JP2651769B2 - Heat recovery combustion equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the improvement of heat recovery and combustion equipment, and more particularly, to the treatment of waste fuel, which is accompanied by a large amount of dust in flue gas, and is converted into fuel or coal, petroleum coke, etc. as fuel. Boilers and hot air generators or municipal waste,
The present invention relates to an improvement of a heat recovery combustion facility provided with a waste heat boiler and an exhaust gas type air preheater (one that preheats combustion air by exhaust gas) among incinerators for incinerating sludge and various industrial wastes such as industrial wastes.

[0002]

2. Description of the Related Art Conventionally, this type of technology uses a stoker (grate) furnace or a rotary kiln furnace as a combustion device so that incombustibles in combustion products are not scattered as much as possible, and the generated combustion exhaust gas has At the entrance of a heat exchanger such as a boiler or air preheater that recovers thermal energy, a pre-daster such as a cyclone should be placed to collect dust and reduce the dust concentration flowing into the heat exchanger as much as possible. Was common. FIG. 3 shows a general flow sheet.

In FIG. 3, auxiliary fuel 14 refers to fuel such as gas or oil for a burner 29 used to raise the internal temperature of the combustion apparatus 1 to a temperature range where ignition or ignition occurs. In addition, the cooling water 17 is used to prevent the flue gas from becoming too hot and damaging the refractory, and preventing the dust from melting or sintering and causing the flue, the heat transfer surface, and the inner wall of the device to be scaled. Spray directly into exhaust gas, usually 900-1
It is for cooling to below 000 ° C. The combustion air 16 is not concentrated and supplied at one location, but is added separately at two locations, that is, at least on the lower surface of the portion where the combustion material is charged and on the way the combustion exhaust gas flows to the outlet of the combustion device. The former is called primary combustion air, and the latter is called secondary combustion air. The amount of primary combustion air is reduced slightly before and after the theoretical air amount, and the combustion products are burned in a reduced state to suppress the generation of fuel NOx, that is, the conversion of nitrogen contained in the combustion products into nitrogen oxides. In addition, intense combustion occurs in the primary combustion air blowing section, which locally raises the temperature to prevent the grate or refractory from being damaged by heat or a chemical reaction. Since the amount of the primary air is only slightly less than the theoretical air amount and is incomplete combustion, secondary air is added later to complete combustion with an appropriate excess air ratio.

[0004] The air preheater 8 recovers heat from the flue gas to preheat the combustion air and simultaneously cools the flue gas. The air preheater 8 improves the heat balance of the combustion device 1 and raises the temperature to facilitate combustion of the burned material. The heat recovery rate of the waste heat boiler 7 is increased, and the exhaust gas is cooled to a temperature equal to or lower than the allowable temperature limit of the dust collector 9 such as a bag filter. In FIG. 3, only the primary combustion air is used, but the secondary combustion air is also passed through the exhaust gas type air preheater to promote the secondary combustion and sometimes reduce the exhaust gas temperature. In addition, a scrubber or an electric dust collector is attached to the dust collecting device 9.
When used for bag filters, usually 150-250
In some cases, an air preheater is not installed because the temperature is as high as 200 to 350 ° C. Non-combustible material 13 from combustion device 1
Emissions are usually made by extinguishing, cooling, and sealing the exhaust gas through a water seal or the like, and then discharged outside. The other ash discharging device 5 discharges dust while sealing exhaust gas with a rotary valve, a double damper, or the like.

[0005]

Recently, the adoption of fluidized bed combustors has gradually begun to become popular. Conventional stoker furnaces and rotary kiln furnaces have extremely limited calorific values and physical properties of target combustibles, and those with excessive calorific values can damage or damage the grate or refractory by melting or deforming them or generating clinkers. If the heat generation amount is too small, it is discharged without being burned, so that the processing amount is drastically reduced and the auxiliary fuel is increased. Further, if the type of combustion material is different from oil, sludge, plastic, garbage, etc., it is necessary to select the type of combustion furnace according to the difference. On the other hand, a fluidized bed combustor accepts both sludge and garbage, from waste oil to waste liquid, without any damage even if the calorific value is high or low, and the heat balance is determined by the balance of the average calorific value of the received combustion products. Has an excellent side.

[0006] In this method, a fluidized bed fluidized by primary combustion air blown from the bottom with sand heated to a combustion temperature of about 600 to 850 ° C is formed at the bottom, and rises from the fluidized bed in a space called an upper free board section. The sand is dropped and returned to the fluidized bed, and the secondary combustion is performed by the secondary combustion air. Since the fuel is burned, it is possible to select the properties of the burned material and the calorific value as described above. The remaining incombustible material is taken out of the furnace together with the sand from the bottom of the fluidized bed, and sieved by a trommel (rotating horizontal cylindrical sieve) or a vibrating sieve into sand of 2 to 5 mm or less and a larger incombustible material. The sand is returned to the furnace, and the incombustibles are discharged. If there are many staples, nails, wires, tacks, etc. in the incombustibles, they are easily caught and clogged by the sieve, so it is common to place a magnetic separator upstream of the sieve to remove iron. The pressure difference between the bottom of the fluidized bed and the outside can be controlled by using a cooling chute with a length of 1 to 2 m without using dampers and cooling the sand and incombustibles and filling the chute with sand. The method of suppressing the pressure difference is convenient because there is no problem such as biting.

In this fluidized bed, unlike conventional rotary kilns and stoker furnaces, since it is dried and burned while being violently crushed with sand, incombustible substances discharged from the furnace bottom are clean and completely burned without dust, and can be handled completely. On the other hand, on the other hand, there is an increase in the number of substances that are scattered together with the exhaust gas from the fluidized bed to the freeboard section and out of the combustion apparatus. In addition, the fluidized sand itself collides with each other, or is subjected to thermal shock in contact with a combustible material or a waste liquid, and becomes worn and fine, and scatters as dust. Non-combustible sand contained in combustibles is assimilated with sand without being discharged even in the outside classification, so if the amount is large, the amount of sand gradually increases, but if it is small, Due to the decrease, it becomes necessary to replenish the sand, and the amount of dust scattered from the combustion device increases accordingly. Most of the dust particles scattered generally have a particle size of less than about 500 μm, but there are many particles having a particle size larger than this due to scattering of sand due to the boiling phenomenon of the fluidized bed.

For this reason, as in the prior art, if the dust is removed as much as possible by a cyclone or other pre-duster and then the dust is passed through a heat recovery device such as a waste heat boiler or an air preheater, the metal part of the cyclone is severely worn by the large dust particles. occured. Also, when only a fine particle having a diameter as small as 10 μm or less that passes through the cyclone flows into the heat recovery device, it gradually adheres to the heat transfer surface and forms a heat insulating layer that is very light and thus difficult to peel off. For this reason, heat exchange was prevented and soot blow had to be operated frequently. For this reason, if the heat transfer surface is worn out due to soot blowing or if a waste heat boiler is used, a reduction in the amount of recovered steam due to the soot blowing and a change in the amount of steam generated by the soot blowing during the soot blowing can be avoided, and there is no waste heat boiler. The air preheater alone required an air or steam source for soot blowing.

In addition, since the amount of exhaust gas during soot blowing fluctuates abruptly by the amount of the soot blow fluid, stable operation of the equipment is impaired, and fluctuations in exhaust gas pressure fluctuate greatly or exceed the capacity of the exhaust gas treatment equipment, resulting in harmful gas. In order to avoid problems such as a decrease in removal efficiency and dust collection efficiency, it was necessary to perform an operation of reducing the combustion amount and narrowing the exhaust gas flow rate prior to soot blowing in order to avoid such a situation. In particular, when a substance containing a large amount of non-combustible material of 10 μm or less such as sludge is included in the combusted material, the rate of forming the heat insulating layer on the heat transfer surface is large, which is a serious problem. The present invention provides a heat recovery and combustion facility capable of efficiently removing dust having a large particle diameter from a combustion device and preventing abrasion due to dust in a heat recovery chamber in order to solve the above problems. The task is to provide.

[0010]

In order to solve the above-mentioned problems, in the present invention, a combustion exhaust gas generated from a fluidized bed combustion device is supplied to an inclined duct having an average flow velocity of 12 to 20 m / s during rated operation. In the heat recovery and combustion equipment, which guides the sedimentation chamber and then flows from the sedimentation chamber to the heat recovery device, the sedimentation chamber has an inflow port on the upper surface, and the central portion has a flow path cross-sectional area that is larger than that of the duct to increase the average flow velocity. 8 to 14 at rated operation
m / s, the bottom of which forms an ash discharge hopper whose wall surface is at an angle of more than 50 ° with respect to the horizontal plane, and an ash discharge device is provided at the lowest part. An outlet nozzle for the heat recovery device is provided at a position where the exhaust gas flowing into the duct from the outlet does not reach, and the cross-sectional area of the flow path of the outlet nozzle is smaller than the cross-sectional area of the settling chamber flow path. In the above, it is preferable to provide means for circulating the ash discharged from the settling chamber ash discharge device to the fluidized bed combustion device. Also, the inclined duct is preferably inclined at least 40 ° when it rises according to the exhaust gas flow, and at least 30 ° when it descends.

[0011]

It is said that the dust accompanying the exhaust gas has a wear effect up to 200 μm or more, which cannot follow the change in the exhaust gas flow direction. According to the present invention, by providing a settling chamber, it is possible to separate and remove dust having a large particle diameter by the impact dust collection effect by changing the exhaust gas flow direction, and selectively remove dust having a particle diameter of 200 μm or more as described above. To prevent abrasion due to dust on the heat transfer surface called ash cut.

Further, in the heat recovery chamber, 2
The amount of particles having a large momentum of at least 00 μm and having abrasion is small, and relatively large particles having a particle size of 50 to 200 μm are mixed as compared with those obtained by dusting with a cyclone or the like. For this reason, dust adhering to the heat transfer surface has a relatively high bulk density, and is easily separated by vibration, airflow, or the like. As a result, the average dust deposition amount is reduced,
The required frequency of soot blow is reduced, it is easily washed off by soot blow, and the strength of soot blow is weakened. Become.

Further, the duct from the fluidized bed combustion device is also inclined and the flow velocity is set to be as large as 12 to 20 m / s. Even if sand or rough dust from the fluidized bed settles and separates, the dust moves by gravity or exhaust gas flow and accumulates. I try not to do it. As a result, the high-concentration scattering of coarse dust unique to a fluidized bed combustion device causes coarse dust to be mixed into exhaust gas, and as a result, coarse dust is mixed into dust attached to the heat transfer surface. The effect of promoting dust separation is enhanced.
In addition, dust does not necessarily hinder heat transfer due to adhesion, but has a heat radiation promoting function of receiving heat of exhaust gas and converting it to radiant heat.

According to the empirical values of the present inventors, there are many data in which high dust exhaust gas discharged from the fluidized bed radiates about 70% of the black body, and is twice as large as exhaust gas with little dust. Heat transfer in a high temperature region can be obtained. In addition, dust has the effect of disturbing and thinning the boundary layer with respect to the boundary layer occupying most of the heat transfer resistance between the exhaust gas and the heat transfer surface. , 2 to 3 times the heat transfer coefficient. In addition, since the radiant heat transfer is enhanced, the radiant heat transfer is originally less likely to be reduced by the attached dust layer and is less affected by the attached dust, which is advantageous for the equipment of the present invention. The sedimentation chamber removes and separates those having a size of 200 to 500 μm or more which cannot follow the change in the direction of the exhaust gas flow, while those having a size less than 200 μm are positively entrained. The purpose of this is different from that of dust that can be removed by the centrifugal separation effect and the collision dust collection effect as described above.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to the drawings, but the present invention is not limited thereto. Embodiment 1 FIG. 1 shows a schematic process diagram of a heat recovery combustion facility of the present invention. FIG. 2 shows an enlarged sectional view of the settling chamber used in FIG. In the figure, a fluidized bed combustion apparatus 1 comprises a fluidized bed section 2 and a freeboard section 3, and a combustion product 14 is burned in a fluidized bed 2 in which fluidized sand is fluidized by primary combustion air 16a. In step 3, secondary combustion is performed by introducing the secondary combustion air 16b.

The incombustibles are discharged from the bottom of the fluidized bed together with the fluidized sand by a take-out chute 10, introduced into a sieving device 12 by a discharge conveyor 11 and sieved into incombustibles 13 and fluidized sand. 25 is circulated to the combustion device 1. Replenishment of the fluidized sand is performed from 18. The auxiliary fuel 15 is
The cooling water 17 is added to raise the temperature of the fluidized bed 2 to a temperature range necessary for combustion, and the cooling water 17 is used to maintain the temperature of the free boat section 3 at an appropriate temperature.

The exhaust gas discharged from the fluidized bed combustion device 1 passes through the inclined duct 19 and enters the settling chamber 4. The exhaust gas flow that has entered the sedimentation chamber 4 from the duct goes straight 26 as shown in FIG.
The dust particles 27 having a size of about 00 μm or more collide with the wall of the ash discharge hopper 24 at that time, are captured and enter the ash discharger 5 from the lowest nozzle, and are discharged to the outside from 5. Since the wall surface of the ash discharge hopper 24 is at an angle of 50 ° or more, even if it bounces, only a few particles jump upward and get on the exhaust gas flow again. Is captured by The exhaust gas flow after the collision is disturbed and flows into the waste heat boiler 7 of the heat recovery device while accelerating.

As described above, the drift of the exhaust gas is reduced by the re-acceleration effect and the effect of changing the direction of the exhaust gas flow. Waste heat boiler 7
The exhaust gas heat-exchanged through the duct 21 enters the air preheater 8 through the duct 21, heats the combustion air 16 and lowers the temperature from itself to the dust collector 9, where it is collected and discharged as clean air. 22. In the waste heat boiler 7 and the air preheater 8 which are heat recovery devices, since relatively large particles of 50 to 200 μm are mixed in the exhaust gas, dust adhering to the heat transfer surface has a relatively high bulk density. It easily rises and peels off due to vibration, airflow, etc. Particles discharged from the settling chamber 4
From the ash discharge device 5, the fluidized bed combustion device 1 is switched by the switching device 6.
Or discharged as collected fly ash 23. The ash discharged from the waste heat boiler 7, the air preheater 8, and the dust collecting device 9 passes through the ash discharging device 5 and collects fly ash 23.
Is discharged as

As a result, depending on the case, it is possible to maintain the conventional heat recovery without particularly removing soot from dust and without increasing the heat transfer area in equipment. Also, in equipment where the amount of fluidized sand may decrease and replenishment must be performed, the ash discharged from the sedimentation chamber has a coarse particle size and a particle size close to that of fluidized sand.
Is provided to reduce the average particle size of sand in the fluidized bed to activate the flow and accelerate the combustion reaction rate in the fluidized bed, and to discharge the fluid out of the system. In order to reduce the amount of sand, it is possible to reduce or eliminate the need for supplementary sand, which is practically advantageous.

[0020]

As described above, according to the present invention, by providing the sedimentation chamber, dust having a particle diameter of 200 μm or more can be selectively removed, and wear of the heat transfer surface due to dust can be prevented. In addition, since relatively large particles are mixed in the heat recovery chamber, dust adhering to the heat transfer surface can be easily separated, enabling stable operation for a long period of time. Was.

[Brief description of the drawings]

FIG. 1 is a schematic process diagram of a heat recovery combustion facility of the present invention.

FIG. 2 is an enlarged sectional view of a settling chamber used in FIG.

FIG. 3 is a schematic process diagram of a conventional heat recovery and combustion facility.

[Explanation of symbols]

1: fluidized bed combustion apparatus, 2: fluidized bed section, 3: free board section, 4: settling chamber, 5: ash discharger, 6: switching apparatus, 7:
Waste heat boiler, 8: air preheater, 9: dust collecting device, 10: take-out chute, 11: discharge conveyor, 12: sieving device, 1
3: non-combustible, 14: combustion, 15: auxiliary fuel, 16: combustion air, 17: cooling water, 18: auxiliary sand, 19: inclined duct, 20, 21: duct, 22: exhaust gas, 23: trapping Fly ash, 24: Ash discharge hopper, 25: Circulating sand, 26: Exhaust gas flow, 27: Trajectory of mixed sand, 28: Cyclone,
29: Burner

Claims (2)

(57) [Claims] 1. A flue gas generated from a fluidized bed combustor is led to a settling chamber by an inclined duct having an average flow velocity of 12 to 20 m / s during rated operation, and then flows from the settling chamber to a heat recovery device. In the heat recovery and combustion equipment, the settling chamber has an inflow port on the upper surface, and the central portion thereof has a flow path cross-sectional area larger than that of the duct so that the average flow rate is 8 to 14 during rated operation.
m / s, the bottom of which forms an ash discharge hopper whose wall surface is at an angle of more than 50 ° with respect to the horizontal plane, and an ash discharge device is provided at the lowest part. Characterized in that an outflow nozzle to the heat recovery device is provided at a position where the exhaust gas flow flowing into the duct from the outside does not emerge, and the cross-sectional area of the flow path of the outflow nozzle is smaller than the cross-sectional area of the settling chamber flow path. Facility. 2. The heat recovery and combustion equipment according to claim 1, wherein the settling chamber ash discharging device has means for circulating the discharged ash to a fluidized bed combustion device.