The dairy industrysteam and condensate systems

2

The well managed use of high quality steamis a major factor in the efficient productionof high grade dairy products

What is steam used for?Raw milk is processed into a wide variety of dairyproducts which include: pasteurised milk, cheese,butter and yoghurt.

In the modern dairy, steam is used in a variety ofprocesses to promote chemical reactions and physicalchanges in raw milk and to help maintain clean, sterileconditions.

The need for high quality steamSteam is used because it is an efficient carrier ofheat.

It is produced in the boiler and carried to the dairyprocessing plant by a pipework distribution system. Ateach process steam transfers its heat and condensesback to condensate.

A very important property of saturated steam is thatits temperature is directly related to its pressure.Therefore, the temperature of many processes canbe accurately controlled by controlling the pressure ofthe steam. Pressure bar g

Steam saturationcurve

00 2 4 6 8 10 12 14 16

Tem

pera

ture

°C

200

150

100

50

250

To enable accurate control of temperatures, it isessential to deliver high quality, dry saturated steamto the process at the correct pressure. Any entrainedmoisture or incondensable gases in the steam canlower its heat content and impair the heat transferrate. This will make accurate control difficult and insome cases it may not even be possible to achievethe desired process temperatures.

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Spirax Sarcoin the dairy industry

For most of the 20th century Spirax Sarco has been the leaderin improving steam plant efficiency, providing knowledge

and high quality products to all branches of industry,including the dairy industry.

We understand that the dairy industryhas its particular needs and problems and that

each application within the industry should be lookedat individually.

We provide solutions to problems throughout thecomplete steam and condensate system in the dairy industry,

anywhere in the world.

To produce high grade dairy products whilst maintaining low production costs, it is essential that dairyprocesses are operated as efficiently as possible, making effective use of the heat available in the steam.

To achieve this, it is necessary to consider the design and operation of the complete steam and condensatesystem, taking into account the individual requirements of each process, the local environment and the varietyof dairy products manufactured. Consideration should also be given to future expansion plans and plans toupgrade existing equipment.

Steamdistribution

Steam controland

management

Condensatemanagement

Steamgeneration

The complete system

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Spirax Sarco and steam generation

Cold water make-up controlsBoiler feedtanksFeedtank controlsDeaerator headsAir vents and vacuum breakersFeedtank recirculation systemsBoiler blowdown heat recovery systemsVent headsSteam injection systemsBoiler blowdown systemsBlowdown vesselsBlowdown inlet manifoldsLevel controls and alarm systemsTDS control systemsTDS measurementFeedpump check valvesSample coolersFlash vesselsResidual blowdown heat exchangersCooling water systemsSteam main start-up systemsCondensate contamination detection systemsCondensate dump valves

Supplied by Spirax Sarco

steam flash steam condensate

Steam leaving the boiler house should contain aslittle moisture and incondensable gases as possible.This ensures that the maximum amount of heat isavailable and minimises the risk of pipeline andequipment damage from waterhammer.

Spirax Sarco has the expertise to help you producehigh quality steam from your boilers, at the mosteconomical cost, with a wide range of productsspecifically designed for the boiler house, allmanufactured to the highest standards.

Technical and sales literature is available on thesubject of boiler house applications and equipmentupon request.

An essential part of boiler house design and operationis to ensure that the boiler operates at the highestpossible efficiency. Every effort should be made torecover and reuse the heat available from secondarysources such as boiler blowdown.

Your local Spirax Sarco engineer will be able to helpand offer advice on how this can be achieved.

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Spirax Sarco relay point

Airvent

Steamflow

Steamflow

Condensate out

Steam distribution

Condensate can be removed by means of a separatoras shown in the illustration of a pressure reducingstation, and in the case of long distribution runs, arelay drain point should be installed. Provision shouldalso be made for removing air and incondensablegases from the steam distribution system throughstrategically placed thermostatic air vents.

From the boiler house the steam is carried to processeswithin the dairy by the distribution system, where itshould be available at the correct pressure, in sufficientquantity and in the best possible condition.

It is important that the pipework carrying steam fromthe boiler house to the equipment is sized correctly.Cost effective steam distribution depends uponkeeping pipe sizes to a minimum. Steam velocityshould be at a reasonable level and the pressure dropkept to a minimum. This means designing for thehighest acceptable distribution pressure between theboiler house and the areas of steam usage, thendropping pressure at the working area to the levelsrequired for maximum heat transfer, efficiency andsafety.

Spirax Sarco pressure reducing stations are designedspecifically to match this task and to assist you inenergy management. Spirax Sarco will be happy toadvise on your distribution pipework sizing.

To ensure that radiation losses are kept to a minimumthe steam distribution system should be insulated.Even when insulated some radiation losses will occur,with some steam condensing and forming condensatein the pipework.

It is important that this condensate is removed so thatthe steam arriving at the process equipment is as dryas possible. The removal of condensate from thedistribution pipework is also necessary to preventdamage from waterhammer. This occurs when slugsof condensate are propelled along the pipeline atsteam velocity.

Steam fromboiler

Air vent

Steam trap set

Pressure reducing valve station

Steam header

Separator

Spirax Sarco pressure reducing valve station

High pressure steam

Reducedpressuresteam

Steam trap set

The cause of waterhammer

If it is not removed, a slug of condensate can develop and becarried along the pipe at steam velocity.

Condensate forms due to radiation losses from the pipe

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Spirax Sarco and

Hot watercirculationVacuum breaker

Steam trap set

Pasteuriser

Condensate

Steam

Spirax Sarco pasteuriser control equipment

Pneumatic actuatedvalve with positioner

Unpasteurised mi

Pasteurised milk

Pneumaticvalve with p

Raw milk

Chiller Holding tank

Pre-heating

Pasteurisation

Pasteurisation / homogenisation

Pasteurisation / homogenisation

Separator Past

7

the dairy industry

lk

Cooling water in

Cooling water out

actuatedpositioner

Spirax Sarco direct UHT controls

Steam trap set

Pressure reducing valve set

Steam

UHT ring nozzle injector

Condensate

Condensate

Spirax Sarcohygienic

steam trap

Milk tohomogeniser

Clean steam filter

Pre-heated milk

teurisation / homogenisation

Cream pasteurisation Butter maker

EvaporatorSpray dryer

Incubator tankBulk starter tank

Processing and ripening

Cheese vat

Steam injector Expansion vessel Homogeniser

Yoghurt

UHT milk

Cheese

Milk powder

Condensedmilk

Butter

Pasteurisedmilk

Cream

Skimmedmilk

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Where is steam used

Airvent

Steam flow

Flow computer

Steam flow

Spirax Sarco steam metering station

Condensate out

Steam pressure control

Various outputsAlarms

TimersR232C Interface

Spiraflometer

Steam trap set

Wafer checkvalve

Separator

Steam flow measurement

In a dairy, saturated steam is normally generated atbetween 11 bar and 17 bar. It should be distributed atthe highest possible pressure to keep the distributionpipework as small as possible, and then reduced inpressure to meet individual process requirements.

Different types of steam pressure reducing valves areavailable, from simple direct acting valves to the more

flexible pneumatic actuator, valve and electro /pneumatic positioner combinations.

The type of system required depends on the needs ofthe process. Spirax Sarco supplies many differenttypes of steam pressure control systems and canadvise on the best choice for a particular application.

Measuring steam flow can provide vital information forthe accurate costing and monitoring of productionprocesses.Spirax Sarco Spiraflo meters are specifically designedfor use on steam systems to give consistent, accurate

information about the flowrate, pressure andtemperature of steam.

Spirax Sarco can also provide other types of flowmetersuitable for many fluids and gases.

Steam is used in the dairy for indirect heating, directheating and sterilization processes. It is essential thatin all of these applications high quality steam isavailable at the correct temperature and pressure.These applications will include:

Hot water heaters.

Indirect plate heat exchangers.Clean in place (CIP) units.Sterilize in place (SIP) systems.Steam jacketed vessels for processing butter oil.

Direct UHT sterilisers used to pasteurise milk athigher temperatures.

Air heater batteries which provide hot air for spray

drying and can drying.

Multi-effect evaporators used to producecondensed milk.Aseptic storage to provide a sterile barrier onproduct change over in pipework and tanks.Dairy effluent holding tanks (waste fat) are keptwarm to prevent solidification prior to disposal.

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Plate heat exchangers

Pneumatic actuatedvalve with positioner

Vacuumbreaker

Air vent

Controller

Sensor

Steam trap setSteam trap set

Steam trap set

Flash steamrecovery vessel

Condensate

Flash steamto preheater

Preheater Heater

Spirax Sarco air heater control system with flash steam preheater

Steam flow

Heated air tospray dryer

Plate heat exchangers are used throughout the dairyin a variety of heating and cooling applications.

For heating applications steam is frequently used asthe primary medium. It is easily controlled and itsexcellent heat carrying properties allow pipe andexchanger sizes to be kept to a minimum.

A temperature control valve constantly adjusts theprimary steam flowrate and pressure to compensatefor fluctuations in the secondary fluid's inlet flowrateand temperature. This will ensure the product flowfrom the exchanger is always at the correcttemperature.

When steam gives up its heat it condenses and thiscondensate must be drained immediately to allowsteam to continue to enter the exchanger and carryon the process. If condensate is allowed to remain in

the exchanger, poor temperature control will resultand there will be an increased possibility of damagefrom waterhammer.

If the correct type of steam trap is selected, andprovided the pressure in the steam space of anexchanger is higher than the pressure in thecondensate return system, condensate will drain fromthe exchanger as soon as it has formed.

However, pressure inside the steam space of a plateheat exchanger is never constant, and may fall into avacuum condition under light loads.

When the pressure within the condensate return systemis greater than the pressure within the exchanger steamspace, the exchanger is described as being in a 'stall'condition. In this condition condensate will not be able todrain from the exchanger.

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Temperature control

Steam

Water

Level control system

Condensate

Steam trap set

Self-actingtemperature

control

Pressure reducingvalve station

Spirax Sarco hot water tank controls

Spirax Sarco plate heat exchanger temperature control and condensate drainage

Pneumatic valve andactuator with positioner

Plate heat exchanger

Pressurepoweredpump

Steam supplyto pump

Condensate

Steam flow

Secondaryflow out

Secondaryflow in

Controller

Steamtrap

A simple and effective solution to this common problemis to install a combination pump/steam trap unit. Thiswill ensure that condensate is drained from the heatexchanger under both normal and 'stall' operatingconditions.

Condensate

Spirax Sarco can advise on whether a 'stall' conditionmay occur on a heat exchange application and how toensure its adverse effects are avoided.

Many of the steam using processes in the dairy willrequire a temperature control system to ensure thatthe product is heated up to and maintained at thecorrect temperature.

Spirax Sarco provide many different types oftemperature control system and will be able to

recommend the most suitable for each of the manydifferent processes.

A simple, robust self-acting control system will oftenbe the most suitable for a hot water tank, while a moresophisticated electro / pneumatic system will berequired for pasteurisation or a UHT process.

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Clean steam

Condensate managementCondensate return

The final stage in condensate management is to returnas much condensate to the boiler house as possible.

Even after flash steam has been recovered, the lowpressure condensate still contains sensible heat - over400 kJ /kg at atmospheric pressure; and will require nofurther boiler feed treatment before it re-enters theboiler.

Methods of returning condensate can include simplegravity return systems, electric pumping systems orsystems incorporating the versatile pressure poweredpump.

Spirax Sarco will be pleased to advise on themost cost effective means of achieving ahighly efficient condensate return system.

Low pressure flash steam

Steam trap set

Condensate fromhigh pressuresteam

Spirax Sarco flash steam recovery set

Condensate out

Flash vessel

Vent

Condensate in

Spirax Sarco pressure powered pumpcondensate return unit.

Condensate out

Overflow

Pressurepoweredpump

Clean steam is widely used in the dairy industry toreduce the risk of product or process contamination,not only during UHT sterilisation but also during theCIP and SIP processes.

Spirax Sarco provide a wide range of stainless steelproducts designed for use on clean steam systems,

including the filters necessary to provide culinary gradesteam from process steam.

The stainless steel construction of Spirax Sarco cleansteam products ensures the risk of contamination isreduced and that sanitary conditions are maintained.

Heat recoveryApproximately 31 % of the heat used to generatesaturated steam at 17 bar remains in the condensatewhen the steam condenses. In effective condensatemanagement, consideration should be given torecovering and using as much of this heat as possible.

Flash steam recoveryFlash steam is released from condensate when itspressure falls. Typically this happens when it passesfrom the process, through a steam trap, to a lowpressure condensate system. Low pressurecondensate has a smaller sensible heat content thanhigh pressure condensate and this sudden excessheat content will cause some of the condensate to'flash off' into steam at the lower pressure.

The recovery of this flash steam using flash vesselscan be used to supplement the steam supply toapplications that require low pressure steam.

CM Issue 2SB-GCM-10

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Spirax-Sarco Limited, Charlton House,Cheltenham, Gloucestershire, GL53 8ER UK.

Tel: +44 (0)1242 521361 Fax: +44 (0)1242 573342E-mail: Enquiries@SpiraxSarco.com

Internet: www.SpiraxSarco.com© Copyright 2000 Spirax Sarco is a registered trademark of Spirax-Sarco Limited

Spirax Sarco provides knowledge,service and products worldwide for the

control and efficient use of steam and otherindustrial fluids in the dairy industry.

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