360 400

FIGURE 2 Typical centrifugal pump characteristic curves versus flow rate or capacity. (m3/h = 0.277 X gpm; m = 0.305 X ft; kW = 0.746 X hp) (Flowserve Corporation

• Will the pulsating flow of a piston pump be detrimental to system operation? Will a pulsation dampener take care of this problem?

• Is the liquid clean enough to avoid premature wear on pistons and cylinders?

For high flow and high head combinations, a multi-stage centrifugal pump can be used. Various designs of this type of pump are available with a wide range of prices reflecting special designs for a whole range of applications (high temperature, cryogenic, water, hydrocarbon, and so on).

Low Flow with Precise Flow Adjustment Ability For low-flow applications where accurate flow metering is necessary, a proportioning pump is appropriate. This type of pump can also be provided with variable flow capability. Certain types of gear, plunger, and diaphragm pumps can also be used in combination with a variable speed drive for flow rate regulation.

Low Available Net Positive Suction Head If the available net position suction head (NPSHA) is low, specially designed centrifugal pumps can be considered. Depending upon how low the NPSHA is, either a horizontal end suction with a suction inducer or a horizontal double suction arrangement may be applied. A vertical turbine pump may also be used, either immersed in the process fluid (possibly in a tank or vessel) or in a specially designed vessel (known as a suction can) that can be installed below grade to increase the NPSHA.

Code and Industry Standard Requirements The design, construction, rating, and testing of most pumps used in refining and chemical industries are governed by standards such as API (American Petroleum Institute), ASME (American Society of Mechanical Engineers), the Hydraulic Institute, NFPA (National Fire Protection Association), PIP (Process Industry Practices), ISO (International Organization for Standardization) and various other international standards. The severity of the service in which the pump will be applied, as well as the location of the plant, will determine which industry standard (or standards) will be used, if any.

In the case of a fire pump service, NFPA compliance might be mandatory to meet the user's insurance company requirements. If a pump will be installed in an oil refinery or chemical plant, either API or ASME standards will be applied depending on the severity of the service and client preferences. International standards such as DIN (German), BS (British), JIS (Japanese), or ISO can also be used. These standards are intended to provide a pump with a level of quality to match the needs and expectations of the end user of the equipment. It is obvious that the quality requirement for an emergency feed water pump in a nuclear power plant needs to be much more stringent than a potable water booster pump in an office building. The quality issues covered by these codes/standards ranges from detailed design issues to inspection and performance testing requirements.

Fluid Characteristics Fluid characteristics such as viscosity, density, vapor pressure, volatility, chemical stability, solid content, and entrained gases are important factors to be considered for proper pump selection. Pumps are available to handle a full range of fluid types. A positive displacement progressing cavity pump can be used to pump toothpaste, peanut butter and shampoo, but it will not usually be a good choice for pumping water or gasoline. A rotary, variable displacement piston pump is a good choice for a hydraulic control system, but not for a potable water application. A rotary sliding vane pump can be successfully applied for pumping hot asphalt and for limited application in a lube oil system.

Making the best pump selection for a certain fluid application is often difficult. Previous successful experience is usually the best guideline for proper pump selection. This information can be obtained from end users, from process licensers, and from pump manufacturers. Recommendations from all of these sources should be carefully considered.

Pump Materials Material selection is affected both by the pumped fluid and the environment. Resistance to corrosion and erosion are of prime importance. The engineer must determine which material is most suitable and economical for a particular service. This requires that an evaluation be made comparing the more expensive longer life material to a less expensive material, which may provide a shorter pump life. Requirements such as continuous or intermittent operation, critical or non-critical service and plant life cycle should be considered when selecting materials.

Pumps are commonly available in cast iron, ductile iron, bronze, carbon steel, alloy steels, and in some cases composite materials or special alloys such as Monel, Hastelloy, or Titanium. In addition to the importance of pump design life, safety must also be considered when selecting materials. Cast iron construction is not used for pressure casing parts of pumps that are to handle flammable or hazardous liquids because cast iron is brittle and subject to fracture when thermally shocked. For these services, pressure-casing parts must be high strength ductile materials such as carbon or alloy steel.

Driver Selection The choice of driver type for a pumping service is as important as the pump selection. Factors that affect the driver choice are capital cost, driver type availability, operating reliability and the availability and cost of utilities.

Constant speed electric motors are most economical when only the first cost is considered. Often there is excess steam available within a facility that, when compared to the cost of electricity, will justify the extra cost of a steam turbine. Reliability requirements may necessitate the use of both a steam driven main pump and an electric motor driven back-up pump. In the case of firewater pumps, a battery-start, diesel-fueled internal combustion engine is needed to be completely independent of plant utilities. More expensive variable speed electric motors can sometimes be justified if the pump is operated well below its design conditions and there is the potential for significant savings in power.

There are other factors that should be considered when selecting the pump driver. The capital cost as well as the installation cost is more expensive for a steam turbine due to required piping. Steam turbines also require more maintenance during plant life, which may be undesirable to the owner. Selection based on past proven performance and selection to match existing plant equipment to minimize spare part inventory is a common consideration.

Air-operated diaphragm-type pumps are available in relatively small capacities, and these can be particularly effective in hazardous area classifications where use of electric motors may be undesirable.

Other Equipment Supply Decisions For both technical and commercial reasons, the purchaser may decide to purchase the pump/driver combination in various ways.

The pump and driver may be purchased separately. This may be advantageous if either the pump or driver (but not both) can be purchased locally. This will save shipping costs and possibly allow the purchaser to meet client requirements for locally manufactured content for a project. Separate purchase of drives on large capital projects can also lead to quantity price discounts and limited spare part inventories.

The purchaser must consider the risk associated with the separate purchase of the pump and driver. Equipment installation and alignment problems (with resulting start-up delay) are more probable than when the pump vendor takes single source responsibility for the purchase and skid mounting of all components.

If the decision is made to purchase the driver separately from the pump, the pump manufacturer can provide the equipment for block mounting or provide a skid on which the driver can be installed in the field. Either way, additional shop inspection is recommended to verify dimensions for field interface. It should be noted that pump manufacturers may purchase a high volume of electric motors and obtain greater discounts than most operating companies and engineering contractors.

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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