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Investigation on high-pressure metal hydride hydrogen compressors
International Journal of Hydrogen Energy 32 (2007) 4011 – 4015 www.elsevier.com/locate/ijhydene
Investigation on high-pressure metal hydride hydrogen compressors X.H. Wang ∗ , Y.Y. Bei, X.C. Song, G.H. Fang, S.Q. Li, C.P. Chen, Q.D. Wang Department of Materials Science and Engineering, Zhejang University, Hangzhou 310027, China Received 26 September 2006; received in revised form 2 March 2007; accepted 2 March 2007 Available online 30 April 2007
Abstract It is well known that metal hydrides can be used to compress hydrogen. In the present study, AB5 type and AB2 type multicomponent hydrogen storage alloys have been studied for the purpose of high-pressure hydrogen compression. A single stage metal hydride hydrogen compressor with hydrogen compression rate of 40 L/min and a double stage compressor with hydrogen compression rate of 20 L/min were designed and built to produce high-pressure hydrogen. The single-stage compressor produces high-pressure hydrogen around 45 MPa from 4 MPa feed gas, when hot oil at 170 ◦ C is used as the heat source. The double-stage compressor rather needs only hot water to produce 45 MPa hydrogen. 䉷 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. Keywords: Metal hydride; Hydrogen storage alloy; Hydrogen compressor; High-pressure hydrogen
1. Introduction
2. Experimental details
Hydrogen fuel cell vehicle received much attention in the past years, and lightweight high-pressure hydrogen storage tank seems to be the main onboard hydrogen storage technology at present stage. In the developed countries, great efforts have been taken in the area of lightweight high-pressure hydrogen storage tank and large progress has been made recently. With the development of high-pressure hydrogen storage technology, it is of interest to develop high efficiency hydrogen compression technology. It is well known that a metal hydride hydrogen compressor has many advantages over traditional compressors such as no moving parts, non-noise, no pollution to the compressed hydrogen [1–8]. However, the hydrogen storage alloys used in most cases of thermal desorption compressors have not been optimized, and LaNi5 or La(NiAl)5 hydrogen storage alloy is generally selected, and the product hydrogen pressure reported is usually less than 15 MPa. In this paper, we report our recent results about the singlestage and double-stage hydride compressors which can produce 45 MPa hydrogen from 4 MPa feed gas.
The Ce-rich mischmetal (Mm) is composed of La 23.8%, Ce 48.6%, Pr 8.1%, Nd 16.8%, others 2.7%. The purity of the metallic elements for sample preparation is as follows: Ni, Cr and Mn are 99.9% pure, La and Ti are 99% pure, V and Ca are 99.5% and 98% pure, respectively. Hydrogen used for hydrogenation/dehydrogenation properties measurement is 99.999% pure. Rare earth-based alloys were prepared in an RF induction furnace under the protection of Ar. TiCr 2 -based alloys were prepared by RF levitation melting. Samples were mechanically crushed into fine powder in air, and then introduced into a stainless steel reactor for the measurements of hydrogen storage properties. The p–c–T curves were determined by the constant volume and pressure difference method. Prior to p–c–T measurements, several hydriding/dehydriding cycles were carried out to ensure the samples were fully activated. The details of p–c–T measurements were described elsewhere [9,10]. During the compression tests, cold oil (293 K) and hot oil (443 K) were used as the cooling and heating sources for the singlestage compressor, but only water is used for the double-stage compressor.
∗ Corresponding author: Tel./fax: +86 571 87951152.
E-mail address: [email protected] (X.H. Wang).
0360-3199/$ - see front matter 䉷 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2007.03.002
4012
X.H. Wang et al. / International Journal of Hydrogen Energy 32 (2007) 4011 – 4015
3. Results and discussion 3.1. Single stage compressor The purpose of this study was to develop MHHCs to produce high-pressure hydrogen ((> 40 MPa) with relatively lowpressure hydrogen feed gas (3.0–4.0 MPa). In order to reach
P/MPa
10
1
298 K
0.1 0
1
2
3
4 H/M
5
6
7
Fig. 1. p–c–T curves of MmNi5 –H system.
such a target under mild conditions, the alloy selected should have relatively high hydrogen absorption/desorption plateau pressure under ambient temperature. MmNi5 meets this requirement; however, this alloy has the disadvantages of bad activation properties and large pressure hysteresis. Fig. 1 shows the p–c–T curves of the MmNi5 alloy. The pressure hysteresis factor (Hf = ln(Pa /Pd )) reaches as high as 1.62. Moreover, the alloy is difficult to activate. It does not absorb hydrogen under 8.0 MPa hydrogen pressure for 24 h, but slowly absorb hydrogen when the applied hydrogen pressure exceeds 12.0 MPa. Our previous investigation [5,6,9] revealed that partial substitution of Mm with Ca improves the activation properties as well as the plateau pressures. And it seems that the optimum Ca substitution content is 0.2–0.3. To further improve the properties of the alloy, we tried to use La to partially substitute Mm. Therefore, we prepared and characterized Mm0.8−x Ca0.2 Lax Ni5 (x = 0.0.7) series alloys. Table 1 summarized the main properties of the alloys. It is clearly seen from Table 1 that the pressure hysteresis of the alloys is remarkably improved after partial substitution of Mm by Ca and La. Moreover, as La content increases, the plateau pressure decreases, and the hysteresis factor also decreases. This may be caused by the fact that the cell volume of the alloys increases due to the increase of La/Ce ratio. Furthermore, the activation properties of the alloys are remarkably improved after partial substitution of Mm by Ca and La. In addition, to further improve the hysteresis properties, we also tried to use Al to partially substitute
Table 1 Main properties of AB5 type alloys Alloy
Hydrogen capacity (wt%)
Pd (MPa) 20 ◦ C
Pa (MPa) 20 ◦ C
Hysteresis factor (ln(Pa /Pd )) 20 ◦ C
MmNi5 Mm0.7 La0.1 Ca0.2 Ni5 Mm0.5 La0.3 Ca0.2 Ni5 Mm0.3 La0.5 Ca0.2 Ni5 Mm0.2 La0.6 Ca0.2 Ni5 Mm0.1 La0.7 Ca0.2 Ni5 Mm0.7 La0.1 Ca0.2 (Ni4.95 Al0.05 )
1.4 1.35 1.35 1.35 1.35 1.35 1.3
1.45 1.88 1.33 1.19 0.93 0.73 1.76
7.33 4.19 2.47 1.92 1.25 0.96 2.45
1.62 0.81 0.61 0.49 0.30 0.27 0.33
10
P/MPa
P/MPa
10
1
1
283 K 293 K 308 K 323 K
0
1
2
3 4 H/M
5
6
283 K 293 K 308 K 323 K
0
1
2
3 4 H/M
5
Fig. 2. p–c–T curves of Mm0.7 Ca0.2 La0.1 (Ni4.95 Al0.05 )–H system. (a) Absorption; (b) desorption.
6
X.H. Wang et al. / International Journal of Hydrogen Energy 32 (2007) 4011 – 4015
H2 compressor reactor
4013
cold/hot oil outlet
high-pressure H2 outlet
low-pressure H2 inlet oil jacket cold/hot oil inlet
Fig. 3. Schematic diagram of single stage compressor.
100 80 60 10 P (MPa)
P/MPa
40
20
10 8 6
10°C 20°C 30°C
1
4 0.0
0.5
1.0
1.5 H/M
2 0
50
100 T /°C
150
200
2.0
2.5
3.0
Fig. 5. p–c–T curves of Ti1.1 Cr 1.5 Mn0.4 V0.1 –H system.
Fig. 4. Hydrogen pressure as a function of temperature during compression.
Ni. The results are also shown in Table 1. With the consideration of plateau characteristics and hysteresis factor, we select Mm0.7 Ca0.2 La0.1 (Ni4.95 Al0.05 ) as the compression alloy. Fig. 2 shows the p–c–T curves of Mm0.7 Ca0.2 La0.1 (Ni4.95 Al0.05 )–H system. The alloy can be activated under 4.0 MPa at room temperature by 3–5 absorption/desorption cycles. Its hydrogen desorption plateau pressure at 20 ◦ C is around 2.45 MPa, and the enthalpy of dehydriding, Hd , calculated from the middle plateau pressure in Fig. 1 according to van’t Hoff equation is −24.5 kJ/molH2 . With Mm0.7 Ca0.2 La0.1 (Ni4.95 Al0.05 ) as the compression alloy, a compressor with hydrogen capacity of 1000 L was designed and built. The reactor was made of steel tubes with 38 mm outer diameter and 6 mm wall thickness. Cool and hot oil was used as the heat exchange medium. Fig. 3 shows the schematic diagram of the compressor. Fig. 4 shows the output hydrogen pressure as a function of oil temperature. The compressor can be saturated with hydrogen under 4.0 MPa hydrogen pressure when cool oil was circulated, and high-pressure hydrogen with pressure of around 45 MPa could be produced when hot oil with temperature of around 170 ◦ C was circulated. The hydrogen compression rate is around 40 L/min.
P (MPa)
10
1
40°C 30°C 20°C
0.1 0
1
2
3 H/M
4
5
6
Fig. 6. p–c–T curves of Mm0.2 La0.6 Ca0.2 Ni5 –H system.
3.2. Double stage compressor For safety purpose, we further explored the possibility of producing high-pressure hydrogen (45 MPa) by using hot water
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X.H. Wang et al. / International Journal of Hydrogen Energy 32 (2007) 4011 – 4015
5 MPa low-pressure H2 inlet
cold/hot oil outlet
cold/hot oil outlet
H2 compressor reactor
15 MPaH2
cold/hot oil inlet
oil jacket
45 MPa high-pressure H2 outlet
cold/hot oil inlet
Fig. 7. Schematic diagram of double stage compressor.
50
40
30 P (MPa)
as the heat exchange medium. In this case, it seems impossible to produce 45 MPa hydrogen from the feed gas with pressure of around 4.0 MPa. Thus we tried to use a double-stage compressor. Because the plateau pressure of Ti-based AB2 type alloys can be regulated in a wider range, it is reasonable to select an alloy from the above AB5 type alloys for the low-pressure stage, and to develop an AB2 type alloy for the high-pressure stage. TiCr 2 alloy has a high plateau pressure, but it has the disadvantages of bad activation properties and small effective hydrogen capacity. To overcome these demerits, we designed the alloy composition with Ti super stoichiometry and partially substituting Cr with transition metals such as Mn and V, namely, Ti1+x Cr 2−y (Mn, V)y (x = 0.0.2; y = 0.4.0.8). The results indicate that as the Mn content x increases, the plateau pressure decreases, hydrogen storage capacity increases slightly, but the pressure hysteresis increases remarkably. When Cr is partially substituted by V, the alloys maintain low hysteresis, but the plateau pressure decreases remarkably. With consideration of the plateau pressure, we finally select Ti1.1 Cr 1.5 Mn0.4 V0.1 as the high-pressure alloy. Fig. 5 is the p–c–T curves of Ti1.1 Cr 1.5 Mn0.4 V0.1 –H system. The hydrogen absorption/desorption plateau pressures at 20 ◦ C are 6.85 and 5.9 MPa, respectively. The enthalpy of dehydriding, Hd , is −23.5 kJ/molH2 . Among the above AB5 type alloys, with consideration of both the plateau characteristics and the matching properties with Ti1.1 Cr 1.5 Mn0.4 V0.1 alloy, Mm0.2 La0.6 Ca0.2 Ni5 is suitable for the low-pressure alloy. Its hydrogen absorption plateau pressure at 20 ◦ C is around 1.25 MPa and hydrogen desorption plateau pressure is around 9.86 MPa at 99 ◦ C. Its p–c–T curves are shown in Fig. 6. With the alloy pair Mm0.2 La0.6 Ca0.2 Ni5 /Ti1.1 Cr 1.5 Mn0.4 V0.1 , a double-stage compressor prototype was designed and built with water as the cooling and heating medium. Fig. 7 shows the schematic diagram of the double-stage compressor. The low-pressure stage compressor was composed of a steel tube with 38 mm outer diameter and 3 mm wall thickness, and the high-pressure stage compressor was composed of a steel tube with 38 mm outer diameter, 6 mm wall thickness. Fig. 8 shows the compression curves of the double-stage compressor. After the low-pressure stage compressor is saturated with hydrogen under around 4.0 MPa pressure, it is then heated by circulating hot water to produce hydrogen with pressure of around 10 MPa. And thus produced high-pressure hydrogen is then
20
10
1st stage 2nd stage
0 0
5
10
15 20 t (min)
25
30
35
Fig. 8. Compression curves of Mm0.2 La0.6 Ca0.2 Ni5 /Ti1.1 Cr 1.5 Mn0.4 V0.1 alloy pair.
input into the high-pressure stage compressor. In this period of time, the high-pressure compressor is cooled by circulating cold water to make the alloy absorb hydrogen. Finally, hot water is circulated into the high-pressure stage compressor, and hydrogen with pressure of around 45 MPa is produced. The hydrogen compression rate is about 20 L/min. 4. Conclusions The properties of AB5 type (MmLaCa)(NiAl)5 alloys and AB2 type Ti1+x (CrMnV)2 alloys are studied for the purpose of hydrogen compression. With the optimized alloys a singlestage hydride hydrogen compressor and a double-stage hydride hydrogen compressor were designed and built. For the singlestage compressor, product hydrogen with pressure of around 45 MPa can be produced from 4 MPa feed gas when hot oil of 170 ◦ C is used as the heat exchange medium. While for the double-stage compressor, only hot water is needed to produce 45 MPa high-pressure hydrogen. Acknowledgment This work was supported by the foundation of Hitech Research and Development Program of China (No. 2006AA05Z129).
X.H. Wang et al. / International Journal of Hydrogen Energy 32 (2007) 4011 – 4015
References [1] Wang QD, Chen CP, Lei YQ. The recent research, development and industrial applications of metal hydrides in the People’s Republic of China. J Alloys Compd 1997;253–254:629–35. [2] Chen CP, Ye Z, Wu J, Wang QD. The properties and some applications of the hydride hydrogen-compression alloy (CaMmCu)(NiAl)5 Zr0.05 . Zeitshrift Phys Chem 1994;183:251–8. [3] Au M, Wang QD. Rare earth-nickel alloy for hydrogen compression. J Alloys Compd 1993;201:115–9. [4] Nomura K, Akiba E, Ono S. Development of a metal hydride compressor. J Less-Common Met 1983;89:551–8. [5] Ivanovsky AI, Kolosov VI, Lototsky MV, Solovey VV, Shmalko YF. Metal hydride thermosorption compressor with improved dynamic characteristics. Int J Hydrogen Energy 1996;21:1053.
4015
[6] Muthukumar P, Maiya MP, Murthy SS. Parametric studies on a metal hydride based single stage hydrogen compressor. Int J Hydrogen Energy 2002;27:1083–8. [7] Dehouche Z, Grimard N, Laurencelle F, Goyette J, Bose TK. Hydride alloys properties investigations for hydrogen sorption compressor. J Alloys Compd 2005;399:224–36. [8] Laurencelle F, Dehouche Z, Goyette J, Bose TK. Integrated electrolyser—metal hydride compression system. Int J Hydrogen Energy 2006;31(6):762–8. [9] Wang XH, Chen RG, Zhang Y, Chen CP, Wang QD. Hydrogen storage alloys for high-pressure suprapure hydrogen compressor. J Alloys Compd 2006;420:322–5. [10] Wang XH, Wang CY, Chen CP, Wang QD. Stability of AB5 -type hydrogen storage alloys. J Alloys Compd 2006;420:107–10.
Investigation on high-pressure metal hydride hydrogen compressors X.H. Wang ∗ , Y.Y. Bei, X.C. Song, G.H. Fang, S.Q. Li, C.P. Chen, Q.D. Wang Department of Materials Science and Engineering, Zhejang University, Hangzhou 310027, China Received 26 September 2006; received in revised form 2 March 2007; accepted 2 March 2007 Available online 30 April 2007
Abstract It is well known that metal hydrides can be used to compress hydrogen. In the present study, AB5 type and AB2 type multicomponent hydrogen storage alloys have been studied for the purpose of high-pressure hydrogen compression. A single stage metal hydride hydrogen compressor with hydrogen compression rate of 40 L/min and a double stage compressor with hydrogen compression rate of 20 L/min were designed and built to produce high-pressure hydrogen. The single-stage compressor produces high-pressure hydrogen around 45 MPa from 4 MPa feed gas, when hot oil at 170 ◦ C is used as the heat source. The double-stage compressor rather needs only hot water to produce 45 MPa hydrogen. 䉷 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. Keywords: Metal hydride; Hydrogen storage alloy; Hydrogen compressor; High-pressure hydrogen
1. Introduction
2. Experimental details
Hydrogen fuel cell vehicle received much attention in the past years, and lightweight high-pressure hydrogen storage tank seems to be the main onboard hydrogen storage technology at present stage. In the developed countries, great efforts have been taken in the area of lightweight high-pressure hydrogen storage tank and large progress has been made recently. With the development of high-pressure hydrogen storage technology, it is of interest to develop high efficiency hydrogen compression technology. It is well known that a metal hydride hydrogen compressor has many advantages over traditional compressors such as no moving parts, non-noise, no pollution to the compressed hydrogen [1–8]. However, the hydrogen storage alloys used in most cases of thermal desorption compressors have not been optimized, and LaNi5 or La(NiAl)5 hydrogen storage alloy is generally selected, and the product hydrogen pressure reported is usually less than 15 MPa. In this paper, we report our recent results about the singlestage and double-stage hydride compressors which can produce 45 MPa hydrogen from 4 MPa feed gas.
The Ce-rich mischmetal (Mm) is composed of La 23.8%, Ce 48.6%, Pr 8.1%, Nd 16.8%, others 2.7%. The purity of the metallic elements for sample preparation is as follows: Ni, Cr and Mn are 99.9% pure, La and Ti are 99% pure, V and Ca are 99.5% and 98% pure, respectively. Hydrogen used for hydrogenation/dehydrogenation properties measurement is 99.999% pure. Rare earth-based alloys were prepared in an RF induction furnace under the protection of Ar. TiCr 2 -based alloys were prepared by RF levitation melting. Samples were mechanically crushed into fine powder in air, and then introduced into a stainless steel reactor for the measurements of hydrogen storage properties. The p–c–T curves were determined by the constant volume and pressure difference method. Prior to p–c–T measurements, several hydriding/dehydriding cycles were carried out to ensure the samples were fully activated. The details of p–c–T measurements were described elsewhere [9,10]. During the compression tests, cold oil (293 K) and hot oil (443 K) were used as the cooling and heating sources for the singlestage compressor, but only water is used for the double-stage compressor.
∗ Corresponding author: Tel./fax: +86 571 87951152.
E-mail address: [email protected] (X.H. Wang).
0360-3199/$ - see front matter 䉷 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2007.03.002
4012
X.H. Wang et al. / International Journal of Hydrogen Energy 32 (2007) 4011 – 4015
3. Results and discussion 3.1. Single stage compressor The purpose of this study was to develop MHHCs to produce high-pressure hydrogen ((> 40 MPa) with relatively lowpressure hydrogen feed gas (3.0–4.0 MPa). In order to reach
P/MPa
10
1
298 K
0.1 0
1
2
3
4 H/M
5
6
7
Fig. 1. p–c–T curves of MmNi5 –H system.
such a target under mild conditions, the alloy selected should have relatively high hydrogen absorption/desorption plateau pressure under ambient temperature. MmNi5 meets this requirement; however, this alloy has the disadvantages of bad activation properties and large pressure hysteresis. Fig. 1 shows the p–c–T curves of the MmNi5 alloy. The pressure hysteresis factor (Hf = ln(Pa /Pd )) reaches as high as 1.62. Moreover, the alloy is difficult to activate. It does not absorb hydrogen under 8.0 MPa hydrogen pressure for 24 h, but slowly absorb hydrogen when the applied hydrogen pressure exceeds 12.0 MPa. Our previous investigation [5,6,9] revealed that partial substitution of Mm with Ca improves the activation properties as well as the plateau pressures. And it seems that the optimum Ca substitution content is 0.2–0.3. To further improve the properties of the alloy, we tried to use La to partially substitute Mm. Therefore, we prepared and characterized Mm0.8−x Ca0.2 Lax Ni5 (x = 0.0.7) series alloys. Table 1 summarized the main properties of the alloys. It is clearly seen from Table 1 that the pressure hysteresis of the alloys is remarkably improved after partial substitution of Mm by Ca and La. Moreover, as La content increases, the plateau pressure decreases, and the hysteresis factor also decreases. This may be caused by the fact that the cell volume of the alloys increases due to the increase of La/Ce ratio. Furthermore, the activation properties of the alloys are remarkably improved after partial substitution of Mm by Ca and La. In addition, to further improve the hysteresis properties, we also tried to use Al to partially substitute
Table 1 Main properties of AB5 type alloys Alloy
Hydrogen capacity (wt%)
Pd (MPa) 20 ◦ C
Pa (MPa) 20 ◦ C
Hysteresis factor (ln(Pa /Pd )) 20 ◦ C
MmNi5 Mm0.7 La0.1 Ca0.2 Ni5 Mm0.5 La0.3 Ca0.2 Ni5 Mm0.3 La0.5 Ca0.2 Ni5 Mm0.2 La0.6 Ca0.2 Ni5 Mm0.1 La0.7 Ca0.2 Ni5 Mm0.7 La0.1 Ca0.2 (Ni4.95 Al0.05 )
1.4 1.35 1.35 1.35 1.35 1.35 1.3
1.45 1.88 1.33 1.19 0.93 0.73 1.76
7.33 4.19 2.47 1.92 1.25 0.96 2.45
1.62 0.81 0.61 0.49 0.30 0.27 0.33
10
P/MPa
P/MPa
10
1
1
283 K 293 K 308 K 323 K
0
1
2
3 4 H/M
5
6
283 K 293 K 308 K 323 K
0
1
2
3 4 H/M
5
Fig. 2. p–c–T curves of Mm0.7 Ca0.2 La0.1 (Ni4.95 Al0.05 )–H system. (a) Absorption; (b) desorption.
6
X.H. Wang et al. / International Journal of Hydrogen Energy 32 (2007) 4011 – 4015
H2 compressor reactor
4013
cold/hot oil outlet
high-pressure H2 outlet
low-pressure H2 inlet oil jacket cold/hot oil inlet
Fig. 3. Schematic diagram of single stage compressor.
100 80 60 10 P (MPa)
P/MPa
40
20
10 8 6
10°C 20°C 30°C
1
4 0.0
0.5
1.0
1.5 H/M
2 0
50
100 T /°C
150
200
2.0
2.5
3.0
Fig. 5. p–c–T curves of Ti1.1 Cr 1.5 Mn0.4 V0.1 –H system.
Fig. 4. Hydrogen pressure as a function of temperature during compression.
Ni. The results are also shown in Table 1. With the consideration of plateau characteristics and hysteresis factor, we select Mm0.7 Ca0.2 La0.1 (Ni4.95 Al0.05 ) as the compression alloy. Fig. 2 shows the p–c–T curves of Mm0.7 Ca0.2 La0.1 (Ni4.95 Al0.05 )–H system. The alloy can be activated under 4.0 MPa at room temperature by 3–5 absorption/desorption cycles. Its hydrogen desorption plateau pressure at 20 ◦ C is around 2.45 MPa, and the enthalpy of dehydriding, Hd , calculated from the middle plateau pressure in Fig. 1 according to van’t Hoff equation is −24.5 kJ/molH2 . With Mm0.7 Ca0.2 La0.1 (Ni4.95 Al0.05 ) as the compression alloy, a compressor with hydrogen capacity of 1000 L was designed and built. The reactor was made of steel tubes with 38 mm outer diameter and 6 mm wall thickness. Cool and hot oil was used as the heat exchange medium. Fig. 3 shows the schematic diagram of the compressor. Fig. 4 shows the output hydrogen pressure as a function of oil temperature. The compressor can be saturated with hydrogen under 4.0 MPa hydrogen pressure when cool oil was circulated, and high-pressure hydrogen with pressure of around 45 MPa could be produced when hot oil with temperature of around 170 ◦ C was circulated. The hydrogen compression rate is around 40 L/min.
P (MPa)
10
1
40°C 30°C 20°C
0.1 0
1
2
3 H/M
4
5
6
Fig. 6. p–c–T curves of Mm0.2 La0.6 Ca0.2 Ni5 –H system.
3.2. Double stage compressor For safety purpose, we further explored the possibility of producing high-pressure hydrogen (45 MPa) by using hot water
4014
X.H. Wang et al. / International Journal of Hydrogen Energy 32 (2007) 4011 – 4015
5 MPa low-pressure H2 inlet
cold/hot oil outlet
cold/hot oil outlet
H2 compressor reactor
15 MPaH2
cold/hot oil inlet
oil jacket
45 MPa high-pressure H2 outlet
cold/hot oil inlet
Fig. 7. Schematic diagram of double stage compressor.
50
40
30 P (MPa)
as the heat exchange medium. In this case, it seems impossible to produce 45 MPa hydrogen from the feed gas with pressure of around 4.0 MPa. Thus we tried to use a double-stage compressor. Because the plateau pressure of Ti-based AB2 type alloys can be regulated in a wider range, it is reasonable to select an alloy from the above AB5 type alloys for the low-pressure stage, and to develop an AB2 type alloy for the high-pressure stage. TiCr 2 alloy has a high plateau pressure, but it has the disadvantages of bad activation properties and small effective hydrogen capacity. To overcome these demerits, we designed the alloy composition with Ti super stoichiometry and partially substituting Cr with transition metals such as Mn and V, namely, Ti1+x Cr 2−y (Mn, V)y (x = 0.0.2; y = 0.4.0.8). The results indicate that as the Mn content x increases, the plateau pressure decreases, hydrogen storage capacity increases slightly, but the pressure hysteresis increases remarkably. When Cr is partially substituted by V, the alloys maintain low hysteresis, but the plateau pressure decreases remarkably. With consideration of the plateau pressure, we finally select Ti1.1 Cr 1.5 Mn0.4 V0.1 as the high-pressure alloy. Fig. 5 is the p–c–T curves of Ti1.1 Cr 1.5 Mn0.4 V0.1 –H system. The hydrogen absorption/desorption plateau pressures at 20 ◦ C are 6.85 and 5.9 MPa, respectively. The enthalpy of dehydriding, Hd , is −23.5 kJ/molH2 . Among the above AB5 type alloys, with consideration of both the plateau characteristics and the matching properties with Ti1.1 Cr 1.5 Mn0.4 V0.1 alloy, Mm0.2 La0.6 Ca0.2 Ni5 is suitable for the low-pressure alloy. Its hydrogen absorption plateau pressure at 20 ◦ C is around 1.25 MPa and hydrogen desorption plateau pressure is around 9.86 MPa at 99 ◦ C. Its p–c–T curves are shown in Fig. 6. With the alloy pair Mm0.2 La0.6 Ca0.2 Ni5 /Ti1.1 Cr 1.5 Mn0.4 V0.1 , a double-stage compressor prototype was designed and built with water as the cooling and heating medium. Fig. 7 shows the schematic diagram of the double-stage compressor. The low-pressure stage compressor was composed of a steel tube with 38 mm outer diameter and 3 mm wall thickness, and the high-pressure stage compressor was composed of a steel tube with 38 mm outer diameter, 6 mm wall thickness. Fig. 8 shows the compression curves of the double-stage compressor. After the low-pressure stage compressor is saturated with hydrogen under around 4.0 MPa pressure, it is then heated by circulating hot water to produce hydrogen with pressure of around 10 MPa. And thus produced high-pressure hydrogen is then
20
10
1st stage 2nd stage
0 0
5
10
15 20 t (min)
25
30
35
Fig. 8. Compression curves of Mm0.2 La0.6 Ca0.2 Ni5 /Ti1.1 Cr 1.5 Mn0.4 V0.1 alloy pair.
input into the high-pressure stage compressor. In this period of time, the high-pressure compressor is cooled by circulating cold water to make the alloy absorb hydrogen. Finally, hot water is circulated into the high-pressure stage compressor, and hydrogen with pressure of around 45 MPa is produced. The hydrogen compression rate is about 20 L/min. 4. Conclusions The properties of AB5 type (MmLaCa)(NiAl)5 alloys and AB2 type Ti1+x (CrMnV)2 alloys are studied for the purpose of hydrogen compression. With the optimized alloys a singlestage hydride hydrogen compressor and a double-stage hydride hydrogen compressor were designed and built. For the singlestage compressor, product hydrogen with pressure of around 45 MPa can be produced from 4 MPa feed gas when hot oil of 170 ◦ C is used as the heat exchange medium. While for the double-stage compressor, only hot water is needed to produce 45 MPa high-pressure hydrogen. Acknowledgment This work was supported by the foundation of Hitech Research and Development Program of China (No. 2006AA05Z129).
X.H. Wang et al. / International Journal of Hydrogen Energy 32 (2007) 4011 – 4015
References [1] Wang QD, Chen CP, Lei YQ. The recent research, development and industrial applications of metal hydrides in the People’s Republic of China. J Alloys Compd 1997;253–254:629–35. [2] Chen CP, Ye Z, Wu J, Wang QD. The properties and some applications of the hydride hydrogen-compression alloy (CaMmCu)(NiAl)5 Zr0.05 . Zeitshrift Phys Chem 1994;183:251–8. [3] Au M, Wang QD. Rare earth-nickel alloy for hydrogen compression. J Alloys Compd 1993;201:115–9. [4] Nomura K, Akiba E, Ono S. Development of a metal hydride compressor. J Less-Common Met 1983;89:551–8. [5] Ivanovsky AI, Kolosov VI, Lototsky MV, Solovey VV, Shmalko YF. Metal hydride thermosorption compressor with improved dynamic characteristics. Int J Hydrogen Energy 1996;21:1053.
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