Two-stage Gasification Process Research Articles

Simulation Research on the Fixed-Bed Gasification Process in a Two-Stage Combined Gasifier

The novel two-stage gasification process that is combined entrained-flow for first stage and fixed-bed for second stage was shown in the study. The benefit of the second stage was to recycle the sensible heat from first stage syngas and enhance the energy utilization. The fixed-bed gasification reaction of second stage was individually investigated by numerical simulation. The simulated results were validated well with the experimental data in terms of gas concentration, gas flow rate, and carbon conversion. The distributions of velocity, temperature, gas concentration, solid mass fraction, and carbon conversion during the gasification process were analyzed. The influences of coal amount and particle size in the second stage on gasification reactivity were also discussed in the study. Results showed that the gas temperature was reduced and the effective gas concentration increased when first stage syngas flowing through the second stage coal layer. The increase of coal amount of second stage showed a more significant heat recovery, but the heating rate and ultimate carbon conversion would be reduced. The increase of particle size resulted in the decreasing of effective gas concentration and gas–solid reaction rate, which was attributed to the change of specific surface area and the increase heat transfer resistance from the particle surface to inside.

Energy and exergy analysis of gas production from biomass intermittent gasification

In this paper, thermochemical biomass intermittent gasification was performed in a fluidized-bed reactor with pure steam as gasification agent. A single fluidized bed two-stage gasification process, also known as intermittent gasification process, which involves the time segregated hybridization of coal-combustion and steam biomass-gasification stages in the same vessel, was employed. This research aims to explore the influences of gasification temperature (T) and steam-biomass ratio (S/B) on composition, energy and exergy distribution, as well as energy and exergy conversion efficiencies of the product gas (biomass-gas). Over the ranges of the test conditions used, the total concentration of H2 and CO in the biomass-gas varies between 57.9% and 80.8%, and the exergy and energy efficiencies of the biomass-gas are in the ranges of 54.61%–35.52% and 82.91%–60.78%, respectively. The results show that the chemical exergy values of the biomass-gas are 13.50 to 17.71 times as the corresponding physical exergy values, whereas the chemical energy values are 6.91 to 9.45 times as the corresponding physical energy values. The total energy values of the biomass-gas are higher than the corresponding exergy values, this result in higher energy efficiencies of the biomass-gas. Higher temperature contributes to higher CO and H2 content, physical and chemical energy values, physical and chemical exergy values, as well as energy and exergy efficiencies of the biomass-gas. The steam to biomass ratio is optimal in the intermediate levels for maximal energy and exergy efficiencies of the biomass-gas.

The influence of partial oxidation mechanisms on tar destruction in TwoStage biomass gasification

TwoStage gasification of biomass results in almost tar free producer gas suitable for multiple end-use purposes. In the present study, it is investigated to what extent the partial oxidation process of the pyrolysis gas from the first stage is involved in direct and in-direct tar destruction and conversion. The study identifies the following major impact factors regarding tar content in the producer gas: oxidation temperature, excess air ratio and biomass moisture content. In a experimental setup, wood pellets were pyrolyzed and the resulting pyrolysis gas was transferred in a heated partial oxidation reactor and oxidized between 800 and 1050°C with excess air rations between 0 and 0.7 and fuel moisture content between 8% and 30%. The gas composition was analyzed before and after oxidation by means of gas chromatography and mass spectrometry. The tar compounds were sampled by solid phase adsorption and determined by stable isotope dilution analysis. The results have shown that partial oxidation reduces and converts primary tars into low molecular weight, polycyclic aromatic hydrocarbons (PAHs), primarily naphthalene. At temperatures above 950°C practically all phenol is converted. The resulting PAH tar compounds are readily converted in the subsequent char-bed of the TwoStage gasification process and the partial oxidation process thus contributes directly as well as in-directly to the overall tar destruction. A high temperature and excess air ratios contribute positively to the direct tar destruction and a high moisture content of the biomass enhances the decomposition of phenol and inhibits the formation of naphthalene. This enhances tar conversion and gasification in the char-bed, and thus contributes in-directly to the tar destruction.

Gas Upgrading in a Downdraft Fixed-Bed Reactor Downstream of a Fluidized-Bed Coal Pyrolyzer

A new two-stage gasification process, consisting of a fluidized-bed (FB) pyrolyzer and a downdraft fixed-bed (DFB) gasifier, has been proposed to gasify powder coal for fuel gas production with low tar generation. Aiming at developing the new technology, this paper investigated the means for coal pyrolysis gas upgrading, with the focus on tar removal by both thermal cracking with or without the presence of oxygen and catalytic cracking or reforming over a char bed in a fixed-bed reactor downstream of a FB coal pyrolyzer. The presence of oxygen and the adoption of a char bed evidently facilitated the tar removal performance and also improved the produced fuel gas quality. Analyzing the tar sample collected at the outlet of the tar removal reactor with gas chromatography-mass spectrometry (GC-MS) clarified that the oxidation by O(2) and the char-catalyzed reforming both exhibited certain selectivity to the tar-containing chemical species. In addition, the property of char played an important role on its catalytic activity. The higher the specific surface area, the better the activity of char for removing tar. The spent char showed a much reduced specific surface area of micropores but evidently elevated the specific surface area of mesopores, even by up to 3 times. The tests with the metal oxides impregnated onto the demineralized char demonstrated that both Ca and Fe oxides enabled better catalytic activity for tar removal than Na and Mg oxides. This study clarified as well that the viable operating conditions for tar removal in a char bed were at 1100 degrees C with an excessive air ratio (ER) of 0.04 and gas residence time above 1.3 s.

Experimental simulation of hard coal underground gasification for hydrogen production

The main objective of this study was the assessment of the feasibility of applying the underground hard coal gasification in the production of a hydrogen-rich gas. In the course of the experiment the so-called two-stage gasification process in which oxygen and steam were supplied to the reaction zone separately in alternate stages was investigated. For this purpose a special surface reactor has been constructed, in which the underground conditions were to be imitated both in respect to the coal seam and the surrounding rock layers. The surface simulation of the underground gasification was carried out on extra large coal samples, which allowed the recreation of near real underground conditions. In the reactor an experiment lasting almost 7days has been performed, with the average hourly gas yields of 7.8m3/h and 9.2m3/h for the oxygen and the steam gasification stages, respectively. The average hydrogen concentration during the oxygen stage (heating up) was 15.28% with the maximum of 54.4%. The average hydrogen concentration during the steam stage was 53.77% with the maximum of 62.90%. Thus the feasibility of hydrogen-rich gas production in the process of underground gasification of hard coal has been demonstrated. During the course of the surface experiment an original and unprecedented database of temperature profiles has been acquired which now constitutes an invaluable source of thermodynamic information for the prospective underground gasification activities.

Coal Pyrolysis in a Fluidized Bed for Adapting to a Two-Stage Gasification Process

Coal pyrolysis is generally performed in atmospheres without oxygen and at temperatures below 650 °C for producing pyrolysis liquid and gas. To support the development of a new two-stage gasificati...

Optimum operating conditions for a two-stage gasification process fueled by polypropylene by means of continuous reactor over ruthenium catalyst

We studied fuel gas production by means of pyrolysis and steam reforming of waste plastics for applications in solid oxide fuel cells. More specifically, we evaluated the effects of pyrolytic gasification temperature, catalyst content, steam reforming temperature, and weight hourly space velocity for a Ru catalyst used in a 60 g h − 1 -scale continuous experimental apparatus, which consisted of a tank reactor for pyrolysis and a packed-bed catalytic reactor for steam reforming. Polypropylene (PP) pellets were used as a model waste plastic. Ru/γ-Al 2O 3 catalysts with two different Ru contents were investigated. To suppress residue formation, the optimum operating temperature of the pyrolyzer was 673 K. To ensure suppressed coke formation, sufficient carbon conversion to gaseous products, and minimized heat loss from the reactor, the optimum operating conditions for the reformer were determined to be 903 K and 0.11 g-sample g-catalyst − 1 h − 1 with a 5 wt.% Ru/γ-Al 2O 3 catalyst. The composition of the gas produced with the 5 wt.% catalyst was almost the same as that predicted by chemical equilibrium laws, and it was applicable for a direct hydrocarbon fuel cell.

P-204 バイオマスの2段階ガス化チャーガス化炉におけるタールの分解特性について(ポスター発表)

P-204 バイオマスの2段階ガス化チャーガス化炉におけるタールの分解特性について(ポスター発表)

加圧二段ガス化システム(EUP)

Waste plastics require the huge final disposal dump, or in case of incineration, chlorine contained in them generates poisonous substances such as dioxins. Pressurized two-stage gasification process (EUP) is a chemical recycling technology of waste plastics in place of fossil raw materials, and is contributing to the reduction of CO2 emissions.

EnergyAnswers' Operating Business acquired by Covanta

The EU landfill and Waste Framework directives are driving new approaches to waste management in the UK, away from landfilling and mass-burn incineration, which has been regarded as the main alternative to landfilling. The objective of this study is to compare the environmental impacts of three dual-stage advanced energy-from-waste technologies, i.e. gasification and plasma gas cleaning, fast pyrolysis and combustion and gasification with syngas combustion, with those associated with conventional treatments for municipal solid waste, i.e. landfill with electricity production and incineration with electricity production. Results show that the two-stage gasification and plasma process has a significantly better overall environmental performance than the conventional waste treatment technologies and somewhat better than a more modern incineration plant, exemplified by a plant under commissioning in Lincolnshire in the UK. The benefits of the gasification and plasma process arise primarily from its higher net electrical efficiency.

Thermodynamic Analysis of Supplementary-Fired Gas Turbine Cycles

This paper presents an analysis of the possibilities for improving the efficiency of an indi-rectly biomass-fired gas turbine (IBFGT) by supplementary direct gas-firing. The supplementary firing may be based on natural gas, biogas or pyrolysis gas. Intuitively, supplementary firing is expected to result in a high marginal efficiency. The paper shows that depending on the application, this is not always the case. The interest in this cycle arises from a recent demonstration of the feasibility of a two-stage gasification process through construction of several plants. The gas from this process could be divided into two streams, one for primary and one for supplementary firing. A preliminary analysis of the ideal, recuperated Brayton cycle shows that for this cycle any supplementary firing will have a marginal efficiency of unity per extra unit of fuel. The same result is obtained for the indirectly fired gas turbine (IFGT) and for the supplementary-fired IFGT. These results show that the combination of external firing and internal firing have the potential of reducing or solving some problems associated with the use of biomass both in the recuperated and the indirectly fired gas turbine: The former requires a clean, expensive fuel. The latter is limited in efficiency due to limitations in material temperature of the heat exchanger. Thus, in the case of an IBFGT, it would appear be very appropriate to use a cheap biomass or waste fuel for low temperature combustion and external firing and use natural gas at a high marginal efficiency for high temperature heating. However, it is shown that this is not the case for a simple IBFGT supplementary-fired with natural gas. The marginal efficiency of the natural gas is in this case found to be independent of temperature ratio and lower than for the recuperated gas turbine. Instead, other process changes may be considered in order to obtain a high marginal efficiency on natural gas. Two possibilities are discussed: Integration between an IFGT and pyrolysis of the biofuel which will result in a highly efficient utilization of the biomass, and integration between external biomass firing, and combined internal biomass and natural gas firing.

Advanced two-stage gasification system. 1. Experimental results

This paper, which describes an advenced two-stage gasification system, consists of two parts: part 1 describes the experimental results, and part 2 describes the process evaluation. In part 1, Avco's concept of two-stage coal gasification that utilizes very rapid coal pyrolysis is reviewed. Its potential technical and economic advantages are also reviewed. The system design studies (part 2) show that, when the experimental data on the rapid pyrolysis operation are incorporated into a two-stage gasification process design, distinct economic advantages over available single-stage processes can be projected