Pump and cooling tower energy performance

Energy Performance of Pumps and Cooling Towers

Prepared By: Maulik Bhagat

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Pumps

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Outline:Outline:

Introduction

Type of pumps

Assessment of pumps

Energy efficiency opportunities

Used for:

•Domestic, commercial, industrial, agricultural services

•Municipal water and wastewater services

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IntroductionIntroduction

Pump have two main purposes• Transfer liquid

from source to destination

• Circulate liquid around a system

Main pump components

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• Prime movers: electric motors, diesel engines, air system

• Piping to carry fluid

• Valves to control flow in system

• Other fittings, control, instrumentation

End-use equipment

• Heat exchangers, tanks, hydraulic machines

Main pump components

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• Head• Resistance of the system

• Two types: static and friction

Pumping System Characteristics

destination

source

Statichead

Static Head

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• Difference in height between source and destination

• Independent of flow

Statichead

Flow

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• Resistance to flow in pipe and fittings

• Depends on size, pipes, pipe fittings, flow rate, nature of liquid

• Proportional to square of flow rate

Frictionhead

Flow

Friction head

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Type of PumpsType of Pumps

Pump Classification

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Positive Displacement Pumps

• Reciprocating pump• Displacement by reciprocation of piston

plunger

• Used only for viscous fluids and oil wells

• Rotary pump• Displacement by rotary action of gear,

cam or vanes

• Several sub-types

• Used for special services in industry

Positive Displacement Pumps

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Positive Displacement Pumps

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Rotodynamic pumps

• Mode of operation• Rotating impeller converts kinetic energy

into pressure to pump the fluid

• Two types• Centrifugal pumps: pumping water in

industry – 75% of pumps installed

• Special effect pumps: specialized conditions

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Centrifugal Pumps

How do it work?

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Assessment of pumpsAssessment of pumps

• Pump shaft power (Ps) is actual horsepower delivered to the pump shaft

• Pump output/Hydraulic/Water horsepower (Hp) is the liquid horsepower delivered by the pump

How to Calculate Pump Performance

Hydraulic power (Hp):Hp = Q (m3/s) x Total head, hd - hs (m) x ρ (kg/m3) x g (m/s2) / 1000

Pump shaft power (Ps):Ps = Hydraulic power Hp / pump efficiency ηPump

Pump Efficiency (ηPump): ηPump = Hydraulic Power / Pump Shaft Power

• Absence of pump specification data to assess pump performance

• Difficulties in flow measurement and flows are often estimated

• Improper calibration of pressure gauges & measuring instruments

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Difficulties in Pump Assessment

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Energy Efficiency OpportunitiesEnergy Efficiency Opportunities

1. Selecting the right pump

2. Controlling the flow rate by speed variation

3. Pumps in parallel to meet varying demand

4. Eliminating flow control valve

5. Eliminating by-pass control

6. Start/stop control of pump

7. Impeller trimming

Cooling Tower

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Outline:Outline:

Introduction

Types of cooling towers

Assessment of cooling towers

Energy efficiency opportunities

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IntroductionIntroduction

A cooling tower is an equipment used to reduce the temperature of a water stream by extracting heat from water and emitting it to the atmosphere.

Component of Cooling Tower

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• Frame and casing: support exterior enclosures

• Fill: facilitate heat transfer by maximizing water / air contact

• Splash fill

• Film fill

• Cold water basin: receives water at bottom of tower

Components of a cooling tower

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• Drift eliminators: capture droplets in air stream

• Air inlet: entry point of air

• Nozzles: spray water to wet the fill

• Fans: deliver air flow in the tower

Components of a cooling tower

• Natural Draft Cooling Tower

• Mechanical Draft Cooling Tower

• Forced Draft Cooling Tower

• Induced Draft Cooling Tower

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Types of Cooling TowersTypes of Cooling Towers

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Performance Parameters

1. Range

2. Approach

3. Effectiveness

4. Cooling capacity

5. Evaporation loss

6. Cycles of concentration

7. Blow down losses

8. Liquid / Gas ratio

Assessment of Cooling TowersAssessment of Cooling Towers

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1. Range

Difference between cooling water inlet and outlet temperature:

Range (°C) = CW inlet temp – CW outlet temp

High range = good performance

Ran

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Hot Water Temperature (In)

Cold Water Temperature (Out)

Wet Bulb Temperature (Ambient)

(In) to the Tower(Out) from the Tower

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2. Approach

Difference between cooling tower outlet cold water temperature and ambient wet bulb temperature:

Approach (°C) = CW outlet temp – Wet bulb temp

Low approach = good performance

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Hot Water Temperature (In)

Cold Water Temperature (Out)

Wet Bulb Temperature (Ambient)

(In) to the Tower(Out) from the Tower

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3. Effectiveness

Effectiveness in %

= Range / (Range + Approach)

= 100 x (CW temp – CW out temp) / (CW in temp – Wet bulb temp)

High effectiveness = good performance

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Hot Water Temperature (In)

Cold Water Temperature (Out)

Wet Bulb Temperature (Ambient)

(In) to the Tower(Out) from the Tower

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4. Cooling Capacity

Heat rejected in kCal/hr or tons of refrigeration (TR)

= mass flow rate of water X specific heat X temperature difference

High cooling capacity = good performance

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Hot Water Temperature (In)

Cold Water Temperature (Out)

Wet Bulb Temperature (Ambient)

(In) to the Tower(Out) from the Tower

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5. Evaporation Loss

Water quantity (m3/hr) evaporated for cooling duty

= theoretically, 1.8 m3 for every 10,000,000 kCal heat rejected

= 0.00085 x 1.8 x circulation rate (m3/hr) x (T1-T2)

T1-T2 = Temp. difference between inlet and outlet water

Ran

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Hot Water Temperature (In)

Cold Water Temperature (Out)

Wet Bulb Temperature (Ambient)

(In) to the Tower(Out) from the Tower

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6. Cycles of concentration (C.O.C.)

Ratio of dissolved solids in circulating water to the dissolved solids in make up water

Depend on cycles of concentration and the evaporation losses

Blow Down = Evaporation Loss / (C.O.C. – 1)

7. Blow Down Losses

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8. Liquid Gas (L/G) Ratio

Ratio between water and air mass flow rates

Heat removed from the water must be equal to the heat absorbed by the surrounding air

L(T1 – T2) = G(h2 – h1)

L/G = (h2 – h1) / (T1 – T2)

T1 = hot water temp (oC)

T2 = cold water temp (oC)

Enthalpy of air water vapor mixture at inlet wet bulb temp (h1) and outlet wet bulb temp (h2)

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Energy Efficiency OpportunitiesEnergy Efficiency Opportunities

1. Selecting a cooling tower

2. Fills

3. Pumps and water distribution

4. Fans and motors

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