Application of membrane filter press in food industry
The development of filter plate is from traditional plate and frame filtration to later box filtration and then to membrane filtration. Its development track is mainly to improve the solid content of filter cake and water washing effect.
The filtration principle of the filter plate of the filter press is that a filter cake layer is formed on the surface of the filter cloth, and then the filter cake layer is used as the filter layer to filter the materials and let the water pass through. With the extension of time, the filter cake layer close to the filter cake is drier than the filter cake in the middle part, so the water permeability is greatly reduced, resulting in obvious deficiencies in the traditional plate frame and box filtration:
1. In the later stage, the pressure of the feed pump increases greatly, wasting energy consumption.
2. In this filtration cycle, 70% dehydration effect can be achieved in the first 30% of the time, and only 30% effect can be achieved in the next 70% of the time. The filtration time is greatly prolonged, but the effect is average.
3. The filter cake is dense and does not form a uniform filter cake washing channel, which is not conducive to subsequent filter cake washing.
In membrane filtration, two membrane plates are added at both ends of the filter plate, so that a pressing chamber is formed between the membrane plate and the filter plate, and a filtering chamber is formed between the membrane plate and the outside. Stop feeding when only 70% of the feed is, and the filter chamber does not need to be fully filled. At this time, the press medium (high-pressure air or high-pressure water) is introduced into the press chamber to squeeze the membrane towards the filter chamber, so as to achieve the purpose of filtration and dehydration. Its advantages:
1. The filtration cycle is greatly shortened and the filtration cycle of each batch of materials is shortened, so as to greatly improve the utilization rate of equipment and output.
2. Since low-pressure feeding and high-pressure pressing are advocated, the solid content of filter cake is greatly improved.
3. The pre pressing technology is used in the pressing process, which makes the filter cake form evenly, which is conducive to water washing, greatly reduces the water consumption, and the impurities in the filter cake are easier to be taken away by water.
At present, the application of membrane filtration technology in food is mainly divided into three categories:
1. After fermentation, the concentrated bacterial residue is dehydrated. Applications in this field include citric acid, beer, lactic acid, sucrose, glucose, etc.
2. Filtration of edible oil, especially palm oil.
3. Dehydration of edible gum, especially agar and carrageenan.
Beer is more and more popular as a nutritional and hobby drink. Beer contains a variety of carbohydrates, proteins, vitamins and hundreds of volatile aroma components, which are easy to decompose, denature and volatilize after heating. Filter press filtration can not only remove bacteria, but also will not cause the loss of nutrients in the permeate, so it maintains the freshness and refreshing characteristics of the original wine.
The preferred filter membrane in the beer industry is the ultrafiltration membrane with cellulose triacetate as the membrane material. The price of the filter press of this material is limited to ph3-8, the temperature below 50 ° C and the pressure below 0.4MPa, otherwise the membrane will be damaged. Proper selection of operating conditions can not only save time and labor, but also ensure the maximum utilization of the filter membrane within its service life, so as to maximize the filtration efficiency. Operating conditions include flow rate, pressure, temperature, etc.
The application of filter cloth in honey processing is relatively exquisite. Different filter cloth mesh plays a different role in promoting the nutritional value of honey. In the process of honey processing, it needs to be filtered through coarse filtration and fine filtration. Coarse filtration is mainly used to filter out wax chips, larvae, bee carcasses and other large impurities. Fine filtration further removes impurities with smaller particle size than flower powder particles, so as to make the honey more clear. However, it will also cause the loss of plant pollen in honey to varying degrees, hinder the judgment of honey and reduce the quality.
As for the pollen, which is an important part of the nutritional value of honey, the membrane filter press is obviously not desirable. If the filter mesh can be selected according to the size of different plant pollen on the premise of filtering out impurities and suspended solids, the pollen in honey can be preserved to the greatest extent, but it also increases the technical difficulty of processing, and the filter mesh of different plant pollen needs to be further discussed. After this experiment, we found that the filter cloth of mechanical filter press uses the same mesh filter cloth for filtration, the size of pollen grains of different plant pollen is different, and the reduction rate of different plant pollen is also different after filtration. However, filtering with 60 filter cloth can not only effectively remove impurities and suspended solids in honey, but also make most honey preserve high pollen content and concentration.###