Vacuum drying – Nothing works without drying

Drying is a mass transfer process consisting of the removal of water or another solvent by evaporation from a solid, semi-solid or liquid. Vacuum is a region with a gaseous pressure much less than atmospheric pressure.

The earth’s atmosphere exerts a pressure upon us (known as the atmospheric pressure), which can be measured in a number of ways. At sea level the standard pressure is described in different units as: 101,300 Pascals; 1,103 millibar; 760 Torr; 760 mm of Hg; 29.92” of Hg;14.7 psia.

In the approximate vacuum range from about one Torr to near atmosphere, typical applications are mechanical handling, vacuum packing and forming, gas sampling, filtration, degassing of oils, concentration of aqueous solutions, impregnation of electrical components, distillation, and steel stream degassing.

Vacuum-based industrial applications

Industrial vacuum applications range from mechanical handling (such as the manipulation of heavy and light items by suction pads) to the deposition of integrated electronic circuits on silicon chips.

At lower pressures down to about 10-4 torr, many metallurgical processes such as melting, casting, sintering, heat treatment, and brazing can derive benefit. Chemical processes such as vacuum distillation and freeze-drying also need this range of vacuum. Freeze-drying is used extensively in the pharma industry to prepare vaccines and antibiotics and to store skin and blood plasma. The food industry freeze-dries coffee mainly, although most foods can be stored without refrigeration after freeze-drying, and this technique is receiving widespread acceptance.

The pressure range down to about 10-6 Torr is used for cryogenic (low-temperature) and electrical insulation. It is used in the production of lamps; television picture tubes, X-ray tubes; decorative, optical, and electrical thin-film coatings; and mass spectrometer leak detectors.

In thin-film coating, a metal or compound is evaporated under high vacuum from a source onto a base material or substrate. The base material is generally plastic for decorative coatings; glass for optical coatings; and glass ceramic, or silica for electrical coatings.

To achieve vacuum high enough for thin-film coating and for other industrial uses requiring pressures down to 10-6 torr, a pumping system consisting of an oil-sealed rotary pump and a diffusion pump is used. The oil-sealed rotary pump (sometimes referred to as forepump) ‘roughs’ the chamber down to a pressure of about 0.1 Torr, after which the roughing valve is closed. The fore valve and high-vacuum baffle valve are then opened so that the chamber is evacuated by the diffusion pump and rotary pump in series.

Salient features

Why vacuum drying?

Vacuum drying is recommended for materials that could get damaged or have its properties changed when exposed to high temperatures. The vacuum removes the moisture while preventing the oxidation or explosions that can occur when certain materials combine with air. Vacuum drying is also ideal in situations where a solvent must be recovered or where materials must be dried to very low levels of moisture.

Why use vacuum dryers?

• Vacuum drying process requires less energy and so it reduces the environmental impact and economic cost for drying the products
• It works faster than any other drying methods and thus saves considerable amount of time
• Vacuum drying tends to retain the integrity of the original products without damaging it with heat. For foods, this can be valuable as other drying processes can degrade quality of the food and thereby reduce its appeal
• Using vacuum drying equipment also prevents workers’ exposure to health risks like fumes and explosions

What are vacuum tray dryers?

It involves heating the shelves inside the vacuum chamber. This technique can apply heat indirectly to the product by forcing physical contact with the shelf. A hot medium flows through the shelves, thus enabling it to conduct heat to the tray placed on the shelves.

Why vacuum tray dyers? (Also called cabinet dryers)

• Conduction-based drying
• Intelligent design of heating shelf for maximum conduction of medium
• Drying without contamination
• Faster and energy efficient method of drying
• Reduces batch time and saves cost

Vacuum tray dryer

Promas vacuum tray dryers are most commonly used as batch dryers. Vacuum tray dryers are of two types-cylindrical and rectangular cross section. The boxes are loaded and unloaded via a door. Inside them are several heating plates mounted one above the other with fixed gap between them on which the product is placed in trays.

Water heating system

The top of the bottom heating plates and trays should be as smooth as possible to permit optimal heat transfer between the plates and products. The heating medium flowing through the heating plates should be water or thermal oil. The distance between the heating plates is determined primarily by the surface loading and the foaming of the products in the case of food products. The preheating phase is very important in order that the drying curve and the foaming of the product are identical throughout the cabinet. The dimensioning of the vacuum systems is an important factor in the design of drying cabinet systems.

Salient features

Our unique feature is the inclusion of an online cartridge filter post cyclone separator for product recovery and for ensuring a better life of oil sealed vacuum pump thus cutting costs of the user considerably. Shown in image below

Water heating system:

The vacuum system accessories used for the drying system

KF flanges and fittings

KF flanges and fittings

A vacuum flange is a flange at the end of a tube used to connect vacuum chambers, tubing and vacuum pumps to each other. Vacuum flanges are used for scientific and industrial applications to allow various pieces of equipment to indirect via physical connections and for vacuum maintenance, monitoring and manipulation from outside a vacuum’s chamber. Several flange standards exist Klein Flange (KF) Quick Flange (QF) or NW, sometimes also as DN.

Introduction

KF vacuum systems employ components with metric interface dimensions which have been defined by the International Standards Organisation (ISO). This ensures a high degree of compatibility between components obtained from different sources. Vacuum ISO KF are compatible with Klein Flange (KF) types. Use ISO KF for tube sizes DN16 to DN50. Our standard range of KF flanges and fittings are manufactured from 304 (1.4301) stainless steel. ISO KF constitutes an economical system of reusable interfacing stainless steel vacuum fittings and components for 19.1, 25.4, 38.1and 50.8mm OD tubing. Assemblies are usable to 10-8mbar. Maximum temperature for sustained use is 150°C. They are ideal for vacuum systems requiring regular assembling and disassembling. Each vacuum seal is made by compression of an O-ring on a centering ring between mating flanges. The seal is made in seconds by finger-closure of a wing nut on the all-metal hinged SS 304 clamp. The ISO KF family of modular building block components includes all commonly used standard fittings, feed-throughs and accessories. Reducing flanges are available to connect different size components. Mating flanges are offered to interface with pipe and other flange systems including LF and CF.

ISO KF Flanges and fittings

Features

• Quick connection and disconnection
• 316L (1.4301) stainless steel fittings
• All SS 304/ 316 clamps
• Viton O-ring bakeable to 150°C
• Single wing nut closure
• ISO compatible

Specifications

• Material fittings -304/316 stainless steel, TIG welded
• Clamps- Aluminium
• Standard O-rings Du Pont Viton fluoroelastomer
• Vacuum O-ring compression by uniform pressure application around the 15° outer flange surfaces
• Flanges ISO standard dimensions 360° rotatable
• Four standard flange sizes for use with four tube sizes
• Tube bore sizes 12.7, 15.8, 22.1, 38.1 and 50mm
• Maximum temperature 150°C
• Components seusable and interchangeable with other ISO
• Dimension components of the same size

Clamps

Hinged clamp assemblies are the most commonly used method for making ISO KF vacuum seal connections. Prior to clamping, flanges can be rotated 360° and accept self-centering ring seals. Pressure is applied uniformly around the 15°outer surface of both flanges by finger-tightening. The single wing nut until the first metal-to-metal contact is made between the spacing lips of the centering ring and the inner surface of the mating flanges. This compresses the O-ring between the flanges and makes the vacuum seal.

Centering rings

Centering ring assemblies are placed between two ISO flanges with matching outer diameters. The widest portion of the centering ring rests inside a capture groove on the flange and the O-ring rests on the flat polished surface outside the capture groove. On a blank flange, the groove seen on the face of a flange is the capture groove, with the O-ring making contact with this flange face just outside the groove.

Features

• Fastens ISO KF of comparable size
• Quick make and break
• Stainless steel wing nut and bolt
• SS304 construction
• Requires centering ring with elastomer gasket.

Way forward in drying

Usage for drying operations will rise as the demand for energy efficient, faster, environmentally friendly and cost effective drying technologies continue to increase worldwide.