Supercritical water gasification (SCWG) is an innovative hydrothermal technique, employing supercritical water (SCW, T≥374oC, P≥22.1 MPa) as the reaction media, to convert wet biomass or aqueous organic waste directly into hydrogen (H2)-rich synthetic gas (syngas). In the first stage of this research, a secondary pulp/paper-mill sludge (SPP, provide by AbitibiBowater Thunder Bay Operations) was gasified at temperatures of 400-550oC for 20 to 120 min in a high-pressure batch reactor for H2 production. The highest H2 yield achieved was 14.5 mol H2/kg SPP (on a dry basis) at 550oC for 60 min. In addition, SPP exhibited higher H2-generation potential than sewage sludges, likely attributed to its higher pH and higher volatile matter and alkali salt contents. In the second stage, a novel two-step process for sludge treatment was established. The first step involved the co-liquefaction of SPP with waste newspaper in a batch reactor at varying mixing ratios, aimed at converting the organic carbons in the feedstocks into valuable bio-crude and water-soluble products. The highest heavy oil (HO) yield (26.9 wt%) was obtained at 300oC for 20 min with a SPP-to-newspaper ratio of 1:2. This co-liquefaction process transformed 39.1% of the carbon into HOs, where 16.3% of the carbon still remained in the aqueous waste. Next, an innovative Ru0.1Ni10/γ-Al2O3 catalyst (10 wt% Ni, Ru-to-Ni molar ratio=0.1), with long-term stability and high selectivity for H2 production, was developed for the SCWG of 50 g/L glucose, where no deactivation was observed after 33 h on stream at 700oC, 24 MPa and a WHSV (weight hourly space velocity) of 6 h-1. The H2 yield was maintained at ~50 mol/kg feedstock. The addition of small amounts of Ru to Ni10/γ-Al2O3 was found to be effective in enhancing Ni dispersion and increasing the reducibility of NiO. Finally, the Ru0.1Ni10/γ-Al2O3 catalyst together with an activated carbon (AC) supported catalyst (Ru0.1Ni10/AC) were utilized for treating the aqueous by-product from sludge-newspaper co-liquefaction using a continuous down-flow tubular reactor. More than 90% of the carbon in the waste was destroyed at 700oC with the highest H2 yield of 71.2 mol/kg carbon noted using Ru0.1Ni10/AC. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2011-04-27 17:20:49.193

In this thesis a fluidized bed containing a draft tube has been studied with the aim of developing the apparatus for coal gasification. The process has the capability of producing synthesis quality gas using air for combustion, and of being able to accomodate poor quality coal feeds containing heavy fines loads. These advantages arise from two special features of a draft tube fluidized bed. In the first place, the bed may be operated as two separate and independent reaction zones, one contained within the draft tube and the other in the annulus region surrounding it. As a result, the gasification reactions may be carried out in one compartment and the combustion reactions in the other, allowing the useful gasification products to be taken off separately and undiluted with the combustion flue gases. Secondly, the fluidized material in the bed may be induced to circulate up the draft tube and down the annulus. These circulating solids provide the heat carrier from the combustion to the gasification zones within the bed. Furthermore, circulation of the bed in this way leads to a much longer residence time of fine particles within the bed and results in a high fine coal utilization efficiency. In order to achieve these benefits in practice, it is necessary to separate the gases supplied to and emitted from the draft tube from those of the annulus, but at the same time allowing free movement of solids between these regions. The thesis deals with how this may be accomplished in three parts: Firstly, the principles underlying division of a fluidized bed with a draft tube into discrete reaction zones are formulated, and strategies for achieving zonal separation, based on these arguments, are experimentally tested. As a result a reactor configuration and operating conditions suitable for coal gasification have been empirically identified. Secondly, a model describing the bulk circulation of solid material in the bed is presented, for the draft tube operating in the slugging mode. This model allows the average solids residence time and the particle velocities in the annulus and draft tube to be predicted, provided that slug velocities and spacings are known. The necessary correlations between hydrodynamic behaviour and the system properties are available in the literature for round nosed and wall slugs, but not for square nosed slugs, which appear to be characteristic in the apparatus used here. The third part consequently examines the square nosed slugging regime, and a theory to describe this behaviour, based on interparticle stress analysis, is presented. This regime is identified as having significant advantage over other bubbling modes because of the high dense phase gas flow rates which are sustained, and the resulting improved gas-solid contacting. The three models together mathematically describe the operation of the draft tube fluidized bed, allowing gas partition between the annulus and the draft tube regions as well as solids circulation to be predicted, for different bed configurations and operating conditions. The predictions compare well with experimental results. The last part of the thesis deals with the application of the system to coal gasification on a one ton coal per day pilot plant. A high quality gas, containing up to 80% CO + H2, (balance CO2), has been produced by steam gasification in the draft tube, using air for the combustion reaction in the annulus. The H2/CO ratio can be varied from about 1 to 3, by changing the operating temperature of the reactor. / Thesis (Ph.D.)-University of Natal, Durban, 1984.

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The purpose of this research was to investigate the feasibility of installing gasification based combined heat and power plants in the New Zealand wood processing industry. This is in accordance with Objective Four of the BIGAS Consortium. This thesis builds on previous work on Objective Four (Rutherford, 2006) where integration into MDF (Medium Density Fibreboard) was investigated. The previous research identified the most suitable form of combined heat and power was a BIG-GE (Biomass Integrated Gasification Gas Engine) process, due to both lower capital investment and overall breakeven electricity production cost. This technology has therefore been adopted, and the investigation has been carried further in this research to incorporate integration into sawmills and LVL (Laminated Veneer Lumber) plants. It is recognised, however, especially when reviewing overseas successes and failures, that the base economics are only one factor in the feasibility of a plant. The research, therefore, has moved further to investigate New Zealand policy, the power market, lower capital alternatives and novel methods of integration. The conclusion of the study is gasification based combined heat and power plants in the New Zealand wood processing industry can be equal or better in economic terms than other forms of renewable generation, however, the application is very niche. Lower capital cost alternatives, stable and low priced biomass feed and a favourable power market in regards to distributed generation is key to the viability of such a plant. Government policy is favourable towards biomass gasification due to the target of 90% electrical generation by renewable resources by 2025. Distributed generation is also encouraged in the Government’s forward strategy. However, the technology has advanced further overseas due to capital grants and a premium paid for ‘green’ electricity. While the technology may be economic in its own right, active government support would lower the perceived risk increasing the likelihood of an investor taking interest in an initial project.

Biomass gasification may be an attractive alternative for meeting future energy demand. Although gasification is a mature technology, it has yet to be fully commercialised due to tar formation. This study focuses on the tar mitigation in gas produced in an atmospheric bubbling fluidised bed (ABFB) gasification system. Previous studies indicated significant tar variability along the system. In this work the experimental procedure has been improved for reliable results and better understanding of tar variability in the producer gas. After having introduced a new sample point for tar analysis to the system, experimental results indicated tar reduction in the gasifier, probably due to continuous accumulation of char and ash in the bed, as well as in the ceramic filter owing to thermal and catalytic effects. Iron-based materials, provided by Höganäs AB, were applied in a secondary catalytic bed reactor for tar decomposition in the producer gas. It was found that tar concentration depends on catalytic and gasification temperatures and catalyst material. When changing the gasification temperature from 850 °C to 800 °C the conditions in the producer gas also changed from reductive to oxidative, transforming the initial metallic state of catalyst into its oxidised form. It may be concluded that the catalysts in their metallic states in general exhibit a better tar cracking capacity than their corresponding oxides. Due to the low reactivity of petroleum coke, an alternative may be to convert it in combination with other fuels such as biomass. Co-gasification of petroleum coke and biomass was studied in this work. Biomass ash in the blends was found to have a catalytic effect on the reactivity of petroleum coke during co-gasification. Furthermore, this synergetic effect between biomass and petcoke was observed in the kinetics data. / <p>QC 20141022</p>

There have been many studies in the energy field to achieve different goals such as energy security, energy independence and production of cheap energy. The consensus of the general population is that renewable energy sources can be used on a short-term basis to compensate for the energy requirement of the world. However, the prediction is that fossil fuels will be used to provide the majority of energy requirements in the world at least on a short-term basis. Coal is one of the major fossil fuels and will be used for a long time because there are large coal reservoirs in the world and many products such as hydrogen, ammonia, and diesel can be produced using coal. In the present study, the performance of a clean energy system that combines the coal gasification and alkaline water electrolyzer concepts to produce hydrogen is evaluated through thermodynamic modeling and simulations. A parametric study is conducted to determine the effect of water ratio in coal slurry, gasifier temperature, effectiveness of carbon dioxide removal, and hydrogen recovery efficiency of the pressure swing adsorption unit on the system hydrogen production. In addition, the effects of different types of coals on the hydrogen production are estimated. The exergy efficiency and exergy destruction in each system component are also evaluated. Although this system produces hydrogen from coal, the greenhouse gases emitted from this system are fairly low.

Biomass, as a renewable energy resource, can be utilized to generate chemicals, heat, and electricity. Compared with biomass combustion, biomass gasification is more eco-friendly because it generates less amount of green gas (CO2) and other polluting gases (NOx and SO2). This research is focused on biomass gasification using a circulating fluidized bed. In the gasifier, fully fluidized biomass particles react with water vapor and air to generate syngas (CO and H2). A comprehensive model, consisting of three modules, hydrodynamics, mass transfer and energy transfer modules, is built to simulate this process using ANSYS Fluent software and C programming language. In the hydrodynamics module, the k-epsilon turbulence equations are coupled with the fluctuating energy equation to simulate gas-particle interaction in the turbulent flows occurring in the riser. In the mass transfer and energy transfer modules, heat transfer and mass transfer in turbulent flows are simulated to solve for the profiles of temperature and species concentration in the gasifier. The impacts of thermal radiation, water gas shift reaction (WGS), equivalence ratio (ER), and char combustion product distribution coefficient are also investigated to gain deeper understanding of biomass gasification process.

The modern concept of “biorefinery” is dominantly based on chemical pulp mills to create more value than cellulose pulp fibres, and energy from the dissolved lignins and hemicelluloses. This concept is characterized by the conversion of biomass into various bio-based products. It includes thermochemical processes such as gasification and fast pyrolysis. In thermo-mechanical pulp (TMP) mills, the feedstock available to the gasification-based biorefinery is significant, including logging residues, bark, fibre material rejects, bio-sludges and other available fuels such as peat, recycled wood and paper products. On the other hand, mechanical pulping processes consume a great amount of electricity, which may account for up to 40% of the total pulp production cost. The huge amount of purchased electricity can be compensated for by self-production of electricity from gasification, or the involved cost can be compensated for by extra revenue from bio-transport fuel production. This work is to study co-production of bio-automotive fuels, bio-power, and steam via gasification of the waste biomass streams in the context of the mechanical pulp industry. Ethanol and substitute natural gas (SNG) are chosen to be the bio-transport fuels in the study. The production processes of biomass-to-ethanol, SNG, together with heat and power, are simulated with Aspen Plus. Based on the model, the techno-economic analysis is made to evaluate the profitability of bio-transport fuel production when the process is integrated into a TMP mill.The mathematical modelling starts from biomass gasification. Dual fluidized bed gasifier (DFBG) is chosen for syngas production. From the model, the yield and composition of the syngas and the contents of tar and char can be calculated. The model has been evaluated against the experimental results measured on a 150 KWth Mid Sweden University (MIUN) DFBG. As a reasonable result, the tar content in the syngas decreases with the gasification temperature and the steam to biomass (S/B) ratio. The biomass moisture content is a key parameter for a DFBG to be operated and maintained at a high gasification temperature. The model suggests that it is difficult to keep the gasification temperature above 850 ℃ when the biomass moisture content is higher than 15.0 wt.%. Thus, a certain amount of biomass or product gas needs to be added in the combustor to provide sufficient heat for biomass devolatilization and steam reforming.For ethanol production, a stand-alone thermo-chemical process is designed and simulated. The techno-economic assessment is made in terms of ethanol yield, synthesis selectivity, carbon and CO conversion efficiencies, and ethanol production cost. The calculated results show that major contributions to the production cost are from biomass feedstock and syngas cleaning. A biomass-to-ethanol plant should be built over 200 MW.In TMP mills, wood and biomass residues are commonly utilized for electricity and steam production through an associated CHP plant. This CHP plant is here designed to be replaced by a biomass-integrated gasification combined cycle (BIGCC) plant or a biomass-to-SNG (BtSNG) plant including an associated heat &amp; power centre. Implementing BIGCC/BtSNG in a mechanical pulp production line might improve the profitability of a TMP mill and also help to commercialize the BIGCC/BtSNG technologies by taking into account of some key issues such as, biomass availability, heat utilization etc.. In this work, the mathematical models of TMP+BIGCC and TMP+BtSNG are respectively built up to study three cases: 1) scaling of the TMP+BtSNG mill (or adding more forest biomass logging residues in the gasifier for TMP+BIGCC); 2) adding the reject fibres in the gasifier; 3) decreasing the TMP SEC by up to 50%.The profitability from the TMP+BtSNG mill is analyzed in comparison with the TMP+BIGCC mill. As a major conclusion, the scale of the TMP+BIGCC/BtSNG mill, the prices of electricity and SNG are three strong factors for the implementation of BIGCC/BtSNG in a TMP mill. A BtSNG plant associated to a TMP mill should be built in a scale above 100 MW in biomass thermal input. Comparing to the case of TMP+BIGCC, the NR and IRR of TMP+BtSNG are much lower. Political instruments to support commercialization of bio-transport fuel are necessary. / Gasification-based Biorefinery for Mechanical Pulp Mills

Biomass is an alternative to fossil fuels that has a lower impact on the environment and is thus of great interest to replace fossil fuels for energy production. There are several technologies to convert the stored energy in biomass into useful energy and this thesis focuses on the process of gasification. The purpose of this thesis is to investigate how the prediction accuracy of gas composition in a kinetic model for fluidized bed gasifier is affected when hydrodynamic parameters are introduced into the model. Two fluidized bed gasifier models has therefore been set up in order to evaluate the affects: one model which only considers the kinetics of a gasifier and a second model which includes both the kinetics and the hydrodynamic parameters for a bubbling fluidized bed. The kinetic model is represented by an already existing kinetic model that is originally derived for a downdraft gasifier which has quite similar biomass gasification processes as fluidized bed gasifiers. Gas residence time differs between the two gasifier types and the model has thus been calibrated by introducing a time correction factor in order to use it for fluidized bed gasifiers and get optimum results. Two sets of experimental data were used for comparison between the two models. The models were compared by comparing the results of the predicted gas composition yield and the amount of unreacted carbon after the reactor at various equivalence ratios (ER). The result shows that the model that only considers reaction kinetics yields best agreement with the experimental data that have been used. One reasons as to why the kinetic model gives a better prediction of gas composition is due to the fact that there are higher reactant concentrations available for chemical reactions in the kinetic, in comparison to the combined model. Less reactant concentrations in the combined model is a result of the bed in the combined model consisting of two phases, according to the two-phase theory of fluidization that have been adapted. Both phases contain gases but the bubble phase is considered solid free, chemical reactions occur therefore only in the emulsion phase since the kinetic model is based on gas-solid reactions. The model that only contains reaction kinetics considers only one phase and all concentrations are available for chemical reactions. Higher char conversion is thus achieved in the model that only contains reaction kinetics and higher gas concentrations are produced.