Belt Presses, Decanters
and Disk Stack Centrifuges
Since the mid 50's, Flottweg has been well known in the field of mechanical liquid solid separation. Starting with applications in the chemical and pharmaceutical industry and the disposal of sewage, more and more processes in the food industry have been developed since the early 70's. With the beginning of the production of belt presses in 1976, activities in the food industry have been intensified considerably.
As a result, approximately 50% of the turnover of 50 million German Mark are obtained in this industry. Due to the high export rate of 70%, Flottweg has established its own offices in many foreign countries, i.e. in North America, Russia, China, France, Spain and the United Kingdom. In the following well-known processes and latest developments are described with belt presses, decanters and centrifuges and their combination in modern and efficient processing lines.
Cloudy Apple Juice: The demand for natural products is increasing constantly. As far as fruit juices are concerned, cloudy apple juice is of great importance. Light colors as well as a high and stable turbidity are the main features of cloudy apple juice. To get these characteristics, a combination of belt press, heater and centrifuge has been tested and well established.
The mill is directly installed above the feed box of the belt press. This arrangement will ensure that crushing and extraction of the apples are completed within 2-3 minutes. In this way, browning reactions are largely avoided. Immediate heating afterwards will inactivate polyphenol, oxidases and petolytic enzymes. In this way, both the light colour of the juice and the pectic substances which are needed for stabilizing the turbidity can be preserved. Subsequently, a separator is used to adjust the turbidity degree of the final product and to improve its stability.
Liquefaction: To ensure optimum utilization of the raw material, a secondary extraction of the pomace has been installed in many companies. The pomace is reslurried with condensate, and - when required - with enzymes and, after an appropriate residence time, extracted again. Using belt presses yields of 92% of soluble solids are possible. A decanter instead of a belt press may possibly be an interesting alternative.
Using enzymes for total liquefaction instead of normal mash enzymes the yield of the total systems can be increased up to more than 95%. This combination allows optimum processing of the raw material both qualitatively (high-quality cloudy juice) and quantitatively (maximum yield).
Processing of Berries, By-products: The installation of a decanter can offer further benefits to the processor. Besides apples, the decanter can be used for the processing of berries and by-products. In this way, both the rate of capacity utilization and the plant economy can be improved. The yield of the total system (decanter plus belt press) will amount up to 95% w/w of the soluble solids.
Regarding by-products, mainly fining lees and UF retentate are concerned. In both cases, a decanter replaces the vacuum rotary filter. The processes become more simple and the consumption of kieselguhr is enormously reduced. Without using kieselguhr, much less waste is produced which has to be disposed. The clarified liquid is discharged with solids contents below 1% v/v. The dry solids discharge is approximately 30%.
Vegetable Juices: Over the years, the consumption of vegetable juices, especially carrot juices, is increasing. As for fruit juices, natural products are preferred. This means that an enzymatic treatment of the mash has to be avoided. Lower yields without enzymes could be compensated by continual improvement in decanter technology. Using decanters of latest design, yields of up to 78% w/w are possible, even without enzymes.
Citrus Processing: During the production of citrus juices and by-product like pulp wash concentrate or cloudy peel products, decanters and centrifuges are used in processing stages. They are mainly used for the separation of particles and the reduction of the pulp content of the products. During the products of citrus oil, centrifuges are used for the concentration and purification of the essential oil. In the first step, the oily emulsion is concentrated from 1 to 3% up to 50 to 80% of oil content by means of an automatic discharge centrifuge (desludger). A second centrifuge, the so-called polisher, finally removes water and solids.
Processing of Exotic Fruits: For the production of juices and concentrates from exotic fruits, decanters and centrifuges have been tried and tested many times. For example, decanters and centrifuges are used for the adjustment of different product qualities like high pulp, medium pulp and low pulp concentrate during pineapple processing. Decanters are used to remove the undesirable components of mango and guava juice. A Flottweg Tricanter is the heart of a coconut processing line. The Tricanter, a three-phase decanter, separates in one step coconut grates, coconut milk and coconut fat. Removing the fat content improves the shelf life of the final products, for example, the coconut syrup. At the same time, a high quality by-product (coconut fat) is produced.