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Gas and particle flow characteristics in the gas reversing chamber of a syngas cooler for a 300 MWe IGCC process
Accepted Manuscript Gas and Particle Flow Characteristics in the Gas Reversing Chamber of a Syngas Cooler for a 300 MWe IGCC Process Sangbin Park, In-Soo Ye, Junho Oh, Changkook Ryu, Ja Hyung Koo PII:
S1359-4311(14)00324-X
DOI:
10.1016/j.applthermaleng.2014.04.060
Reference:
ATE 5584
To appear in:
Applied Thermal Engineering
Received Date: 17 September 2013 Accepted Date: 23 April 2014
Please cite this article as: S. Park, I.-S. Ye, J. Oh, C. Ryu, J.H. Koo, Gas and Particle Flow Characteristics in the Gas Reversing Chamber of a Syngas Cooler for a 300 MWe IGCC Process, Applied Thermal Engineering (2014), doi: 10.1016/j.applthermaleng.2014.04.060. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Highlights
-The gas reversing chamber of a syngas cooler in a 300MWe Shell IGCC was studied -The flow smoothly turned downward without strong circulations in the upper part
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-A correlation of Nu for convection was derived for operation loads between 50-100 %
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-Impaction of fly slag particles to the wall was not expected to cause serious erosion
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Gas and Particle Flow Characteristics in the Gas Reversing Chamber
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of a Syngas Cooler for a 300 MWe IGCC Process
3 Sangbin Parka, In-Soo Yea, Junho Oha, Changkook Ryua*, Ja Hyung Koob
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a
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b
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Construction, Daejeon, 305-811, Republic of Korea
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*Corresponding author, Tel: +82-31-299-4841, Fax: +82-31-290-5889, E-mail: [email protected]
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School of Mechanical Engineering, Sungkyunkwan University, Suwon 440-746, Republic of Korea Coal Conversion System Development Team, Corporate R&D Institute, Doosan Heavy Industries &
10 Abstract
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The gas reversing chamber (GRC) is the top part of a syngas cooler in the Shell coal gasification
13
process, in which the quenched syngas flowing from the gasifier is turned downward into evaporator
14
channels. Using computational fluid dynamics (CFD), this study investigated the detailed gas/particle
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flow and heat transfer characteristics in the GRC of an integrated gasification combined cycle (IGCC)
16
process with 300MWe capacity for operational loads between 50 - 100%. The gas flow rapidly
17
changed its direction to downward after impinging onto the wall opposite to the inlet. This led to the
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formation of a higher velocity region along the opposite side, increasing the gas flow rate in the outer
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channel of the evaporator. In contrast, a region with low velocity below 2 m/s developed towards the
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inlet side above the evaporator, which may lead to the significant deposition of fly slag particles onto
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the structural elements. Larger wall heat flux appeared along the main gas stream with a maximum of
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180 kW/m2 at full load. Convection accounted for about 70% of the total heat transfer rate, of which
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the coefficient was correlated to Nu=8.778 Re0.435Pr0.3. Many particles impinged onto the wall along
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the main gas stream, especially at the joint connecting the transfer duct and the GRC. However,
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erosion by fly slag was not expected to be significant, mainly due to the reduced gas velocity at the
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high operating pressure (43 bar).
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Keywords: Coal gasification; Fly slag; Gas reversing chamber; IGCC; Syngas cooler
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1. INTRODUCTION
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Coal gasification is a versatile technology to produce electricity or various chemical feedstocks (such
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as transportation fuels, substitute natural gas, fertilizers, hydrogen, etc.) by converting the
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carbonaceous coal into CO and H2 rich syngas [1]. The integrated gasification combined cycle (IGCC)
34
process utilizes the syngas for efficient electricity production by using both gas and turbines. The
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process can be further integrated with CO2 capture and storage (CCS) [2-4]. Key IGCC plants
36
operating with coal and coke include NUON’s Buggenum (Shell process; The Netherlands), Wabash 1
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River (ConocoPhilips; US), ELCOGAS’s Puertollano (Prenflo; Spain), Tampa Electric’s Polk power
2
station (Texaco; US), Nakoso (MHI; Japan), and Duke Energy’s Edwardsport (GE; USA) [5-7].
3 For IGCC technology to become more competitive, increasing plant availability is a crucial issue.
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Many operational problems in commercial processes are associated with the coal ash [8, 9]. Most
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large-scale gasification plants employ entrained flow gasifiers with dry or slurry feeding. Due to the
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high temperature during gasification, the ash from pulverized coal becomes molten and is mostly
8
deposited onto the gasifier walls, forming a slag layer. It is important to maintain the membrane wall
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covered by the liquid slag layer for protection of the material from thermal and chemical attack. Also,
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the liquid slag should be continuously discharged from the gasifier without blocking the slag tap. For
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continuous discharge, the liquid slag viscosity near the slag tap should be kept low by maintaining a
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sufficiently high gas temperature. Flux consisting mostly of CaCO3 is also added to the coal/N2 stream
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to control the ash composition and viscosity. The fraction of ash and flux not captured on the wall
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leaves the gasifier, which is called fly slag. The syngas and fly slag are quenched by water or recycled
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cold syngas [10-13] to prevent material damage by hot syngas and to solidify the fly slag. In the heat
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recovery and cooling process of syngas for gas cleaning, it is essential to prevent the deposition of fly
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slag, which causes corrosion, and, blockage if severe.
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For large-scale gasification processes, the details of the gas and particle flow characteristics
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downstream of a gasifier have rarely been reported. Yu et al. at the East China University of Science
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and Technology investigated the flow and heat transfer in an industrial-scale radiant syngas cooler
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using CFD [14], and compared the performance of syngas coolers aligned below a gasifier [15]. For
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the Shell coal gasification process, the authors recently presented the details of gas quench system
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including the flow and heat transfer characteristics [16]. The quenched syngas enters a syngas cooler
25
(SGC) which incorporates a series of evaporators. The syngas flowing upward in the gas quench
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needs to be directed downward in the upper part of the SGC. This part is referred to as a gas reversing
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chamber (GRC) [17]. The syngas is then distributed into long and straight evaporator channels. Due to
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the rapid change of the gas flow direction and complex structural elements inside the GRC, the
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deposition of particles, corrosion and erosion are the operational concerns in the process. The heat
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transfer in the GRC is also important since the whole part is made of membrane wall tubes.
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This study presents the gas/particle flow and heat transfer characteristics in the GRC of the SGC in a
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300 MWe IGCC process using computational fluid dynamics (CFD). For operational loads of 50 -
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100 %, the detailed gas flow was investigated with fly slag particles of various sizes. From the results,
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the wall heat transfer rate was modeled into a simple empirical rate in the form of the Nusselt number
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for the development of a process model. The behaviors of slag particles were analyzed with focus on
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the wall impaction and erosion propensity. 2
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2.1 Gas Reversal Chamber
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Fig. 1a shows a schematic of the gasification block for a Shell coal gasification process for IGCC with
5
a capacity of 300 MWe. In the quench pipe/transfer duct, hot syngas at ~1550 oC from the gasifier is
6
immediately mixed with quench gas at ~250 oC recycled from downstream for gas quenching. A
7
description of the process with details of the flow and heat transfer characteristics in the quench
8
pipe/transfer duct have been described in the authors’ previous study [16]. The mixed syngas then
9
enters the SGC in a tall vertical cylindrical shape for heat recovery by steam and cooling for gas
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cleaning processes. SGC consists of the GRC on the top and a series of helical coil evaporators for the
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production of high-pressure (HP) and medium-pressure (MP) steam.
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Fig. 1b shows a schematic of the GRC. The upward gas flow from the transfer duct (diameter 1.6 m)
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inclined with an angle of 45o enters the upper part of the GRC. The flow is then rapidly turned
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downward to enter six vertical channels of the evaporator made of helical coils tubes. The GRC has a
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diameter of 1.9 m and a height 9.4 m with an entire section made of membrane tube walls for the
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evaporation of HP water. Four sets of HP water tubes from the side wall enter the support cross
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located about 0.7 m above the evaporator. The tubes leaving the support cross vertically are connected
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to the helical coil channels. The central part of the evaporator is blocked by a baffle to increase the gas
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velocity in the channels for the prevention of particle deposition, corrosion and decreases in the heat
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transfer rate.
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Table 1 presents a summary of the operating conditions at the inlet of the GRC considered in this
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study. The operational load was varied from 50 to 100% to investigate the effects of the change in the
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flow rate on the heat transfer and particle behavior within a wide operational range. The flow rate and
26
composition of the syngas for each load were based on the design values, while the temperature was
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determined from the assessment of heat transfer in the quench pipe and transfer duct upstream [16].
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Since the load was determined by the energy content of the syngas supplied to the gas turbine, the
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syngas flow rate increased almost linearly with the load from 56.6 kg/s at 50% to 113.1 kg/s at 100%.
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The concentration of CO2 was higher at lower operational loads as a result of a slight increase in the
31
O2/coal ratio. This was mainly to maintain the gasifier at sufficiently high temperatures for the
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formation and discharge of liquid slag on the wall. The inlet temperatures were the enthalpy-averaged
33
values of the gas profiles at the exit of the transfer duct [16]. The flow rates of fly slag ranged from
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0.92 to 1.83 kg/s. This corresponded to 30% of the total coal ash and flux in the gasifier, while the
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remainder was discharged as liquid slag through the slag tap in the gasifier. The operating pressure
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was fixed at 43 bar (absolute).
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The CFD for the gas flow in the GRC required considerations of the energy, momentum, turbulence
4
and radiation in addition to the particle flows of the fly slag. The modeling methods were identical to
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those in the previous study for the quench pipe/transfer duct [16]. Since this study was focused on the
6
averaged flow and heat transfer properties, the turbulence was predicted by the realizable k-ε model
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[18]. The overall results were not influenced by the choice of turbulence model when compared to
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those for the k-ω model, as described in the Supplementary Information. Radiation was solved by the
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discrete ordinate method with discretization for the radiative transfer equation by 5 divisions and 3
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pixels in both the polar and azimuthal directions [19]. The gas absorption coefficient was predicted by
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the weighted sum of the gray gases model [20]. The fly slag particles in the hot syngas were tracked in
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the Lagrangian frame for a total of 44,632 particles with a stochastic method for consideration of the
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turbulence. The particles consist of eight size fractions ranging from 2 µm to 100 µm in diameter. The
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particles had a fixed density of 2800 kg/m3 and emissivity of 0.83 [21]. A commercial code, FLUENT
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version 6.3, was used for the simulations [22].
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For the average operating conditions given in Table 1, the distributions of the syngas properties on the
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inlet plane of the GRC depended on the flow characteristics in the upstream equipment. Therefore,
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detailed inlet conditions were determined from separate simulations for the quench pipe/transfer duct
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as described in the previous study [16]. The profiles of gas temperature, velocity, and turbulence at the
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outlet of transfer duct were prescribed as the inlet conditions of the GRC. The particle injection at the
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inlet for each size fraction was also based on the results, and was implemented by a user-defined
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function (UDF) of the CFD code.
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The top and side walls and the supporting cross were simplified as a conducting wall boundary with
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an overall heat transfer coefficient of 5000 W/m2K and an outer temperature of 339 oC (the saturation
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temperature of HP water/steam). The HP evaporator channels below the support cross consisted of
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many helical coil tubes connected by fins. Since the detailed geometry of the tubes was too complex
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to be included in the mesh, they were simplified as flat walls. Although the evaporator was not the
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focus of this study, the first 3 m of the height was included to consider its influence in the lower part
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of the GRC. In order to address the resistance by the channels to the gas flow in the GRC, the pressure
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drop estimated for the entire length of the first evaporator was specified by using a porous jump
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condition at 0.5 m above the outlet.
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The mesh was constructed for the GRC using 1,493,502 hexahedral cells. Some structural parts near
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the evaporator were not considered in the mesh due to the complex geometry, such as soot blowers
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and leading tubes from the support cross to the helical coils. The results of the grid sensitivity test are 4
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provided in the Supplementary Information. The mesh for the GRC inlet plane was identical to that
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for the transfer duct [16] and, therefore, the inlet profiles generated were imported without adjustment.
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In the discrete phase, the particles colliding on the wall were reflected, after the mass, velocity and
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incident angle of each particle were recorded for the evaluation of wall erosion by a UDF. The
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calculation method for erosion is explained in Section 3.3.
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7 2.3 Analysis of heat transfer
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Establishing a model of heat transfer for the GRC using the CFD results is useful when a fast-
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response process simulation is performed for the process [23]. In heat transfer theory, the influence of
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gas velocity on the convection coefficient (h) or Nusselt number (Nu) is incorporated by a correlation
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of the Reynolds number (Re) and Prandtl number (Pr). Since the GRC did not have a common flow
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configuration, the simplest form of the correlation was used in this study, as follows:
hD = C Rem Pr n k
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(1)
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Taking the natural log of both sides, it was expressed into a linear equation of (ln Re) to fit the
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convection heat transfer rate predicted by the simulations.
(
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ln Nu = ln C Pr n + m ln Re
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(2)
The physical properties required for Nu, Re, and Pr were evaluated for the average temperature of the
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GRC.
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2.4 Evaluation of erosion propensity
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Erosion of the wall by impinging particles is a potential issue in the GRC due to a rapid change in the
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flow direction and large concentrations of fly slag. Erosion takes place by the mechanisms of cutting
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wear and plastic deformation. The overall mass rate (Merosion) of metal eroded by these mechanisms
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was expressed for the mass flow rate (Mp) and the normal velocity component (V sin α) of the
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impinging particles, as follows [25].
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M erosion =
Kx 4.95 ρ m ρ 1p/ 2
σ
3/ 2 y
M p (V sin α )
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(3)
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The fractional term in this equation was constant, since the material properties involved had fixed
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values. Based on this equation, the erosion propensity (ferosion) per unit area was defined on each wall
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face cell as shown below:
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f erosion = ∑ M p ,i (Vi sin α i ) / A 3
(4)
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where the subscript i represents each impinging particle, and A the wall face area. It was evaluated
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through a UDF for the particle phase during simulations. Using the predicted ferosion, the rate of the 5
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erosion depth (herosion, m/s or mm/yr) was then estimated as follows.
herosion
4.95 1 / 2 M& erosion Kx ρ p = = f erosion Aρ m σ y3 / 2
(5)
3 Mbabazi et al. [25] used a value of 0.47 for the constant K for coal ash in conventional combustion
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boilers. The actual value of K for fly slag would be lower, since most particles were once molten due
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to the very high temperatures in the gasifier (above 1500 oC at the gasifier exit), and became spherical
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[26]. The value for slag density (ρp) used was 2800 kg/m3. The wall material was inconel alloy which
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typically has a yield strength (σy) of well over 200 MPa at 340 oC. Therefore, this value was used for
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conservative estimation. In the fly slag, the coal ash had a silica content (x) of 0.5-0.6, while the flux
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consisted of CaO and MgO with a negligible silica content. Ignoring the fraction of flux in fly slag, x
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was assumed to be 0.6 again for conservative simulation. Then, the fractional term in the equation for
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heroson became about 7.01×10-10. For ferosion of 1, the corresponding value of herosion was 0.022 mm for
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one year of operation.
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3. RESULTS AND DISCUSSION
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3.1 Gas flow characteristics
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Fig. 2 shows the contours of the gas velocity and temperature on selected cross-sections for
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operational loads of 100% and 50%. The gas flow in the transfer duct was concentrated more in the
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upper half due to the bend between the quench pipe and the transfer duct. As soon as it entered the
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GRC, the flow rapidly lost its upward momentum and turned downward with both loads. The gas
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stream mostly flowed to the opposite side of the inlet (indicated as ‘A’ in Fig. 2a), where the
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maximum velocity magnitude became higher than that for the inlet. This flow pattern may cause
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excessive impingement of the fly slag onto the wall, which is discussed later. On the horizontal cross-
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sections, a fraction of the gas flowed along the side wall (‘B’), and the velocity magnitude was also
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relatively high. Below the main gas stream, a weak circulation zone (‘C’) was developed. The gas
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flow entering at the top section of the GRC (‘D’) above the inlet level was very weak, with a velocity
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magnitude of less than 0.5 m/s. Although the flow pattern was similar, the gas velocity at 50% load
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was less than 3 m/s. Such low velocities may lead to the accumulation of fly slag particles on the
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structural elements inside such as the support cross and water tubes. Therefore, the use of soot
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blowers is essential, which typically inject high-pressure N2 produced from the air separation unit.
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In the contours of the gas temperature (Fig. 2b), the temperature was gradually decreased by the heat
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transfer to the membrane wall. The contours were similar to those for the gas velocity since the main
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gas streams retained higher temperatures than the regions with lower velocities. However, the
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temperature became more uniform than the velocity when the gas approached the evaporator channels. 6
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The enthalpy-averaged gas temperatures leaving the GRC were 749 oC and 679 oC with loads of 100%
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and 50%, respectively. This corresponded to temperature drops of 32 oC and 47 oC. The details of the
3
heat transfer are discussed in the next section.
4 Fig.3 shows plots of the gas velocity distribution and flow rate entering the six evaporator channels.
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Channel #1 is the innermost one while channel #6 is adjacent to the membrane wall of the SGC. The
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GRC was not long enough to reach a uniform distribution of gas flow between the evaporator
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channels. Fig. 3a shows that the gas velocity at channel #6 was the largest, being about 20% larger
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than that for channel #1. When multiplied by the cross-sectional area, channel #6 had a flow rate
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about twice that of channel #1.
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Fig. 4 shows the total heat flux on the wall for operational loads of 50 % and 100 %. The heat flux
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was larger along the main gas stream and peaked on the wall opposite to the inlet. The peak value was
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about 180 kW/m2 at 100 % load, and 100 kW/m2 at 50%. It then gradually decreased as the gas
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temperature dropped and progressed downward. The heat flux increased again at the inlet of the
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evaporator by an increase in the gas velocity due to the blockage at the central part. However, the heat
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transfer for the evaporator section requires further investigation, since it was simplified in this study
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to consider only its influence on the gas flow in the GRC.
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In order to identify the contributions of convection and radiation, the GRC was divided into 10
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horizontal sections and the average heat flux was calculated. The results are shown in Fig. 5 for the
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normalized height. The total heat flux reached a peak at H = 0.5 in all cases, as expected from the
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contours in Fig. 4. It also exhibited a wide variation with respect to the load, but the radiative heat
25
flux was relatively steady at about 14 - 34 kW/m2.
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Table 2 shows the total and convective heat transfer rates and enthalpy-averaged gas temperature at
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the GRC exit for the different operational loads. The total heat transfer rate ranged from 5.05 MWth
29
(at 50 % load) to 7.70 MWth (100 % load). Convection was dominant over radiation, representing
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66.6 - 71.0 % of the total. The temperature drop on the GRC was larger at 50% load (46.6 oC) than at
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100% load (32.4 oC)
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The results of convective heat transfer were further analyzed into a correlation for Nu using Eq.(1).
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For the operational loads, the values of Nu ranged from 3276 to 4343 for Re of 0.92×106 to 1.77×106.
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Fig. 6 shows the plot of ln Nu vs. ln Re. It was fitted to ln (Nu)= 2.112 + 0.435 ln (Re). When the
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exponent n for Pr in Eq.(2) was fixed to a typical value of 0.3, C became 8.778. The exponent m for
37
Re was 0.435, which was lower than that for fully developed turbulent flows (0.8) [24]. This implies 7
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was 75 % of that at 100 % load (4343), while the ratio would be 59% in a straight tube. It was because
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the convection in the upper part of the GRC was less influenced by the change in the operational load,
4
as shown in Figs. 4 and 5. The error in Nu predicted by the curve-fit was less than 1.5%.
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3.3 Particle behaviors and erosion characteristics
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Fig. 7 shows the particle trajectories color-encoded by residence time. The trajectories are similar
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overall to the gas flow pattern shown in Fig. 2. Most particles escaped the GRC within 2 seconds at
9
100 % load, while many particles stayed for more than 5 seconds at 50%. The particles in the upper
10
part of the inlet at 50% load became stagnant in the region indicated as ‘A’ in Fig. 7a, and fell
11
downward due to the low gas velocity or drag force. Many of these particles became mixed with those
12
being carried by the main gas stream, as can be identified from the overlaps of the trajectories. The
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particle concentration was low in the inlet side above the evaporator (‘B’) in both cases, but ash
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deposition was more likely in this region due to the low gas velocities.
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Although not clearly seen in Fig. 7, many particles impinged onto the wall due to the rapid change of
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flow directions. As described in Section 2.4, the erosion propensity by the fly slag particles was
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evaluated using ferosion during CFD. Fig. 8 illustrates the contours of ferosion on the wall for loads of 100%
19
and 75%. The results at loads of 60 % and 50 % are not shown here, since the range of ferosion became
20
insignificant. In all cases, ferosion was higher on the side wall close to the inlet (indicated as ‘A’ in Fig.
21
8a) than the wall on the opposite to the inlet (B). At a load of 100%, the peak value of ferosion about 20
22
appeared along the joint connecting the transfer duct and GRC with different curvatures. The gas
23
velocity near the side wall around the joint was also high, as shown in Fig. 2a, since the cross-section
24
expanded for the flow from the duct to the GRC. The sum of particle flow rates impinging onto the
25
wall represented 11.4 % of the input at full load. Multiplying ferosion by 0.022 mm/yr as determined in
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Section 2.4, this corresponded to a maximum erosion rate (herosion) of 0.44 mm/yr. Since this was for
27
one year of continuous operation at full load, erosion was not considered significant. The main reason
28
for the low erosion rate was the reduced velocity (V) due to the high operating pressure (43 bar). In
29
order to prevent possible erosion at the joint, however, it would be desirable to design the wall from
30
the transfer duct to expand smoothly to the GRC. Another region for potential erosion was around the
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inlet of the evaporator channels (‘C’) where the gas velocity was increased by the narrowed cross-
32
section. The proportion of larger particles was slightly higher in the channel adjacent to the wall
33
compared to inner channels due to the larger inertia. However, this requires further investigation since
34
the geometry around the region was simplified in this study. The peak of ferosion at ‘D’ in Fig. 8a was
35
not meaningful, since it was due to the sudden pressure drop assigned to the imaginary plane, as
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described in Section 2.2. ferosion rapidly decreased at 75% load (Fig. 8b) due to the decreases in the
37
particle velocity and mass flow rate. Therefore, erosion would not be an issue at lower operational
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loads.
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4. CONCLUSIONS
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The gas and particle flow characteristics and heat transfer in the GRC of a 300 MWe IGCC process
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were investigated using CFD. The key findings are as follows:
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-The gas flow rapidly changed its direction to downward after impinging onto the wall opposite to the
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inlet. This led to the formation of a higher velocity region along the wall, increasing the gas flow rate
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in the outer channel of the evaporator.
-Low velocity regions also developed in the region above the evaporator channels to the GRC inlet
11
side, with a velocity lower than 2 m/s even at full load. Therefore, the role of soot blowers is
12
important for preventing excessive particle accumulation.
13
-Convection was the dominant mode of heat transfer, accounting for about 70% of the total heat
14
transfer rate. It had a wide variation (39 – 146 kW/m2) along the height, while radiative heat flux was
15
relatively steady between 14 - 34 kW/m2. The convection coefficient was correlated to Nu=8.778
16
Re0.435Pr0.3 for loads of 50-100%.
17
- Due to the rapid change in the flow direction, many fly slag particles impacted the wall surface,
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especially near the inlet and along the main gas. However, the wall erosion was not expected to be
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significant, mainly because the gas velocity was reduced by the high operating pressure of 43 bar.
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ACKNOWLEDGEMENT
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This work was supported by the program for the Development of 300 MW class Korean IGCC
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demonstration plant technology of the Korea Institute of Energy Technology Evaluation and Planning
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(KETEP) and Doosan Heavy Industries and Construction funded by the Korea government Ministry
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of Knowledge Economy (2011951010001A).
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NOMENCLATURE
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A
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C
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D
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K
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Merosion rate of mass eroded, kg/s
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Mp
particle mass flow rate, kg/s
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Nu
Nusselt number
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Pr
Prandtl number
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Re
Reynolds number
area of wall face cell, m2 constant
diameter of GRC, m constant
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velocity magnitude, m/s
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ferosion
erosion propensity
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herosion
rate of erosion, m/s
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i
each impacting particle
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k
thermal conductivity of gas, J/m/K
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m
exponent for Re
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n
exponent for Pr
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x
silica content in a particle (kg/kg)
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Greek
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α
impact angle, rad
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ρm
density of the metal, kg/m3
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ρp
densities of particle, kg/m3
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σy
yield stress of the metal, N/m2
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REFERENCES
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[1] G. J. Stiegel, R. C. Maxwell, Gasification technologies: the path to clean, affordable energy in the
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21st century, Fuel Process. Technol. 71 (2001) 79–97.
[2] M. Prins, R. van den Berg, E. van Holthoon, E. van Dorst, F. Geuzebroek, Technological
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developments in IGCC for carbon capture, Chem. Eng. Technol. 35 (2012) 413-419. [3] M. Kanniche, R. Gros-Bonnivard, P. Jaud, J. Valle-Marcos, J-M. Amann, C. Bouallou, Pre-
23
combustion, post-combustion and oxy-combustion in thermal power plant for CO2 capture, Appl.
24
Therm. Eng. 30 (2010) 53-62.
25
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[4] E. Martelli, T. Kreutz, M. Carbo, S. Consonni, D. Jansen, Shell coal IGCCS with carbon capture: Conventional gas quench vs. innovative configurations, Appl. Energ. 88 (2011) 3978-3989.
27
[5] S. J. Mills, Coal gasification and IGCC in Europe, CCC/113. IEA Clean Coal Centre, 2006.
28
[6] R. Fernando, Coal gasification, CCC/140, IEA Clean Coal Centre, 2008.
29
[7] Duke Energy, Edwardsport Integrated Gasification Combined Cycle (IGCC) Station, available at
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http://www.duke-energy.com/about-us/igcc.asp (accessed on 27 August, 2013) [8] P. Wang, M. Massoudi, Slag behavior in gasifiers. Part I: influence of coal properties and gasification conditions, Energies 6 (2013) 784-806. [9] National Energy Technology Laboratory, Wabash River coal gasification repowering project: a DOE assessment, DOE/NETL-2002/1164, US Department of Energy, Pittsburgh, PA, 2002. [10] C. C. Segerstrom, Shell Oil Company, Interchangeable quench gas injection ring, United States Patent 4859213, Aug. 22, 1989. 10
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[11] H. Morehead, Siemens gasification and IGCC update. PowerGEN International, Orlando FL, 2-4 December, 2008. [12] S. V. B. van Paasen, Technology development for Shell coal gasification. 5th Int. Freiberg Conf. on IGCC & XTL Technologies. Leipzig, Germany, 21-24 May, 2012. [13] K. Uebel, U. Guenther, F. Hannemann, U. Schiffers, H. Yilmaz, B. Meyer, Development and
6
engineering of a synthetic gas cooler concept integrated in a Siemens gasifier design, Fuel, in press
7
(2013).
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[14] G. Yu, J. Ni, Q. Liang, Q. Guo, Z. Zhou, Modeling of multiphase flow and heat transfer in radiant
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syngas cooler of an entrained-flow coal gasification, Ind. Eng. Chem. Res. 48 (2009) 10094-10103.
10
[15] J. Ni, G. Yu, Q. Guo, Z. Dai, F. Wang, Modeling and comparison of different syngas cooling
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types for entrained-flow gasifier, Chem. Eng. Sci. 66 (2011) 448–459
[16] I.-S. Ye, S. Park, C. Ryu, S. K. Park, Flow and heat transfer characteristics in the syngas quench system of a 300 MWe IGCC process, Appl. Therm. Eng. 58 (2013) 11-21.
[17] Shell Oil Company, Process for treating syngas using a gas reversing chamber, US Patent
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US4859214, 1989.
[18] T-H. Shih, W. W. Liou, A. Shabbir, Z. Yang, J. Zhu, A new k-ε eddy-viscosity model for high
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Reynolds number turbulent flows - model development and validation. Computers Fluids 24 (1995)
18
227–238.
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[19] E. H. Chui, G. D. Raithby, Computation of radiant heat transfer on a non-orthogonal mesh using the finite-volume method. Numer. Heat Tranf. B-Fundam. 23 (1993) 269-288.
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[20] T. F. Smith, Z. F. Shen, J. N. Friedman, Evaluation of coefficients for the weighted sum of gray gases model. J Heat Tranf. 104 (1982) 602–608. [21] K. C. Mills, J. M. Rhine, The measurement and estimation of the physical properties of slag
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formed during coal gasification: 2.properties relevant to heat-transfer, Fuel 68 (1989) 904-910.
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[22] Fluent Inc., Fluent 6.3 user guide. Lebanon, New Hampshire, 2006.
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[23] F. Casella, P. Colonna, Dynamic modeling of IGCC power plants, Appl. Therm. Eng. 35 (2012)
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91-111.
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[24] F. P. Incropera, D. P. Dewitt, T. L. Bergman, A. S. Lavine, Fundamentals of heat and mass transfer. 6th ed., John Wiley & Sons, 2008. [25] J. G. Mbabazi, T. J. Sheer, R. Shandu, A model to predict erosion on mild steel surfaces impacted by boiler fly ash particles, Wear 257 (2004) 612-624. [26] B. E. Lee, C. A. J. Fletcher, M. Behnia, Computational prediction of tube erosion I coal fired power utility boilers, Trans. ASME 121 (1999) 746-750.
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List of Tables
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Table 1. Summary of operating conditions at the inlet of the GRC considered in this study
5
Table 2. Heat transfer rates on the wall and the exit gas temperature in the GRC.
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List of Figures
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Fig. 1. Schematic of the gasification block and GRC in a Shell coal gasification process.
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Fig. 2. Contours of velocity magnitude and temperature on selected cross-sections for operational
13
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loads of 100% and 50%.
Fig. 3. Distribution of gas velocity and flow rate in the evaporator channels.
15
Fig. 4. Contours of wall heat flux for operational loads of 100% and 50%.
16
Fig. 5. Average wall heat flux along the vertical direction.
17
Fig. 6. Curve-fit for Re vs. Nu using the CFD results.
18
Fig. 7. Trajectories of selected particles (color: residence time [sec])
19
Fig. 8. Erosion propensity on the wall for operational loads of 100% and 75%.
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Fig. A1. Comparison of the wall heat flux between three meshes with different numbers of cells.
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Fig. A2. The mesh constructed for the GRC (1,493,502 hexahedral cells).
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Table 1. Summary of operating conditions at the inlet of the GRC considered in this study Operation load (%)
50
Flow rate (kg/s) o
75
90
100
67.9
84.8
101.8
113.1
743
761
774
782
55.2
57.2
59.2
59.2
7.2
6.1
5.1
5.1
27.1
28.1
28.5
28.5
10.4
10.4
8.5
7.2
7.2
0.92
1.10
1.37
1.65
1.83
56.6
Average temp. ( C)
726
CO (vol.%)
55.2
CO2 (vol.%)
7.2
H2 (vol.%)
27.1
N2 (vol.%)
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Fly slag flow rate (kg/s)
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Syngas
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Table 2. Heat transfer rates on the wall and the exit gas temperature in the GRC. 50
60
75
90
100
Total heat transfer rate (MW)
5.05
5.60
6.42
7.18
7.70
Convective heat transfer rate (MW)
3.31
3.73
4.38
5.01
5.47
Exit temperature (oC)
679
701
724
740
749
41.7
37.3
34.1
32.4
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Operation load (%)
46.6
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Temperature drop (oC)
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Gas Reversal Chamber (GRC)
Syngas Cooler
Quench gas ~250oC
HP Steam
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Air Syngas O2
N2 Coal
Milling
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Gas Cleaning
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(a) Gasification block
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Support cross
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HP water
HP Evaporator (6 channels of helical coil #1-inner, #6-outer)
Porous jump
Syngas (to a series of evaporators)
(b) Gas reversal chamber (GRC) Fig. 1. Schematic of the gasification block and GRC in a Shell coal gasification process.
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(a) Velocity magnitude
(b) Temperature Fig. 2. Contours of velocity magnitude and temperature on selected cross-sections for operational loads of 100% and 50%.
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Gas velocity (m/s)
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Load 100% Load 75% Load 50%
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Evaporator channel #
(a) Gas velocity
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Evaporator channel #
(b) Mass flow rate Fig. 3. Distribution of gas velocity and flow rate in the evaporator channels.
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(a) Load 100%
(b) Load 50%
Fig. 4. Contours of wall heat flux for operational loads of 100% and 50%.
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1.0
Load 100% Load 75% Load 50%
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Radiation
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Average wall heat flux (kW/m )
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Fig. 5. Average wall heat flux along the vertical direction.
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ln (Nu)
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13.75
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ln (Re)
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Fig. 6. Curve-fit for Re vs. Nu using the CFD results.
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(a) Load 100%
(b) Load 50%
Fig. 7. Trajectories of selected particles (color: residence time [sec])
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(a) Load 100%
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(b) Load 75%
Fig. 8. Erosion propensity on the wall for operational loads of 100% and 75%.
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ACCEPTED MANUSCRIPT Gas and Particle Flow Characteristics in the Gas Reversing Chamber of a Syngas Cooler for a 300 MWe IGCC Process Sangbin Parka, In-Soo Yea, Junho Oha, Changkook Ryua*, Ja Hyung Koob a
School of Mechanical Engineering, Sungkyunkwan University, Suwon 440-746, Republic of Korea Coal Conversion System Development Team, Corporate R&D Institute, Doosan Heavy Industries & Construction, Daejeon, 305-811, Republic of Korea *Corresponding author, Tel: +82-31-299-4841, Fax: +82-31-290-5889, E-mail: [email protected]
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GRID SENSITIVITY AND METRIC In order to assess the grid sensitivity, three meshes were constructed using different numbers of cells: coarse (362,457 hexahedral cells), medium fine (769,713 cells) and fine meshes (1,493,502 cells). The simulation for the grid sensitivity test was carried out for the operational load of 100% in Table 1. Instead of using the profiles at the inlet, the average values were prescribed for temperature, velocity, particle concentration and other properties. Fig. S1 shows the distribution of wall heat flux for the three meshes. Compared to the wall heat flux for the fine mesh, the difference in the average value was 3.7% in the coarse mesh. It was reduced to 1.7% in the medium fine mesh, which was satisfactory. For a minimized grid sensitivity, the fine mesh shown in Fig. S2 was adopted for the simulations in this study.
1.0
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0.8
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2
Wall heat flux (kW/m )
Fig. S1. Comparison of the wall heat flux between Fig. S2. The mesh constructed for the GRC three meshes with different numbers of cells. (1,493,502 hexahedral cells).
Fig. S3 shows the mesh metric in terms of Jacobian determinant and minimum internal angle for the hexahedral cells in the fine mesh used. The determinants were over 0.82 for 98% of the cells and the lowest value was 0.53, indicating that the mesh was reasonably regular. The minimum internal angle was over 60 o for 90% of the cells while the smallest value was about 24o. Skew cells were found near the joint where the two cylinders of the transfer duct and GRC were connected. In general, a minimum angle greater than 18 o and determinant greater than 0.2 are acceptable for most commercial solvers. [ANSYS, 2008]
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mesh number (%)
mesh number (%)
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EFFECTS OF TURBULENCE MODELS Fig. S4 compares the average heat flux on the wall predicted with the realizable k-ϵ model and the shear stress transport (SST) k-ω model. Both models are known to better predict the swirl, circulating or jet flows than the standard models. The two models had the similar trend of heat flux along the GRC wall. Although the heat flux was slightly higher for the SST k-w model in the upper part above the inlet, the difference in the overall heat transfer rate was within 1.2%. Therefore, the use of the realizable k-ϵ model was acceptable for the comparative study of time-averaged trends in flow and heat transfer between different operational cases. 1.0
Realizable k-ε model SST k-ω model
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0.4
0.2
0.0 0
50
100
150
200
2
Wall heat flux (kW/m )
Fig. S4.Comparison of heat flux for the realizable k-ϵ and SST k-ω models. References [ANSYS, 2007] ANSYS Inc., ANSYS ICEM CFD 11.0 Tutorial Manual, January 2007, Cannonsburg, PA 15317, USA.
S1359-4311(14)00324-X
DOI:
10.1016/j.applthermaleng.2014.04.060
Reference:
ATE 5584
To appear in:
Applied Thermal Engineering
Received Date: 17 September 2013 Accepted Date: 23 April 2014
Please cite this article as: S. Park, I.-S. Ye, J. Oh, C. Ryu, J.H. Koo, Gas and Particle Flow Characteristics in the Gas Reversing Chamber of a Syngas Cooler for a 300 MWe IGCC Process, Applied Thermal Engineering (2014), doi: 10.1016/j.applthermaleng.2014.04.060. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Highlights
-The gas reversing chamber of a syngas cooler in a 300MWe Shell IGCC was studied -The flow smoothly turned downward without strong circulations in the upper part
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-A correlation of Nu for convection was derived for operation loads between 50-100 %
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-Impaction of fly slag particles to the wall was not expected to cause serious erosion
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Gas and Particle Flow Characteristics in the Gas Reversing Chamber
2
of a Syngas Cooler for a 300 MWe IGCC Process
3 Sangbin Parka, In-Soo Yea, Junho Oha, Changkook Ryua*, Ja Hyung Koob
4 5 6
a
7
b
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Construction, Daejeon, 305-811, Republic of Korea
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*Corresponding author, Tel: +82-31-299-4841, Fax: +82-31-290-5889, E-mail: [email protected]
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School of Mechanical Engineering, Sungkyunkwan University, Suwon 440-746, Republic of Korea Coal Conversion System Development Team, Corporate R&D Institute, Doosan Heavy Industries &
10 Abstract
12
The gas reversing chamber (GRC) is the top part of a syngas cooler in the Shell coal gasification
13
process, in which the quenched syngas flowing from the gasifier is turned downward into evaporator
14
channels. Using computational fluid dynamics (CFD), this study investigated the detailed gas/particle
15
flow and heat transfer characteristics in the GRC of an integrated gasification combined cycle (IGCC)
16
process with 300MWe capacity for operational loads between 50 - 100%. The gas flow rapidly
17
changed its direction to downward after impinging onto the wall opposite to the inlet. This led to the
18
formation of a higher velocity region along the opposite side, increasing the gas flow rate in the outer
19
channel of the evaporator. In contrast, a region with low velocity below 2 m/s developed towards the
20
inlet side above the evaporator, which may lead to the significant deposition of fly slag particles onto
21
the structural elements. Larger wall heat flux appeared along the main gas stream with a maximum of
22
180 kW/m2 at full load. Convection accounted for about 70% of the total heat transfer rate, of which
23
the coefficient was correlated to Nu=8.778 Re0.435Pr0.3. Many particles impinged onto the wall along
24
the main gas stream, especially at the joint connecting the transfer duct and the GRC. However,
25
erosion by fly slag was not expected to be significant, mainly due to the reduced gas velocity at the
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high operating pressure (43 bar).
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Keywords: Coal gasification; Fly slag; Gas reversing chamber; IGCC; Syngas cooler
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1. INTRODUCTION
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Coal gasification is a versatile technology to produce electricity or various chemical feedstocks (such
32
as transportation fuels, substitute natural gas, fertilizers, hydrogen, etc.) by converting the
33
carbonaceous coal into CO and H2 rich syngas [1]. The integrated gasification combined cycle (IGCC)
34
process utilizes the syngas for efficient electricity production by using both gas and turbines. The
35
process can be further integrated with CO2 capture and storage (CCS) [2-4]. Key IGCC plants
36
operating with coal and coke include NUON’s Buggenum (Shell process; The Netherlands), Wabash 1
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River (ConocoPhilips; US), ELCOGAS’s Puertollano (Prenflo; Spain), Tampa Electric’s Polk power
2
station (Texaco; US), Nakoso (MHI; Japan), and Duke Energy’s Edwardsport (GE; USA) [5-7].
3 For IGCC technology to become more competitive, increasing plant availability is a crucial issue.
5
Many operational problems in commercial processes are associated with the coal ash [8, 9]. Most
6
large-scale gasification plants employ entrained flow gasifiers with dry or slurry feeding. Due to the
7
high temperature during gasification, the ash from pulverized coal becomes molten and is mostly
8
deposited onto the gasifier walls, forming a slag layer. It is important to maintain the membrane wall
9
covered by the liquid slag layer for protection of the material from thermal and chemical attack. Also,
10
the liquid slag should be continuously discharged from the gasifier without blocking the slag tap. For
11
continuous discharge, the liquid slag viscosity near the slag tap should be kept low by maintaining a
12
sufficiently high gas temperature. Flux consisting mostly of CaCO3 is also added to the coal/N2 stream
13
to control the ash composition and viscosity. The fraction of ash and flux not captured on the wall
14
leaves the gasifier, which is called fly slag. The syngas and fly slag are quenched by water or recycled
15
cold syngas [10-13] to prevent material damage by hot syngas and to solidify the fly slag. In the heat
16
recovery and cooling process of syngas for gas cleaning, it is essential to prevent the deposition of fly
17
slag, which causes corrosion, and, blockage if severe.
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For large-scale gasification processes, the details of the gas and particle flow characteristics
20
downstream of a gasifier have rarely been reported. Yu et al. at the East China University of Science
21
and Technology investigated the flow and heat transfer in an industrial-scale radiant syngas cooler
22
using CFD [14], and compared the performance of syngas coolers aligned below a gasifier [15]. For
23
the Shell coal gasification process, the authors recently presented the details of gas quench system
24
including the flow and heat transfer characteristics [16]. The quenched syngas enters a syngas cooler
25
(SGC) which incorporates a series of evaporators. The syngas flowing upward in the gas quench
26
needs to be directed downward in the upper part of the SGC. This part is referred to as a gas reversing
27
chamber (GRC) [17]. The syngas is then distributed into long and straight evaporator channels. Due to
28
the rapid change of the gas flow direction and complex structural elements inside the GRC, the
29
deposition of particles, corrosion and erosion are the operational concerns in the process. The heat
30
transfer in the GRC is also important since the whole part is made of membrane wall tubes.
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This study presents the gas/particle flow and heat transfer characteristics in the GRC of the SGC in a
33
300 MWe IGCC process using computational fluid dynamics (CFD). For operational loads of 50 -
34
100 %, the detailed gas flow was investigated with fly slag particles of various sizes. From the results,
35
the wall heat transfer rate was modeled into a simple empirical rate in the form of the Nusselt number
36
for the development of a process model. The behaviors of slag particles were analyzed with focus on
37
the wall impaction and erosion propensity. 2
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3
2.1 Gas Reversal Chamber
4
Fig. 1a shows a schematic of the gasification block for a Shell coal gasification process for IGCC with
5
a capacity of 300 MWe. In the quench pipe/transfer duct, hot syngas at ~1550 oC from the gasifier is
6
immediately mixed with quench gas at ~250 oC recycled from downstream for gas quenching. A
7
description of the process with details of the flow and heat transfer characteristics in the quench
8
pipe/transfer duct have been described in the authors’ previous study [16]. The mixed syngas then
9
enters the SGC in a tall vertical cylindrical shape for heat recovery by steam and cooling for gas
10
cleaning processes. SGC consists of the GRC on the top and a series of helical coil evaporators for the
11
production of high-pressure (HP) and medium-pressure (MP) steam.
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Fig. 1b shows a schematic of the GRC. The upward gas flow from the transfer duct (diameter 1.6 m)
14
inclined with an angle of 45o enters the upper part of the GRC. The flow is then rapidly turned
15
downward to enter six vertical channels of the evaporator made of helical coils tubes. The GRC has a
16
diameter of 1.9 m and a height 9.4 m with an entire section made of membrane tube walls for the
17
evaporation of HP water. Four sets of HP water tubes from the side wall enter the support cross
18
located about 0.7 m above the evaporator. The tubes leaving the support cross vertically are connected
19
to the helical coil channels. The central part of the evaporator is blocked by a baffle to increase the gas
20
velocity in the channels for the prevention of particle deposition, corrosion and decreases in the heat
21
transfer rate.
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Table 1 presents a summary of the operating conditions at the inlet of the GRC considered in this
24
study. The operational load was varied from 50 to 100% to investigate the effects of the change in the
25
flow rate on the heat transfer and particle behavior within a wide operational range. The flow rate and
26
composition of the syngas for each load were based on the design values, while the temperature was
27
determined from the assessment of heat transfer in the quench pipe and transfer duct upstream [16].
28
Since the load was determined by the energy content of the syngas supplied to the gas turbine, the
29
syngas flow rate increased almost linearly with the load from 56.6 kg/s at 50% to 113.1 kg/s at 100%.
30
The concentration of CO2 was higher at lower operational loads as a result of a slight increase in the
31
O2/coal ratio. This was mainly to maintain the gasifier at sufficiently high temperatures for the
32
formation and discharge of liquid slag on the wall. The inlet temperatures were the enthalpy-averaged
33
values of the gas profiles at the exit of the transfer duct [16]. The flow rates of fly slag ranged from
34
0.92 to 1.83 kg/s. This corresponded to 30% of the total coal ash and flux in the gasifier, while the
35
remainder was discharged as liquid slag through the slag tap in the gasifier. The operating pressure
36
was fixed at 43 bar (absolute).
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ACCEPTED MANUSCRIPT 1 2.2 Computational fluid dynamics
3
The CFD for the gas flow in the GRC required considerations of the energy, momentum, turbulence
4
and radiation in addition to the particle flows of the fly slag. The modeling methods were identical to
5
those in the previous study for the quench pipe/transfer duct [16]. Since this study was focused on the
6
averaged flow and heat transfer properties, the turbulence was predicted by the realizable k-ε model
7
[18]. The overall results were not influenced by the choice of turbulence model when compared to
8
those for the k-ω model, as described in the Supplementary Information. Radiation was solved by the
9
discrete ordinate method with discretization for the radiative transfer equation by 5 divisions and 3
10
pixels in both the polar and azimuthal directions [19]. The gas absorption coefficient was predicted by
11
the weighted sum of the gray gases model [20]. The fly slag particles in the hot syngas were tracked in
12
the Lagrangian frame for a total of 44,632 particles with a stochastic method for consideration of the
13
turbulence. The particles consist of eight size fractions ranging from 2 µm to 100 µm in diameter. The
14
particles had a fixed density of 2800 kg/m3 and emissivity of 0.83 [21]. A commercial code, FLUENT
15
version 6.3, was used for the simulations [22].
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For the average operating conditions given in Table 1, the distributions of the syngas properties on the
18
inlet plane of the GRC depended on the flow characteristics in the upstream equipment. Therefore,
19
detailed inlet conditions were determined from separate simulations for the quench pipe/transfer duct
20
as described in the previous study [16]. The profiles of gas temperature, velocity, and turbulence at the
21
outlet of transfer duct were prescribed as the inlet conditions of the GRC. The particle injection at the
22
inlet for each size fraction was also based on the results, and was implemented by a user-defined
23
function (UDF) of the CFD code.
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The top and side walls and the supporting cross were simplified as a conducting wall boundary with
26
an overall heat transfer coefficient of 5000 W/m2K and an outer temperature of 339 oC (the saturation
27
temperature of HP water/steam). The HP evaporator channels below the support cross consisted of
28
many helical coil tubes connected by fins. Since the detailed geometry of the tubes was too complex
29
to be included in the mesh, they were simplified as flat walls. Although the evaporator was not the
30
focus of this study, the first 3 m of the height was included to consider its influence in the lower part
31
of the GRC. In order to address the resistance by the channels to the gas flow in the GRC, the pressure
32
drop estimated for the entire length of the first evaporator was specified by using a porous jump
33
condition at 0.5 m above the outlet.
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The mesh was constructed for the GRC using 1,493,502 hexahedral cells. Some structural parts near
36
the evaporator were not considered in the mesh due to the complex geometry, such as soot blowers
37
and leading tubes from the support cross to the helical coils. The results of the grid sensitivity test are 4
ACCEPTED MANUSCRIPT 1
provided in the Supplementary Information. The mesh for the GRC inlet plane was identical to that
2
for the transfer duct [16] and, therefore, the inlet profiles generated were imported without adjustment.
3 4
In the discrete phase, the particles colliding on the wall were reflected, after the mass, velocity and
5
incident angle of each particle were recorded for the evaluation of wall erosion by a UDF. The
6
calculation method for erosion is explained in Section 3.3.
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7 2.3 Analysis of heat transfer
9
Establishing a model of heat transfer for the GRC using the CFD results is useful when a fast-
10
response process simulation is performed for the process [23]. In heat transfer theory, the influence of
11
gas velocity on the convection coefficient (h) or Nusselt number (Nu) is incorporated by a correlation
12
of the Reynolds number (Re) and Prandtl number (Pr). Since the GRC did not have a common flow
13
configuration, the simplest form of the correlation was used in this study, as follows:
hD = C Rem Pr n k
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14
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(1)
15
Taking the natural log of both sides, it was expressed into a linear equation of (ln Re) to fit the
16
convection heat transfer rate predicted by the simulations.
(
)
ln Nu = ln C Pr n + m ln Re
17
(2)
The physical properties required for Nu, Re, and Pr were evaluated for the average temperature of the
19
GRC.
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2.4 Evaluation of erosion propensity
22
Erosion of the wall by impinging particles is a potential issue in the GRC due to a rapid change in the
23
flow direction and large concentrations of fly slag. Erosion takes place by the mechanisms of cutting
24
wear and plastic deformation. The overall mass rate (Merosion) of metal eroded by these mechanisms
25
was expressed for the mass flow rate (Mp) and the normal velocity component (V sin α) of the
26
impinging particles, as follows [25].
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M erosion =
Kx 4.95 ρ m ρ 1p/ 2
σ
3/ 2 y
M p (V sin α )
3
(3)
28
The fractional term in this equation was constant, since the material properties involved had fixed
29
values. Based on this equation, the erosion propensity (ferosion) per unit area was defined on each wall
30
face cell as shown below:
31
f erosion = ∑ M p ,i (Vi sin α i ) / A 3
(4)
i
32
where the subscript i represents each impinging particle, and A the wall face area. It was evaluated
33
through a UDF for the particle phase during simulations. Using the predicted ferosion, the rate of the 5
ACCEPTED MANUSCRIPT 1 2
erosion depth (herosion, m/s or mm/yr) was then estimated as follows.
herosion
4.95 1 / 2 M& erosion Kx ρ p = = f erosion Aρ m σ y3 / 2
(5)
3 Mbabazi et al. [25] used a value of 0.47 for the constant K for coal ash in conventional combustion
5
boilers. The actual value of K for fly slag would be lower, since most particles were once molten due
6
to the very high temperatures in the gasifier (above 1500 oC at the gasifier exit), and became spherical
7
[26]. The value for slag density (ρp) used was 2800 kg/m3. The wall material was inconel alloy which
8
typically has a yield strength (σy) of well over 200 MPa at 340 oC. Therefore, this value was used for
9
conservative estimation. In the fly slag, the coal ash had a silica content (x) of 0.5-0.6, while the flux
10
consisted of CaO and MgO with a negligible silica content. Ignoring the fraction of flux in fly slag, x
11
was assumed to be 0.6 again for conservative simulation. Then, the fractional term in the equation for
12
heroson became about 7.01×10-10. For ferosion of 1, the corresponding value of herosion was 0.022 mm for
13
one year of operation.
14
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3. RESULTS AND DISCUSSION
16
3.1 Gas flow characteristics
17
Fig. 2 shows the contours of the gas velocity and temperature on selected cross-sections for
18
operational loads of 100% and 50%. The gas flow in the transfer duct was concentrated more in the
19
upper half due to the bend between the quench pipe and the transfer duct. As soon as it entered the
20
GRC, the flow rapidly lost its upward momentum and turned downward with both loads. The gas
21
stream mostly flowed to the opposite side of the inlet (indicated as ‘A’ in Fig. 2a), where the
22
maximum velocity magnitude became higher than that for the inlet. This flow pattern may cause
23
excessive impingement of the fly slag onto the wall, which is discussed later. On the horizontal cross-
24
sections, a fraction of the gas flowed along the side wall (‘B’), and the velocity magnitude was also
25
relatively high. Below the main gas stream, a weak circulation zone (‘C’) was developed. The gas
26
flow entering at the top section of the GRC (‘D’) above the inlet level was very weak, with a velocity
27
magnitude of less than 0.5 m/s. Although the flow pattern was similar, the gas velocity at 50% load
28
was less than 3 m/s. Such low velocities may lead to the accumulation of fly slag particles on the
29
structural elements inside such as the support cross and water tubes. Therefore, the use of soot
30
blowers is essential, which typically inject high-pressure N2 produced from the air separation unit.
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31 32
In the contours of the gas temperature (Fig. 2b), the temperature was gradually decreased by the heat
33
transfer to the membrane wall. The contours were similar to those for the gas velocity since the main
34
gas streams retained higher temperatures than the regions with lower velocities. However, the
35
temperature became more uniform than the velocity when the gas approached the evaporator channels. 6
ACCEPTED MANUSCRIPT 1
The enthalpy-averaged gas temperatures leaving the GRC were 749 oC and 679 oC with loads of 100%
2
and 50%, respectively. This corresponded to temperature drops of 32 oC and 47 oC. The details of the
3
heat transfer are discussed in the next section.
4 Fig.3 shows plots of the gas velocity distribution and flow rate entering the six evaporator channels.
6
Channel #1 is the innermost one while channel #6 is adjacent to the membrane wall of the SGC. The
7
GRC was not long enough to reach a uniform distribution of gas flow between the evaporator
8
channels. Fig. 3a shows that the gas velocity at channel #6 was the largest, being about 20% larger
9
than that for channel #1. When multiplied by the cross-sectional area, channel #6 had a flow rate
10
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about twice that of channel #1.
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11 3.2 Heat transfer characteristics
13
Fig. 4 shows the total heat flux on the wall for operational loads of 50 % and 100 %. The heat flux
14
was larger along the main gas stream and peaked on the wall opposite to the inlet. The peak value was
15
about 180 kW/m2 at 100 % load, and 100 kW/m2 at 50%. It then gradually decreased as the gas
16
temperature dropped and progressed downward. The heat flux increased again at the inlet of the
17
evaporator by an increase in the gas velocity due to the blockage at the central part. However, the heat
18
transfer for the evaporator section requires further investigation, since it was simplified in this study
19
to consider only its influence on the gas flow in the GRC.
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In order to identify the contributions of convection and radiation, the GRC was divided into 10
22
horizontal sections and the average heat flux was calculated. The results are shown in Fig. 5 for the
23
normalized height. The total heat flux reached a peak at H = 0.5 in all cases, as expected from the
24
contours in Fig. 4. It also exhibited a wide variation with respect to the load, but the radiative heat
25
flux was relatively steady at about 14 - 34 kW/m2.
26
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Table 2 shows the total and convective heat transfer rates and enthalpy-averaged gas temperature at
28
the GRC exit for the different operational loads. The total heat transfer rate ranged from 5.05 MWth
29
(at 50 % load) to 7.70 MWth (100 % load). Convection was dominant over radiation, representing
30
66.6 - 71.0 % of the total. The temperature drop on the GRC was larger at 50% load (46.6 oC) than at
31
100% load (32.4 oC)
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32 33
The results of convective heat transfer were further analyzed into a correlation for Nu using Eq.(1).
34
For the operational loads, the values of Nu ranged from 3276 to 4343 for Re of 0.92×106 to 1.77×106.
35
Fig. 6 shows the plot of ln Nu vs. ln Re. It was fitted to ln (Nu)= 2.112 + 0.435 ln (Re). When the
36
exponent n for Pr in Eq.(2) was fixed to a typical value of 0.3, C became 8.778. The exponent m for
37
Re was 0.435, which was lower than that for fully developed turbulent flows (0.8) [24]. This implies 7
ACCEPTED MANUSCRIPT that Nu in the GRC was less proportional to the change in Re. For example, Nu at 50 % load (3276)
2
was 75 % of that at 100 % load (4343), while the ratio would be 59% in a straight tube. It was because
3
the convection in the upper part of the GRC was less influenced by the change in the operational load,
4
as shown in Figs. 4 and 5. The error in Nu predicted by the curve-fit was less than 1.5%.
5 6
3.3 Particle behaviors and erosion characteristics
7
Fig. 7 shows the particle trajectories color-encoded by residence time. The trajectories are similar
8
overall to the gas flow pattern shown in Fig. 2. Most particles escaped the GRC within 2 seconds at
9
100 % load, while many particles stayed for more than 5 seconds at 50%. The particles in the upper
10
part of the inlet at 50% load became stagnant in the region indicated as ‘A’ in Fig. 7a, and fell
11
downward due to the low gas velocity or drag force. Many of these particles became mixed with those
12
being carried by the main gas stream, as can be identified from the overlaps of the trajectories. The
13
particle concentration was low in the inlet side above the evaporator (‘B’) in both cases, but ash
14
deposition was more likely in this region due to the low gas velocities.
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15
Although not clearly seen in Fig. 7, many particles impinged onto the wall due to the rapid change of
17
flow directions. As described in Section 2.4, the erosion propensity by the fly slag particles was
18
evaluated using ferosion during CFD. Fig. 8 illustrates the contours of ferosion on the wall for loads of 100%
19
and 75%. The results at loads of 60 % and 50 % are not shown here, since the range of ferosion became
20
insignificant. In all cases, ferosion was higher on the side wall close to the inlet (indicated as ‘A’ in Fig.
21
8a) than the wall on the opposite to the inlet (B). At a load of 100%, the peak value of ferosion about 20
22
appeared along the joint connecting the transfer duct and GRC with different curvatures. The gas
23
velocity near the side wall around the joint was also high, as shown in Fig. 2a, since the cross-section
24
expanded for the flow from the duct to the GRC. The sum of particle flow rates impinging onto the
25
wall represented 11.4 % of the input at full load. Multiplying ferosion by 0.022 mm/yr as determined in
26
Section 2.4, this corresponded to a maximum erosion rate (herosion) of 0.44 mm/yr. Since this was for
27
one year of continuous operation at full load, erosion was not considered significant. The main reason
28
for the low erosion rate was the reduced velocity (V) due to the high operating pressure (43 bar). In
29
order to prevent possible erosion at the joint, however, it would be desirable to design the wall from
30
the transfer duct to expand smoothly to the GRC. Another region for potential erosion was around the
31
inlet of the evaporator channels (‘C’) where the gas velocity was increased by the narrowed cross-
32
section. The proportion of larger particles was slightly higher in the channel adjacent to the wall
33
compared to inner channels due to the larger inertia. However, this requires further investigation since
34
the geometry around the region was simplified in this study. The peak of ferosion at ‘D’ in Fig. 8a was
35
not meaningful, since it was due to the sudden pressure drop assigned to the imaginary plane, as
36
described in Section 2.2. ferosion rapidly decreased at 75% load (Fig. 8b) due to the decreases in the
37
particle velocity and mass flow rate. Therefore, erosion would not be an issue at lower operational
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loads.
2 3
4. CONCLUSIONS
4
The gas and particle flow characteristics and heat transfer in the GRC of a 300 MWe IGCC process
5
were investigated using CFD. The key findings are as follows:
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-The gas flow rapidly changed its direction to downward after impinging onto the wall opposite to the
8
inlet. This led to the formation of a higher velocity region along the wall, increasing the gas flow rate
9
in the outer channel of the evaporator.
-Low velocity regions also developed in the region above the evaporator channels to the GRC inlet
11
side, with a velocity lower than 2 m/s even at full load. Therefore, the role of soot blowers is
12
important for preventing excessive particle accumulation.
13
-Convection was the dominant mode of heat transfer, accounting for about 70% of the total heat
14
transfer rate. It had a wide variation (39 – 146 kW/m2) along the height, while radiative heat flux was
15
relatively steady between 14 - 34 kW/m2. The convection coefficient was correlated to Nu=8.778
16
Re0.435Pr0.3 for loads of 50-100%.
17
- Due to the rapid change in the flow direction, many fly slag particles impacted the wall surface,
18
especially near the inlet and along the main gas. However, the wall erosion was not expected to be
19
significant, mainly because the gas velocity was reduced by the high operating pressure of 43 bar.
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ACKNOWLEDGEMENT
22
This work was supported by the program for the Development of 300 MW class Korean IGCC
23
demonstration plant technology of the Korea Institute of Energy Technology Evaluation and Planning
24
(KETEP) and Doosan Heavy Industries and Construction funded by the Korea government Ministry
25
of Knowledge Economy (2011951010001A).
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NOMENCLATURE
28
A
29
C
30
D
31
K
32
Merosion rate of mass eroded, kg/s
33
Mp
particle mass flow rate, kg/s
34
Nu
Nusselt number
35
Pr
Prandtl number
36
Re
Reynolds number
area of wall face cell, m2 constant
diameter of GRC, m constant
9
ACCEPTED MANUSCRIPT V
velocity magnitude, m/s
2
ferosion
erosion propensity
3
herosion
rate of erosion, m/s
4
i
each impacting particle
5
k
thermal conductivity of gas, J/m/K
6
m
exponent for Re
7
n
exponent for Pr
8
x
silica content in a particle (kg/kg)
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1
Greek
11
α
impact angle, rad
12
ρm
density of the metal, kg/m3
13
ρp
densities of particle, kg/m3
14
σy
yield stress of the metal, N/m2
15 16
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REFERENCES
18
[1] G. J. Stiegel, R. C. Maxwell, Gasification technologies: the path to clean, affordable energy in the
20 21
21st century, Fuel Process. Technol. 71 (2001) 79–97.
[2] M. Prins, R. van den Berg, E. van Holthoon, E. van Dorst, F. Geuzebroek, Technological
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developments in IGCC for carbon capture, Chem. Eng. Technol. 35 (2012) 413-419. [3] M. Kanniche, R. Gros-Bonnivard, P. Jaud, J. Valle-Marcos, J-M. Amann, C. Bouallou, Pre-
23
combustion, post-combustion and oxy-combustion in thermal power plant for CO2 capture, Appl.
24
Therm. Eng. 30 (2010) 53-62.
25
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[4] E. Martelli, T. Kreutz, M. Carbo, S. Consonni, D. Jansen, Shell coal IGCCS with carbon capture: Conventional gas quench vs. innovative configurations, Appl. Energ. 88 (2011) 3978-3989.
27
[5] S. J. Mills, Coal gasification and IGCC in Europe, CCC/113. IEA Clean Coal Centre, 2006.
28
[6] R. Fernando, Coal gasification, CCC/140, IEA Clean Coal Centre, 2008.
29
[7] Duke Energy, Edwardsport Integrated Gasification Combined Cycle (IGCC) Station, available at
30 31 32 33 34 35 36
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http://www.duke-energy.com/about-us/igcc.asp (accessed on 27 August, 2013) [8] P. Wang, M. Massoudi, Slag behavior in gasifiers. Part I: influence of coal properties and gasification conditions, Energies 6 (2013) 784-806. [9] National Energy Technology Laboratory, Wabash River coal gasification repowering project: a DOE assessment, DOE/NETL-2002/1164, US Department of Energy, Pittsburgh, PA, 2002. [10] C. C. Segerstrom, Shell Oil Company, Interchangeable quench gas injection ring, United States Patent 4859213, Aug. 22, 1989. 10
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[11] H. Morehead, Siemens gasification and IGCC update. PowerGEN International, Orlando FL, 2-4 December, 2008. [12] S. V. B. van Paasen, Technology development for Shell coal gasification. 5th Int. Freiberg Conf. on IGCC & XTL Technologies. Leipzig, Germany, 21-24 May, 2012. [13] K. Uebel, U. Guenther, F. Hannemann, U. Schiffers, H. Yilmaz, B. Meyer, Development and
6
engineering of a synthetic gas cooler concept integrated in a Siemens gasifier design, Fuel, in press
7
(2013).
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5
8
[14] G. Yu, J. Ni, Q. Liang, Q. Guo, Z. Zhou, Modeling of multiphase flow and heat transfer in radiant
9
syngas cooler of an entrained-flow coal gasification, Ind. Eng. Chem. Res. 48 (2009) 10094-10103.
10
[15] J. Ni, G. Yu, Q. Guo, Z. Dai, F. Wang, Modeling and comparison of different syngas cooling
13 14 15 16
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types for entrained-flow gasifier, Chem. Eng. Sci. 66 (2011) 448–459
[16] I.-S. Ye, S. Park, C. Ryu, S. K. Park, Flow and heat transfer characteristics in the syngas quench system of a 300 MWe IGCC process, Appl. Therm. Eng. 58 (2013) 11-21.
[17] Shell Oil Company, Process for treating syngas using a gas reversing chamber, US Patent
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US4859214, 1989.
[18] T-H. Shih, W. W. Liou, A. Shabbir, Z. Yang, J. Zhu, A new k-ε eddy-viscosity model for high
17
Reynolds number turbulent flows - model development and validation. Computers Fluids 24 (1995)
18
227–238.
20 21 22
[19] E. H. Chui, G. D. Raithby, Computation of radiant heat transfer on a non-orthogonal mesh using the finite-volume method. Numer. Heat Tranf. B-Fundam. 23 (1993) 269-288.
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[20] T. F. Smith, Z. F. Shen, J. N. Friedman, Evaluation of coefficients for the weighted sum of gray gases model. J Heat Tranf. 104 (1982) 602–608. [21] K. C. Mills, J. M. Rhine, The measurement and estimation of the physical properties of slag
24
formed during coal gasification: 2.properties relevant to heat-transfer, Fuel 68 (1989) 904-910.
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[22] Fluent Inc., Fluent 6.3 user guide. Lebanon, New Hampshire, 2006.
26
[23] F. Casella, P. Colonna, Dynamic modeling of IGCC power plants, Appl. Therm. Eng. 35 (2012)
28 29 30 31 32 33
91-111.
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[24] F. P. Incropera, D. P. Dewitt, T. L. Bergman, A. S. Lavine, Fundamentals of heat and mass transfer. 6th ed., John Wiley & Sons, 2008. [25] J. G. Mbabazi, T. J. Sheer, R. Shandu, A model to predict erosion on mild steel surfaces impacted by boiler fly ash particles, Wear 257 (2004) 612-624. [26] B. E. Lee, C. A. J. Fletcher, M. Behnia, Computational prediction of tube erosion I coal fired power utility boilers, Trans. ASME 121 (1999) 746-750.
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List of Tables
3 4
Table 1. Summary of operating conditions at the inlet of the GRC considered in this study
5
Table 2. Heat transfer rates on the wall and the exit gas temperature in the GRC.
6
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7 8 9
List of Figures
10
Fig. 1. Schematic of the gasification block and GRC in a Shell coal gasification process.
12
Fig. 2. Contours of velocity magnitude and temperature on selected cross-sections for operational
13
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11
loads of 100% and 50%.
Fig. 3. Distribution of gas velocity and flow rate in the evaporator channels.
15
Fig. 4. Contours of wall heat flux for operational loads of 100% and 50%.
16
Fig. 5. Average wall heat flux along the vertical direction.
17
Fig. 6. Curve-fit for Re vs. Nu using the CFD results.
18
Fig. 7. Trajectories of selected particles (color: residence time [sec])
19
Fig. 8. Erosion propensity on the wall for operational loads of 100% and 75%.
20
Fig. A1. Comparison of the wall heat flux between three meshes with different numbers of cells.
21
Fig. A2. The mesh constructed for the GRC (1,493,502 hexahedral cells).
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Table 1. Summary of operating conditions at the inlet of the GRC considered in this study Operation load (%)
50
Flow rate (kg/s) o
75
90
100
67.9
84.8
101.8
113.1
743
761
774
782
55.2
57.2
59.2
59.2
7.2
6.1
5.1
5.1
27.1
28.1
28.5
28.5
10.4
10.4
8.5
7.2
7.2
0.92
1.10
1.37
1.65
1.83
56.6
Average temp. ( C)
726
CO (vol.%)
55.2
CO2 (vol.%)
7.2
H2 (vol.%)
27.1
N2 (vol.%)
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Fly slag flow rate (kg/s)
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Syngas
60
13
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Table 2. Heat transfer rates on the wall and the exit gas temperature in the GRC. 50
60
75
90
100
Total heat transfer rate (MW)
5.05
5.60
6.42
7.18
7.70
Convective heat transfer rate (MW)
3.31
3.73
4.38
5.01
5.47
Exit temperature (oC)
679
701
724
740
749
41.7
37.3
34.1
32.4
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Operation load (%)
46.6
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Temperature drop (oC)
14
ACCEPTED MANUSCRIPT
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Gas Reversal Chamber (GRC)
Syngas Cooler
Quench gas ~250oC
HP Steam
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Quench Pipe
Air Syngas O2
N2 Coal
Milling
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~1550oC
ASU
Gasifier
MP Steam
Gas Cleaning
Slag
Quench gas Clean syngas
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(a) Gasification block
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Gas Reversal Chamber
Support cross
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HP water
HP Evaporator (6 channels of helical coil #1-inner, #6-outer)
Porous jump
Syngas (to a series of evaporators)
(b) Gas reversal chamber (GRC) Fig. 1. Schematic of the gasification block and GRC in a Shell coal gasification process.
15
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(a) Velocity magnitude
(b) Temperature Fig. 2. Contours of velocity magnitude and temperature on selected cross-sections for operational loads of 100% and 50%.
16
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10
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6
4
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Gas velocity (m/s)
8
2
0 1
2
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Load 100% Load 75% Load 50%
3
4
5
6
Evaporator channel #
(a) Gas velocity
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Mass flow rate (kg/s)
20
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5
Load 100% Load 75% Load 50%
0 1
2
3
4
5
6
Evaporator channel #
(b) Mass flow rate Fig. 3. Distribution of gas velocity and flow rate in the evaporator channels.
17
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(a) Load 100%
(b) Load 50%
Fig. 4. Contours of wall heat flux for operational loads of 100% and 50%.
18
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1.0
Load 100% Load 75% Load 50%
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0.6
0.4
0.0
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0.2
Radiation
Normalized Height
0.8
50
100
150
200 2
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Total
Average wall heat flux (kW/m )
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Fig. 5. Average wall heat flux along the vertical direction.
19
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8.6
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8.4
y = 2.112 + 0.435 x (R2=0.986)
ln (Nu)
8.2
7.8
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7.6 13.50
13.75
14.00
14.25
14.50
ln (Re)
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Fig. 6. Curve-fit for Re vs. Nu using the CFD results.
20
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(a) Load 100%
(b) Load 50%
Fig. 7. Trajectories of selected particles (color: residence time [sec])
21
(a) Load 100%
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(b) Load 75%
Fig. 8. Erosion propensity on the wall for operational loads of 100% and 75%.
22
ACCEPTED MANUSCRIPT Gas and Particle Flow Characteristics in the Gas Reversing Chamber of a Syngas Cooler for a 300 MWe IGCC Process Sangbin Parka, In-Soo Yea, Junho Oha, Changkook Ryua*, Ja Hyung Koob a
School of Mechanical Engineering, Sungkyunkwan University, Suwon 440-746, Republic of Korea Coal Conversion System Development Team, Corporate R&D Institute, Doosan Heavy Industries & Construction, Daejeon, 305-811, Republic of Korea *Corresponding author, Tel: +82-31-299-4841, Fax: +82-31-290-5889, E-mail: [email protected]
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GRID SENSITIVITY AND METRIC In order to assess the grid sensitivity, three meshes were constructed using different numbers of cells: coarse (362,457 hexahedral cells), medium fine (769,713 cells) and fine meshes (1,493,502 cells). The simulation for the grid sensitivity test was carried out for the operational load of 100% in Table 1. Instead of using the profiles at the inlet, the average values were prescribed for temperature, velocity, particle concentration and other properties. Fig. S1 shows the distribution of wall heat flux for the three meshes. Compared to the wall heat flux for the fine mesh, the difference in the average value was 3.7% in the coarse mesh. It was reduced to 1.7% in the medium fine mesh, which was satisfactory. For a minimized grid sensitivity, the fine mesh shown in Fig. S2 was adopted for the simulations in this study.
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Fig. S1. Comparison of the wall heat flux between Fig. S2. The mesh constructed for the GRC three meshes with different numbers of cells. (1,493,502 hexahedral cells).
Fig. S3 shows the mesh metric in terms of Jacobian determinant and minimum internal angle for the hexahedral cells in the fine mesh used. The determinants were over 0.82 for 98% of the cells and the lowest value was 0.53, indicating that the mesh was reasonably regular. The minimum internal angle was over 60 o for 90% of the cells while the smallest value was about 24o. Skew cells were found near the joint where the two cylinders of the transfer duct and GRC were connected. In general, a minimum angle greater than 18 o and determinant greater than 0.2 are acceptable for most commercial solvers. [ANSYS, 2008]
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(a) (b) Fig. S3 Mesh quality metric of the fine mesh used: (a) Jacobian determinant and (b) minimum internal angle.
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EFFECTS OF TURBULENCE MODELS Fig. S4 compares the average heat flux on the wall predicted with the realizable k-ϵ model and the shear stress transport (SST) k-ω model. Both models are known to better predict the swirl, circulating or jet flows than the standard models. The two models had the similar trend of heat flux along the GRC wall. Although the heat flux was slightly higher for the SST k-w model in the upper part above the inlet, the difference in the overall heat transfer rate was within 1.2%. Therefore, the use of the realizable k-ϵ model was acceptable for the comparative study of time-averaged trends in flow and heat transfer between different operational cases. 1.0
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Fig. S4.Comparison of heat flux for the realizable k-ϵ and SST k-ω models. References [ANSYS, 2007] ANSYS Inc., ANSYS ICEM CFD 11.0 Tutorial Manual, January 2007, Cannonsburg, PA 15317, USA.