Article pubs.acs.org/IECR
Separation of Carbon Dioxide from Coal Gasification-Derived Gas by Vacuum Pressure Swing Adsorption Katarzyna Labus, Stanisław Gryglewicz,* and Jacek Machnikowski Division of Polymer and Carbonaceous Materials, Faculty of Chemistry, Wrocław University of Technology, ul.Gdańska 7/9, 50-344 Wrocław, Poland ABSTRACT: A mixture of 20% CO2, 50% CO, 25% H2, and 5% CH4, which reflects the gas composition from coal gasification, was subjected to vacuum pressure swing adsorption (VPSA) in order to remove CO2 from the gas fuel. Zeolites and activated carbons were used as adsorbents. The performance of the VPSA process was assessed through the CO2 recovery and productivity and the product purity. A strong correlation between the working capacity of an adsorbent expressed on a volumetric basis and the amount of CO2 produced in the VPSA process was found. It was demonstrated that the rinse of an adsorbent with CO2 before evacuation in the VPSA process allows obtaining activated carbons comparable to that of superior adsorbents such as zeolite 13X. CO2 purity of 95% with a 75% recovery were obtained at ambient temperature and pressure of 1.5 bar for KOHactivated carbon with a highly developed narrow microporosity.
1. INTRODUCTION The separation of CO2 and other gases from gas streams is a necessary operation in many important tonnage processes and perspective in the power industry. Almost 42% of industrial CO2 emission derives from energy conversion, mainly from the conventional coal-fired power plant.1 Coal combustion results in about 50% higher CO2 emission compared to the combustion of natural gas per unit of generated energy. Therefore, there are many studies on the separation of CO2 from flue gases (CO2/N2).2−7 The reduction of CO2 emission can be achieved by introducing clean coal technologies such as coal gasification. The precombustion technology designed to fuel decarbonization is particularly promising. First, the coal is subjected to gasification using a mixture of water vapor and oxygen. The gaseous product of coal gasification is a mixture of CO, H2, CO2, and CH4. By removing CO2 from coal gasification-derived gas, it is possible to obtain an excellent fuel that emits very small amounts of CO2 during combustion compared to a direct combustion of coal. There are three major separation techniques used for the removal of CO2, that is, absorption in amines, membrane separation, and adsorption on solid adsorbents. The most currently used method of removing CO2 from industrial gas streams is the absorption in the solution of amines. This approach is below the expectations because of its great energy consumption linked with the regeneration of the absorbent solution, problems with corrosion of apparatus, and chemical degradation of the amine solution.8 The membrane processes9 is potentially an attractive gas separation technology due to the energy saving and easy installation. It is a prospective method that is currently not used in a wide range of the industry. Vacuum pressure swing adsorption (VPSA) technology is promising because of its low energy requirements and simplicity.10,11 This technology is based on solid, regenerative adsorbents. It does not use chemicals, which may pollute the environment. The process of regeneration of an adsorbent does © 2014 American Chemical Society
not require delivery of heat. Desorption of the adsorbed gas occurs under reduced pressure, typically up to 0.01−0.05 bar. The crucial task for the effective removal of CO2 is selection of a suitable adsorbent. It should have a strong affinity for CO2, a large sorption capacity (per unit of volume), and a high selectivity toward CO2. It is also important that the affinity of the adsorbent for CO2 should not be too high, otherwise the regeneration step will be more expensive.12 Moreover, the adsorbent is required to have the capability for rapid adsorption and desorption for the adsorbed gas, low heat of adsorption, and suitable textural properties.13,14 The material used in packed columns must also be in the form of granules with reasonable mechanical strength to reduce the pressure drop.15 There are various materials considered as adsorbents for the CO2 removal process. In commercial practice, activated carbons, zeolites, and titanosilicate molecular sieves are mainly applied. The use of surface-modified adsorbents, such as metal organic frameworks (MOFs) and mesoporous silicas, has been also reported.8,9,16 Generally, the biggest advantage of the zeolites is greater equilibrium adsorption selectivity for CO2, as compared to activated carbon,17 and thus, zeolites are generally preferred.18−20 However, this difference decreases when the adsorption pressure increases. The adsorption process performed using zeolites is slightly dependent on the pressure. Such properties of zeolites are an outcome of metal cations presence in their composition and thus the appearance of an electromagnetic field, which interacts with an especially high molecular quadrupole moment of the CO2 molecule.21,22 Zeolites are strongly hydrophilic materials. Removing adsorbed water requires a temperature close to 280−300 °C. In principle, it is not possible to use the zeolites for the separation of CO2 from the water vapor-containing gas stream. Received: Revised: Accepted: Published: 2022
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degassed overnight at 300 °C. N2 adsorption isotherms were used to determine the total pore volume (VT), Brunauer− Emmett−Teller (BET) surface area (SBET), and the development of microporosity (0.7−2.0 nm). The micropore volume (VDR) and the average micropore width (L0) were calculated by applying the Dubinin−Radushkevich and Stoeckli equations,26 respectively, to the adsorption in the p/p0 range from 2 × 10−5 to 0.05. For evaluation of ultramicropores (95%) and a high concentration of CO2 (purity >95%) in order to avoid loss of valuable gas components. Although CO2 is a small molecule of linear structure, it has a large quadrupole moment. This feature allows for penetrating into the pores with a small size that results in a strong interaction with the surface of adsorbent and high adsorption capacity.8,25 CO and CH4 show an intermediate adsorption affinity that may complicate the CO2 separation process. Their presence in the final product is highly undesirable.16 In turn, hydrogen is a poor adsorbing gas, especially in presence of other adsorbates (competition effect). The goal of this work is to remove CO2 from coal gasification-derived processing gas, consisting of 50% CO, 25% H2, 20% CO2, and 5% CH4, using the VPSA technique. A series of activated carbons of different porous texture and zeolites were tested as adsorbents for this purpose. The VPSA process was optimized in order to increase the CO2 purity and recovery with the highest productivity. The influence of adsorption pressure and rinse with CO2 upon the effectiveness for CO2 removal was determined.
2. EXPERIMENTAL SECTION 2.1. Characterization of Adsorbents. 2.1.1. Adsorbents. A range of adsorbents were investigated in this study: four commercial activated carbons: Norit R2030CO2 (N), Sorbonorit K4 (S) (Norit Co.), Oxorbon K20J (O) (Donau Carbon Co.), and Berkosorb (B) (PICA Co); two zeolites: 13X (Alfa Aesar Co.) and 5A (Serva); and laboratory prepared activated carbon A-CS800-2 (A-CS). 2.1.2. Preparation of Activated Carbon. Bituminous coal from the Szczygłowice mine (S) was used for the preparation of A-CS. The parent material was pyrolyzed in a horizontal tube reactor at the final temperature of 800 °C for 2 h. The resultant coke was grounded and sieved to prepare a size fraction of 0.63−1.25 mm. In the next step, a physical mixture of anhydrous KOH and the prepared coke in the weight ratio of 2:1 was placed in a nickel boat and heated at a rate of 10 °C min−1 to the final temperature of 800 °C and soaked for 1 h under nitrogen flow. The reaction product was washed with a 10% solution of HCl and distilled water and dried at 120 °C for 3 h. 2.1.3. Textural Properties. A porous structure of adsorbents was evaluated by N2 adsorption at −196 °C using ASAP2020 (Micromeritics). Prior to the measurement, the sample was
Figure 1. Scheme of the apparatus used in this study: (1) gasholder; (2) adsorber; (3, 4) mass flow controller; (5) gas analyzer; (6, 7) pressure gauge; (8) vacuum pump.
unit system was constructed of stainless steel column (1.5 cm i.d. and 50 cm height) and lines (1/4′). The adsorption column has a volume amounted to 100 cm3. The constant flow rate was monitored by two mass flow controllers. The composition of gas was measured by an electric mass analyzer (GAS 3000, Atut Co.) with an infrared detector. The process was carried out at 25 °C under a constant flow (1000 cm3/min) and at different 2023
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Figure 2. Scheme of the single-column VPSA and VPSA/CO2 processes.
pressures (1.5, 4, 6, and 11 bar) in the column packed with an adsorbent. The separation of CO2 from a mixture of 50% CO, 25% H2, 20% CO2, and 5% CH4 was performed using VPSA and VPSA/ CO2. The single-column VPSA and VPSA/CO2 processes were carried out according to the scheme presented in Figure 2. Before testing, the apparatus was evacuated with a vacuum pump and filled with hydrogen to atmospheric pressure. The proposed VPSA separation process consists of the following steps: (1) cocurrent feed Pressurization up to the adsorption pressure (pads); (2) cocurrent Adsorption I up to 2% CO2 in the gas leaving the adsorber, under constant adsorption pressure (pads); (3) cocurrent Adsorption II up to equalize the concentration of CO2 with the feed gas (20% CO2) at adsorption pressure (pads); (4) cocurrent blowdown (Desorption I) to a half of the adsorption pressure (1/2pads); (5) countercurrent blowdown (Desorption II) to the atmospheric pressure; (6) countercurrent Evacuation by the vacuum pump from 1 to 0.06 bar to remove the adsorbed gas. In the case of VPSA/CO2, before evacuation, the adsorbent bed was rinsed with pure CO2 at atmospheric pressure until 98% CO2 at the outlet of the column was reached. The efficiency of the CO2 separation process was assessed in terms of recovery, purity, and productivity of CO2.
Figure 3. N2 adsorption isotherms at −196 °C for the studied samples.
Table 1. Textural Parameters and Bulk Density of the Studied Adsorbentsa
3. RESULTS AND DISCUSSION 3.1. Characterization of the Adsorbents. A porous structure of an adsorbent has the crucial impact on the adsorption process. The N2 adsorption isotherms determined at −196 °C for the studied adsorbents are presented in Figure 3. The shape of the isotherms indicates that all adsorbents are microporous in their nature. A sharp knee of an isotherm proves a very high contribution of micropores for A-CS, B, and N, whereas a gentle bend corresponds to wider micropores, as observed for S and O. The porous structure parameters calculated from the N2 adsorption isotherms are given in Table 1. The studied materials differ significantly in their porous texture. The BET surface area is between 473 and 1344 m2/g. The total pore
adsorbent
SBET (m2/g)
VT (cm3/g)
VDR (cm3/g)
L0 (nm)
bulk density (g/cm3)
N O S B A-CS 5A 13X
715 1290 1210 1101 1344 473 664
0.30 0.71 0.71 0.46 0.56 0.24 0.33
0.28 0.46 0.45 0.42 0.54 0.20 0.28
0.78 1.69 1.90 0.95 0.82 n.d. n.d.
0.55 0.42 0.46 0.52 0.31 0.78 0.71
a
SBET, BET surface area; VT, total pore volume; VDR, micropore volume; L0, average micropore width; n.d., not determined.
volume ranges from 0.24 to 0.71 cm3/g, with a micropore fraction of 0.63−0.96. The differences in the microporosity development between the tested ACs are also reflected in the average micropore width that ranges from 0.78 to 1.90 nm. ACS has both the highest BET surface area and micropore volume with an average pore width of 0.82 nm. S and O carbons show slightly lower SBET and VDR; however, their micropores are over 2-fold wider. The studied zeolites have both lower surface area and micropore volume compared with the ACs. 2024
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It should be noted that the ACs with a highly developed porosity have lower bulk density, which may lead to a lower adsorption capacity on a volumetric basis compared with that expressed on a weight basis. From a practical point of view, an evaluation of the potential of the adsorbents of being cycled using VPSA should be done on a volumetric basis. 3.2. Adsorption Capacity and Selectivity. The performance of the adsorbents in terms of their selectivity for CO2 was assessed by comparing the adsorption capacities determined separately for CO2, CO, and CH4 at an ambient temperature in the pressure range 4−11 bar. Under such conditions, the adsorbed amount of hydrogen was barely measurable; hence, hydrogen was excluded from further considerations. The volumetric adsorption capacities for CO2, CH4, and CO at pressures of 4, 6, and 11 bar at 25 °C are given in Table 2.
Figure 4. Selectivity for CO2 over CO as a function of the adsorption pressure.
Table 2. Adsorption Capacities for CO2, CH4, and CO (cm3 of Gas/cm3 of Adsorbent) CO2
CH4
The tests have been carried out for pure gases, which eliminates competitive adsorption. Therefore, the obtained data does not well describe the phenomena occurring in the process of a simultaneous adsorption of multiple components from a gas mixture. Furthermore, only a fraction of micropores takes part in the gas separation process in reality, which is responsible for the so-called “working capacity” of an adsorbent restored repeatedly in a quick desorption process. After the first cycle, the narrowest micropores get blocked and are not involved in the VPSA process. 3.3. Working Capacity. The CO2 working capacity and retentivity at 25 °C for the studied adsorbents are given in Table 3. The CO2 retentivity reflects the micropores that are
CO
gas pressure (bar) adsorbent
4
6
11
4
6
11
4
6
11
N O S B A-CS 5A 13X
41 31 30 54 44 65 70
49 45 44 70 58 69 76
58 74 69 92 74 74 84
19 13 12 22 17 17 10
24 18 17 29 22 22 15
31 27 26 41 31 31 23
8 13 9 22 17 25 17
11 17 12 30 23 31 23
17 27 20 43 33 40 33
Table 3. Adsorbed Amount of CO2 under Different Outgassing Conditions for the Tested Adsorbents (cm3 of Gas/cm3 of Adsorbent)
The zeolites (13X and 5A) show the highest ability of CO2 adsorption at pressure up to 4 bar, followed by B and A-CS carbons. An increase of the pressure to 11 bar lead to a more than 2-fold rise of the CO2 adsorption capacity for ACs and only a 10% increase for zeolites. This clearly confirms a slight impact of pressure on the adsorption process in case of the usage of zeolites. The different relation was found for CO and CH4 adsorption. All adsorbents, including the ACs and the zeolites, show similar behavior; that is, the adsorbed amount of gases increased almost linearly with the adsorption pressure; however, the absolute absorption amount was much lower than for CO2. It agrees with the results reported previously for a series of ACs.28 In our work, a 2-fold increase in the adsorption capacity of CO and CH4 can be observed when the pressure increases from 4 to 11 bar. The relationship between the CO2 selectivity and the adsorption pressure for all adsorbents is shown in Figure 4. The CO2 selectivity of an adsorbent was calculated as the ratio of the adsorption capacity for CO2 and the adsorption capacity for CO. It was found that the selectivity for CO2 over CO is in the range 1.5−5.5, which means that the adsorbed amount of CO2 is 1.5−5.5 times higher than that of CO under the same conditions. Except for the O carbon, the selectivity decreases with an increasing adsorption pressure. Among the studied adsorbents, the N carbon is characterized by the highest selectivity for CO2 in the whole range of applied pressures, which may be ascribed to its smallest micropores (L0 = 0.78 nm). The zeolites show worse performance in the selective removal of CO2 compared with N. In particular, the zeolite 5A presents the lowest selectivity among all adsorbents, indicating the uselessness of micropores with a width of 0.5 nm in the selective separation of CO2 form a mixture of CO2 and CO.
total capacity
working capacity
outgassing conditions sample
1.0 × 10−5 bar, 250 °C
6.0 × 10−2 bar, 25 °C
retentivity
N O S B A-CS 5A 13X
28.1 14.9 13.9 33.6 25.6 67.9 81.4
21.6 12.7 11.7 26.0 20.0 15.2 31.2
6.5 2.2 2.2 7.6 5.6 52.7 50.3
filled in with CO2 up to 6.0 × 10 −2 bar and do not contribute to the adsorption−desorption cycles. The CO2 retentivity of the ACs ranges from 2.2 to 7.6 cm3/cm3, while it is significantly higher for the zeolites. Despite its high retentivity, the zeolite 13X shows the highest working capacity among the tested adsorbents. In order to learn which micropores contribute to the retentivity, the pore volume distribution of the ACs was determined by applying the density functional theory method to the CO2 adsorption isotherms measured at 0 °C. A careful analysis of the pore volume distribution and the CO2 adsorbed up to 6 × 10−2 bar at 25 °C revealed that the micropores with a width below 0.6 nm are responsible for the retentivity. This is supported by a very high correlation coefficient of a linear regression (R2) for the relationship between the volume of CO2 adsorbed up to the pressure of 6 × 10−2 bar at 25 °C and the volume of micropores with a width below 0.6 nm (V SBET > 1350 m2/g) and micropore fraction in the total pore volume (VDR/VT > 0.9) and an average micropore width in the range 0.82−0.95 nm (Table 1). It is interesting to note that the superior adsorbents (zeolite 13X, B, and A-CS) show the highest working capacity (Table 3). Moreover, a linear relationship between the amount of CO2 produced (desorbed) in the VPSA process (Product 6, Figure 2) and the working capacity can be observed (Figure 6). Due to their best performance in the VPSA process, the zeolite 13X and the activated carbons B and A-CS were selected for further study to determine the influence of the VPSA process conditions on the effectiveness of CO2 separation from processing gas obtained by coal gasification. 3.5. Influence of the VPSA Process Conditions. In this section, the influence of the adsorption pressure in the range 1.5−11 bar and CO2 rinse on the effectiveness of CO2 removal from a mixture of 20% CO2, 50% CO, 25% H2, and 5% CH4 has been investigated. All runs were carried out at 25 °C under 2026
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Figure 7. Influence of the adsorption pressure in the VPSA process on the (a) recovery, (b) purity, and (c) productivity of CO2 for the selected adsorbents.
Figure 8. Influence of the adsorption pressure in the VPSA/CO2 process on the (a) recovery, (b) purity, and (c) productivity of CO2 for the selected adsorbents.
enhances the product purity to a high extent, particularly at low adsorption pressures. In the case of A-CS, as an example, the CO2 purity increased from 66% to 95% at 1.5 bar with a high 85% recovery. An increase in the CO2 concentration in the final product compensates for the loss of the process efficiency
The results of the VPSA experiments demonstrate that, among the tested adsorbents, the zeolite 13X exhibits the best CO2 separation performance in terms of productivity and purity with a recovery comparable to ACs. The rinse of an AC bed with CO2 before the vacuum desorption (VPSA/CO2) 2027
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capture from flue gas in an existing coal-fired power plant. Chem. Eng. Sci. 2013, 101, 615−619. (5) Plaza, M. G.; Garcia, S.; Rubiera, F.; Pis, J. J.; Pevida, C. Postcombustion CO2 capture with a commercial activated carbon: Comparison of different regeneration strategies. Chem. Eng. J. 2010, 163, 41−47. (6) Chou, C. T.; Chen, C. Y. Carbon dioxide recovery by vacuum swing adsorption. Sep. Purif. Technol. 2004, 39, 51−65. (7) Aaron, D.; Tsouris, C. Separation of CO2 from flue gas: A review. Sep. Sci. Technol. 2005, 40, 321−348. (8) Huang, Q.; Eić, M. Commercial adsorbents as benchmark materials for separation of carbon dioxide and nitrogen by vacuum swing adsorption process. Sep. Purif. Technol. 2013, 103, 203−215. (9) Yang, H.; Xu, Z.; Fan, M.; Gupta, R.; Slimane, R. B.; Bland, A. E.; Wright, I. Progress in carbon dioxide separation and capture: A review. J. Environ. Sci. 2008, 20, 14−27. (10) Rufford, T. E.; Smart, S.; Watson, G. C. Y.; Graham, B. F.; Boxall, J.; Diniz da Costa, J. C.; May, E. F. The removal of CO2 and N2 from natural gas: A review of conventional and emerging process technologies. J. Pet. Sci. Eng. 2012, 94−95, 123−154. (11) Tagliabue, M.; Farrusseng, D.; Valencia, S.; Aguadom, S.; Ravon, U.; Rizzo, C.; Corma, A.; Mirodatos, C. Natural gas treating by selective adsorption: Material science and chemical engineering interplay. Chem. Eng. J. 2009, 155, 553−566. (12) Dantas, T. L. P.; Luna, F. M. T.; Silva, I. J., Jr.; Azevedo, D. C. S.; Grande, C. A.; Rodrigues, A. E.; Moriera, R. F. P. M. Carbon dioxide−nitrogen separation through adsorption on activated carbon in a fixed bed. Chem. Eng. J. 2011, 169, 11−19. (13) Plaza, M. G.; Garcia, S.; Rubiera, F.; Pis, J. J.; Pevida, C. Separation of CO2 from flue gas: A review. Chem. Eng. J. 2010, 163, 41−47. (14) Marsh, H.; Rodriguez-Reinoso, F. Activated Carbon; Elsevier: Amsterdam, The Netherlands, 2006. (15) Silva, J. A. C.; Schoumann, K.; Rodrigues, A. E. Sorption kinetics of CO2 and CH4 in binderless beads of 13X zeolite. Microporous Mesoporous Mater. 2012, 158, 219−228. (16) Sircar, S.; Golden, T. C.; Rao, M. B. Activated carbon for gas separation and storage. Carbon 1996, 34 (1), 1−12. (17) Zhang, Z.; Zhang, W.; Xia, Q.; Li, Z. Adsorption of CO2 on zeolite 13X and activated carbon with higher surface area. Sep. Sci. Technol. 2010, 45, 710−719. (18) Chue, K. T.; Kim, J. N.; Yoo, Y. J.; Cho, S. H.; Yang, R. T. Comparison of activated carbon and zeolite 13X for CO2 recovery from flue gas by pressure swing adsorption. Ind. Eng. Chem. Res. 1995, 34, 591−598. (19) Choi, W. K.; Kwon, T. I.; Yeo, Y. K.; Lee, H.; Song, H. K. S.; Na, B. K. Optimal operation of the pressure swing adsorption (PSA) process for CO2 recovery. Korean J. Chem. Eng. 2003, 20, 617−623. (20) Kikkinides, E. S.; Yang, R. T.; Cho, S. H. Concentration and recovery of carbon dioxide from flue gas by pressure swing adsorption. Ind. Eng. Chem. Res. 1993, 32, 2714−2720. (21) Sircar, S. Separation of methane and carbon dioxide gas mixtures by pressure swing adsorption. Sep. Sci. Technol. 1988, 23, 519−529. (22) Cavenati, S.; Grande, C. A.; Rodrigues, A. E. Upgrade of methane from landfill gas by pressure swing adsorption. Energy Fuels 2005, 19, 2545−2555. (23) Yang, H.; Gong, M.; Chen, Y. Preparation of activated carbons and their adsorption properties for greenhouse gases: CH4 and CO2. J. Nat. Gas Chem. 2011, 20, 460−464. (24) Drage, T. C.; Blackman, J. M.; Pevida, C.; Snape, C. E. Evaluation of activated carbon adsorbents for CO2 capture in gasification. Energy Fuels 2009, 23, 2790−2796. (25) D’Alessandro, D. M.; Smit, B.; Long, J. R. Carbon dioxide capture: Prospects for new materials. Angew. Chem., Int. Ed. 2010, 49, 6058−6082. (26) Stoeckli, F.; Daguerre, E.; Guillot, A. The development of micropore volumes and widths during physical activation of various precursors. Carbon 1999, 37, 2075−2077.
(productivity). The level of rinse operation can be considered as a specific regulator of CO2 concentration in the final product. This process provides an environmentally friendly fuel with a low CO2 content. Taking into account the presence of water vapor in the feed stream, A-CS seems to be very promising for separation of CO2 from coal gasification-derived gas.
4. CONCLUSIONS The VPSA process was found to be an effective method of CO2 separation from a mixture of CO, CO2, H2, and CH4 simulating the processing gases from coal gasification. Among the studied adsorbents, the zeolite 13X, the commercial activated carbon B, and KOH-activated carbon A-CS have shown the best performance in the separation of CO2. The superior ACs were distinguished by a well-developed microporous structure with an average pore width of about 1 nm and the highest working adsorption capacity. It was revealed that the very narrow pores (below 0.6 nm) do not contribute to the quick adsorption−desorption processes. There is a strong correlation between the working capacity and the amount of CO2 produced in the VPSA process (6 bar). The obtained VPSA results indicate that, with an increasing adsorption pressure, the CO2 recovery and productivity decreases, while the product purity increases. The performance of the zeolite 13X was better than that of the B and A-CS carbons in terms of productivity and purity of the final product. The maximum CO2 purity of 97% with a 58% recovery was obtained for the zeolite 13X at a high adsorption pressure (11 bar). The rinse of the activated carbons with CO2 prior to the evacuation (VPSA/CO2) resulted in a considerable increase of the CO2 purity, to 95% from 67% with a 75% recovery at a significantly lower pressure (1.5 bar), maintaining a high productivity of 90 L/(L·h). A beneficial effect of the CO2 rinse was observed for the ACs under all tested adsorption pressures. The VPSA/CO2 process, which applies a water-resistant activated carbon as the adsorbent, provides an environmentally friendly fuel with a low CO2 content.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The work was performed in the frame of the project “The development of coal gasification technology for the efficient production of fuels and electricity”, Task 2.3.2, financially supported by NCBiR (Poland).
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REFERENCES
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