The oxygen gets out of puff
Deaeration systems and carbonating
plant
Deaeration and carbonation are essential elements in
beverage production. Oxygen dissolved in beverages affects the taste and
shortens the shelf life. To reduce the oxygen content to an acceptable level,
the ingredients or the finished product are deaerated. The carbonation of
drinks serves to enhance their taste and to increase their shelf life.
In the following article, various deaeration systems and
carbonation processes are described.
The simplest way of deaerating liquids is to store them in
tanks for a certain length of time. During this dwell time, air trapped in the
liquid can rise to the surface and escape. This procedure is used principally
with preliminary and intermediate products, e.g. sugar solution or syrup base.
The method can reduce oxygen content to an acceptable level, i.e. values of
around 3 mg O2 per litre. If deaerated water is then also used, the
finished beverage will show good values.
Air that has been introduced into the liquid during the
process of conveying it is removed in pre-run vessels or air separators. This
is air that has got into the pipes during the switch-over from one tank to
another, or when vessels or drums are emptied by suction. The pre-run vessels
are as a rule installed upstream of the transfer pumps. If there were no
pre-run vessels, the pumps would distribute the air finely throughout the
product.
To extract finely distributed air or dissolved oxygen from
liquids, it is necessary to use deaeration equipment. This may operate on one
of a variety of principles:
- hot deaeration with a partial vacuum,
- hot deaeration or cold deaeration through carbonation,
- cold deaeration under a vacuum,
- cold deaeration via filter modules.
Which of the different types of apparatus is used depends
on the product and the residual oxygen values required, as described below.
Hot deaeration of fruit
juices
For fruit juices, the hot deaeration method is used, the
pressure in the deaeration vessel being kept slightly below atmospheric
pressure. It is the finished beverage that is deaerated. Deaeration takes place
in a vessel containing a partial vacuum, into which the product is sprayed
after having been heated to around 50° C. These systems are equipped with
cooling coils in the suction pipe to recoup flavour, since flavourings
evaporate during the treatment. The condensate runs back into the vessel.
These are elaborate systems, since when the equipment is
started up the product first has to be heated in the circuit. The need to
recoup flavour is an additional complication. There is a high level of product
loss at the start-up and running down of the plant. However, the equipment is
easy to integrate into pasteurisation equipment.
Hot deaeration of water with CO2
input
By contrast to the fruit juice equipment described above,
hot deaeration systems for water work without a vacuum. They generally consist
of two columns which the water runs through one after the other.
The water is heated to approx. 75° C and introduced into
the columns. By means of a regeneration stage in the heat exchanger, heat is
regained on cooling. In a further stage, the water is cooled to the desired
temperature.
The water is sprayed into the deaeration columns in a fine
spray, and slowly trickles down over the column packing. CO2 flows in the
opposite direction, from bottom to top, causing the oxygen to be released. In
addition, between the first and second deaeration stages CO2 is injected
through a nozzle, bringing about the intimate mixing of water and CO2 and
further enhancing the deaeration effect. The water level in the deaeration
columns is always kept constant. The heating of the water also serves to
eliminate germs.
The proper functioning of the equipment is monitored by
flow, level and oxygen sensors. Such plant can also be operated as cold
deaeration equipment with higher residual o xygen values. This eliminates the
heat exchanger, which uses a lot of energy.
The introduction of CO2 leads to a slight carbonation of
the water. The plant can therefore not be used in the production of still
beverages. Such a hot deaeration plant achieves residual oxygen values of <
0.02 mg O2 per litre, and is therefore particularly suitable for use in the
brewing industry.
Vacuum deaeration
Vacuum deaeration involves dosing with CO2 in one or two
stages. The two-stage plant consists of two horizontal vessels arranged one
above the other, a vacuum pump, a circulating pump and an extractor pump. The
vessels are fitted with spray nozzles. When they are in operation, the vessels
are evacuated by the vacuum pump. The absolute pressure in the vessels amounts
to around 0.05 bars.
The water to be deaerated enters the lower deaeration tank
via the water inlet valve, being finely sprayed by special nozzles. In the
deaeration plant the vacuum causes a large proportion of the dissolved oxygen
to be released and sucked out.
After this first stage of deaeration a circulating pump
transfers the water to the upper deaeration tank, where it is once again finely
sprayed. On the way to the upper tank the water is dosed with a particular
quantity of CO2, depending on the value set. The partial pressure reduction
leads to the release of more of the oxygen that is still dissolved in the
water.
The deaerated water is then conveyed out of the upper
deaeration tank by the extractor pump. The gas mixture released in the upper
deaeration tank (consisting largely of CO2 with only a little oxygen) flows
through an aperture in the pipe into the lower deaeration vessel, where it is
directed in contraflow to the water that is sprayed in and sucked off by the
vacuum pump. This contraflow in the lower deaeration vessel also enhances the
effectiveness of the first stage of deaeration. The amount of CO2 required for
deaeration depends on the desired residual oxygen content of the water and the
water temperature.
With the GEA Diessel DIOX 2 water deaeration plant a residual
oxygen value of less than 0.05 mg O2 per litre can be achieved at a water
temperature of 12° C. This requires a CO2 input of only 0.5 g per litre of
water. If the water temperature is higher, correspondingly less CO2 is
required.
The inflow of water is controlled by means of the level in
the lower vessel. Any excess water that is not extracted by the extractor pump
flows back from the upper deaeration tank into the lower deaeration tank
through the aperture in the pipe, and is thus recirculated by the circulating
pump.
This arrangement has the advantage that if there are short
breaks in production when no deaerated water is required, the entire volume of
water is kept circulating between the upper and lower vessel. The plant
therefore does not need to be switched off, and supplies perfectly deaerated
water again immediately after each break.
As an alternative to the traditional vacuum pumps, dry
running vacuum pumps can also be used. This cuts operating costs; but the
acquisition costs are higher.
Filtration of water
The filter modules consist of a large number of hollow
microporous polypropylene fibres. The water flows around the exterior of the
fibres. The pores in the fibres let only gas permeate; water does not pass
through them. The gas is sucked out of the pores by a vacuum pump. The
additional loading of the fibres with CO2 or nitrogen enhances the oxygen
extraction.
The use of these filter modules enables low residual oxygen
values of less than 0.01 mg O2 per litre to be achieved. The value attainable
depends on the number of filters and the throughput. The filter modules are
suitable for a maximum throughput of 40,000 litres per hour.
Carbonation of beverages
The last stage in the production of beverages is
carbonation, when CO2 is added to the finished beverage. The heart of the plant
is the “saturator”, by which the gas is finely distributed throughout the
liquid. In order to enable the gas to be dissolved, either a long pipe to act
as a settling length or a pressure tank is installed downstream of the
saturator, this being the feature distinguishing two kinds of plant.
Carbonation plant with pressure tank
The essential component of the plant, in addition to the
mixing tank, is the saturator, which works on the venturi principle. After the
completion of blending the drink is introduced into the saturator by a pressure
booster pump. The flow speed through the saturator is kept constant in the
optimum working range by a regulator. The partial vacuum created in the
saturator provides the desired suction effect for the CO2. The increase in the
flow speed for a short time also guarantees the fine distribution of the
gaseous CO2, and thus homogeneous blending in the product. CO2 is introduced
into the saturator from the pressure tank, the constant pressure of which
guarantees the even carbonation of the beverage. This procedure also ensures
that there is no loss of CO2 on introduction.
The carbonation of the beverage essentially depends
on the pressure of the vessel, which is set at a value determined as a function
of the CO2 value required for the particular beverage; the pressure is only
slightly higher than the saturation pressure of the product. Plant of this kind
can be constructed for different rates of flow, and adapted to the installed
filling capacity. GEA Diessel builds such plant with throughputs of between
10,000 and 70,000 litres per hour.
The carbonation plant incorporates an analysis unit to
check the essential product data - CO2 content, conductivity for the acid
content and Brix value - as the last continuous check before filling. This data
is recorded and monitored to ensure that it lies within the predetermined
limits.
The pressure tank, in combination with an upstream mixing
plant, also serves as a buffer vessel in order to compensate for possible “stop
and go” operation of the filling unit.
The heart of the carbonation plant is
the “saturator”, by which the gas is finely distributed throughout the liquid.
In order to enable the gas to be dissolved, either a pipe to act as a settling
length or a pressure tank is installed downstream of the saturator.
Carbonation plant with saturation
length
Plant with a saturation length is mainly used to add carbon
dioxide to beer. CO2 is introduced into the product through the saturator and
extremely finely distributed, so that it can then be dissolved in the
saturation length immediately downstream. The CO2 throughput is controlled by a
regulating valve. The CO2 content at any time is determined by the CO2 metering
device at the end of the saturation length. If it deviates from the desired
value the control unit can influence the regulating valve accordingly.
GEA Diessel builds such plant with throughputs of between
100 and 700 hl per hour. The plant can be supplemented by analysis equipment
for original gravity or alcohol content, allowing the product to be monitored.
Summary
The modern deaeration and carbonation systems that are
available today provide everything that the beverage industry requires in
respect of the values and levels of accuracy required for the various products.
GEA Diessel has many years of experience with the systems described, and will
advise users on the planning of new production facilities or the modernisation
of existing equipment. The right equipment will be selected in dialogue between
the operator and the equipment manufacturer.
The Author:
Gerhard Bohne, born 1950,
initially trained as an electrician; further training for the qualification
“state-examined electrical technician”; has worked for GEA Diessel (formerly
Diessel) since 1977; group leader in the Design Department and project manager;
since 2000 responsible for preparing quotations in the Sales Department.