Fluidization of palm kernel shell,palm oil fronds,and empty fruit bunches in a swirling fluidized bed gasifier

The increased biomass utilization has triggered the use of palm oil waste as fuel for gasification in Malaysia. In this study, pioneering work was conducted on three types of palm oil wastes namely palm kernel shell (PKS), palm oil fronds (POF), and empty fruit bunches (EFB). Minimum air velocity (U_mf) required for fluidization of the tested biomass was determined experimentally in a swirling fluidized bed, by considering the effect of bed weight, density, particle size, fluidized bed height, pressure drop, and bed voidage. It was revealed that higher the particle size the smaller will be the voidage, which consequently affects the minimum fluidization velocity. U_mf was increased with a decrease in voidage size. However, a direct relationship was found between particle size and U_mf. Overall highest U_mf was determined for EFB followed by POF and PKS. Fluidized bed height was increased by decreasing the particle size regardless of the biomass type. Highest unsettled bed height was obtained with PKS on account of its low density among all the test fuels. It was concluded that optimization of the fluidized bed for each type of biomass, particle size, and density is explicitly required for a low-cost energy conversion process.     

Hydrogen for oil refining via biomass indirect steam gasification: energy and environmental targets

The energy and CO₂ consequences of substitution of a fossil-fuel-based hydrogen production unit with a biomass-based process in a large European refinery are studied in this study. In the base case, the biomass-based process consists in atmospheric, steam–blown indirect gasification of air-dried woody biomass followed by necessary upgrading steps. The effect of gradually substituting the current refinery hydrogen production unit with this process on global energy and CO₂ targets is estimated first. Few process concepts are studied in further detail by looking at different degrees of heat integration with the remaining refinery units and possible polygeneration opportunities. The proposed process concepts are compared in terms of energy and exergy performances and potential reduction in refinery CO₂ emission also taking into account the effect of marginal electricity. Compared to the base case, an increase by up to 8 % points in energy efficiency and 9 % points in exergy efficiency can be obtained by exploiting process integration opportunities. According to energy efficiency, steam production appears the best way to use excess heat available in the process while electricity generation through a heat recovery steam cycle appears the best option according to exergy efficiency results. All investigated cases yield to significant reduction in CO₂ emissions at the refinery. It appears in particular that maximal emission reduction is obtained by producing extra steam to cover the demand of other refinery units if high efficiency marginal electricity scenarios are considered.     

Using biomass as an energy source with low CO2 emissions

This work deals with the carbon dioxide cycle and emissions from biomass incineration under a hydrogen production context. It is proposed to use the thermal energy obtained by biomass combustion to produce water steam, which afterwards would be converted into hydrogen by high temperature electrolysis (HTE). In France, the thermal energy potential from nonvalorised biomass reaches almost 6.5 Mtep. In this study, the potential avoided carbon emissions are quantified as well as the feasible hydrogen production capacity based on the steam supplied by the incineration units. Results show that carbon consumption in hydrogen production by steam methane reforming (SMR) or biomass incineration–HTE process is almost equivalent between both processes. However, the hydrogen produced by the biomass incineration–HTE process used to fuel vehicles, would lead to a decrease of 135 Mt of carbon from fossil origins yearly, in contrast to SMR.     

Numerical study of hydrogen production by the sorption-enhanced steam methane reforming process with online CO<Subscript>2</Subscript> capture as operated in fluidized bed reactors

A three-dimensional (3D) Eulerian two-fluid model with an in-house code was developed to simulate the gas-particle two-phase flow in the fluidized bed reactors. The CO₂ capture with Ca-based sorbents in the steam methane reforming (SMR) process was studied with such model combined with the reaction kinetics. The sorption-enhanced steam methane reforming (SE-SMR) process, i.e., the integration of the process of SMR and the adsorption of CO₂, was carried out in a bubbling fluidized bed reactor. The very high production of hydrogen in SE-SMR was obtained compared with the standard SMR process. The hydrogen molar fraction in gas phase was near the equilibrium. The breakthrough of the sorbent and the variation of the composition in the breakthrough period were studied. The effects of inlet gas superficial velocity and steam-to-carbon ratio (mass ratio of steam to methane in the inlet gas phase) on the reactions were studied. The simulated results are in agreement with the experimental results presented by Johnsen et al. (2006a, Chem Eng Sci 61:1195–1202).     

Synthesis of an integrated biorefinery via the C–H–O ternary diagram

An integrated biorefinery is designed to handle a wide variety of feedstocks (mainly biomass) and can produce a broad range of products (e.g., biofuel, biochemicals, etc.) via multiple conversion pathways and technologies. Gasification is recognized as one of the most promising technologies for initial processing of biomass. It uses thermal energy to convert the biomass feedstock into a gaseous mixture, which is also known as syngas, consisting mainly of carbon dioxide (CO₂), steam (H₂O), methane (CH₄), carbon monoxide (CO) and hydrogen (H₂). It is noted that the composition of syngas, especially the ratio of H₂ to CO, is crucial when the syngas is further converted to liquid fuels and chemicals. In this work, a graphical targeting approach for the evaluation of gas phase equilibrium composition of biomass gasification is proposed. Based on the targeted composition, a conceptual design of an integrated biorefinery can be systematically developed.     

Thermodynamic Analysis of the Gasification of Municipal Solid Waste

This work aims to understand the gasification performance of municipal solid waste (MSW) by means of thermodynamic analysis. Thermodynamic analysis is based on the assumption that the gasification reactions take place at the thermodynamic equilibrium condition, without regard to the reactor and process characteristics. First, model components of MSW including food, green wastes, paper, textiles, rubber, chlorine-free plastic, and polyvinyl chloride were chosen as the feedstock of a steam gasification process, with the steam temperature ranging from 973 K to 2273 K and the steam-to-MSW ratio (STMR) ranging from 1 to 5. It was found that the effect of the STMR on the gasification performance was almost the same as that of the steam temperature. All the differences among the seven types of MSW were caused by the variation of their compositions. Next, the gasification of actual MSW was analyzed using this thermodynamic equilibrium model. It was possible to count the inorganic components of actual MSW as silicon dioxide or aluminum oxide for the purpose of simplification, due to the fact that the inorganic components mainly affected the reactor temperature. A detailed comparison was made of the composition of the gaseous products obtained using steam, hydrogen, and air gasifying agents to provide basic knowledge regarding the appropriate choice of gasifying agent in MSW treatment upon demand.     

Pretreatment methods for gasification of biomass and Fischer–Tropsch crude production integrated with a pulp and paper mill

In this paper, the influence on the system performance and greenhouse gas (GHG) emissions of different biomass pretreatment methods before gasification and Fischer–Tropsch (FT) crude production was evaluated. Entrained flow gasification has the benefit of producing a practically tar-free synthesis gas with nearly complete carbon conversion. This gasifier type requires a relatively dry fuel, with small particle size, at high pressure. The size can be acquired by milling, which is energy intensive and feeding is challenging. Torrefaction of biomass facilitates milling; it thus requires less electricity, however, the torrefaction process requires heat. Pyrolysis decomposes the biomass into gaseous, liquid, and solid parts, respectively. This further makes feeding easier, but comes with a greater heat demand than torrefaction. The impact of the different pretreatment methods on the overall energy system has been evaluated using process integration methodology. The results show that the excess heat from an FT process with a biomass input of 300 MW_HHV can replace the bark boiler in a large chemical pulp and paper mill, producing 350,000 tonnes of bleached paperboard annually. With the preconditions given for this study, thermal pretreatment of biomass may be beneficial in terms of wood-to-FT crude efficiency, with efficiencies up to 68 %, assuming 40 % electrical efficiency. Pretreatment using pyrolysis performed the best in regards to GHG emissions, if CO₂ from acid gas removal was vented, while milling, with an annual reduction of around 700,000 tonnes of CO₂,_eq, had the best results if the CO₂ was captured and sequestrated.     

Numerical simulation of gas-solid flows in fluidized bed gasification reactor

A numerical model for simulating a fluidized bed gasifier should include appropriate parameters to capture the dynamics of gas-solid flows, gasification kinetics and the interaction between these two. The focus of the present study is to analyze the effects of coal gasification chemistry models reported in literature on the prediction of product gas composition in a fluidized bed gasification reactor. Numerical results are validated against the experimental data available in literature. The validated model is used to examine the available chemical kinetics schemes for water gas shift reaction, steam methane reforming reaction and char heterogeneous reactions. It is also used to assess the effects of hydrodynamic models parameters such as drag model, particle-particle restitution coefficient and specularity coefficient on exit gas composition. Results show that the predictions of product gas composition are notably affected by the choices of the kinetics schemes for water gas shift and steam methane reforming reactions. Systematic analysis using the available choices to simulate initial processes such as moisture removal, volatile and tar cracking is reported. Drag models and the value of specularity coefficient are shown to have no effect on product gas composition, and the particle-particle restitution coefficient slightly influences the predicted gas composition.     

Parametric study of co-gasification of ternary blends of rice straw,polyethylene and polyvinylchloride

Parametric study of co-gasification of rice straw (RS), high-density polyethylene (PE) and Polyvinylchloride (PVC) was carried out to investigate the effect of temperature, flow rate of steam, typical plastics and their blends on the quality and volume of synthetic gas. The additions of plastic enhance H₂ content in the synthetic gas. The study found that increase in temperature increases the yield of synthetic gas, H₂ and CO content and lower heating value (LHV) of synthetic gas. The steam to biomass ratio seems to have a very small effect on gas composition. Likewise the increase in PE content in the feed blend increases the hydrogen content and gas yield. Similar results were obtained by increasing PVC content. Co-gasification experiments of ternary blends of RS, PE and PVC were also conducted. The ternary blends of 20 % RS, 40 % PE, 40 % PVC produced synthetic gas with higher H₂ content, higher synthetic gas production rate and higher LHV of synthetic gas. This work confirms that synergistic interactive effect takes place during the co-gasification of ternary blends of PE, PVC and RS due to volatile-char interaction and mineral catalytic effects. This work also suggests that carefully designed co-gasification unit can handle waste with varying composition of biomass and plastic to produce improved quantity as well as quality of synthetic gas.     

Hydrogen production through catalytic low-temperature bio-ethanol steam reforming

As a provider of our energy requirements, hydrogen seems to be one of most promising fuels, in particular when used to feed PEM fuel cells. When produced from a renewable source, it has got the potential to reduce the dependence on non-renewable fossil fuels and lower the amount of harmful emissions. Ethanol steam-reforming (ESR) reaction is an interesting option to obtain a H₂- and CH₄-rich stream with a low content of CO, combining the deep knowledge of the technology with the advantage of the biomass-derived feedstock. Thermodynamic analysis has indicated that the most interesting operating range to enhance the H₂ production and minimize CO and coke formation requires low pressure, high temperature, and high water-to-ethanol molar ratio. On the other hand, despite its endothermic nature, ESR could be carried out at low temperature, to increase overall thermal efficiency, even if at these conditions the catalyst's deactivation, due to coking and sintering phenomena, is not negligible. The main objective of this study is to investigate on the activity, stability, and durability of bimetallic Pt–Ni and Pt–Co catalysts supported on CeO₂ for low-temperature bio-ESR reaction. The catalysts have been prepared through different methods and with an optimized metal's content. They have also been characterized with various physico-chemical characterization tests, and the catalytic studies have been carried out in a lab-scale apparatus. While evaluating the effects on the catalysts' performances of preparation method, reaction temperature, space time, and water-to-ethanol molar ratio, the selected catalysts were found effective for the production of H₂ by steam reforming at low temperature. In particular, the Pt/Ni/CeO₂ catalyst shows a perfect agreement with equilibrium calculations yet at low contact times, although some carbon deposition occurs. Also the cobalt-based catalysts appear attractive. The relative rates of carbon growth versus gasification have been studied, and ascending water contents were used to study the effect of steam addition in the feed stream. An in-depth investigation of the reaction mechanism and the evaluation of the kinetic parameters will be crucial to complete the study of the proposed process.     

Supercritical water synthesis of nano-particle catalyst on TiO2 and its application in supercritical water gasification of biomass

ABSTRACT

Hydrogen production by catalytic gasification in supercritical water (SCW) is a promising way to utilise biomass resource. Supercritical water not only provides homogeneous and rapid reaction environment for the biomass gasification but also causes catalyst agglomeration problems. In order to prepare activity and stable catalyst for biomass gasification in supercritical water, supercritical water synthesis method was utilised and the preparation method was investigated. Ni, Co, Zn and Cu metal elements were loaded on TiO₂ particles which was proved to be hythothermally steady in supercritical water. And nano-particles were successfully made. Based on gas chromatography/mass spectrometer (GC/MS), scanning electron microscopy, energy dispersive spectrometer (EDS) and X-ray diffraction analysis methods, it turned out that metal catalysts have a uniform spherical structure with diameter around 30 nm. Metal catalysts synthesised with supercritical hydrothermal method showed certain catalytic effects. Ni catalyst had the best performance in stability while Zn catalyst possessed highest hydrogen yield.     

Towards cleaner technologies: emissions reduction, energy and waste minimisation, industrial implementation

This editorial introduces and provides an overview of a Special Issue dedicated to the jubilee 10th Conference of Process Integration, Modelling and Optimization for Energy Saving and Pollution Reduction—PRES’07. It contains thirteen selected papers covering various fields of cleaner technologies and environment policy problems. The technologies address recent developments in CO₂ capture in Combined Cycle power plants, CO₂ reduction in pulp and paper mills, process efficiency increases combined with energy savings at a mill, distillation separation enhancements and emissions control at gas plants, pre-combustion decarbonisation for polygenertion from fossil fuels, minimisation of CO₂ emissions in steam and power plants, a study of co-pyrolysis of biomass and plastic wastes, waste-to-energy system design (with a focus on incineration and gasification technologies), optimal design of wastewater treatment systems, and integrated production of sugar and biofuels from sugar beet. Among these topics, The Special Issue includes demonstration of the technologies in the form of Advanced Case studies.     

Superstructure-based synthesis and optimisation of an oil palm eco-industrial town: a case study in Iskandar Malaysia

Malaysia is one of the world’s top edible oil producers, having more than 5.23 million hectares of palm oil plantations and more than 400 palm oil mills. The oil palm industry produces millions of tonnes of biomass waste during harvesting and mill processing. This paper presents an oil palm eco-industrial town (EIT) that integrates a palm oil mill with nine downstream oil palm-based industries, as well as a community. The downstream industries produce various types of products such as crude palm oil, bio-fertiliser, bio-gas, bio-diesel, bio-pellet, medium-density fibreboard (MDF), and are also involved in the paper industry, and livestock production. Through the concept of industry symbiosis, the oil palm EIT promotes energy and material sharing among the industries and the community to reduce energy consumption, virgin material consumption, and waste generation. Therefore, this concept could provide economic and environmental benefits to upstream industries (utilisation of biomass), downstream industries (conversion of biomass to valuable products), and the community (job creation). In this work, a multi-objective linear programming model is formulated to maximise economic performance, while minimising waste generation in the oil palm EIT. The applicability of the model is demonstrated using a case study in Iskandar Malaysia (IM). The optimised model suggests that the most efficient way to utilise abundant oil palm biomass is via the production of crude palm oil, MDF, bio-paper, paper, bio-gas, and bio-diesel. The model could assist decision makers to identify the sub-industries in the EIT that would promote sustainability in the oil palm industry.     

耦合显热回收过程的Shell气流床粉煤气化过程模拟研究

为优化Shell气化炉的气化性能,利用Aspen Plus软件建立了Shell气流床粉煤气化过程的平衡模型,包括热解、燃烧、气化、冷煤气激冷与废热锅炉显热回收4个模块,研究了氧煤比和水蒸气煤比对Shell气化炉气化性能的影响。结果表明:随着氧煤比的增加,H₂和CH₄含量降低,CO₂含量先缓慢增加后快速增加,CO含量和冷煤气效率呈现先增加后减小的趋势;随着水蒸气煤比的增加,H₂和CO₂含量增加,CO和CH₄含量下降,冷煤气效率先迅速增加而后缓慢下降;神府煤最佳的氧煤比和水蒸气煤比分别为0.86和0.05。     

A novel pilot-scale production of fuel gas by allothermal biomass gasification using biomass micron fuel (BMF) as external heat source

A novel pilot-scale allothermal biomass gasification system integrating steam gasification, thermal cracking, and catalytic reforming aiming at fuel gas production was developed. Biomass micron fuel (BMF) was used as external heat source by combusting with air in the combustor. Biomass feedstock was gasified with steam, and then, tar in the produced gas was decomposed by thermal cracking and catalytic reforming. The waste heat of high-temperature flue gas and fuel gas was recovered and used for biomass feedstock pre-heating and steam generation, respectively. The fuel gas yield is 1.36 Nm³/kg with lower heating value of 11.61 MJ/Nm³. An overall energy analysis of the system was also investigated. The results showed that the cold gas efficiency and energy conversion efficiency in this system are 88.11 and 63.59 %, respectively. Meanwhile, combustion of BMF accounts for 25.66 % of the total energy input.     

Effect of DC steam plasma on gasifying carbonized waste

A feasibility study has been conducted to determine whether steam plasma can be used for the treatment of carbonized wastes, such as the carbide of the hazardous waste. The gasification which was often called “water gas reaction” was studied to reduce the volume and weight of wastes and to produce the combustible gas like hydrogen from them by using steam plasma. In this study, the thermal plasma generated by DC plasma was used as a heat source, where steam was added to react with carbon. Graphite was used as a test piece instead of carbonized wastes. The weight of the test piece was measured before and after treatment to decide the weight reduction during the experiment. The gas produced in the reaction was analyzed. The result indicated that it is possible to reduce the weight of graphite and to produce the combustible gas from graphite by using the DC steam plasma.     

Hydrogen production from methane steam reforming: parametric and gradient based optimization of a Pd-based membrane reactor

In this work three mathematical models for methane steam reforming in membrane reactors were developed. The first one is a steady state, non isothermal, non isobaric and one dimensional model derived from material and energy balances and validated using experimental data from the literature. It is referred as full model. The influence of two different intrinsic kinetics available, as well as, the influence of five important parameters on methane conversion (X_CH4_{\mathrm{CH}_{4}}) and hydrogen recovery (Y_H2_{\mathrm{H}_{2}}) were parametrically evaluated through simulations. The second model, referred as meta-model, was obtained though the response surface technique. This meta-model was included into a constrained optimization problem solved using NPSOL. The third model, referred as a simplified model, takes into account only mass balances from the full model. Using this model, a gradient based method (DIRCOL) was used to perform the optimization of the sum of methane conversion and hydrogen recovery. High methane conversions and hydrogen recoveries were reached through these methodologies.     

基于熔融盐加热的甲烷蒸汽重整制氢反应器的熵产生率和氢气产率分析

太阳能热化学储能能够有效解决太阳能时间和空间分布不均的问题。在工业甲烷蒸汽重整反应器模型的基础上,利用有限时间热力学理论建立了基于熔融盐加热的甲烷蒸汽重整反应器（steam methane reforming reactor heated by molten salt,MS-SMRR）模型,得到了MS-SMRR的设计参数,并分析了MS-SMRR的几何参数和操作参数对氢气产率和总熵产生率的影响规律。结果表明：在氢气产率一定时,逆流参考反应器比顺流参考反应器的总熵产生率低,且消耗的熔融盐少;增大熔融盐进口温度和减小反应混合物进口压力能够显著提高MS-SMRR的氢气产率。研究结果对实际MS-SMRR的优化设计具有一定的理论指导意义。     

Coke deposition on and removal from metals and heat-resistant alloys under steam-cracking conditions

The kinetics of coke formation and its removal from nickel, copper and alloys have been studied and the results correlated with the morphology of the deposits. Coke deposition from hydrogen-propylene-steam was fast on nickel and slower on copper and the alloys. The deposition on nickel was filamentary in appearance, resulting from a heterogeneously catalysed process, whereas the deposit on the alloys and on non-catalytic copper was essentially uniform. On the alloys, protection appeared to result from the production of scales, containing predominantly Cr₃C₂ and Cr₂O₃, on the surface. At the same time, carburization of the alloy was reduced, apparently as a result of the formation of a silicon-enriched layer at the base of the scale. Steam was found to have little effect on coke formation. However, in the absence of gas-phase hydrocarbons, coke gasification by steam was rapid for nickel but several orders of magnitude slower for the alloys. The main effect of steam is to aid in the formation of scales that are protective against coking and carburization, by promoting oxide formation.     

Optimization of an experimental membrane reactor for low-temperature methane steam reforming

The systematic and rigorous model-based optimization of the configuration and operating conditions of a methane membrane steam reforming reactor for hydrogen production is performed. A permeable membrane with Pd–Ru deposited on a ceramic dense support is used to selectively remove the produced hydrogen from the reaction zone. The shifted chemical equilibrium towards hydrogen production enables the achievement of high methane conversion at relatively low reactor temperature levels. Steam reforming takes place over a Ni–Pt/CeZnLa ceramic foam-supported catalyst that ensures better thermal distribution, at an operating temperature of 773 K and a pressure of 10⁶ Pa. A nonlinear, two-dimensional, and pseudo-homogeneous mathematical model of the membrane fixed-bed reactor is developed and subsequently validated using experimental data. For model validation purposes, two sets of experiments have been performed at the experimental reactor installed at CPERI/CERTH. The first set of experiments aims to investigate membrane permeability in order to estimate the parameters involved in the applied Sieverts law. The second set of experiments explores the performance of the membrane reactor at different steam to carbon ratios and total inlet volumetric flowrates. The derived mathematical model, consisted of mass, energy, and momentum balances that consider both axial and radial gradients of temperature and concentration, is then utilized within a model-based optimization framework that calculates the optimal operating conditions for the highly interactive reactor system. The optimal steam to carbon ratio and sweep gas flow rate that minimize the overall methane utilization (i.e., reformed methane and equivalent methane for heating purposes) are calculated for a range of hydrogen production rates. Τhe optimal reactor design configuration described by the length of the catalyst zone is also obtained for a given pure hydrogen production rate.