KR100636881B1 - Chemical-looping combustor using circulating fluidized bed with double loops - Google Patents

Abstract

A medium circulating combustion furnace using a circulation layer of a dual path is provided to sufficiently secure reaction of medium particles by increasing the stay time of the medium particles in an air reactor. A medium circulating combustion furnace using a circulation layer of a dual path includes a bubble flow layer air reactor(22), a bubble flow layer reduction reactor(21), two medium circulating ascent pipes(23), a non-mechanical valve(24), and a cyclone(25). The bubble flow layer air reactor provides a heat radiating reaction region for oxidizing a metal. The bubble flow layer reduction reactor provides a heat absorbing reaction region for reducing a metal oxidation material. Solid particles are circulated between the two bubble flow layers and are moved to another reaction region.

Description

Chemical-Looping Combustor Using Circulating Fluidized Bed with Double Loops}

1 is a schematic diagram schematically showing a conventional general circulating fluidized bed media circulating combustion furnace;

2 is a schematic diagram schematically showing a media circulating combustion furnace using a dual-path circulating fluidized bed according to an embodiment of the present invention;

3A and 3B are graphs showing changes in conversion rate with time of reduction and oxidation reactions of each particle according to one embodiment of the present invention;

Figure 4 is a graph showing the composition of the gas discharged from the media circulating combustion furnace using a double-pass circulating fluidized bed according to an embodiment of the present invention; And

5 is a graph showing the conversion rate of methane and the oxygen transfer capacity of the particles in a media circulating combustion furnace using a dual-path circulating fluidized bed according to an embodiment of the present invention.

* Explanation of symbols for main parts of drawings *

11 ... fuel reactor (lower tube) 12 .. air reactor (rising tube)

13 ... non-mechanical valve (loop seal) 14 ... cyclone

21 ... fuel reactor (bubble fluidized bed) 22 ... air reactor (bubble fluidized bed)

23 ... riser 24 ... non-mechanical valve (seal pot)

25 ... cyclone

The present invention relates to a media circulating combustor using a dual-path circulating fluidized bed, and more particularly, to a media circulating type that can directly separate carbon dioxide in order to facilitate the treatment of carbon dioxide in a thermal power plant that is a major carbon dioxide emission source. A new type of circulating fluidized bed media circulating combustion system is proposed to increase the thermal efficiency of the combustion process.

At the 2nd World Meteorological Conference in Geneva in November 1990, most developed countries agreed to maintain at least 1990 levels of CO ₂ and other greenhouse gases by 2000. Rio in Brazil Korea has concluded a climate change agreement that promises to establish countermeasures before causing even greater disasters, including over-consumption of energy due to global warming and extreme weather, resulting in increased concentrations of atmospheric CO ₂ . Joined in December.

In December 1997, the Kyoto Protocol was adopted by the Conference of Contracting Parties to reduce its greenhouse gas emissions to 1990 levels by 2000. In order to reduce the cost of achieving these reduction targets, Kyoto mechanisms were introduced to allow the purchase and sale of greenhouse gas reductions as a commodity, and sinks were recognized. As a result, the obligation to reduce greenhouse gases has become effective as an internationally binding international law, and it is in fact not an environmental convention but a de facto economic convention. Accordingly, in the case of CO ₂ , efforts to suppress, eliminate or convert to useful compounds have been increased.

Until now, various researchers have suggested various processes for recovering CO ₂ emitted from thermal power plants, but most of them are expensive and have high energy loss. Depending on the system, 13-37% energy loss occurs in the conventional thermal power generation process, and the CO ₂ recovery cost is very high, such as $ 18-72 / m ³ CO ₂ depending on the process.

In order to cope with this problem, a study on chemical looping combustion (CLC) is underway. The medium-circulating combustion technology is a cutting-edge technology that can fundamentally block the generation of NOx, separate CO ₂ into a high concentration, and at the same time enable high-efficiency energy recovery, which can simultaneously achieve energy saving, air pollution prevention, and CO ₂ reduction. Reactor forms for media circulating combustion are considered fluidized beds with good gas-solid contact, good heat and mass transfer, and easy process maintenance.

Most of the circulating fluidized bed type circulating combustors proposed so far have considered the riser of the high speed fluidized bed as the oxidation reactor and the low speed bubble fluidized bed as the reduction reactor. Oxygen donor particles, ie, metal oxides, which are layer materials, are oxidized in an oxidation reactor, which is a riser, and then act as oxygen donors. The metal oxide oxidizes the fuel in the gaseous form by passing it to the reduction reactor, which is a slow fluidized bed. In the reaction system proposed so far, the high-speed injection gas of the riser is the driving force for circulating the particles.

As a media circulating combustion furnace using a circulating fluidized bed reactor, as shown in FIG . 1 , when the air introduced into the air reactor 12 meets with the metal as the circulating medium and the oxygen donor to oxidize the metal, the oxygen becomes a metal oxide. The donor particles rapidly raise the riser by using the flow velocity of the air injected at high speed, and then pass the fuel reactor 11. The metal oxide particles passed to the fuel reactor 11 meet with the gaseous fuel to cause a reduction reaction to be separated from the oxygen, where the oxygen generated burns the fuel. Oxygen donor particles that have been reduced and returned to the metal state are transferred back to the air reactor 12, where it is oxidized again in the air reactor to achieve a cyclic process of becoming a metal oxide. This allows the particles to continue to circulate, delivering oxygen to the fuel to perform combustion.

In the air reactor 12 of the reaction system as described above, only the oxygen component which does not react with the metal particles and the oxygen component which is not injected into the reaction is discharged, and the fuel reactor 11 separately enters the gas other than the gaseous fuel. Gas is burned and only CO ₂ and water vapor emitted are emitted. Since CO ₂ in the fuel reactor 11 can be easily recovered through condensation of water vapor, it is expected to be an economical process compared to the absorption method, adsorption method, membrane separation method, and the like, which are conventional CO ₂ recovery technologies.

However, the conventional reactor takes an air reactor, which is an oxidation region of the particles, as the riser, so that the residence time of the particles in the riser is very short and does not satisfy the time required for the oxidation reaction. In order to solve this problem, a method of increasing the pressurization type or the amount of the medium has been devised, but this method has the problem of causing additional economic burden on the initial power plant construction.

Therefore, the present inventors have studied diligently to solve the problem that the conventional reaction system does not satisfy the reaction time required for the oxidation reaction of the metal particles, and as a result, both the oxidation reaction zone and the reduction reaction zone are bubble fluidized beds, and the two reaction zones are In the case of the concentric ring, the residence time of the media particles is increased, and the reaction of the particles is sufficiently performed, resulting in high combustion efficiency. Thus, the initial construction of the power generation facility and the material cost can be reduced, and the heat transfer is efficiently performed. Confirmed and completed the present invention.

Therefore, the present invention increases the residence time of the media particles in the air reactor to sufficiently secure the reaction of the particles, increase the high combustion efficiency and heat transfer efficiency between the two reaction zones, while reducing the initial construction and material cost of the power plant, NOx, etc. It is an object of the present invention to provide a medium-circulating combustion furnace using an environment-friendly double-path circulation fluidized bed capable of separating and collecting carbon dioxide and the like with little generation of by-product gas.

In order to achieve the above object, the present invention, the bubble fluidized bed air reactor in the form of a cylinder providing an exothermic reaction zone for oxidizing the metal by air; A bubble fluidized bed reduction reactor in the form of an annular tube which surrounds the bubble fluidized bed air reactor 22 in the form of an annular tube and provides an endothermic reaction zone for reducing the metal oxide by fuel; Two medium circulating risers (23) designed to circulate solid particles between the two bubble fluidized beds and pass them to another reaction zone; A non-mechanical valve (24) installed between each of the two bubble fluidized beds and the two risers, and designed to circulate only the solid particles without mixing the gas between the two bubble fluidized beds; And a cyclone 25 for discharging the exhaust gas generated in the two bubble fluidized beds or collecting the fine particles, respectively, installed on top of the two bubble fluidized beds. .

Hereinafter, the present invention will be described in detail.

The media circulating combustion furnace using the dual-path circulating fluidized bed according to the present invention sets the dual bubble fluidized bed in which the two reaction zones in the air reactor and the fuel reactor are separated in the form of an annular tube having concentric circles as the reaction zone. Specifically, the combustion furnace is a bubble fluid bed air reactor; Bubble fluidized bed fuel reactor; Two risers; A non-mechanical valve installed at a connection portion of each reactor and each riser; And a cyclone for exhausting exhaust gas or collecting fine particles.

Both the air reactor zone and the fuel reactor zone are set to bubble fluidized beds. In addition, in order to optimize the heat transfer of the exothermic oxidation reaction and the endothermic reduction reaction, the two regions are manufactured by separating and arranging the inner and outer parts in the form of a concentric ring.

The bubble fluidized bed air reactor is a hollow tubular oxidation reactor inside an annular tube, and provides an exothermic reaction zone for oxidizing a metal by air. Oxygen donor particles, ie, metal oxides, which are layer materials, oxidize and circulate in this region and act as oxygen donors. The metal oxide oxidizes the fuel in the gaseous form by removing oxygen from the reduction bubble, that is, the bubble fluidized bed fuel reactor, which is another bubble fluidized bed.

The bubble fluid bed air reactor is designed as an oxidation reactor in the form of a bubble fluid bed, unlike a conventional reaction system. Thus, in the reactivity of the oxygen donor particles, the oxidation reaction can also achieve a sufficient oxidation reaction rate while at the same time the reaction time of the reduction reaction level.

The bubble fluidized bed fuel reactor region provides an endothermic reaction zone for reducing fuel as an annular tube shape surrounding the outer wall of the hollow tubular air reactor. By arranging the two bubble fluidized beds in a concentric annular tube shape, heat transfer from the air reactor, which is an exothermic reaction, to the fuel reaction, which is a reducing reaction, can be effectively increased.

In order to smoothly transport the oxygen donor particles between the two zones, two risers are respectively installed at the connection site between the bubble fluidized bed air reactor and the bubble fluidized bed fuel reactor. One riser of the risers serves to transport oxygen donor particles, ie, metal oxide particles, generated in the air reactor to the fuel reactor, and the other riser of the risers is an oxygen donor generated in the fuel reactor. It is responsible for transporting the particles to the air reactor.

In addition, a non-mechanical valve, preferably a seal-pot-shaped group seal, is placed at the connection of the two reaction zones and prior to entry of the riser to prevent the mixing of gas between the two reaction zones during transport of oxygen donor particles. Install each one.

The loop seal is a non-mechanical control valve that controls solid injection by varying the aeration rate. In the present invention, a seal seal in the form of a seal-pot may be selected. The seal pot-type group seal is configured to block entry of the gas discharged from each reactor zone, and to allow the reaction particles to be accumulated downward to be flooded to another zone.

The cyclone is designed to be placed on top of each of the bubble fluidized bed reactors. The cyclone includes a gas outlet designed to discharge gas generated in the two bubble fluidized beds and a means for collecting fine particles. Thereby, the outflow of the scattering particles generated during the bubble fluidized bed reaction can be prevented, and exhaust gas such as CO ₂ can be easily separated and discharged and collected.

In the present invention, a gas dispersion plate capable of injecting gas at a high speed at each base of the device may be installed. This injects the gas at high speed to influence the formation of the bubble fluidized bed according to the present invention, as well as to provide a driving force for the reaction and circulation of the particles.

In the present invention, the metal oxide particles used as the oxygen donor while circulating between the fuel reactor and the air reactor are not particularly limited as being used to react the gas through oxidation and reduction, but preferably bentonite, NiO and Fe ₂ O ₃ may be supported by TiO ₂ or Al ₂ O ₃ as a carrier.

The metal oxide is preferably a particle having an initial particle size distribution in the range of 106 to 150 μm with improved abrasion resistance as particles having sufficient redox rate and physical strength against wear. This is a particle size set in accordance with the fuel injection flow rate and the air injection flow rate in the range in which the fluidized bed formation conditions of the particles are easy.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention. However, the following embodiment illustrates the best mode preferred in the present invention, and of course, the content of the present invention is not limited or limited to only the following embodiment.

1 is a schematic diagram schematically showing a conventional general circulating fluidized bed circulating combustion furnace as a comparative example, and it can be seen that the conventional reactor simultaneously takes an air reactor, which is an oxidation region of particles, as a riser.

2 is a schematic diagram schematically showing a media circulating combustion furnace using a double-pass circulating fluidized bed according to an embodiment of the present invention.

The fuel uses methane, the main component of natural gas, which is most widely used as a gaseous fuel that is easy to apply to circulating combustion. As the metal oxide medium, NiO-Fe ₂ O ₃ / bentonite solid particles are used, and the size thereof is set to 106 to 150 µm.

In FIG. 2 , air is injected through a dispersion plate at the base of the layer of oxidation reactor 22 filled with solid particles of the metal. The metal is oxidized by air, and the oxidized metal oxide enters the lower seal pot-type group seal 24, and the gases N ₂ and O ₂ generated in the oxidation reactor are discharged through the outlet of the cyclone 25 or Are collected separately. Only the metal oxide particles are transferred to the riser 23 while the metal oxide is separated from air, which is an oxidizing gas, in the group seal. The metal oxide, which has risen along the riser 23, passes over to the circle reactor 21 in the form of an annular tube and meets with the methane, which is the combustion gas injected through the dispersion plate at the base of the reduction reactor 21, to generate combustion. The combustion gases carbon dioxide, carbon monoxide and water vapor enter the cyclone 25 and are collected, and the metal oxide itself is reduced and separated again through the reverse seals 24 and transported back to the tubular air reactor, which is then oxidized again. One cycle is achieved by going through the form. As this cycle is repeated, the oxygen donor particles, ie, metal oxides, which are circulating media, serve to adsorb and desorb oxygen and to transfer oxygen, and gaseous fuel is combusted.

In the bubble reactors (21, 22), the particles have a long residence time in the reactor while the continuous ascending and descending movement, in the riser 23, a high-speed fluidized bed particles are dispersed by a high flow rate, the main reaction is It is passed to the air reactor 22 and the fuel reactor 21 which are the bubble fluidized beds which take place. At this time, the pressure gradient is different for each part of the reactor, and this pressure gradient is the driving force for controlling the particle circulation in the circulating fluidized bed reactor. In addition, this pressure balance must be well circulated smoothly in the reactor.

< Example  1> Oxidation / Reduction of Oxygen Donor Particles

(1) Preparation of Oxygen Donor Particles

1) bentonite As carrier  Manufacture of one particle

Bentonite was used as a carrier to change the component ratios of NiO and Fe ₂ O ₃ . Bentonite was provided by Donghae Chemical. It was prepared by directly mixing the powder of industrial NiO (Japan Chemical) and Fe ₂ O ₃ (Wonil Chemical) and bentonite powder as a material to react with the actual oxygen. Bentonite as a carrier occupies 40% by weight, and the powder was mixed so that the sum of the NiO and Fe ₂ O ₃ masses was 60% by weight. Here, the mass ratios of NiO and Fe ₂ O ₃ were divided into five types, 4: 0, 3: 1, 2: 2, 1: 3, and 0: 4. Secondary distilled water was mixed with the well mixed powder to make a paste. The second distilled water was infused with 30-40 mL per 100 g of the mixed powder. The paste was dried in an oven preheated to 110 ° C. for 24 hours to completely remove moisture, and then fired for 6 hours in an air atmosphere at a 1,000 ° C. heating furnace. The calcined mass was pulverized in a mortar and then sifted into particles of 106-150 μm and used in the experiment.

As a result of comparing the wear characteristics of the metal oxide particles thus prepared, the particle size distribution before and after abrasion is relatively well within a desired range, and it is effective to reduce the loss of particles from abrasion when _the ratio of NiO and Fe ₂ O3 is 3: 1. It was. In this case, NiO-Fe ₂ O ₃ / bentonite (NiO: Fe ₂ O ₃ = 3: 1) was analyzed by X-ray diffractometer (XRD; X-Ray Diffractometer) to determine the crystal structure, NiFe ₂ O ₄ , The main oxygen carriers of NiO and Fe ₂ O ₃ have been found.

2) TiO ₂ To As carrier  Manufacture of one particle

Each powder was mixed to form a mass ratio of 40 wt% TiO ₂ (Degussa P25), 60 wt% NiO or Fe ₂ O ₃ , and then the mixture was mixed with secondary distilled water to form a paste. Here, the distilled water was injected with 70 mL per 100 g of the mixed powder. The paste was dried and pulverized in the same manner as in the case where the bentonite of the above (1) was directly mixed with a powder by a carrier, and then particles having the same particle size were taken.

3) Al ₂ O ₃ To As carrier  Manufacture of one particle

40% by weight of Al ₂ O ₃ (Aldrich Co.), NiO or Fe ₂ O ₃ similar to the case of using TiO ₂ as the carrier Each powder was mixed to achieve a mass ratio of 60% by weight, and then, distilled water was mixed with the well mixed powder to make a paste. Here, the distilled water was injected with 15 mL per 100 g of the mixed powder. Since the preparation was carried out in the same manner as in the case of TiO ₂ .

(2) Oxidation / Reduction Reaction Test of Oxygen Donor Particles

The oxidation / reduction reaction of the prepared particles was carried out in a thermobalance reactor. In order to examine the reactivity according to the support, oxidation and reduction of each particle were performed under the same temperature condition of 850 ° C.

Reactivity was calculated by the following equation through the concept of oxidation fraction.

Here, m is the weight of the test sample, m _red is calculated the weight of when fully reduced value, m _ox is the weight of when fully oxidized, since use of that oxide particles in the experimental m _ox is the weight of the initial sample Set to.

Results of examining the reactivity of the particles according to the carrier are shown in FIGS . 3A and 3B . As can be seen in Figures 3a and 3b , it can be seen that the particles mixed with NiO is more reactive than the particles mixed with Fe ₂ O ₃ . When the initial reaction proceeded quickly, Al ₂ O ₃ , bentonite, TiO ₂ showed excellent properties in the order of support, but when the reaction proceeded for a long time, the conversion of bentonite was much higher.

< Example  2> Reaction characteristics of the medium circulation combustion furnace of the present invention

Using the apparatus shown in FIG . 2 , NiO-Fe ₂ O ₃ / bentonite particles having a diameter of 106 to 150 μm of NiO: Fe ₂ O ₃ = 3: 1 were introduced into the oxygen donor particles, and the circulation amount thereof was 13 kg / m ^2. Operation was set to s. Air was injected into the oxidation reactor through a dispersion plate, and the gas injected into the reduction reactor was fuel gas CH ₄ (99.999%). The flow rate of the injected gas was set at 5 cm / s. Before the gas was introduced into the reactor, the gas was injected into the oxidation reactor and the reduction reactor, respectively, while being heated to 500 ° C. through a heat transfer device, and the reaction was set at 850 ° C. during operation. Air was injected into the group seal and the riser leading to the oxidation reactor. Sikyeoteuna rupssil and riser induced a reduction reactor, each injection of CO ₂ gas in the cylinder, in the actual process can be used to recycle the CO ₂ generated in the reduction reactor at a high purity. At this time, the flow rate of the riser was set to 100 cm / s so that the high-speed fluidized bed state can be maintained.

The circulating combustion characteristics of the media, such as the conversion of methane, were analyzed by the exhaust gas. The gas from the reduction reactor was examined by gas chromatography (GC; HP5890). In gas analysis, CO ₂ , CO, and H ₂ were analyzed to determine the combustion efficiency by looking at the amount of CO or H ₂ from incomplete combustion. For the quantitative analysis, a small amount of Ar gas was flowed into the injection gas to serve as a tracer gas. Gas chromatography apparatus used a molecular sieve (5A column (6 ft-length)).

The gas coming out of the oxidation reactor theoretically said that NOx component would not occur, but it was confirmed by the NDIR type NO analyzer for verification.

Figure 4 shows the result when the medium circulation combustion reaction under the above conditions. That is, all of CH ₄ was converted into CO ₂ and CO, which was not detected at all, and H ₂ , which may occur during side reactions, was also not detected. H ₂ was not detected in all subsequent reactions, so the illustration of H ₂ was omitted in all figures.

Here, it was confirmed that all of CH ₄ is not converted into CO _2, and CO of about 0.3 to 0.6% is generated. However, the conversion to CO _{2 was} about 99.5% or more, indicating that the combustion reaction proceeded smoothly. At the beginning of the reaction, the reaction was not stabilized and showed an uneven trend, but after the reaction proceeded for more than 10 minutes, it was confirmed that the reaction was found to show a certain result.

5 shows the conversion rate of CH ₄ and the oxygen donating ability of the oxygen donor particles. Under these conditions, CH ₄ was converted 100%, and the oxygen donating ability was constant at about 99.8%. Oxygen donating ability is a factor expressed by the following equation.

Only N ₂ and O ₂ were present in the composition of the gases exiting the oxidation reactor. Based on the composition of the gas, CO ₂ was not emitted at all according to the existing purpose, and it was confirmed that gas separation between both reactors was well performed.

In addition, although NO was generated through the detection of NO, the concentration of NO was 5 ppm or less, which is within the error range of the analyzer, so that NO _x was hardly generated.

This proved that the objective of medium-circulating combustion, where CO ₂ was withdrawn from the source and NO _x was not produced by low temperature operation, was smoothly achieved. Here, since there was no generation of by-product gas due to side reactions and poor operation, such as CO ₂ and NOx in the gas discharged from the oxidation reactor, the figure of the gas composition is not shown separately.

The media circulating combustion furnace using the dual-path circulating fluidized bed of the present invention having the above configuration has not only no gas back mixing phenomenon between both reaction zones, but also shows a high combustion efficiency because the combustion reaction is effectively performed at a low level of side reactions. It is economical because carbon dioxide can be easily separated without the need for additional energy or additional equipment for the separation of carbon dioxide, and heat is generated in the air reaction zone because each reaction zone is made in the form of a concentric ring. Effective transfer to the fuel reaction zone reduces the amount of additional heat applied externally, providing an economical effect in terms of thermal efficiency. In addition, the present invention can be used in the catalyst production and catalyst operation technology, such as FCC catalyst process, IGCC desulfurization catalyst, gas-high fluidized bed reactor, chemical process, various industrial processes, such as chemical and power plant scale reactor using circulating fluidized bed technology It can be extended to apply. In particular, the present invention is an environmentally friendly technology for reducing the carbon dioxide emissions can be said to be more economical.

Claims (5)

A bubble fluidized bed air reactor 22 in the form of a cylinder providing an exothermic reaction zone for oxidizing the metal by air; A bubble fluidized bed reduction reactor in the form of an annular tube which surrounds the bubble fluidized bed air reactor 22 in the form of an annular tube and provides an endothermic reaction zone for reducing the metal oxide by fuel; Two medium circulating risers (23) designed to circulate solid particles between the two bubble fluidized beds to be passed to another reaction zone; A non-mechanical valve (24) installed between each of the two bubble fluidized beds and the two risers, and designed to circulate only the solid particles without mixing the gas between the two bubble fluidized beds; And And a cyclone (25) for discharging the exhaust gas generated in the two bubble fluidized beds or collecting the fine particles, respectively installed on top of the two bubble fluidized beds. 2. The dual-pass circulating fluidized bed according to claim 1, wherein a gas dispersion plate for injecting a gas responsible for the reaction and transport of the particles is installed at the base of the two reactors, the two risers, and the two non-mechanical valves. Circulating Combustion Furnace 2. The media circulating furnace according to claim 1, wherein the non-mechanical valve (24) is a seal seal in the form of a group seal. [Claim _2] The circulating medium of claim 1, wherein the metal oxide is bentonite, TiO ₂ or Al ₂ O ₃ as a carrier, and supports NiO and Fe ₂ O ₃ particles. Combustion furnace. 5. The media circulating combustion furnace according to claim 4, wherein the particle diameter of the metal oxide particles is in the range of 106 to 150 mu m.

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