Compressor Arrangement and Location

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Compressor house should be located near the battery limits to facilitate ease in maintenance and operation. Compressors shall be located to keep suction lines as short as possible. The gas compressors shall be located downwind side of furnace so that leaks are not blown towards furnace. In general compressors are to be located under shed. When compressors are located under shed, sides to be kept fully open for the low shed or shed, however, in case of hydrogen compressors located under the sheds provision for top venting from compressor sheds shall be provided. Gas compressors should have roofing and open from sides to avoid accumulation of heavier vapours/gases on the floor of compressor house.

In case of a turbine driven compressor, if exhaust steam is condensed, turbine and compressor need to be located at an elevated level and condenser to be located below turbine.

Large centrifugal compressors may be elevated sufficiently for piping and auxiliaries to be located below main operating platforms. Smaller compressors may be grade mounted
with piping and auxiliaries arranged for convenient access and maintenance.

A major consideration in centrifugal compressor location is the lube and seal oil console. It must be accessible from a road, must be lower than the compressor to allow gravity drain of oil to the consoles oil tank. Intercoolers & Knockout pots may be kept within/outside the Compressor house shed, but, shall be kept near compressor house.

Lube and seal oil consoles shall be located adjacent to, and a minimum distance from, the compressor.

No Shelter

Because many acceptable variations of a centrifugal compressor area are possible, the version presented below must be explained.

Briefly the area includes three centrifugal machines with separate lube oil consoles (driven by condensing steam turbines), two inter coolers, three suction drums, a surface condenser and two vertical condensate pumps.

Because there are three condensing steam turbines operating at low steam pressure, minimizing the length of the exhaust line to the surface condenser should be one of the first goals a layout designer considers.

  1. The surface condenser is located just to the south of the compressor operating platform.
  2. The lube oil console for compressor 1 is located to the west of the surface condenser, which permits the return line to drain to the oil reservoir without obstruction.
  3. Consequently, the area directly east of the surface condenser can be used to pull the tube bundle.
  4. The vertical condensate pumps are located just to the south of the condenser and should straddle the centre line of the hot well outlet nozzle.
  5. The distance between the condenser and the pumps is dictated by pump operation and maintenance requirements as well as piping flexibility.
  6. The suction drums for compressors 1 and 2 are located along the equipment line just to the west of the operating platform.
  7. Often the outlet line of the suction drum to the compressor suction nozzle requires a flow meter with straight run lengths upstream and downstream.
  8. This arrangement permits the natural configuration of the line to satisfy the meter requirements.
  9. The intercooler for compressor 1 is located at grade below the platform, with clear access to the south of tube removal.
  10. The lube oil console for compressor 2 is located just to the east of the compressor at grade level below the operating platform.
  11. If there is insufficient room to maintain the console, removable grating must be provided at the operating platform level, which prohibits any other use for this area.
  12. Compressor 3 has an inter-cooler mounted directly below the machine, which is supplied by the vendor. Again ample access must be provided for tube removal.
  13. The lube oil console for compressor 3 is located just outside and clear of the operating platform to the east. Again, a free-draining oil return line to the console must be provided.
  14. The suction drum for compressor 3 is on the equipment line to the east of the operating platform.
  15. Access to the operating platform is by two stairways at opposite ends of the area, allowing emergency exit.
  16. Each machine has a control panel that is placed along the north edge of the operating platform.
  17. Because there is no shelter over this particular area, all major maintenance is handled by mobile equipment.

Enclosed Structure

The arrangement shown here consists of three electric-motor driven reciprocating compressors as well as air blowers, suction drums, inter-coolers, control panels, and one lube oil console.

Because the compressors are two different sizes, electric motors have been lined up to permit the power-supply conduit to run straight east and west, regardless of whether it runs directly below the operating platform or below grade.

  1. Compressor 1 has three cylinders with a separate lube oil console that is located directly to the north, below the operating platform.
  2. A removable section of the platform should be provided for maintenance above the unit. This are must be kept clear of any obstruction.
  3. Compressors 2 and 3 are identical four-cylinder machines that have integral lube oil consoles mounted directly onto the compressor frame.
  4. Each compressor has a control panel located along the north wall.
  5. An area along the north compressor wall is reserved for valve stems, which are located below the floor and extend to a distance of approximately 3 ft (1000 mm) above the platform floor.
  6. A sleeper runs east and west outside the north wall for all compressor piping, which vibrates a great deal because of reciprocating compressor operation and therefore must be laid as close to the grade as possible.
  7. If the operating valves are located outside the building, a catwalk should be provided to allow access during operation.
  8. The suction drums and intercoolers are located across from the sleeper area.
  9. In a totally enclosed building, all compressor maintenance is handled by travelling crane.
  10. The operating floor stops one bay before the east wall, which allows a drop zone for maintenance. Mobile equipment must be brought into this area from the south or east. Roll-up doors are generally provided for this purpose.
  11. Each of the three electric motors require air from the outside to cool the motors. Electric motors within the building do not always require this type of cooling.
  12. Access to the operating area of this structure is accomplished by stairway and doors along the north wall both at the west end and close to the east end and to the south wall at the west end.
  13. An additional stairway at the east end permits operators or maintenance personnel to enter the drop zone or to access the area under the operating floor.

Elevation of Machines

This section deals with the problems that must be addressed when the elevations of both centrifugal and reciprocating compressors are set.

When separate lube oil consoles are used, a free-draining line from the machine to the lube oil reservoir must be maintained.

Centrifugal Compressors

The type of driver and associated equipment items as well as the straight run requirements of the compressor inlet piping are the major factors that set the final elevation of the machines.

Following figures show the following :

  1. Arrangement A shows bottom mounted nozzles.
  2. Arrangement B shows top mounted nozzles.
  3. Arrangement C shows surface condenser mounted directly below the turbine which is common when only one turbine is being serviced.
  4. Arrangement D shows a top nozzle that allows the exhaust steam line to run to a surface condenser servicing multiple turbines.
  5. By selecting compressor arrangement A or B and placing its match line against the turbine match-line arrangement C or D, a designer can review the governing criteria for setting machine elevations.
  6. In addition, consideration must be given to miscellaneous equipment e.g. as shown in arrangement a in first drawing.

Reciprocating Compressors

Reciprocating machines are located as close to grade as possible because of the extreme vibration in the piping system.

Minimum elevation is established by following steps as shown in figure below.

  1. Sleeper – Usually set to 12 to 18 in (300 to 450 mm) above grade.
  2. Header size – Established on the piping and instrumentation diagram.
  3. Minimum distance required to enter the header with the largest line to and from the compressor.
  4. The pulsation dampener – Designed by the compressor vendor.
  5. Minimum clearance required between the dampener and floor steel.
  6. Maximum depth of the floor steel – set by the structural engineer.
  7. Dimension from the centreline of the dampener to the face of the nozzle – set by vendor.
  8. Bottom of the compressor baseplate to the centreline of the compressor shaft – set by the vendor.

Equipment Layout for Compressor Inter and After Coolers

Inter-coolers :

  1. Coolers are primarily used to reduce the operating temperature within a compressor circuit, which allows the use of a smaller machine with fewer cylinders.
  2. These coolers may vary in size and type (e.g. shell and tube, air coolers and U-tube) and should be located as close to the compressor as practical.
  3. In some reciprocating compressor arrangements, the cooler may be mounted on and directly over the compressor by the vendor, but they are usually located by the engineering contractor close to the machine or stage suction drum.

Following figure shows a centrifugal compressor with its inter-cooler and interconnecting piping between stages as supplied by the vendor.

Following figure shows reciprocating compressor with all components, including the inter-cooler, supplied separately by the contractor.

Further reference can be made to following figure where the intercooler to compressor 1 is mounted separately at grade, parallel to the compressor shaft.

The intercooler to compressor 3 is mounted at grade, perpendicular to the centreline of the shaft, and is supplied by the vendor.

After Coolers :

  1. After-coolers are used to reduce the operating temperature of the gas when it leaves the compressor, whether it continues through additional process equipment or enters a pipeline in which it must have a specific temperature.
  2. Aftercoolers may be located farther away from the compressor than shown in figure below because the primary piping does not return to the cooler.

Following figure shows the typical aftercooler PID.

Compressor Housing and Platform Requirements

When a compressor is covered- partially or totally enclosed by a shelter or structure – many elements determine how the layout must be approached.

The factors to consider are :

  1. Operation : The plant operations personnel need room to walk safely around the machine. They must have access to valves, switches and gauges and must be able to see all gauges, lights and dials on the control panels.
  2. Maintenance : All principal components to be removed during major maintenance must be able to be lifted by the travelling crane, swung laterally to the clear area and removed from the building.
  3. Climate Conditions : Installation in temperate climates may require only a roof that provides limited protection from the elements. In warmer climates, a curtain wall structure may be the right application. A curtain wall has a complete roof and four sides that are open from the operating level to a height of 8 ft (2400 mm). The roof blocks the sun for most of the day while allowing cooler breezes to pass through the structure. This installation may also be used in areas with significant rainfall. Totally enclosed structures are usually provided in severely cold climates.
  4. Safety : The housing must have easy access throughout, ample ventilation as protection from potentially dangerous gas leaks, and a sufficient number of doors and stairways in the event of an emergency.
  5. Economics : The area inside the building should be large enough to satisfy all other factors and no larger, unless specifically requested by a client to accommodate future equipment within the structure.

Drawing below shows how to size a building, regardless of what type of machine is used; the example is for a centrifugal gas compressor. The elements to be sizes are discussed in following sections.

  1. Floor Elevation : The operating floor elevation is established by making all standard allowances around and above equipment and providing the usually headroom below all horizontal piping runs and conduits, as shown by blocks E and F.
  2. Building Width : The width of the building is established by first allowing space for the largest compressor train. There must be adequate room between the steam turbine, lube oil drain piping, and any miscellaneous piping that may be arranged along the adjacent wall as shown by block C. At the compressor end, there must be sufficient room for the operators and any routine maintenance as shown by block B. Although the operator must have access to the front of the control panel, it may also be necessary to allow access to the rear of the panel for maintenance, shown as clearance D.
  3. Building Elevation : The elevation of the building is further established by determining the size of the clear maintenance area (shown as X and Y). This area must accommodate the largest single piece to be maintained at a minimum elevation above all operating floor requirements as shown clearance A. The alternative maintenance area may be used if this area is clear throughout the length of the building.
  4. Hook Centerline Elevation : The layout designer determines the centreline elevation of the hook. The maximum lifted load must be supplied to the structural engineer or building contractor to furnish the correct travelling crane. The eave elevation is then set on the basis of the clearance of the crane selected.
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