A typical Piping Design Basis specifies various aspects of furnace layout such as location of furnace itself, forced draft fans, trenches, control panels, stack etc. as follows.
Heaters should be located up wind at one corner of the unit, so that gases from process and hydrocarbon areas cannot be blown into the open flames by prevailing winds. Space should be provided for removal and cleaning of heater tubes, soot blowers, air preheater baskets, burners, fans and other related serviceable equipment besides approach for crane, Areas around the heaters shall be graded for guiding spills away from process equipment.
Forced Draft Fans
Forced Draft fans shall be located away from process equipment from where they are likely to suck hydrocarbon vapors.
No trenches or pits which might hold flammables should extend under the furnace and connections with underground drain system should be sealed over an area 15 meters from the furnace walls.
The local control panel for soot blower control and flue gas analyzer only should be located on and near the process heater.The rest of controls should be taken to control room.
Heater stack shall be a minimum of 4500 mm above any platform within a radius of 15 Meters.
Access shall be provided at burner observation ports, process piping instrument connections, stack instruments and tube observation doors. Platforms shall be provided at lance doors and soot blowers.
Pressure relief doors and tube access doors shall be free so as not to blow into adjacent equipment.
Arrange piping to permit burner removal by providing break-up flanges in the piping. Burner valves shall be located close to the peepholes for operation so that adjustment can be made while observing the flame from working level. Piping to burners shall be arranged so that there are no pockets & shall distribute equal and sufficient quantity of oil/gas to all burners. Only flexible metallic SS (SS316/SS304) hoses shall be used for burner piping if required.
Snuffing Steam Piping
Block valves for emergency, snuffing steam valve shall be located 15 Meters away from the heater, preferably on the upwind side of the heater.
Piping from various passes of heater outlet nozzles should preferably be symmetrical. Transfer line from heater to column shall be as short as possible, without pockets, free draining and with minimum bends. No piping shall be routed in the tube withdrawl area. If unavoidable, break up flanges shall be provided in the piping for removal. Nozzle forces and moments to be as per API 560.
As well as complying with stress analysis results, the following general criteria must be considered :
- When choosing and positioning supports adjacent to the nozzles, if an anchor has not been provided by the manufacturer, it is necessary to provide supports which will not stop the expansion of the coil, as foreseen in the stress analysis calculations.
- Where spectacle blinds or dismantling spools are inserted, both the upstream and downstream piping spool must be adequately supported considering also the conditions of dismantled spool.
- Avoid the support obstructing the walking floors of service platforms.
When supports connected tot he heater structure are to be provided, the information related to their position and loads will be communicated to Mechanical Department for their transmission to the Manufacturer.