High Pressure Coal Research Articles

High pressure CO2 gasification of Morupule coal: Kinetics and morphological development of chars

A direct gasification approach, coupling pyrolysis and gasification, was employed to study the kinetics of Morupule coal gasification in CO2 using a wire-mesh reactor (WMR) at elevated pressures (up to 20 bara) and temperatures of 900 °C and 1000 °C. A novel non-destructive analytical technique based on X-Ray computed tomography (CT) was used, for the first time, in conjunction with scanning electron microscopy (SEM) to unravel the morphological evolution of pyrolysis and gasification chars produced from the WMR. Lower total volatile yields were obtained at high pressures compared to atmospheric pressure for 0 s (quenching the reaction upon reaching temperature) holding time experiments. A temperature dependence of the gasification reaction rate at elevated pressures was observed. At 900 °C, increasing the pressure beyond 10 bara did not yield a commensurate increase in the reaction rate. Further increases in pressure to 20 bara at 1000 °C led to a pronounced increase in the reaction rate. The applicability of the Langmuir – Hinshelwood (L – H) rate model was investigated and showed a suitable characterisation of the gasification kinetics driven by a CO2 chemisorption-limited reaction mechanism. X-Ray CT imagery reveal the development of an internal macroporosity produced by the explosive release of volatiles during pyrolysis. In contrast, SEM images indicate that high pressure coal gasification is characterised by the development of micropores, with a rapid consumption of the outer char surface.

Optimization Design and Numerical Investigation on Ball Valve of High Pressure Coal Slurry Pump

The charging flow rate fluctuation of the coal slurry pump was caused by the ball valve. In this study, the reconstruction was established to increase the circulation area surrounding the valve ball, the valve limiter was redesigned. The numerical simulation of the structure and performance of the ball valve is carried out with the new limiter structure, getting the flow resistance and the operational parameters The simulation results showed that the new limiter can effectively eliminate the flow fluctuation caused by the old limiter, the reform was successful to bring huge economic benefits to the plant.

Design and Development of a High-Pressure Coal and Biomass Feeder

Coal and biomass pyrolysis and gasification has gained importance in the last few decades for synthetic fuel synthesis, which is a promising solution to the current energy crisis. Efficient fuel feed is necessary to the coal and biomass utilization processes. Common gasification systems employ large-scale slurry feeders to inject the fuel into the gasifier vessel. The presence of excess water in the slurry mixture demands a large energy input that reduces the overall process efficiencies. Dry feed systems are attractive alternatives to slurry feed systems to achieve higher efficiencies. However, high pressures inherent to most gasifier systems and difficulties with particle handling contribute to unpredictable mass flow rates. In this study, the behavior of coal and biomass dry feed has been investigated using a novel, motor-driven screw feeder designed to operate at high pressures. Experimental mass flow rate results were compared with existing theoretical models. The experiments were conducted for three types of feedstock: bituminous coal (< 150 μm), anthracite coal (< 44 μm), and coconut char (< 50 μm). The calibration study at high pressure shows repeatable results and close agreement with theoretical calculations. The results suggest that dry feeding of pulverized material under high-pressure conditions can be accomplished given careful optimization of the system parameters. This technology of high-pressure particle handling is extremely transformative and would ultimately benefit various industries including pharmaceuticals, biofuel refineries, and pulverized coal power plants.

Experimental investigation of high temperature and high pressure coal gasification

Pyrolysis and gasification behavior is analyzed at operation conditions relevant to industrial scale entrained flow gasifiers. A wire mesh reactor and the Pressurized High Temperature Entrained Flow Reactor (PiTER) are used to measure volatile yield of Rhenish lignite, a bituminous coal and German anthracite at high temperature and high pressure. In the wire mesh reactor at 1000 °C a significant influence of pressure on volatile yield is observed. For lignite the volatile yield (daf) decreases from 57 wt% at atmospheric pressure to 53 wt% at 5.0 MPa. In the same pressure interval the volatile yield of the bituminous coal strongly decreases, whereas no significant influence of pressure on the volatile yield of anthracite is detected. In entrained flow experiments (PiTER) at higher temperature and 0.5 MPa an enhanced devolatilization of the lignite is observed. At 1200 °C, the maximum volatile yield is 62 wt% and it increases to 67 wt% at 1400 °C. In entrained flow gasification experiments with Rhenish lignite a high level of conversion is measured at atmospheric pressure and at 0.5 MPa. At both pressures, coal conversion increases with temperature and residence time. The highest conversion of 96 wt% is achieved at a particle residence time of 1.3 s, at a temperature of 1600 °C, and a pressure of 0.5 MPa. The experimental results show a large influence of operation parameters on pyrolysis and gasification behavior of Rhenish lignite. The volatile release in the pyrolysis stage and the high level of conversion after a short residence time indicate that Rhenish lignite is suitable for gasification in an entrained flow reactor. The reactivities of char samples that are collected from the hot reaction zone of the PiTER are measured in a pressurized thermogravimetric analyzer (PTGA) at lower temperature (600–850 °C). The pyrolysis temperature in the entrained flow experiments significantly influences the reaction rate in the PTGA at lower temperature. With increasing pyrolysis temperature (1200–1600 °C) a continuous loss of reactivity is observed.

Influence of coal thermoplastic properties on coking pressure generation: Part 2 – A study of binary coal blends and specific additives

A number of coal blends and pitch/coal blends were evaluated using rheometry, thermogravimetric analysis and microscopy to confirm and further elucidate the coking pressure mechanism previously proposed by Duffy et al. (2007) [1]. We confirm that blending a low rank, high fluidity, low coking pressure coal, with a high rank, low fluidity, high coking pressure coal can significantly reduce the coking pressure associated with the latter. Interestingly, blending does not necessarily result in a fluidity that is midway between that of the two coals; sometimes the fluidity of the blend is less than that of the low fluidity coal, especially when the coals are significantly different in rank. This occurs because the increase in complex viscosity ( η*) through resolidification of the low rank, high fluidity coal counteracts the reduction in η* resulting from softening of the high rank, low fluidity coal. It has also been confirmed that the η* of the resultant blend can be estimated from the η* of each component coal using a logarithmic additivity rule commonly employed for polymer blends. Polarised light microscopy has indicated that the degree of mixing between coals of different rank is minimal, with fusion restricted to the particle surface. It is therefore inappropriate to think of such a coal blend in the same way as a single coal, since each component coal behaves relatively independently. This limited fusion is important for understanding the coking pressure mechanism for blends. It is proposed here that the lower rank coal, which softens at lower temperature, is able to expand into the interparticle voids between the high rank coal that is yet to soften, and these voids can create channels for volatiles to traverse. Then, and importantly, when the high rank coal begins to expand, the pore structure developed in the resolidified structures of the low rank coal can facilitate removal of volatiles, while the resolidified material may also act as a suitable sorbent for volatile matter. This is considered to be the primary mechanism by which coal blending is able to alleviate coking pressure, and applies to addition of inert material also. Addition of a coal tar pitch was found to increase fluidity but also to extend the thermoplastic range to lower temperatures. This caused an increase in the swelling range, which was accompanied by a long plateau in η*, a feature which has previously been observed for certain high fluidity, high pressure coals. Elasticity and η* at the onset of expansion were also higher for both the pitch impregnated coals and the high pressure blends, which supports previous findings for singly charged high pressure coals, and confirms the potential use of such criteria for identifying potentially dangerous coals/blends.

Hydrogasification characteristics of bituminous coals in an entrained-flow hydrogasifier

The characteristics of hydrogasification to generate substitute natural gas (SNG) by using various bituminous coals such as Alaska, Cyprus, Curragh, and Datong have been determined in an entrained-flow hydrogasifier (0.025 m I.D.×1 m high) with high pressure coal feeder and data acquisition system. The effects of reaction pressure (60–80 atm), reaction temperature (600–800 °C) and H 2/coal ratio (0.3–0.5) on composition of product gas and carbon conversion have been determined. The concentration of SNG and carbon conversion increased with an increasing of reaction pressure and temperature, but the carbon conversion and concentration of each bituminous coal were quite different because of different coal properties. Also the H 2/coal ratio affected the carbon conversion and the concentration of SNG.

03/01616 Volatiles release and porosity evolution during high pressure coal pyrolysis: Tomeczek, J. and Gil, S. Fuel, 2003, 82, (3), 285–292

03/01616 Volatiles release and porosity evolution during high pressure coal pyrolysis: Tomeczek, J. and Gil, S. Fuel, 2003, 82, (3), 285–292

High-Pressure Coal Pyrolysis in a Drop Tube Furnace

To obtain useful and reliable pyrolysis data under high pressures, continuous pyrolysis experiments were carried out using a drop tube furnace. To ascertain the reliability of data, a mass balance during pyrolysis was carefully checked. The pyrolysis data obtained in this equipment was compared with previous results, and it was found that the weight loss observed in the drop tube furnace was somewhat larger than those obtained with other apparatuses. The experimental results were compared with those predicted by three pyrolysis models. Although discrepancies between predictions and experimental results were observed under a certain condition, the agreement between the experimental weight losses with three predictions was fairly good at 800 °C and 1 MPa with all the models. Product distribution was also reasonably predicted with the Flashchain model. It is desirable to further improve the models by comparing their predictions with more extensive and reliable experimental data.

Volatiles release and porosity evolution during high pressure coal pyrolysis

The kinetics of porosity and of porous structure evolution have been examined during enhanced pressure (0.1–3.0 MPa) pyrolysis for two subbituminous coals on the basis of volatiles release. It has been found that both the volatiles mass release and char porosity decrease with pyrolysis pressure. The behaviour of three pore size groups, 5–30, 30–300 and 300–5000 nm, were observed during pyrolysis. An almost total elimination of the first group (5–30 nm) was found so that the porosity build up was entirely within the third size group (300–5000 nm), particularly at 1 MPa pressure. During the stage of most intensive devolatilization the release of volatiles precedes the porosity evolution.

97/05161 Development of the moving granular bed filter: Haas, J. C. et al. Proc. Annu. Int. Pittsburgh. Coal Conf., 1996, 13, (2), 1290–1295

The moving bed granular is being developed under the auspices of the US Dept. of Energy. Recent activity focused on three areas: the development of chemically reactive filter media for the removal of alkali and particulate from high temperature, high pressure coal gas streams; cold flow tests of filter components; and the design and fabrication of a filter for testing at DOE`s Power Systems Development Facility. Screening test of clay sorbents for alkali and selected trace metals have identified the most promising sorbents. Extrusion and disk pelletization are used to produce sorbent pellets. Results on pellet strength and reactivity are presented. Cold flow tests addressed filter scale-up issues of gas distribution, filter medium flow and filter medium size. Results from the cold flow tests have been incorporated in the design of the filter to be test at the Power System Development Test Facility.

Materials performance in coal gasification environments

Two exposures were carried out in the gasifier of the Westinghouse Process Development Unit to evaluate the performance of a wide variety of candidate construction materials for hostile high temperature, high pressure coal gasification environments. The test materials included highly alloyed iron-, cobalt-, and nickelbase alloys as well as packaluminized iron-base alloxs. The corrosion damage was assessed, and the corrosion processes taking place were investigated in order to interpret the data obtained from the surveillance tests. In addition, corrosion rates and mechanisms were compared between the two pilot plant exposures and a laboratory simulation test, to determine if laboratory data can be extrapolated to predict materials life in pilot plant environments. The results showed that although consistent kinetic data cannot be obtained by combining all three tests, materials performance can be evaluated qualitatively. Also, the corrosion mechanisms operating during the pilot plant exposures and the laboratory experiments were found to be similar.

Analysis of the Chemical Structure of Coal by Means of Investigation on the high Pressure Hydrogenolysis Reaction Mechanism (IV)

Classification and determination of various oxygen containing groups in high pressure coal hydrogenolysis products was attempted. First the total OH group was trimethylsilylated and the silica in the produced trimethyl sikyl ether was determined by atomic absorption anakysis and at the sametime R-NH2 which undergoes silylation was measured and corrected. Next, using a different method the phenolic hydroxyl group was measured. Based on the above data, it became possible to divide the oxygen in the samples into ether type, phenolic hydroxyl type and alchohoholic hydroxyl type which were measured accordingly.Further the changes accompanying the course of hydrogenolysis of these oxygen containing structures were followed, and we arrived at the opinion that the phenolic hydroxyl group is produced by dissociation of ether type oxygen accompanying decrease the molecular weight arising from hydrogenolysis. Further, it was recognized that the hydroxyl group were removed along with the reaction course.

Mechanism of High Pressure Coal Hydrogenolysis of Taiheiyo Coal

Mechanism of High Pressure Coal Hydrogenolysis of Taiheiyo Coal

Analysis of the Chemical Structure of Coal by Means of Investigation on the High Pressure Hydrogenolysis Reaction Mechanism

High resolution NMR spectroscopy and other physical methods have been used for the study of the chemical structure of coal with the aid of chemical ultimate analysis by the conventional combustion method (JIS) and pyrolysis. However, a more precise ultimate analysis with special reference to oxygen is necessary in order to obtain a truly accurate determination of the chemical structure of coal. In the present report, a discussion was made on the precision of the fast neutron activation analysis for the determination of oxygen content of high pressure coal hydrogenolysis products. The following conclusionswere obtained.(1) A relative error of 2% was achieved by the present neutron activation analysis using gold as the internal standard and solid paraffine and graphite as diluents. It was demonstrated that the method is applicable in the determination of more than 0.2mg of oxygen in a sample of 200mg.(2) The relative error of the pyrolysis method was found to be 1-9% depending on the level of oxygen content in the samples. This method is applicable to samples containing more than 1.0% of oxygen.(3) Oxygen content determined indirectly by the combustion method results in a generally overestimation because of incomplete combustion of the samples used in our present work.