JPH0128608B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a felt cloth suitable for being attached to a belt press type dehydrator to dewater various types of sludge, such as digested and washed sludge, excess sludge, and raw sludge. As a device for dewatering various types of sludge, a pair of endlessly connected belt-like cloths are wound around a number of rollers and moved in opposite directions, and the sludge is sandwiched between the belt-like cloths and squeezed. A belt press type dehydrator for dewatering is known, and conventionally, a monofilament fabric made of synthetic fibers has been used as the above-mentioned cloth. However, recent belt press type dehydrators are equipped with a mechanism that applies high tension to the cloth, a pressure belt mechanism that presses another belt on the outside of the cloth, or a filter press mechanism, and are equipped with a mechanism that applies high tension to the cloth, a pressure belt mechanism that presses another belt on the outside of the cloth, or ^a filter press mechanism. As the squeezing process has come to be carried out at high pressures, the above-mentioned monofilament woven fabrics suffer from the disadvantages that the fabrics are clogged by the high-pressure sludge, resulting in clogging, and that the cake cannot be peeled off. It was hot. In order to eliminate this drawback, attempts have been made to use thin monofilament yarns in the warp and weft of the above-mentioned woven fabric to densify the structure and smooth the surface, but in this case,
There were problems such as poor dewatering in the gravity dewatering section and sludge seeping out (side leak). On the other hand, in order to improve the peeling of the cake, one of the pair of cloths is a synthetic fiber fabric, and the other is a textile base fabric overlaid with a fine denier polyamide fiber web, and the felt is bonded by needling. It has been proposed to use cloth (see Japanese Unexamined Patent Publication No. 103797/1983). In this case, negative pressure is generated inside the cake and felt cloth immediately after passing through the nip point of the rotating drum and pressing roller, but of these negative pressures, the negative pressure inside the cake is the negative pressure inside the felt cloth. , a portion of the liquid is called back from the felt cloth side to the cake side by the above-mentioned negative pressure and capillary action and moves to the boundary between the two, helping to peel off the cake. However, as shown in FIG. 1, the conventional felt cloth is made by needling a base fabric 3 woven using warp yarns 1 and weft yarns 2 and a web 4 made of one type of fine denier polyamide fiber. Since the upper felt part 6 made of only polyamide fibers is formed on the base fabric layer part 5 made of the base fabric 1 and polyamide fibers, the base fabric layer part below the upper felt part 6 is 5 has a denser structure, and the filtration is controlled by this base fabric layer portion 5. Therefore, the solid content in the sludge accumulates in the upper felt portion 6, which has a relatively coarse structure, and clogging progresses. In addition, since the back surface of the felt cloth, that is, the back surface of the base fabric layer portion 5, is formed relatively smooth and its unevenness is small, when a plain roller with a smooth surface is used as the pressing roller, the back surface of the felt cloth is The liquid adhered closely to the surface of the roller, and there was no place for the liquid to escape, resulting in an inconvenience in that excessive water was recalled and the moisture content of the cake increased. By improving the conventional felt cloth described above, this invention has good cake removal properties due to liquid recall, and also prevents clogging when sludge is dehydrated at a high pressure of 10 kg/cm ² or more. This belt has a low flow rate, allows liquid to flow out smoothly even when using a smooth-surfaced squeezing roller, has good dimensional stability, and is effective even on sludge that is highly viscous and difficult to filter, such as excess sludge. The present invention provides felt cloth for press-type dehydrators. That is, the present invention provides a felt cloth for a belt press type dehydrator, which is formed by overlaying a thermoplastic synthetic fiber web on a base fabric made of filament yarn of synthetic fibers and needling, in which the base fabric has warp or weft yarns. It is woven using synthetic monofilament yarn on one side and synthetic monofilament twisted yarn or multifilament yarn on the other, and the thermoplastic synthetic fiber web is layered in order on the base fabric. It consists of two types: a thick denier thermoplastic synthetic fiber web and a fine denier thermoplastic synthetic fiber web. This is a felt cloth for belt press type dehydrators, which is characterized by being formed into a texture. An embodiment of the present invention will be explained below with reference to FIG. A double weave base fabric 13 is woven by the warp yarns 11 and the weft yarns 12, and a comparatively thick denier synthetic fiber web 14 is layered on this base fabric 13 and bonded by needling. A comparatively fine denier synthetic fiber web 15 is layered on top and bonded by needling again, and by these entanglements, a base fabric layer portion 16, a lower layer felt portion 17 and an upper layer felt portion 18 are formed in order from the bottom. At this time, the texture is formed densely in the upper layer felt portion 18 and coarsely in the base fabric layer portion 16, and the voids between the fibers are formed in the upper layer felt portion 1.
8. The lower layer felt portion 17 and the base fabric layer portion 16 are enlarged in this order, and the sludge reaches the upper layer felt portion 1.
8 and passed through the upper felt portion 18 is prevented from being trapped by the lower felt portion 17 and the base fabric layer portion 16. Therefore, most of the solids that have passed through the upper felt portion 18 pass through the lower felt portion 17 and the base fabric layer portion 16 together with the liquid, and as a result, the solids accumulate in these portions and cause eye damage. No clogging occurs. And the upper layer felt part 18
When clogging occurs, solid matter can be removed by washing and restoration can be easily performed. Furthermore, the presence of the upper felt portion 18 and the lower felt portion 17 provides a calling action similar to that of conventional felt cloth, so that the cake can be easily peeled off. Note that by using polyamide fibers with good hydrophilicity as the synthetic fibers constituting the upper layer felt portion 18, the cake releasability can be further improved. The above base fabric 13 has warp 11 or weft 12
It is woven into a relatively coarse net by using monofilament yarns made of synthetic fibers on one side and twisted yarns of monofilament yarns or multifilament yarns made of synthetic fibers on the other side. In particular, it is preferable to use synthetic fiber monofilament yarn with a relatively thick denier for the weft yarn 12 and to use a relatively thin monofilament twisted yarn for the warp yarn 11. This increases the rigidity of the base fabric 13 and increases the stiffness during use. In addition to withstanding tension and maintaining good dimensional stability, the base fabric layer portion 16 is made relatively coarse to facilitate the passage of liquid, and the back surface of the felt cloth is made to have large irregularities to facilitate contact with the squeezing roller. Prevents adhesion,
Moreover, the upper thick denier synthetic fiber web 14
It is possible to strengthen the interlacing bond with the needle and prevent breakage of the needle during needling. On the other hand, when monofilament yarn is not used, base fabric 1
3) lacks rigidity, lacks dimensional stability, expands in the length direction and contracts in the width direction during use, causing fluctuations in dehydration conditions, and furthermore, the back surface of the felt cloth becomes smooth, making the surface of the squeezing roller difficult. On the other hand, when only monofilament yarn is used, synthetic fiber web 1
The bonding force with 4 is weakened, and the needle is more likely to break during needling. Note that by using filament yarns of polyester fibers for the warp yarns 11 and weft yarns 12, the dimensional stability of the felt cloth can be further improved. As explained above, the present invention uses monofilament yarns made of synthetic fibers for the warp or weft of the base fabric, and uses two yarns of different thickness for the synthetic fiber web.
Since it is formed into a dense structure with an upper layer felt part using different types of synthetic fiber webs, it has good peelability of the cake due to the liquid recall effect, and it can be dehydrated at a high pressure of 10 kg/cm ² or more. It is less prone to clogging and has excellent dimensional stability, and the liquid flows out smoothly even when using a squeezing roller with a smooth surface. Therefore, it is also used for dewatering highly viscous and difficult-to-pass sludge with small particle size, concentration of 2.5% or less, and crude fiber content of 5% or less, such as digested and washed sludge, excess sludge, raw sludge, and putrid sludge. be able to. In addition, it goes without saying that it can be used for only one of a pair of cloths or for both. Next, a more specific explanation will be given using an experimental example. Experimental Example Three types of fabrics, Example 1, Comparative Example 1, and Comparative Example 2, shown in Table 1 below were prepared. however,
In Table 1, "mono" in the warp and weft columns refers to monofilament yarn, and "multi"
indicate multifilament yarns, respectively. Also,
The thickness of the monofilament yarn is shown in diameter (mm), and the thickness of the multifilament yarn is shown in denier (d). Incidentally, in Example 1, the back surface was burnt and treated with resin, and the base fabric of Comparative Example 1 was treated with resin.

【table】

[Table] A pair of each of the fabrics of Example 1, Comparative Example 1, and Comparative Example 2 was attached to a belt press type dehydrator, and Experiment 1 and Experiment 2 were conducted under the conditions shown in Table 2 below. Note that all rollers other than the drive roller were plain rollers with smooth surfaces.

[Table] The results of Experiment 1 and Experiment 2 are shown in Table 3 and Table 4, respectively. However, the unit of air permeability is cc/min/ ^cm2 .

【table】

[Table] Next, the above Example 1, Comparative Example 1 and Comparative Example 2
Experiment 3 was conducted on the cloth under the conditions shown in Table 5 below. The results are shown in Table 6.

【table】

【table】

[Table] As can be seen from the table above, the fabric of Comparative Example 1 was
If the squeezing roller is a plain roller, there is no place for the liquid to escape and the liquid will not be discharged sufficiently.
When the pressure is removed, a large amount of moisture is recalled, resulting in a high moisture content of the dehydrated cake. On the other hand, in Example 1, the liquid was discharged smoothly, so an appropriate amount of water was recalled, and a cake with good peelability and a low water content was obtained. This means that
It shows that the rough base fabric layer portion and the lower felt portion act as a liquid drainage path. In addition, when dehydration is performed at a pressure of about 10 Kg/cm ² , Comparative Example 2
The liquid will bleed through the cloth, making it unusable. In addition, the fabric of Comparative Example 1 caused a large amount of clogging, especially in the dense base fabric part, and this clogging was not cleared even by washing.
Air permeability is extremely reduced. Although the felt cloth of Example 1 was slightly clogged in the upper felt portion, it was easily restored by washing.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional felt cloth, and FIG. 2 is a sectional view of an embodiment of the present invention. 11: warp, 12: weft, 13: base fabric, 1
4: Thick denier thermoplastic synthetic fiber web, 1
5: Fine denier thermoplastic synthetic fiber web, 1
6: Base fabric layer part, 17: Lower layer felt part, 1
8: Upper layer felt part.

Claims (1)

[Claims] 1. In a felt cloth for a belt press type dehydrator, which is formed by layering a thermoplastic synthetic fiber web on a base fabric made of synthetic filament yarn and needling, the above base fabric is synthesized in either the warp or the weft. A thick denier thermoplastic fabric, which is woven using monofilament yarns of fibers and twisted yarns of monofilament yarns or multifilament yarns of synthetic fibers on the other side, and the thermoplastic synthetic fiber web is layered in order on the base fabric. It consists of two types: a synthetic fiber web and a fine denier thermoplastic synthetic fiber web, and the upper layer felt portion made of the fine denier thermoplastic synthetic fiber web is formed into a denser structure than the base fabric layer portion containing the above-mentioned base fabric. A felt cloth for belt press type dehydrators.