A heat recovery system

Abstract

The present invention discloses a heat recovery system, including a main steam pipeline, an additional pipeline, a feedwater heater, and a steam-side regulating valve arranged on the additional pipeline, wherein the steam-side regulating valve is used to regulate the main steam in the additional pipeline, so as to control the extraction pressure after the steam-side regulating valve to control the outlet temperature of the feedwater heater to meet the required final feedwater temperature. This system solves the problems of low coal powder burnout rate, black smoke from fuel oil, low-temperature condensation, ash blockage, corrosion and other equipment in the tail flue during the startup phase without setting an additional steam extraction port on the steam turbine, and can also ensure that the unit can be put into the SCR denitration device before being connected to the grid, and prolong the life of the SCR catalyst.

Description

Technical Field

[0001] The invention relates to the field of thermal power generation, and in particular to a heat recovery system. Background Art

[0002] At present, my country's electricity is mainly peaked by thermal power generating units, and low-load operation of thermal power generating units has become the norm. With the official release of my country's "13th Five-Year Plan for Power Development (2016-2020)", "strengthening peak capacity construction and improving system flexibility" has become one of the important tasks of thermal power generating units, which means that higher requirements are put forward for the deep peaking and system flexibility of thermal power generating units. Even the concept of "ultra-low load operation" has been proposed in the industry. In fact, when thermal power generating units are operated at low load, there are many problems such as environmental protection, safety, and economy, including the need to withdraw the SCR denitrification device from operation, the problem of boiler water power instability, boiler combustion instability, and low cycle efficiency.

[0003] Chinese patent ZL201110459533.2 discloses an adjustable feedwater heat recovery system, that is, compared with the traditional steam turbine generator set, the final stage steam extraction pressure set on the high-pressure cylinder is higher than the conventional maximum steam extraction pressure of the high-pressure cylinder; and a steam extraction regulating valve is set on the final stage steam extraction pipeline, and then the feedwater is reheated through the feedwater heater. During operation, the final stage steam extraction can be adjusted through the valve, so as to keep the pressure after the steam extraction regulating valve basically unchanged when the unit changes load, and the temperature of the boiler feedwater is kept basically unchanged through the final stage feedwater heater.

[0004] However, the system and method provided by the patent still have shortcomings. Due to the sliding pressure operation of the unit, the pressure of the steam extraction port is also relatively low when the unit reaches the ultra-low load and startup stage, and it is still unable to meet the requirement of denitrification without shutting down the operation during the startup stage or the ultra-low load stage. In addition, for subcritical units, due to the low pressure parameters themselves, there will be a problem of shutting down the operation due to failure to meet the denitrification requirements during the low load stage. More importantly, the system and method provided by the patent also have application limitations, and cannot be directly applied to units without additional steam extraction ports for steam turbines.

[0005] On the other hand, modern thermal power generating units are equipped with bypass systems to meet the requirements of unit start-up and shutdown, accident conditions, etc. When the unit is started, starting from the ignition of the boiler, a large amount of steam generated by consuming coal and fuel oil is finally sent to the condenser through the bypass system until the turbine inlet steam quality is qualified and the steam parameters meet the start-up conditions, the turbine starts to start, and finally to the grid, the bypass is finally closed. The cold start of a traditional thermal power generating unit takes about 8-10 hours from ignition to grid connection. During this period, a large amount of steam is sent to the condenser through the bypass system. Although the working fluid is recovered, the heat is lost. In addition, there are also problems such as low coal powder burnout rate, black smoke from fuel oil, and low-temperature condensation, ash blockage, and corrosion in the air preheater of the tail flue during the startup stage. Summary of the invention

[0006] In view of this, in order to comprehensively solve the above-mentioned problems faced in the ultra-low load and startup stages and the shortcomings of the existing adjustable water supply heat recovery system, the present invention provides a heat recovery system.

[0007] The present invention provides a heat recovery system, characterized in that it comprises:

[0008] Main steam pipe;

[0009] High pressure cylinder;

[0010] a final-stage feedwater heater using the main steam in the main steam pipeline as a heat source;

[0011] The final stage steam extraction pipeline connects the high-pressure cylinder and the final stage feedwater heater;

[0012] An additional pipeline added to the main steam pipeline, wherein the additional pipeline is connected to the feedwater heater;

[0013] The steam-side regulating valve arranged on the additional pipeline is used to regulate the main steam in the additional pipeline to control the extraction steam pressure after the steam-side regulating valve to control the outlet temperature of the feed water heater to meet the required final feed water temperature.

[0014] Furthermore, it also includes isolation valves respectively arranged on the final stage steam extraction pipeline and the additional pipeline;

[0015] Furthermore, it also includes an additional adjustable post-final-stage feedwater heater, which is arranged at the rear of the final-stage feedwater heater according to the water flow direction; the additional pipeline connects the main steam pipeline and the additional adjustable post-final-stage feedwater heater.

[0016] Furthermore, it also includes at least one water-side regulating valve, and the water-side regulating valve is connected in parallel with the additional adjustable rear final-stage feedwater heater.

[0017] The heat recovery system of the present invention has the following advantages and effects:

[0018] 1. The present invention does not require the setting of additional steam turbine extraction ports, including subcritical units. In normal operation stages of the units at different loads, due to the high main steam pressure, the main steam can still have sufficient pressure to meet the requirements of increasing the final feed water temperature and meeting the denitrification operation requirements under the ultra-low load pressure of the units.

[0019] 2. The system of the present invention can be put into use during the startup phase of the unit, and can recover a portion of the heat of the large amount of steam originally sent to the condenser through the bypass system, which can be used to supplement the heating of the boiler feed water during the startup phase, thereby increasing the feed water temperature and indirectly further supplementing the preheating of the entire boiler, which can greatly reduce the fuel oil and coal consumption during the startup phase. Since the system can be put into use during the startup phase, it also solves the problems of low coal powder burnout rate, black smoke from fuel oil, low-temperature condensation, ash blockage, corrosion of the air preheater of the tail flue, etc. during the startup phase, and can ensure that the unit can be put into the SCR denitration device before being connected to the grid, and can also extend the life of the SCR catalyst.

[0020] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a system schematic diagram of specific embodiment 1 of the present invention.

[0022] Figure 2 It is a system schematic diagram of specific embodiment 2 of the present invention.

[0023] Figure 3 It is a system schematic diagram of specific embodiment 3 of the present invention.

[0024] Among them: 1-final stage steam extraction port; 10-final stage steam extraction pipeline; 11-final stage feedwater heater; 2-main steam pipeline; 3-other conventional systems; 4-high pressure cylinder; 5-final feedwater; 6-water side regulating valve; 01-additional pipeline; 02-steam side regulating valve; 03-additional adjustable final stage feedwater heater; 04, 04' isolating valve. DETAILED DESCRIPTION

[0025] Example 1

[0026] Figure 1 This is a system schematic diagram of a specific embodiment 1 of the present invention. In this embodiment, on the basis of the final stage steam extraction port 1, the final stage steam extraction 10, the final stage feed water heater 11, and the main steam pipeline 2, an additional pipeline 01, a steam side regulating valve 02 on the additional pipeline, and an additional adjustable post-final stage feed water heater 03 are added.

[0027] The additional adjustable rear final stage feedwater heater 03 is connected to the main steam pipeline 2 through the additional pipeline 01, and the steam side regulating valve 02 is arranged on the additional pipeline 01. The steam side regulating valve 02 is used to regulate the main steam in the additional pipeline 01, and the feedwater temperature at the outlet of the additional adjustable rear final stage feedwater heater 03 is controlled by controlling the pressure after the steam side regulating valve 02.

[0028] The control method of the present invention is described in detail by taking an example of a 1000MW unit in a power plant, wherein the steam turbine is an ultra-supercritical single-shaft, once-reheated, four-cylinder, four-exhaust condensing steam turbine.

[0029] For example, the main steam parameters under the rated condition (1000WM) of the unit are 27MPa / 600℃. During the unit operation stage, as the unit load decreases, the pressure entering the additional adjustable final feedwater heater is controlled at about 8.5MPa by adjusting the steam side regulating valve to maintain the final feedwater temperature at about 300℃.

[0030] During the startup phase of the unit, starting from the ignition of the boiler, the steam generated by consuming coal and fuel oil can enter the additional adjustable final-stage feed water heater 03 through the additional pipeline 01 to further supplement the heating of the boiler feed water, thereby increasing the feed water temperature during the startup phase and reducing the inlet under-enthalpy of the water-cooled wall during the startup phase, thereby solving the problem of hydrodynamic instability during the startup phase, creating favorable conditions for the rapid startup of the unit, and ultimately achieving a significant reduction in startup energy consumption. It also solves the problems of low pulverized coal burnout rate, black smoke from fuel oil, and low-temperature condensation, ash blockage, and corrosion in the air preheater of the tail flue generated during the traditional startup phase, and ensures that the unit can be put into the SCR denitrification device before being connected to the grid. In addition, it can also extend the life of the SCR catalyst.

[0031] Example 2

[0032] Figure 2 This is a system schematic diagram of a specific embodiment 2 of the present invention. In this embodiment, based on the final stage steam extraction port 1, the final stage steam extraction 10, the final stage feed water heater 11, and the main steam pipeline 2, an additional pipeline 01, a steam side regulating valve 02 on the additional pipeline, an additional adjustable post-final stage feed water heater 03, and a water side regulating valve 6 are added.

[0033] The main difference between this embodiment and embodiment 1 is that a water-side regulating valve 6 is added, which is connected in parallel with the additional adjustable final-stage feedwater heater 03. Therefore, the additional adjustable final-stage feedwater heater 03 can be designed as a partial-capacity feedwater heater to reduce the cost of the heater.

[0034] The only difference between the method of using the system of this embodiment and that of embodiment 1 is that the final feed water temperature is the feed water temperature after the outlet of the additional adjustable final feed water heater 03 and the outlet of the water side regulating valve 6 are mixed. The rest are the same and will not be repeated here.

[0035] Example 3

[0036] Figure 3 This is a system schematic diagram of a specific embodiment 3 of the present invention. In this embodiment, based on the final stage steam extraction port 1, the final stage steam extraction 10, the isolation valve 04' on the final stage steam extraction 10, the final stage feed water heater 11, and the main steam pipeline 2, an additional pipeline 01, a steam side regulating valve 02 on the additional pipeline, and an isolation valve 04 are added.

[0037] The main difference between this embodiment and embodiment 1 is that there is no additional adjustable final-stage feedwater heater 03, and an isolation valve 04 is added to the additional pipeline, so that during the high-load operation of the unit, if the system is not needed, the isolation valve 04 can be used to close it. When the unit load is low to a certain extent or during the unit startup stage, the final-stage feedwater temperature cannot meet the requirements of the denitrification device operation. At this time, the isolation valve 04 can be opened to switch to this system. At the same time, the isolation valve 04' on the final-stage extraction steam is closed, and the main steam is throttled through the regulating valve 02. Since the main steam pressure itself is relatively high, sufficient feedwater temperature can be ensured. Otherwise, the method of using the system of this embodiment is consistent with that of embodiment 1, and will not be repeated here.

[0038] The above describes in detail the preferred specific embodiments of the present invention. It should be noted that the heat recovery system of the present invention can have a variety of combinations depending on whether a water side regulating valve is configured on the water side, whether an additional adjustable rear final stage feed water heater is provided, and whether the additional adjustable rear final stage feed water heater has different capacities.

[0039] It should be understood that ordinary technicians in this field can make many modifications and changes based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by technicians in this technical field based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the existing technology should be within the scope of protection determined by the claims.

Claims

1. A heat recovery system, Features: include Main steam pipe; High pressure cylinder; a final-stage feedwater heater using the main steam in the main steam pipeline as a heat source; The final stage steam extraction pipeline connects the high-pressure cylinder and the final stage feedwater heater; An additional pipeline added to the main steam pipeline, wherein the additional pipeline is connected to the feedwater heater; The steam-side regulating valve arranged on the additional pipeline is used to regulate the main steam in the additional pipeline during the unit startup phase or low-load phase, so as to control the extraction steam pressure after the steam-side regulating valve to control the outlet temperature of the feed water heater to meet the required final feed water temperature.

2. A heat recovery system as claimed in claim 1, Features: It also includes isolation valves respectively arranged on the final stage steam extraction pipeline and the additional pipeline.

3. A heat recovery system as claimed in claim 2, It is characterized in that It also includes an additional adjustable rear final stage feedwater heater, which is arranged at the rear of the final stage feedwater heater according to the water flow direction; the additional pipeline connects the main steam pipeline and the additional adjustable rear final stage feedwater heater.

4. A heat recovery system as claimed in claim 3, Features: It also includes at least one water-side regulating valve, which is connected in parallel with the additional adjustable rear final-stage feedwater heater.

Images