Systems for supplying CO2 gas to facilities requiring CO2 or mixtures containing CO2, such as slaughterhouses or greenhouses for growing plants

Abstract

The present invention relates to a method for supplying CO2 gas to a site equipped with an installation (20) requiring CO2 or a mixture containing CO2, such as a slaughterhouse or a greenhouse for growing plants, characterized by the following steps: a boiler (4) capable of supplying hot water to the site is arranged on the site, said boiler performs a process of oxy-combustion between fuel (14) and pure oxygen (1), the oxygen supplied to the boiler being obtained from a source of liquid oxygen present on the site, and part 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

[Technical Field]

[0001] The present invention relates to processes and installations using gaseous CO2, especially in the food processing industry, including in particular the beverage sector, modified atmospheres for the preservation of foodstuffs, or the anesthesia of poultry in slaughterhouses, or the cultivation of plants in greenhouses. [Background technology]

[0002] The demand for CO2 in developed countries is still increasing (especially for the uses mentioned above). This CO2 results mainly from fertilizer and methanol (by-product) plants or from hydrogen production plants. The availability of this molecule is therefore becoming important due to frequent shutdowns of fertilizer production plants and geopolitical tensions, which in turn have a strong impact on the price of gas.

[0003] It is then commonly observed that in many countries, due to these frequent crises, greenhouse growers, for example, have not been supplied with commercial CO2 for several months of the year in recent years, which, as is well understood, has a direct impact on their productivity. This is coupled with strong environmental constraints imposed by the desire of developed countries to reduce greenhouse gas emissions, which will directly affect the methods for CO2 production by encouraging the search for solutions aimed at reducing carbon dioxide emissions. Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention attempts to provide an innovative solution for producing CO2 at the actual site of this CO2 user. As will be understood in more detail below, the invention proposes to use items of equipment for the generation of heat (boilers) that are conventionally present at such sites by converting them to oxy-fuel combustion. In this way, the heat produced by the boiler comes from the production of CO2 and is therefore considered "unavoidable heat" in a legal sense.

[0005] Oxy-fuel combustion is a combustion process in which the oxidant gas is no longer air but "pure" oxygen (i.e., generally characterized by a purity of more than 95%, and for liquid oxygen, more than 99%). Oxy-fuel combustion (thus using oxygen and not air) has already been adopted by certain industries operating at high temperatures (glassworks, cement plants, metallurgical plants, etc.) as it offers several advantages, among which may be mentioned: · Reduction in flue gas volume due to reduction / elimination of nitrogen ballast. · Increased thermal efficiency is directly related to reduced flue gas volume (due to less heat loss in the flue gas). · Enhancement of heat transfer due to two phenomena: increased flame temperature and increased radiative heat flow due to flue gases essentially consisting of emitted gases (CO2, H2O). Reduction of polluting emissions of thermal NOx or dioxins (related to the reduction in the volume of oxidizer). In the specialist literature, improvements in the range of 10% to 40% are reported here with respect to fuel. Heating of the oxidizer and fuel also allows a reduction in the consumption of the latter.

[0006] In particular, the objective is to increase the CO2 content of the combustion flue gas by removing the nitrogen ballast, which therefore contains mainly CO2 and water. The purer the oxygen used in the combustion, the closer the combustion flue gas is to a binary H2O / CO2 mixture. The main step in capturing CO2 then consists in condensing the water. Another important advantage is the reduction in the volume of flue gas to be treated. Residual pollutants are less diluted than in combustion in combustible air. [Means for solving the problem]

[0007] The present invention therefore relates to a site equipped with a boiler that uses CO2 and is also able to supply hot water to the site, this boiler, in particular a condensing boiler, employing oxy-fuel combustion between a fuel (CH4, C3H8, etc.) and pure oxygen, the oxygen supplied to the boiler being obtained from a source of liquid oxygen present on site, then, according to the invention, recovering all or part of the CO2 contained in the flue gases produced by the boiler and carrying out heat exchange between said flue gases and the liquid oxygen in an exchanger.

[0008] In particular, the invention is credited with proposing to utilize the "free" low temperature of liquid oxygen already present on site to purify and possibly liquefy the CO2 present in the flue gas produced by the boiler, without the contribution of electrical energy normally required for such a change of state (by compression / expansion).

[0009] The "pure" CO2 thus obtained (captured) in gaseous or liquid form can be stored (sequestered) for subsequent use at the site under consideration, or can be used as a "just-in-time stream" to "synchronize" with the hot water requirements and thus the operation of the boiler.

[0010] The heat exchanger used can be, by way of example, a plate or tubular exchanger. In the exchanger, the change of state of the CO2, which is liquid at 20 bar / -20°C, is achieved by lowering the temperature.

[0011] Condensing gas boilers operate on the same principle as conventional boilers, but in addition make it possible to utilize all the energy generated during gas combustion. In conventional boilers, the central heating water circuit is heated by the combustion of natural gas. Condensing gas boilers utilize the energy contained in the combustion flue gases. The flue gases released during natural gas combustion contain water vapor, which condenses and releases heat. The return water from the heating circuit is heated by this energy, and the water released during condensation (condensate) is discharged via a wastewater system.

[0012] As an example, for anesthesia of chickens or pigs, the CO2 requirement may be advantageously considered to be synchronized with the hot water requirement. The reduced temperature obtained by cryogenic reforming of liquid oxygen allows the CO2 gas to be purified (e.g., at 20 bar and -20°C, only CO2 is liquid). As a further example, in other applications, such as greenhouses for growing plants, it is advantageous to store liquid CO2 in conventional CO2 tanks for later use. As an example, in the case of a tomato greenhouse, the greenhouse grower heats the greenhouse at night and therefore produces CO2 at night, whereas CO2 is required for photosynthesis during the day and therefore needs to be stored in cryogenic tanks.

[0013] Of course, the skilled person is aware of the existence of a state of the art that can be exemplified in particular by documents JP 2009-203860 and WO 2022 / 070125 relating to power plant or generator type installations, for example in document JP 2009-203860, in which a turbine (10) is fed with a supercritical fluid, for example nitrogen or for example CO2, in which the fluid discharged by combustion is purified of its CO2 by exchange with liquid oxygen, and the CO2 thus recovered is led to a suitable tank ("water goes to a waste water reservoir 83 and carbon dioxide goes to a waste carbon dioxide reservoir 84") for environmental reasons (zero emissions of CO2, the ozone layer, etc.).

[0014] In all cases, These prior art documents do not include an oxy-fuel fired boiler for supplying hot water to a given site. These prior art documents do not describe situations where the hot water consuming site also requires gaseous CO2 or a gas mixture containing CO2 for items of equipment at the site (e.g., a slaughterhouse or a greenhouse for growing plants). - These prior art documents do not describe the use of CO2 recovered in the flue gases of a boiler to supply such items of equipment that consume CO2.

[0015] The present invention then provides a process for supplying gaseous CO to a facility requiring CO or a mixture containing CO, for example a slaughterhouse or a site equipped with a greenhouse for growing plants, comprising the following steps: a boiler is available on-site that is capable of supplying hot water to the site, the boiler employing oxy-fuel combustion between fuel and pure oxygen, the oxygen supplied to the boiler being obtained from a source of liquid oxygen present on-site; - the CO2 contained in the flue gas produced by the boiler is totally or partially recovered, and heat exchange between the flue gas and liquid oxygen is carried out in an exchanger.

[0016] The present invention therefore also relates to a process and apparatus for the purification and liquefaction of CO2 on-site at the user's site, achieved by the cryogenic modification of liquid oxygen present on-site. This liquefaction of CO2 can be preceded by one or more treatments of the flue gas by physical and / or chemical and cryogenic separation methods aimed at: heating the oxygen and fuel gas to improve combustion and reduce nitrogen oxide emissions; - condensing the steam from the flue gases and recovering the heat or potential energy of condensation (by reducing the temperature of the flue gases, the steam is converted into liquid water); - To remove dust (refractory dust) that may be generated by the boiler furnace.

[0017] As an example, oxy-fuel combustion with methane requires 64 g of oxygen per 16 g of CH4, producing 36 g of water, which are easily separated, and 44 g of CO2. The O2 / CO2 ratio is therefore 64 / 44 = 1.45. CO2 requires approximately 85 kcal / kg to change 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 refrigeration capacity available is therefore (71.7 x 1.45) + 103 kcal to liquefy 1 kg of CO2.

[0018] The above-mentioned advantages of using liquid oxygen allow users of such oxy-fuel combustion to finance a significant portion (indeed, even all) of the oxygen required for combustion. Knowing that the choice of CO2 sequestration is to reform this gas for processes that customarily use commercially available CO2, the user now has access to widely competitive CO2, and further, because the source is captured on-site, the user is reducing their CO2 emissions by reducing their consumption of CH4 and by not using a "commercial" source of CO2. [Brief explanation of the drawings]

[0019] [Figure 1] Attached Figure 1 shows an example of an item of equipment suitable for carrying out the present invention when used in the field under consideration for tunnel anesthesia in poultry. In this installation, operation was carried out under conditions where the CO2 requirement was synchronized with the hot water requirement. The hot water was used to pluck the poultry feathers, and the gaseous CO2 was used to put the poultry to sleep. In this case, there was no need to liquefy the CO2. DETAILED DESCRIPTION OF THE INVENTION

[0020] The nomenclature of the elements present in this Figure 1 is as follows: -1: Liquid oxygen storage. -2: O2 vaporizer: This exchanger 2 carries out a heat exchange between the flue gas and liquid oxygen, the temperature of which is reduced therein, usually to a temperature close to 2°C, in order to remove as much water as possible and then retain the CO2. -3: Plate for adjusting the injection of O2 and CH4. -4: Boiler. -5: Burner. -6: Module for analysis of flue gases. -7: Cryogenic purifier. -8: low-pressure turbine (turbine 8 makes it possible to suck up the flue gases coming from exchanger 7 and send them into tunnel 20, and also counteracts the pressure drop that occurs in the various previous stages). -9: Regulating valve (controlled by the anesthesia tunnel; if the tunnel is blocked, the gas is sent to the outside, while the more CO2 the tunnel needs, the more the valve opens towards the tunnel's circuit). -10: CH4 heater (this heater makes it possible to heat the fuel gas before sending it to the burner). -11: O2 heater (this heater allows the oxygen to be heated before being sent to the burner). -12: Flue gas condenser (allows the water to be heated before being sent to the boiler). -13: Tap water or drilling water, heated for use on-site, but this water is at a low temperature (generally 10-20°C) and can also reduce the temperature of the flue gases at the boiler outlet. -14: Fuel required to heat water through a boiler; this fuel can also be heated to increase combustion efficiency. -20:Anesthetic tunnel for poultry.

[0021] An example of what is done in the various items of equipment present in FIG. 1 and providing the thermal properties of the fluids involved at each stage, data representing only one example, which is merely illustrative of the items of equipment and operating conditions used herein, is described in detail below. In the boiler 4, tap water enters it at a temperature of around 25°C and leaves it at a temperature of around 85°C, and flue gases leave the boiler at a temperature of around 220°C. At the heater 10, the fuel gas enters at a temperature of around 15°C and leaves at a temperature of around 95°C, and the flue gas leaves this element 10 at a temperature of around 210°C. At the heater 11, oxygen enters at a temperature of around 5°C and leaves it at a temperature of around 95°C, and the flue gas leaves this element 11 at a temperature of around 200°C. In the condenser 12, tap water enters it at a temperature of around 5°C and leaves it at a temperature of around 25°C, and the flue gases leave this element 12 at a temperature of around 90°C (the exchanger 12 thus makes it possible to recover heat from the flue gases and preheat the water entering the boiler (condensing boiler principle)). In exchanger 2, oxygen enters at a temperature around -183°C and leaves at a temperature around +5°C, and flue gas leaves this element 2 at a temperature around +2°C. At this stage, the water is completely condensed and only CO2 remains. In element 7, tap water enters it at a temperature of around 15°C and leaves it at a temperature of around 5°C, and flue gases leave this element 7 at a temperature of around 10°C (exchanger 7 therefore makes it possible to increase the temperature of the CO2 by about 10-12°C after removing the water from it, which is required for such anaesthetic applications according to current legislation).

[0022] In what follows, we consider the example of a 40 ton / h slaughterhouse that anesthetizes under the following conditions: - 5g CO2 requirement per kg of poultry. -To produce 10000 chickens per hour, taking into account that each chicken weighs an average of 2.2 kg, we get a CO2 requirement of 110 kg per hour, hence 2500 mol / h of CO2 and hence 2500 x 2 = 5000 mol / h of oxygen, i.e. 160 kg of oxygen. -2500 mol CH4 x 16 = 40 kg CH4 per hour. Combustion of methane at -25°C produces 39.77 MJ / m 3 (55.53MJ / kg), or 11.05kWh / m 3 Consider that (15.42kWh / kg=616kWh) of energy is released. -The weight of CO2 released per mole of octane consumed is 44g. -The ratio of methane consumption / CO2 emissions is 44 / 16 = 2.75g. -1kg of methane emits 2.75kg of CO2. -20% savings in CH4 (energy savings due to absence of nitrogen + T°C increase in oxidizer / fuel, radiative transfer): (616 / 100) x 20 = 123 kW -123 x 0.10 euros per kW of gas (a price that can be considered as a reference) = 12.3 euros per hour Under the conditions of this simulation, it is possible to pay for part of the oxygen for the production of CO2 with savings on natural gas. 160 x 0.088€ per kg = 214.08€ per hour · 14.08 - 12.3 = 1.78 euros / 110 kg of CO2, i.e. 1.78 / 110 x 1000 = 16.1. The cost of CO2 will be 16.1 euros / tonne · No savings in terms of combustion, but the cost of CO2 is around 134.5€ / tonne (compared to around 150€ / tonne for commercial CO2).

[0023] In this field of tunnels for poultry anesthesia, it is generally considered desirable to achieve a CO2 content in the tunnel of at least 55%, and therefore it is necessary to emphasize the fact that in air / CH4 combustion it is not possible to achieve sufficient values ​​of CO2 in the flue gas (the presence of nitrogen in the combustion air limits the CO2 concentration to 11.5%).

[0024] An example of a tunnel poultry anesthesia facility is shown in detail in FIG. 1, where operation was performed under conditions in which the CO2 requirement was synchronized with the hot water requirement. Hot water is used to pluck the poultry, and gaseous CO2 is used to put the poultry to sleep; therefore, liquefying CO2 is not necessary here. However, liquefying CO2 is useful in other applications, such as greenhouse growers, whose CO2 requirements correspond to plant photosynthesis during the day, while the greenhouse heating requirement is primarily effective overnight (when the greenhouse is colder). Therefore, it is advantageous for these users to liquefy CO2 at night for distribution during the day (in sunlight). Exchanger 2 is then configured to be lowered to -20°C and 20 bar by adding a compressor to the inlet of exchanger 2; then, means 8 no longer has any reason to be in such applications (note that this "greenhouse grower" variant is not represented in FIG. 1).

[0025] The exchanger 2 for carrying out such liquefaction may also be a cryogenic condenser, which is a heat exchanger operating at low temperatures, in which the gaseous effluent resulting from the industrial process enters the interior of a shell-and-tube and then passes through a series of baffles around a finned tube bundle through which liquid cryogen circulates.

[0026] As already mentioned, CO2 is a gas that changes state to a solid phase at pressures approaching 4.7 bar, and therefore it is necessary to avoid approaching this pressure. Pressures between 16 bar and 20 bar are economically advantageous, while a temperature of -20°C requires little capital investment in terms of insulation. Therefore, the pair "20 bar, -20°C" is generally considered to represent the best compromise.

Claims

1. CO ２ or CO ２ Equipment (20) requiring a mixture containing gaseous CO2, for example, a slaughterhouse or a site with a greenhouse for plant cultivation. ２ A process for supplying the following measures: - Within the site, a boiler (4) capable of supplying hot water to the site is available, and this boiler employs oxygen fuel combustion between fuel (14) and pure oxygen (1), and the oxygen supplied to the boiler is obtained from a liquid oxygen (1) source present at the site. - The CO contained in the flue gas generated by the boiler ２ All or part of it is recovered, and heat exchange takes place between the flue gas and the liquid oxygen in the exchanger (2). According to the configuration of the aforementioned exchanger and according to the use to be performed at the site under consideration, CO ２ While it becomes possible to recover it in its gaseous or liquid form, in this exchange, all or part of the water contained in the flue gas is purified. A process characterized by the implementation of [the specified method].

2. CO2 is recovered in this way. ２ The process according to claim 1, characterized in that the substance is in gaseous form and is stored (isolated) for subsequent use at the site under consideration, or is used as a "just-in-time flow" that "synchronizes" with the required amount of hot water.

3. CO2 is recovered in this way. ２ It is in liquid form and is intended for subsequent use at the site under consideration as liquid CO ２ The process according to claim 1, characterized in that it is stored in a tank for use.

4. The exchanger in which heat exchange between the flue gas and the liquid oxygen takes place is configured to convey the flue gas entering the exchanger under the pressure and temperature conditions that enable liquefaction of the CO present in these flue gases. Thus, the low temperature of the liquid oxygen present at the site is utilized, which is characterized in that it does not require the contribution of electrical energy that is usually necessary for such a change of state. The process according to claim 3. ２ configured to convey the flue gas entering the exchanger under the pressure and temperature conditions that enable liquefaction of the CO present in these flue gases. Thus, the low temperature of the liquid oxygen present at the site is utilized, which is characterized in that it does not require the contribution of electrical energy that is usually necessary for such a change of state. The process according to claim 3.

5. CO ２ The process according to claim 2, wherein the equipment required is equipment for anesthetizing poultry or other animals before slaughter.

6. CO ２ The aforementioned equipment requiring CO is equipment for cultivating plants in a greenhouse, ２ The amount of CO2 needed for heating is essentially daytime, whereas the requirement for heating the greenhouse is essentially nighttime, and CO2 is recovered in liquid form during the night, i.e., during the boiler's operating phase. ２ This CO2 is what the greenhouse needs during the daytime. ２ Liquid CO2 is used for the purpose of ２ The process according to claim 3 or 4, wherein the contents are stored in a tank for use.

7. Prior to the heat exchange between the flue gas and the liquid oxygen, the following actions are taken: - To improve the combustion occurring in the boiler and reduce the emission of nitrogen oxides, the oxygen and fuel gas are heated, - Condensing the vapor of the flue gas, - To remove dust that may be generated by the furnace of the boiler, The process according to any one of claims 1 to 5, characterized in that one or more of the flue gases (12, 11, 10, 7, etc.) are treated by physical and / or chemical and / or cryogenic separation methods for the purpose of performing one or more of the following.

8. CO ２ or CO ２ Equipment (20) requiring a mixture containing gaseous CO2, for example, a slaughterhouse or a site with a greenhouse for plant cultivation. ２ The apparatus is for supplying CO, and the site is equipped with a boiler (4) that can provide hot water to the site, and this boiler employs oxygen fuel combustion between fuel (14) and pure oxygen (1), and the oxygen supplied to the boiler is obtained from a liquid oxygen (1) source present at the site, and the apparatus is equipped with a boiler (4) that can provide hot water to the site, and this boiler employs oxygen fuel combustion between fuel (14) and pure oxygen (1), and the oxygen supplied to the boiler is obtained from a liquid oxygen (1) source present at the site, and the CO contained in the flue gas produced by the boiler ２ Recovery of all or part of the CO2 recovered in this manner, and the CO2 ２ In order to enable supply to the equipment using the above, a heat exchanger (2) is provided that enables heat exchange between the flue gas and the liquid oxygen, The aforementioned exchanger, according to the use to be performed at the site under consideration, CO ２ The apparatus is characterized in that it is possible to recover the gaseous or liquid form of the water, while also being configured to purify all or part of the water contained in the flue gas during this exchange.

9. The heat exchanger (2), which enables heat exchange between the flue gas and the liquid oxygen, uses the CO present in these flue gases. ２ The apparatus according to claim 8, configured to transport the flue gas entering the exchanger under pressure and temperature conditions that enable the liquefaction of the liquid oxygen, and thus utilizing the low temperature of the liquid oxygen present at the site, which does not require the contribution of electrical energy that is normally required for such a change in state.

10. The device is equipped with means for processing the flue gas (12, 11, 10, 7, etc.) before reaching the exchanger, and the processing means performs the following actions: - To improve the combustion occurring in the boiler and reduce the emission of nitrogen oxides, the oxygen and fuel gas are heated, - Condensing the vapor of the flue gas, - To remove dust that may be generated by the furnace of the boiler, The apparatus according to claim 8 or 9, characterized by employing a physical and / or chemical and / or cryogenic separation method for the purpose of performing one or more of the following.

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