Heat exchange system and method

A method of controlling a fluid flow towards a control valve in a heat exchange system for heating a first fluid by means of a second fluid, said heat exchange system comprising:

• a first fluid circuit comprising an upstream end, a downstream end and an intermediate portion therebetween, said first fluid circuit being for allowing the first fluid to flow from said first fluid circuit upstream end to said first fluid circuit downstream end;
• a second fluid circuit comprising an upstream end, a downstream end and an intermediate portion therebetween, said second fluid circuit for allowing the second fluid to flow from said second fluid circuit upstream end to said second fluid circuit downstream end;
• a flooded heat exchanger wherein said intermediate portions of said first and second fluid circuits are in adjacent, thermally-conductive contact for allowing heat transfer from the second fluid to the first fluid;
• and
• the control valve being provided on said second fluid circuit downstream of said flooded heat exchanger, for controlling a flow rate of the second fluid through said second fluid circuit, whereby said flooded heat exchanger is capable of being flooded in an adjustable proportion within said second fluid circuit intermediate portion to adjust the heat transfer rate from said second fluid to said first fluid;
• said method comprising the steps of:
• providing a steam detection device comprising at least one temperature sensor and associated signal output circuitry configured to generate a signal indicative of vapor-phase steam presence and connected to said second fluid circuit downstream of said flooded heat exchanger, for detecting if steam is present in said second fluid circuit downstream of said flooded heat exchanger;
• providing a fail-closed/normally closed valve on said second fluid circuit downstream of said flooded heat exchanger, said fail-closed/normally closed valve having an opened condition where it allows fluid flow to said circuit control valve, and a closed condition where it blocks fluid flow to said control valve;
• continuously forcing said fail-closed/normally closed valve into its closed condition with a normally closed mechanism;
• providing a fail-closed/normally closed valve actuator that controls said fail-closed/normally closed valve between said opened and closed conditions;
• maintaining, with said fail-closed/normally closed valve actuator, said fail-closed/normally closed valve in its opened condition under normal heat exchange operating conditions of said heat exchange system against the action of said normal closed mechanism;
• and
• if steam is detected in said second fluid circuit at the position of said steam detection device by said steam detection device, ceasing to maintain said fail-closed/normally closed valve in said opened condition with said fail-closed/normally closed valve actuator to switch said fail-closed/normally closed valve to its closed condition to shut off fluid flow towards said second fluid circuit downstream end.

A heat exchange system comprising:

• a flooded heat exchanger where a first fluid in a first fluid circuit is heated by a second fluid in a second fluid circuit;
• a control valve at a downstream end of said flooded heat exchanger on said second fluid circuit;
• a steam detection device comprising at least one temperature sensor and associated signal output circuitry configured to generate a signal indicative of vapor-phase steam presence and connected to said second fluid circuit downstream of said heat exchanger;
• a fail-closed/normally closed valve located on said second fluid circuit downstream of said flooded heat exchanger, said fail closed/normally closed valve have opened and closed conditions and comprising a normally closed mechanism continuously biasing said fail closed/normally closed valve towards said closed condition;
• and
• a fail-closed/normally closed valve actuator that controls said fail-closed/normally closed valve to maintain it in its opened condition against action of said normally closed mechanism;
• wherein if steam is detected in said second fluid circuit downstream of said flooded heat exchanger, said fail-closed/normally closed valve actuator will switch said fail closed/normally closed valve to its closed condition to shut off fluid flow to said control valve.