SE533563C2 - Procedure for extracting energy from organic waste - Google Patents

Description

533 563 Disadvantages of known technology Because chemicals are used in society and the spread of bacteria, viruses and parasites of various kinds, many of them are found in municipal biosludge. It can be mentioned that within the EU there are about 110,000 commercial chemicals registered. The National Research Council, USA, has classified 10 million. chemicals. Many of the chemicals are hazardous to health and therefore residues of municipal sludge should not be laid on land surfaces. In addition, it has been shown that when spreading in fields, an odor spreads which disturbs the surroundings.

When extracting biogas, an energy yield of only about 1 MWh per tonne of organic matter is obtained. Incineration of digestate (biosludge) has been tried, but due to the high content of water, it has not been possible to obtain economics during incineration. However, in the process described in patent SE 523 787, it is possible to dewater to dry contents above 50%.

Description of the invention The invention comprises vital process steps such as thickening, production of methane gas, dewatering, combustion and / or gasification. Apparatus and their function will be described in the following with reference to Figure 1.

Drainage 1 from animal stables, treatment plants or a toilet seat is taken to a digestion chamber 2 in which biogas 3 is formed in the form of methane. A digestate is obtained as a residual product, so-called biosludge 4. The digestate obtained after production of the biogas is dissolved in large volumes of water. Since it is included in accordance with the invention to burn the digestate, water must be evaporated. This is done by mechanically filtering and / or dewatering in one or more steps. In preferred embodiments of the invention, the suspension is thickened to a dry matter content of from about 5% to about 25% by means of a drum filter or centrifuge.

A characteristic part of the invention is that the partially thickened digestate 6 is fed to a press 7 or double wire machine fi further evaporation of water so that the dry matter content exceeds 48%. In accordance with patent specification SE 523 787, before dewatering, the digestate can be mixed with dewatering-promoting material in particulate form, such as modified sawdust. This alternative is marked with a dashed arrow 8-i tig. Another way that can be applied is to freeze the digestate in accordance with patent specification SE 528 781 and carry out the dewatering after thawing. 533 563 3 Dewatered sludge 9 with a dry content of more than 48% is passed on to an incinerator 10 whose size varies as required. When burning only the digestate, of course, a smaller incinerator is required than when burning the digestion in a mixture with other materials. Preferably, the second material should consist of so-called biofuel, such as wood, bark and bio-oil.

During combustion, destruction of synthetic chemicals is obtained. As a residual product, ash 11 is obtained, which contains oxides of, among others, calcium, potassium and phosphorus. Within the scope of the invention, granules or pellets are produced from the ash.

The energy generated during combustion is used as heat 12 and / or to generate electricity 13.

As an alternative to combustion, gasification can be used, which converts carbon compounds to carbon monoxide and hydrogen gas. Two energy-rich gases which through synthesis can form new high-quality products, such as synthetic diesel.

Execution example in the treatment plant Knorthem, approximately 300 tonnes of dry sludge is handled annually, which is approximately 7500 tonnes / ms at a dry matter content of 4%. After biogas generation, the digestate (4) in a decanter centrifuge (5) is thickened to a dry matter content of 23% in 2% (actual).

Since the content of water in the biosludge (6) was still too large to be incinerated, the digestate sludge was pressed in a press (7) with two pistons with continuous lines for removal of liquid, which was returned to the digestion chamber (2) by means of line 14. The recirculation means that additional biogas could be generated as the digestion process is seldom complete.

Prior to pressing, the digestate was mixed with modified sawdust (8) so that the mixture contained 40% by weight of sawdust. After pressing, the dry content was 57% while the dry content of the mixture before pressing was 32.8%.

The theoretical energy value at a dry matter content of 57% is approximately 4 MWh per tonne of digestate based on organic matter. The theoretical contribution from the digestate was as much as 2.4 MWh (0.6x4.9).

According to the invention, it is thus possible to extract about 1 MWh in the production of biogas and in combustion about 2.4 MWh, i.e. a total of 3.4 MWh. The theoretical recovery rate is thus around 70%.

When firing the mixture in ÖviksEnergi AB's biofuel boiler in Bredbyn, it could be stated that the emptying of the digestate and chip mixture from the container and the feed to the fireplace worked smoothly. 533 563 The combustion of the mixture proceeded normally and it was particularly surprising that coatings in the boiler room decreased and that the ash became easy to handle in the form of free powder. According to calculations, a normal heat exchange was obtained during combustion or about 4.4 MWh per tonne of organic matter (digestate + shavings).

Granules were made from the ash in a rotating drum. The granules obtained were relatively evenly sized (3-8 mm) and surprisingly strong (high density).

The ash contained a surprisingly high content, 6.5%, of P2O5 (phosphorus pentaoxide), 6.2% CaO (quicklime) and 3.5% K2O (potassium oxide). The economic value of the ash could be taxed at at least SEK 600 / tonne. No residues of organic matter could be found in the ash, which showed that the combustion had destroyed synthetic substances. Due to the fact that the ash is alkaline, no viruses, bacteria or parasites could be found in the residual product ash.

Advantages of the invention The invention is of great importance in the effort to create a better environment in a more resource-efficient society.

After thickening of the digestate, which is obtained after the production of biogas, a material is obtained which, when burned, can generate energy. Thus, a considerable amount of energy can be extracted from the residual product, digestate (biosludge) by generating biogas and combustion or alternatively pre-gasifying of digestate. By returning extruded liquid to the digester, a slightly higher yield of biogas is obtained.

Particularly valuable is that from a public health point of view, an efficient destruction of potentially dangerous chemicals, viruses, bacteria and parasites is obtained.

Another advantage of the process according to the invention is that a valuable residual product is obtained in the form of high-value gas containing valuable chemicals, which can be used for cultivation.

Claims (1)

A process comprising recovering energy in various forms from suspensions (1) containing organic matter, characterized in that the organic material is treated in a combination of integrated steps, in which, as a first step, biogas (3) is recovered by digestion of the organic material after which the digestate (4) obtained after digestion in a second step is thickened to dry matter contents in the range 5-25% after which the partially thickened digestate in a third step (6) is mixed with dewatering agent (8) before a fourth step comprising mechanical dewatering (7) to a dry matter content of at least 48%, whereby squeezed liquid (14) is fed to the digestion chamber (2) before a fifth step in the form of thermal treatment during simultaneous destruction of chemicals. Process according to Claim 1, characterized in that modified sawdust is used as the dewatering-promoting agent (8). Process according to Claims 1 and 2, characterized in that the thermal treatment comprises gasification of the concentrated organic material (9). Process according to claims 1-3, characterized in that the generated gas is used for generating heat and / or electricity. Process according to claims 1-3, characterized in that the generated biogas is used to be converted into organic compounds. Process according to claims 1 and 2, characterized in that the thermal treatment comprises combustion (10) of the concentrated organic material. Process according to Claim 6, characterized in that the energy generated during combustion is converted into heat and / or electricity (1, 2.13). Process according to Claim 6, characterized in that the ash (1 L) obtained after incineration is converted into granules.