Pump Selection

Introduction

There has been a situation in which a group of engineers has been asked to propose a piping configuration for a liquid transport system. In this case, the liquid being transported is Ethanol at a constant temperature of 25°C. This fluid should go, from a tank at a certain pressure, down to a pump and all the way up again into a reactor. The pipe dimensions and the desired flowrate have been given and they are:

Shed 40 NPS 2 in

Q = 5.28 dm3/s = 0.00528 m3/s

Even though the piping configuration is up to the group of workers, these engineers have been given certain specifications of some materials and contents of the piping system. For example, they have to include some gate valves in some certain points of the system in order to control the flow rateof the fluid transported.
This group has been asked to select, at their own choice, a specific centrifugal pump for the system. After creating the piping configuration, the engineers must create a system curve, and a pump curve based on the energy requirements. There have been several other limitations: the pump should not cavitate and they must make a choice of the pump in terms of its efficiencyor BHP. In addition to these specifications, the annual operating cost of this particular pump should be calculated and reported.
The objective of this project is to make a decision, a very important one, on a selection of a centrifugal pump based on its efficiency and, also, being aware of its annual cost.
Piping Configuration

Restrictions:
* The liquid must reach the reactor with apressure of 3 atm (abs).
* The storage tank is maintained at atmospheric pressure
* The storage tank liquid level is 1 m above the pump
* The tank exit pipe must be vertical and should have a gate valve fully-open close to the tank exit
* A gate valve fully-open before the pump
* A pressure gauge P1 between the gate valve and the pump
* A check valve after the pump followedby a globe valve fully-open (for throttling the flow)
* A pressure gauge P2 after the globe valve
* A gate valve fully-open before the reactor entrance and a pressure gauge P3 between the gate valve and the reactor
* The reactor must be 3 m above the pump
After checking the piping specifications listed above, the team has been up to a piping system and the design is the following.Fig. 1. Piping configuration Design
Fig. 1. Piping configuration Design

Process

At first the data sheet in the Excel file was created. In this sheet, the known values of the pipe dimensions were captured. With the Schedule 40 and NPS, looking it in tables for piping values, the inside diameter could be read. Then, with that certain diameter, the area of the pipe was calculated.
Fig 2.Pipe Properties
Fig 2. Pipe Properties

At the same time, the fluid properties (ethanol) were read. Density, viscosity, temperature and the vapor pressure for the given temperature (25 C) were captured. Then the mass flow rate was calculated.
Fig 3. Fluid Properties
Fig 3. Fluid Properties

To calculate the system curve, first, the properties of the commercial steel (pipe material) and theinitial pressure drop and elevation change were needed. **Note: This data is just from the tank all the way to the reactor (p1 – p3).

Fig 4. System properties
Fig 4. System properties

Also, the team needed to know the specific (L/D) of each of the fittings that would be proposed. These fittings are for the elbows in the system, the gate valves, globe valves, and check valves. The one forstraight pipe (sp) was calculated with the formula below.
Table 1. Fittings (L/D)
Table 1. Fittings (L/D)



So, after having each individual (L/D) the (L/D) eq was calculated with the formula shown below.

The next step was to read and calculate the friction coefficients (k). These coefficients are constant for the entrance and exit of the pipe to the tank and reactor respectively

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