Combustion method and installation with optimized energy recuperation

Abstract

Combustion method and installation in which an oxygen-rich oxidant is preheated by exchange of heat with a heat-transfer fluid, upstream of the combustion chamber, in which method and installation an auxiliary gas is heated by heat exchange with a first proportion of the hot flue gases discharged from the chamber, and in which method and installation the heat-transfer fluid comprises a mixture of at least a proportion of the heated auxiliary gas with a proportion of hot flue gases.

Claims

1. A process for the combustion, in a combustion chamber, of a fuel with a preheated oxygen-rich oxidant with generation of heat and hot flue gases inside said combustion chamber, wherein the process comprises the steps of: discharging the hot flue gases from the combustion chamber, wherein the resulting discharged flue gases contain residual heat; recovering residual heat by heating an auxiliary gas by heat exchange with at least a part of the discharged hot flue gases in an auxiliary heat exchanger, with a hot auxiliary gas and tempered flue gases being obtained, introducing at least a first part of the hot auxiliary gas into a main exchanger in which oxygen-rich oxidant is preheated by heat exchange with a first heat-exchange gas comprising said at least a first part of the hot auxiliary gas, with a preheated oxidant and a tempered heat-exchange gas being obtained; and supplying the preheated oxygen-rich oxidant to the combustion chamber for the combustion of the fuel, wherein a portion of the discharged hot flue gases is not introduced into the auxiliary exchanger and is instead mixed with said at least a first part of the hot auxiliary gas before it is introduced into the main exchanger in order to increase the thermal energy content of the first heat-exchange gas.

2. The process as claimed in claim 1, wherein the first heat-exchange gas consists of a mixture of hot auxiliary gas and the portion of the discharged hot flue gases.

3. The process as claimed in claim 1, wherein the auxiliary gas is a predominantly inert gas, preferably chosen from steam, CO.sub.2 and the mixtures of these two gases.

4. The process as claimed in claim 1, wherein the auxiliary gas is chosen from air or a mixture of air with a predominantly inert gas.

5. The process as claimed in claim 1, wherein the content of discharged hot flue gases of the first heat-exchange gas is less than or equal to 30 vol %.

6. The process as claimed in claim 1, wherein the ratio by volume of, on the one hand, discharged hot flue gases to, on the other hand, the first hot auxiliary gas in the first heat-exchange gas is less than or equal to 45 vol %.

7. The process as claimed in claim 1, wherein the combustion chamber is a melting chamber, a refining chamber, a melting/refining chamber or a combustion chamber of a boiler.

8. The process as claimed in claim 7, wherein the combustion chamber is a glass melting chamber, a glass refining chamber or a glass melting/refining chamber.

9. A process for the combustion, in a combustion chamber, of a fuel with a preheated oxygen-rich oxidant with generation of heat and hot flue gases inside said combustion chamber, the process comprising the steps of: discharging the hot flue gases from the combustion chamber, said discharged flue gases containing residual heat; recovering residual heat by heating an auxiliary gas by heat exchange with at least a part of the discharged hot flue gases in an auxiliary heat exchanger, with a hot auxiliary gas and tempered flue gases being obtained; introducing at least a first part of the hot auxiliary gas into a main exchanger in which oxygen-rich oxidant is preheated by heat exchange with a first heat-exchange gas comprising said at least a first part of the hot auxiliary gas, with a preheated oxidant and a tempered heat-exchange gas being obtained; and supplying the preheated oxygen-rich oxidant to the combustion chamber for the combustion of the fuel, wherein the process further includes: a first mode of operation in which the first heat-exchange gas does not comprise discharged hot flue gases, and a second mode of operation in which a portion of the discharged hot flue gases is not introduced into the auxiliary exchanger and is instead mixed with said at least a first part of the hot auxiliary gas before it is introduced into the main exchanger in order to increase the thermal energy content of the first heat-exchange gas.

10. The process as claimed in claim 9, wherein, in the first mode of operation, the heat-exchange gas consists of hot auxiliary gas.

11. An installation comprising a combustion chamber, a first heat exchanger, referred to as auxiliary exchanger, and a second heat exchanger, referred to as main exchanger, the combustion chamber being provided with injectors for the injection of a fuel and for the injection of an oxidant into the combustion chamber and with an outlet for flue gases; the auxiliary exchanger comprising, on the one hand, an inlet for hot flue gases and an outlet for tempered flue gases and, on the other hand, an inlet for auxiliary gas to be heated and an outlet for hot auxiliary gas, the outlet for hot flue gases of the combustion chamber being fluidly connected to the inlet for hot flue gases of the auxiliary exchanger; and the main exchanger comprising, on the one hand, an inlet for hot heat-exchange gas and an outlet for tempered heat-exchange gas and, on the other hand, an inlet for oxidant to be preheated and an outlet for preheated oxidant, the outlet for hot auxiliary gas of the auxiliary exchanger being fluidly connected to the inlet for hot heat-exchange gas of the main exchanger, the outlet for preheated oxidant being fluidly connected to at least one of the injectors of the combustion chamber, wherein the installation also comprises a pipeline configured to fluidly connect the outlet for hot flue gases to the inlet for the hot heat-exchange gas of the main exchanger in parallel with the auxiliary exchanger, so as to enable the flow of a controlled part of the hot flue gases resulting from the outlet for flue gases toward the inlet for the hot heat-exchange gas of the main exchanger.

12. The installation as claimed in claim 11, wherein the injectors for the injection of fuel and oxidant are incorporated in burners and/or injection lances.

13. The installation as claimed in claim 11, wherein the combustion chamber is a melting chamber, a refining chamber, a melting/refining chamber or the combustion chamber of a boiler, preferably a glass melting chamber, a glass refining chamber or a glass melting/refining chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the invention and are therefore not to be considered limiting of the invention's scope as it can admit to other equally effective embodiments.

(2) The FIGURE represents a diagrammatic representation in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

(3) The present invention is illustrated by the example below, reference being made to the FIGURE, which is a diagrammatic representation of an installation suitable for the implementation of a combustion process according to the invention.

(4) In the present example, the process according to the invention is more particularly combined with the process described in the unpublished coexisting patent application FR 1363 459 of the applicant company.

(5) Said process makes it possible to limit the costs of the items of equipment used for the preheating of oxidant by the use of a first exchanger for the heating of an oxygen-rich oxidizer, followed by second exchanger for the preheating of the oxidant, said oxidant being obtained by mixing the oxidizer heated in the first exchanger with a predominantly inert gas upstream of the second exchanger.

(6) The installation comprises a melting chamber, for example a glass melting chamber, 100 equipped with burners 200 for the combustion of a fuel, such as natural gas, with an oxygen-rich oxidant. Although just one burner is shown in FIG. 1, such a melting chamber generally comprises several burners. This combustion generates heat and flue gases inside the chamber 100. The heat generated by this combustion is used for the melting of glass former in the chamber 100. The flue gases are discharged from the chamber by an outlet for flue gases 300. The discharged flue gases are hot (typically of the order of 1200 C. to 1600 C.) and contain a not insignificant amount of residual heat.

(7) The present invention makes possible an optimized recovery and exploitation of the residual heat. At least a part of the discharged hot flue gases are introduced into an auxiliary exchanger 10 in which air used as auxiliary gas 21 (known hereinafter as auxiliary air) circulates.

(8) When only a part of the hot flue gases is introduced into the auxiliary exchanger 10, this part advantageously corresponds to at least 70 vol %, preferably at least 75 vol % and more preferably at least 80 vol % of the discharged flue gases.

(9) In the auxiliary exchanger 10, the auxiliary air is heated by heat exchange with the hot flue gases. Hot auxiliary air 22, typically at a temperature of 600 C. to 900 C., and tempered flue gases 12 are thus obtained. The hot auxiliary air is introduced into a main exchanger 40b in which the oxygen-rich oxidant 42, typically a gas consisting for at least 90 vol % of oxygen, preferably for at least 95 vol %, circulates.

(10) Inside the main exchanger 40a, 40b, the oxidant is preheated by heat exchange with a hot heat-exchange gas 23 which comprises at least a part of the hot auxiliary air 22.

(11) Hot oxidant 43 and tempered heat-exchange gas 45 are thus obtained.

(12) The hot oxidant is supplied to at least one of the burners 200 of the combustion chamber 100 and preferably to all of the burners 200 of the chamber 100.

(13) In the FIGURE, just one exchanger 40b is shown. However, the installation can comprise several main exchangers 40a and 40b and in particular several examples of the exchanger 40b which is connected to the burner(s) 200. In this case, each main exchanger 40b preferably feeds a limited number of burners 200 with hot oxidant. For example, a main exchanger 40b can be combined with each of the burners 200 of the chamber 100 using oxygen-rich oxidant.

(14) According to the present invention, it is possible to increase the heat supplied to the main exchanger 40a and 40b by replacing hot auxiliary air as heat-exchange fluid 23 with a mixture of hot auxiliary air with discharged hot flue gases. To this end, a part 13 of the discharged hot flue gases is not introduced into the auxiliary exchanger 10 for the heating of the auxiliary gas.

(15) This part 13 of the hot flue gases is, on the contrary, mixed with the hot auxiliary air 22 (or only with the part of the hot auxiliary air which is introduced into the main exchanger 40a and 40b for the preheating of the oxidant 42).

(16) In this way, it is possible to preheat the oxidant to a greater temperature and/or to preheat a greater flow rate of the oxidant. It is possible to preheat the oxidant in a single stage by introducing cold oxidant, for example at ambient temperature, into the exchanger 40b and by heating said oxidant up to its final temperature in the main exchanger 40b before supplying it to the burner(s) 200.

(17) However, in the example illustrated in FIG. 1, the preheating of the oxidant is carried out in two stages. An oxygen-rich gas 41 is first introduced into an exchanger 40a additional to the main exchanger in which said rich gas 41 is heated by heat exchange with a part 24 of the hot auxiliary air up to a first temperature.

(18) A partially heated rich gas and a tempered auxiliary air stream 44 are thus obtained. The partially heated rich gas 42 is then introduced as oxidant 42 into the main exchanger 40b.

(19) It is also possible to further increase the thermal energy of the rich oxidant 42 before it is introduced into the main exchanger 40b by mixing a limited amount of the hot auxiliary air with the partially heated rich gas, said mixture then being introduced as rich oxidant 42 into the main exchanger 40b.

(20) The disadvantage of this option is a slight reduction in the oxygen content of the -rich oxidant 42, 43. This method and its advantages are described in more detail in the abovementioned co-existing patent application.

(21) A part 25 of the hot auxiliary air is also used for the preheating of the fuel 3, for example natural gas, in a heat exchanger 30 referred to as fuel exchanger.

(22) Preheated fuel 32, which is subsequently supplied to the burner(s) 200 of the combustion chamber 100, and a third stream of tempered auxiliary air 33 are thus obtained.

(23) While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step. The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

(24) Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of comprising). Comprising as used herein may be replaced by the more limited transitional terms consisting essentially of and consisting of unless otherwise indicated herein.

(25) Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

(26) Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

(27) Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

(28) All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.