Some studies on a solid state sulphur probe for coal gasification system

Measurements on the solid electrolyte cell(Ar -b H2 ~ H2S/CaS + CaF2 ~- ( P t ) / / C a F 2 / / ( P t )-~- CaF2 ~ CaS/H2S ~- H2 ~- At) show that the emf of the cell is directly related through the Nernst equation to the difference in sulfur potentials established at the two Ar ~- H2 ~ H2S/electrode interfaces. The electrodes are designed to convert the sulfur potential gradient across the calcium fluoride electrolyte into an equivalent fluorine potential gradient with the aid of the reaction, CaF2(s) ~ 1~ S2(g)-e CaS(s) ~- F2(g). The response time of the probe varies from approximately 9 hr at 990~ to 2.5 hr at 1225~ The conversion of calcium sulfide and/or calcium fluoride into calcium oxide should not be a problem in anticipated commercial coal gasification systems. Suggestions are presented for improving the cell for such commercial applications.

Intelligent prediction of ground vibration in coal formations using ANN

The present paper details the prediction of blast induced ground vibration, using artificial neural network. The data was generated from five different coal mines. Twenty one different parameters involving rock mass parameters, explosive parameters and blast design parameters, were used to develop the one comprehensive ANN model for five different coal bearing formations. A total of 131 datasets was used to develop the ANN model and 44 datasets was used to test the model. The developed ANN model was compared with the USBM model. The prediction capability to predict blast induced ground vibration, of the comprehensive ANN model was found to be superior.

Burning Low Volatile Fuel in Tangentially Fired Furnaces with Fuel Rich/Lean Burners

Pulverized coal combustion in tangentially fired furnaces with fuel rich/lean burners was investigated for three low volatile coals. The burners were operated under the conditions with varied value N-d, which means the ratio of coal concentration of the fuel rich stream to that of the fuel lean stream. The wall temperature distributions in various positions were measured and analyzed. The carbon content in the char and Nox emission were detected under various conditions. The new burners with fuel rich/lean streams were utilized in a thermal power station to burn low volatile coal. The results show that the N-d value has significant influences on the distributions of temperature and char burnout. There exists an optimal N-d value under which the carbon content in the char and the Nox emission is relatively low. The coal ignition and Nox emission in the utilized power station are improved after retrofitting the burners.

Numerical Simulation of Nox Formation in Coal Combustion with Inlet Natural Gas Burning

A full two-fluid model of reacting gas-particle flows and coal combustion is used to simulate coal combustion with and without inlet natural gas added in the inlet. The simulation results for the case without natural gas burning is in fair agreement with the experimental results reported in references. The simulation results of different natural gas adding positions indicate that the natural gas burning can form lean oxygen combustion enviroment at the combustor inlet region and the NOz concentration is reduced. The same result can be obtained from chemical equilibrium analysis.

Interactions of CO, HCl, and Sox in Pulverised Coal Flames

The effect of HCl and SO_2 on CO oxidation in pulverised coal flames was investigated experimentally and kinetically in an entrained flow combustion reactor. Two bituminous coals (German 'Goettelborn' and a Polish coal) were used as fuels with a feeding rate of 1 or 1.5 kg/h. HCl or SO_2 is introduced into the reactor premixed with the primary air. Experimental results indicate that HCl addition may inhibit CO oxidation in coal flames and increases CO emission. Reducing temperature in the reactor will enhance the inhibitory effect of HCl on CO oxidation. The measured CO profiles along the reactor height clearly show that the addition of HCl may inhibit CO oxidation. In the experimental range of SO_2 addition. The inhibiting effect of SO_2 on CO oxidation is less significant than HCl. A detailed kinetic mechanism is used to model the reactions. And the controlling reactions are analysed.

The production of separate streams of pure hydrogen and carbon dioxide from coal via an iron-oxide redox cycle

A chemical looping process using the redox reactions of iron oxide has been used to produce separate streams of pure H2 and CO2 from a solid fuel. An iron oxide carrier prepared using a mechanical mixing technique and comprised of 100wt.% Fe2O3 was used. It was demonstrated that hydrogen can be produced from three representative coals - a Russian bituminous, a German lignite and a UK sub-bituminous coal. Depending on the fuel, pure H2 with [CO] ≲50vol.ppm can be obtained from the proposed process. The cyclic stability of the iron oxide carrier was not adversely affected by contaminants found in syngas which are gaseous above 273K. Stable quantities of H2 were produced over five cycles for all three coals investigated. Independent of the fuel, SO2 was not formed during the oxidation with steam, i.e. the produced H2 was not contaminated with SO2. Since oxidation with air removes contaminants and generates useful heat and pure N2 for purging, it should be included in the operating cycle. Overall, it was demonstrated that the proposed process may be an attractive approach to upgrade crude syngas produced by the gasification of low-rank coals to pure H2, representing a substantial increase in calorific value, whilst simultaneous capturing CO2, a greenhouse gas. © 2010 Elsevier B.V.

Studies of the Effect of a Coal Concentrator on NO Formation in Swirling Coal Combustion

To develop low-pollution burners, the effect of a coal concentrator on NO formation in swirling coal combustion is studied using both numerical simulation and experiments. The isothermal gas-particle two-phase velocities and particle concentration in a cold model of swirl burners with and without coal concentrators were measured using the phase Doppler particle anemometer (PDPA). A full two-fluid model of reacting gas-particle flows and coal combustion with an algebraic unified second-order moment (AUSM) turbulence-chemistry model for the turbulent reaction rate of NO formation are used to simulate swirling coal combustion and NO formation with different coal concentrators. The results give the turbulent kinetic energy, particle concentration, temperature and NO concentration in cases of with and without coal concentrators. The predicted results for cold two-phase flows are in good agreement with the PDPA measurement results, showing that the coal concentrator increases the turbulence and particle concentration in the recirculation zone. The combustion modeling results indicate that although the coal concentrator increases the turbulence and combustion temperature, but still can remarkably reduce the NO formation due to creating high coal concentration in the recirculation zone.

Coflow jets with large velocity difference - a new aerodynamic principle of flame stabilization and combustion intensification

A new aerodynamic principle of flame stabilization and combustion intensification, the coflow jets with large velocity difference, is described. One or more small high-velocity jets of air or steam, injected off the axis and in the same direction as the low-velocity main fuel-air flow into the combustor, create a large recirculation zone of high turbulence intensity in which the combustibles and high temperature gases are effectively mixed, so that stable and intensive combustion can be maintained even for fuels with poor ignition. A pulverized coal combustor based on the principle mentioned above is shown to be characteristic of excellent combustoom and a simple structure. A number of precombustors of this type are in operation at some power stations and industrial boilers of China. Using such precombustor, successtul startups and part-load operation of the boilers have become available under conditions of unpreheated air and low-grade coal with volatiles as low as 15% and ash content as high as 30%. This principle shows good promise as an attractive new technology of combustion.

Income risk of EU coal-fired power plants after Kyoto

Coal-fired power plants may enjoy a significant advantage relative to gas plants in terms of cheaper fuel cost. Still, this advantage may erode or even turn into disadvantage depending on CO2 emission allowance price. This price will presumably rise in both the Kyoto Protocol commitment period (2008-2012) and the first post-Kyoto years. Thus, in a carbon-constrained environment, coal plants face financial risks arising in their profit margins, which in turn hinge on their so-called "clean dark spread". These risks are further reinforced when the price of the output electricity is determined by natural gas-fired plants' marginal costs, which differ from coal plants' costs. We aim to assess the risks in coal plants' margins. We adopt parameter values estimated from empirical data. These in turn are derived from natural gas and electricity markets alongside the EU ETS market where emission allowances are traded. Monte Carlo simulation allows to compute the expected value and risk profile of coal-based electricity generation. We focus on the clean dark spread in both time periods under different future scenarios in the allowance market. Specifically, bottom 5% and 10% percentiles are derived. According to our results, certain future paths of the allowance price may impose significant risks on the clean dark spread obtained by coal plants.

煤粉燃烧中NO_x和SO_x生成的详细反应机理模拟

采用详细化学反应机理与CFD方法耦合的煤粉燃烧数值模拟程序,计算了煤粉燃烧过程中CO,NOx和SOx等的浓度分布特性.通过与实验对照,验证了数值模拟方法的可靠性,并分析了燃烧温度和煤粉细度等因素对于NO生成的影响.结果表明温度对于NO的生成影响较大,随着温度的增加, NO的生成浓度明显增加;对于不同煤种,可能存在一个温度点,这时NO的生成速率将非常快;在计算范围内,温度对SO2的最终生成浓度没有明显影响,而只影响SO2的释放过程.煤粉细度对于NO生成有较小的影响.

The Characteristics of Semi-Cokes --The Solid Residues from Coal Partial Gasification

In this paper the proximate analysis and ultimate analysis of sulfur in different semi-cokes generated from Rizhao bituminous coal and Beijing anthracite under different temperatures is done. Also the tendency of the contents of volatile, ash, fixed carbon and sulfur in different semi-cokes along with the different preparation temperatures is studied. Then the combustion experiment of semi-cokes in the drop-tube furnace system was carried out, and the kinetic parameters of different semi-cokes ware calculated.

Chemical equilibrium analysis and CFD simulation of coal combustion and NOx formation

A full two-fluid model of reacting gas-particle flows with an algebraic unified second-order moment (AUSM) turbulence-chemistry model is used to simulate Beijing coal combustion and NOx formation. The sub-models are the k-epsilon-kp two-phase turbulence model, the EBU-Arrhenius volatile and CO combustion model, the six-flux radiation model, coal devolatilization model and char combustion model. The blocking effect on NOx formation is discussed. In addition, the chemical equilibrium analysis is used to predict NOx concentration at different temperature. Results of CID simulation and chemical equilibrium analysis show that, optimizing air dynamic parameters can delay the NOx formation and decrease NOx emission, but it is effective only in a restricted range. In order to decrease NOx emission near to zero, the re-burning or other chemical methods must be used.