14-12-2012, 05:28 PM
INTRODUCTION TO BOILERS
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Boiler is a metal container in which a liquid is heated and changed into a vapor. Most boilers change water into the vapor steam. Steam is used to heat buildings and processes. It changes from vapor to liquid form as it delivers heat into a room or building, giving off even more heat as a result. Some heating systems, called hydronic systems, circulate hot water rather than steam. However, the heat source in these systems is still referred to as a boiler. Steam produced in boilers is also used in steam turbines and for refining oil or drying paper.The process of heating a liquid until it reaches it's gaseous state is called evaporation.
Heat is transferred from one body to another by means of
(1) radiation, which is the transfer of heat from a hot body to a cold body through a conveying medium without physical contact,
(2) convection, the transfer of heat by a conveying medium, such as air or water and
(3) conduction, transfer of heat by actual physical contact, molecule to molecule.
The heating surface is any part of the boiler metal that has hot gases of combustion on one side and water on the other. Any part of the boiler metal that actually contributes to making steam is heating surface. The amount of heating surface a boiler has is expressed in square feet. The larger the amount of heating surface a boiler has the more efficient it becomes.
BOILER TYPES:
There are virtually infinite numbers of boiler designs but generally they fit into one of two categories:
Firetube or as an easy way to remember "fire in tube" boilers, contain long steel tubes through which the hot gasses from a furnace pass and around which the water to be changed to steam circulates.
In the fire-tube boiler, gases flow through tubes surrounded by water. This type of boiler is used in most steam locomotives, in small factories, and sometimes in heating homes.
In a firetube boiler the heat (gasses) from the combustion of the fuel passes through tubes and is transferred to the water which is in a large cylindrical storage area.
STEAM BOILER SYSTEMS:
The feedwater system provides water to the boiler and regulates it automatically to meet the demand for steam. Valves provide access for maintenance and repair. The steam system collects and controls the steam produced in the boiler. Steam is directed through piping to the point of use. Throughout the system steam pressure is regulated using valves and checked with steam pressure gauges. The steam and feedwater systems share some components. 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. All fuels are combustible and dangerous if necessary safety standards are not followed. Fuels commonly used are nuclear fusion, electricity, the wastes of certain processes and fossil fuels. The approximate heat value of certain fossil fuels: