Vacuum boosters for drying applications

Drying is a process of removal of a liquid from a solid mixture by thermal means. Under this article, we shall not consider mechanical methods, such as filtration, centrifuging, pressing, etc. of liquid removal from solids. Various drying process & techniques are extensively used in the various Process industry, Pharmaceutical industry, Food processing industry, Dye & Chemical industry, Perfumes & Permitted Food additive industry etc primarily to achieve one or more of the following,

• Product concentration.
• Purification by removal of unwanted volatile elements.
• Solvent recovery.
• To increase shelf life and to facilitate further processing and permit proper utilization of the final product.
• To reduce shipping costs by reducing weight of the product.
• To reduce the rate of biological decay.
• To enhance the value of by products of a process.

Drying is an important and widely used process in the industry. Often it is a major cost center in process operations. The reason for this is the high-energy requirement for the removal of water. Typically, to remove 1 kg of water, we require 540 kcals of energy [latent heat of vaporization of water] plus at least another 60 kcals to take care of sensible heat requirements. Hence, regardless of the nature of process, we must supply at least 600 kcals for every kg of water removed from the material. This, therefore, demands high-energy inputs and for this reason the process efficiency must be maintained as high as possible.

The cheapest energy source is the sun. That is why many industries take recourse to sun drying. For example, in small food industry, chillies, ginger, etc., are all sun-dried; in the textile industry, fabrics and yarn are often sun-dried; in the ceramic industry, freshly moulded bricks and blocks are sun dried. Very often, most process requirements demand continuous working, independent to the weather conditions or time of the day. So there is a vast body of ovens, dryers, drying tunnels, dehydrators, etc., to take care of industrial drying processes. While these techniques are well known, their use is now being replaced by Low-pressure, Low temperature drying techniques, which have the advantage of enabling the drying process to be carried out at low temperatures. This process results in optimum energy utilization, lesser thermal exposure & damage to the product and very often, improved quality. In fact, it is possible to dry a product at sub-zero temperatures (Freeze drying) by simply reducing the pressure to an appropriate value for carrying out the process. Freeze Drying, most widely adopted process today in food processing industry is based on the same principle. Amongst the many advantages of low pressure drying techniques over oven-techniques, some are: -

• Drying time is accelerated drastically.
• Solvent recoveries are possible, resulting in substantial savings.
• Reduces pollution.
• Minimizes oxidation losses and product degradation due to reduced Thermal exposure.
• Wide range of operating temperatures can be selected to suit the product/process requirements.

For example, conventionally Katha (an essential ingredient of paan masala and paan), is dried by traditional cold room drying process. It is kept in cold rooms for over a period of about 24 days, with cold dry air blowing over it. The moisture levels are reduced from typically 50% + to about 12-15%. The temperature in the cold room is maintained at slightly above 0 degrees C, throughout the process time. However, by dopting low pressure drying techniques, this period an be reduced substantially. This would not only save energy requirements but also reduce the huge inventory hold-ups. Katha is a high-priced product and shortening of the process time ould result in substantial savings otherwise involved. Shorter process times also reduce possibility of fungus/moulds/bacteria attacks. Similarly Drying of various other products, such as Gelatin, Meat, Milk products, Green bodies etc, can also benefit by this fast process.

A vacuum Booster, when used in conjunction with any of the above, over comes all the associated limitations and increases the overall process efficiency by increasing the vacuum and pumping speeds with relatively very little extra energy.