The Application of Rotary Vacuum Filter in Sugar Production

Sugar production is a process whereby sugar is extracted from sugar cane stalks or sugar beet tubers by physical and chemical means to remove impurities and produce a finished sugar product containing high purity sucrose.

The whole process of sugar production includes squeezing, purification, evaporation, boiling, centrifugation, drying and packaging.

Sugar production from sugar cane (using sulfurous acid) mainly consists of:

1. Pre-treatment and pressing of sugar cane to extract juice

The first pre-treatment before pressing is to chop the cane stems into pieces with a rotating cane knife, or to tear the cane apart without extracting the juice with a hammer mill type ripper. The press is usually a series of five three-roller presses, through which the crushed sugar cane is continuously squeezed out of the juice. The juice from the 5th press is pumped back to the 4th press by adding warm water; the juice from the 4th press is pumped back to the 3rd press; the juice from the 3rd press is pumped back to the 2nd press; the juice from the 2nd and 1st presses is mixed and the coarse residue is removed to obtain a mixed juice. The pressing process is also known as osmotic pressing and the bagasse from the 5th press is often used to fuel boilers or as a raw material for paper and other industries.

2. Purification.

The juice from the press is turbid and acidic, with a very complex composition, with non-sugar substances in addition to more sucrose. The simple purification method is to add lime as a clarifying agent, adjust the PH value and control the temperature, so that some non-sugar precipitation and precipitation, after adding flocculation auxiliaries, in the sedimentation pond after slow-flow sedimentation and filtration to get clear juice, the sediment is filtered through the filterless cloth vacuum suction filter unit, the juice is returned to the sedimentation pond for sedimentation, and the removed filter cake is called filter mud, which can be used as fertilizer. This is the traditional lime method, which yields raw sugar, which requires further processing.

To obtain arable white sugar that meets international standards, a more complex process has to be used, with sulphite and carbonic acid methods, with phosphoric acid sulphite being the main method currently used for sugar cane raw materials and carbonic acid for sugar beet raw materials. This means that in addition to using the lime method, sulphur dioxide or carbon dioxide and phosphoric acid are added to induce more precipitation in the sugar juice, remove more non-sugar components and reduce the colour value. The phosphoric acid sulphite method uses lime and sulphur dioxide as the main clarifying agents and phosphoric acid as a secondary clarifying agent to improve the purity of the clear juice.

3. Evaporation.

The clarified cane juice concentration is about 13~15°Bx, crystallization needs five effects of evaporation to concentrate the clear juice to about 65°Bx syrup, which needs to consume a lot of boiler steam and evaporate a lot of water from the syrup, the 1st and 2nd effects are pressure evaporation, the latter 3 effects are vacuum evaporation, the evaporation process also produces a lot of secondary steam, which can be supplied for sugar cooking and cane juice heating. This process is called evaporation.

4. Boil Suger

The syrup is evaporated in the vacuum tank until the sugar is saturated and the crystalline seeds are added to become the core of the crystallization. As the water evaporates more syrup is added to maintain the proper saturation concentration to make the crystals continue to grow and the syrup forms a thick material called sugar paste. The sugar paste is discharged into the crystal aid box for further crystallisation, called crystal aid.

5.Split honey

The process of boiling sugar is commonly used in three systems of boiling sugar, the syrup is added to a small amount of A diluted honey and back soluble sugar paddle, the crystal seed (seed) is B sugar paste, concentrated into A sugar paste, help crystal after the upper suspension centrifuge filter type separation to get the finished white sugar (A sugar); the solution produced before water washing is not carried out, called A original honey; the solution produced by high-speed cleaning of sugar crystal with high-temperature clean water called A washed honey. Raw honey is diluted and used to cook B and C paste and B sugar paste; A washed honey is diluted and used to back-cook A sugar paste and C paste. A sugar should extract the maximum amount of sugar and reduce the amount of back-boiling.

B seed paste is boiled and added to the high green syrup to make B massecuite, after helping crystals to split honey by continuous cone basket centrifuge, the resulting crystals are B sugar (B sugar), stirred and dissolved with sugar paddle to become sugar paste, as the seed of A massecuite; the resulting B molasses is used to boil C massecuite. A good boiling of the B massecuite will improve the quality of the product and help to increase the boiling recovery rate.

C paste is added to B honey and C honey to make C sugar paste, and after helping the crystals to split the honey by continuous cone basket centrifuge, the resulting crystals are C sugar, i.e. brown granulated sugar, which can become finished products directly, or can be dissolved back into C massecuite and used to cook A massecuite; the resulting C honey, also called waste honey, can be used as other industrial raw materials such as alcohol and yeast. C massecuite is of low purity, has a high viscosity, is difficult to crystallise and takes a long time to cook, so the maximum amount of sugar should be extracted to reduce the purity of the waste honey.

The filter cloth-free vacuum suction filter has no sewage discharge, high production efficiency, low dry filtration mud transfer rate and a high degree of automation, and can be widely used in the sedimentation pond mud filtration of sulphite sugar mills.

The drum is mainly composed of a cylindrical stainless steel shell, a plastic partition and a stainless steel screen. The drive system uses a frequency converter to drive the drum, which improves the adaptability to the production by adjusting the running speed. The slurry tank is used to store the slurry and form the contact between the drum and the slurry. The stirring device is mainly used to stir the juice and prevent it from sinking to the bottom. The juice extraction system consists of a juice extraction pipe and a vacuum distribution device, which is mainly used for the extraction of filtered juice. The washing device is mainly used for washing the mud layer, diluting and taking away the sugar contained in the mud, to reduce the translucency of the dry mud. The vacuum distribution device mainly distributes the vacuum on the drum surface of the filter suction machine to meet the requirements of the suction and filtration process. The mud scraping device scrapes off the mud from the drum surface.

When the filterless cloth vacuum suction filter machine is working, the low vacuum area of the drum is in direct contact with the mud, and due to the pressure difference generated by the vacuum, the mud is pumped through the stainless steel screen, and most of the solid insoluble substances cannot pass through the mesh holes on the surface of the screen to gradually form a filter mud layer, while the sugar solution is filtered through the capillary tubes of the filter mud layer and the holes of the screen to obtain a clearer filter juice, which is gathered in the low vacuum tank; then the filter mud layer enters the high vacuum area with the drum. The washing device sprays hot water evenly on the filter mud layer to dilute and take away the sugar inside, while the water in the filter mud will be dried up to the maximum after this area so that the various indicators of the filter mud meet the process requirements and the diluted juice is gathered to the high vacuum tank; the filtered juice from the high and low vacuum pumping irrigation is gathered in the open box or balance tank and pumped to the special filter juice processing system by the pumping pump to further process the filtered juice. or return to the previous cleaning process for reprocessing. The filtrate is stripped off in the resting area by a scraping device.

a. mud tank

b. stirrer

c. converter

d. scraping device

I. Low vacuum zone

II. High vacuum zone

III. Suspended zone

Main physical indicators of the filterless cloth vacuum suction filter:

1. Dry filter mud translucency ≤5% on average

   
   

2. Wet filter mud water content ≤75% on average

   
   

3. Processing capacity:

• In areas with high purity of sugar cane, such as Guangxi, plants with good

  purification control are about 35~45 tons/square, i.e. 55 square suction filter
  

  machines can meet 2200~2500 tons/day squeezing capacity.

• In areas similar to Yunnan, a factory with good purification control will have a

  capacity of 30~33 tons/square, i.e. a 55-square suction filter machine can meet

  1500~1800 tons/day squeezing capacity.