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Use of Coal Drying to Reduce Water Consumed in Pulverized Coal Power Plants Quarterly Report: July-September

Description: Low rank fuels such as subbituminous coals and lignites contain significant amounts of moisture compared to higher rank coals. Typically, the moisture content of subbituminous coals ranges from 15 to 30 percent, while that for lignites is between 25 and 40 percent, where both are expressed on a wet coal basis. High fuel moisture has several adverse impacts on the operation of a pulverized coal generating unit. High fuel moisture results in fuel handling problems, and it affects heat rate, mass rate (tonnage) of emissions, and the consumption of water needed for evaporative cooling. This project deals with lignite and subbituminous coal-fired pulverized coal power plants, which are cooled by evaporative cooling towers. In particular, the project involves use of power plant waste heat to partially dry the coal before it is fed to the pulverizers. Done in a proper way, coal drying will reduce cooling tower makeup water requirements and also provide heat rate and emissions benefits. The technology addressed in this project makes use of the hot circulating cooling water leaving the condenser to heat the air used for drying the coal (Figure 1). The temperature of the circulating water leaving the condenser is usually about 49 C (120 F), and this can be used to produce an air stream at approximately 43 C (110 F). Figure 2 shows a variation of this approach, in which coal drying would be accomplished by both warm air, passing through the dryer, and a flow of hot circulating cooling water, passing through a heat exchanger located in the dryer. Higher temperature drying can be accomplished if hot flue gas from the boiler or extracted steam from the turbine cycle is used to supplement the thermal energy obtained from the circulating cooling water. Various options such as these are being examined in …
Date: October 1, 2005
Creator: Levy, Edward
Partner: UNT Libraries Government Documents Department

Use of Coal Drying to Reduce Water Consumed in Pulverized Coal Power Plants Quarterly Report: July-September 2003

Description: This is the third Quarterly Report for this project. The background and technical justification for the project are described, including potential benefits of reducing fuel moisture, prior to firing in a pulverized coal boiler. A description is given of the equipment, instrumentation and procedures being used for the fluidized bed drying experiments. Laboratory data are presented on the effects of bed depth on drying rate. These show that drying rate decreased strongly with an increase in bed depth as the settled bed depth varied from 0.25 to 0.65 m. These tests were performed with North Dakota lignite having a 6.35 mm (1/4 inch) top size, constant inlet air and heater surface temperatures, constant rate of heat addition per unit initial mass of wet coal and constant superficial air velocity. A theoretical model of the batch dryer is described. This model uses the equations for conservation of mass and energy and empirical data on the relationship between relative humidity of the air and coal moisture content at equilibrium. Outputs of the model are coal moisture content, bed temperature, and specific humidity of the outlet air as functions of time. Preliminary comparisons of the model to laboratory drying data show very good agreement.
Date: October 1, 2003
Creator: Levy, Edward K.; Caram, Hugo; Yao, Zheng & Feng, Gu
Partner: UNT Libraries Government Documents Department