The choice of process heating technology is a tradeoff of first cost, operating cost, maintenance and maintainability, control, emissions, and product quality. While fossil fuels have been the traditional choice for steam and water heating, electric heaters and boilers are gaining popularity for providing hot water or steam, as well as direct process use. The advantages are that they can be positioned right at the point of use and thereby eliminate fuel handling and storage concerns, reduce or even eliminate the concerns over fires, and eliminates the need for the flue or exhaust fan for products of combustion. In some cases, the environmental restrictions on the site can also be solved by switching from fossil fuels to electric technologies.
The most common types of electric processing are simple resistance heaters, similar to the elements in your home oven or toaster. There are also electric infrared, dielectric (e.g., microwave), and induction devices. The induction heaters have gained widespread appeal in the billet heater applications since they have the advantage of uniformly heating a piece of material across the entire cross section. Induction and infrared are also widely used where selectively heating only precise areas or depths of the materials is needed.
Electric devices can also be used for heat recovery. Heat wheels and run-around systems are used for recovering waste heat from exhaust streams to be used to warm incoming air. The run-around system can also be used for preheating process water. And, the industrial heat pump can recover waste heat from either the exhaust stream, the plant's liquid effluent or the plant cooling water. Depending on the temperature of the water delivered and the temperature of the heat source, the economics of this device can be extremely attractive since the heat recovered is much less costly than the normal heat supply.
Much of the energy for hot water processes such as cleaning and plating, is used to replace losses from the tank. Tank losses through the wall can be reduced with appropriate insulation. Losses from the surface can be reduced by a layer of plastic balls floating on the surface.
