Process for optimizing the operation of a plug-flow fermenter for the anaerobic fermentation of organic wastes

Abstract

A process for optimizing the operation of a plug-flow fermenter for the anaerobic fermentation of organic wastes, wherein the plug-flow fermenter comprises a horizontally oriented fermenter tank and a stirrer, which stirrer comprises a stirrer shaft which traverses the interior of the fermenter tank in an axial manner and multiple paddles which are arranged on the stirrer shaft and protrude radially and also a drive, and the fermentation material is moved in the fermenter tank by means of the stirrer.

Claims

1. A process for optimizing the operation of a plug-flow fermenter for an anaerobic fermentation of organic wastes, wherein the plug-flow fermenter comprises a horizontally oriented fermenter tank and a stirrer, which stirrer comprises a stirrer shaft which traverses the interior of the fermenter tank in an axial manner and multiple paddles which are arranged on the stirrer shaft and protrude radially and also a drive, and fermentation material is moved in the fermenter tank by means of the stirrer, wherein a) at least one parameter characteristic of a particular operating state of the plug-flow fermenter is measured, b) a particular measurement value A.sub.actual obtained in a) is compared with a predefined nominal value A.sub.nominal, and c) depending on a deviation of the measurement value A.sub.actual from the nominal value A.sub.nominal, a rotational speed of the stirrer shaft, a rotational direction of the stirrer shaft and/or a dry-substance portion of the fermentation material is adjusted.

2. The process as claimed in claim 1, wherein the adjustment of the dry-substance portion of the fermentation material is done via an amount of wetting agent introduced into the fermenter tank.

3. The process as claimed in claim 1, wherein the rotational speed of the stirrer shaft, the rotational direction of the stirrer shaft and/or the dry-substance portion of the fermentation material is regulated in step c) depending on the deviation of the measurement value A.sub.actual from the nominal value A.sub.nominal.

4. The process as claimed in claim 1, wherein a range within which the rotational speed of the stirrer shaft is adjusted is between 0 and 10 revolutions per minute.

5. The process as claimed in claim 1, wherein the dry-substance portion of the fermentation material is within a range between 5 to 99%.

6. The process as claimed in claim 1, wherein at least one of the following parameters A1) to A4) is measured in step a): A1: the torque and/or the power of the drive; A2: at least one temperature present in the fermenter tank; A3: the flow rate and/or the composition of the fermentation material at at least one point in the fermenter tank; and/or A4: the composition and/or the amount of gas generated by the anaerobic fermentation.

7. The process as claimed in claim 6, wherein parameter A1 is measured in step a) and in the following order if the measurement value A1.sub.actual, as obtained in step a), of the torque or the power is higher than a predefined maximum value A1.sub.max, the rotational speed is reduced, the torque or the power is measured at reduced rotational speed and if the value A1.sub.actual,red, measured at reduced rotational speed, is still higher than A1.sub.max, the torque or the power is further reduced, whereupon the measurement of the torque or the power at further reduced rotational speed and the subsequently performed further reduction of the rotational speed are repeated at least once, or multiple times, as desired and/or the rotational direction of the stirrer shaft is changed.

8. The process as claimed in claim 7, wherein, subsequent to the change in the rotational direction of the stirrer shaft, the rotational direction is changed after a period t.

9. The process as claimed in claim 6, wherein, if the measurement value A1.sub.actual, as obtained in step a), of the torque or the power is lower than a predefined minimum value A1.sub.min, the rotational speed is reduced and the reduced rotational speed is maintained so long as the measurement value A1.sub.actual is lower than A1.sub.min.

10. A plug-flow fermenter for an anaerobic fermentation of organic wastes, wherein the plug-flow fermenter comprises a horizontally oriented fermenter tank and a stirrer, which stirrer comprises a stirrer shaft which traverses the interior of the fermenter tank and multiple paddles which are arranged on the stirrer shaft and protrude radially and also a drive and which stirrer is suited to moving fermentation material in the fermenter tank, wherein the plug-flow fermenter additionally comprises at least one measurement mechanism for the determination of at least one parameter characteristic of a particular operating state of the plug-flow fermenter as well as a regulator designed to adjust a rotational speed of the stirrer shaft, a rotational direction of the stirrer shaft and/or a dry-substance portion of the fermentation material on the basis of the measurement value obtained or a deviation of the measurement value from a predefined nominal value.

11. The plug-flow fermenter as claimed in claim 10, wherein the regulator is present in the form of or as part of a regulation unit designed to regulate the rotational speed of the stirrer shaft, the rotational direction of the stirrer shaft and/or the dry-substance portion of the fermentation material on the basis of the measurement value obtained or the deviation of the measurement value from the nominal value.

12. The plug-flow fermenter as claimed in claim 10, wherein the drive is a motor, more particularly an asynchronous motor, to which a frequency converter has been assigned.

Description

(1) The invention will be further illustrated on the basis of the figures, where:

(2) FIG. 1 shows a diagram of a regulation system in accordance with the process of the present invention; and

(3) FIG. 2 shows a graph in which torque values (in % at the frequency converter) have been plotted against the drive power that is present in each case, and in which, moreover, nominal values at different rotational speeds of the stirrer shaft have been defined.

(4) According to FIG. 1, the process according to the invention is carried out by using a plug-flow fermenter 10 which comprises a horizontally oriented fermenter tank 12 and a stirrer 14.

(5) The stirrer 14 comprises a stirrer shaft 16 which traverses the interior of the fermenter tank 12 in an axial manner and multiple paddles 18 which are arranged on the stirrer shaft and protrude radially and also a drive 20 which is, in this specific case, present in the form of an asynchronous motor 200, to which a frequency converter 22 has been assigned. Apart from that, arranged on the radially outer end of the paddles 18 are blades 24 which are designed to mix the fermentation material and, as a result, to support the conveyance of the fermentation material toward the fermenter outlet.

(6) In the exemplary embodiment shown in FIG. 1, the torque M.sub.actual [%] at the frequency converter 22 is measured in a step a) at a present rotational speed n.sub.actual [rpm] of the stirrer shaft 16.

(7) The measurement value obtained is compared with a nominal value M.sub.nominal [%], specifically a nominal value range, in a step b).

(8) If the result of this comparison is that the determined value of the torque or the power is above a maximum value of the nominal value range (case A), this for instance possibly being the case in the event of a relatively high dry-substance content of the fermentation material, the system is relieved by giving the frequency converter 22 the signal, via adjustment means 26 in the form of a regulation unit 260, to reduce the rotational speed in step c) to the value n.sub.nominal,new.

(9) Subsequently, the torque to be applied for the reduced rotational speed n.sub.nominal,new of the stirrer shaft 16 is determined and compared with the maximum value M.sub.max.

(10) If the torque is still too high, this indicates congestion of the fermentation material. This can be countered by repeating multiple times the reduction of the rotational speed with the subsequent measurement of the torque to be applied at reduced rotational speed and with the comparison of the torque with the maximum value until the torque is below the maximum value. Alternatively, the rotational direction of the stirrer shaft can also be changed. Depending on the design of the paddles and blades possibly arranged thereon, a plowing action can therefore be obtained in order to disperse the congestion of the fermentation material. Moreover, if the excessively high torque is inter alia a result of fermentation material constituents congested on the paddles, changing the rotational direction can achieve a loosening and ultimately a removal of said constituents from the paddles.

(11) By contrast, if it is established in step b) that the torque is below a minimum value of the nominal value range (case B), this indicates an underload of the system. This is responded to by minimizing the rotational speed to a minimum rotational speed or completely switching it off and thus switching the drive to an energy-saving mode.

(12) Alternatively or additionally, it is conceivable, on the basis for instance of the composition of the fermentation material at at least one point in the fermenter tank and/or after exit from the fermenter tank, to draw conclusions as to whether the mixing in the fermenter tank (at reduced rotational speed) is sufficient.

(13) The different scenarios are represented in the graph according to FIG. 2, where a nominal value range between 50 and 80% and a minimum rotational speed of 0.2 revolutions per minute (rpm) have been predefined for the torque at the frequency converter.

(14) If the result of the determination of the torque is that it, at a rotational speed of the stirrer shaft of 0.6 rpm, is 95% and thus too high, the rotational speed is reduced, the rotational speed being reduced to 0.4 rpm in the specific example, whereupon the torque is redetermined and compared with the nominal value or the maximum value of the nominal value range.

(15) By contrast, if, at a present rotational speed of 0.4 rpm, a drive power is ascertained which is below a predefined minimum value, in this specific case below 6 kW, the rotational speed is minimized and the system is thus switched to an energy-saving mode.

(16) In the example shown in the graph, the rotational speed is successively reduced from the mentioned 0.4 rpm to 0.2 rpm.

LIST OF REFERENCE SIGNS

(17) 10 Plug-flow fermenter 12 Fermenter tank 14 Stirrer 16 Stirrer shaft 18 Paddles 20; 200 Drive; asynchronous motor 22 Frequency converter 24 Blades 26; 260 Adjustment means; regulation unit