Calorific Value Of Product Gas Research Articles

Two-stage fluidized bed gasification enhanced with oxidative pyrolysis for low-tar producer gas from biomass

Oxidative pyrolysis of fuel was adopted to configure an advanced two-stage fluidized bed gasification system, aiming to produce low-tar producer gas efficiently. A series of tests were carried out to investigate the effect of oxygen allocation in supply on gasification of pine chips in terms of both efficiency and producer gas quality. Compared with the case without pre-oxidation, coupling oxidative pyrolysis increased gas volume fraction of CO, CH4, and CnHm while decreasing that of CO2 and H2 in the produced gas. Further analysis showed that adopting oxidative pyrolysis reduced fuel gas yield, but the tar in the produced gas was lighter. The generated tar is easily transformed into small-molecule combustible gas by the catalytic action of hot char, thus increasing the calorific value of product gas. The long-term operation of the pilot plant presents a great steady continuous running with a minimum tar content in the producer gas of 1.3 g/Nm3. The above-mentioned results thus well verified the technical advantage and feasibility of the two-stage fluidized bed gasification with oxidative pyrolysis.

Coal pyrolysis under varied atmospheres and temperatures in a moving-bed pyrolyzer for blue-coke production

To solve the prevailing problems in industrial blue-coke production such as the low utilization of coal and the low calorific value of product gas, a novel blue-coke production technology using slack coal has been proposed. The coarse coal in the feed is pyrolyzed in a moving-bed pyrolyzer with the gasification gas (G-gas) from the fluidized gasification of the fine coal as the heat carrier, so that high-quality blue-coke, tar and gas are obtained. To elucidate the effect of G-gas on pyrolysis, the coarse coal pyrolyses in a moving-bed pyrolyzer were investigated under steam, CO2 and G-gas atmospheres in the temperature range of 500–800 °C. Compared to N2 atmosphere, the steam increased the tar yield below 700 °C due to the enhanced water-gas shift reaction. The CO2 increased the tar yield around 600–700 °C because of the restrained decomposition of calcite in the coal. Above 600 °C, the coke's partial gasification under the reactive atmospheres led to increased gas yield and decreased coke yield; meanwhile, the specific surface area of the coke increased and the electrical resistivity decreased. The contribution of the reactive atmospheres was in the same order of their reactivities, i.e. steam > G-gas > CO2.

Experimental study on evaluation of underground coal gasification with a horizontal hole using two different coals

Underground coal gasification (UCG) is a technique to extract coal energy with heat energy and combustible gases through chemical reactions in the underground gasifier. In this study, an application of a coaxial UCG system with a horizontal hole is discussed by means of the model UCG experiments with a large-scale simulated coal seam having dimensions of 550 × 600 × 2740 mm. The two types of coal having 30.18 MJ/kg of calorific value with 7.9% of ash (type 1) and 22.66 MJ/kg of calorific value with 28.3% of ash (type 2) were used for the experiments to evaluate the effect of coal quality on temperature distribution of the gasification area and product gas quality. The oxygen-enriched air was used. The injection rate of the gasification agents was elevated during the experiments to analyze the effect on the product gas. The results show that the gasification area is expanded along the wall of a coaxial hole, not upwards for the type 2 coal with high ash content. The average calorific value of product gas for types 1 and 2 is 8.05 MJ/m3 and 6.91 MJ/m3 respectively, while an increase of injection flow rate produces an improvement of the calorific value for both types of coal. Additionally, it is suggested that the reacted carbon and the product gas volume can be estimated with the volume of oxygen injected regardless of the coal quality if the gasification efficiency and the reaction temperature are similar. These results help to estimate several important parameters, e.g. reacted coal amount, recovered gas volume, and recovered energy from the coal when the actual field implementation is designed.

CO2-O2 gasification of a bituminous coal in circulating fluidized bed

CO2 as a gasifying agent can fully or partly replace N2 for coal gasification. In this study, the effect of the replacement of N2 by CO2 and the effect of O2/C molar ratio on gasification performance were investigated via experiments as well as thermodynamic equilibrium calculations. Experiments were performed in a bench-scale self-heated circulating fluidized bed (CFB) gasifier with O2 volume percentage of 21%. The results showed the Boudouard reaction was strongly enhanced when N2 in air is replaced by CO2. At the O2/C molar ratio of 0.39, the replacement of N2 by CO2 induced an increase in concentration of CO+H2, yield of CO+H2, calorific value of product gas, carbon conversion and cold gas efficiency, which is mainly due to the enhancement of Boudouard reaction. Though the elevated O2/C molar ratio from 0.39 to 0.64 accelerated the combustion proportion, the yield of H2+CO was improved in CO2-O2 gasification. Meanwhile the cold gas efficiency increased from 43.8% to 58.6% in CO2-O2 gasification, and showed greater improvement than that in air gasification. The enhancement of Boudouard reaction with the replacement of N2 by CO2 was further strengthened by the increase in O2/C molar ratio. The variation of gas composition in CO2-O2 gasification experiments was predicted by thermodynamic equilibrium calculations, and the increase in the yield of CO+H2 was verified when N2 in air was replaced by CO2 in a gasifying agent.

Gasification of high-ash Indian coal in bubbling fluidized bed using air and steam – An experimental study

In this experimental study, gasification characteristics of Indian coals having high ash content (>35%) in a bubbling fluidized bed reactor, using air and steam as the gasification agents under atmospheric pressure, are presented. The thermal power output of the gasification device has been varied in the range of 80–100kW. The ratio of the actual mass flow rate of air supplied to the stoichiometric air mass flow rate (required for complete combustion) has been varied in the range of 0.25–0.35. The ratio of mass flow rate of steam to that of coal has been varied from 0.15 to 0.25. Effects of air and steam flow rates on the calorific value of product gas, carbon conversion and cold gas efficiency have been studied in detail. For high-ash Indian coals, supply of steam produces positive effect as all the metrics such as calorific value of product gas, carbon conversion and cold gas efficiency increases with increase in the steam supply rate.

Thermodynamic modelling of supercritical water gasification: Investigating the effect of biomass composition to aid in the selection of appropriate feedstock material

A process model developed in Aspen Plus®, was used for the thermodynamic modelling of supercritical water gasification (SCWG) using a wide variety of biomass materials as feedstock. The influence of the composition of the biomass material (in terms of carbon, hydrogen and oxygen content) on various performance indicators (such as gas yields, cold gas efficiency, calorific value of product gas and heat of reaction), were determined at various temperatures (600, 700 and 800°C) and biomass feed concentrations (5, 15 and 25wt.%). Generalised contour plots, based on the biomass composition, were developed for these performance indicators to provide the thermodynamic limits at various operating conditions. These plots can aid in the selection or screening of potential biomass materials and appropriate operating conditions for SCWG prior to conducting experimental work.

Pyrolysis of Orimulsion: A Comprehensive Model Based on Chemical Equilibrium

The purpose of this study was to investigate the influence of water content on the concentration of Orimulsion pyrolysis products, calorific value of product gas, cold gas efficiency, and coke formation coefficient. To achieve this objective, a numerical algorithm, based on thermochemical equilibrium, was developed to simulate the pyrolysis process. To improve the model accuracy, the model was first modified by a common method available in the literature. The modified model in the term of products yield was compared with the experiments literature and observed a reasonable agreement between the numerical results and experimental data. The produced gas HHV in pyrolysis process was found to be sensitive to water content, while cold gas efficiency and the coke formation coefficient were less sensitive. Finally, based on the simulated results, an optimal condition is suggested to improve produced gas HHV in Orimulsion pyrolysis process.

Gasification of refuse derived fuel in a fixed bed reactor for syngas production

Steam gasification of two different refuse derived fuels (RDFs), differing slightly in composition as well as thermal stability, was carried out in a fixed-bed reactor at atmospheric pressure. The proximate and ultimate analyses reveal that carbon and hydrogen are the major components in RDFs. The thermal analysis indicates the presence of cellulose and plastic based materials in RDFs. H2 and CO are found to be the major products, along with CO2 and hydrocarbons resulting from gasification of RDFs. The effect of gasification temperature on H2 and CO selectivities was studied, and the optimum temperature for better H2 and CO selectivity was determined to be 725 degrees C. The calorific value of product gas produced at lower gasification temperature is significantly higher than that of gas produced at higher process temperature. Also, the composition of RDF plays an important role in distribution of products gas. The RDF with more C and H content is found to produce more amounts of CO and H2 under similar experimental conditions. The steam/waste ratio showed a notable effect on the selectivity of syngas as well as calorific value of the resulting product gas. The flow rate of carrier gas did not show any significant effect on products yield or their distribution.

Equilibrium and kinetic modeling of char reduction reactions in a downdraft biomass gasifier: A comparison

The thermodynamic and kinetic modeling of char reduction reactions in a downdraft (biomass) gasifier has been presented. Mass and energy balance are coupled with equilibrium relations or kinetic rate parameters (using varying char reactivity factor) in order to predict status of un-converted char in addition to gas composition, calorific value, conversion efficiency, exit gas temperature, endothermic heat absorption rate and gasifier power output. Both modeling predictions are compared against experimental data for their validity. The influence of char bed length and reaction temperature in reduction zone has been examined. CO and H 2 component, calorific value of product gas and the endothermic heat absorption rate in reduction zone are found to be sensitive with reaction temperature, while char bed length is less sensitive to equilibrium predictions. For present case, all char conversion takes place at critical reaction temperature of 932 K for equilibrium, while for kinetic modeling critical reaction temperature and critical char bed length of 950 K and ∼25 cm have been identified, comparing the predictions. The critical reaction temperatures and critical char bed length also depend on inlet components composition and initial temperature supplied to the reduction reaction zone model.

4308 石炭ガス化炉最適運転支援システムの開発(S62-2 高効率石炭火力発電(2),S62 高効率石炭火力発電)

A system which can automatically obtain online plant status data and calculate an optimal operating condition refering to gasification performance evaluation functions is suggested by the authors in this paper. Optimization calculations with non-linear programming are performed in the system for operating conditions of a entrained flow coal gasifer under three gasifier's loads. Constraint of temperature inside the gasifier, calorific value of prodcut gas and amount of recycled char, are imposed on each calculation. The temperature inside the gasifier reflects taking into account a discharge of molten slag from the gasifier. Calorific value of product gas is refered to specifications of gas turbine combustor. Amount of recycled char is restricted within the capacity of recycling system of the plant. Fluctuation of air ratio is also taken into account in the optimization calculation. Results show that improvement of gasifier performance can be done in each gasifier's load, such as 0.28MJ/m^3N increase in calorific value of product gas in 100% load and 0.43 MJ/m^3N increase in 80% load, though optimal condition in 70% load cannot be found. It is confirmed that the system is effective for the assessment of the gasifier's operating condition and performance.

Modelling of an entrained flow coal gasifier. 2. Effect of operating conditions on reactor performance

The entrained flow gasification model developed in Part 1 was used for parametric studies to provide a better understanding of the reactor performance in terms of coal conversion, product gas composition, calorific value and temperature profiles throughout the reactor under various operating conditions (feed flow rate, particle size and system pressure). The results suggest that the critical parameters in gasification are the steam-to-coal and oxygen-to-coal feed ratios and the gasifier pressure. The maximum reactor temperature could be controlled by the concentration of steam in the feed, but its location was strongly dependent on pressure. In terms of throughput and calorific value of product gas, the performance of the gasifier would be improved with lower steam and oxygen feed rates and higher system pressure; in terms of conversion, it would be improved with higher system pressure. No experiments were performed to verify the simulation, but the results are consistent with those of previous investigations.

Development of Pressurized Coal Partial Combustor. Characteristics of 7T/d Gasifier with Various Coal-Feed Ratios.

A pressurized coal partial combustor (P-CPC) with two-stage coal supply was tested to elucidate the characteristics of a 7T-coal/d air-blown coal gasifier. As the secondary coal-feed ratio (2ry coal/total coal) was increased, the following phenomena were observed, indicating depression of the coal gasification reaction ; (1) decrease of CO and H2 concentrations, (2) decrease of calorific value of product gas, (3) increase of hydrocarbon (CH4 + C2H6) content, (4) decrease of carbon conversion efficiency. Secondary coal supply is effective for stable slag discharge and the prevention of the slagging problem in a reductor due to the rapid temperature drop of molten slag. In conclusion, as long as stable slag discharge is obtained, it is effective to lower the 2ry coal-feed ratio to promote the coal gasification reaction, resulting in, for example, higher calorific value of the product gas.