Set of iron combustion honeycomb modules for application in decarbonized energy production

Abstract

A thermal energy production system by metal combustion, characterized in that it comprises a set of iron combustion reactors arranged in a honeycomb pattern. The reactors may consist of iron particle burners followed by their combustion chamber and surrounded by a circuit containing a heat transfer fluid. See Figure 5

Description

Title of the invention: Set of iron combustion honeycomb modules for application in the production of decarbonized energy. FIELD OF THE INVENTION

[0001] The present invention relates to a system for producing thermal energy by combustion of metals for application to the production of decarbonized energy in stationary applications or for mobility. It also relates to a process for producing thermal energy implemented in this system. STATE OF THE ART

[0002] Most current heating systems (natural gas, propane, butane, or fuel oil boilers) use fuels that emit CO2. Furthermore, the rising cost of energy and the risk of shortages due to the energy dependencies of many countries worldwide are driving the search for green alternative energy sources for residential and commercial heating. The use of wood for heating also presents a significant risk of deforestation if responsible and sustainable forest management practices are not adopted.

[0003] In this context, the combustion of metallic particles, as detailed in the article "Direct combustion of recyclable metal fuels for zero-carbon heat and power," Applied Energy, 2015 by JF Bergthorson, is a proposed solution for producing CO2-free combustion for all types of energy production applications. Metallic fuels (magnesium, aluminum, iron) have the advantage of generating only solid metal oxides during combustion, which are easily recovered in a combustion system. These oxides can then be recycled using renewable energy via an inert anode electrolysis process or a zero-CO2 thermochemical reduction process using solar energy.

[0004] The combustion of metallic particles is historically known in aerospace propulsion applications and also in documents US8100095B2 for internal and external combustion automotive applications. A major problem with iron combustion is the time required to burn all the particles. Some companies are developing iron combustion systems with lengths exceeding ten meters in height for only a few MW. However, a reactor of this type is compatible with very few industrial installations or vehicles due to its great height. It is therefore important to modify the design of this system to make it compatible with a large majority of industrial installations. The advantage of having several small power reactors Equivalent to a single large reactor, the goal is to reduce the required length of each reactor so that the particles have time to burn. Since, at lower power outputs, with a diameter equivalent to that of a single reactor (the equivalent diameter providing the cross-sectional area for airflow which, combined with the chosen length and total airflow rate, determines the residence time necessary for the oxidation of iron particles, specifically chosen for the single reactor), the flow velocity is lower (reduced air requirement with decreased power), meaning the particles need less distance to burn. Another advantage of using multiple reactors instead of increasing the diameter of a single reactor (to decrease the flow velocity and shorten the reactor) is that the heat exchange surface area will be larger, thus maximizing the compactness of the heat exchanger.Integrating heat exchangers into the enlarged combustion chamber (to use the option with a single enlarged reactor) is not feasible due to the heavy fouling associated with the highly particle-laden flow.

[0005] The main object of the invention is to provide a modular assembly of iron combustion reactors, thereby reducing the height of the system compared to a single reactor of equal power, allowing the integration of iron combustion systems into a wide variety of industrial applications. Description of the invention

[0006] The invention comprises a set of reactors arranged in a honeycomb pattern to minimize the height of the combustion system and facilitate the large-scale industrialization of a wide range of boilers (50 kW to several MW). DESCRIPTION OF FIGURES

[0007] Other features and advantages will become apparent from the following description of a particular, non-limiting embodiment of the invention, made with reference to the figures in which

[0008] [Fig.1] is a schematic representation of the combustion system composed of a set of reactors.

[0009] [Fig.2] is a schematic representation of the combustion system composed of a a set of reactors surrounded by a hexagonal casing.

[0010] [Fig.3] is a schematic representation of the combustion system consisting of a set of reactors with a distribution of exhaust tubes around the main reactors.

[0011] [Fig.4] is a schematic representation of the nest-like combustion system of bees with several possible module geometries.

[0012] [Fig.5] is a schematic representation of the combustion system with a platform including the filtration system, heat recovery and the injector. DETAILED DESCRIPTION

[0013] SI is an assembly of reactors 1 composed of iron particle burners followed by their combustion chamber and surrounded (or within the chamber) by a circuit containing a heat transfer fluid (each reactor may have its own heat exchanger circuit, potentially each having a different function (different fluid and / or temperatures for heat and / or electricity), or be in contact with the same heat recovery circuit or be immersed together in a tank containing a heat transfer fluid (e.g., water). All of these reactors feed into a filtration system 3, either sedimentation or cyclone type (each reactor may have its own filtration system or share the same one). A block 4 may supplement the filtration of 3 by adding a cyclone and bag or HEPA filters.Placing a filter at the outlet of each reactor would be possible, but sharing a single filter into which all the reactors would discharge seems simpler to implement. The heat exchanger system 2 can accommodate several types of heat transfer fluids depending on the application requirements. This system can be used for stationary applications (boiler rooms, steam generators, power plants) or mobile applications (boat engines, airships, etc.).

[0014] The preliminary sizing of each combustion chamber (also called a reactor) is based on the desired residence time of the gas within it and the available height for such a reactor at the installation site (the number of reactors will also depend on the available surface area in the boiler room and their relative positioning – aligned in a single row, in several rows, circularly, or otherwise, depending on the available space configuration). The law allowing the preliminary sizing of each reactor solely based on the gas flow rate is: D total xt res HxS = —:-- jV r

[0015] H is the equivalent height of each reactor

[0016] S is the surface area of ​​the air passage cross-section in each reactor

[0017] D_total is the total volumetric flow rate of oxidant under normal conditions required to oxidize the iron particles while maintaining an air-fuel ratio (iron-oxygen ratio relative to stoichiometry) ranging from 0.2 to 1. An additional flow rate may be considered to regulate the temperature of the hot gases. The total volumetric flow rate must be corrected for an average temperature in the exhaust gases (gas expansion factor).

[0018] t_res is the residence time of the target gas in each of the reactors to reach an oxidation level targeted by the designer (except for a vertical reactor with top-down particle injection, because the effect of gravity reduces this time). This Residence time can also be determined by the heat exchange time required to sufficiently cool the flow. The purpose of this formula is to provide an indication that gives a rough idea of ​​the sizing of each reactor.

[0019] N_r is the number of reactors and is therefore strictly greater than 1

[0020] For example, if we want to reduce the height of the single reactor by a factor of 5, while maintaining the total power and the cross-sectional area, we will need to install 5 reactors that share the total air flow rate. It might be preferable to also reduce S and increase the number of reactors to maximize the surface area for heat exchange with the heat transfer fluid circulating between the reactors (double-walled or immersed heat exchange circuit). The equation above shows that without the possibility of using multiple reactors, the only degree of freedom to compensate for the reduction in height (without changing the power and residence time) is the air passage area.However, dividing the height by 5 implies multiplying the cross-section by 5, at the expense of a smaller heat exchange surface area or fouling of the heat exchangers if they are immersed in the hot flow in direct contact with the particles (to maximize the exchange surface area). The advantage of the multi-reactor design lies precisely in this respect. It is even possible to imagine reactors of slightly different dimensions, as long as the principles of modularity and compactness are respected. The main idea is to give engineers more freedom in their design of an iron combustion system, which otherwise has characteristics that make it poorly suited for integration into existing boiler rooms (which are usually 3 to 5 meters high with a power output between 200 kWth and 5 MWth).

[0021] One particular case, common in iron combustion systems, concerns the two-phase flow from top to bottom in the vertical reactor. The sedimentation velocity of the particles must be taken into account in the constraint related to the minimum residence time of the particles in order to maximize their oxidation rate and cooling. Indeed, in the case of iron, this velocity for particles with a diameter d50 between 20 and 60 pm is not negligible, even quite high. And the minimum residence time of the particles is dictated by the oxidation time and the cooling time of the oxides to avoid sintering and agglomeration.

[0022] Let's take an example, if we divide the output into 5 reactors of 200 kW (70 cm diameter) instead of one 1 MW reactor that is 9 meters high (1.15 m diameter). With an average iron particle velocity of 60 cm / s. In the case of the 5 reactors, each sharing the air flow to achieve a total output of 1 MW (at an air-fuel ratio of 0.8), the particle velocity (gas velocity + sedimentation velocity) reaches approximately 1.05 cm / s in the first case and 1.44 m / s in the second case. It is necessary Therefore, a reactor 6.5 m high instead of 9 meters to maintain the same residence time of the particles.

[0023] In addition to ensuring that a minimum residence time is respected, it is necessary to ensure that the dimensions (diameter and height) of the reactor allow for optimal heat exchange in the first peripheral heat exchanger. To maximize the heat recovered by the heat exchanger by convection, one can use: Q = 41 * A * AT' (where A is the total surface area of ​​the heat exchanger, h is the convection coefficient, and h is the temperature difference between the inlet and outlet).

[0024] Reducing the height, without changing the reactor diameter, necessarily reduces the amount of heat recovered in the primary heat exchanger. Reducing the diameter accordingly is beneficial for increasing the convection coefficient h, which depends on the Reynolds number (h proportional to the Nusselt constant) of the flow and is inversely proportional to the diameter (h = Nu*k / D). This is true despite the reduction in the heat exchange surface area caused by the decrease in diameter. Theoretically, the height (to reach the desired 3-4 meters) and the diameter of the multi-reactor can therefore be further reduced until the minimum particle residence time threshold is reached while maintaining equivalent heat exchange (even if it means increasing the number of reactors).The constraint for a single reactor is that the combined reduction in diameter and height significantly reduces the residence time of the particles, which can amount to a few hundred milliseconds, insufficient for preheating, burning, and cooling the iron particles. Hence the advantage of being able to distribute the flow rate across different reactors (with smaller diameters) in order to achieve a sufficient residence time and, incidentally, increase the exchange surface area.

[0025] We conducted a comparative simulation of a single 1 MW reactor versus a multi-reactor system, the aim being to maintain the particle residence time between 1.5 and 3 seconds and to ensure the same heat recovery rate while reducing the height from 9 to 4 meters. The degrees of freedom are therefore the diameter and the number of reactors. The simulation yielded the following results: Parameter Single Reactor 5 reactors 10 reactors 20 reactors 20 reactors Number of reactors 1 5 10 20 20 Heat exchanger tube diameter (mm) 70 25 35 35 38 Heat exchanger loop diameter 1000 550 650 450 250 Reactor diameter (mm) 1100 600 700 500 300 Height (mm) 9000 4000 4000 4000 4000 Gas velocity, m / s 3.3 2.2 0.77 0.75 2 Particle residence time, s 3 1.46 3.5 3.52 1.7 Heat transfer surface area, m2 79 19*5 22.57*10 15.6*20 8.6*20 Coefficient Heat transfer coefficient (W / m²-K) 3.9 3.1 1.3 1.6 6 Overall heat transfer coefficient (W / m²-K) 3.8 3.1 1.29 1.6 5.8 Heat transfer rate (kW) 503.4 95.1*5=475 49*10 34*20 46*20

[0026] If the height were to be reduced from 9 to 4 meters on a single reactor and the particle residence time and heat recovery rate maintained, the only degree of Therefore, freedom is the diameter, and the equation has no optimal solution. A trade-off must be made between the residence time and the heat recovery rate described in this table from simulations: Parameter Single Reactor (9m) Single Reactor (4m) Single Reactor (4m) Diameter of a heat exchanger loop 70 70 200 Reactor diameter (mm) 1000 1700 500 Height (mm) 1100 1800 700 Gas velocity, m / s 9000 4000 4000 Particle residence time, s 3.3 1.25 31.9 Heat transfer area, m2 3 3.13 0.32 Heat transfer coefficient W / m2-K 79 56.6 21 Overall heat transfer coefficient, W / m2-K 3.9 1.3 30 Heat transfer rate, kW 3.8 1.3 18 Diameter of a heat exchanger loop 503.4 174 498

[0027] A compromise must therefore be made between combustion efficiency (or a sufficient reduction in particle temperature) and the heat recovery rate if a single 4-meter-high reactor is desired. Indeed, reducing the height to 4 meters implies significantly reducing the diameter to 700 mm to recover the same amount of heat as in the 9-meter-high reactor (to increase the gas velocity and therefore the heat transfer coefficient), resulting in a residence time of 320 ms. This is partly due to the fact that iron combustion generates a large quantity of high-temperature oxide particles that cannot allow for efficient heat recovery with a heat exchanger immersed in the flow (due to the risk of reactor fouling). Combined with the fact that the cumulative preheating / combustion / cooling of particles is longer (often requiring more than 1.5-2 seconds) than fossil fuels.

[0028] For accurate preliminary sizing of the multi-reactor, a minimum particle residence time (taking into account the sedimentation rate in the case of a vertical multi-reactor system with top-down powder injection) and the maximum desired height for a compact system must be established as constraints. The diameter of each reactor will then depend on the desired number of reactors (a large number of reactors increases the risk of partial failures, although without complete boiler shutdown) and the desired level of heat recovery in the main peripheral heat exchanger (the convective heat transfer coefficient is strongly dependent on the diameter). The thermal power / reactor diameter ratio must also be considered, because if it is too high, the system may become excessively fouled with particles.

[0029] S2 in [Fig. 2] is a set of reactors, the outer casing of which has a hexagonal shape to facilitate the addition of other sets of reactors around the periphery in order to form a honeycomb thermal power plant. The advantage of this configuration would be the ability to increase the capacity of a power plant as the application's needs change.

Claims

Demands

1. A system for producing thermal energy by combustion of metals, characterized in that it comprises a set of iron combustion reactors (1) arranged in a honeycomb pattern.

2. Production system according to the preceding claim, characterized in that the reactors (1) are composed of iron particle burners followed by their combustion chamber and surrounded by a circuit (2) containing a heat transfer fluid.

3. Production system according to the preceding claim, characterized in that each reactor (1) has its own heat exchanger circuit (2).

4. Production system according to claim 2, characterized in that the reactors (1) are together in contact with the same heat recovery circuit (2).

5. Production system according to claim 2, characterized in that the reactors (1) are immersed together in a tank (2) containing a heat transfer fluid.

6. Production system according to any one of the preceding claims, characterized in that the set of reactors (1) leads to a filtration system (3) by sedimentation or of the cyclone type.

7. A method for producing thermal energy by burning metals, implemented in a thermal production system according to any one of the preceding claims.