A frequency conversion control method for circulating fan in sintering waste heat recovery system

Abstract

The present invention discloses a frequency conversion control method for a circulating fan of a sintering waste heat recovery system, which specifically includes the following steps: step 1, calculating the cooling temperatures T1 and T2 of the sintered ore at the ends of the first and second stages of the ring cooler under the design working conditions; step 2, obtaining the actual temperatures T'0, T'1, and T'2 of the sintered ore at the upper part of the ring cooler under the operating conditions; step 3, judging whether |T2'-T2|≥10°C or |T1'-T1|≥10°C is established, and if so, proceeding to step 4, and if not, proceeding to step 6; step 4, calculating The optimal cooling air volume Q'1 and Q'2 required for the first and second stages of the ring cooler; Step 5, calculate the optimal operating speed N' of the circulating fan based on the optimal cooling air volume Q'1 and Q'2 obtained in Step 4; Step 6, adjust the operating frequency of the circulating fan to N' in Step 5; adjust the damper opening of the first and second stage cooling air ducts of the ring cooler, and control the opening ratio to first stage opening / second stage opening = Q'1 / Q'2; Step 7, wait for 10 minutes after the adjustment is completed, and return to Step 2 to perform the circulation judgment after the working conditions stabilize.

Description

Technical Field

[0001] The invention belongs to the technical field of waste heat recovery and relates to a frequency conversion control method for a circulating fan in a sintering waste heat recovery system. Background Art

[0002] The sintering waste heat recovery system recovers waste heat from the sintering ring cooler flue gas to drive a steam turbine. The specific process involves piping high-temperature flue gas from the first and second stage chimneys of the ring cooler into a waste heat boiler. After heat exchange in the boiler, the flue gas is cooled to approximately 120-140°C. The flue gas is then pressurized by a circulating fan and discharged through the chimney or returned to the ring cooler inlet for cooling the sintered ore.

[0003] During actual operation, many factors affect the air volume of the circulating fan, such as fluctuations in the sintering production load and changes in ambient temperature caused by seasonal changes. To facilitate the adjustment of the circulating fan load, the circulating fans in the waste heat recovery system generally adopt a variable frequency speed regulation operation mode. During operation, if the production load fluctuates or environmental factors change, the operator needs to observe the flue gas temperature and flue gas flow rate of the annular cooler chimney and other measurement points. Based on experience, the operator needs to determine whether the speed needs to be adjusted, and then manually adjust the fan operating frequency. After the system stabilizes, the operator will observe and judge again until the operator determines that the operating parameters have reached the ideal state.

[0004] The current adjustment method has the following problems: the adjustment process requires human intervention and cannot achieve automatic control of the fan frequency; manual adjustment requires a high level of experience from the operating personnel and is prone to operational errors; due to the lack of reliable algorithm support, the actual adjustment effect of manual adjustment is often not optimal. If the fan air volume is too large or too small, it will lead to low waste heat recovery efficiency or increased system energy consumption. Summary of the Invention

[0005] The purpose of the present invention is to provide a frequency conversion control method for a circulating fan in a sintering waste heat recovery system, so as to solve the problems of low automation and poor adjustment accuracy in a manual adjustment method.

[0006] The technical solution adopted by the present invention is a frequency conversion control method for a circulating fan in a sintering waste heat recovery system, which specifically includes the following steps:

[0007] Step 1: Calculate the cooling temperatures T1 and T2 of the sintered ore at the ends of the first and second stages of the ring cooler under the design conditions;

[0008] Step 2: Obtain the actual temperatures T'0, T1', and T'2 of the sintered ore at the upper portion of the ring cooler under operating conditions;

[0009] Step 3: Determine whether |T2'-T2|≥10℃ or |T1'-T1|≥10℃ is true. If so, proceed to step 4; if not, proceed to step 6.

[0010] Step 4: Calculate the optimal cooling air volumes Q1' and Q'2 required for the first and second stages of the ring cooler;

[0011] Step 5: Calculate the optimal operating speed N' of the circulating fan based on the optimal cooling air volumes Q1' and Q'2 obtained in step 4;

[0012] Step 6: Adjust the operating frequency of the circulating fan to N' in step 5; adjust the damper opening of the first and second cooling air ducts of the ring cooler, and control the opening ratio to be first opening / second opening = Q1' / Q'2;

[0013] Step 7: After the adjustment is completed, wait for 10 minutes. After the working conditions are stable, return to step 2 for loop judgment execution.

[0014] In step 1, according to the parameters of the sintering ring cooler and the supporting blower, the cooling temperatures T1 and T2 of the sintered ore at the end of the first and second stages of the ring cooler under the design working conditions are calculated by formulas (1) and (2):

[0015]

[0016]

[0017] Where:

[0018] T0—temperature of sintered ore before cooling, unit: °C, generally 750-800 °C; T1—cooling temperature of sintered ore at the end of the first stage of the ring cooler, unit: °C; T2—cooling temperature of sintered ore at the end of the second stage of the ring cooler, unit: °C; C0—specific heat of sintered ore at the temperature corresponding to T0, unit: J / (kg·°C); C1—specific heat of sintered ore at the temperature corresponding to T1, unit: J / (kg·°C); C2—specific heat of sintered ore at the temperature corresponding to T2, unit: J / (kg·°C); Q1—designed cooling air volume of the first stage of the ring cooler, unit: Nm 3 / h; Q2—designed cooling air volume of the second stage of the ring cooler, unit: Nm 3 / h;T k0 —The cooling air temperature entering the wind box under the ring cooler, unit ℃; T k1 —Flue gas temperature discharged from the chimney of the ring cooler, unit: °C; T k2 —Flue gas temperature discharged from the second stage chimney of the ring cooler, unit: °C; k1 —Flue gas temperature of the first stage of the ring cooler T k1 The corresponding specific heat capacity of air, unit is J / (m3·℃); C k2 —Flue gas temperature of the first stage of the ring cooler T k2The corresponding specific heat capacity of air, unit is J / (m3·℃); k is the heat exchange coefficient between the cooling air and the sintered ore in the ring cooler, which is taken as 0.95; M is the designed cooling capacity of the ring cooler, unit is t / h.

[0019] The average specific heat capacity C0, C1, and C2 of sintered ore are calculated according to C=a+bT, where a and b are coefficients related to the composition of the sintered ore; T is the temperature of the sintered ore, in °C; and C is the calculated specific heat capacity of the sintered ore, in J / (kg·°C).

[0020] The cooling air temperature T entering the lower wind box of the ring cooler k0 The average outdoor air temperature is 20℃; the flue gas temperature T k1 The flue gas temperature T k2 It is 280~330℃.

[0021] In step 4, the optimal cooling air volumes Q1' and Q'2 required for the first and second stages of the annular cooler are calculated according to the following formulas (3) and (4):

[0022]

[0023]

[0024] in:

[0025] Q′1—Optimal cooling air volume of the first stage of the ring cooler calculated based on the measured sinter temperature, unit Nm 3 / h; Q′2—optimal cooling air volume of the second stage of the ring cooler calculated based on the measured sinter temperature, unit Nm 3 / h; T′0—the measured temperature of the sinter before cooling, unit: °C; T1'—the measured temperature of the sinter at the end of the first stage of the ring cooler, unit: °C; T′2—the measured temperature of the sinter at the end of the second stage of the ring cooler, unit: °C; C'0—the specific heat of the sinter at the temperature corresponding to T′0, unit: J / (kg·°C); C1'—the specific heat of the sinter at the temperature corresponding to T1', unit: J / (kg·°C); C'2—the specific heat of the sinter at the temperature corresponding to T′2, unit: J / (kg·°C); M'—the output of sinter entering the ring cooler under actual operating conditions, unit: t / h.

[0026] The cooling air temperature T entering the lower air box of the ring cooler in step 4 k0 The flue gas temperature discharged from the waste heat boiler of the ring cooler is 120~140℃.

[0027] In step 5, the optimal operating speed of the circulation fan is calculated by formula (5),

[0028]

[0029] Where: N' is the optimal operating speed of the fan; N is the design speed of the fan; Q b is the designed air volume of the fan; λ is the air leakage rate of the ring cooler, which is 5% to 15%.

[0030] The beneficial effects of the present invention are:

[0031] Automatic frequency conversion control of the circulating fan improves the system's automation level. It enables precise control of the fan frequency to optimize system energy consumption. The optimal operating frequency can be directly determined through a calculation model and adjusted immediately, improving regulation efficiency and response speed. This prevents misoperation caused by human error or lack of experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a flow chart of the frequency conversion control method of the circulating fan of the sintering waste heat recovery system of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] like Figure 1 A method for frequency conversion control of a circulating fan in a sintering waste heat recovery system is shown, which is characterized by comprising the following steps:

[0035] Step 1: Calculate the cooling temperatures T1 and T2 of the sintered ore at the ends of the first and second stages of the ring cooler under the design conditions;

[0036] Step 2: Obtain the actual temperatures T'0, T1', and T'2 of the sintered ore at the upper portion of the ring cooler under operating conditions;

[0037] Step 3: Determine whether |T2'-T2|≥10℃ or |T1'-T1|≥10℃ is true. If so, proceed to step 4; if not, proceed to step 6.

[0038] Step 4: Calculate the optimal cooling air volumes Q'1 and Q'2 required for the first and second stages of the ring cooler;

[0039] Step 5: Calculate the optimal operating speed N' of the circulating fan based on the optimal cooling air volumes Q'1 and Q'2 obtained in step 4;

[0040] Step 6: Adjust the operating frequency of the circulating fan to N' in step 5; adjust the damper opening of the first and second cooling air ducts of the ring cooler, and control the opening ratio to the first opening / second opening = Q'1 / Q'2;

[0041] Step 7: After the adjustment is completed, wait for 10 minutes. After the working conditions are stable, return to step 2 for loop judgment execution.

[0042] In step 1, according to the parameters of the sintering ring cooler and the supporting blower, the cooling temperatures T1 and T2 of the sintered ore at the end of the first and second stages of the ring cooler under the design working conditions are calculated by formulas (1) and (2):

[0043]

[0044]

[0045] Where:

[0046] T0—temperature of sintered ore before cooling, unit: °C, generally 750-800 °C; T1—cooling temperature of sintered ore at the end of the first stage of the ring cooler, unit: °C; T2—cooling temperature of sintered ore at the end of the second stage of the ring cooler, unit: °C; C0—specific heat of sintered ore at the temperature corresponding to T0, unit: J / (kg·°C); C1—specific heat of sintered ore at the temperature corresponding to T1, unit: J / (kg·°C); C2—specific heat of sintered ore at the temperature corresponding to T2, unit: J / (kg·°C); Q1—designed cooling air volume of the first stage of the ring cooler, unit: Nm 3 / h; Q2—designed cooling air volume of the second stage of the ring cooler, unit: Nm 3 / h;T k0 —The cooling air temperature entering the wind box under the ring cooler, unit ℃; T k1 —Flue gas temperature discharged from the chimney of the ring cooler, unit: °C; T k2 —Flue gas temperature discharged from the second stage chimney of the ring cooler, unit: °C; k1 —Flue gas temperature of the first stage of the ring cooler T k1 The corresponding specific heat capacity of air, unit is J / (m3·℃); C k2 —Flue gas temperature of the first stage of the ring cooler T k2 The corresponding specific heat capacity of air, unit is J / (m3·℃); k is the heat exchange coefficient between the cooling air and the sintered ore in the ring cooler, which is taken as 0.95; M is the designed cooling capacity of the ring cooler, unit is t / h.

[0047] The average specific heat capacity C0, C1, and C2 of sintered ore are calculated according to C=a+bT, where a and b are coefficients related to the composition of the sintered ore; T is the temperature of the sintered ore, in °C; and C is the calculated specific heat capacity of the sintered ore, in J / (kg·°C).

[0048] The cooling air temperature T entering the lower wind box of the ring cooler k0 The average outdoor air temperature is 20℃; the flue gas temperature T k1 The flue gas temperature T k2 It is 280~330℃.

[0049] In step 4, the optimal cooling air volumes Q1' and Q'2 required for the first and second stages of the annular cooler are calculated according to the following formulas (3) and (4):

[0050]

[0051]

[0052] in:

[0053] Q′1—Optimal cooling air volume of the first stage of the ring cooler calculated based on the measured sinter temperature, unit Nm 3 / h; Q'2—optimal cooling air volume of the second stage of the ring cooler calculated based on the measured sinter temperature, unit Nm 3 / h; T′0—the measured temperature of the sinter before cooling, unit: °C; T1'—the measured temperature of the sinter at the end of the first stage of the ring cooler, unit: °C; T′2—the measured temperature of the sinter at the end of the second stage of the ring cooler, unit: °C; C'0—the specific heat of the sinter at the temperature corresponding to T′0, unit: J / (kg·°C); C'1—the specific heat of the sinter at the temperature corresponding to T1', unit: J / (kg·°C); C'2—the specific heat of the sinter at the temperature corresponding to T′2, unit: J / (kg·°C); M'—the output of sinter entering the ring cooler under actual operating conditions, unit: t / h.

[0054] The cooling air temperature T entering the lower air box of the ring cooler in step 4 k0 The flue gas temperature discharged from the waste heat boiler of the ring cooler is 120~140℃.

[0055] In step 5, the optimal operating speed of the circulation fan is calculated by formula (5),

[0056]

[0057] Where: N' is the optimal operating speed of the fan; N is the design speed of the fan; Q b is the designed air volume of the fan; λ is the air leakage rate of the ring cooler, which is 5% to 15%.

[0058] The cooling temperatures T1 and T2 of the sintered ore at the ends of the first and second stages in step 1 may be given values ​​directly based on experience without calculation, without affecting the calculation and execution of subsequent steps.

[0059] The above algorithm was used to simulate the relevant data of a waste heat recovery project of an annular cooler. The specific results are as follows:

[0060] The original design parameters of a ring cooler are: the temperature of the ore before cooling T0 = 750 ° C, the cooling air volume Q1 = 202500 Nm 3 / h, second stage cooling air volume Q2 = 202500Nm 3 / h, ambient temperature T k0 =20℃, the flue gas temperature T k1 =410℃, second stage flue gas temperature T k2 =330℃, the cooling capacity of the ring cooler is M=364t / h. The specific heat capacity of air is obtained by consulting the physical property table according to the corresponding temperature, where C0=1067J / (kg·℃), C1=996J / (kg·℃), and C2=882J / (kg·℃). The specific heat capacity of sintered ore is calculated according to C=a+bT, where a=646.85, b=0.559. It can be calculated that C0=1066J / (kg·℃), C1=966J / (kg·℃), and C2=882J / (kg·℃). Substituting the above data into formulas (1) and (2), we can obtain:

[0061]

[0062]

[0063] The above T1 and T2 values ​​are the cooling temperatures of the sintered ore at the end of the first and second stages under the design conditions of the ring cooler.

[0064] Comparative working condition 1: Adjustment using the method described in the present invention

[0065] Assume that the output of sintered ore changes during actual operation. The measured output is M' = 338t / h. The temperature of the ore before cooling is consistent with the design value T0' = 750℃, corresponding to C0' = 1066J / (kg·℃). However, the measured temperature of the sintered ore deviates greatly from the design temperature. Both |T2'-T2| and |T1'-T1| are greater than 10℃. According to the control process, the air volume needs to be corrected. At this time, the cooling air temperature of the ring cooler (exhaust gas temperature of the waste heat boiler) T k0 =120℃, the flue gas temperature T k1 =410℃, second stage flue gas temperature T k2 =330℃ Calculate the optimal air volume using formulas (3) and (4):

[0066]

[0067]

[0068] Given that the design speed of the circulating fan is N = 1500r / min, the design air volume is Q b =650000Nm 3 / h, and then the optimal operating speed of the circulation fan is obtained through formula (5).

[0069]

[0070] Adjust the fan operating speed to the above value through the automatic control system, and adjust the first and second stage damper openings proportionally. Wait for 10 minutes and repeat the test until the system runs stably.

[0071] Comparison condition 2: manual adjustment

[0072] When manual adjustment is used, it is usually impossible to predict the exact speed that needs to be adjusted, and adjustments can only be made through continuous trial and error until the system approaches the optimal working condition.

[0073] Assume that after repeated attempts, the operator finally controls T1 and T2 at 590℃ and 450℃ respectively, the first stage ore temperature deviates from the preset target by 20℃, and the second stage ore temperature deviates from the preset target by 30℃. At this time, the corresponding circulating fan speed is about 1200r / min, and the first stage flue gas volume is 253000Nm 3 / h, temperature 410℃, second stage flue gas volume 245000Nm 3 / h, temperature 330℃.

[0074] If the flue gas from the first and second stages under the above two comparison conditions is used for waste heat recovery power generation, the technical and economic benefit analysis corresponding to the two conditions is as follows:

[0075]

[0076] Compared with comparison condition 2, the power generation of comparison condition 1 increased by 1041kW, the power consumption of the circulating fan increased by 374kW, and the power generation increased by 667kW per hour.

[0077] From the above analysis, it can be seen that by adopting the method described in the present invention, the fan speed and the ore temperature can be accurately controlled, the system can be quickly adjusted to the optimal state, the system automation level can be improved, and the waste heat power generation can be increased.

Claims

1. A frequency conversion control method for a circulating fan in a sintering waste heat recovery system, characterized in that: The specific steps include: Step 1: Calculate the cooling temperatures T1 and T2 of the sintered ore at the ends of the first and second stages of the ring cooler under the design conditions; Step 2: Obtain the actual temperature of the sintered ore before cooling in the upper part of the ring cooler under the operating conditions , Actual measured temperature of sintered ore at the end of the first stage of the ring cooler , Actual temperature of sintered ore at the end of the second stage of the ring cooler ; Step 3: Determine whether |T2'-T2|≥10℃ or |T1'-T1|≥10℃ is true. If so, proceed to step 4; if not, proceed to step 6. Step 4: Calculate the optimal cooling air volume required for the first and second stages of the ring cooler and ; Step 5: Optimal cooling air volume obtained according to step 4 and , calculate the optimal operating speed of the circulation fan ; Step 6: Adjust the operating frequency of the circulating fan to the value in step 5. ; Adjust the damper opening of the first and second stage cooling air ducts of the ring cooler, and control the opening ratio to be the first stage opening / the second stage opening = ; Step 7: After the adjustment is completed, wait for 10 minutes. After the working conditions are stable, return to step 2 for loop judgment execution.

2. The method for frequency conversion control of a circulating fan in a sintering waste heat recovery system according to claim 1, characterized in that: In step 1, according to the parameters of the sintering ring cooler and the supporting blower, the cooling temperatures T1 and T2 of the sintered ore at the end of the first and second stages of the ring cooler under the design working conditions are calculated by formulas (1) and (2): （1） （2） Where: T0—temperature of sintered ore before cooling, unit ℃, generally 750~800℃; T1—cooling temperature of sintered ore at the end of the first stage of the ring cooler, unit ℃; T2—cooling temperature of sintered ore at the end of the second stage of the ring cooler, unit ℃; C0—specific heat of sintered ore at the temperature corresponding to T0, unit J / (kg·℃); C1—specific heat of sintered ore at the temperature corresponding to T1, unit J / (kg·℃); C2—specific heat of sintered ore at the temperature corresponding to T2, unit J / (kg·℃); Q1—designed cooling air volume of the first stage of the ring cooler, unit Nm 3 / h; Q2—designed cooling air volume of the second stage of the ring cooler, unit: Nm 3 / h;T k0 —The cooling air temperature entering the wind box under the ring cooler, unit ℃; T k1 —Flue gas temperature discharged from the chimney of the ring cooler, unit: °C; T k2 —Flue gas temperature discharged from the second stage chimney of the ring cooler, unit: °C; k1 —Flue gas temperature of the first stage of the ring cooler T k1 The corresponding specific heat capacity of air, unit is J / (m3·℃); C k2 —Flue gas temperature of the first stage of the ring cooler T k2 The corresponding specific heat capacity of air, unit is J / (m3·℃); k is the heat exchange coefficient between the cooling air and the sintered ore in the ring cooler, which is taken as 0.95; M is the designed cooling capacity of the ring cooler, unit is t / h.

3. The frequency conversion control method for the circulating fan of the sintering waste heat recovery system according to claim 2 is characterized in that: The specific heat of the sintered ore C0, C1, and C2 is calculated according to C=a+bT, where a and b are coefficients related to the composition of the sintered ore; T is the temperature of the sintered ore, in °C; and C is the calculated specific heat capacity of the sintered ore, in J / (kg·°C).

4. The frequency conversion control method for a circulating fan in a sintering waste heat recovery system according to claim 2 is characterized in that: The cooling air temperature T entering the lower wind box of the ring cooler k0 The average outdoor air temperature is 20℃; the flue gas temperature T k1 The flue gas temperature T k2 280~330℃.

5. The frequency conversion control method for a circulating fan in a sintering waste heat recovery system according to claim 1, characterized in that: In step 4, the optimal cooling air volume required for the first and second stages of the ring cooler and Calculate according to the following formulas (3) and (4): (3) (4) in: —The optimal cooling air volume of the first stage of the ring cooler calculated based on the measured sinter temperature, unit Nm 3 / h; —The optimal cooling air volume of the second stage of the ring cooler calculated based on the measured sinter temperature, unit Nm 3 / h; —The measured temperature of the sintered ore before cooling, in °C; —The measured temperature of the sintered ore at the end of the first stage of the ring cooler, in °C; —The measured temperature of the sintered ore at the end of the second stage of the ring cooler, in °C; -correspond Specific heat of sintered ore at temperature, unit: J / (kg·℃); -correspond Specific heat of sintered ore at temperature, unit: J / (kg·℃); -correspond Specific heat of sintered ore at temperature, unit: J / (kg·℃); M'—output of sintered ore entering the ring cooler under actual operating conditions, unit: t / h.

6. The frequency conversion control method for the circulating fan of the sintering waste heat recovery system according to claim 5 is characterized in that: The cooling air temperature T entering the lower wind box of the ring cooler in step 4 is k0 The flue gas temperature discharged from the waste heat boiler of the ring cooler is 120~140℃.

7. The method for frequency conversion control of a circulating fan in a sintering waste heat recovery system according to claim 1, characterized in that: In step 5, the optimal operating speed of the circulating fan is calculated by formula (5): （5） in: is the optimal operating speed of the fan; N is the design speed of the fan; Fan design air volume; The air leakage rate of the ring cooler is 5%~15%.

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