A method for selecting the height of a tertiary air duct arrangement

Abstract

The application discloses a method for selecting the height of a tertiary air duct, and relates to the technical field of air duct height selection. base The method comprises the following steps: step one, obtaining required basic parameters; step two, determining whether the tertiary air duct needs to be arranged according to the reference hearth average temperature parameter (T base ); and step three, calculating the arrangement height (△H) of the tertiary air. The method is based on the hearth structure, temperature field and other working condition parameters of different furnace types, optimizes the arrangement height of the tertiary air, ensures that the normal-temperature tertiary air can form sufficient turbulent mixing with high-temperature flue gas in the hearth after being sprayed into the hearth, promotes complete burnout of unburned components of garbage, avoids disturbance to the stability of the main combustion zone, the reduction zone and the inlet of the first flue, and achieves the dual targets of low-pollutant emission and combustion efficiency.

Description

Technical Field

[0001] This application relates to the technical field of duct layout height selection, and in particular to a method for selecting the layout height of tertiary air ducts. Background Technology

[0002] Currently, medium and large-sized municipal solid waste mechanical grate incinerators (single furnace capacity ≥ 500 t / d) in developed areas of southern my country generally face two major technical challenges during operation: First, the furnace temperature is too high. With the improvement of people's living standards, the lower heating value of municipal solid waste has significantly increased compared to the project design, directly leading to a higher overall temperature in the flue area of ​​the incinerator, deviating from the thermal load value of the waste heat boiler, and causing adverse phenomena such as overheating and coking during operation. Second, the uniformity of the flow field and temperature field inside the furnace is insufficient. Due to the large furnace space scale of these medium and large-sized grate incinerators, the airflow movement and heat transfer process inside the furnace are complex, resulting in uneven distribution of temperature and concentration fields, which in turn increases the difficulty of pollutant emission control.

[0003] These two major technical challenges result in existing incinerators having a concentrated high-temperature zone within the furnace, which overlaps with the oxygen-rich zone, leading to a concentrated combustion area, uneven airflow mixing in the upper part of the furnace, and the coexistence of localized oxygen deficiency and overheating. Furthermore, both thermal and fuel-based NOx are easily generated. Therefore, when applying staged air combustion technology, it is necessary to consider the rational arrangement of the tertiary air to ensure its penetration and mixing capacity while improving furnace temperature stability. Thus, as a key supplementary means in the application of staged air combustion, the parameter design of the tertiary air directly affects the combustion stability within the furnace, pollutant emission levels, and operating energy consumption.

[0004] In existing technical solutions, tertiary air is often preheated before being blown into the furnace, or high-temperature flue gas from recirculation is extracted and used as tertiary air. This requires additional energy consumption and equipment to achieve high-temperature tertiary air. While using ambient temperature air for tertiary air can reduce operating and investment costs, the selection of the tertiary air arrangement height often relies on engineering experience, resulting in poor adaptability of this technology under different waste calorific values ​​and furnace types. It is also prone to problems such as insufficient tertiary air mixing capacity or affecting furnace temperature stability. Summary of the Invention

[0005] The purpose of this application is to provide a method for selecting the height of the tertiary air duct, in order to solve the problem that the selection of the height of the tertiary air duct often relies on engineering experience, which leads to poor adaptability of the technology under different waste calorific values ​​and different furnace types, and is prone to problems such as insufficient tertiary air mixing capacity or affecting furnace temperature stability.

[0006] The method for selecting the height of a tertiary air duct arrangement provided in this application adopts the following technical solution: A method for selecting the height of a tertiary air duct layout includes the following steps: Step 1: Obtain the required basic parameters: (1) Incinerator design parameters: design capacity, secondary air system layout; (2) Actual operating parameters of the incinerator during long-term stable operation: DCS furnace average temperature (T) actual ), actual processing volume; Step 2: Based on the baseline furnace average temperature parameter (T) base Determine whether tertiary air ducts are needed: The reference furnace average temperature parameter reflects a clear signal that the local waste calorific value deviates significantly from and is higher than the original design value, and serves as an approximate temperature criterion for whether to install tertiary air. In actual long-term operation, the average temperature T of the DCS furnace is... actual Greater than the reference furnace average temperature T base The incinerator is equipped with tertiary air ducts; the average temperature T of the DCS furnace is... actual Less than the reference furnace average temperature T base The incinerator does not require the installation of tertiary air ducts; Step 3: Calculate the arrangement height (△H) of the tertiary wind: The arrangement height of the tertiary air is based on the arrangement position of the secondary air duct of the incinerator. The height difference between the tertiary air duct and the secondary air duct is mainly related to the average temperature of the DCS furnace during actual operation.

[0007] Furthermore, in step three, the specific formula for calculating the tertiary wind arrangement height is as follows: ; The following are the detailed definitions and values ​​of each parameter: △H: The height difference between the locations of the secondary air duct and the tertiary air duct; H max : The maximum allowable value of △H; T base Reference temperature parameter; A: Height ratio correction value; k: Temperature change rate coefficient (°C) -1 ; T actual : The average furnace temperature obtained from actual measurement in °C.

[0008] Furthermore, in the specific formula for calculating the height of the tertiary wind arrangement, ΔH takes a value from 2.5m to 4.5m; and H max The value is then 4.5m.

[0009] Furthermore, Tbase The value is set to 1050℃; the T base The choice of 1050℃ is based on the average furnace temperature data obtained from dozens of municipal solid waste incinerators.

[0010] Furthermore, based on simulation comparison, A is set to 2m.

[0011] Furthermore, the optimal value of k is 0.02℃. -1 .

[0012] Furthermore, take T actual The values ​​need to be measured over a long period of time and averaged.

[0013] Compared with the prior art, the beneficial effects of this application are as follows: The selection method in this application is based on the furnace structure and internal temperature field of different furnace types. It optimizes the arrangement height of the tertiary air to ensure that after the ambient temperature tertiary air is injected into the furnace, it can form a sufficient turbulent mixture with the high temperature flue gas in the furnace and promote the complete combustion of unburned components of the waste. At the same time, it can avoid disturbing the stability of the main combustion zone, reduction zone, and flue gas inlet in the combustion zone, thus taking into account both the goals of low pollutant emissions and combustion efficiency.

[0014] Meanwhile, the core advantage of this application lies in: ① Strong design system: Establish a set of parameter design methods to replace experience-based debugging; ② Wide adaptability: It can cover the working conditions of mechanical grate furnaces with relatively high calorific value under different furnace types; ③ Excellent staged combustion effect: Through reasonable design, the tertiary air can fully mix with the high-temperature flue gas in the furnace and promote complete combustion, while avoiding disturbance to the combustion stability of the main combustion zone. It takes into account both low nitrogen emissions and combustion efficiency, and at the same time meets the furnace temperature control of 3T above 850℃. Detailed Implementation

[0015] The following provides a further detailed description of this application.

[0016] This application discloses a method for selecting the height of the tertiary air duct arrangement. This method involves a scheme for ambient temperature tertiary air in waste incineration (single furnace capacity ≥ 500 t / d), applicable to mechanical grate furnaces burning high-calorific-value waste. Under the premise of applying deep air staged combustion, this scheme proposes a method for selecting the height of the tertiary air duct arrangement. Its core lies in: optimizing the tertiary air arrangement height based on the furnace structure, furnace temperature field, and other operating parameters of different furnace types. This ensures that after the ambient temperature tertiary air is injected into the furnace, it can form sufficient turbulent mixing with the high-temperature flue gas inside the furnace, promoting complete combustion of unburned components of the waste, while avoiding disturbance to the stability of the main combustion zone, reduction zone, and primary flue inlet, thus achieving the dual goals of low pollutant emissions and combustion efficiency.

[0017] Specifically, in this embodiment, the selection method includes the following steps: Step 1: Obtain the required basic parameters: (1) Incinerator design parameters: design capacity, secondary air system layout; (2) Actual operating parameters of the incinerator during long-term stable operation: DCS furnace average temperature (Tactual), actual throughput; More specifically, the incinerator's designed throughput is obtained from the corresponding project's design documents (such as boiler operation procedures); the secondary air system's layout is obtained from the corresponding project's boiler plant design drawings; and the actual throughput is obtained from the corresponding project's production operation data (such as daily production report statistics).

[0018] The above parameters serve as the basic input for calculating the selection method of the layout height of the tertiary air duct.

[0019] Step 2: Based on the baseline furnace average temperature parameter (T) base Determine whether tertiary air ducts are needed: In this step, the baseline furnace average temperature parameter reflects a clear signal that the local waste calorific value deviates significantly from and is higher than the original design value, and serves as an approximate temperature criterion for whether to install tertiary air. Furthermore, in actual long-term operation, at the average temperature T in the DCS furnace... actual Greater than the reference furnace average temperature T base The incinerator is equipped with tertiary air ducts; at the DCS furnace average temperature T actual Less than the average furnace temperature T base The incinerator does not require the installation of tertiary air ducts.

[0020] Step 3: Calculate the arrangement height (△H) of the tertiary wind: The height of the tertiary air supply directly affects the airflow organization and distribution within the furnace, thus influencing combustion stability such as furnace temperature. Furthermore, the height of the tertiary air supply depends on the average furnace temperature. If aged waste or sludge is co-fired for a long period, the overall calorific value is low, and tertiary air supply may not be necessary. However, for high-calorific-value waste, the overall furnace temperature is higher, requiring the tertiary air supply to be positioned and appropriately raised, away from the high-temperature combustion zone.

[0021] Specifically, the height of the tertiary air arrangement is based on the arrangement position of the secondary air duct of the incinerator. The height difference between the two positions is closely related to the average temperature of the DCS furnace during actual operation. The design principle is to ensure that after the ambient temperature tertiary air is injected into the furnace, it can achieve full mixing with the flue gas in the furnace, precise oxygen replenishment, and complete combustion of unburned components of the waste, while avoiding disturbance to the stability of key temperature points in the furnace.

[0022] Specifically, in step three, the formula for calculating the height of the tertiary wind arrangement is as follows: ; The following are the detailed definitions and values ​​of each parameter: △H: The height difference between the secondary air duct and the tertiary air duct. The value of △H is between 2.5m and 4.5m. H max : The maximum allowable value of △H, and H max The value is 4.5m; T base Reference temperature parameter, T base The value is set to 1050℃; A: Height ratio correction value, based on simulation comparison, A is set to 2m; k: Temperature change rate coefficient (°C) -1 And the optimal value of k is 0.02℃. -1 ; T actual The actual measured average furnace temperature (°C) is used in this formula, where T is taken as... actual The values ​​need to be measured over a long period of time and averaged.

[0023] More specifically, for the height ratio correction value A and the temperature change rate coefficient k.

[0024] The value of k is a constant obtained by fitting the data after simulation.

[0025] A represents the range of △H, with a value of 2 = 4.5m - 2.5m.

[0026] Meanwhile, in the specific formula for calculating the height of the tertiary wind arrangement, the reference temperature parameter T... base Why choose 1050℃? Specifically, T baseThe choice of 1050℃ is based on the average furnace temperature data obtained from dozens of municipal solid waste incinerators (≥500 tons / day). Example 1:

[0027] The following example uses a 500-ton / day furnace as an example, where the actual average furnace temperature T is... actual When fixed, T base The effect of deviating from 1050℃.

[0028] Additionally, the installation height is specified as follows: Given a 500-ton / day municipal solid waste incinerator, the design height for the tertiary air duct is to be above the existing secondary air duct. Based on the parameters in the above formula: H... max =4.5m, A=2m, T base =1050℃, k=0.02℃ -1 When T actual The values ​​are as follows, and the corresponding design heights of the tertiary air ducts are shown in the table below: Example 2:

[0029] (1) Why is the allowable height difference 2.5 to 4.5 m? According to the simulation, the tertiary air duct is arranged 2.5m to 4.5m above the secondary air duct.

[0030] When ΔH is less than 2.5m, due to the small height difference between the air ducts, the tertiary air mixes rapidly with the secondary air after entering the furnace. This results in premature entry, which damages the staged combustion structure, interferes with the mixing function of the secondary air, and provides oxidant too early, failing to inhibit the formation of fuel-type NOx.

[0031] When ΔH is greater than 4.5m, the position of the tertiary air duct will be too high. At this time, the space in the combustion zone may be insufficient, the mixing effect of the tertiary air on the upper part of the furnace will be weakened, resulting in incomplete CO combustion; and it is impossible to guarantee that all flue gas stays at ≥850℃ for more than 2 seconds, thereby destroying the original flue conditions for inhibiting dioxin resynthesis.

[0032] The table below uses the parameters of a 500-ton / day mechanical grate furnace as an example: Of the four cases in the table above, cases 1 and 4 are beyond the scope of this application. Cases 2 and 3 satisfy the requirements for flue gas residence time, ensure uniform oxygen mixing, and reduce local overheating.

[0033] Therefore, the selection method of this application is based on the furnace structure, furnace temperature field and other operating parameters of different furnace types, and optimizes the arrangement height of the tertiary air to ensure that after the ambient temperature tertiary air is injected into the furnace, it can form a full turbulent mixing with the high temperature flue gas in the furnace and promote the complete combustion of unburned components of the waste, while avoiding disturbance to the stability of the main combustion zone, reduction zone and flue gas inlet of the combustion zone, thus taking into account the dual goals of low pollutant emissions and combustion efficiency.

[0034] Meanwhile, the core advantage of this application lies in: ① Strong design system: Establish a set of parameter design methods to replace experience-based debugging; ② Wide adaptability: It can cover the working conditions of mechanical grate furnaces with relatively high calorific value under different furnace types; ③ Excellent staged combustion effect: Through reasonable design, the tertiary air can not only form a full turbulent mixture with the high-temperature flue gas in the furnace and promote complete combustion, but also avoid disturbing the combustion stability of the main combustion zone in the combustion zone. It takes into account both low nitrogen emissions and combustion efficiency, and at the same time meets the requirements of the 3T principle of combustion control (i.e., temperature, time, turbulence) to control the furnace temperature above 850℃.

[0035] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for selecting the height of a tertiary air duct arrangement, characterized in that: Includes the following steps: Step 1: Obtain the required basic parameters: (1) Incinerator design parameters: design throughput, secondary air system layout; (2) Actual operating parameters of the incinerator during long-term stable operation: DCS furnace average temperature (Tactual), actual throughput; Step 2: Based on the baseline furnace average temperature parameter (T) base Determine whether tertiary air ducts are needed: The reference furnace average temperature parameter reflects a clear signal that the local waste calorific value deviates significantly from and is higher than the original design value, and serves as an approximate temperature criterion for whether to install tertiary air. In actual long-term operation, the average temperature T of the DCS furnace is... actual Greater than the reference furnace average temperature T base The incinerator is equipped with tertiary air ducts; the average temperature T of the DCS furnace is... actual Less than the reference furnace average temperature T base The incinerator does not require the installation of tertiary air ducts; Step 3: Calculate the arrangement height (△H) of the tertiary wind: The arrangement height of the tertiary air is based on the arrangement position of the secondary air duct of the incinerator. The height difference between the tertiary air duct and the secondary air duct is mainly related to the average temperature of the DCS furnace during actual operation.

2. The method for selecting the arrangement height of a tertiary air duct according to claim 1, characterized in that: In step three, the specific formula for calculating the tertiary wind arrangement height is as follows: ； The following are the detailed definitions and values ​​of each parameter: △H: The height difference between the locations of the secondary air duct and the tertiary air duct; H max : The maximum allowable value of △H; T base Reference temperature parameter; A: Height ratio correction value; k: Temperature change rate coefficient (°C) -1 ; T actual : The average furnace temperature obtained from actual measurement in °C.

3. The method for selecting the arrangement height of a tertiary air duct according to claim 2, characterized in that: In the specific formula for calculating the height of the tertiary wind arrangement, ΔH takes a value from 2.5m to 4.5m; and H max The value is then 4.5m.

4. The method for selecting the arrangement height of a tertiary air duct according to claim 2, characterized in that: T base The value is set to 1050℃; the T base The choice of 1050℃ is based on the average furnace temperature data obtained from dozens of municipal solid waste incinerators.

5. The method for selecting the arrangement height of a tertiary air duct according to claim 2, characterized in that: Based on simulation comparison, the value of A is 2m.

6. The method for selecting the arrangement height of a tertiary air duct according to claim 2, characterized in that: The optimal value of k is 0.02℃ -1 .

7. The method for selecting the arrangement height of a tertiary air duct according to claim 2, characterized in that: Take T actual The value needs to be measured over a long period of time and the average value is taken.

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