Boiler flue gas waste heat deep recovery energy-saving system

Abstract

The invention discloses a boiler flue gas waste heat deep recovery energy-saving system. According to the system, an air spraying device is arranged on a boiler air inlet pipeline, and a flue gas humidifying and cooling device is arranged on a smoke exhaust flue; a water circulation pipeline is arranged among the flue gas heat exchanger, the air spraying device and the flue gas humidifying and cooling device, condensate water generated after waste heat of flue gas is recycled through the flue gas heat exchanger firstly enters a condensate water tank, and then part or all of the condensate water is conveyed to the air spraying device and the flue gas humidifying and cooling device. By spraying and humidifying air and flue gas, deep recovery of flue gas waste heat is achieved, and the system is simple in structure, small in implementation difficulty and suitable for different application environments.

Description

Technical Field

[0001] This invention relates to the field of energy conservation, environmental protection and flue gas waste heat recovery, specifically to a deep waste heat recovery and energy-saving system for boiler flue gas. Background Technology

[0002] Coal-fired boilers or gas-fired boilers are common boiler equipment used for heating, bathing and other purposes. Common coal-fired boilers and gas-fired boilers include hot water boilers and steam boilers.

[0003] Coal-fired boilers typically produce flue gas with high sulfide content, which is usually reduced using wet desulfurization technology. However, even after wet desulfurization, the flue gas from coal-fired boilers still contains a high amount of water vapor. Similarly, gas-fired boilers, influenced by the chemical composition of their fuels, also produce flue gas with high water vapor content. Furthermore, since the flue gas temperature of both coal-fired and gas-fired boilers is usually at or above the saturation temperature of water vapor, the flue gas water vapor contains a significant amount of latent heat. Analysis shows that the latent heat of water vapor in the flue gas of coal-fired or gas-fired boilers accounts for as much as 10-11% of the fuel's calorific value. Currently, there is a lack of effective measures for recovering and utilizing this waste heat, resulting in substantial energy waste. Therefore, the in-depth recovery and utilization of waste heat from coal-fired or gas-fired boilers, including latent heat of water vapor, is of great significance for energy conservation and emission reduction.

[0004] To recover and utilize the waste heat from boiler flue gas, the current conventional approach is to use hot water as a carrier and simultaneously install a heat pump and a flue gas-water heat exchanger. The flue gas-water heat exchanger is installed on the flue gas pipeline, and the waste heat from the flue gas is recovered through the hot water carrier and then sent to the heat pump unit to extract the waste heat from the flue gas. However, this method has many technical problems in practice, such as (1) the heat pump requires a high-grade heat source to drive it; (2) the heat pump is expensive, requires a large investment, and has a long investment recovery period; (3) the heat pump requires additional space, is greatly limited by space, and is difficult to use for retrofitting the pipeline systems of existing hot water boilers or steam boilers.

[0005] In response to practical problems, the inventors of this application have previously disclosed two improved systems: (1) A waste heat recovery system is disclosed in patent CN114278956B, which installs an air heater on the boiler air inlet pipe and a flue gas heat exchanger on the boiler flue gas outlet flue. Heating water first enters the air heater to heat the air, and the cooled heating water then enters the flue gas heat exchanger to exchange heat with the flue gas. The heated heating water is then sent back to the boiler, thereby recovering the waste heat in the low-temperature flue gas. When the amount of waste heat recovered from the flue gas is small, the system does not need to drive a heat source, that is, it does not need to install a heat pump. (2) Another waste heat recovery system is disclosed in CN221464409U, which is equipped with an air spray device and an air heater in the boiler air inlet pipe, and a flue gas heat exchanger in the boiler flue gas duct. A heat transfer medium is installed between the air heater and the flue gas heat exchanger. The heat transfer medium and the flue gas exchange heat in the flue gas heat exchanger. The heat of the low temperature flue gas is transferred to the heat transfer medium. After absorbing the heat of the flue gas, the heat transfer medium enters the air heater to heat the air. The heated air enters the boiler, thereby realizing the deep recovery of the waste heat of the flue gas. That is, the waste heat of the flue gas is transferred to the heat transfer medium, and the heat transfer medium transfers the heat to the air and enters the boiler with the air.

[0006] Further optimizing boiler flue gas waste heat recovery and utilization systems to achieve both deep recovery of boiler flue gas waste heat and practical engineering feasibility, enabling the transformation of existing boiler pipeline systems, while also improving boiler efficiency, reducing fuel consumption, simplifying system structure, reducing investment, and increasing return on investment remains a key focus in this field. Summary of the Invention

[0007] This application aims to provide a deep flue gas waste heat recovery system that can ensure the recovery of flue gas waste heat while greatly simplifying the system structure, making it adaptable to different industrial plants and application scenarios.

[0008] To achieve the above objectives, according to one embodiment of the present invention, the technical solution provided is as follows:

[0009] A deep waste heat recovery and energy-saving system for boiler flue gas includes:

[0010] An air spray device and an air heater are installed sequentially on the boiler air inlet duct;

[0011] Install a flue gas heat exchanger on the boiler exhaust duct;

[0012] After being humidified by the air spraying device, the air enters the air heater for heat exchange and temperature increase, and finally enters the boiler;

[0013] All or part of the heating water enters the air heater to heat the air, and the cooled heating water enters the flue gas heat exchanger to exchange heat with the flue gas.

[0014] The heated heating water enters the boiler or is heated again in the heating network heater;

[0015] A water circulation pipeline is installed between the flue gas heat exchanger and the air spray device. The condensate produced after the flue gas recovers waste heat through the flue gas heat exchanger enters the condensate tank, and then some or all of the condensate is transported to the air spray device.

[0016] Preferably, the deep recovery and energy-saving system for waste heat from boiler flue gas further includes: a flue gas humidification and cooling device and a flue gas heat exchanger are sequentially installed on the boiler's flue gas duct; after the flue gas is humidified by the flue gas humidification and cooling device, the water vapor content in the flue gas increases or reaches saturation, and then it enters the flue gas heat exchanger to exchange heat with cold water to recover the waste heat of the flue gas; the flue gas is discharged after the waste heat is recovered.

[0017] In this invention, the humidification and cooling device is used to atomize and / or vaporize the spray water, and then spray it into the flue gas, so as to increase the water vapor content in the flue gas or reach saturation, thereby increasing the water dew point temperature of the flue gas.

[0018] Preferably, in the deep recovery and energy-saving system for waste heat from boiler flue gas, a water circulation pipeline is installed between the flue gas heat exchanger and the flue gas humidification and cooling device. The condensate from the flue gas in the flue gas heat exchanger enters the condensate tank, and then some or all of the condensate is transported to the flue gas humidification and cooling device, reducing the need for additional spray water.

[0019] More preferably, the condensate generated after the flue gas recovers waste heat through the flue gas heat exchanger enters a condensate tank. Part of the condensate is then sent to an air spray device, and the rest is sent to a flue gas humidification and cooling device. By using the condensate tank to collect the condensate from the flue gas and then using it to spray and humidify the air and flue gas, the need for additional spray water is reduced.

[0020] In this invention, the air heater and flue gas heat exchanger are indirect heat exchangers, such as plate heat exchangers and tube heat exchangers.

[0021] Preferably, the air heater and flue gas heat exchanger are plate heat exchangers.

[0022] Plate heat exchangers are characterized by high heat transfer coefficient, compact structure, small footprint, and flexible layout. They are not limited by the structure and layout of boiler flue gas ducts and air inlet pipes, and have strong engineering adaptability, which can well meet the retrofit requirements of various new and old boiler systems.

[0023] In this invention, the heating network heater is a partitioned heat exchanger.

[0024] The present invention does not impose any particular restrictions on the type of air spraying device and flue gas humidification and cooling device. They can be spraying devices commonly used in the prior art, such as tubular sprayers, shower head sprayers, ring pipe multi-hole sprayers, nozzles with liquid atomization function, etc.

[0025] Preferably, the air spray device and the flue gas humidification and cooling device are nozzles, which have the function of atomizing liquid.

[0026] In this invention, there is no limit to the number of air spray device, flue gas humidification and cooling device, flue gas heat exchanger, and heating network heater; there can be one or more.

[0027] This invention does not particularly limit the type of boiler; it is applicable to coal-fired boilers, gas-fired boilers, or oil-fired boilers. In practical applications, it can be a hot water boiler, a steam boiler, or a waste incinerator.

[0028] This invention does not impose any particular restrictions on the flue gas duct of the boiler. This invention is applicable to flue gas ducts of various types of boilers. The flue gas duct can be a vertical flue gas duct or a horizontal flue gas duct. It can be the original flue gas duct of the boiler or a modified flue gas duct.

[0029] This invention does not impose any particular restrictions on the boiler's air intake pipe. This invention is applicable to various types of boiler air intake pipes. The air intake pipe can be a vertical air intake pipe or a horizontal air intake pipe, and can be the original air intake pipe of the boiler or a modified air intake pipe.

[0030] The beneficial effects of this invention are:

[0031] Compared with existing technologies, which suffer from low waste heat recovery rates from flue gas, high costs of heat pump units, high operating and maintenance costs, complex structures, large footprints, strong spatial and environmental constraints, and poor engineering adaptability, this invention has the following advantages:

[0032] (1) Spraying and humidifying the boiler intake air increases the water content in the air, thereby increasing the air's heat capacity and allowing the air to recover more heat from the heating water return water. The increased water content in the air also increases the water vapor content in the flue gas produced by boiler combustion, thus increasing the flue gas's heat release capacity. With this increased heat release capacity, under the same flue gas temperature drop, 50-90% more heat can be recovered from the flue gas.

[0033] (2) A flue gas humidification and cooling device is installed before the flue gas heat exchanger to increase the water vapor content in the flue gas and increase the water dew point temperature. The amount of waste heat recovered in the first heat exchange stage (cooling section) is reduced, and the amount of waste heat recovered in the second heat exchange stage (condensation section) is increased, thereby improving the heat transfer coefficient of the flue gas heat exchanger, reducing the heat exchange area, reducing the equipment weight, reducing equipment investment, saving floor space, and thus facilitating equipment installation.

[0034] (3) The system has a simple structure, is easy to implement, and has high energy efficiency in waste heat recovery.

[0035] (4) While deeply recovering the waste heat of boiler flue gas, it improves boiler efficiency and reduces fuel consumption.

[0036] (5) The present invention adopts a partition wall heat exchanger, which has the characteristics of compact structure, small footprint and flexible layout. It is not limited by the structure and layout of boiler flue gas duct and air inlet duct during use, and has strong engineering adaptability. It can well meet the transformation needs of various new and old boiler systems. Attached Figure Description

[0037] Figure 1 : A schematic diagram of the structure of the deep recovery and energy-saving system for waste heat from flue gas in Embodiment 1 of the present invention.

[0038] Figure 2 : A schematic diagram of the structure of the deep recovery and energy-saving system for waste heat from flue gas in Embodiment 2 of the present invention.

[0039] Figure 3 : A schematic diagram of the structure of the deep recovery and energy-saving system for waste heat from flue gas in Embodiment 3 of the present invention.

[0040] Figure 4 : A schematic diagram of the structure of the deep recovery and energy-saving system for waste heat from flue gas in Embodiment 4 of the present invention.

[0041] Figure 5 : A schematic diagram of the structure of the deep recovery and energy-saving system for waste heat from flue gas in Embodiment 5 of the present invention.

[0042] Figure 6 : A schematic diagram of the structure of the deep recovery and energy-saving system for waste heat from flue gas in Embodiment 6 of the present invention.

[0043] Explanation of reference numerals in the attached figures:

[0044] 1-Boiler; 2-Fan; 3-Air heater; 4-Air spray device; 5-Flue gas heat exchanger I; 6-Condensate tank; 7-Spray water pump; 8-Flue gas humidification and cooling device; 9-Flue gas heat exchanger II; 10-Heating network heater. Detailed Implementation

[0045] In response to the technical problems existing in practice, the inventors of this application have previously disclosed two improved systems: (1) A waste heat recovery system was disclosed in patent CN114278956B, which sets up an air heater on the boiler air inlet pipe and a flue gas heat exchanger on the boiler flue gas outlet flue. The heating water first enters the air heater to heat the air, and the cooled heating water then enters the flue gas heat exchanger to exchange heat with the flue gas. The heated heating water is then sent back to the boiler, thereby recovering the waste heat in the low-temperature flue gas. (2) Another waste heat recovery system is disclosed in CN221464409U, which is equipped with an air spray device and an air heater in the boiler air inlet pipe, and a flue gas heat exchanger in the boiler flue gas duct. A heat transfer medium is installed between the air heater and the flue gas heat exchanger. The heat transfer medium and the flue gas exchange heat in the flue gas heat exchanger. The heat of the low temperature flue gas is transferred to the heat transfer medium. After absorbing the heat of the flue gas, the heat transfer medium enters the air heater to heat the air. The heated air enters the boiler, thereby realizing the deep recovery of the waste heat of the flue gas. That is, the waste heat of the flue gas is transferred to the heat transfer medium, and the heat transfer medium transfers the heat to the air and enters the boiler with the air.

[0046] The system disclosed in patent CN114278956B is more suitable for industrial devices with small amounts of waste heat recovery from flue gas. When the amount of waste heat recovery from flue gas is large, heat pump technology is required.

[0047] The system disclosed in patent CN221464409U can guarantee the amount of waste heat recovered from flue gas, has a wider range of applicable scenarios, and eliminates the need for heat pumps and driving heat sources compared to conventional systems, but requires the installation of a heat transfer medium water system.

[0048] Based on prior inventions, this invention further optimizes the waste heat recovery system and proposes the technical solution of this invention.

[0049] The technical solution provided by this invention involves installing an air spraying device on the boiler's air inlet duct. After the air is sprayed and humidified by the air spraying device, the water content in the air increases, and the air's heat absorption capacity increases. Under the same air temperature rise, the air can absorb more heat from the heating water. After the air enters the air heater and is heated by the heating water, the air temperature rises. At the same time, the liquid water in the air vaporizes into gaseous water. After the air enters the boiler and is burned, it produces flue gas. The water vapor content in the flue gas also increases, and the heat release capacity of the flue gas increases. That is, under the same flue gas temperature drop, 50-90% more heat can be recovered from the flue gas.

[0050] The heating water, in whole or in part, enters an air heater to heat the air. After cooling, the water enters one or more flue gas heat exchangers to exchange heat with the flue gas, absorbing its waste heat. The heated water is then further heated by a boiler or heating network heater before being supplied externally. This process recovers waste heat from the flue gas and increases the temperature of the boiler's intake air and the heating water.

[0051] Furthermore, a flue gas humidification and cooling device is installed before the flue gas heat exchanger. Before the flue gas exchanges heat with the heat exchanger, it is sprayed to humidify and cool the flue gas, so that the water vapor content in the flue gas increases or reaches saturation. Then it enters the flue gas heat exchanger for heat exchange. The first heat exchange stage (cooling section) is partially or completely transformed into the second heat exchange stage (condensation section), which greatly improves the heat exchange capacity. Under the condition of recovering the same amount of heat, the heat exchange area of ​​the heat exchanger can be significantly reduced.

[0052] The principle of setting up a flue gas humidification and cooling device is that flue gas water heat exchange recovery of flue gas waste heat includes two heat exchange stages:

[0053] The first heat exchange stage is the cooling section. During the flue gas cooling process, no liquid water is precipitated, that is, there is no phase change, until the temperature reaches the water dew point.

[0054] The second heat exchange stage is the condensation stage, where the flue gas begins to cool down from the water dew point temperature, during which liquid water is precipitated, i.e., a phase change occurs.

[0055] For example, when the flue gas temperature drops from 75°C to 30°C and the flue gas water dew point temperature is 40°C, the first heat exchange stage (cooling stage) is when the flue gas temperature drops from 75°C to the dew point temperature of 40°C, and there is no phase change in the flue gas; in the second heat exchange stage (condensation stage), the flue gas temperature drops from the dew point temperature of 40°C to 30°C, and condensate is released in the flue gas, and the water in the flue gas undergoes a phase change.

[0056] In the first heat exchange stage (cooling stage), the heat exchange between flue gas and water is a phase-change-free process. Due to the small gas phase heat transfer coefficient, the overall heat transfer coefficient in the first heat exchange stage is very small.

[0057] In the second heat exchange stage (condensation stage), the heat exchange between flue gas and water involves phase change, specifically flue gas condensation and water heat exchange. The heat transfer coefficient of flue gas condensation is much larger than that of gas-phase cooling in the first heat exchange stage (cooling stage). Therefore, the total heat transfer coefficient of the second heat exchange stage (condensation stage) is about ten times larger than that of the first heat exchange stage (cooling stage).

[0058] The inventive concept of this application differs from the conventional understanding in the field. Conventionally, a greater temperature difference between the flue gas entering a heat exchanger and the cooling medium is considered to result in greater heat transfer capacity, or a smaller heat exchanger area. Water spraying for humidification lowers the flue gas inlet temperature, which conventionally leads to the assumption that this reduces the heat transfer capacity of the heat exchanger, or that a larger heat exchanger area is needed to recover the same amount of heat. However, this is a misconception.

[0059] This invention uses a humidification and cooling spray device to lower the flue gas temperature while simultaneously increasing or saturating the water vapor in the flue gas, thereby raising the flue gas dew point temperature. The effect is that the first heat exchange stage (cooling section) is partially or completely transformed into the second heat exchange stage (condensation section). Since the heat transfer coefficient of condensation is about ten times greater than that of cooling, and much greater than the decrease in temperature difference caused by the reduction in flue gas temperature, the heat exchange area required to recover the same amount of heat after humidification and cooling is significantly reduced. The heat exchange area of ​​the flue gas heat exchanger using this spray humidification and cooling method is reduced by more than 30% compared to traditional flue gas heat exchangers.

[0060] In this invention, an air spray device and a flue gas humidification and cooling device work together to enhance the heat exchange capacity of the entire system. The air spray device increases the water content in the boiler intake air, thereby increasing the air's heat capacity and heat carrying capacity. The air heater heats the sprayed and humidified air while evaporating liquid water into vapor water. The water vapor entering the boiler with the air is heated by combustion, cooled by heat transfer, and then discharged from the boiler with the flue gas. The increased water vapor temperature and flue gas saturation in the flue gas are thus improved, and the dew point temperature of the flue gas also increases accordingly. The discharged flue gas is further cooled and humidified by the flue gas humidification and cooling device, further reducing the flue gas temperature, increasing the water vapor content, and further increasing the water dew point temperature. Before entering the heat exchanger, the water in the flue gas has already vaporized, resulting in a comprehensive improvement in the heat exchange capacity of the entire system. While recovering the same amount of heat, the required heat exchange area of ​​the flue gas heat exchanger is reduced.

[0061] Furthermore, the flue gas waste heat recovery system is equipped with a condensate tank and a spray water pump. The condensate that is released from the flue gas during cooling in the flue gas heat exchanger is collected in the condensate tank and then pumped to an air spray device and / or a flue gas humidification and cooling device, thereby realizing the recycling of the condensate and reducing the need for additional spray water.

[0062] The present invention will now be further described with reference to the accompanying drawings, but the following embodiments do not constitute a limitation of the present invention.

[0063] Example 1

[0064] Figure 1 This invention illustrates a deep waste heat recovery system for flue gas, comprising:

[0065] An air spray device 4, an air heater 3, and a fan 2 are sequentially installed on the air inlet pipe of boiler 1.

[0066] Install a flue gas heat exchanger I5 on the boiler exhaust duct;

[0067] After being sprayed and humidified by the air spray device 4, the air enters the air heater 3 for heat exchange and temperature increase, and finally enters the boiler 1;

[0068] All heating water enters the air heater 3 to heat the air. After cooling, the heating water enters the flue gas heat exchanger I5 to exchange heat with the flue gas. After recovering the waste heat of the flue gas, it is heated up and then enters the boiler 1.

[0069] A water circulation pipeline is installed between the flue gas heat exchanger I5 and the air spray device 4. The condensate generated after the flue gas recovers waste heat through the flue gas heat exchanger I5 first enters the condensate tank 6, and then part or all of the condensate is transported to the air spray device 4 by the spray water pump 7.

[0070] After air is humidified by an air spray humidifier, the water content in the air increases, thus increasing its heat absorption capacity. The air then enters the air heater, where all the heating water is fed to heat the air. After being heated by the heating water, the air temperature rises, and the liquid water in the air vaporizes into gaseous water. This air then enters the boiler and is burned to produce flue gas. The water vapor content in the flue gas also increases, thus increasing its heat release capacity.

[0071] In some implementations, a condensate treatment device is installed at the outlet of the condensate tank, and the treated condensate is wholly or partially transported to the air spray device.

[0072] This system uses a condensate tank to collect condensate from the flue gas, and then uses the condensate to spray and humidify the air. This not only improves the utilization rate of condensate, but also reduces the need for additional spray water devices, achieving the effects of simplifying the system and reducing costs while increasing efficiency.

[0073] Example 2

[0074] Figure 2 This invention illustrates another deep waste heat recovery system for flue gas provided by the present invention. The difference between this system and Embodiment 1 is that: part of the heating water enters the air heater 3 to heat the air; the cooled heating water then enters the flue gas heat exchanger I5 to exchange heat with the flue gas, recovering waste heat from the flue gas before being heated and then entering the boiler 1. The other part of the heating water directly enters the boiler 1.

[0075] Example 3

[0076] Figure 3 This invention illustrates another deep waste heat recovery system for flue gas provided by the present invention. The difference between this system and Embodiment 1 is that a flue gas humidification and cooling device 8 is installed before the flue gas heat exchanger I5. The flue gas is sprayed, humidified, and cooled by the flue gas humidification and cooling device 8. During this process, the sprayed water enters the flue gas after atomization and / or vaporization, or undergoes atomization and / or vaporization after entering the flue gas, to increase or saturate the water vapor content in the flue gas before entering the flue gas heat exchanger I5 to exchange heat with heating water and recover waste heat from the flue gas. The flue gas is then discharged after waste heat recovery.

[0077] A water circulation pipeline is installed between the flue gas heat exchanger I5 and the flue gas humidification and cooling device 8. The condensate from the flue gas in the flue gas heat exchanger I5 first enters the condensate tank 6, and then a portion of the condensate is transported to the air spray device 4 by the spray water pump 7, while the remaining portion is transported to the flue gas humidification and cooling device 8.

[0078] In some embodiments, the system is equipped with a dust removal device and a water washing device. After dust removal and water washing, deep recovery of waste heat from the flue gas is then implemented. The dust removal device and water washing device can be a tubular sprayer, a showerhead sprayer, a ring-tube multi-hole sprayer, or a nozzle with liquid atomization function, etc., whose function is to use water to wash away pollutants or dust. However, its function is completely different from the purpose of the humidification and cooling device described in this application. The type, state, and method of spraying the liquid are different, and the effects achieved are also different.

[0079] In some implementations, after the flue gas is discharged from the boiler, it first enters a flue gas humidification and cooling device, and then enters one or more flue gas heat exchange devices.

[0080] In other embodiments, after the flue gas is discharged from the boiler, it first enters one or more flue gas heat exchangers, then one or more flue gas humidification and cooling devices, and then enters one or more flue gas heat exchangers again.

[0081] In other embodiments, a condensate treatment device is provided at the outlet of the condensate tank, and the treated condensate is transported to an air spray device and / or a flue gas humidification and cooling device.

[0082] Example 4

[0083] Figure 4 This invention illustrates another deep waste heat recovery system for flue gas provided by the present invention. The difference between this system and Example 3 is that: part of the heating water enters the air heater 3 to heat the air; the cooled heating water then enters the flue gas heat exchanger I5 to exchange heat with the flue gas, recovering waste heat from the flue gas before being heated and then entering the boiler 1. The other part of the heating water directly enters the boiler 1.

[0084] Example 5

[0085] Figure 5 This invention provides another deep waste heat recovery system for flue gas. Compared with embodiment 3, the difference is that a flue gas heat exchanger II9 is ​​added between boiler 1 and flue gas humidification and cooling device 8. Heating water enters flue gas heat exchanger I5 and flue gas heat exchanger II9 in sequence to recover waste heat from the flue gas before entering boiler 1.

[0086] In this embodiment, both flue gas heat exchanger I and flue gas heat exchanger II are plate heat exchangers.

[0087] Example 6

[0088] Figure 6 This invention provides another deep waste heat recovery system for flue gas. Compared with embodiment 3, the difference is that the deep waste heat recovery system for flue gas adds a heat network heater 10. The heating water is heated by the flue gas heat exchanger and then enters the heat network heater 10. Inside the heat network heater 10, the heating water exchanges heat with the steam generated by the boiler 1, and the heated waste water is supplied externally.

[0089] In this embodiment, boiler 1 is a steam boiler, and the heat network heater is a wall-mounted heat exchanger.

[0090] Test case

[0091] The deep waste heat recovery system for flue gas in Example 3 was tested. Comparing the differences between the present invention and the conventional process, under the condition of recovering an equal amount of waste heat from the flue gas, the system exhibits the following characteristics: flue gas temperature of 98°C, flue gas water dew point temperature of 41°C, cold water inlet temperature of 22°C, cold water outlet temperature of 34°C, and flue gas temperature reduced to 38°C after waste heat recovery.

[0092] Test 1: Traditional process, without humidification and cooling devices.

[0093] Without humidification and cooling devices, the heat transfer temperature difference is 30℃, and the heat transfer coefficient is 74W / m. 2 At ℃, the required heat exchange area for the flue gas heat exchanger is approximately 2200 m². 2 .

[0094] Test 2: The addition of a humidification and cooling device increased the water vapor content in the flue gas, but it did not reach saturation.

[0095] The temperature of the flue gas before humidification and cooling was 98℃, and the temperature of the flue gas after humidification and cooling was 60℃, while the water dew point temperature of the flue gas increased to 46℃.

[0096] The results show that the heat transfer temperature difference is 16℃, and the heat transfer coefficient is 218W / m. 2 At ℃, the required heat exchange area for the flue gas heat exchanger is approximately 1300 m². 2 .

[0097] Test 3: A humidification and cooling device was added, and the water vapor content in the flue gas reached saturation.

[0098] The temperature of the flue gas before humidification and cooling was 98℃, and the temperature after humidification and cooling was 48℃, which is the water dew point temperature of the flue gas.

[0099] The results show that with a heat transfer temperature difference of 15℃, the heat transfer coefficient is 566W / m. 2 At ℃, the required heat exchange area for the flue gas heat exchanger is approximately 560m². 2 .

[0100] The above tests show that the flue gas waste heat deep recovery system provided by the present invention can effectively improve the recovery and utilization rate and reduce the area of ​​the heat exchange device.

[0101] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0102] The present invention has been described in detail above. Specific examples have been used in the specification to illustrate the principles and implementation methods of the present invention. However, the examples are only used to help understand the present invention and should not be construed as limiting the present invention.

Claims

1. A deep waste heat recovery and energy-saving system for boiler flue gas, comprising: An air spray device and an air heater are installed sequentially on the boiler air inlet duct; Install a flue gas heat exchanger on the boiler exhaust duct; After being humidified by the air spraying device, the air enters the air heater for heat exchange and temperature increase, and then enters the boiler; All or part of the heating water enters the air heater to heat the air, and the cooled heating water enters the flue gas heat exchanger to exchange heat with the flue gas. The heated heating water enters the boiler or is heated again in the heating network heater; A water circulation pipeline is installed between the flue gas heat exchanger and the air spray device. The condensate produced after the flue gas recovers waste heat through the flue gas heat exchanger enters the condensate tank, and some or all of the condensate is transported to the air spray device.

2. The boiler flue gas waste heat deep recovery energy-saving system as described in claim 1, characterized in that, Also includes: A flue gas humidification and cooling device and a flue gas heat exchanger are installed sequentially on the boiler's flue gas exhaust duct. After the flue gas is humidified by the flue gas humidification and cooling device, the water vapor content in the flue gas increases or reaches saturation. Then, it enters the flue gas heat exchanger to exchange heat with the heating water and recover the waste heat of the flue gas. The flue gas is discharged after the waste heat is recovered.

3. The boiler flue gas waste heat deep recovery energy-saving system as described in claim 2, characterized in that, A water circulation pipeline is installed between the flue gas heat exchanger and the flue gas humidification and cooling device. The condensate from the flue gas in the flue gas heat exchanger first enters the condensate tank, and then some or all of the condensate is transported to the flue gas humidification and cooling device.

4. The boiler flue gas waste heat deep recovery energy-saving system as described in claim 3, characterized in that, After the flue gas recovers waste heat through the flue gas heat exchanger, the resulting condensate first enters the condensate tank. Then, part of the condensate is transported to the air spray device, and part of the condensate is transported to the flue gas humidification and cooling device.

5. The boiler flue gas waste heat deep recovery energy-saving system as described in any one of claims 1-4, characterized in that, Air heaters are indirect heat exchangers; flue gas heat exchangers are indirect heat exchangers; and heating network heaters are indirect heat exchangers.

6. The boiler flue gas waste heat deep recovery energy-saving system as described in any one of claims 1-4, characterized in that, The air spraying device and the flue gas humidification and cooling device are tubular sprayers, shower head sprayers, ring pipe multi-hole sprayers or nozzles.

7. The boiler flue gas waste heat deep recovery energy-saving system as described in any one of claims 1-4, characterized in that, The air heater and flue gas heat exchanger are plate heat exchangers; the air spray device and flue gas humidification and cooling device are nozzles.

8. The boiler flue gas waste heat deep recovery energy-saving system as described in any one of claims 1-4, characterized in that, A condensate treatment device is installed at the outlet of the condensate tank.

9. The boiler flue gas waste heat deep recovery energy-saving system as described in claim 1, characterized in that, Includes one or more air spray devices.

10. The boiler flue gas waste heat deep recovery energy-saving system as described in claim 2, characterized in that, It includes a flue gas humidification and cooling device and a flue gas heat exchanger; or it includes a flue gas humidification and cooling device and multiple flue gas heat exchangers; or it includes multiple flue gas humidification and cooling devices and multiple flue gas heat exchangers.

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