What is a Boiler?
The boiler is commonly defined as a closed vessel into which water is heated to the point it is converted into steam at the imperative pressure. The main function of the boiler is either to produce hot water or steam. The Hot water boiler heats water for the domestic or commercial purpose of heating and hot water supply, whereas Steam boilers generate steam to power turbines for power generation and other various industrial heating applications.
To understand the steam generation effects using a boiler, try thinking about the steam powering a turbine. When steam is made to flow through the turbine blades, the force turns the blades and accelerates the turbine.
Working Principle of a Boiler
The boiler is a closed vessel, where the water is stored. Hot gasses are formed by burning fuel in the furnace. These glasses are made to come in contact with the water vessel, the point where the heat transfer takes place between the steam and water. Thus, the boiler’s basic principle is to convert water into steam with heat energy. There are various types of boilers available to use for different purposes.
Fuel for boilers
The three most common types of fuel used in steam boilers, are coal, oil, and gas. However, industrial or commercial waste is also used in certain boilers, along with electricity for electrode boilers.
Coal
Coal is the generic term given to a family of solid fuels with a high carbon content. There are several types of coal within this family, each relating to the stages of coal formation and the amount of carbon content. These stages are:
- Peat.
- Lignite or brown coals.
- Bituminous.
- Semi bituminous.
- Anthracite.
Oil
Oil for boiler fuel is created from the residue produced from crude petroleum after it has been distilled to produce lighter oils like gasoline, paraffin, kerosene, diesel or gas oil. Various grades are available, each being suitable for different boiler ratings; the grades are as follows:
- Class D - Diesel or gas oil.
- Class E - Light fuel oil.
- Class F - Medium fuel oil.
- Class G - Heavy fuel oil.
Gas
Gas is a form of boiler fuel that is easy to burn, with very little excess air. Fuel gases are available in two different forms:
- Natural gas - This is gas that has been produced (naturally) underground. It is used in its natural state, (except for the removal of impurities), and contains a high proportion of methane.
- Liquefied petroleum gases (LPG) - These are gases that are produced from petroleum refining and are then stored under pressure in a liquid state until used. The most common forms of LPG are propane and butane.
Boiler Systems
The boiler system comprises feed water system, steam system and fuel system. The feed water system provides water to the boiler and regulates it automatically to meet the steam demand. Various valves provide access for maintenance and repair. The steam system collects and controls the steam produced in the boiler. Steam is directed through a piping system to the point of use. Throughout the system, steam pressure is regulated using valves and checked with steam pressure gauges. The fuel system includes all equipment used to provide fuel to generate the necessary heat. The equipment required in the fuel system depends on the type of fuel used in the system. A typical boiler room schematic is shown below.
The water supplied to the boiler that is converted into steam is called feed water. The two sources of feed water are: (1) Condensate or condensed steam returned from the processes and (2) Makeup water(treated raw water) which must come from outside the boiler room and plant processes. For higher boiler efficiencies, the feed water is preheated by economizer, using the waste heat in the flue gas.
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| Figure: Boiler Systems |
Applications of the Boiler
Boiler applications are indispensable in many industries. Hot water boilers can be used for hot water supply (like bathing hot water) and heating. It is also used in hotels, urban heating systems, accommodation areas, office buildings, farms, and planting greenhouses.
Steam boilers can be used for cooling, heating, cleaning, humidification, and in production processes and also can be used for power generation. Steam boilers can be used in industries like feed, food processing, textile, paper, building materials, metal smelting, heating engineering, and many more.
The cogeneration boilers application is gradually increasing, and steam boilers are also used for generating power, and auxiliary machines like heat exchangers are used for heating purposes. Now, biomass cogeneration is a new trend.
Some Additional Applications of the Boiler Can Be Given as the Following
- Refineries and distilleries
- Thermal power plants
- Sugar plants
- FMCG (Fast Moving consumer goods)
- Health care industries
- Pharmaceutical industries