Suppliers of cool air
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fans, industrial fan motors, big industrial fans, large industrial
ventilators, industrial blower systems, explosion proof ventilation
fans, rooftop fans and ventilators, shop fans, building ventilation
fans. Industrial process ventilation
fans and utility blowers, OEM blower / fan wheel blades, compact
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backward inlined and radial blowers and fan ventilators. Quick ship of
centrifugal and axial aluminum and steel centrifugal pressure blowers
and tubeaxial / vaneaxial fan ventilators.
Industrial blowers, fans and ventilators, high temperature blowers,
high pressure fans and blowers. Sales of centrifugal and axial process
fans, blowers and ventilators.
fan blower ventilator pressure industrial centrifugal axial
explosion proof high pressure temperature Buffalo Twin City Greenheck
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Air can be supplied to the combustion process by natural or mechanical
draft. Natural draft simply refers to the use of a chimney or stack to
induce an upward flow of air. The stack effect pulls air into the
combustion chamber. The amount of airflow depends on the stack’s height
and diameter, the prevailing wind velocity, and the resistance of the
burner mechanism or fuel bed itself. The demand for air-cleaning
apparatus on combustion systems, particularly oil and coal, has
increased the overall system resistance to such an extent that natural
draft alone is seldom sufficient.
The burning of gas, oil, coal, or other combustible material requires
air. When the end result of the burning is to be an efficient
combustion process, in compliance with Federal and State Clean Air Act
requirements, the volume of supply air must be reliably controlled.
Insufficient air volume will result in wasted fuel and excessive
particulate along with potentially explosive gases in the exhaust
system. Too much air increases the amount of heat carried up the stack
by the excess draft. Either extreme increases the cost and difficulty
of controlling exhaust emissions.
Mechanical draft refers to the use of fans or blowers to create airflow
through the combustion area. When mechanical draft is incorporated, the
chimney or stack is used primarily to direct the exhaust gases up and
away where they will not be a nuisance. Because wind velocity and
direction are less important, the combustion process can be much more
carefully controlled. Mechanical draft is accomplished in one of two
ways: when air is blown or forced into the combustion chamber it is
known as forced draft, when the air is drawn through the combustion
chamber it is called induced draft. When both forced and induced draft
are used, the system is termed a balanced-draft system.
Generally, the fans or blowers used for induced-draft applications are
larger and more expensive than those used for similar forced-draft
applications. The combustion process itself creates gases and elevated
temperatures that expand the exhaust airstream, requiring fans with
greater volumetric capacity than would be required on the supply side
of the combustion process to supply clean, ambient air. Also, the hot
exhaust serves to lower the density of the airstream, so density
corrections must be applied to the fan static pressure (SP) to overcome
the actual system resistance. The fact that the exhaust or flue gases
are hot often requires induced-draft fans to be of a construction
suitable for higher temperatures.
The first induced-draft fans were applied to hand-fired, solid-fuel
boilers where the combustion chamber had to be at a negative pressure
to permit the operator to shovel in fuel. When oil and gas became
primary fuel sources, boiler designers were able to seal the combustion
chambers. As a result, forced draft fans became popular. The advantages
were lower fan power and fans handling clean air (no corrosion or
abrasion) at ambient conditions. These factors encouraged the use of
airfoil fans, further reducing power consumption. This led to the
almost universal use of pressurized firing in gas, oil, and pulverized
coal boilers.
Forced draft fans and blowers are common for cast iron firetube and
small water tube boilers. The fan or blower serves to provide the air
and the velocity necessary for the fuel-to-air mixture to enter the
actual combustion chamber. When used in conjunction with induced draft,
the forced-draft fan is often called the primary air fan since it
provides the primary combustion supply air. The induced-draft fan
provides the airflow necessary to overcome system resistance and
exhaust the flue gases. Some combustion systems draw hot, perhaps dirty
air from other processes. Forced draft fans for such systems are called
gas recircula tion fans, and must be selected for the rigorous
conditions under which they will operate.
Radial-blade fans were at one time commonly used for induceddraft
service. However, as pollution requirements have become more stringent
and control devices have been added to reduce flue gas particulates
(ahead of the induced draft fan), radial-tip blade or even
backwardly-inclined fans have become popular due to their higher
efficiencies and higher volumetric characteristics. The exception to
this is where high efficiency scrubbers are used and the pressure
requirements are increased to where the radial-bladed fans are more
suited.
