Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F22—STEAM GENERATION
  • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
  • F22B1/00—Methods of steam generation characterised by form of heating method
  • F22B1/02—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers
  • F22B1/18—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers the heat carrier being a hot gas, e.g. waste gas such as exhaust gas of internal-combustion engines
  • F22B1/1853—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers the heat carrier being a hot gas, e.g. waste gas such as exhaust gas of internal-combustion engines coming in direct contact with water in bulk or in sprays
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
  • F01K25/00—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for
  • F01K25/08—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for using special vapours
  • F01K25/10—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for using special vapours the vapours being cold, e.g. ammonia, carbon dioxide, ether
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E20/00—Combustion technologies with mitigation potential
  • Y02E20/34—Indirect CO2mitigation, i.e. by acting on non CO2directly related matters of the process, e.g. pre-heating or heat recovery

Definitions

• the present invention relates to a system and method for making the combustion processes which take place in industrial plants such as furnaces for metals or glass, ceramics, cement products or similar applications which require thermal energy generated by combustion of fossil gas such as methane in a combustion chamber more efficient.
• the invention is mainly addressed to applications of the OXY-Fuel type where the combustion agent is pure oxygen instead of atmospheric air and the thermodynamics of the combustion process causes the combustion fumes to be released from the combustion chamber at high temperatures (of the order of 1500°C) and are mostly composed of carbon dioxide and steam.
• the invention can also be advantageous when applied to combustion processes using air as an oxidizer, the primary use is envisaged with pure oxygen power plants as it has been found that there is a large margin for improvement in the efficiency and the characteristics of the fumes are suitable for the treatment of the fumes themselves both in terms of exploitation of the enthalpy content and recovery of at least part of the substances contained therein by recirculation and mixing with the fuel.
• the applicant has observed how the energy profile in the combustion chamber is such that, by operating with the best possible mix of methane and oxygen at room temperature (25°C), the process efficiency is about 67% against the production of high temperature fumes and particular composition as anticipated above.
• Units and systems for recovery of the enthalpy content of fumes are known in the state of the art which exploit, for instance, a unit operating by means of a closed reversible thermodynamic cycle engine of the Rankine or Hirn type, or a cycle composed by a compression and an adiabatic expansion and two isobars, the use of which advantageously allows the heat to be transformed into work and therefore into electrical energy by means of a generator; this solution is also referred to as an engine thermodynamic cycle or, if the cycle is carried out with an organic fluid, Organic Rankine Cycle (ORC).
• ORC Organic Rankine Cycle
• thermodynamic cycle involves the action of a pump to raise the pressure, then an isobaric heating thanks to the heat recovered from the fumes until dry or overheated saturated steam is obtained, then expanded in a turbine and then iso thermally-iso barically condensed. The result is therefore obtained of recovering heat from the fumes with a simple and easy to implement cycle.
• the reforming process takes place using steam and is also referred to as "steam reforming” or Steam Methane Reforming (SMR) in the case the fossil gas is methane.
• steam reforming is commonly carried out by mixing a certain quantity of steam from an external source with methane: it will be seen later how the invention described here also allows the steam contained in the combustion fumes to be reused without resorting or resorting only in part to an external source and therefore also limiting the environmental impact resulting from the plant operation.
• the invention provides for feeding the steam reforming process with a percentage of fumes mixed with fuel gas and steam: this has a double positive value:
• the fumes contain a high percentage of H2O already in the form of steam useful for guaranteeing the steam to carbon (S/C) ratio of the process fluid entering the SMR reactor.
• the reformer requires a supply of steam, with a steam-to-carbon (S/C) ratio between 1 .5 and 4, preferably around 1 .9-2.3 and again more preferably equal to 2.
• the present invention therefore has the object of overcoming the technical problems known to the state of the art and of achieving these and other objectives and this object is achieved with a combustion process efficiency unit of a combustion chamber of industrial plants operating by oxy-combustion of natural gas in accordance with claim 1 .
• the first heat exchanger is chosen by the person skilled in the art with characteristics suitable for the temperature and flow rate of the incoming combustion fumes and can be a device such as for instance a boiler.
• the invention also comprises a second heat exchanger for transferring part of the energy contained by said fumes in the form of heat to increase the temperature of an oxygen flow aimed for said combustion chamber, preferably arranged downstream of the reforming unit according to a path of the fumes which from the combustion chamber go towards a discharge or an external collection unit.
• the invention also relates to a method for improving the efficiency of combustion chambers operating in industrial plants such as furnaces for metals or glass, ceramics, cement products, said method comprising the steps of:
• the three steps are performed simultaneously with the path of the combustion fumes emitted from the combustion chamber towards the exhaust or towards the collection point outside the plant and which initially enter a first heat exchanger to then exit and be conveyed towards a reforming unit and finally towards a second heat exchanger.
• said water source comprises at least in part liquid water obtained by condensation of the combustion fumes.
• the method comprises the further step of recovering part of the thermal energy of the fumes through a closed reversible thermodynamic cycle, preferably of the Rankine or Hirn type and even more preferably using organic type working fluids.
• FIG. 1 The attached drawing tables from 1 to 3 show, respectively in each figure, the block diagrams of generic glass processing plants according to three different embodiments of the invention which implement possible embodiments of the invention itself but are not to be considered as limiting the invention.
• Figure 4 illustrates the plant of figure 1 in a specific configuration of the operating parameters.
• a glass furnace is shown provided with a combustion chamber 2 and fed by fuel intended for one or more burners by means of one or more burner nozzles (not visible in the figure) positioned inside said combustion chamber according to the prior art and not further described here.
• the furnace operates with oxy-combustion (Oxyfuel type furnace) or a combustion technique using pure oxygen, although the use with ambient air possibly enriched by substances capable of improving the combustion process is not precluded.
• a combustion process efficiency unit is illustrated for a glass furnace having a combustion chamber 2, which is fed by a flow of combustion oxygen 22 and by a flow of fuel 21 , composed of a mixture based on methane gas.
• the combustion flow 22 coming from a source 13 external to the plant and made available in gaseous form and at room temperature (for instance at a temperature of about 25°C), is heated by heat exchange by a heat exchanger 7 which withdraws energy in the form of heat from the combustion fumes 202 (already subjected to recovery treatment) and, once heated, it is conveyed into the combustion chamber 2.
• the fuel 21 is also made available to the same combustion chamber 2, which in the context of the invention is a mixture based on fossil gases (preferably Methane CH4), part of the exhaust fumes 203 and superheated steam 14.
• fossil gases preferably Methane CH4
• the exhaust fumes are addressed towards a first heat exchanger or boiler 3 intended to raise the temperature of the water coming from a water source 11 , vaporising it and bringing it to a known temperature thus obtaining superheated steam 14.
• this boiler has been sized in such a way that, with water from the source 1 1 at a temperature of 25°C, the steam 14 is overheated to a temperature of about 500°C.
• This superheated steam 14 is then mixed by a mixer 4 which also receives as input the content of a part 203 of the exhaust fumes 201 and a methane gas flow coming from a source 12.
• the methane gas source delivers a flow of gas at 25°C while about 30% of the fumes is conveyed to the mixer 3. This allows, in addition to mixing with steam at 500°C, to obtain a mixture of fuel at a temperature of about 720°C whose composition is mostly made up of methane, carbon dioxide and water with the exception of residual impurities in a percentage normally lower than 1 %.
• the fuel mixture thus obtained is subjected to a gas treatment process by means of a unit 5, aimed at purifying the fuel mixture and preparatory to maintaining the operating life of the reformer 6 which is located downstream in the path of the fuel mixture towards the combustion chamber 2.
• This treatment has as its objective the reduction or neutralization of the chemical substances dispersed in the fumes and/or in the gas entering the mixer 4 such as for instance the desulphurisation of the gas, the reduction of hydracids such as hydrochloric acid or hydrogen sulphide commonly present as a result of the production processes of fossil gases or syngas.
• a gas treatment process by means of a unit 5, aimed at purifying the fuel mixture and preparatory to maintaining the operating life of the reformer 6 which is located downstream in the path of the fuel mixture towards the combustion chamber 2.
• This treatment has as its objective the reduction or neutralization of the chemical substances dispersed in the fumes and/or in the gas entering the mixer 4 such as for instance the desulphurisation of the gas, the reduction of hydracids
• the reforming technique which, through an endothermic reaction between fuel molecules and water molecules, causes the breaking of the bonds between carbon-hydrogen atoms and the formation of molecules with a higher energy content (H2, CO) to increase the calorific value of the fuel flow 21.
• This technique is implemented in the reformer 6 and supported in terms of energy requirements (providing heat to the reformer for the endothermic reaction) thanks to a heat exchange which cools the exhaust fumes once they have been conveyed into the reformer.
• the fumes 204 entering the reformer 6 (downstream of the withdrawal of the fumes intended for the mixer 4) have a temperature of about 1280°C and release heat until they drop to about 605°C at the reformer outlet.
• the retained heat is effectively reused to increase the calorific value of the fuel.
• the fumes contain a high percentage of H2O already in the form of steam useful for guaranteeing the steam to carbon (S/C) ratio of the process fluid entering the SMR reactor.
• the reformer requires a supply of steam, with a steam-to-carbon (S/C) ratio between 1 .5 and 4, preferably around 1 .9-2.3 and again more preferably equal to 2.
• S/C steam-to-carbon
• the final fuel mixture, indicated with 21 is then conveyed to feed the combustion in the combustion chamber 2 using the gaseous oxygen previously heated by the second heat exchanger 7 as comburent.
• the temperature of the oxygen leaving the exchanger 7 is raised from 25°C to about 600°C while the exhaust fumes 203 are lowered to about 400°C starting from an inlet temperature of 605°C to the exchanger 7.
• the temperature of the superheated oxygen may be a few units of degree lower considering the inefficiencies of the actual devices.
• thermodynamic unit 1 10 with relative electric generator 120.
• the fumes from the combustion chamber 2 not reused in the fuel mixture pass first into the reformer 6 and then into the thermodynamic unit 110 to then flow into a chimney for discharge or treatment.
• This residual part with reference to the ambient temperature and pressure conditions, is approximately 26% of the calorific value entering the furnace, and is available for the ORC system, which manages to recover about a further 10% of the calorific value entering the furnace.
• thermodynamic recovery unit 110 a further stage is provided for treating the combustion fumes leaving the second exchanger 7 before they are conveyed to the thermodynamic recovery unit 110; this treatment, carried out according to known techniques, has as its objective the reduction or neutralization of the chemical substances dispersed in the combustion fumes coming from the combustion chamber 2 and also the reduction of the polluting and harmful agents for the operation of the unit 1 10 such as for instance acidic gases, such as hydrochloric acid or hydrogen sulphide or other compounds of the exhaust fumes which are generated by combustion in chamber 2.
• acidic gases such as hydrochloric acid or hydrogen sulphide or other compounds of the exhaust fumes which are generated by combustion in chamber 2.
• a condensation unit 9 is provided which is arranged downstream of the thermodynamic unit 110 and in any case in the terminal of the path of the combustion fumes from the combustion chamber 9 towards the exhaust; advantageously, this unit allows the recovery of water dispersed in the form of steam in the exhaust fumes so as to be made available as a source of water addressed to the first exchanger 3 according to one or more of the embodiments described up to now.
• this further step is extremely advantageous in terms of efficient use of the combustion process also in favor of reusing the combustion products, not only because part of the fumes is recirculated as a fuel mixture but also because it is possible to extract a part of the other components of the combustible gas mixture from the non-reused part of the fumes.
• the use of two heat exchangers, of the further transfer of heat to the reformer 6 and to the thermodynamic unit 110 leads to an advantageous lowering of the temperature of the fumes which can therefore be treated by condensation by working at relatively low temperatures. In one embodiment, these temperatures are close to 100°C and the condenser 9 is able to generate a quantity of water condensed at 25°C about 40% of which is used at the inlet to the first heat exchanger 4.
• the energy produced by the electric generator 120 is used for the operation of an electrolyser from which, by a known electrolysis process, the separation of water molecules into dihydrogen molecules (H2) and oxygen (O2) is obtained.
• H2 dihydrogen molecules
• O2 oxygen
• the electrolyser produces molecules of dihydrogen (H2) which can integrate the fuel (in the mixing phase in mixer 4), effectively adding gas with a high calorific value obtained from the electrolysis of water, electrolysis which is fed by the energy recovered by the heat exchanger unit object of the invention.
• H2 dihydrogen
• a unit for the desulphurisation of the fuel used in the furnace is introduced.
• the desulphurizer operates being powered by hydrogen and the desulphurization process is particularly effective when applied to the fuel before any reforming operation.
• the chemical steam reforming reactor of the same contains a catalyst which is poisoned by the sulfur compounds present in the gas (typically: the odorizer) and which would have a very short life without the upstream desulfurization process.
• the excess hydrogen produced by the electrolyser and not used by the desulphurizer can then be fed directly to the furnace, for instance mixed with the mixture leaving the reforming unit.
• the hydrodesulphurization which requires dihydrogen to be carried out, can advantageously be fed by the dihydrogen molecules coming from the electrolyser which, as mentioned, is energized at least in part indirectly by the heat recovered from the fumes 205.

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• 2022
  • 2022-07-11 IT IT102022000014524A patent/IT202200014524A1/it unknown
• 2023
  • 2023-07-05 WO PCT/IB2023/056969 patent/WO2024013617A2/en not_active Ceased
  • 2023-07-05 EP EP23761980.4A patent/EP4555197A2/de active Pending

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