JP6461677B2 - Dehydration method - Google Patents

Description

  The present invention relates to a technique for dehydrating water contained in a treatment object using a hydrophilic solvent such as an organic solvent, using a hydrated material such as sludge as the treatment object.

  Conventionally, as a device for dewatering sludge generated from a sewage treatment plant, a water purification plant, a factory wastewater treatment facility, a civil engineering construction site, etc., there are various devices such as a centrifugal dehydrator and a filter press. However, depending on the properties of the sludge, it is difficult to remove moisture from the sludge.

  For this reason, for example, in the invention described in Patent Document 1, a volatile organic solvent such as methanol, ethanol, isopropyl alcohol or the like is added to the concentrated mud obtained after the coagulation sedimentation treatment. The organic solvent mixed mud is dehydrated, and the evaporation of the added organic solvent promotes the evaporation of water remaining in the dehydrated sludge, thereby reducing the water content of the dehydrated sludge.

  The invention described in Patent Document 2 includes a filtration step of filtering a slurry through a filter cloth to form a filter cake, a pressing step of pressing the filter cake through the filter cloth to form a press cake, A vacuum heating and drying process in which the pressed cake is heated and held under a negative pressure through a cloth and dried. The pressure of the squeezing is gradually reduced to the non-squeezing pressure at which the compaction of the squeezed cake does not substantially occur.

  The invention described in Patent Document 3 dehydrates organic sludge mixed with an organic solvent that is liquid and volatile under normal temperature and normal pressure with a dehydrator equipped with a heating means. The sludge is heated to a first predetermined temperature equal to or higher than the boiling point of the organic solvent, the organic solvent mixed in the organic sludge is vaporized, and the organic solvent is discharged from the dehydration unit and collected.

JP2011-2000811 JP-A-2005-270828 JP2014-193438

  By the way, when dewatering sewage sludge or the like to a moisture content of 60% or less, for example, after performing a dehydration operation to a certain moisture content, a drying process by heating or the like is performed. There is more rational in terms of time and mechanical strength than lowering and squeezing out the water (liquid) in the sludge.

However, it is necessary to provide a dryer separately from the dehydrator, and the apparatus becomes large, and a process of transferring the object to be processed from the dehydrator to the dryer occurs, resulting in a large heat loss.
In addition, in the vacuum heating drying process in which the pressed cake is heated and dried under a negative pressure while being heated, the diaphragm for pressing is stuck to the filter cloth, and the drying effect of the treatment object cannot be sufficiently obtained. There was a problem.

  In a state where the diaphragm is separated from the object to be processed, there is a problem that a sufficient amount of heat is not transmitted from the heating source to the object to be processed, and the temperature of the object to be processed is lowered below the temperature that effectively contributes to drying.

  The present invention solves the above-described problems, and an object of the present invention is to provide a dehydration method capable of sufficiently exerting a drying effect by heating.

In order to solve the above-described problems, the dehydration method of the present invention uses a pressing means while heating the processing object while dehydrating the processing object mixed with the hydrophilic solvent with a heating type dehydrator. The pressing process of pressing and compressing the object and the drying process for promoting the volatilization of the solvent from the processing object in a state where the pressing means and the processing object are separated are repeated, and the temperature of the processing object is set to the upper limit. When the temperature reaches the temperature, the drying process is performed, and when the temperature of the processing object reaches the lower limit set temperature, the pressing process is performed. The upper limit set temperature is below the temperature rise limit of the processing object determined by the temperature of the heat source that heats the processing object. The lower limit temperature is set to a temperature equal to or higher than the boiling point of the solvent.
In the dehydration method of the present invention, when a processing object that has been stirred and mixed with a hydrophilic solvent is dehydrated by a heating-type dehydrator, the processing object is pressurized and pressed by a pressing means while the processing object is heated. The pressing step and the drying step for promoting the volatilization of the solvent from the processing object in a state where the pressing means and the processing object are separated are repeated, and the temperature of the processing object rises from the lower limit set temperature to the upper limit set temperature. The pressing process is performed for the required heating time, and the drying process is performed for the necessary drying time required for the temperature of the processing object to fall from the upper limit set temperature to the lower limit set temperature. The temperature is set to be equal to or lower than the temperature rise limit of the object to be treated, which is determined by the temperature of the heat source for heating, and the lower limit temperature is set to a temperature equal to or higher than the boiling point of the solvent.

In the dehydration method of the present invention, the upper limit set temperature is set to be equal to or lower than the boiling point of water.
In the dehydrating method of the present invention, a heating filter press is used as a heating type dehydrating device, and warm water is used for heating the heating filter press.

  As described above, according to the present invention, the processing object is heated in the pressing process to give sensible heat to the solvent and moisture, and in the drying process, the pressing means and the processing object are separated to form a space, Volatilization of the solvent and evaporation of water from the processing object heated in the pressing process are promoted. That is, by repeating the squeezing step and the drying step at a predetermined interval, the processing object is opened to the space between the pressing means and contacted with the surrounding atmosphere while giving the amount of heat necessary for drying the processing object. By making it dry, drying can be accelerated | stimulated and drying time can be shortened.

The schematic diagram which shows the absorption dehydration apparatus in embodiment of this invention The graph figure which shows the temperature change of the process target object in embodiment of this invention Schematic diagram showing the operation of the filter press in the same embodiment Schematic diagram showing the operation of the filter press in the same embodiment Schematic diagram showing the operation of the filter press in the same embodiment Graph diagram showing experimental results

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, a processing object 101 in a heating filter press is organic sludge generated from a sewage treatment plant, a water purification plant, a factory wastewater treatment facility, or the like, and here is a dehydrated cake.

  The absorbing liquid 103 used in the absorption dehydrating apparatus 102 is a hydrophilic solvent. Here, an alcoholic solvent that is liquid at normal temperature and normal pressure, such as methanol and ethanol, is used as the hydrophilic solvent.

  The absorption dehydration apparatus 102 has a circulation system that goes around the absorption liquid storage tank 104, the stirring tank 105, the dehydration apparatus 106, the solvent recovery apparatus 107, and the solvent regeneration apparatus 108, and the absorption liquid 103 circulates in the circulation system. .

The absorption liquid storage tank 104 stores the absorption liquid 103, and adjusts the concentration of the solvent by adding a new solvent or dilution water as necessary.
The agitation tank 105 forms an agitation unit that agitates and mixes the absorbing liquid 103 supplied from the absorbing liquid storage tank 104 and the organic sludge 101 with a rotating agitating blade, and takes charge of the agitation process of making the organic sludge 101 into a solid-liquid mixed phase mixture. It promotes the contact between the water contained in the organic sludge 101 and the solvent of the absorbing liquid 103.

  The dehydrator 106 is responsible for a dehydration step of dehydrating the solid-liquid mixture in the stirring tank 105, and here, a heating filter press is used. The warming filter press warms the filter plate with hot water of about 90 ° C., raises the temperature of the solid-liquid mixture in the filter cloth disposed in the filter chamber between the filter plates to 65 to 78 ° C. or higher, and The dehydration process dehydrates the filtrate-containing absorption liquid 1 as a dehydrated filtrate by dehydrating the pressure. The filtrate-containing absorption liquid 1 is a gas-liquid mixed fluid containing the moisture of the organic sludge 101, the liquid phase of the absorption liquid 103, and the organic solvent in the gas phase.

The solvent regeneration device 108 is responsible for a regeneration step of separating the water from the filtrate-containing absorbent in the solvent recovery device 107 to regenerate the absorbent 103.
In this dehydration method, the cell membrane of the organic matter in the organic sludge is dissolved and damaged by the organic solvent, so that the water contained in the cell membrane in the organic matter can be dehydrated, and the water content of the organic sludge is easily reduced. Is a way that can be. In addition, since the viscosity of water decreases due to heating, the rate of dehydration and desolvation from the organic sludge during dehydration increases. Furthermore, since a liquid alcohol solvent at room temperature and normal pressure is used, there is no need to pressurize the organic sludge mixed with the organic solvent in the pressure vessel, so that troublesome safety management related to the first type pressure vessel is not required. It is also a method.

  As shown in FIGS. 3 to 5, each filter plate 1 of the heating filter press includes a recess 2 formed on one surface of the front and back, a warming water passage 3 formed on the other surface, and a diaphragm disposed in the recess 2. 4 and a pressurized water passage 5 communicating with the space of the recess 2 surrounded by the diaphragm 4, the heated water passage 3 and the pressurized water passage 5 are heated water supply passage 7 for supplying warm water 6, and warm water discharge for discharging the warm water 6. Connected to route 8.

  Between the filter plates 1 and 1, filter cloths 9 are doubled, and sludge injection passages (not shown) for supplying the organic sludge 11 to be treated 101 to the filter chambers 10 between the filter cloths 9 are provided. The filter plate 1 is formed.

  Although not shown, the heating filter press is provided with a fixed frame on the outside of the filter plate 1, and the filtrate that communicates with the sludge inlet that communicates with the sludge inlet passage of the adjacent filter plate 1 and the filtrate discharge passage. A discharge port is formed. A solvent recovery device 107 is connected to the filtrate recovery passage, and the solvent recovery device 107 recovers the vaporized solvent from the filtrate in the filter chamber or from the dehydration, and a fan or vacuum device that makes the filter chamber have a negative pressure. Consists of. This solvent recovery device 107 can recover not only gas but also dehydrated filtrate.

Further, in the heating filter press, the filter plate 1 is provided with a thermometer 13 for measuring the temperature of the organic sludge 11 that is the processing object 101, and is pressurized based on the temperature measured by the thermometer 13. A control device is provided for switching between a pressing process for dehydration and a drying process for releasing pressure, and for controlling the supply of hot water to the heating filter press.
The filtrate containing the hydrophilic solvent from the filter press is sent to a solvent recovery device, where the solvent is recovered and regenerated in a distillation tower, thereby constituting a dehydration system as a whole.

Hereinafter, the operation of the above configuration will be described.
Filtration Step As shown in FIG. 3, in the filtration step, the organic sludge 11 to be treated with a solvent passes through the sludge injection passages (not shown) of each filter plate 1 and is injected into each filter chamber 10 and filtered. Filter through cloth 9. In this state, the filter plate 1, the diaphragm 4, the filter cloth 9 and the organic sludge 11 are in continuous contact, and the filter plate 1 is heated to a predetermined temperature by the hot water 6 supplied from the hot water supply passage 7 to the warming water passage 3. At the same time, the organic sludge 11 in the filter chamber 10 is also heated to a predetermined temperature. (See the filtration process in Fig. 2)
Pressing process (pressing 1)
In the squeezing step (squeezing 1) after performing the filtering step, as shown in FIG. 4, hot water 6 is supplied from the hot water supply passage 7 to the warming water passage 3 and the pressurized water passage 5 of each filter plate 1, and the diaphragm 4 is The organic sludge 11 in the filter chamber 10 is squeezed and dehydrated by expanding from the inner side in contact with the warm water toward the outer side in contact with the organic sludge 11. (Refer to the process of pressing 1 in FIG. 2)
At this time, the filtrate containing the dehydrated solvent is discharged, and the inside of the filter chamber 10 is sucked into a negative pressure for solvent recovery. Moreover, since the temperature of organic sludge is normal temperature at this time, the time for raising to predetermined temperature becomes longer than the below-mentioned pressing process (refer to pressing 2-5 of FIG. 2).

Even during such a pressing process, the hot water 6 continues to heat the organic sludge 11 via the diaphragm 4.
Drying process (drying 1)
After performing a pressing process (pressing 1), it heats, performing slurry blow etc., and when an organic sludge 11 reaches upper limit preset temperature, a drying process (drying 1) is performed. The upper limit set temperature is set below the temperature rise limit of the organic sludge 11 determined by the temperature of the warm water 6 which is a heat source for heating the organic sludge 11, and here the upper limit set temperature is set below the boiling point of water.

As shown in FIG. 5, in a state where the warm water 6 is passed through the warming water passage 3, the supply of the warm water 6 to the pressurized water passage 5 is stopped, and the warm water 6 in the inner space of the diaphragm 4 is discharged to the warm water discharge passage 8. Then, the pressurization by the hot water 6 is released, the diaphragm 4 is contracted and separated from the filter cloth 9, and a drying space 12 is formed between the diaphragm 4 and the filter cloth 9. (See the drying 1 process in FIG. 2)
At this time, the heated organic sludge 11 is opened to the drying space 12 through the filter cloth 9 and comes into contact with the atmosphere, whereby the evaporation of the solvent and the evaporation of the water are promoted.

Pressing process (press 2)
When the drying step (drying 1) is performed and the organic sludge 11 reaches the lower limit set temperature, the pressing step (pressing 2) is performed in the same manner as the pressing 1. The lower limit set temperature is set to a temperature equal to or higher than the boiling point of the solvent. (Refer to the process of pressing 2 in FIG. 2)
Thereafter, after repeating the squeezing step and the drying step (see squeezing 3-5 and drying 2-5 in FIG. 2), the warm water 6 in the inner space of the diaphragm 4 and the warm water 6 in the warming water passage 3 are discharged and the filter plate 1 is discharged. Open the plate.

  In this way, the organic sludge 11 to be treated is heated in the pressing step to give sensible heat to the solvent and moisture, and the diaphragm 4 and the organic sludge 11 are separated from each other in the drying step to form a drying space 12. While accelerating the volatilization of the solvent and evaporation of water from the organic sludge 11 heated in the pressing step and repeating the pressing step and the drying step at a predetermined interval, while giving the heat necessary for drying the organic sludge 11 The organic sludge 11 can be opened to the drying space 12 and brought into contact with the surrounding atmosphere to promote drying, achieve the target moisture content, and shorten the drying time.

Moreover, the flow of gas is produced by making the inside of the filter chamber 10 into a negative pressure, and drying is promoted. Since air enters through the filter cloth 9 that contacts the end of the diaphragm 4, it is not necessary to provide a separate air inlet.
(Experimental example)
Using a heating filter press, an experiment was conducted on how the moisture content changes by repeating the pressing process and the drying process using temperature as an index.

  An experiment was conducted using a sewage sludge having a water content of 80% and methanol mixed at a ratio of 1: 1 to the sewage sludge and stirred and mixed. As a comparative example, one pressing operation was performed after filtration, and an experiment was conducted in which the time from filtration to pressing and cleaving was continued for about 50 minutes. At this time, the water content after dehydration was about 40%.

The operation of FIG. 2 is a diagram of the optimum operating state of the pressing process and the drying process of the experiment conducted with the goal of reducing the moisture content to about 30%.
In order to accurately measure the temperature of the object to be processed 101, a thermocouple was inserted between the filter cloths 9 of the filter press and measured. Further, the pressing process (pressing 2-5) and the drying process (drying 2-5) are as shown in FIG. 6, and at the time of re-pressing, a predetermined temperature that is considered to be reachable from warm water (about 90 degrees) used for heating. It went until it became (about 85 degree | times). When the temperature did not rise to the predetermined temperature, it was judged that the temperature was sufficiently warmed when the temperature gradient became small. In the drying process, the period until the temperature gradient of the object to be processed becomes small was defined as the drying process. This is judged from the fact that while the evaporation is actively performed, the temperature is drastically decreased due to the removal of latent heat by the evaporation, but when the evaporation is stopped, the absorption of the heat accompanying the evaporation is reduced. FIG. 2 shows the experimental results obtained by optimizing the time required for this step and repeating the steps to obtain the target moisture content. At this time, the dehydration rate reached about 30%, and the time required for dehydration was almost the same, but the moisture content decreased about 10%.

  In the present embodiment, the temperature of the organic sludge 11 is used as an index for control, but the required heating time and the number of pressing and drying steps required for the temperature of the organic sludge 11 to rise from the lower limit set temperature to the upper limit set temperature. The squeezing process is performed in advance for the required heating time, and the necessary drying time required for the temperature of the object to be processed to fall from the upper limit set temperature to the lower limit set temperature is determined in advance by experiment etc. The drying process is performed for the time required for drying. Even in this control, the target moisture content is achieved by repeatedly performing the pressing step and the drying step.

  In this embodiment, the temperature index is controlled using the temperature itself as an index, but a temperature gradient may be used as an index. When the temperature gradient is observed during heating, it can be determined that the heating of the object to be processed 101 is almost completed when the temperature gradient becomes gentle. Therefore, even when the temperature of the hot water used for heating changes It becomes the structure which can judge the end of temperature.

  In the present embodiment, the diaphragm 4 and the filter cloth 9 are separated from each other by draining warm water in the drying process. However, in order to ensure separation, the warm water is drained, and then the negative pressure is further positively separated. It can also be made. As the negative pressure means, a solvent recovery device 107 can be used.

  In the present embodiment, the temperature of the organic sludge 11 in the furnace chamber is measured by the thermometer 13 provided in the filter plate 1, but it can also be indirectly measured from the temperature on the hot water side of the diaphragm 4. For example, the temperature rise at the time of heating is measured on the inlet side and outlet side temperature of the hot water, and if the temperature on the outlet side becomes substantially the same as that on the inlet side, it can be determined that the organic sludge 11 has been heated to the set temperature. Note that the method of directly measuring the temperature of the object to be processed as in the above experimental example is the most accurate method of measuring the temperature.

  In the present embodiment, a heating filter press that heats with warm water is exemplified, but the heating is not limited to warm water, and any heat source such as steam or heating oil may be used. The dehydrator is not limited to a filter press, and may be any dehydrator that has a function of releasing pressure and releasing pressure while heating, such as a screw press provided with an overheating source on a shaft or screw blade.

DESCRIPTION OF SYMBOLS 1 Filter plate 2 Recessed part 3 Warm water passage 4 Diaphragm 5 Pressurized water passage 6 Warm water 7 Warm water supply route 8 Warm water discharge route 9 Filter cloth 10 Filter chamber 11 Organic sludge 12 Drying space 13 Thermometer 101 Object 102 Absorption dehydration device 103 Absorption Liquid 104 Absorbing liquid storage tank 105 Stirring tank 106 Dehydrating apparatus 107 Solvent recovery apparatus 108 Solvent regenerating apparatus

Claims (4)

When dehydrating the processing object stirred and mixed with the hydrophilic solvent with a heating-type dehydrator, a pressing step of pressing the processing object with the pressing means while pressing the processing object and pressing, and a pressing means The drying process that promotes the volatilization of the solvent from the processing object is repeated in a state where the processing object is separated, and the drying process is performed when the temperature of the processing object reaches the upper limit set temperature. When the lower limit temperature is reached, the pressing process is performed,
A dehydration method characterized in that the upper limit set temperature is set to be equal to or lower than the temperature rise limit of the process target determined by the temperature of the heat source for heating the process target, and the lower limit set temperature is set to a temperature equal to or higher than the boiling point of the solvent. When dehydrating the processing object stirred and mixed with the hydrophilic solvent with a heating-type dehydrator, a pressing step of pressing the processing object with the pressing means while pressing the processing object and pressing, and a pressing means Repeating the drying process that promotes the volatilization of the solvent from the processing object in a state where the processing object is separated from the processing object, the heating necessary for the temperature of the processing object to rise from the lower limit set temperature to the upper limit set temperature is necessary. Perform the pressing process over time, perform the drying process over the required drying time necessary for the temperature of the object to be processed to fall from the upper limit set temperature to the lower limit set temperature,
A dehydration method characterized in that the upper limit set temperature is set to be equal to or lower than the temperature rise limit of the process target determined by the temperature of the heat source for heating the process target, and the lower limit set temperature is set to a temperature equal to or higher than the boiling point of the solvent. The dehydration method according to claim 1 or 2, wherein the upper limit set temperature is set to be equal to or lower than the boiling point of water. The dehydration method according to claim 3 , wherein a warming filter press is used as a warming-type dehydrating device, and warm water is used for warming the warming filter press.

Images