2. 2
The well managed use of high quality steam
is a major factor in the efficient production
of high grade dairy products
What is steam used for?
Raw milk is processed into a wide variety of dairy
products which include: pasteurised milk, cheese,
butter and yoghurt.
In the modern dairy, steam is used in a variety of
processes to promote chemical reactions and physical
changes in raw milk and to help maintain clean, sterile
conditions.
The need for high quality steam
Steam is used because it is an efficient carrier of
heat.
It is produced in the boiler and carried to the dairy
processing plant by a pipework distribution system. At
each process steam transfers its heat and condenses
back to condensate.
A very important property of saturated steam is that
its temperature is directly related to its pressure.
Therefore, the temperature of many processes can
be accurately controlled by controlling the pressure of
the steam. Pressure bar g
Steam saturation
curve
0
0 2 4 6 8 10 12 14 16
Temperature°C
200
150
100
50
250
To enable accurate control of temperatures, it is
essential to deliver high quality, dry saturated steam
to the process at the correct pressure. Any entrained
moisture or incondensable gases in the steam can
lower its heat content and impair the heat transfer
rate. This will make accurate control difficult and in
some cases it may not even be possible to achieve
the desired process temperatures.
3. 3
Spirax Sarco
in the dairy industry
For most of the 20th century Spirax Sarco has been the leader
in improving steam plant efficiency, providing knowledge
and high quality products to all branches of industry,
including the dairy industry.
We understand that the dairy industry
has its particular needs and problems and that
each application within the industry should be looked
at individually.
We provide solutions to problems throughout the
complete 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 dairy
processes 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 condensate
system, taking into account the individual requirements of each process, the local environment and the variety
of dairy products manufactured. Consideration should also be given to future expansion plans and plans to
upgrade existing equipment.
Steam
distribution
Steam control
and
management
Condensate
management
Steam
generation
The complete system
4. 4
Spirax Sarco and steam generation
Cold water make-up controls
Boiler feedtanks
Feedtank controls
Deaerator heads
Air vents and vacuum breakers
Feedtank recirculation systems
Boiler blowdown heat recovery systems
Vent heads
Steam injection systems
Boiler blowdown systems
Blowdown vessels
Blowdown inlet manifolds
Level controls and alarm systems
TDS control systems
TDS measurement
Feedpump check valves
Sample coolers
Flash vessels
Residual blowdown heat exchangers
Cooling water systems
Steam main start-up systems
Condensate contamination detection systems
Condensate dump valves
Supplied by Spirax Sarco
steam flash steam condensate
Steam leaving the boiler house should contain as
little moisture and incondensable gases as possible.
This ensures that the maximum amount of heat is
available and minimises the risk of pipeline and
equipment damage from waterhammer.
Spirax Sarco has the expertise to help you produce
high quality steam from your boilers, at the most
economical cost, with a wide range of products
specifically designed for the boiler house, all
manufactured to the highest standards.
Technical and sales literature is available on the
subject of boiler house applications and equipment
upon request.
An essential part of boiler house design and operation
is to ensure that the boiler operates at the highest
possible efficiency. Every effort should be made to
recover and reuse the heat available from secondary
sources such as boiler blowdown.
Your local Spirax Sarco engineer will be able to help
and offer advice on how this can be achieved.
5. 5
Spirax Sarco relay point
Air
vent
Steam
flow
Steam
flow
Condensate out
Steam distribution
Condensate can be removed by means of a separator
as shown in the illustration of a pressure reducing
station, and in the case of long distribution runs, a
relay drain point should be installed. Provision should
also be made for removing air and incondensable
gases from the steam distribution system through
strategically placed thermostatic air vents.
From the boiler house the steam is carried to processes
within the dairy by the distribution system, where it
should be available at the correct pressure, in sufficient
quantity and in the best possible condition.
It is important that the pipework carrying steam from
the boiler house to the equipment is sized correctly.
Cost effective steam distribution depends upon
keeping pipe sizes to a minimum. Steam velocity
should be at a reasonable level and the pressure drop
kept to a minimum. This means designing for the
highest acceptable distribution pressure between the
boiler house and the areas of steam usage, then
dropping pressure at the working area to the levels
required for maximum heat transfer, efficiency and
safety.
Spirax Sarco pressure reducing stations are designed
specifically to match this task and to assist you in
energy management. Spirax Sarco will be happy to
advise on your distribution pipework sizing.
To ensure that radiation losses are kept to a minimum
the steam distribution system should be insulated.
Even when insulated some radiation losses will occur,
with some steam condensing and forming condensate
in the pipework.
It is important that this condensate is removed so that
the steam arriving at the process equipment is as dry
as possible. The removal of condensate from the
distribution pipework is also necessary to prevent
damage from waterhammer. This occurs when slugs
of condensate are propelled along the pipeline at
steam velocity.
Steam from
boiler
Air vent
Steam trap set
Pressure reducing valve station
Steam header
Separator
Spirax Sarco pressure reducing valve station
High pressure steam
Reduced
pressure
steam
Steam trap set
The cause of waterhammer
If it is not removed, a slug of condensate can develop and be
carried along the pipe at steam velocity.
Condensate forms due to radiation losses from the pipe
6. 6
Spirax Sarco and
Hot water
circulation
Vacuum breaker
Steam trap set
Pasteuriser
Condensate
Steam
Spirax Sarco pasteuriser control equipment
Pneumatic actuated
valve with positioner
Unpasteurised mi
Pasteurised milk
Pneumatic
valve with p
Raw milk
Chiller Holding tank
Pre-heating
Pasteurisation
Pasteurisation / homogenisation
Pasteurisation / homogenisation
Separator Past
7. 7
the dairy industry
lk
Cooling water in
Cooling water out
actuated
positioner
Spirax Sarco direct UHT controls
Steam trap set
Pressure reducing valve set
Steam
UHT ring nozzle injector
Condensate
Condensate
Spirax Sarco
hygienic
steam trap
Milk to
homogeniser
Clean steam filter
Pre-heated milk
teurisation / homogenisation
Cream pasteurisation Butter maker
Evaporator
Spray dryer
Incubator tankBulk starter tank
Processing and ripening
Cheese vat
Steam injector Expansion vessel Homogeniser
Yoghurt
UHT milk
Cheese
Milk powder
Condensed
milk
Butter
Pasteurised
milk
Cream
Skimmed
milk
8. 8
Where is steam used
Air
vent
Steam flow
Flow computer
Steam flow
Spirax Sarco steam metering station
Condensate out
Steam pressure control
Various outputs
Alarms
Timers
R232C Interface
Spiraflo
meter
Steam trap set
Wafer check
valve
Separator
Steam flow measurement
In a dairy, saturated steam is normally generated at
between 11 bar and 17 bar. It should be distributed at
the highest possible pressure to keep the distribution
pipework as small as possible, and then reduced in
pressure to meet individual process requirements.
Different types of steam pressure reducing valves are
available, 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 of
the process. Spirax Sarco supplies many different
types of steam pressure control systems and can
advise on the best choice for a particular application.
Measuring steam flow can provide vital information for
the accurate costing and monitoring of production
processes.
Spirax Sarco Spiraflo meters are specifically designed
for use on steam systems to give consistent, accurate
information about the flowrate, pressure and
temperature of steam.
Spirax Sarco can also provide other types of flowmeter
suitable for many fluids and gases.
Steam is used in the dairy for indirect heating, direct
heating and sterilization processes. It is essential that
in all of these applications high quality steam is
available 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 at
higher temperatures.
Air heater batteries which provide hot air for spray
drying and can drying.
Multi-effect evaporators used to produce
condensed milk.
Aseptic storage to provide a sterile barrier on
product change over in pipework and tanks.
Dairy effluent holding tanks (waste fat) are kept
warm to prevent solidification prior to disposal.
9. 9
Plate heat exchangers
Pneumatic actuated
valve with positioner
Vacuum
breaker
Air vent
Controller
Sensor
Steam trap setSteam trap set
Steam trap set
Flash steam
recovery vessel
Condensate
Flash steam
to preheater
Preheater Heater
Spirax Sarco air heater control system with flash steam preheater
Steam flow
Heated air to
spray dryer
Plate heat exchangers are used throughout the dairy
in a variety of heating and cooling applications.
For heating applications steam is frequently used as
the primary medium. It is easily controlled and its
excellent heat carrying properties allow pipe and
exchanger sizes to be kept to a minimum.
A temperature control valve constantly adjusts the
primary steam flowrate and pressure to compensate
for fluctuations in the secondary fluid's inlet flowrate
and temperature. This will ensure the product flow
from the exchanger is always at the correct
temperature.
When steam gives up its heat it condenses and this
condensate must be drained immediately to allow
steam to continue to enter the exchanger and carry
on the process. If condensate is allowed to remain in
the exchanger, poor temperature control will result
and there will be an increased possibility of damage
from waterhammer.
If the correct type of steam trap is selected, and
provided the pressure in the steam space of an
exchanger is higher than the pressure in the
condensate return system, condensate will drain from
the exchanger as soon as it has formed.
However, pressure inside the steam space of a plate
heat exchanger is never constant, and may fall into a
vacuum condition under light loads.
When the pressure within the condensate return system
is greater than the pressure within the exchanger steam
space, the exchanger is described as being in a 'stall'
condition. In this condition condensate will not be able to
drain from the exchanger.
10. 10
Temperature control
Steam
Water
Level control system
Condensate
Steam trap set
Self-acting
temperature
control
Pressure reducing
valve station
Spirax Sarco hot water tank controls
Spirax Sarco plate heat exchanger temperature control and condensate drainage
Pneumatic valve and
actuator with positioner
Plate heat exchanger
Pressure
powered
pump
Steam supply
to pump
Condensate
Steam flow
Secondary
flow out
Secondary
flow in
Controller
Steam
trap
A simple and effective solution to this common problem
is to install a combination pump/steam trap unit. This
will ensure that condensate is drained from the heat
exchanger under both normal and 'stall' operating
conditions.
Condensate
Spirax Sarco can advise on whether a 'stall' condition
may occur on a heat exchange application and how to
ensure its adverse effects are avoided.
Many of the steam using processes in the dairy will
require a temperature control system to ensure that
the product is heated up to and maintained at the
correct temperature.
Spirax Sarco provide many different types of
temperature control system and will be able to
recommend the most suitable for each of the many
different processes.
A simple, robust self-acting control system will often
be the most suitable for a hot water tank, while a more
sophisticated electro / pneumatic system will be
required for pasteurisation or a UHT process.
11. 11
Clean steam
Condensate management
Condensate return
The final stage in condensate management is to return
as much condensate to the boiler house as possible.
Even after flash steam has been recovered, the low
pressure condensate still contains sensible heat - over
400 kJ/kg at atmospheric pressure; and will require no
further boiler feed treatment before it re-enters the
boiler.
Methods of returning condensate can include simple
gravity return systems, electric pumping systems or
systems incorporating the versatile pressure powered
pump.
Spirax Sarco will be pleased to advise on the
most cost effective means of achieving a
highly efficient condensate return system.
Low pressure flash steam
Steam trap set
Condensate from
high pressure
steam
Spirax Sarco flash steam recovery set
Condensate out
Flash vessel
Vent
Condensate in
Spirax Sarco pressure powered pump
condensate return unit.
Condensate out
Overflow
Pressure
powered
pump
Clean steam is widely used in the dairy industry to
reduce the risk of product or process contamination,
not only during UHT sterilisation but also during the
CIP and SIP processes.
Spirax Sarco provide a wide range of stainless steel
products designed for use on clean steam systems,
including the filters necessary to provide culinary grade
steam from process steam.
The stainless steel construction of Spirax Sarco clean
steam products ensures the risk of contamination is
reduced and that sanitary conditions are maintained.
Heat recovery
Approximately 31 % of the heat used to generate
saturated steam at 17 bar remains in the condensate
when the steam condenses. In effective condensate
management, consideration should be given to
recovering and using as much of this heat as possible.
Flash steam recovery
Flash steam is released from condensate when its
pressure falls. Typically this happens when it passes
from the process, through a steam trap, to a low
pressure condensate system. Low pressure
condensate has a smaller sensible heat content than
high pressure condensate and this sudden excess
heat content will cause some of the condensate to
'flash off' into steam at the lower pressure.
The recovery of this flash steam using flash vessels
can be used to supplement the steam supply to
applications that require low pressure steam.
