THERMODYNAMICS - LAB MANUAL ( B-TECH KUK)

Study of boilers

INTRODUCTION:-

The boiler mountings are added on the boiler for its safe working. While accessories are added on the boiler to improve its performance.

BOILER MOUNTINGS:-

The boiler mounting are the part of the boiler and are required for proper functioning. In accordance with the Indian Boiler Regulations of the boiler mounting is essential fittings for safe working of the boiler.

1. Safety valve:- 2 Numbers.

2. Water level indicator:- 2 Numbers.

3. Pressure Gauge:- 1 Numbers.

4. Steam stop valve:- 1Numbers.

5. Feed check valve.

6. Blow off cock

7. Main Hole.

8. Mud Hole.

9. Fusible plug.

.10. High pressure and low water safety valve on Lancashire and Cornish

Boiler.

Safety valve:-

Safety valves are located on the top the boiler. They guard the boiler against the excessive high pressure of steam inside the drum. If the pressure of the steam in the boiler drum exceed the working pressure, then the safety valve allow to blow off certain quantity of steam to atmosphere. Thus the pressure of steam in the drum falls. The escape of steam makes a audio noise to warn the boiler attendant.

There are 4 types of safety valve.

1. Dead weight safety valve.

2. Spring loaded safety valve.

3. Lever loaded safety valve.

4. High steam& low water safety valve.

1). Dead weight safety valve:-

It is vary similar to dead weigh (whistle) loaded on pressure cooker& functions in similar way. A gun metal valve resets on gun metal seat. The gun metal seat is mounted on steel steam pipe. The valve is fastened to weight carrier. The total weights in the form of cylindrically disc are placed on the carrier. Therefore the total weight placed on the carrier is acting downward. This is the weight of cast iron carrier & valve itself.

2). Spring Loaded Safety Valve:-

The dead weight safety valve cannot be used on locomotive & marine boiler as the jerks, pitching, rolling may change the load on the valve & it can open frequently under working pressures. The spring loaded safety valve is used on locomotive, marine and high pressure boiler.

3). Lever loaded safety valve:-

The body of the valve is fattened on the top of the boiler shell. A gun metal is placed in steam passage formed in the casting. A cast iron lever attached to a fulcrum on one end & loaded by weight on other end keeps the valve on sheets in closed position.

4). Water level indicator:-

Water level indicator is located in front of boiler in such a position that the level of water can easily be seen by attendant. Two water level indicators are used on all boilers. A water level consists of a metal tube& a strong glass tube with marking. The upper & lower ends of these tubes are connected to two gun metal hollow pipes.

5).Fusible plug:-

It is very important safety device, which protects the fire tube boiler against over heating. It is located just above the furnace in the boiler.. During the normal boiler operation, the fusible plug is covered by water& its temp. does not rise to its melting state. But when the water level falls too low in the boiler, it uncovers the fusible plug. The furnace gases heat up the plug & fusible plug melts, the inner plug falls down.

6).Feed check valve:-

The feed check valve is fitted to the boiler, slightly below the working level in the boiler, it is used to supply high pressure feed water to boiler. It also prevents the returning of feed water from the boiler if feed pump fails to work. A feed check consists of two valves: feed valve& check valve as shown in fig

7).Steam stop valve:-

The steam stop valve is located on the highest part of the steam space. It regulates the steam supply to use. The steam stop valve can be operated manually or automatically. A hand operated steam stop valve is shown in fig..

BOILER ACCESSORIES:-

The accessories are mounted on the boiler to increase its efficiency. These units are optional on an efficient boiler. With addition of accessories on the boiler the plant accessories also increases. The following accessories used on a modern boiler.

1. Super heater

2. Economiser

3. Air preheated

1)SUPER HEATER: -

It is heat exchanger in which heat of combustion products is used to dry the wet steam& to increase its temp. During superheating the steam, pressure remains constant, its temp & volume increase. Basically a super heater consists of a set of small diameter four tubes in which steam flows & takes up the heat from the hot flue gases

2)ECONOMISER:-

An Economiser is a heat exchanger used for heating the feed water before it enter the boiler the economizer recovers some of waste heat of hot flue gases going to chimney. It helps in improving the boiler efficiency. It is placed in the path of flue gases at the near end of the boiler just before air preheater. The most popular economizer is greens economizer.

3)AIR PREHEATER:

The function of an air preheater is similar to economizer. It recovers some portion of the waste heat of hot flue gases going to chimney & transfers same to the fresh air before it enter the combustion chamber. Due to preheating of air, the furnace temp. increases. It results in rapid combusting of fuel with less soot, smoke& ash.

NAME

FUNCTION

1. Safety valve 2. Water level indicator 3. Pressure gauge 4. Steam stop valve 5. Feed check valve 6. Blow off cock 7. Man hole 8. Mud hole 9. Fusible plug 10. Dual function safety valves, high pressure and low water safety valve.

1. Do no allow boiler pressure to rise beyond its safe pressure. 2. Show working level of water in the boiler. 3. Indicates workings pressure of the boiler. 4. Regulates the amount of outgoing steam. 5.Checks the amount of feed water going to the boiler and does not allow its return. 6. Allow to drain water from the boiler. 7.Allow a person to go inside the boiler drum for repair etc. 8.Facilitates removal of heavy impurities settled in the boiler drum. 9.Stop the boiler if its heating surface if its overheated due to low water level. 11. Allows escape of steam in case of (1) Unsafe higher pressure (2) Unsafe water level.