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computer
controller for supersaturation in
sugar boiling process |
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computer
controller for supersaturation in
sugar boiling process |
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1. function this device is used for the automatic control of
the sugar boiling process of different strikes (a.b.c and grain strikes). it
works automatically to measure and indicate the supersaturation of the mother
liquor in the massecuite, and hold it in a suitable range. this provides proper
conditions for the growth of crystals, making the crystals grow faster and more
uniform, and preventing the formation of false grains and conglomerates, thus
yielding fine strikes. with the help of this device, good quality and high rate
of sugar product can be obtained, along with a shorter boiling time and lower
steam consumption. 2. main principle
1. in
accordance with the principle of sugar boiling, the main factor affecting the
sugar boiling process is the supersaturation of the mother liquor in the strike,
and the most important key to this process lies in controlling suitable
supersaturation of the strike. 2. the supersaturation of the mother liquor in the boiling strike depends
on its temperature, purity and the absolute pressure in the pan, and a
mathematical relation exists. based on plenty of practical data and handled by a
computer, a new mathematical model has been established.
3. the temperature of the strike and the absolute pressure in the pan are
measured with precise and sensitive sensors. the purity of the mother liquor is
preset in the computer with several curves according to practical experiences.
from these three input data, the computer figures out the current
supersaturation and displays it immediately and consecutively. 4. during the boiling period of a strike, the computer compares the
measured value of supersaturation with that preset in the computer, and controls
the actuator to open or close the feeding valve or water valve, holding the
supersaturation of the strike in the stipulated range. 5. when necessary, the operator can enter a command to the computer, and
change the controlling value of supersaturation, which the computer follows. 6. the reference curves of supersaturation
preset in the computer are worked out according to the principle of sugar
boiling and the practical tests on the spot. various curves are offered to meet
different requirements. the preset purity curve of the mother liquor in the
strike is estimated by experiences based on the purities of the strike and
molasses as well as the course of boiling. several curves are available for
selection. 3.
advantages
and features: 1. this device can indicate the supersaturation itself of the mother
liquor in the boiling strike at all times (whereas other kinds of boiling
controller cannot indicate this figure, but only other relatives such as
conductivity or fluidity). this makes the controlling of the sugar boiling
process stricter and more visualized.
2. the device is of high accuracy, good
stability, re-producibilily and reliability, and is easy to manage.
3. it is of wide adaptability, suitable for the
boiling of all kinds of strike. various controlling programs are offered to suit
different working conditions. 4. the whole system is simpler in structure, without movable part except
for valves, so it is not liable to be damaged and is easy to maintain. 5. it can use either the time provided by the computer itself or the
level in the pan as the fundamental variety of the controller (selected by the
client), thus the system has widely adaptability for different working
conditions. 6. the main parameters of the boiling process are recorded automatically
and consecutively. this makes it convenient to check and investigate the
process. adjusting is easy to make at any time. 7. a vacuum control system is provided for the pan-condenser to maintain
a steady vacuum in the pan, thus achieving better results. 8. this device serves a vacuum pan separately, and several sets of them
can form a centralized control and supervision system. 4. main parts of the system 1. absolute pressure transmitter 2. temperature transmitter 3. level indicator (optional) 4. microprocessor based controller 5. recorder 6. electric operator 7. current to pneumatic converter 8. pneumatic control valve 9. front opened control cabined with switch and signal apparatus. 5.
direction
for use a. use in seed striking 1. close all connecting valves of the pan, raise the vacuum, drawn in
material in accordance with the requirement of purity until it covers the
calandria, put on steam to bring it to the boil, then turn on the device. 2. regulate the vacuum in a suitable range (620-660 mm hg is recommended)
and the steam valve at a moderate opening. 3. select a purity curve according to the purity of the material and a
control curve of supersaturation. 4. turn the selection switch at "seeding", and set the feeding
valve and water valve at proper opening. 5. when the supersaturation displayed on the screen of the computer rises
to about 1.0, prepare for seeding. empty the basin and add a little alcohol in
it. 6. when the supersaturation raises to 1.1, pour the seed slurry into the
basin. draw it into the pan when the supersaturation reaches 1.15-1.20. 7. then the controller works automatically according to the required
supersaturation preset in the software. the water valve opens when the
supersaturation rises to a certain upper limit, and then closes when it drops to
a certain lower limit. this operation repeats 3 times (or less if the operator
desires) to provide well conditions for the crystals to grow and steadily. 8. turn the selection switch to "going up". regulate the
openings of the water valve and feeding valve properly again. then the device
controls the feeding to follow the preset curve of supersaturation, and the
strike goes up gradually.
9. when the grain strike reaches the planned
volume and concentration, turn off the device, close all valves and drop the
strike as usual. b.
use in massecuite-bioling (with magma) 1. when the pan is ready, draw in seed magma until it covers the
calandria, and open the steam valve. after
boiling, open the bypass water valve to coordinate the water-evaporating rate. 2. check the seed magma. if necessary, treat it with water to make the crystals more uniform in size distribution and proper in quantity. then close the bypass water valve, and turn on the device. 3. select a proper controlling curve and a purity curve. turn the switch
on "control" position. 4. set the feeding valve and water valve at proper opening. 5. during the first stage of "control" for several minutes,
check the concentration of the strike in the pan frequently. if necessary,
readjust the preset concentration or replace the control curve. 6. the succeeding processes: feeding, bringing together, tightening and final concentrating are controlled by the computer. after that, turn off the device, close all valves and drop the strike as usual. c. note 1. when this device is first used in a pan or for a new kind of strike,
practical tests and adjustments should be made, by which the optimum control
curve of supersaturation is ascertained, and then it is saved in the computer
for use. 2. the suitable opening of feeding valve, water valve and steam valve for
various strike boiling are also determined through practical tests. the
additional corresponding measuring and controlling system can be offered at the
client's request. 3. all kinds of molasses used for boiling must
have been treated in the dilution tank by steam and water to dissolve the
existing fine grains before
being drawn into the pan.
4. the boiling pan
should work at a vacuum not exceeding 700mm hg but not lower than 600mm hg.
5. the vacuum pan
should have well circulation. better results can be achieved if a stirrer is
provided. |
