High-pressure Wire-mesh Reactor Research Articles

Linking char reactivity to structural and morphological evolution during high pressure pyrolysis of Morupule coal

Understanding the influence of pressure on char physicochemical properties and reactivity during pyrolysis is principal for the design and optimisation of coal gasification technologies. This work investigated the pyrolysis behaviour of Morupule coal at various pressures and temperatures in a high-pressure wire-mesh reactor (HPWMR). The effect of pressure was pronounced at 600 and 800 °C, resulting in lower total volatile yields at higher pressures due to the repolymerisation of volatiles. Although graphitisation was limited during the heating period, an increase in the concentration of ordered structures was observed during holding at 1000 °C. Marked blowholes on the char surface suggested an explosive bubble transport phenomenon during pyrolysis. Chars produced during the ramping period under high pressure showed higher combustion reactivities than their low-pressure counterparts. However, prolonged holding at peak temperature produced chars of similar reactivity, with their CO2 gasification reactivity found to be independent of pyrolysis pressure.

Advances in the development of wire mesh reactor for coal gasification studies

In an effort to further understand the coal gasification behavior in entrained-flow gasifiers, a high pressure and high temperature wire mesh reactor with new features was recently built. An advanced LABVIEW-based temperature measurement and control system were adapted. Molybdenum wire mesh with aperture smaller than 70 mum and type D thermocouple were used to enable high carbon conversion (>90%) at temperatures >1000 degrees C. Gaseous species from wire mesh reactor were quantified using a high sensitivity gas chromatography. The material balance of coal pyrolysis in wire mesh reactor was demonstrated for the first time by improving the volatile's quantification techniques.

Development of a Bench-Scale High-Pressure Fluidized Bed Reactor and Its Sequential Modification for Studying Diverse Aspects of Pyrolysis and Gasification of Coal and Biomass

This paper reviews the design, operation, and sequential modifications of a bench-scale high-pressure fluidized bed reactor system, capable of diverse pyrolysis and gasification applications, all based on the same hardware platform. The reactor is small: 34 mm i.d. and 504 mm high. The mechanical design is relatively simple and inexpensive, featuring direct electrical heating to avoid the use of a separate furnace. The reactor body is made of a high-strength alloy, with 1000 h creep resistance at maximum design conditions (1000 °C and 3.0 MPa). The design thus obviates the use of a “cold” pressure casing. The system can be operated by a single person and has demonstrated ability to generate fuel reactivity and product distribution data rapidly and cheaply, using a wide range of solid fuels. In batch operation, conversions achieved during coal pyrolysis and gasification experiments were comparable with results from a high-pressure wire-mesh reactor, indicating nearly single-particle behavior. The system has been modified for continuous feeding (∼3 g min −1), to study the effect of reaction conditions on the fate of fuel-N, during the gasification of coal and sewage sludge (to 3.0 MPa). The work showed that steam plays a primary role in the formation of NH 3 from both volatile-N and char-N. HCN concentrations were found to depend strongly on the residence time at temperature and on the extent of contact with heated bed solids. A quartz lining allowed the determination of extents of trace element emissions during gasification. Above 900 °C, enhanced depletion of Ba, Pb, and Zn in bed solids was accompanied by enrichment of fines, collected in a downstream filter. The system was subsequently modified to enable a slug of coal to be injected and bed solids discharged (1−3.0 MPa) from the fluidized bed under controlled conditions and precise solid residence times in the bed. The reactivities of the chars were measured as a function of “residence time at temperature” and were observed to decrease with increasing temperature, time, pressure, and particle size. At 1000 °C, coal char reactivities were found to diminish by nearly a factor of 4 within 10 s. The study confirmed and extended prior work carried out in a high-pressure wire-mesh reactor. The system was subsequently configured for pyrolyzing waste plastic material at low temperatures. Altering the electrode positions enabled changing the position of the heated zone, enabling trouble-free injection of polymer samples at temperatures up to 600 °C. The aim of these experiments was to investigate the potential to produce liquid fuel precursors from pure and mixed waste plastics. In its latest incarnation the system has been further modified for performing oxy-fuel gasification experiments.

The Zero Emission Carbon Concept (ZECA): Extents of Reaction with Different Coals in Steam/Hydrogen, Tar Formation and Residual Char Reactivity

A high pressure wire mesh reactor has been modified to investigate the reactions underlying the zero emission carbon concept (ZECA) process. This is a novel power generation concept that involves producing hydrogen from coal. An earlier paper has described the concept, the wire mesh reactor used for laboratory scale tests, and results of tests with H2 and He. In this paper, results of tests with a range of coals are described, together with tar emission and char reactivity measurements. The tests with a range of coals (from lignite through to bituminous have shown that the performances of the different fuels do vary widely, but not as a direct function of their rank. With lignites, high conversions were achieved in a H2/steam mixture. Lower conversions were apparent with the other coals. However, reaction conditions were not optimized to achieve the highest conversion level. Pittsburgh No. 8 coal (high volatile bituminous) was also found to be reactive, whereas Wyodak (sub-bituminous) and Daw Mill (bituminous) coals had a similar reactivity to each other, but lower than the other fuels tested. The amount of primary tar was measured, by collection in a cooled trap, immediately above the wire mesh. This is material formed during the release of the volatiles with only a limited time for further reaction. Slightly higher quantities of tar were measured during tests with H2 than with He. Residual char reactivities declined with increasing temperature and hold time at peak temperature, although steam did appear to have an activation effect at low formation hold times.

Zero-Emission Carbon Concept (ZECA): Equipment Commissioning and Extents of the Reaction with Hydrogen and Steam

A high-pressure wire-mesh reactor has been modified to investigate the reactions underlying the zero-emission carbon concept (ZECA) process. This is a novel power generation concept that involves producing hydrogen from coal. The first step involves reacting coal in a steam−hydrogen mixture to form primarily CH4. The product gas is then steam-reformed and shifted to maximize the H2 content. CO2 is removed by the carbonation of CaO, to give a nearly pure stream of H2. The CaCO3 is calcined in a separate reactor to release the CO2 stream for storage. This paper outlines initial results from experiments simulating the carbon−hydrogen and carbon−steam reactions taking place in the gasifier. Experiments were carried out under inert gas (pyrolysis) and under reactive gas atmospheres. Extents of the reaction were calculated by subtracting the weight loss during pyrolysis from conversions in a reactive atmosphere under otherwise the same experimental conditions. Therefore, data presented in this way show the impact on the level of conversion caused by the presence of H2. It has not been possible to directly measure the amount of CH4 formed with this type of reactor. Initial results have shown that under 7 MPa of pure hydrogen, at temperatures between 750 and 1050 °C, and with a 10 s hold time, between 15 and 25% (w/w, daf) of Daw Mill coal (U.K.) reacted with H2. Rates of the reaction were rapid during the pyrolytic stage, the first few seconds of the test, but then rapidly declined to low values. Preliminary tests have been performed to assess the impact of the reaction with steam under the ZECA conditions. The data indicate extents of the reaction that are greater than those achieved in H2 alone, so that, when the two reactants are present together, moderate to high overall conversions were achieved with the bituminous coal.

Pyrolysis and CO2 Gasification of Chinese Coals in a High-Pressure Wire-Mesh Reactor under Conditions Relevant to Entrained-Flow Gasification

A high-pressure wire-mesh reactor has been successfully re-commissioned to operate at high temperatures (up to 2000 °C) and pressures (up to 30 bara) for characterization of coal samples under conditions relevant to entrained-flow gasification. A sample of coal supplied by the Thermal Power Research Institute (China) has been tested. Pyrolysis yields increased as the temperature increased and decreased as the pressure increased. The extent of gasification at low temperature (1000 °C for 1 s) must have been low, because the weight losses in CO2 and helium did not differ greatly. Nevertheless, the gasification yields at high temperature (1500 °C and 1 s) were significant, and near-complete conversion of the sample occurred in CO2. Non-isothermal thermogravimetric analysis of residual char clearly showed an increased thermal deactivation with increased temperature and pressure. The coupled use of the high-pressure wire-mesh reactor and the thermogravimetric analyzer has potential as a laboratory tool to assess the reactivity of coals to be used in entrained-flow gasifiers.

The fate of injectant coal in blast furnaces: The origin of extractable materials of high molecular mass in blast furnace carryover dusts

Abstract The aim of the work was to investigate the fate of injectant coal in blast furnaces and the origin of extractable materials in blast furnace carryover dusts. two sets of samples including injectant coal and the corresponding carryover dusts from a full sized blast furnace and a pilot scale rig have been examined. The samples were extracted using 1-methyl-2-pyrrolidinone (NMP) solvent and the extracts studied by size exclusion chromatography (SEC). The blast furnace carryover dust extracts contained high molecular weight carbonaceous material, of apparent mass corresponding to 107-108 u, by polystyrene calibration. In contrast, the feed coke and char prepared in a wire mesh reactor under high temperature conditions did not give any extractable material. Meanwhile, controlled combustion experiments in a high-pressure wire mesh reactor suggest that the extent of combustion of injectant coal in the blast furnace tuyers and raceways is limited by time of exposure and very low oxygen concentration. It ...

00/02313 CO 2 and steam-gasification in a high-pressure wire-mesh reactor: the reactivity of Daw Mill coal and combustion reactivity of its chars

00/02313 CO 2 and steam-gasification in a high-pressure wire-mesh reactor: the reactivity of Daw Mill coal and combustion reactivity of its chars

00/00134 CO 2 and steam-gasification in a high-pressure wire-mesh reactor: the reactivity of Daw Mill coal and combustion reactivity of its chars

00/00134 CO 2 and steam-gasification in a high-pressure wire-mesh reactor: the reactivity of Daw Mill coal and combustion reactivity of its chars

Factors governing reactivity in low temperature coal gasification. Part 1. An attempt to correlate results from a suite of coals with experiments on maceral concentrates

This paper reports on the first stage of a study attempting to develop laboratory scale tests for the reliable determination and eventual prediction, of the effect of coal properties on the performance of coals in air blown gasifiers. The pyrolysis and gasification behaviour of a suite of coals have been matched, using a high-pressure wire-mesh reactor (WMR), with those of maceral enriched samples. Reaction conditions were selected to simulate those of the pilot-scale gasifier stage of the Air Blown Gasification Cycle operated by British Coal. Subsequent stages of the study have examined the role of mineral matter and char morphology. The suite of coals previously tested in the pilot scale reactor were originally selected to represent coals of a wide geographical spread, a limited range of properties and were commercially available in the EU. The maceral enriched samples were obtained from different coals, but were of similar rank to those examined in this study. Short hold time experiments (10 s) have been carried out in the laboratory scale reactor. Three distinct types of behaviour have been identified—arising from competing influences of the reactivity of the base char, the impact of secondary char deposition and the effect of melting on the reactivity of the ageing particles. The relative combustion reactivity of the residual chars was measured in an atmospheric pressure TGA test. The reactivities were all low, but differences were apparent between the different samples and were consistent with the observed gasification behaviour. The use of maceral analysis to predict the behaviour of the whole coals has been examined. Extrapolation from maceral behaviour was found to give reasonable estimates of the behaviour under pyrolysis conditions, but predictions of gasification behaviour were not reliable.

CO 2 and steam-gasification in a high-pressure wire-mesh reactor: the reactivity of Daw Mill coal and combustion reactivity of its chars

Interrelationships between extents of coal gasification, char gasification and combustion reactivities have been examined as a function of CO 2 and steam pressure and holding time. Experiments have been carried out in a high-pressure wire-mesh reactor equipped with a steam injection facility. Evidence has been presented linking minima in weight loss vs. reactive gas pressure curves with deactivation as a result of secondary char deposition. At longer times, extents of gasification were about 2–3 times higher in steam compared to CO 2. With increasing reactivity of the ambient gas, the minimum in the weight loss vs. pressure curve appears only at the shortest reaction times. At higher pressures, reactivities between zero and 10 s were lower than those between 10 and 20 s. These data are novel and support the suggestion that a relatively unreactive layer of re-polymerised tar tends to slow down the gasification of the main body of the char in the initial stages – until it is itself consumed. Combustion reactivities of pyrolysis and gasification chars decrease with increasing pressure. When exposed to a temperature of 1000°C, combustion reactivities of chars were found drop rapidly within about 10 s to relatively low and stable values. The end values were independent of pressure and composition of the reactive gas. The results are relevant to the design of pilot and commercial scale reactors. On the basis of limited available evidence, it appears that secondary char deposition caused by tar re-polymerisation plays an increasingly significant effect with increasing particle size.

Coal Gasification in CO2 and Steam: Development of a Steam Injection Facility for High-Pressure Wire-Mesh Reactors

The development of a steam injection facility and a new control system for steam gasification experiments in a high-pressure wire-mesh reactor have been described. The design is based on preheating the steam path to prevent condensation during experiments. Steam is allowed to contact the coal sample only instants before the temperature of the sample is ramped. Results from experiments in helium, CO2, and steam at pressures up to 30 bar (1000 °C s-1 to 1,000 °C) have been compared for experiments extending to 60 s at peak temperature. The occurrence of a minimum in the conversion vs pressure diagrams, previously observed by numerous researchers, appears to be related to the reactivity of the gasifying agent and the holding time. The minimum, observed at shorter holding times in steam compared to CO2, appears related to the consumption of secondary char deposited during the pyrolysis stage. At 10 and 20 bar, the sample appears to be completely consumed in steam in about 60 s, while after 60 s in CO2, the pr...

Internal consistency of coal gasification reactivities determined in bench-scale reactors: effect of pyrolysis conditions on char reactivities under high-pressure CO2

Relationships between char preparation conditions and CO2-gasification conversions have been examined using a wire-mesh, a fluidised-bed and a ‘hot-rod’ (fixed-bed) reactor. Conversions from the direct gasification of untreated coal have been compared with those from the gasification of chars prepared: (i) in-situ under helium in each reactor, before switching over to CO2; and (ii) from gasification in all three reactors of a char sample, pre-prepared in the fixed bed reactor. Conversions from direct gasification were slightly higher than experiments where samples were first pyrolysed in situ and gasified under CO2 in the same reactor. In some cases, conversions were within experimental error. Under these conditions and within several percentage points, the pyrolysis and gasification steps may be considered as additive. Lower overall conversions observed in the hot-rod reactor have been attributed to the combined effect of: (i) formation of a low reactivity char—owing to tar-solids contact leading to secondary char deposition; and (ii) poor contact between char and the reactive gas. In the wire-mesh and the fluidised-bed reactors, direct CO2-gasification conversions were considerably larger than those determined using the common sample of char, pre-prepared in the hot-rod (fixed-bed) reactor. This sharp drop in overall conversion shows that care must be taken in interpreting reactivity data from ‘two-reactor, two-step’ procedures where char preparation conditions are not identical to those of the gasification step. A broadly linear relationship has been observed between conversions from a pilot plant reactor and direct CO2-gasification in the bench-scale high-pressure wire-mesh reactor. Despite differences between operating parameters in the two reactors, the results suggest that data from the wire-mesh reactor may be successfully used to compare relative coal reactivities under pilot-plant gasification conditions.

Pyrolysis and Gasification in a Bench-Scale High-Pressure Fluidized-Bed Reactor

A bench-scale high-pressure fluidized-bed reactor designed for pyrolysis, gasification, and combustion experiments (up to 1000 °C, 40 bar) has been constructed and commissioned. The system is intended to generate fuel reactivity data rapidly and cheaply, under realistic experimental conditions; it is relatively simple to construct and capable of operation by a single researcher. The reactor body (Incoloy Alloy 800HT, 34 mm i.d., 504 mm long) serves as the resistance heater and is designed to withstand the reaction pressure, obviating use of a “cold” pressure casing. The reactor is lined with a loosely fitting quartz tube to limit corrosion and catalytic effects. Sample (up to 2000 mg) is held between two air actuated valves and injected batchwise (“single-slug”) through a water-cooled probe. The design of the reactor allows determination of tar/oil and char yields. Exhaust gases are passed through a dryer before entering the analytical stage. The present report focuses on equipment design and preliminary data from pyrolysis and gasification experiments with Daw Mill coal (UK) at up to 1000 °C and 30 bar. Extents of gasification were calculated by subtraction of total volatile yields in CO2 from mass loss during pyrolysis in helium, performed under otherwise identical conditions. Combustion reactivities of chars were determined in an atmospheric pressure TGA instrument. A number of design adjustments have been described, enabling total volatile yields from the FB reactor to match those from a high-pressure wire-mesh reactor. As expected, tar yields from the fluidized-bed reactor were significantly lower than those from the wire-mesh instrument, due to longer residence times of volatiles in the bed of solids and the reactor freeboard.

Combustion and gasification reactivities of hydropyrolysis chars: Effect of pressure and heating rate

The combustion and CO 2-gasification reactivities of chars from Linby (UK) and Pittsburgh No.8 (USA) coals have been determined in an atmospheric pressure TGA-apparatus. The chars have been prepared in a newly configured high-pressure wire-mesh reactor under pressures ranging from atmospheric to 150 bar, at heating rates between 1 and 1000 K s −1. Yields of tar, total volatile and char are presented and discussed. The combustion reactivities of chars prepared under hydrogen have been observed to go through a minimum around pyrolysis pressures of 20 bar. By contrast, the CO 2 gasification reactivities of chars prepared under H 2 at 700 °C have been observed to increase initially as a function of pressure and to stabilise above 40 bar: however, reactivities of chars prepared at 850 °C were found to increase with H 2 pressure only up to about 20 bar and then to drop sharply. Limited data for pyrolysis under He are also presented for comparison with the effect of H 2 on the process.

Development of a gas-sweep facility for the direct capture of pyrolysis tars in a variable heating rate high-pressure wire-mesh reactor

A variable heating rate high-pressure wire-mesh pyrolysis/hydropyrolysis reactor has been configured to permit the continuous passage of gas through the sample holder in order to remove volatiles away from the reaction zone. The introduction of the gas-sweep facility, hitherto not available at elevated pressures, was made possible by the development and installation of a flow-smoothing section beneath the sample holder. This served to reduce turbulence within the gas stream and even out heat transport from the wire-mesh to the flowing gas. Positive tar recovery was achieved at pressures between 2.5 and 150 bar, at heating rates ranging from 1 to 2500 K s −1 and temperatures up to 850 °C

Experimental study of coal pyrolysis and hydropyrolysis at elevated pressures using a variable heating rate wire-mesh apparatus

A high-pressure wire-mesh reactor has been developed with a heating rate range from 1 to 1000 K/s, and the capability of applying extended isothermal holding times (up to 200 s at 600 o C has been used). These improvements to the range of conditions that can be covered with this type of instrument have been achieved by the use of computerized feedback temperature control and the provision of water cooling for the internal electrode assembly. Experiments using samples of Linby and Pittsburgh No. 8 coals have shown that, as inert gas pressure is raised, the effect of increased heating rates, almost completely disappears. In high-pressure hydrogen slow heating (5 K/s) can even give higher total volatile yields than rapid (1000 K/s) heating with short holding times, though this was found possibly to be due to the greater time available for char hydrogasification during heating