Method for adjusting airflow uniformity of denitration inlet flue flow field

Abstract

The invention provides a denitration inlet flue flow field airflow uniformity adjusting method, and relates to the technical field of flue gas treatment and purification, and the method comprises the following steps: 1, arranging a plurality of guide plates in a horizontal expansion section of a flue; and step 2, partitioning the ammonia spraying area, and isolating and partitioning the flue. The plurality of guide plates are arranged in the horizontal expansion section of the flue, so that the air flow form at the air spraying hole of the ammonia spraying grid is greatly optimized, the rotational flow at the air spraying hole disappears, and the air flow uniformity in an ammonia spraying area is obviously improved. The flue is separated and partitioned, so that the flow velocity uniformity of flue gas in the flue is improved, and the distribution uniformity of the flue gas flowing to different sub-regions is improved, so that the distribution uniformity of ammonia gas in each sub-region is improved, and the ammonia escape rate is reduced. And a herringbone mixer is replaced by the disc mixer, so that the mixing uniformity of the ammonia gas and the flue gas is further improved, the utilization rate of the ammonia gas is improved, and the escape rate of the ammonia is further reduced.

Description

Technical Field

[0001] The invention relates to the technical field of flue gas treatment and purification, and in particular to a method for adjusting airflow uniformity in a flue flow field at a denitration inlet. Background Art

[0002] At present, the power industry is comprehensively implementing ultra-low emission standards for coal-fired power plants, requiring NOx emission indicators to be no higher than 50mg / Nm3; the latest deep emission reduction policies in some regions require NOx emission concentrations to be no higher than 30mg / Nm3; for some advanced power generating units, even an environmental protection leading indicator requirement of no higher than 20mg / Nm3 is proposed. In my country's planning, the Ministry of Ecology and Environment also clearly regards NOx emission reduction as one of the key indicators for improving air quality. It can be foreseen that the requirements for NOx emission indicators of coal-fired power plants will become more and more stringent in the future, and the problem that follows is a substantial increase in the escape rate of denitrification ammonia. Ammonia escaped from coal-fired boilers reacts with SO3, water vapor, etc. in flue gas to generate ammonium bisulfate, and SO3 in flue gas reacts with water vapor to generate sulfuric acid. These two substances will condense and adhere to fly ash during the cooling process of the flue gas flowing through the downstream rotary air preheater, causing ash blockage in the air preheater.

[0003] According to the survey, the main reason for the blockage of air preheaters and low-temperature economizers of thermal power generating units is the adhesion of ammonium bisulfate and ash. The currently commonly used SCR denitrification device, whether using liquid ammonia or urea, will inevitably produce ammonium bisulfate. The main reason for the production of ammonium bisulfate in the SCR denitrification device is that the cross-section of the flue gas at the ammonia spraying grid at the denitrification inlet is relatively uneven when the ammonia spraying amount is relatively uneven. In some areas, due to the small amount of flue gas and the high amount of ammonia spraying, the ammonia escape increases and the air preheater is blocked. Summary of the invention

[0004] The present invention provides a method for adjusting the airflow uniformity of the flue flow field at a denitrification inlet, which is used to solve the defects in the prior art that the amount of ammonia sprayed is relatively uneven when the cross-section of the flue gas at the denitrification inlet ammonia spray grid is uneven, and the amount of ammonia sprayed is high in some areas due to the small amount of flue gas, resulting in increased ammonia escape and blockage of the air preheater.

[0005] In one aspect, the present invention provides a method for adjusting the uniformity of airflow in a flue flow field at a denitration inlet, comprising:

[0006] Step 1: Arrange a plurality of guide plates in the horizontal expansion section of the flue;

[0007] Step 2: Partition the ammonia spraying area and isolate the flue.

[0008] Preferably, step 2 further comprises replacing the herringbone mixer with a disc mixer.

[0009] Preferably, step 2 comprises:

[0010] Step 21: Divide the ammonia spraying area into a plurality of sub-areas based on the average distribution of geometric dimensions of the ammonia spraying area in the horizontal direction;

[0011] Step 22: setting a group of independently controlled ammonia spraying grids in each sub-area;

[0012] Step 23: Divide the flue from the flue at the tail end of the boiler to the outlet of the ammonia injection grid into a number of sub-flues according to the method of evenly dividing the geometric dimensions in the horizontal direction, and the sub-flues correspond to the sub-areas one by one.

[0013] Preferably, step 22 further includes:

[0014] Step 221: installing a first gas sensor at the smoke inlet of each sub-area;

[0015] Step 222: obtaining a theoretical ammonia injection amount for each sub-area based on the detection result of the first gas sensor;

[0016] Among them, Q i is the theoretical ammonia injection amount of the ith sub-area; is the concentration of nitrogen oxides in the flue gas at the entrance of the i-th sub-area; Q iR is the flue gas flow rate at the entrance of the i-th sub-area; ε is the denitrification efficiency;

[0017] Step 223: installing a second gas sensor at the smoke outlet of each sub-area;

[0018] Step 224: correcting the theoretical ammonia injection amount of each sub-area based on the detection result of the second gas sensor to obtain the actual ammonia injection amount;

[0019] Q is =Q i (1-δ i +τ); where Q is is the actual ammonia injection amount of the ith sub-area; Q i is the theoretical ammonia injection amount of the i-th sub-area; δ i is the ammonia escape rate at the outlet of the ith sub-area; τ is the preset minimum margin ratio of ammonia supply.

[0020] Preferably, the first gas sensor is used to detect the smoke concentration at the air inlet of the sub-area; the second gas sensor is used to detect the ammonia concentration at the air outlet of the sub-area.

[0021] Preferably, it also includes:

[0022] Step 3: Regularly evaluate the denitrification status of the flue gas. When the denitrification status of the flue gas does not meet the requirements, clean the flue;

[0023] Step 4: After the flue cleaning is completed, re-evaluate the denitrification status of the flue gas. If the denitrification status of the flue gas still does not meet the use requirements, shut down the flue for maintenance.

[0024] Preferably, step 3 comprises:

[0025] Step 31: setting a number of flow velocity measuring points inside the flue, the flow velocity measuring points being used to detect the flow velocity of the flue gas;

[0026] Step 32: Obtain the ammonia escape rate at the outlet of each sub-area;

[0027] Step 33: Obtain the flue gas flow rate at the inlet of each sub-area and the total flue gas flow rate of the boiler tail flue;

[0028] Step 34: Calculate the flue gas denitrification state evaluation parameter, and determine the flue gas denitrification state based on the flue gas denitrification state evaluation parameter;

[0029] If the flue gas denitrification state assessment parameter is greater than a preset danger threshold, it is judged that the flue gas denitrification state does not meet the use requirements, otherwise it is judged that the flue gas denitrification state meets the use requirements.

[0030] Preferably, step 31 calculates the flue gas denitrification state assessment parameter based on the following formula:

[0031]

[0032] Among them, P is the flue gas denitrification state assessment parameter; α, β, and γ are the weighted calculation coefficients of ammonia escape rate, flue gas distribution uniformity, and flow velocity uniformity, respectively; μ s is the current actual ammonia escape rate; μ b is the preset maximum allowable ammonia escape rate; V is the average value of the flow velocity measurement values ​​of all flow velocity measurement points; y is the preset standard flue gas flow rate; ln is the logarithmic function with e as the base; e is a natural constant; T s is the current flue gas temperature; T0 is the preset optimal flue gas temperature; M is the total number of velocity measurement points; V j is the velocity detection value of the jth velocity measurement point; V0 is the maximum allowable value of velocity fluctuation; N is the total number of sub-areas; Q i is the smoke flow rate of the ith sub-area; Q s is the total flue gas flow rate in the boiler tail flue.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] By setting up several guide plates in the horizontal expansion section of the flue, the airflow pattern at the jet outlet of the ammonia injection grid is greatly optimized, the swirl at the jet outlet disappears, and the airflow uniformity in the ammonia injection area is significantly improved. By isolating and zoning the flue, the uniformity of the flue gas flow rate inside the flue is improved, and the distribution uniformity of the flue gas to different sub-areas is improved, thereby improving the distribution uniformity of ammonia in each sub-area and reducing the ammonia escape rate. By using a disc mixer to replace the herringbone mixer, the mixing uniformity of ammonia and flue gas is further improved, thereby increasing the ammonia utilization rate and reducing the ammonia escape rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] In addition, in the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes, and do not specifically refer to the order or sequence, nor are they used to limit the present invention. They are only used to distinguish components or operations described with the same technical terms, and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions and technical features between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0039] Example 1

[0040] The embodiment of the present invention provides a method for adjusting the airflow uniformity of a denitration inlet flue flow field, comprising:

[0041] Step 1: Arrange a plurality of guide plates in the horizontal expansion section of the flue;

[0042] Step 2: Divide the ammonia spraying area into zones and isolate the flue into zones.

[0043] Preferably, the method further comprises replacing the herringbone mixer with a disc mixer.

[0044] The beneficial effects of the above technical solution are:

[0045] By arranging a number of guide plates in the horizontal expansion section of the flue, the airflow pattern at the jet outlet of the ammonia injection grid is greatly optimized, the swirl at the jet outlet disappears, and the airflow uniformity in the ammonia injection area is significantly improved.

[0046] By isolating and zoning the flue, the uniformity of the flue gas flow rate inside the flue is improved, and the uniformity of the distribution of flue gas to different sub-areas is improved, thereby improving the uniformity of ammonia distribution inside each sub-area and reducing the ammonia escape rate.

[0047] By using a disc mixer to replace the herringbone mixer, the mixing uniformity of ammonia and flue gas is further improved, thereby increasing the ammonia utilization rate and reducing the ammonia escape rate.

[0048] Example 2

[0049] Based on Example 1, step 2 includes:

[0050] Step 21: Divide the ammonia spraying area into a plurality of sub-areas based on the average distribution of geometric dimensions of the ammonia spraying area in the horizontal direction;

[0051] Step 22: setting a group of independently controlled ammonia spraying grids in each sub-area;

[0052] Step 23: Divide the flue from the flue at the tail end of the boiler to the outlet of the ammonia injection grid into a number of sub-flues according to the method of evenly dividing the geometric dimensions in the horizontal direction, and the sub-flues correspond to the sub-areas one by one.

[0053] Preferably, step 22 further includes:

[0054] Step 221: installing a first gas sensor at the smoke inlet of each sub-area;

[0055] Step 222: obtaining a theoretical ammonia injection amount for each sub-area based on the detection result of the first gas sensor;

[0056] Among them, Q i is the theoretical ammonia injection amount of the ith sub-area; is the concentration of nitrogen oxides in the flue gas at the entrance of the i-th sub-area; QiR is the flue gas flow rate at the entrance of the i-th sub-area; ε is the denitrification efficiency;

[0057] Step 223: installing a second gas sensor at the smoke outlet of each sub-area;

[0058] Step 224: correcting the theoretical ammonia injection amount of each sub-area based on the detection result of the second gas sensor to obtain the actual ammonia injection amount;

[0059] Q is =Q i (1-δ i +τ); where Q is is the actual ammonia injection amount of the ith sub-area; Q i is the theoretical ammonia injection amount of the i-th sub-area; δ i is the ammonia escape rate at the outlet of the ith sub-area; τ is the preset minimum margin ratio of ammonia supply.

[0060] Preferably, the first gas sensor is used to detect the smoke concentration at the air inlet of the sub-area; the second gas sensor is used to detect the ammonia concentration at the air outlet of the sub-area.

[0061] In this embodiment, the denitration efficiency is calculated based on the historical operation data of the denitration system.

[0062] In this embodiment, the minimum margin ratio of ammonia supply refers to the minimum ratio of ammonia supply that needs to be additionally supplied to ensure the denitrification effect of flue gas under the condition that the ammonia supply satisfies the complete reaction between ammonia and nitrogen oxides in the flue gas.

[0063] The beneficial effects of the above technical solution are:

[0064] By setting a first gas sensor at the delayed entrance of each sub-area, the ammonia injection amount is theoretically adjusted based on the input flow rate of the flue gas and the nitrogen oxide concentration, so as to improve the compatibility of the ammonia injection amount with the flue gas flow rate and the flue gas concentration, and reduce the ammonia escape rate. The ammonia concentration at the gas outlet of the sub-area is detected by the second gas sensor, so as to obtain the ammonia escape rate of each sub-area, and then the ammonia injection amount of each sub-area is feedback-adjusted, so as to further achieve accurate control of the ammonia injection amount and further reduce the ammonia escape rate of each sub-area. When the ammonia injection amount is feedback-adjusted, the minimum margin ratio of the ammonia supply is introduced when calculating the actual ammonia injection amount, so as to ensure that the ammonia supply always meets the denitrification demand for the flue gas, and ensure the denitrification effect of the flue gas while reducing the ammonia escape rate.

[0065] Example 3

[0066] On the basis of any one of Embodiments 1-2, further comprising:

[0067] Step 3: Regularly evaluate the denitrification status of the flue gas. When the denitrification status of the flue gas does not meet the requirements, clean the flue;

[0068] Step 4: After the flue cleaning is completed, re-evaluate the denitrification status of the flue gas. If the denitrification status of the flue gas still does not meet the use requirements, shut down the flue for maintenance.

[0069] Preferably, step 3 comprises:

[0070] Step 31: setting a number of flow velocity measuring points inside the flue, the flow velocity measuring points being used to detect the flow velocity of the flue gas;

[0071] Step 32: Obtain the ammonia escape rate at the outlet of each sub-area;

[0072] Step 33: Obtain the flue gas flow rate at the inlet of each sub-area and the total flue gas flow rate of the boiler tail flue;

[0073] Step 34: Calculate the flue gas denitrification state evaluation parameter, and determine the flue gas denitrification state based on the flue gas denitrification state evaluation parameter;

[0074] If the flue gas denitrification state assessment parameter is greater than a preset danger threshold, it is judged that the flue gas denitrification state does not meet the use requirements, otherwise it is judged that the flue gas denitrification state meets the use requirements.

[0075] Preferably, step 31 calculates the flue gas denitrification state assessment parameter based on the following formula:

[0076]

[0077] Among them, P is the flue gas denitrification state assessment parameter; α, β, and γ are the weighted calculation coefficients of ammonia escape rate, flue gas distribution uniformity, and flow velocity uniformity, respectively; μ s is the current actual ammonia escape rate; μ b is the preset maximum allowable ammonia escape rate; V is the average value of the flow velocity measurement values ​​of all flow velocity measurement points; y is the preset standard flue gas flow rate; ln is the logarithmic function with e as the base; e is a natural constant; T s is the current flue gas temperature; T0 is the preset optimal flue gas temperature; M is the total number of velocity measurement points; V j is the velocity detection value of the jth velocity measurement point; V0 is the maximum allowable value of velocity fluctuation; N is the total number of sub-areas; Q i is the smoke flow rate of the ith sub-area; Q s is the total flue gas flow rate in the boiler tail flue.

[0078] The beneficial effects of the above technical solution are:

[0079] By regularly evaluating the denitrification effect of the flue gas, the efficient denitrification effect of the flue gas is guaranteed. When the denitrification effect of the flue gas does not meet the requirements, it is presumed that the dust accumulation inside the flue has affected the airflow uniformity and flue gas distribution uniformity of the flue gas, resulting in a decrease in the denitrification effect. By cleaning the flue, the dust accumulation inside the flue is reduced, so that the airflow uniformity and flue gas distribution uniformity of the flue gas are improved, thereby optimizing the denitrification effect. If the denitrification effect of the flue after cleaning still cannot meet the requirements, it is judged that the flue has deformation, damage and other faults, and the flue is repaired through shutdown inspection and maintenance, thereby ensuring excellent flue gas airflow uniformity and flue gas distribution uniformity.

[0080] When calculating the flue gas denitrification status assessment parameters, the accuracy of the assessment results is improved by considering the impact of three factors on the denitrification effect: escape rate, flue gas distribution uniformity and flue gas flow rate uniformity. By comprehensively considering the impact of multiple factors on the denitrification effect, the denitrification effect is used as the main factor for judgment, ensuring excellent denitrification effects, reducing the frequency of flue maintenance, and reducing the workload of staff.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for adjusting the uniformity of the airflow in the flue flow field at the inlet of denitrification, characterized in that: include: Step 1: Arrange a plurality of guide plates in the horizontal expansion section of the flue; Step 2: Partition the ammonia spraying area and isolate the flue.

2. A method for adjusting airflow uniformity of a denitration inlet flue flow field according to claim 1, characterized in that: Step 2 also includes replacing the herringbone mixer with a disc mixer.

3. The method for adjusting the airflow uniformity of the denitration inlet flue flow field according to claim 1, characterized in that: Step 2 includes: Step 21: Divide the ammonia spraying area into a plurality of sub-areas based on the average distribution of geometric dimensions of the ammonia spraying area in the horizontal direction; Step 22: setting a group of independently controlled ammonia spraying grids in each sub-area; Step 23: Divide the flue from the flue at the tail end of the boiler to the outlet of the ammonia injection grid into a number of sub-flues according to the method of evenly dividing the geometric dimensions in the horizontal direction, and the sub-flues correspond to the sub-areas one by one.

4. A method for adjusting airflow uniformity of a denitration inlet flue flow field according to claim 3, characterized in that: Step 22 also includes: Step 221: installing a first gas sensor at the smoke inlet of each sub-area; Step 222: obtaining a theoretical ammonia injection amount for each sub-area based on the detection result of the first gas sensor; Among them, Q i is the theoretical ammonia injection amount of the ith sub-area; is the concentration of nitrogen oxides in the flue gas at the entrance of the i-th sub-area; Q iR is the flue gas flow rate at the entrance of the i-th sub-area; ε is the denitrification efficiency; Step 223: installing a second gas sensor at the smoke outlet of each sub-area; Step 224: correcting the theoretical ammonia injection amount of each sub-area based on the detection result of the second gas sensor to obtain the actual ammonia injection amount; Q is =Q i (1-δ i +τ); where Q is is the actual ammonia injection amount of the ith sub-area; Q i is the theoretical ammonia injection amount of the i-th sub-area; δ i is the ammonia escape rate at the outlet of the ith sub-area; τ is the preset minimum margin ratio of ammonia supply.

5. A method for adjusting airflow uniformity of a denitration inlet flue flow field according to claim 4, characterized in that: The first gas sensor is used to detect the smoke concentration at the air inlet of the sub-area; the second gas sensor is used to detect the ammonia concentration at the air outlet of the sub-area.

6. A method for adjusting airflow uniformity of a denitration inlet flue flow field according to claim 1, characterized in that: Also includes: Step 3: Regularly evaluate the denitrification status of the flue gas. When the denitrification status of the flue gas does not meet the requirements, clean the flue; Step 4: After the flue cleaning is completed, re-evaluate the denitrification status of the flue gas. If the denitrification status of the flue gas still does not meet the use requirements, shut down the flue for maintenance.

7. A method for adjusting airflow uniformity of a denitration inlet flue flow field according to claim 6, characterized in that: Step 3 includes: Step 31: setting a number of flow velocity measuring points inside the flue, the flow velocity measuring points being used to detect the flow velocity of the flue gas; Step 32: Obtain the ammonia escape rate at the outlet of each sub-area; Step 33: Obtain the flue gas flow rate at the inlet of each sub-area and the total flue gas flow rate of the boiler tail flue; Step 34: calculating a flue gas denitrification state evaluation parameter, and determining the flue gas denitrification state based on the flue gas denitrification state evaluation parameter; If the flue gas denitrification state assessment parameter is greater than a preset danger threshold, it is judged that the flue gas denitrification state does not meet the use requirements, otherwise it is judged that the flue gas denitrification state meets the use requirements.

8. A method for adjusting airflow uniformity of a denitration inlet flue flow field according to claim 7, characterized in that: Step 31 calculates the flue gas denitrification state assessment parameter based on the following formula; Among them, P is the flue gas denitrification state assessment parameter; α, β, and γ are the weighted calculation coefficients of ammonia escape rate, flue gas distribution uniformity, and flow velocity uniformity, respectively; μ s is the current actual ammonia escape rate; μ b is the preset maximum allowable ammonia escape rate; V is the average value of the flow velocity measurement values ​​of all flow velocity measurement points; y is the preset standard flue gas flow rate; ln is the logarithmic function with e as the base; e is a natural constant; T s is the current flue gas temperature; T0 is the preset optimal flue gas temperature; M is the total number of velocity measurement points; V j is the velocity detection value of the jth velocity measurement point; V0 is the maximum allowable value of velocity fluctuation; N is the total number of sub-areas; Q i is the smoke flow rate of the ith sub-area; Q s is the total flue gas flow rate in the boiler tail flue.

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