Indirect fluid heater

A heater for heating a flow of a first gas, comprising:

• a vessel containing a heat transfer fluid;
• a heat source tube passing through the vessel and being at least partially immersed in the heat transfer fluid, the heat source tube being suppliable with a heated second gas, the heat source tube configured to allow the heated second gas to flow along and inside the heat source tube to evaporate the heat transfer fluid;
• and
• at least one heat exchanger connectable to a source of the first gas, the at least one heat exchanger arranged so that the first gas can be heated by the evaporated heat transfer fluid,
• wherein the at least one heat exchanger comprises at least one heat transfer tube connectable to the source of the first gas so that the first gas is directed to flow inside the at least one heat transfer tube, the at least one heat transfer tube being arranged to be heated by the evaporated heat transfer fluid,
• wherein the heater further comprises a burner to supply the heated second gas to the heat source tube, and a control system for controlling a vessel pressure of the vessel and a fluid temperature of the heat transfer fluid, the control system configured to operate the vessel with the fluid temperature in a range of 40° C. to 90° C. and with the vessel pressure in an absolute pressure range of 50 mbar to 340 mbar, the control system comprising a digital controller incorporating a thermo-controller,
• wherein the vessel is an evaporator vessel, the at least one heat exchanger further comprising a condenser vessel in fluid communication with the evaporator vessel via a piping circuit to allow the heat transfer fluid to flow between the evaporator vessel and the condenser vessel in the piping circuit, the at least one heat transfer tube passing through the condenser vessel of the at least one heat exchanger, the evaporator vessel, the condenser vessel, and the at least one heat transfer tube together comprising a sealed fluid system operating under vacuum with the vessel pressure in the absolute pressure range of 50 mbar to 340 mbar, the sealed fluid system employing a fixed mass of the heat transfer fluid held under vacuum in the absolute pressure range of 50 mbar to 340 mbar,
• wherein the heat source tube has an inlet where the heat source tube enters the evaporator vessel from the burner and an outlet where the heat source tube leaves the evaporator vessel, and the heat source tube is tapered along a length of the heat source tube located within the evaporator vessel in a direction from the inlet to the outlet, the heat source tube including at least two straight sections and at least one curved section, the heat source tube defining a sinuous path, the tapering of the heat source tube decreasing a surface area of the heat source tube thereby promoting compactness of the heat source tube.

A heater for heating a flow of a first fluid, comprising:

• a vessel containing a heat transfer fluid;
• a heat source tube passing through the vessel and being at least partially immersed in the heat transfer fluid, the heat source tube being suppliable with a heated gas, the heat source tube configured to allow the heated gas to flow along and inside the heat source tube to evaporate the heat transfer fluid;
• and
• at least one heat exchanger connectable to a source of the first fluid, the at least one heat exchanger arranged so that the first fluid can be heated by the evaporated heat transfer fluid,
• wherein the at least one heat exchanger comprises at least one heat transfer tube connectable to the source of the first fluid so that the at least one heat transfer tube is configured such that an entirety of the first fluid received from the source of the first fluid is directed to flow inside the at least one heat transfer tube and through the at least one heat exchanger, the at least one heat transfer tube arranged to be heated by the evaporated heat transfer fluid,
• wherein the heater further comprises a burner to supply the heated gas to the heat source tube, and a control system for controlling a vessel pressure in the vessel and a fluid temperature of the heat transfer fluid, the control system configured to operate the vessel with a vessel temperature in a range of 40° C. to 90° C. and with the vessel pressure in an absolute pressure range of 50 mbar to 340 mbar, the control system comprising a digital controller incorporating a thermo-controller,
• wherein the vessel is an evaporator vessel, the at least one heat exchanger further comprising a condenser vessel in fluid communication with the evaporator vessel via a piping circuit to allow the heat transfer fluid to flow between the evaporator vessel and the condenser vessel in the piping circuit, and the at least one heat transfer tube passing through the condenser vessel of the at least one heat exchanger, the evaporator vessel, the condenser vessel, and the at least one heat transfer tube together comprising a sealed fluid system operating under vacuum with the vessel pressure in the absolute pressure range of 50 mbar to 340 mbar, the sealed fluid system employing a fixed mass of the heat transfer fluid held under vacuum in the absolute pressure range of 50 mbar to 340 mbar,
• wherein one or more temperature sensors are provided to measure a temperature of the first fluid after it has passed through the heat transfer tube, or after it has passed through the heat transfer tube and undergone pressure let-down or to measure the temperature of the heat transfer fluid in the vessel or condenser vessel, and wherein the control system is further configured to control a circulation rate of the heated gas based on an output of one or more of the temperature sensors.