PROCESS FOR THERMOPROCESSING A CHARGE

Abstract

Process for thermoprocessing a non-gaseous charge in a furnace (13), whereby) carbon dioxide released by the charge during said thermoprocessing, a non-zero fraction (7) of the flue gas (6) which contains said released carbon dioxide being combined with hydrogen (3) and subjected to a rWGS reaction with said hydrogen (3), whereafter the reaction product (9) of the rWGS reaction is supplied to the furnace (13) as fuel.

Claims

1.-15. (canceled)

16. A process for thermoprocessing a charge, comprising: introducing a non-gaseous charge to be thermoprocessed into a furnace, heating the furnace by means of combustion of fuel with oxidant, said fuel and oxidant being supplied to the furnace at regulated supply rates, generating an atmosphere in the furnace, said atmosphere comprising of a gaseous mixture comprising (a) combustion gas generated by the combustion of the fuel with the oxidant and (b) carbon dioxide released by the charge during thermoprocessing, withdrawing the thermoprocessed charge from the furnace and evacuating the gaseous mixture as flue gas from the furnace, wherein hydrogen is supplied to the process and a non-zero fraction of the flue gas containing at least 50% vol and at most 100% vol CO.sub.2 is combined with at least part of the supplied hydrogen and subjected to a rWGS reaction with said hydrogen in a rWGS reactor, wherein at least part of the CO.sub.2 in the fraction is converted into CO, and: the reaction product of the rWGS reaction is supplied to the furnace as part or all of the fuel to be combusted.

17. The process according to claim 16, the fraction of the flue gas further comprising: at least 80% vol CO.sub.2, and/or from 0 to 20% vol H.sub.2O H.sub.2O.

18. The process according to claim 16, wherein the fraction of the flue gas is a dehumidified flue-gas fraction.

19. The process according to claim 16, wherein heat is recovered from the evacuated flue gas and supplied to the rWGS reaction.

20. The process according to claim 19, wherein heat recovered from the evacuated flue gas is supplied to the rWGS reaction by using said recovered heat to heat the fraction of the flue gas upstream of the rWGS reactor and/or to heat the at least part of the supplied hydrogen upstream of the rWGS reactor and/or to heat the combined fraction of the flue gas and the at least part of the supplied hydrogen upstream of the rWGS reactor and/or to heat the rWGS reactor.

21. The process according to claim 16, wherein heat is recovered from the evacuated flue gas and used for oxidant preheating, and/or fuel preheating, and/or drying and/or preheating of the charge to be thermoprocessed.

22. The process according to claim 16, wherein a further part of the hydrogen supplied to the process is injected into the furnace as additional fuel admixed with and/or separately from the reaction product of the rWGS reaction.

23. The process according to claim 16, wherein a gaseous hydrocarbon-containing fuel is supplied to the process and injected into the furnace as additional fuel admixed with and/or separately from the reaction product of the rWGS reaction.

24. The process according to claim 22, wherein the amount of additional fuel injected into the furnace is automatically regulated so that an instantaneous combustion heat requirement of the furnace is met by the combustion of the reaction product of the rWGS reaction together with the combustion of the injected additional fuel.

25. The process according to claim 16, wherein the oxidant has an oxygen content of 70% to 100% vol.

26. The process according to claim 16, wherein the fuel is combusted with the oxidant in multiple flames and/or by staged combustion.

27. The process according to claim 16, wherein the process is a glass-melting process and solid glass-forming material to be melted is introduced into the furnace as the non-gaseous charge to be thermoprocessed, carbon dioxide is released into the furnace atmosphere by the glass-forming material during thermoprocessing, and wherein the molten glass is withdrawn from the furnace as the thermoprocessed charge.

28. The process according to claim 27, wherein the furnace is heated simultaneously by means of: a) the combustion of fuel with oxidant, and b) electrodes immersed in the glass-forming material.

29. The process according to claim 28, wherein between 5 and 50% of the energy supplied to the furnace is supplied to the furnace by means of the electrodes.

30. The process according to claim 28, wherein between 30 and 95 of the energy supplied to the furnace is supplied to the furnace by means of the electrodes.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0098] For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

[0099] FIG. 1 shows a schematic flow diagram of a particular embodiment of the process according to the invention applied to a glass-melting furnace.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0100] Furnace 13 is a glass-melting furnace into which solid glass-forming material is continuously introduced at a feed end and from which molten glass is continuously withdrawn at the opposite end of the furnace (not shown). Furnace 13 is heated by the combustion of fuel with oxidant above the charge of glass-forming material, thereby introducing combustion gases into the furnace atmosphere.

[0101] In addition, electric power 10 may be supplied to electrodes (not shown) in furnace 13 to boost the heat supply to the furnace.

[0102] As the glass-forming material is heated and melts, it releases a range of compounds into the furnace atmosphere, including a significant amount of CO.sub.2.

[0103] As the furnace is not air-tight, there is an inevitable ingress 11 of air into the furnace, said ingress air forming also part of the furnace atmosphere.

[0104] The thus obtained mixture of gases is continuously evacuated from the furnace as flue gas stream 6 at a temperature of about 1450? C. The CO.sub.2 content of the evacuated flue gas stream 6 lies around 42% vol.

[0105] Residual heat is recovered from evacuated flue gas stream 6 in heat exchanger 6a, whereby the temperature of the flue gas decreases to about 512? C., i.e. well above the condensation temperature of the water vapour present in said flue gas stream 6.

[0106] Cooled flue gas stream 6b is divided into two parts: recycle flue gas stream 12 and rest stream 8, which is evacuated from the process. The need to evacuate rest stream 8 from the process arises in particular because new CO.sub.2 is continuously released by the charge in furnace 13 and evacuated therefrom as part of the flue gas. Without rest stream 8, the amount of CO.sub.2 in the process would continue to accumulate. Such a purge is also required to evacuate nitrogen introduced by the ingress air from the process. Rest stream 8 may, for example, be subjected to one or more cleaning steps before being released into the atmosphere. However, if possible, rest stream 8 will be subjected to CCUS, as a further measure to reduce the carbon footprint of the glass-melting process.

[0107] In condenser 15, recycle stream 12 is further cooled to cause water to be condensed therefrom, thereby increasing the CO.sub.2 content in the gaseous phase. The condensed water is removed as stream 5.

[0108] The at least partially dehumidified recycle stream 7 has a CO.sub.2 content of around 70% vol and is sent to rWGS reactor 14.

[0109] In addition to recycle stream 7, hydrogen stream 3 is also sent to rWGS reactor 14, where CO.sub.2 from recycle stream 7 reacts with hydrogen from stream 3 as follows:

CO.sub.2+H.sub.2?=CO+H.sub.2O.

[0110] The resulting rWGS reaction product stream 9, which contains both CO and H.sub.2, is injected as fuel into furnace 13 to generate a flame coverage of the glass-forming material in furnace 13, which more closely resembles the flame coverage obtained by means of combusting hydrocarbon fuel, than would a hydrogen flame, but without the additional CO.sub.2 emissions of hydrocarbon combustion.

[0111] A stream 2 of oxygen-rich oxidant, more specifically industrial purity oxygen, is preheated in heat exchanger 2a before the preheated oxidant stream 2b is sent to furnace 13 and injected therein as combustion oxidant for the combustion of fuel.

[0112] Optionally, CO.sub.2 from an external source may also be supplied to rWGS reactor 14 in addition to recycle stream 7. In the illustrated embodiment, additional CO.sub.2-containing stream 4 is mixed with hydrogen stream 3 in static mixer 16 and the mixed H.sub.2+CO.sub.2 stream is supplied to rWGS reactor 14, where it is combined with recycle stream 7 and subjected to the rWGS reaction.

[0113] Optionally, additional fuel(s) may be supplied to furnace 13, in addition to rWGS reaction product stream 9. In the illustrated embodiment, additional fuel stream 1 is preheated in heat exchanger 1a and preheated additional fuel stream 1b is sent to furnace 13 and injected therein so as to be combusted in the furnace with part of preheated oxidant stream 2b.

[0114] Additional fuel stream 1, 1b may be a hydrocarbon-containing fuel stream, preferably made from renewable origin. Additional fuel stream 1, 1b may advantageously also be a hydrogen stream which is injected into furnace 13 without first being subjected to the rWGS reaction.

[0115] Reference number 17 designates the heat recovery assembly of the illustrated process. By means of said heat recovery assembly, residual heat present in evacuated flue gas stream 6 is recovered by means of heat exchanger 6a and used (a) as a heat source for the rWGS reaction in reactor 14, (b) as a heat source for preheating oxidant stream 2 in heat exchanger 2a and (c) when additional fuel is supplied to the furnace, as a heat source for preheating additional fuel stream 1 in heat exchanger 1a.

[0116] In the simplified schematic representation of the FIGURE, the different steps of the heat-recovery process are shown separately for reasons of clarity. However, it will be appreciated that, as discussed earlier, the heat recovery step of heat exchanger 6a is necessarily connected with heat supply steps to the rWGS reaction in reactor 14 and the preheating steps of heat exchangers 1a and 2a which rely on the heat recovered in the heat recovery step. In addition, any one of said steps may consist of multiple substeps. For example, the heat recovery step of heat exchanger 6a may comprise a high-temperature heat recovery substep followed by a low temperature heat recovery substep. A person skilled in the art will, however, appreciate, as also discussed hereabove, heat recovered during different heat-recovery substeps may be used in different heat supply steps. The step of supplying recovered heat to the rWGS reaction in rWGS reactor 14 may, for example, consist of supplying heat to reactor 14 or may also comprise a substep of heating dehumidified recycle stream 7 upstream of rWGS reactor 14.

[0117] It will be appreciated that embodiments of the type illustrated in FIG. 1 are not limited to glass-forming processes, but may be applied to other methods for thermoprocessing a charge, whereby the charge releases CO.sub.2 during thermoprocessing and whereby high-temperature flue gas, containing said released CO.sub.2 is evacuated from the furnace in which said thermoprocessing takes place.

[0118] By using the process according to the invention, the CO.sub.2 which is released by the glass-forming material, which normally contributes to the energy losses of the glass-melting process, is at least in part recycled and used to improve the heating of the charge in the furnace. In addition, the invention also permits an optimized use of the residual heat present in the furnace flue gas.

[0119] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.