|
in the early fifties, there were only three mechanized sugar factories in guangdong province with a total grinding capacity of about
3,000 tons of cane per day (tcd) and with an annual sugar output of less than 50,000 tons. only two products, sugar and alcohol, were produced, and the sugar
quality and its recovery were not satisfactory.
1. forty years of change
through a great deal of effort based on domestic
capabilities in the past 40 years, the entire situation has changed a lot. the
annual sugar output in the last 2 years has exceeded 2 million tons and the
total grinding capacity l80,000 tcd. over 30 kinds of products are manufactured,
including sugar products, paper and pulp products, alcoho1, sodium glutamate,
high activity dry yeast, edible yeast, g1acial, acetic acid, ethy1 acetate,
butyl acetate, furfural, medium density fiber board, particle board,
electricity, soft drinks and some precious biochemical products including
ribonucleic acid, nucleotide, adenosine triphosphate (atp), cytidine
triphosphate(ctp), polyinosinate-polycytidylate, etc. the quality of products
and all technical-economical indices have been improved enormously.
most of the plantation white sugar is of low color value,
usually l00-150 icumsa units, and even 60-100 icumsa units can be obtained when
necessary. milling extraction reaches 96-97% and total recovery 86-89%, steam
consumption is reduced to 40-45% on cane.
the cane sugar industry in guangdong province has
developed into a completely integrated system, including sugar cane breeding and
p1anting, sugar and by-products manufacture, scientific research, plant and
machinery designing, machine manufacture and installation, education and
training of professional personnel, and products sales. thousands of people are
involved in the industry. with great amounts of various products and economic
benefits, this industry has been playing an important role in guangdong
province's economy.
many technical innovations have been carried out, and some
new processes and equipment have been developed in our sugar factories,
resulting in higher quality of products, higher efficiency and lower raw
material and energy consumption.
the principa1 technical developments in our sugar industry
are described briefly in the following sections.
2. milling station
many of our sugar mills run safely with a working time
ratio of over 99.5% in the grinding period, and achieve high extraction of
96-97%, whereas the imbibition of water is lower than 20 % on cane. there have
been major measures adopted.
cane preparation has been much strengthened. cane knives
have been improved in construction and they rotate with a direction against the
moving of the cane carrier. also, a new style of disintegrator has been
developed.
the mill sets are installed with high accuracy. the
working openings of the feed and the discharge roller are kept suitable, thus
getting a proper charge distribution on these rollers. roller shaft is made from
high strength forged steel, and the shell from highly wear-resistant cast iron.
they are accurately machined and then assembled. this enables a long service
life to be achieved: the shaft being over l0 years and the shell 2-4 years.
the hydraulic pressure and running velocity applied to
each mill are determined appropriately. considering the practical situation of
the milling tandem and the requested grinding rate, as well as the property of
the cane fiber and its preparation, the foregoing figures are-calculated, then
they are further adjusted in practice.
donnelly chutes are installed in front of each mill to
improve cane feeding. pressure feeder are provided for the first and the last
mill, and underfeed roller for other mil1s. they improve the performance of
mills greatly.
a lotus roller serves as the top roller. messchaert
grooves and scrapers are arranged suitably to ensure juice draining as well.
an effective imbibition system with compound and
recircu1ating imbibition is used, so that the pol of bagasse is reduced to lower
than 2%.
a new style of milling machine with spherical roller
bearings has been developed successfully; it saves l0% of mill power consumption
in comparison with the conventional mill and has easy maintenance and a clean
working site.
3. clarification station
most sugar factories in guangdong produce plantation white
sugar by means of sulphitation. because of a series of technical measures
app1ied, the clarification efficiency has been raised considerably, thus
resulting in substantial improvements in product quality and sugar recovery.
sulphitators of injecting self suction type and self
melting sulfur furnaces have been developed successfully by our engineers,
whereby high levels of juice sulphiting(1.2-1.6g so2/liter or even
higher), and high absorbing ratio (over 98%) are achieved. they work smoothly
and are easy to manage.
a neutra1 or slight basic reaction is kept in the whole
clarification process, instead of acidic sulphitation. this minimizes the
sucrose inversion and increases the removal of impurities, decreasing the
calcium and ash content in clarified juice.
phosphoric acid of suitable amount is added into the mixed
juice in accordance with the concrete conditions, which achieves a good
cooperative effect together with sulphurous acid.
suitable floccu1ants with high efficiency-are used when
necessary; in order to obtain clearer juice, reduce the volume of mud juice,
shorten the settling time, and eliminate the difficulty of refractory juice
treatment.
the construction and operation of the clarifier have been
improved to reduce the retention time of juice in the clarifier and increase its
working flexibility.
cloth-covered vacuum filter is applied. its fi1trate is
clear and enters evaporator directly, instead of returning to mixed juice, which
minimizes the sucrose inversion and prevents the objectionable re-circulation of
impurities.
simulated juice clarification experiments in the
laboratory are often undertaken. through these tests, and concerning the
composition and nature of the juice, the working conditions of the clarification
process are determined properly.
4. evaporation station
in most of our sugar factories, the evaporation station
not only works as a concentrator to make the juice thicken into syrup, but also
plays a ro1e of secondary boiler. this works as a center of supplying vapors
from different effects to juice heaters and vacuum pans. this makes the best use
of steam and reduces its consumption.
quintuple-effect evaporators are applied, and the vapors
bled from the preceding four effects are used for different heaters and pans.
the pressure and temperature of these effects are raised appropriately for more
effective use of vapors.
a new condensate collecting and flashing system is
employed to guarantee smooth drainage of all condensates and to reclaim their
heat energy for further utilization.
the juice in evaporators is kept at low level, which,
decreases the hydrostatic loss, increases heat transfer efficiency, shortens the
retention time of juice, and reduces the sucrose inversion and color formation
in evaporators.
the syrup concentration is usually kept as high as 62-65%,
and even 68-70% in advanced factories, resulting in lower total steam
consumption.
all evaporators are cleaned at regular intervals. extreme
high-pressure hydraulic cleaners are used to remove the scale thoroughly.
stainless steel tubes are employed when possible. they have a slippery surface
with less sca1e adherence and have long service life.
the whole production process is strictly controlled to
keep the use of steam and vapor uniform.
5. syrup clarification
the traditional method of syrup clarification is
sulphiting to a slight acidity. a newly improved phosflotation process developed
by our experts is more effective, removing the suspensoid and a part of ash and
colloidal material in the syrup. this results in higher quality product and
better boiling house performance. this improved process is characterized by:
special measures used to promote the reaction of
phosphoric acid and lime to complete, which results in a higher clarification
effect and lower residual phosphate and calcium content in final syrup.
a unique method of syrup aerating provides very minute and
uniform air bubbles, whose amount can be easily adjusted to an optimum level.
a new type of clarifier designed to have a large floating
area but less height, providing good separating effect with short retention
time. the layout of the system designed properly to ensure smooth and stable
operation.
6. boiling house
the work of the boiling house is vital to the product
quality and sugar recovery. the keys lie in a proper boiling system, good
boiling performance and equipment, and advanced technical innovation.
a three-boiling system with flexib1e variation is used
generally, while a four-boiling system is for high purity syrup. the pan flow
diagram in different periods is arranged according to the purity of syrup and
the product requirements, following a principle of recovering as much as
possible from a strike (on the basis of fulfilling quality requirements), and
reducing the amount of subsequent strikes.
the quality of seed crystals is improved. a new procedure
is applied to produce uniform and tidy seed crystals with a suitable amount.
full seeding is practiced in sugar boiling, with strict control of the seed and
strike boiling.
a "homogeneous nucleator by organic solvent and
ultrasonic wave" (chinese patent) has been developed to make very tidy
sugar seed, which obviously improves the quality of the sugar product.
a new developed "computer controller for
super-saturation in sugar boiling process" serves to indicate directly the
super-saturation of mother liquor in the strike and to control exactly the
boiling process. with this device, good quality strikes can be obtained, even by
a new worker.
the circulation in the vacuum pan is improved with a
mechanical stirrer. an advanced style "middle-installed stirrer"
(chinese patent) is a new and simpler structure, higl1er efficiency, easier and
less cost, with safe running and less power consumption. it is the best choice
for the improvement of old equipment because of its special design, also it can
be used for new equipment.
7. other sections of the boiling house
the main innovations are as follows:
crystallizers for c strikes are water-cooled style with
high efficiency. cold water is used to cool down the massecuite, letting more
sugar deposit; whereas in the final stage, hot water can be put on to raise the
strike temperature for easy curing.
automatic or semi-automatic controlled batch centrifugals
are used for a strikes. because of its large size, high running speed, and high
number of charge cycles, this machine has a good curing effect and large output.
when the curing operation is over, the driving motor brakes the centrifugal
basket re-generatively, that is, the motor feeds electric energy back into the
power supply network, thus reducing the electric consumption considerably.
a highly effective "vibrated-fluidized bed sugar
drier and cooler" has been developed. with this machine, the sugar products
are dried and cooled to low residual moisture and temperature, suitable for
sugar storing to minimize the deterioration and caking in the warehouse. this
machine causes little abrasion damage to the crystal surface, along with
providing high heat efficiency and excellent flexibility.
before packing, the sugar is weighed automatically with a
device of high accuracy and easy operation.
8. raw sugar refining
many improvements have been practiced in the raw sugar
refining process. this has resulted in great progress in white sugar quality and
recovery. superior white sugar with a low-color value of about 60 incumsa unit
can now be produced, even from raw sugar of poor quality; and a high boiling
recovery of 95-96%, depending on the raw sugar quality, can be achieved. the
main measures are as follows:
raw sugar is affinated to remove the molasses on the
surface of raw crysta1s. double flotation process is used to clarify the melt
liquor, giving a high-color removal of 70-80% and high quality syrup. two
methods can be selected:
l. sulphitation-floatation and phosflotation process.
2. carbonation-floatation and phosflotation process, which
uses co2, produced from the alcohol production as the main chemical
to replace so2 and has higher clarification efficiency as well as
lower cost.
3. five
boiling systems are used. measures are adopted to increase the yields of a
strike and decrease the quantity of low purity materials.
9. power station
medium
pressure boiler-generator sets with high thermal efficiency are employed to
reduce the fuel consumption.
because of a series of energy saving measures adopted,
less steam and fuel are required. in a factory in which uses bagasse as the only
fuel, surplus bagasse of about 7-10 % on cane can be left over, mainly depending
on the fiber content of the cane and the production situation.
if all the bagasse in the plant serves as raw material for
other products, coal is used as fuel instead.
|
