Fuels for Furnaces.

FUELS

The selection of the best fuel should be based upon a study of the
comparative prepared costs, cleanliness of operation, adaptability to
temperature control, labor required, and the effects of each fuel upon the
material to be heated and upon the furnace lining. Attention must be
paid to the quantity to be burned in each burner, the atmosphere (fuel /
air ratio) desired in the furnace, and the uniformity of temperature distribution
required, which determines the number and the location of the
burners. Common methods of burning furnace fuels are as follows:

Solid Fuels (Almost Entirely Bituminous Coals)

Coal was once a common fuel for industrial furnaces, either hand-fired,
stoker-fired, or with powdered coal burners. With the increasing necessity
for accurate control of temperature and atmosphere in industrial
heating, coal has been almost entirely replaced by liquid and gaseous
fuels. It can be expected that methods will be developed for the production
of a synthetic gas (natural-gas equivalent) from coal.

Liquid Fuels (Fuel Oil and Tar)

To burn liquid fuels effectively, first it is necessary to atomize the oil
into tiny droplets which then vaporize and burn. Atomization can be
accomplished mechanically or with the aid of steam or air. With heavy
oils and tar, it is important to maintain the proper viscosity of the oil at
the atomizer by preheating the fuel.
For larger industrial burners, combustion air is supplied by fans of
appropriate capacity and pressure. Combustion air is induced with some
smaller burner designs.

Gaseous Fuels

Burners for refined gases (natural gas, synthetic gas, coke-oven gas, clean
producer gas, propane, butane):
Two-pipe systems: Include blast burners (open or closed setting), nozzle
mixing, luminous flame, excess air (tempered flame), baffle, and
radiant-tube burners, all for low-pressure gas and air.
Premix systems: Air and gas mixed in a blower and supplied through
one pipe.
Proportioning low-pressure mixers: Air and gas supplied under pressure
and proportioned automatically (air aspirating gas or gas inspirating
air). The resulting mixture is burned in tunnel burners, radiant-cup,
baffle, radiant-tube, ribbon, and line burners.
Pilot flames are generally used to ensure ignition for gas and oil
burners. Insurance frequently requires additional safety provision in two
main categories: an interconnected pressure system to prevent lighting
if any burner in a zone is open, and burner monitors using heat or light
to permit ignition.
Burners for crude gas (raw producer-gas, blast-furnace gas, or cokeoven
gas):
Simple mixing systems with large orifices and simple mechanisms
which cannot become clogged by tar and dirt contained in these gases.
Separate gas and air supplies to the furnace, with all mixture taking
place within the furnace.