Low-rank coal low-temperature drying method based on air source heat pump

Abstract

The application discloses a low-rank coal low-temperature drying method based on an air source heat pump and relates to the technical field of energy and environmental engineering. The method comprises the following steps: crushing and grinding the low-rank coal, preheating ambient air, heating the ambient air to form a drying medium through a heat pump condenser, countercurrently or multistage cross-flow drying in a gas-solid fluidized bed at a wind speed of 0.1-5 m / s, dynamically adjusting and controlling the wind speed, temperature, feeding speed and coal laying thickness according to online moisture content, temperature and humidity data through a PLC system, discharging waste gas to a heat regenerator and a heat pump evaporator after dust removal, recovering latent heat and condensing and dehumidifying, recycling the dehumidified air after heat regeneration and mixing with fresh air to form a closed or semi-closed hot air system. The application has the advantages of low drying energy consumption, high energy efficiency ratio, high latent heat recovery rate and low influence of ambient temperature, and effectively solves the problems of high energy consumption, easy spontaneous combustion, great pollution, unstable low-temperature working condition and waste of waste heat of the traditional low-rank coal drying.

Description

Technical Field

[0001] This invention belongs to the field of energy and environmental engineering technology, and specifically relates to a low-temperature drying method for low-rank coal based on an air source heat pump. Background Technology

[0002] With the deepening of my country's energy structure transformation and the strategy of clean and efficient utilization of coal, the upgrading and utilization of low-rank coal, as an important fossil resource with abundant reserves, has become an effective way to alleviate dependence on oil and ensure energy security. Low-rank coal generally has characteristics such as high intrinsic moisture (30-60%), high oxygen content, and low calorific value, which not only significantly reduces combustion efficiency and increases transportation and processing costs, but also causes energy waste and pollutant emissions during pyrolysis, gasification, and other conversion processes. Therefore, developing a low-rank coal drying technology that can balance dehydration efficiency, safety, and environmental friendliness is a prerequisite for realizing its high-value utilization.

[0003] Currently, dewatering of low-rank coal mainly relies on two technologies: mechanical dewatering and thermal drying. Among them, thermally driven drying is the mainstream dewatering method. Although mechanical dewatering can be used as a preliminary treatment, it is difficult to reduce the moisture content to below 30% due to the fineness of coal particles and the density of the filter cake. While traditional flue gas or electric heating drying can achieve deep dewatering, it generally suffers from high energy consumption, low thermal efficiency, and excessively high operating temperatures (often exceeding 150°C), which can easily induce oxidation or even spontaneous combustion of low-rank coal. At the same time, it is accompanied by the emission of large amounts of dust and harmful gases, making it difficult to meet the requirements of green and low-carbon development.

[0004] In recent years, with the continuous development of technology, air source heat pump technology has been widely used in the drying processes of agricultural products, food, and chemical industries due to its advantages such as high energy efficiency (COP can reach 3-5), environmental protection, and safety. However, it still has some problems in the drying of low-rank coal: on the one hand, the evaporator is prone to frosting in low-temperature environments, leading to a decrease in heating performance and a decline in system stability; on the other hand, the drying process lacks a dynamic response mechanism to changes in coal quality and environmental parameters, making it difficult to achieve coordinated optimization of hot air parameters and material state. In addition, the latent heat in high-temperature and high-humidity exhaust gas is usually directly discharged, resulting in energy waste, while the open airflow circulation also exacerbates heat loss and dust dispersion.

[0005] Therefore, there is an urgent need for a low-rank coal drying method that integrates preheating control, closed-loop latent heat recovery, intelligent parameter matching, and low-temperature safe operation to solve the problems of existing technologies in terms of energy efficiency, safety, and adaptability. Summary of the Invention

[0006] To address the aforementioned shortcomings in existing technologies, this invention provides a low-temperature drying method for low-rank coal based on an air-source heat pump, effectively solving the problems of high energy consumption, easy spontaneous combustion, significant pollution, unstable low-temperature operation, and waste of waste heat associated with traditional low-rank coal drying.

[0007] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is: to provide a low-temperature drying method for low-rank coal based on an air source heat pump, comprising the following steps: S1. Grind the low-rank coal and preheat the air. Then, reheat the preheated air to obtain a drying medium. S2. The drying medium obtained in step S1 is introduced into a gas-solid fluidized bed to dry low-rank coal. The exhaust gas enters the dust collector through the circulating air duct for dust removal. After dust removal, it enters the regenerator, where it exchanges heat with the low-temperature dry air that is about to enter the condenser, allowing it to absorb the waste heat of the high-temperature exhaust gas and rise in temperature, thereby improving the heat utilization rate. Then, it is condensed and precipitated in the evaporator to achieve dehumidification and obtain preheated dry air.

[0008] Furthermore, in step S1, the particle size after grinding is 0.4-0.6 mm.

[0009] Furthermore, in step S1, the particle size after grinding is 0.5 mm.

[0010] Furthermore, in step S1, the particle size control of low-rank coal is achieved through two-stage crushing and screening. The jaw crusher and the double roll crusher crush the raw coal to less than 1-2 mm, and then the ball mill further refines it to 0.4-0.6 mm.

[0011] The beneficial effects of adopting the above-mentioned further measures are: increasing its specific surface area and improving heat and mass transfer efficiency. This particle size control strategy ensures that coal particles are heated evenly during the subsequent drying process, avoiding local overheating or uneven drying due to particle size differences.

[0012] Furthermore, in step S1, the ambient air entering the system is preheated using an electric heating device.

[0013] Furthermore, in step S1, the preheated air temperature is 10-20 ℃.

[0014] The beneficial effects of adopting the above-mentioned further solutions are: reducing the heating load of the subsequent heat pump condenser and improving the system's start-up stability and energy efficiency under low-temperature conditions.

[0015] Furthermore, in step S1, the preheated air is introduced into the condenser side of the air source heat pump system, and is reheated by the heat released by the phase change of the refrigerant inside the condenser.

[0016] Furthermore, in step S1, the air temperature after secondary heating is 60-80℃.

[0017] Furthermore, in step S1, the air source heat pump unit adopts two-stage compression or gas injection enthalpy enhancement technology, which can still operate stably when the ambient temperature is as low as -10°C, and the condensing temperature is maintained in the range of 60-80°C.

[0018] The beneficial effect of the above-mentioned further solutions is that they fully utilize the high energy efficiency ratio of heat pumps to maximize heat output per unit of energy consumption.

[0019] Furthermore, in step S2, the drying medium is fed into a drying device containing pretreated low-rank coal for continuous drying at 60-80℃.

[0020] Furthermore, in step S2, the wind speed is 0.1-5 m / s.

[0021] Furthermore, in step S2, the drying device is a gas-solid fluidized bed. The drying chamber is equipped with a multi-channel temperature and humidity sensor and an online moisture content detection module to collect real-time data on the internal temperature, relative humidity and real-time moisture content of the coal sample. The signals are transmitted to the PLC control module, which dynamically adjusts the hot air temperature (60-80℃), air velocity (0.1-5m / s) and coal spreading thickness (10-50mm) according to a preset algorithm.

[0022] Furthermore, in step S2, when the drying device is a gas-solid fluidized bed, the bed body is made of stainless steel, the opening rate of the bottom air distribution plate is controlled at 25-35%, the air distribution uniformity is good, and the fluidization air velocity can be steplessly adjusted within the range of 0.1-5 m / s, so that the coal particles are fully fluidized in the bed, which enhances the gas-solid contact effect, shortens the drying cycle, inhibits the formation of local hot spots, and avoids coal particle agglomeration.

[0023] Furthermore, in step S2, the online moisture content detection module is built based on the principle of near-infrared spectroscopy analysis. It emits infrared light of a specific wavelength to irradiate the coal seam and collects diffuse reflection signals, detecting changes in reflected light intensity. Combined with a pre-calibrated moisture-light intensity relationship model, it calculates the current moisture content of the coal sample in real time, achieving a detection accuracy of ±1% and a response time of less than 30 seconds. The ash concentration monitoring unit uses laser scattering to measure the mass concentration of suspended dust in the circulating gas in real time, with a detection range of 0-500 mg / m³. 3 With an accuracy of ±5%, it provides a basis for explosion-proof early warning and parameter linkage adjustment.

[0024] Furthermore, in step S2, the PLC control module has a built-in multivariable collaborative control model that integrates fuzzy PID control, feedforward compensation, and dynamic optimization algorithms. Based on real-time monitoring of drying chamber temperature, humidity, coal sample moisture content, and ash concentration data, it synchronously adjusts the output frequency of the fan inverter, the opening degree of the heat pump expansion valve, the compressor speed, the feeding rate of the feeding mechanism, and the air volume distribution of the air distribution plate to form a closed-loop rapid response mechanism, effectively improving the drying rate and process stability.

[0025] Furthermore, in step S2, the high-temperature and high-humidity exhaust gas discharged from the drying device is introduced into a high-efficiency dust removal unit for dust removal.

[0026] Furthermore, in step S2, the high-efficiency dust removal unit is designed as a multi-stage series structure. A cyclone separator is set at the front end to remove large dust particles, and a bag filter with a membrane filter bag is configured at the rear end to capture fine particles. The dust collector is equipped with a pulse back-flushing cleaning system, and the cleaning cycle is automatically triggered according to the differential pressure sensor signal to ensure continuous operation capability.

[0027] Furthermore, in step S2, the exhaust gas after removing coal dust particles enters the regenerator and the air source heat pump evaporator in sequence. In the regenerator, it undergoes preliminary heat exchange with the low-temperature dry air that is about to enter the condenser. In the evaporator, it is cooled to below the dew point to achieve water vapor condensation and precipitation.

[0028] Furthermore, in step S2, the air source heat pump evaporator adopts a structure of hydrophilic aluminum foil fins and copper tube expansion joints. An inclined condensate guide groove and an automatic drain valve are set at the bottom of the evaporator to ensure that the condensate is discharged in time and to avoid liquid accumulation and corrosion.

[0029] Furthermore, in step S2, the low-temperature dry air that has been cooled and dehumidified by the evaporator is reintroduced into the other side of the regenerator to absorb the waste heat of the high-temperature exhaust gas and rise in temperature, forming preheated dry air.

[0030] Furthermore, in step S2, the outlet of the gas-solid fluidized bed, the circulating air duct, and the inlet of the dust removal unit are equipped with a CO concentration sensor, an O2 concentration sensor, a surface temperature monitoring probe, and an ash concentration sensor.

[0031] The aforementioned air source heat pump drying system includes: a gas-solid fluidized bed, a dust collector after drying, a regenerator, an electromagnetic expansion valve, a condenser, a compressor, and an evaporator. The condenser and evaporator are connected to the compressor via the electromagnetic expansion valve and the compressor, respectively. The condenser is connected to the gas-solid fluidized bed via a circulating fan, the circulating fan is connected to the dust collector via a circulating fan, and the dust collector is connected to the regenerator via a circulating fan.

[0032] In summary, the present invention has the following beneficial effects: 1. This invention achieves efficient dehydration of low-rank coal within a safe temperature range of 60-80 ℃ by constructing a highly closed low-temperature drying system based on an air source heat pump, effectively reducing the risk of coal oxidation and spontaneous combustion caused by high-temperature drying.

[0033] 2. This invention adopts a three-stage heat energy cascade utilization mechanism of "preheating + heat pump heating + high-efficiency regeneration", which significantly improves the regeneration efficiency and the overall energy efficiency of the system. Compared with traditional electric heating or coal-fired drying methods, the energy saving effect is obvious. Moreover, the closed-loop airflow circulation design effectively curbs dust overflow, heat loss and environmental pollution.

[0034] 3. This invention introduces a multivariate collaborative control model and real-time ash concentration monitoring to achieve dynamic and precise control of the drying process and explosion-proof early warning linkage, which greatly improves the drying rate and operational safety. In addition, the deep recovery of latent heat of waste gas and the reuse of condensate further enhance the comprehensive utilization efficiency of resources, making it suitable for large-scale industrial upgrading of low-rank coal and showing good application prospects. Attached Figure Description

[0035] Figure 1 Here is a flowchart of the drying process; Figure 2 This is a flowchart of the waste gas recirculation treatment process; Figure 3 This is a schematic diagram of the overall monitoring principle. Figure 4 This is a schematic diagram of the structure of an air source heat pump; Among them, 1. gas-solid fluidized bed; 2. dust collector; 3. regenerator; 4. electromagnetic expansion valve; 5. condenser; 6. compressor; 7. evaporator; 8. circulating fan; 9. circulating fan; 10. circulating fan. Detailed Implementation

[0036] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0037] Example 1 A method for low-temperature drying of low-rank coal based on an air-source heat pump includes the following steps: S1. Particle size control of low-rank coal is achieved through two-stage crushing and screening. Jaw crushers and double-roll crushers crush the raw coal to less than 1-2 mm, and then the ball mill further refines it to 0.5 mm. An electric heating device preheats the ambient air entering the system. The feed rate is precisely controlled by a frequency converter. Ambient air is drawn in through the fresh air inlet and first enters the electric heating preheating section. This section is equipped with a finned tube electric heater with a power of 15 kW, which can rapidly heat the ambient air to 15°C for continuous low-temperature drying. The temperature of the preheated air is monitored in real time by a PT100 platinum resistance temperature sensor, and the signal is fed back to the PLC control module for dynamic adjustment of the electric heater's output power to ensure stable preheating temperature. Air is introduced into the condenser side of the air source heat pump system. Inside the condenser, the air is reheated by the heat released from the refrigerant's phase change, raising the air temperature to 60-80℃ and forming a dry medium. The air source heat pump unit uses two-stage compression or gas injection enthalpy enhancement technology, allowing for stable operation even at ambient temperatures as low as -20℃. The condensing temperature is maintained in the 60-80℃ range, with a coefficient of performance (COP) of no less than 3.0. Environmentally friendly R32 or R290 refrigerants are used. The system is equipped with an oil separator and oil return device to ensure the long-term reliability of the compressor. The preheated air enters the heat pump condenser, a coaxial heat exchanger. High-temperature, high-pressure refrigerant vapor flows through the inner tube, while dry air flows through the outer tube. The refrigerant undergoes a phase change within the condenser, condensing from a gaseous state to a liquid state, releasing a large amount of latent heat and heating the air to the target temperature of 60-80℃. The thermodynamic efficiency of this process is quantified by the coefficient of performance (COP), calculated using the following formula:

[0038] Where Qh represents the heat released by the condenser (kW), and Wcomp represents the compressor input power (kW). Under normal operating conditions, when the ambient temperature is 5℃ and the condensing temperature is 70℃, the system COP can reach over 3.2. The heat pump unit is equipped with a fully enclosed scroll compressor with a built-in variable frequency drive, which can steplessly adjust the speed according to the drying load requirements, thereby dynamically matching the heat output. The system is also equipped with a high-efficiency oil separator, installed between the compressor exhaust port and the condenser, with a separation rate of not less than 98%. The separated lubricating oil is returned to the compressor crankcase through a capillary oil return device to prevent lubricating oil from accumulating in the heat exchanger and affecting the heat transfer efficiency. The outlet temperature of the drying medium is monitored in real time by a high-precision thermocouple (K type), and the data is transmitted to the PLC control module for closed-loop adjustment of the compressor frequency and expansion valve opening to ensure that the hot air temperature fluctuation range is controlled within ±2℃. S2. The drying medium is fed into the drying device containing pretreated low-rank coal at a wind speed of 1 m / s. The drying device adopts a gas-solid fluidized bed structure to ensure that the coal particles are in a good fluidized state during the drying process. The contact method between the drying air and the coal sample is countercurrent or multi-stage crossflow arrangement. The drying chamber is equipped with multi-channel temperature and humidity sensors, online moisture content detection module and ash concentration monitoring unit to collect data on the temperature, relative humidity, real-time moisture content of the coal sample and suspended ash concentration in the circulating gas in real time, and transmit the signals to the PLC control module. The PLC control module is based on a multivariable collaborative control model, integrating fuzzy PID algorithm and dynamic response prediction mechanism. It dynamically adjusts the hot air temperature, air supply speed, feeding speed and coal spreading thickness according to the real-time monitoring data. The coal spreading thickness is 10-50 mm, realizing precise, intelligent and high-speed control of the drying process. The drying device is a gas-solid fluidized bed, the bed body is made of 304 stainless steel, the opening diameter is 1 mm, and the air distribution uniformity error is less than 5%. Fluidizing air is provided by a centrifugal fan, with an adjustable speed ranging from 0.1 to 5 m / s, ensuring that coal particles are fully fluidized within the bed and enhancing gas-solid contact. Multiple temperature and humidity sensors are arranged along the height of the drying chamber, each containing a PT100 temperature probe and a capacitive humidity sensor. The online moisture content detection module is based on near-infrared spectroscopy, emitting infrared light with wavelengths of 1450-1940 nm to penetrate the coal seam and detecting changes in reflected light intensity. Combined with a pre-calibrated moisture-light intensity relationship model, the current moisture content of the coal sample is calculated in real time, with an accuracy of ±0.5%. The ash concentration monitoring unit uses laser scattering, with a 650 nm semiconductor laser as the light source and a silicon photodiode as the detector, to measure the suspended dust concentration in the circulating gas in real time, with a detection range of 0-500 mg / m³. 3 Accuracy ±5%. All sensor signals are transmitted to the PLC control module via shielded cables. The PLC control module has a built-in multivariable collaborative control model, integrating fuzzy PID control, feedforward compensation, and dynamic optimization algorithms. Based on real-time monitoring data of drying chamber temperature, humidity, coal sample moisture content, and ash concentration, it synchronously adjusts the output frequency of the fan inverter, the opening of the heat pump expansion valve, the compressor speed, the feeding rate of the feeding mechanism, and the air volume distribution of the air distribution plate. In actual use, when the rate of decrease in moisture content is lower than the set threshold, the system automatically increases the hot air temperature by 1-2℃ and increases the wind speed by 0.5 m / s; when the ash concentration exceeds 200 mg / m³, the system automatically increases the hot air temperature by 1-2℃ and the wind speed by 0.5 m / s. 3 When this occurs, the feed rate will automatically decrease by 10% to reduce dust generation. The coal sample drying rate can be estimated using the formula:

[0039] Where M is the moisture content of the coal sample (kg), t is the time (s), k is the mass transfer coefficient (m / s), and A is the effective drying area (m²). 2X represents the current moisture content (kg water / kg dry coal), and Xe represents the equilibrium moisture content (kg water / kg dry coal). At a drying temperature of 60-80℃, the equilibrium moisture content Xe can be reduced to below 5%, ensuring efficient drying. The coal layer thickness is controlled at 30mm by adjusting the distributor speed and scraper height to ensure moderate bed resistance and uniform drying. The high-temperature, high-humidity exhaust gas discharged from the drying unit is first introduced into a high-efficiency dust removal unit, where bag filters or electrostatic precipitators remove the coal dust particles carried within, preventing dust deposition in subsequent heat exchange equipment and avoiding blockages or reduced heat exchange efficiency. The purified exhaust gas sequentially enters the regenerator and the air source heat pump evaporator. In the regenerator, it undergoes preliminary heat exchange with the low-temperature dry air that is about to enter the condenser, recovering some sensible heat. Subsequently, the exhaust gas enters the evaporator, where it is cooled to below the dew point on the surface of the evaporator coils, achieving condensation and precipitation of water vapor, thus completing the dehumidification process. At the same time, the latent heat in the exhaust gas is absorbed by the refrigerant to drive the heat pump cycle. The condensed liquid water is collected and can be used for system cooling water replenishment or other non-potable purposes in the plant area, realizing the recycling of water resources. The high-efficiency dust removal unit is designed with a multi-stage series structure. A cyclone separator is set at the front end to remove large dust particles with a diameter greater than 10 μm, and a bag filter dust collector with a membrane filter bag is set at the rear end to capture fine particles. The filter bag material is PTFE membrane polyester needle-punched felt, with a filtration efficiency of greater than 99.9%. The system pressure drop is controlled within 1200 Pa. The dust collector is equipped with a pulse back-flushing cleaning system. The cleaning cycle is automatically triggered according to the inlet and outlet pressure difference sensor signals. When the pressure difference exceeds 800 Pa, the cleaning program is started to ensure continuous operation capability. The purified exhaust gas (temperature approximately 55℃, relative humidity 95%) first enters the hot-side channel of the regenerator, where it undergoes cross-flow heat exchange with the low-temperature, dry air (approximately 35℃) from the evaporator. The regenerator employs a plate-fin structure made of corrosion-resistant aluminum alloy, and guide vanes are installed on both sides of the airflow channel to optimize the flow field distribution and reduce flow resistance. The heat recovery efficiency ηrec of the regenerator is defined as:

[0040] Wherein, Tin,hot and Tout,hot are the inlet and outlet temperatures (°C) of the high-temperature exhaust gas, respectively, and Tin,cold is the inlet temperature (°C) of the low-temperature air. Under normal operating conditions, the regeneration efficiency is not less than 80%. The exhaust gas (approximately 45°C) after preliminary cooling by the regenerator enters the air source heat pump evaporator. This evaporator adopts a structure of hydrophilic aluminum foil fins and copper tube expansion joints, with a fin spacing designed to be 2.2mm to adapt to long-term operation under high-humidity exhaust gas conditions and prevent excessively rapid frosting and poor drainage. The refrigerant absorbs heat and evaporates in the evaporator, cooling the exhaust gas to below the dew point (typically 30°C to 35°C), causing water vapor to condense and precipitate. An inclined condensate drainage channel and automatic drain valve are installed at the bottom of the evaporator to ensure timely discharge of condensate into the collection tank, preventing liquid accumulation and corrosion. Simultaneously, after water quality testing, the condensate can be used for cooling tower makeup or watering of factory roads, achieving water resource recycling. The low-temperature dry air, cooled and dehumidified by the evaporator, is reintroduced into the other side of the regenerator, absorbing residual heat from the high-temperature exhaust gas and heating up to form preheated dry air. This preheated air is then mixed with a certain proportion of fresh... Ambient air is mixed, with the mixing ratio set at 20-80% based on the humidity requirements of the system's operating phase, or automatically adjusted by feedback signals from humidity sensors to maintain the humidity balance of the circulating air within the system. The final mixed air re-enters the condenser and is heated to become a drying medium, thus forming a highly closed hot air circulation system. This minimizes heat loss to the external environment and improves overall thermal efficiency. Low-temperature dry air (approximately 30°C, 40% relative humidity) flowing from the evaporator enters the cold-side channel of the regenerator, absorbing waste heat from the hot-side exhaust gas and rising to approximately 45°C, becoming preheated dry air. This air then enters the fresh air mixing section, where it is mixed proportionally with the preheated fresh ambient air. The fresh air mixing section is equipped with an electrically operated proportional regulating valve, whose opening is automatically adjusted by the PLC control module based on feedback signals from the return air humidity sensor. For example, in the initial drying stage when the coal sample has a high moisture content, the system sets the fresh air ratio to 30% to regulate the system's gas composition and humidity level, preventing the accumulation of volatile components. In the later stages of drying, the fresh air ratio can be reduced to 20% to maximize heat recovery. The mixed air (temperature approximately 50℃) re-enters the heat pump condenser and is heated to 60℃ to 80℃, completing a full closed-loop cycle. CO concentration sensors, O2 concentration sensors, surface temperature monitoring probes, and ash concentration sensors are installed at the gas-solid fluidized bed outlet, circulating air duct, and dust removal unit inlet. Sensors detect CO concentrations exceeding 50 ppm, abnormal increases in coal sample surface temperature exceeding 85℃, or persistent ash concentrations in the circulating gas exceeding 300 mg / m³. 3When the system is activated, it automatically initiates a three-level interlock protection mechanism: first, it reduces the feed rate and hot air temperature; second, it increases the inert gas (nitrogen) injection flow rate; and finally, in extreme cases, it cuts off the heat source and initiates an emergency venting procedure, effectively preventing dust explosions or coal powder spontaneous combustion accidents. The nitrogen storage tank is connected to the drying device via a solenoid valve, and the injection flow rate is precisely regulated by a mass flow controller. Simultaneously, this invention also includes a remote monitoring and data management platform, connected to the PLC control system via an industrial Ethernet network, to collect and store operating parameters in real time, including temperature curves, humidity changes, energy consumption data, ash concentration trends, fault records, and control command logs. The historical data storage period can be flexibly set, supporting big data-based operational trend prediction, energy efficiency assessment, and preventative maintenance reminders, improving the system's intelligent operation and maintenance level. The waste gas recirculation treatment flow chart of this invention is shown below. Figure 1 As shown in the diagram, the overall monitoring principle framework is as follows: Figure 2 As shown in the diagram, the structure of an air source heat pump is as follows: Figure 3 As shown.

[0041] The aforementioned air source heat pump includes: a gas-solid fluidized bed 1, a dust collector 2, a regenerator 3, an electromagnetic expansion valve 4, a condenser 5, a compressor 6, and an evaporator 7. The condenser 5 and evaporator 7 are connected via the electromagnetic expansion valve 4 and compressor 6, respectively. The condenser 5 is connected to the gas-solid fluidized bed 1 via a circulating fan 8. The gas-solid fluidized bed 1 is connected to the dust collector 2 via a circulating fan 9. The dried dust collector 2 is connected to the regenerator 3 via a circulating fan 10. A schematic diagram is shown below. Figure 4 As shown.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for low-temperature drying of low-rank coal based on an air-source heat pump, characterized in that, Includes the following steps: S1. Grind the low-rank coal and preheat the air. Then, reheat the preheated air to obtain a drying medium. S2. The drying medium obtained in step S1 is introduced into a gas-solid fluidized bed to dry low-rank coal. The exhaust gas enters the dust collector through the circulating air duct for dust removal. After dust removal, it enters the regenerator, where it exchanges heat with the low-temperature dry air that is about to enter the condenser, allowing it to absorb the waste heat of the high-temperature exhaust gas and rise in temperature, thereby improving the heat utilization rate. Then, it is condensed and precipitated in the evaporator to achieve dehumidification and obtain preheated dry air.

2. The method for low-temperature drying of low-rank coal based on an air-source heat pump as described in claim 1, characterized in that, In step S1, the particle size after grinding is 0.4-0.6 mm.

3. The method for low-temperature drying of low-rank coal based on an air-source heat pump as described in claim 1, characterized in that, In step S1, the preheated air temperature is 10-20 ℃.

4. The method for low-temperature drying of low-rank coal based on an air-source heat pump as described in claim 1, characterized in that, In step S1, secondary heating is performed in the air source heat pump system.

5. The method for low-temperature drying of low-rank coal based on an air-source heat pump as described in claim 1, characterized in that, In step S1, the air temperature after secondary heating is 60-80℃.

6. The method for low-temperature drying of low-rank coal based on an air-source heat pump as described in claim 1, characterized in that, In step S2, the wind speed during drying is 0.1-5 m / s.

7. The method for low-temperature drying of low-rank coal based on an air-source heat pump as described in claim 1, characterized in that, In step S2, the coal layer thickness is 10-50 mm during drying.

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