Waste heat recovery system

A waste heat recovery apparatus installed in a processing system, the latter having of an exhaust stack through which exhaust gases are discharged, and a recipient fluid which can be beneficially heated at a point remote from said exhaust stack, said waste heat recovery system comprising:

• (a) a first heat exchanger disposed within said exhaust stack such that said exhaust gases flow across its surfaces;
• (b) a second heat exchanger disposed at said point remote from said exhaust stack such that said recipient fluid flows across its surfaces, the inlet of said second heat exchanger being in communication with the outlet of said first heat exchanger and the outlet of said second heat exchanger being in communication with the inlet of said first heat exchanger through conduit means, so as to define a closed flow circuit;
• (c) a heat transfer fluid adapted to circulate within said closed flow circuit;
• (d) a reservoir for storing said heat transfer fluid in communication with said closed flow circuit;
• (e) means for forcing said heat transfer fluid to circulate through said closed flow circuit, said forcing means being disposed serially within said closed flow circuit;
• (f) means for controlling the temperature of said heat transfer fluid at at least two critical points within said closed flow circuit, said temperature control means being coupled thereto and comprising:
• (i) at least two temperature transducers, each located at a point which the temperature of said heat transfer fluid is critical;
• (ii) a temperature controller responsive to an out-of-balance condition due to a change in the desired temperature of said fluid at any of said critical points, said temperature controller being electrically coupled to said transducers and adapted to output an electrical control signal when said out-of-balance condition is detected;
• and (iii) a solenoid operated temperature control valve disposed serially in said closed flow circuit, the position of said valve determining the rate of flow of said heat transfer fluid therein, said solenoid being electrically coupled to the output of said controller so that the position of said valve is controlled by said control signal;
• (g) means for controlling the pressure of said fluid, said pressure control means being in communication with said closed flow circuit and comprising:
• (i) a by-pass flow circuit comprising conduit means coupled between the inlet of said second heat exchanger and said reservoir;
• (ii) a solenoid-operated pressure control valve disposed serially in said by-pass flow circuit, the position of said valve determining the rate of flow of said heat transfer fluid therein;
• and (iii) a pressure transducer located at a point within said by-pass flow circuit, said pressure transducer being adapted to output a second electrical control signal responsive to the pressure detected, said second control signal being electrically coupled to said solenoid;
• whereby, said heat transfer fluid absorbs waste heat from said exhaust gases as they pass through said first heat exchanger and releases said recovered waste heat to said recipient fluid as it passes through said second heat exchanger, the temperatures of said fluid at said critical points being maintained substantially within their desired ranges by said temperature controller and temperature valve adjusting the rate of flow of said fluid;
• and said temperature control valve adjusting the rate of flow of said fluid;
• and the pressure of said fluid being maintained substantially within its desired range by said pressure transducer and pressure control valve adjusting the rate of flow of said fluid through said by-pass flow circuit.