Fermenter for biogas plants, comprising a submersible motor-driven stirrer vertically adjustable by means of a motor

Abstract

A fermenter for biogas plants, including a submersible motor-driven stirrer that can be vertically adjusted by means of a motor. During operation of the biogas plant, the fermenter is filled, to a level, with substrate that is to be fermented, and the agitator blades of the submersible motor-driven stirrer are fully immersed in the substrate. According to the invention, a level gauge is provided, by means of which the level of the substrate is detected and a corresponding level measuring signal is generated as an actual level signal. Furthermore, a control device is provided, to which the level measuring signal is fed and which controls the vertically adjusting motor for the submersible motor-driven stirrer in such a way when a lower level is detected that the stirrer is lowered and the agitator blades continue to be fully immersed in the substrate.

Claims

1. A biogas plant fermenter comprising: a cover; a vertically motor-adjustable, submersible motor stirrer, wherein during operation of the biogas plant, the fermenter is filled to a level (H.sub.1) with substrate to be fermented, the submersible motor-driven stirrer with its agitator blades being fully immersed in the substrate; a filling level gauge attached to said cover and spaced from a top surface of the substrate such that the filling level gauge does not contact the substrate, said filling level gauge being configured to detect the actual filling level (H.sub.1) of the substrate by directly measuring the substrate level and generating a corresponding filling level measuring signal as an actual level signal; and a control device configured to receive the filling level measuring signal and when a lower filling level (H.sub.1′) is detected, actuates the height-adjusting motor for the submersible motor stirrer so as to lower it far enough for the agitator blades to continue to be totally immersed in the substrate.

2. The biogas plant fermenter according to claim 1, wherein the filling level gauge comprises a mechanically operating sensor with at least one of a floater and a displacer, each having a position transmitter or a limit value switch.

3. The biogas plant fermenter according to claim 1, wherein the filling level gauge comprises at least one of an ultrasonic echo-sounder impulse device, a non-contact gamma radiator with counter tube chain and a hydrostatic tube for a bubbler system.

4. The biogas plant fermenter according to claim 1, wherein the control device includes a control function incorporated in a plant control.

5. The biogas plant fermenter according to claim 1, wherein the submersible motor stirrer is height-adjustable by means of a motor at a vertical assembly holder and by means of a rope winch.

6. The biogas plant fermenter according to claim 5, wherein the assembly holder is accommodated in the upper region in a dome-shaped servicing well into which the submersible motor stirrer can be displaced upwardly.

7. A biogas plant fermenter comprising: a cover; a vertically motor-adjustable, submersible motor stirrer, wherein during operation of the biogas plant, the fermenter is filled to a level (H.sub.1) with substrate to be fermented, the submersible motor-driven stirrer with its agitator blades being fully immersed in the substrate; a filling level gauge attached to said cover and spaced from a top surface of the substrate such that the filling level gauge does not contact the substrate, said filling level gauge being configured to detect the actual filling level (H.sub.1) by directly measuring the substrate level and generating a corresponding filling level measuring signal as an actual level signal; and a control device configured to receive the filling level measuring signal and when a lower filling level (H.sub.1′) is detected, actuates the height-adjusting motor for the submersible motor stirrer so as to lower it far enough for the agitator blades to continue to be totally immersed in the substrate, wherein the filling level gauge includes a sensor and is configured to detect a free space height (H.sub.3) between the sensor and the substrate level by way of a free space height signal which is transmitted to a control unit of the control device where by subtraction from the total height (H.sub.0) the current filling level (H.sub.1)
H.sub.1=H.sub.0−H.sub.3 is determined, wherein via a height adjuster at the control unit a height adjusting signal is transmitted to the control unit corresponding to a desired level value (H.sub.2) for the submersible stirrer to actuate the height-adjusting motor by way of a height-adjusting signal such that the submersible motor stirrer assumes such desired value level (H.sub.2) measured up to the topmost agitator blade tip, wherein with a superimposed control as a safety control against the agitator blades emerging, a comparison is performed in the control unit between the signals of the current filling level height (H.sub.1) and the desired value level (H.sub.2) stored in the control unit, such that when the filling level (H.sub.1) is higher than the desired value level (H.sub.2), no further control procedure is carried out, wherein when the currently sensed filling level height (H.sub.1′) is lower than the desired value level (H.sub.2), an automatic control procedure occurs independently of the preset height adjustment signal, and wherein the submersible motor stirrer is lowered down far enough until the current setting height (H.sub.2′) of the submersible motor stirrer is lower than the current filling level height (H.sub.1′) by a height differential amount X such that
H.sub.1′=H.sub.2′+X and thus the agitator blades are totally immersed in a stirring operation.

8. The biogas plant fermenter according to claim 7, wherein the height differential amount X can be preset at the control unit.

9. The biogas plant fermenter according to claim 7, wherein the superimposed control procedure for the immersion safeguard of the agitator blades is carried out every time as an X-value difference is exceeded.

10. The biogas plant fermenter according to claim 7, wherein the control device includes a control function incorporated in a plant control.

11. The biogas plant fermenter according to claim 7, wherein the submersible motor stirrer is height-adjustable by means of a motor at a vertical assembly holder and by means of a rope winch.

12. The biogas plant fermenter according to claim 11, wherein the assembly holder is accommodated in the upper region in a dome-shaped servicing well into which the submersible motor stirrer can be displaced upwardly.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in more detail by way of a drawing.

(2) FIG. 1 is a fragmentary elevation view of an embodiment of the present fermenter.

DETAILED DESCRIPTION

(3) FIG. 1 schematically shows a sectional view of a biogas plant fermenter 1 having an agitator device 2. The fermenter 1 contains a fermentable substrate 3 with liquid and solid biomass contents. Although the present fermenter 1 comprises a concrete cover 4 as the fermenter ceiling, it might be covered with a film roof as known per se. The concrete ceiling is provided with a maintenance and mounting hole 5. The stirring device 2 consists of a submersible motor stirrer 6 with a horizontally oriented agitator shaft where, in the present three-blade arrangement, agitator blades 7 are attached.

(4) The submersible motor stirrer 6 is retained at a vertical assembly holder to be height-adjustable via a rope winch 9.

(5) Above the maintenance and mounting hole 5 covered by a cover plate 10 a servicing well 11 (drawn schematically in dashed lines) mounted gas-tight and having a door 12 is arranged. The assembly holder 8 passes through this servicing well 11 and it can be rotated by a crank 13 for angular adjustment of the submersible motor stirrer 6. Moreover the rope winch 9 is attached at the assembly holder 8 in the upper region of the servicing well 11 such that after removing the cover plate 10 the submersible motor stirrer 6 can be pulled upwardly into the servicing well 11 region for maintenance and repairs. Height adjustment of the submersible motor stirrer 6 occurs by actuating an electrically operated height adjustment motor 14 coupled with the rope winch 9. Actuating occurs through a control unit SG emitting a corresponding height adjustment signal HS to the height adjusting motor 14, for example an electrical stepper motor. The desired height adjustment of the submersible motor stirrer 6 is specified at the control unit SG by way of a height adjusting signal HE. Said height adjusting signal HE may be specified for example manually by way of a manual control or else in the scope of a stirring program with changing height adjustments.

(6) In the presently illustrated case the filling level of the fermenter 1 or the substrate level is shown at H.sub.1. The current level adjustment of the submersible motor stirrer 6 (up to the topmost tip of an agitator blade 7 this is the diameter D of the agitator blade arrangement) as preset by the level adjustment signal HE is shown at H.sub.2. The agitator blades 7 are obviously totally immersed in the substrate 3 during a stirring function wherein a height differential amount X is maintained between the top agitator blade position and the substrate level.

(7) The fermentation process depends on a plurality of parameters, such as the biomass type, material feed, temperature, intensity of stirring, etc., such that the substrate filling level can noticeably fluctuate during operation. Such operational fluctuation with a lowered substrate level to the filling level H.sub.1′ is indicated in dashed lines in the FIGURE. Obviously the agitator blades 7 of the submersible motor stirrer 6 would emerge above the substrate level during stirring in the case of height adjustment H.sub.2. To prevent this a filling level gauge 15 is additionally arranged, presently as an ultrasonic echo sounder in the region of the fermenter cover, presently e.g. the cover plate 10 so as to detect the free space height H.sub.3 between the filling level gauge 15 and the substrate level, and a corresponding electrical free space height signal FM is transmitted to the control unit SG. There, by means of subtracting the variable free space height H.sub.3 from the invariable total height H.sub.0, the variable current filling level H.sub.1 is determined and captured.

(8) In the case that the filling level H.sub.1 is higher than the preset desired value level H.sub.2 corresponding to the height adjustment signal HE, the agitator blades 7 are totally immersed for a good stirring effect. In contrast thereto, a superimposed control procedure is carried out if according to the FIGURE the substrate level drops to a height H.sub.1′ (shown in dashed lines) such that the agitator blades 7 would then emerge. To this end a comparison is carried out in the control unit between the current height adjustment of the submersible motor stirrer 6, which is captured in the control unit SG, and the currently measured, dropped filling level height H.sub.1′. If the dropped filling level height H.sub.1′ is lower than the current vertical position of the submersible motor stirrer 6, the control unit SG emits a height adjusting signal HS for a lowering function of the submersible motor stirrer 6 until the current setting height H.sub.2′ is again lower than the current filling level height H.sub.1′ by a height differential amount X. It is thus automatically ensured that during stirring the agitator blades 7 do not emerge above the substrate level.