ENM 202 - Facilities Engineering

Machinery

1) Explain the steps that you would take in the design and/or operation of a pumping system toavoid the possibility of cavitation.

2) Explain the steps taken in a pumping system to attain the desired operating point for thesystem when

(i) the pump is driven by a fixed speed motor, and,

(ii) when the pump is driven by either a variable speed motor or a turbine.

3) Explain the phenomena of surge in a compressor and describe the design and/or operationalsteps that you would take to avoid surging.

Fluid Mechanics

1. Water flowing in a pipeline 4 m above datum level has a velocity of 12 m/s and is at a gauge

pressure of 36 kN/m2. If the mass density of water is 1000 kg/m3, what is the total energy per unit

weight of the water at this point? Assume Acceleration due to Gravity to be 9.81 m/s2 (Ans: 15.01 m)

2. The Main Oil Line Pump is located on an offshore platform. The elevation of pump is 50 meters

above Mean Sea Level. The jacket is located in 100 meter water depth. Assume the datum at the

base of the jacket to be 50 meters below the bottom of the jacket.

The MOL – discharge pressure of 2000 kPa – delivers 100,000 bbls of oil per day via a 10” pipe to a

terminal. The route of the line drops down to 25 meters above the datum. The highest elevation of

the subsea line is 100 meters above datum. The terminal reception is at an elevation of 160meters

above datum.

Draw a sketch of the pipeline route and calculate the pressures at the following three points:

(1) At the lowest point of the route (Ans: 3373.416 kPa)

(2) At the highest point of the route subsea. (Ans: 2784.816 kPa)

(3) The pressure at reception at the terminal. (Ans: 2313.936 kPa)

Assume that there is no loss due to friction. See attached Table for conversion factors

Acceleration due to gravity = 9.81 m/s2; Density of oil = 800 kg/m3

3. The suction pipe of a pump rises from a sump at a slope of 1 in 5 and water passes through at 1.8

m/s. If dissolved air is released when the pressure falls to more than 70 kN/m2 below atmospheric

pressure, find the greatest practicable length of pipe neglecting friction. Assume that the water in

the sump is at rest. Assume the density of water to be 1000 kg/m3. (Ans: 35.54 m)

4. The Main export pump at an oil reception terminal is located 50 meters above the Datum. It

exports 1,250,000 bbls per day of oil via a 36” landline. The line has to cross a land elevation of 150m

above datum. The reception point is located 75m above datum. The pressure in the line should

never drop below 2000 kPa in order to avoid gases being released from the oil. Assume that there

are no friction losses.

(1) Calculate the discharge pressure of the export pump (Ans: 2784.79 kPa)

(2) The pressure at the reception point. (Ans: 2588.59 kPa)

Density of oil=800 Kg/m3; Acceleration due to Gravity = 9.81 m/s2

5. A Main Oil Export pump – Discharge Pressure 2500 kPa – exports 1,500,000 bbls per day via a 30”

land over a long distance. An intermediate pump is located half way along the line generating a head

of 50m. The total length of the pipe suffers from a friction head loss of 25m. Assume that the

location of both the export pump and the terminal are 10m above Mean Sea Level and the location

of the intermediate pump is 60 meters above Mean Sea Level.

Density of oil=860 Kg/m3; Acceleration due to Gravity = 9.81 m/s2

(1) Calculate the pressure of the oil at arrival at the terminal. (Ans: 2710.9 kPa)

(2) Calculate the suction pressure of the intermediate pump. (Ans: 1972.7 kPa)

Pump Theory

Exercises

Exercise 1 – Pressure due to liquid height

An open cylindrical tank contains a liquid to a height of 8 meters. If the density of the liquid is 1.25 X

103 kg/m3, what is the pressure exerted by the liquid at the bottom of the tank?

If 1 Pa = 145.04 X 10-6 psig, calculate the pressure in psig.

(Ans: 98.1 kPa; 14.228 psig)

Exercise 2 – Equivalent Head of water

What height of water is necessary to exert a pressure of 1kPa at a temperature of 60 0 C? (Density of

water at 60 0 C = 983.2 kg/m3) (Ans: 0.1037 m)

Exercise 3 - Equivalent Head of water

The pressure at the discharge of a water pump is 100 psig and the temperature of the water is 80

Deg C. Find the equivalent HEAD in Feet. (Data – Gravitational acceleration g = 32.174 ft/s2; Density

of water at 80 Deg C = 60.65 lb/ft3) (Ans: 237.42 ft)

Exercise 4 – Total Static Head

A pump takes suction from an open tank located 2 meters above the pump. The tank water level is

3.5 meters. The pump discharges into the bottom of an open tank that is 8 meters above the pump.

When the pump is shut down the suction valve is closed. The discharge pressure gauge reads 130

kPa. Assuming the water is at 4 Deg C (density of water at 4 Deg – 1X103 kg/m3), what is

(a) the level in the discharge tank (Ans: 5.26 m)

(b) the total static head of the pump (Ans: 7.76 m)

Exercise 5 – Total Static Head

A rotary pump draws oil from a sump and delivers it into a storage tank. The level in the sump is 2 m

below the base of the storage tank and the level in the tank is 4.5 m. If the pump sits 1m above the

base of the tank and discharges into the side of the tank at a height of 3m what is the total static

head of the pump? (Ans: 6.5 m)

Exercise 6 – Pressure Head

A feed water pump is operating at a pressure of 700 kPa. If the water enters the boiler at a

height of 8m above the pump and 30 cm below the boiler water level, what is the discharge head of

the pump? Ignore the effects of temperature. (Ans: 79.7 m)

Exercise 7 - Pressure Head

Calculate the pressure differential across the pump in a pressurised water system if the liquid level in

the suction vessel is 3 m below the pump and the vessel has a gas blanket of 45 kPa the discharge

pressure head is 150 m and the discharge level is 18,5 m above the pump. (Ans: 1636.42 kPa)

Exercise 8 – Friction Head

Schedule 40 steel pipe, 50.8 mm diameter is used to construct a piping system. The length of piping

is 100 m and there are 4 standard elbows, 2 tees one Gate and Globe Valve. If the flow is

25Litres/Sec, what is the friction head of the system?

Useful data from tables: Equivalent resistance (length of pipe of same diameter) for Sch. 40 Pipe and

fittings:

Friction loss at 25 L/Sec Flow = 36.5 (m water/25 m of pipe)

Elbows = 1.68; Tees = 3.35; Globe Valve = 17.4; Gate Valve = 0.37 (Ans: 191.53 m)

Exercise 9 – Velocity Head

If a centrifugal pump is required to move 10,000 kg of water at a velocity of 12 m/sec through a 5 cm

diameter line, what velocity head must be considered in the pump design? (Ans: 7.34 m)

Exercise 10 – Total Head

A vacuum evaporator has an absolute pressure of 25 kPa. The level in the evaporator is 10 m above

the centreline of the pump. The pump discharges into a storage tank located 20 m above the pump

with the discharge point 6 m above the bottom of the tank and a pressure blanket of 100 kPa

(gauge). Liquid velocities are 3 m/s in the suction piping and 4 m/s in the discharge line. Friction loss

in the suction line is 0.5 m and in the discharge line is 1.8 m.

(a) Using Bernoulli’s equation, calculate the head generated by the pump assuming the density of

the liquid to be (i) 967.5 Kg/m3 and (ii) 1000 kg/m3

(Ans: (i) 37. 69 m (ii) 37.087))

(b) Calculate the TOTAL dynamic head for the pump. Assume the liquid density to be 1000 Kg/m3

(Ans: 37.098 m)

Useful Data from tables: Atmospheric pressure = 101.3 kPa

Exercise 11 – Pump Power

A pump is required to move 30,000 Litres/Min of water at 40 Deg C from a cooling pond to a water

tower. The Total Head required to be produced by the pump has been calculated as 22.5 m.

assuming a pump efficiency of 80%, calculate the power of the motor required to drive the pump.

The density of water at 40 Deg C is given as 990 kg/m3 (Ans: 136.573kW)

Exercise 12 – Water Hammer

Assume that a pump delivers water to a tank of 60 m above the pump. During a power failure the

pump discharge check valve gets stuck in the open position for a few moments, then slams shut.

Before the check valve closes, water begins to flow backwards through the pump with a velocity of

10 m/s. if the speed of sound in water is 1469 m/s at 15.6 Deg c, what is the water hammer head

pressure? (Ans: 15279 kPa or 2216.3 psi)