Oxygen-steam Gasification Research Articles

Методичний підхід до обґрунтування способу газифікації кам’яного вугілля для виробництва синтетичних моторних палив

The aim of the article is to substantiate the most suitable method of gasification of Ukrainian hard coal for further production of synthetic motor fuel. For this substantiation, a methodical approach has been developed, the use of which has allowed to obtain the following results. As a raw material base, the article recommends long-flame coal of the Western Donbass, located on the territory of the Dnepropetrovsk region, where powerful enterprises for the extraction and enrichment of coal operate. The most common methods of coal gasification in the world are analyzed: Lurgi (counter-current steam-oxygen gasification of large-lump coal (or briquettes) in a stationary bed), Siemens (direct-flow steam-oxygen gasification in the pulverized coal stream), Texaco (direct-flow oxygen gasification in the flow of coal-water pulp). For each of these methods, material balances have been developed; the composition and quality of the generated gas, the possibilities of organizing the production of the necessary energy resources, the level of emissions of harmful substances into the atmosphere and wastewater discharge have been evaluated. A methodology for calculating the composition of generator gas is proposed, which takes into account the composition of the blast (content of oxygen, water vapor or water). All calculations were performed for an enterprise with a coal capacity of 550 thousand tons of working weight per year. Based on the calculations and comparison of their results, the Texaco method is recommended for industrial implementation. The advantages of this method are as follows: the absence of a stage of steam production for gasification, the scarcity of the water cycle, which practically excludes the formation of wastewater, and the possibility of using contaminated water from other sources for gasification; the highest total content of hydrogen and carbon monoxide in the resulting synthesis gas; the maximum assimilated capacity of production reactors and the largest number of capacities created in the world using this technology; utilization of the heat of the resulting gas to obtain a large amount of electric and thermal energy.

Техніко-економічна оцінка різних способів газифікації бурого вугілля для виробництва синтетичного моторного палива

The aim of the article is to assess the feasibility of organizing the production of synthesis gas from brown coal, the reserves of which in Ukraine are sufficient. As a raw material base, the article considers the coal of the Novo-Dmytrivske deposit, which is located on the territory of the Kharkiv region. The balance reserves of brown coal in categories A + B amount to 284.4 million tons and in category C1 – to 95.6 million tons, that is, a total of 380 million tons. The average technical analysis data for the deposit are as follows: moisture per working weight is 51.2%; ash content per dry weight is 19.4%; the total sulfur content is 2.45%. The elemental composition of the coal of this deposit is characterized by the following data: carbon – 68.0%, hydrogen – 6.0%, oxygen – 23.0%, sulfur, nitrogen and other elements – 3.0%. To achieve the goal, the properties of coal of this deposit have been examined and the following technologies of coal gasification have been analyzed: Lurgi process (counter-current steam-oxygen gasification of coarse coal (or briquettes) in a stationary bed); Prenflo process (direct-flow steam-oxygen gasification in a pulverized coal stream); Texaco process (direct-flow oxygen gasification in a coal-water pulp stream). For each of these processes, material balances have been developed; the quality of gas synthesis, the possibility of organizing the production of the necessary energy resources, the level of emissions of harmful substances into the atmosphere, and the main technical and economic indicators have been evaluated. The calculations were made for an enterprise with a coal capacity of 9 million tons of actual weight per year. Based on the calculations made, the Lurgi process is recommended for industrial implementation. The advantages of this process are: the lowest temperature and pressure of the gasification process; a wider range of products obtained during gasification; almost optimal syngas composition in terms of H2 : CO ratio; the lowest emissions of carbon dioxide generated during coal gasification and preparation of synthesis gas for further use; the lowest production cost of prepared synthesis gas; the lowest specific capital investments (per 1 thousand m3 of prepared synthesis gas). The inexpediency of using the Texaco process for the gasification of brown coal is substantiated, as well as the directions for improving the Prenflo process for its further use in the gasification of brown coal of the Novo-Dmytrivske deposit are determined.

Effects of inherent AAEMs on catalytic gasification of biomass with large particle size under oxygen-steam atmosphere

Oxygen-steam gasification of biomass is a promising technology because of its ability to improve syngas quality and reduce energy consumption. In this study, a fixed-bed reactor is employed to assess the effects of inherent alkali and alkaline earth metals (AAEMs) on the catalytic gasification of candlenut wood with large particle size under the oxygen-steam atmosphere. Two grain directions, radial and axial, are considered for candlenut wood. Various characterization techniques, SEM, X-ray CT, BET, and FTIR, are employed to analyze biochar samples. GC-MS and GC are determined to tar and syngas respectively. The results show that char yield from biomass with axial grain is higher. Acid-washing removes alkali metals (K and Na) better from biomass with axial grain than radial grain, and vice versa for alkaline earth metals (Ca and Mg). In terms of the gasified chars derived from acid-washed biomass, AAEMs content gradually decreases along the end surface and radial direction, which could also be observed from the 3D reconstruction of X-ray CT images. In all samples, micropores (0–10 µm) dominate and are distributed along the grain direction. In general, pores of 20–30 µm and above 30 µm comprise a minor proportion. Inherent AAEMs facilitate an augmentation in char yield as well as BET and total pore volume of gasified char. AAEMs and grain direction have a slight effect on functional groups of gasified chars. Certain organic matter species and content in tar are remarkably affected by the grain direction, since the discrepancies of pore structure and specific surface area. Acid-washing pretreatment augments the content and organic species of M2-M4 compounds (containing 2–4 benzene rings) in the tar. K and Na significantly boost the char steam gasification, water-gas shift, and steam-tars reforming reactions. A decrement in concentrations of H2 (14.49% and 13.35%), CH4 (0.51% and 0.89%), and CO2 (2.32% and 1.37%) in syngas derived from acid-washed samples are acquired, respectively, compared to that of biomass samples with radial and axial grains. However, a reduction of 4.09% and 1.53% in syngas calorific value could be obtained. The CnHx volume fraction is significantly affected by grain direction and AAEMs, with axial grain yielding a higher volume fraction of C2H4 (49.07%), C2H2 (71.29%), and C3H8 (127.36%) from acid-washed sample than that of radial grain.

Pilot-scale study of sorption-enhanced gasification of sewage sludge

Sustainable management and disposal alternatives for sewage sludge (SS) should be pursued due to the substantial increment in its global production, as well as due to the raising interest in the renewable energy and synthetic fuels deployment. Since SS present high moisture (>95 % wt.), drying would play an essential role in SS management. In this work, SS pre-treated in a solar-drying facility has been successfully used as feedstock in a 30 kWth bubbling fluidised-bed (BFB) gasification pilot plant operating under Sorption Enhanced Gasification (SEG) conditions, i.e. using CaO as bed material and steam as gasifying agent. The influence of key operating SEG parameters (such as temperature, steam-to-carbon ratio and sorbent-to biomass proportion) in the syngas yield and composition (H2, CO, CO2, CH4, CxHy, H2S, COS, NH3 and tars) has been carefully assessed. As a matter of comparison, steam-oxygen gasification conditions have been also tested in the facility using solar-dried SS as feedstock. The results obtained demonstrate the possibility of producing a syngas with high H2 contents of 70–73 vol% and relatively low CO and CO2 contents (i.e. 2–3 vol% and 8 vol% respectively).

Modelling and simulation of fluidized bed steam-oxygen gasification of sewage sludge using thermochemical equilibrium and experimental data

This paper presents a gasifier model to describe steam-oxygen gasification of sewage sludge, as well as simulations to assess the process performance. The gasifier model was set up in the Aspen Plus® software and uses a combined equilibrium and empirical approach. A comparison of the model’s predictions with experimental data showed sufficient accuracy to describe the process The oxygen demand (oxygen ratio) of the gasifier and the cold gas efficiency were found to be highly dependent on various operation parameters, thus a comprehensive sensitivity study was presented. To obtain the relevant gasifier temperature of 850 °C using dried sewage sludge, an oxygen ratio of 0.33 and a cold gas efficiency of 0.65 was calculated. Syngas stoichiometry described by the H2/CO-ratio was found to be adjustable by altering the steam to carbon ratio nSC, which enables to tailor the syngas composition to suit the desired downstream application. The simulations predicted that the water-free syngas has a N2 concentration of 0.04 m3m−3 that originated from fuel-bound nitrogen, which needs to be considered for downstream syngas application. A limestone addition of 0.03 kg limestone per kg fuel was calculated to be the optimum in terms of high cold gas efficiency as well as tar and sulfur reduction. Overall, steam-oxygen gasification was characterized as a promising conversion process.

Negative emission power plants: Techno-economic analysis of a biomass-based integrated gasification solid oxide fuel cell/gas turbine system for power, heat, and biochar co-production—part 2

In our previous work (Part I), we evaluated the thermodynamic models of the biomass-fed integrated gasification solid oxide fuel cell system with a carbon capture and storage (BIGFC/CCS) unit. In this work (Part II), the techno-economic analysis of the proposed negative emission power plants is carried out. Levelized cost of electricity, net present value (NPV), payback period, internal rate of return (IRR), and levelized cost of negative carbon (LCNC) are the key economic parameters evaluated. The results of a series of sensitivity analysis show the impact of gasification agents and stepwise increase in biochar co-production on the performance of the system. The total overnight cost is estimated to be 6197 $/kW and 5567 $/kW for the air and steam-oxygen gasification BIGFC/CCS systems, respectively. Steam-oxygen gasification is found to be more economically beneficial than air gasification one for all of the cases studied. Economically viable biochar co-production cases are identified to ascertain the influence of capital cost, operating cost, biomass cost, plant capacity factor, and tax. Moreover, the effect of the carbon credit scenario on the economic indicators is also reported. The results show that the most effective economic performance from the steam-oxygen gasification case reported an NPV of 3542 M$, an IRR of 24.2%, and a payback period of 3.3 years, with an LCNC of -322.5$/t of CO2. Compiling the results from Part I and Part II shows that it is easier to achieve negative emission using the steam-oxygen gasification of a BIGFC/CCS system. These results are expected to be helpful for stakeholders in identifying appealing negative emissions power plant projects for near and long-term future investments.

A two-stage circulated fluidized bed process to minimize tar generation of biomass gasification for fuel gas production

This study tested a two-stage circulated fluidized bed process consisting of a downer for pyrolysis of biomass and a riser for char gasification and tar removal to produce fuel gas containing tar below 100 mg/Nm3 from pine chips using steam-oxygen (not N2-oxygen) as the agent. A pilot facility treating 15 kg/h biomass was run at different equivalent ratios (ERs) and steam-to-biomass ratios (S/Bs). Under the typical conditions of S/B = 0.15 and ER = 0.3, the produced fuel gas contained (in volume) 21.64% CO, 21.97% CO2, 15.34% H2, 18.59% CH4, 1.49% CnHm and 1.83 g/Nm3db tar. A long-tern running of the pilot pant realized a tar content low as 95.5 mg/Nm3db in the produced gas. These results thus well verified the technology feasibility for low-tar biomass fuel production via the two-stage circulated fluidized bed steam-oxygen gasification.

Negative Emission Power Plants: Thermodynamic Modeling and Evaluation of a Biomass-Based Integrated Gasification Solid Oxide Fuel Cell/Gas Turbine System for Power, Heat, and Biochar Co-Production—Part 1

This article is the first of a two-part series presenting the thermodynamic evaluation and techno-economics of developing negative-emission power plants. The aim of this research is to evaluate the potential of biochar co-production in negative-emission power plants based on biomass-fed integrated gasification solid oxide fuel cell systems with carbon capture and storage (BIGFC/CCS) units. The influence of two gasification agents, namely, air and steam-oxygen, on the proposed system is investigated. In Part I, we present the thermodynamic models. A sensitivity analysis is carried out to investigate the system response to stepwise increase in biochar co-production (up to 10% by weight). Providing a secondary oxy-combustor in the steam-oxygen gasification case has been shown to be a solution to meet the heat requirements of the allothermal gasification process. A comprehensive exergy analysis indicated significant efficiency improvement for the steam-oxygen gasification case. The results show that the biomass steam-oxygen gasification yields the higher electrical exergy efficiency (48.3%) and combined heat and power (CHP) exergy efficiency (54.6%) for the similar rates of biochar co-production. The specific power output per unit of CO2 stored is 2.65 MW/(kg/s) and 3.58 MW/(kg/s) for the air and steam-oxygen gasification cases, respectively, when the biochar is co-produced at 10% by weight for the given biomass flow of 20 kg/s. Moreover, the total CO2 stored due to the proposed system is calculated as 133.9 t/h, and it is estimated to remove 1.17 Mt of CO2 from the atmosphere annually (when the biochar-based carbon storage is also considered). The models are used for the techno-economic analysis presented in Part II of the series.

Experimental simulate on hydrogen production of different coals in underground coal gasification

Research on hydrogen production from coal gasification is mainly focused on the formation of CO and H2 from coal and water vapor in high-temperature environments. However, in the process of underground coal gasification, the water gas shift reaction of low-temperature steam will absorb a lot of heat, which makes it difficult to maintain the combustion of coal seams in the process of underground coal gasification. In order to obtain high-quality hydrogen, a pure oxygen-steam gasification process is used to improve the gasification efficiency. And as the gasification surface continues to recede, the drying, pyrolysis, gasification and combustion reactions of underground coal seams gradually occur. Direct coal gasification can't truly reflect the process of underground coal gasification. In order to simulate the hydrogen production laws of different coal types in the underground gasification process realistically, a two-step gasification process (pyrolysis of coal followed by gasification of the char) was proposed to process coal to produce hydrogen-rich gas. First, the effects of temperature and coal rank on product distribution were studied in the pyrolysis process. Then, the coal char at the final pyrolysis temperature of 900 °C was gasified with pure oxygen-steam. The results showed that, the hydrogen production of the three coal chars increased with the increase of temperature during the pyrolysis process, the hydrogen release from Inner Mongolia lignite and Xinjiang long flame coal have the same trend, and the bimodality is obvious. The hydrogen release in the first stage mainly comes from the dehydrogenation of the fat side chain, and the hydrogen release in the second stage mainly comes from the polycondensation reaction in the later stage of pyrolysis, and the pyrolysis process of coal contributes 15.81%–43.33% of hydrogen, as the coal rank increases, the hydrogen production rate gradually decreases. In the gasification process, the release of hydrogen mainly comes from the water gas shift reaction, the hydrogen output is mainly affected by the quality and carbon content of coal char. With the increase of coal rank, the hydrogen output gradually increases, mainly due to the increasing of coal coke yield and carbon content, The gasification process of coal char contributes 56.67–84.19% of hydrogen, in contrast, coal char gasification provides more hydrogen. The total effective gas output of the three coal chars is 0.53–0.81 m3/kg, the hydrogen output is 0.3–0.43 m3/kg, and the percentage of hydrogen is 53.08–56.60%. This study shows that two-step gasification under the condition of pure oxygen-steam gasification agent is an efficient energy process for hydrogen production from underground coal gasification.

Технічні й економічні аспекти створення підгалузі з виробництва синтетичного рідкого палива в Україні

The article proves that today Ukraine finds itself in a situation where it depends solely on imported supplies of light oil products to meet its motor fuel needs, which is unacceptable from the point of view of the country’s energy and national security, and the solution to this problem lies in the plane of organization of motor fuel production from the country’s own natural resources. The purpose of the study is to substantiate the technical and economic foundations for creating a synthetic motor fuel subsector in Ukraine. To achieve this aim, the authors define the classification of alternative motor fuels; provide a comparative description of the energy content and scope of use of different types of motor fuels, and also provides comparative characteristics of synthetic along with the best grades of natural oil; assess the compliance of synthetic gasoline and diesel fuel with the Euro-4 standard; considers the technical-operational advantages of synthetic analogues of oil fuel over other alternatives. Based on the carried out analysis, the article proves that, given the limited resource capabilities of Ukraine’s motor fuel production from oil and natural gas, the production of synthetic liquid motor fuel (SLMF) from coal raw materials should be recommended for development in the country; the raw material base for the production of synthetic liquid fuel is researched. The article also analyzes the peculiarities of methods and specific technologies for producing synthetic liquid motor fuel from coal and determines that the technology of synthesizing synthetic liquid motor fuel using the Fischer-Tropsch method with preliminary production of synthesis gas by steam-oxygen gasification of coal is advisable for development in Ukraine. Taking this into account, the resource and product balance of the full cycle of synthetic liquid fuel production is formed, a general production scheme of the industry subsector of SLF in Ukraine is developed, technical-economic characteristics of the national and regional industrial complexes for the production of SLF are presented, and the structure of the subsector for the production of SLF in the country is proposed.

Production of H2-Rich Syngas from Oxygen-Steam Gasification of Biomass Using Modified Red Mud Extract as Catalyst

Oxygen-steam gasification of biomass catalyzed by modified iron-rich red mud extract is firstly performed in our work. During the impregnation of the modified red mud extract (MRME), the pore structure characteristics and thermal behavior of the maize straw changed significantly. The influence of MRME on syngas quality, gas yield, and thermal efficiency were performed in a lab-scale gasification reactor. The results showed that higher temperature, sufficient MRME addition, appropriate equivalent ratio (ER) and a small amount of steam all promoted syngas quality and energy conversion. For maximum economic efficiency, the optimal rate of MRME addition is 30% weight ratio to maize straw. The optimal level of ER was found to be 0.23, and the maximum energy conversion ratio was 82.4% at 800 °C with optimal levels of MRME addition and ER. Compared with the raw maize straw gasification at the same operating condition, the content of H2 increased from 17.32% to 33.77%, and CO raised from 22.89% to 35.11%. It seems that the red mud extract catalyst has the potential for using as an economic efficiency industrially catalyst for high quality and H2-riched syngas production from biomass gasification.

Steam-oxygen gasification of sewage sludge: Reduction of tar, H2S and COS with limestone as bed additive

Biogenic residue conversion to fuel and chemicals via fluidized bed gasification and synthesis is a promising pathway allowing biogenic residues to replace fossil carbon sources. This study focuses on sewage sludge gasification with the application of limestone as bed additive for tar, H2S and COS reduction. Experiments were conducted in a 20 kW fuel input bubbling fluidized bed facility with steam and oxygen as gasification agents. The syngas composition, considering the concentrations of H2, CO, CO2, CH4, CxHy, H2S, COS, NH3 and tar species, was determined for different limestone to fuel ratios. The results show that the produced syngas has high H2 and CO concentrations of up to 0.37 m3 m−3 and 0.18 m3 m−3 respectively and is thus suitable for synthesis. Tar species from sewage sludge gasification are characterized by various methods and differ from those from wood gasification. It was found that a small additive ratio of ~0.06 kg kg−1 (limestone to fuel ratio) is sufficient to reduce heavy tar species up to 75%, and with higher additive ratios, light tar species can also be partially reduced. Moreover, H2S and COS capture is demonstrated, with H2S and COS concentrations decreasing by 40%–65% with increasing limestone additive ratio. The ammonia (NH3) concentration was not affected by the additive. This study concludes that limestone addition is an effective and low cost measure to mitigate tar related facility problems and to reduce the downstream tar and sulfur cleaning efforts.

Production of Motor-Fuel Hydrocarbon Fractions from Sunflower Husk Biomass

The production of synthetic hydrocarbons from sunflower husk biomass including the stages of gasification and the Fischer–Tropsch (FT) synthesis of hydrocarbons was studied. It was found that H2/CO = 2 was an optimal ratio for the production of motor-fuel hydrocarbon fractions, and steam–oxygen gasification provided a minimum concentration of ballast components in the synthesis gas. The synthesized hydrocarbons mainly consisted of gasoline and diesel fractions and contained to ~60% isomeric structures.

Reforming of toluene as a tar model compound over straw char containing fly ash

The present work focuses on confirming that straw char containing fly ash (SCFA) produced from steam–oxygen gasification (SOG) of straw pellets has the potential to be reused as a tar–reforming catalyst in the original process. The catalytic activity and reforming selectivity of SCFA was evaluated with toluene as a tar model compound in the presence of steam and hydrogen in a lab–scale fixed bed reactor at high temperature up to 900 °C. The kinetic results showed that SCFA was effective in toluene reforming with a complete toluene conversion at a space time of 0.05 kg h m−3 under 850 °C and a steam volume fraction of 15%. On the other hand, when hydrogen was present, the significant effect of hydrogen on toluene reforming was demonstrated by the formation of benzene through hydrodealkylation reaction. The volumetric ratio of H2O to H2 was an essential parameter that decided the selectivity of toluene reforming. Although the coexist of toluene and hydrogen would inhibit the gasification, SCFA was proved to be gasified during toluene reforming. The surface migration and agglomeration of inorganics due to gasification also resulted in the change of catalytic activity and reforming selectivity through time. In conclusion, this study demonstrated the potential utilization of SCFA derived from the SOG process as a tar–reforming catalyst to enhance the overall performance of the SOG process.

Nonstationary Steam–Oxygen Gasification of Solid Fuel in a Fixed Bed Under Pressure

A two-dimensional model of nonstationary steam–oxygen gasification of solid fuel in a fixed bed has been constructed, which took into account the interphase convective heat transfer, radiative-conductive heat transfer of the solid phase, radiative and conductive heat transfer of the bed with the reactor wall, heterogeneous and homogeneous chemical reactions, gravity force, and the aerodynamic drag force. The influence of the process parameters on the thermochemical treatment of the Shubarkol’ bituminous long-flame coal under a pressure of 3 MPa at ratios of the mass fractions of the steam–oxygen mixture components H2O/O2 = 45/55, 40/60, and 72/28 was studied.

Exergetic, economic and carbon emission studies of bio-olefin production via indirect steam gasification process

The indirect steam gasification of biomass to olefins (IDBTO) coupled with CO2 utilization was proposed and simulated. Energy and exergy efficiencies, net CO2 emissions, and economic evaluation were performed against IDBTO as well as the direct oxygen-steam gasification of biomass to olifins (DBTO). The influences of unreacted gas recycling fraction (RU) and CO2 to dry biomass mass ratio (CO2/B) on the thermodynamic performance of the processes were also studied. The results showed that the yields of olefins of DBTO and IDBTO were 17 wt% and 19 wt%, respectively, the overall energy and exergy efficiencies of the IDBTO were around 49% and 44%, which were 8% and 7% higher than those of the DBTO process, respectively. A higher RU was found favor higher energy and exergy efficiencies for both routes. Besides, for the IDBTO process, it is found that the addition of CO2 to gasification system led to an improvement in both energy efficiency and exergy efficiency by around 1.6%. Moreover, life-cycle net CO2 emission was predicted to be −4.4 kg CO2 eq./kg olefins for IDBTO, while for DBTO, it was −8.7 kg CO2 eq./kg. However, the quantitative economic performance of IDBTO was superior to that of the DBTO process.

Modelling of Substitute Natural Gas production via combined gasification and power to fuel

The combination of water electrolysis and solid fuel gasification offers the substitution of Air Separation Unit, the reduction or elimination of water gas shift catalytic system and acid gas removal technology. Subsequently, the direct utilisation of CO2, which otherwise would be emitted during production and its conversion to valuable fuels in combination with energy storage are achieved. Steam gasification and steam-oxygen gasification in different operating conditions and scales are combined with electrolysers with the aim to define optimum efficiencies towards SNG production and reduction of direct CO2 emissions. Modelling and comparison of 6 different cases for steam and steam-oxygen gasification process, gas cleaning and conditioning technologies focusing on tar removal, activated carbon, water gas shift, and acid gas removal technologies with potassium carbonate and MDEA are investigated. Capture ratios are balanced with and without water gas shift reactor according to the requirements of SNG synthesis. The efficiency of gasification and power to SNG ranges between 57.67% and 63.43% for the optimum cases with low pressure steam/oxygen gasification and electrolysers sized according to oxygen demand and according to the oversized electrolysers case respectively. The overall energy conversion resulted in an energy conversion efficiency of 72.83% and 73.51% with the production of steam.

Oxygen–steam gasification of karanja press seed cake: Fixed bed experiments, ASPEN Plus process model development and benchmarking with saw dust, rice husk and sunflower husk

This article aims at investigating the oxygen–steam gasification of Karanja press seed cake using experimental and modeling studies and compare the results of these studies with those for other feedstocks such as rice husk, sawdust, and sunflower husk. The experimental work was conducted in a fixed bed reactor and the process simulation model was created in ASPEN Plus. Finally, validation and benchmarking exercise were conducted by validating the ASPEN Plus model using experimental results. A general agreement was found between the experimental results and ASPEN Plus process model results with a maximum variation of ±4%. Furthermore, sensitivity analyses were carried out to understand the effects of parameters such as gasification temperature, ER (equivalence ratio), and SBR (steam to biomass ratio) on synthesis gas composition, LHV (lower heating value) and CGE (cold gas efficiency). The optimal values of ER and SBR in this study were found to be 0.23 and 0.3, respectively. The CGE was found to increase with an increase in the temperature. Values of CGE and LHV were found to be as high as 95% and ∼12 MJ/Nm3, respectively at 1000 °C for all feedstocks. The optimum SBR value was found to vary from 0.3 to 0.7 for H2/CO variation in the range of ∼0.83–1.0.

Entrained-flow gasification of torrefied tomato peels: Combining torrefaction experiments with chemical equilibrium modeling for gasification

The purpose of the present study is to quantify the impact of torrefaction pretreatment on the quality of the product gas arising from the gasification with steam and steam-oxygen mixtures of non-woody biomass in high-temperature entrained flow reactors. To this aim, a chemical equilibrium model for biomass gasification was adopted, which allowed predicting the product gas composition as a function of process temperature, equivalence ratio, steam-to-biomass ratio and biomass elemental composition. A global sensitivity analysis with respect to the model input parameters was performed to assess the impact of torrefaction and gasification operating conditions on the quality of the product gas in terms of heating value and composition metrics typically adopted in the process industry (H2/CO ratio, stoichiometric module, etc.). In particular, the gasification of raw tomato peels and related torrefied solids resulting from fluidized bed torrefaction tests performed under light (200 °C and 30 min), medium (240 °C and 30 min) and severe (285 °C and 30 min) conditions was investigated using ultimate analysis data in the model. Results of this analysis highlighted that the quality of product gas arising from the oxygen-steam gasification of torrefied and untreated tomato peels did not differ very much, although torrefied feedstocks produced more H2 and CO and less CO2 than the parent one. This suggests that, despite the significant benefits it determines in biomass feeding, grinding and storage, the torrefaction pretreatment provides only a marginal improvement in the product gas quality. Equilibrium simulations made available in the present study can be useful for a better understanding of the controlling variables that rule gasification processes in addition to act as a point of reference for more complex simulations of the high temperature entrained flow gasification of biomass with oxygen-steam mixtures.

Simultaneous production of CH4-rich syngas and high-quality tar from lignite by the coupling of noncatalytic/catalytic pyrolysis and gasification in a pressurized integrated fluidized bed

An integrated fluidized bed (IFB) reactor with a two-stage configuration has been developed to process small-size coal particles for the simultaneous production of CH4-rich syngas and high-quality tar, in which coal pyrolysis occurred in an upper transport bed (TB) within an atmosphere mixing steam and syngas generated by steam-oxygen gasification of coal or char in a lower fluidized bed (FB). The coupling effect was investigated by combining non-catalytic/catalytic pyrolysis and gasification in a pressurized IFB. Having TB pyrolysis obviously raised CH4 yield (also its content in producer gas) and tar yield. The respective contributions to CH4 formation from the TB pyrolysis and FB gasification were mainly relevant to operating pressure and Ca(OH)2 catalyst. Raising pressure facilitated CH4 formation. When lignite was treated without catalyst, the contribution from TB pyrolysis was greater than that from FB gasification as hydropyrolysis was intensified by pressure in H2-rich gas atmosphere from the FB gasifier. Adding catalyst into lignite reversed their contributions. The FB catalytic gasification formed more CH4 because Ca(OH)2 functioned well asa catalyst for CH4 formation in pressurized gasification. With elevated pressure or/and the addition of Ca(OH)2, pyrolysis tar yield decreased in different degrees but its quality was improved. With the combination effect of pressure and Ca(OH)2, producer gas from the tested IFB reactor was highly rich in CH4 to reach 10.8vol%, with as well a high H2/CO ratio of 2.3 that is suitable for making SNG. The obtained tar had its light tar content as high as 95wt%.