A load shedding method for power grid of a dual-series coal chemical production process enterprise

Abstract

The present invention proposes a load shedding method for the power grid of a dual-series coal chemical production process enterprise, including: step 1, classifying different process load intervals according to whether the dual-series operation is carried out and the degree of influence on the production process; step 2, classifying the loads in each load interval according to the complexity of the production process interlocking, and arranging all load intervals in order of priority; step 3, calculating the load that can be cut in each level according to the classification results; calculating the load that needs to be cut according to the power before the tripping of the section connected with the large power grid; step 4, combining the power shortage that the enterprise power grid can bear, comparing the load that needs to be cut with the load that can be cut in each level, and selecting the load that can be cut in accordance with the principle of under-cutting in an accumulative manner to perform the cutting operation. This method does not require manual intervention, and can maximize the guarantee of the continuous safe and stable operation of the power grid and production process of the coal chemical enterprise after the sudden disconnection from the large power grid, effectively reducing economic losses and improving economic benefits.

Description

Technical Field

[0001] The present invention relates to the field of frequency control of coal chemical power systems, and in particular to a grading and automatic precise load shedding method applicable to a power grid of a dual-series coal chemical production process enterprise. Background Art

[0002] At present, the power grid of coal chemical enterprises is generally weakly connected to the large power grid, and mainly powered by self-provided units. Once the power grid of coal chemical enterprises is disconnected from the large power grid, it is easy to cause power shortages of varying degrees in the chemical system process under the isolated grid. If effective measures are not taken, it will cause a chain reaction such as rapid drop in frequency and voltage, and in severe cases, it will cause unit tripping and uncontrolled shutdown of production lines due to power outages. The restart time after abnormal shutdown is long, and the economic losses are huge. In addition, the shutdown of the entire plant caused by sudden failures of coal-to-gas or coal-to-oil production lines may also cause other secondary accidents, such as equipment damage, raw material leakage and environmental pollution, and even fire, explosion, personal injury and other serious consequences. The current response measures often adopt the method of manual emergency command and processing, that is, when the grid is disconnected under various conditions, the dispatcher will manually cut off the load step by step on the spot according to the system operation status at that time through manual instructions. The problems of the above method are: (1) The response speed is too slow; (2) It is difficult to achieve power balance by cutting off the power supply of the chemical area, which is easy to cause over-cutting behavior and power and frequency swing oscillation; (3) It is easy to send wrong instructions and misoperation under tense conditions, which further deteriorates the system. In fact, the load reduction operation implemented by human judgment and issuing instructions lacks scientific accuracy and cannot meet the requirements of stable operation of the system. Therefore, the research on the reasonable solution of the safety problems of units and chemical production systems under sudden grid disconnection with the large power grid has positive and far-reaching significance.

[0003] At present, both large power grids and enterprise power grids have precedents of using control systems to solve power grid frequency problems. However, no solutions have been proposed for frequency problems and chemical series process shutdown problems that may be caused by sudden disconnection of coal chemical enterprise power grids from large power grids. Summary of the invention

[0004] The purpose of the present invention is to provide a load shedding method for the power grid of a dual-series coal chemical production process enterprise, which can solve the problem of sudden disconnection of the power grid of a coal chemical enterprise which is weakly connected to the large power grid and mainly powered by self-provided units, resulting in unit tripping and production process shutdown caused by low frequency and low voltage of the isolated grid, through a method of automatic and accurate load shedding in stages and levels.

[0005] In order to achieve the above objectives, the technical solutions adopted in this application are as follows:

[0006] A method for shedding load of a power grid applicable to a dual-series coal chemical production process enterprise comprises the following steps:

[0007] Step 1: Classification of cuttable loads: According to whether the coal chemical production process is operated in dual series, the load intervals of different processes are divided into m levels in order of the degree of influence on the coal chemical production process from small to large, and the i-th level is represented by D i (i=1-m);

[0008] Step 2: Classification of cuttable loads: According to the order of interlocking complexity of coal chemical production process from small to large, the load is divided into n levels in each load interval, where the i-th level and the j-th level are represented as: M ij (i=1~m, j=1~n), the corresponding load power that can be cut is Pkq ij (i = 1 ~ m, j = 1 ~ n), all load intervals are arranged in order of priority;

[0009] Step 3: Calculation of load shedding: Calculate the shedding load in each level according to the grading results. The total shedding load in the ith level is: According to the power before tripping of the section connected with the large power grid, calculate the load shedding amount Pxq;

[0010] Step 4: Select the load that can be cut: Combine the power shortage Pset that the grid can bear, compare the load that needs to be cut Pxq with the load that can be cut in each gear, and select the load that can be cut in a certain gear D. i , then in the first gear D1 to the gear D i Within the range, the shelving load is selected in a cumulative manner according to the under-cutting principle to perform the shedding operation.

[0011] Furthermore, in step 1, according to whether the coal chemical production process is operated in dual series, and according to the degree of influence on the coal chemical production process, the method for grading different process load intervals is as follows:

[0012] (1) When the operating condition is dual-series operation, the load shedding is divided into 5 levels D1 to D5, namely: dual-series operation to protect dual-series level, dual-series operation to protect single-series level, dual-series operation to protect public system level, dual-series operation to protect public system + sequentially cutting off some plant and station levels, and chemical dual-series operation to protect thermal power system level;

[0013] (2) When the operating condition is single series operation, the load shedding is divided into 4 levels D1~D4, namely: single series operation to protect the single series level, single series operation to protect the public system level, single series operation to protect the public system + sequentially cutting off some power stations level, and single series operation to protect the thermal power system level.

[0014] Furthermore, the dual series operation maintains the dual series gear position, and after the partial load is removed, the dual series process continues to produce without affecting it, but only affects the production efficiency;

[0015] The double series operation guarantees a single series gear, and on the basis of the load shedding of the double series operation guarantees a double series gear, after cutting off part of the load of any series, it will not affect the production of the other series process, and the series process whose load is cut off can maintain the operation of the public system;

[0016] The dual-series operation guarantees the public system gear position. On the basis of the load that can be cut at the dual-series operation guarantee single-series gear position, after cutting off part of the load of the remaining series, the public system operation of the two series processes is not affected. The two series resume operation within the preset time, and the loss of intermediate products in the production process is small.

[0017] The dual-series operation guarantees the public system + sequentially cuts off some plant and station gears. On the basis of the load that can be cut off in the dual-series operation guarantee single-series gear, all loads of some specific plants and stations are cut off, and only the basic operation load of the public system of the two series of processes is maintained. Even if the two series resume operation within the preset time, the loss of intermediate products in the production process is relatively large;

[0018] The chemical industry's dual-series operation to protect the thermal power system gear position, on the basis of dual-series operation to protect the public system + sequentially cutting off part of the load that can be cut at the plant and station gear positions, further cuts off part of the load to maintain partial normal operation of the two series of process thermal power systems. The two series of processes have basically stopped, but the self-contained power plant can quickly resume operation within a certain period of time.

[0019] The single series operation guarantees the single series gear position. After the part of the load is removed, it does not affect the continuous production of the series process, but only affects the production efficiency;

[0020] The single series operation guarantees the public system gear. On the basis of the load shedding of the single series operation guarantee series gear, after cutting off part of the load of the series, the public system operation of the series process is not affected. The series resumes operation within the preset time, and the loss of intermediate products in the production process is small.

[0021] The single series operation to protect the public system + sequentially cut off some plant and station gears, on the basis of the load that can be cut off at the gear of the single series operation to protect the public system, cut off all the loads of some specific plants and stations, and only maintain the basic operating load of the public system of the series process. Even if the series resumes operation within the preset time, the loss of intermediate products in the production process is relatively large;

[0022] The single series operation to protect the thermal power system gear is based on the single series operation to protect the public system + sequentially cutting off some of the plant and station gears that can cut off the load, and then cutting off part of the load to only maintain the normal operation of part of the thermal power system of this series of processes. This series of processes has basically stopped, but the self-contained power plant can quickly resume operation within the preset time.

[0023] Furthermore, in step 4, the power shortage Pset that the power grid can bear is the upward frequency regulation capability of all self-provided units of the enterprise power grid at one time.

[0024] Furthermore, the step 4 also includes determining whether the power grid of the dual-series coal chemical production process enterprise is suddenly disconnected from the large power grid, and if so, performing load shedding operation, otherwise not performing load shedding operation.

[0025] Furthermore, the determination of whether the power grid of the dual-series coal chemical production process enterprise is suddenly disconnected from the large power grid is determined by a low-frequency auxiliary criterion: when the frequency is lower than the frequency threshold Fgl and the delay is greater than the time threshold Tgl, it is determined that the power grid of the dual-series coal chemical production process enterprise is suddenly disconnected from the large power grid.

[0026] Furthermore, the step 4 specifically includes:

[0027] Determine whether the required load shedding amount Pxq is within the range of [0, Pset]. If so, no load shedding is required. If not, compare the required load shedding amount with the load shedding amount under different load shedding gear levels to determine the corresponding load shedding gear. Then, perform load shedding control according to the load priority within the load shedding range included in the load shedding gear:

[0028] 1) If the difference between the load to be cut and the power shortage that the grid can bear is less than or equal to the total load that can be cut in the first gear D1 That is, Pxq-Pset<=Pkq1, then the maximum priority Nmax of the selected load is determined to be the first priority M of the load that can be cut. 1j Within the range, that is, Nmax <= M 1j ; Select the load interval Pkq by cumulative method 11 ~Pkq 1x (x=1~k,k<=n), until the total amount of load cut Pqq is greater than or equal to the load to be cut minus the power shortage that the power grid can bear, that is,

[0029] 2) If the difference between the load shedding amount and the power shortage that the grid can bear is greater than the (i-1)th level D (i-1) Total load that can be cut and less than or equal to the i-th level D i Total load that can be cut Pkq (i-1)<Pxq-Pset<=Pkq i , then determine the maximum priority Nmax of the selected load to be cut in the i-th gear. ij (j=1~n) range, that is, Nmax<=M ij (j=1~n); select load Pkq by accumulation 11 ~Pkq ix (x=1~k,k<=n), until the total amount of load cut Pqq is greater than or equal to the load to be cut minus the power shortage that the power grid can bear, that is,

[0030] After adopting the above plan, there are obvious effects:

[0031] (1) It can effectively solve the problem of sudden disconnection of the power grid of coal chemical enterprises with weak interconnection with the main power grid and self-provided power supply units, resulting in unit tripping and production process shutdown caused by low frequency and low voltage of isolated grid;

[0032] (2) Realize the safe and stable operation capability of the coal chemical enterprise power grid to automatically adapt to the dual-series and single-series operation modes of the coal chemical production process;

[0033] (3) Implement a method for grading and classifying the load that can be cut in the coal chemical enterprise power grid, which can minimize the impact on the coal chemical production process while cutting the load, and improve the coal chemical process's ability to continue to operate safely and stably in the event of a power grid accident;

[0034] (4) The coal chemical enterprise power grid can automatically, quickly and accurately cut off the phase power load, quickly reach a new power balance, ensure the minimum under-cutting of the load, improve the accuracy of frequency control, and facilitate the frequency recovery of the coal chemical enterprise power grid in the event of a sudden isolated network. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A flow chart of a load shedding method for a power grid of a dual-series coal chemical production process enterprise provided in an embodiment of the present application;

[0036] Figure 2 Logic diagram of the control algorithm for the automatic and precise load shedding method in different grading and classification of power grids in coal chemical enterprises. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0038] Figure 1The present invention provides a method for shedding load of a power grid of a dual-series coal chemical production process enterprise, including the following steps:

[0039] Step S1, the cuttable load classification link: according to whether the coal chemical production process is operated in dual series, the different process load intervals are divided into m grades according to the degree of influence on the coal chemical production process from small to large, and the i-th grade is represented by D i (i=1~m).

[0040] According to whether the coal chemical production process is operated in dual series, and according to the degree of influence on the coal chemical production process, the method of grading different process load intervals is as follows:

[0041] (1) When the operating condition is dual-series operation, the load shedding is divided into 5 levels D1 to D5, namely: dual-series operation to protect dual-series level, dual-series operation to protect single-series level, dual-series operation to protect public system level, dual-series operation to protect public system + sequentially cutting off some plant and station levels, and chemical dual-series operation to protect thermal power system level;

[0042] (2) When the operating condition is single series operation, the load shedding is divided into 4 levels D1~D4, namely: single series operation to protect the single series level, single series operation to protect the public system level, single series operation to protect the public system + sequentially cutting off some power stations level, and single series operation to protect the thermal power system level.

[0043] Step S2, grading of cuttable loads: According to the order of interlocking complexity of coal chemical production process from small to large, the load is divided into n levels in each load interval, where the i-th level and the j-th level are represented as: M ij (i=1~m, j=1~n), the corresponding load power that can be cut is Pkq ij (i=1~m, j=1~n).

[0044] Specifically, load classification is performed in each load interval, and the priority of the first load interval D1 is M 1j (j=1~n), the second gear D2 can cut the load interval priority is M 2j (j=1~n), the third gear D3 load shedding interval priority is M 3j (j=1~n), and so on, the i-th file D i The priority of the load shedding interval is M ij (i=1~m, j=1~n).

[0045] Step S3, calculation of load shedding: Calculate the shedding load in each level according to the grading results. The shedding load in the i-th level is The load shedding amount Pxq is calculated based on the power before the section connected to the large power grid trips.

[0046] Specifically, according to the cut-off load classification result in step S1 and the cut-off load classification result in step S2, the total cut-off load in the first level D1 is calculated as The total load that can be cut in the second gear D2 is calculated as The total load that can be cut in the third gear D3 is calculated as Calculate the D of the i-th gear i The total load that can be cut is Calculate the mth level D m The total load that can be cut is

[0047] Step S4, load shedding selection: Combined with the power shortage Pset that the power grid can bear, according to the comparison between the load shedding amount Pxq and the load shedding amount in each gear, select the load shedding in a certain gear D. i , then in the first gear D1 to the gear D i Within the range, according to the under-cutting principle, the shelving load is selected in an accumulative manner to perform shedding operations. Specifically include:

[0048] Determine whether the required load shedding amount Pxq is within the range of [0, Pset]. If so, no load shedding is required. If not, compare the required load shedding amount with the load shedding amount under different load shedding gear levels to determine the corresponding load shedding gear. Then, perform load shedding control according to the load priority within the load shedding range included in the load shedding gear:

[0049] 1) If the difference between the load to be cut and the power shortage that the grid can bear is less than or equal to the total load that can be cut in the first gear D1 That is, Pxq-Pset<=Pkq1, then the maximum priority Nmax of the selected load is determined to be the first priority M of the load that can be cut. 1j Within the range, that is, Nmax <= M 1j ; Select the load interval Pkq by cumulative method 11 ~Pkq 1x (x=1~k,k<=n), until the total amount of load cut Pqq is greater than or equal to the load to be cut minus the power shortage that the power grid can bear, that is,

[0050] 2) If the difference between the load shedding amount and the power shortage that the grid can bear is greater than the (i-1)th level D (i-1) Total load that can be cut and less than or equal to the i-th level D i Total load that can be cut Pkq (i -1) <Pxq-Pset<=Pkq i , then determine the maximum priority Nmax of the selected load to be cut in the i-th gear. ij(j=1~n) range, that is, Nmax<=M ij (j=1~n); select load Pkq by accumulation 11 ~Pkq ix (x=1~k,k<=n), until the total amount of load cut Pqq is greater than or equal to the load to be cut minus the power shortage that the power grid can bear, that is, like Figure 2 The figure shows the control algorithm logic diagram of the automatic and precise load shedding method in different grading and classification of the power grid of a coal chemical enterprise.

[0051] In a preferred embodiment, the power shortage Pset that the power grid can bear is the upward frequency regulation capability of all self-provided units of the enterprise power grid at one time.

[0052] In a preferred embodiment, step S4 further includes determining whether the power grid of the dual-series coal chemical production process enterprise is suddenly disconnected from the large power grid, and if so, performing a load shedding operation, otherwise not performing a load shedding operation. Determining whether the power grid of the dual-series coal chemical production process enterprise is suddenly disconnected from the large power grid is determined by a low-frequency auxiliary criterion: when the frequency is lower than the frequency threshold Fgl, and the delay is greater than the time threshold Tgl, it is determined that the power grid of the dual-series coal chemical production process enterprise is suddenly disconnected from the large power grid.

[0053] In some embodiments, a hard pressure plate is also provided as a condition for determining whether the coal chemical chemical series is in single-series operation or dual-series operation. By determining that the coal chemical chemical series is in single-series operation, the "single-series operation" hard pressure plate needs to be put in, and by determining that the chemical series is in dual-series operation, the "single-series operation" hard pressure plate needs to be withdrawn. In order to ensure the single-series operation of the chemical dual-series and minimize the impact on chemical production, it is determined manually based on the on-site situation that the "selected A series" hard pressure plate needs to be put in if the A series can be cut; and the "selected A series" hard pressure plate needs to be withdrawn if the B series can be cut.

[0054] In some embodiments, the dual series operation to protect the dual series gear, the dual series operation to protect the single series gear, the dual series operation to protect the public system gear, the dual series operation to protect the public system + sequentially cut off some plant and station gears, the chemical dual series operation to protect the thermal power system gear, the single series operation to protect the single series gear, the single series operation to protect the public system gear, the single series operation to protect the public system gear, the single series operation to protect the public system gear + sequentially cut off some plant and station gears, and the single series operation to protect the thermal power system gear are divided as follows:

[0055] Double series operation maintains double series gear position. After cutting off this part of the load, it will not affect the continued production of the double series process, but only affect the production efficiency.

[0056] Double-series operation guarantees single-series gear position. On the basis of the load shedding capability of double-series operation and double-series gear position, after part of the load of any series is cut off, it will not affect the continued production of the other series process, and the series process with the load cut off can maintain the operation of the public system.

[0057] The dual-series operation ensures the public system gear. On the basis of the load that can be cut at the dual-series operation single-series gear, after cutting off part of the load of the remaining series, the public system operation of the two series processes is not affected. The two series resume operation within the preset time, and the loss of intermediate products in the production process is small.

[0058] Double-series operation protects the public system + cuts off some plant and station gears in turn. On the basis of the load that can be cut by the double-series operation single-series gear, all the loads of some specific plants and stations are cut off, and only the basic operating load of the public system of the two series of processes is maintained. Even if the two series resume operation within the preset time, the loss of intermediate products in the production process will be large.

[0059] The chemical industry's dual-series operation maintains the thermal power system gear. On the basis of dual-series operation to protect the public system + sequentially cutting off some of the loads that can be cut off at the plant and station gears, another part of the load is cut off to maintain partial normal operation of the two series of process thermal power systems. The two series of processes have basically stopped, but the self-contained power plant can quickly resume operation within a certain period of time.

[0060] Single series operation guarantees the single series gear position. After cutting off this part of the load, it will not affect the continued production of this series of processes, but only affect the production efficiency;

[0061] Single series operation guarantees the public system gear. On the basis of the load shedding of the single series gear, after cutting off part of the load of the series, the public system operation of the series process is not affected. The series resumes operation within the preset time, and the loss of intermediate products in the production process is small.

[0062] Single series operation to protect the public system + sequentially cut off some plant and station gears. On the basis of the load that can be cut when the single series is operated to protect the public system gear, all loads of some specific plants and stations are cut off to only maintain the basic operating load of the public system of the series process. Even if the series resumes operation within the preset time, the loss of intermediate products in the production process is relatively large;

[0063] A single series of operations protects the thermal power system gear. On the basis of a single series of operations to protect the public system + sequentially cutting off some of the loads that can be cut off at the plant and station gears, another part of the load is cut off to maintain the normal operation of part of the thermal power system of this series of processes. This series of processes has basically stopped, but the self-contained power plant can quickly resume operation within the preset time.

[0064] The load shedding method of the present application is introduced below with a practical embodiment:

[0065] 1. Determine whether the coal chemical production process is in dual-series operation according to the state of the hard pressing plate, and then classify different process load intervals according to the production requirements and process limitations of the coal chemical production line and the degree of influence on the coal chemical production process;

[0066] According to the order of interlocking complexity of coal chemical production process from small to large, the loads are graded in each load interval, and all load intervals are arranged in order of priority;

[0067] The results of the grading are:

[0068] (1) When the operating condition is dual-series operation, the load shedding is divided into 5 levels D1~D5, namely: D1 level chemical dual-series operation to protect dual series (priority 1~80), D2 level chemical dual-series operation to protect single series (priority 1~250), D3 level chemical dual-series operation to protect public system (priority 1~400), D4 level chemical dual protection public + sequentially cut 10kV phenol recovery, methanation, purification device (priority 1~410), D5 level chemical dual-series operation to protect thermal power system (priority 1~420).

[0069] (2) When the operating condition is single series operation, the load shedding is divided into 4 levels D1~D4, namely: D1 level chemical single series operation to protect the single series (priority 1~80), D2 level chemical single series operation to protect the public system (priority 1~400), D3 level chemical single series to protect the public + sequentially cut off 10kV phenol recovery, methanation, and purification devices (priority 1~410), D4 level chemical single series operation to protect the thermal power system (priority 1~420).

[0070] 2. According to the classification results, the load that can be cut in each level is summarized, and according to the operation status of the chemical process series,

[0071] (1) There are 5 load shedding gears when the chemical double series is running. The total load shedding capacity of the first gear is The total load shedding capacity of the second gear is The load that can be cut in the third gear is The load that can be cut in the 4th gear is The load that can be cut in the 5th gear is

[0072] (2) When the chemical single series is running, there are 4 load shedding gears. The total load shedding capacity of the first gear is The total load shedding capacity of the second gear is The load that can be cut in the third gear is The load that can be cut in the 4th gear is

[0073] 3. Calculate the load shedding amount Pxq based on the power before the tripping of the interconnection section with the large power grid; then compare the load shedding amount Pxq with the load shedding amount in each gear based on the power shortage Pset that the enterprise power grid can bear, and select the load shedding amount in a certain gear D. i , then in the first gear D1 to the gear D iWithin the range, according to the under-cutting principle, the shelving load is selected in an accumulative manner to perform shedding operations. Specifically include:

[0074] Determine whether the required load shedding amount Pxq is within the range of [0, Pset]. If so, no load shedding is required. If not, compare the required load shedding amount with the load shedding amount under different load shedding gear levels to determine the corresponding load shedding gear. Then, perform load shedding control according to the load priority within the load shedding range included in the load shedding gear:

[0075] If the difference between the load to be cut and the power shortage that the power grid can bear is less than or equal to the total load Pkq1 of the first gear D1 that can be cut, that is, Pxq-Pset<=Pkq1, then the maximum priority Nmax of the selected load to be cut is within the range of 80 of the first gear that can be cut, that is, Nmax<=80; the load interval Pkq is selected by accumulation. 11 ~Pkq 1x (x<=80), until the total amount of load cut Pqq is greater than or equal to the load to be cut minus the power shortage that the power grid can bear, that is, And so on.

[0076] 4. When the above load is cut to the last level to protect the thermal power system, the specific method is to take decoupling measures to ensure that the single unit thermal power system and some non-cuttable loads are protected, including ensuring that the 35kV gasification unit oil transformer, 35kV thermal power cycle water oil transformer, and 10kV air separation station incoming line cannot be cut off;

[0077] 5. When selecting load shedding in the D2 gear of the dual series operation, it is required that the shedding load interval of the chemical series A or B can be selected according to the coal chemical operation conditions;

[0078] 6. When the load interval of the 10kV three-level pump station in the above D1 file is cut off, its two 35kV side incoming power supplies must be cut off at the same time;

[0079] 7. When the 10kV phenol recovery, methanation, purification and gasification devices in the above-mentioned dual-series D4 gear and single-series D3 gear are cut off, due to the quick cut-off of their 10kV incoming power supplies, the two 35kV side incoming power supplies corresponding to each load substation need to be cut off at the same time.

[0080] 8. When the 10kV sewage treatment, gasification circulating water, purification circulating water, thermal power circulating water and air separation circulating water in the above-mentioned dual-series D5 gear and single-series D4 gear are cut off, due to the quick cutting of their 10kV incoming power supply, the two 35kV side incoming power supplies corresponding to each load substation need to be cut off at the same time.

Claims

1. A load shedding method for a power grid of a dual-series coal chemical production process enterprise, characterized in that: The steps include: Step 1: Classification of cuttable loads: According to whether the coal chemical production process is operated in dual series, the load intervals of different processes are divided into m levels in order of the degree of influence on the coal chemical production process from small to large, and the i-th level is represented by D i (i=1-m); specifically as follows: (1) When the operating condition is dual-series operation, the load shedding is divided into 5 levels D1 to D5, namely: dual-series operation to protect dual-series level, dual-series operation to protect single-series level, dual-series operation to protect public system level, dual-series operation to protect public system + sequentially cutting off some plant and station levels, and chemical dual-series operation to protect thermal power system level; (2) When the operating condition is single series operation, the load shedding is divided into 4 gears D1 to D4, namely: single series operation to protect the single series gear, single series operation to protect the public system gear, single series operation to protect the public system + sequentially cut off some power stations gear, single series operation to protect the thermal power system gear; Step 2: Classification of cuttable loads: According to the order of interlocking complexity of coal chemical production process from small to large, the load is divided into n levels in each load interval, where the i-th level and the j-th level are represented as: M ij (i=1~m, j=1~n), the corresponding load power that can be cut is Pkq ij (i = 1 ~ m, j = 1 ~ n), all load intervals are arranged in order of priority; Step 3: Calculation of load shedding: Calculate the shedding load in each level according to the grading results. The total shedding load in the ith level is: According to the power before tripping of the section connected with the large power grid, calculate the load shedding amount Pxq; Step 4: Select the load that can be cut: Combine the power shortage Pset that the grid can bear, compare the load that needs to be cut Pxq with the load that can be cut in each gear, and select the load that can be cut in a certain gear D. i , then in the first gear D1 to the gear D i Within the range, according to the under-cutting principle, the shelving load is selected in an accumulative manner to perform shedding operation; specifically, the following are included: Determine whether the required load shedding amount Pxq is within the range of [0, Pset]. If so, no load shedding is required. If not, compare the required load shedding amount with the load shedding amount under different load shedding gear levels to determine the corresponding load shedding gear. Then, perform load shedding control according to the load priority within the load shedding range included in the load shedding gear: 1) If the difference between the load to be cut and the power shortage that the grid can bear is less than or equal to the total load that can be cut in the first gear D1 That is, Pxq-Pset<=Pkq1, then the maximum priority Nmax of the selected load is determined to be the first priority M of the load that can be cut. 1j Within the range, that is, Nmax <= M 1j ; Select the load interval Pkq by cumulative method 11 ~Pkq 1x (x=1~k,k<=n) until the selected total load removal Pqq is greater than or equal to the load to be removed minus the power shortage that the power grid can bear, that is, 2) If the difference between the load shedding amount and the power shortage that the grid can bear is greater than the (i-1)th level D (i-1) Total load that can be cut and less than or equal to the i-th level D i Total load that can be cut Pkq (i-1) <Pxq-Pset<=Pkq i , then determine the maximum priority Nmax of the selected load to be cut in the i-th gear. ij (j=1~n) range, that is, Nmax<=M ij (j=1~n); select load Pkq by accumulation 11 ~Pkq ix (x=1~k,k<=n), until the total amount of load cut Pqq is greater than or equal to the load to be cut minus the power shortage that the power grid can bear, that is, 2. The load shedding method according to claim 1, characterized in that: The dual series operation maintains the dual series gear position, and after cutting off part of the load, it does not affect the continuous production of the dual series process, but only affects the production efficiency; The double series operation guarantees a single series gear, and on the basis of the load shedding of the double series operation guarantees a double series gear, after cutting off part of the load of any series, it will not affect the production of the other series process, and the series process whose load is cut off can maintain the operation of the public system; The dual-series operation guarantees the public system gear position. On the basis of the load that can be cut at the dual-series operation guarantee single-series gear position, after cutting off part of the load of the remaining series, the public system operation of the two series processes is not affected. The two series resume operation within the preset time, and the loss of intermediate products in the production process is small. The dual-series operation guarantees the public system + sequentially cuts off some plant and station gears. On the basis of the load that can be cut off in the dual-series operation guarantee single-series gear, all loads of some specific plants and stations are cut off, and only the basic operation load of the public system of the two series of processes is maintained. Even if the two series resume operation within the preset time, the loss of intermediate products in the production process is relatively large; The chemical industry double series operation protection thermal power system gear position, on the basis of double series operation protection public system + sequentially cutting off part of the load that can be cut at the plant and station gear position, cut off part of the load, only maintain the normal operation of part of the thermal power system of the two series process, the two series process has basically stopped, but the self-provided power plant can quickly resume operation within a certain period of time; The single series operation guarantees the single series gear position. After the part of the load is removed, it does not affect the continuous production of the series process, but only affects the production efficiency; The single series operation guarantees the public system gear. On the basis of the load shedding of the single series operation guarantee series gear, after cutting off part of the load of the series, the public system operation of the series process is not affected. The series resumes operation within the preset time, and the loss of intermediate products in the production process is small. The single series operation to protect the public system + sequentially cut off some plant and station gears, on the basis of the load that can be cut off at the gear of the single series operation to protect the public system, cut off all the loads of some specific plants and stations, and only maintain the basic operating load of the public system of the series process. Even if the series resumes operation within the preset time, the loss of intermediate products in the production process is relatively large; The single series operation to protect the thermal power system gear is based on the single series operation to protect the public system + sequentially cutting off some of the plant and station gears that can cut off the load, and then cutting off part of the load to only maintain the normal operation of part of the thermal power system of this series of processes. This series of processes has basically stopped, but the self-contained power plant can quickly resume operation within the preset time.

3. The load shedding method according to claim 1, characterized in that: In step 4, the power shortage Pset that the power grid can bear is the upward frequency regulation capability of all self-provided units of the enterprise power grid at one time.

4. The load shedding method according to claim 1, characterized in that: The step 4 also includes determining whether the power grid of the dual-series coal chemical production process enterprise is suddenly disconnected from the large power grid, and if so, performing a load shedding operation, otherwise not performing a load shedding operation.

5. The load shedding method according to claim 4, characterized in that: The determination of whether the dual-series coal chemical production process enterprise power grid is suddenly disconnected from the large power grid is determined by a low-frequency auxiliary criterion: when the frequency is lower than the frequency threshold Fgl and the delay is greater than the time threshold Tgl, it is determined that the dual-series coal chemical production process power grid is suddenly disconnected from the large power grid.

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