Control of biogas plants

Abstract

A method and an apparatus for producing biogas from organic matter including a container (1) which is charged with fermentation substrate by a delivery system (13). At least one stirring mechanism (2) is arranged in the container. The feedback value of at least one measurable variable is detected and transmitted to a control unit (4). A reference variable is also provided to the control unit. The control unit calculates the deviation of the feedback value from the reference value, and actuating variables which modify the power input of the stirring mechanism and/or the composition of the container contents and/or the flow behavior of the container contents are adjusted as a function of the deviation.

Claims

1. A method for producing biogas from organic substances in a biogas generating system which includes a regulating unit and a fermenter container having a height to diameter ratio lower than 0.5 arranged to receive substrate being supplied to the container by a feed system, there being arranged in the container at least one agitator mechanism arranged to generate a horizontal flow of the organic substances in the container, the method including detecting an actual value of at least one measurement quantity indicative of a dynamic viscosity of the substrate at the at least one agitator mechanism, transmitting the actual value detected at least one measurement quantity to a regulating unit in which there is stored a setpoint value indicative of a reference substrate viscosity that is a function of at least one of a size of the container, a type of the at least one agitator mechanism and a position of the at least one agitator mechanism in the container, calculating with the regulating unit a deviation of the actual value from the setpoint value and, as a function of said deviation, increasing the dynamic viscosity of the substrate in the container by controlling at least one of an amount of power introduced to the substrate in the container by the at least one agitator mechanism, a composition of the substrate in the container, a composition of the substrate being fed into the container, and amount of substrate being at least one of added to and recirculated into the container, and a flow behavior of the container contents, the flow behavior being varied by addition of at least one of a chemical and a biologically-active mechanism to the substrate.

2. The method as claimed in claim 1, wherein the gas mass flow generated is detected as an additional measurement quantity.

3. The method as claimed in claim 1, wherein the methane gas fraction is detected as an additional measurement quantity.

4. The method as claimed in claim 1, wherein performance data of a machine/assembly which processes the biogas are detected as an additional measurement quantity.

5. The method as claimed in claim 1, wherein the extent of a floating layer which forms is detected as an additional measurement quantity.

6. The method as claimed in claim 1, wherein the biogas residue potential in a fermentation residue is detected as an additional measurement quantity.

7. The method as claimed in claim 1, wherein the regulating unit varies the rotational speed of the agitator mechanism.

8. The method as claimed in claim 1, wherein the regulating unit actuates at least one additional agitator mechanism.

9. An apparatus for producing biogas from organic substances, said apparatus comprising: a container having a height to diameter ratio of 0.5; a feed system configured to supply fermentation substrate to said container; at least one agitator mechanism arranged to generate a horizontal flow of the organic substances in said container; a measurement device for measuring a quantity indicative of a dynamic viscosity of the fermentation substrate in the container at the at least one agitator mechanism; and a regulating unit configured to receive from said measurement device the measured value of the quantity indicative of a dynamic viscosity of the fermentation substrate at the at least one agitator mechanism and having stored therein, a setpoint value of a quantity indicative of a reference substrate viscosity that depends on at least one of a size of the container, a type of the at least one agitator mechanism and position of the at least one agitator mechanism in the container; wherein said regulating unit is configured to calculate a deviation of the measured value of said at least one quantity indicative of the dynamic substrate viscosity at the at least one agitator from the setpoint value and of the quantity indicative of the reference substrate viscosity, control as a function of said deviation an increase in the dynamic viscosity of the substrate at the at least one agitator mechanism of at least one of an amount of power being introduced to the substrate in the container by the at least one agitator mechanism, a composition of the substrate in the container, a composition of the substrate being fed into the container, and amount of substrate being at least one of added to and recirculated into the container, and a flow behavior of the container contents, the flow behavior being varied by addition of at least one of a chemical and a biologically-active mechanism to the substrate.

10. The apparatus as claimed in claim 9, wherein a gas mass flow generated in the apparatus is detected as a measurement quantity.

11. The apparatus as claimed in claim 9, wherein the methane gas fraction of a gas generated in the apparatus is detected as a measurement quantity.

12. The apparatus as claimed in claim 9, wherein performance data of a machine/assembly which processes biogas generated in the apparatus are detected as a measurement quantity.

13. The apparatus as claimed in claim 9, wherein the extent of a floating layer which forms in the container is detected as a measurement quantity.

14. The apparatus as claimed in claim 9, wherein the biogas residue potential of a fermentation residue in the container is detected as a measurement quantity.

15. The apparatus as claimed in claim 9, wherein the regulating unit varies the rotational speed of the agitator mechanism.

16. he apparatus as claimed in claim 9, wherein the regulating unit actuates at least one additional agitator mechanism.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be described in further detail hereinafter with reference to illustrative embodiments shown in the accompanying drawing figures, in which:

(2) FIG. 1 shows a perspective view of a container for biogas production, and

(3) FIG. 2 shows a diagrammatic illustration of the regulation of a plant for biogas production.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(4) FIG. 1 illustrates a cylindrical container 1 for producing biogas. Other container forms are likewise possible. The ratio of the largest diameter to the height of the container is lower than 0.5. Positioned in the container 1 are two agitator mechanisms 2, the propellers 3 of which generate a mostly horizontal flow of the fermentation substrate in the container 1. The agitator mechanisms 2 or their propellers 3 are arranged at different heights inside the container 1. An additional agitator mechanism 11 is cut in, as required.

(5) FIG. 2 shows a diagrammatically illustrated regulating unit 4 for a method for producing biogas. This may be a stored-program control (SPS) or another regulating system.

(6) The regulating unit 4 has a signal input region 5 and a signal output region 6. The signals of the data which are detected during measurements of the method are conducted to the signal input region 5. Data from various process-monitoring sensors 7, 8, 9, 10, 15, 17 and from the agitator mechanisms 2 are processed in the regulating unit 4. The signal output region 6 is operatively connected to process-influencing assemblies. Process-influencing assemblies are the agitator mechanisms 2, 11, a fermenter heating unit 12, a feed system 13 and a recirculation unit 14. These are controlled such that individual process parameters can be optimized with the aim of a maximum methane yield.

(7) The following sensors may be used for process monitoring: at least one sensor for viscosity measurement 7, one or more sensors for flow velocity measurement 8, at least one floating layer detector 9, a gas quantity meter 10, a unit 15 for fermentation residue analysis and at least one unit 17 for determining the flow behavior of the fermentation substrate.

(8) The sensor 7 serves for detecting the viscosity. To determine the viscosity, measurement data which are determined via the agitator mechanisms 2 may also be used. Alternatively or additionally, it is possible to employ a separate flow behavior determination unit 17. Flow behavior determination may in this case take place individually or simultaneously at a plurality of locations. The determination of the flow behavior is necessary in order to avoid too critical a flow behavior in the container 1 in terms of relevant process parameters and also damage to all the agitator mechanisms 2, 11 used in the process and to optimize their specific energy consumption. The velocity generated in the fermentation substrate is of major importance in optimizing between the gas yield and the specific energy consumption.

(9) The sensor 8 is used for velocity measurement in the container 1. In this case, the velocity can take place at different locations by means of one or more velocity determinations.

(10) The formation of a floating layer is monitored by means of a detector 9. Since a floating layer top has an adverse effect upon the emission of biogas from the fermentation substrate, its occurrence must be avoided or it must be destroyed as soon as possible after it has occurred. For this purpose, for example, an additional agitator mechanism 11 can be cut in and/or the rotational speed of one or more main agitator mechanisms 2 can be varied. This gives rise to flow turbulence which dissolves the floating layer.

(11) The generated gas mass flow is detected by a gas mass meter 10. If the gas mass falls below a specific level, the regulating unit 4 adapts the introduction of power by the agitator mechanisms 2, 11. The aim of fermentation is to utilize as large an amount of the biogas potential of the substrate as possible.

(12) The fermentation residues are collected in a fermentation residue store 16. The determination of the biogas residue potential in the fermentation residue is carried out by means of the unit 15 and is a further possible reference quantity for the regulating unit 4 and for the regulation of the agitator mechanisms 2, 11. Determination of the biogas residue potential may take place at various locations in the plant. If a specific biogas residue potential is overshot in the fermentation residue, the regulating unit 4 adapts the process-influencing assemblies 2, 11, 12, 13, 14 to the process conditions.

(13) Basically, all the data from the signal input region 5 are processed in the regulating unit 4. The processing of the data takes place on the basis of a stored algorithm. This algorithm assumes the task of determining from the input quantities the values for controlled quantities determined from them. The controlled quantities determined are used to control the process-influencing assemblies 2, 11, 12, 13, 14 from the signal output region 6.

(14) Signals for regulating various manipulated quantities emanate from the signal output region 6. Consequently, for example, the agitator mechanisms 2 are activated, and their rotational speed can be regulated.

(15) In the absence of movement on the surface of the fermentation substrate, a floating layer may be formed. Moreover, the absence of movement may cause the substrate or fermentation substrate to be fed in to be distributed only insufficiently in the container 1.

(16) When new substrate is supplied or if a floating layer has occurred, an additional agitator mechanism 11 can be cut in or regulated. The heating unit 12 supplies heat to the container 1 when new substrate is being fed in. The substrate is supplied by the feed system 13. The fodder quantity can consequently be adapted to the process parameters. Overfodder of the container 1 with substrate would have an adverse effect upon the flow behavior in the container 1 and therefore on methane production. If the flow behavior changes adversely, the fodder quantity is reduced and/or other controlled quantities, such as, for example, the velocity or recirculate quantity, is/are varied.

(17) If fodder quantities are too low, insufficient substrate is available for methane formation. With the aid of a gas mass meter 10 and/or an analysis of the biogas residue potential in the fermentation residue, this state is detected and foddering with substrate is induced. The method has a recirculation unit 14 by means of which it is possible to add recirculate in a metered manner. A higher substrate turnover and an increased biogas yield are thereby achieved.

(18) The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the described embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations within the scope of the appended claims and equivalents thereof.