Pump and Fan systemPresented ByJ.Nagesh KumarSr.Dy.DirectorNational Productivity CouncilAIP,Ambattur,Chennai-98npcaip@vsnl.com

Centrifugal Pumps

Energy Balance for a Typical Pumping System

Operating Point Defined

Unsafe Safety AllowanceSystem heads should be estimated as accurately as possibleDo not add a margin for safety to the system headIn trying to match the over specified head, a larger pump will be recommended by the supplierThe larger pump will operate at a higher capacity point (as required by the actual system head)This can overload the pump motor and require greater throttling

Efficiency Curves

Operation with ThrottlingAB

Typical pump characteristic curves

The affinity law for a centrifugal pumpFlow:Q1 / Q2 = N1 / N2Example: 100 / Q2 = 1750/3500Q2 = 200 m3/hrHead:H1/H2 = (N12) / (N22)

Example:100 /H2 = 1750 2/ 3500 2

H2 = 400 m

Flow Control StrategiesBypass valveZero savingsThrottle outputIncreased system pressure dropMove system curve and reduces efficiencyEffect less in flat H-Q curveTrim impellerBuy a new pumpVariable speed driveMost efficientPower varies as cube of speedDifferent flow rates without affecting efficiency

Why Oversized Pump ?Safety margins were added to the original calculations. Several people are involved in the pump buying decision and each of them is afraid of recommending a pump that proves to be to small for the job. It was anticipated that a larger pump would be needed in the future, so it was purchased now to save buying the larger pump later on. It was the only pump the dealer had in stock and you needed one badly. He might have offered you a "special deal" to take the larger size. You took the pump out of your spare parts inventory. Capital equipment money is scarce so the larger pump appeared to be your only choice. You purchased the same size pump as the one that came out of the application and that one was over sized also.

Energy conservation measuresConduct water balance minimise water consumptionAvoid idle cooling water circulation in DG sets, compressors, refrigeration systems In multiple pump operations, judiciously mix the operation of pumps and avoid throttlingHave booster pump for few areas of higher headReplace old pumps by energy efficient pumpsIn the case of over designed pump, provide variable speed drive, trim / replace impeller or replace with correct sized pump Remove few stages in multi-stage pump with over designed head

Energy Savings OpportunitiesGive efficiency of the pump due consideration while selecting a pump.Select pumps to match head flow requirements.Select a motor to match the load with high efficiency.Optimize the piping design.Monitor all important system parameters like: motor kW, pump head, flow temperature.Use pumps in series and parallel so that mismatch in system design or variations in operating conditions can be handled properly.

Energy Savings Opportunities (Contd.)Use variable speed drives for variations of flow due to process requirement.If the head flow is higher than needed by 5 to 15%, (i) The existing impeller should be trimmed to a smaller diameter, (ii) or a new impeller with a smaller diameter is to be put.In multistage pumps, add or remove stages to the existing pump, allowing an increase / decrease in delivered head of flow, if required.

Air conditioning SystemResinoid plant

Cold Well

Hot Well

Resinoid Moulding

Recirculated cooled air

Recirculated cooled and washedair

46 TR x 2nos in operation

Annual Savings Rs.3 lakhs

Avoid Cold well PumpsResinoid plant

Hot Well

Resinoid Moulding

Recirculated cooled air

Recirculated cooled and washedair

46 TR x 2nos in operation

New line

Open circuit pumping system (Existing)Cold WellHot WellCalibratorPiercing pressElongatorPush BenchReelerStretch reducing millMandrel bar cooling

Scale pitSettling Tank

Settling Tank

Pressure Sand Filter350 m3/hr25 m45 kw195 m3/hr50 m41 kw175 m3/hr20 m18 kw5 kw x 2 no

Open circuit pumping system (Proposed)Cold WellHot WellCalibratorPiercing pressElongatorPush BenchReelerStretch reducing millMandrel bar cooling

Scale pitSettling Tank

Settling Tank

Pressure Sand Filter350 m3/hr25 m45 kw195 m3/hr50 m41 kw175 m3/hr20 m18 kw5 kw x 2 no

Closed circuit pumping system Cold WellRotary hearth furnaceWalking beam furnaceRoll down furnaceSpiral fin weldingNitrogen generatorNormalising furnaceTempering FurnaceAir compressorsHydraulic systems

Return water sump600 m3/hr20 m48 kw60 m3/hr50 m110 kwSwitch off during 6-9 AM & PM

Existing cooling water system for tube plantReturn water sump

Final compounding mill

Warming mill

Feeding mill

Extruder

8 m3/hr2.5 m3/hr0.4 m3/hr0.23 m3/hr

Extruder die cooling

3 m3/hr

Extruder conveyor cooling

9.4 m3/hr100 TR10 HPActual - 6 kWHP - 7.5Actual - 4 kWH - 22 mQ - 16m3/hrHP - 20Actual - 11 kWH - 29 mQ - 23 m3/hrK41423HP - 10Actual - 6 kWH - 29 mQ - 17m3/hrHP - 20Actual - 16.2 kWH - 56 mQ - 15 m3/hrHP - 20Actual - 12 kWH - 39 mQ - 23 m3/hr

Modified cooling water system for tube plantReturn water sump

Final compounding mill

Warming mill

Feeding mill

Extruder

8 m3/hr2.5 m3/hr0.4 m3/hr0.23 m3/hr

Extruder die cooling

3 m3/hr

Extruder conveyor cooling

9.4 m3/hr100 TR10 HPActual - 6 kWHP - 7.5Actual - 4 kWH - 22 mQ - 16m3/hrHP - 20Actual - 11 kWH - 29 mQ - 23 m3/hrK414HP - 10Actual - 6 kWH - 29 mQ - 17m3/hrHP - 20Actual - 16.2 kWH - 56 mQ - 15 m3/hrHP - 20Actual - 12 kWH - 39 mQ - 23 m3/hrModified pumping systemHP - 3Actual 1.4 kWH - 22 mQ - 17m3/hr

Dump Chest to Belcore(Existing Practice)10 m120 m3/hr Kw

10 m120 m3/hr Kw

DumpChestBelcoreHD CleanerBelcore Feed Chest

Connect HD cleaner pump outlet to Belcore feed pump10 m120 m3/hr Kw

10 m120 m3/hr Kw

DumpChestBelcoreHD Cleaner

Centrifugal fans

Difference between fans, blowers and compressorsAs per ASME the specific pressure, i.e, the ratio of the discharge pressure over the suction pressure is used for defining the fans, blowers and compressors as highlighted below :

Energy audit of fanCollect fan and motor specifications with ducting networkMeasure motor power inputMeasure fan and motor speedMeasure static pressure at various points in the ductMeasure total and static pressure and compute flowEstimate the system efficiency and check fan operating point

Fan and Blower Controls The volume of air moved by fans and blowers is adjusted in four basic ways:Changing the rotational speed is the most efficient. If the volume requirement is constant, it can be achieved by selecting appropriate pulley sizes. If the volume varies with the process, adjustable-speed drives can be used.Changing the blade angle is a method used with some vane-axial fans.Restricting the airflow is accomplished with dampers or valves which close off the airflow at the inlet or outlet. Inlet vanes, which swirl the air entering the centrifugal fan or blower, are more efficient than dampers or butterfly valves.Venting the high-pressure air, or recirculating it to the inlet, is often used with positive-displacement blowers. It is sometimes used with fan systems, but is the least efficient method as there is no reduction in the air being moved.

What to Look for in the FieldOverall system efficiency will be determined by the type of fan or blower, its interaction with the air distribution system, and the method of control.Determine whether the right type of fan or blower is used for an application. Is your fan or blower is providing the best efficiency and performance in a given application.The efficiency of a system depends on the number and type of bends and restrictions. Sharp bends, especially, increase the resistance the fan or blower must overcome. Bends and restrictions near the inlet or outlet seriously degrade capacity and efficiency. With a properly selected fan or blower and well-designed air distribution system, the method of control is the main thing determining energy efficiency. In systems requiring constant air volume, the speed of a belt-driven fan or blower should be adjusted by proper selection of pulley sizes, and equipment should operate only when needed. In systems requiring variable airflow, an adjustable-speed control is most efficient.

Energy conservation in fans Match fan capacity to demanddownsizing, pulley change, VSD..Avoid unnecessary demandexcess air reductionidlingReduce pressure dropsRemove redundant ductsModify ducting with minimum bendsDrive system Provide direct drive where possibleReplace V-belt by flat beltReplace with energy efficient fansRegular preventive maintenance

Checklist for energy savings in Fans and Blowers Use smooth, well-rounded air inlet cones for fan air intakes. Avoid poor flow distribution at the fan inlet. Minimize fan inlet and outlet obstructions. Clean screens, filters, and fan blades regularly. Use airfoil-shaped fan blades. Minimize fan speed. Use low-slip or no-slip belts. Check belt tension regularly.

Checklist for energy savings in Fans and Blowers (contd.)Use variable speed drives for large variable fan loads. Use energy-efficient motors for continuous or near-continuous operationEliminate ductwork leaks. Turn fans off when they are not needed. Blowers Use smooth, well-rounded air inlet ducts or cones for air intakes. Minimize blower inlet and outlet obstructions.

Checklist for energy savings in Fans and Blowers (contd.)Clean screens and filters regularly. Minimize blower speed. Use low-slip or no-slip belts. Check belt tension regularly. Eliminate variable pitch pulleys. Use variable speed drives for large variable blower loads. Use energy-efficient motors for continuous or near-continuous operation. Eliminate ductwork leaks. Turn blowers off when they are not needed.

Flow control

Impact of speed reduction

Use of VSD: Boiler ID fan case study

Use of VSD: Boiler ID fan case study(contd.)

Twin Benefits due to fan speed controlThermax Boiler

6 TPH10.75 Kg/cm2Coconut shell fired

HopperCoconut shell crusherEconomiserDustCollectorPrimary Air FanSecondary Air FanInduced Draft FanDamper14 % O29 % O2

Energy saving in Boiler ID fan by speed reduction through pulley change

Regulate with dampers in each equipment 30 HP dust collector in Resinoid plant

Ask the participants to list some pump applications.Centrifugal pumps account for the vast majority of pumps applications in industry.Centrifugal pumps give energy to the fluid by centrifugal action. They rely on the flow of fluid to create a seal to prevent fluid flowing backward through the pump. The volute is the most common centrifugal. The impeller vanes generally curve backwards, but radial and forward vanes are used.The velocity head of the fluid is converted into pressure head.

Pumps are components of pumping systems, which also include motors, drives, piping and valves. Typically much less than half the electricity input to a pumping system is converted into useful movement of fluid. The rest is dissipated by the various components that make up the system. Energy losses are still greater when the system is not operating at its design point. Thus, there appears to be to be a considerable potential for saving electricity, both by improving component efficiencies and through better system design.

The system curve is a plot of system resistance vs flow. Once the operating point ie flow and pressure are determined, the pump has to be selected by superimposing the pump curve to intersect with the operating point on the system curve. The characteristic curve of a centrifugal pump is shown in the figure. The pump has to be selected so that it will operate at its best efficiency point. Oversizing of flow during initial selection creates can cause efficiency point to shift resulting reduced operational efficiency of the pump. Also the oversized pump needs to be throttled to meet the reduced flow condition.Selection of a pump is vital to energy efficiency in operations later. Allowances and liberal factors of safety enhances the capacity and head requirement. In actual operation the pump will be oversized leading to throttling.Use the white board and do the following

Assume that we need to pump 68 m3/hr. to a 47 meter head with a pump that is 60% efficient at that point.Liquid Power - 68 x 47 / 360 = 8.9 KwWhere 360 is a constantShaft Power - 8.9 / 0.60 = 14.8 KwWhere 0.6 is the efficiency at that pointMotor Power - 14.8 / 0.9 = 16.4 KwWhere 0.9 is the motor efficiencyAs shown in the drawing, we should be using impeller "E" to do this, but we have an oversized pump so we are using the larger impeller "A" with the pump discharge valve throttled back to 68 cubic meters per hour, giving us an actual head of 76 meters. Now our Kilowatts look like this:68 x 76 / 360 = 14.3 Kw being produced by the pump, and 14.3 / 0.50 = 28.6 Kw required to do this. Subtracting the amount of kilowatts we should have been using gives us: 28.6 - 14.8 = 13.8 extra kilowatts being used to pump against the throttled discharge valve. Extra energy used - 8760 hrs/yr x 13.8 = 120,880 kw. = $ 10,000/annumIn this example the extra cost of the electricity could almost equal the cost of purchasing two or three pumps.

This is just similar to fans that we have seen in the last session. The normal operating point A is what the pump had been designed for. But to accommodate lower flow, the flow is throttled leading to an incremental pressure drop. The flow at B is less than flow at A but has been achieved at the cost of additional head which involves waste of energy.For centrifugal pumps the laws that are applicable to fans are also applicable for pumps. Flow is proportional to speed, Head proportional to square of head and power to the cube of speed.Varying flow requirements can be met by conventional and low cost options such as by pass control or throttle control. But both these methods are highly energy inefficient. There are occasions when you might want to permanently change the amount of fluid you are pumping, or change the discharge head of a centrifugal pump. This can be economically achieved by trimming the impeller or replacing the pump with a reduced size of the impeller or at the worst replacing the pump itself.The most efficient way to deal with varying flows is by means of a variable speed drive. This ensures that the pump always operates at the best efficiency point and eliminates the need for any throttling. The virtue of this method is that it reduces the energy input to the system instead of dumping the excess. With decreasing costs in power electronics the variable speed drives are becoming more popular today.

The normal mistakes done in selecting a pump is given above. Remember that the cost of operating an inefficient pump is many times more than the pump cost itself.As a first step, a water balance has to be made out quantifying requirements for various uses. Once this is done analysis needs to be made to reduce or recycle water. Reducing water consumption is the simplest way to save energy.Also look for standby equipment and equipment which are not in operation, but utilising water. For example a DG set which operates only during emergency might have water getting circulated for cooling. Such uses can be curtailed.Just to meet one or two applications where a higher pressure is required, the entire pumping system may be operating at a higher head. Reduce the pressure and provide booster pumps for such applications.

First you should be sure of the flow and head requirements and then select the pump to operate in this point at maximum efficiency.The motor has to be selected so that the loading is maintained high. Energy efficient motor can be considered during new installations.Provide appropriate meters and log data so that analysis becomes easy.Where large variations are expected, multiple pumps have to be judiciously selected and operated for maximum efficiency.Variable speed drives can be considered only where continuous fluctuations are expected.Each pump casing has provision for replacement with lower or higher size impellers up to a certain limit and varies with manufacturer. Flow changes can be met by changing the impeller or trimming the existing impeller.In multistage pumps such as boiler feed pumps, too high a pressure than requirement can be dealt by removing a few stages of the pump.If fans rated for a higher flow rate, but a lesser flow is actually required: then flow reduction is effected by the following methodsRecirculation: Venting the high-pressure air, or recirculating it to the inlet, is often used with positive-displacement blowers. It is sometimes used with fan systems, but is the least efficient method as there is no reduction in the air being moved.Damper: Restricting the airflow is accomplished with dampers or valves which close off the airflow at the inlet or outlet. Inlet vanes, which swirl the air entering the centrifugal fan or blower, are more efficient than dampers or butterfly valves. VFC: Variable speed fluid coupling. Motor speed is constant but the fluid coupling speed changes thus changing the speed of fan.VFD: Variable frequency drive which varies the speed of the motor itself

Changing the blade angle is a method used with some vane-axial fansChanging the rotational speed is the most efficient. If the volume requirement is constant, it can be achieved by selecting appropriate pulley sizes. If the volume varies with the process, adjustable-speed drives can be used.

Existing conditionThis is a coconut shell fired boiler. Boiler is operating with damper 100 % opening. Excess air is around 200 % with an oxygen level of 14 %.This means too much air is being supplied to the boiler. Improved ConditionThe excess air was reduced by closing the damper by 50 % and excess air was reduced to 75 %. Now the fuel consumption reduced by 5%. Not only that. We have reduced the air by closing the damper which has incurred a unnecessary pressure loss. Now how can we reduce the power of the fan ?Existing condition The ID fan is in oversized condition for the existing operating load.So the minimum cost option is to reduce the motor pulley and reduce the fan speed. The motor pulley was reduced from 8 to 6.

Energy consumption in existingCondition (Damper control)26 kW

After reducing the motor pulleyTo 6 (damper fully open)14 kW

Annual saving12 x 8000

96,000 kWHSpeed reduction by pulley change can give only one fixed speed. Since the boiler is operating at constant load speed reduction through pulley change is the appropriate option. Where boiler load fluctuates a variable speed drive (inverter) may be installed. The speed can be varied according to load. The speed control can be effected in relation to fuel feeder RPM.The savings with variable speed drive will be marginally more becauseThe motor and fan can be directly coupled thus eliminating the v-belt losses