Hydrogen energy production from disposable chopsticks by a low temperature catalytic gasification

This study investigates the comparison of various mineral catalysts on the enhancement of energy yield efficiency with low temperature catalytic gasification of disposable chopsticks. The experiments were carried out in a fluidized bed reactor by controlling the temperature and keeping it within the range of 600 °C–800 °C. The mineral catalysts, such as aluminum silicate, zeolite and calcium oxide (CaO) were used as the experimental catalysts for enhancing energy yield in this research. According to the experimental results, the gasification temperature is a critical factor for improving the gas yield and quality. In general, a higher temperature provides more favorable conditions for thermal cracking and enhances the gas yield and quality. The hydrogen content produced from the tested biomass gasification by various catalysts slightly increased from 11.77% to 14.57%. Furthermore, the lower heating value of synthesis gas increased from 9.28 MJ/Nm³ to 9.62 MJ/Nm³, when the fluidized bed reactor temperature operated at 600 °C and the tested catalysts addition. That is, the catalytic gasification has good energy yield performance for enhancing higher energy content of synthesis gas in a lower-temperature catalytic fluidized bed reactor. Compared with the hydrogen production efficiency, the addition of a calcium based catalyst can reduce bed agglomeration tendency, but it also improves the energy yield in this research.     

Gasification of biomass: comparison of fixed bed and fluidized bed gasifier

Gasification as a thermochemical process is defined and limited to combustion and pyrolysis. A systematic overview of reactor designs categorizes fixed bed and fluidized bed reactors. Criteria for a comparison of these reactors are worked out, i.e. technology, use of material, use of energy, environment and economy. A utility analysis for thermochemical processes is suggested. It shows that the advantages of one of the reactor types are marginal. An advantage mainly depends on the physical consistency of the input. As a result there is no significant advantage for the fixed bed or the fluidized bed reactor.     

Evaluation of municipal wastes as secondary fuels through co-combustion with woody biomass in a fluidized bed reactor

Co-combustion of two municipal waste materials (food waste and bio-solids) with an agricultural residue was carried out in a fluid bed unit, for investigating the thermal exploitation of these wastes for energy production. The reactivity of the fuels was studied by thermogravimetric analysis, while temperature profiles, gaseous emissions and combustion efficiency were determined under different operating conditions of the fluid bed reactor. By blending municipal solid waste or sewage sludge with olive stone burnout was improved, nevertheless even at high percentages of these wastes in the mixture combustion efficiency was very good, ranging between 98.5 and 99.5%. A reduction in excess air from 50 to 30%, or an increase in fuel feeding, resulted in higher SO₂ and NO_x emissions. SO₂ levels from olive stone/municipal solid waste blends were negligible, while those of NO_x exceeded emission guidelines. To meet legislation without any extra measures, generally the share of municipal solid waste in the mixture should be up to 10%, reactor loading for all mixtures below 0.72 kg/h and excess air over 40%.     

Coal gasification development and commercialization of the texaco coal gasification process

The development of the Texaco coal gasification process utilizing an entrained bed downflow slagging gasifier is discussed. the advantages of the process including its simplicity and lack of formation of environmentally unacceptable and undesirable by-products are emphasized. Treatment of the crude gasification product gas to produce a clean gas for use as fuel or as feed stock for chemical manufacture is also covered. Status of the commercialization of the process is included.     

Effect of fluidization/gasification parameters on hydrogen generation in syngas during fluidized-bed gasification process

This study discusses the influence of fluidization and gasification parameters on the hydrogen composition in syngas. For gasification conditions, when Stage 1 and Stage 2 gasifier temperature is 900 °C, the hydrogen content in syngas is 35.59 mol.% when the activated carbon is used as bed material. For using zeolite as bed material, the hydrogen content is 38.25 mol.%. The hydrogen content is higher than that under other conditions, but if the Steam/Biomass ratio is increased to 0.6, the hydrogen content resulted from zeolite as bed material is the highest 39.38 mol.%. For fluidization parameters, when Stage 2 bed material size is changed to 0.46 mm, no matter the bed material is activated carbon or zeolite, the hydrogen content in syngas is the best among three particle sizes. In terms of operating gas velocity, when gas velocity is 1.5 U_mf, the hydrogen content is higher. For fluidization parameters, the two bed materials can increase hydrogen content in syngas effectively in Stage 2 fluidized bed, and their effects are similar to each other. However, considering the fluidization parameters, the hydrogen content in syngas when activated carbon is used as bed material is better than that when the zeolite is used.     

Metals flow analysis applied to the hydrogen production by catalytic gasification of plastics

Gasification processes can play a key role in the clean energy production from fossil and non-conventional fuels because of its transformation in a synthetic gas (syngas) rich in hydrogen and carbon monoxide. Fluidized bed reactors, both bubbling and circulating, allow to use a catalytic or reacting solid material in partial or total substitution of the bed in order to promote the dehydrogenation of the fuel. Depending on the operating conditions of reactor and of fuel type, the catalyst has a strong influence on the hydrogen yield; otherwise, the effect of catalyst add to a fluidized bed can decrease during the experimental run due to its progressive deactivation. The experimental tests demonstrated that the utilization of olivine as bed material, recognized in the literature as a good catalyst for gasification process of biomass and plastics, improves the dehydrogenation of the recycled polyethylene used as fuel by producing a hydrogen-rich syngas and a coke layer on the bed particles. The tests also indicated that the olivine was not capable to catalyse the dehydrogenation process for long time because of loss of metals diffused and linked to the carbonaceous solid (coke). A Substance Flow Analysis has been applied to the experimental data in order to evaluate the Hydrogen Recovery Efficiency for the gasification tests and to follow the repartition of metals (Fe, Ni, Mg) in the input/output streams and in the bed. The limited duration of the steady state regime as observed during the tests with olivine indicated a progressive reduction of the catalytic action correlated to the loss of metals. In other words, the use of olivine allows to obtain very high hydrogen concentration in the producer gas but for a limited time and without the possibility to recover its catalytic capacity by thermal or mechanical regeneration due to the progressive loss of metals responsible of polymer dehydrogenation. This experimental result is strictly correlated to the utilization of polyethylene as fuel. This evidence has been confirmed by analysis on olivine and fines elutriated by the reactor and showed, in this work, by a material balance on metals.     

Effect of agglomeration/defluidization on hydrogen generation during fluidized bed air gasification of modified biomass

This study presents the effect of particle agglomeration on syngas emission during the biomass air gasification process. Various operating conditions such as operating temperature, equivalence ratio (ER), and amount of bed materials are employed. The concentrations of H₂ and CO increase along with the operating time as agglomeration begins, while CO₂ decreases at the same time. However, there is no significant change in the emission concentration of CH₄ during the defluidization process. The lower heating value increases while the system reaches the agglomeration/defluidization under various operating parameters. When the system reaches the agglomeration/defluidization process, the LHV value sharply increases. The results are obtained when the system reaches agglomeration/defluidization. The temperature increases while bed agglomeration occurs. A higher temperature increases the production of H₂ and CO, contributing to the LHV calculation.     

A two phase model of high temperature steam-only gasification of biomass char in bubbling fluidized bed reactors using nuclear heat

A two phase biomass char steam gasification kinetic model is developed in a bubbling fluidized bed with nuclear heat as source of energy. The model is capable of predicting the temperature and concentration profiles of gases in the bubble, emulsion gas and solid phases. The robust model calculates the dynamic and steady state profiles, as well as the complex parameters of fluidized bed. Three pilot scale gasifiers were simulated in order to see the effect of the H/D ratio and the bed heating dynamics in the gasification kinetics, these parameters are found to be really important in order to enhance the water-gas shift reaction, and consequently, the hydrogen production. For the system modeled, hydrogen is the principal product of the steam-only gasification, as reported in the literature data. The carbon dioxide yield seems to be smaller than the ones in other works, but these differences are due principally to the energy source (no combustion is conducted) and that char (no oxygen in the solids) was used as the carbon source.     

Promising components of waste-derived slurry fuels

The paper presents the results of experimental studies of energy (calorific value, ignition delay times and threshold ignition temperatures, duration and temperature of combustion) and environmental (CO₂, NO_x and SO_x emission) characteristics of fuel slurries based on pulverized wood (sawdust), agricultural (straw), and household (cardboard) waste. Wastewater from a sewage treatment plant served as a liquid medium for fuels. Petrochemical waste and heavy oil were additives to slurries. The focus is on obtaining the maximum efficiency ratio of slurry fuel, calculated taking into account environmental, cost, energy and fire safety parameters. All slurry fuels were compared with typical coal-water slurry for all the parameters studied. A comparison was also made between slurries and traditional boiler fuels (coal, fuel oil). The relative efficiency indicator for waste-based mixtures was varied in the range of 0.93–10.92. The lowest ignition costs can be expected when burning a mixture based on straw, cardboard and oil additive (ignition temperature is about 330 °C). The volumes of potential energy generated with the active involvement of industrial waste instead of traditional coal and oil combustion are forecasted. It is predicted that with the widespread use of waste-derived slurries, about 43% of coal and oil can be saved.     

Combustion and pollutant emissions characteristics of Camellia oleifera shells in a vortexing fluidized-bed combustor

Because of their saponin content, Camellia oleifera shells cannot be directly discarded. However, this eco-unfriendly agricultural waste is suitable for use as a fuel. A comparison between the combustion of crushed C. oleifera shell (CCS) and pelletized C. oleifera shells (PCS) was carried out in a pilot-scale fluidized-bed. Both directly combustion and flue gas recirculation (FGR) combustion modes were employed. The effects of particle size and the FGR ratio on the combustion behavior and pollutant emissions characteristics were also investigated. Results show that the combustion efficiencies for both CCS and PCS are higher than 99%. The combustion fraction in the bed region of CCS and PCS-6 are 55% and 85%, respectively, resulting in different combustion and pollutant emission characteristics. CCS has smaller CO and NO emissions and higher PCDD/Fs concentration of the fly ash compared with those of pelletized fuels. However, considering the material bridging in the feeding process of CCS, using pellets as the fuel is a better choice. The CO emissions increase while dioxin and furan emissions decrease with an increase in FGR ratio. The lowest NO emissions (about 150 ppm) of the three pelletized fuels combustion were achieved at an FGR ratio of 42%. In addition, all the pollutant emissions are lower than the minimum standards required for municipal solid waste (MSW) incinerators in Taiwan.     

Techno-economic analysis and life cycle assessment of hydrogen production from different biomass gasification processes

The paper presents techno-economic analyses and life cycle assessments (LCA) of the two major gasification processes for producing hydrogen from biomass: fluidized bed (FB) gasification, and entrained flow (EF) gasification. Results indicate that the thermal efficiency of the EF-based option (56%, LHV) is 11% higher than that of the FB-based option (45%), and the minimum hydrogen selling price of the FB-based option is $0.3 per kg H₂ lower than that of the EF-based option. When a carbon capture and liquefaction system is incorporated, the efficiencies of the EF- and FB-based processes decrease to 50% and 41%, respectively. The techno-economic analysis shows that at a biomass price of $100 per tonne, either a minimum price of $115/tonne CO_2e or a minimum natural gas price of $5/GJ is required to make the minimum hydrogen selling price of biomass-based plants equivalent to that of commercial natural gas-based steam methane reforming plants. Furthermore, the LCA shows that, biomass as a carbon-neutral feedstock, negative life cycle GHG emissions are achievable in all biomass-based options.     

Autothermal chemical looping reforming process of different fossil liquid fuels

The autothermal Chemical-Looping Reforming (a-CLR) is a process where syngas is produced with two main advantages; there are captured CO₂ emissions and the heat required for the syngas production is generated by the process itself. A Ni-based material is used as oxygen carrier circulating between two fluidized bed reactors: the fuel and air reactors. In this work, the auto-thermal conditions in a global H₂ production process, integrated by the a-CLR process and a Water Gas Shift reactor, using different liquid fossil fuels were theoretically determined. The hydrogen production per mol of carbon in the fuel was similar for all fossil fuels, taking a value of 2.2 at the optimal operating temperature (700 °C). In addition, the possibility of working at low temperature for a maximum H₂ production was experimentally demonstrated in a continuous 1 kW_th a-CLR unit.     

Comparison of green waste gasification performance in updraft and downdraft fixed bed gasifiers

This study aimed to investigate the gasification potential of municipal green waste in different fixed-bed gasifier configurations as updraft and downdraft. Both reactor systems were constructed from stainless-steel with a cyclone separator to increase synthesis gas yield and reduce tar production. Green waste collected from parks and gardens by Manisa Metropolitan Municipality, Turkey, was used in the experiments. After full-characterization of green waste, gasification experiments were performed above 700 °C to produce syngas with more than 40% (volumetric) H₂ and heating value around 12.54 MJ/Nm³. Dry air (DA) and pure oxygen (PO) were used as gasification agents. DA was applied with the flow-rates ranged between 0.4 and 0.05 L/min while the flow-rate of PO was 0.01 L/min. The maximum H₂ production as 45 vol% was obtained in downdraft reactor while it was about 51 vol% in updraft system. CH₄ production was obtained as higher value (app. 19 vol%) in downdraft reactor than that (13 vol%) in the updraft one. In the experiments with DA above 700 °C, the H₂/CO ratio varied between 1 and 3, and in the experiments with PO, it increased up to a maximum value of 4. The study has found a suitable set of gasification process parameters for two reactor systems. Therefore, the findings have been compared and discussed in detail.     

Hydrogen production via CaO sorption enhanced anaerobic gasification of sawdust in a bubbling fluidized bed

This paper presents the experimental results of CaO sorption enhanced anaerobic gasification of biomass in a self-design bubbling fluidized bed reactor, aiming to investigate the influences of operation variables such as CaO to carbon mole ratio (CaO/C), H₂O to carbon mole ratio (H₂O/C) and reaction temperature (T) on hydrogen (H₂) production. Results showed that, over the ranges examined in this study (CaO/C: 0-2; H₂O/C: 1.2-2.18, T: 489-740 °C), the increase of CaO/C, H₂O/C and T were all favorable for promoting the H₂ production. The investigated operation variables presented different influences on the H₂ production under fluidized bed conditions from those obtained in thermodynamic equilibrium analysis or fixed bed experiments. The comparison with previous studies on fluidized bed biomass gasification reveals that this method has the advantage of being capable to produce a syngas with high H₂ concentration and low CO₂ concentration.     

桦甸油页岩的流化床燃烧特性

根据实验室研究结果和理论计算,介绍了桦甸油页岩的物理、化学特性以及桦甸油页岩在流化床内的着火、燃烧和燃烬等技术特征,为更大规模利用桦甸油页岩提供了基础。     

Combustion of isolated bubbles in an elevated-temperature fluidized bed

Combustion of isolated bubbles was investigated with a laboratory-scale fluidized-bed reactor. Two different combinations of oxygen and argon were employed as the fluidizing gas. Single bubbles of methane were injected into an incipiently fluidized bed maintained at elevated temperatures. Gas composition inside the bubbles was measured using a suction probe connected to an on-line mass spectrometer, and the temperature of the bubbles was monitored using a fast-response thermocouple. The effects of bed particle type, particle size, bubble size, bed temperature, and oxygen concentration in the emulsion phase were examined for bed temperatures between 923 and 1203 K. A theoretical model of homogeneous combustion within the bubble phase was developed for comparison to the experimental results. The model accounted for the heat and mass transfer between bubble and emulsion phases, but only considered combustion within the bubble. The results indicated that small bubble size and high oxygen concentrations in the emulsion phase enhanced bubble-phase combustion. The bed temperature also proved to be an important parameter, with higher temperatures promoting bubble combustion, but unlike some other investigations, no critical ignition temperatures were observed in either experiments or model results. The fluidized bed's particle size and particle composition influence the heat and mass-transfer coefficients, and therefore the bubble-phase combustion, but these have a smaller influence than bed temperature and bubble size. Model results for bubble-phase gas composition and temperature compared favorably with the experimental measurements.     

污泥在流化床中的焚烧特性研究

本文研究了高水分、低热值的污泥在流化床中的结团特性、着火特性。考察了床温、污泥水分、辅助燃料、给料粒径、流化风速对污泥结团的影响，比较了多种不同污泥的结团情况，并运用中间相理论对污泥结团机理作了初步分析。试验结果对于污泥流化床焚烧的基础理论和应用研究都有着重要意义。     

Numerical simulation of hydrogen production by gasification of large biomass particles in high temperature fluidized bed reactor

Biomass as a renewable fuel compared to fossil fuels usually contains high moisture content and volatile release. Hydrogen production by large particle biomass gasification is a promising technology for utilizing high moisture content biomass particle in the high temperature fluidized bed reactor. In the present work, simulation of large particles biomass gasification investigated at high temperature by using the discrete phase model (DPM). Combustible gases with homogeneous gas phase reactions, drying process with a heterogeneous reaction, primary and secondary pyrolysis with independent parallel-reaction by using two-competing-rate model to control a high and low temperature were used. During the thermochemical process of biomass, gaseous products containing of H₂, H₂O, CH₄, CO and CO₂ was obtained. The effects of concentration, mole and mass fraction and hydrodynamics effects on gaseous production during gasification were studied. The results showed that hydrodynamic effect of hot bed is different from cold bed. Concentration and molar fraction of CO and H₂ production by continually and stably state and small amount of CO₂, H₂O, and CH₄ was obtained. The hydrodynamic of bed plays the significant role on the rate of gaseous products.     

Combustion of gel fuels based on organic gellants

The phenomena involved in the combustion of non-metallized organic-gellant-based gelled fuels were investigated. The droplet combustion was photographed using a high-speed digital video camera. Experiments were conducted also with a number of control fuels that were prepared especially for simulating different phenomena occurring during combustion. The organic-gellant-based gel fuel droplet is characterized by a gellant layer formed on the droplet surface because of phase separation, resulting in bubbling and jetting. Phase separation is most likely the phenomenon that dominates the combustion process. The use of control fuels confirms that phase separation is not unique to gel fuels.     

Pyrolysis pretreatment of biomass for entrained-flow gasification

The biomass for entrained-flow gasification needs to be pretreated to significantly increase its heating value and to make it more readily transportable. The pyrolysis pretreatment was conducted in a lab scale fixed-bed reactor; the reactor was heated to elevate the temperature at 5 °C/min before holding at the desired pyrolysis temperature for 1.5 h a fixed time. The effects of pyrolysis temperature on the yield, composition and heating value of the gaseous, liquid and solid products were determined. The pyrolysis removed most oxygenated constituents of rice straw while significantly increased its energy density. Meantime, it changes the physical properties of biomass powders. The results show that the angle of repose, the angle of internal friction of semi-char decrease obviously; the bulk density of semi-char is bigger than that of biomass. This could favor the feeding of biomass. Considering yield and heating value of the solid semi-char product and the feeding problem, the best pyrolysis temperature was 400 °C. The results of this study have confirmed the feasibility of employing pyrolyzed biomass for entrained-flow gasification; they are useful for the additional studies that will be necessary for designing an efficient biomass entrained-flow gasification system.