MAPSA Company with a long history in designing and manufacturing practical pumps and pumps used in oil and gas, petrochemical, power generation and water treatment with below applications:

–    Refining and petrochemical services

–    Crude oil transfer

–    Process transfer

–    Boiler feed

–    Water injection

–    High-temperature applications

–    General industrial services

Is now able to design and produce BB5 pumps.

Design and manufacturing of pumps will be done according to the latest version of 3D design software; CFD and Finite-Element.

BB5 pumps which has been ordered by Tehran Refinery Co. after routine tests according to standard API 610 is now installed and operational.

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Abstract: Centrifugal pumps can be used in many applications, but in order to operate reliably, with optimal energy use and maximum life span, a pump’s design characteristics must suit the intended service. Correct pump selection is the first step to ensure this.

Introduction

Operational versatility is an outstanding feature of centrifugal pumps that has contributed to their extended use in a wide range of applications. But, although a centrifugal pump can serve many different operating conditions, it will not provide suitable and satisfactory performance in all of them.

In order for a pump to run correctly, without wasting energy or sustaining internal damage, its design characteristics must be suitable for the intended service. Therefore, the correct selection of the pump is the first step in guaranteeing efficient and appropriate performance, reliable operation and a reasonably long life span.

In spite of the existence of a large volume of literature concerning the selection of pumps, there are still essential aspects that are sometimes overlooked, leading to an inadequate selection. The main purpose of this article is to review the most important technological details to be defined before seeking a quotation for a new centrifugal pump, the aspects to be included in the enquiry and those to be carefully checked in the offers received before taking the decision as to which is the best pump to fulfil the required service.

Preliminary Definitions

The initial selection process for any pump should include the following steps:

  1. Definition of the technological process outline and main process parameters such as flow, pressure and temperature.
  2. Determination of the required pumping services.
  3. Complete description of the fluid to be handled in each pumping service (type of fluid, temperature, density, viscosity, corrosiveness, erosiveness, vapor pressure, solids in suspension, toxicity, volatility).
  4. Plot of general layout of the plant and determination of available space in three dimensions.
  5. General arrangement and dimensions of the piping according to the recommended velocities for each fluid and type of pipe.
  6. Determination of elevation for suction and discharge points or vessels relative to the center line of the pump.
  7. Preliminary calculation of friction losses and plotting of system characteristic curve. Consider allowance for future corrosion of pipes.
  8. Definition of the working parameters of the pump, namely, capacity, head, suction and discharge pressures, taking into account any possibility of variations in pressure or temperature at different pumping conditions.
  9. Determination of any possible exceptional start, stop or running conditions.
  10. Determination of available NPSH.
  11. Preliminary selection of the pump type, design, position, driver, type of sealing, and cooling of seal and bearings if required.
  12. Determination of the type of drive unit (electric motor, steam turbine, etc.) and its main operating parameters. In the case of an electric motor, special attention should be paid to its efficiency (only high-efficiency motors should be specified) and to the advisability of using a variable speed drive (VSD).

Minimum specifications required for pump quotation request
• Service: hot water circulating pumps
• Type of pump: centrifugal
• Preferred position of the shaft: horizontal
• Fluid: treated water, pH: 9.5
• Corrosive/erosive agent: no
• Normal pumping temperature: 185°C; maximum: 195°C
• Density at pumping temperature: 881 kg/m3
• Viscosity at pumping temperature: 1.68 x 10-7 m2/s
• Vapor pressure at pumping temperature: 1.123 MPa
• Normal capacity at pumping temperature: 105 m3/h
• Rated capacity at pumping temperature: 120 m3/h
• Minimum operating flow: 45 m3/h.
• Rated differential head (water at 20°C): 111.3 m
• Rated differential head (corrected for the density): 126.3 m
• Maximum suction pressure: 1.37 MPa
• Discharge pressure: 2.46 MPa
• Maximum discharge pressure allowed by the process: 2.58 MPa
• NPSH available: 20 m
• Preferred rotational speed: 3000 rpm
• Shaft sealing: packing
• Seal cooling: yes
• Bearing cooling: yes
• Cooling fluid available: treated water, 35°C
• Construction materials: according to the manufacturing standards taking into account the pump design and operating conditions indicated above.
Drive: electric motor with the following features:
• Phases: 3
• Start: delta-star
• Voltage: 400 V; voltage tolerance: ±10%
• Frequency: 50 Hz; frequency tolerance: ±4%
• Efficiency class: EFF 1
• Minimum protection: IP 55 for tropical conditions
• Type of service: continuous, industrial, heavy
• Operating conditions: 24 hours/day, 6 days/week
• Starting: not less than 3 starts per hour. Interval between starts could be as short as 30 seconds.
• Power: suitable for the whole Q-H curve of the pump.
Environmental conditions:
• Maximum temperature: 40°C
• Minimum temperature: 10°C
• Relative humidity: 85%.
• Altitude: 100 m above sea level
• Location of installation: under shed, without walls

In the authors’ experience, the buyer should take the preliminary definitions highlighted in item 11 and include them in the technical specifications of the bid request sent to the suppliers. This action should not eliminate the possibility and advisability of communication and exchange of criteria between buyer and seller leading to mutually agreed changes.

After gathering all the information outlined in the 12 items listed above, the buyer will be ready to prepare the specifications for the quotation request. According to the API 610 standard, a good practice is to fill in as much information as possible in the data sheet shown in its appendix. Undoubtedly, this data sheet is a valuable document for pump owners, which is why its length has increased from one page in the Fifth Edition (March 1971) to five pages in the Eighth Edition (August 1995).

Scope of supply

  • Pump
  • Induction electric motor (with VSD if required)
  • Steel base plate, common to pump and motor
  • Flexible coupling
  • Protection of mobile parts
  • Counter flanges, neck type UNI/DIN for welding to ANSI Schedule 40 pipes.
  • Technical documentation, which should include: complete data sheets for pump and driver as stated by API 610; drawings and specifications for driver, coupling and pump; materials specifications; characteristic curves; installation, operation and maintenance instructions; lubrication instructions; spare parts recommendations; and so on.
  • Inspection and testing certificates as per the scope stated by API 610

The above first box shows the data that must be included in the technical specification. The data shown relate to an actual pump whose selection will be discussed in the case study to be presented in the second article in this two-part series. The second box shows the required scope of supply.

Nevertheless, the previously listed information is not enough. Operational requirements are of the upmost importance, and therefore should be defined with the maximum accuracy. Frequently, capacity and head are established only for normal and maximum values without taking into account that the pump could run through a wide range of capacities and that the process may not allow pressure differences beyond certain limits. This is just the case in the example to be presented in the next article. This condition will obviously force an arrangement to be found to fulfil that basic requirement with the highest possible efficiency. Several options could be considered, such as choosing a pump whose Q-H (capacity–head) characteristic curve is flat enough to satisfy the conditions imposed by the process; using several pumps in parallel; or using a VSD.

It may happen that the option adopted entails the pump running in a capacity range wider than the recommended 80% – 110% of the flow at the best efficiency point (BEP), losing not only efficiency but also reliability, as shown in Figure 1.

Additionally, the minimum safe flow recommended by the manufacturer for the pump should be clearly stated in order to prepare the system to ensure the safe, continuous operation of the pump when the process flow demand is lower than that value.

Figure 1. Adverse effects of operating away from the BEP (reproduced from Ref. 2).

Centrifugal pumps can be used in many applications, but in order to operate reliably, with optimal energy useDownload file