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Plate Heat Exchanger in Cane Sugar Processing
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Plate heat exchangers have been widely used in many industries. Many sugar factories in Europe, America, South Africa and India also use it to heat the juice, exfoliate the juice, the syrup molasses before the tank, and the final molasses cooling (before the honey tank). With the good effect, some sugar mills try to heat the mixed juice with plate heat exchanger also. Below are some examples of good applications.

For Clear Juice Heating

The Dalton Sugar Mill in South Africa uses plate heat exchangers with 44 plates, each with a heating area of 0.79 m2. The flow rate of the clear juice is 130t/h, heated from 92°C to 104°C, the saturation temperature of the used steam is 111°C, and the heat transfer coefficient is 3400W/m2.K. The pressure drop of the clear juice through the heat exchanger is 76 kPa; when used, the steam valve is not fully opened. That is, the actual temperature difference is still small, and the heat transfer coefficient is also higher. The juice heater is turned on after five weeks of continuous operation, and there is some sludge deposition inside. There is a black film on the plate surface, which is easy to wash away with water.

In the German Nande sugar factory, the amount of beet juice is 600t/h. Before the clear juice enters the evaporation tank, it is heated in 4 stages by 4 plate heat exchangers. The juice vapor of the 1~4 effect evaporation tank is used as the heat source, and the temperature reached by each stage is heated. It is only 3 ° C lower than the juice vapor temperature and finally reaches 127 ° C.

In the 1980s, Guangzhou Huaqiao Sugar Factory (carbonic acid method) applied a plate heat exchanger to heat the clear juice. The plate area was 0.79m2, 50 pieces were installed, and the effective heating area was 37.9m2. Using the first juice steam, the juice content is 117t/h, the juice temperature is 68.7°C, the juice temperature is 100.7°C, the temperature rise is 32°C, the steam inlet temperature is 114.2°C, the drainage temperature is 108.4°C, and the heat transfer coefficient K is 4010W/m2. .K, the pressure drop of the clear juice through the heat exchanger is 36 kPa. Its outlet water temperature is about 6 ° C lower than the inlet steam temperature, and there is a little water in the tank. If the drainage is smooth, the K value will be higher. The equipment was dismantled and inspected after more than ten days of continuous use, and most of the surface of the sheet was still as smooth as new. There is very little dirt and can be wiped off with a soft cloth.

The Shunde Sugar Factory (sulfuric acid) sugar factory in Guangdong uses a plate heat exchanger with a plate area of 1.07 m2, which is used as the third stage heating of the clear juice. The average amount of cane juice is 254t/h, the temperature of using waste steam is 129~130°C, the temperature of juice before heating is 106~108°C, the temperature after heating is 120~126°C, and the heat transfer coefficient is 2400~3900 W/m2.K.

Guangdong Zhujiang Ganhua Plant uses a plate heat exchanger for the first-grade heating of the clear juice, and the heat transfer area is 35m2. After heating, the juice temperature is only 2 to 4 ° C lower than the steam temperature. After 15 days, the temperature difference is 4 to 6 ° C, and the heating temperature is higher than the 60 m 2 tube heater used. Its heat transfer coefficient is 2700 ~ 4000W / m2.K.

Another sulphite sugar factory uses a plate heat exchanger with a plate area of 0.36m2 and 90 pieces. The effective heat transfer area is 31.68m2. The juice is heated by the first juice steam. The average measured data for seven days is: clear juice flow rate 37.2. t/h, juice temperature 76 ° C, juice temperature 107 ° C, temperature rise 31 ° C, steam inlet temperature 113 ° C, steam condensation water temperature 112.5 ° C, heat transfer coefficient 2300W / m2.K. After more than ten days of disassembly, the surface of the plate has very little deposit and can be washed off with water and a soft brush.

The heat transfer performance of the heated juice by the plate heat exchanger is more than double that of the tubular type, so that the heat transfer area used can be reduced by half or more. Here, it is better to use the first effect juice, and there is a certain energy saving effect compared with heating using waste steam. In the case that the heat exchanger has good performance and is close to the evaporation can, the juice is heated by the juice vapor to make the temperature of the juice close to the juice vapor temperature, only 3 to 5 ° C lower, which can basically meet the needs of evaporation. Heating with juice vapor can also prevent the coking of sugar juice caused by excessive steam temperature. Some sugar factories in China use waste steam. Some factories have been seriously coked due to careless operation, and the char is difficult to remove.

For Mixed Juice Heating

The Dalton Sugar Mill in South Africa uses a plate heat exchanger to heat the mixed juice, 50 pieces. Use two months, clean once a week, cane juice flow 103 ~ 130t / h, from 72 ~ 76 ° C heating to 94 ~ 97 ° C, the use of waste steam saturation temperature of 109 ~ 111 ° C, heat transfer coefficient of 2900 ~ 3380W /m2.K, the pressure drop of the cane juice is 0.05-0.1 MPa. When the machine is shut down, the interior is deposited by sediment and sugarcane, and there is a thin layer of scale on the board surface, but less than the tube heater, it can be washed with water and brushed. Each work shift is “backwashed” and some of the sediment can be washed away. However, it is preferable to remove the fibrous impurities in the cane juice by sieving.

For materials containing more solid suspended solids such as mixed juice, the use of a wide flow channel plate heat exchanger is better. A foreign sulfite process sugar factory, using this heat exchanger and the third effect evaporation juice steam heating mixed juice and sulfur smoked juice, can run continuously for 30 days, the juice pressure used is very low, only 40kPa absolute pressure, The steam temperature is 75 °C. The heat transfer coefficient reaches 2090~2440W/m2.K, and its heating area is less than half of the tube type.

Two beet sugar factories in Poland (more than 2,000 tons of beet processed per day), in the mid-1990s, used a wide-gap plate heat exchanger, using the juice vapor of the boiling sugar can (temperature about 60 ° C) to heat the exudation juice, by The temperature was raised to about 50 ° C at about 30 ° C, then ash was added and heated again to about 88 ° C with steam and third juice. It works well and can be used continuously for one season. After shutdown, it can be sprayed with high-pressure water to remove all deposits on the surface of the sheet. It utilizes a large number of low temperature heat sources to significantly reduce the fuel consumption of the sugar mill.

The wide-gap plate heat exchanger can use a low-temperature juice steam with vacuum as a heat source to heat the low-temperature cane juice, which has greater energy-saving value.

For Molasses Cooling

The cooling of molasses before entering the storage tank is a key measure to prevent deterioration of the molasses during storage. However, the viscosity of molasses is large, heat transfer is difficult, and the use of a general heat exchanger is not effective.

The use of plate heat exchangers in South Africa and Australia to test the cooling of molasses is better. Both the Gladhow Sugar Mill and the Sezela Sugar Mill in South Africa use plate heat exchangers to cool the molasses. Molasses flow in a single pass in the device, and the cooling water passes in five passes. They used a plate size of 1556 × 416 mm, the number of plates was 96 and 160, respectively, the heat transfer area was 50 and 83 m2, the processed molasses amount was 11.5 and 12.6 t / h, respectively, and the molasses hammer was about 81. The temperature of the molasses is cooled from 59.8 ° C to 42.8 ° C, the latter is cooled from 62.1 ° C to 36.7 ° C, the inlet and outlet temperatures of the cooling water are 30.2 and 36.3 ° C, the latter is 23.3 and 46 ° C, and the cooling water consumption is 13.8. And 6.1t/h; the heat transfer coefficients are 96.3 and 112W/m2.K, respectively. The heat exchanger needs to be washed once a month with water.

The Bingera sugar factory in Australia used a plate heat exchanger manufactured by GEA in Germany to cool the molasses, model B12, with 149 V-shaped corrugated plates measuring 1400×400 mm, heat exchange area of 67.6 m2, molasses and Water is a one-way flow. The actual amount of molasses is 10~15t/h, the temperature of molasses is reduced from 57-62°C to about 37°C, and the temperature of cold water used is 32-35°C. The amount of water is automatically adjusted according to the temperature, which is 1.5~3 times of the amount of molasses. The heat transfer coefficient is 200 ~ 550 W/m2.K. The pressure drop of molasses is 50-150 kPa. The equipment is in normal operation during the whole season (with the inspection and cleaning in the middle), and the stainless steel sheet (model 316SS) has no visible corrosion. The cold water used should be cleaned. The lower temperature river water was tried, but soft deposits were formed between the plates, which affected heat transfer.



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