DE102014113413B3 - Method for controlling a biogas plant and regulating device - Google Patents

Abstract

The invention relates to a method for controlling a biogas plant, wherein the biogas plant has a supply device for feeding a substrate into a fermenter and a gas utilization device, wherein the method comprises the following steps: setting a target value for a gas volume flow, which are made available to the gas utilization device by determining, by means of an optical measuring device, a substrate parameter of the substrate supplied to the fermenter for processing to biogas, determining an expected value for a gas volume flow that can be generated with the substrate based on the determined substrate parameter, comparing the setpoint with the expected value, and Adjusting the supply of the substrate depending on the result of the comparison. Furthermore, the invention relates to a control device for controlling a biogas plant.

Description

The invention relates to a method for controlling a biogas plant and a control device.

background

In biogas production, which is also referred to as fermentation, substrate is converted to biogas, organic residues and heat under anaerobic conditions. The substrate consists mainly of proteins, carbohydrates and fats. Biogas production is characterized by four steps, which are influenced by different bacteria. The details of biogas production are known.

A control and regulation procedure for biogas plants is in the document EP 2 559 750 A1 disclosed. It is determined a mass balance of the inflow and outflow of the fermenter. The controlled variables (feed parameters) are determined in the laboratory. In addition, parameters of the substrate can be determined by near-infrared spectroscopy.

The document DE 10 2006 053 863 A1 discloses a control method for a biogas plant based on target variables. Using a simplex algorithm, the target sizes are optimized.

The prior art has the disadvantage that the determination of controlled variables takes a long time, often several days. The controlled variables are only determined every few days or weeks. An adaptation of the biogas plant is therefore time delayed.

Summary

The task is to provide improved technologies for controlling a biogas plant.

This object is achieved by the method according to independent claim 1 and the control device according to independent claim 10. Further embodiments are the subject of the dependent claims.

In one aspect, a method for controlling a biogas plant is disclosed. The biogas plant has a supply device for supplying a substrate into a fermenter and a gas utilization device. The method comprises the following steps: setting a desired value for a gas volume flow, which is to be made available to the gas utilization device, determining a substrate parameter of the substrate, which is supplied to the fermenter for processing into biogas, by means of an optical measuring device, determining an expected value for a gas volume flow which can be generated with the substrate based on the determined substrate parameter, comparing the setpoint with the expected value and adjusting the supply of the substrate depending on the result of the comparison.

According to a further aspect, a control device for controlling a biogas plant is disclosed with an optical measuring device and a data processing device, which is coupled with the optical measuring device for data technology. The optical measuring device is designed to determine by means of an optical measurement a substrate parameter of a substrate, which is supplied to a fermenter of the biogas plant. The data processing device is designed to determine an expected value for a gas volume flow on the basis of the determined substrate parameter, to compare the expected value with a desired value for the gas volume flow and to adjust a supply of the substrate as a function of the result of the comparison.

The optical measuring device can be designed to determine the substrate parameter on-line, ie in real time. This allows an adjustment of the substrate supply also in real time and an on-demand feeding of the system. By means of the optical measuring device, one or more substrate parameters can be determined.

Upon the supply of the substrate, the amount and / or the composition of the substrate can be adjusted. The substrate may comprise cereals, maize silage, manure (e.g., cattle manure, pig manure) and cosubstrate. Some substrate-specific parameters are named below: The fresh mass FM is the substrate mass in its original form. This contains mainly raw water and dry matter. The dry substance TS contains all energy-containing constituents of the substrate. The dry substance contains a combustible and a non-combustible portion. Crude ash (XA) is the proportion which is non-combustible. The organic dry matter (oTS) is the difference between the dry matter and the crude ash (oTS = TS - XA). Furthermore, the substrate may contain crude protein (XP), crude fat (XL), crude fiber (XF), raw char and starch (XS).

It can be provided that a portion of the substrate removed from the fermenter is recirculated to the fermenter as recirculation, wherein furthermore a recirculation parameter of the recirculate is determined by means of the optical measuring device and the expected value for the gas volume flow is determined taking into account the recirculation parameter.

The supply device may have a mixing device, for example a circular dissolver. A first optical sensor of the optical measuring device can be arranged in a line upstream of the mixing device. The substrate parameter and, if present, the recirculation parameter can be determined by means of the first optical sensor.

It can be provided that a parameter from the following group is determined as substrate parameter and / or as recirculation parameter: fermentable organic dry substance, crude fiber, crude protein, crude lignin and nitrogen-rich extract substances.

The supply device may have a conveying device, for example a climbing screw. A second optical sensor of the optical measuring device can be arranged in the conveying device. By means of the second optical sensor, a mixing parameter of the substrate can be determined. Based on the mixing parameter, the mixing ratio of the supplied substrate can be optimized.

The optical measuring device can be formed as a near-infrared spectroscopy (NIRS) measuring device. Near-infrared spectroscopy is a physical analysis technique based on short-wavelength infrared spectroscopy. Near infrared spectroscopy, like other vibrational spectroscopy, is based on the excitation of molecular vibrations by electromagnetic radiation in the (near) infrared range. In NIRS, detection takes place in the near infrared (760-2500 nm or ca. 13,000-4,000 cm ^-1 ). In this range are overtone or combination vibrations of the molecular fundamental vibration from the middle infrared. The overtone and combination bands are not directly interpreted during the analysis of samples, but evaluated using statistical methods. For quantitative determinations, previously data sets with known content or known concentrations of the substance of interest are prepared (calibration).

For the expected value, an energy content, a biogas formation potential and / or a methane formation potential can be determined.

According to one embodiment it can be provided that the substrate is supplied continuously and the supply of the substrate is adjusted continuously.

According to a further embodiment it can be provided that by means of the optical measuring device a process parameter is determined, which represents an advance of the fermentation of the substrate. The process parameter may be the ratio between the volatile organic acids (FOS) and the total inorganic carbon (TOC). This allows an additional process control of the fermentation. Constant FOS / TAC values indicate good biogas production.

The operation of the biogas plant by means of the control system is very low maintenance. There is no longer any lengthy experience of the plant operator necessary because the gas yield no longer needs to be calculated by hand, but is determined independently by the process and control system. Furthermore, a silage change is much easier adaptable, since the feeding acts, for example, on the FoTS content of the substrate mixtures. If a silage change takes place, the feeding period changes automatically.

The aforementioned features of the method can be transferred to the control device in an analogous manner.

Description of exemplary embodiments

In the following, embodiments will be explained in more detail with reference to figures of a drawing. Show it:

1 a schematic representation of a NIRS measurement,

2 an embodiment of a NIRS measuring system,

3 an energy balance in the fermenter,

4 a fermenter model for Matlab / Simulink,

5 a switch model for switching the gas yield calculations,

6 an energy balance and connection to the OPC server,

7 a model for the energy requirement calculation of a feeding cycle,

8th a model for calculating the energy yield of liquid manure,

9 a model for the energy demand calculation of the CHP, the torch and the digestate storage and

10 a model for calculating the number of cycles after the energy balance.

The biogas plant is divided into three operating units. The first operational unit includes acceptance, buffering and substrate delivery. The second operating unit comprises the fermenter and the digestate storage. The third operating unit includes the CHP, the torch, the district heating connection and the power supply.

First operating unit: acceptance, buffering and substrate feed

In the first operating unit, the substances to be fermented (pig or cattle slurry, cereals, corn, recirculate and water) are assumed. The manure is introduced from the receiving container. In the receiving container, a filling and withdrawal option for manure is mounted. The respective amount of liquid manure is determined by determining the mixing ratio. About the dry-set pump, the manure from the receiving container to the mixing container (circular dissolver) is supplied, which is on load cells. The circular dissolver is crucial for effective mixing of the substrate.

When the calculated amount is reached, the pumping process is stopped. The acceptance of the maize silage takes place via the solids intake in the building with push floor, mechanical rollers and cross auger. The corn silage is fed into the circular dissolver via a plug screw. As overfill protection, a rotary wing monitor is used.

If the task area is overfilled, all drives of the task conveyor are switched off. Only after falling below the limit level previously shut down drives are switched on again. Required sludge suspension is removed from the recirculation shaft with the pump and fed to the mixing vessel. (Silage) water is removed from the Silagesaftschaft by means of the submersible motor pump. If this is empty, water from the well is fed by means of the submersible pump to the circular dissolver. From the grain silo, flour is added to the flour storage container by means of a closed conveyor spiral via the hammer mill. The flour is then fed from the flour feed via the screw conveyor to the circular dissolver. After the last material has been introduced, the entire fermentation substrate is homogenized in the circular dissolver. The complete homogenization of the mixture takes about 2 minutes. The duration of the homogenization can be set via the process control system. When the stirring process has ended, the fermentation substrate is transferred into the fermenter by means of the eccentric pump.

Kreis-Dissolver

For the mixing and digestion of the substrates in the biogas plant is the circular dissolver (KD), for example, the company Envitec AG.

The Circular Dissolver is a 3 m ³ container in which a cutting blade and a stirrer blade mounted on the same shaft are driven by a 75 kW motor. The speed at the maximum power of the engine is about 1000 l / min. During the mixing within the circular dissolver occurs a so-called donut effect (similar to a food processor), which allows rapid mixing of the corn and the cereal.

The solids are pulled down and hit open by the cutting blade and digested. By digesting the substrates, the microbacteria should better disintegrate the substrates. In addition, the substrate is homogenized by the digestion. The circular dissolver enables a substrate saving by higher gas yields. Furthermore, agitator power is saved in the fermenter and the higher fermenter utilization leads to shorter residence times. The circular dissolver starts with a minimum filling weight of 1800 kg and has a maximum filling weight of 3200 kg. The optimum filling level during feeding is around 380 mm after mixing the substrates and a mixing time of approx. 2 minutes. The stirrer blade should be completely covered, as otherwise no complete mixing of the corn takes place. The distance from the beginning of the shaft to the stirrer blade of the circular dissolver is therefore of great importance. The distance is for example 62.5 cm.

It is necessary to adjust the residual weight after pumping the substrate to 250 kg in order to achieve complete mixing of the substrates. The correct filling of the circular dissolver is of great importance, as it can lead to complete failure of the system, if the corn is not completely stirred. The reason for this is that the maize piled up and compressed in the ascending screw. The screw can not turn any further and after a short time the motor protection of the ascending screw is activated. If the dry matter content of corn changes, its mass fraction within the KD must be adjusted so that the TS content of the freshly mixed substrate does not rise above 13.5% kg TS (ensuring pumpability).

Second operating unit: fermentation and digestate storage

The fermentation is carried out as a fully mixed continuous flow reactor in the mesophilic temperature range between 40 ° C and 42 ° C. For this purpose, the fermenter is provided. The substrate is supplied via a substrate line which ends above the liquid level in the fermenter. The supply depends on the control of the pumping process. The fermenter contains three height-adjustable stirrers. The fermentation volume of the fermenter is 1990m ³ . The fermenter also has a 350m ³ gas storage. The gas pressure within the gas reservoir is continuously measured. The temperature of the fermenter is kept constant by means of the fermenter heater. For internal desulphurisation, air is fed to the fermenter through an air blower. A pH probe is installed at the sampling tap of the fermenter. It is part of the regulatory system. According to the supplied amounts of substrate (volume) a corresponding volume of digestate is passed through a submerged in the fermentation liquid overflow line in the digestate storage. For the mixing of the fermentation substrate in the mixing tank a fouling suspension from the Rezi-shaft is needed. The digestate pump feeds the digestate storage. Via a biogas displacement line, the digestate storage tank is connected to the fermenter. The digestate storage also has a gas pressure measurement. The Rezi shaft is filled via a separate transfer with dipping into the fermenter. The digestion suspension is fed to the circular dissolver via the substrate pump. The Rezi shaft, with a filling volume of approx. 1.5m ^3, is designed as a PEHD container with insulation and aluminum sheet cladding.

Third operating unit: CHP

The operating unit CHP contains a gas analysis, for example from Awite. The gas analysis determines the volume contents of CH ₄ , H ₂ S and O _{2 of} the biogas. After the gas analysis, the biogas is compressed in a gas compressor and led to the torch or CHP. To balance the biogas streams an ultrasonic volume flow meter (FIC torch) is installed, for example, the company E + H, to determine the gas consumption of the torch in the biogas line to the torch.

The torch has a power of 1600 kW. The CHP (for example, the company Jenbacher) has a power of 625 kW and has a power measurement and a kilowatt counter. The exhaust gas burned in the CHP is fed to a thermoreactor for afterburning. The electric power of the CHP is fed into the grid via a generator. The heat of the CHP is passed through a heat exchanger to the district heating network and fermenter heating. The unused heat goes over a table cooler.

Optical measuring device

For example, a TENIRS measuring system from m-u-t Agri Solution GmbH (m-u-t) can be used as an optical measuring device. m-u-t has a large data pool of reference data that allows for more accurate and stable calibration models. The database contains u. a Data on maize and grass silage (NaWaRo's), slurry and fermenter contents (such as FOS / TAC, TS and oTS). The NIR spectrometer has a wavelength range of 1000 nm to 1700 nm. A central unit is connected to two measuring heads with sapphire measurement windows, which are connected to the NIR spectrometer using fiber optic cables. The NIR spectrometer has a resolution of approx. 16 nm. The NIRS system is connected to the process control system via Profibus. The measuring system is calibrated for the values of TS, oTS and FoTS for the substrates corn, recirculate, manure and the fresh substrate mixture. For the process control of the biogas plant, a further calibration of the process parameter FOS / TAC in the recirculation stream takes place. To calibrate the NIRS measuring system, samples are taken and analyzed in the laboratory. In addition to the calibration, 12 reference samples are analyzed each year (one sample each month). The NIRS measuring system can perform up to 20 measurements per minute. For each sample several individual spectra can be recorded. The only condition is the correct assignment of the samples to the spectra. The measured data are stored in the internal database of the central unit and can be called up externally. For the configuration of the NIRS system the parameters integration time, averaging count, cycle time, network interface setting and channel selection are adjusted. The TENIRS system independently performs white references (WR) and dark references (DR).

A TENIRS system is installed to record the NIR spectra in the liquids (manure, recirculate and substrate mix) and corn silage. The TENIRS system consists of two NIR probes connected to the central unit via fiber optic cables. The central unit contains the spectrometer. The first measuring head is used for the real-time analysis of the feed parameters of the mixed substrate mixture, the liquid manure and for the measurement of the recirculated material. The analysis of the recirculate also serves to control the process stability of the fermenter via the process parameters FOS, TAC. The second measuring head is installed in the ascending screw to the circular dissolver and serves to optimize the mixture composition within the circular dissolver NIRS analysis of the maize silage feed parameters (solid). The data transmission of the measured data from the central unit takes place via a Profibus connection to the process control system. To calibrate the NIRS measuring system, two additional sampling samples will be installed. The individual components of the NIRS measuring system are described in more detail below.

Central unit: The central unit is mounted in the mixing cellar of the biogas plant in good reach (distance up to 15 m) to the NIR measuring heads. The central unit contains the spectrometer and must therefore be protected from dirt and moisture. The central unit is therefore installed in an additional protective cabinet (600mm × 600mm × 400mm with transparent front glass) and mounted on the wall. After installation of the central unit, the Ethernet connection, Profibus connection and power supply must be connected.

NIR measuring head recirculation, manure and substrate: The first NIR measuring head is installed after the substrate pump (on the pressure side) and in front of the T piece in the direction of the circular dissolver or fermenter in a horizontal position in the recirculation or substrate line. The flange connection of the first NIR measuring head has been specially manufactured and welded with an extruder.

The distance from the 90 ° elbow to the middle of the sensor is approx. 500 mm. This corresponds to the recommendation of a flow contact length L of 4 to 5 times the pipe diameter D.

Sampling for the substrate and recirculated stream is installed at a distance of about 300 mm after the NIR sensor in the flow direction. For the sampling of liquids, a piping system made of PE with ball valve is installed. Sampling is used to remove the recirculated material, manure and substrate.

NIR measuring head - corn: The second NIR measuring head is installed in the ascending screw to the circular dissolver and is used for NIRS measurement of corn silage.

Here, the distance between the entry of the transverse screw (beginning of the ascending screw) to the NIR sensor is 1500 mm. The second sample for the removal of maize silage is installed at a distance of approx. 500 mm from the NIR sensor (in the direction of flow) and is designed in stainless steel (V4A) and has a fire service connection in DN63. The NIR sensor and the sampling tap are both installed in the 5 o'clock position (45 °) in the auger to avoid the measurement of deposits.

Data transmission and connection to the process control system via Profibus: The PLC programming of the measuring system can be carried out with the STEP 7 programming language. Within the central unit, the switching of the sensors takes place. Depending on which sensor is currently being controlled, the bus measured values of the central unit are transmitted via Profibus DP to the S7 controller. For this purpose, a request model for the process control system can be programmed, which requests the measurement of the respective material flow to the central unit. The central unit then changes to the desired NIR sensor and supplies the process control system with the process values. The maize silage is measured continuously as soon as the screw conveyor is in operation. The measurement of the recirculated material starts at 50% of the set value of recirculate at each feeding cycle. On the other hand, the measurement of the substrate mixture takes place only when a weight of 1000 kg plus the residual fill weight is reached during feeding. The remaining filling weight is the weight, which remains after feeding in the circular dissolver (usually between 250 kg and 350 kg). These programming measures can be used to avoid measuring errors due to residues or old substrates in the line. The measurement of manure analogous to the recirculate is possible, but not implemented, since the composition of the manure is relatively constant compared to the recirculate and the substrate mixture. Nevertheless, the slurry must be sampled so that additional manure can be measured. The process values are written in three different file blocks (DB) and visualized in the process control system (DCS). The parameters apply to all substance analyzes (liquid manure, recirculate, substrate and maize). The values of the NIRS sensor are recorded during each pumping operation (manure, recirculation and substrate) after flushing the pipeline, as described above, and then written to the archive. The updating of the NIRS parameters within the PLS is carried out only upon request by the PLS and only during the performance of the measurement. After completion of the measurement, the measured value within the DCS remains constant until the next measurement. The data is stored in the PLS for about three months. To load new calibration models onto the system, the NIRS system is connected to the Internet via Ethernet.

Calibration of the NIRS measuring system

To create the calibration two methods are needed. As primary method, the analytical values from the sampling serve. The measurements of the NIR spectra, on the other hand, serve as a secondary method. Calibration is essentially a complex statistical analysis. Statistical evaluation is done with the unscrambler software from Camo. As a first step, the collection of Data sets (feed analyzes and NIR spectra). This is followed by data preparation (SNVD preprocessing) in which the light scattering is corrected and the NIR drift is normalized over the wavelength. The correction of the light scattering takes place via a combination of SNV (Standard Normal Variant), which scales the absorption spectra and a baseline correction (Detrend). Modeling must then be determined from the SNVD-corrected values. For this purpose, an estimation function is determined by the method MPLS (Multiviate Partial Least Square). Furthermore, there is an outlier control (Local Outlier Factor). The distinction of the substrate composition is made by a principal component analysis called Principal Component Analysis (PCA). The PCA is a kind of support vector machine (SVM) and acts as a classifier. PCA is a method of multivariate statistics. Principal component analysis is used to structure, simplify, and illustrate large data sets by approximating a variety of statistical variables with a smaller number of highly meaningful linear combinations (principal components).

• 1. Test des Betriebsstatus des Messkopfes über das Controlpanel der Zentraleinheit. Es muss ein grüner Kreis um den Tab sein. Sollte der Kreis rot sein, muss zuvor die automatische Messung des NIR-Kopfes gestartet werden. Dies erfolgt durch das Drücken des Start-Buttons über den Touchscreen.
• 2. Genaues Timing der Probenahme.
• 3. Bei gewünschter Probenahme muss sofort über den Bildschirm Start Sampling gedrückt werden. Danach wird das Substrat in der Drop-down-Liste ausgewählt. Sofort danach muss die Probenummer eingegeben werden. Danach vergibt das System der Probenummer einen ersten Zeitstempel.
• 4. Dann werden die Proben gezogen.
• 5. Nach erfolgter Probenahme ist die pH- und Temperaturmessung durchzuführen (testo 205-Einhand-pH-/Temperatur-Messgerät).
• 6. Optional kann dann der pH-Wert im System eintragen werden.
• 7. Es sollte darauf geachtet werden, dass die Messdauer des Systems nicht zu kurz ist. Angemessen ist eine Messdauer von mindestens 30 Sekunden und maximal zwei Minuten.
• 8. Nach erfolgter Messung muss im System der Button Save Sample getippt werden. Es wird gleichzeitig ein weiterer Zeitstempel vergeben. Die Probenahme ist damit abgeschlossen.

For the calibration of the substrate mixture 30 samples are needed, for recirculation 45 samples and for manure 25 samples. The calibration of corn silage is based on 100 samples. Sampling is divided into several sub-steps. In the following, these sub-steps are listed.

• 1. Test the operating status of the measuring head via the control panel of the central unit. There must be a green circle around the tab. If the circle is red, the automatic measurement of the NIR head must first be started. This is done by pressing the Start button on the touch screen.
• 2. Accurate timing of sampling.
• 3. If sampling is required, press Start Sampling immediately on the screen. Thereafter, the substrate is selected in the drop-down list. Immediately thereafter, the sample number must be entered. Thereafter, the system gives the sample number a first timestamp.
• 4. Then the samples are drawn.
• 5. After sampling, the pH and temperature measurement must be carried out (testo 205 single-handed pH / temperature measuring instrument).
• 6. Optionally, the pH value can then be entered in the system.
• 7. Care should be taken that the measurement time of the system is not too short. A measuring time of at least 30 seconds and a maximum of two minutes is appropriate.
• 8. After successful measurement, the button Save Sample must be tapped in the system. At the same time another time stamp will be given. The sampling is completed.

It is important that the reference samples are clearly registered in the database of the measuring system (choice of sampling program with correct sample number). To check if the system has saved the sample correctly, the action should be checked in the log entries of the system.

The equipment and materials used during sampling are listed below.

Corn:

• - Industrial vacuum cleaner, OBI Cleaning wet and dry vacuum cleaner NTS 20, power 1,400W
• - Vacuum cleaner hose extension with fire service connection
• - Wooden stick for breaking the plug inside the sampling tap
• - pH and temperature measurement, testo 205 single-handed pH / temperature measuring device
• - Freezer bag with zipper, volume of 1 l
• - Freezer, temperature of -18 ° C

Liquids:

• - pH and temperature measurement, testo 205 one-hand pH / temperature measuring instrument, Testo AG
• - LDPE wide-mouth bottles, volume of 1 liter, Carl Roth GmbH and Co. KG
• - LDPE wide-mouth bottles, volume of 0.5 l, Carl Roth GmbH and Co. KG
• - Commercially available 20 l canister with enlarged outlet opening

Sampling of corn silage: For sampling, a 2-inch connection with manual valve is installed at 5 o'clock in the ascending screw. Before sampling, the plug must be broken inside the ascending screw with a wooden stick. Thereafter, an industrial vacuum cleaner is connected via a fire service connection by means of a vacuum cleaner hose extension. It takes the removal of the corn until the industrial vacuum cleaner is completely filled. After opening the vacuum cleaner, the pH and temperature measurement should be carried out with the handset. Once the pH and temperature measurements have been taken, the NIRS measurement is stopped by means of the touch screen of the central unit. As sample material only the upper layer of maize within the vacuum cleaner is used so that no residual deposits are analyzed. The corn is placed in a 1 liter zippered freezer bag (about 4 handfuls) and placed in the freezer at a temperature of -18 ° C within 10 minutes and frozen. It should be ensured that the remaining air is pressed out beforehand. The dust cleaner is to be cleaned after the sampling with hot water and then to dry. Sampling of the liquids: Before sampling the liquid media (liquid manure, fresh substrate and recirculate), the sampling line (PE) must first be emptied. For a 20 l canister is completely filled with material from the PE line. Afterwards the sampling can take place. For this a 5 l bucket is filled with the sample material. When sampling manure, in addition to the 20 l canister, another 5 l bucket must be used to discharge. The liquid samples (manure, fresh substrate and recirculate) are finally placed in a 1 liter LDPE wide-mouth bottle. The bottle is easy to depress and then fill up. This can lead to outgassing in the bottle, so that the lab has fewer problems opening the bottle. After sampling, the canister and buckets are cleaned with hot water and air dried.

• – Gülle: Anpassung der Fütterungsmenge auf mind. 400 kg, damit man ungefähr 1 min zur Probenahme hat. Weiterhin wird eine weitere Person zur Hilfe genommen, damit die Probenahme gleichzeitig zur Bedienung des TENIRS-Systems abläuft. Die Probenahme startet direkt nachdem der Schieber der Gülleleitung geöffnet wird und die Pumpe anfängt die Gülle zu pumpen.
• – Rezirkulat: Die Probenahme beginnt wenige Sekunden nachdem die Schieber sich geöffnet haben und Rezirkulat gepumpt wird. Die Probenahme ist spätestens nach Erreichen des Füllgewichtes des Kreis-Dissolvers von 2000 kg zu stoppen, da kurz danach das Füllen des Kreis-Dissolvers mit Getreide beginnt.
• – Mais: Die Probenahme des Maises startet sobald der Motor der Steigschnecke angeschaltet wird und sollte nach ca. 1 Minute beendet werden.
• – Substrat: Die Probenahme des angemaischten Substratgemisches startet nachdem die Pumpe den Abpumpvorgang des Kreis-Dissolvers gestartet hat.

Timing and peculiarities of the sampling: As already mentioned, the time of sampling is very important. The timing of the sampling should be chosen as follows:

• - manure: adjusting the feeding quantity to at least 400 kg, so that one has about 1 min for sampling. Furthermore, another person is taken to help, so that the sampling takes place simultaneously to operate the TENIRS system. The sampling starts immediately after the slide of the manure line is opened and the pump starts to pump the manure.
• - Recirculation: Sampling starts a few seconds after the valves have opened and recirculate is pumped. The sampling must be stopped at the latest after reaching the filling weight of the circle dissolver of 2000 kg, because shortly after the filling of the circular dissolver with cereals begins.
• - Corn: The sampling of the corn starts as soon as the engine of the ascending screw is switched on and should be finished after approx. 1 minute.
• Substrate: The sampling of the mixed substrate mixture starts after the pump has started the pumping process of the circular dissolver.

From maize silage a variety of parameters are to be determined. The parameters are not analyzed wet-chemically, but are determined by means of an already existing NIRS calibration.

There are the parameters TS, OTS, XA, N _ges , C _ges , NH ₄ -NO ₃ , FOS, TAC, acetic acid, propionic acid, iso-butyric acid, butyric acid, iso-valeric acid, valeric acid, caproic acid and the acetic acid equivalent for all 45 Rezirkulatproben certainly. For 20 samples, the quantity and trace elements of the recirculated matter are further analyzed.

The parameters TS, VS, XA, N _ges, C _sat, NH ₄ -NO _3, FOS, TAC be determined for the slurry. The analysis of the acid and quantity or trace elements can not be carried out for the manure.

In contrast to the feed analysis of maize silage, wet chemical analyzes are carried out for the calibrated substrate mixture for the calibration. It will _org, the parameters TS, XA, N _tot, NH ₄ -NO _3, C _ges and the parameters XP, XL, XF, NDF, ADF _org, ADL _org determined and, in addition analogous to the analysis of the liquid manure and the Rezirkulates Parameters FOS, TAC analyzed. The enzyme-soluble organic substance (ELOS) is determined by comparison with the nitrogen-free extractives (NfE). It is assumed that ELOS is 1.04 times larger than NfE.

On a random basis, additional analyzes of the substrates are carried out. For the liquid substrates manure, recirculate and substrate mixture, the TS content and the FOS / TAC index are to be determined. Of the corn silage, only the TS value is to be determined. To determine the TS content, use the laboratory analyzer ORImat310. The FOS / TAC index is determined by means of the automatic titration unit TIM840.

In the biogas plant 1, three different operating regulations are implemented. In the first operation schedule according to the daily schedule (TEP), the number of feedings per day (mixing cycles) is set manually and from this the interval duration of the feedings is calculated. The second control feeds the biogas plant to the biogas pressure in the fermenter. The two control methods are described in detail in Kuhnla 2013.

NIRS control system

To optimize the biogas plant, the fermenter of the biogas plant is balanced. With the aid of the NIRS measuring system, the feed measured values of the recirculated material and the substrate mixture are determined continuously and in real time. These are used for the "Energy Balance" control system. The aim of the regulation is the dynamic calculation of the number of feeding cycles per day. It is assumed that a needs-based substrate supply leads to an increased gas yield by the bacteria within the fermenter. The energetic balancing of the fermenter determines the substrate requirements of the bacteria. The energy content of the substrate and the recirculate is determined by the fermentable organic dry substance (FoTS). The feed intake must be adjusted so that the energy input corresponds to the energy requirement of the CHP. To control the effectiveness of the energy balance control, the biogas plant will be retrofitted using the Volumetric flow meters of the torch (FICFackel) and the CHP (FICBHKW) accounted for. If the feed quantity is too high, it can lead to overproduction of biogas that is either burned (torch) or lost through overpressure protection. This should be avoided by means of the control system according to energy balance. The biogas volume flow of the CHP is therefore specified as the setpoint (eg 300 m ³ / h). If the number of feedings per day is minimized, it is possible to save on a substrate (maize, liquid manure, grain) and, on the other hand, the energy consumption of circular dissolvers and pumps can be minimized. For the energy balance, only the fermentable portion of the material streams (substrate, fermenter outlet) is used. It is assumed that the remaining non-gas forming portion of the streams is completely converted to bacterial mass or can be considered inert.

Since only the directly fermentable portion of the material flows is considered, the energy requirement of the bacteria E _bacteria = 0 can be set.

This results in the following energy balance around the fermenter: E _{substrate mixture, fermentable} = E _{fermenter outlet} + E _biogas

The mass flow of the fermenter outlet in the fermenter _outlet can be determined by means of the mass balance around the fermenter: m _{fermenter outlet} = m _substrate - m _biogas

To determine the _biogas mass flow in _biogas , a constant density of the biogas ρ _biogas = 0.00128 t / m ^{3 is} assumed.

The setpoint of this control according to energy balance is the desired _biogas volume flow V _Biogas; By means of the density of biogas ρ _biogas and the setpoint of the _biogas volume flow V _{biogas; setpoint} the _biogas mass flow m _biogas can be calculated: m _biogas = ρ _biogas · V _biogas;

The calibrated NIRS measurements are used to determine the fermentable content of the material streams. The process parameter FoTS of the recirculated material and substrate mixture from the NIRS measuring system is used. The proportion of the fermentable organic dry matter of the NIRS system is referred to below as x _FoTS . For balancing, the FoTS amount of the substrate x _{FoTS; substrate} and the FoTS amount of the recirculated material x _{FoTS; recirculate} are used. It is assumed that the composition of the recirculated material and the composition of the fermenter outlet are identical. It thus applies: x _{FoTS; fermenter outlet} = x _{FoTS; recirculate}

Subsequently, the fermentable mass of the substrate _mixture m _{FoTS; Substrate} m _{FoTS; substrate} = m _substrate x _{FoTS; recirculate} and the fermenter _outlet m _{FoTS; fermenter outlet} m _{FoTS; fermenter outlet} = m _substrate · x _{FoTS; recirculate} be calculated.

The NIRS system continuously determines the process parameters of the substrate and the fermenter outlet. The controllable part of this balance is the added energy of the substrate mixture. The aim of the regulation is thus to determine the duration of the feeding intervals. In order to achieve the desired biogas volume flow, it is necessary first of all to determine the fermentable mass of a cycle m _{FoTS; Z which} can be converted into biogas. For this purpose, the fermentable mass of the substrate _mixture m _{FoTS, substrate is taken off} from the fermentable mass of the fermenter _outlet m _{FoTS, fermenter outlet} : m _{FoTS; Z} = m _{FoTS; substrate} - m _{fermenter outlet}

According to Weißbach (Weißbach 2008), it is possible to directly determine the fermentation-forming biogas from the amount of fermentable organic dry matter FoTS by means of the specific biogas-forming _potential SBY _{FoTS; Weissbach} . Thus, the biogas volume flow of a feeding cycle V _{BG-FoTS; Z; normalized} can be calculated according to the following equation: V _{BG-FoTS; Z; normalized} = m _{FoTS; Z} * SBY _{FoTS; Weissbach}

Dividing the desired biogas volume flow V _{BG setpoint} with the biogas volumetric flow rate of a feeding cycle just calculated gives the number of required cycles per hour. Z _hour = V _{BG setpoint} / V _{BG-FoTS; normalized; Z}

To convert the number of cycles per hour Z _hour into the number of cycles per day Z _day must be multiplied by 24: Z _day = Z _hour · 24

One day has 1440 minutes. To determine the desired feeding interval, the number of minutes of a day must be divided by the calculated number of cycles per day Z _day : F = 1440 / Z _day

Since it is possible to calculate values which are extremely high or small, an upper and a lower barrier are built in to limit the feeding intervals F _min and F _max . The upper and lower barriers can be changed by the plant operator. The minimum of the feeding interval F _min is the total duration of the feeding until the substrate mixture is pumped out. The total duration of the feeding results from the duration D for filling the circular dissolver with manure (about 30 seconds), recirculate (about 2 minutes), cereals (about 30 seconds) and corn (about 3 minutes), as well as the duration for the mashing of the substrate mixture (about 3 minutes) and for the subsequent pumping out of the substrate mixture (about 3 minutes): F _min = D _manure + D _{recirculation} + D _grain + D _corn + D _mixing + D _pumping = 15 min

The maximum of a feeding interval F _max should be chosen between 40 and 50 min.

Process simulation / fermenter model and OPC server

For the dynamic simulation of the anaerobic fermentation of the biogas plant, the numerical fermenter model based on the Anaerobic Digestion Model no. 1 (ADM1) by Beermann (Beermann 2008). As an extension of the model, the inhibition function for propionic acid is implemented. In addition, Matlab / Simulink's OLE for ProcessControll (OPC) Toolbox is used to enable dynamic transfer of the process control NIRS measurement to the fermentor model.

Adjustments to the fermenter model: The fermenter model from Beermann is used for process simulation and adapted at several points. A Simulink model is added to describe the propionic acid inhibition because propionic acid inhibition was not considered in the existing model. Furthermore, the import function of the input data of the model via Excel is replaced by the real-time transmission of the input data via the Matlab OPC Toolbox. All necessary material data of liquid manure, recirculate, grain and maize are now transferred directly from the process control system to the Simulink model. This enables a real-time simulation of the biogas plant. Furthermore, the model Energy Balance will be added. This model determines the number of necessary cycles of feeds for optimal substrate yield and gas yield. It can be changed over several manual switches, the gas yield forecast. The following gas yield calculations can be selected: calculation according to Amon (Amon 2003 and Amon 2007), to TS, to Weißbach (Weißbach 2008) and to Mukengele (Mukengele 2013). The advantage of this is that you can determine the best-functioning model during real-time operation of the biogas plant. In the following some calculation models of the adapted fermenter model are presented. The adapted fermenter model is referred to below as ADM1EnergyBalance. The feed data of the NIRS system are transmitted via Profibus to the process control system. The process data is stored and written on a Siemens WinCC OPC server. Another OPC server is used to transfer this data to the Matlab OPC Tool. The Matlab OPC tool has a Simulink interface that allows you to further process the data of the OPC server directly in Simulink. The Matlab OPC Toolbox in Simulink contains three blocks. The first OPC-Config block is used to set the communication between the MatrikonOPC server and the OPCClient of the Matlab OPC Toolbox. With the other two blocks, data can be read (OPC Read) and written (OPC Write) on the OPC server. Thus, the results of the ADM1EnergyBalance can be transferred directly to the process control system and, among other things, the number of feedings can be adjusted depending on the calculation model. The 6 schematically displays the MatrikonOPCServer used for communication with the Matlab OPC Toolbox. The figure shows, among other things, the feed values of the NIRS system and the real-time readings of the biogas volume flows FIC.

The ADM1EnergyBalance, as the name implies, consists of two main modules. The first module consists of the fermenter model by Beermann (Beermann 2008) and the connections of the real-time data of the PLS ( 4 ).

Among other things, the temperature T ₀ , the gas volume V _gas and the initial concentration within the fermenter c _{0 of} the ADM1 are transmitted via the OPC server and processed in the model. Furthermore, the feed data of the NIRS system is used directly (green Simulink block). The second module carries out the energy balance around the biogas plant. With the aid of the OPC Toolbox, the feed values of the NIRS system are continuously read (OPC Read) and used directly for the energy balance. In the energy balance model, the fermenter is balanced in the same way as the Energy Balance NIRS control system.

The energy demand of the CHP is also used as the setpoint in the ADM1EnergyBalance. The calculation of the energy requirement is in the 9 seen.

In addition, the real-time measurements of the volumetric flow meters (FICBHKW, FIC torch, FIC residual storage) are used to determine the real energy requirement. Should an overproduction of the biogas plant lead to the gas flare being switched on, the energy balance automatically reduces the number of feeding cycles. The 10 shows the model for calculating the number of feeding cycles per day Z _day or the feeding interval

The features disclosed in the specification, the claims, and the figures may be relevant to the implementation of embodiments both individually and in any combination with one another.

Bibliography:

• Amon 2003: Amon, Th; Kryvoruchko, V; Amon, B; Moitzi, G; Lyson, D; Hackl, E; Jeremic, D; Zollitsch, W; Pötsch, E: Optimization of biogas production from energy crops maize and clover grass. In: Final Report July (2003)
• Amon 2007: Amon, Thomas; Amon, Barbara; Kryvoruchko, Vitaliy; Zollitsch, Werner; Mayer, Karl; Gruber, Leonhard: Biogas production from maize and dairy cattle manure - influence of biomass composition on the methane yield. In: Agriculture, Ecosystems & Environment 118 (2007), No. 1, pp. 173-182
• Beermann 2008: Beermann, Jan: Development of a numerical model for the simulation of anaerobic fermentation in biogas plants based on ADM1, University of Hannover, diploma thesis, April 2008
• Weißbach 2008: Weißbach, F .: The Assessment of the Gas Forming Potential of Renewable Resources. In: International Science Conference Biogas Science 2009 Volume 3 (2008), p. 517
• Mukengele 2013: Mukengele, Mike: Energy Balance - Calculation GE. 2013
• Kuhnla 2013: Kuhnla, Karsten: Development of an application program for the control of the biogas plant Bitterfeld 1 based on Simatic Step 7, HS Merseburg, Dissertation, October 2013

Claims (10)

A method of controlling a biogas plant, the biogas plant having a supply device for feeding a substrate into a fermenter and a gas utilization device, the method comprising the following steps: Setting a nominal value for a gas volume flow which is to be made available to the gas utilization device, Determining a substrate parameter of the substrate, which is supplied to the fermenter for processing into biogas, by means of an optical measuring device, Determining an expected value for a gas volume flow that can be generated with the substrate based on the determined substrate parameter, - Compare the setpoint with the expected value and Adjusting the supply of the substrate depending on the result of the comparison. A method according to claim 1, wherein a discharged from the fermenter portion of the substrate is supplied to the fermenter as recirculation, further a Rezirkulatparameter the recirculation is determined by means of the optical measuring device and the expected value for the gas flow rate is determined taking into account the Rezirkulatsparameters. Method according to claim 1 or 2, wherein the supply device has a mixing device, wherein a first optical sensor of the optical measuring device is arranged in a line upstream of the mixing device and wherein the substrate parameter and, if present, the recirculation parameter are determined by means of the first optical sensor. Method according to one of the preceding claims, wherein the supply means comprises a conveyor, wherein in the conveyor a second optical sensor of the optical measuring device is arranged and wherein by means of the second optical sensor, a mixing parameter of the substrate is determined. Method according to one of the preceding claims, wherein the optical measuring device is formed as Nahinfrarotspektroskopie-measuring device. Method according to one of the preceding claims, wherein a parameter from the following group is determined as a substrate parameter and / or as Rezirkulatparameter: fermentable organic dry matter, crude fiber, crude protein, Rohlignin and nitrogen-rich extractives. Method according to one of the preceding claims, wherein for the expected value, an energy content, a biogas formation potential and / or a methane formation potential is determined. Method according to one of the preceding claims, wherein the substrate is fed continuously and the supply of the substrate is adjusted continuously. Method according to one of the preceding claims, wherein by means of the optical measuring device, a process parameter is determined, which represents an advance of the fermentation of the substrate. Control device for controlling a biogas plant with - an optical measuring device and - a data processing device, which is coupled with the optical measuring device, wherein - the optical measuring device is designed to determine by means of an optical measurement a substrate parameter of a substrate which is fed to a fermenter of the biogas plant and - the data processing device is designed to determine an expected value for a gas volume flow on the basis of the determined substrate parameter, - compare the expected value with a nominal value for the gas volume flow and - adjust a supply of the substrate as a function of the result of the comparison.

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