The dry syngas purification process developed for oxy-fuel integrated gasification combined cycle (IGCC) power generation removes hydrogen halides (HCl, HF) with pelletized sodium-aluminate sorbents and sulfur species (H2S, COS) with a regenerable honeycomb zinc-ferrite sorbent in fixed beds at about 450 °C and ~1 MPa, avoiding the efficiency penalty of wet scrubbing. The originating 2017 study by Kobayashi and Akiho derived the bench-scale reactor design from accelerated laboratory breakthrough tests (about 900 ppm HCl feed, shallow beds, single-week tests at reduced pressure) and left explicit gaps: halide-sorbent kinetics at actual plant impurity concentrations and space velocities, variable-space-velocity breakthrough mapping for the halide sorbents, long-duration cyclic durability, and validation with actual syngas from an O2/CO2-blown gasifier. Follow-on work by the same group in 2019 then demonstrated the bench facility on real gasifier syngas for an initial cyclic run and for 46 hours of five desulfurization cycles, with verified halide and sulfur removal and no carbon deposition, closing the initial-validation gap. What remains open is completion of this validation at plant-representative conditions: halide-sorbent kinetics and bed-sizing relations at plant HCl/HF concentrations (plant syngas is expected around 150 ppm HCl, whereas the bench gasifier's actual syngas contained only about 0.1-2 ppm and the accelerated lab tests used about 900 ppm) across the intended space-velocity range; long-duration, many-cycle operation establishing sorbent durability, cumulative regeneration completeness, and carbon-deposition behavior; and the scale-up confirmation these data enable.

Background

Integrated gasification combined cycle (IGCC) power generation gasifies coal into a fuel gas (syngas, a mixture of mainly CO, H2, CO2, H2O and CH4) that is burned in a gas turbine, with waste heat driving a steam turbine. In the oxy-fuel IGCC variant, under development by the Central Research Institute of Electric Power Industry (CRIEPI, Japan) and partners in a program supported by the New Energy and Industrial Technology Development Organization (NEDO, Japan) and targeting net thermal efficiency above 42% on a higher-heating-value (HHV) basis, the gasifier is blown with oxygen diluted by recycled exhaust gas instead of air, so that the gas turbine exhaust becomes a concentrated CO2 stream (about 93 vol%) ready for capture. Coal-derived syngas contains trace impurities — the halides HCl and HF and the sulfur species H2S and COS — that must be reduced to sub-ppm levels to protect the gas turbine and downstream equipment. Conventional wet scrubbing cools, dries and re-heats the gas, which destroys part of the efficiency advantage; dry syngas purification instead removes the acid gases with solid sorbents at the operating temperature (~450 °C) and pressure (~1 MPa) of the gas leaving the gasifier.

The process trains two sorbent beds in series. The halide unit is a packed bed of pelletized porous sodium-aluminate sorbent (SAS), which irreversibly captures chlorine and fluorine as NaCl and NaF; its performance is quantified by the chlorination ratio RCl=NCl/NNaR_{\mathrm{Cl}} = N_{\mathrm{Cl}}/N_{\mathrm{Na}}, the molar ratio of captured chlorine to sodium in a sampled sorbent mass, measured by ion chromatography and inductively coupled plasma (ICP) optical emission spectroscopy. The sulfur unit uses a honeycomb-shaped regenerable sorbent of zinc ferrite (ZnFe2O4\mathrm{ZnFe_2O_4}–SiO2 on a TiO2 support), which removes H2S and COS by sulfidation (conversion measured by the molar uptake ratio S/(Zn+Fe)) and is then restored by cyclic operation: three fixed-bed reactors rotate through sulfidation, oxidative regeneration (diluted air releasing the sulfur as SO2), and reduction steps, so that one reactor is always cleaning gas while the others regenerate. A key chemical risk in CO/CO2-rich syngas at 450 °C is carbon deposition (carbon formation via the reverse Boudouard reaction, 2CO → C + CO2, and related C–H–O equilibria), which can physically destroy the zinc-ferrite sorbent; the countermeasure is to blend exhaust gas (CO2/H2O) into the desulfurization feed to push the gas composition out of the carbon-forming regime. Fixed-bed reactor sizing is governed by the space velocity (volumetric gas flow per unit bed volume, in h^-1) at which the reaction front remains inside the bed: a breakthrough curve (outlet concentration versus time) shows when the front reaches the bed exit, and the front thickness determines the minimum safe bed depth.

A laboratory lineage established the pieces before 2017: exhaust circulation to prevent carbon deposition (Kobayashi, Nakao and Oki, 2014; Kobayashi and Nakao, 2015), carbon behavior over desulfurization cycles (Kobayashi and Akiho, 2016), the porous sodium-aluminate halide sorbent (Kobayashi, Akiho and Nakao, 2015), and the honeycomb zinc-ferrite sorbent tested across space velocities from 1880 to 9390 h^-1 with sulfidation conversion near 0.80 before breakthrough (Kobayashi and Akiho, 2017). The originating study of this problem (Kobayashi and Akiho, 2017, Journal of Environmental Management 203:925-936) combined accelerated halide breakthrough tests (~900 ppm HCl, 450 °C, space velocities near 4000 h^-1, shallow ~52 mm beds, chlorination ratios 0.93-0.98) with the honeycomb desulfurization data to derive a preliminary bench-scale design: a halide bed of 1.3 kg of 3x4 mm sodium-aluminate pellets with a 168 h service time, and a three-reactor honeycomb desulfurization unit with 4 h desulfurization steps, for a plant syngas assumed to contain about 150 ppm HCl, 15 ppm HF, 620 ppm H2S and 150 ppm COS. The paper's own stated limitation was that the bench-scale facility — the first ever to demonstrate halide and sulfur removal with fixed beds on actual syngas from an O2/CO2-blown gasifier — was still to be built and operated, that the halide tests were run at accelerated (not plant) concentrations without a variable-space-velocity sweep, and that long-duration cyclic durability was undemonstrated.

The intended demonstration then took place: Kobayashi, Akiho, Ozawa and Nakajima (2019) operated the bench-scale dry acid gas removal facility (halide packed bed upstream of the three-reactor zinc-ferrite unit) on real O2/CO2-blown gasifier syngas at 450 °C and about 0.98 MPa, first for an initial cyclic run with 1 h reactor-switching steps (Applied Energy 252:113402) and then for 46 h of five complete sulfidation-regeneration-reduction cycles with 3 h steps (Fuel 250:144-153). Halide removal reduced HCl and HF to very low outlet levels (Fourier-transform infrared (FTIR) gas analysis plus spent-sorbent analysis), sulfidation kept outlet H2S and COS below 1 ppm, spent-sorbent carbon contents stayed at or below the fresh baseline, and regeneration released the absorbed sulfur consistently. A companion laboratory breakthrough test of the sodium-aluminate sorbent at 0.98 MPa and 450 °C with simulated syngas reached complete breakthrough after about 59 h with 98% sodium conversion. However, the actual bench gasifier syngas contained only about 0.1-2 ppm HCl — far below the ~150 ppm expected at plant scale — and the papers themselves state that longer-duration multi-cycle operation, accurate inlet impurity monitoring, and extended testing remain to be performed. Kobayashi consolidated the development, including scale-up strategies, in a 2020 Elsevier monograph. The unresolved target is therefore the completion of the process validation at plant-representative impurity concentrations, space velocities, and durations.

Problem Statement

Complete the experimental validation of the dry syngas purification process for oxy-fuel IGCC power generation with CO2 capture, at plant-representative conditions, so that the remaining scale-up questions for pilot or commercial deployment can be closed. The common objective unifying the requested results is to establish, at plant-representative conditions, the operating envelope and durability of the two-sorbent fixed-bed train (upstream sodium-aluminate halide removal; downstream regenerable honeycomb zinc-ferrite desulfurization) that has so far been demonstrated with actual O2/CO2-blown gasifier syngas only in short-duration runs (an initial cyclic run with 1 h switching steps, and 46 h / five cycles at 450 °C, ~0.98 MPa abs). The requested results, which jointly serve this objective, are: (1) quantified halide-sorbent reaction kinetics and breakthrough behavior at actual plant impurity concentrations — the 2017 design basis assumes plant syngas of about 150 ppm HCl and 15 ppm HF, whereas the accelerated laboratory tests used ~900 ppm HCl and the bench gasifier's actual syngas contained only ~0.1-2 ppm HCl — across the halide-bed space-velocity range of the plant design basis — anchored to the accelerated-test condition near 4000 h^-1 — with the lower and upper bounds of the required sweep stated and justified by the answer against the fixed-bed design constraint that the chlorination front remain inside the bed for the full 168 h service time at the plant HCl/HF levels — sufficient to determine the chlorination-front thickness and the required bed depth as functions of space velocity and feed concentration; (2) long-duration cyclic operation with actual O2/CO2-blown gasifier syngas — for at least the 168 h halide-bed service time of the 2017 design — well beyond the demonstrated initial five desulfurization/regeneration/reduction cycles (~46 h) — with steady multi-cycle scheduling; plant-representative halide levels while preserving the real gasifier syngas's interfering species and water content — establishing sorbent mechanical and chemical durability, cycle-to-cycle capacity retention, cumulative regeneration completeness (residual sulfur/sulfate trends), and carbon-deposition behavior under extended steady operation and transient start-up with exhaust circulation; and (3) using (1) and (2) to confirm the reactor sizing, cycle schedule, and operability as the design basis for scale-up; pilot-plant heat-balance verification and demonstration-plant start-up confirmation are staged by the program as subsequent phases and lie outside this problem's completion boundary. The kinetics relations determine the reactor geometry, and the long-duration campaign of (2) tests that geometry and the sorbents under the resulting duty. Both requested results are at plant-representative conditions: (1) at plant HCl/HF concentrations, and (2) on the actual O2/CO2-blown gasifier syngas itself, held at plant-representative halide concentrations. The source papers identify the longer duration of multiple cyclic operation of the bench-scale facility on actual syngas as the remaining step.

References

  1. Makoto Kobayashi and Hiroyuki Akiho (2017), "Dry syngas purification process for coal gas produced in oxy-fuel type integrated gasification combined cycle power generation with carbon dioxide capturing feature", Journal of Environmental Management 203:925-936, DOI 10.1016/j.jenvman.2017.05.067, https://doi.org/10.1016/j.jenvman.2017.05.067 (PMID 28599799)
  2. Makoto Kobayashi, Hiroyuki Akiho, Yasushi Ozawa, and Akira Nakajima (2019), "Verification of proper operation of dry acid gas removal process on syngas derived by O2/CO2-blown gasifier", Applied Energy 252:113402, DOI 10.1016/j.apenergy.2019.113402, https://doi.org/10.1016/j.apenergy.2019.113402
  3. Makoto Kobayashi, Hiroyuki Akiho, Yasushi Ozawa, and Akira Nakajima (2019), "Evaluation of dry acid gas removal process on bench scale test facility coupled with syngas produced by O2/CO2-blown gasifier", Fuel 250:144-153, DOI 10.1016/j.fuel.2019.03.136, https://doi.org/10.1016/j.fuel.2019.03.136
  4. Makoto Kobayashi (2020), "Dry Syngas Purification Processes for Coal Gasification Systems", Elsevier, 1st edition, October 18, 2020, ISBN 9780128188668, https://shop.elsevier.com/books/dry-syngas-purification-processes-for-coal-gasification-systems/kobayashi/978-0-12-818866-8 (chapters include "Process development" DOI 10.1016/b978-0-12-818866-8.00006-9, "Scaling-up strategies" DOI 10.1016/b978-0-12-818866-8.00007-0, and "Applications of dry syngas purification" DOI 10.1016/b978-0-12-818866-8.00008-2)
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  8. Makoto Kobayashi and Hiroyuki Akiho (2017), "Performance evaluation of honeycomb shaped sorbent for sulfur removal in advanced oxy-fuel IGCC power generation plant", Fuel 203:1015-1025, DOI 10.1016/j.fuel.2017.02.087, https://doi.org/10.1016/j.fuel.2017.02.087
  9. Makoto Kobayashi and Hiroyuki Akiho (2016), "Carbon behavior in the cyclic operation of dry desulfurization process for oxy-fuel integrated gasification combined cycle power generation", Energy Conversion and Management 125:70-79, DOI 10.1016/j.enconman.2016.03.024, https://doi.org/10.1016/j.enconman.2016.03.024
  10. Makoto Kobayashi and Yoshinobu Nakao (2015), "Inhibition and elimination of carbon deposition in dry gas desulfurization process under oxy-fuel IGCC derived coal gas environment", Fuel 152:19-28, DOI 10.1016/j.fuel.2015.02.092, https://doi.org/10.1016/j.fuel.2015.02.092
  11. Makoto Kobayashi, Yoshinobu Nakao, and Yuso Oki (2014), "Exhaust circulation into dry gas desulfurization process to prevent carbon deposition in an Oxy-fuel IGCC power generation", Energy Conversion and Management 87:1315-1323, DOI 10.1016/j.enconman.2014.06.013, https://doi.org/10.1016/j.enconman.2014.06.013
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