Abstract: This invention makes an optimal control of an air separator for any set value of a product quantity by inputting a necessary product quantity, calculating a minimum necessary raw air quantity by use of the capacity of the air separator and its operating condition and using this quantity as a set value for a raw air quantity adjustment loop.

Abstract: A method for the temperature balancing control of a plurality of heat exchangers wherein, in case of operating the heat exchangers connected in parallel, the temperatures of a medium to-be-heated on the outlet sides of the respective heat exchangers are balanced. According to the method, the temperatures of the same positions of the heat exchangers except for the inlets thereof for the medium to-be-heated are sensed, the respective sensed values are compared with a temperature setting value so as to calculate control signals, all the control signals are subsequently revised so that the maximum value among the control signals may agree with a preset control reference value, and temperature regulation means disposed for the respective heat exchangers are controlled on the basis of the revised control signals.

Abstract: A gas liquefying system of the type in which a compressed gas is divided into a part which is to be used for the generation of cold heat and a part which is to be liquefied, the part of the gas for generation of cold heat being introduced into a high-pressure expansion turbine to generate the cold heat and, after an adjustment of the temperature thereof at the outlet of the high-pressure expansion turbine, supplied to a low-pressure expansion turbine to further generate the cold heat while becoming the returning gas of a low temperature, the returning gas being supplied to a liquefier to liquefy the part of gas to be liquefied.

Abstract: A temperature control method for a reversing type heat exchanger group wherein an outlet temperature of reheating gas of an arbitrarily selected reversing type heat exchanger which serves as a reference in the reversing heat exchanger group is rendered equal in value to a reference control temperature set beforehand in such a manner so as to satisfy the sweeping temperature difference. The outlet temperatures of the reheating gas in the other reversing type heat exchangers of the reversing type heat exchanger group are rendered equal in value to the outlet temperature of the reheating gas in the reversing type heat exchanger serving as the reference. Thus, the temperature of the cold end of all of the reversing type heat exchangers of the reversing type heat exchanger group are caused to be balanced equally whereby ice and dry ice deposited on the feed water channels can be effectively removed by a sweeping action.