Method and apparatus for reducing NO.sub.x emissions in industrial thermal processes
AssigneeSouthern California Gas Company
InventorKlaus H. Hemsath
Life of this patent
Estimating the term…
Abstract
Nitrous oxide emissions are reduced in an industrial thermal process and system which operates a gas fired burner at substantially sub-stoichiometric conditions to produce products of combustion rich in combustibles and control flame temperatures at temperatures which do not exceed predetermined levels. Completion air at stoichiometric proportions is subsequently employed to burn the combustibles. Regenerative and recuperative means to cool gases after each partial combustion step are used to extract heat and use is in conventional heating processes. A novel regenerative heat exchange system is used to extract heat from the gases so that the gases never exceed a temperature whereat nitrous oxide formation tends to occur.
Claims20
An industrial thermal process for heating work with reduced NO.sub.x emissions comprising the following sequential steps:
- a) combusting a gaseous fuel with combustion air at a sub-stoichiometric ratio which is sufficient to generate a reducing atmosphere having products of combustion rich in hydrogen and carbon monoxide combustibles,
- b) while immediately cooling the atmosphere to a predetermined temperature by passing same through a tortuous heat treat path wherein removed heat is used to heat work and wherein oxygen in said atmosphere continues to react with said products of combustion to produce an atmosphere substantially free of NO.sub.x, and
- c) thereafter adding completion air to said reducing atmosphere which is sufficient to combust said hydrogen and carbon monoxide combustibles while continuously controlling the temperature of said gaseous products by regulating the rate at which said gases receive said completion air to be below said predetermined temperature whereat NO.sub.x tends to occur.
An industrial thermal process for heating work with reduced NO.sub.x emissions comprising the following sequential steps:
- a) combusting a gaseous fuel with combustion air at a sub-stoichiometric ratio which is sufficient to generate a reducing atmosphere rich in hydrogen and carbon monoxide combustibles;
- b) removing a portion of the heat generated in step (a);
- c) adding completion air to said reducing atmosphere which is sufficient to combust said hydrogen and carbon monoxide combustibles, while controlling the temperature of said gaseous products in steps (b) and (c) to be below a predetermined temperature whereat NO.sub.x tends to occur;
- d) directly contacting said gases with cool objects to effect heat transfer therewith to control the gas temperature by providing a plurality of heat transfer objects rolling within a sealed, closed loop track, said track arranged so that a first portion thereof extends within a sealed furnace in heat transfer relationship with work disposed therein and a second portion thereof is insulatedly removed from said first portion, said second portion having a first segment adjacent the point where said objects enter the first track portion in said furnace enclosure and a second segment contiguous with said first segment and adjacent the point where said objects leave said first track portion in said furnace enclosure;
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- e) performing steps a-d in said second track portion and reducing the temperature of said objects by indirect heat transfer to the work in said first track portion.
A thermal system for heating work to a predetermined temperature comprising:
- a) a furnace having a sealed furnace enclosure in which work to be heated is placed;
- b) a casing having an uninsulated first portion extending within said furnace enclosure and a second portion insulated from said furnace enclosure, said casing defining a continuous, sealed closed loop track extending through said first and second portions each of which is defined by an entry point and an exit point and arranged so that the entry point of one portion is adjacent the exit point of the other portion;
- c) a plurality of heat transfer objects within said track and means for moving said objects about said track from said entry to said exit points of said portions;
- d) burner means generally adjacent said exit point of said second portion for firing products of combustion from said exit point towards said entry point of said second portion;
- e) burner regulator means controlling the ratio of fuel and combustion air to said burner means to assure substoichiometric combustion of said burner means to produce products of combustion having hydrogen and carbon monoxide as elements thereof;
- f) completion air means intermediate said exit and entry points of said second portion for supplying combustion air in stoichiometric proportion at controlled flow rates to assure combustion of said hydrogen and carbon monoxide whereby said objects are heated in said second portion from contact with said products of combustion and cooled in said first portion from said work while the temperature of said products of combustion are controlled by contact with said objects to assure that said products of combustion do not exceed a predetermined temperature to minimize formation of NO.sub.x emissions.
An industrial process for generating a heated gas with minimal NO.sub.x content for heating work comprising the steps of:
- a) combusting natural gas with combustion air at substoichiometric proportions sufficient to generate a reducing atmosphere having products of combustion rich in hydrogen and carbon monoxide combustibles;
- b) immediately cooling said atmosphere to a first predetermined temperature by directly contacting said atmosphere with cool objects providing a tortuous flow path to establish a sufficient reaction time whereby said products of combustion continue to react with oxygen to produce an atmosphere rich in combustibles with substantially no NO.sub.x, and
- c) thereafter adding completion air to said reducing atmosphere sufficient to combust said hydrogen and carbon monoxide combustibles while continuously controlling the temperature at a second predetermined temperature and the rate of flow of said completion air to minimize the formation of NO.sub.x.
Dependencies are inferred from the claim text.