Water leaves a cooling tower system in one of four ways.Įvaporation: The primary function of the tower and the method that transfers heat from the cooling tower system to the environment.ĭrift: A small quantity of water may be carried from the tower as mist or small droplets. In this system phase transformation is absent means water is directly converted into the steam at these pressure and temperature.The thermal efficiency and longevity of the cooling tower and equipment depend on the proper management of recirculated water. This circulation in boiler is applicable to the boilers which are operating at critical pressure. To regulate the flow through various tubes, orifice plates are used. If the Operating pressure of boiler is between 180 kg/cm2 to 200 kg/cm2 then circulation in boiler is to be assisted with mechanical pumps, to overcome frictional losses. Therefore natural circulation is limited to boiler with drum operating pressure around 175 kg/cm2. Thus the hydrostatic head available will not be able to overcome the frictional resistance for a flow corresponding to the minimum requirement of cooling of water wall tubes. Circulation takes place at such a rate that the driving force and frictional resistance are balanced.Īs the pressure increases, the difference in density between water and steam decreases. This density difference is the driving force, for the mixture. The Down comer contains relatively cold water, whereas the riser tubes contain a steam & water mixture, whose density is comparatively less. The circulation, in this case, takes place on the basis of thermo-siphon principle. These boilers have to respond quick load changes. Medium pressure industrial boilers adopted higher circulation ratio. Circulation ratio is higher side as the density difference between steam & water is high. Circulation ratio for utility high pressure boilers is between 6 to 9. The value of circulation ratio varies from 6 to 30 in industrial boilers. Separated steam from steam drum is sent to the turbine. This mixture is continuously rises till it reaches back to the steam drum. The ratio of the weight of water to the weight of steam in the mixture leaving the heat absorption surface is called circulation ratio. Heat absorbed in water wall is latent heat of vaporization creating a mixture of steam and water. When water rises upside in tubes, a portion of the water is converted into steam and continue to rise upwards as a mixture of steam and water. Water rises through water wall tubes are exposed to furnace heat. Advertisementsĭown comer pipes are outside the boiler furnace while water walls are inside the furnace. Water inside the drum flows down through down comer pipes and distributed by bottom header to water walls. Normally steam drum water level is maintained around 50%.It means steam drum is half filled with water & remaining 50% above the water level contains steam. Steam drum acts as a pressure vessel and separates steam and water from steam water mixture. Feed water flows through economizer gets further heated by flue gas and enters into the steam drum. It is also called the boiling point of water. Saturation temperature means the temperature at which water vaporization is starts for a given pressure. Here temperature of the boiler feed water is around the saturation temperature corresponding to its pressure. ![]() Water circulation in boiler can be classified in three different types of systems.īoiler feed water which is pumped with high pressure boiler feed water pumps first reaches at economizer. Types of water circulation in industrial steam water tube boilers: Advertisements
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