Case Study:
Bunge Canada, Toronto, Ontario
There
are many processes, some of which use heat and others which exhaust heat
at different times, making re-use of the heat most difficult to achieve.
At the
Bunge Canada plant where edible oils are manufactured up to10,000 Lbs/Hr
of steam is produced in one Hydrogenation process which is an exothermic
reaction where gaseous hydrogen is adsorbed by the edible oil to produce
Hydrogenated Oil.
The
process is heated with steam to bring the oil up the temperature at which
the reaction becomes exothermic. The high pressure supply steam is turned
off and condensate or re-circulated water is used to cool the reaction and
keep the temperature under control.
At first
10,000 Lbs/Hr of steam is produced because the amount of hydrogen being
adsorbed is at its maximum and after an hour the rate has decreased to
several hundred Lbs/Hr.
The steam
pressure produced by the reaction is controlled at 15 psig so as to be
useful in other sections of the plant and every effort is made to avoid
exhausting steam to the atmosphere.
There
is a second Hydrogenation process which produces less steam at less
frequent intervals and it is important to use the steam produced at the
second unit as well.
There are
many processes in the plant which can use hot water or steam for heating
the product.
A
steam heated propylene glycol system will keep outdoor edible oil storage
tanks warm using 15 psig steam produced in the process.
Arrangements were made to pipe some of the excess steam, reduced to 5
psig, back to the deaerator in the main boiler room - 400 Ft distant - to
preheat the feedwater rather than using steam from the main steam header
in the boiler room.
The
Solution
Over a
period of three years Bill Dawson and the Bunge plant Engineer examined
all of the plant processes and designed a system to save excess heat.
Because
the heat produced by the process and the heat required to heat the product
occur at different times and at different rates the heat produced in
excess of the current needs is stored as hot water in the following: -
One
existing 15,000 US Gal insulated, vented storage tank stores water at 180
F. A second 15,000 US Gal insulated storage tank contains water at 160 F
which is used for cooling the edible oil after it has been heated to the
required process temperature.
Large
circulating pumps and heat exchangers were installed to deliver either hot
water (180 F) or cold water (160 F) to the various heat exchangers to heat
or cool processes.
Excess
steam from the process at 15 psig will be used to heat the water for the
hot water tank and when the tank is full and there are no other processes
to use hot water, the steam will be vented to the atmosphere.
More
excess 15 psig steam will be vented to the atmosphere in summer because of
lower requirements for heating – particular for the outside edible oil
storage tanks.
Computer Control System
A
computerized control system was developed on site to control the complex
heat recovery system described above.
Expected Savings
When the
system is fully implemented in April, 2006 the main boiler steam loads are
expected to be reduced by 1/3 to 1/2 - with most savings occurring in
winter.
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your efficiency,
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