SE524263C2 - Solid fuel production from mixture of sludge and combustible material, comprises impregnating solid fuel with hydrophobic material - Google Patents

Abstract

A solid fuel product is impregnated with at least one hydrophobic material. The production of a fuel in granular, pellet or briquette form, uses a mixture of sludge obtained from a sewage works or industrial purification plant, with one or more combustible materials such as sawdust, peat, bark, paper pulp and/or lignin. The solid fuel is impregnated with one or more hydrophobic materials, e.g. tallow oil, resin oil, paraffin, waxes or rape seed oil.

Description

524 263 z When evaporating water from a mixture of sludge and bio-oil, it has proved difficult to maintain an even temperature in the mixture due to a thickening being obtained, which substantially complicates the stirring. In addition, it has been shown to offer significant problems to remove excess bio-oil with known pressing technology.

DESCRIPTION OF THE INVENTION Technical solution The invention is preferably used for the manufacture of granules, pellets or briquettes which contain sludge from municipal and / or industrial treatment plants. The sludge must have a dry matter content of at least 15%. Such sludge is preferably mixed with materials such as biofuels, which in mixture with sludge can be converted into, for example, granules. Examples of materials include peat, wood shavings, bark and fi bristles from lignocellulosic materials or only wood lignin (obtained as a residual product after digestion or hydrolysis of lignocellulosic materials). After mixing with such a component, the common dry matter content should exceed 30% and preferably be higher than 35%. To increase the fuel value, rapeseed oil, paraffin, resin and / or pine oil, which are added by the process according to the invention, can be advantageously added.

The included material should preferably be reduced to a relatively easy-to-handle size. According to the invention, the size of individual particles should be reduced so that the maximum size can pass a sieve with a hole diameter of 5 mm and preferably less than 3 mm. Particles that do not pass the sieve can be returned to a reduction machine (grinder).

In many cases it can be advantageous to feed the raw materials to a mixing and homogenizing device. To achieve good results, a double-axis so-called paddle mixer, double-screw fi FROTAPULPER brand or the mixing device described in U.S. Patent 4,908,101. It is possible to add binders to these devices if desired. Suitable binders include lignosulfonate, carbohydrates such as sugar, starch and whey. In some cases, a small amount of biofuel ash (max. 10% by weight) may be involved.

The mixing and homogenizing device can in its simplest design in principle consist of a cement mixer or simply of a rotating drum which is provided on its inside with so-called bafs, which usually consist of long narrow jaws which sit along the edges or slightly obliquely in relation to the axis of the drum. The residence time can be regulated by changing the inclination of the drum in the axial direction.

After thorough homogenization (mixing), the goods are fed to a granulation device which forms the material into spherical units. A granulating drum or a rotating plate can be used to granulate the mixture. I fi g. I and 2 show with sketches examples of a drum 1 and a plate 2. A dry-drawn embodiment of the invention constitutes the use of a continuously operating drum whose cross-section shows a number of inwardly facing bowls (concave inside) 3 integrated into a circle with irregular periphery in accordance with what is shown in fi g. The design of the bowls means that the material to be granulated is brought to follow the bowls during the rotation. The hemispherical shape of the bowls causes the granules to rotate within each bowl. The residence time in the drum can be varied by changing the inclination of the drum and / or by changing the speed. 524 263 s »| ø | ».N Furthermore, the drum can be supplemented with nozzles 4 for application of an additional component, such as some type of a hydrophobic substance (pine oil, resin oil, wax or rapeseed oil).

The granules which are produced can, in general, have the same dry matter content as the raw material had at the entrance to the granulation device. Through handling, however, it may happen that the dry matter content increases by a few percentage points during the granulation.

Within the scope of the invention, the granules can also be dried inside the drum. The drying can advantageously be carried out with the help of flue gases, hot air or with superheated water vapor. In some cases, it may be advantageous to resort to indirect drying.

The granules obtained according to the invention should have a substantially spherical shape. The diameter of the granules can vary over a wide range. Suitable diameter can range from about 2 mm up to 50 mm.

Characteristic of the invention is that the granules, with or without moisture, are impregnated with, among other things, pine oil, resin oil, waxes or rapeseed oil. This impregnation is carried out at temperatures higher than 50 ° C and preferably at temperatures higher than 100 ° C. In special cases, the granules can be treated (impregnated) for a time which allows an evaporation of excess water from the granules. Final drying of the impregnated granules can take place at any temperature. If the granules have been impregnated with, for example, tall oil, drying at temperatures above 100 ° C is preferred. At high temperatures, faster drying is obtained, which results in hard granules. Granules prepared according to the invention can be ground and used for powder firing.

The granules should, after drying, have a TS content exceeding 60% and preferably exceed a TS content of 80%. For long-term storage, the TS content must be at least 85%.

In the following, applications of the invention will be demonstrated with the aid of Figure I.

EXAMPLE 1 Sawdust from Domsjö Sawmill was ground in a hammer mill to obtain a flour-like shaving. More specifically, the chips contained over 50% by weight of fmt chips, which passed a sieve with a mesh size of 2 mm. Biosludge from a treatment plant in Ömsköldsvik municipality and the ground sawdust were treated in a mixing and homogenizing device 5. The weight fraction of dry-dried biosludge was 50% and the weight fraction of dry-dried sawdust was 50%.

The dry matter content (TS content) of the biosludge was measured at 23% and the TS content of the chips at 72%. After thorough mixing and homogenization, a TS content of 34.8% was obtained. A surprising and positive effect was that the smell from the sludge practically disappeared.

The mixture of chips and sludge was fed to a press 6 for partial dewatering. Thereby a surprisingly high dry content was achieved. Thus, it was found that the dry content became 59%. The relatively dry mixture was fed via the transport screw 7 to a granulation drum 1 for producing granules (round balls). By the rotation of the mixture in the specially designed drum, the nearest globular granules were obtained, the diameter of which varied from 8 mm to 20 mm.

In order to sort the granules by size, they were passed through a sieve 8 directly connected to the granulation drum. The mantle surface of the sieve had holes whose diameter was 12 mm.

Granules 9 with a diameter of less than 12 mm were placed in a bath 10 of tall oil which had been heated up to 170 ° C. After 60 seconds, the granules had increased in weight by about 50% due to the absorption of tall oil. The granules were then dried at a temperature of 155 ° C. 524 263 4 The drying was carried out in an oven 11 with air flow. Dried granules became surprisingly hard and after soaking in water only an insignificant water uptake could be noted. Granules 12 with a diameter of 2 12 mm (passed the sieve 8) were also treated in the same way as the smaller granules. In this experiment a lower weight gain could be noted than for the smaller granules (312 mm). Thus, after 60 seconds, a weight gain of 38% versus 50% was obtained for the smaller granules.

EXAMPLE 2 In this experiment the same apparatus as described in Example 1 was used.

Biosludge from a treatment plant in Ömsköldsvik municipality and a partially dried mixed peat with different degrees of humidification (according to von Post 3-8) were treated in the mixing and homogenization device 5. The proportion of dry-dried biosludge was 50% by weight and the weight proportion of dry-dried peat was 50 %. The dry matter content (TS content) of biosludge was measured at 23% and the TS content of peat at 78%. After thorough mixing and homogenization, a sample for TS content was taken and a value of 35.5% was obtained.

The mixture of peat and sludge was fed to the press 6 for partial dewatering. Thereby a surprisingly high dry content was achieved. Thus, it was found that the dry matter content was 57%. The relatively dry mixture was passed via the transport screw 7 to the granulation tube 1 for the production of granules (round balls).

By rotating the mixture in the specially designed drum, almost globular granules were obtained, the diameter of which was 6-16 mm. In order to sort the granules by size, they were passed through the sieve 8 directly connected to the granulation drum. The mantle surface of the sieve had holes whose diameter was 10 mm.

Granules with a diameter of less than 10 mm were placed in the bath 10 of tall oil which had been heated up to 170 ° C. After 60 seconds, the granules had increased in weight by about 55% due to the absorption of tall oil. The granules were then dried in an oven 11 at a temperature of 155 ° C.

Dried granules became surprisingly hard and after soaking in water only insignificant water uptake could be noted. Granules with a diameter of 20 mm (passed the sieve 8) were also treated in the same way as the smaller granules. In this experiment a lower weight gain could be noted than for the smaller granules (§12 mm). Thus, after 60 seconds, a weight gain of 41% versus 55% was obtained for the smaller granules.

Advantages Applying the present invention achieves a number of advantages. Thus, valuable fuel can be produced from sludge. In addition, with the help of the special granulation drum, granules of even size and high quality can be prepared. Particularly advantageous is that in mixture with other materials granules of sludge can be produced which are taken directly from treatment plants. After drying, granules with high strength are obtained, which makes them storage-resistant and durable during transport and spreading. This also makes granules prepared according to the invention advantageous from a work environment point of view. Not least with regard to the fact that they emit a small amount of dust. In a mixture with shavings and peat, the smell from the sludge is also eliminated.

Claims (1)

524 263 s' Pat. characterized in that produced granules, pellets or briquettes are impregnated with one or more hydrophobic substances. selected from the group tall oil a, resin oil a, paratin, wax or rapeseed oil. Process according to Claim 1, characterized in that the impregnation is carried out by immersion in the hydrophobic substance. Process according to Claim 2 and 2, characterized in that the dry matter content of the fuel before the treatment with hydrophobic substances exceeds 30%. Process according to Claims 1 to 3, characterized in that the treatment with hydrophobic substances is carried out at temperatures higher than 50 ° C and preferably higher than 100 ° C. Process according to one of Claims 1 to 4, characterized in that the fuel or the treatment with hydrophobic substances is dried at temperatures higher than 80 ° C to expel water.