System for supplying co2 gas to a facility that requires co2 or a mixture comprising co2, such as an abattoir or a greenhouse for cultivating plants

Abstract

The invention relates to a method for supplying CO2 gas to a site comprising a facility (20) that requires CO2 or a mixture comprising CO2, such as an abattoir or a greenhouse for cultivating plants, characterised by the following steps: a boiler (4) capable of supplying hot water to the site is arranged within the site, said boiler carrying out the process of oxycombustion between a fuel (14) and pure oxygen (1), the oxygen that supplies the boiler being obtained from a liquid oxygen source present on the site; some or all of the CO2 contained in the flue gas produced by the boiler is recovered by transferring heat between the flue gas and the liquid oxygen in an exchanger (2).

Description

[0001] System for supplying gaseous CO2 to an installation requiring CO2 or a mixture containing CO2, such as a slaughterhouse or a greenhouse for growing plants

[0002] The present invention relates to processes and installations using gaseous CO2, particularly in the agri-food industry.

[0003] This field includes the beverage sector, modified atmospheres for the preservation of food products, the anesthesia of poultry in slaughterhouses, and even the cultivation of plants in greenhouses.

[0004] The need for CO2 in developed countries is still increasing (especially for the applications mentioned above).

[0005] This CO2 is mainly produced by fertilizer and methanol (by-product) plants, as well as hydrogen production plants. The availability of this molecule is therefore becoming critical due to frequent shutdowns of fertilizer production plants and geopolitical tensions, which then have a strong impact on the price of gas.

[0006] We then commonly observe in many countries, due to these frequent crises, the fact that, for example, greenhouse growers have not been supplied with merchantable CO2 for several months a year in recent years, which, understandably, has a direct impact on their productivity.

[0007] Added to this are strong environmental constraints, due to the desire of developed countries to reduce greenhouse gas emissions, which will directly impact CO2 production methods, by promoting the search for solutions aimed at reducing the carbon footprint.

[0008] The present invention aims to propose an innovative solution for producing CO2 on the site of a user of this CO2.

[0009] As will be seen in more detail below, the present invention proposes to use the heat production equipment (boilers) traditionally present on such sites, by converting it or them to oxycombustion. In this way, the heat produced by the boilers will come from the production of CO2 and will therefore be considered as “waste heat” within the meaning of the legislation.

[0010] Oxycombustion is a combustion process in which the combustion gas is no longer air but “pure” oxygen (i.e. characterized by a purity generally greater than 95%, and 99% for liquid oxygen).

[0011] Oxy-combustion (i.e. with oxygen and not air) is already used by certain industries operating at high temperatures (glassworks, cement works, metallurgical plants, etc.) because it brings a certain number of advantages, including:

[0012] • Reduction in the volume of fumes thanks to the reduction / elimination of nitrogen ballast.

[0013] • The increase in thermal efficiency directly linked to the reduction in the volume of fumes (due to lower thermal losses in the fumes).

[0014] • The intensification of heat transfers thanks to two phenomena: the increase in flame temperature and the increase in radiation heat fluxes due to fumes mainly composed of emitting gases (CO2, H2O).

[0015] • Reduction of pollutant emissions such as thermal NOx or dioxins (linked to the reduction in the volume of oxidant). The specialist literature announces savings of 10 to 40% on fuel. Heating the oxidant and the fuel also allows a reduction in the consumption of the latter.

[0016] The objective is to increase the CO2 content of combustion fumes by eliminating the nitrogen ballast, as these fumes then contain mainly CO2 and water. The purer the oxygen used for combustion, the closer the combustion fumes become to a binary H2O / CO2 mixture. The main step in CO2 capture then consists of condensing the water.

[0017] Another important advantage is the reduction in the volume of fumes to be treated. Residual contaminants are less diluted than in combustion in combustible air.

[0018] According to the present invention, we are therefore interested in sites using CO2, also equipped with a boiler capable of supplying hot water to the site, this boiler, in particular a condensing boiler, implementing oxy-combustion between a fuel (CH4, C3H8, etc.) and pure oxygen, the oxygen supplying the boiler being obtained from a source of liquid oxygen present on the site.

[0019] And then, according to the present invention, all or part of the CO2 contained in the fumes produced by the boiler is recovered by organizing, in an exchanger, a heat exchange between said fumes and the liquid oxygen.

[0020] It is indeed the merit of the present invention to have proposed to take advantage of the "free" frigories of the liquid oxygen already present on the site, to purify and in certain cases liquefy the CO2 present in the fumes produced by the boiler, this without the supply of electrical energy which would normally be necessary for such a change of state (by compression expansion).

[0021] The “pure” CO2 thus obtained (recovered) in its gas or liquid form can be stored (sequestered) for later use on the site in question, or used “just in time”, in a flow “synchronized” with the need for hot water and therefore the operation of the boiler.

[0022] The heat exchanger used can be, for example, a plate exchanger or a tubular exchanger.

[0023] Within the exchanger, due to the lowering of the temperature, a change of state of the CO2 takes place, which is liquid at 20 bars / - 20°C.

[0024] The operation of a condensing gas boiler follows the same principle as a traditional boiler and also allows you to take advantage of all the energy produced during the combustion of the gas.

[0025] In a conventional boiler, the central heating water circuit is heated by the combustion of natural gas. The condensing gas boiler takes advantage of the energy contained in the combustion fumes. The fumes emitted during the combustion of natural gas contain water vapor, which condenses, releasing heat. The return water from the heating circuit is heated using this energy, and the water released during condensation (condensates) is evacuated via the wastewater network. For example, for the anesthesia of chickens or pigs, the need for CO2 is advantageously synchronized with the need for hot water; the temperature drop obtained by recovering the frigories of liquid oxygen makes it possible to purify the CO2 gas (at 20 bars and -20°C, for example, only the CO2 will be liquid).

[0026] As an example, for other applications, such as greenhouses for growing plants, it is advantageous to store liquid CO2 in a traditional CO2 tank for use at another time.

[0027] As an example for tomato greenhouses, greenhouse growers heat the greenhouse at night, therefore producing CO2 at night, while they require CO2 during the day for photosynthesis, so it is necessary to store the CO2 in a cryogenic tank.

[0028] Of course, the person skilled in the art is aware of the existence of a prior state of the art, which can be illustrated in particular by documents JP2009 / 203860 and W02022 / 070125, which relate to installations of the power plant or generator type, where, for example, in document JP2009 / 203860 a turbine (10) is supplied with a supercritical fluid, for example nitrogen, or for example CO2, where the fluid released by combustion is purified of its CO2 by exchange with liquid oxygen, the CO2 thus recovered is directed to a suitable reservoir (“Water goes to the waste water reservoir 83 and carbon dioxide goes to the waste carbon dioxide reservoir 84”), for environmental reasons (zero CO2 emissions, ozone layer, etc.).

[0029] In all cases:

[0030] - these previous documents do not cover an oxycombustion boiler supplying a given site with hot water;

[0031] - these earlier documents do not describe a situation where this hot water consuming site also requires for equipment on this site (such as a slaughterhouse or a greenhouse for growing plants), gaseous CO2 or a mixture of gases containing CO2; - these earlier documents do not describe the use of CO2 recovered from the boiler fumes to supply such CO2 consuming equipment.

[0032] The present invention then relates to a method for supplying gaseous CO2 to a site comprising an installation requiring CO2 or a mixture comprising CO2, such as a slaughterhouse or a greenhouse for growing plants, characterized by the implementation of the following measures: a boiler is provided within said site capable of supplying hot water to the site, this boiler implementing oxy-combustion between a fuel and pure oxygen, the oxygen supplying the boiler being obtained from a source of liquid oxygen present on the site; all or part of the CO2 contained in the fumes produced by the boiler is recovered by organizing, in an exchanger, a heat exchange between said fumes and the liquid oxygen.

[0033] The present invention therefore also relates to a method and apparatus for purifying and liquefying CO2, on the user site, by using the frigories of the liquid oxygen present on the site.

[0034] This liquefaction of CO2 may be preceded by one or more treatments of the flue gases using physical and / or chemical separation methods, but also cryogenic methods, aimed at: heating the oxygen and the combustible gas, to improve combustion and reduce the release of nitrogen oxides; condensing the water vapor from the flue gases and perfectly recovering the heat of condensation or latent energy (by lowering the temperature of the flue gases, the water vapor transforms into liquid water). removing any dust generated by the boiler hearth (refractory dust).

[0035] For example, Oxy-Combustion with methane requires 64g of oxygen for 16g of CH4 and will produce 36g of water which will be easily separated and 44g of CO2. The O2 / CO2 ratio is therefore 64 / 44 = 1.45. CO2 requires approximately 85 Kcal / kg to go from +20°C to -20°C (20 bar). Liquid oxygen releases 71.7 Kcal / kg at 8 bar from its liquid form at a temperature of -30°C. The theoretical cooling capacity available is therefore (71.7 x 1.45) + 103 Kcal to liquefy one kg of CO2.

[0036] The advantages of using liquid oxygen mentioned above allow the user of such oxycombustion to finance a good part (or even all) of the oxygen required for combustion. Knowing that the choice of CO2 sequestration is to valorize this gas on processes which usually use commercial CO2, the user here has a largely competitive CO2, this user has also reduced his CO2 emissions by reducing his CH consumption and by not using a "commercial" source of CO2, since the source is recovered on site.

[0037] The attached [Figure 1] illustrates an example of equipment suitable for implementing the invention, in the case of use on the site in question for anesthetizing poultry in a tunnel. In the case of this installation, we worked in conditions where the need for CO2 is synchronized with the need for hot water: hot water is used to pluck the poultry and gaseous CO2 is used to sedate the poultry. In this case it was not necessary to liquefy the CO2.

[0038] The nomenclature of the elements present in this Figure 1 is as follows:

[0039] 1: liquid oxygen storage.

[0040] 2: O2 vaporizer: this exchanger 2 carries out the heat exchange between the fumes and the liquid oxygen, the temperature of the fumes is lowered to a temperature typically close to 2°C to remove as much water as possible, and thus keep CO2.

[0041] 3: O2 and CH4 injection control board.

[0042] 4: boiler.

[0043] 5: burner.

[0044] 6: flue gas analysis module. 7: cryogenic purifier.

[0045] 8: low pressure turbine (turbine 8 allows the fumes from exchanger 7 to be sucked in and sent into tunnel 20, also countering the pressure losses occurring in the various previous stages).

[0046] 9: regulation valve (which is controlled by the anesthesia tunnel, if the tunnel is stopped the gases are sent outside, while the more CO2 the tunnel requires the more the valve opens towards the tunnel circuit).

[0047] 10: CH4 heater (this heater heats the combustible gas before sending it to the burner).

[0048] 11: O2 heater (this heater heats the oxygen before sending it to the burner).

[0049] 12: flue gas condenser (allows the water to be heated before being sent to the boiler).

[0050] 13: town water or borehole, which will be heated for use on the site, but this water, which is cold (generally 10 to 20°C), also allows the temperature of the fumes leaving the boiler to be lowered.

[0051] 14: fuel needed to heat the water, by the boiler, this fuel can also be heated to increase the combustion efficiency.

[0052] 20: poultry anesthesia tunnel.

[0053] Let us detail in the following what occurs in the different equipment present in Figure 1, as well as an example of implementation giving the thermal characteristics of the fluids involved in each stage, data representing only an example of implementation which are only illustrative of the equipment and operating conditions used here:

[0054] - At boiler 4: the town water enters at a temperature of around 25°C and leaves at a temperature of around 85°C, the fumes leave the boiler at a temperature of around 220°C.

[0055] - at the level of the heater 10, the combustible gas enters at a temperature close to 15°C and leaves at a temperature close to 95°C, and the fumes leave this element 10 at a temperature close to 210°C. - at the level of the heater 11, the oxygen enters at a temperature close to 5°C and leaves at a temperature close to 95°C, and the fumes leave this element 11 at a temperature close to 200°C.

[0056] - at the level of the condenser 12, the city water enters at a temperature of around 5°C and leaves at a temperature of around 25°C, and the fumes leave this element 12 at a temperature of around 90°C (The exchanger 12 therefore makes it possible to recover calories in the fumes and preheats the water which will enter the boiler (principle of condensing boilers)).

[0057] - at the level of exchanger 2, the oxygen enters at a temperature close to -183°C and leaves at a temperature close to +5°C, and the fumes leave this element 2 at a temperature close to +2°C. At this stage, the water is completely condensed, only CO2 remains.

[0058] - at element 7, the city water enters at a temperature of around 15°C and leaves at a temperature of around 5°C, and the fumes leave this element 7 at a temperature of around 10°C (exchanger 7 therefore makes it possible to raise the temperature of the CO2 to around 10-12°C after removing the water, which is required for such anesthesia applications according to current legislation).

[0059] Let us consider in the following the example of a 40 ton / h slaughterhouse, anesthetizing under the following conditions:

[0060] A CO2 requirement of 5g per kg of poultry

[0061] For a production of 10,000 chickens per hour, considering chickens weighing on average 2.2 kg each, we obtain a requirement of 110 kg of CO2 per hour, hence 2500 mol / h of CO2, and therefore 2500 x 2 = 5,000 mol / h of oxygen, i.e. 160 kg of oxygen.

[0062] 2500 mol of CH4 x 16 = 40 kg of CH4 per hour.

[0063] Considering that the combustion of methane at 25°C releases an energy of 39.77 MJ / m 3 (55.53 MJ / kg), or 11.05 kWh / m 3 (15.42 kWh / kg= 616 KWh).

[0064] The mass of CO2 released per mole of octane consumed is 44 g.

[0065] The ratio of methane consumption to CO2 emissions is 44 / 16 = 2.75 g.

[0066] 1 kg of methane releases 2.75 kg of CO2. A gain of 20% on CH4 (energy gain with absence of nitrogen + increase in T°C of oxidant / fuel, radiative transfers): (616 / 100)x20=123 Kw

[0067] 123 x 0.10€ per Kw gas (price that can be considered as a reference) = 12.3€ per hour

[0068] Under the conditions of this simulation, the gain on natural gas makes it possible to pay for part of the oxygen for the production of CO2:

[0069] • 160 x 0.088€ per kg = 14.08€ O2 per hour

[0070] • 14.08 - 12.3 = 1.78€ for 110 kg of CO2 or 1.78 / 110 x 1000 = 16.1.

[0071] • Which comes to a CO2 cost of €16.1 / Tonne

[0072] • If no gain occurs on combustion, the price of CO2 is around €134.5 per tonne (compared to around €150 / Tonne for commercial CO2).

[0073] In this field of poultry anesthesia tunnels, it is generally considered that the aim is to achieve a CO2 content in the tunnel of at least 55%.

[0074] And therefore it is necessary to emphasize the fact that an air / CH4 combustion would not allow sufficient CO2 values ​​to be reached in the fumes (the presence of nitrogen in the combustion air limits the concentration to 11.5% of CO2).

[0075] In Figure 1, we have just developed in detail the example of a poultry anesthesia installation in a tunnel, where we worked under conditions where the need for CO2 is synchronized with the need for hot water: hot water is used to pluck the poultry and gaseous CO2 is used to sedate the poultry, it is therefore not necessary here to liquefy the CO2.

[0076] But in other applications, it will be useful to liquefy CO2, for example, let's cite the case of using CO2 for greenhouse growers, the need for CO2 corresponds to the photosynthesis of the plant, therefore during the day, while the need to heat the greenhouse is mainly effective during the night (when it is colder).

[0077] So for these users it is advantageous to liquefy the CO2 at night to distribute it during the day (in sunlight).

[0078] We will then configure the exchanger 2 to go down to -20°C and 20 bars, having added a compressor to the inlet of the exchanger 2, the means 8 then no longer having any reason to exist in such an application (we will note that this “greenhouse” variant is not shown in Figure 1).

[0079] The exchanger 2 to carry out such liquefaction can also be a cryo-condenser, which is a heat exchanger operating at low temperature, the gaseous effluent from the industrial process enters inside a shell, then travels through a series of baffles, around a finned tubular bundle in which a liquid cryogen circulates.

[0080] As has been said, CO2 is a gas which changes state into a solid phase at a pressure close to 4.7 bar, so it is necessary to avoid approaching this pressure.

[0081] A pressure between 16 bar and 20 bar is economically favorable, while a temperature of -20°C requires little investment in terms of insulation.

[0082] It is therefore generally considered that the “20 bar, -20°C” pair represents the best compromise.

Claims

CLAIMS 1. A method for supplying gaseous CO2 to a site comprising an installation (20) requiring CO2 or a mixture comprising CO2, such as a slaughterhouse or a greenhouse for growing plants, characterized by the implementation of the following measures: a boiler (4) is provided within said site, capable of supplying hot water to the site, this boiler implementing oxy-combustion between a fuel (14) and pure oxygen (1), the oxygen supplying the boiler being obtained from a source of liquid oxygen (1) present on the site; all or part of the CO2 contained in the fumes produced by the boiler is recovered by organizing, in an exchanger (2), a heat exchange between said fumes and the liquid oxygen.

2. Method according to claim 1, characterized in that the CO2 thus recovered is in its gaseous form and it is stored (sequestered) for later use on the site in question, or else used “in a just-in-time” flow, in a flow “synchronized” with the need for hot water.

3. Method according to claim 1, characterized in that the CO2 thus recovered is in its liquid form and it is stored in a tank for liquid CO2 for subsequent use on the site in question.

4. Method according to claim 3, characterized in that said exchanger in which a heat exchange is organized between said fumes and liquid oxygen is configured to bring the fumes entering the exchanger under pressure and temperature conditions allowing the liquefaction of the CO2 present in these fumes, thus taking advantage of the frigories of the liquid oxygen present on the site, this without the need for an input of electrical energy which would normally be necessary for such a change of state.

5. Method according to claim 2, wherein said installation requiring CO2 is an installation for anesthetizing poultry or other animals, before slaughter. Method according to claim 3 or 4, wherein said installation requiring CO2 is a greenhouse plant cultivation installation, where the need for CO2 occurs essentially during the day, while the need to heat the greenhouse occurs essentially during the night, the CO2 recovered in liquid form during the night, i.e. during the boiler operation phase, being stored in a liquid CO2 tank for use of this CO2 during the day when the greenhouse requires it. Method according to one of the preceding claims, characterized in that said heat exchange between said fumes and liquid oxygen is preceded by one or more fume treatments (12, 11, 10, 7, ...) by physical and / or chemical and / or cryogenic separation methods, aimed at carrying out one or more of the following actions: heating the oxygen and the combustible gas, to improve the combustion taking place in the boiler and reduce the release of nitrogen oxides; condensing the water vapor from the fumes; removing any dust generated by the boiler hearth.Device for supplying gaseous CO2 to a site comprising an installation (20) requiring CO2 or a mixture comprising CO2, such as a slaughterhouse or a greenhouse for growing plants, a site which comprises a boiler (4) capable of supplying hot water to the site, this boiler implementing oxy-combustion between a fuel (14) and pure oxygen (1), the oxygen supplying the boiler being obtained from a source of liquid oxygen (1) present on the site, characterized in that it comprises a heat exchanger (2), making it possible to organize a heat exchange between said fumes and the liquid oxygen to allow the recovery of all or part of the CO2 contained in the fumes produced by the boiler, and the supply using this CO2 thus recovered from said installation. Device according to claim 8, characterized in that the CO2 thus recovered is in its liquid form and in that the device comprises means for storing the CO2 thus recovered in liquid form for subsequent use on the site in question. Device according to claim 8, characterized in that the CO2 thus recovered is in its gaseous form and in that the device comprises means for storing the CO2 thus recovered for subsequent use on the site in question.Device according to claim 8 or 9, characterized in that said heat exchanger (2) making it possible to organize a heat exchange between said fumes and liquid oxygen is configured to bring the fumes entering the exchanger under pressure and temperature conditions allowing the liquefaction of the CO2 present in these fumes, thus taking advantage of the frigories of the liquid oxygen present on the site, this without the need for an electrical energy supply which would normally be necessary for such a change of state. Device according to one of claims 8 to 11, characterized in that it comprises means (12, 11, 10, 7, ...) for treating the fumes before they reach the exchanger, treatment means using physical and / or chemical and / or cryogenic separation methods, aimed at carrying out one or more of the following actions: heating the oxygen and the combustible gas, to improve the combustion taking place in the boiler and reduce the release of nitrogen oxides; condensing the water vapor from the fumes; removing any dust generated by the boiler hearth.

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