A steam heat source drying system heat energy cascade utilization and waste heat recovery device

Abstract

The present application belongs to the technical field of drying auxiliary equipment, and particularly relates to a steam heat source drying system heat energy gradient utilization and waste heat recovery device. In the present application, the main heating unit is sequentially provided with a circulating water preheating module, a water vapor mixing heating module and a steam heating module in the air flow direction. Since the circulating water temperature, the temperature of the steam-containing condensed water and the steam temperature are sequentially increased, the circulating water preheating module, the water vapor mixing heating module and the steam heating module realize gradient heating of the air, fully utilize the steam heat, and can heat the air temperature to close to the saturation temperature of the supersaturated steam heat source, so that the drying efficiency of the subsequent drying process is higher. In addition, the present application utilizes the waste heat recovery device to recover the heat of the steam and the condensed water to heat the circulating water, realizes the heat recovery and utilization, and eliminates the steam in the condensed water; the preheating of the circulating water preheating module reduces the temperature difference between the water vapor mixing heating module and the heated gas, and avoids the water hammer phenomenon.

Description

Technical Field

[0001] This invention belongs to the technical field of drying auxiliary equipment, specifically relating to a device for the cascade utilization of thermal energy and waste heat recovery in a steam heat source drying system. Background Technology

[0002] Large-scale drying systems are frequently used in modern factories. In order to ensure product quality and drying efficiency, reduce energy consumption, and ensure safe and stable production, these systems are becoming increasingly complex, and the reliability requirements for equipment, processes, and control systems are becoming increasingly stringent.

[0003] Large factories often have their own power plants, supplying various production workshops with saturated steam and highly superheated steam, depending on the power plant's heat and power balance requirements. Large-scale drying systems, addressing the varying requirements of materials at different stages of drying, cooling, conveying, and storage, often utilize multiple steam heat sources and employ multiple heating units, each with different heating requirements. Therefore, the condensate parameters discharged from different heating units within a large-scale drying system vary significantly. Furthermore, due to start-up, shutdown, and stable production requirements, the condensate drainage systems of large-scale drying systems may sometimes open bypasses to discharge steam into the condensate pipeline. From an equipment usage perspective, condensate drain valves often experience 1% to 3% steam leakage over long-term use, and the pressure drop and flash evaporation of condensate discharged from the heating units at different pressures also generate flash steam. Therefore, for large and complex drying systems, the simultaneous discharge of steam and condensate into the condensate drainage pipelines frequently occurs, increasing the difficulty of subsequent processing.

[0004] For large-scale drying systems, condensate from all sources is typically discharged into a centralized condensate tank located within the plant area for storage. The tank is equipped with a vent pipe on top to release any leaks or flash vapors carried in the condensate into the atmosphere. This method results in significant energy waste, and the released water vapor causes safety issues and visual pollution.

[0005] In actual production, the steam-water mixture in the condensate drain pipe is also introduced into the first or first few plates of the cold air inlet section of the main hot air heater unit of the drying system to condense the steam in the condensate and reduce the temperature of the condensate, which is then discharged into the centralized condensate tank in the factory area.

[0006] Existing large-scale drying systems have numerous technical problems with their steam heating processes and equipment:

[0007] 1. Existing drying systems either directly discharge condensate into the environment or centrally store condensate in a condensate tank located within the plant area. This results in excessively high condensate temperatures, and any leaks or flash vapors within the condensate are directly released into the atmosphere. Both scenarios lead to significant energy waste; the released water vapor also poses safety risks and causes visual pollution. Furthermore, excessively high condensate temperatures can reduce the suction capacity of the condensate transfer pump or even prevent it from functioning properly.

[0008] 2. The waste heat recovery method of passing the condensate discharged through the drainage system into the first or first few plates of the hot air heat exchanger to absorb the exhaust steam and reduce the temperature of the condensate is subject to water hammer when the steam entrained in the condensate condenses rapidly, which affects the service life of the equipment.

[0009] 3. Especially for finned tube air heat exchanger assemblies in large-scale drying systems, a large amount of ambient air is directly drawn for heating. Due to the significant seasonal variations in ambient temperature and humidity, the operating conditions of the heat exchanger are complex and variable. Particularly in northern regions during winter, when ambient temperatures are generally below -10℃, the entry of a steam-water mixture into the heat exchange fins located at the air inlet can cause severe water hammer.

[0010] In addition, insufficient condensate flow and heat can cause excessive heat exchange in the first few heat exchangers, which can easily lead to localized freezing and cracking of the heat exchange tubes. Summary of the Invention

[0011] The purpose of this invention is to solve the above-mentioned problems and provide a device for the cascade utilization of thermal energy and waste heat recovery in a steam heat source drying system. In this invention, the main heating unit is sequentially arranged according to the airflow direction, including a circulating water preheating module, a water-steam mixing heating module, and a steam heating module. Since the temperature of the circulating water is lower than that of the steam-containing condensate, and the temperature of the steam-containing condensate is lower than that of the steam, the circulating water preheating module, the water-steam mixing heating module, and the steam heating module sequentially heat the air in a cascade manner, fully utilizing the heat of the steam and heating the air to near the supersaturated steam heat source temperature, resulting in higher drying efficiency in subsequent drying processes. Furthermore, this invention utilizes a waste heat recovery device to recover the heat from the steam and condensate to heat the circulating water, achieving heat recovery and eliminating waste steam in the condensate. The preheating by the circulating water preheating module reduces the temperature difference between the water-steam mixing heating module and the heated gas, avoiding water hammer and improving the safety of the entire device.

[0012] The technical problem to be solved by the present invention is achieved by the following technical solution: a steam heat source drying system heat energy cascade utilization and waste heat recovery device, including a main heating unit, a waste heat recovery unit, a circulating water pump and a first drain valve;

[0013] The main heating unit is provided with a circulating water preheating module, a water-steam mixing heating module and a steam heating module in sequence according to the airflow direction. The steam heating module is provided with a first steam pipe at the inlet and a first steam trap at the outlet. The outlet of the first steam trap is connected to the inlet of the water-steam mixing heating module through a first steam-liquid pipe and the outlet of the first steam trap is connected to the first steam-liquid inlet of the waste heat recovery unit through a second steam-liquid pipe.

[0014] A first throttle valve is installed on the first vapor-liquid pipeline, a second throttle valve is installed on the second vapor-liquid pipeline, and the outlet of the water-vapor mixing heating module is connected to the first vapor-liquid inlet through a third vapor-liquid pipeline;

[0015] The waste heat recovery unit is equipped with circulating water. The circulating water outlet of the waste heat recovery unit is connected to the water inlet of the circulating water preheating module. The circulating water pump is located between the waste heat recovery unit and the circulating water preheating module. The water outlet of the circulating water preheating module is connected to the circulating water inlet of the waste heat recovery unit.

[0016] The waste heat recovery unit is used to recover steam and condensate and exchange heat between the steam, condensate, and circulating water. During the heat exchange process, when the condensate contains a large amount of steam, water hammer may still occur in the water-steam mixing heating module. In this case, the condensate in the first steam trap can be partially or completely sent into the waste heat recovery unit by switching valves to separate and absorb the exhaust steam. Specifically, the first and second throttle valves are used to control the proportion of the condensate and steam mixture output from the first steam trap to the waste heat recovery unit and the water-steam mixing heating module. The corresponding control of the first and second throttle valves is mainly adjusted according to whether water hammer occurs in the water-steam mixing heating module. Water hammer will occur when there is too much steam in the condensate or when the inlet air temperature of the main heating unit is too low. If water hammer does not occur, it is preferable to input all the condensate and steam mixture output from the first steam trap into the water-steam mixing heating module; when water hammer occurs, the second throttle valve is opened to allow part of the condensate and steam mixture to enter the waste heat recovery unit to raise the circulating water temperature until the water hammer disappears.

[0017] The technical solution of the present invention also includes: the waste heat recovery unit is provided with an interconnected waste steam absorption chamber and a condensate mixing and cooling chamber from top to bottom, the circulating water is stored in the condensate mixing and cooling chamber, and the waste steam absorption chamber is provided with a waste steam absorption layer above the circulating water liquid surface along the cross-section.

[0018] The first vapor-liquid inlet is located below the exhaust vapor absorption layer;

[0019] The circulating water inlet of the waste heat recovery unit is located above the waste steam absorption layer. To achieve the recovery and utilization of condensate and steam, a waste steam absorption layer is set along the cross-section of the waste steam absorption chamber, located above the circulating water surface. Since the first vapor-liquid inlet is located below the waste steam absorption layer and the circulating water inlet is located above the waste steam absorption layer, after the condensate-steam mixture and circulating water are discharged into the waste heat recovery unit, the condensate mixes with the circulating water below. The steam rises and passes through the waste steam absorption layer, while the circulating water entering from the circulating water inlet falls and passes through the waste steam absorption layer. The steam and the cooled circulating water achieve sufficient heat exchange in the waste steam absorption layer, thereby being absorbed and heating the cooled circulating water.

[0020] The technical solution of the present invention also includes: the waste heat recovery unit is provided with a nozzle connected to the circulating water inlet above the waste steam absorption layer;

[0021] The waste heat recovery unit has a first spray pipe connected to the first vapor-liquid inlet below the exhaust steam absorption layer, positioned above the circulating water surface. Due to the poor flowability of the circulating water within the waste heat recovery unit, to ensure sufficient heat exchange between the circulating water and steam after heat exchange, a nozzle connected to the circulating water inlet is installed above the exhaust steam absorption layer to evenly spray the circulating water onto the exhaust steam absorption layer. The first spray pipe, located below the exhaust steam absorption layer and connected to the first vapor-liquid inlet, ensures that the steam rises evenly during spraying and is evenly absorbed by the exhaust steam absorption layer, thus uniformly heating the circulating water falling from above. Condensate is sprayed into the air by the first spray pipe, dispersing into droplets. This condensate mixes evenly with the water droplets falling from the exhaust steam absorption layer in the air, achieving rapid heat exchange. Furthermore, the condensate droplets sprayed by the first spray pipe fall onto the circulating water surface below, also achieving rapid heat exchange with the circulating water below, thus quickly increasing the circulating water temperature.

[0022] The technical solution of the present invention also includes: a second heating unit;

[0023] The second heating unit is provided with a second steam pipe at its inlet and a second steam trap at its outlet. The outlet of the second steam trap is connected to the inlet of the water-steam mixing heating module via a fourth steam-liquid pipe. A fourth throttle valve is provided on the fourth steam-liquid pipe.

[0024] The outlet of the second steam trap is connected to the second vapor-liquid inlet of the waste heat recovery unit through the fifth vapor-liquid pipeline. The second vapor-liquid inlet is located below the exhaust steam absorption layer. A fifth throttle valve is installed on the fifth vapor-liquid pipeline.

[0025] The waste heat recovery unit has a second spray pipe connected to the second vapor-liquid inlet below the waste steam absorption layer, and the second spray pipe is located above the circulating water surface. A second heating unit is typically installed in the drying system as an internal heat exchanger assembly inside the dryer or granulator. Since the second heater also uses steam for heating, the condensate discharged through the second steam trap also contains steam and a large amount of heat energy, which needs to be recovered and utilized.

[0026] When the water-vapor mixing heating module does not experience water hammer, the condensate and steam mixture discharged from the second steam trap is fed into the water-vapor mixing heating module through the fourth vapor-liquid pipeline for direct heating of the air.

[0027] When water hammer occurs in the water-vapor mixing heating module or when the circulating water temperature in the waste heat recovery unit is too low, the condensate and steam mixture discharged from the second steam trap is fed into the waste heat heater through the fifth vapor-liquid pipe and the second vapor-liquid inlet to heat the circulating water. This raises the preheating temperature of the air by the circulating water preheating module, reduces the temperature difference between the air and the condensate and steam mixture, and thus eliminates the water hammer problem. The condensate parameters of the main heating unit and the second heating unit are relatively similar, allowing them to be mixed and used together.

[0028] One or more second heating units can be installed as needed.

[0029] The technical solution of the present invention also includes: a third heating unit;

[0030] The third heating unit has a third steam pipe at its inlet and a third steam trap at its outlet. The outlet of the third steam trap is connected to the third steam-liquid inlet of the waste heat recovery unit via a sixth steam-liquid pipe. The third steam-liquid inlet is located below the exhaust steam absorption layer. In a drying system, the third heating unit is typically used as an auxiliary heating unit. The steam heat source input through the third steam pipe has a low temperature, resulting in less condensate. Therefore, it is directly fed into the waste heat recovery unit for recycling through the third steam-liquid inlet. For example, the third heating unit is used for heating steam in pneumatic air supply, regenerating steam in dehumidifiers, and heating compressed air. The heating temperature at these points generally does not exceed 100℃, the usage is much smaller, and the condensate temperature is also lower, so a lower-grade heat source can be used. Because the condensate volume is small, the water temperature is low, and the steam content is also low, there is no need to install a separate spray pipe; it can be directly connected to the waste heat recovery unit. It is also unsuitable to mix the condensate from the main heating unit and the second heating unit, as the parameter differences are significant, and it may even cause water hammer in the condensate pipe.

[0031] One or more third heating units can be installed as needed.

[0032] The technical solution of the present invention also includes: a first level gauge, a first temperature sensor, a water injection pipe, and a drainage pipe;

[0033] The first level gauge, water injection pipe, and drainage pipe are installed on the waste heat recovery unit;

[0034] The first level gauge is used to monitor the level of circulating water in the waste heat recovery unit. Before the system starts, a certain level of circulating water is injected into the waste heat recovery unit by opening the water injection valve on the water injection pipe to ensure that the pump starts initially and forms a water circulation between the waste heat recovery unit and the circulating water preheating module. The first level gauge is used to monitor the level of circulating water in the waste heat recovery unit. The level signal is used to automatically or manually control the opening or closing of the drain valve on the drain pipe (or the level signal is used to control the speed of the circulating water discharge pump) to discharge the circulating water, thereby achieving fixed level control or high and low level control, that is, ensuring that the level of circulating water is at the set level or within the set level range.

[0035] The first temperature sensor is installed on the waste heat recovery unit or on the conveying pipeline between the waste heat recovery unit and the circulating water preheating module. The first temperature sensor is used to monitor the outlet temperature of the circulating water in the waste heat recovery unit. When the first temperature sensor detects that the temperature of the circulating water in the waste heat recovery unit is lower than the set lower limit temperature, it indicates that the heat supplemented by the recovered condensate and steam to the circulating water cannot meet the heat exchange requirements of the circulating water preheating module. At this time, the flow rate, temperature, or steam ratio of the steam-water mixture entering from the gas-liquid inlet can be increased to increase the temperature of the circulating water and meet the heat exchange efficiency requirements of the circulating water preheating module.

[0036] When the first temperature sensor detects that the temperature of the circulating water in the waste heat recovery unit is higher than the set upper limit temperature, it indicates that the temperature of the circulating water is higher than the operating temperature required by the circulating water pump. At this time, the flow rate, temperature or steam ratio of the steam-water mixture entering from the gas-liquid inlet can be reduced, or the water injection valve on the water injection pipe can be opened to inject cooling water of a certain temperature into the waste heat recovery unit so that the temperature of the circulating water is kept within the operating temperature range of the circulating water pump.

[0037] The technical solution of the present invention also includes a circulating water discharge pump, which is installed on the drainage pipe. The discharge rate of the circulating water is controlled by the circulating water discharge pump.

[0038] The drainage pipe is separate from the circulating water pipe and can be operated independently to discharge the circulating water, reducing the power requirement of the circulating water pump. The circulating water pipe only needs to use a lower power pump, saving electricity.

[0039] The technical solution of the present invention also includes: a breathing valve;

[0040] The waste heat recovery unit has an vent above the exhaust steam absorption layer, and a breather valve is installed on the vent. Existing condensate recovery tanks have vents above them primarily to discharge excess steam to prevent positive pressure, or to draw in air to prevent negative pressure. To avoid safety risks and steam contamination, the steam needs to be led out to a safe outdoor location. In this invention, since the exhaust steam has been effectively absorbed, the gas inside the waste heat recovery unit can be led out through the vent and connected to the breather valve nearby, preventing the tank from being pressurized and eliminating steam emissions.

[0041] The technical solution of the present invention also includes: the exhaust steam absorption layer is a filler absorption layer made of a material that is resistant to the temperature of water vapor and severe temperature fluctuations;

[0042] The exhaust steam absorption layer includes corrugated packing, wire mesh packing, or random metal packing.

[0043] The technical solution of the present invention also includes: a third throttling valve is provided on the third vapor-liquid pipeline. The main function of the third throttling valve is to cooperate with the first throttling valve to disconnect the water-vapor mixing heating module from the entire device, so as to prevent water leakage to the hot air side or the environment when the water-vapor mixing heating module is damaged by water hammer.

[0044] The inventive concept of this invention:

[0045] Depending on the underlying principle, water hammer in steam systems can be classified into two types:

[0046] 1. Direct water hammer: Commonly seen in conveying pipelines, high-speed steam flows over the surface of condensate to create "waves". When the "waves" cover the entire pipeline or have a sufficient windward area, the condensate will be pushed by the steam to form water bombs.

[0047] The flow velocity of a normal water system is between 2 m / s and 3 m / s, while the flow velocity of steam reaches 25 m / s to 40 m / s. When the water bomb is propelled by steam and flows through bends, valves, and other equipment at a velocity of 25 m / s to 40 m / s, the water bomb will stop, releasing a large amount of energy and causing damage to the pipes and valves.

[0048] 2. Collapse water hammer: Commonly seen in condensate pipes. When steam enters the condensate, the steam bubbles dissipate heat and condense, and their volume decreases instantly. Especially in low-pressure condensate pipes, due to the low pressure of the secondary steam, the volume of the secondary steam condenses instantly shrinks to 1 / 1000 of its original size. At this time, the "vacuum area" formed by the steam condensation causes the surrounding condensate to instantly fill this area. Under the action of this suction force, the condensate collides with each other, forming "collapse water hammer".

[0049] The present invention utilizes a waste heat recovery device to release and recover the exhaust steam in the condensate in the drying system, thereby avoiding "collapse water hammer" in the circulating pipes of the circulating water preheating module.

[0050] In addition, the present invention preheats the air through a circulating water preheating module, reducing the temperature difference between the air and the water vapor mixing heating module, and avoiding "crushing water hammer" in the water vapor mixing heating module.

[0051] Furthermore, this invention heats the air in stages through a circulating water preheating module, a water-steam mixing heating module, and a steam heating module. While keeping the steam heat source temperature constant, it further increases the temperature of the hot air that is finally introduced into the drying system, thereby improving energy utilization and subsequent drying efficiency.

[0052] Compared with the prior art, the beneficial effects of the present invention are:

[0053] 1. With the steam heat source provided by the plant, the device of this application can make full use of the heat of the steam to increase the drying air inlet temperature, so that the temperature of the heated gas is close to the saturation temperature of the supersaturated steam heat source, which can be used in the subsequent drying system to obtain higher thermal efficiency of hot air drying.

[0054] 2. By using the exhaust steam in the primary condensate to heat the circulating water, the circulating water is introduced into the circulating water preheating module of the main heating unit to heat the low-temperature ambient air. This effectively solves the water hammer phenomenon that may occur during heat exchange of steam-water mixtures, as well as the problem of localized freezing and cracking of heat exchange tubes. It improves the stability of the operation of large finned air heat exchangers, especially in winter, and saves on equipment replacement and maintenance costs.

[0055] 3. Since the circulating water does not contain exhaust steam, a high-flow-rate forced circulation is achieved using a circulating water pump. The flow velocity within the heat exchange tubes is several times higher than that of directly using primary condensate for heat exchange, thus increasing the heat transfer coefficient of each heat exchange tube. Furthermore, by rationally setting the number of heat exchangers in the circulating water preheating module, the temperature of the condensate can be effectively reduced. The temperature of the condensate discharged from the system can be lowered to below 50℃, which is 20-30℃ lower than existing systems. Moreover, the condensate does not contain steam, resulting in significant energy savings and reduced consumption. The absence of steam emissions also eliminates safety issues and visual pollution caused by water vapor, simplifying engineering design.

[0056] In addition, the condensate temperature is lowered below the maximum allowable temperature of the water pump to ensure the normal and reliable operation of the water pump when delivering condensate. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the thermal energy cascade utilization and waste heat recovery device of the steam heat source drying system described in Embodiment 1 of the present invention;

[0058] Figure 2 This is a schematic diagram of the thermal energy cascade utilization and waste heat recovery device of the steam heat source drying system described in Embodiment 2 of the present invention;

[0059] Figure 3 This is a schematic diagram of the structure of the steam heat source drying system heat energy cascade utilization and waste heat recovery device described in Embodiment 3 of the present invention;

[0060] In the diagram, 1 is the main heating unit, 2 is the waste heat recovery unit, 3 is the circulating water pump, and 4 is the first drain valve.

[0061] 1001 Circulating water preheating module, 1002 Water-steam mixing heating module, 1003 Steam heating module, 10031 First steam pipeline;

[0062] 5 First vapor-liquid pipeline, 51 First throttle valve, 6 Second vapor-liquid pipeline, 61 Second throttle valve, 7 Third vapor-liquid pipeline, 71 Third throttle valve;

[0063] 2001 Exhaust vapor absorption chamber, 2002 Condensate mixing and cooling chamber, 2003 Exhaust vapor absorption layer;

[0064] 20001 First vapor-liquid inlet, 20002 Second vapor-liquid inlet, 20003 Third vapor-liquid inlet;

[0065] 8 nozzles, 9 first spray pipe;

[0066] 10 Second heating unit, 101 Second steam pipe, 11 Second steam trap, 12 Fourth vapor-liquid pipe, 121 Fourth throttle valve, 13 Fifth vapor-liquid pipe, 131 Fifth throttle valve, 14 Second spray pipe;

[0067] 15 Third heating unit, 151 Third steam pipe, 16 Third steam trap, 17 Sixth vapor-liquid pipe;

[0068] 18 First level gauge, 19 First temperature sensor, 20 Water injection pipe, 21 Drainage pipe;

[0069] 201 Water injection valve, 211 Drain valve;

[0070] 22. Circulating water drain pump, 23. Breathing valve, 24. Air vent. Detailed Implementation

[0071] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The steam trap of the present invention includes a steam trap body and components such as a shut-off valve, a bypass valve, and auxiliary valves, not all of which are shown in the accompanying drawings.

[0072] Example 1

[0073] like Figure 1 As shown, a steam heat source drying system thermal energy cascade utilization and waste heat recovery device includes a main heating unit 1, a waste heat recovery unit 2, a circulating water pump 3, and a first drain valve 4.

[0074] The waste heat recovery unit 2 is equipped with a circulating water inlet, a circulating water outlet, a first vapor-liquid inlet 20001, a water injection port, and a drain port.

[0075] The main heating unit 1 is provided with a circulating water preheating module 1001, a water-steam mixing heating module 1002 and a steam heating module 1003 in sequence according to the airflow direction. The steam heating module 1003 is provided with a first steam pipe 10031 at its inlet and a first steam trap 4 at its outlet. The outlet of the first steam trap 4 is connected to the inlet of the water-steam mixing heating module 1002 through a first steam-liquid pipe 5. The outlet of the first steam trap 4 is connected to the first steam-liquid inlet 20001 of the waste heat recovery unit 2 through a second steam-liquid pipe 6.

[0076] A first throttle valve 51 is installed on the first vapor-liquid pipeline 5, and a second throttle valve 61 is installed on the second vapor-liquid pipeline 6. The outlet of the water-vapor mixing heating module 1002 is connected to the first vapor-liquid inlet 20001 through a third vapor-liquid pipeline 7. A third throttle valve 71 is installed on the third vapor-liquid pipeline 7.

[0077] The waste heat recovery unit 2 is equipped with circulating water. The circulating water outlet of the waste heat recovery unit 2 is connected to the water inlet of the circulating water preheating module 1001. The circulating water pump 3 is located between the waste heat recovery unit 2 and the circulating water preheating module 1001. The water outlet of the circulating water preheating module 1001 is connected to the circulating water inlet of the waste heat recovery unit 2.

[0078] The waste heat recovery unit 2 is used to recover steam and condensate and exchange heat between the steam, condensate and circulating water.

[0079] Specifically, the waste heat recovery unit 2 is provided with an interconnected waste steam absorption chamber 2001 and a condensate mixing and cooling chamber 2002 from top to bottom. The circulating water is stored in the condensate mixing and cooling chamber 2002. The waste steam absorption chamber 2001 is provided with a waste steam absorption layer 2003 located above the circulating water surface along its cross-section.

[0080] The first vapor-liquid inlet 20001 is located below the exhaust vapor absorption layer 2003.

[0081] The circulating water inlet of the waste heat recovery unit 2 is located above the waste steam absorption layer 2003.

[0082] The waste heat recovery unit 2 is equipped with a nozzle 8 connected to the circulating water inlet above the waste steam absorption layer 2003.

[0083] The waste heat recovery unit 2 has a first spray pipe 9 connected to the first vapor-liquid inlet 20001 below the waste steam absorption layer 2003, and the first spray pipe 9 is located above the circulating water surface. Condensate containing a high amount of water vapor or with a water temperature close to its boiling point is evenly sprayed onto the cross-section of the preheating recovery unit 1 tank, achieving good separation between steam and water, and ensuring sufficient heat exchange with the circulating water droplets sprayed from the waste steam absorption layer 2003.

[0084] A circulating water spray assembly is installed in the exhaust steam absorption chamber 2001 to uniformly spray circulating water onto the exhaust steam absorption layer 2003, ensuring that the exhaust steam absorption layer 2003 is fully wetted. The height of the exhaust steam absorption layer 2003 can be calculated; the cross-sectional area of ​​the exhaust steam absorption chamber 2001 is related to the exhaust steam volume, and the cross-sectional flow velocity is generally <1.5m / s; the circulating water is evenly distributed and falls after passing through the entire cross-section of the exhaust steam absorption layer 2003, mixing with the primary condensate evenly sprayed to the same location and then cooling down. Similarly, the spray assembly for spraying the primary condensate is located below the exhaust steam absorption chamber 2001. In addition to enhancing the heat exchange between the circulating water droplets and the primary condensate droplets, it also plays a role in uniformly distributing steam. Because the operating conditions of the drying system fluctuate greatly, when the exhaust steam flow rate is very low, it cannot be evenly distributed through its own diffusion. It needs to be achieved through the arrangement of the spray device so that the exhaust steam can be evenly absorbed by the circulating water when it passes evenly upward through the exhaust steam absorption layer 2003, and the circulating water can also be evenly heated.

[0085] The steam heat source drying system heat energy cascade utilization and waste heat recovery device also includes a first liquid level gauge 18, a first temperature sensor 19, a water injection pipe 20 and a drainage pipe 21.

[0086] The first level gauge 18, the water injection pipe 20, and the drainage pipe 21 are installed on the waste heat recovery unit 2. The water injection pipe 20 is connected to the water injection port, and the drainage pipe 21 is connected to the drainage port.

[0087] A water injection valve 201 is provided on the water injection pipe 20, and a drain valve 211 is provided on the drain pipe 21.

[0088] The first level gauge 18 is used to monitor the level of circulating water in the waste heat recovery unit 2.

[0089] The first temperature sensor 19 is installed on the waste heat recovery unit 2 or on the conveying pipeline between the waste heat recovery unit 2 and the circulating water preheating module 1001. The first temperature sensor 19 is used to monitor the outlet water temperature of the circulating water in the waste heat recovery unit 2.

[0090] The steam heat source drying system's heat energy cascade utilization and waste heat recovery device also includes a circulating water discharge pump 22, which is installed on the drain pipe 21 to discharge excess condensate. When controlling the discharge of circulating water using liquid level control, an automatic control valve (including an automatic regulating valve and an automatic on / off valve) can be used as the drain valve 211, or the speed of the circulating water discharge pump 22 can be controlled by a frequency converter. If the former, an automatic control valve needs to be installed after the circulating water discharge pump 22 as the drain valve 211, which can also serve as a check valve, or a separate check valve can be installed. If the latter, a check valve needs to be installed after the circulating water discharge pump 22 to prevent backflow.

[0091] The steam heat source drying system heat energy cascade utilization and waste heat recovery device also includes a breather valve 23.

[0092] The waste heat recovery unit 2 is provided with an exhaust port 24 above the exhaust steam absorption layer 2003, and a breather valve 23 is provided on the exhaust port 24.

[0093] The exhaust steam absorption layer 2003 is a packing absorption layer made of a material resistant to water vapor temperature and drastic temperature fluctuations. Specifically, the exhaust steam absorption layer 2003 is a corrugated packing made of metal.

[0094] Working principle:

[0095] The main heating equipment of large-scale drying systems typically consists of multiple finned heat exchangers connected in series. Air is drawn from the atmosphere, and especially in northern regions where winter temperatures often reach -10℃ to -20℃, severe water hammer often occurs when steam or steam-containing condensate from steam traps is directly introduced to heat the cold air. Furthermore, the heat exchange tubes of large heat exchangers are very long, leading to icing at the tube ends. Both of these conditions can cause water hammer cracking or freezing cracking of the heat exchange tubes in the first or subsequent one or two heat exchangers, affecting the normal operation of the equipment.

[0096] This invention pressurizes the circulating water in the waste heat recovery unit 2 using a circulating water pump 3 and forces it to circulate between the circulating water preheating module 1001 and the waste heat recovery unit 2. The spray assembly of the waste heat recovery unit 2 separates the primary condensate from each heat exchange unit into steam and water. The exhaust steam enters the exhaust steam absorption layer 2003 and is absorbed by the circulating water cooled by the circulating water preheating module 1001, thereby increasing the temperature of the circulating water. At this time, the temperature of the condensate in the waste heat recovery unit 2 is below the saturation temperature of water at normal pressure, so it does not contain water vapor. When it is circulated back to the circulating water preheating module 1001 for heat exchange, the water hammer phenomenon is eliminated. Furthermore, the circulation volume of the circulating water is much greater than the flow rate of the primary condensate, ensuring sufficient heat supply. This makes the outlet water temperature of the circulating water preheating module 1001 much higher than the freezing point. The increase in the flow velocity inside the circulating water preheating module 1001 tubes not only improves the heat transfer coefficient inside the heat exchange tubes but also avoids dead flow zones, thereby preventing tube freezing.

[0097] After being heated by the circulating water preheating module 1001, the air temperature rises above zero degrees Celsius, eliminating the risk of pipe freezing. After the temperature difference between the air and the water-steam mixing heating module 1002 is reduced, the heat exchange process becomes gentle. At this time, when the steam-containing condensate output by the steam heating module 1003 through the first steam trap 4 is introduced into the water-steam mixing heating module 1002 for heat exchange, it can effectively absorb the exhaust steam without causing water hammer.

[0098] During the heat exchange process, when the condensate contains a lot of steam, the water-steam mixing heating module 1002 may still produce water hammer. At this time, the condensate of the main heating unit 1 can be partially or completely sent into the waste heat recovery unit 2 by switching the valve to separate and absorb the exhaust steam.

[0099] Steam from the steam source enters the steam heating module 1003 of the main heating unit 1 to further heat the hot air that has been heated by the circulating water preheating module 1001 and the water-steam mixing heating module 1002. In this embodiment, the outlet air temperature usually does not exceed the saturation temperature of the steam, which is suitable for drying systems with low requirements for inlet air temperature.

[0100] For superheated steam with high superheat provided by the plant, the device of this application can fully utilize the sensible heat of the superheated steam to increase the inlet air temperature for drying, thereby achieving higher thermal efficiency in hot air drying. For example, for common superheated steam at 220°C and 0.5 MPa(G), with a saturation temperature of 158.8°C and a superheat greater than 60°C, the waste heat recovery device of this embodiment can achieve an exhaust air temperature of approximately 145°C-155°C when using both saturated steam and superheated steam. The condensate discharge temperature can be reduced to approximately 60°C.

[0101] Example 2

[0102] like Figure 2As shown, the difference from Embodiment 1 is that the steam heat source drying system heat energy cascade utilization and waste heat recovery device further includes a second heating unit 10.

[0103] The waste heat recovery unit 2 is provided with a second vapor-liquid inlet 20002.

[0104] The second heating unit 10 is provided with a second steam pipe 101 at its inlet and a second steam trap 11 at its outlet. The outlet of the second steam trap 11 is connected to the inlet of the water-steam mixing heating module 1002 via a fourth steam-liquid pipe 12. A fourth throttle valve 121 is provided on the fourth steam-liquid pipe 12.

[0105] The outlet of the second steam trap 11 is connected to the second steam inlet 20002 of the waste heat recovery unit 2 through the fifth steam-liquid pipeline 13. The second steam inlet 20002 is located below the exhaust steam absorption layer 2003. The fifth steam-liquid pipeline 13 is equipped with a fifth throttle valve 131.

[0106] The waste heat recovery unit 2 is provided with a second spray pipe 14 connected to the second vapor-liquid inlet 20002 below the waste steam absorption layer 2003, and the second spray pipe 14 is located above the circulating water surface.

[0107] In this embodiment, the second heating unit 10 generally refers to the largest heating unit other than the main heating unit 1. Similarly, its condensate can also be introduced into the water-vapor mixing heating module 1002 of the main heating unit 1. The condensate from the water-vapor mixing heating module 1002 is sprayed into the waste heat recovery unit 2 through the spray assembly. The second heating unit 10 can be a steam heat exchanger installed in the main bed of the drying system, with a heating effect secondary to that of the main heating unit 1. The steam source of the second heating unit 10 can be the same as or different from that of the main heating unit 1. When the second heating unit 10 has a strict upper limit on the steam temperature, such as when it is limited by the temperature resistance of the material, or when the required heating temperature is lower than that of the main heating unit 1, its heat source does not need to be a high superheat steam heat source.

[0108] During the heat exchange process, when the condensate contains a lot of steam, the water-steam mixing heating module 1002 may still produce water hammer. At this time, the condensate of the second heating unit 10 can be partially or completely sent into the waste heat recovery unit 2 by switching the valve to separate and absorb the exhaust steam.

[0109] Example 3

[0110] like Figure 3 As shown, the difference from Embodiment 1 is that the steam heat source drying system heat energy cascade utilization and waste heat recovery device also includes a third heating unit 15.

[0111] The waste heat recovery unit 2 is equipped with a third vapor-liquid inlet 20003.

[0112] The third heating unit 15 is provided with a third steam pipe 151 at its inlet and a third steam trap 16 at its outlet. The outlet of the third steam trap 16 is connected to the third steam inlet 20003 of the waste heat recovery unit 2 via a sixth steam-liquid pipe 17. The third steam inlet 20003 is located below the exhaust steam absorption layer 2003.

Claims

1. A device for cascade utilization of thermal energy and waste heat recovery in a steam heat source drying system, characterized in that: The main heating unit (1), the waste heat recovery device (2), the circulating water pump (3) and the first steam trap (4) are arranged in sequence along the air flow direction. The main heating unit (1) is sequentially provided with a circulating water preheating module (1001), a water-vapor mixing heating module (1002) and a steam heating module (1003) along the air flow direction, the steam heating module (1003) is provided with a first steam pipeline (10031) at the inlet, the steam heating module (1003) is provided with a first steam trap (4) at the outlet, the outlet of the first steam trap (4) is connected with the inlet of the water-vapor mixing heating module (1002) through a first steam-liquid pipeline (5), and the outlet of the first steam trap (4) is connected with a first steam-liquid inlet (20001) of the waste heat recovery device (2) through a second steam-liquid pipeline (6). The first steam-liquid pipeline (5) is provided with a first throttling valve (51), the second steam-liquid pipeline (6) is provided with a second throttling valve (61), and the outlet of the water-vapor mixing heating module (1002) is connected with the first steam-liquid inlet (20001) through a third steam-liquid pipeline (7). The waste heat recovery device (2) is provided with circulating water, the circulating water outlet of the waste heat recovery device (2) is connected with the water inlet of the circulating water preheating module (1001), the circulating water pump (3) is arranged between the waste heat recovery device (2) and the circulating water preheating module (1001), and the water outlet of the circulating water preheating module (1001) is connected with the circulating water inlet of the waste heat recovery device (2). The waste heat recovery device (2) is used for recycling steam and condensate water and performing heat exchange between the steam, the condensate water and the circulating water. The first throttling valve (51) and the second throttling valve (61) are used for controlling the proportion of the condensate water and the steam mixture output by the first steam trap (4) to the waste heat recovery device (2) and the water-vapor mixing heating module (1002), so as to avoid the water hammer phenomenon. The waste heat recovery device (2) is sequentially provided with a steam absorption cavity (2001) and a condensate water mixing cooling cavity (2002) which are communicated with each other from top to bottom, the circulating water is stored in the condensate water mixing cooling cavity (2002), and the steam absorption cavity (2001) is provided with a steam absorption layer (2003) above the liquid level of the circulating water along the cross section. The first steam-liquid inlet (20001) is located below the steam absorption layer (2003). The circulating water inlet of the waste heat recovery device (2) is located above the steam absorption layer (2003).

2. The apparatus for cascade utilization of heat energy and recovery of waste heat of a steam heat source drying system according to claim 1, characterized in that: The waste heat recovery device (2) is provided with a spray head (8) connected with the circulating water inlet above the steam absorption layer (2003). The waste heat recovery device (2) is provided with a first spray pipe (9) connected with the first steam-liquid inlet (20001) below the steam absorption layer (2003), and the first spray pipe (9) is located above the liquid level of the circulating water.

3. The apparatus for cascade utilization of heat energy and recovery of waste heat of a steam heat source drying system according to claim 1, characterized in that: The second heating unit (10) is further included. The second heating unit (10) is provided with a second steam pipe (101) at the inlet, and is provided with a second steam trap (11) at the outlet, and the outlet of the second steam trap (11) is connected with the inlet of the water-steam mixed heating module (1002) through a fourth vapor-liquid pipe (12), and the fourth vapor-liquid pipe (12) is provided with a fourth throttling valve (121); The outlet of the second steam trap (11) is connected with the second vapor-liquid inlet (20002) of the waste heat recovery device (2) through a fifth vapor-liquid pipe (13), and the second vapor-liquid inlet (20002) is located below the steam absorption layer (2003), and the fifth vapor-liquid pipe (13) is provided with a fifth throttling valve (131); The waste heat recovery device (2) is provided with a second spray pipe (14) connected with the second vapor-liquid inlet (20002) below the steam absorption layer (2003), and the second spray pipe (14) is located above the circulating water liquid level.

4. The apparatus for thermal energy cascade utilization and waste heat recovery in a steam heat source drying system according to claim 1, characterized in that: Further comprising a third heating unit (15); The third heating unit (15) is provided with a third steam pipe (151) at the inlet, and is provided with a third steam trap (16) at the outlet, and the outlet of the third steam trap (16) is connected with the third vapor-liquid inlet (20003) of the waste heat recovery device (2) through a sixth vapor-liquid pipe (17), and the third vapor-liquid inlet (20003) is located below the steam absorption layer (2003).

5. The apparatus for thermal energy cascade utilization and waste heat recovery in a steam heat source drying system according to claim 1, characterized in that: Further comprising a first liquid level meter (18), a first temperature sensor (19), a water injection pipe (20) and a drain pipe (21); The first liquid level meter (18), the water injection pipe (20) and the drain pipe (21) are arranged on the waste heat recovery device (2); The first liquid level meter (18) is used for monitoring the liquid level of the circulating water in the waste heat recovery device (2); The first temperature sensor (19) is arranged on the waste heat recovery device (2) or on the conveying pipe between the waste heat recovery device (2) and the circulating water preheating module (1001), and is used for monitoring the outlet water temperature of the circulating water of the waste heat recovery device (2).

6. The apparatus for cascade utilization of heat energy and recovery of waste heat of a steam heat source drying system according to claim 5, characterized in that: Further comprising a circulating water discharge pump (22), which is arranged on the drain pipe (21).

7. The apparatus for thermal energy cascade utilization and waste heat recovery in a steam heat source drying system according to claim 1, characterized in that: Further comprising a breather valve (23); The waste heat recovery device (2) is provided with a vent (24) above the steam absorption layer (2003), and the vent (24) is provided with a breather valve (23).

8. The apparatus for thermal energy cascade utilization and waste heat recovery in a steam heat source drying system according to claim 1, characterized in that: The steam absorption layer (2003) is a filler absorption layer made of a material resistant to water vapor temperature and severe temperature fluctuations; The steam absorption layer (2003) includes corrugated metal filler, wire mesh filler or scattered metal filler.

9. The apparatus for thermal energy cascade utilization and waste heat recovery in a steam heat source drying system according to claim 1, characterized in that: The third vapor-liquid pipe (7) is provided with a third throttling valve (71).

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