working and function of mounting & accessories in boiler

AIM: To study the working and function of mounting & accessories in boiler.

APPARATUS USED: Model of Mounting & accessories in boiler.

THEORY: For efficient operation and maintenance of safety, the boiler equipped with two categories of components and elements.

First categories include the fittings which are primarily indicated for the safety of the boiler and for complete control the process of steam generation. These units are called mountings. The mounting from an integral part of the boiler and are mounted on the body of the boiler itself. The following mountings are usually installed on the boiler.

1. Two safety valve

2. Two water level indicators

3. Pressure gauge

4. Fusible plug

5. Steam stop valve

6. Feed check valve

7. Blow-of cock

8. Man and mud hole

Second categories include the components which are installed to increase the efficiency of the steam power plants and help in the power working of the boiler unit. These fitting are called boiler accessories. The following accessories are given below.

1. Air pre-heater

2. Economiser

3. Super heater

4. Feed pump and

5. Injector

FUNCTION, LOCATION AND WORKING OF MOUNTINGS AND ACCESSORIES.

A) SAFETY VALVE: The function of the safety valve is to permit the steam in the boiler to escape to atmosp0here when pressure in the steam space in the boiler. The safety valve operates in the principle that a valve is pressed against its seat through some agency such as sturt, screw or spring by external weight or force, when the steam force due to boiler pressure acting under the valve exceeds the external force, the valve gets lifted off its seat and some of the steam rushes out until normal pressure is restored again.

The commonly used safety valves are given below:

ii) Lever safety valve

iii) Spring loaded safety valve

iv) High steam-low water safety valve

Figure of Safety valve

B) WATER LEVEL INDICATOR: The function of the water level indicator is to ascertain constantly and exactly the level of water in the boiler shell. It is fitted in the front of the boiler from where it is easily visible to the operator.

Figure of Water Level Indicator

The unit consists of a strong glass tube whose ends pass through stuffing boxes consists of heat resisting rubber packing to prevent leakage steam and water. The flanges are bolted to front end plate of the boiler, the upper flange being fitted to the steam space and the lower to water space in the boiler. There are two cocks namely steam cock and water cock which communicate the boiler shell spaces to the gauge glass tube. When the handle of the cocks are vertical, they are in operation and the water level in the tube corresponds to water level in the shell. A red mark on the glass tube indicates the safe water level.

C) FUSIBLE PLUG: The function of the fusible plug is to extinguish the fire in the event of the boiler shell failing below a certain specified limit. We know that when the water on heating transforms into steam, the level of water in the boiler falls down. If the water is not replenished and the steam generation continues then the parts, which have been uncovered by water uncovered by water may get overheated and subsequently are melted. To safeguard against this eventuality we use fusible plug.

Figure of Fusible Plug

The fusible plug is inserted at the box crown or cover the combustion chamber at the lowest permissible water level.

D) PRESSURE GAUGE: Each boiler has to be provided with a pressure gauge, which record the pressure at which the steam is being generated in the boiler.

Figure of Pressure gauge

The gauge is usually mounted at the front top of the boiler shell or drum. The gauge should to be clearly visible to the attendant so that he can easily record the pressure reading.

E) BLOW OFF COCK: The blow of cock serves to drain out the water from the boiler periodically for any one of the following reasons:

1) To discharge mud, scale and other impurities which settle down at the bottom of the boiler?

2) To empty the boiler for internal cleaning and inspection.

3) To lower the water level rapidly if the level becomes too high.

The unit is fitted at the lowest portion of the boiler. It may be mounted directly to the boiler shell or through an boiler elbow pipe, which is fitted to the boiler shell.

F) FEED CHECK VALVE: The feed check valve has the following two functions to perform:

1. To allow the feed water to pass into the boiler.

2. To prevent the back flow of water from the boiler in the events of the failure of the feed pump.

Figure of Feed check Valve

G) STOP VALVE: The function of the steam stop valve is to shut off or regulate the flow of steam from the boiler to the steam pipe or from the steam pipe to the engine. When used for the former purpose, it is called junction valve. Usually the junction valve means a regulating valve of larger size and a stop valve refers to a regulating valve of smaller size.

Figure of Stop valve

The junction valve is mounted on the highest part of the steam space of the boiler and is connected to the steam pipe, which carries the steam to the engine.

H) MAN HOLES: These are door to allow men to enter inside the boiler for the inspection and repair

I) AIR PREHEATER: Air heater or air pre-heater is waste heat recovery device in which the air on its way to the furnace is raised in temperature by utilizing the heat of the exhaust gases. Air pre-heater are classified into the following two categories.

Figure of Air preheater

· Recuperative Air heater

· Regenerative Air heater

J) ECONOMISER: The economizer is a device, which serves to recover some of the heat being carried by exhaust flue gases. The heat thus recovered is utilized in raised temperature in feed water being supplied to the boiler. If the water is raised and thus there is a saving in the consumption of fuel.

Figure of economizer

The economizer unit is installed in the path of the flue gases between the boiler and the chimney.

K) STEAM SUPER HEATER: The steam generated by a simple boiler in generally wet or at the most dry saturated. Steam super heater is a surface heat exchanger in which the wet steam is first dried at the same temperature and pressure and then raised to temperature above the saturation temperature at constant pressure. Heat of flue gasses utilized in super heating the steam and as the super heater is placed in the path of the flue gasses,

Figure of Super heater

Since superheating result in the increased efficiency and economy of the steam plant.

L) FEED WATER EQUIPMENT: The pressure inside a steaming boiler is high and so the feed water has to be raised in pressure before its entry can be affected in the boiler. Feed pump is a device which raised the pressure of water and forces it into the boiler.