Exergy analysis of renewable light olefin production system via biomass gasification and methanol synthesis

The conceptual light olefin production system from biomass via gasification and methanol synthesis was simulated and its thermodynamic performance was evaluated through exergy analysis. The system was made up of gasification, gas composition adjustment, methanol synthesis, light olefin synthesis, steam & power generation and cooling water treatment. The in-depth exergy analysis was performed at the levels of system, subsystem and operation component respectively. The gasifier and the tail gas combustor were the main sources of irreversibility with exergy destruction ratios of 17.0% and 16.8% of the input exergy of biomass. The steam & power generation subsystem accounted for 43.4% of the overall exergy destruction, followed by 41.0% and 5.69% in the subsystems of gasification and gas composition adjustment respectively. The sensitivity evaluation of the operation parameters of gasifier indicates that the system efficiency could be improved by enhancing syngas yield and subsequent yield of light olefins. The overall exergetic efficiency of 30.5% is obtained at the mass ratios of steam to biomass and O₂-rich gas (95 vol%) to biomass (S/B and O/B) of 0.26 and 0.14 and gasification temperature at 725 °C.     

Hydrogen from Various Biomass Species via Pyrolysis and Steam Gasification Processes

The aim of this study was to assess the scientific and engineering advancements of producing hydrogen from biomass via two thermochemical processes: (a) conventional pyrolysis followed by reforming of the carbohydrate fraction of the bio-oil and (b) gasification followed by reforming of the syngas (H₂ + CO). The yield from steam gasification increases with increasing water-to-sample ratio. The yields of hydrogen from the pyrolysis and the steam gasification increase with increasing of temperature. In general, the gasification temperature is higher than that of pyrolysis and the yield of hydrogen from the gasification is higher than that of the pyrolysis. The highest yields (% dry and ash free basis) were obtained from the pyrolysis (46%) and steam gasification (55%) of wheat straw while the lowest yields from olive waste. The yield of hydrogen from supercritical water extraction was considerably high (49%) at lower temperatures. The pyrolysis was carried out at the moderate temperatures and steam gasification at the highest temperatures. This study demonstrates that hydrogen can be produced economically from biomass. The pyrolysis-based technology, in particular, because it has coproduct opportunities, has the most favorable economics.     

Syngas production from algae biomass gasification: the case of China

A kinetic model of algae gasification for hydrogen production with air and steam as gasification agent and was developed. The developed model was based on kinetic parameters available in the literature. The objective was to study the effect of critical parameters such as reaction temperature, stoichiometric ratio (SR) and steam flow rate (SFR) on H₂/CO ratio in the syngas, hydrogen yield, and lower heating value (LHV) of the produced syngas. Model formulation was validated with experimental results on air-steam gasification of biomass conducted in an atmospheric fluidized bed gasifier. The results showed that higher temperature contributed to lower H₂/CO, while higher SFR resulted in higher H₂/CO. The LHV of producer gas increased with SFR and gasification temperature.     

Exergy analysis of hydrogen production plants based on biomass gasification

Biomass gasification is a promising option for the sustainable production of hydrogen rich gas. Five different commercial or pilot scale gasification systems are considered for the design of a hydrogen production plant that generates almost pure hydrogen. For each of the gasification technique models of two different hydrogen production plants are developed in Cycle-Tempo: one plant with low temperature gas cleaning (LTGC) and the other with high temperature gas cleaning (HTGC). The thermal input of all plants is 10 MW of biomass with the same dry composition. An exergy analysis of all processes has been made. The processes are compared on their thermodynamic performance (hydrogen yield and exergy efficiency). Since the heat recovery is not incorporated in the models, two efficiencies are calculated. The first one is calculated for the case that all residual heat can be applied, the case with ideal heat recovery, and the other is calculated for the case without heat recovery. It is expected that in real systems only a part of the residual heat can be used. Therefore, the actual value will be in between these calculated values. It was found that three processes have almost the same performance: The Battelle gasification process with LTGC, the FICFB gasification process with LTGC, and the Blaue Turm gasification process with HTGC. All systems include further processing of the cleaned gas from biomass gasification into almost pure hydrogen. The calculated exergy efficiencies are, respectively, 50.69%, 45.95%, and 50.52% for the systems without heat recovery. The exergy efficiencies of the systems with heat recovery are, respectively, 62.79%, 64.41%, and 66.31%. The calculated hydrogen yields of the three processes do not differ very much. The hydrogen yield of the Battelle LTGC process appeared to be 0.097 kg (kg_{(dry biomass)})⁻¹, for the FICFB LTGC process a yield of 0.096 kg (kg_{(dry biomass)})⁻¹ was found, and for the Blaue Turm HTGC 0.106 kg (kg_{(dry biomass)})⁻¹.     

Hydrogen production through biomass gasification in supercritical water: A review from exergy aspect

Hydrogen production through supercritical water gasification (SWG) of biomass has been widely studied. This study reviews the main factors from exergy aspect, and these include feedstock characteristics, biomass concentration, gasification temperature, residence time, reaction catalyst, and reactor pressure. The results show that the exergy efficiencies of hydrogen production are mainly in the range of 0.04–42.05%. Biomass feedstock may affect hydrogen production by changing the H₂ yield and the heating value of biomass. Increases in biomass concentrations decrease the exergy efficiencies, increases in gasification temperatures generally increase the exergy efficiencies, and increases in residence times may initially increase and finally decrease the exergy efficiencies. Reaction catalysts also have positive effects on the exergy efficiencies, and the reviewed results show that the effects are followed KOH > K₂CO₃ > NaOH > Na₂CO₃. Reactor pressure may have positive, negative or negligible effects on the exergy efficiencies.     

Exergy analysis of hydrogen production from steam gasification of biomass: A review

Exergy analysis of hydrogen production from steam gasification of biomass was reviewed in this study. The effects of the main parameters (biomass characteristics, particle size, gasification temperature, steam/biomass ratio, steam flow rate, reaction catalyst, and residence time) on the exergy efficiency were presented and discussed. The results show that the exergy efficiency of hydrogen production from steam gasification of biomass is mainly determined by the H₂ yield and the chemical exergy of biomass. Increases in gasification temperatures improve the exergy efficiency whereas increases in particle sizes generally decrease the exergy efficiency. Generally, both steam/biomass ratio and steam flow rate initially increases and finally decreases the exergy efficiency. A reaction catalyst may have positive, negative or negligible effect on the exergy efficiency, whereas residence time generally has slight effect on the exergy efficiency.     

A review on biomass‐based hydrogen production and potential applications

In this paper, a detailed review is presented to discuss biomass‐based hydrogen production systems and their applications. Some optimum hydrogen production and operating conditions are studied through a comprehensive sensitivity analysis on the hydrogen yield from steam biomass gasification. In addition, a hybrid system, which combines a biomass‐based hydrogen production system and a solid oxide fuel cell unit is considered for performance assessment. A comparative thermodynamic study also is undertaken to investigate various operational aspects through energy and exergy efficiencies. The results of this study show that there are various key parameters affecting the hydrogen production process and system performance. They also indicate that it is possible to increase the hydrogen yield from 70 to 107 g H₂ per kg of sawdust wood. By studying the energy and exergy efficiencies, the performance assessment shows the potential to produce hydrogen from steam biomass gasification. The study further reveals a strong potential of this system as it utilizes steam biomass gasification for hydrogen production. To evaluate the system performance, the efficiencies are calculated at particular pressures, temperatures, current densities, and fuel utilization factors. It is found that there is a strong potential in the gasification temperature range 1023–1423 K to increase energy efficiency with a hydrogen yield from 45 to 55% and the exergy efficiency with hydrogen yield from 22 to 32%, respectively, whereas the exergy efficiency of electricity production decreases from 56 to 49.4%. Hydrogen production by steam sawdust gasification appears to be an ultimate option for hydrogen production based on the parametric studies and performance assessments that were carried out through energy and exergy efficiencies. Finally, the system integration is an attractive option for better performance. Copyright © 2012 John Wiley & Sons, Ltd.     

生物质化学链气化联合燃气轮机发电系统模拟

使用Aspen Plus软件对以Fe_2O_3为载氧体的生物质化学链气化系统进行模拟,分析温度、压力、载氧体与生物质摩尔比、水蒸气与生物质摩尔比等因素对合成气制备的影响;对不同生物质的气化条件进行优化;将气化制得的合成气通入M701F燃气轮机中发电,考察系统的发电效率。结果表明:常压下,不同生物质气化的优化温度均在740℃左右,此时制备的合成气冷煤气效率较高;提高反应压力有利于系统热量自平衡,但合成气的冷煤气效率降低;载氧体与生物质摩尔比的优化值与生物质中氧碳摩尔比呈负相关,且达到优化值时,气化环境中氧碳摩尔比在1.25左右;水蒸气通入气化系统后冷煤气效率可提高15.00%～20.00%,主要原因为H_2的产量显著增加,通入水蒸气后的气化环境的氧碳比在1.4左右时,制备合成气的冷煤气效率较高;系统的发电效率在30.00%～37.00%,高于生物质发电效率。     

Enhancement of the quality of syngas from catalytic steam gasification of biomass by the addition of methane/model biogas

In this study, methane and model biogas were added during the catalytic steam gasification of pine to regulate the syngas composition and improve the quality of syngas. The effects of Ni/γ-Al₂O₃ catalyst, steam and methane/model biogas on H₂/CO ratio, syngas yield, carbon conversion rate and tar yield were explored. The results indicated that the addition of methane/model biogas during biomass steam gasification could increase the H₂/CO ratio to about 2. Methane/model biogas, steam and Ni/γ-Al₂O₃ catalyst significantly affected the quality of syngas. High H₂ content syngas with H₂/CO ratio of about 2, biomass carbon conversion >85% and low tar yield was achieved under the optimum condition: S/C = 1.5, α = 0.2 and using Ni/γ-Al₂O₃ catalyst. According to ANOVA, methane and catalyst were the key influencing factors of the H₂/CO ratio and syngas yield, and the tar yield mainly depended on the Ni/γ-Al₂O₃ catalyst. Biogas, as a more environmentally friendly material than methane, can also regulate the composition of syngas co-feeding with biomass.     

Performance of hydrogen and power co-generation system based on chemical looping hydrogen generation of coal

An integrated hydrogen and power co-generation system based on slurry-feed coal gasification and chemical looping hydrogen generation (CLH) was proposed with Shenhua coal as fuel and Fe₂O₃/MgAl₂O₄ as an oxygen carrier. The sensitivity analyses of the main units of the system were carried out respectively to optimize the parameters. The syngas can be converted completely in the fuel reactor, and both of the fuel reactor and steam reactor can maintain heat balance. The purity of hydrogen produced after water condensation is 100%. The energy and exergy analyses of the proposed system were studied. Pinch technology was adopted to get a reasonable design of the heat transfer network, and it is found pinch point appears at the hot side temperature of 224.7 °C. At the given status of the proposed system, the hydrogen yield is 1040.11 kg·h⁻¹ and the CO₂ capture rate is 94.56%. At the same time, its energy and exergy efficiencies are 46.21% and 47.22%, respectively. According to exergy analysis, the degree of exergy destruction is ranked. The gasifier unit has the most serious exergy destruction, followed by chemical looping hydrogen generation unit and the heat recovery steam generator unit.     

生物质费托合成制取液体燃料的仿真及分析

以生物质费托合成制取液体燃料工艺为基础,利用Aspen Plus软件建立其流程的仿真模型,研究各单元操作参数变化对航空煤油产量的影响,并在最优工况下对系统进行能量分析.结果表明:生物质气化单元对航油产量的影响主要来自产物合成气中H2与CO物质的量之比(H2/CO),最优操作条件为T=750℃,P=0.1 MPa,进口水...     

Energy and exergy analysis of biomass gasification at different temperatures

Biomass is usually gasified above the optimal temperature at the carbon-boundary point, due to the use of different types of gasifiers, gasifying media, clinkering/slagging of bed material, tar cracking, etc. This paper is focused on air gasification of biomass with different moisture at different gasification temperatures. A chemical equilibrium model is developed and analyses are carried out at pressures of 1 and 10 bar with the typical biomass feed represented by CH_1.4O_0.59N_0.0017. At the temperature range 900–1373 K, the increase of moisture in biomass leads to the decrease of efficiencies for the examined processes. The moisture content of biomass may be designated as “optimal” only if the gasification temperature is equal to the carbon-boundary temperature for biomass with that specific moisture content. Compared with the efficiencies based on chemical energy and exergy, biomass feedstock drying with the product gas sensible heat is less beneficial for the efficiency based on total exergy. The gasification process at a given gasification temperature can be improved by the use of dry biomass and by the carbon-boundary temperature approaching the required temperature with the change of gasification pressure or with the addition of heat in the process.     

Analysis of syngas production rate in empty fruit bunch steam gasification with varying control factors

Biomass gasification is a prevailing approach for mitigating irreversible fossil fuel depletion. In this study, palm empty fruit bunch (EFB) was steam-gasified in a fixed-bed, batch-fed gasifier, and the effect of four control factors—namely torrefaction temperature for EFB pretreatment, gasification temperature, carrier-gas flow rate, and steam flow rate—on syngas production were investigated. The results showed that steam flow rate is the least influential control factor, with no effect on syngas composition or yield. The gasification temperature of biomass significantly affects the composition of syngas generated during steam gasification, and the H₂/CO ratio increases by approximately 50% with an increase in temperature ranging from 680 °C to 780 °C. The higher H₂/CO ratio at a lower gasification temperature increased the energy density of the combustible constituents of the syngas by 3.43%.     

Hydrogen and syngas yield from residual branches of oil palm tree using steam gasification

Wastes produced during oil palm production from agro-industries have great potential as a source of renewable energy in agriculturally rich countries, such as Thailand and Malaysia. Clean chemical energy recovery from oil palm residual branches via steam gasification is investigated here. A semi-batch reactor was used to investigate the gasification of palm trunk wastes at different reactor temperatures in the range of 600 to 1000 °C. The steam flow rate was fixed at 3.10 g/min. Characteristics and overall yield of syngas properties are presented and discussed. Results show that gasification temperature slightly affects the overall syngas yield. However, the chemical composition of the syngas varied tremendously with the reactor temperature. Consequently, the syngas heating value and ratio of energy yield to energy consumed were found to be strongly dependent on the reactor temperature. Both the heating value and energy yield ratio increased with increase in reactor temperature. Gasification duration and the steam to solid fuel ratio indicate that reaction rate becomes progressively slower at reactor temperatures of less than 700 °C. The results reveal that steam gasification of oil palm residues should not be carried out at reactor temperatures lower than 700 °C, since a large amount of steam is consumed per unit mass of the sample in order to gasify the residual char.     

Numerical study on solar spouted bed reactor for conversion of biomass into hydrogen-rich gas by steam gasification

A solar-powered biomass steam gasification system was developed, in which heat transfer model, flow model and chemical model were constructed to predict the distributions of temperature, pressure, mole fraction of syngas, and solar incident flux. Several key parameters of gasifier were designed to ensure the fluidization stability. Based on the model validation, gasifier performance simulations in the design working conditions were obtained. The effects of the key variable parameters, including the rim angle of the dish collector, steam-to-biomass mass flow ratio, biomass feeding rate and the solar irradiance in the different operation working conditions on the composition of syngas, lower heating value, and efficiencies were investigated. The results reveal that the coupled system implements the best gasification performance in the design conditions which the rim angle, steam-to-biomass mass flow ratio, and biomass feeding rate are set at 60°, 0.4, and 2.5 g/min, while the LHV, carbon conversion, and gasification energy efficiencies are 11.51 MJ/m³, 78.17%, and 93.01%, respectively. The overall energy efficiency considering solar energy is 30.79%.     

Exergy analysis of biomass staged-gasification for hydrogen-rich syngas

Using Aspen Plus simulations, exergy analyses of hydrogen-rich syngas production via biomass staged-gasification are carried out for three configurations, namely, staged-gasification with pyrolysis gas combustion and char gasification (C-1), staged-gasification with pyrolysis gas reforming and char gasification (C-2), and staged-gasification with pyrolysis gas reforming and char combustion (C-3). The results show that, for the gasification and reforming processes, the exergy loss of pyrolysis gas with tar reforming is less than that of char gasification. As for the system, it is conducive to generating hydrogen by making full use of the hydrogen element (H) in biomass instead of the H in water. The benefits of C-1 are that it removes tar and produces higher yield and concentration of hydrogen. However, C-2 is capable of obtaining higher exergy efficiency and lower exergy loss per mole of H₂ production. C-3 theoretically has greater process performances, but it has disadvantages in tar conversion in practical applications. The appropriate gasification temperature (T_G) are in the range of 700–750 °C and the appropriate mass ratio of steam to biomass (S/B) are in the range of 0.6–0.8 for C-1 and C-3; the corresponding parameters for C-2 are in the ranges of 650–700 °C and 0.7–0.8, respectively.     

Integration of solid oxide electrolyser,entrained gasification,and Fischer-Tropsch process for synthetic diesel production: Thermodynamic analysis

A novel integrated renewable-based energy system for production of synthetic diesel is proposed and simulated in this study. This system merges solid oxide electrolyser (SOE), entrained gasification (EG) and Fischer-Tropsch (FT) technologies. Two case scenarios are considered here. In the first case, the electrolyser unite produce syngas through co-electrolysis of steam and carbon dioxide, while in the second case only steam is electrolyzed. The effects of SOEC and EG operating pressure and temperatures on the system performance in each case are investigated and compared. It is shown that the operating condition of electrolyser subsystem has a more considerable effect on the performance of the integrated system as compared to the gasification subsystem. Also waste heat recovery results in about 43 and 2 percentage point increase in energy and exergy efficiency, respectively. It is also shown that internal recovering of oxygen has the best effect on the system performance.     

Effect of supplementary firing options on cycle performance and CO2 emissions of an IGCC power generation system

Supplementary firing is adopted in combined‐cycle power plants to reheat low‐temperature gas turbine exhaust before entering into the heat recovery steam generator. In an effort to identify suitable supplementary firing options in an integrated gasification combined‐cycle (IGCC) power plant configuration, so as to use coal effectively, the performance is compared for three different supplementary firing options. The comparison identifies the better of the supplementary firing options based on higher efficiency and work output per unit mass of coal and lower CO₂ emissions. The three supplementary firing options with the corresponding fuel used for the supplementary firing are: (i) partial gasification with char, (ii) full gasification with coal and (iii) full gasification with syngas. The performance of the IGCC system with these three options is compared with an option of the IGCC system without supplementary firing. Each supplementary firing option also involves pre‐heating of the air entering the gas turbine combustion chamber in the gas cycle and reheating of the low‐pressure steam in the steam cycle. The effects on coal consumption and CO₂ emissions are analysed by varying the operating conditions such as pressure ratio, gas turbine inlet temperature, air pre‐heat and supplementary firing temperature. The results indicate that more work output is produced per unit mass of coal when there is no supplementary firing. Among the supplementary firing options, the full gasification with syngas option produces the highest work output per unit mass of coal, and the partial gasification with char option emits the lowest amount of CO₂ per unit mass of coal. Based on the analysis, the most advantageous option for low specific coal consumption and CO₂ emissions is the supplementary firing case having full gasification with syngas as the fuel. Copyright © 2008 John Wiley & Sons, Ltd.     

Desulfurization and tar reforming of biogenous syngas over Ni/olivine in a decoupled dual loop gasifier

For the production of bio-SNG (substitute natural gas) from syngas of biomass steam gasification, trace amounts of sulfur and tar compounds in raw syngas must be removed. In present work, biomass gasification and in-bed raw gas upgrading have been performed in a decoupled dual loop gasifier (DDLG), with aggregation-resistant nickel supported on calcined olivine (Ni/olivine) as the upgrading catalyst for simultaneous desulfurization and tar elimination of biogenous syngas. The effects of catalyst preparation, upgrading temperature and steam content of raw syngas on sulfur removal were investigated and the catalytic tar reforming at different temperatures was evaluated as well. It was found that 850 °C calcined Ni/olivine was efficient for both inorganic-sulfur (H₂S) and organic-sulfur (thiophene) removal at 600–680 °C and the excellent desulfurization performance was maintained with wide range H₂O content (27.0–40.7%). Meanwhile, tar was mostly eliminated and H₂ content increased much in the same temperature range. The favorable results indicate that biomass gasification in DDLG with Ni/olivine as the upgrading bed material could be a promising approach to produce qualified biogenous syngas for bio-SNG production and other syngas-derived applications in electric power, heat or fuels.     

Comparative exergoeconomic analyses of the integration of biomass gasification and a gas turbine power plant with and without fogging inlet cooling

Inlet cooling is effective for mitigating the decrease in gas turbine performance during hot and humid summer periods when electrical power demands peak, and steam injection, using steam raised from the turbine exhaust gases in a heat recovery steam generator, is an effective technique for utilizing the hot turbine exhaust gases. Biomass gasification can be integrated with a gas turbine cycle to provide efficient, clean power generation. In the present paper, a gas turbine cycle with fog cooling and steam injection, and integrated with biomass gasification, is proposed and analyzed with energy, exergy and exergoeconomic analyses. The thermodynamic analyses show that increasing the compressor pressure ratio and the gas turbine inlet temperature raises the energy and exergy efficiencies. On the component level, the gas turbine is determined to have the highest exergy efficiency and the combustor the lowest. The exergoeconomic analysis reveals that the proposed cycle has a lower total unit product cost than a similar plant fired by natural gas. However, the relative cost difference and exergoeconomic factor is higher for the proposed cycle than the natural gas fired plant, indicating that the proposed cycle is more costly for producing electricity despite its lower product cost and environmental impact.