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Tangential firing

Tangential firing is a method of firing a fuel to heat air inthermal power stations. The flame

envelope rotates ensuring thorough mixing within the furnace, providing completecombustion

and uniform heat distribution.

The most effective method for producing intense turbulence is by the impingement of one flameon another. This action is secured through the use of burners located in each of the four corners

of the furnace, close to the floor or the water-screen. The burner nozzles are so directed that the

streams of coal and air are projected along a line tangent to a small circle, lying in a horizontal

plane, at the center of the furnace. Intensive mixing occurs where these streams meet. Ascrubbing action is present which assures contact between the combustible and oxygen, thus

promoting rapid combustion and reducing carbon loss. A rotative motion, similar to that of a

cyclone, is imparted to the flame body, which spreads out and fills the furnace area. The ignition

at each burner is aided by the flame from the preceding one.

With tangential firing the furnace is essentially the burner, consequently air and coal quantitiesneed not be accurately proportional to the individual fuel nozzle assemblies. Turbulence

produced in the furnace cavity is sufficient to combine all the fuel and air. This continuously

ensures uniform and complete combustion so that test performance can be maintained throughout

daily operation. With other types of firing the fuel and air must be accurately proportioned toindividual burners making it difficult to always equal test results.

With this type of firing, combustion is extremely rapid, and short flame length results. The

mixing is so intense that combustion rates exceeding 35,000 Btu/(ft3h) or 360 kW/m3 are

practical under certain conditions. However, since there is considerable impingement of flame

over the furnace walls it is absolutely necessary that they be fully water-cooled. This sweeping of

the water-cooled surfaces, in the furnace, by the gas increases the evaporation rate. Thus, inaddition to absorption by radiation from the flame envelope, there is transfer by convection, and

the resulting furnace temperatures are lower than with other types of burners, even though the

heat liberation rates may be somewhat higher. Tangentially fired furnaces are usually clean in theupper zone and, as a result, both the furnace and the boiler are comparatively free from

objectionable slag deposits.

(http://en.wikipedia.org/wiki/Tangential_firing)

1. ^Lorenzi, M.E., Otto, ed. Combustion Engineering. 1st ed. New York: ComustionEngineering, INC., 1955. 8.16-8.17.

A furnace in which fuel, such as pulverized coal, is burned, with the fuel and air beingintroduced into the furnace through tangential burners located in each of the four corners thereof

and being directed tangentially to an imaginary circle in the center of the furnace. The invention

will be described with pulverized coal, but is not limited to coal. Combustion gases fromdownstream of the furnace are recirculated back to the furnace, and are also introduced into the

http://en.wikipedia.org/wiki/Thermal_power_stationhttp://en.wikipedia.org/wiki/Thermal_power_stationhttp://en.wikipedia.org/wiki/Thermal_power_stationhttp://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/wiki/Tangential_firing#cite_ref-0http://en.wikipedia.org/wiki/Tangential_firing#cite_ref-0http://en.wikipedia.org/wiki/Tangential_firing#cite_ref-0http://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/wiki/Thermal_power_station

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furnace from the four corners, in a tangential manner. The coal is introduced along with primary

air to be directed at the smallest of a series of concentric imaginary circles; the recirculated gasesare directed tangentially at a somewhat larger imaginary circle; and the secondary air is directed

tangentially at a still larger imaginary circle.

(http://www.freepatentsonline.com/4294178.html)