A method for optimizing the layout of the tertiary air of a utility boiler burner

Abstract

The present invention relates to a method for optimizing the layout of the tertiary air of a utility boiler burner. By rearranging the position of the tertiary air, the optimized distribution of the tertiary air volume is achieved, a calculation method for the parameters of the tertiary air nozzle is provided, and the NO concentration at the boiler outlet is reduced, while avoiding boiler fouling and the decrease of the reheat steam temperature. Select the upper tertiary air: Removing the upper tertiary air takes a longer time than removing the lower reducing zone, which is more conducive to NOx reduction and reduces NOx generation. The number of tertiary air pipes is changed from 2 to 4: Reducing the air volume of a single tertiary air pipe, decreasing the momentum of the tertiary air nozzle after transformation and the impact on the downstream nozzle airflow, preventing the downstream tangential circle of the transformed nozzle from becoming larger, and reducing the risk of fouling. The tertiary air is moved up to the overfire air: 1. Counteracting the downward movement of the furnace flame center caused by the downward movement of the tertiary air, avoiding the decrease of the flue gas temperature at the furnace outlet and the reheat steam temperature. 2. Further reducing the excess air coefficient in the reducing zone, which is beneficial to reducing NOx. x Concentration and avoid boiler coking and the decrease of the reheat steam temperature. Select the upper tertiary air: Removing the upper tertiary air is more conducive to NOx reduction and reduces NOx generation because the reduction zone is longer when the upper tertiary air is removed compared to removing the lower one. The number of tertiary air pipes is changed from 2 to 4: Reducing the air volume of a single tertiary air pipe, decreasing the momentum of the tertiary air nozzle after transformation and the impact on the downstream nozzle airflow, preventing the downstream tangential circle of the transformed nozzle from becoming larger, and reducing the risk of coking. The tertiary air is moved up to the overfire air: 1. Counteracting the downward movement of the furnace flame center caused by the downward movement of the tertiary air, avoiding the decrease of the flue gas temperature at the furnace outlet and the reheat steam temperature. 2. Further reducing the excess air coefficient in the reducing zone, which is beneficial to reducing NOx.

Description

Technical Field

[0001] The present invention relates to the technical field of power generation equipment, and in particular to a burner tertiary air optimization arrangement method to reduce the NOx at the boiler furnace outlet. x concentration, while avoiding boiler coking and reduction of reheat steam temperature. Background Art

[0002] Boilers using a central storage pulverizing system usually have a furnace outlet NO x The concentration is high, the emission reduction pressure is high, and the tertiary air volume is large, resulting in a high excess air coefficient in the reduction zone, which is the cause of NO x One of the reasons for high concentration. Therefore, some modifications adopt the method of moving part of the tertiary air downward to the main burner area, which can reduce the NOx concentration at the furnace outlet and has a good emission reduction effect. However, due to the low temperature and high density of the tertiary air, the downward momentum of the tertiary air is large, and the impact on the primary air downstream of the adjacent corner is large, which can easily cause the primary air downstream of the adjacent corner to deflect and brush the wall, increase the primary air tangent circle, and increase the wall wind speed, thereby causing slagging in the furnace. In addition, after the tertiary air moves downward, the combustion center moves downward, causing the furnace outlet temperature to decrease, which can easily cause the reheat steam temperature to be low. Taking two 320MW units in a power plant as an example, after the tertiary air was moved downward, serious coking occurred, and the reheat steam temperature was more than 10°C lower, and the safety and economy of the unit were significantly reduced. Therefore, its improvement and innovation are imperative. Summary of the invention

[0003] In view of the above situation, in order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a method for optimizing the arrangement of tertiary air in a power station boiler burner, rearrange the tertiary air position, achieve optimal distribution of tertiary air volume, and provide a method for calculating the parameters of the tertiary air nozzle to reduce the NO at the boiler outlet. x concentration and avoid boiler coking and reduction of reheat steam temperature.

[0004] The technical solution provided by the present invention is:

[0005] A method for optimizing the arrangement of tertiary air of a power station boiler burner, including a power station boiler of a central storage type pulverizing system, wherein the burner areas are burnout air, a reduction area, and a main burner from top to bottom, and the tertiary air is in two layers and arranged at the uppermost part of the main burner. The method for optimizing the arrangement of the tertiary air is as follows: selecting the upper layer of tertiary air, dividing one group of two diagonal tertiary air ducts into four branch pipes and moving them downward to a secondary air nozzle of the main burner, and dividing another group of two diagonal tertiary air ducts into four branch pipes and moving them upward to the burnout air area, specifically comprising the following steps:

[0006] Step 1: Determine the location of the three-wind upward nozzle

[0007] The upper-shifted tertiary air nozzle is located below the lowermost overfire air nozzle and adjacent to the lowermost overfire air nozzle. The distance between the upper edge of the upper-shifted tertiary air nozzle and the lower edge of the lowermost overfire air nozzle is the same as the distance between the nozzles of the original main burner;

[0008] Step 2: Determine the parameters of the upper-shifted tertiary air nozzle

[0009] 1. Determine the common load range of the unit;

[0010] 2. Calculate the momentum MV of the overfire air nozzles at high and low loads in the common load range of the unit sofa,H 、MV sofa,L where M is the mass of the nozzle air flow per unit time, and V sofa,H is the air flow velocity of the overfire air nozzle at high load, and V sofa,L is the air flow velocity of the overfire air nozzle at low load. Here, MV is regarded as a whole. MV sofa,H is the momentum of the overfire air nozzle at high load, and MV sofa,L is the momentum of the overfire air nozzle at low load;

[0011] 3. Calculate the mass flow rate m1 and volume flow rate Q1 of the air flow of a single upper-shifted tertiary air nozzle;

[0012] The mass flow rate m and volume flow rate Q of the air flow of a single tertiary air nozzle before transformation can be obtained through experimental tests or the thermal calculation specification of the coal mill. Then, the mass m1 of a single upper-shifted tertiary air nozzle = m / 2, and the volume flow rate Q1 = Q / 2;

[0013] 4. Calculate the area A1 of the upper-shifted tertiary air nozzle based on the condition that the air flow momentum per unit time of the upper-shifted tertiary air nozzle is equal to the average value of the air flow momenta of the overfire air nozzles at high and low loads, that is, m1×Q1 / A1 = (MVsofa,H + MVsofa,L) / 2;

[0014] The overfire air volume is different at different loads of the unit. The overfire air momentum is large at high load and small at low load, while the tertiary air momentum is independent of the load and is close to a constant. Calculate the air flow momenta of the overfire air nozzles at high and low loads respectively in the common load range (Step 2 of Step 2), and make the air flow momentum of the upper-shifted tertiary air nozzle equal to the average value of the air flow momenta of the overfire air nozzles at high and low loads (Step 4 of Step 2), to avoid large differences in the air flow momenta between the upper-shifted tertiary air nozzle and the overfire air at different loads, preventing slagging in the overfire air area;

[0015] 5. Keep the width of the upper-shifted tertiary air nozzle the same as the width L1 of the overfire air nozzle, and calculate the height H1 of the upper-shifted tertiary air nozzle = A1 / L1; thus, the size of the upper-shifted tertiary air nozzle is obtained. During layout, the center of the upper-shifted tertiary air nozzle and the centers of the nozzles of the original main burner are on the same vertical line;

[0016] Step 3: Determine the position of the lower-shifted tertiary air nozzle

[0017] 1. Measure the distance in the upward height direction of the tertiary air nozzle as H, and the measuring positions are all at the center positions of each nozzle.

[0018] 2. Measure the distance in the height direction from each secondary air nozzle of the main burner to the original upper tertiary air. Select the nozzle with the smallest absolute value of the difference from H as the position of the downward-moved tertiary air. At the same time, block the internal pipeline of the original secondary air nozzle.

[0019] Step 4: Determine the parameters of the downward-moved tertiary air nozzle

[0020] 1. Calculate the momentum MV of the primary air nozzle 一次风 ;

[0021] 2. Calculate the mass m2 and volume flow rate Q2 of a single downward-moved tertiary air nozzle;

[0022] Similar to Step 2, through experimental tests or the thermal calculation manual of the coal mill, the air mass flow rate m and volume flow rate Q of a single tertiary air nozzle before transformation can be obtained. Then, the mass m2 of a single upward-moved tertiary air nozzle = m / 2, and the volume flow rate Q2 = Q / 2. In this patent, m1 = m2 and the volume flow rate Q1 = Q2;

[0023] 3. Calculate the area A2 of the downward-moved tertiary air nozzle according to the principle that the air momentum per unit time of the downward-moved tertiary air nozzle is equal to the momentum of the adjacent downstream primary air nozzle, that is, m2×Q2 / A2 = MV 一次风 ;

[0024] 4. The height of the downward-moved tertiary air nozzle is limited by space, which is the height H2 of the original secondary air nozzle. Calculate the nozzle width L2 = A2 / H2, and the center of the downward-moved tertiary air nozzle coincides with the center of the original secondary air nozzle.

[0025] The present invention rearranges the position of the tertiary air to achieve the optimal distribution of the tertiary air volume, provides a calculation method for the parameters of the tertiary air nozzle, reduces the NO x concentration at the boiler outlet and avoids boiler coking and the decrease of the reheater steam temperature. Compared with the prior art, the present invention has the following advantages:

[0026] 1. Select the upper tertiary air: Removing the upper tertiary air has a longer reduction area than removing the lower one, which is more conducive to NOx reduction and reduces NOx generation. The number of tertiary air pipes changes from 2 to 4: Reducing the air volume of a single tertiary air pipe, decreasing the momentum of the tertiary air nozzle after transformation and the impact on the downstream air flow, preventing the downstream tangential circle of the transformed nozzle from becoming larger, and reducing the coking risk. The tertiary air is moved up to the overfire air: 1 offsetting the effect of the downward movement of the tertiary air on the descent of the furnace flame center, avoiding the decrease of the furnace outlet flue gas temperature and the reheater steam temperature. 2 further reducing the excess air coefficient in the reduction area, which is beneficial to reducing NOx.

[0027] 2. The upward shifted tertiary air is located below the overfire air and adjacent to it, ensuring that the pulverized coal in the upward shifted tertiary air has sufficient oxygen and time to burn out, and preventing the carbon content in fly ash from increasing.

[0028] 3. Keep the average momentum of the upward shifted tertiary air equal to that of the overfire air nozzles at high and low loads, avoid the large difference in air flow momentum between the upward shifted tertiary air nozzles and the overfire air at different loads, prevent the air flow impact, and prevent coking in the overfire air area.

[0029] 4. The downward shift distance of the tertiary air is similar to the upward shift distance, which can keep the original designed furnace internal heat load without significant decrease or increase, maintain the stability of the flue gas temperature at the furnace outlet, and prevent the reheat steam temperature from decreasing.

[0030] 5. The momentum of the primary air at different loads is similar. By changing the area of the tertiary air nozzle, keep the momentum of the downward shifted tertiary air equal to that of the adjacent downstream primary air nozzle, avoid the large momentum of the tertiary air impacting the air flow of the primary air nozzle, prevent the primary air tangential circle downstream of the modified nozzle from becoming larger, and prevent coking in the burner area. Description of the Drawings

[0031] Figure 1 This is a schematic diagram of the modification of the embodiment of the present invention. Among them, SOFA1 / 2 / 3 are overfire air, and the rest of the nozzles are main burners. The reduction zone is between the overfire air and the main burners. The top two layers of the main burners are: the upper tertiary air and the lower tertiary air; A / B / C / D / E primary air are all primary air burner nozzles, and the rest are secondary air nozzles. Detailed Embodiment

[0032] The following further describes in detail the specific embodiments of the present invention in conjunction with the drawings and embodiments.

[0033] Embodiment:

[0034] As Figure 1 shown, the burner of a 320MW power station unit boiler is optimized and arranged for the tertiary air modification by the method of the present invention. Select the upper tertiary air, divide one group of 2 diagonal tertiary air pipes into 4 branch pipes and shift them downward to a certain secondary air nozzle of the main burner, and divide the other group of 2 diagonal tertiary air pipes into 4 branch pipes and shift them upward to the overfire air area.

[0035] Step 1. Determine the position of the upward shifted tertiary air nozzle

[0036] Determine the upward shift position of the tertiary air as below the lowest overfire air nozzle and adjacent to it. The distance between the upper edge of the upward shifted tertiary air nozzle and the lower edge of the lowest overfire air nozzle is kept consistent with the distance between the nozzles of the original burner.

[0037] Step 2. Determine the parameters of the upward shifted tertiary air nozzle

[0038] 1. Determine that the common load section of the unit is 50% - 100% ECR;

[0039] 2. Calculate the momentum MV of a single overfire air nozzle per unit time (second) under the 50% ECR condition sofa,H = 248 kgm / s, MV sofa,L = 121 kgm / s;

[0040] 3. The mass and volume flow rates of a single upward shifted tertiary air nozzle are 5.17 kg / s and 4.86 m 3 / s respectively;

[0041] 4. Calculate the area A1 of the upward shifted tertiary air nozzle based on the principle that the momentum of the upward shifted tertiary air nozzle is equal to the average momentum of the overfire air nozzles at high and low loads, that is, 5.17×4.86 / A1 = (248 + 121) / 2, and we get A1 = 0.14 m 2 ; 5. The width of the upward shifted tertiary air nozzle remains the same as the width L1 of the overfire air nozzle, L1 = 0.60 m. Calculate the height H1 = A1 / L1 = 0.23 m; thus, the dimensions of the upward shifted tertiary air nozzle are obtained. At the same time, the center of the upward shifted tertiary air nozzle and the centers of the nozzles of the original burner are on the same vertical line.

[0042] Step 3: Determine the position of the downward shifted tertiary air nozzle

[0043] Measure the upward shift distance of the tertiary air as 4.2 m. The nozzle with the smallest absolute value of the difference between the distance from the center of each secondary air nozzle to the center of the original upper tertiary air nozzle and 4.2 m is the CD2 secondary air nozzle. Block the internal pipeline of the CD2 secondary air nozzle, and the tertiary air moves down to this position.

[0044] Step 4: Determine the parameters of the downward shifted tertiary air nozzle

[0045] 1. Calculate the momentum MV of the primary air nozzle 一次风 = 107 kgm / s;

[0046] 2. The mass and volume flow rates of a single downward shifted tertiary air nozzle are 5.17 kg / s and 4.86 m 3 / s respectively;

[0047] 3. Calculate the area A2 of the downward shifted tertiary air nozzle based on the principle that the momentum of the downward shifted tertiary air nozzle is equal to the momentum of the adjacent primary air nozzle downstream, that is, 5.17×4.86 / A2 = 107, and we get A2 = 0.24 m 2 ;

[0048] 4. The height of the downward shifted tertiary air nozzle is limited by space to the original height H2 of the secondary air nozzle = 0.24 m. Calculate the nozzle width L2 = A2 / H2 = 0.98 m; the center of the downward shifted tertiary air nozzle coincides with the center of the secondary air nozzle at the original position.

[0049] Reform effect of the embodiment:

[0050] 1. The NOx concentration at the furnace outlet before retrofit was 650 mg / Nm 3 , with a relatively high concentration.

[0051] 2. Only the modification of the downward shift of the tertiary air was carried out: only the upper tertiary air was integrally shifted downward to the middle of the furnace. After the retrofit, the NOx concentration at the furnace outlet decreased from 650 mg / Nm 3 to 530 mg / Nm 3 . The NOx emission reduction effect was good, but the actual tangential circle of the primary air downstream of the downward shift nozzle of the tertiary air was 25% larger, the average value of the wall-attached wind speed was 9 m / s, and the furnace was severely coked. The reheat steam temperature decreased from the original 540°C to 530°C, and the safety and economy of the unit were significantly reduced.

[0052] 3. The retrofit of the tertiary air was carried out using this patent: after the retrofit, there was no obvious change in the actual tangential circle size near the upper and lower shift nozzles of each layer of the tertiary air, the wall-attached wind speed of the furnace was less than 5 m / s, there was no obvious coking risk, and no coking accident occurred during the one-year operation of the boiler. The NOx at the furnace outlet decreased to 510 mg / Nm 3 , and the reduction range of NOx was 140 mg / Nm 3 . The reheat steam temperature recovered to 540°C. After the retrofit, the NOx emission reduction effect was significant, and at the same time, boiler coking and the decrease of the reheat steam temperature were avoided, without affecting the safety and economy of the unit.

Claims

1. A method for optimizing the layout of the tertiary air of a power station boiler burner, including a power station boiler with a medium storage pulverizing system, where the burner area from top to bottom is the overfire air, the reduction zone, and the main burner in sequence, and the tertiary air is in two layers and arranged at the uppermost part of the main burner, and is characterized in that, The method for optimizing the layout of the tertiary air is as follows: Select the upper tertiary air. Divide 2 tertiary air pipes in a diagonal group of it into 4 branch pipes and move them down to a certain secondary air nozzle of the main burner, and divide the other 2 tertiary air pipes in a diagonal group into 4 branch pipes and move them up to the overfire air area. It specifically includes the following steps: Step 1: Determine the position of the upward-moved tertiary air nozzle The upward-moved tertiary air nozzle is located below the lowermost overfire air nozzle and adjacent to it. The distance between the upper edge of the upward-moved tertiary air nozzle and the lower edge of the lowermost overfire air nozzle is kept the same as the distance between the nozzles of the original main burner; Step 2: Determine the parameters of the upward-moved tertiary air nozzle 1. Determine the common load section of the unit; 2. Momentum MV of the burnout air nozzles at high and low loads in the common load sections of the computer group sofa,H 、MV sofa,L , where M is the mass of the nozzle air flow per unit time, and V sofa,H is the air flow velocity of the high-load burnout air nozzle, and V sofa,L is the air flow velocity of the low-load burnout air nozzle. Here, MV is regarded as a whole, and MV sofa,H is the momentum of the high-load burnout air nozzle, and MV sofa,L is the momentum of the low-load burnout air nozzle; 3. Calculate the mass flow rate m1 and volume flow rate Q1 of the air flow of a single upward-moved tertiary air nozzle; 4. Obtain the area A1 of the upward-moved tertiary air nozzle according to the condition that the air momentum per unit time of the upward-moved tertiary air nozzle is equal to the average value of the air momenta of the overfire air nozzles at high and low loads, that is, m1×Q1 / A1 = (MVsofa,H + MVsofa,L) / 2; 5. Keep the width of the upward-moved tertiary air nozzle the same as the width L1 of the overfire air nozzle, and calculate the height H1 of the upward-moved tertiary air nozzle = A1 / L1; thus, the size of the upward-moved tertiary air nozzle is obtained. During layout, the center of the upward-moved tertiary air nozzle and the centers of the nozzles of the original main burner are on the same vertical line; Step 3: Determine the position of the downward-moved tertiary air nozzle 1. Measure the distance in the upward height direction of the tertiary air nozzle as H, and the measurement positions are all the center positions of the nozzles; 2. Measure the distances from each secondary air nozzle of the main burner to the original upper tertiary air in the height direction, and select the nozzle with the smallest absolute value of the difference from H as the position of the downward-moved tertiary air. At the same time, the internal pipeline of the original secondary air nozzle is blocked; Step 4: Determine the parameters of the downward-moved tertiary air nozzle 1. Calculate the primary air nozzle momentum MV 一次风 ; 2. Calculate the mass m2 and volume flow rate Q2 of a single downward-moved tertiary air nozzle; 3. Determine the area A2 of the downward shifted tertiary air nozzle based on the principle that the air momentum per unit time of the downward shifted tertiary air nozzle is equal to the momentum of the adjacent downstream primary air nozzle, i.e., m2×Q2 / A2 = MV 一次风 ; 4. The height of the downward-moved tertiary air nozzle is limited by space and is the height H2 of the original secondary air nozzle. Calculate the nozzle width L2 = A2 / H2, and the center of the downward-moved tertiary air nozzle coincides with the center of the secondary air nozzle at the original position.

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