Pressurized Fluidized Bed Gasifier Research Articles

Fragmentation of dolomite bed material at pressurized conditions in the presence of H2O and CO2: Implications for pressurized fluidized bed gasification

Dolomite shows superior tar cracking and anti-agglomeration abilities in gasification processes, while its fragmentation at elevated temperatures is still a major obstacle inhibiting its applications in fluidized bed (FB) applications. To improve the understanding of its performance in pressurized FB gasification, we investigated fragmentation behaviors of crystalline Glanshammar and amorphous Sala dolomite at both isothermal and non-isothermal modes under pressurized H2O and CO2 conditions. A series of tests under various conditions, i.e. pressure, temperature, heating rate, gas atmosphere, and dolomite types, was conducted. The primary fragmentation of Glanshammar is significantly reduced at 10 bar. Dolomite exposed to a PH2O of 10 bar has the lowest fragmentation among all cases. Both dolomites were also loaded into a pressurized fluidized bed gasifier as bed material. Glanshammar exhibits approximately 14% loss of its initial mass of bed, a much higher loss compared to the Sala dolomite with only 5.5%. Fragmentation mechanisms at pressurized conditions in the presence of H2O and CO2 and measures to mitigate dolomite fragmentation in pressurized FB gasifiers are proposed. During gasification, both high operating pressure and high PH2O are beneficial for fragmentation mitigation. To mitigate an initial fragmentation of dolomite during the reactor heating-up stage, a pressurization to the operating pressure before reaching the initial fragmentation temperature of dolomite (400 °C) is recommended. Crystalline dolomite, is the preferred choice, if a pretreatment at a high-pressure using H2O is applied.

Role of cobalt and calcium on coal catalytic hydrogasification in a pressurized fluidized bed

Coal catalytic hydrogasification (CCHG) was carried out in a lab-scale pressurized fluidized bed to study the cobalt-calcium (Co-Ca) catalyst on the gross distribution of products by changing the addition amount of the catalyst. The CH4 formation behaviors and the structure properties of gasified coal char were analyzed to elucidate the role of Co and Ca in the dual catalyst system. Results show that 90.0 wt% of carbon conversion and 77.3 wt% of CH4 yield could be simultaneously achieved in 30 min with the help of 5%Co-1%Ca catalyst through hydrogasification at 850 °C and 3 MPa. Co-Ca dual catalyst triggered coal catalytic hydropyrolysis and coal char catalytic hydrogasification in succession. However, neither individual Co nor Ca had profound catalytic activity towards the condensed aromatic rings in coal structure. Co alone was prone to agglomerate during CCHG, resulting in the inactivation and blockage of the micropore structures. The addition of Ca retarded Co sintering and more importantly mediated Co-C interaction, making Co penetrating into the interior of coal matrix to accelerate the carbon conversion. The catalytic process of CCHG was summarized and the probable interaction between Co-Ca-C was discussed. The findings in this work will provide the theory foundation for the design of the catalyst in the pressurized fluidized bed gasifier.

Novel Model for the Release and Condensation of Inorganics for a Pressurized Fluidized-Bed Gasification Process: Effects of Gasification Temperature.

A model is established to investigate the release and condensation of inorganics for a wood steam/oxygen-blown fluidized-bed gasification process. In the established model, fates of major elements (C, H, O, N, S, and Cl) and minor elements (Al, Ca, Fe, K, Mg, Mn, Na, P, Si, Ti, and Zn) are modeled separately. The composition of gaseous species involving major elements is predicted using Aspen Plus based on a semiempirical model. The release of minor elements and the condensation of inorganics are predicted using software SimuSage. The combination of Aspen Plus with SimuSage is achieved by manually inputting the stream parameters calculated from Aspen Plus into SimuSage. On the basis of this developed model, effects of gasification temperature on the condensation of Na-, K-, and Cl-containing species during gas cooling are studied. Results show that the process model established by combining Aspen Plus and SimuSage is valid and can be used to investigate the release of inorganics during gasification and condensation of inorganics during gas cooling. Under the investigated gasification conditions, regardless of the bed material, there are two temperature ranges within which no salt melt is formed during gas cooling. As the gasification temperature increases, the high-temperature range without salt melt formation becomes successively wider.

Influence of pressure on fluidized bed gasifier: Specific coal throughput and particle behavior

In this work, the influence of pressure on specific coal throughput and particle behavior was investigated. Firstly, mono-gasification of Jincheng anthracite (JCA) and meat and bone meal (MBM) and co-gasification of JCA and MBM were performed in pressurized fluidized bed gasifier pilot plant with a pressure of 0.1–2.6 MPa and a temperature of 900–1050 °C (mono-gasification of MBM at about 750 °C). It was found that the specific coal throughput is approximately directly proportional to the pressure to the power of 0.6–0.75 and co-gasification leads to successful thermochemical conversion of JCA as opposed to mono-gasification. Furthermore, a series of experiments, in a Pseudo-2D cold mode of a pressurized fluidized bed gasifier using an optic fiber probe system, have been performed to investigate the effects of pressure, fluidizing-gas velocity and static bed height on the particle behavior. The bed material used in this study was polystyrene having average diameter of 1.32 mm. It was found that the effect of pressure on vertical local-particle velocities (Vp) at low bed height (LBH) can be ignored at identical excess fluidizing-gas velocity while Vp at high bed height (HBH) decrease slightly with pressure in the lower pressure range (evidently below approximately 1.2 MPa) and increase thereafter. The effects of the fluidizing-gas velocity on Vp at LBH and HBH are also different. However, the effects of static bed height on Vp both at LBH and HBH are the same under pressure.

Selection of dolomite bed material for pressurized biomass gasification in BFB

Dolomite is considered advantageous as bed material in fluidized bed gasification processes, due to its catalytic tar cracking and anti-sintering properties. However, in case of pressurized fluidized bed gasifiers, the use of dolomite is challenging. High temperature in the presence of steam favors the production of clean syngas due to the intensified cracking of tar in the presence of CaO, whereas it simultaneously increases the tendency of fragmentation of dolomite particles after full calcination. The present study was carried out to examine the influence of the properties of dolomite on the stability of dolomite in a pressurized fluidized bed gasifier, with the aim of determining criteria for dolomite selection. Glanshammar dolomite exhibited a better stability in the mechanical strength after calcination, compared to Sala dolomite. The corresponding change of micro-structure that occurred during dolomite chemical transformation was presented. The crystal pattern and Si distribution in the crystal lattice are the possible explanations for the superior performance of the Glanshammar dolomite compared to the Sala dolomite.

Selection of dolomite bed material for pressurized biomass gasification in BFB

Dolomite is considered advantageous as bed material in fluidized bed gasification processes, due to its catalytic tar cracking and anti-sintering properties. However, in case of pressurized fluidized bed gasifiers, the use of dolomite is challenging. High temperature in the presence of steam favors the production of clean syngas due to the intensified cracking of tar in the presence of CaO, whereas it simultaneously increases the tendency of fragmentation of dolomite particles after full calcination. The present study was carried out to examine the influence of the properties of dolomite on the stability of dolomite in a pressurized fluidized bed gasifier, with the aim of determining criteria for dolomite selection. Glanshammar dolomite exhibited a better stability in the mechanical strength after calcination, compared to Sala dolomite. The corresponding change of micro-structure that occurred during dolomite chemical transformation was presented. The crystal pattern and Si distribution in the crystal lattice are the possible explanations for the superior performance of the Glanshammar dolomite compared to the Sala dolomite.

Thermodynamic evaluation of CHP (combined heat and power) plants integrated with installations of coal gasification

Integration of a CHP steam plant with an installation of coal gasification and gas turbine leads to an IGCC-CHP (integrated gasification combined cycle-combined heat and power). Two installations of coal gasification have been analyzed, i.e. pressurized entrained flow gasifier – case 1 and pressurized fluidized bed gasifier with CO2 recirculation – case 2. Basing on the results of mathematical modelling of an IGCC-CHP plant, the algorithms of calculating typical energy indices have been derived. The following energy indices are considered, i.e. coefficient of heat performance and relative savings of chemical energy of fuels. The results of coefficients of heat performance are contained between 1.87 and 2.37. Values exceeding 1 are thermodynamically justified because the idea of cogeneration of heat and electricity based on combining cycles of the heat engine and heat pump the efficiency of which exceeds 1. Higher values concerning waste heat replace more thermodynamically effective sources of heat in CHP plants. Relative savings of the chemical energy of fuels are similar in both cases of IGCC-CHP plants and are contained between the lower value of the CHP (combined heat and power) plants fuelled with coal and higher value of CHP plants fired with natural gas.

Addition of ash to prevent agglomeration during catalytic coal gasification in a pressurized fluidized bed

The agglomeration of potassium-loaded Wangjiata coal during catalytic coal gasification (CCG) was investigated in a bench-scale pressurized fluidized bed. The pressurized pressure-drop sintering technique was employed to understand sintering characteristic in a CO/H2/H2O mixture atmosphere at 3.5MPa. The ash, which was removed the water-soluble potassium compounds from gasification residue, was added to prevent fluidized bed agglomeration. The effects of the addition of ash on the catalytic activity and recovery of K2CO3 catalyst were also evaluated. The results showed that K2CO3 catalyst lowered the sintering temperature of coal ash, and the agglomeration tendencies increased with increasing amount of K2CO3. The presence of K–Ca–Fe phases was responsible for the agglomeration in CCG pressurized fluidized bed gasifier. The sintering temperature of coal ash increased, and no agglomeration occurred after the addition of water-washed ash. A good correlation was established between the sintering temperature and acid/basic (A/B) ratio in CCG atmosphere at 3.5MPa, and the sintering temperature increased with increasing A/B ratio in ash. The addition of water-washed ash did not decrease the gasification activity or water-soluble potassium recovery. This technique effectively prevented agglomeration in the pressurized fluidized bed gasifier.

Application of life cycle thermo-ecological cost methodology for evaluation of biomass integrated gasification gas turbine based cogeneration

Biomass integrated gasification cogeneration is nowadays considered as one of the most attractive technologies for CO2 emission reduction and non-renewable fuel savings. The paper presents application of the Thermo-Ecological Cost (TEC), which expresses the cumulative consumption of non-renewable exergy, for examination of energy and environmental benefits of biomass energy conversion plant based on gasification technology and medium scale recuperative gas turbine. To express the total effect of considered energy conversion systems the TEC is supplemented with the data resulting from Life Cycle Analysis (LCA). Different available gasification technologies and configurations of a cogeneration plant are investigated. Atmospheric fluidized bed gasification (AFB), pressurized fluidized bed gasification (PFB) and allothermal gasification using pure steam as gasification agent (FICFB) are taken into account as well as simple and combined power cycles with the Mercury 50 Solar gas turbine. The results reveal that simple cycle with gas turbine and waste heat recovery water boiler offers better effects than combined cycle configuration. The best performance has been reported for pressurized gasification technology.

H2 rich gas production via pressurized fluidized bed gasification of sawdust with in situ CO2 capture

The continuous increase in energy demand and the growing attention on global warming worldwide have aroused great research interest in a novel near zero emission energy utilization system which is based on CaO sorption enhanced gasification. This paper presents the experimental results of pressurized CaO sorption enhanced sawdust gasification in a self-design pressurized fluidized bed gasifier, aiming to survey the effects of reaction pressure, CaO to carbon mole ratio (CaO/C), steam to carbon mole ratio (H2O/C) and reaction temperature (T) on hydrogen (H2) production under pressurized gasification conditions. Results showed that the pressurized operation not only promoted gasification reactions, but also apparently enhanced CaO carbonation. Within the experimental ranges investigated in this work, H2 fraction and H2 yield were both elevated with the increase in reaction pressure, CaO/C, H2O/C and T. Comparing with previous atmospheric fluidized bed gasification results, pressurized gasification was capable of producing syngas with higher H2 fraction and lower CO2 fraction even at lower CaO/C, H2O/C and T. It was also verified that pressurized operation increased the carbon conversion and cold gas efficiency for CaO sorption enhanced sawdust gasification.

Measurement of Residence Time Distributions of Coal Particles in a Pressurized Fluidized Bed Gasifier (PFBG) using Radio Tracer Technique

A pressurized fluidized bed gasifier (PFBG) system of an integrated coal gasification and combined cycle (ICGCC) plant is designed to behave as a well-mixed flow system for coal; and any deviation from the well-mixed flow condition will deteriorate the performance and efficiency of the gasification system. This paper describes a radiotracer investigation carried out to measure RTDs of coal particles in a pilot-scale PFBG with objectives to determine mean residence time (MRT) of coal/ash particles in the gasifier and estimate degree of mixing at different operating and process conditions. Lanthanum-140 labeled coal (100 gm) was used as a radiotracer. The tracer was instantaneously injected into the coal feed line and monitored at ash and gas outlets of the gasifier using collimated scintillation detectors. The measured RTD was used to determine mean residence time (MRT) of coal particles within the system and simulated using fractional tank-in-series model. The results of simulation indicated that the system behaved as a well-mixed system with undesired bypassing of a small fraction coal particle from the system. The results of the study were used to improve the design of the gasifier and optimize the system.

Measurement of Residence Time Distributions Of Coal Particles in a Pressurized Fluidized Bed Gasifier (PFBG) using Radio Tracer Technique

A pressurized fluidized bed gasifier (PFBG) system of an integrated coal gasification and combined cycle (ICGCC) plant is designed to behave as a well-mixed flow system for coal; and any deviation from the well-mixed flow condition will deteriorate the performance and efficiency of the gasification system. This paper describes a radiotracer investigation carried out to measure RTDs of coal particles in a pilot-scale PFBG with objectives to determine mean residence time (MRT) of coal/ash particles in the gasifier and estimate degree of mixing at different operating and process conditions. Lanthanum-140 labeled coal (100 gm) was used as a radiotracer. The tracer was instantaneously injected into the coal feed line and monitored at ash and gas outlets of the gasifier using collimated scintillation detectors. The measured RTD was used to determine mean residence time (MRT) of coal particles within the system and simulated using fractional tank-in-series model. The results of simulation indicated that the system behaved as a well-mixed system with undesired bypassing of a small fraction coal particle from the system. The results of the study were used to improve the design of the gasifier and optimize the system.

Critical factors for high temperature processing of biomass from agriculture and energy crops to biofuels and bioenergy

The demand for biomass for the production of energy in the forms of electric power, heat, and liquid fuels is growing fast over the last few years worldwide, mainly due to environmental concerns regarding the use of fossil fuels, such as coal, and oil. Agricultural residues, such as wheat straw, olive residue, and corn stover, as well as energy crops, e.g., Arundo donax, miscanthus, and switchgrass gain more and more interest as feedstocks to supply the vast amounts of biomass needed in order to produce the energy and liquid fuels required to fulfill the Kyoto protocol and reduce the environmental burdens of using fossil fuels in our planet. Biomass feedstocks can be converted to energy vectors in high‐efficiency thermochemical systems, such as pressurized fluidized bed boilers and gasifiers coupled with Fischer–Tropsch or other types of liquid fuel synthesis units, supercritical combustion units, and entrained flow combustors or gasifiers. This use is presently limited by the ash‐related problems associated with high‐temperature/high‐pressure environments. Inorganic bioresource constituents, such as alkali metals, chlorine, sulfur, and phosphorus, are the most troublesome elements responsible for several problems occurring. This paper presents a critical discussion regarding the main factors affecting the use of biomass of both agricultural residues and energy crops in high temperatures and high‐efficiency thermochemical conversion systems for the production of energy and liquid fuels. On the basis of an analysis of the particular problems, we identify solutions that could resolve these problems and assist significantly with a much higher production of energy and fuels from various biomass sources in an economical and sustainable way.This article is categorized under: Bioenergy > Science and Materials Energy Policy and Planning > Science and Materials

Co-production system of hydrogen and electricity based on coal partial gasification with CO2 capture

To solve the problems of high cost and low efficiency of conventional co-production system of hydrogen and electricity with low hydrogen-to-electricity ratio, a novel co-production system based on coal partial gasification with CO2 capture is proposed and thermodynamically analyzed. The new system integrates the conceptions of cascade conversion of coal and cascade utilization of syngas to realize the system with high efficiency, low cost, environmental friendliness and flexible hydrogen-to-electricity ratio. The performance of the new system is evaluated by an Aspen Plus model and effects of the operating conditions are also studied. It is found that the system with capturing CO2 of 59.7% and hydrogen-to-electricity ratio of 4.76 holds a high exergy efficiency of 54.3% when the carbon conversion ratio of the pressurized fluidized bed (PFB) gasifier is equal to 0.7. The carbon conversion ratio of the PFB gasifier is a dominant factor to decide the performance of system. In comparison with the series-type co-production system, the parallel-type co-production system and separate production system, the new system proposed in this study has exergy-saving efficiency of 17.7%, 15.1% and 8.9%, respectively.

Fusion Characteristics of Ash Residues from Lignite Gasification

Fusion characteristics of ash residues from Xiaolongtan lignite pressurized fluidized-bed gasification were investigated with ash fusion point detector and sintering temperature analyzer. The results show that the sintering temperature (Ts) and ash fusion temperature (AFT) of three ashes residues decrease from gangue ashes to agglomerate to slag, which result from the differences of mineral type and content in three ash residues, and the decrease of the total basic constituents increases the AFT. The formations of three ash residues during gasification are the interactions among mineral matter and their transformations under high temperature.

Upgrading of Raw Gas from Biomass and Waste Gasification: Challenges and Opportunities

The depletion of fossil fuel-based resources and concerns for increasing emissions of CO2 call for new ways of producing environmentally-friendly substitutes for motor fuels and chemicals. Thermo-chemical conversion of biomass and waste using gasification is a strong candidate to meet these challenges. For efficient and cost-effective application of this technique, novel solutions for hot gas cleaning are needed. This review highlights some important areas for improvement of upgrading technologies for pressurised fluidised bed gasification systems using biomass as a fuel.

Effect of Conical Distributor Parameters on the Fluidisation Characteristics of Cylindrical Fluidised Bed Reactors

Integrated gasification combined cycle (IGCC) is one of the most advanced power generation technologies. The normal approach to design a commercial size pressurised fluidised bed gasifier (PFBG) for IGCC is based on large-scale pilot plant experimentation or scale-up of hydrodynamically similar cold model. The conical distributor is a critical component of PFBG, which affects the hydrodynamic performance of the fluidiser. A correlation to bring out the effect of distributor apex angle a on fluidisation quality has been developed and presented in this paper. The correlation has been validated with that of Antoni Lucas et al. [1]. The average deviation and standard deviations of the correlation are 6.8 and 27%, respectively. The experimental results show that minimum fluidising velocity increases with increase in a. The bed voidage derived from Ergun's equation is found to decrease with increase of a indicating better fluidisation quality. This paper aims to study the fluidisation characteristics of cylindrical fluidised bed reactors with varying apex angle of conical distributor and derive a correlation of Reynolds number at minimum fluidising velocity as a function of Archimedes number and apex angle of the distributor.

プラント規模を考慮したBio-DME製造システムに係るLCA

Objective. In this paper, we focused on Bio-DME (Biomass Di-methyl Ether) in BTL (Biomass-to-Liquid) fuel liquefaction system through a gasification process. Based on the bottom-up methodology, the inventories of CO2 emissions and energy intensities were estimated. In the system boundary, the sub-systems of the pre-processing, the energy conversion, and the fuel transportation were included. Considering the scale and the operational conditions (an inner pressure and a reaction temperature) of BTL plant, the inventories were estimated. Also, the uncertainties in the pre-processing, that is, the moisture content of biomass materials and the transportation distance to the plant were simulated by the Monte Carlo simulation. In the pre-processing, there were three processes of chipping, transportation and dryer. In the energy conversion, we executed the process design on the following two types; the medium scale of BTL plant through pressurized fluidized bed gasification and the small one through BLUE Tower (BT) process were assumed. Both plants have a liquefaction process. Also, due to the process design, the auxiliary power of each plant was considered. In addition, the liquefied fuel (Bio-DME) was assumed to be delivered using a 10 kL tank lorry.Results and Discussion. As the results, in the small scale plat (BT process), CO2 emissions of 45.8-60.5 g-CO2 /MJ and energy intensities of 1.44-1.63 MJ/MJ were obtained. Conversely, In the medium one, CO2 emissions of 22.5-51.6 g-CO2/MJ and energy intensities of 0.29-0.66 MJ/MJ were obtained. Conclusions. From the viewpoint of the environmental statement, Bio-DME was likely to be superior to DME of natural gas origin.

Numerical simulation of coal gasification at circulating fluidised bed conditions

This paper presents modelling results for a new pressurised fluidised bed gasifier concept, called the Power High-Temperature Winkler gasifier (PHTW gasifier). The numerical simulation of the steam/oxygen blown and lignite-fuelled power plant gasifier is performed on the 4800 t/day (1000 MW) at a pressure of 33 bar. The formation of flow pattern, turbulence, product gas composition, temperature, and radiation heat transfer were investigated. Influence of diameter variation on the flow patterns at constant operating conditions is presented. A comparison between the calculation and literature data of similar fluidised bed systems shows good conformance. To anticipate the solid's behaviour, particle concentration, particle size change due to pyrolysis and surface reactions, and particle tracks were modelled using an Eulerian–Lagrangian approach. While varying the total particle mass flow, the pressure drop as a function of reactor height was observed.

The fate of fuel-nitrogen during gasification of biomass in a pressurised fluidised bed gasifier

The distribution of fuel-nitrogen in gases, tar and char from gasification of biomass in a pressurised fluidised bed gasifier was investigated. Four species of biomass: birch, Salix, Miscanthus and Reed canary grass were gasified at 0.4 MPa and 900 °C. Oxygen-enriched nitrogen was used as fluidising agent. As a reference, gasification of Daw Mill coal was also carried out under the same experimental conditions. The experimental results illustrate that both the nature of the original fuels and the chemical structure of the nitrogen in the fuel have influence on the distribution of fuel-nitrogen in gases (NH 3, HCN, NO), tar and char under the employed experimental conditions. The present work also shows that the types of nitrogen heterocyclic compounds (NHCs) in the tar from different kinds of biomass are the same and the major compound is pyridine. However, the distribution of the various NHCs in the tar from the four species of biomass varies: the higher the content of fuel-nitrogen, the higher the concentration of two-ring NHCs in the tar. An effective method for extracting NHCs from the acidic absorption of the product gas was introduced in the present work. The method makes use of solid phase extraction (SPE) by a silica-based C 18 tube to extract the NHCs which subsequently were analysed by gas chromatography (GC) with flame ionisation detection (FID). The recovery and reproducibility of the SPE technique for NHCs is discussed.