Boilers Types and Terms

Boiler Types

• Boilers are machines used to generate hot water or steam.
• Cast iron boilers are modular boilers that are limited to low-pressure steam or hot water applications.
  
• Central boilers provide steam and heat for a larger complex heating system. Central boilers are often housed in a special environment with cooler temperatures surrounding them to prevent overheating.
  
• Double boilers allow for fine-tuned control and provide high thermal efficiency.
  
• Electric boilers are water or water/steam units powered by electricity rather than gas or other fuel.
  
• Firebox boilers use tube attachment techniques that are similar to those of the firetube boiler, but their combustion chambers are not round. Firebox boilers are compact, economical units that are typically used seasonally in low pressure steam or hot water applications in which efficiency is not a primary factor.
  
• Firetube boilers are cylindrical vessels with 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.
  
• Flexible watertube boilers, also called "bent tube boilers," are a common type of boiler valued for their resistance to thermal shock. Flexible watertube boilers are used in low pressure steam or hot water applications and can be a part of a field erectable package.
  
• Gas boilers use natural gas to heat the water and generate the steam necessary for heating applications.
  
• Hot water boilers are boilers whose primary purpose is the production of hot water.
  
• Membrane watertube boilers are compact boilers with high outputs that are used in high or low pressure or hot water applications. Membrane watertube boilers are ideal for applications in which space is limited.
  
• Mobile boilers are used often in temporary shelter environments, such as military camps or for emergency boiler breakdown situations. Mobile boilers can vary greatly in size and capacity and be towed to a location via semi-trucks or small vehicles.
  
• Packaged boilers are units that produce both heat and hot water to an environment.
  
• Steam boilers are boilers whose primary function is to produce steam. Steam boilers are a general type of boiler.
  
• Tubeless boilers are vertical boilers that have the burner located either at the bottom, middle or top. Tubeless boilers are easily operated boilers that have no tubes, but collect the steam over the water in a large jacket or "U" tube.
  
• Vertical boilers are commonly used in steam trucks, buses, trams and portable equipment, such as donkey engines utilized for sawmilling and dock work. The design of the vertical tube boiler lends itself to rough handling while in steam, making it ideal for use in situations in which the work plant has to be moved frequently over rough terrain.
  
• Waste-heat boilers make use of the rejected heat from other processes, such as gas turbines.
  
• Water tube boilers are safe boilers that consist of a header drum to which the water tube pipes connect. The drum and the tubes are usually surrounded by an insulating jacket or brickwork, and the fire and products of combustion are directed to pass through the tubes a multiple number of times, horizontally or vertically.

Boiler Terms

Accumulation Test - A test that measures the relieving capacity of boiler safety relief valves.

Ambient Air - The air that surrounds the equipment.

Aspirating Burner - A burner in which the fuel, in either a gaseous or finely divided form, is burned in suspension. The air for combustion is supplied by bringing it into contact with the fuel as it is drawn through one or more openings by the lower static pressure created by the velocity of the fuel stream.

Boiler Lay-Up - The removal of a boiler from service for a length of time. A boiler may be laid-up dry or wet.

Boiler Pressure - Pressure of the steam of water in a boiler, generally expressed in pounds per square inch (psi) and corresponding temperature.

Boiler Vent - A valved port used to vent air from a full boiler and to prevent a vacuum from forming when the boiler is drained. Boiler vent openings are located on the highest part of the waterside of the boiler.

Bottom Blowdown - The draining of a portion of the water in the boiler in order to remove the heavy sludge that tends to settle at the bottom. This process is done periodically.

BTU (British Thermal Unit) - Amount of heat needed to raise or lower the temperature of one pound of water by one degree Fahrenheit under standard pressure.

By-Pass Line - A pipeline that passes around a control in order to allow the boiler to be operated manually without having to use the control.

Continuous Blowdown - A small, continuously draining stream of water that controls the quantities of impurities in a boiler.

Cut-In Pressure - A pressure control setting at which the boiler automatically turns on.

Equalizer - Connections between parts of a boiler to equalize pressures.

Explosion Door - A door in a furnace or boiler setting that is designed to be opened by a pre-determined gas pressure.

Flash Point - The lowest temperature at which, under specified conditions, fuel oil gives off enough vapor to flash into a momentary flame when ignited.

Furnace - An enclosed space of a boiler in which the fuel undergoes combustion.

Pilot - A flame which is utilized to ignite the fuel at the main burner or burners.

Stack - A vertical conduit that, due to the difference in density between internal and external gases, creates a draft at its base.

Steam - The vapor phase of water, unmixed with other gases.

Vaporization - The change from liquid or solid phase to the vapor phase.