Gasification Medium Research Articles

Iron ore as oxygen carrier improved with potassium for chemical looping combustion of anthracite coal

Chemical looping combustion (CLC) is an innovative combustion technology with inherent separation of CO2 without energy penalty. When solid fuel is applied in CLC, the gasification of solid fuel is the rate-limiting process for in situ gasification of coal and reduction of oxygen carrier. The K2CO3-decorated iron ore after calcinations was used as oxygen carrier in CLC of anthracite coal, and potassium ferrites were formed during the calcinations process. The experiments were performed in a laboratory fluidized bed reactor with steam as a gasification medium. Effects of reaction temperature, K2CO3 loading in iron ore and cycle on the gas concentration, carbon conversion, gasification rate and yields of carbonaceous gases were investigated. The carbon gasification was accelerated during the fast reaction stage between 860°C and 920°C, and the water–gas shift reaction was significantly enhanced in a wider temperature range of 800°C to 920°C. With the K2CO3 loading in iron ore increasing from 0% to 20% at 920°C, the carbon conversion was accelerated in the fast reaction stage, and the fast reaction stage became shorter. The yield of CO2 reached a maximum of 94.4% and the yield of CO reached a minimum of 3.4% when use the iron ore loaded with 6% K2CO3. SEM analysis showed that the K2CO3-decorating in iron ore would cause a sintering on the particle surface of oxygen carrier, and the K2CO3 loading in iron ore should not be too high. Cycle experiments indicate that the K2CO3-decorated iron ore has a relative stable catalytic effect in the CLC process.

Steam and air fed biomass gasification: Comparisons based on energy and exergy

Abstract Results are reported of thermodynamic analyses of a biomass gasification unit in which sawdust is the biomass feed and the gasifying medium is either air or steam. Energy and exergy analyses are performed for the system and each of its components. A parametric study reveals the effect of design and operating parameters on the system's performance and energy and exergy efficiencies. The results show that the adiabatic temperature of biomass gasification significantly changes with the type of the gasifying medium. In addition, the exergy and energy efficiencies are observed to be higher when air is the gasifying medium rather than steam, while the system performance and exergy efficiencies are dependent on the moisture content of the feed biomass. The results are significant because they quantify the strong dependence of biomass gasification, which can be used for syngas or hydrogen production, on moisture content, and gasifying medium.

Updraft fixed bed gasification of mesquite and juniper wood samples

Biomass gasification is being considered as one of the most promising technologies for converting biomass into gaseous fuel. Here we present results of gasification, using an adiabatic bed gasifier with air as gasification medium, of mesquite (Prosopis glandulosa) and redberry juniper (Juniperus pinchotii), two woody species that dominate uncultivated lands in the Southern Great Plains, U.S.A., that may have potential for bioenergy utilization. The effects of equivalence ratio (ER), particle size, and moisture content on the temperature profile, gas composition (CO, CO2, H2, N2, CH4, and C2H6), and higher heating value (HHV) were investigated. As ER decreased from 4.2 to 2.7, the mole composition of the end product gas for mesquite contained: 13–21% CO, 1.6–3% H2, 1–1.5% CH4, 0.4–0.6% C2H6, 60–64% N2, 11–25% CO2, and 1–2% O2. The mole composition of the end product gas for juniper consisted of 21–25% CO, 2.5–3.5% H2, 1.5–1.8% CH4, 0.3–0.5% C2H6, 58–61% N2, 9–12% CO2, and 1–2% O2. The H2 and CO mole percentages decreased with increasing ER while the CO2 and N2 mole percentage increased. After removing N2, the HHV of the end-product gas for mesquite and juniper reached 26 and 27.5% of natural gas HHV, respectively, when ER ≈ 2.7.

Comparison of a pilot scale gasification installation performance when air or oxygen is used as gasification medium 2 – Sulphur and nitrogen compounds abatement

The release of H2S and NH3 into syngas during co-gasification of two coals (German and Polish) mixed with wastes (pine, olive bagasse and polyethylene) was studied. Sulphur and nitrogen contents in feedstock were found to have a great influence on H2S and NH3 concentrations in syngas, as the highest contents of these elements led to the highest releases. Air/steam or oxygen/steam mixtures were used in the gasification medium, keeping constant experimental conditions, including equivalent ratio. However, when air was added instead of oxygen, higher flow rates were used, due to the introduction of nitrogen and thus lower residence times were used. Different H2S and NH3 contents were obtained by changing the gasification medium. In presence of oxygen and steam higher H2S contents and lower NH3 concentrations were obtained than those produced in presence of air and steam. However, after syngas hot treatment in two fixed bed reactors, the first one with dolomite and the second one with a Ni-based catalyst (G-90 B 5) these differences lost significance. On the other hand, different final compositions of H2S and NH3 were obtained for different feedstocks. Those with highest sulphur and nitrogen contents led to the highest final H2S and NH3 contents in syngas.

Underground coal-air gasification based solid oxide fuel cell system

Underground coal gasification (UCG) is a potential clean coal technology which converts coal into combustible gas in situ. The syngas produced from the UCG process using dry air contains more steam, tar and higher hydrocarbons compared to the conventional gasifiers. The focus of the present work is to use solid oxide fuel cells (SOFCs) to produce electrical power efficiently. To this end, a UCG system, based on air alone as the gasifying medium, is integrated with the SOFC system taking advantage of the high temperature exhaust from the latter to reform the syngas for producing hydrogen. Additional power is produced in the conventional way from a steam turbine making use of the unutilized fuel in SOFC. A detailed energy analysis of this system shows more than 4% thermal efficiency gain over an electricity generating system based entirely on a steam turbine cycle.

The Effect of Temperature on the Gasification Process

Gasification is a technology that uses fuel to produce power and heat. This technology is also suitable for biomass conversion. Biomass is a renewable energy source that is being developed to diversify the energy mix, so that the Czech Republic can reduce its dependence on fossil fuels and on raw materials for energy imported from abroad. During gasification, biomass is converted into a gas that can then be burned in a gas burner, with all the advantages of gas combustion. Alternatively, it can be used in internal combustion engines. The main task during gasification is to achieve maximum purity and maximum calorific value of the gas. The main factors are the type of gasifier, the gasification medium, biomass quality and, last but not least, the gasification mode itself. This paper describes experiments that investigate the effect of temperature and pressure on gas composition and low calorific value. The experiments were performed in an atmospheric gasifier in the laboratories of the Energy Institute atthe Faculty of Mechanical Engineering, Brno University of Technology.

Biomass gasification with preheated air: Energy and exergy analysis

Due to the irreversibilities that occur during biomass gasification, gasifiers are usually the least efficient units in the systems for production of heat, electricity, or other biofuels. Internal thermal energy exchange is responsible for a part of these irreversibilities and can be reduced by the use of preheated air as a gasifying medium. The focus of the paper is biomass gasification in the whole range of gasification temperatures by the use of air preheated with product gas sensible heat. The energetic and exergetic analyses are carried with a typical ash-free biomass feed represented by CH1.4O0.59N0.0017 at 1 and 10 bar pressure. The tool for the analyses is already validated model extended with a heat exchanger model. For every 200 K of air preheating, the average decrease of the amount of air required for complete biomass gasification is 1.3% of the amount required for its stoichiometric combustion. The air preheated to the gasification temperature on the average increases the lower heating value of the product gas by 13.6%, as well as energetic and exergetic efficiencies of the process. The optimal air preheating temperature is the one that causes gasification to take place at the point where all carbon is consumed. It exists only if the amount of preheated air is less than the amount of air at ambient temperature required for complete gasification at a given pressure. Exergy losses in the heat exchanger, where the product gas preheats air could be reduced by two-stage preheating.

Fixed bed gasification of dairy biomass with enriched air mixture

Concerns over the depletion of fossil fuels and global warming have increased the need for alternative–renewable energy sources. Biomass is one of the renewable and nonconventional energy sources and it also includes municipal solid wastes and animal wastes. Concentrated animal feeding operations produce large quantity of dairy biomass which might result in land and water pollution if left untreated. Different methods are employed to extract the available energy from the dairy biomass which includes co-firing and gasification. Earlier studies on gasification of dairy manure with different steam fuel ratios resulted in increased production of hydrogen. However, the gas mixture has low heat value due to large amount of diluent nitrogen. In order to enhance gas heat values, dairy biomass was gasified in a medium with enriched oxygen varying from 24% to 28% oxygen on volume basis. The effect of enriched air mixture, equivalence ratio and steam fuel ratio on the performance of fixed bed gasifier was studied. Limited studies were done using a mixture of carbon dioxide and oxygen as the gasification medium in order to explore the possibility of complete separation of CO2 and increase the heating value of gas mixture. The results show that the peak temperature and carbon dioxide production increases with corresponding decrease in carbon monoxide with increase in oxygen concentration in the incoming gasification medium. Higher heating value (HHV) of the gases decreases with increase in equivalence ratio (decrease in oxygen concentration). The gases produced using carbon dioxide and oxygen mixture had a higher HHV when compared to that of air and enriched air gasification.

Experimental research on fuel staging cyclone gasification of wood powder

Fuel staging cyclone gasification of wood powder was studied in a cyclone gasifier using air as the gasifying medium. A part of fuel was fed into the upper part of the gasifier, where main part of oxidation reactions took place. Another part of fuel was fed into the lower part of the gasifier. The high temperature flue gas and particles in the upper part of the gasifier were forwarded into the lower part of the gasifier to provide endothermic heat for fuel pyrolysis and reduction reactions. The influences of fuel staging, the equivalence ratio and fuel distribution on temperature profiles, composition, lower heating value and tar content of the produced gas, energy transformation including carbon conversion and cold gasification efficiency, were investigated in this study. The optimum range of equivalence ratio is 0.26–0.29 and the staged fuel ratio is not more than 20%. The lower heating value of the produced gas, the fuel gas production and the tar content are 5.36–5.77MJ/Nm3, 1.70–1.84Nm3/kg and 2.15–2.39g/Nm3, respectively. While the cold gas efficiency is about 61%.

Experimental Investigation of Lignin Decomposition and Char Structure During CO2 and H2O/N2 Gasification

Characterization of the char pore structure resulting from thermal decomposition of lignin during TGA processing in both CO2 and H2O/N2 media was performed using an Hitachi 4700 scanning electron microscope. Lignin, the more thermally resilient structural component of ligno-cellulosic biomass feedstocks, was found to undergo more complete conversion to volatiles during thermal processing in a CO2 as compared to a H2O/N2 gasification medium. The pyrolytic char created during CO2 thermal treatment exhibited a more porous surface and an intricate channel structure that enabled the CO2 molecules to access the inner volume and provided a channel network for escaping volatiles. This resulted in a more complete solid to gas conversion of the char during CO2 gasification. Both a greater surface pore density and a wider pore size distribution was observed in those chars undergoing thermal decomposition in CO2.

Coal and Biomass Partial Gasification and Soot Properties in an Atmospheric Fluidized Bed

Using air as the gasification medium, one kind of coal and one kind of biomass partial gasification studies were carried out in a laboratory-scale atmospheric fluidized bed with the various operating parameters. The effects of the O/C ratio, biomass/(coal + biomass) (Fb/Fm) ratio, and bed temperature on the fuel gas compositions and the high heating value (HHV) were reported in this paper. The results show that the concentrations of carbon monoxide, hydrogen, and methane and the HHV decrease with the rise of the O/C ratio and the decline of the Fb/Fm ratio for coal and biomass partial gasification. A rise of the bed temperature favors the semi-gasification reaction of coal, but the concentrations of carbon monoxide and methane and the HHV decrease with the rise of the bed temperature, except hydrogen. In addition, the gas HHVs are between 1.0 and 3.3 MJ N–1 m–3. The gas yield and carbon conversion increase with the O/C ratio, Fb/Fm ratio, and bed temperature. The atomic percentage of carbon increases and the atomic percentage of oxygen decreases with the rise of the O/C ratio in fly ash. The concentration of soot decreases along with the O/C ratio in fly ash.

Comparison of a pilot scale gasification installation performance when air or oxygen is used as gasification medium 1. Tars and gaseous hydrocarbons formation

It is predictable that in the near future fossil fuels will continue to have the greatest contribution to energy production. Thus, it is necessary to develop and improve technologies that ensure low CO2 emissions. Oxy-gasification is one of such technologies, as the use of oxygen instead of air will allow solving the problem of nitrogen dilution effect in syngas and consequently will simplify the process of CO2 capture. On the other hand, the use of oxygen will increase investment costs, as an oxygen production unit will have to be added to the overall installation, and operation costs will also rise, due to the extra energy necessary for oxygen production. Apart from this, it is important to check the performance of installations initially designed to operate with air, when retrofitted to use oxygen and to analyse the effect that this change may have on syngas composition. In this work the effect of gasification agent on syngas composition, including tar content was determined during co-gasification of two types of coals (German and Polish) mixed with several wastes, like pine, olive bagasse and polyethylene (PE). Air and steam or oxygen and steam mixtures were used as gasification agent, keeping constant ER (equivalent ratio), that is to say, for each coal and wastes blend the oxygen flow was the same for both gasification agents. However, when oxygen was used, gas flows fed into the gasifier were lower than those used in presence of air, which means that residence times were higher than when air was used. Therefore, syngas presented lower hydrocarbons contents and higher CO2 concentrations, probably because there was more time for reactions to occur in presence of oxygen.

Results with a bench scale downdraft biomass gasifier for agricultural and forestry residues

A small scale fixed bed downdraft gasifier system to be fed with agricultural and forestry residues has been designed and constructed. The downdraft gasifier has four consecutive reaction zones from the top to the bottom, namely drying, pyrolysis, oxidation and reduction zones. Both the biomass fuel and the gases move in the same direction. A throat has been incorporated into the design to achieve gasification with lower tar production. The experimental system consists of the downdraft gasifier and the gas cleaning unit made up by a cyclone, a scrubber and a filter box. A pilot burner is utilized for initial ignition of the biomass fuel. The product gases are combusted in the flare built up as part of the gasification system. The gasification medium is air. The air to fuel ratio is adjusted to produce a gas with acceptably high heating value and low pollutants. Within this frame, different types of biomass, namely wood chips, barks, olive pomace and hazelnut shells are to be processed. The developed downdraft gasifier appears to handle the investigated biomass sources in a technically and environmentally feasible manner. This paper summarizes selected design related issues along with the results obtained with wood chips and hazelnut shells.

Generation of hydrogen rich gas through fluidized bed gasification of biomass

The objective of this study was to investigate the process of generating hydrogen rich syngas through thermo chemical fluidized bed gasification of biomass. The experiments were performed in a laboratory scale externally heated biomass gasifier. Rice husk had been taken as a representative biomass and, steam had been used as the fluidizing and gasifying media. A thermodynamic equilibrium model was used to predict the gasification process. The work included the parametric study of process parameters such as reactor temperature and steam biomass ratio which generally influence the percentage of hydrogen content in the product gas. Steam had been used here to generate nitrogen free product gas and also to increase the hydrogen concentration in syngas with a medium range heating value of around 12 MJ/Nm3.

Thermodynamic optimization of biomass gasification for decentralized power generation and Fischer–Tropsch synthesis

Abstract In recent years, biomass gasification has emerged as a viable option for decentralized power generation, especially in developing countries. Another potential use of producer gas from biomass gasification is in terms of feedstock for Fischer–Tropsch (FT) synthesis – a process for manufacture of synthetic gasoline and diesel. This paper reports optimization of biomass gasification process for these two applications. Using the non–stoichometric equilibrium model (SOLGASMIX), we have assessed the outcome of gasification process for different combinations of operating conditions. Four key parameters have been used for optimization, viz. biomass type (saw dust, rice husk, bamboo dust), air or equivalence ratio (AR = 0, 0.2, 0.4, 0.6, 0.8 and 1), temperature of gasification (T = 400, 500, 600, 700, 800, 900 and 1000 °C), and gasification medium (air, air–steam 10% mole/mole mixture, air–steam 30%mole/mole mixture). Performance of the gasification process has been assessed with four measures, viz. molar content of H2 and CO in the producer gas, H2/CO molar ratio, LHV of producer gas and overall efficiency of gasifier. The optimum sets of operating conditions for gasifier for FT synthesis are: AR = 0.2–0.4, Temp = 800–1000 °C, and gasification medium as air. The optimum sets of operating conditions for decentralized power generation are: AR = 0.3–0.4, Temp = 700–800 °C with gasification medium being air. The thermodynamic model and methodology presented in this work also presents a general framework, which could be extended for optimization of biomass gasification for any other application.

Dynamic experimental simulation of hydrogen oriented underground gasification of lignite

The main goal of the study presented in the paper was to experimentally demonstrate the feasibility of lignite gasification to hydrogen-rich gas under the underground conditions simulated in the ex situ reactor. The in situ gasification conditions were simulated both in respect to the coal seam and the surrounding stratum. In the 54-h experiment the process of lignite gasification with oxygen and steam as gasifying medium was tested. The experiment was initially divided into three stages: the ignition stage, the oxygen stage and the steam stage. The gas produced in the steam gasification stage was characterized by the calorific value of 7.8 MJ/m 3 and average hydrogen content of 46.3 vol.%. Unfortunately a rapid decrease in the temperature levels and in the amount of produced gas proved that the tested lignite of 53 vol.% moisture content was not suitable for steam gasification. A great amount of thermal energy was consumed for water evaporation which led to a considerable heat loss. An addition of stoichiometric amount of water in the system by adding steam caused the seam to extinguish. Thus only oxygen could be used as the gasifying medium in the gasification of the tested lignite. The average calorific value of gas produced in the stable operation during oxygen gasification stage equaled 5.2 MJ/m 3 with the average gas production rate of 16.0 m 3/h and the average hydrogen content in the produced gas of 26.4 vol.%.

Exergy analysis of hydrogen production from biomass gasification

For a given set of operating conditions, the hydrogen production from biomass gasification can be improved through optimization of the operating parameters and efficiencies. The present approach can predict hydrogen production via biomass gasification in a range of 10–32 kg/s from biomass (sawdust wood). The biomass is introduced to a gasifier at an operating temperature range of 1000–1500 K. Also, 4.5 kg/s of steam at 500 K is used as gasification medium. Results indicate that improvement in hydrogen production from biomass steam gasification depending on the amount of steam and quantity of biomass feeding to the gasifier as well the operating temperature. Over the range of feeding biomass, the hydrogen yield reaches 80–130 g H 2/kg biomass while in the operating temperature examined, the hydrogen yield reaches 80 g H 2/kg biomass. On mole basis it is found that, in the first range of H 2 varies from 51 to 63% in the studied range of feeding biomass in existing 4.5 kg/s from steam while H 2 gets to 51–53% in existing of 6.3 kg/s from steam.

Air gasification characteristics of coir pith in a circulating fluidized bed gasifier

The gasification characteristics of coir pith are studied in a circulating fluidized bed gasifier using air as the gasifying medium. The effect of various parameters such as temperature, Equivalence Ratio (ER), and Oxygen/Carbon ratio (O/C) on gas yield, gas composition, gas heating value, carbon conversion, cold gas and overall thermal efficiency is studied. The ERs employed in the study are 0.18, 0.21, 0.24 and 0.31. It has been found that temperature has an influence on the cracking reactions, as indicated by the increased yield of hydrogen. The maximum yield of hydrogen is obtained at a temperature of 1028.6 °C, and as the Equivalence Ratio (ER) increased, hydrogen yield decreased. The gas yield also increased with increase in temperature and ER. Also it has been observed that the gas heating value increases with increase in temperature and decrease in ER. Carbon conversion is found to increase with increase in temperature and increase in ER. It is found that the increase in temperature favours both the cold gas thermal and overall thermal efficiencies. Also the cold gas and overall thermal gasification efficiencies decrease with increase in Equivalence Ratio.

D201 SOLID CARBON FEEDSTOCK GASIFICATION USING CO_2 SIMULATION AND EXPERIMENT(Biomass-4)

The concept of using CO_2 as a gasification medium has been investigated both theoretically and experimentally. The theoretical investigation was done using Aspen[○!R] Plus simulations to explore and understand the impact of CO_2 on an integrated gasification combined cycle (IGCC) plant and the gasifier performance. The results show that a steam to carbon ratio of 1.5 provides a hydrogen output from the gasifier of 1.15 kg hr^<-1> while generating about 14 kW of electricity per kmol hr^<-1> of carbon from a SOFC using the portion of the CO generated that was not needed to drive the reforming reactions. However recycling up to 25% of CO_2 into the gasifier produces about 15% more hydrogen, while using 20% less CO for combustion to drive the gasification reactions. The IGCC simulations show that the addition of CO_2, from the high pressure compressor, does not change the CGE. The baseline CGE using steam gasification of Spring Creek coal (9338 BTU lb^<-1>) is 65.0% whereas replacing the steam with CO_2 resulted in a CGE of 65.1%. Moreover, the H_2O/CO was reduced from 4.2 for steam gasification to 2.0 for CO_2 gasification, which is the minimum necessary to enable efficient operation of water gas shift reactors. Validation tests over a CO_2 concentration range from 0% to 100% by volume resulted in a significant enhancement in the CO evolution above 700℃. However the CO_2 introduction suppressed the H_2 production at temperatures above 700℃, indicating a delayed effect on H_2 suppression. All biomass test samples showed similar mass decay behavior and were completely exhausted by 900°-1000℃. Finally, CO_2 gasification of various biomass and municipal solid waste (MSW) feedstocks has yielded similar results to those obtained using coal.

Ultra-High Temperature Steam Gasification of Biomass and Solid Wastes

Experimental results are presented on the gasification of several waste products using high-temperature steam as the gasification media. Four cellulose-rich surrogate waste products (paper, cardboard, and wood pellets) were gasified with high-temperature steam at different temperatures in the range of 700 to 1,100°C. Gasification is an efficient method for clean conversion of waste to hydrogen-rich syngas having moderate heating value, and producing negligible soot and tars during its conversion. Although gasification is a relatively old technique, it has not been examined at ultrahigh gasification temperatures. Paper, cardboard, and other cellulose-rich waste products represent a majority share of municipal solid waste. Basic chemistry of gasification and main reactions propelling the process are presented here. The experimental facility used provided pure steam or steam–oxygen mixtures from the combustion of hydrogen and oxygen at very high temperatures. The role of the chemical composition of the feeds...