Combustion Of Coal-water Fuels Research Articles

Coal-water suspensions: preparation, properties, characteristics (a brief overview)

RELEVANCE. A review of the current state of research on coal-water slurries in Russia and abroad is presented. Coal-water slurries are promising alternative types of energy fuels. Their use in the energy sector will allow generating thermal and electrical energy. It is possible to use a fairly wide range of substances as components of such fuels. One of the preferred types are various waste. The analysis of modern literature has shown a fairly wide range of directions for the study of multicomponent coal-water slurries.THE PURPOSE. To provide information on the current state of research in the field of technologies for the preparation, spraying and combustion of coal-water fuels, as well as on existing and promising additives to such slurries.METHODS. The study was carried out by the method of collecting and structuring information.RESULTS. The review of the current state of research in the field of technologies for the preparation, spraying and combustion of coal-water fuels, as well as existing and promising additives to such slurries, was carried out. It was found that additives of liquid combustible waste and biomass contribute to reducing the ignition delay time. At the same time, such additives do not reduce the quality characteristics of spraying multicomponent coal-water slurries. A number of components reduces the amount of emissions of combustion products of such fuels into the atmosphere. The influence of additives and components of coal-water slurries on their characteristics and properties was analyzed. It was shown that liquid components contribute to the intensification of ignition and combustion processes. In addition, their introduction into the fuel composition has a positive effect on the rheological properties of slurries, the characteristics of their spraying, combustion and the concentration of harmful emissions.CONCLUSION. Coal-water slurries are promising alternative types of energy fuels. The introduction of combustible components into the composition of coal-water slurries can significantly improve the rheological properties, which can improve the storage and transportation characteristics of such fuels. The established positive characteristics and properties of coal-water slurries provide prerequisites for the full-scale introduction of such fuels into industrial power engineering.

Energy recycling of pyrolysis water as a part of coal‐water fuel

Under research, there is a combustion process of multicomponent coal-water fuel (CWF) that was conducted with mixing ratio of coal, pyrolysis, and technical water. The pyrolysis water was extracted through pyrolysis oil settling, where the oil was obtained from pyrolysis of wood waste. Ignition and combustion of CWF samples were carried out in a combustion chamber at heating medium temperatures (Tg = 600-1000°C, with an interim step of 50°C). Gas-phase combustion products were analyzed with a flow-line gas analyzer. Technical water in CWF composition was replaced with pyrolysis one that was acted to raise the reactive capacity. It resulted in reducing the ignition delay time τi (by an average of 25%) and the minimum ignition temperature (from 440°С to 393°С, reliance on a CWF composition). In addition, increase in flame combustion time was recorded by an average of 20%, as well as dependence on a heating medium temperature and a CWF composition. In the case when a CWF liquid-phase component was completely replaced with the pyrolysis water, the significant increase in heat value by 2.14 MJ/kg was observed. According to the data of the flow-line gas analyzer, we concluded that the CWF combustion based on the pyrolysis water was accompanied by less NOx emission (by an average of 22%) but more CO and CO2 amount (by an average of 1.4 and 1.2, respectively). It was found according to the results of the energy balance assessment that application of pyrolysis water in CWF composition leads to a decrease in fuel consumption for heat production by 16.7%.

The Main Regularities of Ignition and Combustion of Coal-Water Fuels Produced from Brown, Flame and Gas Coals

An experimental investigation was carried out of coal-water fuel (CWF) drops ignition and combustion. CWF examples were produced by using of coal of different metamorphic stages, including brown coal, flame coal, and gas coal. The processes of combustion and ignition of CWF took place in the air. Time-temperature dependences of ignition and combustion processes were obtained; basic stages of CWF combustion were established and investigated; combustion completeness was defined and ash residue structure and properties were investigated during the experimental research. Influence of the working medium temperature on the time duration of each burning stage was defined. Generalization of results was carried out. It is shown, that duration of the volatiles combustion stage doesn’t depend on the medium temperature and stay constant for each of coal grade. Time interval before CWF ignition can be described with power-type dependence, which is identical for all metamorphic stages of coal. The maximum temperature of CWF combustion grows linearly in respect to the medium temperature in the oven.

Improvement of coal-water fuel combustion characteristics by using of electromagnetic treatment

Using of coal-water slurries as fuel for heat and power generation is interesting for researchers for a long time. Coal-water fuel (CWF) application has two major aspects of investigation: rheological properties to provide its transportation and atomization; and improvement of fuel combustion parameters. CWF combustion characteristics improvement can be achieved with the help of different physical and chemical methods. Influence of electromagnetic field on the structure and properties of hydrocarbon fuels is known. However, influence of electromagnetic treatment on the combustion parameters of coal-water fuel produced from coal of different metamorphic stages was not investigated before.Experimental investigations of coal-water fuel combustion parameters: ignition time, time-temperature correlations, ignition temperature, maximal temperature of flame and others were performed. Fuels produced from coal of 6 basic metamorphic stages, which cover a wide range from Brown coal to Anthracite, were used for research. Investigations were carried out in two cases: without fuel pre-treatment with an electromagnetic field, and with it. It is shown in the article that electromagnetic pre-treatment of coal-water fuel improves fuel ignition and combustion stability, increases combustion process efficiency and reduces the total time of fuel burning.

Effect of fuel treatment on Coal-Water Fuel Combustion

Three methods of improving spray fineness by fuel treatment were investigated—1) the heating of the Coal Water Fuel (CWF) under pressure to produce steam as the pressure drops during passage of the CWF through the atomizer nozzle, 2) the absorption of CO2 gas in the CWF to produce a similar effect, and 3) the addition of a chemical additive which will cause microexplosions in the droplets upon heating. These treatments are expected to produce disruptive atomization, i.e., the disintegration of slurry droplets subsequent to their leaving the atomizing nozzle and, hence, to yield better burnout and finer fly ash particle size distribution upon combustion. The effects of disruptive atomization upon CWF spray size distribution were studied using a spray test chamber equipped with a laser diffraction particle size analyzer; the data were fitted to the Rosin-Rammler particle size distribution function. The combustion characteristics of the treated CWFs were investigated in the MIT Combustion Research Facility. The spray chamber tests established that thermally-assisted atomization produced reductions both in the mean droplet size and in the mass fraction of large particles in the spray. For fuel delivery temperatures up to 100°C this effect is attributable to lowered fuel viscosity, while further heating of the CWF (to 150°C in these experiments) produces disruptive atomization. In-flame measurements and high speed cine pictures made during combustion tests provided detailed information for comparisons of treated and untreated CWF. Thermally-assisted atomization was the most effective of the methods studied for improving carbon conversion efficiency and reducing fly ash particle size. CO2 and picric acid addition techniques showed substantial improvements but they were less effective.

A mechanistic model of Coal-Water Fuel Combustion

The various stages of combustion of coal-water fuels (CWF) (formulated from bituminous coals) such as drying, pyrolysis and char burning were studied in an experimental-theoretical investigation. Measurements were made in a 1.5 MW CWF turbulent diffusion flame to determine the spatial distributions of gas velocity, temperature, and gaseous species concentrations. Particulate samples, collected at several axial stations in the flame, were analyzed for their size distribution, density, and mass fractions of the residual volatile and ash. This formed the basis for the development of a mechanistic model to describe the transformations of a CWF droplet in the flame. A mathematical model which quantitatively predicts the changing properties of the CWF droplet was used to compute the progress of combustion of three particle size ranges, for the measured temperature and oxygen concentration distribution in the experimental flame. The model follows the regression of a drying interface in the droplet, and describes quantitatively the heating of the already dry outer shell while the interstitial water from the core is still evaporating. For calculations of particle heatup and pyrolysis, the particle specific heat is varied with temperature in the range 1200 to 2500 J /(kg K). The initial weight of the sampled particles is back-calculated from their physical and chemical analyses. Model predictions are compared with the progress of combustion of flame samples (adjusted for the varying initial weight) of the same size range in two regions. Close to the burner, where CWF particles are mainly evaporating and devolatilizing, attention is focussed on the smaller particle sizes (53–75 μm, 75–90 μm and 106–125 μm) which constitute the bulk of the sample in that zone. In the tail end region of the flame, char burnout of the larger particle sizes (150–180 μm, 180–212 μm and 212–250 μm) is considered.

The Performance of Fabric Filters in a Pilot Baghouse During Coal Water Fuel Combustion Trials

Energy, Mines and Resources, Canada, together with the New Brunswick Electric Power Commission (N.B. Power) and Cape Breton Development Corporation have undertaken a program in eastern Canada to demonstrate coal-water fuel (C.W.F.) technology for electric utility boilers. The successful results of the C.W.F. demonstration in N.B. Power’s Chatham Generating Station led to a continuation of the program in a 20-MWe compact oil-designed utility boiler in Charlottetown, P.E.I. during the latter part of 1986 and early 1987. Based upon the results of the Charlottetown demonstration an evaluation of C.W.F. for a larger utility boiler (in the 90–150-MWe range) is planned. An essential feature of the Charlottetown demonstration, and any subsequent use of C.W.F., is the containment of the particulate emissions which arise from use of coal in the boiler. This paper describes tests which were undertaken at Chatham, using a pilot-scale baghouse, in order to be able to specify equipment, materials and operating procedures for the Charlottetown C.W.F. demonstration.

Coal-water fuel (CWF) project at Yukong

Coal-water fuel (CWF), one of the newer fluid fuels, can be stored, transported, and burned like oil, and will be competitive in price with No. 6 fuel oil. Yukong Ltd, Korea's largest petroleum refiner, has set up a demonstration project to develop CWF commercialization in Korea. This project, scheduled for completion by the end of 1986, includes the construction of a 600-(BPD) CWF plant, the modification of a 68-ton/hr oil-designed boiler, and the completion of a CWF combustion test.