FIRE TUBE BOILERS BASIC AND TUTORIALS


A fire tube boiler, as the name suggests, has the hot flue gases from the combustion chamber, the chamber in which combustion takes place, passing through tubes and out the boiler stack. These tubes are surrounded by water.


The heat from the hot gases transfers through the walls of the tubes and heats the water. Fire tube boilers may be further classified as externally fired, meaning that the fire is entirely external to the boiler or they may be classified as internally fired, in which case, the fire is enclosed entirely within the steel shell of the boiler.

Two other classifications of fire tube boilers are wet-back or dryback. This refers to the compartment at the end of the combustion chamber.

This compartment is used as an insulating plenum so that the heat from the combustion chamber, which can be several thousand degrees, does not reach the boiler’s steel jacket. If the compartment is filled with water it is known as a wet-back boiler and conversely, if the compartment contains only air is called a dry-back boiler.

Still another grouping of fire tube boilers is by appearance or usage. The two common types used today in HVAC heating systems are the marine or Scotch marine boiler and the firebox boiler. The marine boiler was originally used on steam ships and is long and cylindrical is shape.

The firebox boiler has a rectangular shape, almost to the point of being square. A Scotch marine fire tube boiler has the flame in the furnace and the combustion gases inside the tubes. The furnace and tubes are within a larger vessel, which contains the water and steam.

Fire tube boilers are also identified by the number of passes that the flue gases take through the tubes. Boilers are classified as two-, three- or four-pass. The combustion chamber is considered the first pass.

Therefore, a two-pass boiler would have one-pass down the combustion chamber looping around and the second pass coming back to the front of the boiler and out the stack. A three-pass boiler would have an additional row of tubes for the gas to pass through going to the back of the boiler and out the stack.

A fourpass boiler would have yet another additional row of tubes for the gas to pass through going to the front of the boiler and out the stack. An easy way to recognize a two-, three- or four-pass boiler is by the location of the stack. A two- or four-pass boiler will have the stack at the front, while a three-pass boiler will have the stack at the back.

Fire tube boilers are available for low and high pressure steam, or hot water applications. The size range is from 15 to 1500 boiler horsepower (a boiler horsepower is 33,475 Btuh). HVAC fire tube boilers are typically used for low pressure applications.

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1 comment:

albina N muro said...

A fire tube boiler, as the name suggests, has the hot flue gases from the combustion chamber, the chamber in which combustion takes place, passing through tubes and out the boiler stack. These tubes are surrounded by water. boiler installation in Birmingham

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