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CO2 hydrate cooling system and LCC analysis for energy transportation application
Accepted Manuscript CO2 hydrate cooling system and LCC analysis for energy transportation application Jae Woo Choi, Shol Kim, Yong Tae Kang PII:
S1359-4311(15)00787-5
DOI:
10.1016/j.applthermaleng.2015.07.084
Reference:
ATE 6889
To appear in:
Applied Thermal Engineering
Received Date: 3 June 2015 Revised Date:
20 July 2015
Accepted Date: 21 July 2015
Please cite this article as: J.W. Choi, S. Kim, Y.T. Kang, CO2 hydrate cooling system and LCC analysis for energy transportation application, Applied Thermal Engineering (2015), doi: 10.1016/ j.applthermaleng.2015.07.084. 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.
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transportation application
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CO2 hydrate cooling system and LCC analysis for energy
Jae Woo Choi 1, Shol Kim 1, Yong Tae Kang 1 *
School of Mechanical Engineering, Korea University,
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Anam-dong, Seongbuk-gu, Seoul 136-701, Korea
=================================== (*) Corresponding author. Tel : +82-2-3290-5952 Fax: +82-2-926-9290 e-mail: [email protected]
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Abstract Recently, many researchers have investigated alternative refrigerants in order to replace
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CFC and HCHC refrigerants. One of the alternative refrigerants is CO2 hydrate slurry that has a large latent heat (507 kJ/kg). In this study, we carry out an economic evaluation of the CO2 hydrate cooling system by Life-cycle cost (LCC) analysis technique. LCC consists of the
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key parameters such as initial cost (IC), energy cost (EC) and maintenance cost (MC). Total LCC for a district cooling system (DCS) and CO2 hydrate cooling systems is compared for
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long distance energy transportation application. It is found that the total LCC for the CO2 hydrate cooling system is only a half of that of the DCS based on the cooling capacity of 5000 RT, the transportation distance of 10 km, and the service life of 20 years. It is concluded that the optimum transportation pipe diameters for CO2 hydrate and DCS are 200mm and 400mm,
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respectively, for the present basis conditions. It is also concluded that the effect of the pump power rate of the DCS on the total LCC is 2.5 times higher than that of the CO2 hydrate
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cooling system.
Keywords
CO2 hydrate; Cooling application; Economic assessment; Energy transportation.
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NOMENCLATURE : diameter, 10-3 m
EC
: energy cost, $
f
: friction factor
h
: time, s
i
: interset rate
i*
: actual interest rate, %
IC
: initial investment cost, $
L
: length, km
LCC
: life cycle cost, $
MC
: maintenance cost, $
T
: temperature, oC
t
: time, year
V
: velocity, m s-1
W
: work, kW
: heat transfer rate, kW
m&
P
: pressure, kPa
∆
: pressure drop, kPa
Re
: Reynold’s number
h
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: specific heat, kJ kg-1 oC-1
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Cp
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D
: enthalpy difference, kJ kg-1
: mass flow rate, kg s-1
3
ACCEPTED MANUSCRIPT : temperature difference, oC
T
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: volumetric flow rate, m3 s-1
ρ
: density, kg m-3
μ
: viscosity, kg m-1 s-1
: roughness, mm
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: price escalation rate
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α
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Greek
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1. INTRODUCTION
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The problems of global environmental pollution are getting more and more serious as a result of rapid industrial development [1]. Furthermore, due to the depletion of energy sources, many countries are carrying out policies for efficient energy use such as the
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diversification of energy sources and the development of alternate energy.
As solutions to these problems, the efficiency and diversification of energy sources through
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the use of hybrid heat pumps [2] and absorption refrigerating machines [3-4] are being studied. CFC- and HCFC-based refrigerants destroy the ozone layer when they are leaked to the atmosphere [5]. Therefore, the Montreal Protocol was agreed and entered into force by many countries. At present, the first generation natural refrigerants were revived and
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alternative refrigerants are being actively researched [6-7]. The alternative refrigerants must be environment-friendly while having excellent thermophysical characteristics. In light of this, CO2 hydrate has an advantage due to its characteristic of high latent heat. A recent study
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by Vasilescu and Infante [8] investigated the use of CO2 hydrate slurry as an alternative refrigerant. Hydrates are formed as solid phase by the combination of gas and water
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molecules under a low temperature and high pressure condition. Since 1810 when Sir Humphrey Davy discovered the existence of chlorine hydrate (Cl2․6H2O), over 130 gas molecules including the hydrocarbon gas which is the main component of natural gas have been reported to form the gas hydrates by combining with water molecules [9]. The existence of natural gas hydrates was revealed in a study by Hammerschmidt in 1934, which found that the blocking of a gas transmission line at a higher temperature than the freezing point of water was by the natural gas hydrates created inside the pipe. Natural gas hydrates began to 5
ACCEPTED MANUSCRIPT receive attention after this study. Lately, a technology for artificially producing hydrates was developed and its applications for natural gas hydrates and CO2 hydrates are being researched [10]. For last few decades, interest in the applications of gas hydrates for potential application
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technologies such as the capture, isolation, storage, and transportation of carbon dioxide has been increasing [11]. Salem Jerbi et al. [12] investigated the rheological characteristics of CO2 hydrate slurry to use it as a secondary refrigerant in refrigeration systems. Shi and Zhang
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[13] proposed a cooling system that used TBAB hydrates as a refrigerant and Marinhas et al. [14] conducted a modeling study on the latent heat of CO2 hydrate slurry. These hydrates
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have advantages in that it has no corrosion problem which is a shortcoming of the wet process using amines and no chemical reaction [15]. Furthermore, CO2 hydrates cost less than the CO2 capture method using chemical absorption and are simple to preserve and store due to their self-preservation effect. In addition, unlike the conventional chemical absorption
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method which requires high heat source temperature in the process of separating absorbent and carbon dioxide, hydrates can be easily isolated by a small temperature difference [16]. Whereas the dissociation heat amounts of ice, R11, and R141b are 333 kJ/kg, 334 kJ/kg, and
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344 kJ/kg, respectively, the dissociation heat amount of CO2 hydrate is 501 - 507 kJ/kg [17], this is much higher than the others. Due to this reason, CO2 hydrates can be used as a
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secondary refrigerant [18]. In this study, the economic efficiency of the CO2 hydrate system is assessed and compared with the cost of the conventional district cooling system (DCS). For economic assessment, the life cycle cost (LCC) analysis that calculates the initial investment, energy and maintenance costs for the total lifetime is used. The LCC analysis represents an engineering decision making technique to select the optimal solution that can minimize the total lifecycle cost [19]. In this study, therefore, the costs of the conventional DCS and the CO2 hydrate system are compared through the LCC analysis. Furthermore, the total costs of 6
ACCEPTED MANUSCRIPT the DCS and the CO2 hydrate cooling system for the capacity of 5000 RT, transportation distance of 10 km and operation period of 20 years are analyzed. The sensitivity analysis is also carried out for the pipe diameter, operation period, pump power change rate, and
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transportation distance.
2. TRANSPORATATION METHODS
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Figure 1 shows the concepts of the sensible heat transportation by temperature difference
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and the latent heat transportation by phase change [20]. Fig. 1.(a) illustrates the long-distance transportation of cool water by the conventional sensible heat transportation method. As the sensible heat method uses temperature difference, it requires a high mass flow rate of the chilled water or a high temperature difference in order to achieve a large heat transfer rate. Another disadvantage of this method is the need for expensive insulation materials due to the
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high temperature difference. Fig. 1.(b) shows the latent heat transportation method. The latent heat transportation refers to the use of heat generated from concentration difference or phase
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change for energy transportation but not from the temperature difference. When concentration difference is used, the cost of energy transportation can be minimized because energy can be
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transported at ambient temperature by the concentration difference. Another advantage is that there is no need to consider the thermal heat insulation. In the case of energy transportation using the phase change, a smaller mass flow rate is required compared to the sensible heat method due to the large latent heat capacity. Therefore, the latent heat transportation can achieve a large heat than for rate with a low mass flow rate, and thus save the LCC cost because the pump power rate and pipe diameter can be reduced.
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3. CO2 HYDRATE COOLING SYSTEM
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For an economic assessment of the CO2 hydrate system, it is directly compared with the heat transport system of the DCS that is being operated in South Korea, and the optimum condition which has the lowest LCC is determined.
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Figure 2 shows a schematic of a DCS [21]. The steam turbine is operated by the heat generated from the primary generator using a gas turbine and by the high temperature and
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pressure steam generated from the boiler. The heat energy discharged from the turbines is extracted and used for industrial steam in factories. Large-scale cogeneration plants produce hot water instead of steam, which is supplied for heating to apartment complexes and large buildings. In summer, they supply hot water to operate H2O/LiBr absorption refrigerating
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machines to provide cooling for commercial and business facilities. Figure 3 shows a schematic of the CO2 hydrate cooling system developed in the present study. The methanol absorption and regeneration process can selectively produce highly pure
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CO2 gas from the syngas [22]. The methanol absorption and regeneration process discharges CO2 gas, and this CO2 enters the regenerator to be dissociated from the water, and introduced
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to the hydrate reactor to form the CO2 hydrate. The formed hydrate slurry is sent to the CO2 dissociation unit and CO2 gas is dissociated through the heat exchange with the chilled water around 12 oC which is supplied from the district cooling zone. The chilled water of 12 oC is cooled down to around 7 oC and supplied to the local complex for cooling application. The biggest difference between these two systems is the energy transportation method. As explained in Fig. 1, the DCS uses sensible heat transportation whereas the CO2 hydrate 8
ACCEPTED MANUSCRIPT cooling system uses latent heat transportation method. Therefore, the LCC analysis focuses on the transportation method while other facilities are assumed to be the same conditions. In other words, only the transportation facilities are considered in the economic assessment of
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the DCS and the CO2 hydrate cooling system. The main conditions for the economic assessment of the DCS and the CO2 hydrate cooling system are a cooling capacity of 5000 RT, a transportation distance of 10 km, and an
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operation period of use of 20 years. The basis conditions including the working fluid, mass
each system are summarized in Table 1.
4. LCC ANALYSIS
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A. Analysis period
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flow rate, pipe diameter, pipe type and roughness, pump efficiency, and operation period of
The LCC analysis in this study adopts the prices in October 2014 and the analysis period is set to 20 years which is the standard for thermal power plants based on the corporate tax. The
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construction period for the system is set to 2 years based on the typical construction period in the conventional district energy projects. Therefore, the target period for the LCC analysis is
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set to be from October 2014 until September 2036.
B. Major cost
For operation times of the two systems, around-the-clock operation for 90 days (2160 hours) during the cooling period (from June 15 to September 15) is assumed. The energy equation for 5000 RT is as follows; the heat capacity of the DCS is determined by applying equation (1) for sensible heat, and the heat capacity for the CO2 hydrate cooling system is 9
ACCEPTED MANUSCRIPT determined by applying equation (2) for latent heat = ∆
(1)
= ℎ
(2)
In equation (1), denotes the mass flow rate of the chilled water, the specific heat,
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and ∆ the temperature difference. In equation (2), denotes the mass flow rate of the CO2 hydrate and ℎ the latent heat capacity. The pump work rate is calculated by equation (3). = ∆
(3)
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where, the head loss (∆P) and the friction factor (f) during a turbulent flow can be calculated using equations (4) and (5) below. Furthermore, the Reynolds number (Re)
∆ =
( )
= −2.0 $%& ' *.+ + 345 6
0
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Re =
.-
./
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required for calculating the coefficient of friction can be determined by using equation (6). (4) (5) (6)
Consequently, the total of the pump work rates of the system is as follows: W8,:;:<= = W8 + W8
(7)
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where and denote pump work from each pump.
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For the calculation method, the present value method which converts the prices based on the current value is adopted. The present value method calculates the future cost by converting them to the current values. The reason for using this method is that the two systems have the same lifecycle. Table 2 lists the interest rate, the price escalation rate, and the actual interest rate, which are typically considered for economic assessment. For the interest rate and price escalation rate, the 10 year average values for 2004-2013 published by the National Statistics Office are used [23]. The price escalation rate is also based on the 10
ACCEPTED MANUSCRIPT consumer general price index published by the National Statistics Office [23]. The actual interest rate (i*) considering the price escalation rate(>) is calculated by equation (8). i∗ =
AB
AC
−1
(8)
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Table 3 lists the initial investment, energy, and maintenance costs which comprise the LCC. The initial investment cost (IC) does not need the value conversion because it is a current price, but the energy cost (EC) and maintenance cost (MC), which are paid every year, must
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be calculated by equation (9) [24]. LCC: = IC + ∑::N EC: J1 + i∗ KL: + ∑::N MC: J1 + i∗ KL:
(9)
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All the prices considered in the IC are decided by referring to the Price Reference Table of the Korea Price Information (Dec. 1 to 10, 2014) [25]. Table 4 shows the pump cost that are selected by considering the lift head and flow rate. The pumps have different prices depending on the type and vendor during the pump investigation process. For the water
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flowing in the pipes, $ 0.775 per m3 is applied in accordance with the industrial charging system for water supply [26]. Furthermore, for the energy cost, the industrial power price is
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used by referring to the Price Reference Table (November 21, 2013) of KEPCO [27].
5. LCC ANALYSIS RESULTS
For LCC analysis, the IC, EC, MC, and other costs are added up to determine the total cost and the minimum LCC is selected. Then sensitivity analysis is carried out according to pipe diameter, transportation distance, operation period, and pump power rate.
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ACCEPTED MANUSCRIPT A. Selection of minimum LCC Figures 4 and 5 show the IC, EC, MC, and total LCC analysis results of the CO2 hydrate cooling system and the DCS. The minimum LCC is determined based on the transport pipe diameter because the pipe diameter is the most important parameter for energy transportation
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system, which directly affects IC, EC and MC. For the basis conditions of the cooling capacity of 5000 RT, the transportation distance of 10 km, and the operation period of 20 years, the lowest total LCC of the DCS is estimated about $ 7,351,024 at the pipe diameter of
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400 mm. For the CO2 hydrate cooling system, the lowest total LCC is estimated about
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$ 3,549,253 at the pipe diameter of 200 mm. In particular, the ICs of the DCS and the CO2 hydrate system are $ 4,952,591 and $ 2,573,511, respectively, so the IC of the CO2 hydrate cooling system is lower by $ 2,379,080. This is because the CO2 hydrate system can achieve the same heat capacity with a lower flow rate due to its high latent heat capacity, thus can reduce the pipe diameter which gives a significant effect on the IC. Moreover, the ECs of the
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CO2 hydrate cooling system and the DCS are $ 157,791 and $ 824,344 respectively, so the EC of the CO2 hydrate cooling system is lower by about $ 666,553. As can be seen in Figs. 4 and 5, it is found that EC is the main cost at a smaller pipe
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diameter than the optimum diameters (200mm for CO2 hydrate cooling system and 400mm
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for DCS) while IC becomes the primary cost at a larger pipe diameter than the optimum diameters. This is because the EC including the pump power becomes significant for the smaller pipe diameters while the IC including the materials cost does significant for the larger pipe diameters. Based on the comparisons of Figs. 4 and 5, it is found that the total LCC of the CO2 hydrate cooling system ($ 3,549,235) is about 1/2 times compared to that of the DCS ($ 7,351,024).
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ACCEPTED MANUSCRIPT B. Sensitivity Analysis The LCC analysis has uncertainty because the future costs are predicted [28]. To supplement this problem, a sensitivity analysis is performed. The parametric ranges for
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sensitivity analysis for the pipe diameter, transportation distance, the number of operation years, pump power rate, and actual interest rate are listed in Table 5. Typically, the operation period for district cooling system ranges 15-20 years depending on the transportation distance. The operation period was selected 5, 10, 15 and 20 for long distance energy transportation in
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the present study. The range of pipe diameter was selected based on the optimum pipe
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diameter. Typically, the energy transportation distance ranges 10-50 km, and a huge pump is placed every 10 km for DCS. This is why the transportation distance was selected 10, 20, 30, 40 and 50 km in the present study. As for the pumping power change rate, the reference performance of the pump was set 0%, and the sensitivity analysis was performed for every 5% change between -15% and +15%. The actual interest change rate depends on unexpected
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accidents such as the oil price change and it actually changes within ±3%. Figure 6a shows the total LCC variations for each pipe diameter. The LCC analysis results
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show that the total LCC of the CO2 hydrate cooling system decreases until the pipe diameter of 200 mm before rising again. The total LCC at the pipe diameter of 400 mm become higher
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than that at 100 mm. In the case of DCS, the total LCC decreases until the pipe diameter of 400 mm and it rises again. The total LCC of the DCS becomes lower than that of the CO2 hydrate cooling system from the pipe diameter of 400 mm. This can be explained by two reasons. The first reason is that the CO2 hydrate cooling system has a higher IC at the same diameter condition because it uses carbon steel pipes for pressure service and therefore the IC of CO2 hydrate cooling system increases significantly with increasing the pipe diameter as shown in Fig. 4. The second reason is that the EC of the DHCS sharply decreases from 13
ACCEPTED MANUSCRIPT 300mm because the pressure drop decreases significantly with increasing the pipe diameter. Therefore, it is concluded that the optimum transportation pipe diameters for CO2 hydrate and DCS are 200 mm and 400 mm, respectively, for the present basis conditions summarized in
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Table 1. Figure 6b shows the total LCC as a function of the operation period. The total LCC of the CO2 hydrate cooling system increases by about $ 213,210 whenever the number of used years
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increases by 5 years, whereas that of the DHCS increases by about $ 632,860. Therefore, the total LCC difference between two systems gradually increases as the operation period
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becomes longer.
Figure 6c shows the total LCC as a function of transportation distance. It is found that whenever the transportation distance increases by 10 km, the total LCC increases by $ 7,240,000 for the DCS and $ 3,495,660 for the CO2 hydrate cooling system. This is because
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the IC, MC, and EC increase as the transportation distance increases, resulting in a higher total LCC of the DCS. For this reason, the total LCC difference between two systems sharply
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increases as the transportation distance becomes longer. Figure 7a shows the LCC variations as a function of pump power change rate for the CO2
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hydrate cooling system. It is found that 5% change of the pump power rate changes the cost by about $ 7,889, which is only about 0.22% of the total LCC of the CO2 hydrate cooling system. Therefore, it could be concluded that the effect of the pump power rate on the total LCC is not significant.
Figure 7b shows the LCC variations as a function of pump power change rate for the DCS. In the case of the DCS, 5% change of the pump power rate changes the cost by about
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ACCEPTED MANUSCRIPT $ 41,217, which is also only about 0.56% of the total LCC. Therefore it is concluded that the effect of the pump power rate of the DCS on the total LCC is 2.5 times higher than that of the CO2 hydrate cooling system even though it does not affect the total LCC significantly.
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Figure 8 shows the total LCC variation as a function of actual interest change rate. The price escalation rate and the interest rate change when the unpredictable market situations occur such as the sudden change in the international oil price or other fluctuations in the
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global market. Therefore, a sensitivity analysis for the actual interest rate could reduce the uncertainty in the LCC. The sensitivity analysis results show that when the interest rate
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changes by 1%, the total LCCs of the DCS and the CO2 hydrate cooling system are affected by 5.83% and 4.9%, respectively. The reason for this is that the EC and MC, which are paid every year, are affected by the actual interest rate. Furthermore, there is an uncertainty in the selection of pump when the IC is estimated. However, the percentages of pump cost in the
impact on the total LCC. 6. CONCLUSIONS
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LCC of the two systems are only 0.44% and 0.58%, respectively, which do not have much
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From the LCC analysis of the DCS using sensible heat transportation method and the CO2 hydrate cooling system using the latent heat transportation method, the following conclusions
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are drawn.
1) The CO2 hydrate cooling system is an economic alternative solution to the conventional DCS. It is found that the total LCC for the CO2 hydrate cooling system is only a half of that of the DCS based on the cooling capacity of 5000 RT, the transportation distance of 10 km, and the service life of 20 years. 2) It is found that the energy transportation of the latent heat method (CO2 hydrae cooling 15
ACCEPTED MANUSCRIPT system) can save the energy cost by about $ 666,553 compared to the sensible heat method (DCS). 3) It is found that EC is the main cost at a smaller pipe diameter than the optimum
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diameters while IC becomes the primary cost at a larger pipe diameter than the optimum diameters.
4) It is concluded that the optimum transportation pipe diameters for CO2 hydrate and
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DHCS are 200mm and 400mm, respectively, for the present basis conditions.
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5) It is concluded that the effect of the pump power rate of the DCS on the total LCC is 2.5 times higher than that of the CO2 hydrate cooling system.
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ACKNOWLEGEMENT
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This work was supported by the Korea CCS R&D Center (KCRC) grant funded by the Korea government (Ministry of Science, ICT & Future planning) (No.NRF-2014M1A8A1049304).
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(2004) 63-70.
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Fig. 1. Types of heat transportation
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Fig. 2. Schematic diagram of the district cooling system (DCS)
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Fig. 3. Schematic diagram of the CO2 hydrate cooling system
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LCC IC MC EC
10000
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6000 4000 2000 0 200
300
400
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100
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3
Cost [10 $]
8000
500
Diameter [mm]
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Fig. 4. LCC of the CO2 hydrate cooling system vs. pipe diameter
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LCC IC MC EC
30000
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20000
3
Cost [10 $]
25000
15000
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10000 5000 200
300
400
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Diameter [mm]
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Fig. 5. LCC of the DCS vs. pipe diameter
25
500
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30000
Hydrate system DCS system
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20000 15000 10000 5000 100
200
300
400
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0
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3
Total cost [10 $]
25000
500
Diameter [mm]
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Fig. 6a. Total LCC variations for each pipe diameters
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Hydrate system DCS system
7000
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3
Total cost [10 $]
6000 5000 4000
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3000 2000 10
15
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5
20
Period [year]
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Fig. 6b. Total LCC as a function of operation period
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Hydrate system DCS system
35000
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25000
3
Total cost [10 $]
30000
20000 15000
5000 20
30
40
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10
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10000
50
Distance [km]
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Fig. 6c. Total LCC as a function of transportation distance
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3500 3000
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3
Cost [10 $]
2500 LCC IC MC EC
2000 1500
500 -15
-10
-5
0
5
10
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0
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1000
15
Power power change rate [%]
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Fig. 7a. LCC variations as a function of pump power change rate for the CO2 hydrate cooling system
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7000 6000
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3
Cost [10 $]
5000
LCC IC MC EC
4000 3000
1000 -15
-10
-5
0
5
10
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0
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2000
15
Power power change rate [%]
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Fig. 7b. LCC variations as a function of pump power change rate for DCS.
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8000
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6000 5000 4000 3000
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3
Total cost [10 $]
7000
Hydrate system DCS system
2000 -2
-1
0
1
2
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-3
3
Actual interest change rate [%]
AC C
EP
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Fig. 8. Total LCC variations as a function of actual interest change rate
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ACCEPTED MANUSCRIPT List of figure captions
Types of heat transportation
Fig. 2.
Schematic diagram of the district cooling system (DCS)
Fig. 3.
Schematic diagram of the CO2 hydrate cooling system
Fig. 4.
LCC of the CO2 hydrate cooling system vs. tube diameter
Fig. 5.
LCC of the DCS vs. pipe diameter
Fig. 6a.
Total LCC as a function of pipe diameters
Fig. 6b.
Total LCC as a function of operation period
Fig. 6c.
Total LCC as a function of transportation distance
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Fig. 1.
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Fig. 7a. LCC variations as a function of pump power change rate for the CO2 hydrate cooling system.
Fig. 7b.
LCC variations as a function of pump power change rate for the DCS.
Fig. 8. LCC variations as a function of actual interest change rate
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List of Tables
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Table 1 Basis conditions
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Table 2 Life cycle cost factors
Table 4 Pump cost of both systems
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Table 3 Life cycle cost components
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Table 5 Parametric ranges for sensitivity analysis
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Table 1 Basis conditions DCS
Working fluid
How water
Hydrate slurry
Mass flow rate [kg/s]
207.8
37.2
Diameter [mm]
400
Type of pipe
Insulation pipe
Roughness [mm] Period [years]
Carbon steel pipe
85
85
0.046
0.046
20
5000
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Capacity [RT]
200
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Efficiency of pump[%]
Hydrate
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Items
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Transportation length [km]
34
10
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Table 2 Life cycle cost factors 2004-2013
Interest rate(i)
4.1 %
Price escalation(>)
2.91 %
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Investigation period
Actual Interest rate(i*)
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EP
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1.15 %
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Table 3 Life cycle cost components Life cycle cost components Labor cost, pump, Solution, Pipe, Insulation, Storage Tank
Energy cost (EC)
Pump power rate
Maintenance cost (MC)
2% of equipment cost [24]
AC C
EP
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Initial installation cost (IC)
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Table 4 Pump cost of both systems [25]
Number of pumps[EA]
2
Cost[$]/EA
21741
CO2 hydrate
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DCS
2
7858
AC C
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System
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Table 5 Parametric ranges for sensitivity analysis
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Sensitivity parameters 5, 10, 15, 20
Diameter[mm]
100, 200 ,300, 400, 500
Distance[km]
10, 20, 30, 40, 50
Pump power change rate[%]
-15, -10, -5, 0, 5, 10, 15
Actual interest change rate[%]
-3, -2, -1, 0, 1, 2, 3
AC C
EP
TE D
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Period[years]
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Highlights
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1. The CO2 hydrate system is an economic alternative solution to the conventional DCS. 2. The optimum pipe diameters for CO2 hydrate and DCS are 200 and 400mm, respectively. 3. The pump power rate of the DCS is 2.5 times higher than that of CO2 hydrate system.
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4. Total LCC for CO2 hydrate cooling system is only a half of that for the DCS.
S1359-4311(15)00787-5
DOI:
10.1016/j.applthermaleng.2015.07.084
Reference:
ATE 6889
To appear in:
Applied Thermal Engineering
Received Date: 3 June 2015 Revised Date:
20 July 2015
Accepted Date: 21 July 2015
Please cite this article as: J.W. Choi, S. Kim, Y.T. Kang, CO2 hydrate cooling system and LCC analysis for energy transportation application, Applied Thermal Engineering (2015), doi: 10.1016/ j.applthermaleng.2015.07.084. 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
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transportation application
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CO2 hydrate cooling system and LCC analysis for energy
Jae Woo Choi 1, Shol Kim 1, Yong Tae Kang 1 *
School of Mechanical Engineering, Korea University,
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1
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Anam-dong, Seongbuk-gu, Seoul 136-701, Korea
=================================== (*) Corresponding author. Tel : +82-2-3290-5952 Fax: +82-2-926-9290 e-mail: [email protected]
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Abstract Recently, many researchers have investigated alternative refrigerants in order to replace
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CFC and HCHC refrigerants. One of the alternative refrigerants is CO2 hydrate slurry that has a large latent heat (507 kJ/kg). In this study, we carry out an economic evaluation of the CO2 hydrate cooling system by Life-cycle cost (LCC) analysis technique. LCC consists of the
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key parameters such as initial cost (IC), energy cost (EC) and maintenance cost (MC). Total LCC for a district cooling system (DCS) and CO2 hydrate cooling systems is compared for
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long distance energy transportation application. It is found that the total LCC for the CO2 hydrate cooling system is only a half of that of the DCS based on the cooling capacity of 5000 RT, the transportation distance of 10 km, and the service life of 20 years. It is concluded that the optimum transportation pipe diameters for CO2 hydrate and DCS are 200mm and 400mm,
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respectively, for the present basis conditions. It is also concluded that the effect of the pump power rate of the DCS on the total LCC is 2.5 times higher than that of the CO2 hydrate
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cooling system.
Keywords
CO2 hydrate; Cooling application; Economic assessment; Energy transportation.
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NOMENCLATURE : diameter, 10-3 m
EC
: energy cost, $
f
: friction factor
h
: time, s
i
: interset rate
i*
: actual interest rate, %
IC
: initial investment cost, $
L
: length, km
LCC
: life cycle cost, $
MC
: maintenance cost, $
T
: temperature, oC
t
: time, year
V
: velocity, m s-1
W
: work, kW
: heat transfer rate, kW
m&
P
: pressure, kPa
∆
: pressure drop, kPa
Re
: Reynold’s number
h
SC M AN U
TE D
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: specific heat, kJ kg-1 oC-1
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Cp
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D
: enthalpy difference, kJ kg-1
: mass flow rate, kg s-1
3
ACCEPTED MANUSCRIPT : temperature difference, oC
T
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: volumetric flow rate, m3 s-1
ρ
: density, kg m-3
μ
: viscosity, kg m-1 s-1
: roughness, mm
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: price escalation rate
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α
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Greek
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1. INTRODUCTION
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The problems of global environmental pollution are getting more and more serious as a result of rapid industrial development [1]. Furthermore, due to the depletion of energy sources, many countries are carrying out policies for efficient energy use such as the
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diversification of energy sources and the development of alternate energy.
As solutions to these problems, the efficiency and diversification of energy sources through
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the use of hybrid heat pumps [2] and absorption refrigerating machines [3-4] are being studied. CFC- and HCFC-based refrigerants destroy the ozone layer when they are leaked to the atmosphere [5]. Therefore, the Montreal Protocol was agreed and entered into force by many countries. At present, the first generation natural refrigerants were revived and
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alternative refrigerants are being actively researched [6-7]. The alternative refrigerants must be environment-friendly while having excellent thermophysical characteristics. In light of this, CO2 hydrate has an advantage due to its characteristic of high latent heat. A recent study
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by Vasilescu and Infante [8] investigated the use of CO2 hydrate slurry as an alternative refrigerant. Hydrates are formed as solid phase by the combination of gas and water
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molecules under a low temperature and high pressure condition. Since 1810 when Sir Humphrey Davy discovered the existence of chlorine hydrate (Cl2․6H2O), over 130 gas molecules including the hydrocarbon gas which is the main component of natural gas have been reported to form the gas hydrates by combining with water molecules [9]. The existence of natural gas hydrates was revealed in a study by Hammerschmidt in 1934, which found that the blocking of a gas transmission line at a higher temperature than the freezing point of water was by the natural gas hydrates created inside the pipe. Natural gas hydrates began to 5
ACCEPTED MANUSCRIPT receive attention after this study. Lately, a technology for artificially producing hydrates was developed and its applications for natural gas hydrates and CO2 hydrates are being researched [10]. For last few decades, interest in the applications of gas hydrates for potential application
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technologies such as the capture, isolation, storage, and transportation of carbon dioxide has been increasing [11]. Salem Jerbi et al. [12] investigated the rheological characteristics of CO2 hydrate slurry to use it as a secondary refrigerant in refrigeration systems. Shi and Zhang
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[13] proposed a cooling system that used TBAB hydrates as a refrigerant and Marinhas et al. [14] conducted a modeling study on the latent heat of CO2 hydrate slurry. These hydrates
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have advantages in that it has no corrosion problem which is a shortcoming of the wet process using amines and no chemical reaction [15]. Furthermore, CO2 hydrates cost less than the CO2 capture method using chemical absorption and are simple to preserve and store due to their self-preservation effect. In addition, unlike the conventional chemical absorption
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method which requires high heat source temperature in the process of separating absorbent and carbon dioxide, hydrates can be easily isolated by a small temperature difference [16]. Whereas the dissociation heat amounts of ice, R11, and R141b are 333 kJ/kg, 334 kJ/kg, and
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344 kJ/kg, respectively, the dissociation heat amount of CO2 hydrate is 501 - 507 kJ/kg [17], this is much higher than the others. Due to this reason, CO2 hydrates can be used as a
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secondary refrigerant [18]. In this study, the economic efficiency of the CO2 hydrate system is assessed and compared with the cost of the conventional district cooling system (DCS). For economic assessment, the life cycle cost (LCC) analysis that calculates the initial investment, energy and maintenance costs for the total lifetime is used. The LCC analysis represents an engineering decision making technique to select the optimal solution that can minimize the total lifecycle cost [19]. In this study, therefore, the costs of the conventional DCS and the CO2 hydrate system are compared through the LCC analysis. Furthermore, the total costs of 6
ACCEPTED MANUSCRIPT the DCS and the CO2 hydrate cooling system for the capacity of 5000 RT, transportation distance of 10 km and operation period of 20 years are analyzed. The sensitivity analysis is also carried out for the pipe diameter, operation period, pump power change rate, and
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transportation distance.
2. TRANSPORATATION METHODS
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Figure 1 shows the concepts of the sensible heat transportation by temperature difference
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and the latent heat transportation by phase change [20]. Fig. 1.(a) illustrates the long-distance transportation of cool water by the conventional sensible heat transportation method. As the sensible heat method uses temperature difference, it requires a high mass flow rate of the chilled water or a high temperature difference in order to achieve a large heat transfer rate. Another disadvantage of this method is the need for expensive insulation materials due to the
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high temperature difference. Fig. 1.(b) shows the latent heat transportation method. The latent heat transportation refers to the use of heat generated from concentration difference or phase
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change for energy transportation but not from the temperature difference. When concentration difference is used, the cost of energy transportation can be minimized because energy can be
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transported at ambient temperature by the concentration difference. Another advantage is that there is no need to consider the thermal heat insulation. In the case of energy transportation using the phase change, a smaller mass flow rate is required compared to the sensible heat method due to the large latent heat capacity. Therefore, the latent heat transportation can achieve a large heat than for rate with a low mass flow rate, and thus save the LCC cost because the pump power rate and pipe diameter can be reduced.
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3. CO2 HYDRATE COOLING SYSTEM
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For an economic assessment of the CO2 hydrate system, it is directly compared with the heat transport system of the DCS that is being operated in South Korea, and the optimum condition which has the lowest LCC is determined.
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Figure 2 shows a schematic of a DCS [21]. The steam turbine is operated by the heat generated from the primary generator using a gas turbine and by the high temperature and
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pressure steam generated from the boiler. The heat energy discharged from the turbines is extracted and used for industrial steam in factories. Large-scale cogeneration plants produce hot water instead of steam, which is supplied for heating to apartment complexes and large buildings. In summer, they supply hot water to operate H2O/LiBr absorption refrigerating
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machines to provide cooling for commercial and business facilities. Figure 3 shows a schematic of the CO2 hydrate cooling system developed in the present study. The methanol absorption and regeneration process can selectively produce highly pure
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CO2 gas from the syngas [22]. The methanol absorption and regeneration process discharges CO2 gas, and this CO2 enters the regenerator to be dissociated from the water, and introduced
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to the hydrate reactor to form the CO2 hydrate. The formed hydrate slurry is sent to the CO2 dissociation unit and CO2 gas is dissociated through the heat exchange with the chilled water around 12 oC which is supplied from the district cooling zone. The chilled water of 12 oC is cooled down to around 7 oC and supplied to the local complex for cooling application. The biggest difference between these two systems is the energy transportation method. As explained in Fig. 1, the DCS uses sensible heat transportation whereas the CO2 hydrate 8
ACCEPTED MANUSCRIPT cooling system uses latent heat transportation method. Therefore, the LCC analysis focuses on the transportation method while other facilities are assumed to be the same conditions. In other words, only the transportation facilities are considered in the economic assessment of
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the DCS and the CO2 hydrate cooling system. The main conditions for the economic assessment of the DCS and the CO2 hydrate cooling system are a cooling capacity of 5000 RT, a transportation distance of 10 km, and an
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operation period of use of 20 years. The basis conditions including the working fluid, mass
each system are summarized in Table 1.
4. LCC ANALYSIS
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A. Analysis period
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flow rate, pipe diameter, pipe type and roughness, pump efficiency, and operation period of
The LCC analysis in this study adopts the prices in October 2014 and the analysis period is set to 20 years which is the standard for thermal power plants based on the corporate tax. The
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construction period for the system is set to 2 years based on the typical construction period in the conventional district energy projects. Therefore, the target period for the LCC analysis is
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set to be from October 2014 until September 2036.
B. Major cost
For operation times of the two systems, around-the-clock operation for 90 days (2160 hours) during the cooling period (from June 15 to September 15) is assumed. The energy equation for 5000 RT is as follows; the heat capacity of the DCS is determined by applying equation (1) for sensible heat, and the heat capacity for the CO2 hydrate cooling system is 9
ACCEPTED MANUSCRIPT determined by applying equation (2) for latent heat = ∆
(1)
= ℎ
(2)
In equation (1), denotes the mass flow rate of the chilled water, the specific heat,
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and ∆ the temperature difference. In equation (2), denotes the mass flow rate of the CO2 hydrate and ℎ the latent heat capacity. The pump work rate is calculated by equation (3). = ∆
(3)
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where, the head loss (∆P) and the friction factor (f) during a turbulent flow can be calculated using equations (4) and (5) below. Furthermore, the Reynolds number (Re)
∆ =
( )
= −2.0 $%& ' *.+ + 345 6
0
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Re =
.-
./
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required for calculating the coefficient of friction can be determined by using equation (6). (4) (5) (6)
Consequently, the total of the pump work rates of the system is as follows: W8,:;:<= = W8 + W8
(7)
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where and denote pump work from each pump.
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For the calculation method, the present value method which converts the prices based on the current value is adopted. The present value method calculates the future cost by converting them to the current values. The reason for using this method is that the two systems have the same lifecycle. Table 2 lists the interest rate, the price escalation rate, and the actual interest rate, which are typically considered for economic assessment. For the interest rate and price escalation rate, the 10 year average values for 2004-2013 published by the National Statistics Office are used [23]. The price escalation rate is also based on the 10
ACCEPTED MANUSCRIPT consumer general price index published by the National Statistics Office [23]. The actual interest rate (i*) considering the price escalation rate(>) is calculated by equation (8). i∗ =
AB
AC
−1
(8)
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Table 3 lists the initial investment, energy, and maintenance costs which comprise the LCC. The initial investment cost (IC) does not need the value conversion because it is a current price, but the energy cost (EC) and maintenance cost (MC), which are paid every year, must
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be calculated by equation (9) [24]. LCC: = IC + ∑::N EC: J1 + i∗ KL: + ∑::N MC: J1 + i∗ KL:
(9)
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All the prices considered in the IC are decided by referring to the Price Reference Table of the Korea Price Information (Dec. 1 to 10, 2014) [25]. Table 4 shows the pump cost that are selected by considering the lift head and flow rate. The pumps have different prices depending on the type and vendor during the pump investigation process. For the water
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flowing in the pipes, $ 0.775 per m3 is applied in accordance with the industrial charging system for water supply [26]. Furthermore, for the energy cost, the industrial power price is
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used by referring to the Price Reference Table (November 21, 2013) of KEPCO [27].
5. LCC ANALYSIS RESULTS
For LCC analysis, the IC, EC, MC, and other costs are added up to determine the total cost and the minimum LCC is selected. Then sensitivity analysis is carried out according to pipe diameter, transportation distance, operation period, and pump power rate.
11
ACCEPTED MANUSCRIPT A. Selection of minimum LCC Figures 4 and 5 show the IC, EC, MC, and total LCC analysis results of the CO2 hydrate cooling system and the DCS. The minimum LCC is determined based on the transport pipe diameter because the pipe diameter is the most important parameter for energy transportation
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system, which directly affects IC, EC and MC. For the basis conditions of the cooling capacity of 5000 RT, the transportation distance of 10 km, and the operation period of 20 years, the lowest total LCC of the DCS is estimated about $ 7,351,024 at the pipe diameter of
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400 mm. For the CO2 hydrate cooling system, the lowest total LCC is estimated about
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$ 3,549,253 at the pipe diameter of 200 mm. In particular, the ICs of the DCS and the CO2 hydrate system are $ 4,952,591 and $ 2,573,511, respectively, so the IC of the CO2 hydrate cooling system is lower by $ 2,379,080. This is because the CO2 hydrate system can achieve the same heat capacity with a lower flow rate due to its high latent heat capacity, thus can reduce the pipe diameter which gives a significant effect on the IC. Moreover, the ECs of the
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CO2 hydrate cooling system and the DCS are $ 157,791 and $ 824,344 respectively, so the EC of the CO2 hydrate cooling system is lower by about $ 666,553. As can be seen in Figs. 4 and 5, it is found that EC is the main cost at a smaller pipe
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diameter than the optimum diameters (200mm for CO2 hydrate cooling system and 400mm
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for DCS) while IC becomes the primary cost at a larger pipe diameter than the optimum diameters. This is because the EC including the pump power becomes significant for the smaller pipe diameters while the IC including the materials cost does significant for the larger pipe diameters. Based on the comparisons of Figs. 4 and 5, it is found that the total LCC of the CO2 hydrate cooling system ($ 3,549,235) is about 1/2 times compared to that of the DCS ($ 7,351,024).
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ACCEPTED MANUSCRIPT B. Sensitivity Analysis The LCC analysis has uncertainty because the future costs are predicted [28]. To supplement this problem, a sensitivity analysis is performed. The parametric ranges for
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sensitivity analysis for the pipe diameter, transportation distance, the number of operation years, pump power rate, and actual interest rate are listed in Table 5. Typically, the operation period for district cooling system ranges 15-20 years depending on the transportation distance. The operation period was selected 5, 10, 15 and 20 for long distance energy transportation in
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the present study. The range of pipe diameter was selected based on the optimum pipe
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diameter. Typically, the energy transportation distance ranges 10-50 km, and a huge pump is placed every 10 km for DCS. This is why the transportation distance was selected 10, 20, 30, 40 and 50 km in the present study. As for the pumping power change rate, the reference performance of the pump was set 0%, and the sensitivity analysis was performed for every 5% change between -15% and +15%. The actual interest change rate depends on unexpected
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accidents such as the oil price change and it actually changes within ±3%. Figure 6a shows the total LCC variations for each pipe diameter. The LCC analysis results
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show that the total LCC of the CO2 hydrate cooling system decreases until the pipe diameter of 200 mm before rising again. The total LCC at the pipe diameter of 400 mm become higher
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than that at 100 mm. In the case of DCS, the total LCC decreases until the pipe diameter of 400 mm and it rises again. The total LCC of the DCS becomes lower than that of the CO2 hydrate cooling system from the pipe diameter of 400 mm. This can be explained by two reasons. The first reason is that the CO2 hydrate cooling system has a higher IC at the same diameter condition because it uses carbon steel pipes for pressure service and therefore the IC of CO2 hydrate cooling system increases significantly with increasing the pipe diameter as shown in Fig. 4. The second reason is that the EC of the DHCS sharply decreases from 13
ACCEPTED MANUSCRIPT 300mm because the pressure drop decreases significantly with increasing the pipe diameter. Therefore, it is concluded that the optimum transportation pipe diameters for CO2 hydrate and DCS are 200 mm and 400 mm, respectively, for the present basis conditions summarized in
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Table 1. Figure 6b shows the total LCC as a function of the operation period. The total LCC of the CO2 hydrate cooling system increases by about $ 213,210 whenever the number of used years
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increases by 5 years, whereas that of the DHCS increases by about $ 632,860. Therefore, the total LCC difference between two systems gradually increases as the operation period
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becomes longer.
Figure 6c shows the total LCC as a function of transportation distance. It is found that whenever the transportation distance increases by 10 km, the total LCC increases by $ 7,240,000 for the DCS and $ 3,495,660 for the CO2 hydrate cooling system. This is because
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the IC, MC, and EC increase as the transportation distance increases, resulting in a higher total LCC of the DCS. For this reason, the total LCC difference between two systems sharply
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increases as the transportation distance becomes longer. Figure 7a shows the LCC variations as a function of pump power change rate for the CO2
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hydrate cooling system. It is found that 5% change of the pump power rate changes the cost by about $ 7,889, which is only about 0.22% of the total LCC of the CO2 hydrate cooling system. Therefore, it could be concluded that the effect of the pump power rate on the total LCC is not significant.
Figure 7b shows the LCC variations as a function of pump power change rate for the DCS. In the case of the DCS, 5% change of the pump power rate changes the cost by about
14
ACCEPTED MANUSCRIPT $ 41,217, which is also only about 0.56% of the total LCC. Therefore it is concluded that the effect of the pump power rate of the DCS on the total LCC is 2.5 times higher than that of the CO2 hydrate cooling system even though it does not affect the total LCC significantly.
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Figure 8 shows the total LCC variation as a function of actual interest change rate. The price escalation rate and the interest rate change when the unpredictable market situations occur such as the sudden change in the international oil price or other fluctuations in the
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global market. Therefore, a sensitivity analysis for the actual interest rate could reduce the uncertainty in the LCC. The sensitivity analysis results show that when the interest rate
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changes by 1%, the total LCCs of the DCS and the CO2 hydrate cooling system are affected by 5.83% and 4.9%, respectively. The reason for this is that the EC and MC, which are paid every year, are affected by the actual interest rate. Furthermore, there is an uncertainty in the selection of pump when the IC is estimated. However, the percentages of pump cost in the
impact on the total LCC. 6. CONCLUSIONS
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LCC of the two systems are only 0.44% and 0.58%, respectively, which do not have much
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From the LCC analysis of the DCS using sensible heat transportation method and the CO2 hydrate cooling system using the latent heat transportation method, the following conclusions
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are drawn.
1) The CO2 hydrate cooling system is an economic alternative solution to the conventional DCS. It is found that the total LCC for the CO2 hydrate cooling system is only a half of that of the DCS based on the cooling capacity of 5000 RT, the transportation distance of 10 km, and the service life of 20 years. 2) It is found that the energy transportation of the latent heat method (CO2 hydrae cooling 15
ACCEPTED MANUSCRIPT system) can save the energy cost by about $ 666,553 compared to the sensible heat method (DCS). 3) It is found that EC is the main cost at a smaller pipe diameter than the optimum
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diameters while IC becomes the primary cost at a larger pipe diameter than the optimum diameters.
4) It is concluded that the optimum transportation pipe diameters for CO2 hydrate and
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DHCS are 200mm and 400mm, respectively, for the present basis conditions.
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5) It is concluded that the effect of the pump power rate of the DCS on the total LCC is 2.5 times higher than that of the CO2 hydrate cooling system.
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ACKNOWLEGEMENT
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This work was supported by the Korea CCS R&D Center (KCRC) grant funded by the Korea government (Ministry of Science, ICT & Future planning) (No.NRF-2014M1A8A1049304).
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[6] W.F. Stoecker, J.W. Jones, Refrigeration & Air Conditioning, international edition, 2th ed,
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Mcgraw hill, 1983.
[7] K. Chopra, V. Sahni, R.S. Mishra, Thermodynamic analyses of multiple evaporators vapor compression refrigeration systems with R410A, R290, R1234YF, R502, R404A, R152A and R134A, Int. J. Air-Cond. Ref.22 (2014) 1450003. [8] C. Vasilescu, F.C. Infante, Experimental study of semi-clathrate hydrate slurry in a coil heat exchanger, 4th IIR conference on thermophysical properties and transfer processes of refrigerants, 2013, Paper No. TP-026 17
ACCEPTED MANUSCRIPT [9] Sloan E, Clathrate hydrates of natural gases, 3th rd, chemical industries;2007(1). [10] E.G. Hammerschmidt, Formation of gas hydrates in natural gas transmission lines, Ind Eng Chem. 26 (1934) 851-5.
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[11] H.P. Veluswamy, P. Linga, Macroscopic kinetics of hydrate formation of mixed hydrates of hydrogen/tetrahydrofuran for hydrogen storage, Int J Hydrogen Energ. 38 (2013) 4587-96.
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[12] S. Jerbi, A. Delahaye, J. Oignet, L. Fournaison, P. Haberschill, Rheological properties of CO2 hydrate slurry produced in a stirred tank reactor and a secondary refrigeration loop, Int J
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Refrig. 36 (2013) 1294-301.
[13] X.J. Shi, P. Zhang, A comparative study of different methods for the generation of tetran-butyl ammonium bromide clathrate hydrate slurry in a cold storage air-conditioning system, Appl Energ. 112 (2013) 1393-402.
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[14] S. Marinhas, A. Delahaye, L. Fournaison, D. Dalmazzone, W. Furst, J.P. Petitet, Modelling of the available latent heat of a CO2 hydrate slurry in an experimental loop applied
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to secondary refrigeration, Chem Eng Process. 45 (2006) 184-92. [15] H.P. Veluswamy, R. Kumar, P. Linga, Hydrogen storage in clathrate hydrates: Current
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state of the art and future directions, Appl Energ. 122 (2014) 112-32. [16] S.P. Kang, W.H. Jang, W.E. Jo, Gas hydrate phase equilibria of CO2+H2 mixture in silica gel pores for the development of pre-combustion capture, Clean Technology. 15 (2009) 25864. [17] N. Liu, G. Gong, D. Liu, Y. Xie, Effects of addtives on carbon dioxidehydrate formation, Proceedings of the 6 th International Conference on gas hydrates ICGH 2008, Vancouver, 18
ACCEPTED MANUSCRIPT British columbia, Canada, July 6-10, 2008. [18] X.L. Wang, M. Dennis, L.Z. Hou, Clathrate hydrate technology for cold storage in air conditioning systems, Renew Sust Energ Rev. 36 (2014) 34-51.
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[19] Y.S. Bae, S.Y. Lee, W.T. Kwon, J.M. Jeon, A study on the database for analyzing life cycle cost of road facilities in Seoul, J. Korean Soc. Hazard Mitig. 14 (2014) 99-105.
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[20] Y.T. Kang, A. Akisawa, Y. Sambe, T. Kashiwagi, Absorption heat pump systems for solution transportation at ambient temperature - STA cycle. Energy. 25 (2000) 355-70.
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[21] Y.K. Jo, J.K. Kim, S.G. Lee, Y.T. Kang, Development of type 2 solution transportation absorption system for utilizing LNG cold energy. Int J Refrig. 30 (2007) 978-85. [22] Y.D. Yoo, S.H. Kim, Y.S. Yun, G.T. Jin. Conversion technology from coal to synthetic
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natural gas, Korean Industrial Chemistry News. 12 (2009) 38-57
[23]http://www.index.go.kr/potal/stts/idxMain/selectPoSttsIdxSearch.do?idx_cd=1073&clas_ div=C&idx_sys_cd=540&idx_clas_cd=1,2014.10
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[24] Y.S. Kim, K.S. Kim, Validating the applicability of a simplified correlation method for
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economic evaluation of cooling plants, Korean Journal of Air-Conditioning and Refrigeration Engineering. 14 (2002) 854-62. [25] http://www.kpi.or.kr,2014.12 [26]http://i121.seoul.go.kr/cs/cyber/front/cgcalc/NR_cgCalcPublicPurpose.do?_m=m1_3_3,2 014.10 [27]http://cyber.kepco.co.kr/ckepco/front/jsp/CY/E/E/CYEEHP00101.jsp,2014.10 19
ACCEPTED MANUSCRIPT [28] T.K. Park, A case study on the LCC analysis for the education and research building of seoul national university, Korea Institute of construction engineering and management. 5
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(2004) 63-70.
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Fig. 1. Types of heat transportation
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Fig. 2. Schematic diagram of the district cooling system (DCS)
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Fig. 3. Schematic diagram of the CO2 hydrate cooling system
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LCC IC MC EC
10000
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6000 4000 2000 0 200
300
400
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100
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3
Cost [10 $]
8000
500
Diameter [mm]
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Fig. 4. LCC of the CO2 hydrate cooling system vs. pipe diameter
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LCC IC MC EC
30000
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20000
3
Cost [10 $]
25000
15000
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10000 5000 200
300
400
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Diameter [mm]
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Fig. 5. LCC of the DCS vs. pipe diameter
25
500
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30000
Hydrate system DCS system
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20000 15000 10000 5000 100
200
300
400
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3
Total cost [10 $]
25000
500
Diameter [mm]
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Fig. 6a. Total LCC variations for each pipe diameters
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Hydrate system DCS system
7000
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3
Total cost [10 $]
6000 5000 4000
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3000 2000 10
15
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5
20
Period [year]
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Fig. 6b. Total LCC as a function of operation period
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Hydrate system DCS system
35000
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25000
3
Total cost [10 $]
30000
20000 15000
5000 20
30
40
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10000
50
Distance [km]
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Fig. 6c. Total LCC as a function of transportation distance
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3500 3000
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3
Cost [10 $]
2500 LCC IC MC EC
2000 1500
500 -15
-10
-5
0
5
10
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1000
15
Power power change rate [%]
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Fig. 7a. LCC variations as a function of pump power change rate for the CO2 hydrate cooling system
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7000 6000
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3
Cost [10 $]
5000
LCC IC MC EC
4000 3000
1000 -15
-10
-5
0
5
10
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2000
15
Power power change rate [%]
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Fig. 7b. LCC variations as a function of pump power change rate for DCS.
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8000
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6000 5000 4000 3000
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3
Total cost [10 $]
7000
Hydrate system DCS system
2000 -2
-1
0
1
2
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3
Actual interest change rate [%]
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Fig. 8. Total LCC variations as a function of actual interest change rate
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ACCEPTED MANUSCRIPT List of figure captions
Types of heat transportation
Fig. 2.
Schematic diagram of the district cooling system (DCS)
Fig. 3.
Schematic diagram of the CO2 hydrate cooling system
Fig. 4.
LCC of the CO2 hydrate cooling system vs. tube diameter
Fig. 5.
LCC of the DCS vs. pipe diameter
Fig. 6a.
Total LCC as a function of pipe diameters
Fig. 6b.
Total LCC as a function of operation period
Fig. 6c.
Total LCC as a function of transportation distance
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Fig. 1.
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Fig. 7a. LCC variations as a function of pump power change rate for the CO2 hydrate cooling system.
Fig. 7b.
LCC variations as a function of pump power change rate for the DCS.
Fig. 8. LCC variations as a function of actual interest change rate
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List of Tables
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Table 1 Basis conditions
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Table 2 Life cycle cost factors
Table 4 Pump cost of both systems
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Table 3 Life cycle cost components
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Table 5 Parametric ranges for sensitivity analysis
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Table 1 Basis conditions DCS
Working fluid
How water
Hydrate slurry
Mass flow rate [kg/s]
207.8
37.2
Diameter [mm]
400
Type of pipe
Insulation pipe
Roughness [mm] Period [years]
Carbon steel pipe
85
85
0.046
0.046
20
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Capacity [RT]
200
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Efficiency of pump[%]
Hydrate
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Transportation length [km]
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Table 2 Life cycle cost factors 2004-2013
Interest rate(i)
4.1 %
Price escalation(>)
2.91 %
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Investigation period
Actual Interest rate(i*)
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1.15 %
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Table 3 Life cycle cost components Life cycle cost components Labor cost, pump, Solution, Pipe, Insulation, Storage Tank
Energy cost (EC)
Pump power rate
Maintenance cost (MC)
2% of equipment cost [24]
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Initial installation cost (IC)
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Table 4 Pump cost of both systems [25]
Number of pumps[EA]
2
Cost[$]/EA
21741
CO2 hydrate
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DCS
2
7858
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System
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Table 5 Parametric ranges for sensitivity analysis
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Sensitivity parameters 5, 10, 15, 20
Diameter[mm]
100, 200 ,300, 400, 500
Distance[km]
10, 20, 30, 40, 50
Pump power change rate[%]
-15, -10, -5, 0, 5, 10, 15
Actual interest change rate[%]
-3, -2, -1, 0, 1, 2, 3
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Period[years]
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Highlights
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1. The CO2 hydrate system is an economic alternative solution to the conventional DCS. 2. The optimum pipe diameters for CO2 hydrate and DCS are 200 and 400mm, respectively. 3. The pump power rate of the DCS is 2.5 times higher than that of CO2 hydrate system.
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4. Total LCC for CO2 hydrate cooling system is only a half of that for the DCS.