Plate fin exchangers that are subjected to thermal stress due to steep temperature gradients often fail at the brazed joints. Thermal cycling will do the same thing over time. The style of heat exchanger that is appropriate for this service is highly dependent upon the details of the process gases to which you refer and the pressure drop that can be tolerated. Basic choices include shell and tube, plate, spiral and finned economizer bundles — vendors for these styles of exchangers can be found with a simple web search or by utilizing a manufacturers list such as Thomas Register (American Manufacturers). Other resources for heat exchanger design include “Process Heat Transfer” by Hewitt, Shires and Bott; “Heat Exchangers Selection, Rating and Thermal Design” by Kakac and Liu.