Q. Layout of vessels in plant design?

Layout of vessels needs to allow sufficient spacing for instruments, piping, operations, maintenance and firefighting access.

Vessels operating above 316 °C (600 °F) or above auto-ignition temperature represent an increase risk of fire. Equipment located above vessels containing hydrocarbons operating above 316°C (600°F) or above auto-ignition temperature (whichever is lower) should be protected by measures such as passive fire protection or water sprays.

Internally insulated vessels are more vulnerable to overheating and potential failure when exposed to external fires, so increased spacing is justified.

For very large vessels, consider providing a toe-wall around the vessel a minimum of 3 m (10 ft.) from the vessel shell. No other equipment should be installed within the toe-wall. Toe-wall contained areas shall be adequately drained to prevent hydrocarbon pool fires occurring in the event of major spills. For large multi-level structures, such toe-wall containment and drainage shall be designed to prevent escalation offire to lower levels by burning hydrocarbon fluids. If possible, locate vessels with the largest inventory of fluids at the bottom of the structure to permit faster drainage and fire fighting access. Blowdown and water disengaging drums should be located in a separate unit area to avoid involvement in process unit fires.

Large vessels should be located close to battery limits to allow easy access of mobile lifting equipment. Vessels containing catalyst, resins, filters, cartridges or packing require space for bins or pallets and lifting facilities for filling / emptying of materials. Where a series of beds are involved, access to each bed will be required. Reactors have a substantial top platform with lifting facilities for removal of reactor head and catalyst loading. Reactors can have platforms attached or have an independent access structure.

Towers and columns shall be located in a way that all working platforms and manholes face the access road. Manways shall be on or about a common centerline.

Where vessels are fitted with agitators, lifting facilities shall be provided for motor / agitator blades removal and set down. This can affect building heights. If a travelling crane is used, motor / agitator travel routes should not pass over other equipment.

Permanent access should be provided to manholes and instrumentation on all vessels. Access to platforms from ladders should be by side stepping wherever possible.