The pulverizer plays a pivotal role in coal based thermal power generation. The improper coal fineness or drying reflects a quality-wise deterioration. This results in flame instability, unburnt combustible loss, and a propensity to slagging or clinker formation. Simultaneously, an improper air-coal ratio may result in either the coal pipe choke or the flame impingement, an unbalanced heat release, an excessive FEGT, overheating of the tube metal, etc, resulting on the reduced output and excessive pulverizer rejects. In general, the base capacity of the pulverizer is a function of coal and air quality, conditions of grinding elements, classifier and other internals. The capacity mapping is a process of comparison of standard inputs with actual fired inputs to assess the available standard output capacity of the pulverizer. In fact, this will provide a standard guideline over operational adjustment and maintenance requirement of the pulverizer. The base capacity is a function of grindability; fineness requirement may vary depending upon the volatile matter content of the coal and the input coal size. The quantity and inlet temperature of primary air limits the drying capacity. The base airflow requirement will change depending upon the quality of raw coal and output requirement. It should be sufficient to dry pulverized coal. Drying capacity is also limited by utmost P.A. fan power to supply air. The P.A. temperature is limited by APH inlet flue gas temperature — an increase of this will result in efficiency loss of the boiler. Besides, the higher P.A. inlet temperature can be attained through economizer gas by-pass, the SCAPH, partial flue gas recirculation. The primary air/coal ratio, a variable quantity within the pulverizer operating range, increases with decrease in grindability or pulverizer output and decreases with decrease in volatile matter. Again, the flammability of mixture has to be monitored on explosion limit. Through calibration, the P.A. flow and efficiency of conveyance can be verified. The velocities of coal/air mixture to prevent fallout or to avoid erosion in the coal carrier pipe are dependent on the pulverized coal particle size distribution. Metal loss of grinding elements inversely depends on the YGP index of coal. Besides, variations of dynamic load on grinding elements, wearing of pulverizer internal components affect the available pulverizing capacity and percentage rejects. Therefore, the capacity mapping is necessary to ensure the available pulverizer capacity to avoid overcapacity or under capacity running of pulverizing system, optimizing auxiliary power consumption, This will provide a guideline on the distribution of raw coal feeding in different pulverizers of a boiler to maximize operating system efficiency and control resulting a more cost effective heat rate.

The steam consumption in a turbine within an operating pressure range determines the effectiveness of thermal energy conversion to electric power generation in a turbo-alternator. The low pressure (LP) stage of the steam turbine produces largest amount of steam to shaft-power in comparison to other stages of turbine although susceptible to various additional losses due to condensation of wet steam near penultimate and ultimate stages. The surface deposition in blade is caused by inertial impaction and turbulent-diffusion. With increasing blade stagger angle along the larger diameter of blading, the fractional deposition of wet steam is largely influenced by blade shape. From this background, the aim of this work is to predict the effect of mathematical models through computational fluid dynamics analysis on the characterization of thermodynamic and mechanical loss components based on unsaturated vapor water droplet size and pressure zones in LP stages of steam turbine and to investigate the influence of droplet size and rotor blade profile on cumulative energy losses due to condensation and provide an indication about the possible conceptual optimization of blade profile design to minimize moisture-induced energy losses.

Pulverizers play a pivotal role in coal-based thermal power generation. Improper coal fineness or drying reflects a qualitywise deterioration. This results in flame instability, unburnt combustible loss, and a propensity to slagging or clinker formation. Simultaneously, an improper air-coal ratio may result in either coal pipe choking or flame impingement, an unbalanced heat release, an excessive furnace exit gas temperature, overheating of the tube metal, etc., resulting in reduced output and excessive mill rejects. In general, the base capacity of a pulverizer is a function of coal and air quality, conditions of grinding elements, classifier, and other internals. Capacity mapping is a process of comparison of standard inputs with actual fired inputs to assess the available standard output capacity of a pulverizer. In fact, this will provide a standard guideline over the operational adjustment and maintenance requirement of the pulverizer. The base capacity is a function of grindability; fineness requirement may vary depending on the volatile matter (VM) content of the coal and the input coal size. The quantity and the inlet temperature of primary air (PA) limit the drying capacity. The base airflow requirement will change depending on the quality of raw coal and output requirement. It should be sufficient to dry pulverized coal (PC). Drying capacity is also limited by utmost PA fan power to supply air. The PA temperature is limited by air preheater (APH) inlet flue gas temperature; an increase in this will result in efficiency loss of the boiler. Besides, the higher PA inlet temperature can be attained through the economizer gas bypass, the steam coiled APH, and the partial flue gas recirculation. The PA/coal ratio, a variable quantity within the mill operating range, increases with a decrease in grindability or pulverizer output and decreases with a decrease in VM. Again, the flammability of mixture has to be monitored on explosion limit. Through calibration, the PA flow and efficiency of conveyance can be verified. The velocities of coal/air mixture to prevent fallout or to avoid erosion in the coal carrier pipe are dependent on the PC particle size distribution. Metal loss of grinding elements inversely depends on the YGP index of coal. Besides that, variations of dynamic loading and wearing of grinding elements affect the available milling capacity and percentage rejects. Therefore, capacity mapping is necessary to ensure the available pulverizer capacity to avoid overcapacity or undercapacity running of the pulverizing system, optimizing auxiliary power consumption. This will provide a guideline on the distribution of raw coal feeding in different pulverizers of a boiler to maximize system efficiency and control, resulting in a more cost effective heat rate.

The case study is related to an assessment of derating of power generation capacity of 75 MWe nameplate capacity units due to unavailability of high pressure (HP) heaters of a pulverized coalfired power generating station in India. The generation capacity of the said Power Plant units, which were commissioned since the 1960s onward, was deteriorated due to trouble in the regenerative feed water heating system. The power generating station was consisting of three 75 MWe BTG units and the generated steam from any of the three similar 320 TPH boilers may be fed to any one of 75 MWe turbo generators through available crossover connections. The study summarizes the results of the series of calculation on collected in-situ data to evaluate the performance and efficiency deterioration due to fall in final feed water (FW) temperature at boiler inlet, as per the provisions of standard thermodynamic 1st law based cycle efficiency evaluation practices. The erosion in IP turbine blades degrades the back pressure on the high-pressure turbine with aging and thereby degrades last HP Heater shell pressure resulting degradation in FW temperature. Bypassing HP heaters affects the same way along increasing condenser losses. Cycle heat rate loss is also inevitable due to emergency drip operation, turbine gland steam leakage, makeup water flow in the condenser. These findings discuss the impact on unit heat rate with reference to design and operating data of 75 MWe generating units while HP Heaters were available and the same were partly or fully unavailable causing performance deterioration.

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