CN111718100A - Low-temperature sludge drying method and system - Google Patents
Low-temperature sludge drying method and system Download PDFInfo
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- CN111718100A CN111718100A CN202010605925.4A CN202010605925A CN111718100A CN 111718100 A CN111718100 A CN 111718100A CN 202010605925 A CN202010605925 A CN 202010605925A CN 111718100 A CN111718100 A CN 111718100A
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- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F11/00—Treatment of sludge; Devices therefor
- C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
- C02F11/13—Treatment of sludge; Devices therefor by de-watering, drying or thickening by heating
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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Abstract
The invention relates to a low-temperature sludge drying method and system in the technical field of sludge treatment. The method comprises the steps that waste heat air of wet sludge is sequentially input into a cooling system and a refrigerant system to output high-temperature dry air, the high-temperature dry air is output to a drying chamber chain net conveying system through a circulating air system, the high-temperature dry air and the wet sludge in the drying chain net conveying system are subjected to heat-mass exchange, the waste heat air is output to the cooling system, circulation is formed in the process, and after multiple times of circulation, the wet sludge in the drying chain net conveying system is dried. And adjusting the parameters of the refrigerant system by setting input and output parameters and according to a pre-established mathematical model of the refrigerant system. The key parameters are used for adjusting the parameters of the condenser, the compressor and the evaporator of the refrigerant system, so that the system parameters are adaptive to actual requirements, the working efficiency of the sludge low-temperature dryer system is improved, and more energy conservation and emission reduction are realized.
Description
Technical Field
The invention relates to the technical field of sludge treatment, in particular to a low-temperature sludge drying method and system.
Background
With the rapid development of economy and the continuous improvement of industrialization level in China, the discharge of sewage and sewage is increased, and a large amount of sludge is generated. The sludge contains a large amount of toxic and harmful substances, also contains a large amount of metal ions, and has the characteristics of high water content, complex volume form, difficult transportation and the like. If the food is not handled well, the environment will be damaged greatly, and even the food chain is threatened to cause harm to human beings. At present, the treatment and disposal of sludge become a great environmental protection problem which must be faced in the development process of China. The existing low-temperature sludge drying technology in China is still in the beginning stage of industrial application, and many technologies need further theoretical research and practical inspection. For example, the modeling of the whole low-temperature sludge drying equipment system is realized, and the system optimization theory is realized by using the existing technologies such as intelligent gateway, edge calculation, Internet of things, artificial intelligence algorithm and the like, so that the purposes of intelligence, energy conservation and emission reduction are achieved.
Disclosure of Invention
The invention aims to establish a mathematical model for a condensing system of a sludge low-temperature drying machine system, and provides a sludge low-temperature drying method and a sludge low-temperature drying system.
In order to achieve the above purpose, the invention provides the following technical scheme:
a low-temperature sludge drying method comprises the following steps:
s1, inputting the waste heat air of the wet sludge into a cooling system, carrying out primary condensation dehumidification through the cooling system, and outputting second waste heat air;
s2, sending the second waste heat air into a refrigerant system, sequentially carrying out second condensation dehumidification, first temperature rise and second temperature rise on the second waste heat air in the refrigerant system, and outputting dry hot air to a circulating air system;
s3, outputting dry hot air to the drying chamber chain net conveying system through the circulating air system, carrying out heat and mass exchange between the dry hot air and wet sludge in the drying chain net conveying system, and outputting waste heat air to the cooling system;
s4, drying the wet sludge in the drying type chain-net conveying system through the repeated circulation of the steps S1-S3;
in the process, temperature and humidity parameters of air output by a cooling system of the cooling tower are solved by pre-establishing a mathematical model of heat and mass transfer of the cooling system of the cooling tower; the temperature and humidity parameters of air output by a cooling system of the cooling tower, the temperature and humidity parameters of dry hot air output by a preset refrigerant system and a pre-established mathematical model of the refrigerant system are used for adjusting the parameters of the refrigerant system.
Further, the mathematical model of the refrigerant system is Qout＝Q1+WyWherein Q is1Is the heat absorbed by the evaporator in the refrigerant system, WyIs the actual power consumption, Q, of the compressor in the refrigerant systemoutIs the heat output by the condenser in the refrigerant system.
As a preferred embodiment of the present invention, the parameters of the refrigerant system include: condenser heat transfer area, compressor real power, evaporator heat transfer area.
Further, the heat transfer area of the condenser is calculated by the formula:
wherein Q is1Is the heat absorbed by the evaporator in the refrigerant system, WyK is the heat transfer coefficient, Δ t is the average temperature difference of the condenser in the refrigerant system, which is the power consumption of the compressor in the refrigerant system.
As a preferable scheme of the invention, the calculation formula of the average temperature difference of the condenser is as follows:
wherein, the average temperature difference of the condenser in the delta t refrigerant system, t2The temperature, t, of the second waste heat air entering the condenser of the refrigerant system3Dry hot air is output from the refrigerant system t4The temperature after the second condensation and dehumidification.
As a preferred scheme of the invention, the actual power consumption calculation formula of the compressor is as follows:
wherein Q is1The total heat of the waste heat air absorbed by the evaporator in the refrigerant system, Q2Is the heat absorbed by each kilogram of refrigerant in the evaporator of the refrigerant system, h1Is the enthalpy content, h, in the refrigerant at a pressure of 1000kpa2The enthalpy content of the refrigerant, η, is defined as the isentropic efficiency of the compressor at a pressure value of 3100 kpa.
As a preferred scheme of the invention, the heat transfer area calculation formula of the evaporator is
Wherein Q is1Is the heat absorbed by the evaporator in the refrigerant system, k is the heat transfer coefficient, Δ t' is the average temperature difference of the evaporator in the refrigerant system.
As a preferred scheme of the invention, the average temperature difference calculation formula of the evaporator in the refrigerant system is as follows:
wherein, the average temperature difference of the evaporator in the delta t' refrigerant system, t5The temperature t is the temperature when the waste heat air enters the evaporator after the waste heat air enters the cooling tower system for the first condensation and dehumidification6Is the temperature, t, of the air as it exits the evaporator7The evaporator evaporates the temperature.
Based on the same conception, the invention also provides a sludge low-temperature drying system, which comprises a drying chamber chain network conveying system, a refrigerating system, a refrigerant system and a circulating air system,
the refrigeration system is used for carrying out primary condensation dehumidification on waste heat air of wet sludge, receiving the waste heat air of the wet sludge and outputting second waste heat air;
the refrigerant system receives second waste heat air, and is used for sequentially carrying out second condensation dehumidification on the second waste heat air, carrying out first temperature rise and second temperature rise and outputting dry hot air to the circulating air system;
the drying chamber chain net conveying system is used for conveying the dry hot air to the drying chamber chain net conveying system;
the drying chamber chain network conveying system transmits wet sludge into the drying chamber, so that dry hot air input by the circulating air system and the wet sludge in the drying chamber are subjected to heat-mass exchange, and waste heat air is output to the cooling system;
the parameters of the refrigerant system are adjusted through temperature and humidity parameters of air output by a cooling system of the cooling tower, temperature and humidity parameters of dry hot air output by a preset refrigerant system and a pre-established mathematical model of the refrigerant system; the temperature and humidity parameters of the air output by the cooling system of the cooling tower are obtained by pre-establishing a heat and mass transfer mathematical model of the cooling system of the cooling tower and the temperature and humidity parameters of the waste heat air of the wet sludge.
As a preferable aspect of the present invention, the refrigerant system includes: an evaporator, a heat recoverer, a condenser, a compressor and a control unit,
the evaporator receives the second waste heat air, is used for carrying out secondary condensation dehumidification on the second waste heat air, and outputs low-temperature air to the heat recoverer;
the heat recoverer heats the low-temperature air for the first time to obtain medium-temperature dry air, and the medium-temperature dry air is output to the condenser;
the condenser receives the medium-temperature dry air, carries out secondary temperature rise on the medium-temperature dry air, and outputs dry hot air to the circulating air system;
the compressor is respectively connected with the condenser and the evaporator and is used for compressing low-temperature low-pressure refrigerant gas and discharging high-temperature high-pressure refrigerant gas to the condenser and the evaporator;
the control unit outputs parameters of the refrigerant system according to temperature and humidity parameters of air output by the cooling system of the cooling tower, temperature and humidity parameters of dry hot air output by the preset refrigerant system and a pre-established mathematical model of the refrigerant system, wherein the parameters of the refrigerant system comprise the heat transfer area of a condenser, the actual power of a compressor and the heat transfer area of an evaporator.
Compared with the prior art, the invention has the beneficial effects that:
according to the invention, on the basis of the sludge low-temperature drying method, a mathematical model is established for the condensation process, and in the process of drying wet sludge through air circulation, key parameters of a refrigerant system can be calculated according to the temperature, the moisture content and the relative humidity of waste heat air, the temperature, the moisture content and the relative humidity of high-temperature dry air and the pre-established mathematical model of the refrigerant system, wherein the key parameters are used for adjusting the parameters of a condenser, a compressor and an evaporator of the refrigerant system, so that the system parameters are adapted to actual requirements, the working efficiency of the sludge low-temperature drying machine system is improved, and energy conservation and emission reduction are realized. In addition, the selection of the condenser, the compressor and the evaporator of the refrigerant system can be guided during working, and the cost is saved.
Description of the drawings:
FIG. 1 is a schematic block diagram of a low-temperature sludge drying method according to the present invention;
FIG. 2 is a schematic diagram of the operation of a specific sludge low-temperature drying method and system according to embodiment 1 of the present invention;
FIG. 3 is a simplified one-dimensional model of a mathematical three-dimensional heat and mass model of a cooling system of a cooling tower in accordance with embodiment 1 of the present invention;
FIG. 4 is a diagram of a theoretical cycle T-S of the process in example 1.
The reference numeral 1-drying chamber chain net conveying system, 2-cooling tower cooling system, 21-heat recoverer, 22-water condenser, 23-cooling tower, 24-cooling water circulating pump, 3-refrigerant system, 31-evaporator, 32-condensate water, 33-heat recoverer, 34-compressor, 35-electronic expansion valve, 36-condenser, 4-circulating air system, 5-dry granary and 6-lifting variable frequency regulator.
Detailed Description
The present invention will be described in further detail with reference to test examples and specific embodiments. It should be understood that the scope of the above-described subject matter is not limited to the following examples, and any techniques implemented based on the disclosure of the present invention are within the scope of the present invention.
Example 1
A functional block diagram of a sludge low-temperature drying method is shown in figure 1, waste heat air sequentially passes through a cooling system, a refrigerant system and a circulating air system to output dry hot air to a drying chamber chain network conveying system, the whole process is carried out circularly, and the sludge low-temperature drying method comprises the following steps: waste heat air firstly passes through a refrigerating system to be subjected to first condensation dehumidification, the obtained air enters a refrigerant system again to be subjected to second condensation dehumidification and heat exchange to improve the temperature of the air, high-temperature dry air is obtained through second dehumidification and temperature rise, the high-temperature dry air is conveyed to a drying chamber chain net conveying system through a circulating air system, and the sludge in the drying chamber chain net conveying system is dried in the circulating process.
A specific working principle diagram of the sludge low-temperature drying method and system is shown in fig. 2. The sludge low-temperature dryer system is characterized in that waste heat air with medium temperature and high humidity in a drying chamber enters a heat recoverer of a cooling system of a cooling tower to be subjected to primary condensation dehumidification, then enters an evaporator in a refrigerant system to be subjected to secondary condensation dehumidification, the absolute water content of the obtained low-temperature air is reduced, the low-temperature air at the moment returns to the heat recoverer to be subjected to energy exchange with medium-temperature air in the heat recoverer, primary temperature rise is carried out to obtain medium-temperature dry air, the medium-temperature dry air is output to a condenser of the refrigerant system to be subjected to secondary condensation temperature rise, dry hot air is output to a circulating air system, the circulating air system blows the dry hot air to the surface of sludge, the dry hot air releases heat in the drying chamber to be cooled, moisture of wet sludge is taken away, the wet hot air is output to a cooling. The whole working process forms refrigeration cycle and air cycle through four systems, wherein the refrigeration cycle means that a refrigerant in a refrigerant system is compressed by a compressor to do work and then is converted into high-temperature and high-pressure gas, the high-temperature and high-pressure gas enters an evaporator after being radiated by a condenser, and the heat of water vapor in a drying box is absorbed in the evaporator and then enters the air cycle; the air circulation is that the dry hot air entering the drying chamber chain net conveying system directly contacts with the materials, absorbs moisture in the materials to reduce the temperature, then indirectly contacts with the refrigerant in the evaporator after passing through the cooling tower cooling system, the moisture in the humid air is removed by cooling condensation twice, finally indirectly contacts with the condenser to absorb heat to improve the temperature, the dry hot air is output, and the dry hot air enters the drying chamber chain net conveying system again through the circulating air system.
As shown in FIG. 2, the medium-temperature and high-humidity waste heat air in the drying chamber enters the heat recoverer of the cooling system of the cooling tower to carry out primary condensation dehumidification, and the working process and the principle of the cooling system of the cooling tower are reflected by establishing a heat mass transfer mathematical model. The cooling system of the cooling tower comprises a heat recoverer, a water condenser, the cooling tower and a cooling water circulating pump, waste heat air enters the water condenser to be heated after passing through the heat recoverer, and if in the process of air heat-mass exchange in the water condenser, water and air are subjected to heat-mass exchange in an ideal steady state, and heat-mass transfer among fluid, the environment and the internal structure of the cooling tower is ignored. Based on the counter-flow pattern of the cooling tower, the complex heat and mass transfer mathematical three-dimensional model of the cooling system of the cooling tower is simplified into a one-dimensional model as described in fig. 3, and the heat and mass transfer mathematical one-dimensional model of the cooling system of the cooling tower is obtained according to the energy and mass conservation equation, as shown in the following formula:
madha＝c(p,w)d(mwtw)
dms＝madda
wherein m issIs the mass of the filler; daIs the air mass, unit kg/s; h isaIs the air enthalpy value, unit kJ/kg, mwIs the water flow unit kg/s, twIs the water temperature, unit degree C(p,w)The specific heat capacity of water at constant pressure is expressed in J/(kg ℃).
Accordingly, the energy transfer equation for the air side in the cooling system of the cooling tower is:
wherein the content of the first and second substances,
wherein h ismIs the heat transfer coefficient and has the unit of kg/(m)2S); a is the surface area of the filler in m2/m3(ii) a V is the volume of the packing in the cooling tower and is expressed in m3；heThe enthalpy of saturated air corresponding to the water temperature is expressed in kJ/kg.
Meanwhile, the mass transfer equation between air and water is:
dethe moisture content of saturated air corresponding to the water temperature is expressed in kJ/kg.
Given the relevant parameters of the inlet waste heat air and water condenser (air temperature and humidity, flow rate, water temperature and flow rate), the temperature and humidity of the air output by the cooling system of the cooling tower can be solved by using the mathematical model.
And the air output from the cooling system of the cooling tower enters a refrigerant system to be treated in the second stage. The method aims at the design of a refrigerant system, and can adjust the parameters of the refrigerant system through a pre-established refrigerant system mathematical model according to the temperature, the moisture content and the relative humidity of the air input into the refrigerant system and the temperature, the moisture content and the relative humidity of the dry and hot air output by the refrigerant system, so that the system parameters are adapted to actual requirements, the working efficiency of the sludge low-temperature dryer system is improved, energy is saved, emission is reduced, and the cost is saved.
The drying object is sludge, the initial water content of which is about 80 percent is recorded as X1, the water content of which after the sludge is treated according to the production requirement is recorded as X2, and the initial total mass of the sludge is recorded as M1And the mass of the dried sludge is recorded as M2Then, we can get:
the average dewatering amount of the sludge is:
wherein t is dryThe length of time. In actual industrial production, the initial mass of the sludge M1 is 1000kg, t is 24h, and M2 is 222.2kg, and y is 32.4kg/h according to the formula. According to the requirement of a drying process, the temperature in the drying chamber should reach about 80 ℃, high-temperature and low-humidity dry hot air enters the drying chamber to dry and dehumidify the sludge, and the process is an isenthalpic heat-insulating humidifying process. The air supply temperature is designed to be 80 ℃, the relative humidity phi is designed to be 10%, and the exhaust volume of the circulating air system can be obtained according to the enthalpy-humidity change rule of the air state point
Where Δ d is the enthalpy-humidity change, and the enthalpy-humidity change is generally calculated according to the needs of different regions, and here, an average value L is 3100 kg/h.
The main parameter of the circulating air system is the circulation rate, the circulation rate is obtained by the ratio of the circulating air volume of the communication roadway to the total air volume passing through the working face in the circulating area, and the circulation rate is obtained according to the following formula:
r1 is inlet windage; r2 is the pipeline wind resistance; r3 is outlet windage; p3 is the total air quantity of the system inlet; p1 is the system air volume when no circulation ventilation is carried out; p2 is circulating air volume; f-circulation rate. The total air quantity required from the refrigerant system to the circulating air system can be calculated, and meanwhile, a stable air quantity is formed through the circulating air system, so that a required dry hot air source is provided for the drying chamber.
When the waste heat air enters the condenser, the temperature is set to be t 2-20 ℃, the humidity content d 2-15 g/kg and the relative humidity phi 2-10%, the temperature of the air passing through a refrigerant system is t 3-80 ℃, the relative humidity phi 3-10% and the humidity content d 3-15/kg according to the requirements, and the condensing temperature t4 is 86 ℃ according to the design of the outlet temperature of the condenser and the system temperature difference of 6 ℃. The average temperature difference of the condenser can be obtained:
from the air volume calculated above, the wind speed is the ratio V of the air volume to the cross-sectional area of the pipeline, which is 8m/s, and the heat transfer coefficient k is 30w/(m2 k), then the heat transfer area of the condenser is:
wherein Q isout＝Q1+WyM, wherein WyFor actual power consumption of the compressor, Q1And (4) obtaining a mathematical model of the heat absorbed by the evaporator and the condenser to complete the parameter design of the condenser, thereby guiding the type selection of the condenser.
From the foregoing, it was determined that the condensation temperature was 6 c, i.e., about 86 c, above the condenser exit temperature and the evaporation temperature was about 25 c. Assuming that the evaporator outlet is saturated gas and the condenser outlet is saturated liquid, as shown in fig. 4, if the refrigerant is R22 type, then according to R22 performance parameters:
pressure p1 at a is 1000kpa, specific heat capacity v1 is 0.025m3Kg, enthalpy h 1-450 kJ/kg, entropy s 1-1.80 kJ/(kg k);
pressure p2 ═ 3100kpa, enthalpy h2 ═ 469kJ/kg, entropy s2 ═ s1 ═ 1.80kJ/(kg ×) k at b;
at c, the pressure p3 is 3100kpa, and the enthalpy h3 is 348 kJ/kg;
at D, the pressure p4 is 1000kpa, and the enthalpy h3 is h4 is 348 kJ/kg.
The unit R22 absorbs heat in the evaporator as: q2-h 1-h 4-450-102 kJ/kg.
The total heat Q1 of the evaporator absorbing the waste heat circulating wind is equal to the product of the mass of Q2 and R22.
The isentropic efficiency of the actual compressor is η 60%, then the actual power consumption:
the actual power of the compressor can be obtained through calculation, and the actual power of the compressor can be set or theoretical guidance is made on the model selection of the compressor.
After the waste heat air enters the cooling tower system for the first condensation and dehumidification, the temperature t5 when the waste heat air enters the evaporator is 32 ℃, the relative humidity phi 3 is 40%, the temperature t6 when the waste heat air exits the evaporator is 15 ℃, and the relative humidity phi 4 is 10%. In actual working conditions, the internal temperature of the evaporator is 5 ℃ lower than the temperature of the outlet of the evaporator, the evaporation temperature t7 is 10 ℃, and the internal average heat transfer temperature difference can be obtained:
the heat transfer coefficient k is 25W/(m)2K) the heat transfer area of the evaporator is
And determining the heat transfer area of the evaporator, namely achieving modeling so as to guide the selection of the evaporator.
Example 2
Based on the same conception, the invention also provides a low-temperature sludge drying system which comprises a drying chamber chain network conveying system, a refrigerating system, a refrigerant system and a circulating air system, and is shown in figure 2.
The refrigeration system is used for carrying out primary condensation dehumidification on waste heat air of wet sludge, receiving the waste heat air of the wet sludge and outputting second waste heat air;
the refrigerant system receives the second waste heat air, and is used for sequentially carrying out secondary condensation dehumidification, primary heating, tertiary condensation and secondary heating on the second waste heat air, and outputting high-temperature dry air to the circulating air system;
the circulating air system receives high-temperature dry air and is used for outputting the high-temperature dry air to the drying chamber chain net conveying system, and the circulating air system is also used for providing power for the air to sequentially circulate in the drying chamber chain net conveying system, the refrigerating system, the refrigerant system and the circulating air system;
the drying chamber chain net conveying system transmits wet sludge into the drying chamber, so that high-temperature dry air input by the circulating air system and the wet sludge in the drying chamber are subjected to heat and mass exchange, and waste heat air is output to the cooling system.
Preferably, the refrigerant system includes: an evaporator, a heat recoverer, a condenser, a compressor and a control unit,
the evaporator receives the second waste heat air, is used for carrying out secondary condensation dehumidification on the second waste heat air, and outputs low-temperature air to the heat recoverer;
the heat recoverer is used for performing first temperature rise on the low-temperature air to obtain medium-temperature dry air, outputting the medium-temperature dry air to the condenser, receiving second low-temperature air, performing second temperature rise on the second low-temperature air, and outputting the high-temperature dry air to the circulating air system;
the condenser receives the medium-temperature dry air, carries out third condensation on the Chinese dry air, and outputs second low-temperature air to the heat recoverer;
the compressor is respectively connected with the condenser and the evaporator and is used for compressing low-temperature low-pressure refrigerant gas, discharging high-temperature high-pressure refrigerant gas to the condenser and the evaporator and providing power for the refrigeration cycle;
the control unit outputs parameters of a refrigerant system through a pre-stored refrigerant system mathematical model according to the temperature, the moisture content and the relative humidity of the waste heat air and the temperature, the moisture content and the relative humidity of the high-temperature dry air, wherein the parameters of the refrigerant system comprise the heat transfer area of a condenser, the actual power of a compressor and the heat transfer area of an evaporator.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.
Claims (10)
1. The low-temperature sludge drying method is characterized by comprising the following steps:
s1, inputting the waste heat air of the wet sludge into a cooling system, carrying out primary condensation dehumidification through the cooling system, and outputting second waste heat air;
s2, sending the second waste heat air into a refrigerant system, wherein the second waste heat air is subjected to secondary condensation dehumidification, primary temperature rise and secondary temperature rise in the refrigerant system in sequence, and outputting dry hot air to a circulating air system;
s3, outputting the dry hot air to a drying chamber chain net conveying system through a circulating air system, carrying out heat and mass exchange between the dry hot air and wet sludge in the drying chain net conveying system, and outputting waste heat air to the cooling system;
s4, drying the wet sludge in the drying type chain-net conveying system through the repeated circulation of the steps S1-S3;
in the process, temperature and humidity parameters of air output by a cooling system of the cooling tower are solved by pre-establishing a mathematical model of heat and mass transfer of the cooling system of the cooling tower; and adjusting parameters of the refrigerant system through temperature and humidity parameters of air output by the cooling system of the cooling tower, temperature and humidity parameters of dry hot air output by a preset refrigerant system and a pre-established refrigerant system mathematical model.
2. The low-temperature sludge drying method according to claim 1, wherein the mathematical model of the refrigerant system is Qout＝Q1+WyWherein Q is1Is the heat absorbed by the evaporator in the refrigerant system, WyIs the actual power consumption, Q, of the compressor in the refrigerant systemoutIs the heat output by the condenser in the refrigerant system.
3. The low-temperature sludge drying method according to claim 2, wherein the parameters of the refrigerant system include: condenser heat transfer area, compressor real power, evaporator heat transfer area.
4. The low-temperature sludge drying method according to claim 3, wherein the calculation formula of the heat transfer area of the condenser is as follows:
wherein Q is1Is the heat absorbed by the evaporator in the refrigerant system, WyAnd k is a heat transfer coefficient, and delta t is the average temperature difference of a condenser in the refrigerant system.
5. The low-temperature sludge drying method according to claim 4, wherein the average temperature difference of the condenser is calculated by the following formula:
wherein, the average temperature difference of the condenser in the delta t refrigerant system, t2The temperature, t, of the second waste heat air entering the condenser of the refrigerant system3Is to output dry hot air t from the refrigerant system4The temperature after the second condensation and dehumidification.
6. The low-temperature sludge drying method according to claim 3, wherein the actual power consumption calculation formula of the compressor is as follows:
wherein Q is1The total heat of the waste heat air absorbed by the evaporator in the refrigerant system, Q2Is the heat absorbed by each kilogram of refrigerant in the evaporator of the refrigerant system, h1Is the enthalpy content, h, in the refrigerant at a pressure of 1000kpa2The enthalpy content of the refrigerant, η, is defined as the isentropic efficiency of the compressor at a pressure value of 3100 kpa.
7. The low-temperature sludge drying method according to claim 3, wherein the heat transfer area of the evaporator is calculated according to the formula
Wherein Q is1Absorbed by an evaporator in the refrigerant systemThe heat, k, is the heat transfer coefficient, Δ t', the average temperature difference of the evaporator in the refrigerant system.
8. The low-temperature sludge drying method according to claim 7, wherein the average temperature difference of the evaporator in the refrigerant system is calculated by the following formula:
wherein, the average temperature difference of the evaporator in the delta t' refrigerant system, t5The temperature t is the temperature when the waste heat air enters the evaporator after the waste heat air enters the cooling tower system for the first condensation and dehumidification6Is the temperature, t, of the air as it exits the evaporator7The evaporator evaporates the temperature.
9. A low-temperature sludge drying system is characterized by comprising a drying chamber chain network conveying system, a refrigerating system, a refrigerant system and a circulating air system,
the refrigeration system is used for carrying out primary condensation dehumidification on waste heat air of wet sludge, receiving the waste heat air of the wet sludge and outputting second waste heat air;
the refrigerant system receives the second waste heat air, is used for sequentially carrying out second condensation dehumidification on the second waste heat air, and outputting dry hot air to the circulating air system after first temperature rise and second temperature rise;
the drying chamber chain net conveying system is used for conveying the dry hot air to the drying chamber chain net conveying system;
the drying chamber chain network conveying system transmits wet sludge into the drying chamber, so that the dry hot air input by the circulating air system and the wet sludge in the drying chamber are subjected to heat and mass exchange, and waste heat air is output to the cooling system;
the parameters of the refrigerant system are adjusted through temperature and humidity parameters of air output by the cooling system of the cooling tower, temperature and humidity parameters of dry hot air output by the preset refrigerant system and a pre-established mathematical model of the refrigerant system; and the temperature and humidity parameters of the air output by the cooling system of the cooling tower are obtained by pre-establishing a mathematical model of heat transfer and mass transfer of the cooling system of the cooling tower and the temperature and humidity parameters of the waste heat air of the wet sludge.
10. The low-temperature sludge drying system as claimed in claim 9, wherein the refrigerant system comprises: an evaporator, a heat recoverer, a condenser, a compressor and a control unit,
the evaporator receives the second waste heat air, is used for carrying out secondary condensation dehumidification on the second waste heat air, and outputs low-temperature air to the heat recoverer;
the heat recoverer heats the low-temperature air for the first time to obtain medium-temperature dry air, and the medium-temperature dry air is output to a condenser;
the condenser receives the medium-temperature dry air, carries out secondary temperature rise on the medium-temperature dry air, and outputs dry hot air to the circulating air system;
the compressor is respectively connected with the condenser and the evaporator and is used for compressing low-temperature low-pressure refrigerant gas and discharging high-temperature high-pressure refrigerant gas to the condenser and the evaporator;
the control unit outputs the parameters of the refrigerant system according to the temperature and humidity parameters of the air output by the cooling tower cooling system, the preset temperature and humidity parameters of the dry hot air output by the refrigerant system, and a pre-established mathematical model of the refrigerant system, wherein the parameters of the refrigerant system comprise the heat transfer area of the condenser, the actual power of the compressor and the heat transfer area of the evaporator.
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