Ammonia reforming and combustion system using direct heat storage method

Abstract

An ammonia reforming and combustion system according to one embodiment of the present invention comprises: a thermal facility main body in which ammonia-reformed gas and air for combustion are combusted and combustion exhaust gas is discharged; and a heat storage device including a first heat storage device and a second heat storage device each having a heat storage material. The combustion exhaust gas is directly supplied to the heat storage device, the heat of the combustion exhaust gas is stored in the heat storage material and then discharged, ammonia is directly supplied to the heat storage device after the discharge of the combustion exhaust gas, the ammonia is in direct contact with the heat storage material, and the ammonia-reformed gas, which is reformed by the heat of the heat storage material, is discharged. The first heat storage device and the second heat storage device are alternately operated to supply the combustion exhaust gas discharged from the heat facility body to the first heat storage device to store heat, and supply the combustion exhaust gas to the second heat storage device to store heat. The ammonia may be alternately supplied to any one that stores heat, of the first heat storage device and the second heat storage device, and reformed.

Description

Ammonia reforming and combustion system using direct heat storage

[0001] The present invention relates to a system configuration that recovers the heat of combustion exhaust gas from a heat accumulator and reforms ammonia using the heat.

[0002] Countries and major corporations around the world are announcing carbon neutrality plans, and various research and efforts are underway in Korea to achieve carbon neutrality. Due to a lack of renewable energy-based electricity generation capacity, Korea has no choice but to import significant quantities of carbon-free fuels from abroad. Ammonia, a carbon-free fuel in the form of ammonia, which offers advantages in long-distance transport, is more likely to be introduced than hydrogen, which requires significant energy for liquefaction and is expected to suffer high losses due to vaporization during long-distance transport.

[0003] Ammonia imported domestically can be reformed and separated into hydrogen for use in fuel cell power generation and as automotive fuel. However, high-purity ammonia reforming is costly and energy-intensive, and since high-purity hydrogen is not required for general thermal equipment, ammonia is used as is or after minimal reforming. The composition of the synthesis gas (hydrogen, nitrogen, and ammonia) changes depending on the ammonia reforming rate and the rate of separation and purification of undigested ammonia or nitrogen, which in turn determines combustion characteristics. The greater the reforming rate, the less combustible ammonia is and the more combustible hydrogen is, resulting in improved overall combustion. Furthermore, ammonia is a significant source of fuel NOx, far exceeding thermal NOx, which is primarily generated at high temperatures. Therefore, using gas with a high ammonia reforming rate reduces overall nitrogen oxide (NOx) production. However, the higher the hydrogen content, the higher the risk of flame flashback and increased equipment deterioration and damage due to high-temperature flames.

[0004] On the other hand, if the ammonia content in the fuel is high, it is easy to be extincted due to flame blowout, and the overall thermal efficiency may be lowered due to the low flame temperature. In addition, the large amount of fuel NOx generated may not be able to be handled by the aftertreatment facility that reduces NOx. In addition, operating a high ammonia mixing ratio in a high-temperature combustion facility requires resolving several technical issues, so it is thought that it will be possible only after considerable research. Accordingly, it is judged that ammonia reforming is necessary to some extent in the short term, and while an ammonia reforming system like that in Figure 1 is typically used, it is required to build a high-efficiency reforming system suitable for the thermal facility.

[0005] According to one embodiment of the present invention, a combustion system can be provided that recovers the heat of combustion exhaust gas discharged from a heat facility in a heat accumulator and directly reforms and operates ammonia using the heat.

[0006] The objectives of the present invention are not limited to the above-described scope. Those skilled in the art will have no difficulty understanding the additional objectives of the present invention from the overall content of this specification.

[0007] An ammonia reforming and combustion system according to one embodiment of the present invention comprises a heat facility body in which ammonia reformed gas and combustion air are combusted and combustion flue gas is discharged; and a heat accumulator including a first heat accumulator and a second heat accumulator, each having a heat storage material, wherein the combustion flue gas is directly supplied to the heat accumulator, the heat of the combustion flue gas is stored in the heat storage material and then discharged, ammonia is directly supplied to the heat accumulator after the combustion flue gas is discharged, the ammonia is in direct contact with the heat storage material, and the ammonia reformed gas reformed by the heat of the heat storage material is discharged, the first heat accumulator and the second heat accumulator are operated alternately so that the combustion flue gas discharged from the heat facility body is supplied to the first heat accumulator to be stored, and the combustion flue gas is supplied to the second heat accumulator to be stored, and the ammonia may be alternately supplied to a heat accumulator among the first heat accumulator and the second heat accumulator to be reformed.

[0008] In the above heat facility body, a fuel including at least one selected from the group consisting of LNG, LPG and Oil can be additionally combusted.

[0009] It may further include a first ammonia supply valve arranged in a pipe through which the ammonia is supplied to the first accumulator; a first combustion exhaust gas discharge valve arranged in a pipe through which the combustion exhaust gas is discharged from the first accumulator; a second ammonia supply valve arranged in a pipe through which the ammonia is supplied to the second accumulator; and a second combustion exhaust gas discharge valve arranged in a pipe through which the combustion exhaust gas is discharged from the second accumulator.

[0010] When the first ammonia supply valve is opened, the second combustion exhaust gas discharge valve is opened, and when the second ammonia supply valve is opened, the first combustion exhaust gas discharge valve is opened, and the first ammonia supply valve and the second combustion exhaust gas discharge valve, and the second ammonia supply valve and the first combustion exhaust gas discharge valve can be alternately opened and closed.

[0011] The system may further include a nitrogen supply system for purging residual gas from the first accumulator and the second accumulator toward the thermal equipment body.

[0012] It may further include a heat exchanger in which the combustion air is preheated through heat exchange between the combustion exhaust gas discharged from the first accumulator and the second accumulator and the combustion air supplied to the heat equipment body.

[0013] The above-mentioned heat equipment body may further include a bypass pipe connecting the rear ends of the first combustion exhaust gas discharge valve and the second combustion exhaust gas discharge valve.

[0014] The above heat storage material may be at least one selected from the group consisting of ceramic honeycomb, ceramic ball and porous monolith.

[0015] The combustion air may be at least one selected from the group consisting of air, air with added oxygen, and combustion exhaust gas.

[0016] The opening and closing of the first ammonia supply valve, the second ammonia supply valve, the first combustion exhaust gas discharge valve, and the second combustion exhaust gas discharge valve can be performed when the temperature of the accumulator in which heat is accumulated among the first accumulator and the second accumulator is 800°C to 1200°C.

[0017] According to one embodiment of the present invention, the exhaust gas exhausted from a thermal facility is recovered in a heat accumulator and the heat is used to directly reform ammonia at high temperatures, thereby achieving a high reforming rate and eliminating the need for a separate catalyst. Furthermore, the high ammonia reforming rate can suppress the production of fuel NOx.

[0018] Figure 1 is a schematic diagram showing a conventional ammonia reforming and combustion system.

[0019] FIG. 2 is a schematic diagram of an ammonia reforming and combustion system using a direct heat storage method according to one embodiment, in which heat storage by supplying combustion exhaust gas occurs in a first heat storage unit and ammonia is reformed in a second heat storage unit.

[0020] FIG. 3 is a schematic diagram of an ammonia reforming and combustion system in which, in one embodiment, heat storage by supplying combustion exhaust gas occurs in a second accumulator and ammonia is reformed in a first accumulator.

[0021] FIG. 4 is a schematic diagram of an ammonia reforming and combustion system further including a nitrogen supply system for purging residual gas from the first accumulator and the second accumulator toward the thermal equipment body in one embodiment.

[0022] FIG. 5 is a schematic diagram of an ammonia reforming and combustion system that additionally includes a heat exchanger for heat exchange between combustion exhaust gas and combustion air in one embodiment.

[0023] FIG. 6 is a schematic drawing of an ammonia reforming and combustion system that additionally includes a bypass pipe connecting the heat treatment facility body and the rear ends of the first combustion exhaust gas discharge valve and the second combustion exhaust gas discharge valve in one embodiment.

[0024] Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings. However, the embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0025] According to one embodiment of the present invention, a combustion system is provided that recovers the heat of combustion exhaust gas discharged from a heat facility in a heat accumulator and directly reforms ammonia using the heat.

[0026] In the drawings 2 to 5 described below, the entire inside of the valve is filled in black, indicating that the valve is closed, and the inside of the valve is drawn in white, indicating that the valve is open.

[0027] FIG. 2 is a schematic diagram showing an ammonia reforming and combustion system using a direct storage method according to one embodiment of the present invention.

[0028] The above direct heat storage method refers to a method in which heat recovery of the combustion flue gas is achieved through direct contact between the combustion flue gas and the heat storage material, and then reforming of ammonia is achieved through heat transfer through direct contact between the heat storage material and ammonia. Therefore, the direct heat storage method has higher heat transfer efficiency than the indirect transfer method in which heat is transferred through a heat pipe during the heat transfer process, and can increase the ammonia reforming rate. Furthermore, in one embodiment of the present invention, the combustion flue gas and ammonia are directly supplied to the heat storage device, meaning that the combustion flue gas and ammonia are supplied so that heat transfer occurs through direct contact with the heat storage device, without being supplied through a separate heat pipe. Therefore, the combustion flue gas and ammonia are directly supplied to the heat storage device, and are not limited to a form in which the combustion flue gas and ammonia are supplied to the heat storage device without passing through other equipment. For example, in the process of supplying the combustion exhaust gas directly to the accumulator, it may pass through other equipment in the process arranged between the thermal equipment body (1) and the first accumulator (2-1), and in the process of supplying ammonia directly to the accumulator, it may pass through other equipment in the process arranged in front of the first accumulator (2-1).

[0029] Specifically, in the thermal equipment main body (1), a combustion reaction occurs by ammonia reformed gas and combustion air. In the thermal equipment main body (1), a fuel including at least one selected from the group consisting of LNG, LPG, and oil in addition to the ammonia reformed gas can be additionally combusted. The combustion flue gas discharged from the thermal equipment main body (1) is directly supplied to two or more accumulators including a first accumulator (2-1) and a second accumulator (2-2), the heat of the combustion flue gas is recovered and stored in a heat storage material, and then the low-temperature combustion flue gas is discharged, ammonia is directly supplied and reformed, and the reformed ammonia reformed gas is supplied to the thermal equipment main body (1). While heat storage is performed in the first accumulator (2-1) by the direct supply of the combustion flue gas, ammonia is reformed in the second accumulator (2-2) by the direct supply of the ammonia. The above ammonia reforming is accomplished by direct contact between the storage material and ammonia.

[0030] The above ammonia reforming and combustion system may include a first ammonia supply valve (3-1) arranged in a pipe through which ammonia is supplied to the first accumulator (2-1), a first combustion exhaust gas discharge valve (4-1) arranged in a pipe through which combustion exhaust gas is discharged from the first accumulator, a second ammonia supply valve (3-2) arranged in a pipe through which ammonia is supplied to the second accumulator (2-2), and a second combustion exhaust gas discharge valve arranged in a pipe through which combustion exhaust gas is discharged from the second accumulator.

[0031] In Fig. 2, in the thermal equipment main body (1), a combustion reaction occurs by ammonia reforming gas and the combustion air, and high-temperature combustion flue gas is discharged. When the first combustion flue gas discharge valve (4-1) is opened, the first accumulator (2-1) containing a heat storage material inside is passed through, where it is cooled, and the cooled combustion flue gas is discharged to the stack. Normally, if the combustion flue gas is at the level of 1000°C, the temperature inside the accumulator at the point where the combustion flue gas flows in is at the level of the combustion flue gas, and the temperature at the rear end of the accumulator where the combustion flue gas is discharged is maintained at the level of 100 to 300°C, but this may vary depending on the design and operation.

[0032] When the temperature of the first accumulator (2-1) reaches a temperature similar to that of the flue gas supplied to the first accumulator or before the temperature of the flue gas discharged from the first accumulator reaches a temperature that damages the first flue gas discharge valve (4-1), the first flue gas discharge valve (4-1) closes, thereby cutting off the supply of the flue gas to the first accumulator. At this time, the second flue gas discharge valve (4-2) at the rear end of the second accumulator opens, so that the flue gas is supplied to the second accumulator and then discharged after being cooled in the second accumulator. In this way, the flue gas is alternately supplied to the first accumulator and then supplied to the second accumulator after a certain period of time, and this is continuously repeated. This is defined as "switching", and the time interval for switching is defined as "switching time".

[0033] In Fig. 2, ammonia is supplied to the second accumulator (2-2) through the second ammonia supply valve (3-2) which is opened so as to be supplied to the second accumulator (2-2) to which the flue gas is not supplied. The second accumulator (2-2) to which ammonia is supplied is in a high temperature state due to the high temperature flue gas, and since the ammonia reforming is carried out by direct contact between the accumulator material and ammonia, the supplied ammonia is easily reformed and has a high reforming rate. Accordingly, there is no need to use a separate catalyst. The reformed ammonia reformed gas can be supplied to the thermal equipment body (1) at a higher temperature than the indirect heating method, and this can obtain positive effects such as complete combustion, increased flame stability, and suppression of fuel NOx emissions due to undecomposed ammonia. The reformed ammonia reformed gas is supplied to the thermal equipment body (1) and can be supplied through a burner or a separate hole. Ammonia, like the flue gas, is alternately supplied to the first accumulator and then, after a certain period of time, is switched and supplied to the second accumulator, which is continuously repeated.

[0034] The switching time can be adjusted within the time interval in which the accumulator (2-1, 2-2) reaches a temperature similar to the temperature of the flue gas supplied to the accumulator or the temperature of the flue gas at the rear end of the accumulator (2-1, 2-2) reaches a temperature that may cause a problem in the heat resistance of the flue gas discharge valve (4-1, 4-2). However, the longer the switching time, the higher the temperature of the flue gas discharged from the accumulator (2-1, 2-2), the worse the thermal efficiency. In addition, in the accumulator on the opposite side where ammonia is reformed, the longer the time in which the temperature gradually decreases due to the ammonia reforming reaction of the endothermic reaction, so there is a side effect in which the reforming rate gradually decreases. Accordingly, the switching time needs to be adjusted according to the ammonia reforming rate as well as the thermal efficiency.

[0035] Specifically, the opening and closing of the first ammonia supply valve, the second ammonia supply valve, the first combustion exhaust gas discharge valve and the second combustion exhaust gas discharge valve, i.e., the switching, may be performed when the temperature of the accumulator in which heat is stored by supplying the combustion exhaust gas among the first or second accumulators is similar to the temperature of the combustion exhaust gas, typically 800°C to 1200°C. The ammonia reforming rate in the accumulator in which ammonia reforming is performed among the first or second accumulators may be 50% or more. Since a large amount of fuel NOx may be generated when the ammonia reforming rate is low and un-decomposed ammonia is burned in the thermal equipment body (1), it is preferable that the ammonia reforming rate be maintained at 80% or more. However, this may vary depending on the co-firing ratio with fuel other than the ammonia reformed gas fed into the thermal equipment body (1).

[0036] FIG. 3 schematically illustrates an ammonia reforming and combustion system in which the above-described switching is performed in the embodiment of FIG. 2, wherein the second combustion exhaust gas discharge valve (4-2) at the rear end of the second accumulator (2-2) is opened so that combustion exhaust gas is supplied to the second accumulator (2-2) and discharged after being cooled in the second accumulator. In FIG. 3, ammonia is supplied to the first accumulator (2-1) through the first ammonia supply valve (3-1) which is opened so as to be supplied to the first accumulator (2-1) to which combustion exhaust gas is not supplied, and the reformed ammonia reformed gas is supplied to the thermal equipment body (1), and may be supplied through a burner or a separate hole.

[0037] Fig. 4 schematically illustrates an ammonia reforming and combustion system further including a nitrogen supply system in one embodiment, wherein the combustion system may further include a nitrogen supply system for purging nitrogen from gas remaining inside the first accumulator (2-1) and the second accumulator (2-2) toward the thermal equipment body (1) when the first accumulator (2-1) and the second accumulator (2-2) are switched. The nitrogen supply system includes a nitrogen supply valve (5) for controlling nitrogen supply by opening and closing the valve, and a pipe through which nitrogen is supplied.

[0038] When hydrocarbon fuel is used, the flue gas is composed of CO2, H2O, N2, and several percent of oxygen. Therefore, several percent of oxygen remains in the accumulator to which the flue gas is supplied. If the switch is switched in this state and ammonia is supplied, a combustion reaction may occur until the oxygen present in the high-temperature accumulator is consumed, and if a high level of oxygen remains in the accumulator, a small explosion may occur. In this case, the switch is switched and both ammonia supply valves (3-1, 3-2) are closed for several seconds, and the nitrogen supply valve (5) is opened to supply nitrogen and perform a purge operation to push the remaining oxygen into the thermal equipment body (1) (not shown). After the purge for several seconds is completed, the nitrogen supply valve (5) is closed and ammonia is supplied to enable reforming.

[0039] At this time, the accumulator on the opposite side of the accumulator containing residual oxygen will contain ammonia and its reformed gas (hydrogen and nitrogen) that were being reformed during the switchover. If the flue gas is immediately supplied due to the switchover, the combustible gases hydrogen and ammonia may combust when they meet the oxygen in the flue gas, and the remainder will be discharged into the stack. Ammonia discharged into the stack may cause environmental problems. Accordingly, nitrogen is injected into the accumulator and a purge operation is performed to inject the reformed residual gas into the thermal equipment body (1).

[0040] FIG. 5 is a schematic diagram of an ammonia reforming and combustion system that additionally includes a heat exchanger for heat exchange between combustion flue gas and combustion air in one embodiment. Compared to a conventional regenerator-based method, a method of directly recovering combustion flue gas heat using a heat accumulator has high thermal efficiency because the temperature of the combustion flue gas discharged to the stack is low. Typically, a thermal efficiency improvement of about 10 to 30% can be expected. Furthermore, since the combustion flue gas discharged from the first or second heat accumulator still has a heat source corresponding to a medium-low temperature of 100°C to 300°C, an additional heat exchanger can be installed to preheat the combustion air supplied to the thermal equipment main body (1) or to produce steam that can then be discharged to the stack. That is, as shown in FIG. 5, combustion air can be preheated in the heat exchanger (6) using low-temperature combustion flue gas and then supplied to the thermal equipment main body (1). As a result, the thermal efficiency of the thermal facility can be maximized because the sensible heat of the combustion exhaust gas discharged to the stack is extremely low.

[0041] FIG. 6 is a schematic diagram of an ammonia reforming and combustion system that additionally includes a bypass pipe (7) connecting the heat equipment main body (1) and the rear ends of the first combustion exhaust gas discharge valve (4-1) and the second combustion exhaust gas discharge valve (4-2) in one embodiment. When the combustion exhaust gas is discharged as in the present invention, the pressure inside the furnace may fluctuate due to the opening and closing process of the combustion exhaust gas discharge valves (4-1, 4-2). Accordingly, the flame length and shape of the heat equipment main body (1) may change, and the outside air may leak or inflow of the furnace exhaust gas, which is detrimental to the stability of the facility. In order to prevent this, as shown in FIG. 5, by installing a bypass pipe (7) connected from the heat equipment main body (1) to the rear ends of the combustion exhaust gas discharge valves (4-1, 4-2), the pressure fluctuations can be reduced.

[0042] The first accumulator (2-1) and the second accumulator (2-2) are filled with a heat storage material that has heat resistance that can withstand high-temperature combustion exhaust gas. The heat storage material may be at least one selected from the group consisting of a ceramic honeycomb, a ceramic ball, and a porous monolith. The porosity varies depending on the shape of the heat storage material, and this affects the pressure loss, so the heat storage material can be selected based on the pressure loss and heat resistance performance.

[0043] The combustion air supplied to the above-mentioned thermal equipment body (1) may be a synthesis gas of various compositions containing oxygen. The synthesis gas may be at least one selected from the group consisting of air, air with added oxygen, and combustion exhaust gas, and the oxygen concentration in the synthesis gas may be 21% to 99%.

[0044] [Explanation of symbols]

[0045] 1: Thermal equipment body

[0046] 2-1: First accumulator

[0047] 2-2: Second accumulator

[0048] 3-1: 1st ammonia supply valve

[0049] 3-2: Second ammonia supply valve

[0050] 4-1: First combustion exhaust gas discharge valve

[0051] 4-2: Second combustion exhaust gas discharge valve

[0052] 5: Nitrogen supply valve

[0053] 6: Heat exchanger

[0054] 7: Bypass piping

[0055] 8: Reformer

[0056] As described above, the features of the present invention can be applied in whole or in part to an ammonia reforming and combustion system.

Claims

1. A thermal facility body in which ammonia reformed gas and combustion air are combusted and combustion exhaust gas is discharged; and A heat accumulator comprising a first heat accumulator and a second heat accumulator, each having a heat accumulator material, The above combustion exhaust gas is directly supplied to the accumulator, and the heat of the combustion exhaust gas is stored in the accumulator material and then discharged. After the exhaust of the above combustion gas, ammonia is directly supplied to the accumulator, the ammonia comes into direct contact with the accumulator material, and the ammonia reformed gas reformed by the heat of the accumulator material is discharged. The first accumulator and the second accumulator are operated alternately so that the combustion exhaust gas discharged from the thermal equipment main body is supplied to the first accumulator for heat storage, and the combustion exhaust gas is supplied to the second accumulator for heat storage. A combustion system in which the ammonia is alternately supplied to the first accumulator and the second accumulator and reformed.

2. In paragraph 1, A combustion system in which a fuel including at least one selected from the group consisting of LNG, LPG and Oil is additionally combusted in the above-mentioned heat facility body.

3. In paragraph 1, A first ammonia supply valve arranged in a pipe through which the ammonia is supplied to the first accumulator; A first combustion exhaust gas discharge valve arranged in a pipe through which combustion exhaust gas is discharged from the first accumulator; A second ammonia supply valve arranged in a pipe through which the ammonia is supplied to the second accumulator; and A combustion system further comprising a second combustion exhaust gas discharge valve disposed in a pipe through which combustion exhaust gas is discharged from the second accumulator.

4. In paragraph 3, When the first ammonia supply valve is opened, the second combustion exhaust gas discharge valve is opened, When the second ammonia supply valve is opened, the first combustion exhaust gas discharge valve is opened, A combustion system, wherein the first ammonia supply valve and the second combustion exhaust gas discharge valve, and the second ammonia supply valve and the first combustion exhaust gas discharge valve are alternately opened and closed.

5. In paragraph 1, A combustion system further comprising a nitrogen supply system for purging residual gas from the first accumulator and the second accumulator toward the thermal equipment body.

6. In paragraph 1, A combustion system further comprising a heat exchanger in which the combustion air is preheated through heat exchange between the combustion exhaust gas discharged from the first accumulator and the second accumulator and the combustion air supplied to the heat equipment body.

7. In paragraph 3, A combustion system further comprising a bypass pipe connecting the above-mentioned heat equipment body and the rear ends of the first combustion exhaust gas discharge valve and the second combustion exhaust gas discharge valve.

8. In paragraph 1, A combustion system wherein the above-mentioned heat storage material is at least one selected from the group consisting of ceramic honeycomb, ceramic ball and porous monolith.

9. In paragraph 1, A combustion system wherein the combustion air is at least one selected from the group consisting of air, air with added oxygen, and combustion exhaust gas.

10. In paragraph 3, The opening and closing of the first ammonia supply valve, the second ammonia supply valve, the first combustion exhaust gas discharge valve and the second combustion exhaust gas discharge valve are A combustion system that is performed when the temperature of the accumulator in which heat is stored among the first accumulator and the second accumulator is 800°C to 1200°C.

Images