Paper machine waste heat full recycling system

Abstract

The invention discloses a full waste heat recycling system for a paper machine. The full waste heat recycling system comprises a first gas hood, a first pipeline, a heat exchanger and a steam generator, wherein the first gas hood is used for collecting water-containing tail gas of a drying cylinder of a drying part of the paper machine; the first pipeline is used for collecting the water-containing tail gas collected by the first gas hood; the heat exchanger and the steam generator are each provided with a flow guide pipeline connected with the first pipeline in series and a heat exchange cavity exchanging heat with the flow guide pipeline. A heat exchange chamber outlet of the heat exchanger is connected with a heat exchange chamber inlet of the steam generator through the first compressor, heat collected by a working medium of the heat exchanger is compressed by the compressor and then enters a heat exchange chamber of the steam generator to be released, and fluid in a flow guide pipeline of the steam generator is heated. A flow guide pipeline outlet of the steam generator is connected with a paper machine drying part drying cylinder steam inlet, a flow guide pipeline inlet of the steam generator is connected with a drying cylinder condensation water outlet, condensation water in a drying cylinder and generated water-containing tail gas heat are fully collected and used for heating the condensation water, and full recovery of the condensation water and the heat is achieved.

Description

Technical Field

[0001] The invention relates to a heat exchange system, in particular to a paper machine waste heat full recovery and utilization system. Background Art

[0002] In the papermaking drying process, steam and hot flue gas (flue gas hood) are required for paper drying. The steam in the drying cylinder has two results after drying the paper. The first is that the steam temperature drops and condenses to form saturated water and part of the steam, which is collected by the collection tank. The condensed water has no suitable use. The steam entering the collection tank is led out by the venturi tube and then the heat is recovered. The energy recovery rate of the led-out steam is low; the second is that the water in the paper is evaporated by heat and mixed with the steam and hot flue gas with a temperature drop, and discharged as exhaust gas. The exhaust gas temperature is 50℃~100℃, and it carries a lot of heat. In the prior art, various simple heat exchangers are only set on the exhaust pipe of the drying part of the paper machine to exchange heat with water and recover part of the energy by producing hot water, and the recovery efficiency is very low. The invention patent application with publication number CN 116592619 A discloses a conduction drying system and process for supplying heat to a dryer using a dual heat pump combination. The mechanical compression high-temperature heat pump system recovers all the heat of the drying exhaust gas discharged from the dryer, cools and dehumidifies it, and then heats it back to the dryer as a carrier gas for continued circulation. In this scheme, the exhaust gas is dried and then the energy is recovered, which requires a large amount of desiccant. There is also energy loss in the drying process. The recovered energy reheats the dry air, and the dry air temperature is maintained at 90-100°C, which cannot meet the drying requirements of the paper machine.

[0003] In the papermaking process, the wet part will also produce a large amount of water vapor and hot and humid air. These water vapor and hot and humid air will also carry some heat, and this part of energy also needs to be recycled. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a paper machine waste heat recovery system that can simultaneously realize condensation water and heat recovery.

[0005] Technical solution: The present invention discloses a system for fully recovering and utilizing waste heat from a paper machine, comprising a first air hood for collecting water-containing tail gas from a drying cylinder of a paper machine, a first pipeline for collecting water-containing tail gas, and a heat exchanger and a steam generator connected in series with the first pipeline in sequence; the heat exchanger and the steam generator both have a guide pipeline connected in series with the first pipeline, and a heat exchange chamber for exchanging heat with the guide pipeline; the outlet of the heat exchange chamber of the heat exchanger is connected to the inlet of the heat exchange chamber of the steam generator through a first compressor, and the heat collected by the working medium of the heat exchanger enters the heat exchange chamber of the steam generator after being compressed by the compressor and is released to heat the fluid inside the guide pipeline of the steam generator, the outlet of the guide pipeline of the steam generator is connected to the steam inlet of the drying cylinder of the paper machine, and the inlet of the guide pipeline of the steam generator is also connected to the condensate outlet of the drying cylinder.

[0006] Preferably, the condensate outlet of the drying cylinder is connected to a collection tank, and the bottom outlet of the collection tank is connected to the water supply system of the steam generator. The water supply pump and the pressure device used for water supply in the water supply system are connected in series, and the condensate in the collection tank partially or completely enters the steam generator through the water supply pump and the pressure device.

[0007] Preferably, the top pipeline of the collecting tank is connected to the second compressor, and the outlet of the second compressor is connected to the steam inlet of the drying cylinder. The steam formed inside the collecting tank is compressed and heated by the second compressor and then supplied to the drying cylinder.

[0008] Preferably, the outlet of the steam generator flow guide pipeline is connected through the second pipeline, the top pipeline of the collection tank and the inlet of the second compressor. When the outlet temperature of the steam generator reaches the requirement of the drying cylinder, it directly enters the drying cylinder for reuse. If the outlet temperature of the steam generator is lower, it enters the second pipeline and merges with the outlet steam of the collection tank, and is compressed and heated by the second compressor before returning to the drying cylinder for reuse. The steam generator and the top pipeline of the collection tank form a Venturi structure, so that the steam formed inside the collection tank can be fully sucked out.

[0009] Preferably, the outlet of the guide pipe of the steam generator and the outlet of the second compressor are both connected to the steam inlet of the drying cylinder through the sub-cylinder, and the sub-cylinder inlet is connected to the supplementary steam pipeline. The steam generated in the steam generator is mixed with the steam compressed by the second compressor and enters the drying cylinder for use or is mixed with the supplementary steam before being put into use.

[0010] Preferably, the sub-cylinder is connected to the steam inlet of the drying cylinder via a third pipeline, a branch pipeline is provided on the third pipeline, and the branch pipeline is connected to the drying cylinder via an air heater.

[0011] Preferably, the first pipeline inlet is also connected to a second air hood for collecting the wet tail gas from the wet end of the paper machine.

[0012] Preferably, the flow guiding pipeline of the heat exchanger is provided with a gas outlet, and the gas outlet is connected to a suction fan.

[0013] Preferably, the outlet connection of the heat exchange chamber of the steam generator is in one-way communication with the inlet of the heat exchange chamber of the heat exchanger. The low-temperature and high-pressure working fluid that releases heat in the steam generator enters the heat exchange chamber of the heat exchanger through the throttle valve, and the low-temperature and low-pressure working fluid absorbs the heat of the water-containing tail gas guided by the first pipeline.

[0014] Preferably, in order to prevent the third pipeline from failing, a spare pipeline is connected in parallel to one end of the third pipeline connected to the steam inlet of the drying cylinder.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. Full recovery of condensed water and heat: the condensed water formed in the drying cylinder enters the water supply system of the steam generator and re-forms steam. The heat of the water-containing tail gas generated in the drying cylinder is fully collected and used to heat the condensed water, thereby achieving full recovery of condensed water and heat; 2. The steam temperature formed by the water-containing tail gas is adjusted as needed: the condensed water formed in the drying cylinder can be directly flash evaporated and compressed to form high-temperature and high-pressure steam for use, or it can be heated in the steam generator to form steam and then used, or the two modes can be used in parallel to form mixed steam, or it can be mixed with supplementary steam and then used as steam. Reuse, adjust the steam mode and steam temperature according to different needs; 3. It can recover the heat of the waste hot air / waste hot flue gas discharged from the air hood of the paper machine drying section separately, and can also recover the heat of the waste hot air generated by the dry section and wet section of the paper machine at the same time; 4. Higher efficiency and more energy-saving: reduce the demand for steam in the paper machine system, reduce 30% to 50% of the steam input, reduce the demand for energy in the paper machine system, and increase the output of the paper machine; the heat pump COP can reach 1.5 to 3.4, combined with the recovery of condensate heat, the power consumption per ton of steam is only 1 / 1.5 to 2.4 of that of an ordinary electric boiler, which has a huge energy-saving advantage. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic structural diagram of the first embodiment of the present invention;

[0017] Figure 2 It is a schematic structural diagram of the second embodiment of the present invention. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0019] Example 1: Figure 1 As shown, the present invention discloses a waste heat recovery system for a paper machine, which is mainly composed of a paper machine wet section 2, a dryer cylinder 1, air hoods 3 and 4, a pipeline system 8, a heat pump system, a steam generator 7, etc.

[0020] There are no less than two air hoods. The air hood 4 is connected to the wet section 2 of the paper machine to collect the water-containing tail gas from the wet section of the paper machine. The air hood 3 is connected to the drying cylinder 1 of the drying section of the paper machine to collect the tail gas from the drying section of the paper machine. The tops of the air hoods 3 and 4 are simultaneously connected to the inlet of the pipeline 81, so that the tail gas collected inside the air hoods 3 and 4 is gathered. The outlet of the pipeline 81 is connected to the heat exchanger 5 and the steam generator 7 in series in sequence. The heat exchanger 5 and the steam generator 7 both have a flow guide pipeline connected in series with the pipeline 81 and a heat exchange chamber for heat exchange with the flow guide pipeline. The flow guide pipelines of the heat exchanger 5 and the steam generator 7 are the first and second flow guide pipelines, respectively, and the heat exchange chambers of the heat exchanger 5 and the steam generator 7 are the first and second heat exchange chambers, respectively.

[0021] The inlet of the first flow guiding pipeline is connected to the outlet of the pipeline 81, and the inlet of the second flow guiding pipeline is connected to the outlet of the first flow guiding pipeline, that is, the pipeline 81, the first flow guiding pipeline, and the second flow guiding pipeline are connected in series in sequence.

[0022] The outlet of the first heat exchange chamber is connected to the inlet of the compressor 6, and the outlet of the compressor 6 is connected to the inlet of the second heat exchange chamber. The low-temperature and low-pressure working medium entering the first heat exchange chamber absorbs the heat of the water-containing tail gas inside the first guide pipe, enters the compressor 6, and is converted into a high-temperature and high-pressure working medium by the compressor 6, and then enters the second heat exchange chamber to heat the fluid inside the second guide pipe, so that the fluid inside the second guide pipe forms steam. The outlet of the second heat exchange chamber is unidirectionally connected to the first heat exchange chamber, and the heat exchange working medium can only flow from the second heat exchange chamber to the first heat exchange chamber. The high-pressure and low-temperature working medium that releases heat in the second chamber returns to the first heat exchange chamber through the throttle valve and restores the low-temperature and low-pressure state. The outlet of the second guide pipe is connected to the steam inlet of the drying cylinder 1. The heat exchanger 5 can be a tubular heat exchanger, a plate heat exchanger or a heat pipe heat exchanger. Replace the working medium inside the compressor 6, such as pentane, R245F, CO2, etc., and change the temperature of the compressed working medium. After being compressed by the compressor 6, the temperature of the working medium reaches above 140°C, basically between 140°C and 250°C. The working medium heats the fluid inside the second guide pipe to different temperatures, forming high-temperature steam, which is returned to the drying cylinder 1 for use in drying paper. Using carbon dioxide as the heat exchange working medium, the steam pressure at the outlet of the second guide pipe body can reach 3 to 10 barg, and the temperature can reach 140 to 220°C, which can fully meet the requirements for paper machine drying. Adjust the temperature of the high-pressure and low-temperature working medium that releases heat in the second chamber to make it close to the dew point temperature, so as to fully recover the heat carried by the steam in the wet part of the paper machine.

[0023] The first flow guide pipe of the heat exchanger 5 is provided with a gas outlet, which is connected to the suction fan 15, and the outlet of the suction fan 15 is connected to the exhaust pipe. After heat exchange, the gas temperature inside the first flow guide pipe is lower than the water dew point or even lower, and is discharged into the atmosphere through the suction fan 15 (exhaust fan).

[0024] When drying paper, the drying cylinder 1 will continuously generate high-temperature condensate. In order to recycle this part of condensate, the condensate outlet of the drying cylinder 1 is connected to the inlet of the second guide pipe of the steam generator 7, so that the condensate can be heated to form steam again. Specifically: the condensate outlet of the drying cylinder 1 is provided with a collecting tank 13. The high-temperature condensate generated by the drying cylinder 1 collected by the collecting tank 13 enters the first guide pipe through the bottom outlet of the collecting tank 13 and the water supply system of the steam generator 7. The water supply system includes a water supply pump 12 and a pressurizing device (not shown) connected in series. The water supply pump 12 and the pressurizing device are existing devices and are not described in detail. The condensate in the collecting tank 13 is partially or completely sent to the steam generator 7 through the water supply system to form a water cycle. Part of the steam will be formed inside the collecting tank 13. In order to utilize this part of the steam, the top pipeline 83 of the collecting tank 13 is connected to the inlet of the compressor 10. After the steam inside the collecting tank 13 is compressed by the compressor 10 to increase the temperature and pressure, it is returned to the drying cylinder 1 for use to dry the paper. After compression, the steam pressure can reach 5-30 barg, and the temperature is between 140-300℃. The compressed steam can fully meet the requirements for paper machine drying.

[0025] The working fluid inside the compressor 6 is different, and the fluid inside the second guide pipe will be heated to different temperatures. If the steam temperature and pressure at the outlet of the second guide pipe body do not meet the requirements of the drying cylinder 1, the drying cylinder 1 cannot be used directly. Therefore, the outlet of the second guide pipe is also connected to the inlet of the second compressor 10 through the pipeline 82, the top pipeline 93 of the collection tank 13, and the second compressor 10. If the outlet temperature of the steam generator 7 is low, it enters the pipeline 82, and merges with the steam at the outlet of the top pipeline 83 of the collection tank 13, and is compressed and heated by the second compressor 10 before returning to the drying cylinder 1 for use. The high-temperature steam produced by the steam generator 7 is merged with the steam inside the collection tank 13 through the pipeline 82 and then enters the steam compressor 10. The pipeline 82 and the top pipeline 83 of the collection tank 13 form a Venturi structure, which will produce a suction and airflow effect on the condensate tank 13, have a flash evaporation effect, and maximize the use of the steam inside the collection tank 13.

[0026] The outlet of the compressor 10 is connected to the sub-cylinder 9 through the pipeline 87 and the outlet of the steam generator 7 is connected to the sub-cylinder 9 through the pipeline 85. The sub-cylinder 9 is connected to the steam inlet of the drying cylinder 1 through the pipeline 85. The steam at the outlet of the compressor 10 and the outlet of the steam generator 7 is sent to the sub-cylinder 9 and distributed for use. The inlet of the sub-cylinder 9 is connected to a supplementary steam pipeline, and the steam at the outlet of the compressor 10 and the outlet of the steam generator 7 is mixed with the supplementary steam and then distributed for use.

[0027] A spare pipeline is connected in parallel to one end of the pipeline 85 connected to the steam inlet of the drying cylinder 1 to prevent failure of the pipeline 85. The pipeline 85 is provided with a branch pipeline 86, such as Figure 1The branch pipeline 86 is connected to the drying cylinder 1 through the air heater 14, and the steam enters the air heater 14 from the branch cylinder 9, heats the air sucked by the fan 11, and then sends it into the air hood 3.

[0028] Embodiment 2: This embodiment can also have the following variations: Figure 2 The hot flue gas pipeline is connected to the drying cylinder 1. Part of the hot flue gas discharged by the gas turbine enters the gas hood 3, and part is sent to the waste heat boiler. The water-containing tail gas after drying the paper is sent to the pipeline 81.

Claims

1. A paper machine waste heat full recovery and utilization system, characterized in that: The invention comprises a first air hood (3) for collecting water-containing tail gas from a paper machine dryer cylinder (1), a first pipeline (81) for collecting water-containing tail gas, a heat exchanger (5) and a steam generator (7) which are connected in series with the first pipeline (81) in sequence; the heat exchanger (5) and the steam generator (7) both have a flow guide pipeline connected in series with the first pipeline (81) and a heat exchange chamber for performing heat exchange with the flow guide pipeline; the heat exchange chamber outlet of the heat exchanger (5) is connected to the heat exchange chamber inlet of the steam generator (7) through a first compressor (6); the heat collected by the working medium of the heat exchanger (5) is compressed by the first compressor (6) and then released into the heat exchange chamber of the steam generator (7), thereby heating the fluid inside the flow guide pipeline of the steam generator (7); the flow guide pipeline outlet of the steam generator (7) is connected to the steam inlet of the drying cylinder (1); and the flow guide pipeline inlet of the steam generator (7) is communicated with the condensate outlet of the drying cylinder (1).

2. The paper machine waste heat full recovery and utilization system according to claim 1 is characterized in that: The condensate outlet of the drying cylinder (1) is connected to a collecting tank (13), and the bottom outlet of the collecting tank (13) is connected to the water supply system of the steam generator (7).

3. The paper machine waste heat full recovery and utilization system according to claim 2 is characterized in that: The top pipeline (83) of the collecting tank (13) is connected to the second compressor (10), and the outlet of the second compressor (10) is connected to the steam inlet of the drying cylinder (1).

4. The paper machine waste heat full recovery and utilization system according to claim 3 is characterized in that: The outlet of the flow guide pipeline of the steam generator (7) is connected through the second pipeline (82), the top pipeline (82) of the collection tank (13) and the inlet of the second compressor (10).

5. The paper machine waste heat full recovery and utilization system according to claim 3 is characterized in that: The outlet of the guide pipe of the steam generator (7) and the outlet of the second compressor (10) are both connected to the steam inlet of the drying cylinder (1) through the sub-cylinder (9), and the inlet of the sub-cylinder (9) is connected to a supplementary steam pipeline.

6. The paper machine waste heat full recovery and utilization system according to claim 5 is characterized in that: The sub-cylinder (9) is connected to the steam inlet of the drying cylinder (1) via a third pipeline (85); a branch pipeline (86) is provided on the third pipeline (85); and the branch pipeline (86) is connected to the drying cylinder (1) via an air heater (14).

7. The paper machine waste heat full recovery and utilization system according to claim 1 is characterized in that: The inlet of the first pipeline (81) is also connected to a second air hood (4) for collecting the water-containing tail gas from the wet end (2) of the paper machine.

8. The paper machine waste heat full recovery and utilization system according to claim 1 is characterized in that: The flow guide pipeline of the heat exchanger (5) is provided with a gas outlet, and the gas outlet is connected to the suction fan (15).

9. The paper machine waste heat full recovery and utilization system according to claim 1, characterized in that: The heat exchange chamber outlet of the steam generator (7) is connected to the heat exchange chamber inlet of the heat exchanger (5) in one-way communication.

10. The paper machine waste heat full recovery and utilization system according to claim 6, characterized in that: A spare pipeline is connected in parallel to one end of the third pipeline (85) connected to the steam inlet of the drying cylinder (1).

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