Piping Layout: PipeRack Piping Arrangement Drawing Part-2

YARD PIPING ARRANGEMENT

The plant layout determines the main-yard piping runs. Refer sketch, which shows typical piperack layouts for various plant arrangements.

Piping Layout: PipeRack Piping Arrangement Drawing Part-1

The piperack general arrangement is finalised during the development of overall plot plan. The exact width of the piperack, numbers of levels and elevations, the access and maintenance platforms are finalised during piperack piping study.

Normally, the piperack piping study, with its structural and platform requirements is the first priority item for detail engineering of a process unit. The piperack may be an integral part of a process unit located in the middle of the unit or it may be an arterial part connecting several services of other process unit.

The following data and drawings are required to be studied before starting the detailed design of piperack piping study:

Unit Plot Plan / Overall Plot Plan, Piping and Instrumentation diagrams Plant layout specification, Client specification, Material of construction, Fireproofing requirements

Piping Layout: TankFarm Piping And General Arrangement Drawing Part-2

PUMP LOCATION IN TANKFARM

To determiine the optimum location of pumps, the potential hazards and client preferrence shall be considered.

Fig. illustrates the location of pump within the dyke area with the curb wall height of approx. 400-500mm.

This design protects the pump from minor spillage within the dyke and enable the discharge piping to exit the dyke over the wall and there is no need to have dyke penetration seals.

The piping outside the dyke may run on a piperack or sleepers.The pumps located outside the dyke area are illustrated in Fig.

Tank outlet piping can either penetrate the dyke or pass over the dyke in case the minimum liquid level in the tank do cause cavitation in the pump.

Piping Layout: TankFarm Piping And General Arrangement Drawing Part-1

The study of the tankfarm consisting of a group of tanks shall be carried out keeping the following basic points in consideration.

1. Grouping of tanks,

2. Specification of the content.

3. Capacity of tanks

4. Nature of hazard - fire

- toxic

- explosive

- corrosive

- bulk handling loading

5. unloading

6. Statutory distance

7. Requirement of Dykewall or curbing

8. Dykewall height or curb height calculation

9. Location of Pumps - inside dyke area

- outside dyke area

10. Approach to tank nozzles with valve

11. Approach to tank roof

12. Drainage of dyke area - Sump and pump

13. Road around tankfarm

14. Fire hydrant / monitor requirement

15. Underground system connected to specific system of treatment / disposal

Piping Layout: Heat Exchanger And Condenser Location In Plant And Piping Arrangement

INTRODUCTION

Heat Exchangers are widely used equipments in the chemical, petrochemical and refinery type of plant.  The control of heat within a plant operation is done by direct heat application in a furnace, or   by heat exchange in a shell and tube exchanger / plate heat exchanger.   Types of heat exchanger    may be Shell and Tube, Aircooled (Fin-Fan), Plate    type or Coil type(spiral).

Various process duties of heat exchanger have an effect on the layout aspects viz.

a.        Exchange of sensible heat between two process   fluids.

b.       Cooling with air or water.

c.        Chilling with refrigerated  liquid.

d.       Heating with steam or hot  water.

e.        Condense by water or a cold process   stream.

f.         Vapourising by steam (e.g. column reboiler) or any heat transfer    liquid.

Fixed tube exchangers are used when the temperature differences between shell side and tube side

fluid are small.

Floating head or U-type exchangers are used where there is a  significant  temperature  difference.

Kettle -type reboilers are used for evaporation in case of limiting  pressure  drop,  otherwise  vertical reboilers are used for  evaporation.

Plate heat exchangers are generally used in low-pressure, low temperature applications.  The   plate exchanger occupies less space than shell and tube exchanger for equivalent  heat  exchanger surface.

Aircoolers are used for overhead condensers of column and consist of fin-tube bundles with a header box to each end, having inlet on top of header-box at one end and outlet on bottom of header box at the other  end.

For single pass arrangement of air-cooler exchangers, inlet nozzles are mounted on the top of the header box and the outlet nozzles are located at the opposite end and mounted on the bottom of the header box.For double pass arrangement, the inlet and outlet nozzles are located at the same end.

LOCATION

Exchangers should be located close to the major equipment with  which  it is associated  in PFD  /  P&ID. Reboilers are placed next to their respective towers and condensers are placed over reflux  drums. Exchangers between two distant pieces of process equipment  should be placed at optimal  points in relationship to  piperacks.

Most exchangers are to be located at grade level with elevations to have a clearance of 1m above Finished Ground Level (FGL). Elevated exchangers may be necessary  to  fulfill  the  NPSH  requirement of a downstream centrifugal   pump.

In case of large numbers of heat exchangers, they are grouped in one or more category to save       pipe work, structural work, provision of lifting and maintenance facilities, platform requirement etc. Paired or grouped exchnagers shall be spaced to allow  minimum  450mm  preferrably  600mm  between the outside of adjacent channel or bonnet flanges to facilitate access to flange bolts during maintenance. Adequate  space shall be provided  on either  side of paired  exchanger  and at both  ends of grouped exchanger for control and operator access as illustrated.

Groups of exchangers should be generally located by the alignment of channel nozzles in a vertical plane so as to present an aesthetic   appearance.

The support saddle with oblong holes for provision of thermal expansion are normally located on the saddle farthest from the channel end but the final location depends on the plant layout and the stress analysis of the connected  piping.

Exchanger piping should be as direct and simple as possible by considering alternatives such as arranging exchangers side by side / stacking them for reversing   flows.

Exchangers are sometimes mounted on structures, process columns and other equipment. Special arrangements for maintenance and tube cleaning should be provided in such cases.

ACCESS FOR OPERATION &  MAINTENANCE

Internals of heat exchanger require periodic  cleaning  and  repair.  It is important  that  exchangers and the surrounding piping are arranged to facilitate access to the internal parts.

Horizontal clearance of at least 900mm should be left between exchangers flange to flange or exchanger flanges to piping. Where space is limited, clearance may be reduced between alternate exchangers but in no case clearance over insulation between channel flanges shall be less than 600mm.

The channel ends of exchangers should face the local access road for tube bundle removal and  the shell cover should face the piperack.       Pulled out bundles should not extend over main access road.

A typical exchanger arrangement  with clearance  for access,  operation  and maintenance  is shown.

Access for tube bundle removal is usually 500mm more than the bundle length.

Mobile equipment should be used for handling tube bundles and covers at grade level. Expensive built-in facilities e.g. lifting beams, monorails to be kept     minimum.

Piping layout: Pump Piping And Location

The design of a piping system can have an important effect on the successful operation of a centrifugal pump. Such items as sump design, suction piping design, suction and discharge pipe size and pipe supports must all be carefully considered. A typical horizontal centrifugal pump installation is illustrated.

Selection of the discharge pipe size is primarily a matter of economics. The cost of various pipe sizes must be compared to the pump size and power cost required to overcome the resulting friction head.

Piping Layout: Compressor Piping And General Arrangement Drawing

Compressors are normally located inside a permanent shelter or building (Compressor House) for weather protection. The compressor house can be fully covered by side cladding to grade level if handling non-hazardous materials e.g. air.

For compressor, handling flammable materials, ventilation and weather protection is assured by significant openings upto 2.5m ht. at grade level together with roof ventilators.

Except for lighter than air gases, trenches, pits and similar gas traps should be avoided within gas Compressor House. This will eliminate chances of suffocation or explosion risk due to accumulation of heavy gases in pits.

For open compressor house, the side cladding on all sides should be provided upto 1m below crane level.

The general arrangement of compressor house shall consider the vendor drawings and vendor recommendation, if any, for space and location of auxiliary units.

For compressor house where a number of installations from multiple vendors are to be accommodated, a thorough discussion should be held among the engineers of Piping, Process and Civil discipline to finalize the detail plot plan of the unit.

The clear space between compressors shall be minimum 1.5m or half width of the compressors. The clearance between rows of compressor and at the end of each compressor shall be also 1.5m.Built-in maintenance equipment viz. travelling gantry with overhead crane / monorail with hoist and chain-pulley blocks as well as the drop-out areas shall be provided in the compressor house.

Piping Layout: Drums And Vessel Layout Nozzle Orientation And Platform

The process vessels and drums are cylindrical hollow vessels used in process plants as intermediate containers. They are often used to provide surge volumes for liquid-vapour separations on distillation columns or separating mixtures of immiscible liquids. Other uses are flash drums, condensate and other process liquid collectors and holding drums for additives and chemicals.

The piping study on drums shall consider the general requirements for drum plant layout and provide information required to locate nozzles, instruments, piping and controls for plat forming and operation / maintenance access.

In the first study of plot plan, platform levels and details of vessel elevations are set from process requirements (net positive suction head - NPSH, gravity feed, barometric legs etc.) and from considerations of access for safe and convenient operation and maintenance.

Methods of supporting vessels and operating platforms are detailed. Access for lifting equipment or overhead hoists and trolley beams is arranged for removal of motors, mixers and internal heat exchangers from process vessels. A platform should always be provided for the removal of such heavy items of equipment and for access to manholes, sight glass, light glass etc.