There are many pressure parts and non pressure parts in a water tube boiler, we list the main components of the water tube boiler and their functions.
Steam drum is a collection vessel for steam & water. Here water & steam is separated. It has steam separators. Steam goes from top side to superheater & water goes from the bottom through down comer Mud drum, then to furnace bottom ring headers (bottom water tube boiler steam drum of furnace water wall).
Mud or water drum the lower drum is directly attached to upper steam drum with large no of straight tubes bundles called boiler bank tubes. Solids and mud can settle in this mud drum for removal through periodic blowdown. Some times desuperheater coil also installed in this drum to recover heat from superheated steam. Draining arrangement of this drum is through one or two boiler blowdown connections to control tds or to fully drain the boiler when out of service.
Tubing arrangement around the furnace to extract heat from fuel to generate steam is called water wall circuit. These water walls can be arranged in line arrangement or stagger arrangement. Water walls get the heat from radiation and approximately absorb the 50% of the total heat produced in the furnace.
If the temperature of the steam is above its saturation temperature then it is called superheated platen superheater steam. The super heater (heat exchanger) is used to increase the temperature of the steam. These are bundles of high strength tube which can bear temperature 600C Depending upon the material of tubes Mostly SA-213 is used. In most industrial water tube boilers the superheater is placed where flue gases make their turn from the radiant to the convection section of the boiler.
Economizer (heat exchanger) is the boiler accessory used to recover the heat of flue gas that leaving the boiler by heating feed water. The efficiency of a boiler can be increased with an economizer. 60C rise in feed water temperature with the help of economizer can save up to 1% of fuel.
Air supplied to a boiler for combustion is pre heated with the help of air heater by recovering the heat of waste flue gas that leaves the economizer. 20C rise in temperature of combustion air can save up to 1% of total fuel. Preheated air is also required for the operation of pulverized coal furnaces. Primary air is needed for drying coal in the pulverizer.
For combustion of fuel in the boiler furnace air is drawn from the atmosphere and pushed through the ducts with forced draught fan to furnace where air reacts with fuel and become flue gas, the flue gas is then extracted from the furnace with the help of Induced draught fan. The fan used in large water tube boilers are FD fans, ID fans, Primary air fans, Secondary air fans and Gas recirculation fans.
Other main water tube boiler parts are burning equipment burners and furnace and gas cleaning devices like ESP Cyclone Separators and bag filters.
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