Steam Raising

08 Steam raising (boiler operatiohldesign)

Probability-density function model of turbulent hydrogen flames

01/01772

Hsu. A.T. He, G.-B. Applied Energy, 2000, 67, (l-2), 117-135. Hydrogen combustion Hitracted mich attention recently because of the need for clean alternative energy. For the theoretical/numerical study of hydrogen combustion, there is a need for modelling capabilities for turbulent hydrogen flames. The present work examines the applicability of probability density function (pdf) turbulence models. For the purpose of accurate prediction of turbulent combustion, an algorithm that combines a conventional CFD flow solver with the Monte Carlo simulation of the pdf evolution equation, has been developed. The algorithm is validated using experimental data for a heated turbulent plane jet. A study of Hz-F* diffusion flames has been carried out using this algorithm. Numerical results show that the pdf method is capable of correctly simulating turbulence effects in hydrogen combustion.

Results achieved by the use of renewable energy source with special regard to agriculture. Potentials for state support OllOl773

Bohoczky, F. Energiagardalkodas, 1999, 40, (8) 20-21. (In Hungrian) In a review with no references the importance of biomass production for fuels in Hungary are discussed.

Total costs and benefits of biomass in selected regions of the European Union

01101774

Groscurth, H.-M. er a/. Energy, 2000, 25, (I I), 1081-1095. The paper describes results of the BioCosts project in which a comprehensive analysis of the economic and environmental performance of the energy use of biomass was carried out for selected existing facilities throughout the European Union. It is demonstrated that the appropriately organized use of biofuels has significant environmental advantages compared to the use of fossil fuels. Mitigation of global warming is the largest single incentive to use biofuels. However, only a few technologies are economically competitive under prevailing conditions, while others lead to up to 100% higher energy production costs than fossil fuels. Employment effects of using biofuels are small but positive.

in the literature for this system. The existing models for the production of nitrogen oxides from char-N were also reviewed. A critical analysis of the assumptions made in these models and how they affect the final predictions is presented. Finally, a simplified version of these models was used to perform a parametric analysis evaluating the impact of several parameters on the total conversion of char-N to NO. These parameters include: (1) the rate of NO reduction on the char surface; (2) the rate of carbon oxidation; and (3) early vs. late nitrogen release during the char oxidation process. The results underscore the importance of the reaction of NO reduction on the char surface to the final conversion of char-N to NO.

01101777 Char surface reaction model for pulverized coal combustion Yamamoto, K. et al. Nippon Kikai Gakkai Ronbunshu. B-hen, 1999, 65, (637), 3196-3202. (In Japanese) Experimental and analytical study was performed for surface reaction model that was used for numerical simulation of pulverized coal firing boiler. Combustion efficiency in downstream of premixed flames was examined for a subbituminous coal, two bituminous coals and an anthracite. The influence of SR (stoichiometric ratio), combustion temperature, FR (fuel ratio) and initial particle diameter was examined. Reaction rates of oxidation and gasification? and surface area model of coal char were examined by compartson between experimental and analytical results. The outer surface area was assumed not to be changed during devolatilization, but to be reduced by surface reaction. Effective surface area for reaction was assumed to be decreased when ash content in char was increased. By using this surface area model, comparison of the predicted combustion efficiency with the experimental data showed good agreement for SR 0.5-1.5. Reaction rates were decreased when FR of coal increased. The effect of coal type was significant for gasification reaction. The activation energy of gasification was smaller than the previous study that was obtained without oxygen. The reaction yield by gasification at SR 0.8 was important for numerical simulation of was =lO%, gasification pulverized coal firing boiler. 01101778

Co-firing of asphalt fired dust in pulverized coal

fired boiler

08

STEAM RAISING Boiler operation/design

OlIOl775 A effect of fuel conversion from LSWR to LNG in industrial boiler performance Seo, K.W. Chae, J.O. Nonmunjip - Sanop Kwahak Kiwi Yonguso (Inha Taehakkyo), 1999, 27, 3541.. (In Korean) As regulation of air pollution around the large city becomes stricter, it is necessary that the fuel of the existing industry boiler changed from coal or heavy oil to clean fuel. The combustion characteristics and the efficiency of boiler in the process of fuel conversion from LSWR (low sulphur wax residual) to LNG (liquid natural gas) for the oil boiler are discussed. During the combustion of LNG the heat loss is > 3% due to the increase of the hydrogen contents in the LNG to form HzO. The spray water spent is more than that in the LSWR combustion by a factor of 10, because the amount of the radiation heat transfer is less than that of the convection heat transfer and it caused the over-heating of the superheater and reheater. The boiler efficiency is decreased by 3% and the plant efficiency showed the decrease of 1.26%, due to the increase of the boiler heat loss and the spray water. The boiler vibration is increased due the different combustion characteristics and gas flow pattern.

01101776 Char nitro en conversion: implications to emisslons from coal-8.ued utility boliers Molina, A. et al. Progress in Energy and Combustion Science, 2000, 26, (4-6), 507-53 I. The contribution of nitrogen present in the char on the production of nitrogen oxides during char combustion was analysed. A literature review summarizes the current understanding of the mechanisms that account for the formation of NO and NzO from the nitrogen present in char. The review focused on: (1) the functionalities in which nitrogen is present in the coal and how it evolves during coal devolatilization; (2) the mechanism of nitrogen on the char to the homogeneous phase and its further oxidation to NO; and (3) the reduction of NO on the surface of the char. The critical analysis of these three issues allowed identification of uncertainties and well-founded conclusions observed

Kiga, T. Watanabe, S. FACT (Am. Sec. Mech. Eng.), 1999, I, 95-100. In order to determine whether the dust collected at the electrostatic precipitator (EP) of asphalt fired boilers can be co-fired in pulverized coal fired boilers, laboratory-scale and bench-scale tests were conducted. Test results showed that although dust from asphalt firing had as only a little amount of volatile matter as semi-anthracite or anthracite had, it revealed burn-out properties like bituminous. When it was co-fired with pulverized coal by 2% by heat input, a considerable increase in SOz emission was noted, while NO. emission was somewhat decreased compared with coal firing. From these verifications, the cofiring of dust from asphalt firing in pulverized coal fired boiler was applicable to actural plants so far as the De-SO, system permitted.

01101779 Cofiring biofuel in a PC boiler using direct injection of wood waste Tilfman”, D.A. Battista, J.R. Biomass, Proc. Biomass Konf. Am., 4th. 1999, 2, 1309-1313. Edited by Overend R.P., Chornet E. Power Research Institute (EPRI), the U.S. Department of Energy (USDOE) and ib Federal Energy Technology Center, has developed a demonstration of cofiring at the Seward Generating Station Boiler #12. This demonstration requires construction of a facility to receive, screen, store, and transport the biofuel to the boiler. The facility’s distinctive features include the wood waste receiving system, the silo storage for processed biomass, and the injection system using the centrepipe of the coal burners. The biomass is prepared separately from the coal and transported separately from the coal; however the wood waste is injected into the centre of the coal flame, and burns there for optimum biofuel performance. This demonstration, reflecting two years of cofiring testing, is based upon successful parametric tests conducted in December 1996 and July 1997. These tests documented the effect of cofiring, in the short term, on capacity, efficiency, and emissions. Those results are being evaluated during the long term. Additional, opefational and maintenance issues are being addressed with this demonstration. This paper describes the cofiring system, and it reviews progress to date with preliminary combustion tests.

Combustion of Ekibastuzskii coals at Ekibastuzskii hydropower plant energy blocks 500 MW boilers 01101780

Gordeev, V.V. et al. Teploenergetika (Moscow), 1999, 9, 13-22. (In Russian) The performance of Ekibastuzskii coal fired boilers and various units in the boiler systems is analysed on the basis of operation results. The operation of dust removing system with mills, heaters, combustion characteristics, and NO, emissions are considered. Fuel and Energy Abstracts

May 2601

215

09 Comb&ion

(burners, combustion systems)

01101781 Computational evaluation of low NO, operating conditions in arch-fired boilers Fueyo, N. et al. J. Eng. Gas Turbines Power, 1999, 121, (4), 735-740. In the present paper, a computational model is used to simulate the aerodynamic, thermal, and chemical conditions inside an arch-fired coal boiler. The model is based on the Eulerian-Eulerian concept, in which Eulerian conservation equations are solved both for the gas and the particulate phases. A NO, formation and destruction sub-model is used to calculate the local concentration of NO. The model is used to simulate a range of operating conditions in an actual, 350 MW, archfired boiler, with the aim of reducing, using primary measures, the emissions of NO,. The model results shed some light on the relevant NO.-formation mechanisms under the several operating conditions. Furthermore, they correlate well quantitatively with the available field measurements at the plant, and reproduce satisfactorily the tendencies observed under the different operating modes. State-of-art technology of SCR system for coal fired boiler Nakatani, H.K. et al. FACT (Am. Sot. Mech. Eng.), 1999, 23, 493-496. More than 18 years have passed since the first SCR system for the coal fired plant in the world provided by Mitsubishi was put into commercial operation. During the above period, SCR catalyst has been developed to overcome any difficulties which we experienced, especially because the flue gas contains the large amount of dust compared with gas and oil fired unit. For example, dust plugging, SO2 oxidation rate, pressure loss and erosion have been the main items to be solved. This paper reviews with no references the background of the above items and test result which was conducted before the application to the actual unit to confirm the initial performance and the durability against them. In addition to the above, the efforts to reduce the catalyst volume for coal fired unit by means of the application of smaller pitch catalyst is also presented together with the inspection result of smaller pitch catalyst after the operation. 01101782

01101783 Techno-economic analysis of NO, reduction technologies in p.f. boilers McCahey, S. et al. Fuel, 1999, 78, (14), 1771-1778. The impact of NO, reduction technologies upon a supercritical coal fired p.f. (pulverized fuel) power station has been investigated using Technical, environmental, and the ECLIPSE process simulator. economic assessments were performed, based upon a model of the Amer 9 Power Station at Geertruidenberg, the Netherlands. Selective catalytic reduction (s.c.r.) achieves the largest reduction in NO, emissions, to below 50 mg/N m3, but at an additional electricity cost of 0.21 pence (P)/kWh over the base case. The additional cost for coalover-coal reburning is 0.03 p/kWh, reducing NO, emissions to below 200 mg/N m3. Only high unburnt carbon losses or high-priced reburn coal justify the use of a coal micronizer. Natural gas-over-coal reburning requires an unrealizable natural gas price of f0.98iGJ to compete with coal-over-coal reburning. Gas prices between f1.76/GJ and f1.93/GJ are required for it to compete with s.c.r. Wa and results of optimization of the operation of an OP-430 g oiler in the Potnan Karolin Power Plant for reduction of NO, emission Korzuch, S. et a/. Energetyka, 1999, 53, (7), 337-341. (In Polish) The plant operates two pulverized coal-fired boilers OP-430, 2K and 3K. The boilers are of a tight wall type, each producing 430 t/h steam of 540°C and 13.5 MPa. The primary method deN0, was applied in the boilers, and the modernization was completed in 1997 for the boiler 2K, and, after additional changes, in 1998 for the boiler 3K. During restarting of the boilers optimization of their operation was conducted, including mills, burners and nozzles, and air quantity and its distribution. 01101784

09

COMBUSTION Burners,

combustion

systems

01101785 ‘Heavy’ Species Ludwig-Soret Transport Effects in Air-Breathing Combustion Rosner, D.E. et al. Combustion and Flame, 2000, 123, (4), 547-560. In the combustion community there seems to be a persistent view that Ludwig-Soret (L-S) (thermally driven, non-Fickian) species diffusion will only be important for (011.molecular weight species, such as H and 216

Fuel and Energy Abstracts

May 2001

Hz in HZ/air flames. In the present paper we mobilize and extend some relevant research which, among other things, proves this particular viewpoint to be untrustworthy, replacing it with more robust and readily used criteria tailored to high molecular weight (SC > 1) species. As an immediate corollary of the results presented/discussed here, many previous ‘L-S-free’ theoretical studies of (large of small) ‘Lewis number effects in combustion’ must be re-examined and extended since ‘extreme’ nonunity Lewis number effects and significant L-S transport effects will frequently ‘go together.’ Often, lack of direct experimental information about the relevant thermal d#fuusion ,factor wr, or even complexity of the underlying kinetic theory expressions for aT, are used to ‘justify’ neglecting L-S species transport. To overcome this we suggest and exploit two remarkably simple but rational approximate methods to estimate aT for ‘heavy’ species via the already familiar Schmidt number VA/DB~, in the ideal gas, high temperature limit. We also provide, as a corollary, simple but rational correlations/estimates for anticipating the simultaneous consequences of Fick and LudwigSoret diffusional transport, including appreciable modifications of the recovery factor for mainstream chemical energy in surface-catalysed combustion. Using instructive examples for non-premixed and surfacecatalysed combustion, we demonstrate the importance of L-S transport for heavy fuel vapour species (even the normal paraffins C,,H2,, + z smaller than eicosane (n = 20), as well as for flame intermediates (including soot precursors, such as polycyclic aromatic hydrocarbons (PAHs) up to coronene (C24H12). We conclude that it is not only bona fide soot particles that are appreciably influenced by ‘thermophoresis’ in such laminar diffusion flames - even for coronene we estimate that the dimensionless ‘thermophoretic diffusivity’: a~D~~/v,, is already about 0.47, not far from the particle-limit value of 0.5385. Put another way, in combustion applications the L-S effect, while known to be important for diffusion flames involving H(g) and Hz(g), does not ‘disappear’ for heavier vapours, only to ‘suddenly’ reappear for bona fide nanoparticles (e.g. ‘soot’)! 01101786 A comprehensive biomass combustion model Jones, J.M. et al. Renewable Energy, 1999, 19, (l-2), 229-234. A combustion model for wheat straw is discussed and compared to that of a bituminous coal, Pittsburgh No. 8. The input data into the combustion model for both cases were generated using the FG-DVC (functional group-depolymerization, vaporization, crosslinking) coal devolatilization model, which had been validated in part experimental. The combustion behaviour of the two fuels are investigated using a laminar flow computational fluid dynamics model of a drop-tube furnace. The results indicate that, because of the low calorific nature of the straw volatiles, the combustion takes place at a lower temperature, but with rapid ignition and rapid devolatilization. The straw char is highly microporous with relatively high ash and oxygen contents; consequently, the burnout is quicker than the analogous coal char burnout. 01101787 A multi-fluid model for simulating turbulent gasparticle flow and pulverized coal combustion Guo, Y.C. Chan, C.K. Fuel, 2000, 79, (12), 1467-1476. Based on the pure two-fluid model for turbulent reacting gas-particle flows with combusting pulverized coal particles, a new comprehensive model for pulverized coal combustion was developed by incorporating a modified k-&p model, a general model of pulverized coal devolatilization and a general model of char combustion. Both gasphase and particle-phase conservation equations are described using Eulerian coordinates, and these equations are discretized and integrated in the computational cell. As the first stage of numerical modelling of pulverized coal combustion in the cyclone furnace, threedimensional simulation of turbulent gas combustion and gas-particular flows has been made. The predicted results show that there is a near wall recirculating zone at the bottom of the cyclone furnace, and the recirculating zone enhances ignition and flame stabilization. The predicted tangential velocity distribution of both the gas phase and the particle phase similar to those of the Rankine vortex. 01/01788 Co-firing of coal and straw Overgaard, P. et al. Biomass. Proc. Biomass Cotzf. Am., 4th, 1999, 2, 1299-1305. Edited by Overend R.P., Chornet E. In 1995 Danish utility company MIDTKRAFT converted the 150 MW, pulverized coal-fired Studstrup power station unit 1 into co-firing of coal and straw for technological demonstration purposes. The conversion consisted of establishing a straw per-processing plant with a capacity of 20 tonne/h, corresponding to 20% of the total energy input at full load, and modifying the burner system. After plant commissioning in January 1996, a two-year demonstration programme was initiated. The objective of the programme was to evaluate the influence of co-firing upon boiler plant performance, combustion chemical, heat surface deposits and corrosion, residue quality and emissions. This paper describes the plant conversion and results from the demonstration period. One result from the programme is that the fly ash is not usable in the cement and concrete industry due to a high