| Air Preheater :Heat exchanger device that uses some of the heat in the flue gases to raise the temperature of the air supply to the burners. |
| Breeching:The hood that collects the flue gas at the convection section exit. |
| Bridge:Wall Temperature - The temperature of the flue gas leaving the radiant section |
| Bulk Temperature: The average temperature of the process fluid at any tube cross section. |
| Center Wall:A refractory wall in the radiant section, which divides it into two separate cells. |
| Coil: A series of straight tube lengths connected by 180 o return bends, forming a continuous path through which the process fluid passes and is heated. |
| Convection Section: The portion of a heater, consisting of a bank of tubes, which receives heat from the hot flue gases, mainly by convection. |
| Corbelling: Narrow ledges extending from the convection section side walls to prevent flue gas from flowing preferentially up the side of the convection section, between the wall and the nearest tubes. |
| Crossover:Piping which transfers the process fluid either externally or internally from one section of the heater to another. |
| Damper: A device to regulate flow of gas through a stack or duct and to control draft in a heater. |
| Draft:The negative pressure (vacuum) at a given point inside the heater, usually expressed in inches of water. |
| Excess Air - The percentage of air in the heater in excess of the stoichiometric amount required for combustion. |
| Extended Surface - Surface added to the outside of bare tubes in the convection section to provide more heat transfer area. |
| Film - A thin fluid layer adjacent to a pipe wall that remains in laminar flow, even when the bulk flow is turbulent. |
| Film Temperature - The maximum temperature in the film, at the tube wall. |
| Fire Box - A term used to describe the structure which surrounds the radiant coils and into which the burners protrude. |
| Flue Gas - A mixture of gaseous products resulting from combustion of the fuel. |
| Fouling - The building up of a film of dirt, ash, soot or coke on heat transfer surfaces, resulting in increased resistance to heat flow. |
| Forced Draft - Use of a fan to supply combustion air to the burners and to overcome the pressure drop through the burners. |
| Fired Heater Efficiency - The ratio of heat absorbed to heat fired, on a lower heating value basis. |
| Header Box - The compartment at the end of the convection section where the headers are located. |
| Heat Available - The heat absorbed from the products of combustion (flue gas) as they are cooled from the flame temperature to a given flue gas temperature. |
| Heat Density - The rate of heat transfer per unit area to a tube, usually based on total outside surface area. |
| Heat Duty - The total heat absorbed by the process fluid, usually expressed in MBtu/hr |
| Induced Draft - Use of a fan to provide the additional draft required over that supplied by the stack, to draw the flue gas through the convection section, and any downstream heat recovery equipment. |
| Lower Heating Value (LHV) - The theoretical heat of combustion of a fuel, when no credit is taken for the heat of condensation of water in the flue gas. |
| Mass Velocity - The mass flow rate per unit of flow area through the coil. Typical units are lb/s-sq. ft. |
| Natural Draft - System in which the draft required to move combustion air into the heater and flue gas through the heater and out the stack is provided by stack effect alone. |
| Net Fuel - The fuel that would be required in the heater if there were no radiation losses. |
| One-Side Fired Tubes - Radiant section tubes located adjacent to a heater wall have only one side directly exposed to a burner flame. Radiation to the back side of the tubes is by reflection/ re-radiation from the refractory wall. |
| Pass - A coil that transports the process fluid from fired heater inlet to outlet. |
| Radiant Section - The section of the fired heater in which heat is transferred to the heater tubes primarily by radiation from high-temperature flue gas. |
| Service Factor – A measure of the continuity of operation, generally expressed as the ratio of total running days for a given time period to the total calendar days in the period. |
| Shield Section - The first two tube rows of the convection section. |
| Sootblower - A steam lance (usually movable) in the convection section for blowing soot and ash from the tubes using high-pressure steam. |
| Stack - A cylindrical steel, concrete or brick shell which carries flue gas to the atmosphere and provides necessary draft. |
| Stack Effect - The difference between the weight of a column of high-temperature gases inside the heater and/or stack and the weight of an equivalent column of external air,usually expressed in inches of water per foot of height. |
| Stack Temperature - The temperature of the flue gas as it leaves the convection section,or air preheater directly upstream of the stack. |
| Two-Side Fired Tubes - Radiant section tubes which are exposed on both sides to direct radiation from the burners. |
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