Two-stage Gasification Process Research Articles

Application of modified olivine to a two-stage gasification process to evaluate the effects on hydrogen generation and retention of heavy metals

An environmentally-friendly and efficient waste-to-energy and heavy metal retention system was successfully developed in this study. The natural resource-olivine was applied to be the bed material of second-stage gasifier, and the effects of second-stage gasifier temperature, and steam/biomass ratio on the hydrogen (H2) production ratio of syngas and heavy metal retention were discussed in detail. The optimal hydrogen production ratio (30.3%) was achieved when second-stage temperature, steam/biomass ratio (S/B ratio) were respectively controlled at 900 °C, and 0.25. The characterization analysis results evidenced that the Fe and Mg from pristine olivine and calcined olivine can facilitate the waste-to-hydrogen during the gasification reaction. Moreover, the NiO and Ni loaded on the surface of the calcine olivine could not only facilitate the water–gas shift reaction for H2 production, but also provide strong binding sites for the linkage of ether and cleavage of the C–O bond, leading to formation of CH4. The formed CH4 would be further dissociated over the metallic Ni/olivine, resulting in a significantly improved H2 production efficiency. In general, the order based on the H2 ratio of the syngas at the second-stage was calcined Ni-loaded olivine > calcined olivine > olivine; the heavy metal retention efficiency of three bed materials was in the order of Cu > Pb > Zn.

Two-stage gasification process simulation and optimization of pulverized coal for hydrogen-rich production using Aspen plus

This study proposed a two-stage gasification (TSG) process of pulverized coal to allow for hydrogen-rich (HR) production. The balance flow of this process is constructed using Aspen Plus software. Gasification pressure (GP), steam-coal ratio (SCR), and oxygen-coal ratio (OCR) influences on the process are studied, and the operating conditions are optimized to achieve the maximum hydrogen production. The results show that the GP mainly affects the pyrolysis of pulverized coal in the low-temperature section. Reducing the GP is conducive to hydrogen production. However, it requires heat supplement to raise temperature and maintain the balance of the system. An increase in the SCR is better for hydrogen production, leading to a decrease in the gasification temperature. When the SCR is higher than 0.3, the steam utilization rate decreases obviously. With an increase in the OCR, the gasification temperature continues to increase, and hydrogen production first increases and then decreases, reaching its peak at approximately 0.5. The optimal parameter combination is as follows: the SCR is 0.3; the OCR is 0.53; water is used as the medium for temperature regulation uses, and the water supply is 0.12 kg/kg coal; oxygen is used to raise the temperature of the low-temperature section, and the oxygen supply is 0.18 kg/kg coal. The hydrogen production rate of the optimal working condition is 77.78 g/kg coal, which is 48.38% higher than that of single-stage gasification.

Characteristics of Air Gasification of 10 Different Types of Plastic in a Two-Stage Gasification Process

In this study, air gasification of 10 different types of plastic was conducted using a two-stage gasifier consisting of a fluidized bed gasifier and a tar-cracking reactor filled with activated carbon as a tar removal additive. The study aimed to show characteristics of the producer gases obtained from the two-stage gasification of individual plastics. Ten individual plastics were grouped into four according to their chemical compositional characteristics. In the experiment, product gases having tar contents in the range from 132 mg/Nm3 (ABS) to 0 mg/Nm3 (polyethylene and polyamide) were obtained. In the gasification of plastics having aromatic rings, the productions of char and tar in gas were higher than those of aliphatic plastics. The gasification of aliphatic plastics without heteroatoms, such as polyethylene and polypropylene, favored H2 production and had a maximum value of 26 vol %. Activated carbon played a significant role in lowering the tar content in gas and enhancing H2 production. Plastics having oxygen in their structures (PMMA, PA, PET, PU, and PC) enhanced the CO production. However, gasification of plastics having aromatic rings (PC, PET, and ABS) with sand as the bed material caused bed agglomeration and a severe coke buildup on an activated carbon bed. Dolomite as the fluidized bed material was found to be very effective in solving these operational problems.

Sewage sludge and phytomass co-pyrolysis and the gasification of its chars: A kinetics and reaction mechanism study

This paper presents the kinetics and mechanisms of pyrolysis and gasification processes of sewage sludge and phytomass blends as well as their application in gas conversion. Sewage sludge is a type of combustible waste substance that constitutes a renewable energy source. Mixing sewage sludge with another type of waste biomass can have a beneficial effect on the quality of the fuel produced and may improve the conversion efficiency. Pyrolysis and gasification processes are considered sustainable methods for the production of combustible gas. The two-stage gasification process combining co-pyrolysis and the gasification of “hot” char were studied using a thermogravimetric analyser and a fixed-bed reactor coupled with gas chromatography. The pyrolysis of sewage sludge and Salix viminalis as well as their mixture was performed below the temperature of 900 °C at low heating rates under a nitrogen atmosphere and in non-isothermal conditions. The char gasification experiments were carried out at temperatures of 700, 800 and 900 °C in an atmosphere of air. The effect of the percentage share of Salix viminalis in the tested blends on the pyrolysis process and on the reactivity of “hot” char in the gasification process were investigated. For the tested blends, the kinetic parameters of co-pyrolysis and gasification were determined.

Effects of second-stage bed materials on hydrogen production in the syngas of a two-stage gasification process

This study investigated the effects of various bed materials (silica, biomass-based activated carbon, coal-based activated carbon, and zeolite) used in the second-stage reactor and different gasification conditions on the H2 fraction in the syngas. The equivalence ratio was fixed at 0.3, and the temperature in the first-stage reactor was held constant at 500 °C. Three temperatures were tested in the second-stage reactor, and the steam/biomass ratio was also tested.As shown in the experimental results, the combination of operating temperatures that gives the optimum percentage of H2 in the syngas is 500 °C/900 °C. The highest proportion of H2 formed at S/B = 0.6. As steam passes into the first-stage reactor, the operating temperature and, subsequently, the gasification efficiency can be lowered. The higher operating temperature of the second-stage reactor nevertheless reintroduced steam into the gasification reaction as it entered, raising the H2 content significantly. In addition, for the different bed materials used in the second stage, B-AC yielded the highest proportion of H2 in the syngas exiting the gasifier. The H2 fraction reached 50.96 mol% when S/B = 0.6 and the operation was carried out at 500 °C/900 °C. Among the four different bed materials, silica yielded the lowest H2 proportion of 36.66 mol%.

Property of drying, pyrolysis, gasification, and combustion tested by a micro fluidized bed reaction analyzer for adapting to the biomass two-stage gasification process

In the present research, a concept of fluidized bed two-stage gasification has been proposed to gasify the wet industrial biomass, which decouples the direct gasification of biomass into the main sub-processes of drying, pyrolysis, gasification, and combustion. To better understand the reaction behavior and kinetics of these main sub-processes, a micro fluidized bed reaction analyzer was adopted. Moreover, a kind of water-adsorbing char was chosen to simulate the drying behavior of wet biomass. In the examined temperature range of 1123–1223 K, the processes of pyrolysis and combustion were conducted in the second scale, while that of gasification and drying was in the minute level, dominating the whole gasification process. For the reaction rate, at above 1173 K, they followed the order of pyrolysis > combustion > gasification > drying. The volume reaction model and shrinking core reaction model can be used to describe the process of pyrolysis/gasification and drying/combustion, respectively. For pyrolysis, combustion, drying, and gasification, the calculated activation energies were about 29.51, 62.39, 83.75, 210.23 kJ/mol, respectively. Finally, a schematic diagram of the FBTS gasification process was proposed for treating the wet Chinese distilled grains according to the reaction behavior and kinetics.

Lab-scale and pilot-scale two-stage gasification of biomass using active carbon for production of hydrogen-rich and low-tar producer gas

Laboratory- and pilot-scale two-stage air gasification of various types of biomass was performed to produce hydrogen-rich and low-tar gas. Typical tar removal apparatuses, such as scrubbers and electrostatic precipitators, were not employed and the only tar removal agent used was coal-based active carbon. The hydrogen content of all producer gases was remarkably high, whereas the tar content was low (maximum H2: 29 vol%; minimum tar: 0 mg/Nm3). The producer gases from the pilot-scale experiment also exhibited an exceedingly high hydrogen content and low tar content (maximum H2: 27 vol%; minimum tar: 3.3 mg/Nm3). The pilot-scale operation continued without any external heat supply via autothermal operation. A gas engine was connected to the pilot-scale gasification plant to generate electricity. The generated power ranged from 20 to 35 kWe depending on the type of biomass used. This indicated that the two-stage gasification process could be applied to decentralized power generation. To summarize, the present study provided positive experimental results of the two-stage gasification process in terms of tar reduction, hydrogen production, and power generation. Furthermore, studies on long-term operation are needed to obtain more reliable results.

Assessment of char property on tar catalytic reforming in a fluidized bed reactor for adopting a two-stage gasification process

To well understand the effect of char property on tar catalytic reforming and support the development of two-stage gasification technology for the clean fuel gas production, the roles of pore structure and metal oxide in tar removal behavior were examined and compared on a fluidized bed two-stage reactor. The results show that although both of micro pore and meso pore had a remarkable influence on tar removal efficiency, fuel gas component and distilling fractions in tar, perhaps micro pore played a much more important role. Moreover, the tar removal efficiency did not have a good proportional relationship with the specific surface area of char. For the spent char, the activation treatment in steam was very beneficial to renew the catalytic reforming on tar by increasing the surface area of micro pore and maintain its high gasification activity. Compared to the demineralized char, the char samples that loaded metal oxide by impregnation approach largely promoted the tar removal efficiency, following the rank of Na2O > Fe2O3 > CaO > MgO. For Na2O, it not only had the best catalytic activity on tar, but also greatly promoted the generations of light tar and effective fuel gas, such as H2 and CO. Finally, considering the different effect of pore structure and metal oxide on tar catalytic reforming, a brief mechanism of tar catalytic reforming by char was proposed.

Characteristics comparison of tar from lignite pyrolysis with inherent and simulated moisture for adopting a two-stage gasification process

To utilize low rank coal cleanly and high efficiently, a new fluidized bed two-stage gasification (FBTSG) process, mainly consisting of a FB pyrolyzer and a transport bed gasifier, has been proposed to treat pressurized coal (below 10 mm) with relatively high moisture for the production of clean fuel gas. In this study, a laboratory FB pyrolysis apparatus was adopted to examine the influence of moisture mode on pyrolysis behavior from 600 °C to 900 °C, especially in the yield and property of pyrolysis tar. Two common experimental methods in literatures, namely wet coal with inherent moisture and dried coal with the simulated moisture by introducing steam, were systematically analyzed. Compared to the simulated moisture, inherent moisture in coal can facilitate effectively the generation of tar at 700 °C and 800 °C, and had strong reforming effect on tar conversion to light fraction, leading to more production of light fractions and micro-molecule compounds. All of these differences were much related to the difference in interaction pathway between volatile matter and moisture.

Influences of temperature arrangement on hydrogen production during two-stage gasification process

The effects of temperatures of the first and second stages, equivalence ratio (ER), and steam/biomass (S/B) ratio on the formation of syngas during two-stage gasification were investigated. Experiments conducted with the first and second stages performed at different temperatures showed that the total H2 production rate was optimal when the first and second stages were both operated at 900 °C. The amount of H2 produced increased from 28.8 mol.% in the first stage to 37.4 mol.% in the second stage. When the temperatures of the first and second stages were 500 and 900 °C, respectively, the total H2 production rate increased from 23.9 mol.% in the first stage to 36.8 mol.% in the second stage. Hence, even if the first stage is operated at a lower temperature, leading to lower H2 production rates, operating the second stage at a higher temperature will always help to improve the H2 production rate.

Characteristics of tar abatement by thermal cracking and char catalytic reforming in a fluidized bed two-stage reactor

With respect to the newly proposed fluidized bed two-stage (FBTS) gasification process, the researches on tar thermal cracking and catalytic removal by char bed layer were conducted on a FB two-stage reaction apparatus. It shows that the effect of char on tar removal was much related to the reaction temperature and residence time of tar-containing fuel gas in the tar reformer. Under the tested experimental conditions, increasing reaction temperature and residence time can effectively promote tar abatement and generate more H2, CO and CH4. For catalytic reforming by char, the higher reaction temperature and the longer residence time, the lower tar content in fuel gas. Compared to thermal cracking, catalytic reforming of tar by char was more effective in tar removal efficiency and inhibition of carbon deposition, upgrading the quality of fuel gas. The researches indicated that the suitable operational conditions for tar removal by char in the FB two-stage gasification process were at reforming temperature of 1000 °C, and residence time above 0.9 s.

Characterization and pilot scale test of a fluidized bed two-stage gasification process for the production of clean industrial fuel gas from low-rank coal

To utilize low rank coal efficiently, a fluidized bed two-stage (FBTS) gasification process, mainly consisting of a FB pyrolyzer and a transport FB (TFB) gasifier, has been proposed for the production of clean fuel gas. To verify the feasibility and technical features of this novel gasification technology, a pilot autothermal platform, with a treating capacity of 100 kg/h for coal, was designed and built up. By adopting a kind of lignite from Inner Mongolia, the running state and fuel gas quality were compared systematically under typical operational conditions. The results show that by keeping the reaction temperatures of pyrolyzer and gasifier at around 840 °C and 1000 °C, respectively, the corresponding tar content in fuel gas at the outlets of pyrolyzer and gasifier were 1127 mg/Nm3 and 365 mg/Nm3, reaching a high tar removal efficiency. Under the stable operation state, the volume fractions of CO, H2, CH4 and CO2 in fuel gas were 14.4%, 8.3%, 3.4% and 11.3%, respectively, and the corresponding higher heating value of fuel gas was about 1100 kcal/Nm3. Compared with the tar from pyrolyzer, the heavy oil fraction in tar from gasifier reduced significantly, while the light oil components increased sharply simultaneously, showing significant effect of catalytic reforming by hot char bed on tar removal.

Study of the two-stage gasification process of pulverized coal with a combined countercurrent and concurrent flow system

The paper presents a numerical study of an advanced two-stage gasifier with a combined countercurrent and concurrent flow pattern and dry fuel feed system EAGLE. The Reynolds Stress model was used for the numerical simulation of turbulent flow. We have conducted studies on the influence of upper burner’s inclination angle on heat and mass transfer processes in the gasifier as well as on coal conversion. It is shown that the increase in the upper burner’s inclination angle in the horizontal plane allows intensifying the process of two-stage gasification.

Study of the two-stage gasification process of pulverized coal at the hydrodynamic flow separation

The paper presents a numerical study of advanced two-stage gasifier with a combined countercurrent and concurrent flow pattern and dry fuel feed system EAGLE. The Kuznetsk coal was used as a fuel for the gasifier under study. We have conducted studies on the influence of the inclination angle of the upper burners in horizontal and vertical planes, and the amount of steam supplied, on heat and mass transfer processes in the chamber as well as on the composition of coal-derived gases. It is shown that the increase in the inclination angle of the upper burners in the horizontal plane allows intensifying the process of two-stage gasification and makes it possible decreasing the height of the chamber without sacrifice of the composition of the coal-derived gases.

Fluidized Bed Two-Stage Gasification Process for Clean Fuel Gas Production from Herb Residue: Fundamentals and Demonstration

A new two-stage gasification process, decoupling complex biomass gasification from biomass pyrolysis and char gasification, has been proposed for the production of clean industrial fuel gas. In this work, Chinese herb residues will be used as raw material, and the fundamental studies and demonstration of this process were conducted on an externally heated laboratory two-stage gasification setup and an industrial demonstration plant, respectively. The fundamental studies found that the appropriate operation of the upstream fluidized bed (FB) pyrolyzer occurred at 700 °C and the suitable conditions for effective tar removal in the downstream gasifier were as follows: 850 °C, an equivalent ratio of air (ER) at 0.04, and a retention time of tar-containing fuel gas above 0.9 s. On the basis of these fundamental data, an autothermal demonstration plant treating 600 kg of herb residue per hour was built and successfully commissioned for its continuous running to verify the technology feasibility. The running dat...

Industrial demonstration plant for the gasification of herb residue by fluidized bed two-stage process

A fluidized bed two-stage gasification process, consisting of a fluidized-bed (FB) pyrolyzer and a transport fluidized bed (TFB) gasifier, has been proposed to gasify biomass for fuel gas production with low tar content. On the basis of our previous fundamental study, an autothermal two-stage gasifier has been designed and built for gasify a kind of Chinese herb residue with a treating capacity of 600kg/h. The testing data in the operational stable stage of the industrial demonstration plant showed that when keeping the reaction temperatures of pyrolyzer and gasifier respectively at about 700°C and 850°C, the heating value of fuel gas can reach 1200kcal/Nm3, and the tar content in the produced fuel gas was about 0.4g/Nm3. The results from this pilot industrial demonstration plant fully verified the feasibility and technical features of the proposed FB two-stage gasification process.

Waste-gasification efficiency of a two-stage fluidized-bed gasification system

This study employed a two-stage fluidized-bed gasifier as a gasification reactor and two additives (CaO and activated carbon) as the Stage-II bed material to investigate the effects of the operating temperature (700°C, 800°C, and 900°C) on the syngas composition, total gas yield, and gas-heating value during simulated waste gasification. The results showed that when the operating temperature increased from 700 to 900°C, the molar percentage of H2 in the syngas produced by the two-stage gasification process increased from 19.4 to 29.7mol% and that the total gas yield and gas-heating value also increased. When CaO was used as the additive, the molar percentage of CO2 in the syngas decreased, and the molar percentage of H2 increased. When activated carbon was used, the molar percentage of CH4 in the syngas increased, and the total gas yield and gas-heating value increased. Overall, CaO had better effects on the production of H2, whereas activated carbon clearly enhanced the total gas yield and gas-heating value.

Integrated gasification and plasma cleaning for waste treatment: A life cycle perspective

In the past, almost all residual municipal waste in the UK was landfilled without treatment. Recent European waste management directives have promoted the uptake of more sustainable treatment technologies, especially for biodegradable waste. Local authorities have started considering other options for dealing with residual waste. In this study, a life cycle assessment of a future 20MWe plant using an advanced two-stage gasification and plasma technology is undertaken. This plant can thermally treat waste feedstocks with different composition and heating value to produce electricity, steam and a vitrified product. The objective of the study is to analyse the environmental impacts of the process when fed with seven different feedstocks (including municipal solid waste, solid refuse fuel, reuse-derived fuel, wood biomass and commercial & industrial waste) and identify the process steps which contribute more to the environmental burden. A scenario analysis on key processes, such as oxygen production technology, metal recovery and the appropriate choice for the secondary market aggregate material, is performed. The influence of accounting for the biogenic carbon content in the waste from the calculations of the global warming potential is also shown. Results show that the treatment of the refuse-derived fuel has the lowest impact in terms of both global warming potential and acidification potential because of its high heating value. For all the other impact categories analysed, the two-stage gasification and plasma process shows a negative impact for all the waste streams considered, mainly due to the avoided burdens associated with the production of electricity from the plant. The plasma convertor, key characteristic of the thermal process investigated, although utilising electricity shows a relatively small contribution to the overall environmental impact of the plant. The results do not significantly vary in the scenario analysis. Accounting for biogenic carbon enhanced the performance of biomass and refuse-derived fuel in terms of global warming potential. The main analysis of this study has been performed from a waste management perspective, using 1ton of waste as functional unit. A comparison of the results when 1kWhe of electricity produced is used as functional unit shows similar trends for the environmental impact categories considered.

Life cycle assessment of conventional and two-stage advanced energy-from-waste technologies for municipal solid waste treatment

The EU landfill and Waste Framework directives are driving new approaches to waste management in the UK, away from landfilling and mass-burn incineration, which has been regarded as the main alternative to landfilling. The objective of this study is to compare the environmental impacts of three dual-stage advanced energy-from-waste technologies, i.e. gasification and plasma gas cleaning, fast pyrolysis and combustion and gasification with syngas combustion, with those associated with conventional treatments for municipal solid waste, i.e. landfill with electricity production and incineration with electricity production. Results show that the two-stage gasification and plasma process has a significantly better overall environmental performance than the conventional waste treatment technologies and somewhat better than a more modern incineration plant, exemplified by a plant under commissioning in Lincolnshire in the UK. The benefits of the gasification and plasma process arise primarily from its higher net electrical efficiency.

Study on Gasification Characteristics of Petroleum Asphalt in a Two-Stage Gasifier

The gasification performance of petroleum asphalt in a two-stage gasifier was investigated through experiments and simulations. The analysis results of asphalt samples show that the asphalt has characteristics of high volatile content, high calorific value, and low ash content. Coal pyrolysis model, gas-solid heterogeneous reaction model, gas homogeneous reaction model and Gibbs free energy minimization method were employed to build the two-stage entrained flow gasification model and simulate the asphalt gasification process using Aspen Plus software. The results indicate that the cold gas efficiency of asphalt is 3% higher than that of bituminous coal, while the consumption of coal and oxygen is 40% lower than that of bituminous coal. The gasification performance of asphalt is superior to that of coal. In addition, the cold gas efficiency of asphalt can be increased by about 3% when the two-stage gasification process is employed. The utilization rate of coal in the two-stage gasifier is much higher than that in traditional one-stage gasifier.