Frank Kluger

A Kinetic Model for the Prediction of NO Emissions from staged Combustion of Pulverized Coal

Emissions of nitrogen oxides from coal combustion are a major environmental problem because they have been shown to contribute to the formation of acid rain and photochemical smog. Air staging and the application of low-NOx burners are effective in reducing the In-furnace-formed NOx. Fuel staging, or reburning, is another effective method to reduce NOx emissions in the combustion chamber. For a successful application of these processes on industrial scale, the governing parameters must be evaluated very carefully. Computer modeling is an efficient tool for acquiring a better knowledge of the optimum process parameters. In order to predict NO emissions from furnaces operated with advanced combustion technologies, a knowledge of the fare of coal nitrogen during the combustion process is paramount. An advanced NOx model for staged combustion of pulverized coal is presented. It is closely connected to a coal combustion model that includes primary pyrolysis and secondary reactions of tars formed during primary pyrolysis. The present NOx model takes into account the different pathways of coal nitrogen release during primary and secondary pyrolysis, char, and soot combustion. The subsequent conversions of nitrogen-containing species comprise formation of NO from fuel nitrogen and air nitrogen (thermal NO) as well as reduction of NO by hydrocarbon and NHi radicals, char, and soot. The interaction between turbulence and chemistry is modeled by an advanced eddy dissipation concept (EDC). The NOx model is used to predict NO profiles that are compared to measurements obtained from combustion tests carried out at a bench-scale entrained-flow reactor. Comparisons are made for air-staged and fuel-staged combustion of pulverized coal using methane and coal as reburn fuel.

Thermodynamic Modelling of the Corrosive Deposits in Oxy-Fuel Fired Boilers

The aim to reduce the CO2-emissions has triggered the evaluation of new cycle concepts for power plants. For the coal-fired power plants, the oxy-fuel firing is a promising option for CO2- emission reduction. Here, the combustion takes place in a nitrogen-free atmosphere. The oxygen is separated from the air and burned in near-stoichiometric conditions with the fuel. The gas composition is significantly changed, when the combustion is changed from air-fired to oxy-fuel fired condition. For lignite, the carbon dioxide content is raised from 15 to 59vol% and the watercontent from 10 to ~32%. For the same fuel, the SO2-content in the flue gas increases by a factor of 3-4 to ~0.5%. These changed environmental boundary conditions will affect corrosion life of the materials especially on the water walls and the heat exchanger surfaces. Considering the significant changes in the combustion gas, the composition and the occurrence of the corrosive deposits has been evaluated with the thermodynamic modelling program ‘FactSage’. The chemical compositions of the deposits have been modelled for dried lignite from Germany. The results exhibit that the oxy-fuel firing will give a significant change in the atmosphere as well as in the deposit composition. Consequently, the corrosion rates of current used materials in air fired boilers need to be evaluated for the application in oxy-fuel fired boilers.

Operational Experience With High Efficiency Cyclones: Comparison Between Boiler A and B in the Zeran Power Plant — Warsaw, Poland

The two 450t/h CFB units of the Zeran heat and power plant in Warsaw, Poland, are nearly identical in design, except for the cyclones. While the first CFB unit Zeran A which was commissioned in 1995 had cyclones of a prior design, the second unit Zeran B, which went into operation in late 2001, was equipped with high efficiency cyclones with the latest technological developments. The impact of the cyclone design is clearly visible in the operational data. Due to the high cyclone efficiency, the internal circulation became much higher and the fineness of the circulating particles was shifted to finer particles. As a result, the heat transfer in the furnace was boosted and the temperature profile became more even. This had a significant positive effect on the emissions, especially NOx and on the limestone consumption, which was considerably reduced.Copyright

Pilot Plant Combustion Tests of Low-Volatile and High-Sulphur Coal for the 55 MWel CFBC Cao Ngan Power Plant, Vietnam

Circulating Fluid Bed technology has made a rapid and successful entry into power and steam generation marketplace in many countries. As one of the first CFB based power plants in Vietnam the 2 × 55 MWe Cao Ngan project will follow this trend towards clean coal technology. The Cao Ngan CFB boiler is designed to burn a blend of low-volatile, high-sulphur coals from two local mines complying with strict environmental regulations, 500 mg/Nm3 for SO2 and 300 mg/NM3 for NOx . Combustion tests were carried out at the University of Bochum, Institute of Energy Plant Technology, Germany, in a pilot-CFB combustor (100 kWth ) in order to check the combustion behaviour and the emission characteristics. In these tests a blend of the two different coals was burned at different temperature levels (830 °C, 860 °C, 890 °C) and at each temperature level the desulphurisation efficiency was tested with two different kind of limestone and different Ca/S-ratios: Furthermore the experimental analysis comprised the determination of the conventional emissions (NOx , CO), ignition characteristics for start-up and part load behaviour. During all tests samples of bed and filter ash were taken for further analysis, e.g. burnout, particle size distribution etc.. Earlier comparable combustions tests carried out in the pilot-CFB combustor and large scale CFB boilers has proven, that the results are transferable to large scale commercial plants: This is valid especially for the major emissions e.g. SO2 and NOx . The current paper will explain the design principles and the basic lay-out of the Cao Ngan CFB boiler. In addition, details of the results of combustion tests carried out in a pilot- CFBC at the University of Bochum, Institute of Energy Plant Technology, Germany, will be presented.Copyright