DE102014005667A1 - Apparatus and method for drying fermentation residues - Google Patents

Abstract

For drying fermentation residues from biogas plants or liquid manure, a digestate dryer (GT) has an evaporator (V) with a heating device (HV). The heater (HV) can be heated with steam or hot water. With several fermentation residue dryers (GT) different plant constellations can be realized for an efficient drying of different fermentation residues.

Description

The invention relates to a device and a method for drying fermentation residues.

For the growing number of biogas plants, the disposal of digestate becomes a central issue. Practical and economic concepts must be found for this. Depending on the initial digestate and the desired products, mechanical separation, drying, evaporation and wastewater management methods are used. These individually or in combination operated procedures require in part considerable investment and the use of thermal and electrical energy. On the other hand, storage and application costs can be saved and sometimes proceeds for the fermentation residue products can be achieved. In the case of large-scale plants, digestate treatment can hardly be avoided, and the question of their economic efficiency arises in connection with the entire plant (cf. LOOTSMA, A., T. RAUSSEN (2008): Current methods for processing and recycling digestate. In: Bio and secondary raw material utilization. Material - energetic III. Witzenhausen Institute - News from research and practice. Kassel: K. Wiemer, M. Kern (ed.). Pp. 559-576 .).

The cited reference gives a good overview of the state of the art of drying processes. Combinations of drying methods from mechanical separation and thermal processes using belt, drum, thrust reversing, fluidized bed, or hot steam dryer are frequently used. For the evaporation or for thickening of liquid fermentation residues, downdraft and forced circulation evaporators or multi-stage evaporator boilers with mechanical vapor compression are used. Evaporation systems with vapor compression are also used.

In belt dryer systems used on the market, the fermentation residues are dried by heated air, which is blown over a large area of strip loaded with digestate. The operating principle of these systems is essentially based on evaporation. To achieve high drying performance, high airflow velocities are required. Drying is additionally supported by heating the dry air. However, these air drying processes require large amounts of air which must be generated electrically. This reduces the electrical efficiency of the entire biogas plant. In addition, the drying efficiency is not sufficient to process 100% of the fermentation residues that arise in the biogas plant. In addition, such systems are not hermetically sealed, so that it comes to odor, whereby the exhaust air is additionally loaded with ammonia and particulate matter.

In most processes for digestate drying the digestate must be pretreated by z. For example, be dried using a separator to a dry matter content of 25 percent; or a small portion of the dried material is added. These process steps represent additional expense that degrades the efficiency of the drying.

From the German patent application DE 41 14 667 A1 a method and a device for the treatment in the form of manure present animal waste products is known that consists in that the waste products are first stored in a container for the formation of methane gas, from there continuously supplied to a centrifuge and the solid component obtained there then dried becomes. The separated in the centrifuge liquid component is passed into an evaporator vessel in which the water contained therein is vaporized by vacuum, then re-liquefied in a condenser and fed to the natural water cycle. The waste heat of the condenser is raised by means of a heat pump and then fed to the evaporator boiler. In this, as with all known capacitors, the steam condensation is carried out by conventional heat exchangers, that is, with 2 separate media, which in addition to other disadvantages has a temperature loss and quickly pollute the heat exchanger because of the loaded vapor vapor

The object of the invention is therefore to provide a digestate dryer, which overcomes the disadvantages mentioned.

This object is achieved with a device for drying digestate, which consists of a digestate dryer (GT), this one evaporator vessel with a Gärrestezufluss and a digestate effluent, a steam outlet, a heater with a steam or hot water supply (ZHV) and a condensate or Includes hot water drainage.

An advantageous embodiment of the invention is that the heating device (HV) consists of at least one concentrically arranged around the central axis of the evaporator vessel (V), double-walled plate. This can be an optimal heat transfer to the medium in the evaporator boiler reach.

A further advantageous embodiment of the invention is that the double-walled plates consist of several segments. This facilitates the installation and maintenance of double-walled panels.

Between the concentrically arranged plates, a cleaning device can advantageously be provided, with which the outsides of the double-walled plates are kept clean, so that they are not contaminated by the digestate. As a result, the caking of digestate, which could reduce the heat transfer, avoided.

The cleaning device may comprise brushes which are arranged so that they are arranged parallel to the axis of the evaporator vessel.

An advantageous device for drying fermentation residues consists of at least two arranged in series fermentation residue dryers which are connected to each other via their Gärrestezu- and drains, wherein the heating device of each upstream fermentation residue dryer is connected to the steam outlet of the downstream digestate dryer, wherein in the heater of the upstream condensate dryer resulting condensate is fed to a condensate collection tank.

According to a further advantageous embodiment of the device for drying fermentation residues, at least one solid / liquid separating device (QP) for the fermentation residues (M) is provided between the digestate feed and outflows. If the proportion of solid constituents of the fermentation residues is too high for the drying process or during the drying process, a mechanical separation of the fermentation residues may be useful.

According to a further advantageous embodiment of the apparatus for drying fermentation residues, the digestate discharge of a digestate dryer is connected to the inlet of a secondary fermenter and its outlet is connected to the digestate inflow of the subsequent fermentation residue dryer. A post-fermenter inserted between two digestate dryers has the advantage that a large proportion of the vapor is evaporated from the digestate before the post-fermenter is charged, so that the digestate volume is reduced and therefore the post-fermenter can be made structurally smaller. This additionally reduces the heat requirement in the post-fermenter. In addition, by the upstream evaporation a better digestion of the digestate, i. e. reaches the substrate, resulting in higher gas yields in the post-fermenter.

A further advantageous embodiment of the invention is that the digestate effluent with the input of a Nachgärers whose output is connected to a solid / liquid separator and its liquid output with the Gärrestezufluss the second digestate dryer. Depending on the desired or achieved dry substrate content, it may be useful to make with particular mechanical separation devices, a separation of liquid and solid components. This separation after the post-fermenter NG has the advantage that the slightly volatile ammonia has already been expelled from the digestate / substrate. This results in a much lower odor load and a reduction in ammonia emissions. Overall, the better substrate digestion results in higher gas yields, lower emissions and a reduction in construction costs. Depending on the desired result, it is advantageously possible to optionally provide a secondary fermenter, a solid / liquid separation device, or a secondary fermenter and a solid / liquid separation device between two evaporators.

A further advantageous device for drying fermentation residues results from the use of at least one digestate dryer, wherein the connection of the first digestate dryer is connected to the outlet of a fermenter and the outlet of the last fermentation residue dryer is returned to the fermenter. Due to the achievable continuous drying, respectively thickening of the fermentation residues in the fermenter, a volume reduction of more than 50% can be achieved so that the fermenter only needs to be built half as large.

The methods that can be carried out with the digestate dryer and the devices for drying fermentation residues are defined in the method claims. The digestate dryer, the devices and the methods are described in more detail below with reference to FIGS. Showing:

1 a schematic representation of a digestate dryer GT in three-dimensional view and side view with partially cut jacket of the evaporator vessel V

2 a schematic representation of an apparatus for drying fermentation residues with three successively connected digestate dryers GT1 to GT3

3 a schematic representation of an apparatus for drying fermentation residues with a Nachgärer NG and a separator QP between two digestate dryers

4 a schematic representation of a device for fermentation residue drying with two digestate dryers GT, which are connected in the circuit with a fermenter F.

1 shows a device for drying fermentation residues, which is referred to below as the digestate dryer GT. This consists of an evaporator vessel V, which in 1 Although shown at the top, but actually closed at the top. In the evaporator vessel V are concentrically arranged, double-walled heat exchanger plates DP, as a heater HV. Each of these double-walled plates DP is connected at the upper end with a supply line ZHV and at the lower end with a drain pipe KA. Hot water or steam is fed through the plates via the supply and discharge lines ZHV, KA.

It has been shown that such heat exchangers can be used directly with steam. Due to the resulting in the condensation negative pressure (and the below-mentioned vacuum lines and suction of the condensate), the vapor is sucked at high speed in the heat exchanger plates. As a result, the diameter of the steam lines can be reduced, for example, from 400 mm to 150 mm.

The evaporator vessel V is by means of a - in 1 not shown - pump via a Gärrestezufluss ZG with digestate, for example, from a fermenter or a Nachgärer a biogas plant, or from an upstream fermentation residue dryer GT ( 2 to 3 ) come, loaded. The fermentation residues are then located between the heat exchanger plates DP. The then partially dried fermentation residues are discharged via the digestate effluent AG and further processed as shown below.

In the evaporator vessel V, a three-armed holding device T is fixed at the top and bottom. This takes up the shaft of a likewise three-armed brush holder BT. On the brush holder BT brushes B are attached, which extend parallel to the vertical axis of the evaporator boiler over the length of the heat exchanger plates DP of the heater HV. The brush holder BT is reversely moved over the drive axis A, so that the brushes attached to the three arms each clean a circular segment of the plates. The brushes B are arranged so that the front and back sides of the plates are cleaned.

The digestate dryer GT thus works like a heat exchanger. The heated plates DP heat the digestate. The resulting steam is from a - not shown here for clarity - not shown in the cover of the evaporator vessel V steam outlet pipe off and fed to a further use described below. The heating device HV can be connected with its input VL and its output KA to a hot water circulation device, for example to a combined heat and power plant. If it is heated with steam, the condensate produced by the removal of heat is discharged via the outlet KA.

2 shows a schematic representation of a device for drying fermentation residues with three successively connected digestate dryers GT3 to GT1 (from left to right). The heater HV3 is powered by an external heat source, here via flow and return VL, RL the hot water circulation device of a cogeneration unit CHP. The steam thus generated in the evaporator vessel V3 is supplied via the steam outlet pipe DA of the second heater HV2. Accordingly, the first heater HV1 is supplied with the vapor from the digestate dryer GT2. In this way a cascaded supply of the digestate dryers GT3 to GT1 is achieved with the heat originally generated by the combined heat and power plant CHP.

The fermentation residues M are pumped counter to the circulation of the steam successively through the digestate dryers GT1 to GT3 (in the figure from right to left) and thereby increasingly dried. Before they are pumped from the post-fermenter NG into the digestate dryer GT1, the digestate M can be separated into solid and more or less liquid components by means of a solid / liquid separator QP, for example a mechanical screw separator. In this case, the dry fraction is discharged via the outlet AT of the separator QP. The moisture content is supplied as digestate M via the output AF to the evaporator vessel V1 of the digestate dryer GT1.

The resulting in the heaters HV1 and HV2 condensate is fed into the condensate collection KST1 and KST2 and pumped from there by means of pumps in the condensate line KL.

The steam accumulating in the evaporator boiler V1 is passed through the steam outlet DA1 and the line connection 1.1 a conventional heat exchanger, here a steam condenser K (dash-dotted outline) fed. The condensate accumulating there in the condensate collector KST1 is likewise pumped into the line KL. The heat obtained in the steam condenser K can be supplied to a further use.

Via the line connections 1.2 and 1.3 The steam outlet DA2 and DA3 can be branched off steam and also supplied to the steam condenser K or each a separate heat exchanger and hot water can be generated. For example, if steam is diverted from the evaporator boiler 3, hot water can be obtained with a temperature of about 70 ° C; after this Evaporation vessel V2 of 55 ° C and after the evaporator vessel V1 of 40 ° C.

At each of the condensate collection KST1 to KST3 a vacuum line UA1, UA2, UA3 is connected, which is guided in each case in the condensate line KL. The condensate line KL is, as will be shown later, connected to a vacuum pump, on the one hand, the condensate is pumped and on the other hand, the desired vacuum can be maintained.

The condensation in the heat exchanger plates creates a negative pressure, which affects the respective evaporator vessel V via the steam outlet.

On the one hand, the evaporation process in the evaporators V1 to V3 is controlled via the vacuum connections UA1 to UA3 with the aid of valves and optionally pumps, not illustrated here, by generating and / or maintaining a predefinable negative pressure.

The condensate accumulating in the condensate collection tanks KST1 to KST3 is pumped into the condensate line KL and subjected to further processing, in particular an ammonia separation. For vacuum generation, not necessarily each vacuum line UA1 to UA3 a vacuum pump P1 to P3 must be assigned, but the various vacuums can for example also be set via only one vacuum pump and corresponding valves. These measures are within the skill of the skilled person and are therefore not further illustrated and explained.

Digestate M with the desired dry matter content of z. For example, 25% and can be spent in a fermentation storage, not shown here.

In the embodiment according to 3 is a schematic representation of a device for drying fermentation residues shown in which a post-fermenter NG is arranged with a downstream separator QP between two digestate dryers, here the digestate dryers GT1 and GT2. The evaporator vessel V1 of the digestate dryer GT1 is charged with digestate from a fermenter F. In the evaporator vessel V1, for example, one third of the vapors can be evaporated from the digestate M already. This results in a reduction in volume of the digestate M, which may be for example about 25%, so that only a 25% smaller Nachgärer NG is required. This requires less heat in the post-fermenter NG. In addition, a better substrate digestion is achieved by the evaporation before the secondary fermentation, which has an advantageous effect on the secondary fermentation.

From the post-fermenter NG, the fermentation residues M can be fed directly to the second digestate dryer, or they are, as shown, fed to a separator QP. This separating device can be, for example, a mechanical screw press. But it could also be a centrifuge, etc. are used. The squeezed, relatively solid components (the dry fraction) are fed via the outlet AT for further use or processing. The liquid components are introduced into the evaporator vessel V2 of the digestate dryer GT2. The heating cascade works as described above with reference to 2 The third heating device HV3 of the third fermentation residue dryer GT3 is heated by the waste heat of a cogeneration unit CHKW with hot water and over the resulting in the respective evaporator boilers V3 to V1 steam in each case the upstream evaporator boilers V2 and V1 are heated by their heaters HV2, HV1. The out 2 known capacitor is for clarity in 3 not shown, but may also be part of the device.

It should be noted that a combination of the post-fermenter NG and a mechanical separator QP is not necessarily required and not necessarily at this point. The mechanical separator QP or the post-fermenter NG can also be arranged separately between each two evaporators V1 to V3. It is also possible to use both only a secondary fermenter NG or a mechanical separator QP. The use of a secondary fermenter NG and / or a separator QP in the cascade between the evaporator vessels V3 to V1 can be provided by the skilled person depending on the desired degree of drying.

The separation of the solid and liquid components by the mechanical separation device QP after the post-fermenter NG has the advantage that the slightly volatile ammonia is expelled from the substrate by the evaporation in the digestate dryer V1, and thus significantly less odor nuisance and ammonia emissions incurred. In addition, the better substrate digestion results in a higher gas yield; Furthermore, the reduction of the fermentation residues or of the substrate volume results in lower construction costs, since the secondary fermenter NG can be made smaller.

In the illustration according to 4 Two digestate dryers GT1, GT2 are connected to a fermenter F in the circuit. Such a plant is particularly suitable for the drying of digestate with a high liquid content such as manure. The fermenter F is continuously charged with manure via a slurry pit VG (not shown). From the fermenter F, the manure passes through a cycle through the evaporator boiler V1 and V2 and is then returned to the fermenter F. Due to the continuous feed from the liquid manure pit VG, the dry matter content in the fermenter F remains constant, for example at 10%. Also in this system, the heating of the evaporator boiler V2, V1 as described above. The fermenter F can be heated via a heater HKF. This is fed with steam from the steam outlet DA1 of the evaporator boiler V1. Again, there is the possibility (as based on 2 described), a part of the steam over the connection 1.1 branch off and supply a further heating device.

Through the interaction of heating temperature and negative pressure, the above-described systems can be optimally controlled. Such a scheme is exemplary based on the Appendix 4 described. The heating device HV2 is supplied with hot water via the combined heat and power plant with a flow temperature of 95 ° C. At a corresponding negative pressure, the digestate then evaporates at about 70 ° C. For the heaters HV1 thus again approximately 69 ° C are available. Thus, the thermally generated energy of the combined heat and power plant CHP can be used twice. This is particularly advantageous in the fermentation of manure, as its fermentation process hardly generates heat. In evaporator vessel V1, the vapor evaporates at a corresponding negative pressure at about 60 ° C. Thus, the entire thermally generated energy of the cogeneration plant CHP with a temperature level of just under 60 ° C continues to heat the fermenter F or, as described, external heating devices available.

Via the outlet GLA of the fermenter F the thickened manure is spent in a digestate storage GL.

Representing all other described facilities is in 4 a vacuum pump VP shown, with which the excess condensate is sucked off via the condensate line KL and fed to a condensate treatment plant KA. In the embodiment according to 4 the condensate treatment plant KA is additionally supplied with the condensate from the fermenter F via the line LF.

The necessary components for the devices, such as valves, pumps, sensors, controls, etc. are not shown in the figures. They are part of the expertise of the process engineer, who can design and use them as needed.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 4114667 A1 [0006]

Cited non-patent literature

• LOOTSMA, A., T. RAUSSEN (2008): Current methods for processing and recycling digestate. In: Bio and secondary raw material utilization. Material - energetic III. Witzenhausen Institute - News from research and practice. Kassel: K. Wiemer, M. Kern (ed.). Pp. 559-576 [0002]

Claims (14)

Apparatus for drying fermentation residues consisting of a digestate dryer (GT), this consisting of 1.1. an evaporator vessel (V) with 1.1.1. a digestate inflow (ZG) and a digestate effluent (AG) 1.1.2. a steam outlet (DA) 1.1.3. a heating device (HV) with a steam or hot water supply (ZHV) and a condensate or hot water discharge (KA) Apparatus for drying fermentation residues according to claim 1, characterized in that the heating device (HV) consists of at least one concentrically around the central axis of the evaporator vessel (V) arranged, double-walled plate (DP). Apparatus for drying fermentation residues according to claim 2, characterized in that the double-walled panels (DP) consist of several segments. Apparatus for drying fermentation residues according to claim 2 or 3, characterized in that a cleaning device (BT, B) for cleaning the outer sides of the double-walled plates (DP) is provided. Device for drying fermentation residues according to claim 4, characterized in that the cleaning device (BT, B) brushes (B), which are arranged so that they are arranged parallel to the axis of the evaporator vessel (V). Apparatus for drying fermentation residues with at least two fermentation residue dryers arranged in series (GT1, GT2, GT3) according to one of the preceding claims, characterized in that 6.1. the digestate dryers (GT1, GT2, GT3) are connected to each other via their digestate inflows and outflows (ZG1, ZG2, ZG3, AG1, AG2, AG3), 6.2. the heating device (HV1) of the respectively upstream fermentation residue dryer (GT1) is connected to the steam outlet (DA2) of the downstream fermentation residue dryer (GT2), 6.3. the condensate produced in a heating device (HV1) is fed to a condensate collecting tank (KST). Device for drying fermentation residues according to one of the preceding claims, characterized in that between the Gärrestezu- and effluents (ZG1, ZG2, ZG3, AG1, AG2, AG3) at least one solid / liquid separation device (QP) for the digestate ( M) is provided. Device for drying fermentation residues according to one of the preceding claims, characterized in that a secondary fermenter (NG) is provided at least between two digestate dryers (GT). Device for drying fermentation residues according to claim 8, wherein the post-fermenter (NG) is followed by a solid / liquid separation device (QP) for the fermentation residues (M). Device for drying fermentation residues with at least one digestate dryer (GT1, GT2) according to one of the preceding claims, characterized in that the fermentation residues (M) from a fermenter (F) at least by a digestate dryer (GT) and then returned to the fermenter ( F) are returned. Method for drying digestate with a digestate dryer (GT), comprising an evaporator vessel (V) and a heater (HV) wherein at least two digestate dryers (GT) are arranged in series, wherein 11.1. the respective downstream digestate dryer (GT) is charged with the digestate of the upstream fermentation residue dryer (GT) and 11.2. the heating device (HV2, HV1) of the respectively upstream digestate dryer (GT) is heated with the steam from the respective downstream digestate dryer (GT2, GT1). Method for drying fermentation residues according to Claim 11, characterized in that the fermentation residues (M) are first fed to a post-fermenter (NG) and then to the subsequent digestate dryer (GT). Process for drying fermentation residues according to one of the preceding method claims, characterized in that the fermentation residues (M) in the digestate stream are separated at least once into their solid and liquid components and the liquid constituents are fed to the subsequent digestate dryer (GT). Method for drying fermentation residues with a digestate dryer (GT), comprising an evaporator vessel (V) and a heating device (HV) 14.1. at least one digestate dryer (GT) is charged with the fermentation residues of a fermenter (F) and the fermentation residues dried in the digestate dryers (GT) are returned to the fermenter, wherein 14.2. the upstream fermentation residue dryer (GT1, GT2) is heated with the steam of the downstream digestate dryer (GT1, GT2).

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