THE APPLICATION OF A VARIABLE-AREA JET PUMP TO THE EXTERNAL RECIRCULATION OF HOT FLUE-GASES

A jet pump of special design, having a variable-geometry nozzle, is ap plied to the external recirculation of flue gas in a furnace system. T his new concept improves reliability by eliminating the need for a flu e-gas fan, and enables the recycle of high-temperature gas to be effec ted. Recycle is induced by simply increasing the main air supply press ure by a reasonably modest amount, while the nozzle area of the jet pu mp is reduced by the progressive insertion of a co-axial spear. Detail s are given of the jet pump design. A model of its operating character istics is given, which modifies standard incompressible-flow jet-pump theory such that it can be applied to the large nozzle : mixing-tube a rea ratio designs required for this application. The model is used to predict the jet pump's operating characteristics and the potential per formance envelope of a flue-gas recirculation system. It is demonstrat ed that the amount of hot flue gas that can be recycled rises with ava ilable air-supply pressure but varies inversely with the recycle gas t emperature. Results are given for experiments conducted with two jet p umps, including the use bf hot air and helium to obtain data at variou s density ratios. The results agree well with the proposed model, and confirm the proposed operation of the flue-gas recycle system.