Many industries use steam for heating purposes. Some industries use steam for electrical power generation. Steam is produced in Steam Boilers. There are many types of boilers in use. However, they can be classified into two types:
- Fire tube boiler
- Water tube boiler
Principles of Boiler
All boilers work on the same principle. When water is heated to a boil, steam is produced. This is exactly what happens when we boil water in a kettle. But to produce steam continuously at a pressure, a boiler is used. The boiler is a pressure vessel. The steam it contains must have sufficient pressure in order to be useful.
As water evaporates into steam in the boiler, more water has to be pumped in to replenish it. Evaporated water tends to leave behind salts that can form scales. The water also tends to become acidic at high temperatures and pressures. The water in the boiler has to be treated.
Fire is used to heat up the water in a boiler. Burners are equipment that can be utilized to burn fuels like oil, gas, coal, etc. They have to be in good condition in order to getting the best efficiency from the burning.
The hot gas from the combustion of fuel, after passing through the heating surfaces of the tubes, is led away to the atmosphere through the chimney.
Fire Tube Boiler
These are small, low pressured boilers. The hot gases from the fire pass through the inside of the tubes, while the water is on the outside. Most of these boilers have horizontal tubes where the hot gases can pass through. Some tubes contain swirlers in the form of coiled rods. The speed of the hot gases passing through these swirlers is reduced, and better heat transfer is achieved.
Water Tube Boiler
These are used in large to medium pressured boilers. The hot gases passes through the outside of the tubes. The boiler water is inside the tubes. The tubes are called by different names according to their function. Generating tubes are those directly in the line of the flow of the gases. Water wall tubes are used to line the boiler along its other skin. Superheater tubes are used to heat up saturated steam so that they become superheated. There are also other tubes like downcomer tubes, reheater tubes, desuperheater tubes, and others that serve to control the steam or water in the boiler.
Parts of a Boiler Although the concept of a boiler is simple, it does need to have the following parts:
- Steam Drum
- Burner and Combustion Equipment
- Furnace or Combustion Chamber
- Stack or Chimney
- Water Level Sight Glass
- Safety Valve
- Steam Stop Valve
- Feed Water Valve
- Blowdown Valve
- Manhole Cover and Door