Specifically, this section will discuss:
• The function and components of the fuel gas system.
• The function and components of the fuel oil system.
Fuel Gas System
The most common gaseous fuel is natural gas. Waste gas or gas produced as a process byproduct can also be used. Natural gas is transported through pipelines and is delivered by the suppliers as it is used.
Fuel Oil System
The most common oils used for boiler fuel are the lightweight Number 2 fuel oil and the Number 6 grade of heavy residual fuel oil. It is usually necessary to heat Number 6 fuel oil so that it can be pumped through the system. It is normally not necessary to heat Number 2 fuel oil. Fuel oil is pumped through the fuel oil system, and the boiler control system regulates the BTU input by a control valve. The amount of heat (BTU) liberated per unit quantity of gas or oil is called the Higher-Heat Value (HHV). The HHV for a fuel, typically in units of BTU per pound, can be found in the Combustion Engineering Fuel Burning and Steam Generation Handbook.
GLOSSARY
Air The mixture of oxygen, nitrogen, and other gases that with varying amounts of water vapour, forms the atmosphere of the earth.
Air heater Heat transfer apparatus through which air passes and is heated by a medium of higher temperature, such as the products of combustion (flue gases) or steam.
Air preheater A steam coil or similar heat exchange device used to keep the temperature of the flue gas above its dew point to minimize corrosion to the air heater.
Balanced draft A system of furnace pressure control in which the inlet combustion air flow and the outlet flue gas flow is controlled to maintain the furnace pressure at a fixed value the required velocities, turbulence, and concentration to maintain ignition and combustion of the fuel within the furnace.
Constant speed A fan with a single-speed motor that uses damper control or inlet vane control to Fan vary air flow.
Control Any manual or automatic device for the regulation of a machine to keep it at
Flash evaporator A device that is used with boilers operating at 1000 gal or over to purify boiler water by an evaporation technique.
Forced draft fan A fan that is used to force a flow of air into the boiler furnace.
Fuel A substance that contains combustible materials that are used for generating heat.
Fuel oil Unit of energy management equivalent to energy in a barrel of oil, or equivalent 6,300,000 BTU.
barrels
Furnace Combustion chamber of a boiler.
Heat exchanger A device for transferring heat energy from one medium to another.
Heat of The heat input or enthalpy necessary to convert saturated water to saturated vaporization steam.
HHV Higher Heating Value. The number of heat units that are liberated per unit of quantity of fuel burned.
Induced draft The furnace draft produced by drawing the flue gases out of the furnace by an induced draft fan. The furnace pressure is usually controlled at less than
atmospheric pressure with the fan.
Induced draft A fan that is used to produce a flow of air through the furnace by creating a lower fan pressure. An induced draft fan is commonly used to aid the
exhaust of flue gases.
Intermittent The blowing down of boiler water at intervals to remove suspended solids.
blowdown Intermittent blowdown is achieved by periodically opening a blowoff valve located at the bottom of the mud drum.
Makeup Water that is added to replace losses, blowdown, etc.
Mud drum Lowest boiler drum in which suspended solids collect.
Natural circulation The circulation of water in a boiler that is caused by differences in density.
Natural draft A furnace draft that is caused solely by the effect of the stack.
Nucleate boiling The process of steam bubbles at a tube's inner surface condensing and giving up their heat to raise the temperature of the water.
Oxygen Chemicals that are used to control boiler corrosion.
furnace forced draft fan.
Quality Quality is the percent by weight of vapor in a steam/water mixture.
Recirculation The reintroduction of part of the flowing fluid to repeat the cycle of circulation.
Reverse osmosis A procedure that is used to remove dissolved salts and minerals in a solution.
Risers The tubes that are heated through which the steam/water mixture moves from the lower or mud drum to the boiler drum.
Saturated steam Steam that is at the boiling point temperature that corresponds to a particular pressure, without any water present.
Saturated water Water at the temperature of its boiling point.
Scrubber An apparatus for the removal of solids from gases by entrainment in water.
Specific volume The volume that a pound of steam or water occupies at a given pressure or temperature.
Stack The flue, vent or passage through which smoke or heated air, etc. escapes.
Stack effect The movement of hot flue gases out of the stack caused by differences in density between these flue gases and the cooler air surrounding the stack.
Steam coil air A tubular recuperative air heater in which gas flows vertically through tubes. Air heater flows horizontally across the tubes in order to provide heat transfer.
Steam drum All apparatus within a drum.
internals
Steam quality The percent by weight of vapor in a steam and water mixture.
Superheated Steam that is at a higher temperature than its saturation temperature.
steam
Superheater A device that is used to raise the temperature of steam above its saturation temperature.
Variable speed A fan with a variable speed drive that is used to change speed to vary air flow.
fan