Intelligent regulation and control method for operation of flue gas waste heat gradient utilization system

Abstract

The invention relates to an intelligent operation regulation and control method based on a flue gas waste heat gradient utilization system, and the method comprises the steps: firstly, judging the relation between the water inlet temperature and the minimum operation value of a low-pressure economizer, and carrying out different treatments according to different judgments, so as to guarantee that the water inlet temperature of the low-pressure economizer is not lower than the minimum operation value; and then the flow ratio of outlet water of the low-pressure economizer entering the inlet end and the outlet end of a second low-pressure heater is adjusted according to the unit load, and meanwhile the steam extraction amount of a medium-pressure cylinder of the second low-pressure heater is adjusted. On the premise that safe operation of a boiler is met, through real-time detection and dynamic adjustment, complex and changeable operation conditions can be better adapted, all available waste heat resources are fully utilized, the high-grade steam extraction amount of the system reaches the minimum, the overall performance and the energy-saving effect of the flue gas waste heat gradient utilization system are improved, and the energy-saving effect of the flue gas waste heat gradient utilization system is improved. And the method is suitable for ultra-supercritical units with different powers.

Description

Technical Field

[0001] The present invention relates to the field of flue gas waste heat utilization devices for coal-fired boilers, and particularly to an intelligent operation control method based on a flue gas waste heat cascade utilization system. Background Art

[0002] In order to reduce the flue gas exhaust temperature of coal-fired boilers and maximize the utilization of flue gas waste heat, a flue gas waste heat cascade utilization system is often set at the flue gas output end of coal-fired boilers. The flue gas waste heat cascade utilization system couples the boiler flue gas system with the steam turbine regenerative system, and then uses high-temperature feed water, condensate or closed-circuit circulating water to absorb the flue gas waste heat, reduce the boiler flue gas exhaust temperature, and improve the thermal efficiency of coal-fired units. Currently, in order to reduce the flue gas exhaust temperature of coal-fired boilers and maximize the utilization of flue gas waste heat, one of the disclosed technologies is that the flue gas waste heat cascade utilization system couples the boiler flue gas system with the steam turbine regenerative system, uses high-temperature feed water, condensate or closed-circuit circulating water to absorb the flue gas waste heat, reduces the boiler flue gas exhaust temperature, and improves the thermal efficiency of coal-fired units. In the flue gas waste heat cascade utilization system, the outlet point of the low-pressure economizer is selected based on the temperature difference to ensure the energy-saving effect of the waste heat utilization system and the efficiency of the steam turbine regenerative system. However, this operation method can only judge the outlet temperature of the low-pressure economizer and the temperature of the selected return water point, lacking comprehensive consideration of the whole. This operation method cannot fully explore and utilize all the energy-saving potential of the unit, limits the improvement of the overall thermal efficiency, and does not consider dynamically adjusting system parameters with the change of unit load, which may lead to the inability to achieve the best waste heat utilization effect under different working conditions, and is only applicable to low-power units with more stable operating loads. For high-power ultra-supercritical units, their operating conditions are more complex and variable, and usually require a higher thermal efficiency requirement for the flue gas waste heat cascade utilization system. Therefore, it is necessary to further improve the existing operation method based on the flue gas waste heat cascade utilization system to maximize the energy-saving effect of the system, make it applicable to various types of ultra-supercritical units, and at the same time reduce the operating energy consumption cost. Summary of the Invention

[0003] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a condensate bypass of a flue gas waste heat cascade utilization system and its operation method, which solves the problems of limited energy-saving potential and poor versatility in the existing flue gas waste heat cascade utilization system.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions:

[0005] An intelligent operation control method for a flue gas waste heat cascade utilization system, the flue gas waste heat cascade utilization system includes a first low-pressure heater connected to a first low-pressure cylinder, a second low-pressure heater connected to an intermediate-pressure cylinder, and a low-pressure economizer. The inlet end and the outlet end of the first low-pressure heater are respectively connected to the inlet end of the low-pressure economizer, and the inlet end and the outlet end of the second low-pressure heater are respectively connected to the outlet end of the low-pressure economizer, including the following steps:

[0006] Step S1: Set the minimum operating value of the inlet water temperature of the low-pressure economizer, and detect the inlet water temperature of the low-pressure economizer, and the outlet water temperatures at the inlet end and the outlet end of the first low-pressure heater in real time;

[0007] Step S2: Determine whether the inlet water temperature of the low-pressure economizer is greater than or equal to the minimum operating value;

[0008] If not, adjust the inlet water ratio of the inlet end and the outlet end of the first low-pressure heater entering the low-pressure economizer until the inlet water temperature of the low-pressure economizer is greater than or equal to the minimum operating value;

[0009] If so, maintain the current inlet water ratio;

[0010] Step S3: Obtain the unit load in real time, and adjust the flow ratio of the outlet water of the low-pressure economizer entering the inlet end and the outlet end of the second low-pressure heater respectively according to the unit load, and at the same time adjust the extraction steam amount of the second low-pressure heater from the intermediate-pressure cylinder, where the flow ratio is 0-100%.

[0011] Further, the specific adjustment method of the inlet water ratio is:

[0012] Increase the water flow rate from the outlet end of the first low-pressure heater to the low-pressure economizer; or

[0013] Reduce the water flow rate from the inlet end of the first low-pressure heater to the low-pressure economizer; or

[0014] Increase the water flow rate from the outlet end of the first low-pressure heater to the low-pressure economizer while reducing the water flow rate from the inlet end of the first low-pressure heater to the low-pressure economizer.

[0015] Further, obtain the unit load in real time, and adjust the flow ratio of the outlet water of the low-pressure economizer entering the inlet end and the outlet end of the second low-pressure heater respectively according to the unit load, specifically as follows:

[0016] Step S 31 、Obtain the unit load in real time;

[0017] Step S 32, determine whether the unit load meets the preset range;

[0018] If so, adjust the proportion of the outlet water of the low-pressure economizer entering the inlet end of the second low-pressure heater to decrease until it is 0%, and adjust the proportion of the outlet water of the low-pressure economizer entering the outlet end of the second low-pressure heater to increase until it is 100%;

[0019] If not, adjust the proportion of the outlet water of the low-pressure economizer entering the inlet end of the second low-pressure heater to increase until it is 100%, and adjust the proportion of the outlet water of the low-pressure economizer entering the outlet end of the second low-pressure heater to decrease until it is 0%.

[0020] Further, the judgment step of the preset range is specifically as follows:

[0021] Calculate the average value of the condensate water temperature at the outlet end and the inlet end of the second low-pressure heater;

[0022] Judge whether the outlet water temperature of the low-pressure economizer is greater than or equal to the average value;

[0023] If so, judge that the unit load meets the preset range;

[0024] If not, judge that the unit load does not meet the preset range.

[0025] Further, the minimum value of the preset range is greater than 50%.

[0026] Further, the unit load is obtained in real time, and the proportion of the outlet water of the low-pressure economizer entering the inlet end and the outlet end of the second low-pressure heater is adjusted according to the unit load. Specifically:

[0027] Step S 31 , obtain the unit load in real time;

[0028] Step S 32 , based on a preset rule, when the unit load is higher than the preset range, reduce the flow rate of the outlet water of the low-pressure economizer entering the inlet end of the second low-pressure heater, and increase the flow rate of the outlet water of the low-pressure economizer entering the outlet end of the second low-pressure heater until the unit load meets the preset range;

[0029] When the unit load is lower than the preset range, increase the flow rate of the outlet water of the low-pressure economizer entering the inlet end of the second low-pressure heater, and reduce the flow rate of the outlet water of the low-pressure economizer entering the outlet end of the second low-pressure heater until the unit load meets the preset range;.

[0030] Further, it also includes the discrimination process of the outlet flue gas temperature of the low-pressure economizer:

[0031] Monitor the outlet flue gas temperature of the low-pressure economizer in real time;

[0032] Judge whether the outlet flue gas temperature is lower than the acid dew point warning value, where the acid dew point warning value is greater than the value of the acid dew point, and the acid dew point is the temperature at which the low-pressure economizer produces low-temperature corrosion;

[0033] If so, reduce the inlet water flow rate of the low-pressure economizer based on the water inlet ratio.

[0034] Further, the flue gas waste heat cascade utilization system further includes a third low-pressure heater connected to the second low-pressure cylinder and / or the first low-pressure cylinder, and a fourth low-pressure heater connected to the intermediate-pressure cylinder. The third low-pressure heater is arranged between the first low-pressure heater and the second low-pressure heater, and the fourth low-pressure heater is arranged at the outlet end of the second low-pressure heater. The first low-pressure heater, the second low-pressure heater, the third low-pressure heater and the fourth low-pressure heater form a low-pressure heating flow path;

[0035] The method further includes: adjusting the condensate flow rate flowing in the low-pressure heating flow path and the condensate flow rate flowing through the low-pressure economizer based on the load;

[0036] When the unit load is lower than the preset range, reduce the condensate flow rate entering the low-pressure economizer and increase the condensate flow rate entering the low-pressure heating flow path until the unit load meets the preset range;

[0037] When the unit load is higher than the preset range, increase the condensate flow rate entering the low-pressure economizer and reduce the condensate flow rate entering the low-pressure heating flow path until the unit load meets the preset range.

[0038] In summary, compared with the prior art, the present invention has at least the following beneficial effects:

[0039] The present invention provides an intelligent operation control method for a flue gas waste heat cascade utilization system. First, by judging the relationship between the inlet water temperature of the low-pressure economizer and the minimum operating value, different treatments are taken for different judgments to ensure that the inlet water temperature of the low-pressure economizer is not lower than the minimum operating value. Then, according to the unit load, the flow ratio of the outlet water of the low-pressure economizer entering the inlet end and the outlet end of the second low-pressure heater is adjusted, and at the same time, the extraction steam volume of the second low-pressure heater from the intermediate pressure cylinder is adjusted, realizing the matching of the outlet water temperature of the low-pressure economizer and the outlet water temperature of the second low-pressure heater under different load conditions of the unit. On the premise of ensuring the safe operation of the boiler, through real-time detection and dynamic adjustment, the flue gas waste heat cascade utilization system can keep the inlet water temperature of the low-pressure economizer higher than the minimum operating value all the time, and is optimally configured under different load conditions, and can better adapt to complex and changeable operating conditions, fully utilize all available waste heat resources, minimize the extraction amount of high-grade steam by the system, improve the overall performance and energy-saving effect of the flue gas waste heat cascade utilization system, and can be applied to ultra-supercritical units with different powers. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0041] Figure 1 It is a schematic structural diagram of a flue gas waste heat cascade utilization system provided in an embodiment of the present invention.

[0042] Description of the reference numerals:

[0043] 1, first low-pressure heater; 2, second low-pressure heater; 3, low-pressure economizer; 4, first low-pressure cylinder; 5, intermediate pressure cylinder; 6, third low-pressure heater; 7, fourth low-pressure heater; 8, second low-pressure cylinder. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] The following will clearly and completely describe the technical solutions of the present invention with reference to the drawings. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0045] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0046] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected", "connected to" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0047] The present invention provides an intelligent operation control method for a flue gas waste heat cascade utilization system, wherein, as shown in the attached Figure 1As shown in the figure, the flue gas waste heat cascade utilization system used in the present invention includes a first low-pressure heater 1 connected to the first low-pressure cylinder 4, a second low-pressure heater 2 connected to the intermediate-pressure cylinder 5, and a low-pressure economizer 3. The steam extracted from the first low-pressure cylinder 4 will enter the first low-pressure heater 1 for heat exchange. The high-grade steam in the intermediate-pressure cylinder 5 will be extracted by the second low-pressure heater 2 for heat exchange. The inlet end and the outlet end of the first low-pressure heater 1 are respectively connected to the inlet end of the low-pressure economizer 3. The inlet end and the outlet end of the second low-pressure heater 2 are respectively connected to the outlet end of the low-pressure economizer 3. It should be noted that the condenser first cools and condenses the steam discharged from the steam turbine into water. The condensate water entering the first low-pressure heater 1 has a relatively low temperature. After heat exchange between the first low-pressure heater 1 and the steam extracted from the first low-pressure cylinder 4, the temperature of the condensate water flowing out of the outlet end of the first low-pressure heat exchanger 1 is higher than that of the condensate water at the inlet end of the first low-pressure heat exchanger 1. And the second low-pressure heater 2 extracts the high-grade steam in the intermediate-pressure cylinder 5 to heat the condensate water flowing through the second low-pressure heater 2. Therefore, the temperature of the condensate water flowing out of the outlet end of the second low-pressure heater 2 is higher than that of the condensate water at the inlet end of the second low-pressure heater 2. A part of the condensate water enters the flow paths of each low-pressure heater arranged in a cascade, and the temperature of the condensate water will be gradually increased by each heater. Another part will be guided to the low-pressure economizer 3. The low-pressure economizer 3 uses the waste heat of the flue gas discharged from the boiler to heat the condensate water flowing through it, which can not only recover the heat in the flue gas, but also conduct more suitable heat exchange with the steam extracted from the intermediate-pressure cylinder and the low-pressure cylinder, thereby reducing the loss of high-grade steam in the system and improving the operation efficiency of the system. And, as shown in the appendix Figure 1 As shown, the system is also connected with a flow measurement point (marked in the figure ), a pressure measurement point (marked in the figure ), and a temperature measurement point (marked in the figure ) to detect various data in real time.

[0048] Specifically, an intelligent operation control method based on the flue gas waste heat cascade utilization system includes the following steps:

[0049] Step S1: Set the minimum operating value of the inlet water temperature of the low-pressure economizer 3, and detect the inlet water temperature of the low-pressure economizer 3, and the outlet water temperatures at the inlet and outlet ends of the first low-pressure heater 1 in real time. Herein, the minimum operating value refers to the lowest inlet water temperature that the low-pressure economizer 3 is allowed to receive. When the temperature is lower than this value, the temperature difference between the outlet temperature of the low-pressure economizer 3 and the return water point temperature of the low-pressure economizer 3 will be too large. In order to make up for the insufficient heating of the condensate water caused by the too large temperature difference, the second low-pressure heater 2 or the low-pressure heaters after it need to extract more high-quality steam from the intermediate pressure cylinder 5 to heat the return water of the low-pressure economizer 3. This not only increases the steam consumption but also reduces the energy-saving effect of the flue gas waste heat cascade utilization system. It should be noted that the minimum operating value needs to be determined according to the actual application conditions and system design, and is not limited herein.

[0050] Step S2: Determine whether the inlet water temperature of the low-pressure economizer 3 is greater than or equal to the minimum operating value;

[0051] If not, adjust the inlet water ratio of the inlet and outlet ends of the first low-pressure heater 1 entering the low-pressure economizer 3 until the inlet water temperature of the low-pressure economizer 3 is greater than or equal to the minimum operating value;

[0052] If so, maintain the current inlet water ratio.

[0053] Since the water temperature at the outlet end of the first low-pressure heater 1 is higher than the water temperature at the inlet end of the first low-pressure heater 1, by changing the proportion of the water inflow from the two paths into the low-pressure economizer 3, the inlet water temperature of the low-pressure economizer 3 is increased until it reaches or exceeds the minimum operating value, thereby increasing the outlet water temperature of the low-pressure economizer 3 and reducing the high-quality steam extracted from the intermediate pressure cylinder 5 by the unit.

[0054] Step S3: Obtain the unit load in real time, adjust the flow ratio of the outlet water of the low-pressure economizer 3 entering the inlet and outlet ends of the second low-pressure heater 2 respectively according to the unit load, and at the same time adjust the extraction steam amount of the second low-pressure heater 2 from the intermediate pressure cylinder 5, wherein the flow ratio is 0-100%.

[0055] Specifically, the unit load will affect the operating state of the entire system. Usually, the unit load gradually decreases with the running time of the system, causing the outlet water temperature of the low-pressure economizer 3 to decrease. This will result in an increase in the heat exchange amount of the steam extraction from the steam turbine in the second low-pressure heater 2 or in the subsequent low-pressure heaters, increasing the loss of high-grade steam in the system and thus reducing the energy-saving effect of the flue gas waste heat cascade utilization system. Therefore, to ensure that the control system can respond promptly to the change of the unit load, it is necessary to adjust the flow ratio of the outlet water of the low-pressure economizer 3 entering the inlet end and the outlet end of the second low-pressure heater 2 respectively, where the ratio ranges from 0 to 100%, that is, the outlet water of the low-pressure economizer 3 can be adjusted to enter completely into the inlet end of the second low-pressure heater 2, or the outlet water of the low-pressure economizer 3 can be adjusted to enter completely into the outlet end of the second low-pressure heater 2, or the two-way outlet water flow can be flexibly distributed according to different ratios. At the same time, correspondingly adjust the steam extraction amount of the second low-pressure heater 2 from the intermediate pressure cylinder 5, so that the energy distribution of the system can be flexibly adjusted according to the actual situation of the unit load, improving the energy utilization efficiency.

[0056] It should be noted that when fouling occurs on the flue gas side of the low-pressure economizer 3, it may also cause the outlet water temperature of the low-pressure economizer 3 to decrease. To accurately distinguish whether this situation is caused by fouling or load reduction, on the one hand, it can be judged according to the system temperature change level. If it is a load reduction, the temperature level of the entire system will drop, rather than just the outlet water temperature of the low-pressure economizer 3 dropping. If only the outlet water temperature of the low-pressure economizer 3 drops significantly while the temperature of other parts remains relatively stable, this may be due to the decrease in the local heat exchange efficiency caused by fouling. On the other hand, pressure measuring points are added at the inlet end and the outlet end of the flue gas side of the low-pressure economizer 3 in the system, and it can be judged according to the detected pressure difference between the inlet end and the outlet end of the flue gas side of the low-pressure economizer 3. When the pressure difference is too large and exceeds the normal range, it can be determined that fouling has occurred on the flue gas side of the low-pressure economizer 3. When it is confirmed as a fouling situation, it needs to be cleaned to prevent the fouling from deteriorating further, resulting in more heat being unable to be effectively transferred to the condensate water, thus reducing the thermal efficiency of the entire system.

[0057] The intelligent operation control method based on the flue gas waste heat cascade utilization system provided by the present invention can, on the premise of ensuring the safe operation of the boiler, through real-time detection and dynamic adjustment, enable the flue gas waste heat cascade utilization system to keep the inlet water temperature of the low-pressure economizer 3 higher than the minimum operating value all the time, and optimize the configuration under different load conditions, and can better adapt to complex and changeable operating conditions, make full use of all available waste heat resources, minimize the extraction amount of high-grade steam in the system, effectively improve the overall performance and energy-saving effect of the flue gas waste heat cascade utilization system, and can be applied to ultra-supercritical units with different powers.

[0058] In some embodiments of the present invention, since the condensate water temperature at the outlet end of the first low-pressure heater 1 is higher than that at the inlet end, the specific adjustment method of the water inlet ratio is as follows:

[0059] Increase the water flow rate from the outlet end of the first low-pressure heater 1 to the low-pressure economizer 3; or

[0060] Decrease the water flow rate from the inlet end of the first low-pressure heater 1 to the low-pressure economizer 3; or

[0061] Increase the water flow rate from the outlet end of the first low-pressure heater 1 to the low-pressure economizer 3 and at the same time decrease the water flow rate from the inlet end of the first low-pressure heater 1 to the low-pressure economizer 3, which is suitable for quickly responding to changes in system requirements, such as coping with sudden temperature drops.

[0062] Specifically, by dynamically adjusting the water temperature entering the low-pressure economizer 3, the proportion of low-temperature condensate water that is not fully heated is reduced to ensure that the water inlet temperature of the low-pressure economizer 3 is always within the optimal operating range, so that the water outlet temperature of the low-pressure economizer 3 remains at a relatively high temperature, improving the thermal efficiency and energy-saving effect of the entire system. Among them, the selection of the specific adjustment method of the water inlet ratio can depend on the real-time monitored data and the current operating conditions, which are not limited herein.

[0063] In some embodiments of the present invention, the step of "real-time obtaining the unit load and adjusting the flow rate ratio of the water outlet of the low-pressure economizer 3 entering the inlet end and the outlet end of the second low-pressure heater 2 according to the unit load" is specifically as follows:

[0064] Step S 31 、Real-time obtain the unit load;

[0065] Step S 32 、Judge whether the unit load meets the preset range;

[0066] If so, adjust the flow rate ratio of the water outlet of the low-pressure economizer 3 entering the inlet end of the second low-pressure heater 2 to decrease until it is 0%, and adjust the flow rate ratio of the water outlet of the low-pressure economizer 3 entering the outlet end of the second low-pressure heater 2 to increase until it is 100%, that is, adjust the water outlet point of the low-pressure economizer 3 to the outlet end of the second low-pressure heater 2;

[0067] If not, adjust the flow rate ratio of the water outlet of the low-pressure economizer 3 entering the inlet end of the second low-pressure heater 2 to increase until it is 100%, and adjust the flow rate ratio of the water outlet of the low-pressure economizer 3 entering the outlet end of the second low-pressure heater 2 to decrease until it is 0%, that is, adjust the water outlet point of the low-pressure economizer 3 to the inlet end of the second low-pressure heater 2.

[0068] Specifically, the preset range is the optimal operating load range when the outlet point of the low-pressure economizer 3 is the outlet end of the second low-pressure heater 2. By judging whether the unit load is within the preset range of the unit load, the path of the outlet water of the low-pressure economizer 3 entering the second low-pressure heater 2 is determined according to the judgment result to optimize the heat exchange efficiency. Among them, the judgment method of the unit load can be to directly obtain the current unit load value, or to directly reflect the working state and efficiency of the unit by setting judgment rules, and then infer whether the unit load meets the preset range. The specific judgment method used can be determined according to the actual working conditions and technical requirements, etc., and is not limited here. When the unit load meets the preset range, the inlet and outlet water temperatures of the low-pressure economizer 3 are relatively high. Therefore, allowing the condensed water heated by the low-pressure economizer 3 to directly enter the outlet end of the second low-pressure heater 2 can maximize the utilization of flue gas waste heat and reduce the demand for high-quality steam. When the load does not meet the preset range, the inlet and outlet water temperatures of the low-pressure economizer 3 are relatively low. At this time, introducing the outlet water of the low-pressure economizer 3 into the inlet end of the second low-pressure heater 2 can better balance the heat energy distribution of the system, avoid the problem of too high or too low outlet water temperature of the low-pressure economizer 3, and realize the matching of the outlet water of the low-pressure economizer 3 and the outlet water temperature of the low-pressure heater before the return water point under different load conditions of the unit.

[0069] In some embodiments of the present invention, since the unit load is variable and in order to avoid installing complex sensors and high-precision equipment required for directly measuring the unit load to simplify the system design, the preset range can be indirectly judged by setting judgment rules in advance. The specific steps are as follows:

[0070] Calculate the average value of the condensed water temperature at the outlet end and the condensed water temperature at the inlet end of the second low-pressure heater 2;

[0071] Judge whether the outlet water temperature of the low-pressure economizer 3 is greater than or equal to the average value;

[0072] If so, judge that the unit load meets the preset range, and at this time, adjust the outlet point of the low-pressure economizer 3 to the outlet end of the second low-pressure heater 2;

[0073] If not, judge that the unit load does not meet the preset range, and at this time, adjust the outlet point of the low-pressure economizer 3 to the inlet end of the second low-pressure heater 2.

[0074] In some embodiments of the present invention, the minimum value of the preset range is greater than 50%.

[0075] In some embodiments of the present invention, another implementation manner of the step of "real-time obtaining the unit load and adjusting the flow ratio of the outlet water of the low-pressure economizer 3 entering the inlet end and the outlet end of the second low-pressure heater 2 according to the unit load" is specifically as follows:

[0076] Step S31 1. Obtain the unit load in real time;

[0077] Step S 32 2. Based on a preset rule, when the unit load is higher than the preset range, reduce the flow rate of the outlet water of the low-pressure economizer 3 entering the inlet end of the second low-pressure heater 2, and increase the flow rate of the outlet water of the low-pressure economizer 3 entering the outlet end of the second low-pressure heater 2 until the unit load meets the preset range;

[0078] When the unit load is lower than the preset range, increase the flow rate of the outlet water of the low-pressure economizer 3 entering the inlet end of the second low-pressure heater 2, and reduce the flow rate of the outlet water of the low-pressure economizer 3 entering the outlet end of the second low-pressure heater 2 until the unit load meets the preset range. Among them, the preset rule is the flow rate distribution of the outlet water of the low-pressure economizer 3 entering the inlet end and the outlet end of the second low-pressure heater 2.

[0079] In some embodiments of the present invention, during the operation of the low-pressure economizer 3, when the flue gas temperature is lower than the critical temperature (acid dew point) at which the acidic gas in the flue gas begins to condense into liquid acid, it will cause corrosion of the low-pressure economizer 3 and the tail flue. Therefore, it also includes a process for judging the outlet flue gas temperature of the low-pressure economizer 3:

[0080] 3. Monitor the outlet flue gas temperature of the low-pressure economizer 3 in real time;

[0081] 4. Judge whether the outlet flue gas temperature is lower than the acid dew point warning value. Among them, the acid dew point warning value is greater than the value of the acid dew point, and the acid dew point is the temperature at which the low-pressure economizer 3 generates low-temperature corrosion;

[0082] 5. If so, reduce the inlet flow rate of the low-pressure economizer 3 based on the inlet water ratio.

[0083] Specifically, the greater the inlet flow rate of the low-pressure economizer 3, the greater the heat exchange capacity of the low-pressure economizer 3, and ultimately the lower the outlet flue gas temperature. In order to increase the outlet flue gas temperature of the low-pressure economizer 3 and avoid it approaching or being lower than the low-temperature corrosion point, the total inlet flow rate needs to be reduced. It can be adjusted by the overall opening degree of the inlet valves on the flow paths of the inlet end and the outlet end of the first low-pressure heater 1. On the basis of the inlet water ratio that has been adjusted by the inlet water temperature of the low-pressure economizer 3, the inlet flow rate of the low-pressure economizer 3 is reduced as a whole. It can make full use of the waste heat of the flue gas while preventing the flue gas temperature from being too low to cause low-temperature corrosion, avoiding corrosion and equipment damage, and effectively extending the service life of the low-pressure economizer 3.

[0084] In some embodiments of the present invention, as shown in the appendix Figure 1As shown, the flue gas waste heat cascade utilization system further includes a third low-pressure heater 6 connected to the second low-pressure cylinder 8 and / or the first low-pressure cylinder 4, and a fourth low-pressure heater 7 connected to the intermediate-pressure cylinder 5. The third low-pressure heater 6 is arranged between the first low-pressure heater 1 and the second low-pressure heater 2 to form an intermediate heating link; the fourth low-pressure heater 7 is arranged at the outlet end of the second low-pressure heater 2 to extract higher-grade steam from the intermediate-pressure cylinder 5 to further increase the temperature of the condensate water. The first low-pressure heater 1, the second low-pressure heater 2, the third low-pressure heater 6 and the fourth low-pressure heater 7 form a low-pressure heating flow path. It should be noted that different from the traditional flue gas waste heat cascade utilization system where the water inlet position of the low-pressure economizer 3 is the inlet end of the first low-pressure heater 1 and the outlet end of the third low-pressure heater 6, the system based on the present invention improves the water inlet position of the low-pressure economizer 3 to the inlet end and the outlet end of the first low-pressure heater 1. This is determined by the large flow rate of the condensate water of high-power units and the different proportions of the heat exchange capacity of the low-pressure economizer 3 in the heat exchange of the unit system, and it can be adapted to the flue gas waste heat cascade utilization system at various powers, having strong versatility.

[0085] After the condensate water coming from the condenser enters the flue gas waste heat cascade utilization system, it is divided into two routes. Part of the condensate water enters the low-pressure heating flow path and passes through the first low-pressure heater 1, the third low-pressure heater 6, the second low-pressure heater 2 and the fourth low-pressure heater 7 in sequence; the other part of the condensate water enters the low-pressure economizer 3 to be heated and then returns to the low-pressure heating flow path, and finally passes through the fourth low-pressure heater 7 for further heating. Therefore, in order to ensure that the system can operate efficiently under different load conditions, this method further includes dynamically adjusting the flow rate of the condensate water flowing in the low-pressure heating flow path and the flow rate of the condensate water flowing through the low-pressure economizer 3 according to the unit load. It should be noted that this step needs to be carried out preferentially while maintaining the requirement of the outlet water temperature of the low-pressure economizer 3, specifically as follows:

[0086] Adjust the flow rate of the condensate water flowing in the low-pressure heating flow path and the flow rate of the condensate water flowing through the low-pressure economizer 3 based on the load;

[0087] When the unit load is lower than the preset range, reduce the flow rate of the condensate water entering the low-pressure economizer 3 and increase the flow rate of the condensate water entering the low-pressure heating flow path until the unit load meets the preset range;

[0088] When the unit load is higher than the preset range, increase the flow rate of the condensate water entering the low-pressure economizer 3 and reduce the flow rate of the condensate water entering the low-pressure heating flow path until the unit load meets the preset range.

[0089] Based on the unit load, the condensate flow rate is reasonably adjusted to ensure the optimal distribution of heat energy throughout the system. In particular, diverting a portion of the condensate from the low-pressure economizer 3 and preheating it can significantly reduce the high-quality steam extracted by the second low-pressure heater 2 and the fourth low-pressure heater 7 from the intermediate-pressure cylinder 5.

[0090] It should be noted that the above description uses condensate as the heat exchange medium, but it is not limited to condensate, and other heat exchange media can also be used.

[0091] The above embodiments are only the preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantive changes and substitutions made by those skilled in the art based on the present invention fall within the scope of protection required by the present invention.

Claims

1. An intelligent operation regulation method for a flue gas waste heat cascade utilization system, the flue gas waste heat cascade utilization system comprising a first low-pressure heater connected to a first low-pressure cylinder, a second low-pressure heater connected to an intermediate-pressure cylinder, and a low-pressure economizer, an inlet end and an outlet end of the first low-pressure heater being respectively connected to an inlet end of the low-pressure economizer, an inlet end and an outlet end of the second low-pressure heater being respectively connected to an outlet end of the low-pressure economizer, characterized in that, It includes the following steps: Step S1: Set the minimum operating value of the inlet water temperature of the low-pressure economizer, and detect in real time the inlet water temperature of the low-pressure economizer, and the outlet water temperatures at the inlet and outlet ends of the first low-pressure heater; Step S2: Determine whether the inlet water temperature of the low-pressure economizer is greater than or equal to the minimum operating value; If not, adjust the water inlet ratio of the inlet and outlet ends of the first low-pressure heater entering the low-pressure economizer until the inlet water temperature of the low-pressure economizer is greater than or equal to the minimum operating value; If so, maintain the current water inlet ratio; Step S3: Obtain the unit load in real time, and adjust the flow rate ratios of the outlet water of the low-pressure economizer entering the inlet and outlet ends of the second low-pressure heater respectively according to the unit load, and at the same time adjust the extraction steam amount of the second low-pressure heater from the intermediate pressure cylinder, where the flow rate ratios are 0-100%.

2. The intelligent operation control method based on the flue gas waste heat cascade utilization system according to claim 1, characterized in that, The specific adjustment method of the water inlet ratio is as follows: Increase the water flow rate from the outlet end of the first low-pressure heater to the low-pressure economizer; or Reduce the water flow rate from the inlet end of the first low-pressure heater to the low-pressure economizer; Or Increase the water flow rate from the outlet end of the first low-pressure heater to the low-pressure economizer while reducing the water flow rate from the inlet end of the first low-pressure heater to the low-pressure economizer.

3. The intelligent operation control method based on the flue gas waste heat cascade utilization system according to claim 1, characterized in that Obtain the unit load in real time, and adjust the flow rate ratios of the outlet water of the low-pressure economizer entering the inlet and outlet ends of the second low-pressure heater respectively according to the unit load, specifically as follows: Step S 31 , obtain the unit load in real time; Step S 32 , determine whether the unit load meets a preset range; If so, adjust the flow rate ratio of the outlet water of the low-pressure economizer entering the inlet end of the second low-pressure heater to decrease until it is 0%, and adjust the flow rate ratio of the outlet water of the low-pressure economizer entering the outlet end of the second low-pressure heater to increase until it is 100%; If not, adjust the flow rate ratio of the outlet water of the low-pressure economizer entering the inlet end of the second low-pressure heater to increase until it is 100%, and adjust the flow rate ratio of the outlet water of the low-pressure economizer entering the outlet end of the second low-pressure heater to decrease until it is 0%.

4. The intelligent operation control method based on the flue gas waste heat cascade utilization system according to claim 3, characterized in that, The judgment steps of the preset range are specifically as follows: Calculate the average value of the condensate water temperature at the outlet end and the condensate water temperature at the inlet end of the second low-pressure heater; Determine whether the outlet water temperature of the low-pressure economizer is greater than or equal to the average value; If so, determine that the unit load meets the preset range; If not, determine that the unit load does not meet the preset range.

5. The intelligent operation control method for the flue gas waste heat cascade utilization system according to claim 3, characterized in that The minimum value of the preset range is greater than 50%.

6. The intelligent operation control method for the flue gas waste heat cascading utilization system according to claim 1, characterized in that Obtain the unit load in real time, and adjust the flow rate ratios of the outlet water of the low-pressure economizer entering the inlet and outlet ends of the second low-pressure heater respectively according to the unit load, specifically as follows: Step S 31 Obtain the unit load in real time; Step S 32 Based on a preset rule, when the unit load is higher than a preset range, reduce the flow rate of the outlet water of the low-pressure economizer entering the inlet end of the second low-pressure heater, and increase the flow rate of the outlet water of the low-pressure economizer entering the outlet end of the second low-pressure heater until the unit load meets the preset range; When the unit load is lower than the preset range, increase the flow rate of the outlet water of the low-pressure economizer entering the inlet end of the second low-pressure heater, and reduce the flow rate of the outlet water of the low-pressure economizer entering the outlet end of the second low-pressure heater until the unit load meets the preset range.

7. The intelligent operation control method based on the cascade utilization system of flue gas waste heat according to claim 1, wherein It also includes the discrimination process of the outlet flue gas temperature of the low-pressure economizer: Monitor the outlet flue gas temperature of the low-pressure economizer in real time; Determine whether the outlet flue gas temperature is lower than the acid dew point warning value, where the acid dew point warning value is greater than the value of the acid dew point, and the acid dew point is the temperature at which the low-pressure economizer produces low-temperature corrosion; If so, reduce the inlet water flow rate of the low-pressure economizer based on the water inlet ratio.

8. The intelligent operation control method based on the flue gas waste heat cascade utilization system according to claim 1, characterized in that The flue gas waste heat cascade utilization system further includes a third low-pressure heater connected to the second low-pressure cylinder and / or the first low-pressure cylinder, and a fourth low-pressure heater connected to the intermediate-pressure cylinder. The third low-pressure heater is arranged between the first low-pressure heater and the second low-pressure heater, and the fourth low-pressure heater is arranged at the outlet end of the second low-pressure heater. The first low-pressure heater, the second low-pressure heater, the third low-pressure heater, and the fourth low-pressure heater form a low-pressure heating flow path; The method further includes: adjusting the condensate flow rate flowing in the low-pressure heating flow path and the condensate flow rate flowing through the low-pressure economizer based on the load; When the unit load is lower than the preset range, reduce the condensate flow rate entering the low-pressure economizer and increase the condensate flow rate entering the low-pressure heating flow path until the unit load meets the preset range; When the unit load is higher than the preset range, increase the condensate flow rate entering the low-pressure economizer and reduce the condensate flow rate entering the low-pressure heating flow path until the unit load meets the preset range.

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