The Process Plant Layoutand Piping Design

Process Plant Layout and Piping Design AgendaIntroduction to PlantLayout Design Plant LayoutSpecificationsPlot PlansCompressorsDrumsReactorsTowersStructuresExchangersFurnacesPumpsPipe RacksInstrumentationProcess LiquidStorage TankPipe Stress AnalysisUnderground PipingWhat is a Process Plant ?Miscellaneous

Pumps

The Process Plant Layout and Piping Design Course

Main Menu

Introduction to PumpTerminologyPumps the purpose of pumps is to make fluids flow. Pumps do this by adding energy to the fluid. Added energy increases pressure. Fluid flows from high pressure to low pressure. Pumps add energy by centrifugal action, by pistons, and by rotary action.Centrifugal pump this is the most common type of pump in a process plant. A driver, usually an electric motor but sometimes a turbine, whirls an impeller around the central axis of the pump. As the fluid enters the side of the impeller casing through the suction nozzle, the impeller scoops the fluid up, whirls it around the casing and hurls the fluid out of the discharge nozzle.Reciprocating Pumps used for viscous fluids or for small amounts of fluid flow (such as for process additives) add energy by using a piston instead of the impeller found in centrifugal pumps. Fluid pulsations can cause vibrations in the piping system.

Rotary Pumps these pumps are used for highly viscous liquids that a high-speed impeller cannot push. The liquid is pushed through the pump casing by gears, vanes, or cams. Horizontal and Vertical Pumps Horizontal pumps are the most common. Horizontal pumps have the driver and the impeller at the same elevation connected by a horizontal coupling. Vertical pumps have the driver above the impeller. Vertical pumps are used when NPSH requirements make using horizontal pumps impractical.Net Positive Suction Head - NPSH is one of the most important terms a designer has to know. NPSH is a measure of the pressure drop of the liquid as it moves form the inlet of the pump to the eye of the impeller. NPSH is a characteristic of the pump and is usually determined by manufacturer testing.

Title

Introduction to PumpTerminology (cont)Vapor pressure When the pressure in the pump suction line falls below the vapor pressure of a liquid, the liquid changes to vapor. The pump cannot pump vapor and thus becomes vapor boundAvailable NPSH this term refers to the net pressure available in a given system, based on vessel pressure and static head, minus the liquid vapor pressure and functional losses in the system. The designers goal is to maintain equipment heights and minimize pump suction piping to ensure that the available NPSH is greater than the required NPSH. Insufficient NPSH can reduce pump capacity and efficiency and lead to cavitation damage.Cavitation The rapid collapse of vapor bubbles that can produce noise, result in a loss of head and capacity, and create a sever erosion of the impeller and casing surfaces in the adjacent inlet areas.

Allowable Nozzle Loading This is the maximum amount of stress that the piping configuration may impose on the pump suction and discharge nozzles, as set by the vendor, client or code.API (American Petroleum Institute) pumps this term refers to the horizontal, single-stage pumps found in the petroleum. The standard developed by vendors, contractors, and users entitled API 610 Centrifugal Pumps for General Refinery Service is used to specify pumps for purchase. To a plant layout designer, an API pump is a large, refinery-type pump.

Title

Introduction to Pumps Terminology (cont)TitleHorizontal Centrifugal PumpDouble-acting Piston PumpRotary Pumps

Inline Centrifugal PumpSump Centrifugal Pumps

Introduction to Pumps Terminology (cont)Title

Introduction to PumpsDesign TipsPump Locations along a rackKeep in mind that in setting the pump location your objective is to minimize the length of suction piping while still maintaining enough piping flexibility that the nozzle loads are low during operation. Locating the pumps under the rack is one way to achieve this goal. The problem with pumps under the rack is the potential for hydrocarbon leaks onto the pump motor which may create safety and/or maintenance problems. You can locate pumps outside of the rack (which is often what your client will require). When you do this, be sure that you have accounted for the auxiliary steel that may be needed to support piping going to and from the pump to the pipe rack.

Pump Locations near equipmentPumps operating with exchangers and drums that are located in vertical structures can be placed beneath the structure. Hydrocarbon leakage is usually not a concern in that type of situation. Centrifugal pumps in a vacuum service typically have to be located very close or directly beneath the suction side equipment, which is normally a tower. When locating pumps beneath a tower be sure to account for the potential of spring cans that support the pump causing the pump to be elevated higher than normal. Also, pumps on springs have a tendency to vibrate depending on flow rate. The potential for vibration on spring mounted pumps should be discussed with both your stress engineer and your process engineer on the project

Title

Introduction to PumpsDesign Tips (cont)Pump Locations by typeVertical pumps are more expensive than horizontal pumps. Yet vertical pumps can be the right solution when you have problems achieving NPSH requirements. For example, between a horizontal centrifugal pump and a horizontal vessel you would measure the NPSH distance you have between the centerline elevation of the pump shaft and the bottom tangent line of the vessel. If you were using a vertical pump instead, you would measure the distance between the bottom impeller of the vertical pump which can be located below grade. This would lower the elevation of the horizontal vessel and save significant structural costs.

Pump PipingDo you understand how your specific client plans on doing the maintenance for these pumps? Are they going to use a cherry picker or some kind of A-Frame? Is there the potential for replication of this piping layout elsewhere in the plant? For large numbers of similar systems it may be worth while to design for the largest pipe size and highest temperature and layout all 'close' systems the same way.

Title

Introduction to PumpsDesign Tips (cont)Pump PipingWhen laying out piping on vertical suction and vertical discharge centrifugal pumps, assure that the flanges on the larger valves do not interfere with each other. If they do interfere, but only slightly, the use of eccentric reducers on both suction and discharge lines may offer enough offset to provide the clearance you need.Centrifugal pumps with side suction nozzles are particularly prone to cavitation. A generally accepted rule of thumb is to make sure a minimum of five diameters (5D) of straight run is added to the line before it reaches the suction nozzleWhen a pump suction line comes from below grade, be sure to orient the reducer at the pump nozzle with the flat side up.

Pump Piping SupportsHas the stress engineer determined the location of the supports? For most centrifugal pumps the stress engineer is responsible for locating the support and guide scheme and determining the loads on those supports. The location of these supports can affect how you layout the pipe, and vice versa. Here are some simple rules to follow that will help you predict where the supports will be. For end and side suction pumps, expect an adjustable or spring support to be placed at the first elbow. Since both these types of supports typically need at least 12(300mm.) clearance, maybe more, expect a dummy leg off the first riser from the suction nozzle ONLY IF your bottom of pipe coming from the suction nozzle is low to the grade. On a vertical discharge line some designers turn the pipe fitting to fitting to the horizontal plane until the discharge piping clears the foundation then turn up. It is at this second elbow transitioning from the horizontal to the vertical plane that a vertical dummy leg going to a spring can or adjustable support can be located.

Title

Introduction to PumpsDesign Tips (cont.)Pumps located partially under piperack.Pumps located under piperack.Pumps located outside of rack.

Pumps located under a structure.Title

Introduction to PumpsDesign Tips (cont.) Typical Centrifugal Pump Auxiliary Piping LayoutTypical Centrifugal Pump Primary Piping LayoutTitle

TitleTYPICAL PIPING FOR CENTRIFUGAL PUMPS

Most pumps used in industry are of the centrifugal type. Typical piping and fittings required at a centrifugal pump together with the valves necessary to isolate the pump from the system.

The check valve is required to prevent possible flow reversal in the discharge line. A permanent in-line strainer is normally used for screwed suction piping and a temporary strainer for butt-welded/ flanged piping. The temporary strainer is installed between flanges. A spool is usually required to facilitate removal.

Although centrifugal pumps are provided with suction and discharge ports of cross sectional area large enough to cope with the full rated capacity of the pump, it is often necessary with thick fluids or with long suction lines to use an inlet pipe of larger size than the inlet port, to avoid cavitation. Cavitation is the pulling by the pump of vapor spaces in the pumped liquid, causing reduction of pumping efficiency, noisy running and possible impellor and bearing damage.

Most pumps have end suction and top discharge. Limitations on space may require another configuration, such as top suction with top discharge, side suction with side discharge, etc. Determination of nozzle orientation takes place when equipment layout and piping studies are made.

AUXILIARY, TRIM, or HARNESS PIPINGPumps, compressors and turbines may require water for cooling bearings, for mechanical seals, or for quenching vapors to prevent their escape to atmosphere. Piping for cooling water or seal fluid is usually referred to as auxiliary, trim, or harness piping, and the requirement for this piping is normally shown on the P&ID. This piping is usually shown in isometric view on one of the piping drawings.

In order to cool the gland or seal of a centrifugal pump and ensure proper sealing, it is usually supplied with liquid from the discharge of the pump, by a built-in arrangement, or piped from a connection on the pumps casing. The gland may be provided with a cooling chamber, requiring piped water. If a pump handles hot or volatile liquid, seal liquid may be piped from an external source.

Title

DRAINING

Each pump is usually provided with a drain hub 4 to 6 inches in diameter, positioned about 9 inches in front of the pump foundation on the centerline of the pump. The drain hub is piped to the correct sewer or effluent line. If two small pumps have a common foundation, they can share the same drain hub.

Most centrifugal pumps have base plates that collect any leakage from the pump. The base plate will have a threaded connection which is piped to the drain hub. Waste seal water is also piped to the drain hub.

In outside installations in freezing climates, provide a valved drain from the pumps casing.

Provide a short spool for a -inch drain between the on/ off valve and the check valve, to drain the discharge line. If the valve is large enough, the drain can be made by drilling and tapping a boss on the check valve, in which instance no spool is required.Title

INSTALLATION

Do not route piping over the pump, as this interferes with maintenance. It is better to bring the piping forward of the pump.Leave vertical clearance over pumps to permit removal for servicing sufficient headroom must be left for a mobile crane for all but the smaller pumps, unless other handling is planned.If pumps positioned close to supply tanks are on separate foundations, avoid rigid piping arrangement, as the tanks will settle in the course of time.Locate the pump as closely as practicable to the source of liquid to be pumped from storage tanks, sumps, etc., with due consideration for flexibility of the piping.Position valves for ease of operation placing them so they are unlikely to be damaged by traffic and will not be a hazard to personnel.The foundation may be of any material that has rigidity sufficient to support the pump baseplate and withstand vibration. A concrete foundation built on solid ground or a concrete slab floor is usual. The pump is positioned, the height fixed (using packing), and the grout is then poured. Grout thickness is not usually less than one inch.A pit in which a pump is installed should have a drain, or have a sump that can be drained or pumped out.Make the concrete foundation at least as large as the baseplate, and ensure that concrete extends at least 3 inches from each bolt.Title

VALVES

Valves are line size unless shown otherwise on the P&ID.Use tiling disc or swing check valves for preference.Do not use globe valves for isolating pumps. Suction and discharge line isolating valves are usually gate valves, but may be other valves offering low resistance to flow.

SUCTION LINE

To avoid cavitation, the pump must be at the correct elevation, related to the level or head of the liquid being pumped. If the location of the pump has not previously been established on an equipment arrangement drawing, refer to the engineer involved.

Eccentric reducers are used, and are arranged to avoid: (1) Creating a vapor space. (2) Creating a pocket which would need to be drained. These conditions set the configuration of the reducer - that is, whether it is to be installed top flat or bottom flat.Title

Suction Line (Cont.)

If a centrifugal pump has the suction nozzle at the end (in line with the drive shaft), an elbow may be connected directly to the nozzle at any orientation.

If a pump has the suction nozzle at the side with spilt flow to the impellor provide a straight run of pipe equal to 3 to 5 pipe diameters of the suction line to connect to the nozzle. Alternately, and elbow may be connected to the suction nozzle, but it must be arranged in a plane at 90 degrees to the driving shaft, to promote equal flow to both sides of the impellor. If an elbow must be in the same plane as the driving shaft of the pump, consider the use of turning ( or splitter) vanes to induce more even flow. Uneven flow causes damage to the impellor and bearings.

Route suction lines as directly as possible so as not to starve the pump and incur the risk of cavitation.If the pump draws liquid from a sump at a lower elevation, provide a combined foot valve and strainer. A centrifugal pump working in this situation requires priming initially provide for this by a valved branch near the inlet port, or by other means.Provide a strainer in the suction line. Do not place a temporary startup screen immediately downstream of a valve, as debris may back up and prevent the valve from being closed.Title

DISCHARGE LINE

The outlet pipe for centrifugal and other non-positive displacement pumps is in most cases chosen to be of larger bore than the discharge port, in order to reduce velocity and consequent pressure drop in the line. A concentric reducer or reducing elbow is used in the discharge line to increase the diameter. There is no restriction on the placement of elbows in discharge lines as there is in suction lines.

Provide a pressure connection in the discharge line, close to the pump outlet. It may be necessary to provide a short spool for this purpose if there is no pressure point tapping on the pump discharge nozzle.For locations of drain connections in the discharge line, see figures.

PUMPS WITH SCREWED CONNECTIONS

A pump with screwed connections requires unions in the suction and discharge lines to permit removal of the pump.Title

Centrifugal Pump Piping in ElevationScrewed PipingFlanged Butt-Welded PipingTitle

Piping to Centrifugal Pump - AlternativesScrewed PipingFlanged Butt-Welded PipingSocket-Welded PipingDischarge ManifoldTitle

Centrifugal Pump Piping in Elevation

Centrifugal Pump Piping in Plan

Centrifugal Pump Piping in Plan

Centrifugal Pump Piping in Elevation

Centrifugal Pump Piping in Plan

Centrifugal Pump Piping in Elevation

Centrifugal Pump Piping in Plan (at Reboiler)

Centrifugal Pump Piping in Elevation (at Reboiler)

Metering Pump Piping in Plan

Metering Pump Piping in Elevation