The Steam Generation Process
The process of steam generation starts when the feed water enters the steam drum through both internal tubes and the tubes that surround the furnace. The system of tubes that surrounds the furnace are known as waterwall or floor tubes. The feed water gets heated when passed through these tubes. Addition to this, there are Large-bore downcomer tubes that passes outside of the furnace and are used to circulate water between the drums, to which the tubes are attached from outside of the furnace.
The steam produced in the steam drum is known as wet or saturated steam. This steam cannot be used directly as it contains high amounts of moisture. To make this steam usable, it is first dried and heated with the help of a superheater located within the boiler. Once all the moisture content is removed from the steam, the superheated steam can be supplied to other systems. It is utmostly important to monitor and control the temperature of the superheated steam, or else it can cause damage to the systems to which it is supplied. For this reason, an implement known as an attemperator is used. The attemperator is a kind of cooler which is used to cool down the superheated steam to the right temperature. Thus, all the steam used in various system is taken out from the main steam drum of the boiler.
The energy from the fuel burning are used for various other purposes, the main two are as follows:
- For heating feed water to produce steam
- For superheating the steam from the boiler drum
To increase the efficiency of the boiler, the feed water that enters the boiler is pre-heated with the help of an economizer through which the feed water passes before entering the boiler. The exhaust gas of the boiler is also put to use by making it pass over an air heater, which heats up the combustion air entering the furnace. Thus, even the energy exhausted from the boiler is not allowed to go waste, which increases the overall efficiency of the system.
All these boilers are fitted with various safety fittings and control systems to monitor and control various aspects such as fuel oil flow rate, flow of combustion air, and feed water supply. All these systems should work in co-ordination to supply the amount of steam required by various system. The boiler is also provided with various mountings to ensure safe operation of the boiler.