Furnaces / Heater consist of various parts and piping with different operational modes. Following is a terminology used to describe these aspects of a furnace.
Blowdown Steam :
Blowdown steam is used for tube cleaning or removal of products from the inlet piping in the event of fire.
Blowdown System :
A blowdown system is the piping system used to carry waste away from piping or tubes for disposal.
Breeching referes to duct work that collects flue gases among the furnace box outlet for transmission to stack.
Supplied with air and fuel necessary for combustion, burners heat the product in the tubes in the radiant section of the furnace. The most common types of burners are : gas; air and as; air and oil or gas; and oil which requires air, oil and atomizing steam.
Burner Management Package :
This device is designed to control such burner operations as monitoring purge sequence, igniter and main fuel start-up, pilot flame, main flame, and heater conditions. Limiting devices are built into the package that shut down the furnace if unsafe operating conditions arise.
Clean-out access doors :
Access is provided to the interior of the furnace for maintenance personnel.
Convection Section :
This compartment houses rows of primarily horizontal tubes located downstream from the radiant section that are used for additional heating in a process unit. Passing the hot flue gases over these tubes can provide additional duty. Examples include preheating process streams, steam superheating, and additional steam generation. Provisions must be made to remove these tubes for inspection, repair and replacement.
Crossover Piping :
This piping interconnects the radiant and convection sections and is usually furnished by the furnace vendor.
Located in the stack or duct, this device is used to control drafts in the furnace. Dampers are usually flat plates that rotate on a shaft resting on pillow blocks set in the steel shell, similar to a butterfly valve.
The coke built up in many hydrocarbon furnace tubes during operation is removed by injecting steam and air into the tubes.
Draft gauge :
This instrument is used to check pressure in a furnace.
Explosion doors :
In the event of an explosion in a furnace, doors specifically designed to blow out and protect against major structural failure are provided; they act like safety valves in a piping system.
A header is the fitting that connects two tubes in a flow pattern.
Header boxes :
Most ends of tubes are connected by U-bends that make inspection difficult. Therefore special return fittings with plugged connections are provided that permit inspection and cleaning. Because the removable plugs are subject to leaking, all headers must be completely enclosed in header boxes. Snuffing steam is used to suppress fire in this area.
Peep Doors :
Small doors are provided in the wall or floor of the radiant section to permit visual inspection of burners during start-up or operation.
Small-bore piping configurations connect the radiant tubes to the inlet and outlet headers as shown below.
Radiant Section :
The main compartment of a furnace is the radiant section, in which process streams are heated, usually in vertical tubes, by heat from burners mounted in the walls, roof or floor.
The refractory is made of insulating bricks capable of withstanding high temperatures in furnaces.
Soot Blowers :
Soot blowers are mechanical devices that clean residue build-up on the exterior of the convection tubes. They are usually furnished when oil fired burners are used.
Located downstream from the convection section, the stack is designed to carry flue gases directly to the atmosphere or to divert them through secondary ducts to an air pre-heating system. Stack elevations are usually established by furnace designer to operate on natural drafts. If the height of the stack is increased to suit safety conditions, a fan must be added. If emission probes are needed in a stack, ladders and platforms are added as required.
Snuffing Steam :
This is a steam that is injected into the combustion chambers or header box of a furnace to suppress a fire.
Transfer Line :
The outlet of the process tubes are tied into a piping header called transfer line, which feeds the man process tower.
Piping within the furnace carries the medium to be heated. A radiant coil is shown below.