Patent ID: 12233426

Reference numerals used in the drawings include:AL Exhaust airAS Slurry/waste suspensionBG BiogasFFT Solid-liquid separationRA Reactor dischargeSW Heavy materialsF Flow measurementL Fill level measurementP Pressure measurementV Solids content measurement1Supply pump2Fermentation reactor3Mixing in slurry4Return pump5Hydrocyclone feed pump6Mixing in on suction side of feed pump7Hydrocyclone8Fermentation reactor feed pump9Storage unit10Solid-liquid separation feed pump11Slurry return pump of solid-liquid separation1290° bends13Installation region of pressure sensor

DETAILED DESCRIPTION

A corresponding method procedure is shown inFIG.1. The slurry (waste suspension) is pumped (3) into a return from the fermentation reactor (2) by means of the supply pump (1), the throughput of which is regulated according to the amount of waste suspension produced. The throughput of the return pump (4) is controlled on the basis of a predetermined ratio to the throughput of the supply pump (1) in order to achieve the required reduction in solids content. The resulting mixture, which has a lower solids content than the waste suspension, is supplied (6) to the suction side of the hydrocyclone feed pump (5). The throughputs of the hydrocyclone (7) and its feed pump are a multiple of the sum of the throughputs of the supply pump (1) and the return pump (4) combined, so as to enable several passes of the waste suspension through the separation of heavy materials before it is supplied to the fermentation reactor. The throughput of the feed pump (5) is regulated by means of pressure measurement (P1) in the inlet of the hydrocyclone (7). The suspension which has been freed of heavy materials in the hydrocyclone is returned to the suction side of the hydrocyclone feed pump (5). To ensure a constant pressure loss in the hydrocyclone, the delivery rate of the fermentation reactor feed pump (8) is regulated by means of the pressure measurement (P2) in the outlet of the hydrocyclone (7), in such a way that the pressure difference P1-P2is constant.

Integrating a storage unit into the outlet of the hydrocyclone enables more stable control (seeFIG.2). As a result of the free overflow of the hydrocyclone (7) into the reservoir (9), only one pressure measurement (P) in the inlet of the hydrocyclone is required so as to ensure a constant pressure loss in the hydrocyclone. If the fill level (L) in the storage unit (9) allows it, the fermentation reactor feed pump (8) is controlled on the basis of a predetermined ratio to the throughput of the hydrocyclone feed pump (5), so as to implement a predetermined number of passes through the separation of heavy materials. If a predetermined upper fill level is exceeded in the storage unit (9), the throughput of the fermentation reactor feed pump (8) is regulated as a function of the fill level (L) in the storage unit (9), until the upper fill level in the storage unit (9) is undershot again. The throughput of the fermentation reactor feed pump (8) is then controlled on the basis of the throughput of the feed pump (5) of the system for separating heavy materials.

The storage unit (9) is preferably connected to the exhaust air treatment system. If formation of relevant amounts of methane or hydrogen is expected as a result of anaerobic biological activity in the storage unit, the storage unit should be connected to the biogas collection (FIG.2, dashed line) to improve the biogas yield from the fermentation.

The throughputs of the pumps are controlled via the speed of each pump. In the simple implementation of the method using a storage unit, the speed specifications are determined as follows:The speed of the supply pump (1) is controlled as a function of the accumulating volume of waste suspension.The required speed of the return pump (4) is determined on the basis of:throughput of the supply pump, calculated using the speed of the supply pump, the discharge head determined from the inventory, and the pump characteristic curve stored in the control system,required throughput of the return pump, which is calculated using the ratio of the average dry residue levels in the waste suspension and the return (dry residue levels determined in samples in the laboratory) and the dry residue level which is to be achieved in the mixture of these two material flows andrequired speed of the return pump, which is calculated from the required throughput using a specified discharge head and the pump characteristic curve stored in the control system.The speed of the feed pump (5) for the separation of heavy materials is controlled by measuring the pressure in the inlet of the hydrocyclone (P) in order to ensure the specified pressure loss in the hydrocyclone.In the event that the fill level in the storage unit (9) is below a predetermined upper fill level, the required speed of the fermentation reactor feed pump (8) is determined on the basis of:throughput of the hydrocyclone feed pump (5) is calculated using the speed of the feed pump, the discharge head determined from the inventory, pressure loss in the hydrocyclone, and the pump characteristic curve stored in the control system,required throughput of the fermentation reactor feed pump (8), which is calculated using the throughput of the hydrocyclone feed pump (5) and the predetermined number of passes through the hydrocyclone andrequired speed of the fermentation reactor feed pump (8), which is calculated from the required throughput using the discharge head determined from the inventory and the pump characteristic curve stored in the control system.In the event that the fill level in the storage unit (9) is above a predetermined upper fill level, the required speed of the fermentation reactor feed pump (8) is regulated by means of the fill level measurement (L) in the storage unit, in such a way that the fill level slowly drops until it falls below the specified upper fill level.

A preferred embodiment of the method is equipped with additional measurement technology (FIG.3). In the supply to the hydrocyclone, the solids content of the suspension (V1) is measured as a guide to the dry residue level or viscosity of the suspension. As a function of this measured value, the speed of the return pump (4) is regulated in such a way that the measured solids content corresponds to the setpoint specified by the control system. Alternatively, the solids content can also be measured in the mixture of waste suspension and return (V2) if this enables better control behaviour. Furthermore, flow measurement systems are installed in the supply (F1) to the hydrocyclone and in the supply (F2) to the fermentation reactor. As a result, if the fill level in the storage unit (9) is below a predetermined upper fill level, the speed of the fermentation reactor feed pump (8) can be regulated in such a way that a predetermined ratio of F1to F2is maintained. This ratio approximately corresponds to the number of passes through the system for separating heavy materials, since the mass of the separated heavy materials (SW) is negligible by comparison with the masses of the volume flows F1and F2.

For setting the dry residue level required for optimal separation of heavy materials, the required return can be very high, as a result of the dry residue level in the fermentation reactor. If this causes the hydraulic load on the hydrocyclone to become too high, a second heavy material separator is required. In this case, the dry residue level in the volume flow to be returned can be reduced using solid-liquid separation.FIG.4shows the method according to an exemplary embodiment of the invention with the necessary additions. A solid-liquid separation (FFT) is fed from the fermentation reactor (2) using a pump (10), and separates off a large part of the solids, which mainly contribute to a higher viscosity, at a consistency which can still be pumped. These are then returned to the fermentation reactor using a pump (11). By way of the return pump (4), the generated material flow, which is characterised by a lower dry residue level or lower viscosity than the contents of the fermentation reactor, is returned for blending with the waste suspension (3). As a result of the reduced dry residue level of the material from the fermentation reactor returned for separation of heavy materials, the return pump (4) has to supply less to the separation of heavy materials so as to set the required dry residue level in the inlet of the hydrocyclone (7). This means that an increase in the separation of heavy materials can be avoided or the specified number of passes can be achieved by maintaining the hydraulic load on the hydrocyclone.

By returning a liquid phase, which has been freed of filterable substances by the solid-liquid separation, using the return pump (4), the entry of methanogenic microorganisms into the storage unit (9) is also reduced. This largely prevents the formation of methane and hydrogen in the storage unit. This promotes a connection of the storage unit to the exhaust air treatment system, which brings about operational advantages and can be implemented more cost-effectively.

An advantage of the method procedures described above is that the waste suspension is diluted using contents of the fermentation reactor. This dilution therefore has no influence on the hydraulic holding time nor on the solids holding time in the fermentation reactor. The fermentation reactor can therefore only be designed for the significantly smaller accumulation of waste suspension.

Some embodiments can be implemented as follows:

In the aforementioned waste fermentation plant, the dry residue level of the waste suspension is approximately 11% based on the wet mass (FM) for an accumulation of 37 Mg/h. The dry residue level in the fermentation reactor is approximately 6% by wet mass. Do Carmo Precci Lopes et al. (2021) recommend, in their publication, a dry residue level of 9% by wet mass in the inlet of the hydrocyclone. This dry residue level can be set, in the method procedure described inFIG.1, after combining the waste suspension and recycling in point3by returning 25 Mg of contents of the fermentation reactor per hour. If the dry residue level in the inlet and outlet of the hydrocyclone changes only negligibly as a result of the separation of heavy materials, the dry residue level in the supply to the hydrocyclone corresponds to this value. For a throughput of 310 Mg/h through the system for separating heavy materials, 5 passes through the hydrocyclone can be implemented.

If the dry residue level changes significantly during passage through the hydrocyclone, a method procedure analogous toFIG.3is preferable. If the separation of heavy materials separates off 10% of the dry residue level of the waste suspension, the return pump (4) only has to pump 15 Mg of the fermentation reactor's contents per hour in order to maintain the desired dry residue level of 9% by wet mass in the hydrocyclone inlet. In this case, only 260 Mg/h need to be supplied to the hydrocyclone for 5 passes.

If 37 Mg/h of a waste suspension having a dry residue level of 17% by wet mass is supplied into this process and 10% thereof is separated during the separation of heavy materials, at a dry residue level of 6% by wet mass, 88 Mg/h must be returned to the fermentation reactor in order to set a dry residue level of 9% by wet mass in the inlet of the hydrocyclone. To achieve a number of passes through the hydrocyclone of five, 625 Mg/h must be supplied thereto.

If, in this case, the method procedure is carried out analogously toFIG.4and the dry residue level in the return can be reduced to 2% by wet mass using the solid-liquid separation, only 36 Mg/h must be returned to set the dry residue level in the hydrocyclone inlet to 9% by wet mass. As a result, a throughput of 365 Mg/h through the separation of heavy materials enables a number of passes of five.

Since the number of required passes through the hydrocyclone is largely determined by the ratio of the supply flow for separating heavy materials to the feed flow for fermentation, the usable volume of the storage unit (9) has no influence on it. As a result of the mixing of the waste suspension with contents of the fermentation reactor, this mixture is characterised by methanogenic activity. In order to limit the formation of biogas in the storage unit, the usable volume of the storage unit is limited to ensure the shortest possible holding time. In a preferred embodiment of the method according to the invention, the usable volume of the storage unit is only 1 to 2 times the volume of waste suspension supplied per hour.

Centrifugal pumps are preferably used as the supply pump (1) and feed pump (5) for the separation of heavy materials, as they are available in a very robust and low-wear design. As a result of the hydrostatic pressure in the fermentation reactor and the reduced content of heavy materials in the material flows to be conveyed, the feed pump (8) for the fermentation reactor and the return pump (4), provided that it draws directly from the reactor, are designed as positive displacement pumps.

In a method design according toFIG.1orFIG.2, depending on the operating and installation situation, the design of the return pump as a positive displacement pump may require that the supply pump be designed as a positive displacement pump. In the method design according toFIG.3, this can be avoided. If the return pump is controlled by measuring the solids content of the suspension (V1) in the hydrocyclone inlet, the return can be supplied directly (dashed line) to the storage unit (9).

For a method procedure analogous toFIG.4, the solid-liquid separation feed pump (10) and the pump for returning the solids (11) are positive displacement pumps. In this case, the return pump (4) may be designed as a more cost-effective and lower-wear centrifugal pump. A return (dashed line) directly into the storage unit (9) simplifies the configuration of the return pump and improves the control behaviour, since the back pressure of the return pump changes solely as a function of the delivery rate of this pump.

In the supply to the hydrocyclone, two 90° bends (12) cause the supply flow to be diverted from the vertical flow direction into a horizontal flow direction, and then horizontally, before entering the hydrocyclone. This ensures that the heavy materials are introduced largely tangentially at the wall of the hydrocyclone. The pressure measurement sensor is installed in the supply line laterally just before the hydrocyclone on the opposite side (13), to reduce abrasion. Furthermore, it does not protrude into the suspension flow, but rather is installed offset back a few millimetres from the inner pipe wall to improve its service life (FIG.5).

The mixture of slurry and return from the fermentation reactor is supplied on the suction side of the feed pump (5) of the system for separating heavy materials. This ensures that this centrifugal pump provides good mixing of the three material flows supplied to the hydrocyclone.

While certain exemplary embodiments of the method, device, and apparatus and methods of making and using the same have been shown and described above, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.