Patent ID: 6910878

Claim:
A method of heating a fluid, comprising: (A) providing a heater comprising: (i) a chamber having an outlet for combustion gases produced in said chamber, (ii) at least one fuel nozzle for feeding fuel into said chamber, and proximal nozzle means for feeding oxidant gas proximal to said at least one fuel nozzle to stabilize the flame formed by combustion of the fuel as it emerges from said at least one fuel nozzle, (iii) means for feeding fuel to said at least one fuel nozzle, (iv) means for feeding oxidant gas to said proximal nozzle means, and (v) a conduit at least a portion of which is located within a region of said chamber so that its outer surface is heated by radiation of heat generated by combustion of said fuel within said chamber, said conduit having an inlet end outside said chamber for receiving fluid and an outlet end outside said chamber for discharging fluid outside said chamber, (B) feeding fuel through said at least one fuel nozzle into said chamber and feeding oxidant gas through said proximal nozzle means so as to stabilize the flame formed by combustion of the fuel as it emerges from said at least one fuel nozzle, while feeding oxidant gas into said chamber from a source thereof through a plurality of oxidant gas nozzles spaced further than said proximal nozzle means from said at least one fuel nozzle, and (C) combusting said fuel in said chamber with the oxidant gas fed through said proximal nozzle means and said oxidant gas nozzles, wherein the orientation of the axis of each oxidant gas nozzle with respect to the axis of the at least one fuel nozzle, the aggregate cross-sectional area of said oxidant gas nozzles, and the velocity of the oxidant gas fed through said oxidant gas nozzles, are effective to promote circulation within said chamber of combustion gases produced by combustion of said fuel with said oxidant gas and to provide that the ratio of the peak heat flux to the average heat flux to said conduit in said region during said combustion is lower than said ratio when the same fuel is combusted to obtain the same absorbed duty in the heater provided in step (A) but using only air as the oxidant gas.