Energy recovery from fumes from a melting furnace using a gas turbine and heat exchangers

Abstract

The invention relates to a unit and method for melting in a furnace comprising a combustion-heated melting chamber, in which the air is heated by means of heat exchange with the fumes generated by combustion. The heated air is used in a gas turbine in order to generate electrical and/or mechanical energy. In addition, the effluent from the gas turbine is used to pre-heat the combustion oxygen and/or gaseous fuel upstream of the melting chamber.

Claims

1. A method for melting in a furnace comprising a melting chamber, the method comprising the steps of: preheating at least one combustion reagent chosen from oxygen and gaseous fuel upstream of the melting chamber by exchange of heat with a heat-transfer gas in a primary heat exchanger, thereby obtaining at least one preheated combustion reagent and temperate air; heating the melting chamber by means of combustion using at least one preheated combustion reagent, thus generating heat energy and fumes in the melting chamber; and removing the fumes from the melting chamber and introduced into a secondary heat exchanger to heat compressed air by exchange of heat with the fumes removed from the melting chamber, wherein mechanical and/or electrical energy and a gaseous effluent is generated by means of a gas turbine using the heated compressed air coming from the secondary heat exchanger as oxidant for the gas turbine, and the gaseous effluent from the gas turbine is used as heat-transfer gas for preheating the combustion oxygen and/or the gaseous fuel in the primary heat exchanger.

2. The method of claim 1, wherein the mechanical and/or electrical energy generated by the gas turbine is at least partially supplied to one or more air compressors.

3. The method of claim 2, wherein at least some of the mechanical and/or electrical energy generated by the gas turbine is supplied to at least one air compressor chosen from: an air compressor which feeds the secondary heat exchanger, an air compressor which feeds a unit for separating the gases of the air and another air compressor.

4. The method of claim 1, wherein the melting furnace is a glass furnace.

5. The method of claim 1, wherein some of the preheated gaseous fuel coming from the primary heat exchanger is used by way of oxidant for the gas turbine.

6. A melting furnace installation, the melting furnace comprising: a furnace defining a melting chamber heated by combustion said melting chamber comprising at least one outlet for fumes generated by combustion, a primary heat exchanger for preheating, by exchange of heat between a heat-transfer fluid and either combustion oxygen or gaseous fuel upstream of the melting chamber, said primary exchanger exhibiting (a) an inlet and an outlet for heat-transfer fluid and (b) an inlet and an outlet for combustion oxygen and/or an inlet and an outlet for gaseous fuel, a secondary heat exchanger for heating compressed air by exchange of heat with the fumes coming from the melting chamber, said secondary exchanger exhibiting (a) an inlet and an outlet for compressed air and (b) an inlet and an outlet for fumes, a first air compressor, said air compressor being connected to the compressed air inlet of the secondary exchanger, the installation comprising: connecting the fumes inlet of the secondary exchanger to a fumes outlet of the melting chamber; and connecting the combustion oxygen outlet of the primary exchanger to at least one oxidant injector of the melting chamber and/or the gaseous fuel outlet of the primary exchanger is connected to at least one gaseous fuel injector of the melting chamber, wherein the installation includes a gas turbine having an air intake nozzle and an exhaust, the compressed air outlet of the secondary exchanger being connected to the air intake nozzle of the gas turbine, the exhaust of the gas turbine being connected to the heat-transfer fluid inlet of the primary exchanger, so as to supply the primary exchanger with exhaust gas from the gas turbine by way of heat-transfer fluid.

7. The use of an installation of claim 6 in a method of claim 1.

8. The installation of claim 6, wherein the gas turbine supplies mechanical and/or electrical energy to at least one air compressor.

9. The installation of claim 8, wherein the gas turbine supplies mechanical energy to at least one air compressor by means of a transmission shaft.

10. The installation of claim 8, wherein the gas turbine supplies mechanical and/or electrical energy to at least one air compressor chosen from: the first air compressor, a second air compressor which feeds a unit for separating the gases of the air and another air compressor.

11. The installation of claim 10, wherein the gas turbine supplies mechanical or electrical energy to a unit for separating the gases of the air exhibiting an oxygen outlet connected to at least one oxidant injector of the melting chamber.

12. The installation of claim 11, wherein the oxygen outlet of the unit for separating the gases of the air is connected to the combustion oxygen inlet of the primary heat exchanger.

13. The installation of claim 6, wherein the combustion oxygen outlet of the primary heat exchanger is connected to at least one oxidant injector incorporated into a burner of the melting chamber and/or the gaseous fuel outlet of the primary heat exchanger is connected to at least one fuel injector incorporated into a burner of the melting chamber.

14. The installation claim 6, wherein the combustion oxygen outlet of the primary heat exchanger is connected to at least one oxidant injector incorporated into an oxidant lance of the melting chamber and/or the gaseous fuel outlet of the primary heat exchanger is connected to at least one fuel injector incorporated into a fuel lance of the melting chamber.

15. The installation of claim 6, wherein the melting furnace is a glass furnace.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) For a further understanding of the nature and objects for the present invention, reference should be made to the detailed description, taken in conjunction with the accompanying drawing, in which like elements are given the same or analogous reference numbers and wherein:

(2) FIGS. 1 and 2 are schematic depictions of two examples of an installation and of a method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) The melting furnace 10 is an oxycombustion furnace, heated by a number of oxyburners (not depicted). Said burners are fed with fuel, such as natural gas for example, by the pipe 12 and with combustion oxygen by the pipe 11.

(4) The combustion oxygen is generated by a unit for separating the gases of the air 50 which separates compressed air 51 into a stream of oxygen 52 having an O.sub.2 content of at least 90 vol %, and a stream (not depicted) consisting chiefly of N.sub.2.

(5) The fumes generated by the oxycombustion in the furnace 10 are removed from the melting chamber by the outlet 13, said fumes being at a temperature of between 1000 C. and 2000 C., for example between 1250 C. and 1750 C.

(6) Said fumes are conveyed to a heat exchanger, referred to as secondary heat exchanger 30. The hot fumes enter the secondary exchanger via a fumes inlet 31 and leave via the fumes outlet 32. Inside the secondary exchanger 30, the fumes heat compressed air by exchange of heat, the compressed air being obtained by compressing ambient air 33 to a pressure of between 10 and 20 atm, for example to around 15 atm, in the compressor 34. The compressor 34 may also supply compressed air to the unit for separating the gases of the air 50. The unit 50 may also have an air compressor (not depicted) specifically dedicated to supplying the unit 50 with air.

(7) The compressed air is introduced into the secondary exchanger 30 via an air inlet 35. The heated air 46 leaves the secondary exchange 30 via the air outlet 36 at a temperature of between 600 C. and 800 C.

(8) According to the invention, the heated air coming from the secondary exchanger 30 is used to generate mechanical and/or electrical energy according to the principle of operation of a gas turbine.

(9) Thus, the heated air 46 is introduced into a combustion chamber 41 by the air intake nozzle. In the combustion chamber 41, the heated air is used to burn (gaseous) fuel introduced by the fuel intake 47. The combustion gases thus obtained are at a temperature of 1000 C. to 1600 C., for example between 1200 C. and 1400 C., and are sent to the inlet 43 of an expansion turbine 42.

(10) In the scenarios illustrated, the energy obtained by this expansion of the combustion gases is transmitted: on the one hand to the air compressor 34 in the form of mechanical energy by the transmission shaft 45, and on the other hand to the separation unit 50 in the form of electrical energy via the connection 40.

(11) At the outlet or exhaust of the expansion turbine 42, the combustion gases 44 are at a temperature of 550 C. to 750 C. These combustion gases 44 are introduced into a second heat exchanger, referred to as primary exchanger 20, via the heat-transfer fluid inlet 21 and leave the primary exchanger 20 via the heat-transfer fluid outlet 22.

(12) Just one primary exchanger 20 is depicted in the figures. However, said primary exchanger 20 may be broken down into a series of several primary subexchangers, namely a series of heat-transfer fluid/combustion oxygen exchangers and/or of heat-transfer fluid/gaseous fuel exchangers.

(13) The stream of oxygen 52 coming from the separation unit 50 is introduced into the primary exchanger 20 via the oxygen inlet 23 and leaves the primary exchanger as preheated oxygen via the oxygen outlet 24. A stream of natural gas 60 is introduced into the primary exchanger 20 via the fuel inlet 25 and leaves the primary exchanger by way of preheated natural gas via the fuel outlet 26. Inside the primary exchanger 20, the stream of oxygen 52 is preheated to a temperature of between 350 C. and 650 C., for example to 550 C., by exchange of heat with the combustion gases and the stream of natural gas 60 is preheated to a temperature of between 250 C. and 550 C., for example to 450 C., likewise by exchange of heat with the combustion gases.

(14) The oxygen thus preheated is transported by way of combustion oxygen to the furnace 10 by the pipe 11 and the natural gas thus preheated is transported by way of fuel to the furnace 10 by the pipe 12.

(15) The embodiment illustrated in FIG. 2 differs from that of FIG. 1 in that in FIG. 2 some of the preheated natural gas is used as fuel in the combustion chamber 41.

Example

(16) The present invention and advantages thereof are illustrated in the comparative example below.

(17) The example according to the invention corresponds to the diagram of FIG. 1.

(18) The reference example corresponds to the same diagram except that it has no combustion chamber 41 nor does it have an expansion turbine 42 as described hereinabove, which means to say that it has no gas turbine.

(19) The furnace is a glass melting furnace heated by oxycombustion only with an oxygen consumption of 7000 Nm.sup.3/h and production of approximately 620 t/d of glass.

(20) The electricity consumption of the unit for separating the gases of the air is estimated at 3 MWe.

(21) In the primary exchanger, the oxygen is preheated to 550 C. and the natural gas is preheated to 450 C.

(22) In the primary exchanger, air compressed to 15 atm is heated to 350 C.

(23) In the example according to the invention, the combustion gases leave the combustion chamber 41 at the temperature of 1300 C.

(24) The electrical balance is defined by taking two consumers into consideration: The compression stages of the separation unit 50, and The compression stages of the heat-transfer air.

(25) The following is considered as an energy generating station: The expansion of the combustion gases in the expansion turbine 42.

(26) The material and energy balances calculated show that the invention is capable of generating all the energy required for the production of the stream of oxygen by the separation unit, or even of releasing excess energy, although a consumption of natural gas is nevertheless involved.

(27) The table summarizes the results of the energy consumptions.

(28) TABLE-US-00001 TABLE 1 Energy balances and associated natural gas consumptions reference invention Electrical balance (kWe) 2991 1384 Additional consumption of 00.00 686.80 natural gas (Nm3/h)

(29) There are two scenarios that can be envisaged: a scenario in which the price of electricity is comparable to that of gas (/MWh), a scenario in which the price of electricity is at least three times that of gas (/MWh)

(30) The operating costs include the consumption of electricity and of natural gas.

(31) The investment ratio is calculated on the basis of amortizement over four years with the equipment being available for 8600 hours/year.

(32) Table 2 provides the economic data from these material and energy balances, on the basis of the following prices for natural gas and electricity: natural gas at 40 /MWh and electricity at 70 /MWh.

(33) TABLE-US-00002 TABLE 2 Investment cost calculation (scenario 1) reference invention Electrical balance (kWe) 2991 1384 OPEX (EUR/h) 209.37 159.82 Additional investment 390 (EUR/kWh)
For scenario 2 in which natural gas costs 40 /MWh and electricity 140 /MWh, the economic data are set out in table 3:

(34) TABLE-US-00003 TABLE 3 Investment cost calculation (scenario 2) reference invention Electrical balance (kWe) 2991 1384 OPEX (EUR/h) 418.74 62.92 Additional investment 2798 (EUR/kWh)

(35) 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.

(36) The singular forms a an and the include plural referents, unless the context clearly dictates otherwise.

(37) 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 is defined herein as necessarily encompassing the more limited transitional terms consisting essentially of and consisting of; comprising may therefore be replaced by consisting essentially of or consisting of and remain within the expressly defined scope of comprising.

(38) 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.

(39) 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.

(40) 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.

(41) 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.