- Email: [email protected]
An economic and energy analysis on bio-hydrogen fuel using a gasification process
ARTICLE IN PRESS
Renewable Energy 32 (2007) 80–94 www.elsevier.com/locate/renene
An economic and energy analysis on bio-hydrogen fuel using a gasification process Kiyoshi Dowakia,, Tsuyoshi Ohtab, Yasukazu Kasaharab, Mitsuo Kameyamac, Koji Sakawakic, Shunsuke Morid a
Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510, Japan Aimura Kensetsu Co. Ltd., 186-6 Shimo-Gennyu, Jouetsu, Nigata, 942-0051, Japan c Japan Planning Organization Co. Ltd., 3-20 Kioicho, Chiyoda-ku, Tokyo, 102-0094, Japan d Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510, Japan b
Received 5 August 2005; accepted 20 December 2005 Available online 15 February 2006
Abstract Recently, in Japan, recycling technologies have been developed using waste biomass material. Waste biomass is traded in the waste materials market between users and a third-party, who receives a fee for processing them. This study is an environmental and economic analysis of a biomass energy system, which can produce hydrogen fuel for fuel cells (purity of 99.99%) as an example of an environmental business model. The experimental apparatus was made based on the moving-bed gasifier by the German company, DM2 Inc., and the hydrogen gas yield was measured. Finally, the economic viability of the future hydrogen business was estimated. The experimental results obtained gave the gas concentration of 57.5% in a Steam/Carbon ratio of 1.40 at 900 1C. Assuming the plant scale of 10 t/d, the production amount of hydrogen gas would be 21.3 kg/h. Based on the law concerning waste processing in Japan, a sizeable amount of waste biomass could be expected. Therefore, if the processing fee which is paid to the group (contractor) ranges between 5.0 and 10.0 $/t, and if the whole investment cost is 6 million dollars and the depreciation period is 15
Corresponding author. Current affiliation: Research Institute of Innovative Technology for the Earth (RITE),
9th Floor, No. 3 Toyokaiji Bldg., 2-23-1, Nishi-shimbashi, Minato-ku, Tokyo, 105-0003, Japan. Tel.: +81 3 3437 2850; fax: +81 3 3437 1699. E-mail address: [email protected] (K. Dowaki). 0960-1481/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2005.12.010
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
81
years, the bio-hydrogen production cost using the experimental data would be 5.75–7.86 $/kg-H2 without receiving related subsidies. In a one-third grant proportion, the cost would become 4.60–6.72 $/kg-H2. r 2006 Elsevier Ltd. All rights reserved. Keywords: Moving-bed gasifier; Bio-hydrogen; Waste biomass; Processing fee; Hydrogen production cost; Internal rate of return
1. Introduction In order to solve the environmental problem, decarbonization has received world wide attention. In particular, hydrogen energy, which is produced from renewable energy resources of wind power, hydropower, photovoltaic, solar thermal power, geothermal power and biomass, biomass is the most promising. In Japan, the annual amount of hydrogen gas that was consumed in 2002 was 1.5–2.0 1010 Nm3. Half of this hydrogen energy was produced from fossil fuel. In 2020, the Japanese government has a target of introducing 5 million fuel cell vehicles. If this is realized, the demand for hydrogen gas will increase by approximately 1.4 1010 Nm3 [1]. Hence, hydrogen energy from renewable energy resources is important from the viewpoint of CO2 emissions mitigation. On the other hand, biomass use, in which many people already have an interest, has the properties of being a renewable resource and a carbon neutral resource. The Japanese government has tried to promote biomass energy use in an effort to solve global warming. For instance, the Ministry of Economy, Trade and Industry (METI) predicts biomass energy use of 39.1 PJ in the future energy demand and supply plan in 2010. The Ministry of Agriculture, Forestry and Fisheries (MAFF) also predicts biomass energy use of 110.5–210.1 PJ in the future energy demand and supply plan in 2010 [2]. As there was a plentiful supply of scrap wood in 2002, equal to 2.83 108 m3, a significant way to process that wood was needed [3]. Up until now, the focus has been on the use of biomass resources and biomass energy systems, such as the biomass gasification cogeneration system, which have mainly been developed in Europe. Economic and technological analysis and the advantages of the scale of the plant have already been clarified [4–6]. Likewise, the energy cost of generated power from the biomass energy system has been estimated [7–10]. In these analyses, the benefits of CO2 mitigation and of economic merit were found to be superior to that of the conventional system [7,8]. In this paper, the energy cost of hydrogen gas produced by the gasifier was estimated. Niigata prefecture in Japan was selected as a model area. It has been confirmed that this site has potential for introduction of a biomass energy system, through a previous investigation. That is, the results showing the processing fee on the waste wood (Japanese cedar) and the amount that was available were obtained. The processing fee will be a source of income to the gas company which operates the hydrogen production plant. The sale of produced hydrogen will also be income. That is, the company may be able to earn double income. In addition, for a new environmental energy system such as this proposal, a related subsidy from the government is likely to be available.
ARTICLE IN PRESS 82
K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
Considering the amount of waste wood which would be distributed in the Niigata prefecture area, the available plant-scale would be 10 t/d at most. A moving-bed gasifier was selected as the gasification plant. In Japan, it is thought that a large-scale plant will be successful due to the low energy density of biomass. In the case, it would be necessary to collect the material more widely. However, in Japan which has an abundance of mountainous areas and narrow roads, the transportation cost of waste material would contribute a significant amount to the overall cost. Thus, it is thought that a small-scale plant where the demand side would be close to the supply side (ex. a sawmill or a food factory where a cogeneration system is needed, or a waste processing facility with a hydrogen station for local fuel cell vehicles) was much better from the viewpoint of cost benefits. As a test case, a demonstration-plant was constructed in Tokushima prefecture in 2005 in order to examine the gasification performance. This gasifier has three reactors for preheating, the reforming process and the pyrolysis process [11]. The moving-bed gasifier has the following characteristics; (1) pyrolysis reactions take place in pyrolyzer, (2) pyrolysis gases are reformed by H2O (steam), (3) heat required for their reactions is supplied by combustion of off-gas, Tar and char. With regard to the gasification performance, since gas yields and concentration are dependent upon the kind of material, the operating temperature and the inner pressure, they were examined using the gasifier apparatus which has a reformer and a pyrolyzer. The type of waste wood used was Japanese cedar. Finally, using the experimental results, the gasifier performance was examined, and the production cost and the internal rate of return due to sale of hydrogen gas, was estimated. While a comprehensive economic analysis including chemical experimentation is not included in the previous researches, this paper provides significant data for future biomass use. 2. Gasification experiment 2.1. Summary At the city of Herten in Germany, a moving-bed gasifier, which is owned by DM2 Inc., consists of three reactors: a preheater, a reformer and a pyrolyzer. Hard balls (suitable size: 5–30 mm) which are called ‘‘heat carriers’’ circulate through the reactors. They are usually made from sand, gravel or similar material. The experimental apparatus was fabricated in order to examine gaseous yields through gasification process. The apparatus consists of a pyrolyzer and a reformer made from Inconel. The size of each reactor is as follows: (1) an inner diameter of 100 mm and (2) a height of 300 mm (see Fig. 1). Although the two reactors are not separate, they have the system in which their temperature control can be adjusted precisely. In our apparatus, the balls of heat carriers are fixed so as not to circulate through the reactor, limiting the role of the heat carriers to the heat transfer and/or somewhat a catalyst. Hence, heat carriers are put on the bottom portion in the pyrolyzer and on the middle portion in the reformer. The pipe heated at 130 1C connects the outlet of the reactor to two gas-chromatographs (GC-14A, Shimadzu Inc.). This is done to avoid liquefying H2O of the product gas. By connecting gaschromatographs in series, gas concentrations can be measured every 5 min. A 0.1 g of waste woody particles (size:o0.75 mm) are fed into the pyrolyzer every 30–40 s. Using
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
83
Fig. 1. Schematic of experimental apparatus.
a diaphragm pump, the water (0.1–0.4 ml/min) for reforming is also supplied to the reactor with 150 ml/min of He, which is purge gas. At the same time, our experimental apparatus includes a system whereby the data of the furnace temperature and pressure and feed rate of material can be monitored automatically. Regarding the inner temperature of the furnace, the K-type thermocouple is put into the furnace so that it measures the temperature of product gas directly. In our experiment, balls of MgO as heat carriers were selected (see Photograph 1 and Table 1). Table 2 shows the ultimate analysis of the waste woody material.
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
84
Photo 1. Heat carrier (size:o5 mm).
Table 1 Chemical properties of the heat carriers MgO CaO SiO2 Fe2O3 Al2O3 B2O3 Bulk density
95.00–95.50 1.10–1.50 2.50–3.00 0.10–0.15 0.20–0.25 0.15–0.30
wt% wt% wt% wt% wt% wt%
3.30–3.35
g/cm3
Table 2 Ultimate analysis of the waste woody material (Japanese cedar) Ca Ha Oa Sa Na Cla Asha
50.90 5.90 40.50 0.10 0.52 0.080 2.00
wt% wt% wt% wt% wt% wt% wt%
Heating valuea Moisture content Volatile matter
18.348 8.81 81.5
kJ/kg wt% wt%
a
Dry-base.
In this paper, the effect of gaseous yields is analyzed at 550 and 900 1C changing the amount of added steam. These temperatures are the same as those of the demonstration plant in Germany. The equilibrium constants of shift reaction and methanation reaction were estimated in order to examine the catalytic function due to heat carriers. The nine kinds of gases which can be measured include H2, CO, CO2 CH4, C2H4, C2H6, N2, O2 and H2O. The gas analysis was done by the TCD method using the columns of Molecular Sieve 13X and Porapak N.
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
Concentration [vol.%] (Dry-base)
80.0%
CH4 CO H2
60.0%
85
CO2 C2H4 C2H6
40.0% 20.0% 0.0%
0.13
0.64
1.40 S/C [-]
1.91
2.55
Fig. 2. Result of pyrolysis at 550 1C.
The added water was 0.13, 0.64, 1.40, 1.91 and 2.55 mol-H2O/mol-C, in the case that a steam carbon ratio (S/C) was shown. Also, the reforming temperatures at the time when the equilibrium constants were analyzed were 850, 875, 900, 925 and 950 1C. Here, a steam carbon ratio is defined as the following equation. S=C½molH2 O=molC ¼
Added Steam ½mol=s þ Moisture ½mol=s . Carbon Content of Material ½mol=s
(1)
2.2. Pyrolysis process The gaseous yields of pyrolysis were analyzed while holding the temperature of reactors at 550 1C. The inner pressure was approximately atmospheric pressure during the measurement. The average moisture content of our material was 8.80%. The feed rate was 3.48 mg/s. Fig. 2 shows the concentrations of pyrolysis gases at the time when the added steam was changed from 0.13 to 2.55 of S/C. It was observed that H2 concentration was affected by the added water. However, an over-supply of water could not increase it. The concentration of hydrocarbon increased as the added water increased. At S/C ¼ 0.64, H2 of 66.1% (dry-base) was obtained. Compared with the concentration at another S/C, that was maximum concentration. Although a little increase in H2 concentration was seen due to water, it is thought that the concentration of H2 in the pyrolysis process might be little affected by excess water (see Fig. 2). However, the formation of H2 in the reforming process would be promoted by steam, that is, the reforming reaction. Thus, more water (S/C40.64) may have to be added so that H2O reacts with CH4 and/or CO2 effectively. 2.3. Reforming process Next, the performance of the reforming process was analyzed. The operating temperature was constant at 900 1C and only the added water was changed. The inner average pressure was the same as the pyrolyzer. The moisture content of material was 8.81%. The feed rate of material was 3.32 mg/s on average.
ARTICLE IN PRESS 86
K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
CH4
Concentration [vol.%] (Dry-base)
60.0%
CO
H2
CO2
1.91
2.55
40.0%
20.0%
0.0%
0.13
0.64
1.40 S/C [-]
Fig. 3. Result of reformed gases at 900 1C.
Fig. 3 shows the concentrations of reformed gases at the time when the added steam was changed from 0.13 to 2.55 of S/C. According to Fig. 3, the maximum concentration of H2 was 57.5% at 1.40 of S/C. The concentrations over 1.40 of S/C decreased. That is, more added water did not make a contribution to reforming H2. Likewise, from the viewpoint of plant design, the excess water would decrease the overall energy efficiency. Also, since the generated hydrogen gas has to increase to the purity of 99.99% using the PSA system (Pressure Swing Absorption), for using as the fuel of a fuel cell apparatus, it is much better that the input concentration of hydrogen gas is higher. In this system analysis, it is assumed that the PSA system can create a concentration to 99.99% purity of hydrogen gas, in the case that the H2 concentration of product gas is over 50%. Hence, in the later analysis, the data at the time when the concentration of H2 gas was a maximum was used, that case being when S/C was at 1.40. Using the input rate of material, the added water and some assumptions described below, the chemical reaction in this process can be indicated. The hydrocarbon gases which consist of two or more carbons were not observed. Here, it is assumed that the following reactions in the reactor take place. (1) Carbon of material is divided into gases of CH4, CO and CO2, Tar and char. The hydrocarbon gases over two carbons would no longer exist in the reformer. (2) Although the Tar density was not confirmed as to how much was in our experiment, it could be estimated due to the experimental value using another type of gasifier [12]. According to the report, Tar density in the product-dried gas is represented at the function of operating temperature. In our case of 900 1C, it would be 53.1 g/Nm3. Thus, the product hydrogen gas and its concentration would be 34.3 mol/kg-material and 57.5% (Dry-base), respectively. On the other hand, compared with the designed data [16], the hydrogen gas and its concentration at S/C ¼ 1.31 would be 33.9 mol/kgmaterial and 53.5%, respectively. Hence, this assumption is likely to be reasonable. In future work, using our apparatus to confirm the performance of the gasifier, the weight of Tar will have to be measured. (3) Tar consists of carbon, hydrogen and oxygen. Since the Tar component was unknown, the combination of components was decided so as to satisfy assumption 2).
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
87
That is, using the experimental results, the material balance on gas yields at S/C ¼ 1.40 for 1 kg of waste material can be described as follows. yCH4 1000 xCH4 ¼ ð1 MCÞðM C þ M Ash þ VM 1Þ TarC , (2) ac yCH4 þ yCO þ yCO2 xCO ¼
1000 yCO ð1 MCÞðM C þ M Ash þ VM 1Þ TarC , ac yCH4 þ yCO þ yCO2
xCO2 ¼
yCO2 1000 ð1 MCÞðM C þ M Ash þ VM 1Þ TarC , ac yCH4 þ yCO þ yCO2
xH2 ¼ xCH4
yH2 , yCH4
xH2 O ¼ xCH4
yH 2 O , yCH4
(3)
(4) (5) (6)
TarH ¼
1000M H ð1 MCÞ þ 2W ð4xCH4 þ 2xH2 þ 2xH2 O Þ, aH
(7)
TarO ¼
1000M O ð1 MCÞ þ W ð2xCO2 þ xCO þ xH2 O Þ, aO
(8)
a¼
TarC aC þTarH aH þTarO aO , 273:15RðxCH4 þ xCO2 þ xCO þ xH2 Þ=101325
(9)
where xj, yj, Mi, ai, Tark MC, VM, W, a and R are mole of i component [mol/s], mole fraction of i component, content of j element [%], atomic number of j element, content of k element of Tar, moisture content [%], volatile matter [%], added water [mol/s], Tar density of product dried gas [g/Nm3] and gas constant [J/mol K], respectively. Likewise, using the ultimate analysis result, the measured concentration of each gas and the above assumptions, the chemical reaction at 1.40 of S/C on the gasification process is as follows. Note that the moles of N2, NH3, H2S and HCl which would occur in the reactor were negligible, since they are an extremely small amount. C38:6 H53:4 O23:1 þ 54:1H2 O ! 2:7CH4 þ 9:1CO þ 34:9H2 þ 13:5CO2 þ 39:8H2 O þ Tar þ Char:
ð10Þ
2.4. Equilibrium constants In the gasification process after the pyrolysis reaction, it is usually thought that the following two reactions take place. CO þ H2 O2CO2 þ H2 , CH4 þ H2 O2CO þ 3H2 .
ð11Þ
Using our experimental apparatus, the difference between theoretical temperature and the actual temperature was measured. The temperature difference is known as the approach temperature.
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
88
In Eq. (11), the equilibrium constant of shift reaction Ks and that of methanation reaction Km are represented as DG ðT DTÞ PCO2 PH2 K s ¼ exp , (12) ¼ RT PCO PH2 O DG ðT DTÞ PCH PH O K m ¼ exp ¼ 34 2 , RT PH2 PCO
(13)
Equilibrium Constan lnKs [-]
where DT, R and Pi are the approach temperature [K], gas constant [J/mol K] and the partial pressure of i component [Pa], respectively. The approach temperatures of shift and methanation reactions were analyzed as follows. Without adding water, the concentration of each product gas was measured while changing the temperature from 850 to 950 1C every 25 1C. The operating pressure was atmospheric pressure. As a result, the theoretical and the measured constants are indicated in Figs. 4 and 5. In the end, the average approach temperatures were 193 1C of shift reaction and 211 1C of methanation reaction. Thus, the heat carriers in this respect would not have any catalytic function.
0.600
Theoretical
Measured
Regression Line
0.300 0.000 -0.300 -0.600 -0.900 8.00E-04
8.25E-04 8.50E-04 8.75E-04 Temperature 1/T[1/K]
9.00E-04
Equilibrium Constan lnKm[-]
Fig. 4. Temperature dependence of shift reaction equilibrium.
9.000
Theoretical
Measured
Regression Line
6.000
3.000
0.000 8.00E-04
8.25E-04 8.50E-04 8.75E-04 Temperature 1/T[1/K]
9.00E-04
Fig. 5. Temperature dependence of methanation reaction equilibrium.
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
89
Using the measured data, the equilibrium constants of the shift and methanation reactions were represented in the regression lines (see Figs. 4 and 5). lnðK s Þ ¼ 3:122
4167 ; RT
r2 ¼ 0:823,
(14)
24; 721 ; r2 ¼ 0:954, (15) RT where r2 is a coefficient of correlation. Hence, it is found out that the activation energy [kJ/mol] and the constant [dimensionless] in each reaction were 34.7 [kJ/mol] and 2.27 101 [dimensionless] in shift reaction and 205.5 [kJ/mol] and 9.96 108 [dimensionless] in methanation reaction, respectively. Since the inner pressure of the plant is atmospheric pressure, the estimated gas moles by Eq. (10) have to be modified using the above results (see Eqs. (14) and (15)) and Eq. (16). About the methodology of modification, the gas moles can be re-estimated by solving the non-linear equation as follows (see Eq. (16)): X lnðPi Þ lnðK j Þ ¼ 0, (16) lnðK m Þ ¼ 20:719
i
where Kj is the equilibrium constant in j reaction. 2.5. Performance of the Gasifier Assuming that the inner pressure is a level whereby the reforming temperature and S/C are 0.101 MPa, 900 1C and 1.40, respectively, 1 kg of waste material would produce the gas yields which were modified by Eq. (16), and are shown in Table 3. Next, using the data of Table 3, the heat and material balances were estimated in Fig. 6. Here, it was assumed that the efficiencies of the air blower and the water pump and the recovery efficiency of PSA are 60.0% and 67.3%. The efficiency of PSA is known through the investigation by the Japanese manufacturer. It was also assumed that the specific heat and the heating value of Tar were the same as those of the waste material. According to Fig. 6, when the cold gas efficiency and the H2 recovery efficiency were defined as Eqs. (17) and (18), these values were 55.3% and 33.9%, respectively. In Eq. (17), the external heating value means the added heat from char, Tar and/or off-gas, which are
Table 3 Gaseous yields(S/C ¼ 1.40, 900 1C, 0.101 MPa) Component
Gas yield (mol/kg)
Concentration (vol%)a
CH4 CO H2 CO2 N2
1.80 13.09 34.39 10.40 0.17
3.0 21.9 57.5 17.4 0.3
a
Dry-base.
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
90
Fig. 6. Heat and material balance.
re-fed to the gasifier in order to make up for the lost heat due to an endoergic reaction. Cold Gas Eff: ¼
Product Gas Heating Value ½kJ=s , Input Material ½kJ=s þ External Heating Value ½kJ=s
H2 Recovery Eff: ¼
(17)
Purified H2 ½kJ=s . Input Material Heating Value ½kJ=s þ Auxiliary Power ½kJ=s (18)
3. Economic analysis 3.1. Economic analysis of a bio-hydrogen system Based on an energy analysis of the described system, the product cost of a bio-hydrogen system was estimated.
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
91
Table 4 Performance data of bio-hydrogen plant (10 t/d) Feed (kg/h) (Moisture: 8.81%) Product H2 (kg/h) (Purity: 99.99%) Cold gas efficiencya H2 recovery efficiencya Annual operating hours a
450 21.3 55.3 33.9 6.240
LHV-base.
In this analysis, it was assumed that the plant scale would be 10 t/d and that the annual operating hours would be 6240 h ( ¼ 260 days 24 h). Under these conditions, the product amount of H2 would be 21.3 kg/h. Hence, the performance data of this plant is indicated in Table 4. In making financial preparations for plant operations, the plant cost, labor costs, taxes and other related expenses must be considered. Thus, their costs are set as follows. The capital cost of a bio-hydrogen system, which can be constructed in the near future, would be 6 million dollars. As a basis for this estimate, this figure was arrived at while considering the cost of the demonstration-plant in Tokushima prefecture, in Japan. The depreciation cost of a bio-hydrogen system was calculated by a capital recovery factor methodology, using 3% interest, 15 years of depreciation years and a residual value of 10%. Then, the cost of the bio-hydrogen system is converted to an annual expense. Other costs such as general expenses, maintenance, public welfare, taxes and insurance are estimated as follows [13]:
Annual general expense: the plant cost 10% Annual maintenance: the plant cost 2% Annual public welfare fee: labor cost 18% Annual property tax: the plant cost 1.6% Annual land tax: land cost 0.4% Annual insurance fee: the plant cost 0.57% Value added tax: 5% of the entire purchase amount
It was also assumed that the operator would be 9 persons (2 persons 3 shifts+1 reserve+1 administrator) and that the annual labor expense would be 342,200$. With regard to income, revenues to the plant owner would include the related subsidy, the processing fee of waste material and the sale of H2 gas. In estimating the H2 cost, the processing fee is considered as a parameter; that is, it changes 0, 50 and 100$/t. In addition, in Japan, a related subsidy (a grant rate of 1/2 or 1/3) also can be taken into account at the time of construction of biomass energy systems. Especially, in the case of an environmentally friendly plant, which will be constructed by private companies, the related subsidy is available at the rate of 1/3. Eventually, the H2 product cost would be set so that revenue and expenses will be balanced. Fig. 7 shows the H2 production cost while changing the processing fee from 0 to 100 $/t. As a result, the bio-hydrogen production cost using the experimental data would be
ARTICLE IN PRESS 92
K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
Fig. 7. Result of H2 production cost.
Fig. 8. Result of internal rate of return on bio-hydrogen fuel.
5.75–7.86 $/kg-H2 without the subsidy and that would be 4.60–6.72 $/kg-H2 with the subsidy (see Fig. 7). With the current price of gasoline being 1.16 $/l as of April, 2005 and a gasoline equivalent cost being based on an efficiency gain of 3.0 for hydrogen fuel cell vehicles over current gasoline internal combustion engines vehicles [14], the cost would be 0.47–0.64 $/l without the subsidy and that would be 0.37–0.55 $/l in the case that a related subsidy will be available at the rate of 1/3 of the construction cost. Note that in the case of Japan, half of the gasoline price is made up of a specific tax. Hence, if more fuel cell vehicles are promoted in Japan, and if the sale price is equilibrated with that of conventional cars, bio-hydrogen energy might be widely used. As another point of reference, a comparable report on the costs of representative hydrogen fueling appliances to supply hydrogen to fuel cell vehicles is available in the US, where natural gas is used as the source of hydrogen. The system which consists of a reforming system, hydrogen compressor, storage tanks and dispenser is standard. The differences from the system described in this paper are the hydrogengeneration technologies (steam methane reforming and auto-thermal reforming) and hydrogen purification technologies (pressure swing adsorption and metal membrane). As a result, the production cost of H2 gas for fuel cell vehicles is 3.38 to 4.28 $/kg-H2 [15]. This implies that even if there is another benefit like a subsidy and/or the fee for processing waste material, the hydrogen cost produced from biomass would be higher
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
93
than that from fossil resources. Assuming that more fuel cell vehicles are promoted in the near future and that the price of gasoline increases, or includes a tax similar to the gasoline tax in Japan, bio-hydrogen energy production might go well as an environmental business. Next, the internal rate of return was estimated using a sales price of 14.26 $/kg-H2, which is equivalent to the current price of gasoline (see Fig. 8) [14]. According to Fig. 8, the internal rate of return (IRR) would be positive even if the depreciation period is 6 years, if the plant owner can receive a subsidy at a grant rate of 1/3 of the capital cost. Inversely, the business of hydrogen fuel production without a subsidy would not be successful, even if the plant owner is able to receive a processing fee of 50 $/t or more. If the IRR is positive, the plant owner can obtain benefits by investing in this environmental business. Nowadays, since the gasoline price is rising, the possibility of the environmental business described in this paper prospering, can be, and should be, expanded effectively, by using a related subsidy at an early stage. 4. Conclusion Based on the above analysis results, the following knowledge was obtained. (1) Using the moving-bed gasifier, 0.047 kg-H2/kg-biomass material (purity: 99.99%) can be produced due to a gasification process. (2) The cost of bio-hydrogen is 4.60–7.86 $/kg-H2. Although this cost is higher than that of methane, there is a sufficient possibility of introducing bio-hydrogen, considering the mitigation of CO2 and the introduction of a green tax such as a CO2 tax.
References [1] Ohmori R. Hydrogen production technologies using no fossil fuel resources. Sci Technol Trends Nat Inst Sci Technol Policy 2002;19 (in Japanese). [2] Energy & Environment 2002; 1719 (in Japanese). [3] Forest Agency. Annual Report on Thinned Wood, http://www.rinya.maff.go.jp/seisaku/sesakusyoukai/ kanbatu2/top.htm; 2002. (in Japanese) [4] Papadopoulos DP, Kaitsigiannis PA. Biomass energy surveying and techno-economic assessment of suitable CHP system installations. Biomass Bioenergy 2002;22:105–24. [5] Brammer JB, Bridgwater AV. The influence of feedstock drying on the performance economics of a biomass gasifire-engine CHP system. Biomass Bioenergy 2002;22:271–81. [6] Niessen WR, et al. Evaluation of gasification and novel thermal processes for the treatment of municipal solid waste. Colorado: National Renewable Energy Laboratory; 1996. [7] Dowaki K, Minagawa A, Matsuhashi R, Ishitani H. Evaluation of biomass gasification cogeneration system by using scrap wood in a Sawmill. JIE Japan 2002;81(4):263–73 (in Japanese). [8] Dowaki K, Mori S. A system analysis of a biomass energy system in a Sawmill. JSER Japan 2003;24(3):203–8 (in Japanese). [9] Dowaki K, Mori S, Fukushima C, Asai N. A comprehensive economical analysis concerning biomass gasification systems. IEE Japan 2003;123(10):1670–9 (in Japanese). [10] Dowaki K, Mori S. A system analysis of a biomass energy system in Sawmill. Appl Energy 2005;80(3):327–39. [11] Schmid C, Mu¨hlen H. Staged reforming—a thermal conversion process specifically developed for biomass. In: Proceedings of the second Olle Lindstro¨m Symposium, 1999. p. 75–82.
ARTICLE IN PRESS 94
K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
[12] Development of High Efficiency Conversion Technologies on Biomass Energy. Tokyo: New Energy Development and Industrial Technology Organization (NEDO); 2003 (in Japanese). [13] Annual report on production and sale data of gas business. Tokyo: The Japan Gas Association (JGA); 2001 (in Japanese). [14] Technical Report on World Energy of Net Work (WE-NET) (in Japanese). Second Edition. Tokyo: New Energy Development and Industrial Technology Organization (NEDO); 2002. [15] Myers DB, et al. Cost and Performance Comparison of Stationary Hydrogen Fueling Appliances. In: Proceedings of the 2002 US DOE Hydrogen Program Review. Virginia, 2002. [16] Technical data on the scale of 10 MW, DM2 Inc.; 2003.
Renewable Energy 32 (2007) 80–94 www.elsevier.com/locate/renene
An economic and energy analysis on bio-hydrogen fuel using a gasification process Kiyoshi Dowakia,, Tsuyoshi Ohtab, Yasukazu Kasaharab, Mitsuo Kameyamac, Koji Sakawakic, Shunsuke Morid a
Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510, Japan Aimura Kensetsu Co. Ltd., 186-6 Shimo-Gennyu, Jouetsu, Nigata, 942-0051, Japan c Japan Planning Organization Co. Ltd., 3-20 Kioicho, Chiyoda-ku, Tokyo, 102-0094, Japan d Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510, Japan b
Received 5 August 2005; accepted 20 December 2005 Available online 15 February 2006
Abstract Recently, in Japan, recycling technologies have been developed using waste biomass material. Waste biomass is traded in the waste materials market between users and a third-party, who receives a fee for processing them. This study is an environmental and economic analysis of a biomass energy system, which can produce hydrogen fuel for fuel cells (purity of 99.99%) as an example of an environmental business model. The experimental apparatus was made based on the moving-bed gasifier by the German company, DM2 Inc., and the hydrogen gas yield was measured. Finally, the economic viability of the future hydrogen business was estimated. The experimental results obtained gave the gas concentration of 57.5% in a Steam/Carbon ratio of 1.40 at 900 1C. Assuming the plant scale of 10 t/d, the production amount of hydrogen gas would be 21.3 kg/h. Based on the law concerning waste processing in Japan, a sizeable amount of waste biomass could be expected. Therefore, if the processing fee which is paid to the group (contractor) ranges between 5.0 and 10.0 $/t, and if the whole investment cost is 6 million dollars and the depreciation period is 15
Corresponding author. Current affiliation: Research Institute of Innovative Technology for the Earth (RITE),
9th Floor, No. 3 Toyokaiji Bldg., 2-23-1, Nishi-shimbashi, Minato-ku, Tokyo, 105-0003, Japan. Tel.: +81 3 3437 2850; fax: +81 3 3437 1699. E-mail address: [email protected] (K. Dowaki). 0960-1481/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2005.12.010
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
81
years, the bio-hydrogen production cost using the experimental data would be 5.75–7.86 $/kg-H2 without receiving related subsidies. In a one-third grant proportion, the cost would become 4.60–6.72 $/kg-H2. r 2006 Elsevier Ltd. All rights reserved. Keywords: Moving-bed gasifier; Bio-hydrogen; Waste biomass; Processing fee; Hydrogen production cost; Internal rate of return
1. Introduction In order to solve the environmental problem, decarbonization has received world wide attention. In particular, hydrogen energy, which is produced from renewable energy resources of wind power, hydropower, photovoltaic, solar thermal power, geothermal power and biomass, biomass is the most promising. In Japan, the annual amount of hydrogen gas that was consumed in 2002 was 1.5–2.0 1010 Nm3. Half of this hydrogen energy was produced from fossil fuel. In 2020, the Japanese government has a target of introducing 5 million fuel cell vehicles. If this is realized, the demand for hydrogen gas will increase by approximately 1.4 1010 Nm3 [1]. Hence, hydrogen energy from renewable energy resources is important from the viewpoint of CO2 emissions mitigation. On the other hand, biomass use, in which many people already have an interest, has the properties of being a renewable resource and a carbon neutral resource. The Japanese government has tried to promote biomass energy use in an effort to solve global warming. For instance, the Ministry of Economy, Trade and Industry (METI) predicts biomass energy use of 39.1 PJ in the future energy demand and supply plan in 2010. The Ministry of Agriculture, Forestry and Fisheries (MAFF) also predicts biomass energy use of 110.5–210.1 PJ in the future energy demand and supply plan in 2010 [2]. As there was a plentiful supply of scrap wood in 2002, equal to 2.83 108 m3, a significant way to process that wood was needed [3]. Up until now, the focus has been on the use of biomass resources and biomass energy systems, such as the biomass gasification cogeneration system, which have mainly been developed in Europe. Economic and technological analysis and the advantages of the scale of the plant have already been clarified [4–6]. Likewise, the energy cost of generated power from the biomass energy system has been estimated [7–10]. In these analyses, the benefits of CO2 mitigation and of economic merit were found to be superior to that of the conventional system [7,8]. In this paper, the energy cost of hydrogen gas produced by the gasifier was estimated. Niigata prefecture in Japan was selected as a model area. It has been confirmed that this site has potential for introduction of a biomass energy system, through a previous investigation. That is, the results showing the processing fee on the waste wood (Japanese cedar) and the amount that was available were obtained. The processing fee will be a source of income to the gas company which operates the hydrogen production plant. The sale of produced hydrogen will also be income. That is, the company may be able to earn double income. In addition, for a new environmental energy system such as this proposal, a related subsidy from the government is likely to be available.
ARTICLE IN PRESS 82
K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
Considering the amount of waste wood which would be distributed in the Niigata prefecture area, the available plant-scale would be 10 t/d at most. A moving-bed gasifier was selected as the gasification plant. In Japan, it is thought that a large-scale plant will be successful due to the low energy density of biomass. In the case, it would be necessary to collect the material more widely. However, in Japan which has an abundance of mountainous areas and narrow roads, the transportation cost of waste material would contribute a significant amount to the overall cost. Thus, it is thought that a small-scale plant where the demand side would be close to the supply side (ex. a sawmill or a food factory where a cogeneration system is needed, or a waste processing facility with a hydrogen station for local fuel cell vehicles) was much better from the viewpoint of cost benefits. As a test case, a demonstration-plant was constructed in Tokushima prefecture in 2005 in order to examine the gasification performance. This gasifier has three reactors for preheating, the reforming process and the pyrolysis process [11]. The moving-bed gasifier has the following characteristics; (1) pyrolysis reactions take place in pyrolyzer, (2) pyrolysis gases are reformed by H2O (steam), (3) heat required for their reactions is supplied by combustion of off-gas, Tar and char. With regard to the gasification performance, since gas yields and concentration are dependent upon the kind of material, the operating temperature and the inner pressure, they were examined using the gasifier apparatus which has a reformer and a pyrolyzer. The type of waste wood used was Japanese cedar. Finally, using the experimental results, the gasifier performance was examined, and the production cost and the internal rate of return due to sale of hydrogen gas, was estimated. While a comprehensive economic analysis including chemical experimentation is not included in the previous researches, this paper provides significant data for future biomass use. 2. Gasification experiment 2.1. Summary At the city of Herten in Germany, a moving-bed gasifier, which is owned by DM2 Inc., consists of three reactors: a preheater, a reformer and a pyrolyzer. Hard balls (suitable size: 5–30 mm) which are called ‘‘heat carriers’’ circulate through the reactors. They are usually made from sand, gravel or similar material. The experimental apparatus was fabricated in order to examine gaseous yields through gasification process. The apparatus consists of a pyrolyzer and a reformer made from Inconel. The size of each reactor is as follows: (1) an inner diameter of 100 mm and (2) a height of 300 mm (see Fig. 1). Although the two reactors are not separate, they have the system in which their temperature control can be adjusted precisely. In our apparatus, the balls of heat carriers are fixed so as not to circulate through the reactor, limiting the role of the heat carriers to the heat transfer and/or somewhat a catalyst. Hence, heat carriers are put on the bottom portion in the pyrolyzer and on the middle portion in the reformer. The pipe heated at 130 1C connects the outlet of the reactor to two gas-chromatographs (GC-14A, Shimadzu Inc.). This is done to avoid liquefying H2O of the product gas. By connecting gaschromatographs in series, gas concentrations can be measured every 5 min. A 0.1 g of waste woody particles (size:o0.75 mm) are fed into the pyrolyzer every 30–40 s. Using
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
83
Fig. 1. Schematic of experimental apparatus.
a diaphragm pump, the water (0.1–0.4 ml/min) for reforming is also supplied to the reactor with 150 ml/min of He, which is purge gas. At the same time, our experimental apparatus includes a system whereby the data of the furnace temperature and pressure and feed rate of material can be monitored automatically. Regarding the inner temperature of the furnace, the K-type thermocouple is put into the furnace so that it measures the temperature of product gas directly. In our experiment, balls of MgO as heat carriers were selected (see Photograph 1 and Table 1). Table 2 shows the ultimate analysis of the waste woody material.
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
84
Photo 1. Heat carrier (size:o5 mm).
Table 1 Chemical properties of the heat carriers MgO CaO SiO2 Fe2O3 Al2O3 B2O3 Bulk density
95.00–95.50 1.10–1.50 2.50–3.00 0.10–0.15 0.20–0.25 0.15–0.30
wt% wt% wt% wt% wt% wt%
3.30–3.35
g/cm3
Table 2 Ultimate analysis of the waste woody material (Japanese cedar) Ca Ha Oa Sa Na Cla Asha
50.90 5.90 40.50 0.10 0.52 0.080 2.00
wt% wt% wt% wt% wt% wt% wt%
Heating valuea Moisture content Volatile matter
18.348 8.81 81.5
kJ/kg wt% wt%
a
Dry-base.
In this paper, the effect of gaseous yields is analyzed at 550 and 900 1C changing the amount of added steam. These temperatures are the same as those of the demonstration plant in Germany. The equilibrium constants of shift reaction and methanation reaction were estimated in order to examine the catalytic function due to heat carriers. The nine kinds of gases which can be measured include H2, CO, CO2 CH4, C2H4, C2H6, N2, O2 and H2O. The gas analysis was done by the TCD method using the columns of Molecular Sieve 13X and Porapak N.
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
Concentration [vol.%] (Dry-base)
80.0%
CH4 CO H2
60.0%
85
CO2 C2H4 C2H6
40.0% 20.0% 0.0%
0.13
0.64
1.40 S/C [-]
1.91
2.55
Fig. 2. Result of pyrolysis at 550 1C.
The added water was 0.13, 0.64, 1.40, 1.91 and 2.55 mol-H2O/mol-C, in the case that a steam carbon ratio (S/C) was shown. Also, the reforming temperatures at the time when the equilibrium constants were analyzed were 850, 875, 900, 925 and 950 1C. Here, a steam carbon ratio is defined as the following equation. S=C½molH2 O=molC ¼
Added Steam ½mol=s þ Moisture ½mol=s . Carbon Content of Material ½mol=s
(1)
2.2. Pyrolysis process The gaseous yields of pyrolysis were analyzed while holding the temperature of reactors at 550 1C. The inner pressure was approximately atmospheric pressure during the measurement. The average moisture content of our material was 8.80%. The feed rate was 3.48 mg/s. Fig. 2 shows the concentrations of pyrolysis gases at the time when the added steam was changed from 0.13 to 2.55 of S/C. It was observed that H2 concentration was affected by the added water. However, an over-supply of water could not increase it. The concentration of hydrocarbon increased as the added water increased. At S/C ¼ 0.64, H2 of 66.1% (dry-base) was obtained. Compared with the concentration at another S/C, that was maximum concentration. Although a little increase in H2 concentration was seen due to water, it is thought that the concentration of H2 in the pyrolysis process might be little affected by excess water (see Fig. 2). However, the formation of H2 in the reforming process would be promoted by steam, that is, the reforming reaction. Thus, more water (S/C40.64) may have to be added so that H2O reacts with CH4 and/or CO2 effectively. 2.3. Reforming process Next, the performance of the reforming process was analyzed. The operating temperature was constant at 900 1C and only the added water was changed. The inner average pressure was the same as the pyrolyzer. The moisture content of material was 8.81%. The feed rate of material was 3.32 mg/s on average.
ARTICLE IN PRESS 86
K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
CH4
Concentration [vol.%] (Dry-base)
60.0%
CO
H2
CO2
1.91
2.55
40.0%
20.0%
0.0%
0.13
0.64
1.40 S/C [-]
Fig. 3. Result of reformed gases at 900 1C.
Fig. 3 shows the concentrations of reformed gases at the time when the added steam was changed from 0.13 to 2.55 of S/C. According to Fig. 3, the maximum concentration of H2 was 57.5% at 1.40 of S/C. The concentrations over 1.40 of S/C decreased. That is, more added water did not make a contribution to reforming H2. Likewise, from the viewpoint of plant design, the excess water would decrease the overall energy efficiency. Also, since the generated hydrogen gas has to increase to the purity of 99.99% using the PSA system (Pressure Swing Absorption), for using as the fuel of a fuel cell apparatus, it is much better that the input concentration of hydrogen gas is higher. In this system analysis, it is assumed that the PSA system can create a concentration to 99.99% purity of hydrogen gas, in the case that the H2 concentration of product gas is over 50%. Hence, in the later analysis, the data at the time when the concentration of H2 gas was a maximum was used, that case being when S/C was at 1.40. Using the input rate of material, the added water and some assumptions described below, the chemical reaction in this process can be indicated. The hydrocarbon gases which consist of two or more carbons were not observed. Here, it is assumed that the following reactions in the reactor take place. (1) Carbon of material is divided into gases of CH4, CO and CO2, Tar and char. The hydrocarbon gases over two carbons would no longer exist in the reformer. (2) Although the Tar density was not confirmed as to how much was in our experiment, it could be estimated due to the experimental value using another type of gasifier [12]. According to the report, Tar density in the product-dried gas is represented at the function of operating temperature. In our case of 900 1C, it would be 53.1 g/Nm3. Thus, the product hydrogen gas and its concentration would be 34.3 mol/kg-material and 57.5% (Dry-base), respectively. On the other hand, compared with the designed data [16], the hydrogen gas and its concentration at S/C ¼ 1.31 would be 33.9 mol/kgmaterial and 53.5%, respectively. Hence, this assumption is likely to be reasonable. In future work, using our apparatus to confirm the performance of the gasifier, the weight of Tar will have to be measured. (3) Tar consists of carbon, hydrogen and oxygen. Since the Tar component was unknown, the combination of components was decided so as to satisfy assumption 2).
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
87
That is, using the experimental results, the material balance on gas yields at S/C ¼ 1.40 for 1 kg of waste material can be described as follows. yCH4 1000 xCH4 ¼ ð1 MCÞðM C þ M Ash þ VM 1Þ TarC , (2) ac yCH4 þ yCO þ yCO2 xCO ¼
1000 yCO ð1 MCÞðM C þ M Ash þ VM 1Þ TarC , ac yCH4 þ yCO þ yCO2
xCO2 ¼
yCO2 1000 ð1 MCÞðM C þ M Ash þ VM 1Þ TarC , ac yCH4 þ yCO þ yCO2
xH2 ¼ xCH4
yH2 , yCH4
xH2 O ¼ xCH4
yH 2 O , yCH4
(3)
(4) (5) (6)
TarH ¼
1000M H ð1 MCÞ þ 2W ð4xCH4 þ 2xH2 þ 2xH2 O Þ, aH
(7)
TarO ¼
1000M O ð1 MCÞ þ W ð2xCO2 þ xCO þ xH2 O Þ, aO
(8)
a¼
TarC aC þTarH aH þTarO aO , 273:15RðxCH4 þ xCO2 þ xCO þ xH2 Þ=101325
(9)
where xj, yj, Mi, ai, Tark MC, VM, W, a and R are mole of i component [mol/s], mole fraction of i component, content of j element [%], atomic number of j element, content of k element of Tar, moisture content [%], volatile matter [%], added water [mol/s], Tar density of product dried gas [g/Nm3] and gas constant [J/mol K], respectively. Likewise, using the ultimate analysis result, the measured concentration of each gas and the above assumptions, the chemical reaction at 1.40 of S/C on the gasification process is as follows. Note that the moles of N2, NH3, H2S and HCl which would occur in the reactor were negligible, since they are an extremely small amount. C38:6 H53:4 O23:1 þ 54:1H2 O ! 2:7CH4 þ 9:1CO þ 34:9H2 þ 13:5CO2 þ 39:8H2 O þ Tar þ Char:
ð10Þ
2.4. Equilibrium constants In the gasification process after the pyrolysis reaction, it is usually thought that the following two reactions take place. CO þ H2 O2CO2 þ H2 , CH4 þ H2 O2CO þ 3H2 .
ð11Þ
Using our experimental apparatus, the difference between theoretical temperature and the actual temperature was measured. The temperature difference is known as the approach temperature.
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
88
In Eq. (11), the equilibrium constant of shift reaction Ks and that of methanation reaction Km are represented as DG ðT DTÞ PCO2 PH2 K s ¼ exp , (12) ¼ RT PCO PH2 O DG ðT DTÞ PCH PH O K m ¼ exp ¼ 34 2 , RT PH2 PCO
(13)
Equilibrium Constan lnKs [-]
where DT, R and Pi are the approach temperature [K], gas constant [J/mol K] and the partial pressure of i component [Pa], respectively. The approach temperatures of shift and methanation reactions were analyzed as follows. Without adding water, the concentration of each product gas was measured while changing the temperature from 850 to 950 1C every 25 1C. The operating pressure was atmospheric pressure. As a result, the theoretical and the measured constants are indicated in Figs. 4 and 5. In the end, the average approach temperatures were 193 1C of shift reaction and 211 1C of methanation reaction. Thus, the heat carriers in this respect would not have any catalytic function.
0.600
Theoretical
Measured
Regression Line
0.300 0.000 -0.300 -0.600 -0.900 8.00E-04
8.25E-04 8.50E-04 8.75E-04 Temperature 1/T[1/K]
9.00E-04
Equilibrium Constan lnKm[-]
Fig. 4. Temperature dependence of shift reaction equilibrium.
9.000
Theoretical
Measured
Regression Line
6.000
3.000
0.000 8.00E-04
8.25E-04 8.50E-04 8.75E-04 Temperature 1/T[1/K]
9.00E-04
Fig. 5. Temperature dependence of methanation reaction equilibrium.
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
89
Using the measured data, the equilibrium constants of the shift and methanation reactions were represented in the regression lines (see Figs. 4 and 5). lnðK s Þ ¼ 3:122
4167 ; RT
r2 ¼ 0:823,
(14)
24; 721 ; r2 ¼ 0:954, (15) RT where r2 is a coefficient of correlation. Hence, it is found out that the activation energy [kJ/mol] and the constant [dimensionless] in each reaction were 34.7 [kJ/mol] and 2.27 101 [dimensionless] in shift reaction and 205.5 [kJ/mol] and 9.96 108 [dimensionless] in methanation reaction, respectively. Since the inner pressure of the plant is atmospheric pressure, the estimated gas moles by Eq. (10) have to be modified using the above results (see Eqs. (14) and (15)) and Eq. (16). About the methodology of modification, the gas moles can be re-estimated by solving the non-linear equation as follows (see Eq. (16)): X lnðPi Þ lnðK j Þ ¼ 0, (16) lnðK m Þ ¼ 20:719
i
where Kj is the equilibrium constant in j reaction. 2.5. Performance of the Gasifier Assuming that the inner pressure is a level whereby the reforming temperature and S/C are 0.101 MPa, 900 1C and 1.40, respectively, 1 kg of waste material would produce the gas yields which were modified by Eq. (16), and are shown in Table 3. Next, using the data of Table 3, the heat and material balances were estimated in Fig. 6. Here, it was assumed that the efficiencies of the air blower and the water pump and the recovery efficiency of PSA are 60.0% and 67.3%. The efficiency of PSA is known through the investigation by the Japanese manufacturer. It was also assumed that the specific heat and the heating value of Tar were the same as those of the waste material. According to Fig. 6, when the cold gas efficiency and the H2 recovery efficiency were defined as Eqs. (17) and (18), these values were 55.3% and 33.9%, respectively. In Eq. (17), the external heating value means the added heat from char, Tar and/or off-gas, which are
Table 3 Gaseous yields(S/C ¼ 1.40, 900 1C, 0.101 MPa) Component
Gas yield (mol/kg)
Concentration (vol%)a
CH4 CO H2 CO2 N2
1.80 13.09 34.39 10.40 0.17
3.0 21.9 57.5 17.4 0.3
a
Dry-base.
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
90
Fig. 6. Heat and material balance.
re-fed to the gasifier in order to make up for the lost heat due to an endoergic reaction. Cold Gas Eff: ¼
Product Gas Heating Value ½kJ=s , Input Material ½kJ=s þ External Heating Value ½kJ=s
H2 Recovery Eff: ¼
(17)
Purified H2 ½kJ=s . Input Material Heating Value ½kJ=s þ Auxiliary Power ½kJ=s (18)
3. Economic analysis 3.1. Economic analysis of a bio-hydrogen system Based on an energy analysis of the described system, the product cost of a bio-hydrogen system was estimated.
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
91
Table 4 Performance data of bio-hydrogen plant (10 t/d) Feed (kg/h) (Moisture: 8.81%) Product H2 (kg/h) (Purity: 99.99%) Cold gas efficiencya H2 recovery efficiencya Annual operating hours a
450 21.3 55.3 33.9 6.240
LHV-base.
In this analysis, it was assumed that the plant scale would be 10 t/d and that the annual operating hours would be 6240 h ( ¼ 260 days 24 h). Under these conditions, the product amount of H2 would be 21.3 kg/h. Hence, the performance data of this plant is indicated in Table 4. In making financial preparations for plant operations, the plant cost, labor costs, taxes and other related expenses must be considered. Thus, their costs are set as follows. The capital cost of a bio-hydrogen system, which can be constructed in the near future, would be 6 million dollars. As a basis for this estimate, this figure was arrived at while considering the cost of the demonstration-plant in Tokushima prefecture, in Japan. The depreciation cost of a bio-hydrogen system was calculated by a capital recovery factor methodology, using 3% interest, 15 years of depreciation years and a residual value of 10%. Then, the cost of the bio-hydrogen system is converted to an annual expense. Other costs such as general expenses, maintenance, public welfare, taxes and insurance are estimated as follows [13]:
Annual general expense: the plant cost 10% Annual maintenance: the plant cost 2% Annual public welfare fee: labor cost 18% Annual property tax: the plant cost 1.6% Annual land tax: land cost 0.4% Annual insurance fee: the plant cost 0.57% Value added tax: 5% of the entire purchase amount
It was also assumed that the operator would be 9 persons (2 persons 3 shifts+1 reserve+1 administrator) and that the annual labor expense would be 342,200$. With regard to income, revenues to the plant owner would include the related subsidy, the processing fee of waste material and the sale of H2 gas. In estimating the H2 cost, the processing fee is considered as a parameter; that is, it changes 0, 50 and 100$/t. In addition, in Japan, a related subsidy (a grant rate of 1/2 or 1/3) also can be taken into account at the time of construction of biomass energy systems. Especially, in the case of an environmentally friendly plant, which will be constructed by private companies, the related subsidy is available at the rate of 1/3. Eventually, the H2 product cost would be set so that revenue and expenses will be balanced. Fig. 7 shows the H2 production cost while changing the processing fee from 0 to 100 $/t. As a result, the bio-hydrogen production cost using the experimental data would be
ARTICLE IN PRESS 92
K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
Fig. 7. Result of H2 production cost.
Fig. 8. Result of internal rate of return on bio-hydrogen fuel.
5.75–7.86 $/kg-H2 without the subsidy and that would be 4.60–6.72 $/kg-H2 with the subsidy (see Fig. 7). With the current price of gasoline being 1.16 $/l as of April, 2005 and a gasoline equivalent cost being based on an efficiency gain of 3.0 for hydrogen fuel cell vehicles over current gasoline internal combustion engines vehicles [14], the cost would be 0.47–0.64 $/l without the subsidy and that would be 0.37–0.55 $/l in the case that a related subsidy will be available at the rate of 1/3 of the construction cost. Note that in the case of Japan, half of the gasoline price is made up of a specific tax. Hence, if more fuel cell vehicles are promoted in Japan, and if the sale price is equilibrated with that of conventional cars, bio-hydrogen energy might be widely used. As another point of reference, a comparable report on the costs of representative hydrogen fueling appliances to supply hydrogen to fuel cell vehicles is available in the US, where natural gas is used as the source of hydrogen. The system which consists of a reforming system, hydrogen compressor, storage tanks and dispenser is standard. The differences from the system described in this paper are the hydrogengeneration technologies (steam methane reforming and auto-thermal reforming) and hydrogen purification technologies (pressure swing adsorption and metal membrane). As a result, the production cost of H2 gas for fuel cell vehicles is 3.38 to 4.28 $/kg-H2 [15]. This implies that even if there is another benefit like a subsidy and/or the fee for processing waste material, the hydrogen cost produced from biomass would be higher
ARTICLE IN PRESS K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
93
than that from fossil resources. Assuming that more fuel cell vehicles are promoted in the near future and that the price of gasoline increases, or includes a tax similar to the gasoline tax in Japan, bio-hydrogen energy production might go well as an environmental business. Next, the internal rate of return was estimated using a sales price of 14.26 $/kg-H2, which is equivalent to the current price of gasoline (see Fig. 8) [14]. According to Fig. 8, the internal rate of return (IRR) would be positive even if the depreciation period is 6 years, if the plant owner can receive a subsidy at a grant rate of 1/3 of the capital cost. Inversely, the business of hydrogen fuel production without a subsidy would not be successful, even if the plant owner is able to receive a processing fee of 50 $/t or more. If the IRR is positive, the plant owner can obtain benefits by investing in this environmental business. Nowadays, since the gasoline price is rising, the possibility of the environmental business described in this paper prospering, can be, and should be, expanded effectively, by using a related subsidy at an early stage. 4. Conclusion Based on the above analysis results, the following knowledge was obtained. (1) Using the moving-bed gasifier, 0.047 kg-H2/kg-biomass material (purity: 99.99%) can be produced due to a gasification process. (2) The cost of bio-hydrogen is 4.60–7.86 $/kg-H2. Although this cost is higher than that of methane, there is a sufficient possibility of introducing bio-hydrogen, considering the mitigation of CO2 and the introduction of a green tax such as a CO2 tax.
References [1] Ohmori R. Hydrogen production technologies using no fossil fuel resources. Sci Technol Trends Nat Inst Sci Technol Policy 2002;19 (in Japanese). [2] Energy & Environment 2002; 1719 (in Japanese). [3] Forest Agency. Annual Report on Thinned Wood, http://www.rinya.maff.go.jp/seisaku/sesakusyoukai/ kanbatu2/top.htm; 2002. (in Japanese) [4] Papadopoulos DP, Kaitsigiannis PA. Biomass energy surveying and techno-economic assessment of suitable CHP system installations. Biomass Bioenergy 2002;22:105–24. [5] Brammer JB, Bridgwater AV. The influence of feedstock drying on the performance economics of a biomass gasifire-engine CHP system. Biomass Bioenergy 2002;22:271–81. [6] Niessen WR, et al. Evaluation of gasification and novel thermal processes for the treatment of municipal solid waste. Colorado: National Renewable Energy Laboratory; 1996. [7] Dowaki K, Minagawa A, Matsuhashi R, Ishitani H. Evaluation of biomass gasification cogeneration system by using scrap wood in a Sawmill. JIE Japan 2002;81(4):263–73 (in Japanese). [8] Dowaki K, Mori S. A system analysis of a biomass energy system in a Sawmill. JSER Japan 2003;24(3):203–8 (in Japanese). [9] Dowaki K, Mori S, Fukushima C, Asai N. A comprehensive economical analysis concerning biomass gasification systems. IEE Japan 2003;123(10):1670–9 (in Japanese). [10] Dowaki K, Mori S. A system analysis of a biomass energy system in Sawmill. Appl Energy 2005;80(3):327–39. [11] Schmid C, Mu¨hlen H. Staged reforming—a thermal conversion process specifically developed for biomass. In: Proceedings of the second Olle Lindstro¨m Symposium, 1999. p. 75–82.
ARTICLE IN PRESS 94
K. Dowaki et al. / Renewable Energy 32 (2007) 80–94
[12] Development of High Efficiency Conversion Technologies on Biomass Energy. Tokyo: New Energy Development and Industrial Technology Organization (NEDO); 2003 (in Japanese). [13] Annual report on production and sale data of gas business. Tokyo: The Japan Gas Association (JGA); 2001 (in Japanese). [14] Technical Report on World Energy of Net Work (WE-NET) (in Japanese). Second Edition. Tokyo: New Energy Development and Industrial Technology Organization (NEDO); 2002. [15] Myers DB, et al. Cost and Performance Comparison of Stationary Hydrogen Fueling Appliances. In: Proceedings of the 2002 US DOE Hydrogen Program Review. Virginia, 2002. [16] Technical data on the scale of 10 MW, DM2 Inc.; 2003.