there is disclosed a system for measuring and controlling the concentration of hydrogen in hydrogen recycle processes used in oil refineries and petrochemical plants . the system is intended to reduce the amount of hydrogen and hydrocarbon vapor circulating in such systems , thus reducing the quantity of utilities needed to operate such systems . specifically , there is a savings of compressor power and fuel required for heating . the system is dependent on the recognition that a decrease in cooling medium temperature results in an increase in hydrogen flow , which can be decreased to the minimum permissible without endangering catalyst activity and stability and product yield if hydrogen concentration is monitored , and that partial pressure is the key parameter .