Usually boiler mountings are mounted on the surface of boiler, and boiler accessories are provided either inside or outside of the main boiler tank. The overall efficiency of the boiler is partially depended on the performance of boiler accessories. That is, proper maintanance and opeartion of the boiler with each other and that is why special care should be taken when choosing and operating those boiler accessories and mountings.
Boiler accessories are provided with the boilers for better optimization of the boiler performance and to increase the longevity of the boiler. These are called as the addtional components of boiler, becuase a boiler is able to run without the boiler accessories. But the boiler performance will much higher if appropriate boiler accessories are installed with it. Therefore boiler accessories are the optional units which are installed to increase the efficiency of steam boiler.There are various types of boiler accessories which are used to serve various purposes and they are discussed as follows.
- Economizer: The name of this accessory somehow approaches to the word “Economy”. And this unit is installed to help the economy of power plant. After exhausting, the flue gases goes towards the boiler chimney and afterthat they are released at atmosphere. The economizer recovers some part of waste flue gases from the chimney and this collected hot gases are utilized to heat up the feed water (by heat exchanging method) before entering into the main boiler. This pre heating of feed water saves the fuel and in this way, economizer increases the efficiency of the boiler and improves the economy of the plant. It is installed at the waste flue gas path and just before the air preheater.
- feed water pump: The water is converted into steam inside the boiler. As the steam boiler is a closed vessel, so huge pressure is created inside the boiler which creates a problem for feeding water into the boiler tank. So, feed water pumpsa are used to force the feed water into the boiler tank with high pressure.
- Air pre heater: The function of air pre heater is alomost same as economizer. It collects a part of waste flue gases from chimney and use those hot gases for heat up the air before entering the furnace. In this way the surronding air of furnace is preheated which leads to save in fuel and this high temparature also helps in combusting low quality coals. Preheating of air also helps in rapid combustion and produces less smokes. The air preheater is installed in between the ecomizer and chimney.
- Steam injector: The steam and feed water both are located inside the boiler in very high pressure. A steam injector lifts the feed water and forces it into the boiler. The size and cost of steam injector are small and the operation is silent.
- Steam separator: The generated steam is collected from the top section of a boiler and used for further applications. But thhe steam should be pure and free from water particles. Steam separator is used to rectify the steam from any impurities and the pure steam travelles towards the steam engine or steam turbine.
- Super heater: The generated steam sometime consist of impurities like water partilcles etc. But the steam should be dry and pure before entering into the steam turbine or steam engines. This necessitates the use of super heater. A super heater is a U shaped equpment which collects the heat from hot flue gases and dries the wet steam by applying those hot gases. After the processing, the volume and temparature of steam increases, but the pressure remains constant.
Boiler mountings are the essential part of a boiler. These mountings must be installed with the steam boilers to ensure the safety of the operating personel and to maintain the satisfactory boiler operation and proper functiong. According to the Indian Boiler Act, Boiler mountings are the essential part of the boilers and they must be preinstalled with the boiler. Various types of boiler mountings are discussed as follows.
- Pressure Gauge: The steam is stored into the upper portion of boiler and they are collected from that portion by a valve. The measurement of steam pressure is very important to ensure the safe operation of the boiler. A pressure gauge is a pressure measuring device, and the view panel of this device is installed infront of the boiler. Pressure gauge is connected with the boiler steam zone by a tubular siphon connector and efficiently checks the steam pressure of the boiler. Operator checks the pressure of steam and takes the necessry steps if required.
- Water level indicator: The accurate level of the feed water must be maintained in order to ensure the proper functionality of the boiler. This device is installed at the junction point of steam and water. Two water level indicators are installed with boiler and the front section of those indicators are situated infront of boiler. Boiler operators checks the water level and takes necessary actions if required.
- fusible plug: As the boilers are constantly deals with huge amount of heat, so there is a chance of overheating specially in case of firetube boilers. Therefore, fusible plugs are installed with the boiler and this device acts like a safety fuse. This device is an important safety device and must be installed in order to protect the boiler from the adverse effects of overheating. This device is situated above the boiler furnace. a fusible plug is made up with a gun metal plug which is fixed in a gun metallic frame with fusible metal. When the boiler is operating normally, then the fusible plug is totally covered by the feed water and therefore the fuse metal is kept intact. But whenever the water level is getting low and approaches a safe value, then automatically the fusible plug becomes uncovered and come into the direct contact with hot flue gases. This temparature rise leads the melt the fuse metal. In this way this device protects the boiler from overheating by sensing the heat.
- Blow off cock: The feed water of boiler sometime consists of several types of impurities. After the evaporation of water, some part of them are stored as sedimentation in the bottom portion of boiler. These muds are accomodating the useful parts of water space and therefore must be drained immidiately to maintain the proper operation of boiler. The lever is locked in normal operating condition of boiler, and it is opened when needed. When the valves of this device are kept open, then the high pressure of water flows out the sedimentation instantly.
- Safety valves: Boilers are usually capable to withstand high steam pressure. But a precautionary arrangement should be provided for safety reasons. Therefore safety valves are provided with steam boilers and they are generally mounted on the upper portion of boiler shell where the steam space is located. The contacts are closed when the boiler is operating under normal operating condition. But whenever the steam pressure goes beyond a predetermined safe value, then the valves are opened and realeases the excess amount of steam into the atmosphere.
- Steam stop valve: The generated steam is collected through a pipe from the steam space. Thereafter the steam is used fore several purposes. But there should be a controlling valve of steam, by which the flow of steam can be controlled. So, to fulfill this requirement a steam stop valve is mounted on the uppermost portion of the steam space. This is actually a steam regulating device which can be operated either manually or automatically by a implementing an electronic controller. This valve is considered as an important boiler mounting as this device controlles the steam flow efficiently.
- feed check valve: Water is the most important thing for boiler. The water level is checked by the water level indicator. But additionally a feed check valve is mounted on boiler by which the water is fed from the water feed pump. This device acts like a unidirectional diode. A feed check valve opens in a single direction. The normal water pressure inside the boiler remains constant when the pump is off. Thereafter when the pump is on, water enters into the boiler shell easily by the feed check valve.
Difference in between boiler mountings and boiler accessories
So, all the boiler accessories and boiler mountings are very much important for smooth boiler operation.