Sludge incineration device and method with staged air distribution and flue gas recirculation type rotary kiln

Abstract

The application discloses a sludge incineration device and method for a rotary kiln with staged air distribution and flue gas recirculation, which sends sludge and primary air into the rotary kiln from the kiln head; sends secondary air from the kiln head to the ignition section of the rotary kiln; and sends recirculated flue gas from the kiln head to the stable combustion section of the rotary kiln. The staged air distribution can form an oxygen-deficient fuel-rich zone in the initial combustion stage to inhibit the generation of NO x ; and the remaining air required for combustion is sent in the form of secondary air in the later combustion stage to make the fuel burn out; the flue gas recirculation can moderately reduce the oxygen content in the furnace and strengthen the reducing atmosphere in the combustion zone, which is beneficial to further reducing the emission of NO x in the sludge incineration process. The application uses the staged air distribution and flue gas recirculation, not only reduces the emission of NO x , but also avoids the problem that the SNCR method commonly used in the denitration of the rotary kiln incinerator needs to add ammonia water and external equipment, thereby reducing the operation cost and having good economic efficiency and application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of incineration, in particular to a rotary kiln sludge incineration device and method equipped with staged air distribution and flue gas recirculation and system. BACKGROUND

[0002] At present, sludge incineration equipment includes multi-chamber incinerator, fluidized bed incinerator and rotary kiln incinerator, etc. In view of the characteristics of wide source and complex composition of sludge, rotary kiln incinerator has attracted more and more attention and research due to its strong fuel adaptability and large treatment capacity. Since sludge contains a large amount of nitrogen elements, these nitrogen elements will be converted into NO x pollutants discharged into the atmosphere during the rotary kiln incineration process, so denitration has become an important step in the rotary kiln sludge incineration process.

[0003] At present, the denitration of rotary kiln incinerator mainly adopts selective catalytic reduction (SCR) technology and selective non-catalytic reduction (SNCR) technology, and there is no report on the use of in-furnace combustion control technology. SCR and SNCR need to use ammonia water in the denitration process, and additional ammonia injection equipment is required, and the reaction temperature requirement is also high, which increases the operation cost.

[0004] At present, fluidized bed boilers and pulverized coal furnaces have successfully reduced the emission of NO x by using staged air distribution and flue gas recirculation. Practice shows that by using staged air distribution, a fuel-rich combustion zone is created in the rotary kiln incinerator, which reduces the generation of NO x overall; by using flue gas recirculation, the O2 concentration and temperature level in the rotary kiln incinerator are reduced, thereby reducing the emission of NO x . However, the existing rotary kiln incinerator does not use the method of air staging and flue gas recirculation to reduce the emission of NO x . Fluidized bed incineration mainly relies on the high heat capacity, strong mixing and heat transfer of the high-temperature fluidized bed material in the furnace to quickly heat the waste sent into the furnace to form uniform combustion throughout the bed.

[0005] The combustion characteristics of pulverized coal furnace are that the fuel enters the combustion chamber with air and burns in a suspended state.

[0006] Therefore, these two types of incinerators have good gas-solid mixing characteristics in the furnace.

[0007] The advantage of rotary kiln incinerator is that the incineration temperature is high, the adaptability to the shape and size of waste is wide, and it can be applied to almost any type of hazardous waste, and has the characteristics of flexible operation and adjustment, less failure, safe incineration, etc.

[0008] However, the solid fuel of the rotary kiln incinerator mainly relies on the gravity and the rotation of the cylinder to move in the furnace, so the gas-solid mixing characteristics of the rotary kiln incinerator are not as good as those of the fluidized bed and the pulverized coal furnace.

[0009] For example, in the fluidized bed boiler, the fuel is lifted by the primary air flowing from bottom to top, mixed with the high-temperature bed material in a suspended state, and ignited and burned. The secondary air is generally introduced in the middle of the furnace and enters the furnace axially along the secondary air pipe, playing a role of supplementing combustion and strengthening disturbance. However, for the rotary kiln, since the fuel and the primary air enter the furnace from the kiln head direction, ignition and combustion are required. Therefore, according to the conventional method, the secondary air is introduced from the middle of the furnace, which cannot effectively strengthen the mixing of the fuel and the atmosphere in the furnace, and cannot improve the gas-solid mixing characteristics of the rotary kiln incinerator.

[0010] Therefore, the staged air distribution adopted by the fluidized bed and the pulverized coal furnace cannot be directly applied to the rotary kiln incinerator. SUMMARY

[0011] The purpose of the present application is to solve the problems in the prior art and provide a staged air distribution and flue gas recirculation type rotary kiln sludge incineration device and incineration method which can reduce the emission of NO x , reduce the operating cost and adjust the temperature in the rotary kiln incinerator.

[0012] To solve the above technical problems, the technical method adopted by the present application is as follows: the present application discloses a staged air distribution and flue gas recirculation type rotary kiln sludge incineration device, which comprises a rotary kiln, a waste heat boiler and a recirculation flue gas injection pipe.

[0013] The flue gas discharged from the rotary kiln enters the waste heat boiler and is cooled to form low-temperature flue gas. Part of the low-temperature flue gas is discharged from the waste heat boiler, and the other part is sent into the rotary kiln through the recirculation flue gas injection pipe.

[0014] Further, the gas outlet of the recirculation flue gas injection pipe is arranged in the stable incineration section of the rotary kiln.

[0015] Further, along the circumferential direction of the recirculation flue gas injection pipe, flue gas injection holes are uniformly and equidistantly arranged, so that the low-temperature flue gas enters the rotary kiln along the circumferential direction of the recirculation flue gas injection pipe.

[0016] Further, the rotary kiln is further provided with a primary air pipe and a secondary air pipe; compared with the air outlet of the primary air pipe, the air outlet of the secondary air pipe is deeper into the rotary kiln.

[0017] Further, the central axis of the secondary air pipe is parallel to the central axis of the rotary kiln; along the circumferential direction of the secondary air pipe, flue gas injection holes are uniformly and equidistantly arranged;

[0018] The primary air pipe outlet discharges air along the wall of the primary air pipe; the flow direction of the discharged air is perpendicular to the flow direction of the discharged air of the secondary air pipe.

[0019] Further, a part of the low-temperature flue gas discharged from the waste heat boiler is sent to the tail gas treatment device and then discharged through a chimney.

[0020] The application further discloses a rotary kiln sludge incineration method with a staged air distribution and flue gas recirculation system.

[0021] The low-temperature flue gas formed by cooling the flue gas discharged from the rotary kiln through the waste heat boiler is sent to the stable combustion section of the rotary kiln.

[0022] Further, the ratio between the amount of secondary air entering the rotary kiln and the total air amount is 0-0.4:1.

[0023] Further, the ratio between the flow of the low-temperature flue gas entering the rotary kiln and the flow of the discharged low-temperature flue gas is 0-0.5:1.

[0024] Further, when the low-temperature flue gas enters the rotary kiln, the flue gas temperature of the low-temperature flue gas is below 200 DEG C; and the injection speed of the low-temperature flue gas entering the rotary kiln is 40-50 m / s.

[0025] Advantages:

[0026] 1. The application reduces the emission of NO by recycling a part of the low-temperature flue gas after absorbing heat through the waste heat boiler into the rotary kiln. x Since the waste heat boiler is originally a device in the sludge rotary kiln incineration system, the application does not increase too many additional devices and does not use ammonia water or urea and other additives in the denitration process, thereby saving the operation cost; meanwhile, the application recycles the low-temperature flue gas into the rotary kiln, reduces the temperature level in the rotary kiln and the oxygen concentration in the combustion atmosphere, effectively reduces the emission of NO and effectively avoids over-temperature of the rotary kiln, which is beneficial to the safe operation of the rotary kiln. x

[0027] 2. The application adjusts the mixing condition of fuel and air in the rotary kiln incinerator by setting the primary air and the secondary air and implementing air staging, thereby strengthening the reducing property of the combustion atmosphere in the furnace and reducing the emission of NO. x

[0028] 3. When the recirculated flue gas is injected into the furnace, the recirculated flue gas is injected along the circumferential direction of the end of the recirculated flue gas injection pipe, which can effectively strengthen the mixing of the flue gas in the furnace and make the combustion atmosphere in the furnace more uniform.​​

[0029] The secondary air is sprayed into the furnace through the multiple secondary air spray holes on the circumference of the secondary air pipe end, and is perpendicular to the flow direction of the sludge material and the primary air, so that the mixing of the secondary air and the flue gas in the furnace is enhanced, the residence time of the flue gas in the furnace is prolonged, and the burning is facilitated; and the mixing of the fuel and the combustion atmosphere is more uniform, and the uniform combustion of the fuel is facilitated, and local over-temperature of the rotary kiln is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the overall structure schematic diagram of the sludge incineration device of the rotary kiln with staged air distribution and flue gas recirculation in the application;

[0031] Figure 2 is the structure schematic diagram of the secondary air pipe in the specific embodiment of the application;

[0032] Figure 3 is the structure schematic diagram of the recirculation flue gas spray pipe in the specific embodiment of the application.

[0033] The list of reference signs: 1-air blower, 2-primary air regulating valve, 3-secondary air regulating valve, 4-supporting wheel, 5-driving motor, 6-toothed ring, 7-waste heat boiler, 8-tail gas treatment device, 9-chimney, 10-recirculation air blower, 11-recirculation flue gas regulating valve, 12-wheel belt, 13-rotary kiln, 14-hopper, 15-screw feeder, 16-recirculation flue gas spray pipe, 17-burner, 18-primary air pipe, 19-secondary air pipe. DETAILED DESCRIPTION

[0034] The application will be further described in detail below in combination with the description of the drawings and the specific embodiments.

[0035] EMBODIMENT

[0036] As shown in the drawings, Figures 1-3 the rotary kiln incineration system equipped with the staged air distribution and flue gas recirculation system disclosed in the application sequentially comprises an air blower 1, a primary air regulating valve 2, a secondary air regulating valve 3, a supporting wheel 4, a driving motor 5, a toothed ring 6, a waste heat boiler 7, a tail gas treatment device 8, a chimney 9, a recirculation air blower 10, a recirculation flue gas regulating valve 11, a wheel belt 12, a rotary kiln 13, a hopper 14, a screw feeder 15, a recirculation flue gas spray pipe 16, a burner 17, a primary air pipe 18, and a secondary air pipe 19.

[0037] The gas outlet of the recirculation flue gas spray pipe 16 is arranged at the stable incineration section of the rotary kiln 13.

[0038] The flue gas discharged from the rotary kiln 13 enters the waste heat boiler 7 and is cooled, forming low-temperature flue gas. Part of the low-temperature flue gas is discharged from the waste heat boiler 7 and then sent to the tail gas treatment device 8 and discharged through the chimney 9. The other part is sent to the rotary kiln 13 through the recirculation flue gas nozzle 16.

[0039] As shown in Figure 3 , four flue gas injection holes are evenly and equidistantly arranged along the circumferential direction of the recirculation flue gas nozzle 16, so that the low-temperature flue gas enters the rotary kiln along the circumferential direction of the recirculation flue gas nozzle.

[0040] The rotary kiln 13 is also provided with a primary air pipe 18 and a secondary air pipe 19. The secondary air pipe 19 has a deeper outlet in the rotary kiln 13 than the primary air pipe 18. The central axis of the secondary air pipe 19 is parallel to the central axis of the rotary kiln 13. As shown in Figure 2 , four flue gas injection holes are evenly and equidistantly arranged along the circumferential direction of the secondary air pipe 19.

[0041] The outlet of the primary air pipe 18 is arranged at the end of the pipe wall of the primary air pipe 18. The flow direction of the air discharged from the primary air pipe 18 is perpendicular to the flow direction of the air discharged from the secondary air pipe 19.

[0042] The device burns municipal sludge in the rotary kiln incinerator and reduces the emission of NO x by staged air distribution and flue gas recirculation.

[0043] In the incineration system, the rotary kiln 13 is driven to rotate by the transmission motor 5 and the gear ring 6. The sludge is ignited by the burner 17 after being added to the hearth of the rotary kiln 13 by the screw feeder 15. The fuel quantity and air supply quantity are adjusted to achieve stable combustion of the sludge, and the temperature in the rotary kiln reaches 850-900 DEG C.

[0044] The secondary air fan is used to supply secondary air to the rotary kiln incinerator to meet the needs of complete combustion of the fuel and enhance the reducing property of the combustion atmosphere in the furnace to reduce the generation of NO x .

[0045] The flue gas recirculation fan is turned on, and the flow of the recirculated flue gas is adjusted by the recirculated flue gas regulating valve to reach 0-50% of the total flue gas quantity, so as to reduce the temperature level and oxygen concentration in the hearth of the rotary kiln and thus reduce the emission of NO x .

[0046] The application also discloses a rotary kiln sludge incineration method with staged air distribution and flue gas recirculation.

[0047] Step 1: Start the transmission motor 5 to drive the rotary kiln 13 to rotate around the shaft.

[0048] Step 2: Start the screw feeder 15 to send the sludge into the rotary kiln 13.

[0049] Step 3, start the burner 17;

[0050] Step 4, start the air blower 1 to send in primary air and secondary air;

[0051] Step 5, judge the combustion condition in the furnace by detecting the furnace temperature and oxygen content in the tail flue gas, and adjust the feeding amount and air supply amount to make the sludge burn stably;

[0052] Step 6, adjust the recirculation air blower 10 and the recirculation flue gas adjusting valve 11 to make the recirculation flue gas amount reach 0-50% of the total flue gas amount;

[0053] Step 7, adjust the operation parameters of the rotary kiln 13 incinerator according to the furnace temperature and oxygen content in the tail flue gas to make the sludge burn efficiently and stably, and realize denitration.

[0054] Working principle of the embodiment:

[0055] The rotary kiln incinerator is arranged at a certain slope, the screw feeder and the burner are arranged at the upper end of the rotary kiln, the screw feeder is started to send the sludge into the rotary kiln, due to the slope and uniform rotation of the rotary kiln itself, the sludge will gradually move to the lower end of the rotary kiln after entering the rotary kiln. The burner is started to make the sludge ignite, through the rotation of the rotary kiln itself, the sludge and the combustion atmosphere will be mixed and burned, so that the temperature in the furnace gradually rises, and reaches the rated working condition of 850-900℃.

[0056] The nitrogen content in the sludge is high, mainly in the form of organic matter, under high temperature environment, part of the nitrogen in the sludge will be converted into HCN and NH3 with the volatilization of volatile matter, among which HCN tends to generate N2O, and NH3 tends to generate NO.

[0057] The main reactions of HCN are shown in formula (1)-(3):

[0058] HCN + O → NCO + H (1)

[0059] NCO + O → NO + CO (2)

[0060] NCO+ NO → N2O + CO (3)

[0061] When the reaction temperature rises, the reactions (1) and (2) of HCN oxidation to generate NO will be promoted, and the generation amount of NO increases.

[0062] At different temperatures, NH3 in the furnace will simultaneously undergo reduction reaction and oxidation reaction, as shown in formula (4)-(5):

[0063] 4NH3+ 4NO + O2 → 4N2 + 6H2O (4)

[0064] 4NH3+ 5O2 → 4NO + 6H2O (5)

[0065] When the temperature rises, the oxidation reaction 2 of NH3 will be promoted, resulting in the increase of NO concentration.

[0066] The staged air distribution changes the combustion atmosphere in the furnace, thereby affecting the emission process of NO x . The staged air distribution reduces the oxygen concentration in the fuel-rich zone, which not only reduces the combustion reaction rate and the release rate of nitrogen oxides, thereby inhibiting the generation reaction of NO, but also enhances the reducing atmosphere in the furnace, such as HCN, CO, etc., thereby promoting the reduction reaction of NO. x Therefore, the staged air distribution can reduce the emission of NO

[0067] And the flue gas recirculation can reduce the combustion temperature and oxygen concentration in the furnace, thereby inhibiting the oxidation reaction of HCN and NH3, enhancing the reducing atmosphere in the furnace, and thereby reducing the emission of NO x .

[0068] Specifically, the oxygen content in the outlet flue gas of the rotary kiln incinerator is controlled between 6% and 8%, so that the sludge is completely combusted.

[0069] Among them, the low-temperature flue gas entering the furnace will cause the combustion temperature to drop, and by adjusting the operating parameters, the combustion temperature of the rotary kiln incinerator is stabilized at 850-900℃, so as to take into account the needs of efficient incineration and denitrification.

[0070] Specifically, in order to enhance the mixing of the secondary air and the flue gas in the furnace, the secondary air pipe is installed parallel to the axis of the rotary kiln, and the secondary air is sprayed into the furnace along the four secondary air spray holes at the end of the secondary air pipe, as shown in the accompanying drawings. Figure 2

[0071] The present application realizes efficient incineration of sludge in the rotary kiln incinerator by adjusting the ratio of primary air and secondary air, and takes into account denitrification.

[0072] Specifically, in order to enable the low-temperature flue gas to be uniformly mixed with the combustion in the furnace, the recirculation flue gas spray pipe is installed parallel to the axis of the rotary kiln, and the flow direction of the flue gas into the furnace is not along the axis direction of the flue gas spray pipe, but along the circumferential direction of the recirculation flue gas spray pipe, and the flue gas is sprayed out of the four circular holes on the side of the end of the flue gas spray pipe, as shown in the accompanying drawings. Figure 3

[0073] ​​Because of the combustion of sludge in the furnace, the temperature of the combustion atmosphere in the furnace is already high when the recirculated flue gas is introduced into the furnace, and the viscosity of the gas is large. In order to ensure that the recirculated flue gas has sufficient momentum to fully contact and mix with the atmosphere in the furnace and the sludge, the flow speed of the recirculated flue gas is taken to be 40-50 m / s.

[0074] Specifically, the solid waste residence time is 20-40 minutes, and the flue gas residence time is not less than 10 seconds. If the residence time is too short or too long, the residence time should be adjusted by changing the inclination angle of the rotary kiln or the rotation speed of the furnace tube.

[0075] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A rotary kiln sludge incineration device with staged air distribution and flue gas recirculation, characterized in that: It includes a rotary kiln (13), a waste heat boiler (7), and a recirculating flue gas nozzle (16). The flue gas discharged from the rotary kiln (13) is cooled down after entering the waste heat boiler (7) to form low-temperature flue gas. Part of the low-temperature flue gas is discharged from the waste heat boiler (7), and the other part is sent into the rotary kiln (13) through the recirculated flue gas nozzle (16). The outlet of the recirculated flue gas nozzle (16) is located in the stable combustion section of the rotary kiln (13); Along the circumferential direction of the recirculated flue gas nozzle (16), flue gas outlet holes are provided evenly and equidistantly, so that the low-temperature flue gas enters the rotary kiln along the circumferential direction of the recirculated flue gas nozzle. The rotary kiln (13) is also provided with a primary air duct (18) and a secondary air duct (19); compared with the air outlet of the primary air duct (18), the air outlet of the secondary air duct (19) is deeper into the rotary kiln (13); The central axis of the secondary air duct (19) is parallel to the central axis of the rotary kiln (13); flue gas ejection holes are provided evenly and equidistantly along the circumferential direction of the secondary air duct (19); The air outlet of the primary air duct (18) is discharged along the end of the pipe wall of the primary air duct (18); the air flow direction of the primary air duct (18) is perpendicular to the air flow direction of the secondary air duct (19).

2. The rotary kiln sludge incineration device with staged air distribution and flue gas recirculation according to claim 1, characterized in that: A portion of the low-temperature flue gas is discharged from the waste heat boiler (7), then sent to the tail gas treatment device (8), and finally discharged through the chimney (9).

3. A rotary kiln sludge incineration method equipped with a staged air distribution and flue gas recirculation system, characterized in that: Based on the rotary kiln sludge incineration device with graded air distribution and flue gas recirculation as described in any of claims 1-2, when the rotary kiln (13) is incinerated, sludge and primary air are sent into the rotary kiln (13); secondary air is sent to the ignition section of the rotary kiln to achieve graded air distribution of primary and secondary air. The flue gas discharged from the rotary kiln (13) is cooled by the waste heat boiler (7) and the resulting low-temperature flue gas is sent to the stable combustion section of the rotary kiln (13).

4. The rotary kiln sludge incineration method equipped with a staged air distribution and flue gas recirculation system according to claim 3, characterized in that: The ratio between the secondary air volume entering the rotary kiln (13) and the total air volume is 0~0.4:

1.

5. The rotary kiln sludge incineration method equipped with a staged air distribution and flue gas recirculation system according to claim 3, characterized in that: The ratio between the flow rate of the low-temperature flue gas entering the rotary kiln (13) and the flow rate exiting is 0~0.5:

1.

6. The rotary kiln sludge incineration device and method with staged air distribution and flue gas recirculation according to claim 3, characterized in that: When the low-temperature flue gas enters the rotary kiln (13), the flue gas temperature is below 200°C; the ejection velocity of the low-temperature flue gas entering the rotary kiln (13) is 40~50m / s.

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