(95e) Spiral Flow Heat Exchanger for Heat Recovery from Gases

In process industry the recovery of heat from flue gases or from process gases is desirabal. In number of processes the gas temperature need to be reduced for the downstream processing or to recover the heat. The conventional shell and tube heat exchangers are installed for the heat recoery. The heat transfer efficiency achived in the gas cooling is lower due to the inherent limitation of flow of gases in tube. In order to enhance the heat transfer the inserts are provided in the tube such as spiral cord across the length of tube. The tube inside surface may be corrougated , internal fins provided as techques to enhance the heat transfer. All such techniques result in additional pressure drop in heat exchanger.

The spral tube heat exchanger is a concept in which the tube is made in Horizantal spiral coil, The coil is in single plane. Such coils are connected with Inlet and oulet header through wich tthe water or pocess fluid is allowed to flow. Due to the spiral geomerty of the tude the direction of fluid flow changes resulting in local turbulance. On gas side these coils ae inseted perpendicular to gas flow resulting in bracking the boundary layer in Gas side and also creating the local turbulance. The net result is higher rate in heat transfer. The heat transfer enhancement to the order of 2 to 2.5 times.

The above principal of heat recovery being studied. The five horizal spiral coils of 1.2 meter tube lenth 10 mm O.D. are prepared. The distance between the spiral tube is maintained as 3D. The inlet and outlet of tubes being connected with header. The comple assmbly is made in a sheell of dia 150 mm. The total length accomadetd is 6 met in heat exchanger of size 200 mm x200mmx250mmlong. The water at ambient temperature is allowued to flow through the tube. The Heat exchange is installed in flue gas exhost of Deselgenerating set of 70 KVA. The flue gas temperaure is redused from 450 deg centegrade to 280 degree cenegrade. There is corresponding rise in temperature of water.

The construction is modular, the tube material can be seleced sompitabal with gas and process fluid. The construction is simple. The heat extraction is rae is higher.

Key word : spiral heat exchanger , heat recovery ,hot gases.