CONDENSERS

Description

Condensers are used to remove high concentrations of solvents from gas streams. The cleaned gas may then be recycled, vented to the atmosphere or passed to the next treatment stage. The solvents are concentrated in liquid form and, as such, are suitable for recycling, incineration or disposal.

Condensers are appropriate for solvents with dewpoints between 0 C and -50 C and can be operated continuously or in an intermittent fashion.

There are five main types of condenser - direct-contact, surface, air-cooled, pressurised and cryogenic.

Direct contact condensers provide the least expensive and simplest form of condensation. The gas stream to be treated is brought into direct contact with a spray of cooling fluid. Direct contact condensers are preferred where the condensate is particularly sticky or gummy and would easily foul a surface.

In a surface condenser the exhaust air is passed through a chilled region where the condensible material drips down into a collector.

Air-cooled condensers consist of tubes with fins attached to the outer wall. The fins create a large surface area to encourage heat loss. The gas is passed through the central tube where the condensation takes place.

Pressurised condensers compress the gas before cooling. Sudden cooling on exiting the pressurised region via a nozzle achieves efficient, but expensive, condensation.

In cryogenic condensation, the gas is bubbled through a reservoir of cooled solvent. Differences in the density of ice, the condensate and the solvent allow each fraction to be separated in the reservoir.

Application

Typical applications for condensers arise in the semiconductor, chemical, fertiliser, drying, printing, coating and food industries. Condensers are convenient methods for simultaneously removing contaminants from the gas phase and quenching steam and are often the first stage in an air cleaning system.

Sizing

A typical condenser treating a gas flow of about 20,000 m3/hour would have a 75 kW heat exchanger with a 5 kW recirculation pump. Condensers can handle flows of up to 120,000 m3/hour. A typical cryogenic condenser would have an power requirement of 45 kW.