JP4191442B2 - Sludge freeze / thaw tank - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
Recently, attention has been paid to the effect of freezing and thawing before filtering and dewatering wastewater sludge, sewage sludge, septic tank sludge, human waste, or sludge discharged in the treatment of industrial and landfill wastewater. became. The present invention relates to a sludge freezing / thawing tank used for the sludge freezing / thawing treatment.
[0002]
[Prior art]
Since the sludge usually contains a solid component in a large amount of water, several solid-liquid separation methods such as sedimentation, filtration, and dehydration are appropriately selected and combined, and a large amount of solid component is obtained. Water is removed sequentially, concentrated and dehydrated, and the final solids are composted or finally disposed of, such as landfill and incineration. In many cases, the concentrated sludge is filtered and dehydrated using a pressure filter or the like. However, these sludges have extremely poor filtration / dehydration properties, and a long time is required for the filtration / dehydration treatment.
[0003]
As one means for solving the above-mentioned problems, a freezing / thawing treatment method in which sludge is frozen and thawed in advance, followed by filtration and dehydration has been proposed, and its effect has been recognized. Sludge to be filtered and dewatered is subjected to freezing and thawing treatment, causing sludge particles to aggregate and coarsen, and water retained in the sludge to be dehydrated, followed by filtration and dewatering. Easy to operate. Freezing and thawing treatment is usually performed using a freezing and thawing tank, and a heat transfer tube is provided in the freezing and thawing tank for rapid processing, and as a heat medium for cooling and heating the sludge introduced into the tank. For example, an aqueous solution of calcium chloride, sodium chloride, ethylene glycol or the like is used as brine. When the sludge is frozen, the brine cooled by the refrigerator is called cold brine and flows into the heat transfer tube in the tank. On the other hand, when the frozen brine is thawed, the brine heated with warm water is called warm brine and is alternately flown into the heat transfer tube in the tank to freeze and thaw the sludge in the tank, and batch processing is performed.
[0004]
A basic example of a sludge dewatering system using freezing and thawing treatment is shown in the flow sheet of FIG. According to this example, the raw water 31 containing sludge is guided to the settling basin 32 and the sludge is settled and separated, and then the settled sludge is fed into the concentration tank 33 and separated and concentrated. The concentrated sludge is guided to the freezing / thawing tank 34, and cold brine is allowed to flow through the heat transfer tube 36 in the tank for freezing. Then, the sludge is switched to warm brine for thawing, and the supernatant water 37 is separated and concentrated. The improved sludge is sent to the pressure filter 35 and pressurized and dehydrated.
[0005]
[Problems to be solved by the invention]
The effect of freezing and thawing treatment in sludge filtration and dehydration operations is great, but the time required for the sludge freezing and thawing treatment is long, resulting in a problem of increased equipment and operating costs. To finish the sludge freezing in a short time, it is necessary to reduce the pitch of the heat transfer tubes and increase the number of heat transfer tubes. As a result, the equipment cost, the amount of brine used, the heat loss and the required power for circulation increase. The present invention has been completed as a result of earnestly researching the means for reducing the equipment cost and the operating cost while the operation is completed in a short time in order to effectively execute the freezing / thawing process.
[0006]
[Means for Solving the Problems]
As a means for solving the above-mentioned problems, the present invention is a freezing / thawing tank used for freezing / thawing treatment performed prior to sludge filtration / dehydration, and is bent in a plane passing through the central axis . A sludge freezing / thawing tank is used, in which finned heat transfer tubes formed of a serpentine tube or U-shaped tube and fins mounted in the plane are arranged in parallel or in the same plane.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be specifically described with reference to the drawings. FIG. 1 is a transverse sectional view showing an example of the shape and arrangement of heat transfer tubes in a sludge freezing / thawing tank according to the present invention, and FIG. 2 is a longitudinal sectional view thereof.
[0008]
In the present invention, the sludge to be dehydrated by freezing and thawing may be organic or inorganic, and may be raw sludge that has not been concentrated, or sludge that has been concentrated by the method described above. The upper shape of the freezing / thawing tank may be cylindrical or rectangular, but the bottom is valley-shaped or cone-shaped so that the freezing / thawing tank sludge can be easily discharged. Considering sludge discharge, heat transfer tube arrangement, and manufacturing costs, the upper part should be a square tube and the bottom part should be a valley. A heat transfer tube 1 with fins 2 for flowing cold brine or warm brine is attached in the tank to freeze and thaw sludge. Depending on the nature and components of the frozen sludge, the tank body is usually made of carbon steel to prevent corrosion on the surface, as well as for insulation and cooling, and as a cushioning material to prevent damage to the tank due to volume expansion when the sludge freezes. Adhere foam sponge rubber etc. on the inner surface of the tank. The heat transfer tube 1 is preferably a circular tube because a large external pressure is applied by volume expansion of sludge due to freezing, and a stainless steel tube, a molten aluminum plated tube, or the like is used.
[0009]
The heat transfer tube 1 uses a serpentine tube or a U-shaped tube (helibone type heat exchanger) bent in a zigzag shape in order to efficiently store in the tank and increase the flow rate in the tube to increase the heat transfer coefficient. In order to facilitate the discharge of sludge, the heat transfer tube has a straight pipe portion in the vertical direction, the fin 2 is a simple flat plate, and both diametrical sides of the heat transfer tube 1 along the axial direction, The fins 2 are attached so as to be parallel to or flush with each other.
[0010]
The sludge that is frozen and thawed is sticky, so a few horizontal protrusions can cause a bridge to form when sludge is discharged, preventing sludge from being completely discharged, or air being mixed when sludge is thrown in. There is a risk that the sludge will not be uniformly filled in the tank. Therefore, when the heat transfer tube 1 is a serpentine tube or a U-shaped tube, the heat transfer tubes 1 are arranged in a direction A that is the same or parallel to the bending direction, and the fin 2 is also the center of the (attached) heat transfer tube 1. It is desired to be mounted in the same plane A as the bending direction. You may arrange | position the heat exchanger tube comprised by one snake tube over several parallel rows according to the above. It is better not to attach in the direction where the fin and the heat transfer tube axis direction intersect, or in the direction where planes including the fin intersect each other. It is not preferable from the viewpoint of preventing sludge from adhering and facilitating feeding, discharging and cleaning.
[0011]
The brine temperature during cooling is generally −10 to −20 ° C., and depending on the brine temperature, the cooling surface area including the fin surface is preferably 40 to 50 m ² per ton of sludge.
[0012]
【Example】
In order to understand the present invention in detail, the conventional freezing / thawing tank will be described in detail with reference to an example in which the freezing / thawing tank according to the present invention is modified. It is not limited.
[0013]
Conventional Example and Example A conventional freezing and thawing tank is a SUS304TP having an inner diameter of about 120 cm, an inner height of about 150 cm, and a V-shaped carbon steel square tank with an outer diameter of 27.6 mm. Using tubes, the ends are U-shaped and bent in a zigzag manner 15 times in the same plane at a pitch of about 5.5 cm to form 16 serpentine tubular heat transfer tubes, which are attached in parallel at intervals of about 4.7 cm. It was. The heat transfer area was about 26 m ² .
[0014]
The conventional heat transfer tube of the freezing / thawing tank was manufactured by replacing and attaching a finned heat transfer tube having the same shape as illustrated in FIGS. 1 and 2 to obtain the freezing / thawing tank according to the present invention. More specifically, a SUS304TP tube having an outer diameter of 27.6 mm is used as the heat transfer tube, and the end is U-shaped and bent in a zigzag manner seven times in the same plane at a pitch of about 11 cm. The SUS304 plate having a width of 3.6 cm was used as a fin and welded in the same direction as the bending direction on both sides of the center line of the straight tube portion of the heat transfer tube. The 18 heat transfer tubes were arranged in parallel at intervals of about 4.7 cm. The heat transfer area including the surface of the fin was about 30 m ² .
[0015]
Both of the two types of freeze / thaw tanks were fed with 0.6 tons of sludge and frozen in -15 ° C brine. As a result, the required brine amount is about ½ and the circulation power of the brine is about ½ compared to the conventional freezing / thawing tank, and the time required for freezing under the same conditions is about 10% compared to the conventional tank. It has been shortened, and sludge can be easily charged, discharged and cleaned, improving work efficiency.
[0016]
【The invention's effect】
By effectively attaching fins to the heat transfer tube using the present invention, the number of heat transfer tubes is reduced to about 1/2 compared with the conventional sludge freezing and thawing tank, and the brine to be used accordingly. On the contrary, the amount of treated sludge that can be filled in the tank can be increased by about 5% by volume. Since the total required length of the heat transfer tube can be shortened, the brine flow rate in the tube can be increased to improve the heat transfer rate, and further the time required for the freezing / thawing operation can be shortened. In addition, since the curvature of the U vent can be increased, manufacturing restrictions are eased. In addition, when a flat plate is used for the fin and attachment is performed in one direction, and the heat transfer tube is a U-shaped tube or a serpentine tube, the sludge can be easily filled / discharged and cleaned by being attached in accordance with the bending direction.
[Brief description of the drawings]
FIG. 1 is a transverse sectional view showing an example of the shape and arrangement of heat transfer tubes in a sludge freezing / thawing tank according to the present invention. FIG. 2 is a longitudinal sectional view of the same. FIG. 3 is a freezing / thawing treatment method. Schematic flow sheet exemplifying conventional sludge treatment using slag
1: Heat transfer tube 2: Fin A: The same plane as the bending direction through the center of the heat transfer tube 31: Raw water containing sludge 32: Sedimentation basin 33: Concentration tank 34: Freezing / thawing tank 35: Filtration / dehydrator (pressure filtration 36) Heat transfer tube 37: Supernate water

Claims (1)

Freezing and thawing tank used for freezing and thawing treatment prior to sludge filtration and dewatering, and a serpentine tube or U-shaped tube bent in a plane passing through the central axis, and the plane A sludge freezing and thawing tank, characterized in that finned heat transfer tubes configured with attached fins are arranged in parallel or in the same plane in the tank.

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