ISSN 00406015, Thermal Engineering, 2013, Vol. 60, No. 3, pp. 202–211. © Pleiades Publishing, Inc., 2013. Original Russian Text © D.O. Dunikov, V.I. Borzenko, S.P. Malyshenko, D.V. Blinov, A.N. Kazakov, 2013, published in Teploenergetika.

ENERGY SAVING, NEW, AND RENEWABLE ENERGY SOURCES

Prospective Technologies for Using Biohydrogen in Power Installations on the Basis of Fuel Cells (a Review) D. O. Dunikov, V. I. Borzenko, S. P. Malyshenko, D. V. Blinov, and A. N. Kazakov Joint Institute for High Temperatures, Russian Academy of Sciences, Izhorskaya ul. 13, str. 2, Moscow, 125412 Russia Abstract—The present state of technology for obtaining hydrogen by biological methods and for purifying it is reviewed from the viewpoint of its possible use in kilowattclass power installations. Hybrid membrane sorption biohydrogen purification methods combining membranebased pretreatment and sorptionbased final treatment, also with the use of metal hydrides, should be regarded as the most efficient ones. Keywords: biohydrogen, hydrogen purification, metal hydrides, dark fermentation DOI: 10.1134/S0040601512110043

Increasing the fraction of production and con sumption of electricity with the use of renewable sources of energy (RSEs) from approximately 0.5 to 4.5% (except with hydro power stations with a capac ity of higher than 25 MW), including biopower instal lations, incineration, and garbage processing power facilities in cities, is one of the target objectives in the energy strategy of the Russian Federation [1]. One of the characteristic features of RSEs is that the flow of energy from them is essentially nonuniform in time and space, due to which various methods of energy storage have to be implemented [2]. Hydrogen can be used as an intermediate energy carrier due to its having the highest heating value and due to its being an environmentally clean substance [3, 4]. At present, from 50 [5] to 60 million t [6] of hydro gen per annum is produced around the world; the annual growth of its production is around 4%, and a considerable increase of this growth is expected in the nearest future [6]. The petroleum industry, which according to different estimates uses from 23 [5] to 50% [6] of all produced hydrogen (the larger fraction is typical for industrially developed countries), and the chemical industry, which uses from 40 [6] to 61% [5] of all produced hydrogen for producing ammonia (largely for fertilizers) and up to 9% for producing methanol [5], are the main consumers of hydrogen. Hydrogen is also used for producing other chemical agents and is applied in the metallurgical, radioelec tronic, and food industries. Only insignificant amount of hydrogen is presently used for power generation purposes. The major part of hydrogen is obtained from min erals, mainly from natural gas and coal. At present, catalytic steam reforming of natural gas or naphta is the cheapest and most energyefficient (the efficiency is up to 83%) method for obtaining hydrogen [7]. The cost of hydrogen obtained from natural gas is in the

range $(0.3–1.83)/kg and that obtained from coal, $(2.48–3.17)/kg (in the 2007 prices). Alternative methods are essentially more costly and have not yet become economically efficient under the conditions of massscale production [8]. These methods are not always environmentally safe, and technologies for decarbonizing and storing the carbon dioxide obtained during the hydrogen production process must be worked out for developing clean power engi neering on their basis [9, 10]. A changeover for truly clean hydrogen power engi neering will become possible only if hydrogen is pro duced through the use of renewable sources of energy [11]. Solar and wind have a sufficient potential for covering the needs of the world economy in energy. However, the diffuse nature of the energy obtained from solar and wind imposes essential limitations on a largescale use of these sources due to an avalanche like growth of costs for setting up the necessary infra structure [12]. The energy of biomass produced from collected or cultivated organic materials stands out among other renewable sources of energy for its being accessible and available everywhere. Two main ways in which hydrogen can be obtained from biomass can be pointed out: a thermochemical method, which involves gasification, pyrolysis, reforming, and liquefaction, and a biochemical method, which consists of photosynthesis, fermenta tion, and esterification processes. Figure 1 shows clas sification of methods for reprocessing biomass into hydrogen [10]. Thermochemical methods for produc ing hydrogen have been well elaborated and have been used on industrial scale, whereas biochemical meth ods need further development [13]. In the 2000s, intense studies of the possibility of obtaining hydrogen using biological methods were commenced [14–18]. The term “biohydrogen” means hydrogen obtained not from fossil materials,

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Biochemical methods

Photosynthesis Dark fermentation Fermentation

Ethanol

Esterification

Biodiesel fuel

Anaerobic digestion

Biogas Gasification or reforming

Thermochemical methods

Biomass Pyrolysis

Bio oils

Hydrothermal liquefaction

Biocob

Combustion, turbine units

Electrolysis

H2

Fig. 1. Classification of methods for obtaining hydrogen from biomass [10].

but from biological sources, which is generated during decomposition of organic substances as a product of the living activity of plants, animals, and microorgan isms. An important advantage of this process is that it allows energy to be obtained from organic substrates dissolved in water, such as industrial, agricultural, and domestic effluent waters [19, 20]. Food wastes, grain crop processing products, and livestock farming wastes hold the greatest promise as raw materials for e.g. fermentation processes [21]. Biohydrogen is regarded as fuel for transport vehi cles and independent power installations constructed on the basis of lowtemperature fuel cells. Assessments show that a bioreactor with a volume of 1–10 m3 can support the operation of a 5kW power installation [22], which is quite consistent with the possibilities of an individual facility. Dark fermentation processes, which do not depend on solar energy, seem to hold promise in this respect. Recently, works have been commenced for studying the possibility of construct ing hybrid bioreactors combining dark fermentation and lightdependent production of hydrogen, e.g., by means of purple nonsulfur bacteria [15]. Those who design and commercialize all renewable hydrogen power installations encounter a common problem: the need to develop systems for efficient storage and purification of hydrogen. Hydrogen gen erated in biological systems contains a large quantity of admixtures: the total content of hydrogen in the produced gas does not exceed 50%. For example, anaerobic microorganisms participating in fermenta tion of sugars, starch, or cellulose, produce equal molar volumes of hydrogen and carbon dioxide; in addition, reaction products may contain other admix tures, such as methane, hydrogen sulfide, ammonia, and carbon monoxide [16, 22]. THERMAL ENGINEERING

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Metal hydrides selectively absorbing hydrogen can be used for purifying hydrogen [23–25] by separating it from nonadsorbed gases, including carbon dioxide, and then releasing highpurity hydrogen. Metal hydride systems have performance charac teristics that are well in compliance with the require ments lowtemperature fuel cells impose on hydrogen purity (better than 99.95 vol % [26]). The property of solidphase accumulating materials of selectively absorbing hydrogen, and high reliability, efficiency, and safety of solidphase hydrogen storage and purifi cation systems are factors that help to solve the problem of supplying fuel to independent power installations on the basis of lowtemperature fuel cells. The advantage of using metal hydride hydrogen purification and storage systems jointly with independent power installations is that operation at temperatures and pressures close to standard conditions is possible, so that the heat produced by lowgrade sources like a bioreactor for obtaining hydrogen and a power installation on the basis of low temperature fuel cells can be utilized. In this study, the possibility of using biohydrogen in power installations constructed on the basis of fuel cells was analyzed, and the applicability of the metal hydride technologies developed in the Laboratory of Hydrogen Power Technologies at the Joint Institute for High Temperatures of the Russian Academy of Sciences for purifying biohydrogen was experimen tally investigated. SCIENTIFICTECHNICAL PROBLEMS CONCERNED WITH USING BIOHYDROGEN IN POWER INSTALLATIONS Use of biohydrogen in power installations involves certain difficulties connected with its biological origin:

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—Biogas produced using the dark fermentation technology has a low content of hydrogen, which is rarely more than 50%, although the use of hybrid sys tems is considered that incorporate the biological stage of fixing carbon dioxide by microalgae in a pho tobioreactor, in which the yield of hydrogen is increased to more than 90% [27]. Such hydrogen can not be used in power installations on the basis of fuel cells containing a solidpolymer electrolyte. —Since the process goes at atmospheric pressure, the obtained hydrogen has low partial pressure, due to which the need to install a compressor arises, and, accordingly, larger energy expenditures are required for obtaining the final product. —Certain expenditures of energy for heating are required in order to maintain the optimal temperature in the reactor (above the temperature of surrounding medium). These expenditures, taken together with energy expenditures for compression, may shift the energy balance in the biohydrogen production system toward the negative region for many types of organic wastes [28, 29]. In [30], a pilot bioreactor with a volume of 1.48 m3 was described, which had successfully operated for 200 days. During its operation, the reactor produced up to 5.57 m3 H2 from 1 m3 of the reactor volume a day, and the produced biogas contained from 40 to 52% of hydrogen. Such hydrogen cannot be used in solid polymer fuel cells; moreover, it may lead to their fail ure [31]. Thus, development of renewable hydrogen production systems must be supported by parallel development and integration of hydrogen storage and purification systems [32]. Four basic methods for separating mixtures of hydrogen with other gases are now widely used in the industry, which are based on absorption (both physical and chemical), adsorption, and on membrane and cryogenic separation techniques. The technical and economic indicators of these methods are closely con nected both with the main hydrogen production pro cesses (primarily the methane reforming process) and with the needs of main hydrogen consumers (petro leum refinery and production of ammonia and meth anol). Till the early 1980s, the production of hydrogen through the methane reforming process involved the use of absorption cleaning by washing in a solution of weak alkali or amine (ethanolamine) followed by sub jecting the remainders of CO and CO2 to methaniza tion. The gas produced in this way contained 95–97 vol % of hydrogen, 2–4 vol % of methane, and 0–2 vol % of nitrogen [33]. This technology is discussed in detail in the monograph [34]. Washing of hydrogen in scrubbers is still widely used in the production of ammonia; the advantage of amine absorption is that it concurrently purifies hydrogen from sulfur com pounds, which may be contained in synthesis gas [5].

Since the early 1980s, pressureswing adsorption (PSA) has become the main industrial hydrogen puri fication method. At present, up to 85% of the hydro gen obtained around the world is produced using PSA in the technological cycle [35]. The operating princi ple of PSA is simple: admixtures are selectively sorbed on micro and mesoporous sorbents (zeolites for CH4, CO, and N2; activated carbon for CO2; and silica gel or alumogel for H2O [33]) as the initial mixture comes in contact with adsorbent in a packed column at a pres sure of 2–6 MPa. Purified hydrogen leaves the col umn, after which the adsorbent is regenerated by purg ing it with product gas at reduced pressure. Purging gas can be used as fuel in the technological cycle. Depend ing on the desired value of hydrogen extraction ratio (up to 90%) and product gas purity (higher than 99.9999%) [33], the process can be complicated by using several purification columns. A typical system containing 10 columns can produce hydrogen with purity of 99.999% from the products obtained from steam conversion of methane (77% H2, 22.5% CO2, 0.35% CO, and 0.013% CH4, with a pressure of 2.07 MPa and temperature of 21°C) at a close to the inlet pressure, and with an extraction ratio of up to 86% [35]. Cryogenic purification is mainly used for large scale production of hydrogen from byproducts of petroleum refinery, which contain 30–75% of hydro gen and up to 30% of hydrocarbons (ethane, propane, and alkenes). The initial mixture is dried, and dry gas is cooled to the liquefaction temperatures of different components, which are separated one after another in separators. In purifying initial mixture (at 4 MPa) con taining 33.7% of hydrogen, it is possible to obtain hydro gen with purity of 95%, extraction ratio equal to 85% and hydrocarbon extraction ratio of up to 75% [36]. The membrane separation methods are based on different permeabilities of membranes for individual gases composing a mixture [37]. Purification of hydro gen by means of membranes is the most economically justified method for small flowrates of initial mixture [38]. At present, membrane systems such as polymeric asymmetric membranes Polysep produced by UOP (the United States) and PRISM (developed by Mon santo) that are produced by Air Products and Chemi cals Inc. (the United States) are widely used for extracting hydrogen with purity from 70 to 99% and with an extraction ratio of 70–95% from gas flows in the petroleum refinery industry [33]. The modern state of membrane methods for extracting hydrogen are reviewed in [39]. The table gives a comparison of the main industrial methods used for purifying hydrogen [38]. It should be pointed out that ready industrial solutions, especially cryogenic purification and PSA, were developed pri marily for largescale production of hydrogen and cannot be directly used for purifying small quantities of biohydrogen. The PSA technology allows the high THERMAL ENGINEERING

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Table Indicator

Membrane systems

PSA

Cryogenic systems

Medium

High

Low

Instantaneous

Fast (5–15 min)

Slow

Startup time after making changes

Extremely small (10 min)

1h

8–24 h

Possibility to operate with low load

Up to 10%

Up to 30%

Up to 50%

Reliability

Up to 100%

95%

Limited

Low

High

High

Very high (modular design)

Medium

Very low

Medium

No

High

30–90

75–90

30–75

>1.0

1.5–3.0

>2.0

Raw material flowrate, m3/h

<30000

103–105

>105

Product purity, %

90–98

>99

90–98

Operational flexibility Response

Requirements for the control system Extension ability Value of byproducts Composition of raw material (H2), % Raw material feed pressure, MPa

est purity to be achieved, but it becomes considerably less efficient if initial raw material with a low content of hydrogen is used; in addition, this technology is not readily amenable for scaling to small flows of gas being purified. Works aimed at creating compact PSA sys tems are known [40]; however, they can be used only for carrying out finish purification of hydrogen with a low initial content of impurities. The technology of polymeric membranes can well be scaled in its perfor mance characteristics for use with biohydrogen pro duction systems, but the purity of obtained hydrogen is the limiting factor here, because its level is insuffi cient for use in power installations on the basis of fuel cells. Thus, the problem of purifying hydrogen obtained by biological methods and producing it in quantities sufficient for operation of kilowattclass power instal lations has not been solved as yet, because neither the flowrate of initial mixture produced in bioreactors, nor its pressure and purity comply with the require ments imposed by the industrial purification methods. At present, the possibility of using metal mem branes for purifying hydrogen is being considered owing to their having exceptionally high selectivity [35]. Highpure hydrogen can be obtained using pal ladium membranes; however, these membranes are made with the use of precious metals; they operate at relatively high temperatures (350–500°C), and their performance characteristics degrade when they come in contact with many admixtures [33, 41, 42]. The presence of carbon dioxide may affect their effi ciency; for example, the throughput capacity of the THERMAL ENGINEERING

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composite membrane “Pd + 23%Ag/steel” drops by 10–15% depending on the partial pressure of carbon dioxide [43]. The pressure of initial flow is an important factor influencing the efficiency of using membranes for sep arating hydrogen from mixtures. With a low difference of pressures across the membrane, the ratio of product gas flow to the inlet flow is determined by the ratio of their pressures and not by the membrane selectivity [44]. In order to increase the hydrogen extraction ratio from biogas with the use of highly selective mem branes, it is necessary to essentially increase the pres sure of inlet flow by means of compressors, which may turn to be economically unfeasible. For increasing the throughput capacity of sorption hydrogen purification methods, it was proposed to use absorbents with increased selectivity [32], including metal hydrides, which selectively absorb hydrogen. Various intermetallic alloys can reversibly absorb hydrogen, and their ability to operate at temperatures and pressures close to the standard conditions is their important advantage. Pilot installations for purifying industrial gas flows with the use of metal hydrides were constructed in different countries [45], primarily in production of ammonia [46], and it should be noted that metal hydride technologies can have better energy efficiency than the traditional ones [34, 47]. Admix tures may adversely affect the absorption of hydrogen by metal hydrides. Some substances, such as H2S or CO2 poison the surface of absorbing material particles [48–50]; CO2 can also contaminate metal hydrides [49, 50], and noninteracting “inert admixtures” slow

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Metal hydrides

Product gas H2

Weakly

Nonadsorbed admixtures “Inert”: Ar, He, N2, CH4, C2H6 Weakly interacting: CO2, NH3, C2H4, C3H6 (~1000* cycles)

N2, Ar, O2

H2O, O2

Medium adsorbing gases

CO, CH4, C2H6, C2H4

CO, H2S, SO2,

Strongly adsorbing gases

CO2, H2S, C3H6, C4+, NH3, H2O

adsorbing gases

Chemical interaction (approximately 100* cycles) Surface poisoning (1–2* cycles)

CH3SH H2

Product gas

Initial mixture Fig. 2. Gas and vapor sorption ratio during SCA [39] and during interaction with metal hydrides. *The capacity drops by a factor of 2 at a content equal to 0.1 vol %.

down the hydrogen absorption reaction [51]. Figure 2 shows a comparison of the degree of interaction of dif ferent gases and vapors with sorbents in the case of using SCA and metal hydride purification. As a result, hybrid membraneadsorption methods may turn to be the most efficient hydrogen purifica tion techniques [39], in which gas is subjected to pre treatment using polymeric membranes, and the final treatment is carried out using the sorption methods. The basic process circuit of such system is shown in Fig. 5. Biogas obtained in a dark fermentation biore actor is compressed by a compressor and is forwarded to the membrane purification unit. This unit serves primarily for separating all components except hydro gen and carbon dioxide, which are separated in the sorption purification unit that can operate according to the metal hydride technology. The spent gas can be used in the exhaust utilization system, e.g., by firing the residual hydrogen for heating the bioreactor and metal hydride reactors in the hydrogen desorption process. By now, a lot of studies for optimizing the heat and mass transfer processes in metal hydrides have been carried out, and various types of metal hydride reac tors have been developed [52–62]. Either methods close to PSA [63] or methods for filtering a mixture by passing it through a bed of absorbing alloy [64] can be used for purifying hydrogencontaining gas flow by

means of metal hydrides. The studies carried out by the authors have shown that for purifying hydrogen containing small amounts of admixtures the method involving cyclic discharge of accumulated admixtures from the reactor similar to PSA is the most suitable one, whereas for mixtures having a high content of impurities the method of filtering a mixture by passing it through metal hydride is more efficient [65–68]. AN EXPERIMENTAL STUDY OF THE POSSIBILITY OF SEPARATING HYDROGEN AND CARBON DIOXIDE USING METAL HYDRIDES The experiments for studying purification of gas eous hydrogen from carbon dioxide were carried out at the comprehensive experimental rig of the Joint Insti tute for High Temperatures, Russian Academy of Sci ences (OIVT RAN) [65] using the RKhOP1 flow type metalhydride reactor for storing and purifying hydro gen (Fig. 4). Physically, the RKhOP1 reactor is made as a vertical cylindrical shell with an inner diameter of 57 mm and a height of 247 mm filled with a charge of activated hydrogenabsorbing alloy LaFe0.1Mn0.3Ni4.8 developed at the Moscow State University by S.V. Mitrokhin with coworkers. The alloy charge weight is 1.63 kg, the maximal capacity is 1.36 wt % (246 ln), the heat of hydration reaction is 34.9 kJ per mole of H2, and the equilibrium pressure of hydro THERMAL ENGINEERING

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PROSPECTIVE TECHNOLOGIES FOR USING BIOHYDROGEN IN POWER INSTALLATIONS CO2

207

H2

Compressor Hydrogen accumulator

Exhaust recovery

Biogas

Bioreactor

Membrane purification

Concentrate

Sorption purification Substrate Permeate(H2 + CO2) Wastes

Fig. 3. Basic circuit of the integrated hydrogen purification and storage system.

gen above the alloy is 0.014 MPa at 0°С and 0.42 MPa at 80°С. The results of experiments for separating a mixture containing 50% of hydrogen and 50% of carbon diox ide are shown in Fig. 5. At the reactor charging stage, the mixture of hydrogen with impurity gas (carbon dioxide) is supplied for 240 min to the reactor with a flowrate ranging from 0 to 5 ln/min (see Fig. 5a) through the upper inlet socket at the pressure pin = 0.6 MPa at a thermostat temperature of 0°С. The lower outlet socket is connected with the system for exhausting gases into the atmosphere (pout = 0.1 MPa), and the pressure difference forces the mixture to flow from the inlet to the outlet valve through the bed. As the mixture passes through the bed, the hydrogenabsorbing alloy absorbs the major part of hydrogen causing the temper ature in the bed to grow (Fig. 5e). The flowrate at the out let is limited at a level of 1 ln/min (Fig. 5b). The flowrates are set and measured using flowrate controllers of the LabFlow series produced by Bronkhorst. Once the reactor has been charged with hydrogen, the inlet valve is closed, the thermostat temperature grows to 80°C (see Fig. 5e), and the alloy bed begins to desorb hydrogen, which leaves the reactor through the outlet socket, and the flowrate controller records the gas flowrate. The purity of hydrogen released by the metal hydride was monitored using a Varian CP4900 gas chromatograph (its purity was better than 99.99%). Metal hydrides release hydrogen with a high degree of purity; therefore, the content of admixtures in the gas at the outlet from the experimental section was mainly determined by the extent to which the remainders of mixture were pumped off from the installation’s pipelines. The content of hydrogen in the discharged depleted mixture (see Fig. 5c) is determined by means of a flowtype gas analyzer made on the basis of an AG0012 sensitive element combined with a gas flow THERMAL ENGINEERING

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meter. At the beginning of the charge process, the gas analyzer’s readings show that the discharged mixture does not contain hydrogen. This, together with a growth of temperature in the bed indicates that the alloy particles actively absorb hydrogen. As the alloy is becoming saturated with hydrogen, the hydration reaction slows down (which can be seen from the drop of bed temperature, Fig. 5e), breakthrough of hydrogen through the bed occurs, and the fraction of hydrogen in the discharged mixture begins to grow (see Fig. 5c). In all, 466 ln of mixture (233 ln of H2) was fed to the reactor during the experiment; 254 ln of depleted mix ture was released into the atmosphere through the out let socket, and 212 ln of pure hydrogen was obtained during the discharge process. Thus, the total loss of hydrogen during the purification process was equal to 21 ln of H2; accordingly, the hydrogen extraction ratio in the process was around 91%. In the first 180 min of the process, 190 ln of hydrogen was charged into the reactor, its loss during this period did not exceed 1%, and the main portion of hydrogen losses fell on the final stage of the charge process. This was due to the fact that the bed became saturated with hydrogen over its entire height, and that crisis of heatandmass transfer occurred in the reactor, due to which the hydrogen absorption reaction rate slowed down dra matically and breakthrough of hydrogen through the bed occurred. Clearly, the purification process must be stopped before the onset of crisis. In this case, it will be possible to achieve the highest hydrogen extraction ratios from mixtures with nonadsorbed gases, includ ing carbon dioxide. Such process can be organized e.g., by setting up a cascade system of reactors. In conclusion, it should be pointed out that biolog ical production of hydrogen by means of dark fermen tation may become an efficient method for providing fuel to isolated consumers and a method for purifying organic wastes. The review of materials published in

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Discharge to atmosphere

CFM 4 5 V

V

V PG

CFM PG

3 2

EMV R

1

V H2

CO2

N2

Emp ty

Fig. 4. Schematic diagram of the experimental section. (1) Area for preparing gas mixture, (2) experimental metalhydride reactor RKhOP1, (3) thermostat, (4) flow type gas analyzer, and (5) vacuum pump. Vs are manually operated valves, PG is a pressure gage, EMVs are electromagnetic valves, CFMs are controlling flow meters, and R is a reducer.

the literature shows that active works for developing highperformance bioreactors and microorganisms are being carried out. However, the hydrogen pro duced by them cannot be directly used in power instal lations constructed on the basis of fuel cells with solid polymer electrolyte due to a high content (more than 50%) of impurities, primarily carbon dioxide. The modern industrial hydrogen purification methods are not readily adaptable to the needs of kilo wattclass power installations; therefore, there is a need to develop dedicated purification systems able to purify gas flow containing less than 50% of hydrogen at temperatures and pressure close to standard condi tions. This problem can be solved by using a combined membrane and sorption purification system in which biohydrogen is pretreated by means of polymeric membranes, and final separation of hydrogen and car bon dioxide is carried out by selectively absorbing hydrogen using intermetallic alloys. The advantage of using metal hydrides for purifying hydrogen over other sorption and membrane methods is that this purifica

tion technique features exceptionally high selectivity of the hydrogen purification process and that it can be used at low temperatures and pressures. The possibility of separating a mixture containing 50% of hydrogen and 50% of carbon dioxide in a metal hydride reactor with the use of AB5 intermetallic alloy has been experimentally demonstrated. During the experiment, 466 ln of mixture was purified to hydrogen purity better than 99.99% and with an extraction ratio of around 91%. It has been shown that the loss of hydrogen has a nonlinear dependence on time, and that by reducing load on the sorbent the hydrogen purification process can be carried out with an extrac tion ratio of up to 99%. ACKNOWLEDGMENTS The authors are grateful to the Ministry of the Rus sian Federation for Education and Science for render ing financial support to the investigations (state con tracts nos. 16.516.11.6052, 16.11.516.6103, and NSh THERMAL ENGINEERING

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jin, ln/min

PROSPECTIVE TECHNOLOGIES FOR USING BIOHYDROGEN IN POWER INSTALLATIONS 3 2 1 0

jout, ln/min

(а) 3 2 1 0 (b)

СН2

1.0 0.5 0 (c) p, МPа

0.6 0.4 0.2 0 (d)

t, °C

80 40 0 0

100

200 (e)

300

400 τ, min

Fig. 5. Results of the experiment for separating a mixture containing 50% H2 and 50% CO2 in the RKhOP1 reactor. (a) Flowrate of hydrogen at the reactor inlet jin, (b) flow rate of hydrogen at the reactor outlet jout, (c) volume frac tion of hydrogen in the gas flow at the reactor outlet CH2, (d) pressure in the reactor, and (e) temperature of the ther mostat (the dashedanddotted curve) and at the center of hydrogenabsorbing material bed (the solid line).

3717.2010.8). The authors are also grateful to V.D. Zhemerikin for assistance in carrying out exper imental studies, to S.V. Mitrokhin for development of hydrogen absorbing materials, to I.A. Romanov for the provided experimental data on the properties of hydrogen absorbing materials, and to B.P. Tarasov for the provided information on the effect of admixtures of metal hydrides. REFERENCES 1. “The Energy Strategy of Russia for the Period of Up to 2030, Approved by the Decree of RF Government No. 1715r of November 13, 2009,” Sobr. Zakonod. RF, No. 48, Article 5836 (2009). THERMAL ENGINEERING

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