Types of Industrial Boilers

Boilers are the enclosed vessels in which the water is heated and circulated as hot water or as steam for the generation of power or heat energy. It consists of arrangement of tubes where the water is heated and supplied for the steam for energy production. It acts as a storage tank for hot water. These boilers consist of tubes that are divided into chief classes.

Efficiency:
Boiler or steam boiler efficiency is given by:

This efficiency includes thermal, combustion, fuel to steam efficiencies. It completely depends on size of the boiler. In general the efficiency varies in between 80% to 88%. Some losses are included as incomplete combustion, radiating losses that occurs due to the wall that is surrounding, defective combustion of the gas etc. results in the efficiency range.

Types of boilers
There are mainly two types of boilers as water tube boiler and fire tube boiler.

• Fire tube boiler:
  

In fire tube boiler there are number of tubes through which the hot gases are passed and where the water surrounds these tubes. The tube consists of hot gases passing through them with their immersion into water in a vessel that is closed. In this boiler the closed vessel or shell consists of water through which the hot tubes are passed.

Firetube boilers are often characterized by their number of passes, referring to the number of times the combustion (or flue) gases flow the length of the pressure vessel as they transfer heat to the water. Each pass sends the flue gases through the tubes in the opposite direction. To make another pass, the gases turn 180 degrees and pass back through the shell. The turnaround zones can be either dryback or water-back. In dryback designs, the turnaround area is refractory lined. In water-back designs, this turnaround zone is water-cooled, eliminating the need for the refractory lining. The number of passes the boiler contains affects the boiler efficiency, and its first cost to manufacturer. The more heat transfer surfaces the boiler has, the more efficient it can be. However, this also increases the amount of material it contains and therefore the first cost.

Wet/Water Back and Dry Back

2 pass dry back

3 pass wet back

·         Water tube boiler:

A water tube boiler is a kind of boiler that uses the water that is heated inside the tubes and the surrounded by hot gases around them. It is just reverse to the fire tube boiler where water is heated inside tubes and hot gases surround these tubes.