JP2019126788A - Indirect heating sludge dryer - Google Patents

Abstract

To provide an indirect heating sludge dryer that reduces power consumption and can be made compact without reducing the evaporation rate.SOLUTION: Dryers 100a, 100b receive the sludge to be dried at the receiving port 6, heat and dry the sludge while stirring and transporting it with a plurality of heat transfer blades 5 provided at intervals in the axial direction of the rotating shaft 4, and discharge the sludge from the discharge port, and are arranged to receive the dried sludge discharged from the upstream dryer 100a by the downstream dryer 100b, and the rotating shaft of the upstream dryer 100a has the rotation speed lower than that of the rotating shaft of the downstream dryer 100b.SELECTED DRAWING: Figure 5

Description

  BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an indirect heating type sludge drying apparatus including a plurality of dryers that heat and dry sludge as a waste while transporting it.

  This type of drier is an apparatus for drying water and solvents in raw materials, and is used in various plants such as food production, sewage sludge and waste incineration plants. As the drying method, there are a direct heating method in which hot air is directly applied to the material for drying, and an indirect heating method in which the metal is heated by a heat medium such as steam and the material is dried by the heat transfer. In addition to drying, these dryers are also employed in processing steps such as heating, cooling, baking, roasting, and reaction.

  As the direct drying method, an air flow dryer, a fluidized bed dryer, a rotary dryer or the like is known, and as the indirect heating method, a rotary dryer with a steam pipe (for example, FIG. 5 of Patent Document 1 and Patent Document 2). A groove type stirring dryer (for example, FIG. 4 of Patent Document 1) and the like are known. The indirect heating method has an advantage that the exhaust gas is less than the direct heating method.

  For example, as shown in FIG. 5 of Patent Document 1, a large number of heating pipes extending over the entire length are arranged concentrically in the rotating cylinder as shown in FIG. 5 of Patent Document 1, for example. The heat of the heat medium passed through the inside of the heating pipe is indirectly transferred to the dehydrated sludge which is the object to be treated through the heat transfer body formed by the heating pipe and dried.

  As shown in FIG. 1, a conventional grooved stirrer / dryer 100 is a grooved type (trough type) low-speed agitation type conduction heat transfer dryer, and has a grooved trough 3 having a heat transfer jacket 2. A heat transfer body in which heat transfer blades 5 (also referred to as paddle blades) are arranged at appropriate intervals on a single or a plurality of rotation shafts 4 is rotatably supported. The trough 3 has an inlet 6 at one end for receiving the dewatered sludge which is the treated sludge, and an outlet 7 for discharging the dried sludge at the other end. Further, the heat transfer jacket 2 is provided with a heat medium supply port 8 for supplying a heat medium and a heat medium outlet 9 for discharging the heat medium. The rotating shaft 4 and the heat transfer blade 5 are hollow to communicate the inside, and the heat medium introduced from the heat medium supply port 8 is drained from the heat medium outlet 9 as a drain through the hollow. The The rotation shaft 4 is drivingly connected to the electric motor 11 via the transmission chain 10 and the like outside the trough 3 and is rotationally driven. Furthermore, an exhaust fan (not shown) is provided in the trough 3 in order to discharge water vapor generated by drying, and the carrier gas (external air) is troughed from the carrier gas inlet 12 provided in the trough 3. The gas is sucked into the chamber 3 and the steam as well as the carrier gas is exhausted from the exhaust port 13 provided in the trough 3. The heat transfer jacket 2 is also provided with a jacket heat medium supply port 14 and a jacket heat medium discharge port 15. The trough 3 can also be installed with a downward slope where the side of the outlet 7 is lower.

  In the indirect heating type sludge dryer, steam, heat medium oil, or high temperature water is used as a heat medium, and the heat medium (steam in the example of FIG. 1) supplied from the heat medium supply port 8 has the rotating shaft 4 and heat transfer. While being discharged from the heat medium discharge port 9 through the internal space of the blade 5, it is transported to the discharge port 7 while drying the sludge by contact with the sludge supplied from the receiving port 6, and generated by drying. The steam is exhausted from the exhaust port 13 together with the carrier gas, and the sludge to be dried which is the input raw material (dehydrated sludge) is dried at the outlet 7 to a target moisture content.

Japanese Patent No. 3778422 International Publication No. 2016/088833 Pamphlet Japanese Patent No. 5372187 Japanese Patent No. 6139949

  The conventional indirect heating sludge dryer is widely used as an energy-saving dryer because it can dry wet materials with properties that are difficult to form a fluidized bed or wet materials with strong adhesion, with high thermal efficiency. Stirring and drying machines are employed in drying, heating, cooling, baking, roasting, and reaction processes.

  Since it was thought that the evaporation speed per heat transfer area increased with the number of revolutions of the heat transfer blades constituting the heat transfer body in the grooved stirrer dryer provided with the heat transfer blades, and the apparatus could be made compact as a device. Although attempts have been made to increase the number of revolutions of the thermal wing as much as possible to achieve compactness, there has been a problem that the higher the number of revolutions, the larger the power consumption.

  Therefore, the main object of the present invention is to provide an indirectly heated sludge drying apparatus capable of reducing power consumption and downsizing without lowering the evaporation rate.

  In order to achieve the above object, the indirect heating type dry sludge dryer according to the present invention receives, as a first means, a plurality of sludges to be dried at a receiving port, and a plurality of the sludges are provided at intervals in the axial direction of the rotating shaft. It is equipped with a plurality of dryers that are heated and dried while being stirred and conveyed by the heat transfer blades, and discharged from the discharge port, so that the drying sludge discharged by the upstream dryer is sequentially received by the downstream dryer. It is characterized in that the rotary shaft of the most upstream dryer is rotated at a lower speed than the rotary shaft of the dryer immediately downstream.

  The indirectly heated sludge drying apparatus according to the present invention further includes, as the second means, a temperature detector for detecting an in-machine temperature of each of the plurality of dryers in the first means, and the temperature detection The rotational speed of the rotation shaft of each of the plurality of dryers is set based on the detection value of the device.

  In the indirect heating sludge drying apparatus according to the present invention, as the third means, in the first or second means, the to-be-dried sludge is preheated to 60 ° C. or more and less than 100 ° C. in the most upstream dryer. The rotational speed of the rotary shaft of the dryer on the most upstream side is controlled so as to be discharged from the outlet of the dryer on the most upstream side.

  The indirect heating sludge drying apparatus according to the present invention includes, as a fourth means, in any one of the first to third means, from the intermediate portion between the inlet and the outlet of the upstream dryer. The apparatus further includes a bypass line for bypassing the sludge to be dried and an opening / closing means for opening and closing the bypass line to an intermediate portion between the inlet and the outlet of the dryer downstream.

  In the indirect heating sludge drying apparatus according to the present invention, as the fifth means, in any one of the first to fourth means, each of the plurality of dryers discharges the dried sludge discharged from the discharge port. It further comprises a height adjustable butt for adjusting the emissions.

  According to the present invention, since the rotation shaft of the most upstream dryer is configured to rotate at a lower speed than the rotation shaft of the immediately downstream dryer, it is not affected by the high load of the high viscosity preheating zone, The number of rotations in the evaporation zone and the crushing zone can be increased, and it is possible to obtain the maximum evaporation amount according to the shape of sludge in each machine while suppressing the power consumption.

It is a partially notched front view which shows the conventional indirect heating type sludge dryer. It is a center longitudinal cross-sectional view of FIG. It is a graph which shows the drying test result which measured the sludge moisture content and evaporation rate of each area in a machine using the conventional indirect heating type | formula sludge dryer. It is a schematic diagram which shows the state of the sludge in the apparatus of the conventional indirect heating type sludge dryer. It is a schematic block diagram which shows 1st Embodiment of the indirect heating type | formula sludge dryer which concerns on this invention. It is a schematic block diagram which shows 2nd Embodiment of the indirect heating type | formula sludge dryer which concerns on this invention. It is a schematic block diagram which shows 3rd Embodiment of the indirect heating type sludge dryer which concerns on this invention.

  In order to understand the present invention, first, a drying test using a single conventional ditch type grooved drier (hereinafter referred to as “conventional device”) will be described.

  1 is a graph showing the results of a drying test in which a conventional machine having the structure shown in FIG. 1 is used to rotate the rotating shaft at different predetermined rotation speeds (low speed and high speed) and measure the sludge moisture content and evaporation rate in each area in the machine. Is shown in FIG.

The specifications of the conventional machine used in the test were a heat transfer area of about 10 m ² , a machine length of about 4 m, and a paddle diameter of 300 mm, and saturated steam of about 0.5 MPa was used as a heat medium. As a raw material, sewage sludge with a water content of about 80% was used by dehydration. The moisture content was measured by the method defined in the Sewage Sludge Test Method. The evaporation rate is a value obtained by dividing the amount of evaporated water per time calculated from the sludge moisture content and sludge supply amount at the inlet 6 and outlet 7 of the dryer by the heat transfer area of the dryer. . The rotational speed (low speed, high speed) of the rotating shaft is set such that the power consumption decreases by about 10% at low speed with respect to high speed.

  The evaporation rate shown in FIG. 3 is obtained by collecting sludge at a plurality of collection points in the dryer and dividing the heat transfer area calculated in proportion to the length between each collection point on the graph. (Plotted points are not shown), and the plotted values are indicated by straight lines.

  As can be seen from the graph of FIG. 3, in the conventional machine, the high moisture content zone on the inlet 6 side of the dryer (the range of the number of heat transfer blades up to the 10th) is the one where the heat transfer blade 5 is rotated at a low speed. But the evaporation rate is fast, the heat transfer area is used effectively. However, the lower the speed of rotation of the rotating shaft 4, the smaller the power consumption.

  On the other hand, as shown in the graph of FIG. 3, in the conventional machine, the evaporation speed is faster if the heat transfer blades are rotated at a high speed after the tenth heat transfer blade. However, at high speed rotation, power consumption increases.

  As can be seen from the transition of the moisture content of the dewatered sludge shown in the graph of FIG. 3, these phenomena are the preheating zones of the dewatered sludge up to the 10th heat transfer blade in the conventional machine, and Since the temperature is low and the viscosity is high, it is recognized that rotating the heat transfer blade at low speed is advantageous from the viewpoint of evaporation speed and low power consumption. On the other hand, in the graph of FIG. 3, since the temperature of the sludge rises and the viscosity decreases after the 10th heat transfer blade, the contact between the heat transfer blade and the sludge is higher when the heat transfer blade is rotated at high speed. It is considered that the evaporation rate is faster because the heat transfer effect by the.

  Further, in the conventional machine, the load applied when the heat transfer blade rotates is expected to be dominated by the load at a high moisture content and high viscosity location in the preheating zone on the inlet side. Therefore, it is considered that the load applied to the motor for rotationally driving the heat transfer blades is small even if the motor is rotated at high speed outside the preheating zone.

  The schematic diagram about the state of the sludge in the inside of the conventional machine in FIG. 4 is shown. In the conventional machine, referring to FIG. 1, the temperature detector (thermocouple) is placed in the trough 3 at the front position F (directly under the receiving port), the middle position M (the center in the longitudinal direction in the apparatus), and the rear position R (discharge port). As a result of measuring the temperature when the sludge was dried, the temperature at the front stage F was 60 ° C. or more and less than 100 ° C., the middle stage position Md was about 100 ° C., and the rear stage position R was 90 ° C. It was 120 ° C.

  In the conventional machine, the inside of the machine is roughly divided into four zones. From the receiving side, it is a preheating zone (less than 100 ° C), an evaporation zone (approximately 100 ° C), and a crushing zone (a zone where the clay is decomposed into granules). , Below 100.degree. C.), Finished zone (less than 100.degree. C. in the zone where re-evaporation occurs after granulation). However, if the residence time in the finishing zone is long, drying of the sludge proceeds, and if the sludge water content is less than 20%, the sludge temperature becomes 100 ° C. or higher.

  Based on the experimental result by the said conventional machine, embodiment of this invention is described below, referring FIGS. 5-7. The same or similar components are denoted by the same reference numerals throughout the drawings including the prior art.

  FIG. 5 is a schematic configuration view showing a first embodiment of the indirectly heated sludge dryer according to the present invention. The indirect heating type sludge dryer 1A of the first embodiment includes two dryers 100a and 100b. Each of the dryers 100a and 100b receives the sludge to be dried at the receiving ports 6a and 6b, and agitates the heat transfer blades 5a and 5b provided at intervals in the axial direction of the rotary shafts 4a and 4b. While transporting, heat and dry, and discharge from the discharge ports 7, 7.

  The inlet 6b of the downstream dryer 100b is connected to the outlet 7a of the upstream dryer 100a, and the sludge to be dried discharged from the upstream dryer 100a is disposed so as to be received by the downstream dryer 100b. Yes. In the illustrated example, each of the dryers 100a and 100b has one rotating shaft 4a and 4b, but a plurality of rotating shafts are arranged in parallel in each of the dryers 100a and 100b. A heat transfer blade can also be provided.

  Although details are not shown in FIG. 5, in the dryers 100a and 100b, as in the conventional example shown in FIG. 1, the heat medium is circulated through the hollows of the rotary shafts 4a and 4b and the heat transfer blades 5a and 5b. Thus, the sludge to be dried is indirectly heated by heat transfer, and an electric motor, a heat medium supply port, a heat medium discharge port, an exhaust fan, a heat transfer jacket, and the like that rotationally drive the rotating shaft can be provided.

  In the first embodiment of the present invention, the upstream dryer 100a corresponds to a high viscosity zone corresponding to a preheating zone. The rotational speed of the rotating shaft 4a of the dryer 100a is controlled so that the sludge to be dried is preheated to 60 ° C. or more and less than 100 ° C. and discharged from the discharge port 7a in the upstream dryer 100a.

  In the preheating zone, as already described in the conventional machine, in general, since the filling rate of the sludge to be treated is high, the viscosity is high and the temperature is low, the load (torque) applied by the rotation of the heat transfer blade is large. Therefore, the power consumption can be minimized by operating at a low rotational speed of the rotating shaft 4a. On the other hand, because it is a zone that performs preheating by heat transfer from the heat transfer blade to the sludge, it is not necessary to increase the rotation speed more than necessary and to quickly update the sludge on the surface of the heat transfer blade. However, the evaporation rate may be higher.

  In the first embodiment of the present invention, the downstream drier 100b corresponds to an evaporation zone, a crushing zone and a finishing zone. In the conventional machine, as can be seen from FIG. 4, from the middle stage to the latter stage, the sludge filling rate decreases due to drying, and in order to increase the number of times of contact with the heat transfer blade, increasing the rotation speed increases the evaporation rate. However, since the rotation speed in the preheating zone in the former stage is also increased simultaneously, the evaporation rate in the preheating zone in the former stage is decreased, and the power consumption is increased.

  Therefore, in the first embodiment of the present invention, the rotating shaft 4a of the upstream dryer 100a rotates at a lower speed than the rotating shaft 4b of the immediately downstream dryer 100b, in other words, the rotating shaft of the downstream dryer 100b. 4b is configured to rotate at a speed faster than the rotation shaft 4a of the upstream dryer 100a.

  With such a configuration, the upstream dryer 100a is used for the preheating zone, and the downstream dryer 100b is not affected by the high load of the high viscosity preheating zone, and the number of revolutions in the evaporation zone and the crushing zone is increased. It is possible to obtain the maximum evaporation amount according to the shape of sludge in each machine while suppressing the power consumption. The rotational speed of the rotating shafts 4a and 4b can be adjusted by controlling the number of rotations of a motor (control motor) (not shown) that rotationally drives the rotating shafts 4a and 4b.

  Each of the dryers 100a, 100b can be equipped with a temperature detector T for detecting the in-machine temperature. The temperature detector T can be disposed, for example, in the vicinity of the inlets 6a and 6b, in the vicinity of the outlets 7a and 7b, and at an intermediate position between the inlet and the outlet. Is not limited. The temperature detector T is, for example, a thermocouple, and can be installed on the inner surface of the trough 3 at a position where the sludge to be dried can come in contact with.

  As described above, in the conventional machine, the sludge to be dried is kept at approximately 100 ° C. in the evaporation zone where drying is progressing, so the preheating zone upstream of the evaporation zone is in a state of high viscosity at less than 100 ° C. From the preheating zone to the evaporation zone, the drying progresses gradually, and when the temperature changes again due to the crushing, the drying progresses to a certain extent and the viscosity decreases. However, if the water content is less than 20% in the preheating zone, the temperature becomes 100 ° C. or more.

  Therefore, in the first embodiment of the present invention, it is possible to control the number of rotations of the rotating shafts 4a and 4b according to the detection result of the temperature detector T provided, for example, in the vicinity of the outlet 7b. In this case, if the purpose is to discharge the sludge to be dried from the discharge port 7b with a water content lower than 20% (a state close to absolute drying), the temperature is set to 100 ° C. or higher. For the purpose of discharging from the discharge port 7 in a granular form containing some moisture at about 40%, the set temperature is less than 100 ° C., and the temperature detector T provided in the vicinity of the discharge port 7b is set to the set temperature. The number of rotations of the rotating shafts 4a and 4b is controlled.

  Next, a second embodiment of the indirectly heated sludge dryer according to the present invention will be described with reference to FIG.

  In the indirect heating type sludge dryer 1B of the second embodiment, three dryers 100a, 100b and 100c are arranged in upper and lower three stages, and the outlet 7 of the uppermost stream (uppermost) dryer 100a is directly connected The inlet 6b of the second-stage dryer 100b at the downstream (directly lower stage) is connected, and the inlet of the third-stage dryer 100c at the most downstream (lowermost stage) is connected to the outlet 7b of the second-stage dryer 100b. 6c is connected.

  In the second embodiment of the illustrated example, the conveyance direction in the machine is reversed in the upper and lower stages, but the invention is not limited thereto, for example, the conveyance direction is the same direction and the reception port 6a (6b) from the discharge port 7a (7b, 7c) , 6c) can also be provided with a tilting chute (not shown).

  In the second embodiment, the rotating shaft 4a of the most upstream (uppermost) dryer 100a is configured to rotate at a lower speed than the rotating shaft 4b of the immediately downstream (second-stage) dryer 100b. The rotary shaft 4a of the second stage dryer 100b is configured to rotate at a lower speed than the rotary shaft 4c of the dryer 100c immediately downstream thereof (third stage).

  Each of the dryers 100a, 100b, and 100c is provided with a height-adjustable weir portion 20 for adjusting the amount of dried sludge discharged from the discharge ports 7a, 7b, and 7c.

  As in the second embodiment, by setting the dryer in multiple stages and providing the weir portion 20, it is possible to adjust the to-be-dried sludge filling rate of the second and lowermost stages (third stage), compared with the conventional machine. As a result, the contact frequency between the heat transfer blades 5 and the sludge becomes higher, and the evaporation rate becomes higher than that of the conventional machine. As a result, the average evaporation rate of the entire dryer (the entire multi-stage dryer) compared to the conventional machine is faster for the indirect heating sludge dryer of the present invention. Since it can be made smaller than the conventional machine, the apparatus can be made compact, and the cost can be reduced.

  Next, a third embodiment of the indirectly heated sludge dryer according to the present invention will be described with reference to FIG.

  The indirectly heated sludge dryer 1C according to the third embodiment is a modification of the second embodiment, and is located downstream of the middle portion between the inlet 6a and the outlet 7a of the uppermost stream (uppermost) dryer 100a. A middle portion between the inlet 6b and the outlet 7b of the (second-stage) dryer 100b is provided with a bypass line 21 for bypassing the sludge to be dried, and an opening / closing means 22 for opening / closing the bypass line 21; Furthermore, from the intermediate part between the inlet 6b and the outlet 7b of the second stage dryer 100b to the intermediate part between the inlet 6c and the outlet 7c of the next downstream (third stage) dryer 100c. A bypass line 23 for bypassing sludge and an opening / closing means 24 for opening / closing the bypass line 23 are provided. For example, a slide gate or a rotary valve can be employed as the opening / closing means 22, 24.

  By providing such bypass lines 21 and 23, it is possible to discharge part or most of the inside of the dryers 100a, 100b and 100c to the dryer (downstream) downstream. Thereby, when the amount of input sludge is small or when the water content of dehydrated sludge to be input is low, the water content of the dried sludge discharged can be adjusted or kept constant by adjusting the heat transfer area. .

  The present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the present invention. In the said embodiment, although the dryer showed 2 or 3 embodiment, you may provide 4 or more dryers.

1A Indirect heating sludge dryer 1B Indirect heating sludge dryer 1C Indirect heating sludge dryer 2 Heat transfer jacket 3 Trough 4, 4a, 4b, 4c Rotating shaft 5, 5a, 5b, 5c Heat transfer blades 6, 6a, 6b, 6c Inlet 7, 7a, 7b, 7c Discharge port 8 Heat medium supply port 9 Heat medium discharge port 10 Transmission belt 11 Electric motor 12 Carrier gas inlet 13 Exhaust port 14 Heat medium supply port for jacket 15 Heat medium discharge port for jacket DESCRIPTION OF SYMBOLS 20 heat part 21 bypass line 22 opening-and-closing means 23 bypass line 24 opening-and-closing means 100 grooved stirring dryer 100a dryer 100b dryer 100c dryer T temperature detector

Claims (5)

A plurality of dryers that receive the sludge to be dried at the receiving port, are heated and dried while being stirred and conveyed by a plurality of heat transfer blades provided at intervals in the axial direction of the rotating shaft, and discharged from the discharge port. Prepared,
The drying sludge discharged from the upstream dryer is arranged so as to be sequentially received by the downstream dryer, and the rotational axis of the uppermost dryer is lower than the rotational axis of the dryer immediately downstream. An indirect heating type sludge drying apparatus characterized by being controlled to rotate. A temperature detector for detecting an in-machine temperature of each of the plurality of dryers;
The rotation speed of the rotating shaft of each of the plurality of dryers is set based on the detection value of the temperature detector, The indirectly heated sludge drying device according to claim 1.   The rotational speed of the rotary shaft of the dryer in the most upstream position so that the sludge to be dried is preheated to 60 ° C. or more and less than 100 ° C. in the dryer most upstream and discharged from the outlet of the dryer in the uppermost flow The indirectly heated sludge dryer according to claim 1 or 2, characterized in that A bypass line for bypassing the sludge to be dried from an intermediate part between the inlet and outlet of the dryer upstream to an intermediate part between the inlet and outlet of the dryer next downstream;
Opening and closing means for opening and closing the bypass line;
The indirect heating sludge drying apparatus according to any one of claims 1 to 3, further comprising:   5. The apparatus according to any one of claims 1 to 4, wherein each of the plurality of dryers further includes a height adjustable weir for adjusting the amount of sludge to be dried which is discharged from the discharge port. The indirect heating type sludge drying apparatus as described.