This article is about technical requirement of spacing of process equipment like fired heaters.
Layout and Spacing of Process Equipment
Process Unit Spacing
Equipment in a process unit should be located 30 meter from equipment handling hydrocarbon in adjacent units. This spacing is required to minimize risks due to turnaround maintenance activities in a unit while the adjacent unit remains in service. If the process units are integrated, and therefore shut down simultaneously, the spacing may be reduced to 15 meter.
The minimum distance from a process unit battery limit to an unrestricted plant roadway should be 15 m. Spacing less than 15 m may be considered with the addition of proper mitigation and/or control procedures. For example, requiring vehicle permits on all vehicles that travel on unrestricted plant roadways.
Process equipment should be located at least 60 m from railroad main lines. Spacing to tankage should be as specified in NFPA No. 30. Spur tracks for refinery use should be outside process unit battery limits and 15 m from process equipment, except in coking units.
Fired Heaters
- Fired heaters are a continuous ignition source and require separation of at least 15 m from process equipment containing flammable liquids. Where hydrocarbons are handled at temperatures above auto-ignition or above 260 °C there is little chance of delayed ignition or vapor cloud formation. This allows a reduction in spacing to the minimum required for maintenance and fire fighting. Fired heaters should be located upwind at process unit battery limits or next to road for easy access. The prevailing wind direction should be considered when locating fired heaters to minimize the potential of igniting vapors.
- Locate fired heaters at least 15m from pumps and compressors and from vents that might release ignitable vapors. The spacing should be increased to 22.5m where adjoining vessels will be entered for maintenance while a fired heater remains in operation. Process unit pipeways and the heater’s fuel gas knockout pots should be no less than 7.5m from fired heaters.
- Provisions shall be made for pulling the cleaning tubes and soot blowers. The area allotted for tube removal, either horizontal or vertical, should be shown on the plot plan on the side away from the piping end of the heater. Adequate area shall be provided for necessary equipment, such as cranes.
- The top of vertical tube heaters must have clear areas for removing tubes. Bottom fired heaters should have 2.1 m clearance for burner removal. The area under heaters shall be paved.
- Silica dehydrators (1100 °C) should be spaced 60 meter from hydrocarbon equipment that might release vapors. Given the low operating percentage, the spacing may be reduced to 30m if the plant implements operating procedures to control dehydrator operation during times of maintenance or flange breaks in adjacent units.
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