A dual-system steam pipe network for a large combined device and its balancing method

Abstract

The present application discloses a dual-system steam pipe network for a large combined device and its balancing method, belonging to the technical field of thermal energy of the steam system in chemical plants. Both the first system and the second system of the present invention are steam pipe networks with multiple pressure levels; the first system includes a first steam pipeline, a second steam pipeline, a third steam pipeline, a fourth steam pipeline, and a fifth steam pipeline with pressures decreasing from large to small; the second system includes a first post-constructed steam pipeline, a second post-constructed steam pipeline, a third post-constructed steam pipeline, a fourth post-constructed steam pipeline, and a fifth post-constructed steam pipeline corresponding to the pressures of the first system one by one; among them, the high-pressure and low-low-pressure pipe networks of the first system and the second system are interconnected to form a dual system, and the medium-pressure and low-pressure steam pipe networks corresponding to the first system and the second system are not interconnected with the existing steam pipe networks of the same level; the pressure fluctuation of the steam pipe network in the present application can be controlled within the allowable range of the device compressor and the steam used in the device process, and the device operates stably.

Description

Technical Field

[0001] This application relates to the technical field of thermal energy of steam systems in chemical plants, and particularly relates to a dual-system steam pipe network for a large combined plant and its balancing method. Background Technique

[0002] Most chemical plants use steam as the power to drive turbines, which is more energy-efficient than motors and has more stable operation control. The production of olefins from coal through methanol and the downstream products of olefin production are the most representative industrial routes in modern coal chemical industry, and they developed rapidly as demonstration projects during the 12th Five-Year Plan period. This route has a long process flow, many unit plants, many power equipment involved, and high energy consumption.

[0003] According to the demonstration effect and technical improvement during the 13th Five-Year Plan, the balance of the steam pipe network has been improved to a certain extent, which can meet the stable operation of each steam-consuming device. However, the system energy conservation has not been improved, and there are problems such as poor cascade utilization of steam, rich low-temperature waste heat, and large steam consumption.

[0004] From the actual operation of the steam pipe network, there are also problems such as insufficient balance ability of the steam pipe network to adapt to multi-condition operation, large consumption of high-grade steam, large surplus of low-grade steam, and low overall energy efficiency of the pipe network. Summary of the Invention

[0005] Embodiments of the present invention provide a dual-system steam pipe network for a large combined plant and its balancing method, which solve the problems in the prior art such as insufficient balance ability of the steam pipe network to adapt to multi-condition operation, large consumption of high-grade steam, large surplus of low-grade steam, and low overall energy efficiency of the pipe network. In normal conditions, the balance of each level of the steam pipe network is self-regulated by process means in the embodiments of the present invention. In abnormal conditions, it is adjusted by a desuperheater and pressure reducer. The rich saturated steam produced by methanol synthesis is used as the heat source for the high-pressure boiler feed water heater of the boiler. The steam balance rate of each level of the pipe network during normal operation reaches more than 99.5%, the opening of the desuperheater and pressure reducer is less than 5%, and the pressure fluctuation of the steam pipe network can be controlled within the allowable range of the device compressor and the device process steam consumption, and the device operates stably.

[0006] In a first aspect, embodiments of the present invention provide a dual-system steam pipe network for a large combined plant, including a first system and a second system;

[0007] The first system includes a first steam pipeline, a second steam pipeline, a third steam pipeline, a fourth steam pipeline, and a fifth steam pipeline with decreasing pressure in sequence;

[0008] The second system includes a first post-constructed steam pipeline, a second post-constructed steam pipeline, a third post-constructed steam pipeline, a fourth post-constructed steam pipeline, and a fifth post-constructed steam pipeline that correspond to the steam pipelines of the first system one by one and have decreasing pressure in sequence;

[0009] The first steam pipeline is communicated with the first post-built steam pipeline, and the fifth steam pipeline is communicated with the fifth post-built steam pipeline;

[0010] A first steam-consuming equipment group and a plurality of desuperheating and pressure-reducing valve groups are connected between the first steam pipeline and the second steam pipeline, and a second steam-consuming equipment group and a desuperheating and pressure-reducing valve group are connected between the second steam pipeline and the fourth steam pipeline; A third steam-consuming equipment group is connected between the first steam pipeline and the fourth steam pipeline; The third steam pipeline is connected to the fourth steam pipeline; A fourth steam-consuming equipment group is arranged between the first steam pipeline and the fifth steam pipeline; The outlet end of a desuperheating and pressure-reducing valve group on the first steam pipeline is also connected to the fifth steam pipeline;

[0011] The fourth steam pipeline is connected to the boiler deaeration system, and the fourth steam-consuming equipment group is also connected to the boiler deaeration system, and the boiler deaeration system is connected to the first steam pipeline; A desuperheating and pressure-reducing valve group is connected between the fourth steam pipeline and the fifth steam pipeline;

[0012] A first post-built steam-consuming equipment group and a desuperheating and pressure-reducing valve group are connected between the first post-built steam pipeline and the second post-built steam pipeline; A second post-built steam-consuming equipment group and a desuperheating and pressure-reducing valve group are connected between the second post-built steam pipeline and the fourth post-built steam pipeline; A third post-built steam-consuming equipment group is connected between the second post-built steam pipeline and the fifth post-built steam pipeline; The third post-built steam pipeline is connected to the outlet end of a desuperheating and pressure-reducing valve group on the second post-built steam pipeline, and the outlet end of the third post-built steam pipeline is also connected to the post-built boiler deaeration system, the outlet end of the fourth post-built steam pipeline is also connected to the post-built boiler deaeration system, the post-built boiler deaeration system is connected to the first post-built steam pipeline, and a desuperheating and pressure-reducing valve group is connected between the fourth post-built steam pipeline and the fifth post-built steam pipeline.

[0013] In combination with the first aspect, in a possible implementation manner, the first steam-consuming equipment group connected between the first steam pipeline and the second steam pipeline includes an air separation compressor; The second steam-consuming equipment group connected between the second steam pipeline and the fourth steam pipeline includes a propylene refrigeration compressor and a DMTO reaction gas compressor; The third steam-consuming equipment group connected between the first steam pipeline and the fourth steam pipeline is a DMTO propylene compressor; The fourth steam-consuming equipment group connected between the first steam pipeline and the fifth steam pipeline is a generator set.

[0014] In combination with the first aspect, in a possible implementation manner, the third steam pipeline is a methanol synthesis rich medium-pressure saturated steam pipeline.

[0015] In combination with the first aspect, in a possible implementation manner, the first group of steam-consuming equipment connected between the first post-built steam pipeline and the second post-built steam pipeline includes an air separation compressor, a DMTO propylene compressor, and a methanol plant synthesis compressor;

[0016] The second group of steam-consuming equipment connected between the second post-built steam pipeline and the fourth post-built steam pipeline includes: a methanol boiler feed pump directly connecting the second post-built steam pipeline and the fourth post-built steam pipeline, and also includes a methanol plant flue gas fan, a methanol plant air fan, and a methanol plant purified gas compressor that are only connected to the second post-built steam pipeline;

[0017] The third group of steam-consuming equipment includes a DMTO reaction gas compressor and a propylene chiller connected between the second post-built steam pipeline and the fifth post-built steam pipeline.

[0018] In combination with the first aspect, in a possible implementation manner, the third post-built steam pipeline is located between the fourth post-built steam pipeline and the fifth post-built steam pipeline.

[0019] In combination with the first aspect, in a possible implementation manner, an electric valve and a bidirectional flowmeter are connected between the first steam pipeline and the first post-built steam pipeline, and an electric valve and a bidirectional flowmeter are connected between the fifth steam pipeline and the fifth post-built steam pipeline.

[0020] In a second aspect, an embodiment of the present invention provides a method for balancing a dual-system steam pipe network of a large combined device, based on the dual-system steam pipe network of any one of the above.

[0021] The first steam pipeline and the first post-built steam pipeline are adjusted through interconnection; the interconnection adjustment amount is the steam output of a single boiler;

[0022] The second post-built steam pipeline is adjusted by extracting steam in the form of extraction condensation by an air separation compressor, a methanol combined device compressor unit, and a DMTO propylene compressor, that is, the first post-built steam pipeline extracts steam by doing work and condenses and extracts the steam to the second post-built steam pipeline for steam adjustment;

[0023] The balance of the fourth post-built steam pipeline is adjusted by the load of the methanol plant conversion unit, that is, the steam volume of the fourth post-built steam pipeline is adjusted by operating the load for pipe network adjustment;

[0024] The balance of the fifth post-built steam pipeline steam pipe network is adjusted by extracting steam in the form of extraction condensation by the propylene chiller and the DMTO reaction gas compressor; that is, the second post-built steam pipeline extracts steam by doing work and condenses and extracts the steam to adjust the low-pressure steam.

[0025] Combined with the second aspect, in a possible implementation, under normal conditions, the boiler, power equipment, and process equipment adjust the operating load, and adjust the steam production balance through the interconnection, intercommunication, and mutual supply of steam between the first system and the second system;

[0026] Under abnormal conditions, it is adjusted by means of the desuperheating and pressure reducing valve. The opening of the desuperheating and pressure reducing valve is used to achieve the steam balance of each grade of pipe network.

[0027] Combined with the second aspect, in a possible implementation, the automatic adjustment under normal conditions is based on the full load of the process equipment. When the balance of any grade of steam pipe network changes, the system collects pressure signals and feeds them back to the preset priority order to adjust the balance of steam supply and production; the valves for the interconnection and intercommunication of the dual systems are set to be normally open, and the connected pipe network can achieve the balance between each pipeline through pressure;

[0028] The priority order is as follows: First, adjust the extraction steam volume of the steam-using equipment unit. When the extraction steam volume cannot be balanced, secondly, adjust the load of the process equipment to balance the process steam consumption, and then act on the steam-using equipment unit again; when the adjustable range of the steam-using equipment unit is exhausted, the pipe network is fed back from the fifth steam pipeline to the first steam pipeline level by level, and is fed back from the fifth newly built steam pipeline to the first newly built steam pipeline level by level; at this time, adjust the balance of the first steam pipeline and the first newly built steam pipeline through the boiler operating load. If it is necessary to ensure that the boiler load is greater than 80%, the system will automatically stop the generator set from generating electricity to ensure the boiler operating load and stabilize the S1 steam pipe network;

[0029] The automatic control under abnormal conditions is that when the steam pipe network pressure exceeds the design range, the desuperheating and pressure reducing valve is automatically controlled through the change of the pipe network pressure, and the opening is used to return the steam pressure of each grade of pipe network to the design range to ensure the balance of the pipe network.

[0030] Combined with the second aspect, in a possible implementation, the balanced extraction steam volume of the second newly built steam pipeline is 50% ± 10% of the steam consumption of each corresponding compressor;

[0031] The balance of the fourth newly built steam pipeline is mainly adjusted by the operating load of the methanol unit, and the adjustment range is 20% of the balance of this grade of pipe network;

[0032] The steam adjustment compensation method for the fifth newly built steam pipeline is to set the extraction steam adjustment of the propylene refrigeration machine and the DMTO reaction gas compressor, and the extraction steam volume is 50% ± 10% of the corresponding compressor.

[0033] One or more technical solutions provided in the embodiments of the present invention have at least the following technical effects or advantages:

[0034] In an embodiment of the present invention, the second system is connected to the first system. The second system includes a first newly-built steam pipeline, a second newly-built steam pipeline, a fourth newly-built steam pipeline, and a fifth newly-built steam pipeline that correspond to the first system one by one. The first newly-built steam pipeline is communicated with the first steam pipeline, and the fifth newly-built steam pipeline is communicated with the fifth steam pipeline, realizing the interconnection and intercommunication of the highest and lowest two pressure grade pipe networks with the existing steam pipe network to form a dual system. The balance of each level of steam pipe network in normal operation is self-regulated by process means, and in abnormal conditions, it is regulated by a desuperheating and pressure reducing valve. The saturated steam rich in methanol synthesis in the newly-built system is used as the heat source for the high-pressure boiler feed water heater of the boiler, reducing the limited regulation ability of the second steam pipeline in the first system, the inefficiency of using the third steam pipeline, the excessive regulation of the fifth steam pipeline, the insufficient self-balancing ability of the third steam pipeline in the small methanol system, which has a counterproductive impact on the large consumption of the first steam pipeline, and the lack of close combination of the second steam pipeline and the fourth steam pipeline with the process steam production and use. Finally, it is reflected in the large consumption of the first steam pipeline, the start-up and high-load operation of the desuperheating and pressure reducing valve under normal conditions, insufficient power generation, the long-term surplus of the fifth steam pipeline, the inefficiency of the pipe network, and the poor pipe network regulation and balance ability. The interconnection and intercommunication between the first steam pipeline and the first newly-built steam pipeline of the dual system, and the interconnection and intercommunication between the fifth steam pipeline and the fifth newly-built steam pipeline are realized, ensuring the anti-balance ability of the system. The second steam pipeline and the second newly-built steam pipeline are not interconnected, and the fourth steam pipeline and the fourth newly-built steam pipeline are not interconnected. The second steam pipeline and the second newly-built steam pipeline drive more small turbines and belong to a small and short system pipe network. Its operation stability is mainly controlled by its own system, that is, it coincides with the working conditions of its own system process device. After connection, it will disrupt its own operation instead, posing a greater safety risk; the fourth newly-built steam pipeline is for process steam use, and the system pipe network has a strong anti-fluctuation ability. In addition, considering that the dual system does not start and stop simultaneously, by adjusting the steam production scale of methanol conversion and adjusting the methanol steam conversion boiler feed water turbine to back pressure (the second newly-built steam pipeline - the fourth newly-built steam pipeline), the stability of the system can be guaranteed. At the same time, the connection of the fifth steam pipeline and the fifth newly-built steam pipeline of the dual system can also act on the fourth steam pipeline and the fourth newly-built steam pipeline of the dual system to tend to be stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for describing the embodiments of the present invention 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.

[0036] Figure 1 It is a schematic structural diagram of the dual-system steam pipe network of the large-scale combined device of the present invention.

[0037] Icons: 1 - First system; 2 - Second system; 3 - Interconnection point of high-pressure steam pipelines; 4 - Interconnection point of low-low-pressure steam pipelines. Detailed implementation manners

[0038] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. 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 based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] In the description of the embodiments 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 accompanying drawings, and is only for the convenience of describing the embodiments of 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 of the present invention. The terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance. In addition, the terms "installed", "connected", "connected" 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 or 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 embodiments of the present invention can be understood according to specific circumstances.

[0040] Referring to Figure 1 As shown, the embodiments of the present invention disclose a dual-system steam pipe network for a large combined device, including a first system 1 and a second system 2;

[0041] The first system 1 includes a first steam pipeline S1, a second steam pipeline S2, a third steam pipeline S3, a fourth steam pipeline S4, and a fifth steam pipeline S5 with pressures decreasing in turn;

[0042] The second system 2 includes a first post-constructed steam pipeline S1', a second post-constructed steam pipeline S2', a third post-constructed steam pipeline S3', a fourth post-constructed steam pipeline S4', and a fifth post-constructed steam pipeline S5' that correspond one by one to the steam pipelines of the first system and have pressures decreasing in turn;

[0043] The first steam pipeline S1 and the first post-constructed steam pipeline S1' are connected, and the specific connection point is Figure 1At the interconnection point 3 of the medium and high pressure steam pipelines, the fifth steam pipeline S5 and the fifth newly built steam pipeline S5' are connected, and the specific connection point is the interconnection point 4 of the low and low pressure steam pipelines;

[0044] Between the first steam pipeline S1 and the second steam pipeline S2, the first steam-consuming equipment group and multiple desuperheating and pressure-reducing valve groups (letters F1, F2, and F3 in the figure) are connected. Between the second steam pipeline S2 and the fourth steam pipeline S4, the second steam-consuming equipment group and the desuperheating and pressure-reducing valve group (F4 and F5 in the figure) are connected; between the first steam pipeline S1 and the fourth steam pipeline S4, the third steam-consuming equipment group is connected; the third steam pipeline S3 is connected to the fourth steam pipeline S4; a fourth steam-consuming equipment group is arranged between the first steam pipeline and the fifth steam pipeline; the outlet end of a desuperheating and pressure-reducing valve group F1 on the first steam pipeline is also connected to the fifth steam pipeline S5;

[0045] The fourth steam pipeline S4 is connected to the boiler deaeration system, and the fourth steam-consuming equipment group is also connected to the boiler deaeration system. The boiler deaeration system is connected to the first steam pipeline S1; a desuperheating and pressure-reducing valve group F6 is connected between the fourth steam pipeline S4 and the fifth steam pipeline S5;

[0046] Between the first newly built steam pipeline S1' and the second newly built steam pipeline S2', the first newly built steam-consuming equipment group and the desuperheating and pressure-reducing valve groups f1 and f2 are connected. Between the second newly built steam pipeline S2' and the fourth newly built steam pipeline S4', the second newly built steam-consuming equipment group and the desuperheating and pressure-reducing valve groups f3 and f4 are connected; between the second newly built steam pipeline S2' and the fifth newly built steam pipeline S5', the third newly built steam-consuming equipment group is connected; the third newly built steam pipeline S3' is connected to the outlet end of a desuperheating and pressure-reducing valve group f3 on the second newly built steam pipeline S2', and the outlet end of the third newly built steam pipeline S3' is also connected to the newly built boiler deaeration system. The outlet end of the fourth newly built steam pipeline S4' is also connected to the newly built boiler deaeration system. The newly built boiler deaeration system is connected to the first newly built steam pipeline S1'. A desuperheating and pressure-reducing valve group f5 is connected between the fourth newly built steam pipeline S4' and the fifth newly built steam pipeline S5';

[0047] Through the above solution, the first newly-built steam pipeline S1’ is connected to the first steam pipeline S1, and the fifth newly-built steam pipeline S5’ is connected to the fifth steam pipeline S5, realizing the interconnection of the highest and lowest two pressure-level pipe networks with the existing steam pipe network to form a dual system. The balance of each level of steam pipe network is self-regulated by process means under normal conditions, and the abnormal conditions are adjusted by means of a desuperheating and pressure-reducing valve group. The methanol synthesis rich saturated steam S3’ of the newly-built system is used as the heat source for the high-pressure boiler feed water heater of the boiler, solving the problems that the balance adjustment ability of the second steam pipeline S2 in the first system 1 is limited, the utilization of the third steam pipeline S3 is not energy-saving, the adjustment of the fifth steam pipeline S5 is excessive, the self-balancing ability of the third steam pipeline S3 in the small methanol system is insufficient and has a negative impact on the large consumption of the first steam pipeline S1, the combination of the second steam pipeline S2 and the fourth steam pipeline S4 with the process steam production and use is not tight, and finally it is reflected in the large consumption of the first steam pipeline S1, the desuperheating and pressure-reducing valve starts and operates at high load under normal conditions, the power generation is insufficient, the fifth steam pipeline S5 is in long-term surplus, the pipe network is not energy-saving, and the pipe network adjustment and balance ability is poor. The interconnection of the first steam pipeline S1 and the fifth newly-built steam pipeline S5’ of the dual system is realized to ensure the anti-balance ability of the system. The second steam pipeline S2 and the second newly-built steam pipeline S2’ are not interconnected, and the fourth steam pipeline S4 and the fourth newly-built steam pipeline S4’ are not interconnected. The second steam pipeline S2 and the second newly-built steam pipeline S2’ drive more small turbines and belong to the small and short system pipe network. Its operation stability is mainly controlled by the self-system, that is, it coincides with the working conditions of the self-system process device. After connection, it will disrupt its own operation instead and there are greater safety risks; the fourth steam pipeline 4 and the fourth newly-built steam pipeline S4’ are for process steam use, the system pipe network is large, and the anti-fluctuation ability is strong. In addition, considering that the dual system does not start and stop at the same time, by adjusting the steam production scale of methanol conversion and adjusting the methanol steam conversion boiler feed water turbine to back pressure (from the second newly-built steam pipeline S2’ to the fourth newly-built steam pipeline S4’), the system stability can be guaranteed. At the same time, the connection of the fifth steam pipeline S5 and the fifth newly-built steam pipeline S5’ of the dual system can also make the fourth steam pipeline S4 and the fourth newly-built steam pipeline S4’ of the dual system tend to be stable.

[0048] Among them, the pressures of the first steam pipeline S1 and the first newly-built steam pipeline S1’ are both 10.6±1.28MPa(g), the pressures of the second steam pipeline S2 and the second newly-built steam pipeline S2’ are both 4.0±0.6MPa(g), the pressures of the fourth steam pipeline S4 and the fourth newly-built steam pipeline S4’ are both 1.0±0.2MPa(g), and the pressures of the fifth steam pipeline S5 and the fifth newly-built steam pipeline S5’ are both 0.5±0.1MPa(g); the pressures of the third steam pipeline S3 and the third newly-built steam pipeline S3’ are the rich saturated steam of the methanol plant, with a pressure of 2.2±0.1MPa(g) saturated steam, which is used as the heat source for heating high-pressure boiler feed water to reduce the coal consumption of the boiler for producing high-pressure (S1) steam;

[0049] The high-pressure (first steam pipeline S1 and first post-construction steam pipeline S1'), medium-pressure (second steam pipeline S2 and second post-construction steam pipeline S2') steam, and low-pressure (fourth steam pipeline S4 and fourth post-construction steam pipeline S4') steam are superheated steam, and the very low-pressure (fifth steam pipeline S5 and fifth post-construction steam pipeline S5') steam is saturated steam.

[0050] Optionally, referring to Figure 1 As shown, the first steam-using equipment group connected between the first steam pipeline S1 and the second steam pipeline S2 in the embodiment of the present invention includes an air separation compressor A; the second steam-using equipment group connected between the second steam pipeline S2 and the fourth steam pipeline S4 includes a propylene refrigeration machine D and a DMTO reaction gas compressor C; the third steam-using equipment group connected between the first steam pipeline S1 and the fourth steam pipeline S4 is a DMTO propylene compressor B; the fourth steam-using equipment group connected between the first steam pipeline S1 and the fifth steam pipeline S5 is a generator set E;

[0051] Optionally, the third steam pipeline S3 is a methanol synthesis rich medium-pressure saturated steam pipeline.

[0052] Optionally, the first post-construction steam-using equipment group connected between the first post-construction steam pipeline S1' and the second post-construction steam pipeline S2' includes: an air separation compressor a, a DMTO propylene compressor b, and a methanol plant synthesis compressor g1;

[0053] The second post-construction steam-using equipment group connected between the second post-construction steam pipeline S2' and the fourth post-construction steam pipeline S4' includes: a methanol boiler feed pump g2 directly connecting the second post-construction steam pipeline S2' and the fourth post-construction steam pipeline S4', and also includes a methanol plant flue gas fan g3, a methanol plant air fan g4, and a methanol plant purified gas compressor g5 only connected to the second post-construction steam pipeline S2';

[0054] The third post-construction steam-using equipment group includes a DMTO reaction gas compressor c and a propylene refrigeration machine d connected between the second post-construction steam pipeline S2' and the fifth post-construction steam pipeline S5'.

[0055] The existing system of the steam-using equipment unit is fixed and cannot be changed; the second system includes the steam-using equipment unit including an air separation compressor a, a methanol synthesis compressor g1, and a DMTO propylene compressor b, in a condensing extraction form from S1 to S2; a methanol boiler feed pump g1, in a back-pressure form from S2 to S4; a methanol flue gas fan g3, a methanol air fan g4, and a methanol purified gas compressor g5, in a fully condensing form driven by S2; a propylene refrigeration machine d and a DMTO reaction gas compressor c, in a condensing extraction form from S2 to S5.

[0056] Since the first system adjusts the balance of the S1 and S5 pipe networks through two generator sets, and its extraction steam is used as the heat source for the high-pressure boiler feedwater heater, the S2 pipe network is only adjusted by the air separation unit, the S3 steam is directly reduced in pressure to S4, and the methanol plant adopts a small-system self-balancing (not reflected in the steam balance system); actual operation verification shows that the overall pipe network adjustment and balance ability of the first system is poor, the opening of the desuperheating and pressure-reducing valve under normal conditions is relatively large, and the system is not energy-saving; specifically, the adjustment of the S2 pipe network balance ability is limited, the utilization of S3 is not energy-saving, the adjustment of S5 is excessive and there is a long-term surplus, the self-balancing ability of the methanol small system is insufficient and has a counter-effect on the large consumption of S1, and the S2 and S4 pipe networks are not closely combined with the process steam production and consumption, and finally it is reflected in the large consumption of S1. Due to the large consumption of S1 steam, the steam supply of the generator set is insufficient, and then the power generation is insufficient.

[0057] Therefore, combining the characteristics of the steam pipe network of the first system and the existing deficiencies in operation, the optimization principles of the above-mentioned second system and dual system are determined as follows:

[0058] 1) The steam system should be stable and supply sufficient steam. Being closely associated with the process units is the key to coping with system fluctuations and multi-condition operation; 2) Make the most of the surplus superheated steam produced by the process units and increase the process means to adjust the steam balance; 3) High-pressure steam should be preferentially used for high-power and process-critical equipment units to ensure the stable operation of the process; 4) Medium-pressure steam is associated with the process steam consumption of each process unit and plays a role in balancing and compensating the high- and low-pressure systems. The setting should be stable and reliable; 5) It is not advisable to set up waste heat utilization systems or small steam systems that are irrelevant to the system and isolated; 6) According to the steam balance and its requirements for coping with pipe network fluctuations, combined with process requirements and the reliability of equipment units, select extraction-condensing or back-pressure turbine units, and select the units according to the principle of choosing extraction-condensing for large units and back-pressure for small units; 7) The desuperheating and pressure-reducing valve is used for abnormal condition adjustment, and the opening under normal conditions is maintained at the hot standby opening. The setting scale should be reasonably selected to reduce investment and heat loss; 8) It is necessary to fully consider that the condensate recovery system is greatly affected by the operating conditions of steam users and the condensate cannot be recovered in a short time. When determining the scale of the demineralized water station, elastic margin should be considered to ensure sufficient boiler feedwater.

[0059] According to the above optimization principles, compared with the first system, the research results of the second system and the formation of a dual-steam system are as follows: The first steam pipeline S1 and the fifth steam pipeline S5 of the dual system are interconnected to ensure the system's anti-balance ability, solve the problem of insufficient steam in the first steam pipeline S1 resulting in a low load of the generator set, solve the problem of the single regulation means of the steam pipe network of the first post-constructed steam pipeline S1' in the second system, solve the problem of long-term surplus steam in the fifth steam pipeline S5 in the first system, and at the same time make up for the weak regulation ability of the fifth post-constructed steam pipeline S5'. 2) The pipe networks between the second steam pipeline S2 and the second post-constructed steam pipeline S2', and between the fourth steam pipeline S4 and the fourth post-constructed steam pipeline S4' are not interconnected. Since the second steam pipeline S2 and the second post-constructed steam pipeline S2' drive more small turbines and belong to a small and short system pipe network, their operation stability is mainly controlled by the self-system, that is, it is consistent with the operating conditions of the self-system process unit. Connecting them will instead disrupt their own operation and pose a greater safety risk; The fourth steam pipeline and the fourth post-constructed steam pipeline S4' are for process steam, the system pipe network has a strong anti-fluctuation ability, and considering the non-simultaneous start and stop of the dual system, by adjusting the steam production scale of methanol conversion and adjusting the methanol steam reforming boiler feed water turbine to back pressure (S2'-S4'), the system stability can be guaranteed. At the same time, the connection of the dual systems of S5 and S5' can also act on the dual systems of S4 and S4' to tend to be stable. 3) Reduce the air separation steam extraction volume (S2), change the DMTO propylene compressor B from the original back pressure (S1-S4) to the extraction-condensing form (S1'-S2'), and change the adjustable range of the extraction-condensing gas volume of the methanol synthesis compressor (S1'-S2') to jointly ensure the stability of S2' and break the original design of maintaining the balance of S2 solely through air separation steam extraction; Such a setting makes the correlation between steam balance and process units stronger, and is less affected by the operating conditions of the coal gasification unit. 4) Adjust the two major users, the DMTO reaction gas compressor C and the propylene refrigeration compressor D, from the original extraction-condensing (S2-S4) to the extraction-condensing from S2' to S5', which is more conducive to the stability of the S2' steam pipe network and makes up for the lack of regulation means of S5' at the same time. 5) Change the coal gasification compressor from the original full-condensing driven by the steam of S1 and S1' to the full-condensing driven by the steam of S2 and S2'. This is more in line with the characteristics of the positive correlation between coal gasification and air separation (the steam sources of S1 and S1', and the steam production sources of S2 and S2') and the negative correlation with methane conversion (the steam production source of S1'), realizing the cascade utilization of energy and also being conducive to the stability of the pipe network during operating condition regulation. 6) Determine that the steam of S3' is used as the high heating source for the boiler, and its condensate is sent to the boiler deaerator to make high-pressure boiler feed water. When the quality of this steam is unqualified, its condensate is switched to the desalination station for refining. 7) The desalted water and turbine condensate of the dual system are interconnected to make up for the problem of insufficient elasticity of the desalted water production capacity in the first phase. At the same time, the design elasticity of the desalination station is increased from 120% in the first phase to 150% to cope with the problem of the reduction of turbine condensate.

[0060] The innovation of the present invention lies in that the steam balance regulation is closely related to the operation of the process device and has high flexibility; by connecting the highest and lowest grade pipe networks at both ends, the complementarity and the role of clamping each level of pipe network are obvious, and the steam balance is more stable; it breaks the self-balanced design of the small system in the methanol combined device and eliminates the impact of abnormal conditions in the small system on the large system; the regulation of the S2' steam pipeline no longer depends on the air separation regulation, and the associated process devices are added to share the regulation, which conforms to the operation characteristics of the large-scale coal chemical process; the steam of the third post-constructed steam pipeline S3' (rich production of methanol synthesis) is used as the high heating source for boiler feed water, with obvious energy saving. The key is that this scheme does not damage the steam balance pipe network.

[0061] Optionally, the third post-constructed steam pipeline S3' is located between the fourth post-constructed steam pipeline S4' and the fifth post-constructed steam pipeline S5', which is convenient for connecting the third post-constructed steam pipeline S3 into the large system, rather than just connecting to a certain pipeline, and has a positive effect on the regulation of the entire large system; the post-constructed system is optimized as follows: the rich saturated steam of the methanol device in the post-constructed system (the third post-constructed steam pipeline S3') is no longer directly decompressed to low-pressure steam (the fourth post-constructed steam pipeline S4'), but is used as the heat source for the high-pressure boiler feed water heater of the boiler; the steam balance of the small system inside the methanol device in the post-constructed system (the second system) is no longer independently set, but is considered in the unified steam balance of the dual system; the steam balance setting of the equipment unit in the post-constructed system is no longer closely related to the whole plant device, but is closely related to this process device.

[0062] Optionally, an electric valve and a bidirectional flowmeter are connected between the first steam pipeline S1 and the first post-constructed steam pipeline S1', and an electric valve and a bidirectional flowmeter are connected between the fifth steam pipeline S5 and the fifth post-constructed steam pipeline S5' to achieve the purpose of automatic control and material flow measurement through the electric valve and the flowmeter.

[0063] On the other hand, the embodiment of the present invention provides a method for balancing the steam pipe network of a large combined device's dual system. Based on the above dual-system steam pipe network, the first steam pipeline S1 and the first post-constructed steam pipeline S1' are adjusted through interconnection; the interconnection adjustment amount is the steam production of a single boiler.

[0064] The second post-constructed steam pipeline S2' is adjusted by extracting steam in the form of condensing extraction by the air separation compressor a, the compression unit b of the methanol combined device, and the DMTO propylene compressor c, that is, the first post-constructed steam pipeline S1' does work to extract and condense steam to the second post-constructed steam pipeline S2' for steam regulation.

[0065] The balance of the fourth post-construction steam pipeline S4’ is adjusted by the load of the conversion unit of the methanol plant (the conversion unit belongs to the steam production of the process plant and is not shown in the figure. The conversion unit has no steam-consuming equipment and only produces steam), that is, the steam volume of the fourth post-construction steam pipeline S4’ is adjusted by the operating load for network adjustment; for example, the capacity of the conversion unit of the methanol plant is 130% ± 10% of the conventional design. While meeting the adjustment of the hydrogen-carbon ratio of the methanol plant in a large range, it is mainly used to provide low-pressure (the fourth post-construction steam pipeline S4’) steam to ensure the balance of the steam network of the fourth post-construction steam pipeline S4’; in addition, the fourth post-construction steam pipeline S4’ also adjusts the steam balance through the methanol boiler feed pump g2.

[0066] The balance of the steam network of the fifth post-construction steam pipeline S5’ is adjusted by the extraction steam of the propylene chiller d and the DMTO reaction gas compressor c in the extraction condensing mode; that is, the second post-construction steam pipeline S2’ does work and extracts steam to the low-pressure steam for adjustment. The interconnection capacity of the very low-pressure (the fifth post-construction steam pipeline S5’) steam is not enough to solve the problems of large deviation in steam consumption between winter and summer and poor steam balance strain capacity. The problem is supplemented and solved by setting the extraction steam adjustment of the propylene chiller d and the DMTO reaction gas compressor c in the second system.

[0067] Through the above scheme, after the first steam pipeline S1 and the first post-construction steam pipeline S1’ are interconnected, the network capacity increases by about 1 time, and thus the stability of the network under normal conditions and the flexibility under emergency conditions are greatly improved. The interconnection between the first steam pipeline S1 and the first post-construction steam pipeline S1’ is a two-way flow. Under normal conditions, the mutual steam between S1 and S1’ is a forward flow (that is, the second system flows to the first system), with a flow rate of about 150 t / h to supplement the existing system S1 network. Under accident conditions, when an accident occurs in the existing system resulting in insufficient steam, the steam between S1 and S1’ is a forward flow, with a maximum flow rate of 320 t / h to ensure the stability of the existing system S1 network; under accident conditions, when an accident occurs in the post-construction system resulting in insufficient steam, the steam of S1 is a reverse flow (that is, the first system flows to the second system), with a maximum flow rate of 320 t / h to ensure the stability of the post-construction system S1’ network.

[0068] The steam of the second steam pipeline S2 and the second post-construction steam pipeline S2’ is used as process steam and to drive small-power equipment units. The selection of equipment units is mainly determined by the tightness and operating flexibility of each process plant. The selection of the driving equipment units for S2 and S2’ can be in the extraction condensing form, pure back-pressure extraction steam form or full condensing form; S4 and S4’ are used as process steam and not as steam for driving equipment units; S5 and S5’ are used as process steam and steam for winter pipeline heat tracing.

[0069] The regulation amount of low-low pressure (S5, S5’) steam is the cumulative value of the calculated balance differences in winter and summer. When the existing system and the later-built system operate independently, calculate the respective balance amounts of the two systems in winter and summer, and accumulate the differences in their respective balance amounts. The accumulated amount is the interconnection amount.

[0070] The S4’ pipe network balance of the second system (later-built system) is mainly adjusted by the operating load of the methanol plant (conversion unit). Its characteristics are that under normal conditions, its normal steam production is 65% of the pipe network balance amount. Based on the hydrogen-carbon complementary process requirements of this project, when adjusting the hydrogen-carbon ratio, its load adjustment will reach the range of 55% to 75% of the pipe network balance amount, which has a great impact on the pipe network. The methanol plant eliminates this impact through process relevance internally.

[0071] Optionally, under normal conditions, the steam production balance is adjusted by adjusting the operating load of the boiler, power equipment (such as the aforementioned steam-using equipment group) and process units, and by interconnecting and mutually supplying steam between the first system and the second system; in abnormal conditions, it is adjusted by means of a desuperheater and pressure reducer, and the steam balance of each grade of pipe network is achieved by opening the desuperheater and pressure reducer.

[0072] Optionally, the normal state automatic adjustment is based on the full load of the process unit. When the balance of any grade of steam pipe network changes, the system collects pressure signals and feeds them back to adjust the balance of steam supply and production according to the preset priority order; the interconnection valves of the dual systems are set to be normally open, and the interconnected pipe network can achieve balance between each pipeline through pressure;

[0073] The priority order is as follows: First, adjust the extraction steam volume of the steam-using equipment unit. When the extraction steam volume cannot be balanced, secondly, adjust the process unit load to balance the process steam consumption, and then act on the steam-using equipment unit again; when the adjustable range of the steam-using equipment unit is exhausted, the pipe network is fed back from the fifth steam pipeline S5 to the first steam pipeline S1 level by level, and from the fifth later-built steam pipeline S5’ to the first later-built steam pipeline S1’ level by level; at this time, adjust the balance of the first steam pipeline S1 and the first later-built steam pipeline S1’ by adjusting the operating load of the boiler. If it is necessary to ensure that the boiler load is greater than 80%, the system will automatically stop the generator from generating electricity to ensure the boiler operating load and stabilize the S1 steam pipe network;

[0074] The process unit load is the adjustable range of the local unit or system process of the process unit. The steam balance is achieved through its load adjustment. This kind of load adjustment will not cause changes in the product output of the process unit, or the changes will be restored quickly in a short time. Otherwise, it enters the abnormal condition.

[0075] The abnormal condition automatic control is that when the steam pipe network pressure exceeds the design range, the desuperheater and pressure reducer are automatically controlled through the change of the pipe network pressure, and opened to make the steam pressure of each grade of pipe network return to the design range to ensure the balance of the pipe network.

[0076] Optionally, the balanced extraction steam volume of the second post-construction steam pipeline is 50% ± 10% of the steam consumption of each corresponding compressor;

[0077] The balance of the fourth post-construction steam pipeline is mainly adjusted by the operating load of the methanol plant, and the adjustment range is 20% of the balance of the pipe network at this level;

[0078] The steam adjustment compensation method for the fifth post-construction steam pipeline is to set the extraction steam adjustment of the propylene chiller and the DMTO reaction gas compressor. The extraction steam volume is 50% ± 10% of the corresponding compressor, and the insufficient part is adjusted through interconnection.

[0079] The present invention describes the steam pipe network balance control of the first system and the second system:

[0080] (1) Balance control of the S1 and S1' steam pipe networks: The steam supply of the S1 and S1' pipe networks is provided by 6 boilers in 2 systems. The interconnection of the 2 systems can achieve the instant mutual supply balance of the double-system pipe networks.

[0081] Under normal conditions, the gas production of the 6 boilers is stable. The second system supplies 150 t / h of steam to the first system to ensure full power generation of the first system, and the extraction steam volume of each system's equipment unit is maintained at a certain opening flow rate.

[0082] When it is detected that the pressure of the S1 or S1' pipe network increases or decreases, preferably, the extraction steam volume is first adjusted by 2 generator sets (E), and then the extraction steam volume of 2 air separation units (A or a) corresponding to a certain system is adjusted accordingly. If the pressure of the second system increases or decreases, finally, the extraction steam volumes of the methanol synthesis compressor (g1) and the DMTO propylene compressor (b) of the second system are adjusted. When the extraction steam adjustment volume does not exceed the adjustment range, the system performs self-balancing repair to achieve the rebalancing of the steam pipe network; when the extraction steam adjustment volume exceeds the extraction steam adjustment range of the 2 generator sets (E), an alarm is issued. According to the alarm prompt, the production management adjusts the process unit load and stability; when the extraction steam adjustment volume exceeds the adjustment range of the 2 air separation units (A or a), an alarm is issued. According to the alarm prompt, the production management adjusts the process unit load and stability. The alarm state is eliminated by adjusting the process unit load, and the steam pipe network balance automatically returns to the original state; through the process unit adjustment, if the alarm state of the steam pipe network cannot be eliminated, the steam pipe network enters an abnormal condition.

[0083] When the pressure of the above-mentioned S1 and S1' pipe networks increases or decreases, if it is detected that the boiler outlet pressure changes, it indicates that the steam production of the boiler has changed, and the boiler automatically adjusts its operating load and stability according to the pressure control to ensure the pipe network balance.

[0084] Under abnormal operating conditions, when it is detected that the S1 or S1' pipeline pressure increases beyond the design range, the self-system temperature and pressure reducing device (F3 or f2) is automatically opened according to the pressure control, and the valve opening degree is set according to the pressure value. If another system also detects that the pipeline is overpressured, it will automatically open the self-system temperature and pressure reducing device (f2 or F3); when the temperature and pressure reducing device is opened or opened to the maximum opening, the pipeline pressure continues to rise to the high alarm value, and the steam pipeline enters the accident condition under abnormal conditions. At this time, the steam pipeline high pressure alarm interlock opens the accident temperature and pressure reducing device (F1, F2 or f1) to protect the pipeline; when the pipeline pressure does not trigger the interlock protection, the production management finds the cause and eliminates the problem, the pipeline pressure returns to the design range, and the temperature and pressure reducing device automatically returns to the hot standby state.

[0085] For the above abnormal operating conditions, production management usually chooses to prioritize the stability of the steam balance of a certain system based on the cause of the problem, and will manually control the opening of the temperature and pressure reducer (F3 or f2) to solve and eliminate the problem in a targeted manner.

[0086] (II) Balance control of S2 and S2' steam networks: S2 and S2' networks are not interconnected and operate independently. This description takes the balance of the second system as an example. The steam supply of S2' is provided by the extraction of two air separation units (a), DMTO propylene compressor (b) and methanol synthesis compressor (g1); the steam consumption is consumed by six steam-consuming equipment units (c, g2, g3, g4, g5, d), of which two (c, g2) are extraction condensing type to adjust the steam balance.

[0087] Under normal operating conditions, when it is detected that the pipeline pressure increases or decreases, the steam is extracted and adjusted through two condensing compressors. The balance adjustment mechanism is the same as that of S1 and S1, steam balance adjustment mechanism.

[0088] Normally, the steam network operates relatively stably, and the steam balance can be within the design range through process operation and equipment units. The balance exceeding the design range is mostly caused by S1 network pressure relief or insufficient steam extraction, which is an abnormal operating condition.

[0089] Under abnormal operating conditions, when the S1' pressure relief causes the pressure to rise beyond the design range, the temperature and pressure reducing device (f4) of this stage will be automatically opened; when the S1' steam extraction is insufficient and causes the pressure to be lower than the design range, the upper temperature and pressure reducing device (f2) will be automatically opened; in actual production, whether it is normal operating conditions or abnormal projects, it is preferred to use the automatic control of the S1'-level temperature and pressure reducing device (f2), and the equipment unit steam extraction, process unit load adjustment and the temperature and pressure reducing device (f4) of this stage as auxiliary regulation control.

[0090] (III) Balance of S4 and S4' steam pipelines: The pipeline is controlled without emergency temperature and pressure reducing devices. When the pipeline pressure exceeds the high alarm pressure, the pressure is released through the safety valve interlock.

[0091] The S4 and S4' pipe networks are not interconnected and operate independently. This description takes the balance of the second system as an example. The steam supply of S4' is provided by the back pressure of the methanol steam conversion boiler feed pump (g2) and the process-rich production of the methanol conversion unit, with the latter being the main source. The steam consumption is for the process unit and there is no consumption by equipment units. The steam supply and consumption of the S4' pipe network are not affected by equipment units, and its balance is affected by the process unit.

[0092] In actual production, whether in normal or abnormal conditions, it is preferably controlled automatically by the upstream desuperheater and pressure reducer (f4), with the load adjustment of the process unit and the desuperheater and pressure reducer of this stage (f5) as auxiliary control. There is no accident desuperheater and pressure reducer installed in this pipe network. When the pressure of the pipe network exceeds the high alarm pressure, it is relieved through the interlock of the safety valve.

[0093] (4) Balance control of the S5 and S5' steam pipe networks. The steam supply of S5 and S5' is provided by the extraction steam of the equipment units in two systems, namely 2 generator sets (E), the DMTO reaction gas compressor (c), and the propylene refrigeration compressor (d). The steam consumption is for the process unit and there is no consumption by equipment units. The pipe networks are interconnected to achieve the instant mutual supply balance of the dual-system pipe networks.

[0094] The steam balance control of S5 is mainly ensured by the extraction steam of 2 generator sets (E). S5 is different from other steam pipe networks because it requires tracing steam in winter and there is a large difference in steam consumption between winter and summer. This steam balance is solved through interconnection and mutual supply, and the extraction steam of the DMTO reaction gas compressor (c) and the propylene refrigeration compressor (d) in the second system is used to make up and adjust.

[0095] When operating in summer, the DMTO reaction gas compressor (c) and the propylene refrigeration compressor (d) do not extract steam, and the balance of the dual systems is achieved through the extraction steam of 2 generator sets (E).

[0096] When operating in winter, the DMTO reaction gas compressor (c) and the propylene refrigeration compressor (d) adjust the extraction steam volume to start (the maximum is 45 t / h), and together with the extraction steam of 2 generator sets (E), they jointly ensure the steam balance.

[0097] For the independent operation of the second system, through the extraction-condensing design of the DMTO reaction gas compressor (c) and the propylene refrigeration compressor (d), the steam balance in winter and summer can also be ensured.

[0098] In actual production, whether in normal or abnormal conditions, it is preferably controlled automatically by the upstream desuperheater and pressure reducer (f5), with the load adjustment of the process unit as the auxiliary control.

[0099] There is no accident desuperheater and pressure reducer installed in this pipe network. When the pressure of the pipe network exceeds the high alarm pressure, it is relieved through the interlock of the safety valve.

[0100] After the S1 and S1', as well as S5 and S5' of the dual-system pipe network of the present invention are interconnected, the capacity of the pipe network increases by about 1 time, and the stability of the pipe network under normal conditions and the resilience under abnormal conditions are greatly improved, with an obvious complementary effect.

[0101] For the implementation effect of the present invention, the steam balance rate of each level of the pipe network under normal conditions reaches more than 99.5%, the opening degree of each level of desuperheating and pressure reducing valves is less than 5%, the steam pipe network pressure fluctuation is controlled within the allowable range of the device compressor and the steam used in the device process, and the process device operates stably. The power generation of the existing system reaches full load, the duration of the surplus of S5 steam is reduced, and through comprehensive evaluation, the steam consumption of the dual-system S1 is saved by about 35t per hour, and the economic benefit is relatively ideal (the annual efficiency increase is more than 50 million yuan).

[0102] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, reference can be made to each other. The key point of each embodiment is to illustrate the differences from other embodiments.

[0103] The above embodiments are only used to illustrate the technical solutions of the present application, rather than limiting the present application; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the present application.

Claims

1. A dual-system steam pipe network for a large combined device, characterized in that, It includes a first system and a second system; The first system includes a first steam pipeline, a second steam pipeline, a third steam pipeline, a fourth steam pipeline, and a fifth steam pipeline with decreasing pressure in sequence; among them, the third steam pipeline is a medium-pressure saturated steam pipeline rich in methanol synthesis; The second system includes a first post-constructed steam pipeline, a second post-constructed steam pipeline, a third post-constructed steam pipeline, a fourth post-constructed steam pipeline, and a fifth post-constructed steam pipeline that correspond one-to-one with the steam pipelines of the first system and have decreasing pressure in sequence; The first steam pipeline is connected to the first post-constructed steam pipeline, and the fifth steam pipeline is connected to the fifth post-constructed steam pipeline; A first steam-consuming equipment group and multiple desuperheating and pressure-reducing valve groups are connected between the first steam pipeline and the second steam pipeline, and a second steam-consuming equipment group and a desuperheating and pressure-reducing valve group are connected between the second steam pipeline and the fourth steam pipeline; a third steam-consuming equipment group is connected between the first steam pipeline and the fourth steam pipeline; the third steam pipeline is connected to the fourth steam pipeline; a fourth steam-consuming equipment group is arranged between the first steam pipeline and the fifth steam pipeline; the outlet end of one of the desuperheating and pressure-reducing valve groups on the first steam pipeline is also connected to the fifth steam pipeline; The fourth steam pipeline is connected to the boiler deaeration system, the fourth steam-consuming equipment group is also connected to the boiler deaeration system, and the boiler deaeration system is connected to the first steam pipeline; a desuperheating and pressure-reducing valve group is connected between the fourth steam pipeline and the fifth steam pipeline; A first post-constructed steam-consuming equipment group and a desuperheating and pressure-reducing valve group are connected between the first post-constructed steam pipeline and the second post-constructed steam pipeline; a second post-constructed steam-consuming equipment group and a desuperheating and pressure-reducing valve group are connected between the second post-constructed steam pipeline and the fourth post-constructed steam pipeline; a third post-constructed steam-consuming equipment group is connected between the second post-constructed steam pipeline and the fifth post-constructed steam pipeline; the third post-constructed steam pipeline is connected to the outlet end of a desuperheating and pressure-reducing valve group on the second post-constructed steam pipeline, and the outlet end of the third post-constructed steam pipeline is also connected to the post-constructed boiler deaeration system, the outlet end of the fourth post-constructed steam pipeline is also connected to the post-constructed boiler deaeration system, the post-constructed boiler deaeration system is connected to the first post-constructed steam pipeline, a desuperheating and pressure-reducing valve group is connected between the fourth post-constructed steam pipeline and the fifth post-constructed steam pipeline, and the third post-constructed steam pipeline is located between the fourth post-constructed steam pipeline and the fifth post-constructed steam pipeline; 2. The dual-system steam pipe network of the large combined device according to claim 1, wherein The first steam-consuming equipment group connected between the first steam pipeline and the second steam pipeline includes an air separation compressor; the second steam-consuming equipment group connected between the second steam pipeline and the fourth steam pipeline includes a propylene freezer and a DMTO reaction gas compressor; The third steam-consuming equipment group connected between the first steam pipeline and the fourth steam pipeline is a DMTO propylene compressor; the fourth steam-consuming equipment group connected between the first steam pipeline and the fifth steam pipeline is a generator set.

3. The dual-system steam pipe network of the large combined device according to claim 1, characterized in that, The first post-construction steam-using equipment group connected between the first post-construction steam pipeline and the second post-construction steam pipeline includes: an air separation compressor, a DMTO propylene compressor, and a methanol plant synthesis compressor; The second post-construction steam-using equipment group connected between the second post-construction steam pipeline and the fourth post-construction steam pipeline includes: a methanol boiler feed pump directly connecting the second post-construction steam pipeline and the fourth post-construction steam pipeline, and further includes a methanol plant flue gas fan, a methanol plant air fan, and a methanol plant purified gas compressor only connected to the second post-construction steam pipeline; The third post-construction steam-using equipment group includes a DMTO reaction gas compressor and a propylene refrigerating machine connected between the second post-construction steam pipeline and the fifth post-construction steam pipeline.

4. The dual-system steam pipe network of the large combined device according to claim 1, characterized in that, An electric valve and a bidirectional flowmeter are connected between the first steam pipeline and the first post-construction steam pipeline, and an electric valve and a bidirectional flowmeter are connected between the fifth steam pipeline and the fifth post-construction steam pipeline.

5. A method for balancing a dual-system steam pipe network of a large combined plant, based on the dual-system steam pipe network of any one of claims 1-4, characterized in that The first steam pipeline and the first post-construction steam pipeline are adjusted through interconnection; the interconnection adjustment amount is the steam production amount of a single boiler; The second post-construction steam pipeline is adjusted by extracting steam in the form of extraction condensation by an air separation compressor, a methanol combined plant compressor unit, and a DMTO propylene compressor, that is, the first post-construction steam pipeline performs work to extract and condense steam to the second post-construction steam pipeline for steam adjustment; The balance of the fourth post-construction steam pipeline is adjusted by the load adjustment of the methanol plant conversion unit, that is, the steam amount of the fourth post-construction steam pipeline is adjusted by operating the load for pipe network adjustment; The balance of the fifth post-construction pipeline steam pipe network is adjusted by extracting steam in the form of extraction condensation by a propylene refrigerating machine and a DMTO reaction gas compressor; that is, the second post-construction steam pipeline performs work to extract and condense steam for low-pressure steam adjustment.

6. The method for balancing the dual-system steam pipe network of a large combined device according to claim 5, wherein, Under normal conditions, the steam production balance is adjusted by adjusting the operating load of the boiler, power equipment, and process unit, and by interconnecting and mutually supplying steam between the first system and the second system; In case of abnormal conditions, it is adjusted by means of the desuperheating and pressure-reducing valve, and the steam balance of each grade of pipe network is achieved by opening the desuperheating and pressure-reducing valve.

7. According to the method for balancing a dual-system steam pipe network of a large combined plant as claimed in claim 6, characterized in that The automatic adjustment under normal conditions is based on the full load of the process unit. When the balance of any grade of steam pipe network changes, the system collects pressure signals and feeds them back to adjust the balance of steam supply and production according to the preset priority order; the dual-system interconnection valves are set to be normally open, and the interconnected pipe network can achieve the balance between each pipeline through pressure; The priority order is as follows: First, adjust the extraction steam volume of the steam-using equipment unit. When the extraction steam volume cannot be balanced, secondly, adjust the process unit load to balance the process steam consumption, and then act on the steam-using equipment unit again; when the adjustable range of the steam-using equipment unit is exhausted, the pipe network is fed back to the first steam pipeline step by step through the fifth steam pipeline, and is fed back to the first newly-built steam pipeline step by step through the fifth newly-built steam pipeline; at this time, adjust the balance of the first steam pipeline and the first newly-built steam pipeline through the boiler operation load. If it is necessary to ensure that the boiler load is greater than 80%, the system will automatically stop the generator set from generating electricity to ensure the boiler operation load and stabilize the S1 steam pipe network; The automatic control under abnormal conditions is that when the steam pipe network pressure exceeds the design range, the desuperheating and pressure-reducing valve is automatically controlled through the change of the pipe network pressure, and is opened to make the steam pressure of each grade of the pipe network return to the design range to ensure the balance of the pipe network.

8. The method for balancing the steam pipe network of the dual systems of the large combined device according to claim 7, wherein, The balanced extraction steam volume of the second newly-built steam pipeline is 50% ± 10% of the steam consumption of each corresponding compressor; The balance of the fourth newly-built steam pipeline is mainly adjusted through the operation load of the methanol unit, and the adjustment range is 20% of the balance amount of this grade of pipe network; The steam adjustment compensation method of the fifth newly-built steam pipeline is to set the extraction steam adjustment of the propylene chiller and the DMTO reaction gas compressor, and the extraction steam volume is 50% ± 10% of the corresponding compressor.

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