Blown Gasification Research Articles

Numerical simulation on O<sub>2</sub>-CO<sub>2</sub> blown coal gasifier with elementary reaction modeling of a gas-particle multiphase reacting flow

Numerical simulation on O<sub>2</sub>-CO<sub>2</sub> blown coal gasifier with elementary reaction modeling of a gas-particle multiphase reacting flow

Verification of applicability to wide range coal property of O<sub>2</sub>/CO<sub>2</sub> –blown gasification technology for Oxy-fuel IGCC system

Verification of applicability to wide range coal property of O<sub>2</sub>/CO<sub>2</sub> –blown gasification technology for Oxy-fuel IGCC system

Verification of O<sub>2</sub>/CO<sub>2</sub> –blown gasification technology for oxy-fuel IGCC system

Verification of O<sub>2</sub>/CO<sub>2</sub> –blown gasification technology for oxy-fuel IGCC system

Considerations for oxidant and gasifying medium selection in underground coal gasification

Underground coal gasification (UCG) is a technology for exploiting deep coal resources. A major consideration in the design and operation of UCG is the selection of the oxidant and gasifying medium. Air, enriched-air, steam/oxygen, water/oxygen and CO2/oxygen are potential oxidants for use in UCG. This article provides guidelines for the selection of the oxidant and gasifying medium through a combination of qualitative assessment and the use of a simplified cost model. It is found that air blown operations are popular for demonstration purposes and are favoured for coals at shallow to moderate depths and when project scale is small. Steam/oxygen blown gasification is suitable for coals at shallow to moderate depth and may be favoured when steam can be generated from waste heat sources in an integrated plant. Water/oxygen blown gasification is attractive when operating pressures are high (e.g. in deep coals) and when project scales are large. There is currently limited practical experience with carbon dioxide/oxygen blown gasification in underground coal gasification.

Exposure of 304L and 310S in chlorinating gasification environments

This work examines the difference in behaviour between two austenitic steels, 304L and 310S, in a simulated environment with carbon and oxygen activities typical of the syngas cooler of a steam blown gasifier. The cyclic exposures were performed with and without addition of 500 ppm HCl for a total duration of 960 h. The oxide layers (200–600 nm) were studied using TEM, a focused ion beam microscope with EDX (FIB-EDX), electron back scattered diffraction (EBSD), SEM and X-ray diffraction (XRD). For 304L, a Cr and Ni depleted zone with a ferritic structure was observed below the oxide layer and a thin, manganese rich layer at the metal/oxide interface. For 310S, circular oxide patches were observed on the surface after exposure with HCl. These displayed elevated concentration of Al, Ca and Si, typical of inclusions. Results indicate that the addition of HCl results in a difference in oxide quality and structure but that HCl at the level of this study has little impact on the sound metal thickness.

Steam/oxygen gasification system for the production of clean syngas from switchgrass

A pilot-scale 25kg/h fluidized bed, oxygen/steam blown gasifier and syngas cleaning system was developed to convert switchgrass into clean syngas. The system is rated for operation at gage pressures up to 1bar. The reactor vessel incorporated a novel guard heating system to simulate near-adiabatic operation of large commercial-scale gasifiers, and was effective for gasification temperatures up to 900°C. After removing particulate from the gas stream via cyclones, a warm-gas cleaning operation based on oil scrubbing was used to remove tars. Sulfur compounds were removed via solid-phase adsorption. Ammonia was removed by water scrubbing. Baseline gasification tests with steam and oxygen were conducted at equivalence ratios (ER) between 0.21 and 0.38 using switchgrass as fuel. Measurements on the raw and cleaned syngas included permanent gas composition, C2 hydrocarbons, water, heavy and light tars, gasification residues (char and ash), hydrogen sulfide (H2S), carbonyl sulfide (COS), carbon disulfide (CS2), ammonia (NH3), and the first reported measurements of hydrogen cyanide (HCN) for oxygen/steam blown gasification. Heavy tars were removed with high efficiency by the method employed, although more difficult to remove light tars reduced overall tar removal efficiency to less than 80%. The sulfur scrubbing system demonstrated 99.9% removal efficiency, resulting in less than 200ppb of H2S in the cleaned gas. The NH3 scrubbing system also accomplished greater than 99.9% removal efficiency, resulting in final NH3 concentrations of less than 1ppm.

Combustion Performance in a Semiclosed Cycle Gas Turbine for IGCC Fired With CO-Rich Syngas and Oxy-Recirculated Exhaust Streams

Our study found that burning a CO-rich gasified coal fuel, derived from an oxygen–CO2 blown gasifier, with oxygen under stoichiometric conditions in a closed cycle gas turbine produced a highly-efficient, oxy-fuel integrated coal gasification combined cycle (IGCC) power generation system with CO2 capture. We diluted stoichiometric combustion with recycled gas turbine exhaust and adjusted for given temperatures. Some of the exhaust was used to feed coal into the gasifier. In doing so, we found it necessary to minimize not only CO and H2 of unburned fuel constituents but also residual O2, not consumed in the gas turbine combustion process. In this study, we examined the emission characteristics of gasified-fueled stoichiometric combustion with oxygen through numerical analysis based on reaction kinetics. Furthermore, we investigated the reaction characteristics of reactant gases of CO, H2, and O2 remaining in the recirculating gas turbine exhaust using present numerical procedures. As a result, we were able to clarify that since fuel oxidation reaction is inhibited due to reasons of exhaust recirculation and lower oxygen partial pressure, CO oxidization is very sluggish and combustion reaction does not reach equilibrium at the combustor exit. In the case of a combustor exhaust temperature of 1573 K (1300 °C), we estimated that high CO exhaust emissions of about a few percent, in tens of milliseconds, corresponded to the combustion gas residence time in the gas turbine combustor. Combustion efficiency was estimated to reach only about 76%, which was a lower value compared to H2/O2-fired combustion while residual O2 in exhaust was 2.5 vol%, or five times as much as the equilibrium concentration. On the other hand, unburned constituents in an expansion turbine exhaust were slowed to oxidize in a heat recovery steam generator (HRSG) flue processing, and exhaust gases reached equilibrium conditions. In this regard, however, reaction heat in HRSG could not devote enough energy for combined cycle thermal efficiency, making advanced combustion technology necessary for achieving highly efficient, oxy-fuel IGCC.

Comparison of mass and energy balances for air blown and thermally ballasted fluidized bed gasifiers

Abstract The objective of this study was to compare the mass and energy balances for a conventional air blown fluidized bed gasifier and a ballasted fluidized bed gasifier developed at Iowa State University. The ballasted gasifier is an indirectly heated gasifier that uses a single reactor for both combustion and pyrolysis. Heat accumulated in high-temperature phase change material during the combustion phase is released during the pyrolysis phase to generate producer gas. Gas composition, tar and char contents, cold gas efficiency, carbon conversion, and hydrogen yield per unit biomass input were determined as part of these evaluation. During the pyrolysis phase of ballasted gasification, higher volumetric concentrations of hydrogen and methane were obtained than during air blown gasification. Hydrogen yield for ballasted gasification was 14 g kg −1 of biomass, which was about 20% higher than that obtained during air blown gasification. The higher heating value of the producer gas also reached higher levels during the ballasted pyrolysis phase than that of air blown gasification. Heating value for air blown gasification was 5.2 MJ m −3 whereas the heating value for the ballasted pyrolysis phase averaged 5.5 MJ m −3 , reaching a maximum of 8.0 MJ m −3 . The ballasted gasifier was expected to yield producer gas with average heating value as high as 15 MJ m −3 but excessive use of nitrogen to purge and cool the fuel feeder system greatly diluted the producer gas. Relatively simple redesign of the feeder system would greatly reduce the use of purge gas and may increase the heating values to about 17.5 MJ m −3 . Higher char production per kilogram of biomass was associated with the ballasted system, producing 140 g kg −1 of biomass compared to only 53 g kg −1 of biomass during air blown gasification. On the other hand, tar concentrations in the producer gas were 6.0 g m −3 for ballasted gasification compared to 11.7 g m −3 for air blown gasification. On balance, carbon conversion was found to be higher for air blown gasification. Cold gas efficiencies were somewhat higher for air blown gasification compared to ballasted gasification, although the difference did not appear to be significant.

Numerical investigation on combustion of coal volatiles under various O2/CO2 mixtures using a detailed mechanism with soot formation

The effort for increasing syngas production and reducing soot and CO2 emissions from coal combustion is important for cleaner and more efficient use of coal for energy production. The primary reactions of coal volatiles for soot formation mechanism were numerically investigated under pyrolysis (thermal decomposition), partial oxidation (O2 gasification) and O2/CO2 gasification conditions. Soot formation was modeled in a plug flow reactor (PFR) with a detailed reaction mechanism containing 276 species, 2158 conventional gas phase reactions and 1635 surface phase reactions. The reaction temperature and pressure were maintained in the range 1273–1873K and 0.1–2MPa, respectively. The effect of temperature on product concentrations appeared more significant compared with pressure effect. In the viewpoint of special attention regarding O2/CO2 blown gasification, the effect of O2/CO2 input on the production of major combustion species was investigated. The O2 input became important in reducing PAHs/soot at low temperature. However, if the gas mixture input had a high CO2 concentration, higher temperature and pressure provided in eliminated PAHs/soot and increased CO.

Toward zero emissions from coal in China

China depends for most of its energy on coal – a situation that is likely to persist in the light of the abundance of its coal resources, the paucity of its oil and gas resources, and the reluctance of the government to allow China to become overly dependent on energy imports. The challenge is to find ways to use coal without the enormous air pollution damage caused by current conversion technologies and with greatly reduced carbon dioxide (CO 2 ) emissions. A coal energy system for China is proposed that could ultimately be characterized by near-zero emissions of both air pollutants and greenhouse gases. The key enabling technology is oxygen-blown (O 2 –blown) gasification to generate synthesis gas from coal. This technology is used in commercially ready integrated gasification combined-cycle power plants that can provide electricity with air pollutant emissions as low as emission levels for natural gas combined-cycle plants. O 2 -blown gasification is not yet used in China's energy sector, although the technology is well-established in China's chemical process industry. The key enabling strategy, which would often lead to attractive energy costs without further technological advances, is “polygeneration” – the co-production from synthesis gas of at least electricity and one or more clean synthetic fuels (e.g., dimethyl ether (DME), Fischer-Tropsch (F-T) liquids, hydrogen (H 2 )) and often also chemicals, town gas, and/or industrial process heat. The products of polygeneration could be used in the near term to serve a wide range of energy needs with extremely low levels of air pollutant emissions. In such polygeneration configurations CO 2 can often be produced in relatively pure streams as a co-product as a result of processing to increase the synthetic fuel's hydrogen-to-carbon ratio. In the near term this CO 2 might be used profitably for enhanced oil recovery or enhanced recovery of methane from deep beds of unminable coal where resource recovery opportunities exist. For the longer term the potential exists for evolving the coal energy system to the co-production primarily of electricity and H 2 for serving urban areas, with most of the carbon in the coal ending up as CO 2 that is sequestered in geological reservoirs such as in depleted oil and natural gas fields and deep saline aquifers at low incremental cost – even where there are no opportunities for using the CO 2 for enhanced resource recovery. The H 2 so produced would be used for fueling zero-polluting fuel-cell vehicles, for distributed cogeneration (combined heat and power) applications in stationary fuel cells, and for cooking and heating applications as well. A third clean carbon-based synthetic fuel might also be needed for serving rural markets that would be difficult to serve with H 2 , unless there are breakthroughs in H 2 storage technology. DME is a strong candidate for becoming the “third” clean energy carrier for China. Evolving a coal-based energy system that would be characterized ultimately by near-zero emissions of air pollutants and greenhouse gases would probably involve shifting the center of gravity for central-station power generation to the chemical process industries that would ultimately be co-producing as their major products electricity, H 2 , and (perhaps) DME. Ongoing structural reforms in the electric power sector that encourage greater competition in power generation would facilitate the realization of this vision for coal.

Materials Performance in Solid Fuel Gasification Systems

Solid fuel gasification offers the potential to generate power from coal, waste and biomass with greater efficiencies and far less environmental emissions (SO x , NO x and CO 2 ) than conventional pulverised coal power generation. However, the chemically aggressive fuel gases produced by the various competing gasification technologies have the potential to degrade materials by a number of distinct mechanisms on different components (eg fuel gas coolers, hot gas filters) in the fuel gas paths. A series of realistic laboratory studies of high temperature gaseous corrosion (up to 4000 hours), downtime corrosion and mixed mode corrosion have been carried out with the aim of developing models for the corrosive performance of materials in the fuel gas path of solid fuel gasification systems. Precision metrology methods have been used to generate suitable metal loss data for use in the development of these models. Validation of the models has been carried out by comparing the performance of materials exposed to realistic conditions in air blown gasification pilot plants (on both operational components and probes) with the model predictions.

99/03127 Overview of clean coal technologies and current status of the air blown gasification cycle

99/03127 Overview of clean coal technologies and current status of the air blown gasification cycle

99/03347 The influence of tars on hot gas filter performance in air blown gasification of coal and biomass

99/03347 The influence of tars on hot gas filter performance in air blown gasification of coal and biomass

99/02628 The influence of tars on hot gas filter performance in air blown gasification of coal and biomass

99/02628 The influence of tars on hot gas filter performance in air blown gasification of coal and biomass

97/01059 Development of hot gas filtration for air blown gasification plant

97/01059 Development of hot gas filtration for air blown gasification plant

Grimethorpe filter element performance—the final analysis

A demonstration hot gas filter, funded by the Electric Power Research Institute and installed in a pressurised fluidised bed combustor at Grimethorpe, South Yorkshire, UK was operated for a second period in 1991–92 for the Grimethorpe Topping Cycle Project (GTCP). This project was aimed at assessing the feasibility of running a gas turbine on coal-derived gas as part of the development programme for the Air Blown Gasification Cycle (formerly known as the British Coal Topping Cycle).As in previous studies operation of the filter led to progressive changes to the mechanical properties of the tubular clay-bonded silicon carbide filter elements. In order to explain the mechanisms behind these changes and thus determine operating conditions which influence element properties and performance detailed element characterisation and microstructural studies have been carried out. It has been found that slow bond devitrification and the development of a bond-grit interlayer of cristobalite led to changes in the integrity of the interface, with loss of strength and elastic modulus and a decrease in ultrasonic pulse velocity through the material. Microstructural studies suggest that the combination of the upper temperature of operation (≈ 830°C) and the thermal cycling during reverse pulse cleaning to remove the dust cake results in microcracking. While the strength losses experienced did not result in in-plant element failures, the reliability of the elements would be improved if operation can be limited to a temperature at which devitrification of the element's bond material is minimised.

New Technology Trends for Improved IGCC System Performance

The application of gas turbine technology to IGCC systems requires careful consideration of the degree and type of integration used during the system design phase. Although gas turbines provide the primary output and efficiency gains for IGCC systems, as compared with conventional coal-fired power generation systems, they are commercially available only in specific size ranges. Therefore, it is up to the IGCC system designer to optimize the IGCC power plant within the required output, efficiency, and site conditions by selecting the system configuration carefully, particularly for air separation unit (ASU) integration incorporated with oxygen blown gasification systems. An IGCC system, based on a generic, entrained flow, oxygen blown gasification system and a GE STAG 109FA combined cycle has been evaluated with varying degrees of ASU integration, two fuel equivalent heating values and two gas turbine firing temperatures to provide net plant output and efficiency results. The data presented illustrate the system flexibility afforded by variation of ASU integration and the potential performance gains available through the continued use of gas turbine advances. Emphasis is placed on system design choices that favor either low initial investment cost or low operating cost for a given IGCC system output.