BN-DG-C01A Plant Layout - General Requirements

Table of Contents

1. Process
2. Hazardous and Toxic Areas
3. Economic Considerations
4. Aesthetic Considerations
5. Access
6. Safety
7. Site Considerations
8. External Influences
9. Clearances
10. Paving
11. Elevations
12. Insulation
13. Columns and Drums (Vertical/Horizontal)
14. Exchangers
15. Furnaces and Fired Equipment
16. Pumps
17. Compressors
18. Piping
19. Access to Valves and Instruments
20. Relief Valve Systems
21. Maintenance and Equipment Handling

1. Process

Equipment should be laid out in a sequence to suit the process flow. Fluid flow requirements, for example gravity flow systems, pump suction heads and thermosyphon system, often dictate relative elevations and provoke the need for structures. Limitations of pressure or temperature drop in transfer lines decide proximity of furnaces, reactors, etc.

2. Hazardous and Toxic Areas

Equipment items considered a possible source of hazard should preferably be grouped and located separately, if possible and economic.

Examples are:

Furnaces, flare stacks, or other direct fired equipment containing an open flame; rotating or mechanical equipment handling flammable or volatile liquids which could easily leak or spill.

Equipment handling acids or other toxic materials which could cause damage or danger by spillage, should be grouped and contained within a bunded area.

2.1 Locate Control Rooms

15 meters or more from equipment which in operation or during maintenance can create a hazard. (If not practicable, pressurize). Ensure maximum cable run to any instrument is not more than 90 meters.

2.2 Locate Buildings

Example offices, first-aid rooms, cafeterias, garages, fire station, warehouses, gas holders and work-shops a minimum of 30 meters from any hazard.

Unpressurised substation and switchrooms a minimum of 15 meters from any hazard.

Definition of dangerous areas and their safety requirements shall be in accordance with the Institute of Petroleum Safety Codes, or where this is not recognized, to the applicable National Code(s).

Local bye-laws and Fire Office whose requirements may be more stringent or specific than the above codes shall take precedence.

3. Economic Considerations

Apart from process restrictions, position equipment for maximum economy of pipe-work and supporting steel. As compact a layout as possible with all equipment at grade is the first objective, consistent with standard clearances, construction and safety requirements.

Minimize runs of alloy pipework and large bore pipe without the introduction of expensive expansion devices.

Optimize use of supporting structures in concrete or steel by duplicating their application to more than one item of equipment and ensuring that accessways, platforms, etc., have more than one function. Space saving can be achieved by locating equipment over the piperack. Pumps should in general be located with their motors underneath the main piperack.

4. Aesthetic Considerations

Attention should be paid to the general appearance of the plant. An attractively laid out plant with equipment in straight lines is usually economical. Preference should be given to use of a single central pipeway with a minimum number of side branches, with equipment laid out in rows on either side. Buildings, structures and groups of equipment should form neat, symmetrical, balanced layout, consistent with keeping pipe runs to a minimum.

Towers and large vertical vessels will be arranged in rows with a common center line if of similar size, but line up with a common face if diameters vary greatly. If adjacent to a structure, common face will be on the structure side.

Center lines of exchanger channel nozzles and center lines of pump discharge nozzles should be lined up. Piping around pumps, exchangers and similar ground-level equipment should be run at set elevations, one for north-south and another for east-west elevations wherever possible. (Similar for rack pipe-work). These elevations being to bottom of pipe or underside of shoe for insulated lines. This should also help to achieve a common elevation for off takes from pipeways.

If possible, duplicated streams should be made identical. Handed arrangements should be avoided. Follow this principle for this similar equipment sequences within the process stream, for example, fractionator tower with overhead condensers, reflux drum pumps and reboiler, etc., is a system which could be repeated almost identically for different towers having a different process duty. Advantages are design and construction economy, improved maintenance and operating efficiency.

5. Access

Overall plant arrangement must be reviewed for constructions, operation, safety and maintenance. Consider large items of equipment or towers for which special lifting gear will be required. Provide adequate access to lift these into place. Large equipment positioned close to boundary limits may require erection from outside.

Check to ascertain whether sufficient space will be available at the construction phase.

Operation and maintenance should be reviewed by the eventual operating company. Give consideration to maintenance access to air fins, etc., above pipe tracks.

Consider location of equipment requiring frequent attendance by operating personnel and relative position of control room to obtain shortest and most direct routes for operators when on routine operation.

6. Safety

Provide: Sufficient clear area between critical or high temperature items of equipment. Clear routes for operators with two or more escape ladders or exits at extremities. Clear routes for access by fire-fighting equipment.

Do not Allow: Areas classified as hazardous to overlap the plot limits or extend over railways where open firebox engines are likely to be employed.

7. Site Considerations

Ascertain soil loading considerations and site contours before fixing final layout. Considerable variations occur in allowable soil loads throughout site areas. It may be advantageous to locate heavy equipment in the best soil loading area. Use existing contours, so that the quantity of earth movement due to cut and fill may be substantially reduced by intelligent positioning of the equipment.

8. External Influences

Stacks should preferentially be located so that prevailing winds do not blow smoke over the plant. Try not to locate the plant where it will receive dust, smoke, spray or effluent from a neighboring plant.

Avoid using locations polluted by continuous drift of dust, smoke, etc.

If the plant is to be located in an existing refinery or factory site, line up with existing roads, columns, stacks.

Location of external railways, pipeways, cableways, sewers and drains, etc., may also influence the final orientation of the plant.

When railway facilities are required, avoid boxing in the plant by branch lines.

Hazardous areas from other existing plants or equipment may extend over the plant limit. This could effectively reduce plot size and thus influence the plant layout philosophy.

9. Clearances

(See Table A) Clearances between adjacent plants should at least equal those for primary access roads. The space between edge of any road and nearest equipment must not be less than 1.5 meters.

Adequate road access with properly formed roads must be provided for known maintenance purposes: e.g., compressor house, large machinery areas, reactors or converters where catalyst removal and replacement must be effected.

Equipment requiring infrequent maintenance such as exchanger tube bundles, tower internals, etc., need adequate level clear space for access/removal purposes. The ground need not be specifically built up to take loads other than a surfacing of granite chips or similar, as duckboards, gratings, or other temporary material can be laid at the time when the plant is under maintenance.

10. Paving

Within the process area minimal concrete paving should be supplied for walkways interconnecting major items of equipment, platforms, stairways and buildings.

Paving should be supplied around pumps or other machinery located in the open, underneath furnaces, and any other areas where spillage is likely to occur during normal operation.

Areas containing alkalis acids, or other chemicals or toxic materials should be paved and bunded to prevent spillage spreading. Other areas of the plant are to be graded and surfaced with granite chips or similar material.

11. Elevations

(See Table A) All elevations refer to a nominal 100 meters. The point 100 elevation is taken as the high point of paving in the paved areas. This should be common throughout the plant. Equipment elevations referring to grade elevations of 100 meters are as shown in table A.

12. Insulation

Insulation may be applied to vessel supports or stanchions of structures for fire protection purposes, thus decreasing available free space for access, siting of pipework, instruments or electrical equipment.

In particular, note thickness of insulation of very high temperature or low temperature piping, which may considerably increase effective o/d of pipe to be routed. For low temperature insulation, additional clearance must be provided around control valves, instrumentation, etc. Consider additional weight of insulation and reduced centers of supports necessary to support heavily insulated pipe.

13. Columns and Drums (Vertical/Horizontal)

Columns are usually self-supporting without external structures. Circular or segmental platforms with ladders are supported from the shell. Maximum allowable straight run of ladder before a break platform should not exceed 9 meters.

Factors influencing column elevation are provision of gravity flow system and installation of therm-syphon reboilers. Depending on plant arrangement columns may have to be elevated to a height in excess of the normal requirements to allow for headroom clearance from low level piping off-takes.
Skirt height of all columns or vessels providing suction to pumps, particularly if handling hot or boiling liquids, should be adequate for pump NPSH requirements.

Provide platforms on columns for all valves 3” and above, instrument controllers and transmitters, relief valves, manholes and blinds or spades. Otherwise, access to small valves, indicating instruments, etc., is acceptable by ladder.

Platforms for access to level gauges and controllers should not be provided if underside of supporting steelwork is less than normal headroom clearance from grade. Adjacent columns should be checked, so that platforms do not overlap. For layout, 2.0 to 2.5 meters between shells, depending upon insulation, should suffice. Allow 900 meters minimum clearance between column foundation and adjacent plinth. Provide clearance for removal of internals and attachments, and for davits at top of column if relevant.
Center line of manholes will be 900 mm above any platform.

Horizontal vessels should be located at grade, with longitudinal axis at right angles to the pipeway if possible. Consider saving plot space by changing vessels from the horizontal and by combining vessels together with an internal head. (Subject to project approval). Size and number of access platforms on horizontal vessels shall be kept to a minimum and are not to be provided on horizontal vessels or drum when the top of the vessel is 2.5 meters or less from grade.

Channel end of vessels provided with internal tubular heaters will face towards open space. Withdrawal area must to be indicated on studies, GA’s and Plot Plants. Internal agitators or mixers are to be provided with adequate clearance for removal. Removal area must be indicated on Studies, GA’s and Plot Plants.

14. Exchangers

Tubular exchangers usually have standard length tubes of 2.5, 4, 5, and 6 meters.

Whenever possible locate exchangers at grade to facilitate maintenance and tube withdrawal. Two or more shells forming one unit will be stacked, or otherwise arranged as indicated on the exchanger specification sheet.

Exchangers on dissimilar service may be stacked but never more than three high, except for fin tube type units. Horizontal clearance of at least 900 mm will be left between exchangers or exchangers and piping. Where space is limited, clearance may be reduced between alternate exchangers, providing sufficient space is left for maintenance and inspection access.

Tube bundle removal distance will be minimum tube length plus 900 mm. Minimum removal distance plus 600 mm will be left behind the rear shell cover of floating head exchangers. Where rear shell cover is provided with a davit, allow clearance for full swing of the head. Set overhead vapor exchangers or condensers at such elevation that exchanger is self draining.

Arrange outlets to a liquid hold pot or trap, so that underside of exchanger tubes is above the liquid level in the trap. Arrange exchangers so that fixed end is at the channel end. Vertical exchangers should be set to allow lifting or lowering of tube bundle. Consult Vessel Section as to feasibility of supporting vertical exchangers from associated towers.

Space for tube or bundle withdrawal should be left free, exchanger channels preferably pointing towards access area or road. If exchanger is situated well within the plot, leave a free area and approach for mobile lifting equipment. Preferably air fin exchangers should be located in a separate row outside the main equipment row, remote from the central pipeway. Consider location of air fin exchangers over the central pipeway if plot space if very limited.

15. Furnaces and Fired Equipment

Locate at least 15 meters away from other equipment which could be a source of spillage or leakage of gas.

No pits or trenches permitted to extend under furnaces or any fired equipment and if possible to be avoided in furnace areas.

Ensure ample room at firing front for operation and removal of the burners and for burner control panel if required.

Bottom floor fired furnaces require adequate headroom underneath the furnace. Wall fired furnaces require an adequate platform width with escape routes at each end of the furnace.

Apart from adequate platforming and access to the firing front, other structural attachments and platforming around furnaces should be kept to a minimum. Peep-holes should only be provided where absolutely necessary. Access by means of step ladder is sufficient.

Arrange heaters on common center line wherever possible. Provide unobstructed space for withdrawal. Operation and maintenance platforms should be wide enough to permit a 1.0 meter clear walkway. Escape ladders should be provided on large heaters. Vertical heaters are usually supplied with stub supporting feet, ensure drawings show adequate supports elevated to required height. Headroom elevation from floor level to underside of heater should be 2.3 meters, to provide good firing control operation.

16. Pumps

Locate pumps close to the equipment from which they take suction possibly under structures or with motor ends under a piperack allowing an access aisle for mobile handling equipment. Suction lines are generally larger than discharge lines, to avoid problems arising from low NPSH.

End suction, top discharge is preferable for pumps taking suction directly from tanks or vessels located at grade. Pumps should be arranged in rows with center line of discharges on a common line. Clearances between pumps or pumps and piping shall be a minimum of 900 mm.

17. Compressors

Locate reciprocating compressors, anchors and restrains for pipes in the compressor system on foundations independent of any building, structure or pipe trestle.

Spacing varies with type and duty, pay particular attention to: Withdrawal of engine and compressor pistons, cam shaft, crank shaft and lube oil cooler bundle; cylinder valve maintenance clearance with least possible obstruction from piping supports.

Compressors are generally provided with a degree of shelter, i.e., a sheets building. Keep the sides up to 8 feet above grade, open and vent the ridge to allow for escape of flammable gas which might leak from the machines. Certain types of compressors, owing to the height of the mass foundation above grade level, require a mezzanine floor of the grid construction to avoid trapping any gas, for operation and maintenance.

18. Piping

All piping within a process area should usually be run above grade. Trenched piping to be avoided. Piperacks and supports to be of the simplest form.

Piperacks may contain two layers of pipework. Avoid triple layer of pipeways except for very short runs. Run piping external to the process area at grade on sleepers (300 mm high). (Piping at grade is cheaper but liable to interfere with access).

Locate large bore piping as close to stanchions as possible. Lines requiring a constant fall (relief headers) can be run on cantilevers from piperack stanchions or on vertical extensions to pipe track stanchions.

Run hot line requiring expansion loops on the outside edge of pipeway to permit loops to have greatest width over the pipeway and facilitate nesting. Take-off elevations from pipeways should be at a constant elevation consistent with the range of pipe sizes involved.

Change elevation whenever banks of pipes, either to grade or on piperacks change direction. Elevations to the underside of piperacks will be minimum for operation and mobile maintenance equipment and consistent with clearances.

Open pipe trenches may be used between plants where there is no risk of flammable vapors collecting. It is sometimes convenient to run open trenches alongside roadways. (Soil from the trench can be used to build up the road). Where a pipeway or road changes direction, the pipe is run beneath the road. Occasionally it is permissible to run pipes in trenches to overcome a difficult piping problem. Such trenches should be concreted, drained and covered. Although trenched piping is to be avoided due to the expense and hazards associated with open trenches, underground buried piping is acceptable provided pipe is adequately protected and below the frostline.

Sizing and arrangement of underground piping should be fixed early to ensure that installation is simultaneous with foundation work. (Many drains, sewers and cableways, which do not require attention, are run underground below the frost-line). Leave space for drawboxes on cableways, anchors on underground cooling water pipes and manholes on sewers. Fire mains should be located between the perimeter road and the plant.

19. Access to Valves and Instruments

(See Table A)

All operating valves 3” and larger are to be accessible either from grade or suitable platform with maximum 2.0 meters above working level to center of hand-wheel. Small operating valves can be reached from a ladder. Valves installed for maintenance and shutdown purposes (other than operating) can be reached by portable ladder. Otherwise extension spindles or suitable remote operating gear should be provided, but not on valves 1 ¹/₂” and below. The minimum access to be provided is as shown on Table A.

20. Relief Valve Systems

Closed relief valve systems should be arranged to be self-draining and should not contain pockets where liquids may condense and collect to provide any back pressure.

21. Maintenance and Equipment Handling

Handling facilities are limited to the handling of working parts of equipment which require frequent or routine service and which are inaccessible to mobile handling facilities assumed to be available at the plant. These facilities are not designed to handle heavy parts such as bedplates of rotating machines, rotating equipment, compressors’ bodies, machinery frames, etc. The handling facilities provided are limited as shown on table A -

The design and installation of trolley beams, overhead travelling cranes and hoist trestles is based on lifting the parts to be handled and transporting or lowering them to specified maintenance areas or to grade. From these points they are expected to be removed by skids or hand trucks to other areas more suitable for maintenance.

Tables A

ACCESS CLEARANCES

ELEVATION

VALVE ACCESS

MAINTENANCE FACILITIES

Listing of Instrumentation Which May Assist Initial Layout

Likely Devices and Probable Number Fitted to Various Types of Equipment. Devices and Design Points Affected.

LIST 1)

LIST 1)

LIST 1)

In-line instrument elements:- Flow Elements (Orifice, Plates, Venturi, Turbine, P/D, etc.). Control Valves (Globe, Butterfly, Ball, etc.). Relief Valves. Thermowells. LIST 2)

LIST 2)

LIST 2)

GENERAL NOTE: Instrusive elements and/or spool type installation may call for flow line size due to change due to forces on wetted parts, erosion, noise, deposition of solids in cavities or viscosity.