JPH076609B2 - Circulating fluidized bed combustion method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a circulating fluidized bed combustion method used in boilers and various heating furnaces that burn solid matter such as coal, waste oil, wood chips, and sludge, and liquid fuel. .

[Conventional technology]

Explain conventional fluidized bed combustion method 1. Bubble type fluidized bed combustion method (1) Combustion furnace is composed of fluidized bed, and fluidized material, fuel, air and coal stone are put into the fluidized bed to perform combustion and desulfurization. It is done at the same time.

(2) A heat transfer surface such as a superheater is arranged above the fluidized bed.

2. Circulating fluidized bed combustion method Fuel and air are supplied to the lower part of the combustion furnace, and the solid content in the combustion gas collected from the high temperature part of the boiler is recirculated to the bottom of the combustion furnace, and the combustion furnace together with the fuel and air. After rising from the lower part, the high temperature dust collector installed in the rear flue collects solids, and the clean gas is further sent to the rear flue. The solid matter collected in the above-mentioned high temperature part is re-injected into the combustion furnace after releasing the amount of heat retained by the solid matter to the heat exchanger provided in the recirculation system.

[Problems to be solved by the invention]

1. Bubbling type fluidized bed combustion method (1) Part of the evaporator and superheater in order to absorb a part of the generated heat of all fuel generated in the fluidized bed and maintain the temperature in the fluidized bed at 850 to 900 ° C. Is installed in the fluidized bed. Steel pipes that compose this evaporator and superheater are ash of the above fuel, coal stone,
It is worn by the fluid material, and it is necessary to replace it with a new pipe in a short time or perform overlay repair.

(2) The unburned matter that has flown out of the fluidized bed comes into contact with the heat transfer surface at the upper part of the fluidized bed and is cooled without being burned, and is transported to the outside of the boiler without being burned, resulting in high unburned loss.

(3) Since desulfurization is performed in the fluidized bed, it is necessary to create an oxidizing atmosphere in the fluidized bed. Therefore, the NOx concentration at the combustion furnace outlet becomes high.

2. Circulating fluidized bed combustion method (1) The amount of solid matter carried by the combustion product gas passing through the combustion furnace and the rear flue is 10 to 10% of the amount of fuel injected into the combustion furnace.
Since it is about 100 times, the metal adhesion and dust collector in the combustion furnace and the rear flue heat transfer surface are severely worn.

(2) The dust collector installed in the high temperature part is larger in size than the one installed in the low temperature part, and it is expensive and unreliable because it uses high temperature resistant material. It requires a longer startup time than the temperature rise rate limit.

(3) Since the combustion temperature in the combustion furnace is controlled at 800 to 900 ° C, a large amount of N ₂ O is generated.

[Means for solving problems]

In order to solve the above problems, the present invention provides a circulating fluidized bed combustor in which an overfire air nozzle is provided in an upper space formed by supplying solid fuel, and an additional air nozzle is provided above the overfire air nozzle. Supplying a regulated amount of air in the fluidized bed in the range of 0.3 to 0.8 times the theoretical combustion air amount, supplying the remaining air to the overfire air nozzle and the additional air nozzle, and discharging from the fluidized bed. Of the low temperature particles collected from the exhaust gas, 1 to 5 times the amount of solid fuel supplied to the fluidized bed is recirculated into the fluidized bed to set the installation level of the overfire air nozzle and the additional air nozzle. The present invention provides a circulating fluidized bed combustion method, which is characterized in that a denitration reaction zone having a temperature of 1000 ° C or higher is formed between the temperature and the installation level.

[Action]

The fluidized bed contains low temperature particles containing solid fuel and unburned carbon and 0.
3 to 0.8 times the primary air is supplied, the fuel and unburned carbon are partially combusted and gasified, and the next endothermic reaction occurs.

1) C + O ₂ = CO ₂ + 97,200kcal / moL 2) C + 1 / 2O ₂ = CO + 29,200kcal / moL 3) C + O ₂ 2CO-38,800kcal / moL 4) C + H ₂ O = CO + H ₂ −28,400kcal / moL 5) C + 2H ₂ O ＝ CO ₂ ＋ 2H ₂ -19,000kcal / moL 6) C + H ₂ OCO ₂ ＋ H ₂ ＋ 10,000kcal / moL Endothermic reaction of the above formulas 3), 4), 5) and solid injected into the collected low temperature particles The NOx reducing component (CnHm, NH) is maintained by keeping the inside of the fluidized bed at a reducing atmosphere of 700 to 1000 ° C by returning it to the fluidized bed of about 1 to 5 times the amount of fuel and performing low NOx combustion.
₃ etc.) is generated.

Reducing gas generated in the fluidized bed _{(CO, H 2, CnHm,} NH 3, NHi
Etc.) reacts with a small amount of oxygen supplied by overfire air in the reaction section where the temperature formed between the installation level of the overfire air nozzle and the installation level of the additional air nozzle above the fluidized bed is 1000 ° C. or higher and Causes the denitration reaction shown in. This reaction carries out the reductive decomposition of NO and nitrogen compounds with hydrogen oxide and ammonia when the reducing gas is present in excess of the chemical equivalent of oxygen.

8) NO + NH ₂ → N ₂ + H ₂ O In the above-mentioned high temperature zone of 1000 ° C or higher, the recirculation amount of low temperature particles collected from the exhaust gas should be 1 to 5 times the amount of solid fuel supplied to the fluidized bed. Where N ₂ O is decomposed.

〔Example〕

The present invention will be described based on an embodiment using the apparatus shown in FIG.

The combustion furnace is formed by being surrounded by a combustion furnace wall 1 made of a water cooling wall tube, and the furnace bottom 2 is also formed by a water cooling wall tube. A wind chamber 3 is provided below the furnace bottom 2, and a large number of primary air nozzles 4 are attached to the furnace bottom 2. A fluidized bed 5 is formed on the upper part of the bottom 2 of the furnace, a fuel supply device 6 for charging coal of solid fuel is installed on the combustion furnace wall 1 on the upper part of the fluidized bed 5, and an upper fuel furnace wall 1 is overlaid. A fire air nozzle 7 and an additional air nozzle 8 are provided. A rear flue wall 9 formed of a water-cooled wall pipe is formed adjacent to the combustion furnace to form a rear flue and communicates with the combustion furnace via a combustion furnace outlet 10.
The water cooling wall pipes forming the combustion furnace wall 1 and the rear flue wall 9 are connected to the ceiling drum 11. A plurality of heat exchangers 12 are arranged in the rear flue, and a hopper 13 is arranged below the rear flue. A rear flue outlet 14 is formed in the rear flue wall 9 directly above the hopper 13 and a flue 15 is connected. Flue 15
The wake end is connected to the inlet of the cyclone separator 16, and the gas outlet of the cyclone separator 16 is connected to the flue 17. An air preheater 18 is arranged at the downstream end of the flue 17, and a hopper 19 is arranged below the air preheater.
The flue 20 is connected directly above the hopper 19, and the rear end of the flue 20 is connected to the entrance of the dust collector 21. A flue 22 is connected to the exit of the dust collector 21.

The air outlet part of the air preheater 18 has a damper 23 and a blower on the way.
It communicates with the wind chamber 3 via a primary air supply pipe 25 having 24, and communicates with the overfire air nozzle 7 and the additional air nozzle 8 via a secondary air supply pipe 27 having a blower 26. A discharge pipe 29 having an extraction valve 28 is attached to the hopper portion for discharging the solid content of the cyclone separator 16.
The lower end of the discharge pipe 29 is connected to a solid material injection device 32 to which the downstream end of a high-pressure pipe 31 attached to the outlet of the blower 30 is connected. In addition, a discharge pipe 34 having an extraction valve 33 is attached to the hopper portion for discharging the solid content of the dust collector 21, and the lower end of the discharge pipe 34 has a high pressure pipe 35 attached to the outlet of the blower 30. Is connected to the solid material injection device 36 to which the downstream end thereof is connected. A discharge pipe 37 is branched on the upstream side of the discharge valve 33 of the discharge pipe 34, and a discharge valve 38 is arranged in the middle of the discharge pipe 37.

Solid material empty pipes 39, 40 are attached to the outlets of the solid material injection devices 32, 36, respectively, and the solid material empty pipes 39, 40 are provided at the bottom 2 of the furnace. It communicates with 41 and 42.

A gas temperature detecting device 43 for measuring the temperature of the fluidized bed 5 is provided, a signal of the gas temperature detecting device 43 is transmitted to the controller 44, and the signal of the controller 44 is transmitted to the damper 23, the extraction valve 33,
It is sent as a control signal of a driving means for driving 38.

The solid matter containing unburned carbon, which is introduced from the fuel and solid matter injection nozzles 41 and 42 in an amount of 1 to 5 times the amount of fuel injected from the fuel supply device 6, has a theoretical air amount of 0.3 to 3 in the fluidized bed 5.
The reaction of 1) to 6) above is performed by 0.8 times the amount of primary air, and the fuel is gasified and partially burned to 700 ° C to 1000 ° C.
To form the primary combustion zone of the reducing atmosphere.

By forming this primary combustion zone, generation of NOx due to combustion is suppressed, and denitration in the furnace in a reducing atmosphere is promoted.

The reducing gas or the like generated in the primary combustion zone is introduced into the unburned matter reaction zone below the overfire air nozzle 7 in the upper part of the fluidized bed 5. Here, as in the fluidized bed 5, gasification reaction and partial combustion are performed.

Overfire air is injected from the overfire air nozzle 7. A denitration reaction zone is formed between the level of the overfire air nozzle 7 and the level of the additional air nozzle 8, where the furnace temperature is maintained at 1000 ° C or higher, and the denitration reaction shown in 7) and 8) above is performed. And decomposition of N ₂ O takes place. After that, the unburned component and the remaining reducing gas enter the complete combustion region, and the additional air introduced from the additional air nozzle 8 forms an oxidizing atmosphere in the furnace to promote complete combustion of the unburned gas. Here, the unburned component is completely burned by maintaining the temperature in the furnace at about 900 to 1300 ° C. and securing the gas residence time of 1 to 4 seconds.

The solid content collected by the cyclone separator 16 and the dust collector 21 is introduced into the fluidized bed 5 by an amount of 1 to 5 times as much as the fuel quantity through the solid content injection nozzles 41 and 42 installed in the fluidized bed 5 by air conveyance. To be done. A part of the solid matter collected by the dust collector 21 provided in the low temperature gas section is fed to the fluidized bed 5, and the rest is discharged out of the system. At that time, the extraction valves 33, 38 are output by the signal from the controller 44 which receives the signal from the gas temperature detector 43 so that the gas temperature of the fluidized bed 5 becomes a constant value (for example, 950 ° C.).
The valve opening is adjusted to control the solid matter introduced from the solid matter introduction nozzles 41 and 42 through the solid matter empty pipes 39 and 40.

Further, independently of or in parallel with the above solid amount input control, the opening of the damper 23 is adjusted by a signal from the controller 44 to control the gas temperature of the fluidized bed 5. To control the gas temperature of the fluidized bed 5, there are two methods of adjusting the primary air amount and the recirculation amount of the solid matter collected in the low temperature dust collector. Which one is the main and the rest is the subordinate? It may be determined according to the properties of the fuel, the load, and the regulation value of NOx.

By the above action, without installing a heat transfer surface in the fluidized bed,
Since optimum conditions for NOx control can be created in the fluidized bed and upper part of the combustion furnace, it is possible to supply a boiler with low pollution and high reliability.

The solid matter for recirculation may be the one collected by the hoppers 13 and 19.

Further, the overfire air nozzle 7 and the additional air nozzle 8 are provided in the corner portion, and the diameter of the virtual circle formed by the overfire air introduced from the corner portion is reduced to a small diameter, and the additional air is placed above the virtual circle. It is also possible to carry out the denitration reaction between combustion furnaces in which the diameter of the virtual circle is increased. That is,
The reducing gas remains outside the virtual circle formed by the overfire air. On the other hand, the inner side completely burns with overfire air to generate NOx, but the completely burned gas (a small amount of O ₂ remains) is diffused toward the outer periphery by the centrifugal force from the additional air above. The complete combustion gas diffused to the outer periphery (a small amount of O ₂ remains) is mixed with the reducing gas outside the virtual circle to cause a denitration reaction.

Further, the overfiring air nozzle 7 and the additional air nozzle 8 can be tilted vertically and horizontally in multiple stages of overfiring air injection, whereby a more effective denitration reaction can be performed.

Next, the relationship between the input amount of primary air, the circulating amount of solid matter and the effect will be described with concrete experimental data.

The one shown in FIG. 2 is the primary when the amount of injection from the solid injection nozzles 41 and 42 is changed to 1, 2.5, or 5 times the amount of fuel injected from the fuel supply device 6. It is a graph relating to the average temperature in the fluidized bed 5 with respect to the change in the amount of air supplied from the air nozzle 4 into the fluidized bed 5. From this graph as well, if the air amount is 0.3 to 0.8 of the theoretical air amount,
It can be seen that a low-temperature reducing atmosphere is formed by suppressing the temperature below the softening point of combustion ash at about 700 to 1000 ° C. It is also understood that if the amount of the solid matter added is increased by 5 times or more, the temperature in the fluidized bed 5 becomes too low, so that it cannot be used.

Next, FIG. 3 is a graph showing the combustion efficiency with respect to the circulating amount of solid matter, and it can be seen that when the circulation ratio becomes 1 or less, the combustion efficiency extremely decreases and cannot be used.

FIG. 4 shows the relationship between the air ratio in the fluidized bed obtained in the circulating fluidized bed combustion test furnace and the NOx at the furnace outlet. From Fig. 4, it can be seen that the NOx at the furnace outlet shows the lowest value when the air ratio in the fluidized bed is 0.7. This test has a circulation ratio
The results from 2.0 to 2.6 are shown.

FIG. 5 shows the temperature distribution in the furnace when the recirculation amount was changed in the above test furnace, when the circulation ratio was 0 and 2.45.

From Fig. 5, even if the air ratio in the fluidized bed is the same, changing the circulation ratio changes the temperature distribution in the furnace and suppresses NOx (145
It can be seen that it is possible to operate with ppm reduced to 73 ppm. As shown in this figure, it is important to form a high temperature zone of 1000 ° C or higher in the furnace to reduce NOx. By the way, if the circulation ratio is increased to about 50, which is the same level as the circulating fluidized bed, the heat capacity of the circulating particles increases, The temperature inside the furnace is constant.

〔The invention's effect〕

According to the fluidized bed combustion method of the present invention, the combustion efficiency is 2 to 12%.
It is effective and can reduce NOx generation significantly.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a mode for carrying out the present invention, and FIG.
A graph showing the relationship between the amount of secondary air and the temperature in the fluidized bed, Fig. 3 is a graph showing the relationship between the solid matter circulation amount and combustion efficiency, and Figs. 4 and 5 are tests in a circulating fluidized bed combustion test furnace. It is a graph which shows a result. 4 ... Primary air nozzle, 5 ... Fluidized bed, 6 ... Fuel supply device 7 ... Overfire air nozzle, 8 ... Additional air nozzle 16 ... Cyclone separator, 21 ... Dust collector 41, 42 ... Solid Material injection nozzle.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Manabu Miyamoto 2-5-1, Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. (56) References JP-A-61-106997 (JP-A-62-261808) No.), a microfilm (JP, U) of the details and drawings attached to the application.

Claims (1)

[Claims] 1. A circulating fluidized bed combustor in which an overfire air nozzle is provided in a space above a fluidized bed formed by supplying solid fuel, and an additional air nozzle is provided above the overfire air nozzle. An amount of air adjusted in a range of 0.3 to 0.8 times the amount of combustion air is supplied, the remaining air is supplied to the overfire air nozzle and the additional air nozzle, and is collected from the exhaust gas discharged from the fluidized bed. The temperature between the installation level of the overfire air nozzle and the installation level of the additional air nozzle is 1000 by recirculating 1 to 5 times the amount of solid fuel supplied into the fluidized bed among the generated low temperature particles. A circulating fluidized bed combustion method characterized by forming a denitration reaction zone at ℃ or higher.