CN108609832B - Vacuum cold and hot drying combined sludge drying device and method - Google Patents
Vacuum cold and hot drying combined sludge drying device and method Download PDFInfo
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- CN108609832B CN108609832B CN201810685727.6A CN201810685727A CN108609832B CN 108609832 B CN108609832 B CN 108609832B CN 201810685727 A CN201810685727 A CN 201810685727A CN 108609832 B CN108609832 B CN 108609832B
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- C02F11/00—Treatment of sludge; Devices therefor
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Abstract
The invention discloses a vacuum cold and hot drying combined sludge drying device and method, which comprises the steps of heat convection drying, freeze drying and heat conduction drying which are sequentially carried out, wherein wet sludge (the water content is about 75% -80%) is firstly subjected to heat drying, and the water content is reduced to be thick sludge with the water content of 60% -50%. Through valve switching, vacuum freeze drying is carried out, ice in the sludge sublimates to form water vapor and then is extracted, the water content is further reduced, and finally, deep heat drying is carried out on the sludge again. The invention adopts heat pump cold and hot combined drying technology, uses three-section drying modes of heat convection pre-drying, freeze drying and deep drying, fully exerts the advantages of different drying modes, and improves the sludge drying efficiency under lower energy consumption.
Description
Technical Field
The invention relates to the technical field of sludge drying, in particular to a vacuum cold-hot drying combined sludge drying device and method.
Background
Sludge produced by domestic town sewage treatment plants is generally dehydrated in a filter pressing and centrifugation mode, the water content of a dehydrated mud cake is reduced, but the water content is still higher, the mud amount is large, landfill and incineration disposal are difficult, and further drying of the sludge is needed. In recent years, with the continuous progress of drying technology, combined drying technologies such as solar energy, microwave, vacuum freeze drying and the like based on thermal drying have been developed to some extent.
Sludge drying is usually carried out by deep dehydration in a high-temperature or medium-temperature low-temperature drying mode, according to the sludge drying rate curve, as the water content decreases, the sludge drying rate sequentially passes through a constant speed stage, a first deceleration stage and a second deceleration stage, and simultaneously shows different flow state characteristics. When the water content of the sludge is reduced to 60-50%, the fluid property of the sludge is in a viscous state, the internal water is not easy to evaporate, the required energy consumption is increased rapidly, and the drying efficiency is reduced obviously.
At present, the common solution is to use dry sludge and wet sludge for back mixing, so that the water content of the sludge is reduced to below 50 percent to start drying, the back mixing proportion is higher because the solid content of the wet sludge is generally lower, and in addition, the heat loss of the back mixing process is large, so that the energy consumption is higher.
For example, the number of the cells to be processed,
the vacuum freeze drying has good drying effect, the water content of the material can be reduced to 1%, but the drying process is very long, the energy consumption is higher, the method is not suitable for drying the sludge with higher water content, and the method is usually only selected under the condition that the heat drying cannot be adopted.
Disclosure of Invention
The invention provides a heat pump drying device and a heat pump drying method integrating vacuum freeze drying and heat drying, which adopt a heat pump cold and hot combined drying technology, utilize a three-section drying mode of heat convection predrying, freeze drying and deep drying, fully exert the advantages of different drying modes, and improve the sludge drying efficiency under lower energy consumption.
The vacuum cold and hot drying combined sludge drying device comprises a heat pump system, wherein the heat pump system comprises a compressor and an evaporator, and also comprises a drying system and a heat storage system;
the drying system includes:
the drying box is provided with an air inlet, an air outlet and a vacuum pumping port, the air outlet of the drying box is connected with the evaporator, and the vacuum pumping port is connected with a vacuum pump through a pipeline;
the air inlet pipe of the air pump is connected with the evaporator, the air outlet pipe of the air pump is connected with the air inlet of the drying box, and the drying box, the air pump and the evaporator are sequentially connected into a drying air loop;
the working medium inlet end of the condenser is connected to the compressor through a working medium pipeline, the working medium outlet end of the condenser is connected to the evaporator through a working medium pipeline, and a first expansion valve is arranged on the working medium pipeline connected with the evaporator;
the thermal storage system includes:
a heat storage tank in which a heat storage solution is placed;
the second heat exchanger is arranged in the heat storage box, and a second expansion valve is arranged between the second heat exchanger and the first heat exchanger;
the compressor, the condenser, the first expansion valve, the evaporator and the compressor are sequentially connected into a working medium loop, and a heat convection drying system is formed by the working medium loop and the drying gas loop; the compressor, the second heat exchanger, the second expansion valve, the first heat exchanger and the compressor are sequentially connected into a working medium loop to form a freeze drying system; when the compressor, the first heat exchanger, the second expansion valve, the second heat exchanger and the compressor are sequentially connected into a working medium loop, a heat conduction drying system is formed; the thermal convection drying system, the freeze drying system and the thermal conduction drying system are sequentially switched.
Preferably, the freezing and drying system and the thermal conduction and drying system can be switched by arranging a four-way valve.
Preferably, the condenser and the fan are both arranged at an air inlet in the drying box; the fan is arranged in front of the inner wall of the box body and the condenser and is arranged towards the condenser.
The heat storage solution is sodium chloride solution; and a stirrer is arranged in the heat storage box.
Preferably, an on-line monitoring device is arranged in the drying box. The device is mainly used for detecting the temperature and the pressure in the drying box, and the on-line monitoring device is provided with a visual display.
The invention also provides a vacuum cold and hot drying combined sludge drying method, the sludge to be dried is sent into a drying box, and any one or more of the following drying modes is selected by switching corresponding valves:
(1) Thermal convection pre-drying
The sludge to be dried is sent into a drying box, a compressor, a condenser, a first expansion valve, an evaporator and the compressor are sequentially connected into a working medium loop through controlling corresponding valves, the condenser is positioned in the drying box, meanwhile, an air pump is connected with the evaporator, the air pump is respectively connected with an air inlet and an air outlet of the drying box, the air pump is connected with the evaporator to form a drying gas loop, a fan is started, normal-temperature low-pressure working medium is compressed by the compressor to form a high-temperature high-pressure working medium, the air in the drying box is heated by the condenser to form a high-pressure low-temperature working medium, the high-pressure working medium is depressurized by the first expansion valve to form a supercooled low-pressure working medium, the evaporator acquires the heat of wet air in the drying box and is recovered to form a normal-temperature low-pressure working medium, the next working medium circulation process is carried out, condensed water is discharged out outside the evaporator, and the air heated in the drying box carries out heat convection predrying on the sludge under the action of the fan;
(2) Freeze drying
The method comprises the steps that a compressor, a second heat exchanger, a first heat exchanger and a compressor are sequentially connected into a working medium loop through switching corresponding valves, the first heat exchanger is located in a drying box, the second heat exchanger is located in a heat storage box, a normal-temperature low-pressure working medium is compressed by the compressor to form a high-temperature high-pressure working medium, heat is transferred to a heat storage solution in the heat storage box through the second heat exchanger to form a low-temperature high-pressure working medium, the temperature of the heat storage solution is increased, heat is stored in the heat storage box, the low-temperature high-pressure working medium is depressurized through a second expansion valve to form a supercooled low-pressure working medium, cold is transferred to sludge through the first heat exchanger, water in the sludge is solidified into ice, expansion occurs in a sludge gap, the supercooled low-pressure working medium is recovered into a normal-temperature low-pressure working medium after absorbing heat of the sludge, a next working medium circulation process is performed, and when the temperature of the sludge in the drying box is reduced to-20 ℃ to 0 ℃, a vacuum pump is opened, and the drying box is vacuumized to form a low pressure;
(3) Drying by thermal conduction
When the pressure reduction in the drying oven is less than or equal to 100Pa, the corresponding valves are switched to enable the compressor, the first heat exchanger, the second expansion valve, the second heat exchanger and the compressor to be sequentially connected into a working medium loop, normal-temperature low-pressure working medium is pressurized and heated by the compressor and then condensed on the first heat exchanger, released heat is absorbed by sludge, and energy is provided for the gasification of ice into water vapor; and then the working medium is subjected to pressure relief through a second expansion valve to become a supercooling low-pressure working medium, and the heat in the heat storage box is recovered through a second heat exchanger to become a normal-temperature low-pressure working medium for the next cycle.
For sludge with different water contents, one or two of three drying modes can be adopted.
Preferably, the method further comprises a heat convection deep drying step (4) which is the same as the heat convection drying step. If the sludge after freeze drying is further dried, the heat convection drying can be continued by referring to the mode of the step (1). Because the sludge is freeze-dried and has a certain pore structure, hot air easily enters the sludge to take away residual moisture.
Preferably, the temperature in the drying box is 25-40 ℃ during the heat convection drying and the heat conduction heat pump drying. The temperature of the sludge in the drying oven can be preferably measured by an infrared thermometer.
Preferably, the thermal convection drying time is 1-8 h, the freeze drying time is 1-4 h, and the thermal conduction drying time is 1-4 h in each drying process.
The maximum value of the drying time is that the fact that some sludge can meet the requirement by adopting only one drying mode is considered, so that the time is much longer than the sectional drying time under the multi-mode drying. While the minimum is the minimum drying time in each mode under multi-mode drying conditions, the minimum drying in a single mode will be longer than this time.
For sludge with different qualities, the optimal combination of drying modes and the drying condition parameters are obtained according to experiments, and for most sludge in sewage plants, the drying modes can be sequentially carried out in the modes (1) (2) and (3).
For example, the drying step may be determined according to the raw sludge moisture content and the target moisture content after drying: raw sludge has water content of 85-60%, and is subjected to thermal convection drying or thermal conduction drying; the water content of the raw sludge is 60-40%, and the raw sludge is freeze-dried in vacuum; raw sludge with water content less than 40%, thermal convection drying or thermal conduction drying (preferably thermal conduction drying)
For the selection of thermal convection drying and thermal conduction drying, the sludge wall adhesion performance is determined according to experiments, the water content is reduced, the sludge wall adhesion performance is firstly increased and then reduced, and the highest point is about 60%. Under the condition of the same water content and drying temperature, the sludge with high organic matter content has stronger wall sticking performance. The wall sticking performance of the sludge can be reduced by adopting heat convection drying, but the energy consumption is higher. And the heat conduction, drying and heat transfer efficiency is high, but wall sticking is more likely to occur. The sludge with low organic content is preferably dried by thermal conduction. The sludge with high organic matter content is preferably heat convection dried, in the first drying step, thermal convection drying is preferred, and in the deep drying, thermal conduction drying is preferred.
The sludge with lower organic matter content comprises: sand setting Chi Wuni, materialized sludge, digested sludge and the like.
The sludge with higher organic matter content comprises: primary sedimentation tank sludge, secondary sedimentation tank sludge and humic sludge.
Preferably, the heat storage solution is sodium chloride solution with the mass concentration of 5-35%; the temperature range of the heat storage solution is 0-50 ℃.
The invention also provides a sequencing batch vacuum cold and hot drying combined sludge drying device, which comprises a compressor and at least two sets of drying systems, wherein each set of drying system comprises an evaporator, a drying system and a heat storage system;
the drying system includes:
the drying box is provided with an air inlet, an air outlet and a vacuum pumping port, the air outlet of the drying box is connected with the evaporator, and the vacuum pumping port is connected with a vacuum pump through a pipeline;
the air inlet pipe of the air pump is connected with the evaporator, the air outlet pipe of the air pump is connected with the air inlet of the drying box, and the drying box, the air pump and the evaporator are sequentially connected into a drying air loop;
the working medium inlet end of the condenser is connected to the compressor through a working medium pipeline, the working medium outlet end of the condenser is connected to the evaporator through a working medium pipeline, and a first expansion valve is arranged on the working medium pipeline connected with the evaporator;
the thermal storage system includes:
a heat storage tank in which a heat storage solution is placed;
the second heat exchanger is arranged in the heat storage box, and a second expansion valve is arranged between the second heat exchanger and the first heat exchanger;
the condenser, the first expansion valve and the evaporator of each set of drying system are sequentially connected and connected with the compressor to form a working medium loop, and the working medium loop and a drying gas loop in each set of drying system form a heat convection drying system of the corresponding drying system; the second heat exchanger, the second expansion valve and the first heat exchanger of each set of drying system are sequentially connected and sequentially connected with the compressor to form a working medium loop, so that a freeze drying system corresponding to the drying system is formed; when the first heat exchanger, the second expansion valve and the second heat exchanger of each set of drying system are sequentially connected and sequentially connected with the compressor to form a working medium loop, a heat conduction drying system corresponding to the drying system is formed; each drying system is independently controlled, and the thermal convection drying system, the freeze drying system and the thermal conduction drying system in each drying system are sequentially switched; the heat storage boxes of the drying systems are connected in series through a circulating pump.
The at least two sets of drying systems are connected in parallel with the compressor and independently run among the drying systems; the heat convection drying system, the freeze drying system and the heat conduction drying system in each drying system are operated in sequence; the heat storage boxes of the drying systems are connected in series through a circulating pump.
The invention also provides a sludge drying method for performing sequencing batch vacuum cold and hot drying combination by utilizing the sludge drying device, the sludge to be dried is sent into a drying box of a corresponding drying system, and one or any combination of the following drying modes or three modes are sequentially selected by switching corresponding valves;
(1) Thermal convection pre-drying
The method comprises the steps of starting a thermal convection drying system of a corresponding drying system by controlling a corresponding valve, starting a fan, compressing a normal-temperature low-pressure working medium through a compressor to form a high-temperature high-pressure working medium, heating air in a drying box through a condenser to form a high-pressure low-temperature working medium, releasing pressure through a first expansion valve to form a supercooled low-pressure working medium, acquiring heat of wet air in the drying box through an evaporator, recovering the heat to form the normal-temperature low-pressure working medium, and performing the next working medium circulation process;
(2) Freeze drying
After the heat convection drying is finished, a freeze-drying system corresponding to the drying system is started by switching a corresponding valve, a normal-temperature low-pressure working medium is compressed by a compressor to form a high-temperature high-pressure working medium, heat is transferred to a heat storage solution by a second heat exchanger to form a low-temperature high-pressure working medium, the temperature of the heat storage solution is increased, the heat is stored in a heat storage box, the low-temperature high-pressure working medium is depressurized by a second expansion valve to form a supercooled low-pressure working medium, cold is transferred to sludge by a first heat exchanger, moisture in the sludge is solidified into ice, a sludge gap expands, the supercooled low-pressure working medium is recovered to the normal-temperature low-pressure working medium after absorbing the heat of the sludge, the next working medium circulation process is performed, and when the temperature of the sludge in the drying box is reduced to minus 20-0 ℃, a vacuum pump is opened, and the interior of the drying box is vacuumized to form low pressure;
(3) Drying by thermal conduction
When the pressure reduction in the drying box is less than or equal to 100Pa, a heat pump heat conduction drying system corresponding to the drying system is started by switching a corresponding valve, the normal-temperature low-pressure working medium is pressurized and heated by a compressor and then condensed on a first heat exchanger, and released heat is absorbed by sludge to provide energy for the gasification of ice into water vapor; then the working medium is decompressed by a second expansion valve to become a supercooling low-pressure working medium, and the heat in the heat storage box is recovered by a second heat exchanger to become a normal-temperature low-pressure working medium for the next cycle;
when the temperature of the heat storage solution in each heat storage tank exceeds the range, starting a circulating pump and a corresponding valve to balance the temperature of the heat storage solution in each heat storage tank; and stopping the drying work when all the heat storage solutions exceed the temperature range.
Other related process parameter controls are the same as a single set of control system.
Compared with the prior art, the invention has the following beneficial effects:
the invention adopts a heat pump drying system integrating vacuum freeze drying and thermal drying, and has the following advantages
The beneficial effects are that:
(1) The wet sludge (the water content is about 75% -80%) is firstly dried by heat, and the water content is reduced to the viscous sludge with the water content of 60% -50%. Through valve switching, vacuum freeze drying is carried out, ice in the sludge sublimates to form water vapor and then is extracted, the water content is further reduced, and finally, deep heat drying is carried out on the sludge again.
(2) The evaporator and the condenser of the heat pump are utilized to absorb the heat of the sludge in the refrigerating process and store the heat in the heat storage device, and the heat is transferred to the sludge from the heat storage device in the heating process, so that the heat circulation is realized.
(3) In the freeze drying process, as the volume of the frozen water becomes larger, the porosity of the sludge is increased, the water in the sludge is sublimated and then extracted, the water content is further reduced, and meanwhile, a porous structure is formed, so that a good condition is provided for the subsequent deep heat convection drying.
(4) And the sequencing batch sludge is dried, so that the drying efficiency is improved.
Drawings
Fig. 1 is a schematic diagram of a drying system of a single drying oven of the present invention.
Fig. 2 and 3 are schematic diagrams of the four-way valve in state 1 (fig. 2) and state 2 (fig. 3).
Fig. 4 is a schematic diagram of a drying system of the multiple drying ovens of the present invention.
Reference numerals shown in the drawings are as follows:
1-drying oven 11-condenser 12-fan
13-on-line monitoring device 14-air pump 15-first heat exchanger
21-compressor 22-first expansion valve 23-second expansion valve
24-vacuum pump 25-evaporator 26-four-way valve
27-circulation pump
3-Heat storage tank 31-second heat exchanger 32-stirrer
33-Heat storage solution
41-1 # Valve 42-2 # Valve 43-3 # Valve
44-4 # Valve 45-5 # Valve 46-6 # Valve
47-7 # Valves 48-8 # Valve 49-9 # Valve
410-10 # Valves 411-11 # Valves 412-12 # Valves 413-13 # Valve
Detailed Description
As shown in fig. 1, a single drying oven is taken as an example for explanation, and the drying system of the present invention includes a heat pump part, a drying oven part, a heat storage part, and corresponding piping and valve parts.
The heat pump section comprises a compressor 21, an evaporator 25, a first expansion valve 22 and a second expansion valve 23.
The drying box part comprises a drying box 1, an air pump 14, a vacuum pump 24, a condenser 11, a fan 12, a first heat exchanger 15 and an on-line monitoring device 13 which are positioned in the drying box, wherein the drying box is provided with an air inlet, an air outlet, a vacuumizing port and an air discharging port, the air inlet is connected with an air inlet pipe, and 3 parts are arranged on the air inlet pipe # The valve 43, the air inlet pipe is connected to the air outlet of the air pump 14, the air inlet of the air pump 14 is connected to the air channel outlet of the evaporator 25 through the pipeline, the air channel inlet of the evaporator is connected to the air outlet of the drying box; the vacuumizing port is externally connected with a vacuum pump 24 through a pipeline, and a pipeline connected with the vacuum pump is provided with 5 # A valve 45; the emptying port is connected with an emptying pipeline, and the emptying pipeline is provided with 6 # And a valve 46.
A fan and a condenser are arranged on the drying partThe fan is positioned between the inner wall of the box body and the condenser, the fan blades are arranged towards the condenser, a working medium outlet of the condenser is connected to a working medium inlet of the evaporator through a working medium pipeline, and a first expansion valve 22 is arranged on the working medium pipeline connecting the condenser and the evaporator; the working medium inlet of the condenser is connected with the working medium outlet of the compressor 21 through a working medium pipeline, and the connecting pipeline is provided with a working medium inlet 1 # Valve 41, the working medium outlet of the evaporator is connected with the working medium inlet of the compressor through a working medium pipeline, and 7 is arranged on the working medium pipeline # And a valve 47.
The fan is fixed on the inner wall of the air inlet of the drying box and faces the condenser, the condenser heats the air entering the drying box, and the hot air convects under the action of the fan to dry the sludge; the on-line monitoring device 13 is arranged in the drying oven and is provided with a visual display, and monitors the temperature, the pressure, the humidity and the like in the drying oven in real time.
The heat storage part comprises a heat storage tank 31 with a heat storage solution 33, a stirrer 32 arranged in the heat storage tank and a second heat exchanger 31, and for facilitating the switching of the connection modes of the first heat exchanger and the second heat exchanger, a four-way valve 26 is arranged, a first interface (a interface) of the four-way valve is connected with a working medium outlet of a compressor through a working medium pipeline, and a working medium pipeline connected with the first interface (a interface) and the compressor is provided with 2 # The valve 42, the second interface (b interface) of the four-way valve is connected with one of the connectors of the first heat exchanger, the third interface (c interface) of the four-way valve is connected with the working medium inlet of the compressor, the fourth interface (d interface) of the four-way valve is connected with one of the connectors of the second heat exchanger, and 4 is arranged on the working medium pipeline connecting the third interface and the compressor # The valve 44 is connected between the other connecting port of the first heat exchanger and the other connecting port of the second heat exchanger through a working medium pipeline, and the working medium pipeline connecting the first heat exchanger and the second heat exchanger is provided with a second expansion valve 23.
The two states of the four-way valve are shown in fig. 2 and 3, and the interface a is communicated with the interface d and the interface b is communicated with the interface c in the state 1; and in the state 2, the interface a is communicated with the interface b, and the interface c is communicated with the interface d.
The thermal convection drying system, the freeze drying system and the thermal conduction drying system are sequentially switched.
Sequencing batch drying System consisting of multiple drying systems As shown in FIG. 4, 1 for all drying cabinets # Valves 41 and 2 # The pipeline between the valves 42 is connected in parallel to form a main pipe which is connected with the outlet of the compressor 21, 4 # Valves 44 and 7 # The pipeline between the valves 47 is connected in parallel as a main pipe to the inlet of the compressor 21. The heat storage boxes of all the heat storage devices are connected in parallel with the circulating pump 27 through pipelines, the heat storage solution inlet and outlet of each heat storage box are connected with the inlet and outlet of the circulating pump through pipelines, and valves are respectively arranged on the pipelines and are respectively 8 # Valves 48, 9 # Valves 49, 10 # Valves 410, 11 # Valves 411, 12 # Valves 412 and 13 # Valve 413, at 8 # Valves 48 to 13 # The valve 413 and the circulation pump control the flow of the heat storage solution.
During the drying operation, the mixture is formed by 1 # Valves 41, 2 # The switching of valve 42 and four-way valve 26 allows independent operation of each oven. The operation method is the same as that of a single drying box drying system.
The working mode of the invention is as follows:
all valves are in a closed state by default, and the four-way valve is in a state 1 by default.
(1) Single drying oven drying system
Drying is divided into three stages of thermal convection pre-drying, freeze drying and thermal convection deep drying.
(1) Heat convection predrying: opening 1 # Valves 41, 3 # Valves 43 and 7 # Valve 47, compressor 21,1 # Valve 41 valve 1, condenser 11, first expansion valve 22, evaporator 25,7 # The valve 47 and the compressor 21 are connected in sequence to form a working medium circuit. The fan is started, the normal-temperature low-pressure working medium is compressed by the compressor to form a high-temperature high-pressure working medium, the high-pressure low-temperature working medium is formed after the air in the drying oven is heated by the condenser, the high-pressure low-temperature working medium is decompressed by the first expansion valve 22 to form a supercooled low-pressure working medium, the heat of the wet air in the drying oven is acquired by the evaporator 25, the normal-temperature low-pressure working medium is recovered, and the next working medium circulation process is performed. The air in the drying box is heated to hot air on the condenser, convection is formed between the hot air and the sludge in the drying box by utilizing a fan, the hot air heats the sludge and then brings out moisture to form wet low-temperature air, the wet air is introduced into the evaporator 25 in a negative pressure mode to be condensed to form low-temperature dry air, the low-temperature dry air is returned to the left end of the dryer through the air pump 14, and the condensed water is discharged out of the evaporator.
(2) Freeze drying, shut off 1 # Valves 41 and 7 # Valve 47, open 2 # Valve 42,4 # Valve 44 for making compressors 21, 2 # Valve 42, four-way valve 26 (state 1), second heat exchanger 31, second expansion valve 23, first heat exchanger 15, four-way valve 26 (state 1), 4 # Valve 44 and compressor 21 are connected in sequence to form a working fluid circuit. The normal temperature and low pressure working medium is compressed by the compressor to form a high temperature and high pressure working medium, heat is transferred to the heat storage device by the second heat exchanger 31 to form a low temperature and high pressure working medium, the temperature of the solution in the heat storage device is increased, and the heat is stored in the heat storage device. The low-temperature high-pressure working medium is subjected to pressure relief through the second expansion valve 23 to become a supercooled low-pressure working medium, cold is transferred to the sludge in the first heat exchanger 15, moisture in the sludge is solidified into ice, and a certain expansion occurs in a sludge gap. The working medium absorbs the heat of the sludge and then is recovered into a normal-temperature low-pressure working medium, and the next working medium circulation process is carried out. When the temperature of the sludge is reduced to-20 to 0 ℃,the vacuum pumps 24 and 2 are turned on # And a valve 45. And (5) pumping air in the drying box to form low pressure.
(3) Drying by thermal conduction
When the pressure in the drying oven is less than or equal to 100Pa, the four-way valve 26 is switched from the state 1 to the state 2, and the compressors 21 and 2 are arranged # Valve 42, four-way valve 26 (state 2), first heat exchanger 15, second expansion valve 23, second heat exchanger 31, four-way valves (state 2), 4 # The valve 44 and the compressor 21 are sequentially connected to form a working medium loop to form a thermal conduction heat pump system. The working medium is compressed and heated by the compressor and then condensed on the first heat exchanger 15, and the released heat is absorbed by the sludge to provide energy for the gasification of ice into water vapor. The working medium is then depressurized through the second expansion valve 23 to become a supercooled low-pressure working medium, and the heat in the heat storage device is recovered through the second heat exchanger 31 to become a normal-temperature low-pressure working medium for the next cycle.
In the drying box, after absorbing heat, the sludge is gasified into water vapor, and the water vapor is pumped out by a vacuum pump and discharged out of the system, and meanwhile, the pressure in the drying box is kept to be less than or equal to 100Pa. When freeze drying is completed, vacuum pumps 24 and 5 are turned off # Valve 45 of the metal-containing compound is selected, opening 6 # Valve 46 allows outside air to be sucked into the drying cabinet to restore the internal pressure to normal pressure. All equipment and valves were closed and the four-way valve was adjusted to the initial state (state 1).
(4) Deep drying by heat convection: if the freeze-dried sludge is further dried, the heat convection drying may be continued as described in the above (1). Because the sludge is freeze-dried and has a certain pore structure, hot air easily enters the sludge to take away residual moisture.
(2) Multi-drying-box parallel drying system
When a plurality of drying boxes share one set of heat pump system, 1 of all drying boxes # Valves 41 and 2 # The pipeline between the valves 42 is connected in parallel to form a main pipe which is connected with the outlet of the compressor 21, 4 # Valves 44 and 7 # The pipeline between the valves 47 is connected in parallel as a main pipe to the compressor inlet. All the heat accumulating devices are connected in parallel via the used pipeline and the circulating pump in the order of 8 # Valves 48 to 13 # The valve 413 and the circulation pump 27 control the flow of the heat storage solution.
During the drying operation, the mixture is formed by 1 # Valves 41, 2 # The switching of valve 42 and four-way valve 26 allows independent operation of each oven. The operation method is the same as that of the (1) single drying box drying system.
Example 1
The water content of the feed sludge is 65-80%, and the drying requirement is as follows: the water content of the dried sludge is 20-40 percent: first, (1) heat convection drying is performed, and when the water content of the sludge is reduced to 60%, the sludge is freeze-dried (2).
Example 2
The feed sludge is digested sludge, the water content is 65-80%, the organic matter content is low, and the drying requirement is that: the water content of the dried sludge is below 20 percent: firstly, performing (3) heat conduction drying, when the water content of the sludge is reduced to 60%, performing (2) freeze drying, and when the water content of the sludge is lower than 30%, performing (3) heat conduction drying again.
Example 3
The water content of the feed sludge is 50-60%, and the drying requirement is as follows: the water content of the dried sludge is 20 to 40 percent, and only the freeze drying is carried out (2).
Example 4
The water content of the feed sludge is 50-60%, and the drying requirement is as follows: after the sludge is dried, the water content of the sludge is below 20 percent, the freeze drying is firstly carried out (2), and when the water content of the sludge is below 30 percent, the heat convection drying is then carried out (1).
Example 5
High water content (80%), high organic matter sludge, such as secondary sedimentation tank sludge, drying requirements: the water content is 25%, the first step is selected from thermal convection drying, when the drying is 70%, the second step is freeze drying, when the drying is 40%, the third step is thermal conduction drying, and finally the drying is 25%.
Example 6
Since the three-stage drying time of the sludge is not exactly the same, the time of freeze drying is usually longer, and the time of thermal convection drying and thermal conduction drying is shorter, so that the residence time of the sludge in the drying box is not equal. In addition, in the continuous operation process of the sewage plant, the sludge press filtration intermittently works, and the sludge is press-filtered for 2-3 times a day.
The drying box can be used for freeze drying and heat conduction or heat convection drying, so that a plurality of drying boxes can be used in parallel, sequencing batch sludge drying is realized, and the utilization rate of a sludge drying device is maximized.
Taking a set of heat pump system shared by 3 drying boxes as an example, the results are shown in table 1, namely drying box 1, drying box 2 and drying box 3 from left to right. The sludge drying scheme is as follows: the heat convection drying stage is 2h, the freeze drying stage is 4h, the deep drying stage is 2h, and the specific flow is shown in the table below. A, B, C, D denote the heat convection drying stage, lyophilization stage, deep drying stage and idle, and numerals in parentheses after letters denote sludge batches.
TABLE 1
The drying scheme of this example and as an example only, the actual application should be based on experiments to obtain the optimal drying time, thereby determining the drying process.
The foregoing is merely illustrative of specific embodiments of the present invention, but the technical features of the present invention are not limited thereto, and any changes or modifications made by those skilled in the relevant art within the scope of the present invention are encompassed by the present invention.
Claims (8)
1. The sludge drying method combining vacuum cold and hot drying by utilizing the sludge drying device combining vacuum cold and hot drying is characterized in that the sludge drying device combining vacuum cold and hot drying comprises a heat pump system, a drying system and a heat storage system, and the heat pump system comprises a compressor and an evaporator;
the drying system includes:
the drying box is provided with an air inlet, an air outlet and a vacuum pumping port, the air outlet of the drying box is connected with the evaporator, and the vacuum pumping port is connected with a vacuum pump through a pipeline;
the air inlet pipe of the air pump is connected with the evaporator, the air outlet pipe of the air pump is connected with the air inlet of the drying box, and the drying box, the air pump and the evaporator are sequentially connected into a drying air loop;
the working medium inlet end of the condenser is connected to the compressor through a working medium pipeline, the working medium outlet end of the condenser is connected to the evaporator through a working medium pipeline, and a first expansion valve is arranged on the working medium pipeline connected with the evaporator;
the thermal storage system includes:
a heat storage tank in which a heat storage solution is placed;
the second heat exchanger is arranged in the heat storage box, and a second expansion valve is arranged between the second heat exchanger and the first heat exchanger;
the compressor, the condenser, the first expansion valve, the evaporator and the compressor are sequentially connected into a working medium loop, and a heat convection drying system is formed by the working medium loop and the drying gas loop; the compressor, the second heat exchanger, the second expansion valve, the first heat exchanger and the compressor are sequentially connected into a working medium loop to form a freeze drying system; when the compressor, the first heat exchanger, the second expansion valve, the second heat exchanger and the compressor are sequentially connected into a working medium loop, a heat conduction drying system is formed; the heat convection drying system, the freeze drying system and the heat conduction drying system are switched;
the method for drying the sludge by utilizing the combined vacuum cold and hot drying sludge drying device comprises the steps of feeding sludge to be dried into a drying box, and selecting any one or more of the following drying modes by switching corresponding valves:
(1) Thermal convection pre-drying
The method comprises the steps of switching on a heat convection drying system by controlling a corresponding valve, starting a fan, compressing a normal-temperature low-pressure working medium through a compressor to form a high-temperature high-pressure working medium, heating air in a drying box through a condenser to form a high-pressure low-temperature working medium, releasing pressure through a first expansion valve to form a supercooled low-pressure working medium, acquiring heat of wet air in the drying box through an evaporator, recovering the heat to form the normal-temperature low-pressure working medium, carrying out the next working medium circulation process, discharging condensed water outside the evaporator, and carrying out heat convection predrying on sludge by the air heated in the drying box under the action of the fan;
(2) Freeze drying
Switching to the freeze drying system, compressing the normal-temperature low-pressure working medium through a compressor to form a high-temperature high-pressure working medium, transmitting heat to a heat storage solution in a heat storage box through a second heat exchanger to form a low-temperature high-pressure working medium, increasing the temperature of the heat storage solution, storing the heat in the heat storage box, releasing the pressure of the heat storage solution through a second expansion valve to form a supercooled low-pressure working medium, transmitting cold energy to sludge through a first heat exchanger, solidifying water in the sludge into ice, expanding a sludge gap, recovering the supercooled low-pressure working medium to the normal-temperature low-pressure working medium after absorbing the heat of the sludge, performing the next working medium circulation process, and opening a vacuum pump to vacuumize the interior of a drying box to form low pressure when the temperature of the sludge in the drying box is reduced to minus 20-0 ℃;
(3) Drying by thermal conduction
When the pressure reduction in the drying box is less than or equal to 100Pa, switching to the thermal conduction drying system, pressurizing and heating the normal-temperature low-pressure working medium by a compressor, condensing the working medium on a first heat exchanger, absorbing the released heat by sludge, and providing energy for the gasification of ice into water vapor; and then the working medium is subjected to pressure relief through a second expansion valve to become a supercooling low-pressure working medium, and the heat in the heat storage box is recovered through a second heat exchanger to become a normal-temperature low-pressure working medium for the next cycle.
2. The sludge drying method as claimed in claim 1, further comprising a heat convection deep drying step (4) of the same drying manner as the heat convection drying step.
3. The method for drying sludge according to claim 1, wherein the temperature in the drying oven is 25-40 ℃ in both the thermal convection drying and the thermal conduction heat pump drying.
4. The method according to claim 1, wherein the thermal convection drying time is 1 to 8 hours, the freeze drying time is 1 to 4 hours, and the thermal conduction drying time is 1 to 4 hours in each drying process.
5. The sludge drying method according to claim 1, wherein the heat storage solution is sodium chloride solution with a mass concentration of 5-35%; the temperature range of the heat storage solution is 0-50 ℃.
6. The sludge drying method according to claim 1, wherein the condenser and the fan are both provided at an air inlet in the drying box; the fan is arranged in front of the inner wall of the box body and the condenser and is arranged towards the condenser.
7. The sludge drying method according to claim 1, wherein an on-line monitoring device is provided in the drying oven.
8. The sludge drying method for performing sequencing batch vacuum cold and hot drying combination by utilizing the sludge drying device for performing sequencing batch vacuum cold and hot drying combination is characterized in that the sludge drying device for performing sequencing batch vacuum cold and hot drying combination comprises a compressor and at least two sets of drying systems, wherein each set of drying system comprises an evaporator, a drying system and a heat storage system;
the drying system includes:
the drying box is provided with an air inlet, an air outlet and a vacuum pumping port, the air outlet of the drying box is connected with the evaporator, and the vacuum pumping port is connected with a vacuum pump through a pipeline;
the air inlet pipe of the air pump is connected with the evaporator, the air outlet pipe of the air pump is connected with the air inlet of the drying box, and the drying box, the air pump and the evaporator are sequentially connected into a drying air loop;
the working medium inlet end of the condenser is connected to the compressor through a working medium pipeline, the working medium outlet end of the condenser is connected to the evaporator through a working medium pipeline, and a first expansion valve is arranged on the working medium pipeline connected with the evaporator;
the thermal storage system includes:
a heat storage tank in which a heat storage solution is placed;
the second heat exchanger is arranged in the heat storage box, and a second expansion valve is arranged between the second heat exchanger and the first heat exchanger;
the condenser, the first expansion valve and the evaporator of each set of drying system are sequentially connected and connected with the compressor to form a working medium loop, and the working medium loop and a drying gas loop in each set of drying system form a heat convection drying system of the corresponding drying system; the second heat exchanger, the second expansion valve and the first heat exchanger of each set of drying system are sequentially connected and sequentially connected with the compressor to form a working medium loop, so that a freeze drying system corresponding to the drying system is formed; when the first heat exchanger, the second expansion valve and the second heat exchanger of each set of drying system are sequentially connected and sequentially connected with the compressor to form a working medium loop, a heat conduction drying system corresponding to the drying system is formed; each drying system is independently controlled, and the heat convection drying system, the freeze drying system and the heat conduction drying system in each drying system are switched; the heat storage boxes of the drying systems are connected in series through a circulating pump;
the sludge drying method for performing sequencing batch vacuum cold and hot drying by using the sequencing batch vacuum cold and hot drying combined sludge drying device comprises the steps of feeding sludge to be dried into a drying box of a corresponding drying system, and selecting any one or more of the following drying modes by switching corresponding valves:
(1) Thermal convection pre-drying
The method comprises the steps of starting a thermal convection drying system of a corresponding drying system by controlling a corresponding valve, starting a fan, compressing a normal-temperature low-pressure working medium through a compressor to form a high-temperature high-pressure working medium, heating air in a drying box through a condenser to form a high-pressure low-temperature working medium, releasing pressure through a first expansion valve to form a supercooled low-pressure working medium, acquiring heat of wet air in the drying box through an evaporator, recovering the heat to form the normal-temperature low-pressure working medium, and performing the next working medium circulation process;
(2) Freeze drying
After the heat convection drying is finished, a freeze-drying system corresponding to the drying system is started by switching a corresponding valve, a normal-temperature low-pressure working medium is compressed by a compressor to form a high-temperature high-pressure working medium, heat is transferred to a heat storage solution by a second heat exchanger to form a low-temperature high-pressure working medium, the temperature of the heat storage solution is increased, the heat is stored in a heat storage box, the low-temperature high-pressure working medium is depressurized by a second expansion valve to form a supercooled low-pressure working medium, cold is transferred to sludge by a first heat exchanger, moisture in the sludge is solidified into ice, a sludge gap expands, the supercooled low-pressure working medium is recovered to the normal-temperature low-pressure working medium after absorbing the heat of the sludge, the next working medium circulation process is performed, and when the temperature of the sludge in the drying box is reduced to minus 20-0 ℃, a vacuum pump is opened, and the interior of the drying box is vacuumized to form low pressure;
(3) Drying by thermal conduction
When the pressure reduction in the drying box is less than or equal to 100Pa, a heat pump heat conduction drying system corresponding to the drying system is started by switching a corresponding valve, the normal-temperature low-pressure working medium is pressurized and heated by a compressor and then condensed on a first heat exchanger, and released heat is absorbed by sludge to provide energy for the gasification of ice into water vapor; then the working medium is decompressed by a second expansion valve to become a supercooling low-pressure working medium, and the heat in the heat storage box is recovered by a second heat exchanger to become a normal-temperature low-pressure working medium for the next cycle;
when the temperature of the heat storage solution in each heat storage tank exceeds the range, starting a circulating pump and a corresponding valve to balance the temperature of the heat storage solution in each heat storage tank; and stopping the drying work when all the heat storage solutions exceed the temperature range.
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| CN110240377B (en) * | 2019-06-28 | 2021-11-09 | 西安建筑科技大学 | Fluidized bed sludge drying equipment and method based on freezing wall breaking and hot air drying |
| CN112429933B (en) * | 2020-11-02 | 2022-11-29 | 江苏苏讯新材料科技股份有限公司 | Sludge low-temperature drying treatment process |
| CN113623950A (en) * | 2021-06-21 | 2021-11-09 | 以农环境工程有限公司 | Freezing sublimation garbage treatment process |
| CN115159810B (en) * | 2022-04-24 | 2024-04-09 | 中煤科工清洁能源股份有限公司 | Low-energy-consumption sludge drying system |
| CN114656126B (en) * | 2022-05-25 | 2022-12-27 | 广东沪利环境科技发展有限公司 | Low-temperature vacuum intelligent closed ring plate drying equipment for sludge |
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