|
A pusher centrifuge is a type of filtration technique that offers continuous operation to de-water and wash materials such as relatively in-compressible feed solids, free-draining crystalline, polymers and fibrous substances. It consists of a constant speed rotor and is fixed to one of several baskets. This assembly is applied with centrifugal force that is generated mechanically for smaller units and hydraulically for larger units to enable separation. Pusher centrifuges can be used for a variety of applications. They were typically used in inorganic industries and later, extensively in chemical industries such as organic intermediates, plastics, food processing and rocket fuels. A suspension feed enters the process to undergo pre-acceleration and distribution. The subsequent processes involve main filtration and intermediate de-watering, after which the main filtrate is collected. Wash liquid enters the washing step and final de-watering follows. Wash filtrate is extracted from these two stages. The final step involves discharge of solids which are then collected as the finished product. These process steps take place simultaneously in different parts of the centrifuge. It is widely accepted due to its ease of modification, such as gas-tight and explosion protection configurations. == Applications == Pusher centrifuges are mainly used in chemical, pharmaceutical, food (mainly to produce sodium chloride as common salt) and mineral industries. During the twentieth century, the pusher centrifuge was used for desiccation of comparatively large crystals and solids. Although pushers are typically used for inorganic products, they appear in chemical industries such as organic intermediates, plastics, food processing and rocket fuels. Organic intermediates include paraxylene, adipic acid, oxalic acid caprolactam, nitrocellulose, carboxymethylcellulose, etc. In food processing, pusher centrifugation is used to produce monosodium glutamate, salt, lysine and saccharin. Pusher centrifugation is also used in the plastic industry, contributing to products such as PVC, polyethylene and polypropylene, and a number of other resins. Individual products *Soda Ash—Particle size is commonly beyond 150 µm. Feed slurry usually has 50% solids by weight, and discharged cake has about 4% moisture. *Sodium bicarbonate—Feeds usually contain more than 40% of solids in weight with and crystals generally beyond the particle size of 45 µm. Cake production usually has only 5% water. To achieve such high efficiency of desiccation, requires device modifications. *Paraxylene—Fed as frozen slurry with a particle size ranging from 100 to 400 µm. Purity of 99.9% is available using a single stage long basket design. Considerations and measurements have to be taken to avoid contamination of paraxylene and oil. Lip seals and rod scrapers are used on the shaft seal to eliminate cross-contamination. The feed is purified using a funnel. Vents integrated into process housing ensure that gases moves uninhibited, preventing contamination. *Adipic acid—Undergoes repeated process of crystallisation, centrifugation and remelting to achieve the required purity. Adipic acid crystals are generally larger than 150 µm. nitric acid is reduced from 30% in the feed to 15 ppm in the cake produced. Separation of nitric acid from adipic acid is essential for further treatment. *Cotton seed delinting—Cotton seeds contain fibres that grow and form a ball of lint. This is separated using sulphuric acid, where the lint may be used to produce cotton fibre. Adding sulphuric acid causes the lint to become brittle, hence ensuring that in the subsequent tumbling process de-linting occurs effectively. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pusher centrifuge」の詳細全文を読む スポンサード リンク
|