SE527884C2 - Process for liquid expulsion from suspensions - Google Patents

Abstract

This invention relates to a procedure concerning dewatering of suspensions, in particular, suspensions with a relatively low concentration of organic matter or having a dry solid content of less than 15 %. A distinguishing feature of this invention is that dewatering promoting agents are mixed simultaneously with the suspension as thickening occurs. Examples of materials that increases the concentration of organic matter are among others sawdust, synthetic materials that preferably consist of pulverous polyurethane, ground peat or alternatively ground bark. The weight proportion of the additives amounts to at least 5 weight­% and preferably to at least 10 weight-% of the total weight of the organic matter. The simultaneous dewatering and mixing is performed with the aid of known dewatering mechanisms. An example of this is the water extracting screw. After the partial dewatering the material is transferred to a press for further dewatering to solid contents above 45 %.

Description

527 884 Z A disadvantage of many devices is that they expose the material to excessive compression. * If can damage the material, and parts of the machine equipment itself.

As far as the equipment is concerned, among other things. wires and presses result from excessive mechanical pressures.

Wear increases and the wire or fi lten can even give off. The press rollers can also be damaged. In addition, more energy is required for each increase in working pressure. Secondly, a higher energy output has a negative effect on the external million because it usually requires the input of electrical energy, which in turn is generated by burning, among other things. fossil fuels, which i.a. generates carbon dioxide.

Vidtörtjicknmgwslam fi inmmngwerkicenui fi xgârdetwånstttömmammaterida or the dry matter content exceeds about 25% (rare). Another disadvantage of centrifuges is their relatively low capacity in cleaning with high investment costs.

Screw presses give relatively high dry matter contents, but have the disadvantage that the liquid, which is pressed out, contains much of the material to be thickened. This is due to PW's WW5 * having walls which are relatively large or large slots.

The usual type of spinner is a small spoon material. In other words, the filtrate is relatively pure. However, a significant disadvantage of the drums is the low dry matter content they give. Even after supplementing the filter with press rollers, a very high tonnage content is not achieved.

Description of the invention In accordance with the invention, the suspension to be dewatered is mixed with a solid (hereinafter referred to as an additive) in particulate form. of polymers such as low-density polyurethane or with a bulk density significantly lower than 1 kg / dm ”. Polyurethane is composed of uric acid esters (general formula RQCONH;). The ethyl ester form is usually called urethane. In addition, within the scope of the invention, regenerated cellulose (WETIEK-shntf), sawdust, starch, straw plants such as straw and straw can also be added. Peat, bark and finely divided straw plants can also be added. According to a preferred embodiment of the invention, the additive should be grated or ground into relatively small particles, possibly before partitioning by means of fractionation (sieving) or enrichment of the fine material of the additive.

The intended particle size of the additive is most safely obtained by sieving in one or more steps.

Thus, kanda saddle devices such as shaking sieve, vibration sieve or so-called can be used. wind visibility. oo 0 oo nano o o o oo n c o O I I u n o a u c: noe u o U o o o o I 0 role o o nu non nous Oo o IQ I ul O lo I I OOIIO OI I 527 884 3 The weight percentage of additives can vary within a large range. From an economic point of view, however, the lowest possible proportion of additives is tripled. However, for ß e fi ekt, a weight percentage of at least 5% and preferably more than 10% by weight is required.

In some cases, it may be advantageous to add briquettes, granules or pellets after the thickening of the cake. The method described in, among other things, patent application SE 9904313-5 can be used.

An essential and characteristic part of the invention is that the mixing of the additives described above takes place in an integrated step with simultaneous thickening. This refers to fi liquefaction of liquids which have a relatively low concentration (dry content) of substance, e.g. sludge.

Thus, it is intended to increase suspensions with concentrations of solid material between 0.5% and 15%.

The combination of blending and thickening steps can be performed using known machines. Thus, screw cores with a core or cores without a core can be used, which transport liquid and substance by means of a spiral. In principle, the screw or spiral is surrounded by a tube with openings on its mart surface. The outside or inside of the mantle surface can be covered with a plastic or steel wire. Additional alternatives are dewaterers with rotating paddles or sticks attached to a single-drum shaft. »_ ~. . * LLJJ l fl ll ': LSU ~ _ Fiber sludge in suspension form bio from a paper belt bio-purification stage was fed to a screw drain whose surface had holes with a diameter of 0.2 mm. Water was drained via the mantle surface holes. This results in an increase in concentration from 1.3% to 12.6%.

The filtrate, which flowed out through the holes of the screw press, was found to contain an undesired concentration of dry slurry. Thus, the filtrate contained 3 g of dry powder per liter of liquid.

The sludge in the screw press Rårtjoekade was passed on to a press, which is described in more detail in patent specification 0004557-2. After pressing, a dewatering was obtained which resulted in a dry content of 17.6%. In the form of a suspension in Fiberslam in suspension form, a bio-purification step was carried out, which in the example of thickening according to the known standard single-wave water had a mantle surface with a diameter of 0.2 mm. At the inlet of the screw waterer, spin from a sawmill 527 884 * was added in The sawdust was an ction alction of screened sawdust. The sieve sawdust had a wild share of 64% fi n al- alrtion, which by definition passed a sieve with a hole size of 2 mm. The sawdust had a customs content of 43%.

At fi irsolcet, a surprisingly good mixture was obtained between spin and fi berslam suspension. Even more surprising was the effective thickening the mixture of sawdust resulted in. Thus, a dry matter content of 24% was obtained on samples taken from the outlet of the screw drain. The weight content of sawdust in sack samples taken during six hours was found to be at an average value of 41% and with a spread of 3% by weight. This means that during the initial stage inside the screw drain, the dry matter content was temporarily about 14%. In other words, the dry matter content was increased from about 14% to 24% depending on the dewatering property as such. This observation was confirmed by the fact that the filtrate during analysis was found to contain only 0.8 grams of dry matter per liter of liquid. Despite a relatively high dry matter content (24%) in to the press, a surprisingly large fl wasted dewatering was obtained without the press. Due to the relatively good water fl fate fi without the press, a dry matter content as high as 51.2% was obtained.

Advantages Since it is possible to achieve higher dry matter numbers with the help of the invention, energy can be saved. In addition, any form of energy saving results in a better environment as the use of energy-generating fossil fuels can be reduced. Among other things, carbon dioxide emissions can be reduced in a significant way. Theoretically, a reduction of every other by 1 m ”per: an empty sam means a reduction of romioxiaham (cos) one said 200 kg. According to the invention, the water content can be reduced by about 3 m: (tonnes) perton dry tank sludge In other words, the invention results in a reduction of environmentally damaging CO; with about 600 kg pertons sludge Barai Sweden produces ea200,000 dry tank sludge per year with a water content of 1 million m3 (tons). With the application of the invention, it is not possible to reduce CO-z wood emissions by just over 100,000 tonnes per year.

Claims (1)

A process for liquid expulsion from suspensions with a relatively low concentration of organic material, such as sludge from sewage treatment plants or sludge from pulp and paper mills, characterized in that at the same time as the liquid expulsion in a dewatering means comprising a movable machine part such as a screw, sticks or paddles are added to a dry matter raising substance in particulate form, which substance is then mixed with the suspension, after which the mixture is passed to a drainage step which comprises a press. Process according to Claim 1, characterized in that the blank in particulate form consists of sawdust. Process according to Claim 1, characterized in that the substance in the particulate form consists of synthetic material and preferably contains polyurethane. Process according to Claim 1, characterized in that the substance in the particulate form consists of bark. Process according to Claim 1, characterized in that the substance in particulate form consists of peat. Process according to Claim 1, characterized in that the substance in particulate form consists of the tube. Process according to Claim 1, characterized in that the substance in particulate form consists of straw. Method according to one or more of Claims 1 to 7, characterized in that sawdust, synthetic material, bark, pipes, straw and / or peat in particulate form are optionally mixed with one another. Process according to Claims 1 to 7, characterized in that the proportion by weight of the substance in the panicle form amounts to more than 10% by weight of the total weight of organic material.