System for optimal pressure control in a multi-stage evaporation unit

Claim 2

IN A SYSTEM FOR OPTIMAL PRESSURE CONTROL IN A MULTISTAGE EVAPORATION UNIT HAVING AT LEAST TWO SERIES CONNECTED FIRST AND FINAL EVAPORATORS, THE IMPROVEMENT COMPRISING: A. THE FIRST EVAPORATOR BEING PRECEDED BY FIRST AND SECOND HEAT EXCHANGES, B. SAID FINAL EVAPORATOR BEING A HIGHER-PRESSURE EVAPORATOR RELATIVE TO SAID FIRST EVAPORATOR, C. BOTH SAID FIRST AND SECOND HEAT EXCHANGERS COMPRISE SHELL-AND-TUBE HEAT EXCHANGERS, FOR RECEIVING THE VAPOR EFFLUENT LEAVING SAID HIGHER-PRESSURE EVAPORATOR, D. SUPPLY LINE MEANS FOR PASSING FRESH FEED SOLUTION THROUGH SAID TWO HEAT EXCHANGERS IN WHICH THEY ARE HEATED BY THE VAPOR EFFLUENT FROM SAID FINAL HIGH PRESSURE EVAPORATOR E. THE SHELL PORTION OF SAID SECOND HEAT EXCHANGER RECEIVES THE VAOR EFFLUENT FIRST, F. THE TUBE PORTION OF SAID FIRST HEAT EXCHANGER RECEIVING VAPOR CONDENSATE FROM SAID SECOND HEAT EXCHANGER, G. A THIRD SHELL-AND-TUBE HEAT EXCHANGER IS CONNECTED IN SAID FRESH FEED SOLUTION SUPPLY LINE MEANS IN SERIES WITH SAID FIRST AND SECOND HEAT EXCHAGERS. H. SAID FRESH FEED SOLUTION SUPPLY LINE MEANS BEING CONNECTED TO THE TUBES OF SAID THIRD SHELL-AND-TUBE HEAT EXCHANGER, AND I. A VAPOR EFFLUENT LINE EXTENDING FROM SAID LOW PRESSURE EVAPORATOR TO THE SHELL OF SAID THIRD SHELL-AND-TUBE HEAT EXCHANGER FOR MORE EFFICIENT HEATING OF SAID FRESH FEED SOLUTION AND CONDENSING OF THE VAPORS FROM THE LOW PRESSURE EVAPORATOR.

Claim 3

A pressure control system for a multistage evaporator unit having low and high pressure series-connected evaporators and pump means for drawing liquid solution from the low pressure evaporator to the high pressure evaporator comprising, a. fresh liquid feed solution supply line means for the low pressure evaporator, b. first and second heat exchanger means connected in series in said fresh liquid feed solution supply line means, c. high pressure vapor line means from the high pressure evaporator to a condensate tank, said high pressure vapor line means being first connected to said second heat exchanger means, d. said high pressure vapor line means extending from said second heat exchanger means to said first heat exchanger means before continuing to said condensate tank, a vapor effluent being passed through said high pressure vapor line means, e. said second heat exchanger means being a tube-and-shell heat exchanger means in communication with said high pressure vapor line means for heating said fresh liquid solution for the low pressure evaporator and for supplying condensate and the remaining vaporous portion to said first heat exchanger means, and f. said first heat exchanger means being a shell-and-tube heat exchanger means in communication with said high pressure vapor line means for generating additional condensate for increasing resistance to flow in said first heat exchanger means for maintaining pressure in said high pressure vapor line means to accordingly eliminate the requirement for a control valve and to increase the temperature of the fresh liquid feed to said low pressure evaporator for increased efficiency.

Claim 4

A pressure control system for a multistage evaporator unit having low and high pressure series-connected evaporators and pump means for drawing liquid solution from the low pressure evaporator to the high pressure evaporator comprising, a. fresh liquid feed solution supply line means for the low pressure evaporator, b. first and second heat exchanger means connected in series in said fresh liquid feed solution supply line means, c. high pressure vapor line means from the high pressure evaporator to a condensate tank, said high pressure vapor line means being first connected to said second heat exchanger means, d. said high pressure vapor line means extending from said second heat exchanger means to said first heat exchanger means before continuing to said condensate tank, a vapor effluent being passed through said high pressure vapor line means, e. said second heat exchanger means being a tube-and-shell heat exchanger means in communication with said high pressure vapor line means for heating said fresh liquid solution for the low pressure evaporator and for supplying condensate and the remaining vaporous portion to said first heat exchanger means, and f. said first heat exchanger means being a shell-and-tube heat exchanger means in communication with said high pressure vapor line means for generating additional condensate for increasing resistance to flow in said first heat exchanger means for maintaining pressure in said high pressure vapor line means to accordingly eliminate the requirement for a control valve and to increase the temperature of the fresh liquid feed to said low pressure evaporator for increased efficiency.