Inefficient heat transfer is often the cause for loss of capacity and unscheduled outage.
As mentioned in a previous article, surfaces through which heat passes are called heat transfer surfaces. One example of this is cooling water tube bundles, which take heat from process liquids, hot water or steam. The points at which the heat transfers to the cooling water are the heat transfer surfaces. The transfer in a cooling water system usually takes place in equipment call the heat exchanger.
Heat transfer takes place in the boiler where hot gases from the combustion of fuel transmit levels of intense heat through the boiler tubes to produce steam.
The build-up of any adherent material – scale, corrosion products or micro-organisms – on heat transfer surfaces slows down the exchange of heat.
Poor heat transfer has several effects:
First of all, system capacity is reduced. A 5% reduction in heat transfer means that the plant can achieve only 95% of its potential output. With a cooling system, for example, production lines are slowed down to obtain the required cooling.
There may be an increase in energy consumption. Using the cooling system example again, as a remedial step the plant operator may increase cooling water flow rates. Pumping costs increase because water must be circulated more rapidly in an attempt to restore cooling efficiency. In steam generating systems, as another example, more fuel must be consumed to convert water to steam.
Overheating may cause failure of tubes and other system components. As previously mentioned, this necessitates immediate shutdown of the equipment and repair work. There is also a potential for injury to personnel working in the area of a failure.
In all cases, production costs rise.
As you can see it is important to ensure efficient heat transfer processes and all these factors mentioned above should be kept in mind.