Problem: heat load increases and temperature uniformity decreases in the area of process openings for both indexing (Fig. 1) and continuous equipment (Fig. 2)
Causes: Equipment typically maintained with slight negative to contain process fumes and POC from direct fired heating systems.
Solution: Cross between non-recirculating and recirculating air curtain.
A curtain of air to prevent flow exchange across the process opening. This would use tempered air from a separate fan that supplies air from across a heat exchanger of the system exhaust for energy recovery. The heating of the curtain would help reduce the affect of the air blown across the opening, cooling the internal section of the process just inside the opening. Internal air is not good to use for the curtain since it can include what needs to be contained, and exhausted in the equipment. Also the supply pressure of the equipment typically does not provide for adequate velocities for a good curtain. A separate supply fan would provide the needed velocity to prevent the buoyant exchange across the opening. The curtain flow across the opening would be captured by a collection duct just inside the opening. It would be ducted to the system combustion air source and make up air opening and not recirculated to the curtain supply fan. This would provide for the exchange flow across the opening that is due to the equipment running with a negative pressure (to prevent escape of fumes off the process and also POC). Since this exchange flow from the curtain is captured just below the opening it reduces the temperature effects of the air being brought into the equipment. Since it is tempered from the heat exchanger across the exhaust it would provide an energy savings to the system by recovering exhaust heat and returning it to the make up/combustion air source.