JPH0799250B2 - Fluidized bed combustion method and fluidized bed combustion apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fluidized bed combustion method and a fluidized bed combustion apparatus used for carrying out this combustion method.

(Prior Art) A combustion apparatus for burning coal containing a large amount of sulfur using a fluidized bed has already been proposed. In this conventional fluidized bed combustor, the fluidized bed is a so-called bubbling fluidized bed method (bu
The superficial velocity of the fluidized bed, that is, the flow rate of the combustion air flowing in the fluidized bed per unit time is divided by the cross-sectional area of the fluidized bed to obtain a quotient of 4 to 12
It is made into feet / second (about 120 to 360 cm / second) and has an average particle diameter of about 1000 microns. Coal particles are combusted in the fluidized bed. At this time, limestone or dolomite is added to the fluidized bed as an absorbent to suppress the release of sulfur oxides. This absorbent is added to the fluidized bed as particles with a particle size of 1000-3000 microns, which consists mainly of coal ash, reacted absorbent, partially reacted absorbent and partially burned fuel particles. ing. In addition, a cooling pipe that transfers heat to the steam is arranged in the fluidized bed, and in order to remove the heat from the burned hot gas and lower the temperature of the hot gas, another pipe is provided in the freeboard section above the fluidized bed. Is attached. During operation, fine particles of semi-coke, ash and partially reacted absorbent are separated and released from the fluidized bed.

Most of these particulates are recirculated downstream of the convection heat exchanger to completely burn the fuel particles and more effectively absorb the sulfur oxides in the unreacted absorbent. It is captured by a cyclone and returned to the fluidized bed. At this time, only extremely fine particles are sent from the cyclone to the filter device as overflow and captured. Further, the flow rate in the recirculation path is provided so as to be substantially equal to the total solid content flow rate of the fuel and the absorbent supplied into the combustion device.

However, the above-mentioned conventional combustion device has some problems. First, unburned fuel particles are released from the combustion device, and the combustion efficiency is reduced to about 97%. This is extremely remarkable when burning a fuel having a low volatile content such as petroleum coke having a carbon content of 90% as compared with coal having a carbon content of 42%. Second, in order to meet the requirements of normal air pollution regulations that require low absorption of 90% sulfur oxides, the molar ratio of calcium to sulfur should be at least 3: 1. Need to maintain. Therefore, the sulfur oxides are absorbed only on the surfaces of the relatively large absorbent particles, and most of the inside of the particles are released in an unused state. The third drawback is that these boilers emit nitrogen oxides as pollutants, which are generated from the nitrogen contained in the fuel. In some parts of the United States, nitrogen oxide emissions do not exceed local limits, but in regions such as Southern California, they do.

In contrast, U.S. Pat. No. 4,177,741 discloses a configuration in which circulating particles are agglomerated before returning to a fluidized bed in order to increase the combustion efficiency of a conventional fluidized bed boiler. The agglomerated particles are prevented from blowing out of the fluidized bed and burned. U.S. Pat. No. 4,259,911 shows a configuration in which coal particles and circulating particles are agglomerated prior to entering the fluidized bed. U.S. Pat. No. 4,329,234 discloses a configuration in which a portion of the fluidized bed is removed and the pre-absorption particles are crushed to a diameter of 50 microns to improve the utilization of the absorbent.

Furthermore, German Patent No. 3,023,480 discloses another arrangement which increases the utilization rate of the absorbent and suppresses the sulfur oxides generated from the combustion gas. In this case, the combustion gas particle size of 30 ~
It is passed through a fluidized bed of 200 micron absorbent particles. The superficial velocity of the fluidized bed is 3 to 30 feet / second (about 90 to
900 cm / sec), and the particle density of the fluidized bed is 0.
It is said to be 1 to 10 kg / m ³ . Particles that accompany the high velocity gas are removed by the cyclone and the temperature is 1300-2000 °.
It is returned to the fluidized bed at F (about 704 to 1093 ° C.), and the recirculation flow rate per hour is about 5 times the weight of the fluidized bed.

U.S. Pat. No. 4,111,158 discloses a structure for enhancing the combustion efficiency of a fluidized bed combustion furnace based on the principle of a circulating fluidized bed, and suppressing or removing sulfur oxides and nitrogen oxides. In this case, the superficial velocity of the bubbling fluidized bed combustion furnace is 4
If it is ~ 12 ft / sec, the upper surface of the bubbling fluidized bed is clearly divided, but the superficial velocity is 15-45 ft / sec (about
At 450-1350 cm / sec), the upper surface of the fluidized bed was not clearly divided, and the particle density tended to gradually change from the bottom to the top of the combustor.

The particles contained in the gas stream within the combustor are separated by a recirculation cyclone located downstream of the combustor and introduced at the bottom of the fluidized bed. The particle size is 30-250 microns and the particle density is 10-40 kg / m ³ at the top of the combustor. In this case, no heat is recovered from the particles and gas in the combustor and recirculation path. The tube in the combustion device is easily worn, and the particle density at the place where the tube is installed is lower than the particle density in the bubbling fluidized bed (500 kg / m ³ ), so heat is not effectively transferred to the tube. . Therefore, in the present invention, heat is recovered by taking out a part of the fluidized bed from the bottom of the combustion apparatus and cooling it by another fluidized bed heat exchanger that optimally utilizes the process.

U.S. Pat. No. 3,900,554 discloses a structure in which ammonia is injected to suppress nitrogen oxides without using a catalyst. In this case, the basic gas reaction of ammonia reduces the nitrogen oxides as desired at 1742 to 1832 ° F (about 950 to 1000 ° C), and when the molar ratio of ammonia and nitrogen oxides is 2, It is supposed to be suppressed.

(Problems to be Solved by the Invention) According to the above-mentioned U.S. Pat.No. 4,177,741, circulating particles are agglomerated, and according to U.S. Pat.No. 4,259,911, since coal particles and circulating particles are agglomerated, these particles are in a fluidized bed. It is prevented from blowing out from. Also, U.S. Pat.
According to No. 4, since the particles are crushed, further absorption of sulfur oxides is observed. However, these U.S. patents are merely a modification of the old fluidized bed combustor described above.

Further, according to German Patent No. 3,023,480, it is possible to suitably suppress the sulfur oxides by using fine particles having a large surface area and being actively mixed, but by disposing a cooling pipe in the fluidized bed, heat can be applied to the fluidized bed. The technical idea of recovering from is not reached.

Further, U.S. Pat.No. 4,111,158 discloses a structure for enhancing the combustion efficiency of a fluidized bed combustion furnace based on the principle of a circulating fluidized bed, and suppressing or removing sulfur oxides and nitrogen oxides. According to the patent, no heat is recovered from the particles and gases in the combustor and recirculation path. The tubes in the combustor will be prone to wear, and the particle density at the location of the tubes is lower than the particle density in the bubbling fluidized bed (500 kg / m ³ ), so heat is not effectively transferred to the tubes. There is a fear. Therefore, heat is recovered by removing a portion of the fluidized bed from the bottom of the combustor and cooling it in another fluidized bed heat exchanger that best utilizes the process. As a result, high combustion efficiency is obtained by completely burning the well-mixed small-sized fuel particles in the combustion device and the recirculation path, and the fine combustion particles and the recirculation are used by using the fine absorbent particles. Maintaining the temperature at an effective level throughout the path increases the utilization of the absorbent. Further, there is a feature that generation of nitrogen oxides can be suppressed by sequentially introducing combustion air over the entire length of the combustion device. However, this combustion apparatus has a problem in that a heat exchanger separate from the fluidized bed is required and a large-sized recirculating sacron is required.

Also, according to U.S. Pat. No. 3,900,554, due to the basic gas reaction of ammonia, 1742-1832 ° F (about 950-1000
Nitrogen oxides can be selectively reduced at (° C.) And the molar ratio of ammonia and nitrogen oxides is set to 2.
It is said to be suppressed by 20%. Although this point is acknowledged, this US patent shows that when the molar ratio of ammonia to nitrogen oxides is also 2, it removes 95% of nitrogen oxides when mixed well, as in a recycle cyclone. I am not convinced that I can do it.

The present invention has been made in view of the drawbacks and problems of the conventional fluidized bed type combustion method or fluidized bed type combustion apparatus as described above, and it is possible to obtain high combustion efficiency and to effectively use the absorbent. For the purpose of providing a fluidized bed combustion method and a fluidized bed combustion apparatus used for carrying out the method, wherein sulfur oxides and nitrogen oxides are effectively removed from the combustion gas There is. Further, the present invention provides a fluidized bed combustion method and a fluidized bed combustion apparatus used for carrying out the method, in which the heat transfer coefficient of the cooling pipe arranged in the fluidized bed is increased and the cooling pipe is less worn. That is also the purpose.

In addition to the above objects, another invention is a fluidized bed combustion method in which the capture of sulfur oxides is significantly improved and the release of nitrogen oxides is suppressed, and a fluidized bed combustion apparatus used for carrying out this method. Is intended to provide.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a step of supplying a solid fuel and a liquid fuel containing impurities into a fluidized bed combustion apparatus at atmospheric pressure, inert particles, and ash. Particles and partially combusted fuel particles are crushed rather than burned in the combustor and operated at superficial velocity of 0.5 to 7 ft / sec (15 to 210 cm / sec) and a sieve point located above the combustor. Included in the exhaust gas from the fluidized bed combustor with the process of circulating between the fluidized bed with a cyclone for recirculation of less than 12 microns to form a fluidized bed with an average particle size of 100 to 800 microns. Capturing the particles with a recirculating cyclone and returning to the fluidized bed at a return flow rate of 1 to 5 times the weight of the fluidized bed per hour;
It is configured to include a step of recovering heat from exhaust gas downstream of a cooling pipe arranged in a fluidized bed and a cyclone for recirculation, and a step of removing dust from the exhaust gas stream recovered from heat. It

The invention described in the second aspect of the claims is to supply the absorbent for sulfur oxide during the step of supplying the solid fuel according to the first aspect, whereby the fluidized bed is partially reacted with sulfur oxidation. The invention according to claim 3 is configured so as to include absorbent particles for a product, and the invention according to claim 3 is the process described in claim 1 in which the immediately upstream of the cyclone for recirculation is used. In order to include the step of introducing ammonia into the hot combustion gas stream, the invention described in the fourth aspect of the present invention is re-used during the step of returning to the fluidized bed according to the first aspect of the present invention. It is configured to return the particles captured by a cyclone for circulation directly to the fluidized bed through the inside of the combustion chamber, and the invention described in claim 5 is the invention described in claim 1. During the process of recovering heat, in the fluidized bed combustion device, The invention described in claim 6 is configured to recover heat, and when performing the steps described in claim 1, the fluidized bed combustor is set to 1400 to 1500. Operates at ° F (760-816 ° C), which suppresses the generation of nitrogen oxides due to combustion of fuel particles, and also suppresses nitrogen oxides by semi-coke in the fluidized bed and recirculation, and semi-coke. And in the invention according to claim 7 during the step of forming a fluidized bed according to claim 1,
Keep 40-20% of the particles in the fluidized bed below 200 microns,
As a result, the heat transfer coefficient of the cooling pipe in the fluidized bed is 100-200.
It is configured to raise to BTU / FT ² · HR · F.

The invention described in claim 8 is a fluidized bed combustor at atmospheric pressure, a fuel supply device for supplying liquid fuel containing solid fuel and impurities into the fluidized bed combustor, and the fluidized bed combustor. Inert particles, ash particles and partially burned fuel particles comminuted by burning in a layered combustor and contained in the exhaust gas are trapped and equal to 1 to 5 times the weight of the fluidized bed per hour. A cyclone for recirculation with a sieve point of 12 microns or less returned to the fluidized bed at a return flow rate and a superficial velocity of only 0.5 to 7 feet / second (15 to 210 cm / second) in the fluidized bed combustor. It is composed of a superficial velocity imparting device, a heat recovery device for recovering heat from the fluidized bed of the fluidized bed combustor and the exhaust gas flow, and a filter device for collecting dust from the heat recovered exhaust gas flow. . The invention described in claim 9 is the heat recovery device according to claim 8 in which the heat recovery device is arranged in the fluidized bed and the downstream side of the cyclone for recirculation. The invention according to claim 9 is a cyclone for recirculation according to claim 8 or 9, wherein the heat exchanger is disposed in a combustion device. And a recycle cyclone underflow tube is arranged above the chamber and extends to the fluidized bed in the combustion chamber.

(Operation) Solid fuel or liquid fuel containing impurities is supplied into the fluidized bed combustion apparatus. Inert particles, ash particles and partially burned fuel particles are burnt in a combustion device. Then, these particles are burned and crushed. Then, for example, combustion air is supplied from below the fluidized bed combustion chamber so that the superficial velocity is in the range of 0.5 to 7 feet / second (15 to 210 cm / second). The crushed inert particles, ash particles and partially burned fuel particles contained in the exhaust gas are recycle cyclones with a sieve point of 12 microns or less between the fluidized bed and the cyclone located above the combustion device. Circulate. During this time, the average particle size
A fluidized bed is formed which is in the range 100-800 microns.
Then, the fuel burns. The hot exhaust gas containing particles is supplied to a cyclone for recirculation, and particles having a predetermined size or more are trapped as underflow by the cyclone for recirculation, and are 1 to 5 times the weight of the fluidized bed per hour. A large amount of particles called the return flow rate are returned to the fluidized bed. As a result, most of the particles contained in the hot exhaust gas circulate many times between the combustion chamber and the recycle cyclone located above the combustion device. As a result, the fuel is sufficiently retained in the combustion chamber, and the carbon particles are completely combusted.

The overflow exhaust gas is dedusted and released to the atmosphere. On the other hand, heat is recovered from a cooling pipe arranged in the fluidized bed and exhaust gas downstream of the cyclone for recirculation.

In the invention described in the second aspect of the claims, when the solid fuel is supplied, the absorbent for sulfur oxide is supplied. At this time as well, the fuel is sufficiently retained in the combustion chamber.
The reaction between the sulfur oxide and the absorbent is sufficiently performed. This suppresses sulfur oxides. The third part of the claims
In the invention described in the item 1, ammonia is introduced into the high temperature combustion gas stream immediately upstream of the cyclone for recirculation to decompose nitrogen oxides. The invention described in claim 4 is
The particles captured by the recycle cyclone are returned directly to the fluidized bed through the interior of the combustion chamber. This allows operation at temperatures ideal for combustion or sulfur absorption.

According to the fifth aspect of the invention, heat is recovered only from the fluidized bed in the fluidized bed combustor during the process of recovering heat. For example, the free boat part above the fluidized bed is used for heat recovery. No cooling pipe is provided. This forms an isothermal recirculation path.

According to the sixth aspect of the present invention, the fluidized bed combustor is operated at 1400 to 1500 ° F (760 to 816 ° C), thereby suppressing the production of nitrogen oxides due to the combustion of fuel particles. At the same time, the semi-coke is generated in the fluidized bed and the recirculation while the nitrogen oxides are suppressed by the semi-coke. The invention described in claim 7 maintains 40 to 20% of the particles in the fluidized bed to 200 microns or less, whereby the heat transfer coefficient of the cooling pipe in the fluidized bed is 100 to 200BT.
Increase to U / FT ² , HR, F.

(Examples) Examples of the present invention will be described below with reference to the drawings. In the drawings, an embodiment of a system comprising a fluidized bed combustion device 10 is shown. The fluidized bed type combustion apparatus 10 has a combustion chamber 11, and a fluidized bed B made of particles supported on a dispersion plate 12 is formed inside the combustion chamber 11. Further, the fluidized bed type combustion apparatus 10 includes a cooling pipe 13 arranged so as to be located in the fluidized bed B, a combustion supply passage 14, an absorbent supply passage 15 and a fluidized bed drain 16. . Further, a fluidized air inlet 17 is provided at the bottom of the fluidized bed combustion device 10, and air for fluidizing particles is introduced from the fluidized air inlet 17 into a chamber below the dispersion plate 12. . The hot exhaust gas and fine particles emitted from the surface of the fluidized bed B are free boat parts.
It is sent to the recycle cyclone 21 disposed above the fluidized bed B via the conduit 19 via the line 18. The straight underflow pipe 22 extending downward from the cyclone 21 is sufficiently provided with a head so that fine particles are smoothly returned to the fluidized bed B. In this case, the screen point of the cyclone 21 for recirculation is about 12 microns.

A conduit immediately upstream of the cyclone 21 for recirculation to suppress nitrogen oxides generated when the fuel containing nitrogen is burned.
At 19, an ammonia injector 23 is arranged. And
From this ammonia injector 23, ammonia is injected into the hot exhaust gas stream flowing in the conduit 19. Ammonia is supplied from the ammonia supply tank 24 to the ammonia injector 23. The hot exhaust gas from the cyclone 21 for recirculation is
After being sent to the convection heat exchanger 26 via 25, the heat exhaust gas in the heat exchanger 26 is sent from the heat exchanger 26 to a filter device 27 such as a back house filter, dust is removed and the chimney 28 enters the atmosphere. It is supposed to be released.

Furthermore, in detail, in the fluidized bed combustion method and the fluidized bed combustion apparatus according to the embodiment of the present invention, the superficial velocity of the fluidized bed B, that is, the flow rate of the combustion air flowing through the fluidized bed B per unit time. The quotient obtained by dividing by the cross-sectional area of fluidized bed B is selected within the range of 0.5 to 7 feet / second (about 15 to 210 cm / second), and the diameter of the particles of fluidized bed B is within the range of 45 to 2000 microns. At the same time, 40 to 20% of the particles in the fluidized bed B are operated with a diameter smaller than 200 microns. The particle size distribution of the particles in the fluidized bed B is determined by the size of the dolomite used as the feed material. The particles of fluidized bed B are comminuted by burning in a combustor and operated at a superficial velocity of 0.5 to 7 ft / sec (about 15 to 210 cm / sec) and a sieve located above the combustor. A recycle cyclone having a point of 12 microns or less is repeatedly circulated with the fluidized bed to form a fluidized bed having an average particle size of 100 to 800 microns. Also,
A fluidized bed B is placed through a cooling pipe 13 arranged in the fluidized bed B of high temperature.
The heat transfer coefficient on the outside of the cooling pipe 13 is provided so as to partially remove heat from the
100-200BTU / FT ²・ HR ・ F (B-T-U Hourly Square Foot Degree F, 1BTU / FT ²・ HR ・ F = 1 / 0.2048 kcal / h ・ m
²・ ℃) range.

Further, the solid fuel or the liquid fuel is directly supplied into the fluidized bed B together with the solid fuel. Sulfur absorbent such as limestone or dolomite is also directly fed into the fluidized bed B.

High temperature freeboard part 18 of combustion chamber 11 of fluid combustion device 10.
However, there is no means for adjusting the secondary air flow within the heat transfer surface or freeboard portion 18. A large amount of fine particles are discharged from the fluidized bed B to the freeboard section 18,
Free board part 18 with heat exhaust gas and fine particles mixed
Retain inside for a sufficiently long time to carry out a chemical reaction. Most of the fine particles discharged from the fluidized bed B to the freeboard section 18 are returned to the fluidized bed B again, but a considerable amount of fine particles are sent to the cyclone 21 for recirculation together with the heat exhaust gas flow, and heat is generated in the cyclone 21. It is separated from the gas and returned at a temperature substantially the same as the temperature of the fluidized bed B. The amount of fine particles contained in the hot gas introduced into the recycle cyclone 21 is about 0.5 kg / m ³ . Freeboard section 18 and cyclone 21 for recirculation
In the above, by thoroughly mixing the fine carbon particles and the combustion gas containing a large amount of oxygen and allowing it to stay for a sufficient time,
The carbon particles in the air-fuel mixture are completely burned and released from the cyclone 21 for recirculation. The circulation of the semi-coke particles effectively suppresses the generation of nitrogen oxides at temperatures below 1,400 ° F (about 760 ° C). Similarly, in the freeboard section 18 and the cyclone 21, the sulfur oxides contained in the combustion gas and the fine absorbent particles are sufficiently mixed and stayed for a long time, so that the absorption of the sulfur oxides by the absorbent is performed appropriately. Be seen.

The residence time of the absorbent fine particles in the fluidized bed B is about 1
Seconds, about 3 seconds in the freeboard section 18 and the cyclone 21. The cyclone 21 for recirculation is designed with a sieve point of 5 microns, and most of particles substantially larger than 5 microns are smoothly recirculated to the fluidized bed B through the underflow pipe 22 of the cyclone 21 for recirculation. Is configured to
It is possible to prevent the release of particles larger than 5 microns into the filter device 27. The flow rate of particles captured in the recirculation process is about 20 times the flow rate of the mixed flow of fuel and absorbent supplied into the fluidized bed B, and the flow rate per time is twice the weight of the fluidized bed B. become.

If the fuel contains nitrogen bound to the fuel and it is necessary to suppress nitrogen oxides, a cyclone for repurification circulation
Immediately upstream of the inlet of 21, ammonia is injected into the combustion hot gas stream. 1743-1832 ° F without using a catalyst
Within the range of (about 950-1000 ° C), ammonia can reduce nitrogen oxides as desired with maximum efficiency, but operating fluidized bed B at 1450-1650 ° F (about 788-899 ° C). Afterburn in the freeboard 18 above the fluidized bed B, that is, the temperature rise due to afterburning
Nitrogen oxides are more effectively reduced by being held between 150 ° F (about 0-83 ° C). When ammonia is injected so that the molar ratio of ammonia and nitrogen oxides is 1.5 to 2, good mixing is obtained in the cyclone 21 for recirculation, so 80 to 95% of nitrogen oxides are suppressed. To be done. Under certain conditions nitrogen oxides are suppressed without injecting ammonia. That is, the combustion temperature is 1450 ° F (about
788 ° C) and when the fuel contains a high proportion of fixed carbon, most of the recycled particles are semi-coke (chair). 86% of nitrogen is suppressed and nitrogen oxides are reduced by the coke particles. This reduces the emission of nitrogen oxides due to the nitrogen contained in the fuel.
In addition to this, the following is well known. Ie 1,
Semi-coke produced at 450 ° F (788 ° C) is
It acts to reduce nitrogen oxides in the presence of oxygen. 1,
At 450 ° F (788 ° C), a large amount of semi-coke is separated from the fluidized bed and circulates in the circulation circuit. Some of the 86% nitrogen oxide ions may contribute to the reaction of the hot semi-coke (chair).

The combustion hot gas and dust emitted from the recycle cyclone 21 are sent to the convection heat exchanger 26, and the heat exhaust gas is cooled in the heat exchanger 26 to the emission temperature. Finally, the heat exhaust gas is sent from the heat exchanger 26 to the filter device 27, where dust is removed and released into the atmosphere.

In this case, in the present embodiment, it is difficult to combust, for example, various solid and liquid fuels including petroleum coke having a low volatile content of 90% fixed carbon, or sulfur, nitrogen and a mixture thereof (all are air pollutants). To burn fuel cleanly. Therefore, in the present invention, the fuel is burned while recirculating the large-diameter particles in the fine particles through the high-temperature recirculation path above the bubbling fluidized bed B made of fine particle components.

Using petroleum coke with 90% fixed carbon and a calcium / sulfur molar ratio of 1.8, a combustion efficiency of 99.4% was achieved and 98% of sulfur oxides was suppressed. When the ammonia / nitrogen molar ratio was 2.0, 95% of nitrogen oxides were suppressed.
These effects occur simultaneously in the overall composition of the fluidized bed and circulation mechanism.

Another feature of the invention is to extend the fluidization range to 15: 1. Since the fluidized bed B is composed of fine particles, the minimum fluidization speed of the fluidized bed B is about 0.5 feet / second (about 15 cm / second).

Experimental Example I (when using petroleum coke) Petroleum coke was burned with air in the combustion chamber 11 of the fluidized bed combustion apparatus 10 having the configuration shown in the drawing. The combustion chamber 11 has a fireproof structure and has a diameter of 3 feet (about 90 cm) and a height of 12 feet (about 36 cm).
(0 cm), and a cyclone 21 for recirculation was attached to the upper part of the combustion chamber 11. The fluidized bed B was operated at a depth of 3.5 to 4 feet (about 105 to 120 cm), and the cooling pipe 13 for taking out heat was arranged in the fluidized bed B. The components and calorific value of the petroleum coke used in this experimental example are as follows.

Fixed carbon 89.7% by weight Nitrogen 1.9% by weight Sulfur 2.1% by weight Other volatiles 4.4% by weight Ash 0.3% by weight Moisture 1.6% by weight Calorific value (HHV) 14,270 BTU / LB (1BTU / LB = 1 / 1.8 (kcal / kg) This petroleum coke has a lot of fixed carbon and little volatile matter, so it is difficult to burn. The petroleum coke also contains nitrogen and sulfur which generate nitrogen oxides and sulfur oxides as air pollutants. This petroleum coke has a combustion supply line 14
Is introduced into the fluidized bed B and the particle size of the fuel is mostly 50 to 400
It was in the micron range. Dolomite as a sulfur absorbent was introduced into the fluidized bed B from the absorbent supply passage 15. The components of dolomite are as follows.

Calcium carbonate 56.6 (~ 53.6) wt% Magnesium carbonate 45.5 (~ 43.5) wt% Inert ingredient 0.9 wt% Dolomite particle size was in the range of 4700-1200 microns. It combusted in the fluidized bed B and became fine particles.

Fluidized bed B was initially composed of dolomite with an average particle size of 800 microns. After about 500 hours of combustion, Fluidized Bed B contained ash, spent absorbent and partially absorbed absorbent with an average particle size of about 300 microns. The average superficial velocity of fluidized bed B is 4 feet / second (about 120c
m / sec). In order to maintain the fluidized bed depth at a constant level, it was necessary to periodically discharge the constituent material of the fluidized bed B. The cyclone 21 for recirculation is 5 in the fluidized bed combustion chamber 11.
The underflow tube 22 was designed to capture most of the particles larger than micron, and the underflow tube 22 was also designed to allow the particles to be freely collected in the fluidized bed B without substantial resistance. As a result, the recirculation flow rate of the fine particles became large, and the recirculation flow rate per time became twice the weight of the fluidized bed B and 20 times the solid content supply flow rate. Fuel particles and absorbent particles are
It does not leave the fluidized bed B together with the gas flow until the particle size becomes extremely small, and the fluidized bed B is held in the fluidized bed B and pulverized by the action of the fluidized bed B. By preventing the fuel particles from escaping from the combustion chamber 11, the difficult-to-burn fuel containing about 90% of fixed carbon was completely burned with high efficiency.

Combustion efficiency could be further increased by keeping the recirculation system isothermal. The fuel particles are completely heated in the fluidized bed B to the combustion temperature and are not cooled in either the freeboard section 18 or the cyclone 21. The temperature of fluidized bed B is 1600 ° F (about 87
(1 ℃) and burned with 20-30% excess air, the combustion efficiency was 99.4%. In this case, the temperature rise due to afterburning is 50-100 ° F (about 28-55 ° F) above the temperature of the fluidized bed.
C.) showed a high value.

The crushing of the absorbent particles and their retention in the fluidized bed resulted in a large surface area of the absorbent for absorbing sulfur from the gas in the combustion chamber 11. The molar ratio of calcium and sulfur
At 1.8, 98% of sulfur oxides were suppressed. Combustion chamber 11
Another advantage of the small size of the particles in the
This is to increase the heat transfer coefficient on the surface of the cooling pipe 13 arranged in the fluidized bed B. The heat transfer coefficient of the surface of the cooling pipe 13 is 40 to 60 BTU / HR · FT ² · in the conventional fluidized bed boiler.
While it was F, it became 100-200 BTU / HR · FT ² · F.

In order to control the emission levels of nitrogen oxides in order to pass the air pollution regulations in South California, US, ammonia (NH ₃ ) was injected and mixed with combustion gas upstream of the cyclone 21 for recirculation, which is well known. Nitrogen oxide (NO) was converted to nitrogen and water in the reaction. When the molar ratio of NH ₃ and NO was set to 2, about 95% of NO was suppressed.

Example II (when Utah-produced coal is used as fuel) The same combustion chamber 11 as in Example I was used to burn Utah-produced coal in the same manner. The components and calorific value of this coal are as follows.

Fixed carbon 43% by weight Nitrogen 1.3% by weight Sulfur 0.6% by weight Other volatiles 37.1% by weight Ash 8.0% by weight Moisture 10.0% by weight Calorific value (HHV) 11,500BTU / LB Coal produced in Utah has a large fixed carbon content. It burned more easily than petroleum coke because it had very little volatile content. The size of Utah coal was less than 1 x 5/8 inches (4.12 cm). As the sulfur absorbent, the same dolomite as in Experiment I was used. The components are as follows.

Calcium carbonate 56.6 (~ 53.6)% by weight Magnesium carbonate 45.5 (~ 43.5)% by weight Inert component 0.9% by weight The particle size of dolomite when inserted is in the range of 1,200 to 4,700 microns and burns in fluidized bed B. And it became fine particles. The combustion efficiency of this coal was 99.8% when the excess air of 20% and the temperature of fluidized bed B were 1600 ° F (about 871 ° C). With this coal, only about 20% excess air and 14
It burned at a low temperature such as 00 ° F (about 760 ° C) and had good combustion characteristics. For petroleum coke, excess air
Up to 60%, the desired combustion characteristics could be maintained only at a temperature of 1450 ° F (about 788 ° C). When the combustion is coal and the temperature of fluidized bed B is 1600 ° F (about 871 ° C), the value of the temperature rise due to afterburning on the upper part of fluidized bed B is 10 to 20 ° F (about 6 to 11 ° F).
℃) range was suppressed. Also in this example, as in the case of petroleum coke, sulfur oxides and nitrogen oxides were suppressed.

(Effect of the invention) As described above, according to the present invention, the average particle size of the fluidized bed is 10
Since the superficial velocity is within the range of 0 to 800 microns and the superficial velocity is as low as 0.5 to 7 ft / sec (about 15 to 210 cm / sec), the particle size of the fine particles blown out from the fluidized bed is well selected. The combustion efficiency is improved.

In addition, heat is recovered from the cooling pipe arranged in the fluidized bed and the exhaust gas downstream of the recycle cyclone, and the heat exhaust gas is generated between the fluidized bed and the recycle cyclone as in a conventional combustion device. And since there is no heat transfer surface to cool the particles,
An isothermal recirculation path is formed. Therefore, according to the present invention, it operates at temperatures ideal for combustion or sulfur absorption. This effect is obtained also by the invention described in claim 4 because it includes a step of returning the particles captured by the cyclone for recirculation directly to the fluidized bed through the inside of the combustion chamber. To be

Furthermore, since the average particle size of the fluidized bed is as small as 100 to 800 microns, the heat transfer coefficient of the cooling pipe arranged in the fluidized bed is increased. Further, since the superficial velocity is low, wear of the cooling pipe is also reduced.

In addition, the superficial velocity is 0.5 to 7 feet / second (about 15 to 210 cm /
The average particle size of the fluidized bed can be reduced by operating at a low speed of 10 seconds) and the sieve point located above the combustor is circulated between the fluidized bed and the cyclotron for recirculation of 12 microns or less.
It can be made extremely small, 100 to 800 microns, so that when an absorbent for sulfur oxide is supplied as in the invention described in the second aspect of the claims,
The capture of sulfur oxides is significantly improved.

Further, according to the invention described in claim 3, ammonia is injected at the inlet of the cyclone for recirculation, so that ammonia and nitrogen oxides are well mixed in the cyclone for recirculation. Therefore, the effect that the release of nitrogen oxides is suppressed extremely effectively is added.

According to the invention described in claim 6, the fluidized bed combustion device is operated at 1400 to 1500 ° F (760 to 816 ° C), so that the generation of nitrogen oxides due to the combustion of fuel particles is suppressed. In addition, the effect of producing semi-coke while suppressing nitrogen oxides by the semi-coke in the fluidized bed and the recirculation system is further added. Furthermore, according to the invention described in claim 7, 40 to 20% of the particles in the fluidized bed
Is maintained at 200 microns or less, the heat transfer coefficient of the cooling pipe in the fluidized bed can be increased to 100 to 200 BTU / FT ² · HR · F.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing one embodiment of the present invention. 10 ... Fluidized bed type combustion device, 11 ... Combustion chamber, 12 ... Dispersion plate, 13 ... Cooling pipe, 14 ... Fuel supply passage, 15 ... Absorbent supply passage, 16 ... Fluidized bed drain, 17 …… Fluidized air inlet, 18 …… Free boat part, 19 …… Conduit, 21 …… Recycling cyclone, 22 …… Underflow pipe, 23 …… Ammonia injector, 24 …… Ammonia supply tank, 25 ... Heat exhaust gas conduit, 26 ... Heat exchanger, 27 ... Filter device, 28
... Chimney, B ... Fluidized bed

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Giel Yell. Cooper United States, California 94041 Mountain Biscuit Calderon 279 (72) Inventor Zyon Luis Guirolii United States, California 94019 Half Moon Bay Spind Lift Way 534 (56) Reference JP 54-23225 (JP, A) JP Sho 55-165402 (JP, A) JP 58-173312 (JP, A) JP 60-29847 (JP, B2)

Claims (10)

[Claims] 1. A step of supplying a solid fuel and a liquid fuel containing impurities into a fluidized bed type combustion apparatus at atmospheric pressure, and by burning inert particles, ash particles and partially burned fuel particles in the combustion apparatus. Grinding and operating at superficial velocity of 0.5 to 7 ft / sec (15 to 210 cm / sec), a cyclone for recirculation with a sieve point of 12 microns or less placed above the combustor with fluidized bed Circulate between the two to form a fluidized bed with an average particle size of 100 to 800 microns, and the particles contained in the exhaust gas from the fluidized bed combustor are captured by a recirculation cyclone to A step of returning to the fluidized bed with a return flow rate of 5 times per hour, a step of recovering heat from a cooling pipe arranged in the fluidized bed and exhaust gas downstream of a cyclone for recirculation, and heat recovered The process of removing dust from the exhaust gas stream. To, burning liquid fuel containing solid fuel and impurities, fluidized bed combustion method. 2. An absorbent for sulfur oxides is supplied at the step of supplying solid fuel according to claim 1;
A fluidized bed combustion process whereby the fluidized bed also comprises absorbent particles for the partially reacted sulfur oxides. 3. The process according to claim 1
A fluidized bed combustion method comprising the step of introducing ammonia into a hot combustion gas stream immediately upstream of a recycle cyclone. 4. A fluidized bed combustion method according to claim 1, wherein during the step of returning to the fluidized bed, particles captured by a cyclone for recirculation are directly returned to the fluidized bed through the inside of the combustion chamber. 5. A fluidized bed combustion method according to claim 1, wherein heat is recovered only from the fluidized bed in the fluidized bed combustion apparatus during the step of recovering heat. 6. A fluidized bed combustor is used at a temperature of 1400-1500 ° F. (760 ° C.) when carrying out the steps of the first aspect of the present invention.
~ 816 ℃), thereby suppressing the generation of nitrogen oxides due to combustion of fuel particles and generating semi-coke while controlling nitrogen oxides by semi-coke in the fluidized bed and recirculation path. , Fluidized bed combustion method. 7. The process of forming a fluidized bed as claimed in claim 1, wherein 40 to 20% of the particles of the fluidized bed are kept below 200 microns, thereby cooling tubes in the fluidized bed. Fluidized bed combustion method that increases the heat transfer coefficient of 100 to 200 BTU / FT ² · HR · F. 8. A fluidized bed combustor at atmospheric pressure, a fuel supply device for supplying a liquid fuel containing solid fuel and impurities into the fluidized bed combustor, and combusting in the fluidized bed combustor. Crushed by
Then, the inert particles, ash particles and partially burned fuel particles contained in the exhaust gas are captured and returned to the fluidized bed at a return flow rate per hour equal to 1 to 5 times the weight of the fluidized bed, and the sieve point is 12 microns. The following cyclones for recirculation and 0.5-7 ft / sec (15-210) in the fluidized bed combustor.
(cm / sec), a superficial velocity imparting device for giving a superficial velocity, a heat recovery device for recovering heat from the fluidized bed of the fluidized bed combustor and the exhaust gas flow, and the heat recovered exhaust gas flow A fluidized bed combustion apparatus, comprising: a filter device for collecting dust. 9. The heat recovery device according to claim 8 comprises a cooling pipe arranged in the fluidized bed and a heat exchanger arranged downstream of the cyclone for recirculation. A fluidized bed combustor. 10. The recirculation cyclone according to claim 8 or 9 is arranged above the combustion device, and the underflow pipe of the recirculation cyclone is located inside the combustion chamber. A fluidized bed combustion device that extends to the fluidized bed.