Pumps - Pumps - A GENERAL OVERVIEW FOR CHEMICAL ENGINEERING STUDENTS, Presented by Raja Wajahat

PUMPS

A GENERAL OVERVIEW FOR CHEMICAL ENGINEERING STUDENTS

Presented by Raja Wajahat 1

PUMPS

A pump is a device used to move fluids, such as liquids, gases or slurries.

Usually most of the pumps are used for moving volumes from lower places to higher ones.

Pumps are a part of various residential, industrial and commercial applications

The most common example of use of pumps in our homes is the water pump that runs every morning to draw water from the ground.


USE OF PUMPS

Pumps have two main purposes: Transfer of liquid from one place to another place.

Circulate liquid around a system.


COMPONENTS OF A PUMPING

Pumps. (different types of pumps are explained later)

Prime movers: electric motors, diesel engines or air system.

Piping ;used to carry the fluid

Valves ;used to control the flow in the system

Other fittings , controls and instrumentation

End-use equipment. Examples include heat exchangers, tanks and hydraulic machines.


PUMP FAMILY TREE


TYPES OF PUMPS

POSITIVE DISPLACEMENT PUMPS

CENTRIFUGAL PUMPS


POSITIVE DISPLACEMENT PUMPS

The positive displacement pump is commonly used to feed chemicals into the water or to move heavy suspension , such as sludge.

The power for a large piston pump is generally an electric motor connected to the piston by way of a gear head and connecting rod.


CENTRIFUGAL PUMPS

A centrifugal pump is one of the simplest pieces of equipment in any process plant. shows how this type of pump operates:

Liquid is forced into an impeller either by atmospheric pressure, or in case of a jet pump by artificial pressure.

The vanes of impeller pass kinetic energy to the liquid, thereby causing the liquid to rotate. The liquid leaves the impeller at high velocity.

The impeller is surrounded by a volute casing or in case of a turbine pump a stationary diffuser ring. The volute or stationary diffuser ring converts the kinetic energy into pressure energy.


QUALITIES OF AN IDEAL PUMP?

Performance — the ability to quickly move a high volume of water

Low Downtime — the ability to pass debris without clogging

Durability — the ability to withstand harsh work environments

Value — all of the above features at an economical price


PUMPING FACTORS

The altitude at which a pump is operated

At higher elevations atmospheric pressure is decreased reducing suction lift

Water Temperature As water temperature increases the practical suction lift will decrease,

because warm water contains more entrained air, causing the pump to lose its ability to prime. If the water is too warm, it may be necessary to locate the pump below the water level. It can damage the pump (if exceed of operating temperature)


PUMP TERMINOLOGY


PUMP TERMINOLOGY

Pump performance is measured in volume as gallons per minute and in pressure as head.

The published specifications of most pump manufacturers will list this as maximum suction lift.

Head refers to gains or losses in pressure caused by gravity and friction as water moves through the system It can be measured in lbs/in² (PSI)


PUMP TERMINOLOGY

Static Suction Lift : The vertical distance from the water line to the centerline of the impeller.

Static Discharge Head : The vertical distance from the discharge outlet to the point of discharge or liquid level when discharging into the bottom of a water tank.

Dynamic Suction Head : The static suction lift plus the friction in the suction line. Also referred to as Total Suction Head.

Dynamic Discharge Head : The static discharge head plus the friction in the discharge line. Also referred to as Total Discharge Head.

Total Dynamic Head : The Dynamic Suction Head plus the Dynamic Discharge Head. Also referred to as Total Head.


PUMPING POWER

The power imparted into a fluid increases the energy of the fluid per unit volume.

The power relationship is between the conversion of the mechanical energy of the pump mechanism and the fluid elements within the pump.

In general, this is governed by a series of simultaneous differential equations, known as the Navier–Stokes equations.

However a more simple equation relating only the different energies in the fluid, known as Bernoulli's equation can be used. Hence the power, P, required by the pump:


PUMPING POWER

ΔP is the change in total pressure between the inlet and outlet (in Pa),

Q, the fluid flowrate is given in kg/s

η is the pump efficiency, and may be given by the manufacturer's information, such as in the form of a pump curve, and is typically derived from either fluid dynamics simulation (i.e. solutions to the Navier–Stokes for the particular pump geometry), or by testing.

The efficiency of the pump depends upon the pump's configuration and operating conditions (such as rotational speed, fluid density and viscosity etc.)


PUMPING POWER

The total pressure may have gravitational, static pressure and kinetic energy components; i.e. energy is distributed between change in the fluid's gravitational potential energy (going up or down hill), change in velocity, or change in static pressure.


RESISTANCE OF THE SYSTEM: HEAD

The total head is the sum of static head and friction head

Static head

Static head consists of: Static suction head (hS)

Static discharge head (hd)


FRICTION HEAD (HF)

This is the loss needed to overcome that is caused by the resistance to flow in the pipe and fittings.

It is dependent on : size, condition and type of pipe

number and type of pipe fittings

flow rate

nature of the liquid


FRICTION HEAD (HF)

The friction head is proportional to the square of the flow rate as shown in figure


FRICTION HEAD & STATIC HEAD

In most cases the total head of a system is a combination of static head and friction head as shown in Figures


PUMP PERFORMANCE CURVE

The head and flow rate determine the performance of a pump, which is graphically shown in Figure


PUMP OPERATING POINT

The rate of flow at a certain head is called the duty point.

The pump performance curve is made up of many duty points.

The pump operating point is determined by the intersection of the system curve and the pump curve as shown in Figure


NET POSITIVE SUCTION HEAD (NPSH)

The net positive head available is given by the following equation:

where NPSH(m,u = net positive suction head available at the pump suction, m, P — the pressure above the liquid in the feed vessel, N/m2,

H — the height of liquid above the pump suction, m,

Pf = the pressure loss in the suction piping, N/m2,

Pv = the vapour pressure of the liquid at the pump suction, N/m2,

p — the density of the liquid at the pump suction temperature, kg/m3


POWER REQUIREMENTS FOR PUMPING LIQUIDS

The total energy required can be calculated from the equation:

where W = work done, J/kg, Δz = difference in elevations , m,

ΔP = difference in system pressures , N/m2,

ΔP= pressure drop due to friction, including miscellaneous losses,

and equipment losses, N/m2,

p = liquid density, kg/m3,

g = acceleration due to gravity, m/s2.





If W is negative a pump is required; if it is positive a turbine could be installed to extract energy from the system.

The power is given by:

where m = mass flow-rate, kg/s,

η — efficiency = power out/power in.


PUMP EFFICIENCY

It is the ratio of the power imparted on the fluid by the pump to the power supplied to drive the pump.

Efficiency is a function of the discharge and therefore operating head so its value is not fixed for a given pump.


PUMP EFFICIENCY

The efficiency will depend on the type of pump used and the operating

conditions.

For preliminary design calculations, the efficiency of centrifugal pumps can be

determined using Figure


PUMP EFFICIENCY


PUMPS IN PARALLEL TO MEET VARYING DEMAND

Operating two pumps in parallel and turning one of when the demand is lower, can result in significant energy savings.

Pumps providing different flow rates can be used.

Parallel pumps are an option when the static head is more than fifty percent of the total head


PUMPS IN PARALLEL TO MEET VARYING DEMAND


PUMP TROUBLESHOOTING

If the pump does not deliver enough water: Engine may not be running at the rated speed.

Strainer, inlet valve or the suction line may be clogged.

Suction line or fittings may leak air.

Mechanical seal may be worn and leaking air or water. Check weep hole.

There may be too much clearance between impeller and the volute due to wear. For best performance refer to manufacturer’s recommendations for proper adjustment.



If the pump does not develop enough pressure: Mechanical seal may be leaking. Check weep hole.

There may be too much clearance between the impeller and pump body or volute due to wear. For good performance, refer to the manufacturer’s instructions for proper adjustment.



Every six months, check the impeller for wear, and for clearance between the impeller face and the volute. Refer to the manufacturer’s recommendations. Check the shaft seal for wear, as well as the shaft sleeve. Clean the casing and volute passages.


THANK YOU


Pumps - Pumps - A GENERAL OVERVIEW FOR CHEMICAL ENGINEERING STUDENTS, Presented by Raja Wajahat

Engineering

check weep

dynamic suction

dynamic discharge

static discharge

static head

total head

suction line

pump suction