sugar & sweeteners
TRANSCRIPT
Sugar & Sweeteners
for Beet, Cane &
Special Sugars
Drying & Cooling Plant
P R O C E S S E N G I N E E R I N G
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Few manufacturers offer a greater choice
of dryers and coolers for the sugar and
sweetener industry than Barr-Rosin,
with a range that includes:
• Rotary dryers
• Rotary dryer/coolers
• Rotary coolers
• Dryer/ conditioners
• Fluidised bed dryer/coolers (static)
• Fluidised bed dryer/coolers (vibro)
• Fluidised bed coolers
These are supplied for processing beet,
cane and special sugars, such as:
• dextrose (monohydrate & anhydrous)
• maltitol
• fructose
• other polyols
• coated sugars
• confectionary products
In a world of changingmarkets and new
products, being able to rely on a process
equipment supplier witha broad experience and wide choice of
technologies is essential.Welcome to Barr-Rosin.
Counter-Current Rotary Dryer (evaporative cooler)
This makes full use of the heat from the
incoming sugar for drying, while also
cooling the product. The system generally
requires the lowest airflow and needs
very little additional heat input. When
a very low final sugar temperature is
required (ie.below 25-35ºC), this system
also significantly reduces the duty of the
following ‘secondary’ cooler.
Combined Dryer/Cooler (two zone, central tube type)
This maintains the counter-current
principle throughout both the drying and
cooling zones. It also uses the heat from
the sugar for drying, as well as pre-
heated air from the cooling zone. The
latter is mixed with a small amount of
supplementary drying air, introduced
via a central tube. The system is typically
more suited to high ambient temperature
and humidity conditions (as in cane
sugar regions), where increased quantities
of cooling air may be necessary.
Dryers can be designed for either co-
current or counter-current configuration,
according to the type of sugar processed.
They can also be supplied as combined
units with drying and cooling zones.
The dryer internals are fitted with special
‘sawtooth’ lifting flights, louvres and/or
cross-shelf (cruciform) baffles, as required.
For some applications, surfaces in
contact with the product are ground
and polished.
Combined Dryer/Cooler (central exhaust type)
This combines co-current drying and
counter-current cooling, where the
converging airflows are exhausted from
the centre of the dryer/cooler. Although
the design may permit higher drying
temperatures, which can reduce drum
diameter, the total air flow and drum
length is generally increased. It may be
used for beet and cane as well as certain
‘special’ sugar applications.
Solutions for all
A choice of technologiesFor animal feeds, such as beet pulp,
corn /wheat fibre and DDG, direct fired
Rotary, Ring (flash) and closed circuit
pressurised ‘Steam’ dryers are also
supplied – all specifically designed to
suit the varying product characteristics
and local climatic conditions.
The Rotary Dryer Workhorse of the Industry
Long established as the traditional method
of drying sugar, the rotary dryer is today,
still widely recognised as the most effective
and reliable system available. The simple,
robust design requires less energy, yet
offers greater flexibility than other dryer
types. Because it is less prone to sticking /
caking and more readily accomodates
‘upset’ or variable feed conditions, it is
suitable for a wide range of sugars. An
additional feature is the low headroom
requirement, which often benefits
installation in existing sugar factories.
P R O C E S S E N G I N E E R I N G
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Beet and Cane Sugar Applications
Counter Current
P R O C E S S E N G I N E E R I N G
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These dryers are often used in
conjunction with fluidised bed coolers
(sometimes fitted with ‘in-bed’cooling
tubes) and are supplied with a range of
ancillaries, such as agitated feed vessels,
multi-stage and absolute filters, trommel
screens, cyclones, wet scrubbers and
bag filters.
Special attention is given to the design
and surface finish of product contact
areas, to minimise sticking/caking and
micro-biological contamination.
Rotary CoolerA simple counter-current design can
provide separate cooling or secondary
cooling. This low energy system is
sometimes an appropriate alternative
to a fluidised bed cooler.
Co-Current Rotary DryerThis design is generally more suited
to sugars and sweeteners such as starch
derivatives, coated and confectionary
sugars, which are typically fine and /
or sticky.
Such products often contain higher
moistures – yet are more heat sensitive
and generally supplied at feed
temperatures close to ambient. The
longer co-current design affords the
extended residence times needed for
diffusuion drying / conditioning and
permits the use of higher drying
temperatures, without causing heat
damage or discoloration.
Due to the hygroscopic nature of most
special sugars, air conditioning
equipment is usually required, to reduce
both the temperature and humidity of
the ambient (fluidising) air before it
enters the cooler. However, for certain
applications, the unit can also be
supplied with ‘in-bed’ tube bundles
(heat exchangers) providing additional
but indirect, contact cooling.
By using chilled water through the tubes,
the air volume and cooler size is
significantly reduced, which is
particularly beneficial when the ambient
temperature and humidity is high.
Fluidised Bed Dryer/CoolersFor special applications, such as those
designed for confectionary sugars and
smaller plant capacities, fluidised bed
combined dryer/coolers can be
provided. However, to overcome the
cohesive nature of the sugar at the feed
point, static type fluid bed dryers are
often fitted with a de-aglomerator or
stirring device. Alternatively, a vibrating
bed dryer can be supplied to maintain
the product in a ‘live’ state during the
initial drying phase. These units are
more suitable if there is a wide particle
size distribution, or if integral final
product screening is required.
Fluidised Bed CoolersThis is an efficient, well proven system,
whereby the sugar layer (or bed) is
suspended on a ‘cushion’ of air passing
up through the cooler, via a special
perforated distributor plate. Bubbles
continuously form and collapse within
the bed of material, creating a fluidising
effect that promotes intimate contact and
rapid heat transfer between the cooling
air and sugar. Whereas a fluid bed
system for drying sugar can be prone to
‘blinding and caking’, the vigorous but
gentle handling and cooling of dry sugar
in a fluidised state can actually enhance
the quality of the final product.
Through careful design of the fluid bed
housing and with allowance for
adjustment of the cooling air flow, the
‘fines’ can be removed from the surface
of the product (if required), to produce
a clean, bright crystal.
For most sugar and sweetener
applications these units are of the static
type, since the sugar is free-flowing in
the dry state.
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Co-current
Developing markets
More optionsSpecial Sugar Applications Fluid Bed Systems
page 7
P R O C E S S E N G I N E E R I N G
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consumption, fire risk and final off-gas
volume. Alternatively, in a CHP system,
the dryer may operate on an open-circuit
basis, using turbine exhaust-gas (TEG),
also having the effect of depleting
oxygen to safer levels.
Since the bleed-off volume to
atmosphere is relatively low when
recycling dryer exhaust gases, the duty
of any odour treatment, whether by
scrubber/condenser or Regenerative
Thermal Oxidiser (RTO), is greatly
reduced. This minimises both the
installation and operating costs.
Feed DryersEngineered for Efficiency utilising:-
• Exhaust Gas Recycle
• Turbine Exhaust Gas
• Waste Heat Recovery
• Regenerative Thermal Oxidisers
• Steam drying
Rotary, Ring (or Flash) and closed circuit,
pressurised Steam dryers can be
supplied for a range of animal feeds,
including beet pulp, corn/wheat fibre
and Distillers Dark Grains (DDG).
Direct Fired Rotary DryersThese dryers are of the co-current,
cascade/‘cruciform’ (or cross-shelf) type,
designed for oil/ gas firing and
generally utilise exhaust gas-recycle.
By recycling and reheating a proportion
of the dryer exhaust, this self-inertising
system also reduces energy
Steam DryingHaving originally pioneered the ring
dryer, Barr-Rosin has since developed a
closed circuit system, which combines
the main features of the ring dryer, but
entirely replaces the heated air with
recirculated steam, generated by the
evaporation of water. Steam drying, at
pressures of up to 3 bar g can offer
significant advantages when compared
with direct fired systems, in particular:
• there is no exhaust (or odour)
to atmosphere
• steam is available for other purposes
• there is no potential for fire/explosion
• energy consumption is greatly reduced
• product quality is improved.
Ring DryersThe ring dryer employs the same basic
principle as the flash dryer, but
incorporates a centrifugal classifier. This
allows selective internal recirculation of
semi-dried solids, effectively increasing
the retention-time of larger particles in
the dryer, while finer material (which
dries more rapidly), exits with the
exhaust air. Widely used for animal
feeds, in particular DDGS, these dryers
produce a high quality product.
Again, they are direct fired and utilise
exhaust gas recycle to render the drying
system inert and increase efficiency.
Also, when appropriate, RTO’s are
supplied to treat the bleed-off gases.
By- Products
Different approaches
Sugar & Sweeteners
P R O C E S S E N G I N E E R I N G
Drying & Cooling Plantfor Beet, Cane & Special Sugars
Barr-Rosin is a world leader in industrial
drying technology, combining over one
hundred years of drying experience.
Barr-Rosin is part of the Process
Engineering Division of the GEA Group.