A boiler is a closed vessel in which fluid is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central heating, boiler-based power generation, cooking, and sanitation.
A furnace, referred to as a heater or boiler in British English, is a heating unit used to heat up an entire building. Furnaces are mostly used as a major component of a central heating system. The name derives from Latin word fornax, which means oven. Furnaces are permanently installed to provide heat to an interior space through intermediary fluid movement, which may be air, steam, or hot water. Heating appliances that use steam or hot water as the fluid are normally referred to as a residential steam boiler or residential hot water boiler. The most common fuel source for modern furnaces in North America and much of Europe is natural gas; other common fuel sources include LPG, fuel oil and in rare cases coal or wood. In some areas electrical resistance heating is used, especially where the cost of electricity is low or the primary purpose is for air conditioning. Modern high-efficiency furnaces can be up to 98% efficient and operate without a chimney, with a typical gas furnace being about 80% efficient. Waste gas and heat are mechanically ventilated through PVC pipes that can be vented through the side or roof of the house. Fuel efficiency in a gas furnace is measured in AFUE. Furnaces primarily run on natural gas or electricity. Furnaces that are used to boil water are called boilers.
A fire-tube boiler is a type of boiler in which hot gases pass from a fire through one or (many) more tubes running through a sealed container of water. The heat of the gases is transferred through the walls of the tubes by thermal conduction, heating the water and ultimately creating steam.
A high pressure watertube boiler is a type of boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which boils water in the steam-generating tubes. In smaller boilers, additional generating tubes are separate in the furnace, while larger utility boilers rely on the water-filled tubes that make up the walls of the furnace to generate steam.
A thermal power station is a power station in which heat energy is converted to electric power. In most, a steam-driven turbine converts heat to mechanical power as an intermediate to electrical power. Water is heated, turns into steam and drives a steam turbine which drives an electrical generator. After it passes through the turbine the steam is condensed in a condenser and recycled to where it was heated. This is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different heat sources: fossil fuel, nuclear energy, solar energy, biofuels, and waste incineration are all used. Certain thermal power stations are also designed to produce heat for industrial purposes, for district heating, or desalination of water, in addition to generating electrical power.
Thermosiphon is a method of passive heat exchange, based on natural convection, which circulates a fluid without the necessity of a mechanical pump. Thermosiphoning is used for circulation of liquids and volatile gases in heating and cooling applications such as heat pumps, water heaters, boilers and furnaces. Thermosiphoning also occurs across air temperature gradients such as those utilized in a wood fire chimney or solar chimney.
The steam-electric power station is a power station in which the electric generator is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser. The greatest variation in the design of steam-electric power plants is due to the different fuel sources.
A boiler or steam generator is a device used to create steam by applying heat energy to water. Although the definitions are somewhat flexible, it can be said that older steam generators were commonly termed boilers and worked at low to medium pressure but, at pressures above this, it is more usual to speak of a steam generator.
Yarrow boilers are an important class of high-pressure water-tube boilers. They were developed by Yarrow & Co. (London), Shipbuilders and Engineers and were widely used on ships, particularly warships.
The Stirling boiler is an early form of water-tube boiler, used to generate steam in large land-based stationary plants. Although widely used around 1900, it has now fallen from favour and is rarely seen.
Boilers for generating steam or hot water have been designed in countless shapes, sizes and configurations. An extensive terminology has evolved to describe their common features. This glossary provides definitions for these terms.
A Field-tube boiler is a form of water-tube boiler where the water tubes are single-ended. The tubes are closed at one end, and they contain a concentric inner tube. Flow is thus separated into the colder inner flow down the tube and the heated flow upwards through the outer sleeve. As Field tubes are thus dependent on thermo-syphon flow within the tube, they must thus always have some vertical height to encourage the flow. In most designs they are mounted near-vertically, to encourage this.
Three-drum boilers are a class of water-tube boiler used to generate steam, typically to power ships. They are compact and of high evaporative power, factors that encourage this use. Other boiler designs may be more efficient, although bulkier, and so the three-drum pattern was rare as a land-based stationary boiler.
A cross-tube boiler was the most common form of small vertical boiler. They were widely used, in the age of steam, as a small donkey boiler, for the independent power of winches, steam cranes etc.
A monotube steam generator is a type of steam generator consisting of a single tube, usually in a multi-layer spiral, that forms a once-through steam generator (OTSB). The first of these was the Herreshoff steam generator of 1873.
A steam generator is a form of low water-content boiler, similar to a flash steam boiler. The usual construction is as a spiral coil of water-tube, arranged as a single, or monotube, coil. Circulation is once-through and pumped under pressure, as a forced-circulation boiler. The narrow-tube construction, without any large-diameter drums or tanks, means that they are safe from the effects of explosion, even if worked at high pressures. The pump flowrate is adjustable, according to the quantity of steam required at that time. The burner output is throttled to maintain a constant working temperature. The burner output required varies according to the quantity of water being evaporated: this can be either adjusted by open-loop control according to the pump throughput, or by a closed-loop control to maintain the measured temperature.
A forced circulation boiler is a boiler where a pump is used to circulate water inside the boiler. This differs from a natural circulation boiler which relies on current density to circulate water inside the boiler. In some forced circulation boilers, the water is circulated twenty times the rate of evaporation.
A cornertube boiler is a type of natural circulation water-tube boiler which differentiates itself from other water tube boilers by its characteristic water-steam cycle and a pre-separation of heated steam from the steam-water mixture occurs outside the drum and the unheated downcomers.
A LaMont boiler is a type of forced circulation water-tube boiler in which the boiler water is circulated through an external pump through long closely spaced tubes of small diameter. The mechanical pump is employed in order to have an adequate and positive circulation in steam and hot water boilers.
A Velox boiler is a high pressure, forced circulation, water-tube boiler. It was developed in 1930's by Brown Boveri Company of Switzerland. The first public demonstration of Velox was at VDI Scientific Conference in Berlin on 15 October 1932.
