High-pressure Coal Gasification Research Articles

High pressure CO2 gasification of Morupule coal: Kinetics and morphological development of chars

A direct gasification approach, coupling pyrolysis and gasification, was employed to study the kinetics of Morupule coal gasification in CO2 using a wire-mesh reactor (WMR) at elevated pressures (up to 20 bara) and temperatures of 900 °C and 1000 °C. A novel non-destructive analytical technique based on X-Ray computed tomography (CT) was used, for the first time, in conjunction with scanning electron microscopy (SEM) to unravel the morphological evolution of pyrolysis and gasification chars produced from the WMR. Lower total volatile yields were obtained at high pressures compared to atmospheric pressure for 0 s (quenching the reaction upon reaching temperature) holding time experiments. A temperature dependence of the gasification reaction rate at elevated pressures was observed. At 900 °C, increasing the pressure beyond 10 bara did not yield a commensurate increase in the reaction rate. Further increases in pressure to 20 bara at 1000 °C led to a pronounced increase in the reaction rate. The applicability of the Langmuir – Hinshelwood (L – H) rate model was investigated and showed a suitable characterisation of the gasification kinetics driven by a CO2 chemisorption-limited reaction mechanism. X-Ray CT imagery reveal the development of an internal macroporosity produced by the explosive release of volatiles during pyrolysis. In contrast, SEM images indicate that high pressure coal gasification is characterised by the development of micropores, with a rapid consumption of the outer char surface.

Process for CO2 Capture from High-Pressure and Moderate-Temperature Gas Streams

A novel CO2 capture process was developed using a Mg(OH)2-based sorbent suitable for warm gas CO2 removal from high-pressure coal gasification gas streams. The purpose of this study is to perform a preliminary energy study and develop a method to implement this sorbent in a power plant. The proposed CO2 removal process involves sorption of CO2 at 200–300 °C and regeneration at 385 °C. The operational temperature is ideal for CO2 capture downstream to the water–gas shift reactor in an integrated gasification combined cycle (IGCC) power plant but is applicable to other warm gas cleanup processes as well. This technology offers the ability to fully utilize the potential efficiency increases associated with warm gas clean up. Additionally, the sorbent is able to operate in the presence of steam, which distinguishes it from other technologies that require an energy-intensive drying step prior to CO2 separation. Regeneration is carried out at 280 psi and 400 °C, resulting in a high-pressure CO2 product stream, ...

Experimental investigation of high temperature and high pressure coal gasification

Pyrolysis and gasification behavior is analyzed at operation conditions relevant to industrial scale entrained flow gasifiers. A wire mesh reactor and the Pressurized High Temperature Entrained Flow Reactor (PiTER) are used to measure volatile yield of Rhenish lignite, a bituminous coal and German anthracite at high temperature and high pressure. In the wire mesh reactor at 1000 °C a significant influence of pressure on volatile yield is observed. For lignite the volatile yield (daf) decreases from 57 wt% at atmospheric pressure to 53 wt% at 5.0 MPa. In the same pressure interval the volatile yield of the bituminous coal strongly decreases, whereas no significant influence of pressure on the volatile yield of anthracite is detected. In entrained flow experiments (PiTER) at higher temperature and 0.5 MPa an enhanced devolatilization of the lignite is observed. At 1200 °C, the maximum volatile yield is 62 wt% and it increases to 67 wt% at 1400 °C. In entrained flow gasification experiments with Rhenish lignite a high level of conversion is measured at atmospheric pressure and at 0.5 MPa. At both pressures, coal conversion increases with temperature and residence time. The highest conversion of 96 wt% is achieved at a particle residence time of 1.3 s, at a temperature of 1600 °C, and a pressure of 0.5 MPa. The experimental results show a large influence of operation parameters on pyrolysis and gasification behavior of Rhenish lignite. The volatile release in the pyrolysis stage and the high level of conversion after a short residence time indicate that Rhenish lignite is suitable for gasification in an entrained flow reactor. The reactivities of char samples that are collected from the hot reaction zone of the PiTER are measured in a pressurized thermogravimetric analyzer (PTGA) at lower temperature (600–850 °C). The pyrolysis temperature in the entrained flow experiments significantly influences the reaction rate in the PTGA at lower temperature. With increasing pyrolysis temperature (1200–1600 °C) a continuous loss of reactivity is observed.

Zeolite-Based Process for CO2 Capture from High-Pressure, Moderate-Temperature Gas Streams

A novel CO2 capture process was developed using a zeolite suitable for CO2 removal at warm-gas temperatures in high-pressure coal gasification gas streams. The process involves sorption of CO2 at 150 °C and regeneration at 350 °C. Regeneration at 350 °C removes the moisture absorbed during CO2 sorption. This sorption temperature is ideal for CO2 removal downstream of the water gas shift reactor in an integrated gasification combined cycle (IGCC) power plant but is also applicable to other warm gas cleanup processes. Most solvent-based processes require energy-intensive drying to remove moisture prior to CO2 removal. Using zeolites for CO2 capture at 150 °C and regeneration at 350 °C eliminates the problem with moisture in the gas stream traditionally causing deactivation of the zeolite. The results of using this capture scheme in an IGCC power plant is advantageous because of the high-pressure CO2 product stream and because removal of CO2 and H2O from the syngas generates high-quality H2 for the combustio...

Application of response surface methodology to assess the combined effect of operating variables on high-pressure coal gasification for H 2-rich gas production

Coal gasification was performed by means of a high-pressure fixed bed gasifier fitted with a solids feeding system in continuous mode, using oxygen and steam as gasifying agents. The main aim of the paper was to assess the combined effects of the operating variables (temperature, oxygen and steam concentrations) on high-pressure coal gasification. To this end a face centered central composite design (FCCCD) based on response surface methodology (RSM) was used. The response variables studied were: H 2, CO and syngas production, H 2/CO ratio, cold gas efficiency ( η), and carbon conversion ( X). The study was carried out at temperatures of 900, 950 and 1000 °C, using oxygen concentrations of 5, 10 and 15 vol.%, and steam concentrations of 25, 40 and 55 vol.%. The gasification temperature was found to be the most influential variable, with high temperatures leading to an increase in all the response variables studied. An increase in the oxygen content of the gasifying agent led to a decrease in H 2 and CO production, and cold gas efficiency, whilst carbon conversion was favoured. An increase in steam concentration, on the other hand, favoured the production of H 2 and syngas production, whereas CO production underwent a reduction; cold gas efficiency and carbon conversion were observed to increase. Response surface methodology (RSM) revealed the effects of interaction between the operating variables, which would not have been identified by the traditional “one-factor-at-a-time” method. The models developed successfully fitted the experimental results for all the response variables studied.

In-Situ Desulfurization in a Fluidized-Bed Coal Gasifier

Abstract A high-pressure coal gasification process development unit (PDU) has been used by the Institute of Gas Technology to study in-sim desulfurization in an ash-agglomerating, fluidiied-bed coal gasifier at elevated pressures. Previous work in this area has been limited to pressures up to about 225 psig. The current work extends this pressure range to 400 psig, well within the pressure range of the combustion turbines now being considered for application in integrated gasification combined cycle (IGCC) power plants. The coal used in this study was Pittsburgh No. 8 bituminous coal, and the sorbent used was New Enterprise limestone. Data were collected and analyzed to determine the effects of gasifier pressure and temperature on sulfur capture within the fluidized bed. The optimum temperature for maximum sulfur removal was determined as a function of the partial pressure of CO2 in the fluidized bed.

Materials performance in coal gasification environments

Two exposures were carried out in the gasifier of the Westinghouse Process Development Unit to evaluate the performance of a wide variety of candidate construction materials for hostile high temperature, high pressure coal gasification environments. The test materials included highly alloyed iron-, cobalt-, and nickelbase alloys as well as packaluminized iron-base alloxs. The corrosion damage was assessed, and the corrosion processes taking place were investigated in order to interpret the data obtained from the surveillance tests. In addition, corrosion rates and mechanisms were compared between the two pilot plant exposures and a laboratory simulation test, to determine if laboratory data can be extrapolated to predict materials life in pilot plant environments. The results showed that although consistent kinetic data cannot be obtained by combining all three tests, materials performance can be evaluated qualitatively. Also, the corrosion mechanisms operating during the pilot plant exposures and the laboratory experiments were found to be similar.

Methanol from biomass draws closer to market

A number of projects are under way in the U.S. and abroad that use biomass as a feedstock for the manufacture of fuel-grade methanol. Most of them are based existing technology. And the key to their success will be commercial demonstration. One such project, now in the design stage, is scheduled to be the first commercial, wood-based, liquid fuels production facility in New England. It is being built in a joint program by Evergreen Energy Corp., Waltham, Mass., and Texaco Development Corp. and will adapt Texaco's high-pressure coal gasification system to accept wood as a feedstock. According to William A. Stevenson, president of Evergreen, the only thing left to do is find the best way to gasify the wood; the rest of the technology is on the shelf. The proposed plant would produce 330,000 gal per day of methanol from 3500 tons per day of green wood chips with complete environmental compatibility. Overall efficiency ...

Thermodynamic evaluation of high-pressure coal gasification

Thermodynamic evaluation of high-pressure coal gasification