The invention concerns a reactor for producing biogas.

The invention relates to enhanced utilization of the waste material used in producing biogas. Numerous possibilities exist to utilize the residual sludge produced in the waste material putrifying process, and the aim of the invention was to devise apparatus intended for biogas production in which part of the putrified organic matter can successfully be utilized e.g. as soil amelioration material.

Putrifying is a process in which the organic matter is decomposed by action of bacteria, methane bacteria among others, so that as end product biogas is obtained which may further be burned in boiler plants, or the energy of which can be usefully applied in another way.

Putrifying is a commonly applied method e.g. in treating municipal effluent sludges. Above all, it serves to improve the hygienic quality and drying properties of the sludge, while at the same time the process produces at least the putrifying gas quantity required to satisfy its own heating requirements. As a rule no good enough result has been achieved as regards energy householding. It is however generally known that increasing the gas yield would make the process economically profitable in this sense as well.

Expedients known in prior art enabling the biogas yield to be increased include: elevated process temperature, efficient agitation in the reactors, subdividing the process into sections appropriate for different groups of microbes, regulation of acidity, adding various organic or inorganic nutrients, and eliminating the harmful effects of certain heavy metals or sulphide ions.

It has also been known that methane bacteria require highly reduced

conditions in order to operate, and it is known that oxygen -- either atmospheric or released through chemical reactions -- is toxic to the vital processes of methane bacteria at quite low contents already. Endeavours have therefore been made to prevent entraining of oxygen into the biogas process proper, as efficiently as possible.

Therefore the invention has for object a means which is favourable in its total energy economy. Also an object of the invention is an apparatus by the aid of which the various fractions of the reactor can be utilized. The general aim of the invention is also a biogas- producing apparatus in which the gas production has been success¬ fully enhanced.

As taught by the invention, a reactor has been formed which com¬ prises a vertical shaft for rotating the waste material to be putrified. As taught by the invention, several outlets are provided from the reactor vessel or reactor tank for separating different fractions from the putrified waste material. As taught by the n invention, there has also been formed a biogas reactor in which part of the biogas is conducted to -a point above the sludge input pipe and so-called floatation is applied in order to separate impurities present in the sludge from the surface of the sludge mass proper, whereby the fraction that is separate from the central 5 part of the vessel will be free of impurity particles, whereby it becomes utilizable e.g. in decorative horticultural building.

The biogas reactor of the invention is mainly characterized in that the reactor for producing biogas comprises a rotatable gas Q floatation section disposed in the lower part of the vertical reactor vessel, above the entrance port of the waste material supply pipe, and that the reactor vessel comprises at least three draining ports for fractions of the organic matter being putrified or for particles entering therewith, gravitation-based separation 5 being arranged to take place below the floatation section, advantageously with the structural parts rotating in said lower part aiding the separation.

As taught by the invention, the reactor vessel comprises at least one waste material exit port in the central part of the reactor vessel. Through said exit port waste material is conducted into a drain pipe when desired, and said conduction of waste material is then advantageously accomplished with the aid of compressed air. After the exit port a valve has been provided, the draining of said fraction from the reactor vessel being regulated by opening and closing this valve. As taught by the invention, the reactor may advantageously comprise an exit port for the fraction deposited 0 in the upper part of the sludge mass, disposed adjacent to the upper sludge surface. A valve is again provided in conjunction with said exit port, and thus said fraction can be conducted out from the reactor vessel by opening/closing said valve. Advan¬ tageously, vanes or equivalent are provided adjacent to the upper c sludge mass surface by the aid of which the impurities deposited in the upper part of the sludge mass are transported away from the reactor vessel.

The invention is described in the following, referring to certain n advantageous embodiments of the invention, presented in the figures of the attached drawings, yet to which the invention is not meant to be exclusively confined.

In Fig. 1 is presented a biogas reactor according to the invention, 5 in sectioned view and schematically.

In Fig. 2 is presented a second advantageous embodiment of the biogas reactor of the invention, similarly in sectioned view and schematically. 0

In Fig. 3 is presented a third advantageous embodiment of the biogas reactor of the invention, similarly in elevational view and sectioned.

In Fig. 4 is presented a fourth advantageous embodiment of the invention.

As depicted in Fig. 1, the biogas reactor comprises a feed pipe 1, through which the organic material to be putrified is introduced in the reactor vessel 3 and in its lower part. From the upper part of the reactor vessel 3 departs a gas pipe 4 for carrying the biogas out from the reactor vessel. The biogas is transported further through said pipe 4 e.g. to a burner, ot it is otherwise recovered. In the lower part of the reactor vessel 3 has been disposed a sedimentation unit 8, comprising a gas floatation section 8b, a gas conduction tube 8c and guide vanes 8d. From the gas pipe 4, a side branch 4b branches off from the main branch 4a, and a gas pumping means 5 transports part of the biogas by the branch pipe 4b to below the reactor vessel 3, to the gas conduction tube 8c extending into the reactor vessel 3 and conducting said part of the biogas further to the so-called gas floatation section 8b, which comprises a plurality of nozzle apertures 8b' through which the gas discharges into the material that is being putrified. Separation by gravitation has been arranged to take place below the floatation section 8b with the aid of vanes 8d or other equivalent components moving, advantageously rotating, in said section.

The gas conduction tube 8c is rotated with a mixer motor 6. The gas floatation section 8b, being attached to the gas conduction tube 8c, rotates within the reactor vessel 3, and the biogas dis- charges in the form of bubbles through the nozzle apertures 8b', into the organic matter that is being putrified. Hereby part of the impurities present in the material being putrified e.g. plastic bodies, rise with the bubbles to the surface of the sludge, where they can be separately separated.

With the gas conduction tube 8c, which is rotated with the mixer motor 6, are connected the gas floatation section 8b of the sedi¬ mentation unit 8, and the guide vanes 8d.

The gas floatation section 8b is located substantially above the input port la of the feed pipe 1. The bottom part 3a of the reactor vessel 3 is advantageously conical and the wall surfaces 3a^ of

said conical part are substantially parallel with the lower guide vanes 8d. Heavy particles, such as glass shards and equivalent settle into the settling section 7, and these impurities can be removed with the aid of the sludge removal pump 7a in the settling section 7 and further out from the reactor vessel 3 through the exit 12'. Above the nozzle apertures 8b' of the floatation section 8b in the reactor vessel 3 is located an exit 12" , through which waste material that has been putrified can be removed from the reactor vessel 3 for further removal and utilization. In the very highest part of the reactor, adjacent to the upper sludge surface is located an exit port 12"', through which the impurity fraction can be removed which has been deposited in the upper part of the sludge. For removal of the upper fractions, the removal ports 12" and 12 ¹ " join the duct 13a, and the exit port 12' of the bottom- most fraction joins the duct 13b, said ducts further joining a joint output pipe 13c.

After the exit aperture 12" in the middle has been provided a valve 14" in the exit duct, and after the exit port 12"' of the topmost fraction a valve 14"' has been disposed in the duct section adjoining thereto. It is possible b_y alternatingly opening these valves, to remove the desired fraction through the duct 13a and further through the duct 13c, while the putrified organic matter advantageously departs under gravity action from the reactor vessel 3.

In Fig. 2 is depicted a second advantageous embodiment of the invention. This embodiment differs from that of Fig. 1 in that the reactor vessel 3 comprises a vertical, at least bipartite shaft 13. In the embodiment of the figure, the shaft comprises a first shaft section 15a and a second shaft section 15b. These shaft sections have been joined end to end with a thrust bearing arrange¬ ment 16. At least the lower shaft is so designed that the biogas can be carried therethrough, in the manner shown in Fig. 1, to the gas floatation section 8b. The shaft 15a is advantageously a hollow tube. The topmost shaft 15b is rotated by a motor 17 and the lower¬ most shaft, by the motor 6. The topmost shaft comprises guide

vanes 10a and 10b, which mix the sludge. The motor may rotate the shafts 15a and 15b in the opposite directions, whereby the so- called sedimentation process is enhanced. The end faces of the vanes 10a and 10b are advantageously disposed in a plane, in which they pass by the exit ports 12' and 12" and thereby prevent blocking of the exit apertures. One motor may rotate both shafts 15a and 15b, and over a gear transmission also in opposite directions. The valve 14" has been arranged to open and close the exit port 12" , and the valve 14"' has been arranged to open and close the topmost exit port 12"' .

In Fig. 3 is depicted a third advantageous embodiment of the in¬ vention, in which in the topmost part of the vessel has been in¬ stalled a separate vane 19, rotated by a motor 18. The motor 18 has been mounted in the very top part of the reactor vessel 3, on the top surface of the reactor vessel, and it has been arranged to rotate the shaft 19' of the vane 19. In the plane of the vane 19 is located an exit port 20, through which impurities are removed which have accumulated on the surface in the course of floatation, e.g. plastic articles and other light structural parts.

The central sludge section A of the reactor vessel 3 has, as shown in the figure, two separate exit ports 21 and 22. There is further¬ more an aperture 23 for removal of heavy settled particles, in the lower part of the vessel 2. Therefore, in the case of the reactor of the embodiment of this figure, four different fractions may be extracted from the reactor vessel 3. The lowermost fraction, com¬ prising the heavy impurities which have accumulated in the settling section 7, is removed through the exit port 23. Sludge in various stages of putrification can be removed through the exit apertures 21,22, and through the topmost exit aperture 20 those impurities can be separated from within the vessel which have accumulated on the surface of the sludge section. In conjunction with the exit port 22 has been disposed a valve 26 and with the exit port 21, a valve 25. Similarly, the valve 24 has been installed in conjunction with the exit port 20 and the valve 28 in conjunction with the exit port 23, in the duct 13b. Furthermore, the duct 13a includes

a valve 27 in its lower part.

In Fig. 4, a fourth advantageous embodiment of the invention is depicted, in elevational view and schematically. In the embodiment of the figure, the reactor vessel 3 comprises a first, bottom-most conical, downward tapering wall portion 30 and a second conical wall portion 31, between these conical portions being a portion 3b comprising a straight cylindrical mantle surface. Below the first conical portion 30 lies the lowest part of the biogas reactor vessel 3, enclosed by the cylindrical mantle surface 29, which contains a floatation section 8b and vanes 8d rotated by the shaft 8c. The floatation section with its biogas nozzle apertures 8b' is located substantially close to the point where the portions 29 and 30 of the tank 3 join each other.

The upper part of the tank 30 comprises above the second conical tank portion 31 an uppermost part 32 with straight cylindrical mantle, which encloses within itself a shaft 33 and therewith connected vanes 34 and 35 rotated by a motor 36 and a shaft 33, the ends of these vanes being advantageously arranged to sweep past the fraction removal ports 37 and 38 leading out from the tank section 32, whereby the vanes prevent blocking of the exit ports 37 and 38. In connection with the ducts of the fraction removal ports 37 and 38, valves 39 and 40 have been provided, the desired fraction being removal along the duct 13a by opening and closing these valves.

The tank 3 comprises, below the tank section 29, a settling section 7, and therefrom an exit duct 13b, through which with a cylinder 7b and other action means the fraction is removed with pressure through the aperture 41.

The biogas circulating through the ducts 4 and 4b may be similar as in the preceding embodiments. It is thus understood that part of the biogas is carried to the floatation section 8b by the duct 4b.