An online correction method for the threshold of a wind valve based on a thermal equilibrium model

Abstract

An online correction method for the damper threshold based on a heat balance model, belonging to the technical field of damper control, includes the following steps: Step 1, calculate the volatile density and the total calorific value of the volatile matter according to the volatile components; Step 2, calculate the theoretical combustion-supporting air volume required according to the complete combustion of the volatile matter, the carbon burnout, and the sulfur burnout; Step 3, calculate the total combustion-supporting air volume according to the set air excess coefficient and the theoretical combustion-supporting air volume, etc. The present invention can alleviate the influence of external interference factors of the pot furnace on the furnace calcination process and product quality, and perform online correction on the damper threshold to improve the stability of the combustion control system of the pot furnace.

Description

Technical Field

[0001] The present invention belongs to the technical field of air valve control, and particularly relates to an online correction method for the air valve threshold based on a heat balance model. Background Art

[0002] At present, the annual output of calcined coke in China exceeds ten million tons, and most of it is produced by pot-type furnaces. In recent years, due to the gradual decline in crude oil quality and the continuous improvement of refining technology, as a by-product, the grade of delayed petroleum coke has gradually declined, and the contents of volatile components, sulfur components, etc. in the petroleum coke have increased. A pot-type furnace is an indirect heating furnace that does not require external fuel and uses the combustion of volatile components in the raw materials. The increase in the content of volatile components causes an excess of heat income in the pot-type furnace, leading to many production problems including product quality. Therefore, enterprises abandon the high-temperature preheated air combustion-supporting process and adopt the normal-temperature air combustion-supporting process. The temperature is controlled by controlling the amount of normal-temperature air entering the flue, and at the same time, a pot-type furnace combustion control system is started to automatically adjust the temperature to improve the uniformity of the flue temperature distribution and the product quality uniformity.

[0003] In order to control the amount of normal-temperature combustion-supporting air, an electric valve is set, and the opening of the electric valve is adjusted by the flue temperature feedback to control the temperature. However, generally, domestic calcined coke production enterprises have large production capacities and scales, require a large amount of raw materials, and in order to control costs, there are many raw material suppliers, and the quality of raw materials from different suppliers varies; even for the same supplier, due to different crude oil qualities, the quality of raw materials is also different; and during the production process of calcined coke, factors such as changes in the batching plan and system output adjustment are external interference factors for the pot-type furnace, causing fluctuations in the volatile content and resulting in unstable flue temperature. Summary of the Invention

[0004] In view of the above-mentioned disadvantages and deficiencies of the prior art, the present invention provides an online correction method for the air valve threshold based on a heat balance model to alleviate the influence of external interference factors of the pot-type furnace on the furnace calcination process and product quality, and correct the air valve threshold online to improve the stability of the pot-type furnace combustion control system.

[0005] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0006] An online correction method for the air valve threshold based on a heat balance model, the method is to embed the pot-type furnace heat balance model in the air valve threshold correction program, input or obtain the pot-type furnace production parameters online, calculate the combustion-supporting air volume corresponding to different raw materials according to the heat balance, and further obtain the valve opening by establishing a data model of flue negative pressure - valve opening - air volume, including the following steps:

[0007] Step 1: Calculate the volatile density and the total calorific value of the volatile components according to the volatile component composition;

[0008] Step 2: Calculate the theoretical combustion-supporting air volume required based on the complete combustion of volatile matter, carbon burnout, and sulfur burnout.

[0009] Step 3: Calculate the total combustion-supporting air volume based on the set air excess coefficient and the theoretical combustion-supporting air volume.

[0010] Step 4: Calculate its density, volume flow rate, comprehensive specific heat, and total calorific value parameters based on the gas components entering the flue.

[0011] Step 5: Calculate the flue gas components, flow rate, density, specific heat, and total heat parameters after combustion based on the gas components entering the flue.

[0012] Step 6: Calculate the heat income items and heat expenditure items of the pot furnace to obtain the heat balance model and error.

[0013] Step 7: Calculate the data model of the relationship among the flue negative pressure at the air valve inlet, the air valve opening, and the total combustion-supporting air volume.

[0014] Step 8: Set the balance error to zero, perform iterative calculations to obtain the corrected air excess coefficient, and then obtain the corrected total combustion-supporting air volume.

[0015] Step 9: Based on the total combustion-supporting air volume obtained in Step 8, combine it with the inlet negative pressure - valve opening - total combustion-supporting air volume data model to obtain the valve opening.

[0016] Furthermore, the method further includes Step 10: Determine the final upper limit threshold and lower limit threshold of the air valve based on the obtained valve opening and experience.

[0017] Furthermore, the heat income items of the pot furnace in Step 6 include the combustion heat of combustible gas, the sensible heat of materials and air, the chemical heat of carbon burnout and sulfur burnout; the heat expenditure items include the heat carried away by materials, the heat absorption of moisture, the heat carried away by flue gas, the heat carried away by dust, the heat dissipation of the furnace body, and the heat carried away by circulating cooling water.

[0018] Furthermore, the data model of the relationship among the flue negative pressure at the air valve inlet, the air valve opening, and the total combustion-supporting air volume is as follows:

[0019]

[0020] Furthermore, the upper limit threshold in Step 10 refers to the maximum valve opening set when the air excess coefficient is 2.0 - 2.2. Exceeding this value, the valve continues to open wide, and the amount of air entering is constant, resulting in ineffective operation.

[0021] Furthermore, the lower limit threshold in Step 10 refers to the minimum valve opening set when the air excess coefficient is 1.3 - 1.5.

[0022] The beneficial effects of the present invention are as follows: The method of the present invention can alleviate the external interference factors of the pot furnace, including the influence of changes in raw material types, production output adjustments, formula changes, etc. on the furnace calcination process and product quality, cover as wide a range of volatile matter changes as possible, avoid temperature runaway caused by fluctuations in the volatile matter content, ensure both complete combustion of the volatile matter and the effectiveness of each action of the air valve, improve the anti-interference ability and stability of the combustion control system of the pot furnace, and enhance the adaptability of the pot furnace to the raw material volatile matter. Brief Description of the Drawings

[0023] Figure 1 It is a schematic flow diagram of the online correction method for the air valve threshold based on the heat balance model of the present invention. Detailed Embodiments

[0024] In order to better explain the present invention for easy understanding, the present invention will be described in detail below with reference to the drawings and through specific embodiments.

[0025] As Figure 1 shown, the present invention provides an online correction method for the air valve threshold based on the heat balance model, which embeds the heat balance model of the pot furnace into the air valve threshold correction program, calculates the total amount of combustion-supporting air online by inputting or obtaining online the relevant production parameters of the pot furnace, including the air excess coefficient, etc., and determines the upper limit threshold and lower limit threshold of the air valve by establishing a data model of flue gas duct negative pressure - valve opening - total amount of combustion-supporting air and combining the experience of temperature control experts.

[0026] The heat balance model is established on the basis of material balance, calculates the heat income and heat expenditure of the pot furnace for balance, and iteratively calculates the air excess coefficient and the total amount of combustion-supporting air by setting the balance error to zero.

[0027] The input parameters include the design parameters and statistical data of the pot furnace. The design parameters include the number of furnace body material tanks and the size of the material tanks; the statistical data is the carbonaceous burn-off rate.

[0028] The online obtained parameters include the detection data and laboratory data during production operation. The detection data includes the discharge amount, flue gas outlet temperature and pressure, and ambient temperature. The laboratory data includes the conventional components of the raw material mixture.

[0029] The data model refers to the data relationship among the flue gas duct negative pressure at the air valve inlet, the air valve opening, and the total amount of combustion-supporting air.

[0030] The upper limit threshold refers to the maximum opening of the valve set when the air excess coefficient is 2.0 - 2.2. When exceeding this value, the valve continues to open wider, and the amount of air entering is basically constant, resulting in ineffective operation.

[0031] The lower threshold value mentioned above refers to the minimum opening degree of the valve set when the air excess coefficient is 1.3 - 1.5, which not only ensures the complete combustion of volatile components in the flue but also ensures the one-sided control effect of reducing the flue temperature when the valve opening degree increases.

[0032] It includes the following steps:

[0033] Step 1: Calculate the volatile density and total calorific value of volatile components based on the volatile component composition.

[0034] Step 2: Calculate the theoretical combustion-supporting air volume required based on the complete combustion of volatile components, carbon burnout, and sulfur burnout.

[0035] Step 3: Calculate the total combustion-supporting air volume based on the set air excess coefficient and the theoretical combustion-supporting air volume.

[0036] Step 4: Calculate its density, volume flow rate, comprehensive specific heat, and total calorific value parameters based on the gas components entering the flue.

[0037] Step 5: Calculate the flue gas components, flow rate, density, specific heat, and total heat parameters after combustion based on the gas components entering the flue.

[0038] Step 6: Calculate the heat income items and heat expenditure items of the pot-type furnace to obtain the heat balance model and error.

[0039] Step 7: Calculate the data model of the relationship among the flue negative pressure, valve opening degree, and total combustion-supporting air volume at the air valve inlet.

[0040] Step 8: Set the balance error to zero, perform iterative calculations to obtain the corrected air excess coefficient, and then obtain the corrected total combustion-supporting air volume.

[0041] Step 9: Obtain the valve opening degree based on the total combustion-supporting air volume obtained in Step 8 and in combination with the heat balance model.

[0042] It also includes Step 10: Determine the final upper threshold value and lower threshold value of the air valve based on the obtained valve opening degree and in combination with experience.

[0043] The specific calculation formulas for the various parameters of the pot-type furnace heat balance are well-known techniques in the art. The following mainly introduces the method of obtaining the valve opening degree through heat balance calculation and data model, and the specific heat balance calculation process will not be described.

[0044] Example 1

[0045] The input data includes: the number of pot-type furnace charge pots: 120; the discharge amount per pot: 120 kg / h; the raw material components: volatile matter 11%, sulfur content 0.5%, ash content 0.25%, fixed carbon 88.75%, moisture content 8%; the carbonaceous burnout rate 3%; the volatile matter loss rate 89%, the ash content loss rate 20%, the sulfur content loss rate 22%, the moisture content loss rate 100%, the excess air coefficient 1.5, the flue gas temperature at the outlet of the pot-type furnace 1080 °C, the outlet flue gas pressure -260 Pa; the ambient temperature 35 °C. The following heat balance model is obtained:

[0046]

[0047] Through the heat balance calculation model, on the premise that the heat balance calculation error is "0", the iterative calculation obtains an excess air coefficient of 1.73, the total amount of combustion-supporting air 54744 Nm3 / h, the negative pressure at the inlet of the flue -25 Pa. According to the data model of the negative pressure at the inlet of the flue - valve opening and the total amount of combustion-supporting air (as shown in Table 1), taking the average difference, the corresponding valve opening obtained is 52%.

[0048] Table 1 Data model of negative pressure at the inlet of the flue - valve opening - total amount of combustion-supporting air

[0049]

[0050] According to the calculated excess air coefficient of 1.73, the upper and lower limit thresholds are set in combination with experience and input into the system. According to the upper limit threshold setting principle, the excess air coefficient is 2.2, the total amount of combustion-supporting air 69617 Nm3 / h, the inlet negative pressure -20 Pa. According to the data model shown in Table 1, the upper limit threshold of the air damper is obtained as 72%; according to the lower limit threshold setting principle, the excess air coefficient is 1.5, the total amount of combustion-supporting air 47466 Nm3 / h, the inlet negative pressure -30 Pa. According to the data model, the lower limit threshold of the air damper is obtained as 37%. The opening of the air valve is maintained between the upper and lower thresholds of 37% - 72%, which not only ensures the complete combustion of volatile matter in the flue but also ensures the unilateral control effect of the fire channel temperature reduction when the valve opening is increased.

[0051] Therefore, when the volatile matter content in the raw material is 11%, the corresponding air valve thresholds are 37% and 72% respectively. When the volatile matter content in the raw material changes to 12%, according to the heat balance calculation model and the data model shown in Table 1, the corresponding thresholds modified online by the combustion control system are 42% and 78% respectively. The online correction of the air valve thresholds is realized.

[0052] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any modifications, alterations, substitutions, and variations made by those of ordinary skill in the art to the above embodiments fall within the scope of the present invention.

Claims

1. An online correction method for the air valve threshold based on a thermal equilibrium model, characterized in that The method is to embed the thermal balance model of the pot furnace into the air valve threshold correction program. By inputting or obtaining the production parameters of the pot furnace online, the combustion-supporting air volume corresponding to different raw materials is calculated according to the thermal balance, and the air valve opening is further obtained by establishing a data model of flue gas negative pressure - valve opening - air volume, including the following steps: Step 1: Calculate the volatile density and total calorific value of the volatile according to the volatile components; Step 2: Calculate the theoretical combustion-supporting air volume required according to the complete combustion of the volatile, carbon burnout, and sulfur burnout; Step 3: Calculate the total combustion-supporting air volume according to the set air excess coefficient and the theoretical combustion-supporting air volume; Step 4: Calculate the density, volume flow rate, comprehensive specific heat, and total calorific value parameters of the gas entering the flue according to the gas components entering the flue; Step 5: Calculate the flue gas components, flow rate, density, specific heat, and total heat parameters after combustion according to the gas components entering the flue; Step 6: Calculate the heat income items and heat expenditure items of the pot furnace to obtain the thermal balance model and error; Step 7: Calculate the data model of the relationship among the flue gas negative pressure at the air valve inlet, the air valve opening, and the total combustion-supporting air volume; Step 8: Set the balance error to zero, and iteratively calculate to obtain the corrected air excess coefficient, and then obtain the corrected total combustion-supporting air volume; Step 9: According to the total combustion-supporting air volume obtained in Step 8, combined with the inlet negative pressure - valve opening - total combustion-supporting air volume data model, obtain the air valve opening; 2. The online correction method for the damper threshold based on the thermal balance model according to claim 1, characterized in that: The method further includes Step 10: Determine the final upper limit threshold and lower limit threshold of the air valve according to the obtained air valve opening and in combination with experience; 3. The on-line correction method for the damper threshold based on the thermal equilibrium model according to claim 1, wherein: In Step 6, the heat income items of the pot furnace include the combustion heat of combustible gas, the sensible heat of materials and air, the chemical heat of carbon burnout and sulfur burnout; the heat expenditure items include the heat taken away by materials, the heat absorption of moisture, the heat taken away by flue gas, the heat taken away by soot, the heat dissipation of the furnace body, and the heat taken away by circulating cooling water; 4. The online correction method for the damper threshold based on the thermal equilibrium model according to claim 1, wherein: The data model of the relationship among the flue gas negative pressure at the air valve inlet, the air valve opening, and the total combustion-supporting air volume is as follows:

5. A method for online correction of the damper threshold based on a thermal equilibrium model according to claim 2, characterized in that: In Step 10, the upper limit threshold refers to the maximum opening of the valve set when the air excess coefficient is 2.0 - 2.

2. Exceeding this value, the valve continues to open wide, and the air volume entering is constant, and the operation fails; 6. The online correction method for the damper threshold based on the thermal equilibrium model according to claim 2, wherein: In Step 10, the lower limit threshold refers to the minimum opening of the valve set when the air excess coefficient is 1.3 - 1.5.

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