Industrial Cross Flow Heat Exchangers are used for transferring heat between two gas streams or between a liquid and a gas. Typical examples include stack gas heat recovery as in Waste Heat Recovery Units (WHRU), combustion air preheating and the heating of process fluids.
We have supplied cross flow heat exchangers into a wide wide range of industries ranging the from the heating vegetable oils in the food industry to the vaporising of gases and the heating and cooling of process gases.
In the usual configuration, the hot gas flows over the tubes, taking advantage of the good heat transfer and low pressure drop that this affords. The coolant, either gas or liquid, then passes through the tubes.
We do not have many limitations on the maximum temperature that can be achieved, provided that the hot gas has a high enough temperature. Our main limitations are that we must keep the metal temperatures higher than the dew point of the hot gas and that materials must be chosen for both corrosion resistance and strength at the temperatures involved.
Is the heat source located close to your demand for heat? If it is, then the most economic way may be to mount a cross flow heat exchanger in the hot gas stream, with the fluid to be heated going through the tubes. If not, then you may have to transfer the heat to an intermediate fluid to transport the heat to its destination. In this case the hot gas is used to heat up fluids such as thermal oils, pressurised water or may be used to generate steam.
Having cooled the gas, will a blower be needed to discharge the gasses, as the flue no longer produces natural convection due to the hot gas in it? It is a big and important area where we are able to help both in planning and the manufacture of heat exchangers to perform the duty.
A counter current cross flow heat exchanger can, in theory, achieve 100% efficiency. For example, an ambient air stream could be used to recover heat from a hot gas stream, taking the hot gas stream down close to the temperature of the ambient air. In practice, the size of the unit starts to increase significantly as the outlet temperature on one side approaches the inlet temperature on the other. Additionally, if the hot stream is not dry, as in stack gas, once you reduce the stream below its dew point, a large quantity of water, possibly acidic, will start to condense out.
All is not lost though. If you have a use for low grade heat or are able to put it back into the process, we can achieve solutions to achieve that high efficiency.