Construction method and system for deep recuperation of waste heat in flue gas of utility boiler

Abstract

The present invention belongs to the technical field of waste heat recovery from boiler flue gas, and specifically relates to a construction method and system for a deep heat recovery system of waste heat from flue gas of a power station boiler. In the construction method, the first heat medium water circuit is connected from the condensate water system, and the second heat medium water circuit is connected from the steam turbine regenerative system; the outlet water of the first heat medium water circuit and the inlet water of the second heat medium water circuit are mixed and then enter the second heat medium water heat exchanger; part of the outlet water of the second heat medium water circuit returns to the steam turbine regenerative system, and part of the outlet water is connected to the primary air preheater and the secondary air preheater respectively through the third heat medium water circuit; the outlet water of the third heat medium water circuit enters the second heat medium water heat exchanger; the flow rates of each circuit are adjusted to increase the outlet flue gas temperature of the air preheater to 135 - 185 °C and increase the secondary air hot air temperature by 3 - 15 K. The construction method of the present application realizes the improvement of the waste heat recovery effect of the flue gas, reduces the power supply coal consumption of the unit by about 5 g / kWh, and simultaneously improves the low-load operation performance of the unit.

Description

Technical Field

[0001] The present invention belongs to the technical field of boiler flue gas waste heat recovery, and specifically relates to a construction method and system for a deep heat recovery system of flue gas waste heat in a power station boiler. Background Art

[0002] Efficient recovery of boiler flue gas waste heat is an important research direction for improving the power generation efficiency of coal-fired power generation units. The most direct way to recover flue gas waste heat is to use a low-low temperature economizer to reduce the boiler flue gas temperature from about 130 °C to 85 - 90 °C with condensed water. The heated condensed water returns to the low-pressure heating system. Since the extraction steam volume of the steam turbine is reduced, the work done by the steam turbine increases, thereby improving the cycle efficiency of the unit and reducing the power generation coal consumption. This method has a simple system, but the waste heat recovery efficiency is low. Generally, it can only reduce the power supply coal consumption by about 2 g / kWh, of which 0.5 g / kWh is due to reasons such as the reduction of flue gas resistance after the flue gas temperature is reduced. Since the direct reduction of power generation coal consumption by recovering waste heat usually does not exceed 1.5 g / kWh.

[0003] To improve the effect of flue gas waste heat recovery, a boiler flue gas waste heat recovery system that sets a flue gas bypass in the air preheater area and a flue gas heat exchanger in front of the desulfurization absorption tower has been introduced in China in recent years (see Figure 1 ), and it has been applied to newly built large coal-fired power generation units. This system can recover flue gas waste heat more efficiently and can reduce the power supply coal consumption by about 4 g / kWh according to the design calculation. However, this system has the following problems:

[0004] (1) The primary air does not participate in the recovery of low-temperature flue gas waste heat. The set forced circulation heat pipe system only heats the secondary air, and the primary air directly enters the air preheater. The primary air accounts for about 25% of the total air volume and is not used for cooling low-temperature flue gas and recovering flue gas waste heat in the low-temperature area, which will reduce the effect of flue gas waste heat recovery.

[0005] (2) The outlet air temperature of the air preheater is lower than the working condition without flue gas waste heat recovery, that is, after about 15% of the flue gas bypass, the air temperature for combustion is lower than the original design value, which will lead to a decrease in boiler efficiency and thus an increase in coal consumption. Figure 1 Although the shown recovery system improves the effect of flue gas waste heat recovery by setting a forced circulation heat pipe system to preheat the secondary air and by setting technical means such as a flue gas bypass, the reduction of the outlet air temperature of the air preheater offsets part of the waste heat recovery effect, thus affecting the overall efficiency of flue gas waste heat recovery. The actual operation effect often fails to reach the design value.

[0006] (3) The operation regulation is relatively complex. The operations of each flue gas heat exchanger are interconnected and affect each other, making it difficult to accurately control some important node parameters, so that the flue gas heat exchanger in front of the desulfurization tower cannot be put into operation for a long time, affecting the realization of the energy-saving goal.

[0007] (4) The heat transfer temperature difference of each flue gas heat exchanger and the secondary air preheater is small, so the heating surface is large, especially resulting in high construction cost of the flue gas heat exchanger in front of the desulfurization tower.

[0008] In short, the existing system has a large equipment investment, complex operation, and the energy-saving potential is not fully utilized. At the same time, due to the need to set up a bypass flue gas system, it is difficult to be used for the retrofit of existing units.

[0009] Based on the above problems, how to construct a flue gas waste heat regeneration system to achieve coal saving and improve the cycle efficiency of the unit is an urgent problem to be solved. Summary of the Invention

[0010] To solve the problems in the above-mentioned background technology, the present invention provides a construction method for a deep flue gas waste heat regeneration system of a power station boiler. Through this construction method, the low-temperature flue gas waste heat is efficiently recovered and utilized, and the power supply coal consumption of the unit can be reduced by about 5 g / kWh.

[0011] The first object of the present invention is to provide a construction method for a deep flue gas waste heat regeneration system of a power station boiler. This construction method is based on the deep flue gas waste heat regeneration system of a power station boiler. The system includes an air preheater, an electrostatic precipitator, an induced draft fan, and a desulfurization tower that are sequentially arranged on the main flue.

[0012] The construction method includes: a first heat medium water heat exchanger arranged on the main flue between the induced draft fan and the desulfurization tower, a second heat medium water heat exchanger arranged on the main flue between the electrostatic precipitator and the air preheater. The first heat medium water heat exchanger and the second heat medium water heat exchanger operate in series, and a primary air preheater arranged on the inlet pipeline of the primary air before the air preheater, and a secondary air preheater arranged on the inlet pipeline of the secondary air before the air preheater.

[0013] A first heat medium water circuit is connected to the first heat medium water heat exchanger, and a second heat medium water circuit is connected to the second heat medium water heat exchanger. The heat medium water of the first heat medium water circuit is accessed from the condensate water system, and the heat medium water of the second heat medium water circuit is accessed from the steam turbine regenerative system. The outlet water of the first heat medium water circuit and the inlet water of the second heat medium water circuit are mixed and then enter the second heat medium water heat exchanger. A part of the outlet water of the second heat medium water circuit returns to the steam turbine regenerative system, and the other part of the outlet water is connected to the primary air preheater and the secondary air preheater respectively through a third heat medium water circuit. The primary air preheater is used to heat the primary air, and the secondary air preheater is used to heat the secondary air. The outlet water of the third heat medium water circuit and the inlet water of the second heat medium water circuit are mixed and then enter the second heat medium water heat exchanger.

[0014] The construction method further includes: adjusting the flow rates of the first hot medium water circuit and / or the second hot medium water circuit and / or the third hot medium water circuit to increase the outlet flue gas temperature of the air preheater to 135 - 185 °C; and increasing the heating area of the secondary air to increase the hot air temperature of the secondary air by 3 - 15 K.

[0015] Further, the air preheater includes a primary air preheater and a secondary air preheater disposed on the main flue, and the construction method further includes:

[0016] Changing part of the heating surface of the primary air preheater to be used for preheating the secondary air to form an additional secondary air preheater; the primary air enters the primary air preheater after passing through the primary air heater, and the secondary air enters the secondary air preheater and the additional secondary air preheater after passing through the secondary air heater.

[0017] Further, a water pressurizing pump is provided on the inlet pipeline of the first hot medium water circuit, and the construction method further includes: increasing the flow rate of the inlet pipeline of the first hot medium water circuit through the water pressurizing pump to increase the logarithmic mean temperature difference of heat transfer of the first hot medium water heat exchanger, so as to reduce the heat transfer area of the first hot medium water heat exchanger.

[0018] Further, the third hot medium water circuit includes a primary air hot medium water branch and a secondary air hot medium water branch. The primary air heater is connected to the primary air hot medium water branch, and the secondary air heater is connected to the secondary air hot medium water branch; a primary air heater inlet regulating valve is provided on the primary air hot medium water branch, and a secondary air heater inlet regulating valve is provided on the secondary air hot medium water branch; a hot medium water return regulating valve is provided on the main return line of the second hot medium water circuit;

[0019] The construction method includes: adjusting the hot air temperature of the primary air by adjusting the primary air heater inlet regulating valve and / or the hot medium water return regulating valve; adjusting the hot air temperature of the secondary air by adjusting the secondary air heater inlet regulating valve and / or the hot medium water return regulating valve; adjusting the return water temperature of the second hot medium water heat exchanger by adjusting the primary air heater inlet regulating valve, the secondary air heater inlet regulating valve and / or the hot medium water return regulating valve.

[0020] Further, a first hot medium water heat exchanger inlet valve is provided on the inlet pipeline of the first hot medium water circuit, and a first hot medium water heat exchanger outlet valve is provided on the outlet pipeline of the first hot medium water circuit; the hot medium water of the second hot medium water circuit is connected from the steam turbine regenerative system, and a hot medium water heat exchanger makeup valve is provided on the pipeline before mixing with the hot medium water in the first hot medium water circuit;

[0021] The construction method includes: adjusting the inlet valve of the first hot medium water heat exchanger and / or the outlet valve of the first hot medium water heat exchanger and / or the makeup water valve of the hot medium water heat exchanger and / or the inlet regulating valve of the primary air air preheater and / or the inlet regulating valve of the secondary air air preheater and / or the return water regulating valve of the hot medium water to adjust the flue gas temperature at the inlet of the electrostatic precipitator.

[0022] Furthermore, the construction method is applied to the retrofit of existing units or the construction of new units.

[0023] The second object of the present invention is to provide a deep heat recovery system for the flue gas waste heat of a power station boiler. The system includes an air preheater, an electrostatic precipitator, an induced draft fan, and a desulfurization tower arranged in sequence on the main flue; further, a first hot medium water heat exchanger is arranged on the main flue between the induced draft fan and the desulfurization tower, and a second hot medium water heat exchanger is arranged on the main flue between the electrostatic precipitator and the air preheater. The first hot medium water heat exchanger and the second hot medium water heat exchanger operate in series. An primary air air preheater is arranged on the inlet pipeline of the primary air before the air preheater, and a secondary air air preheater is arranged on the inlet pipeline of the secondary air before the air preheater; the outlet temperature of the air preheater is 135 - 185 °C;

[0024] A first hot medium water circuit is connected to the first hot medium water heat exchanger, and a second hot medium water circuit is connected to the second hot medium water heat exchanger; the hot medium water of the first hot medium water circuit is accessed from the condensate water system, and the hot medium water of the second hot medium water circuit is accessed from the steam turbine heat recovery system; the outlet water of the first hot medium water circuit and the inlet water of the second hot medium water circuit are mixed and then enter the second hot medium water heat exchanger; a part of the outlet water of the second hot medium water circuit returns to the steam turbine heat recovery system, and the other part of the outlet water is connected to the primary air air preheater and the secondary air air preheater respectively through a third hot medium water circuit. The primary air air preheater is used to heat the primary air, and the secondary air air preheater is used to heat the secondary air; the outlet water of the third hot medium water circuit and the inlet water of the second hot medium water circuit are mixed and then enter the second hot medium water heat exchanger.

[0025] Furthermore, the air preheater includes a primary air preheater and a secondary air preheater arranged on the main flue. Part of the heating surface of the primary air preheater is changed to be used for preheating the secondary air to form an additional secondary air preheater;

[0026] The primary air fan is connected to the primary air preheater through the primary air air preheater, and the secondary air fan is connected to the additional secondary air preheater and the secondary air preheater respectively through the secondary air air preheater.

[0027] Furthermore, a water pressurizing pump and a first hot medium water heat exchanger inlet valve are arranged on the inlet pipeline of the first hot medium water circuit, and a first hot medium water heat exchanger outlet valve is arranged on the outlet pipeline of the first hot medium water circuit;

[0028] The heating medium water of the second heating medium water circuit is connected from the steam turbine regenerative system, and a makeup valve for the heating medium water heat exchanger is provided on the pipeline before mixing with the heating medium water in the first heating medium water circuit.

[0029] Further, the third heating medium water circuit includes a primary air heating medium water branch and a secondary air heating medium water branch. The primary air preheater is connected to the primary air heating medium water branch, and the secondary air preheater is connected to the secondary air heating medium water branch.

[0030] A regulating valve for the inlet water of the primary air preheater is provided on the primary air heating medium water branch, a regulating valve for the inlet water of the secondary air preheater is provided on the secondary air heating medium water branch, and a regulating valve for the return water of the heating medium water is provided on the main circuit of the second heating medium water circuit.

[0031] The construction method of the flue gas waste heat deep regeneration system for a power station boiler provided by the present invention is as follows: a first heating medium water heat exchanger is provided behind the induced draft fan and in front of the desulfurization tower to absorb the low-temperature flue gas waste heat; a second heating medium water heat exchanger is provided in front of the electrostatic precipitator. The cooling water of the first heating medium water heat exchanger comes from the condensate system, and the cooling water of the second heating medium water heat exchanger comes from the outlet water of the first heating medium water heat exchanger and the steam turbine regenerative system. The condensate water supplied into the first heating medium water heat exchanger has a temperature of about 40°C, is heated to 70°C by the first heating medium water heat exchanger, and then is supplied to the second heating medium water heat exchanger after being combined with the feed water of the steam turbine regenerative system, with a supply water temperature of about 70°C. The water temperature after being heated by the second heating medium water heat exchanger reaches above 120°C. A part of the outlet water of the second heating medium water heat exchanger returns to the steam turbine regenerative system, replacing part of the extraction steam of the steam turbine regenerative system, enabling this part of the extraction steam to continue to do work in the steam turbine, thereby reducing the coal consumption. The remaining heating medium water enters the primary air preheater and the secondary air preheater respectively to heat the primary air and the secondary air. Then, the primary air and the secondary air continue to enter the air preheater to be heated, enabling both the primary air and the secondary air to effectively participate in the flue gas waste heat regeneration, especially the flue gas waste heat regeneration in the low-temperature part. Since the gas-borne regeneration can directly reduce the input heat brought in by the coal combustion, the boiler efficiency is improved.

[0032] Through the above construction method, the low-temperature flue gas waste heat can be efficiently recovered and utilized, and the power supply coal consumption of the unit can be reduced by about 5 g / kWh. Description of the Drawings

[0033] 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 the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0034] Figure 1 It is the overall structure diagram of the boiler flue gas waste heat recovery system in the prior art;

[0035] Figure 2 This is the overall structure diagram of the deep heat recovery system for the flue gas waste heat of a power station boiler provided by the embodiments of the present invention;

[0036] Wherein: 1 - main flue, 2 - air preheater, 21 - primary air preheater, 22 - additional secondary air preheater, 23 - secondary air preheater, 3 - electrostatic precipitator, 4 - induced draft fan, 5 - desulfurization tower, 6 - first heat medium water heat exchanger, 7 - second heat medium water heat exchanger, 8 - primary air air heater, 9 - secondary air air heater, 10 - first heat medium water circuit, 11 - second heat medium water circuit, 12 - water pressurizing pump, 13 - primary air heat medium water branch, 14 - secondary air heat medium water branch, 15 - primary air air heater inlet regulating valve, 16 - secondary air air heater inlet regulating valve, 17 - heat medium water return regulating valve, 18 - first heat medium water heat exchanger inlet valve, 19 - first heat medium water heat exchanger outlet valve, 20 - heat medium water heat exchanger make-up water valve. Detailed implementation manners

[0037] 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 present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0038] Next, the present invention will be elaborated in detail in conjunction with the attached Figure 1 drawings and specific embodiments.

[0039] A coal-fired power generation unit has two heat recovery systems, namely the boiler flue gas-air heat recovery system and the steam turbine extraction heat recovery system. The functions of the two heat recovery systems are to recover the waste heat to be discharged into the environment and use the high-temperature heat source (furnace) to improve the energy quality for continued work, so it is called heat recovery. When constructing the deep heat recovery system for the flue gas waste heat of a power station boiler, it is necessary to overall optimize the two heat recovery systems to maximize the cycle efficiency of the unit. The flue gas waste heat is used to heat the combustion air and returns to the furnace with the combustion air, which is defined as air-borne heat recovery; the flue gas waste heat is used to heat the working medium water and then returns to the steam turbine heat recovery system with the working medium water, which is defined as water-borne heat recovery; the utilization efficiency is higher when the flue gas waste heat is carried by the combustion air, while the utilization efficiency is lower when the flue gas waste heat is carried by the working medium water, that is, the efficiency of air-borne heat recovery is always higher than that of water-borne heat recovery. During design, it is necessary to reasonably overall optimize the two heat recovery systems to maximize the heat recovery effect of the flue gas waste heat, improve the cycle efficiency of the unit, and reduce the coal consumption for power supply.

[0040] The present invention provides a construction method for a deep recuperation system of the waste heat of the flue gas of a power station boiler. This construction method is implemented based on the deep recuperation system of the waste heat of the flue gas of the power station boiler. The system includes an air preheater 2, an electrostatic precipitator 3, an induced draft fan 4, and a desulfurization tower 5 that are sequentially arranged on the main flue 1. It also includes a first heat medium water heat exchanger 6 arranged on the main flue 1 between the induced draft fan 4 and the desulfurization tower 5, a second heat medium water heat exchanger 7 arranged on the main flue 1 between the electrostatic precipitator 3 and the air preheater 2. The first heat medium water heat exchanger 6 and the second heat medium water heat exchanger 7 operate in series, and a primary air air heater 8 is arranged on the inlet pipeline of the primary air before the air preheater 2, and a secondary air air heater 9 is arranged on the inlet pipeline of the secondary air before the air preheater 2. The settings of the first heat medium water heat exchanger 6, the second heat medium water heat exchanger 7, the primary air air heater 8, and the secondary air air heater 9 in the above system and the series connection of the first heat medium water heat exchanger 6 and the second heat medium water heat exchanger 7 are the basis for maximizing the waste heat recuperation benefit of the flue gas.

[0041] The construction method includes: a first heat medium water circuit 10 is connected to the first heat medium water heat exchanger 6, a second heat medium water circuit 11 is connected to the second heat medium water heat exchanger 7. The heat medium water of the first heat medium water circuit 10 is accessed from the condensate water system, and the heat medium water of the second heat medium water circuit 11 is accessed from the steam turbine regenerative system; the outlet water of the first heat medium water circuit 10 and the inlet water of the second heat medium water circuit 11 are mixed and then enter the second heat medium water heat exchanger 7; a part of the outlet water of the second heat medium water circuit 11 returns to the steam turbine regenerative system, and another part of the outlet water is connected to the primary air air heater 8 and the secondary air air heater 9 respectively through a third heat medium water circuit. The primary air air heater 8 is used to heat the primary air, and the secondary air air heater 9 is used to heat the secondary air; the outlet water of the third heat medium water circuit and the inlet water of the second heat medium water circuit 11 are mixed and then enter the second heat medium water heat exchanger 7;

[0042] The construction method further includes: adjusting the flow rates of the first heat medium water circuit 10 and / or the second heat medium water circuit 11 and / or the third heat medium water circuit to increase the outlet flue gas temperature of the air preheater 2 to 135 - 185 °C; and increasing the heating area of the secondary air to increase the secondary air hot air temperature by 3 - 15 K.

[0043] It should be understood that the increase in the temperature of the working medium water returned by the second heat medium water circuit 11 to the steam turbine regenerative system helps to reduce the heat consumption of the steam turbine. The above construction method of the present application is designed for the system from the perspective of reducing the heat consumption of the steam turbine and improving the boiler efficiency. At the same time, the construction method of this system can not only effectively improve the waste heat recovery effect of the flue gas, but also improve the operation flexibility and environmental protection performance of the unit.

[0044] In a specific embodiment, in combination with specific working conditions using the above construction method, the temperature ts5 of the condensate water fed into the first heat medium water heat exchanger 6 is about 40°C, and after being heated by the first heat medium water heat exchanger 6, the temperature ts6 is about 70°C. Then, it is combined with the feed water (temperature ts0 is 70°C) of the steam turbine regenerative system and supplied to the second heat medium water heat exchanger 7. The supply water temperature ts1 is about 70°C, and the water temperature ts2 after being heated by the second heat medium water heat exchanger 7 reaches above 120°C (that is, the return water temperature reaches above 120°C). A part of the outlet water of the second heat medium water heat exchanger 7 returns to the steam turbine regenerative system, replacing part of the extraction steam of the steam turbine regenerative system, enabling this part of the extraction steam to continue to do work in the steam turbine, thereby reducing the coal consumption. The remaining heat medium water enters the primary air preheater 8 and the secondary air preheater 9 respectively to heat the primary air and the secondary air. Then, the primary air and the secondary air continue to enter the air preheater 2 for heating, enabling both the primary air and the secondary air to effectively participate in the flue gas waste heat regeneration, especially the flue gas waste heat regeneration in the low-temperature part. The airborne heat regeneration can directly reduce the input heat brought in by the coal. In other words, since the temperature of the air returning to the furnace increases after the secondary air is heated by the secondary air preheater 9, the boiler efficiency is improved; at the same time, since the temperature of the working medium water returning to the steam turbine regenerative system increases, the heat consumption of the steam turbine is reduced. The improvement of the boiler efficiency combined with the reduction of the steam turbine heat consumption further improves the cycle efficiency of the unit. By applying the construction method of the present application and reasonably designing the flow rates of the first heat medium water circuit 10, the second heat medium water circuit 11, and the third heat medium water circuit, the cycle efficiency of the unit can be maximally improved.

[0045] It should be emphasized that in the present application, increasing the inlet flue gas temperature T2 of the second heat medium water heat exchanger 7 (that is, the outlet flue gas temperature of the air preheater) is an important parameter for improving the cycle efficiency of the unit. In this scheme, T2 is increased to 135 - 185°C. Increasing T2 will increase the outlet water temperature ts2 of the second heat medium water heat exchanger 7. The increase of ts2 indicates an increase in the return water temperature to the steam turbine regenerative system, which is beneficial to reducing the heat consumption of the steam turbine, thereby reducing the coal consumption. At the same time, increasing T2 also creates conditions for increasing the outlet air temperature of the air preheater 2. Increasing the temperature of the air preheater 2 will increase the hot air temperature t23 of the secondary air. Increasing the hot air temperature of the secondary air means an increase in the airborne heat regeneration share and a corresponding decrease in the waterborne heat regeneration share. After calculation, when the hot air temperature ts23 of the secondary air increases by 10K, the power generation coal consumption of the unit can be reduced by 1g / kWh.

[0046] By implementing the above construction method to achieve efficient recovery and utilization of low-temperature flue gas waste heat, the comprehensive power supply coal consumption of the unit can be reduced by about 5g / kWh.

[0047] The flue gas flow of the embodiment of this application is as follows: The flue gas (T1 = 360 - 370 °C) from the outlet of the boiler economizer is cooled to T2 = 135 - 185 °C after passing through the air preheater; after passing through the second heat transfer medium water heat exchanger 7, the flue gas temperature is reduced to T3 = 85 - 90 °C; after the flue gas passes through the electrostatic precipitator 3 and the induced draft fan 4, due to the blowing and heating effect of the induced draft fan 4, the flue gas temperature rises to about T4 = 95 °C; after the flue gas is cooled by the first heat transfer medium water heat exchanger 6, the flue gas temperature drops to about T5 = 65 °C, and then the flue gas enters the desulfurization tower and is finally discharged from the chimney.

[0048] Refer to Figure 1 , in the prior art, after bypassing about 15% of the flue gas in the bypass flue, the air outlet temperature of the air preheater cannot reach the original design value (the level before the bypass flue is not set), and the air-borne heat regeneration decreases instead of increasing, which will cause the decline of the boiler efficiency and the unit cycle efficiency and reduce the effect of flue gas waste heat recovery. However, in this application, by raising the outlet flue gas temperature of the air preheater to 135 - 185 °C and simultaneously increasing the heating surface area of the secondary air preheater and increasing the share of air-borne heat regeneration, the boiler efficiency and the unit cycle efficiency are improved.

[0049] Specifically, the air preheater 2 includes a primary air preheater 21 and a secondary air preheater 23 arranged on the main flue 1. Since the temperature of the primary air usually does not need to be too high, the temperature of the primary air mainly depends on the requirements of the coal type for drying. The appropriate primary air temperature can be achieved by adjusting the heating surface area of the primary air preheater 21. However, increasing the secondary air temperature is of great significance for reducing the coal consumption for power generation of the unit. When the secondary air temperature increases, especially during low-load operation, it not only helps to stably burn in the boiler and burn out the pulverized coal, improving the operation stability and economy, but also is conducive to organizing staged combustion and reducing the generation of NOx, with good environmental performance. Therefore, the construction method of this application also includes: changing a part of the heating surface of the primary air preheater 21 to preheat the secondary air, forming an additional secondary air preheater 22, that is, while reducing the heating surface area of the primary air preheater 21, increasing the heating surface area of the secondary air preheater. The primary air enters the primary air preheater 21 after passing through the primary air air heater 8, and the secondary air enters the secondary air preheater 23 and the additional secondary air preheater 22 after passing through the secondary air air heater 9. Due to the increase in the heating surface area of the secondary air and the increase in the inlet flue gas temperature of the second heat medium water heat exchanger 7 to 135 - 185 °C, the hot air temperature of the secondary air is increased by 3 - 15 K compared with the conventional situation under the combined action, thereby improving the boiler efficiency and reducing the coal consumption for power generation of the unit. It should be noted that after the secondary air temperature t23 increases, the boiler needs to make adaptive combustion adjustments. On the one hand, it is necessary to try to improve the boiler combustion efficiency and boiler thermal efficiency, and on the other hand, it is necessary to reduce the generation of NOx through deep staged combustion. How to specifically make combustion adjustments is not specifically limited in this application. In addition, the hot air temperature of the secondary air of different units will be different. Therefore, the increase in the hot air temperature of the secondary air by 3 - 15 K in this application is applicable to all units applying the above construction method.

[0050] It is emphasized again that the flue gas waste heat should be used as much as possible to heat the combustion air, especially to heat the secondary air, and the waste heat recovery benefit obtained by increasing the secondary air temperature is the largest. In this application, the heating surface area of the primary air preheater 21 is reduced to avoid too high a hot air temperature of the primary air. At the same time, the heating surface area of the secondary air preheater increases, which can also increase the hot air temperature of the secondary air, thereby improving the boiler efficiency.

[0051] Specifically, a water pressurizing pump 12 is arranged on the water inlet pipeline of the first heat medium water circuit 10. The construction method also includes: increasing the flow rate of the water inlet pipeline on the first heat medium water circuit 10 through the water pressurizing pump 12 (i.e., the condensate pressurizing pump), so as to increase the logarithmic mean temperature difference of the first heat medium water heat exchanger 6 and reduce the heat transfer area of the first heat medium water heat exchanger 6. In a specific embodiment, by increasing the flow rate of the water pressurizing pump 12, the heat transfer temperature difference at the hot end of the first heat medium water heat exchanger 6 can be increased from 10 K to 25 K, and the logarithmic mean temperature difference can be increased from 16.4 K to 25 K. Finally, the heat transfer area of the first heat medium water heat exchanger 6 can be reduced by one-third, and the reduction of the heat transfer area of the first heat medium water heat exchanger 6 can reduce its construction cost.

[0052] It should also be noted that the cold - end heat transfer temperature difference of the second hot - medium water heat exchanger 7 remains basically unchanged, while the hot - end heat transfer temperature difference will increase slightly with the increase of T2. Therefore, although the heat transfer amount increases synchronously with the increase of T2, the heat - exchange area of the second hot - medium water heat exchanger 7 will not increase excessively.

[0053] Specifically, the third hot - medium water circuit includes a primary air hot - medium water branch 13 and a secondary air hot - medium water branch 14. The primary air air preheater 8 is connected to the primary air hot - medium water branch 13, and the secondary air air preheater 9 is connected to the secondary air hot - medium water branch 14. An inlet regulating valve 15 for the primary air air preheater is arranged on the primary air hot - medium water branch 13, an inlet regulating valve 16 for the secondary air air preheater is arranged on the secondary air hot - medium water branch 14, and a hot - medium water return regulating valve 17 is arranged on the main return line of the second hot - medium water circuit 11.

[0054] The construction method includes: by adjusting the inlet regulating valve 15 for the primary air air preheater and / or the hot - medium water return regulating valve 17, the temperature of the primary air hot air is adjusted, and thus the cold air incorporated into the coal - pulverizing system can be cancelled or reduced, reducing irreversible losses; by adjusting the inlet regulating valve 16 for the secondary air air preheater and / or the hot - medium water return regulating valve 17, the temperature of the secondary air hot air is adjusted. By reasonably distributing the flow rate on the secondary air hot - medium water branch 14, the temperature t23 of the secondary air can be adjusted, which is crucial for improving the boiler efficiency and the unit cycle efficiency during low - load operation; by adjusting the inlet regulating valve 15 for the primary air air preheater, the inlet regulating valve 16 for the secondary air air preheater and / or the hot - medium water return regulating valve 17, the return water temperature ts2 of the second hot - medium water heat exchanger 7 is adjusted. The increase of ts2 indicates the increase of the return water temperature to the steam turbine regenerative system, which is beneficial to reducing the heat consumption of the steam turbine, thereby reducing the coal consumption and improving the unit cycle efficiency. Similarly, through the setting of each valve in this application, the adjustable means of the unit are increased and the adjustable range is widened, ensuring greater flexibility in operation. The specific adjustment process is not the focus of this application and will not be elaborated here.

[0055] Specifically, an inlet valve 18 for the first hot - medium water heat exchanger is arranged on the inlet pipeline of the first hot - medium water circuit 10, and an outlet valve 19 for the first hot - medium water heat exchanger is arranged on the outlet pipeline of the first hot - medium water circuit 10. The hot - medium water of the second hot - medium water circuit 11 is connected from the steam turbine regenerative system, and a make - up water valve 20 for the hot - medium water heat exchanger is arranged on the pipeline before mixing with the hot - medium water in the first hot - medium water circuit 10.

[0056] The construction method includes: adjusting the inlet valve 18 of the first heat medium water heat exchanger and / or the outlet valve 19 of the first heat medium water heat exchanger and / or the makeup water valve 20 of the heat medium water heat exchanger and / or the inlet regulating valve 15 of the primary air air preheater and / or the inlet regulating valve 16 of the secondary air air preheater and / or the heat medium water return regulating valve 17 to adjust the flue gas temperature at the inlet of the electrostatic precipitator, so as to ensure the safe operation of downstream equipment.

[0057] Furthermore, the construction method is applied to the retrofit of existing units or the construction of new units. When applied to the retrofit of existing units, there is no need for large-scale demolition, which is convenient for retrofit; when applied to the construction of new units, the equipment requirements are less, the floor area is small, and the cost is low.

[0058] The present invention also provides a deep recuperation system for the waste heat of the flue gas of a power station boiler. The system includes an air preheater 2, an electrostatic precipitator 3, an induced draft fan 4, and a desulfurization tower 5 arranged in sequence on the main flue 1; and further includes a first heat medium water heat exchanger 6 arranged on the main flue 1 between the induced draft fan 4 and the desulfurization tower 5, and a second heat medium water heat exchanger 7 arranged on the main flue 1 between the electrostatic precipitator 3 and the air preheater 2. The first heat medium water heat exchanger 6 and the second heat medium water heat exchanger 7 operate in series, and a primary air air preheater 8 is arranged on the inlet pipeline of the primary air before the air preheater 2, and a secondary air air preheater 9 is arranged on the inlet pipeline of the secondary air before the air preheater 2; the outlet temperature of the air preheater is 135 - 185 °C.

[0059] A first heat medium water circuit 10 is connected to the first heat medium water heat exchanger 6, and a second heat medium water circuit 11 is connected to the second heat medium water heat exchanger 7; the heat medium water of the first heat medium water circuit 10 is connected from the condensate system, and the heat medium water of the second heat medium water circuit 11 is connected from the steam turbine regenerative system; the outlet water of the first heat medium water circuit 10 and the inlet water of the second heat medium water circuit 11 are mixed and then enter the second heat medium water heat exchanger 7; a part of the outlet water of the second heat medium water circuit 11 returns to the steam turbine regenerative system, and the other part of the outlet water is connected to the primary air air preheater 8 and the secondary air air preheater 9 respectively through a third heat medium water circuit. The primary air air preheater 8 is used to heat the primary air, and the secondary air air preheater 9 is used to heat the secondary air; the outlet water of the third heat medium water circuit and the inlet water of the second heat medium water circuit 11 are mixed and then enter the second heat medium water heat exchanger 7.

[0060] Furthermore, the air preheater 2 includes a primary air preheater 21 and a secondary air preheater 23 connected in parallel on the main flue 1. Part of the heating surface of the primary air preheater 21 is changed to be used for preheating the secondary air to form an additional secondary air preheater 22;

[0061] The primary air fan is connected to the primary air preheater 21 through the primary air air preheater 8, and the secondary air fan is connected to the additional secondary air preheater 22 and the secondary air preheater 23 respectively through the secondary air air preheater 9.

[0062] Furthermore, a water pressurizing pump 12 and a first heat medium water heat exchanger inlet valve 18 are provided on the inlet pipeline of the first heat medium water circuit 10, and a first heat medium water heat exchanger outlet valve 19 is provided on the outlet pipeline of the first heat medium water circuit 10;

[0063] The heat medium water of the second heat medium water circuit 11 is connected from the steam turbine regenerative system, and a heat medium water heat exchanger makeup water valve 20 is provided on the pipeline before mixing with the heat medium water in the first heat medium water circuit 10.

[0064] Furthermore, the third heat medium water circuit includes a primary air heat medium water branch 13 and a secondary air heat medium water branch 14. The primary air air preheater 8 is connected to the primary air heat medium water branch 13, and the secondary air air preheater 9 is connected to the secondary air heat medium water branch 14;

[0065] A primary air air preheater inlet regulating valve 15 is provided on the primary air heat medium water branch 13, and a secondary air air preheater inlet regulating valve 16 is provided on the secondary air heat medium water branch 14;

[0066] A heat medium water return regulating valve 17 is provided on the main circuit of the second heat medium water circuit 11.

[0067] The deep heat recovery system for the flue gas waste heat of the power station boiler provided by the present application is constructed by the above construction method, and thus has at least all the beneficial effects brought by the technical solutions of the embodiments of the above construction method, which will not be elaborated here one by one.

[0068] The above further describes the present invention with the aid of specific embodiments. However, it should be understood that the specific description here should not be construed as a limitation on the essence and scope of the present invention. Various modifications made by those of ordinary skill in the art to the above embodiments after reading this specification all fall within the scope protected by the present invention.

Claims

1. A construction method for a deep recuperation system of flue gas waste heat in a power station boiler, characterized in that Based on the realization of the deep heat recovery system for the flue gas waste heat of a power station boiler, the system includes an air preheater, an electrostatic precipitator, an induced draft fan, and a desulfurization tower arranged in sequence on the main flue. The construction method includes: a first heat medium water heat exchanger arranged on the main flue between the induced draft fan and the desulfurization tower, a second heat medium water heat exchanger arranged on the main flue between the electrostatic precipitator and the air preheater, and the first heat medium water heat exchanger and the second heat medium water heat exchanger operate in series; a primary air air preheater arranged on the inlet pipeline of the primary air before the air preheater, and a secondary air air preheater arranged on the inlet pipeline of the secondary air before the air preheater. A first heat medium water circuit is connected to the first heat medium water heat exchanger, and a second heat medium water circuit is connected to the second heat medium water heat exchanger. The heat medium water of the first heat medium water circuit is connected from the condensate water system, and the heat medium water of the second heat medium water circuit is connected from the steam turbine heat recovery system; the outlet water of the first heat medium water circuit and the inlet water of the second heat medium water circuit are mixed and then enter the second heat medium water heat exchanger; a part of the outlet water of the second heat medium water circuit returns to the steam turbine heat recovery system, and the other part of the outlet water is connected to the primary air air preheater and the secondary air air preheater respectively through a third heat medium water circuit; the outlet water of the third heat medium water circuit and the inlet water of the second heat medium water circuit are mixed and then enter the second heat medium water heat exchanger. The construction method further includes: adjusting the flow rate of the first heat medium water circuit and / or the second heat medium water circuit and / or the third heat medium water circuit to increase the outlet temperature of the air preheater to 135 - 185 °C; and increasing the heating area of the secondary air to increase the hot air temperature of the secondary air by 3 - 15 K.

2. The construction method according to claim 1, characterized in that, The air preheater includes a primary air preheater and a secondary air preheater arranged on the main flue, and the construction method further includes: Changing part of the heating surface of the primary air preheater to be used for preheating the secondary air to form an additional secondary air preheater; the primary air enters the primary air preheater after passing through the primary air air preheater, and the secondary air enters the secondary air preheater and the additional secondary air preheater after passing through the secondary air air preheater.

3. The construction method according to claim 1, wherein A water pressurizing pump is arranged on the inlet pipeline of the first heat medium water circuit, and the construction method further includes: increasing the flow rate of the inlet pipeline on the first heat medium water circuit through the water pressurizing pump to increase the logarithmic mean temperature difference of heat transfer of the first heat medium water heat exchanger, so as to reduce the heat transfer area of the first heat medium water heat exchanger.

4. The construction method according to claim 1, characterized in that The third heat medium water circuit includes a primary air heat medium water branch and a secondary air heat medium water branch. The primary air air preheater is connected to the primary air heat medium water branch, and the secondary air air preheater is connected to the secondary air heat medium water branch; a primary air air preheater inlet regulating valve is arranged on the primary air heat medium water branch, and a secondary air air preheater inlet regulating valve is arranged on the secondary air heat medium water branch; a heat medium water return regulating valve is arranged on the main circuit of the second heat medium water circuit. The construction method includes: adjusting the primary air hot air temperature by adjusting the inlet regulating valve of the primary air preheater and / or the return water regulating valve of the heat transfer medium water; adjusting the secondary air hot air temperature by adjusting the inlet regulating valve of the secondary air preheater and / or the return water regulating valve of the heat transfer medium water; and adjusting the return water temperature of the second heat transfer medium heat exchanger by adjusting the inlet regulating valve of the primary air preheater, the inlet regulating valve of the secondary air preheater and / or the return water regulating valve of the heat transfer medium water.

5. The construction method according to claim 4, characterized in that, A first heat transfer medium water heat exchanger inlet valve is provided on the inlet pipeline of the first heat transfer medium water circuit, and a first heat transfer medium water heat exchanger outlet valve is provided on the outlet pipeline of the first heat transfer medium water circuit; the heat transfer medium water of the second heat transfer medium water circuit is connected from the steam turbine regenerative system, and a heat transfer medium water heat exchanger make-up water valve is provided on the pipeline before mixing with the heat transfer medium water in the first heat transfer medium water circuit; The construction method includes: adjusting the inlet regulating valve of the first heat transfer medium water heat exchanger and / or the outlet regulating valve of the first heat transfer medium water heat exchanger and / or the make-up water valve of the heat transfer medium water heat exchanger and / or the inlet regulating valve of the primary air preheater and / or the inlet regulating valve of the secondary air preheater and / or the return water regulating valve of the heat transfer medium water to adjust the flue gas temperature at the inlet of the electrostatic precipitator.

6. The construction method according to claim 1, wherein The construction method is applied to the retrofit of existing units or to new units.

7. A deep heat recovery system for the flue gas waste heat of a power station boiler, characterized in that, The system includes an air preheater, an electrostatic precipitator, an induced draft fan and a desulfurization tower arranged in sequence on the main flue; further included is a first heat transfer medium water heat exchanger provided on the main flue between the induced draft fan and the desulfurization tower, a second heat transfer medium water heat exchanger provided on the main flue between the electrostatic precipitator and the air preheater, the first heat transfer medium water heat exchanger and the second heat transfer medium water heat exchanger operating in series, and a primary air preheater provided on the inlet air duct of the primary air before the air preheater, a secondary air preheater provided on the inlet air duct of the secondary air before the air preheater; the outlet temperature of the air preheater is 135 - 185 °C; A first heat transfer medium water circuit is connected to the first heat transfer medium water heat exchanger, and a second heat transfer medium water circuit is connected to the second heat transfer medium water heat exchanger; the heat transfer medium water of the first heat transfer medium water circuit is connected from the condensate system, and the heat transfer medium water of the second heat transfer medium water circuit is connected from the steam turbine regenerative system; the outlet water of the first heat transfer medium water circuit is mixed with the inlet water of the second heat transfer medium water circuit and then enters the second heat transfer medium water heat exchanger; a part of the outlet water of the second heat transfer medium water circuit returns to the steam turbine regenerative system, and the other part of the outlet water is connected to the primary air preheater and the secondary air preheater respectively through a third heat transfer medium water circuit, the primary air preheater is used to heat the primary air, and the secondary air preheater is used to heat the secondary air; the outlet water of the third heat transfer medium water circuit is mixed with the inlet water of the second heat transfer medium water circuit and then enters the second heat transfer medium water heat exchanger.

8. The deep heat recovery system for the flue gas waste heat of a power station boiler according to claim 7, characterized in that The air preheater includes a primary air preheater and a secondary air preheater arranged on the main flue, and part of the heating surface of the primary air preheater is changed to be used for preheating the secondary air to form an additional secondary air preheater; The primary air fan is connected to the primary air preheater through the primary air air preheater, and the secondary air fan is connected to the additional secondary air preheater and the secondary air preheater respectively through the secondary air air preheater.

9. The flue gas waste heat deep regeneration system for a power station boiler according to claim 7, characterized in that A water pressurizing pump and a primary heat medium water heat exchanger inlet valve are provided on the inlet pipeline of the first heat medium water circuit, and a primary heat medium water heat exchanger outlet valve is provided on the outlet pipeline of the first heat medium water circuit; The heat medium water of the second heat medium water circuit is connected from the steam turbine regenerative system, and a heat medium water heat exchanger makeup water valve is provided on the pipeline before mixing with the heat medium water in the first heat medium water circuit.

10. The deep recuperation system for the waste heat of the flue gas of a power station boiler according to claim 7, characterized in that, The third heat medium water circuit includes a primary air heat medium water branch and a secondary air heat medium water branch. The primary air air preheater is connected to the primary air heat medium water branch, and the secondary air air preheater is connected to the secondary air heat medium water branch; A primary air air preheater inlet regulating valve is provided on the primary air heat medium water branch, a secondary air air preheater inlet regulating valve is provided on the secondary air heat medium water branch, and a heat medium water return regulating valve is provided on the main circuit of the second heat medium water circuit.

Images