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

Abstract

The invention relates to a melting unit and method in which: a melting chamber is heated by means of combustion, the combustion fumes are used to heat the air used as a heat-transfer gas, the heated air is used to pre-heat the combustion oxygen and/or the gaseous fuel, the tempered air resulting from the pre-heating is compressed, the compressed tempered air is heated by means of heat exchange with the combustion fumes, and the mechanical and/or electrical energy is generated by expansion of the heated compressed air.

Claims

1. A method for melting in a furnace comprising a melting chamber, in which method: the melting chamber is heated by means of combustion, thus generating heat energy and hot fumes in the melting chamber, the hot fumes are removed from the melting chamber and air as heat-transfer gas is heated by exchange of heat with hot fumes removed from the melting chamber, thereby obtaining hot air, at least one reagent chosen form oxygen and/or gaseous fuel is preheated by exchange of heat with the hot air, thereby obtaining at least one preheated reagent and temperate air, and the at least one preheated reagent is used as a combustion reagent for heating the melting chamber, characterized in that: the temperate air is compressed in a first air compressor so as to obtain compressed temperate air, the compressed temperate air is heated by exchange of heat with the hot fumes so as to obtain heated compressed air, and mechanical and/or electrical energy is generated by expanding the heated compressed air in an expansion turbine.

2. The method of claim 1, wherein the at least one reagent is preheated by exchange of heat with the hot air in a primary heat exchanger and the heat-transfer gas is heated by exchange of heat with hot fumes removed from the melting chamber in a secondary heat exchanger.

3. The method of claim 2, wherein the compressed temperate air is also heated by exchange of heat with hot fumes removed from the melting chamber in the secondary heat exchanger.

4. The method of claim 2, wherein the compressed temperate air is heated with hot fumes removed from the melting chamber in a tertiary heat exchanger.

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

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

7. A melting installation comprising: a furnace defining a melting chamber heated by combustion and comprising at least one outlet for fumes generated by combustion, a primary heat exchanger for preheating combustion oxygen and/or gaseous fuel upstream of the melting chamber by exchange of heat with air, said primary exchanger exhibiting (a) an inlet and an outlet for heat-transfer gas 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 air by exchange of heat with the fumes coming from the melting chamber, said secondary exchanger exhibiting (a) an inlet and an outlet for air and (b) an inlet and an outlet for fumes, in which installation: the fumes inlet of the secondary exchanger is connected to a fumes outlet of the melting chamber, the combustion oxygen outlet of the primary exchanger is connected 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 fuel injector of the melting chamber, and characterized in that: the air outlet of the primary heat exchanger is connected to an air inlet of a first air compressor, said first air compressor having a compressed air outlet connected to a compressed air inlet of a heat exchanger for heating compressed air by exchange of heat with fumes generated by the combustion in the melting chamber, said heat exchanger having an outlet for heated compressed air, said outlet for heated air being connected to a compressed gas inlet of an expansion turbine for generating mechanical and/or electrical energy by expanding the heated compressed air in the expansion turbine.

8. The installation of claim 7, wherein the secondary heat exchanger is also used as the heat exchanger for heating compressed air.

9. The installation of claim 7, wherein a third heat exchanger, referred to as tertiary heat exchanger, is used as the heat exchanger for heating compressed air.

10. The installation of claim 7, wherein the expansion turbine supplies mechanical and/or electrical energy to at least one air compressor.

11. The installation of claim 10, wherein the expansion 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.

12. The installation of claim 7, wherein the expansion turbine supplies mechanical or electrical energy to a unit for separating the gases of the air and/or an air compressor of a unit for separating the gases of the air, said unit for separating the gases of the air exhibiting an oxygen outlet connected to the combustion oxygen inlet of the primary exchanger.

13. The installation of claim 7, wherein: the combustion oxygen outlet of the primary 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 exchanger of the primary exchanger is connected to at least one fuel injector incorporated into a burner of the melting chamber; and/or in which the combustion oxygen outlet of the primary 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 exchanger is connected to at least one fuel injector incorporated into a fuel lance of the melting chamber.

14. The installation of claim 7, wherein the melting furnace is a glass furnace.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIGS. 1 and 2 are schematic depictions of two examples of an installation and of a method according to the invention using air as heat-transfer gas.

DETAILED DESCRIPTION OF THE INVENTION

(2) The melting furnace comprises an oxycombustion melting chamber 100, heated by a number of oxyburners (not depicted). Said burners are fed with fuel, such as natural gas for example, by the pipe 105 and with combustion oxygen by the pipe 104.

(3) The combustion oxygen is generated by a unit for separating the gases of the air 160 which separates compressed air 161 into a stream of oxygen 40 having an O.sub.2 content of at least 90 vol %, and a stream (not depicted) consisting chiefly of N.sub.2.

(4) The fumes 20 generated by the oxycombustion in the melting chamber 100 are removed from the combustion chamber by the outlet 101, said fumes 20 being at a temperature of between 1000° C. and 2000° C., for example between 1250° C. and 1750° C.

(5) Said hot fumes 20 or at least part 21 of said fumes are conveyed to a first heat exchanger referred to as “secondary heat exchanger” 140. The hot fumes (20, 21) enter the secondary exchanger 140 via a fumes inlet 143 and leave via the fumes outlet 144. Inside the secondary exchanger 140, the fumes heat air 30 by exchange of heat.

(6) The air 30 is introduced into the secondary exchanger 140 via an air inlet 141. The heated air 31 leaves the secondary exchanger 140 via the air outlet 142 at a temperature of between 600° C. and 800° C.

(7) The heated air 31 coming from the secondary exchanger 140 is conveyed to and introduced into a second heat exchanger, referred to as “primary exchanger” 130 via the heat-transfer gas inlet 131.

(8) Just one primary exchanger 130 is depicted in the figures. However, said primary exchanger 130 may be broken down into a series of several primary subexchangers, namely a series of heat-transfer gas/combustion oxygen exchangers and/or of heat-transfer gas/gaseous fuel exchangers.

(9) A stream of oxygen 40 coming from the separation unit 160 is introduced into the primary exchanger 130 via the oxygen inlet 133 and leaves the primary exchanger as preheated oxygen 41 via the oxygen outlet 134. A stream of natural gas 50 is introduced into the primary exchanger 130 via the fuel inlet 135 and leaves the primary exchanger 130 by way of preheated natural gas 51 via the fuel outlet 136.

(10) Inside the primary exchanger 130, the stream of oxygen 40 is preheated to a temperature of between 350° C. and 650° C., for example to 550° C., by exchange of heat with the heated air 31 and the stream of natural gas 50 is preheated to a temperature of between 250° C. and 550° C., for example to 450° C., likewise by exchange of heat with the heated air 31.

(11) The oxygen thus preheated 41 is transported by way of combustion oxygen to the melting chamber 100 by the pipe 104 and the natural gas thus preheated 51 is transported by way of fuel to the melting chamber 100 by the pipe 105.

(12) After it has been used for preheating the oxygen and the gaseous fuel, the temperate heat-transfer gas (air) 32 is removed from the primary exchanger 130 via the air outlet 132.

(13) The temperate air 32 is conveyed to an air compressor 110 in which the temperate air is compressed to a pressure of between 10 and 20 atm, for example to around 15 atm, so as to obtain compressed temperate air 33 at the outlet 112 of the compressor 110.

(14) The compressed temperate air 33 is then conveyed to a heat exchanger to be heated by exchange of heat with hot fumes 20 coming from the melting chamber 100.

(15) In the embodiment illustrated in FIG. 1, the compressed temperate air 33 is thus introduced into the secondary exchanger 140 via the compressed air inlet 153 and the heated compressed air 34 obtained by exchange of heat with the hot fumes 20 is removed from the secondary exchanger 140 by the heated compressed air outlet 154.

(16) In the embodiment illustrated in FIG. 2, the compressed temperate air 33 is introduced into a third heat exchanger referred to as “tertiary exchanger” 150 by the compressed air inlet 153. The hot fumes 20 are split into two fractions 21 and 22. The fraction 21 of hot fumes is introduced into the secondary exchanger 140 for heating the air 30 which is used as a heat-transfer gas. The fraction of hot fumes 22 is introduced into the tertiary exchanger 150 via the hot fumes inlet 151 for heating the compressed temperate air 33 obtained by compression in the compressor 110 of the temperate air coming from the primary exchanger. The temperate fumes are removed from the tertiary exchanger 150 via the fumes outlet 152 and the heated compressed air is removed via the compressed air outlet 154.

(17) Regulating what fraction of hot fumes 21 is sent to the secondary exchanger 140 and what fraction of hot fumes 22 is sent to the tertiary exchanger 150 on the basis of the heat energy required for respectively heating the air 30 used as heat-transfer gas and heating the compressed air makes it possible to optimize the recuperation and exploitation of the heat energy present in the hot fumes 20 leaving the melting chamber 100.

(18) The heated compressed air 34 is then conveyed to the compressed gas inlet 121 of an expansion turbine 120. The expanding of the heated compressed air 34 in this expansion turbine 120 generates mechanical and electrical energy. After expansion, the air is removed from the expansion turbine via the outlet 122.

(19) In the scenarios illustrated, the energy obtained by this expanding of the heated compressed air is transmitted: on the one hand to the air compressor 34 in the form of mechanical energy by the transmission shaft 123, and on the other hand, to the separation unit 160 in the form of electrical energy via the connection 124.

EXAMPLE

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

(21) The example according to the invention corresponds to the diagram in FIG. 1.

(22) The reference example corresponds to the same diagram except that the temperate air 32 coming from the primary heat exchanger 130 is sent directly to the flue.

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

(24) The electric power consumption of the unit for separating the gases of the air is estimated at 3 MWe.

(25) In the primary exchanger 130, the oxygen is preheated to 550° C. and the natural gas is preheated to 450° C.

(26) In the secondary exchanger 140, the air is heated to 650° C.

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

(28) The electrical balance is defined by considering the energy consumption for the compression of air for feeding the separation unit 160, for feeding the secondary exchanger with heat-transfer gas and for compressing temperate air 32 in the compressor 110.

(29) Two scenarios can be envisioned: a scenario in which the price of electricity is 40 /MWh a scenario in which the price of electricity is 140 /MWh

(30) Table 1 provides the economic data derived from these material and energy balances, for scenario 1.

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

(32) TABLE-US-00001 TABLE 1 Investment cost calculation (scenario 1) Reference Invention Electrical balance (kWe) −2991.0 −2347.9 OPEX (EUR/h) 209.37 164.35 Additional investment (EUR/kWh) 2408
For scenario 2 in which natural gas costs 40/MWh and electricity 140/MWh, the economic data are set out in table 2:

(33) TABLE-US-00002 TABLE 2 Investment cost calculation (scenario 2) Reference Invention Electrical balance (kWe) −2991 OPEX (EUR/h) 418.74 328.71 Additional investment (EUR/kWh) 4816

(34) For the reference case, an electrical balance of −2991 kWe is observed. According to the invention, the electrical balance is reduced to −2347.9 kWe, which represents a reduction of over 20%. This shows that the invention offers true economic benefit, particularly in regions where the cost of energy is high.

(35) While the invention has been described 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.