Air-blown Gasification Research Articles

Recent progress in Japan on hot gas cleanup of hydrogen chloride, hydrogen sulfide and ammonia in coal-derived fuel gas

The present review paper highlights on the recent progress in Japan on the hot gas cleanup of HCl, H 2S and NH 3 in raw fuel gas for coal-based, combined cycle power generation technologies. It has been shown that NaAlO 2, prepared by mixing Na 2CO 3 solution with Al 2O 3 sol, can reduce HCl in an air-blown gasification gas from the initial 200 ppm to < 1 ppm at 400 °C, and it is tolerable for 200 ppm H 2S. With regard to the removal of H 2S, studies on the stability and durability of ZnFe 2O 4 sorbent in a simulated fuel gas have indicated the presence of an optimal operation temperature from the viewpoint of the suppression of both vaporization of metallic Zn and carbon formation from CO. High-performance TiO 2-supported ZnFe 2O 4, which can decrease 1000 ppm H 2S to < 1 ppm at 450 °C and 1 MPa, has been developed by the homogeneous precipitation method using a mixture of SiO 2 sol and an aqueous solution of Zn and Fe nitrates, followed by mixing with TiO 2. Although this sorbent is regenerable and durable, the sorption ability should be improved in a syngas-rich fuel gas from an O 2-blown gasifier. A novel method to prepare carbon-supported ZnFe 2O 4 and CaFe 2O 4 by impregnating the corresponding nitrate solution with brown coal has been proposed, and the large desulfurization capacity of almost 100% has been achieved in the removal of 4000 ppm H 2S around 450 °C. The present authors have demonstrated that an Australian limonite rich in α-FeOOH is practically feasible as the catalyst material for the decomposition of 2000 ppm NH 3 in a syngas-rich gas of 25 vol.% H 2/50 vol.% CO at 750 °C, because small amounts of H 2O and CO 2 added to the gas can work efficiently for inhibiting carbon deposition from the CO.

High temperature air-blown woody biomass gasification model for the estimation of an entrained down-flow gasifier

A high temperature air-blown gasification model for woody biomass is developed based on an air-blown gasification experiment. A high temperature air-blown gasification experiment on woody biomass in an entrained down-flow gasifier is carried out, and then the simple gasification model is developed based on the experimental results. In the experiment, air-blown gasification is conducted to demonstrate the behavior of this process. Pulverized wood is used as the gasification fuel, which is injected directly into the entrained down-flow gasifier by the pulverized wood banner. The pulverized wood is sieved through 60 mesh and supplied at rates of 19 and 27kg/h. The oxygen-carbon molar ratio (O/C) is employed as the operational condition instead of the air ratio. The maximum temperature achievable is over 1400K when the O/C is from 1.26 to 1.84. The results show that the gas composition is followed by the CO-shift reaction equilibrium. Therefore, the air-blown gasification model is developed based on the CO-shift reaction equilibrium. The simple gasification model agrees well with the experimental results. From calculations in large-scale units, the cold gas is able to achieve 80% efficiency in the air-blown gasification, when the woody biomass feedrate is over 1000kg/h and input air temperature is 700K.

High temperature air-blown gasification of Korean anthracite and plastic waste mixture

Korean anthracite is too high in ash contents and low in calorific value to be used as an industrial energy source, the demand for anthracite has rapidly decreased and its competitiveness weakened. To overcome the problem, a mixture of Korean anthracite and plastic wastes low in ash and high in calorific value was manufactured. A 1.0T/D fixed bed gasification process was developed to understand the gasification characteristics of the mixtures and secure operation technology using Korean and Chinese anthracite. For the Korean anthracite, the syngas composition and heating value are varied from 10 to 20% and from 300 to 800 kcal/Nm3 as a function of steam/air/fuel ratio. Therefore, it is concluded that Korean anthracite is hard to gasify because of low reactivity. For the Chinese anthracite low ash content and higher heating value than domestic anthracite, the syngas composition was maintained at about 20–40% and the calorific value was 800–1,300 kcal/Nm3. A reformer using high-temperature air/steam was installed just after the gasifier to combust and convert tar and soot into syngas. We confirmed that the amount of generated tar and soot showed a salient difference after running the reformer. In the future, gasification experiments of manufactured mixtures of anthracite and plastic waste using 1.0T/D fixed bed gasifier will be performed.

木質バイオマスの空気吹き高温気流層型ガス化プロセスに関する研究

High temperature air-blown gasification experiment of woody biomass was conducted in an entrained down-flow type gasifire. Air was blown as the gasifying agent instead of oxygen to improve the gasification process performance. To archive the higher temperature (over 1273 K), pulverized wood was used as the feed stock of gasification experiment. Air-blown gasification process was evaluated by measuring temperature in the gasifire and produced gas composition against O/C ratio. Carbon to gas conversion, cold gas efficiency and heating value of produced gas in an air-blown gasification experiment was also calculated. These gasification behaviors were compared with that in oxygen-blown gasification experiment. It was found that gasification process with air could be performed as well as gasification with oxygen.

An Investigation of the Reactivity of Chars Formed in Fluidized Bed Gasifiers: The Effect of Reaction Conditions and Particle Size on Coal Char Reactivity

Coal-derived chars formed during air-blown gasification processes may rapidly lose reactivity, and this can limit the extent of their conversion. To study this effect, a laboratory-scale fluidized bed reactor has been modified to enable char samples to be prepared under strictly controlled conditions of temperature, pressure, particle size, gaseous environment, and residence time. This has been used to gain an insight into the deactivation of the chars as they form and during their subsequent residence time in the bed of the gasifier. The work shows that the char reactivity declines rapidly during its formation as part of the pyrolysis of the coal. This is thought to result from the rapid deposition of secondary, unreactive char within the pores of the material. In this work, it has been shown to occur within the initial 10 s in the reactor, but in reality, this effect probably occurred within 1 s. Temperature, pressure, and particle size have an impact on this process. Subsequently, and over a longer time scale, structural reorganization occurs in the solid char, and this anneals the structure by graphitization. This has been indicated by the identification of graphite, by X-ray diffraction in long-residence-time chars. The presence of steam in the fluidizing gas seemed to reduce the reactivity of small char particles, which could be due to the gasification of the more reactive parts. This effect does not seem to be present in data obtained with larger particles, and this is thought to be due to the greater influence of secondary char deposition in the larger particles. The reactivities of the largest particles formed over the longest time in this work are getting close to the reactivity values seen in char particles formed in a pilot-scale gasifier.

Characteristics of air-blown gasification in a pebble bed gasifier

High temperature air-blown gasification is a new concept to utilize the waste heat from gasifier that is called multi-staged enthalpy extraction technology. This process was developed to solve the economic problems due to air separation costs for the oxygen-blown as a gasifying agent. In this study, we have constructed a pebble bed gasifier and operated it by controlling the pebble size and bed height with three different types of coal (Kideco, Datong and Drayton coal). As a result, we can produce syngas with a calorific value of 700 kcal/Nm3 at an air temperature of 650 °C; the performance of high temperature air gasification was strong in the order of Kideco coal, Datong coal and Drayton coal. Also, from the data of the exterior analysis of slag that is attached to the surface of pebbles, we can know that the iron component is considerably high. This means the increase in restored metallic iron component seems to contribute to the solidification of slag.

More efficient biomass gasification via torrefaction

Wood torrefaction is a mild pyrolysis process that improves the fuel properties of wood. At temperatures between 230 and 300 °C, the hemicellulose fraction of the wood decomposes, so that torrefied wood and volatiles are formed. Mass and energy balances for torrefaction experiments at 250 and 300 °C are presented. Advantages of torrefaction as a pre-treatment prior to gasification are demonstrated. Three concepts are compared: air-blown gasification of wood, air-blown gasification of torrefied wood (both at a temperature of 950 °C in a circulating fluidized bed) and oxygen-blown gasification of torrefied wood (at a temperature of 1200 °C in an entrained flow gasifier), all at atmospheric pressure. The overall exergetic efficiency of air-blown gasification of torrefied wood was found to be lower than that of wood, because the volatiles produced in the torrefaction step are not utilized. For the entrained flow gasifier, the volatiles can be introduced into the hot product gas stream as a ‘chemical quench’. The overall efficiency of such a process scheme is comparable to direct gasification of wood, but more exergy is conserved in as chemical exergy in the product gas (72.6% versus 68.6%). This novel method to improve the efficiency of biomass gasification is promising; therefore, practical demonstration is recommended.

Energy-Recuperative Coal-Integrated Gasification/Gas Turbine Power Generation System

Coal-integrated gasification/gas turbine (CIG/GT) based power plants are well known for achieving electricity more efficient and at a lower cost than direct combustion based power plants. Since the gasification is an endothermic, thermochemical conversion process, it requires heat to proceed. In general, this heat is furnished by internal combustion taking place in the gasifier by virtue of oxygen-blown or air-blown gasification. However, the direct combustion of the solid fuel is seen to be inefficient because of the large amount of exergy destruction posed during the combustion, especially at relatively low temperatures like gasification temperatures. This causes the overall performance deterioration of the CIG/GT system. Therefore, a decrease in the destruction of exergy during the combustion can contribute to improve overall system efficiency. In this paper, an innovative concept of energy-recuperative gasification was proposed and incorporated in the CIG/GT system. The idea is to make use of the waste heat from the gas turbine exhaust as the reaction heat for the gasification instead of the internal combustion. This type of energy recuperation is also called thermochemical recuperation. In addition, the proposed CIG/GT incorporates other effective energy recuperation, including heat and steam recuperation, in order to maximize the generation efficiency. The feasibility of the concept implementation and the system improvement were preliminarily examined and discussed.

An Investigation of the Reactivity of Chars Formed in Fluidized-Bed Gasifiers: Equipment Development and Initial Tests

Chars formed during air and oxygen blown gasification processes have a low reactivity. This is due to changes that occur in the structure and morphology of the original coal during heating. In part, the changes depend on conditions prevailing during the pyrolysis stage and partly on the length of time spent at peak temperature. Previous work in this laboratory has highlighted that the gasification reactivity of a char depends on the conditions of its formation. This means that chars must be prepared under realistic conditions when conducting laboratory scale reactivity studies that are intended to support a larger scale development. This is not easy to do and requires the development of dedicated methods for preparing the char. In this paper, the development of a laboratory-scale test, based on a laboratory-scale spouted bed gasifier, is described that is able to prepare chars under conditions that represent those in an air-blown gasifier. The reactivity of the prepared chars is then examined to identify ...

Thermodynamic equilibrium study of trace element transformation during underground coal gasification

In order to provide theoretical basis for gas cleaning and pollution control thermodynamic equilibrium calculations were performed to predict the partitioning of trace element species under special conditions for underground coal gasification, including both oxygen-steam gasification and air blown gasification under elevated pressures. The trace elements studied include As, Se, Pb, Ni, Cd, Cr, Sb. The results indicate, in the condition of large-section UCG process with oxygen-steam injection, all the elements studied present in the gas phase during gasification stage. Ni and Cr are hardly volatile and tend to condense below 1000 °C. Most of them will be enriched in bottom ash. As, Pb, Cd, Sb totally or partially occur in gas phase in underground gas cleaning system. In cold cleaning system, they exist in condensed phases and tend to be enriched in fly ash, which is beneficial to trace element removal. Se presents in gas phase in the form of H 2Se(g) even in ground cold gas cleaning system. The presence of potassium makes arsenic less volatile due to the formation of K 3AsO 4 and selenium is not affected. Also the amount of gaseous antimony chloride is reduced because of prior formation of alkali metal chloride. Pressure shows a remarkable effect on equilibrium partitioning of As, Se, Sb. With rising pressure, increasing quantities of hydrides of these trace elements are generated due to the enhancement of the reducing atmosphere. At the same time, the condensation points of all the trace elements sharply increase with pressure. It is found that for underground air blown gasification, the gaseous species of trace element sulfide can be easily formed, and the trace elements have lower condensation points than those for oxygen-steam gasification.

3631 空気吹き石炭ガス化炉の性能予測低空気比運転時におけるガス化剤酸素濃度の影響(S54 高効率石炭火力発電技術)

3631 空気吹き石炭ガス化炉の性能予測低空気比運転時におけるガス化剤酸素濃度の影響(S54 高効率石炭火力発電技術)

Biomass-derived hydrogen from an air-blown gasifier

The goal of this research is to produce high concentrations of hydrogen from gasification of biomass. Air-blown gasification of biomass in fluidized bed reactors produces relatively low concentrations of hydrogen (about 8 vol.%). Steam reforming of tars and light hydrocarbons and reacting steam with carbon monoxide via the water–gas shift reaction can increase hydrogen content in the producer gas to almost 30 vol.%. In these experiments, the temperature, space velocity, and steam/gas ratio were varied to determine the effect of these variables on hydrogen production. Characterization of the catalysts by X-ray photoelectron spectroscopy (XPS) and BET analysis was also performed. These analyses showed that coke and small quantities of sulfur and chlorine deposited on the catalysts, although catalytic deactivation was not evident during the tests.

Release of fuel-nitrogen during the gasification of Shenmu coal in O 2

Formation of NH 3, HCN, NO and NO 2 from the gasification of a Chinese coal (Shenmu) in a fluidised-bed/fixed-bed reactor in 4.1% O 2 in argon was investigated. The presence of O 2 even at 673 or 773 K could lead to the gradual gasification of char to form HCN and NH 3. The yields of NH 3 and HCN showed maxima at about 773 K, amounting to 40% of coal-N. In the presence of O 2, the H radicals required for the formation of NH 3 and HCN may be generated from the reactions in the gas phase and within the solid particles. The yields of NO x increased from 773 to 973 K. A non-negligible proportion (∼5%) of coal-N was converted into NO 2 at 773 K through homogeneous and heterogeneous reactions. The yield of NO 2 diminished with increasing temperature. At 1173 K, the reactions between char-N and H 2O (or O/H-containing radicals) formed from the oxidation of char and volatiles led to the formation of NH 3 but not HCN. This route of NH 3 formation is believed to be an important pathway for the formation of NH 3 in an air-blown gasifier.

Stoichiometric, mass, energy and exergy balance analysis of countercurrent fixed-bed gasification of post-consumer residues

Abstract Air-blown gasification studies were conducted on a countercurrent fixed-bed gasifier for municipal residue-based Refuse Derived Fuel (RDF) pellets and compared with the mass and energy performance features of gasifier with other biomass and residual fuels. The mass conversion efficiency and cold gas efficiency (CGE) of the gasifier were observed to be 83% and 73%, respectively for RDF pellets. The higher heating value and global energy content of the producer gas generated from gasification of RDF pellets was observed to be 5.58 MJ Nm −3 and 12.2 MJ kg −1 , respectively. The tar content in the gas generated from RDF pellets was observed to be about 45% less than the tar content in the gas generated from wood chips (WC). Empirical stoichiometric equations were developed to describe the gasification of different fuels. A complete thermodynamic analysis was performed to determine the magnitudes of various inefficiencies and irreversibilities involved in the process. It was evaluated for RDF pellets that 27% of the exergy or available energy input was dissipated in the system due to various irreversibilities taking place in the gasification process. The second law CGE was observed to be highest for RDF pellets i.e. 56% followed by charred soybean straw pellets and WC. Thermal energy in the form of sensible heat energy accounted for 6–7% of the total energy; the available energy accounted for 2–3% of the total energy output of the process.

FIXED-BED GASIFICATION OF FEEDLOT MANURE AND POULTRY LITTER BIOMASS

The U.S. cattle industry is a $175 billion industry with an estimated 100 million cattle. About 10 million head ofthese cattle are in feedlots producing harvestable manure. At the same time, the U.S. poultry industry is the worlds largestproducer and exporter of poultry meat. Not surprisingly, one outcome is the production of a large quantity of manure byproducts,with approximately 60 million tons of dry harvestable animal manure produced annually from confined livestock andpoultry. This article describes a method of extracting energy from feedlot manure or poultry litter biomass either individuallyor combined with each other. High-ash (approximately 45% dry weight basis) feedlot biomass (HFB) and poultry litter biomass(HLB) were gasified in a 10 kW (thermal) fixed-bed, counter-current atmospheric pressure gasifier to generate a mixtureof combustible gases that could be further burned to generate heat. This article discusses the effect of the biomass particlesize on the composition of the product gas leaving the gasifier, the temperature profiles in the fixed bed, and the ash fusionof HFB and HLB during gasification. Air-blown gasification of the biomass fuels yielded a low-Btu gas with a higher heatingvalue of 4.4 0.4 MJ/m3 and an average product gas composition (dry basis) of H2: 5.8 1.7%, CO: 27.6 3.6%, CH4: 1.00.5%, CO2: 6.7 4.3%, and N2: 59.0 7.1%. The overall average equivalence ratio was 2.82 0.43 on a dry ash-freebasis. The experimental results also show that high-alkaline content fuels, such as HLB (Na2O + K2O = 16.7% of ash), canbe gasified by blending with lower-alkaline content fuels, such as HFB (6.0%), to reduce agglomeration in the fuel bedwithout significantly affecting the heating value of the product gas. The gasification of HLB and HFB yields a low-Btu gasthat can be combusted to generate heat for steam or power generation. The process has potential for reducing transportationcosts for traditional cropland-based manure application in some regions.

Thermochemical Generation of Hydrogen from Switchgrass

Thermochemical production of hydrogen is anticipated to be one of the most cost-effective means of producing hydrogen fuel. Switchgrass, a warm-season, perennial grass that is native to many areas of the United States, is an attractive feedstock for this purpose. The goal of this study is to convert switchgrass into hydrogen by the sequential processes of thermal gasification in a fluidized bed reactor, catalytic steam reforming of tars, and the use of water-gas shift catalysts to enhance the concentration of hydrogen. Air-blown gasification of switchgrass produced relatively low concentrations of hydrogen (about 8.5 vol-%). Steam reforming of tars and light hydrocarbons and reacting steam with carbon monoxide via the water-gas shift reaction increased the hydrogen content in the producer gas to 27.1 vol-%. The catalysts used in the steam reformer and water-gas shift reactors were examined at the end of the trials using X-ray photoelectron spectroscopy and BET analysis. These analyses showed changes in pore size and pore size distribution. Although not evident during the tests, eventual degradation of the catalysts can be expected as the result of deposition of coke, sulfur, and chlorine on the catalysts.

03/02382 High-temperature, air-blown gasification of dairy-farm wastes for energy production: Young, L. and Pian, C. C. P. Energy, 2003, 28, (7), 655–672

03/02382 High-temperature, air-blown gasification of dairy-farm wastes for energy production: Young, L. and Pian, C. C. P. Energy, 2003, 28, (7), 655–672

The formation of ammonia in air-blown gasification: does char-derived NO act as a precursor? ☆

Air-blown gasification of coal has received considerable attention worldwide and especially in the UK in conjunction with the Air-Blown Gasification Cycle, an integrated combined cycle which has been developed in recent decades. The cycle has the potential to produce electricity at higher efficiencies and lower emissions than conventional pf plants. However, the formation of ammonia in the gasifier has been identified as a potential problem, as it would contribute to NO x emissions. The formation of ammonia has been studied in a laboratory-scale rig designed and constructed specifically for that purpose. The reactor was a fluidised bed of the spouted bed variety. NH 3, NO and HCN levels could be monitored at different bed heights to trace their formation and conversion. Four coals were gasified at 1000 °C and 0.2 MPa. It was found that the bulk of the NH 3 was formed in the spout and the NH 3 concentration increased progressively with reactor height. Formation of NO was relatively minor and, although both NO and HCN may act as precursors for NH 3 formation in the devolatilisation/partial combustion zone, no evidence was found to suggest they make a significant contribution to any subsequent increase in NH 3 emissions.

High-temperature, air-blown gasification of dairy-farm wastes for energy production

A study was carried out to investigate the feasibility of integrating an advanced gasifier into the operation of a dairy farm for converting biomass wastes into fuel gas that can be used for power production. The disposal/utilization of excess animal wastes is a serious problem facing the dairy industry. Implementation of a gasification system on the dairy farm may provide an economical means of disposing of this waste. In our scheme, an advanced, high-temperature air-blown gasification system is used to convert the waste into synthetic fuel gas. A ceramic regenerative heater supplies the high-temperature air. Results of performance calculations indicated gasification conversion efficiencies of 65–85 % are possible, depending on the gasifier operating configuration. The syngas produced by the gasifier can be used on the farm for generating electricity and heat, or for other energy needs, thus helping to reduce the operating cost of the farm. In a case study, using information collected from an Upstate New York dairy farm, the results showed that gasification of dairy wastes would allow this particular farm to produce more than two times the amount of energy required for self-sufficiency.

Thermodynamics of gas-char reactions: first and second law analysis

In energy transformation processes such as combustion, gasification and reforming of fossil and renewable fuels, the conservation of energy (first law of thermodynamics) as well as the quality of energy (second law of thermodynamics) is important. This study focuses on the conversion of biomass with air and/or steam into gaseous components and char represented by solid carbon (graphite). Energy and exergy (available energy) losses are analysed by calculating the composition of a dry, ash-free typical biomass feed represented by CH 1.4O 0.59N 0.0017 in equilibrium with varying amounts of air and/or steam. The analysis is carried out for adiabatic systems at atmospheric pressure, with input of biomass and air at ambient conditions and steam at atmospheric pressure and temperature of 500 K . For air gasification, energy and exergy in the product gas have a sharp maximum at the point where all carbon is consumed, the carbon boundary point. This is the optimum point for operating an air-blown biomass gasifier. For gasification with steam, operation at the carbon boundary point is also optimal, but thermodynamic process losses hardly increase when adding more steam than required. The efficiency of steam and air-blown gasification was compared using the definition of rational efficiency. Although gasification by steam is more efficient (87.6% vs. 80.5%), this difference is expected to level off if exergy losses for the production of steam are taken into account. The choice between steam and air as a gasifying medium therefore seems to depend more on the required gas compositions. For steam gasification, the product gas contains mainly methane and carbon dioxide, while hydrogen, carbon monoxide, and (at least 38%) nitrogen are the main product gases for air gasification.