WO2020032799A1

WO2020032799A1 - Method and device for biological drying

Info

Publication number: WO2020032799A1
Application number: PCT/NL2019/050523
Authority: WO
Inventors: Franciscus Henricus HORSTINK
Original assignee: Fhp Beheer B.V
Priority date: 2018-08-10
Filing date: 2019-08-08
Publication date: 2020-02-13
Also published as: NL2021457B1

Abstract

In a method and apparatus for biological drying of an organic residue the residue is carried into a reactor space (100) and subjected to a microbial decomposition process. The residue is carried in a first direction through the reactor space while a forced airflow is simultaneously carried in a second direction opposite to the first direction through the reactor space. The forced airflow is partially, and in particular for the greater part, captured and released here from the reactor space via a vapour outlet (22) between an air inlet (20) of the reactor space and a product inlet (105) of the reactor space. Moisture is hereby extracted from the residue and the residue can be removed in an at least partially dried form at a product outlet (110) of the reactor space.

Description

Method and device for biological drying

The present invention relates to a method for biological drying of an organic residue, wherein: the residue is carried into a reactor space; the residue is subjected to a microbial decomposition process; water is extracted from the residue; and the residue is removed in an at least partially dried form at a product outlet of the reactor space.

The invention also relates to an apparatus for biological drying of an organic starting mass, comprising a process reactor with a reactor space and with a product inlet for receiving the starting substance at or close to a top of the reactor space, which reactor space debouches on a bottom side remote from the product inlet into a product outlet where at least partially dried organic mass can be removed.

The starting material applied here is a biologically degradable organic mass which remains as residue from a waste flow of an industrial or agricultural production process. The substances will often be waste products or animal manures, though need not by definition be of biological origin. These substances have as similarity a high moisture content, whereby the substances are usually also biologically unstable and infectious (decay, pathogens). In such a case a significant reduction in mass of the residue, as well as biological stabilization, can be achieved by (biological) drying.

The present invention relates particularly to a method and apparatus for biological drying of starting material, also referred to below as biodrying. Specifically this can relate particularly to processing of:

- dewatered pig manure (raw or fermented)

- dewatered water purification sludge, industrial or communal (raw or fermented)

- dewatered digestate of other (liquid) fermentation

- biodegradable organic waste products from the chemical industry

- abattoir offal and waste.

In addition, liquid biological waste products can be dried as additive in combination with other material. Industrial biodrying traditionally takes place in the form of composting in large centralized installations (apparatuses). The development of smaller installations for industry has not materialized. The development of local installations for biological drying has hitherto remained limited to agricultural applications in the intensive cattle farming sector. This particularly involves the composting of animal manure in a rotating drum. The drum is intended for the purpose of aerating, homogenizing and internal transport of the material for processing. The water vapour released during the process is discharged by a large amount of air being blown thereover. However, these systems require porosity (structure) in the starting material for an effective supply of oxygen. This system is hereby only applicable for particular types of manure, such as poultry manure and cow manure.

The present invention has for its object, among others, to provide a method and apparatus for biological drying which are more widely usable, energy-efficient and, in addition to being suitable for a centralized large-scale application, are also particularly suitable for relatively small- scale decentralized applications.

In order to achieve the stated object a method of the type described in the preamble has the feature according to the invention that during the process the residue is moved in a first direction through the reactor space, that a forced airflow is simultaneously carried in a second direction opposite to the first direction through the reactor space, and that the airflow is partially released from the reactor space between an air inlet and a product inlet.

An apparatus of the above described type has for this purpose the feature according to the invention that the reactor space comprises an air inlet close to the product outlet at the bottom of the reactor space, that the reactor space is provided with ventilator means for maintaining and guiding a forced airflow into the reactor space via the air inlet, and that the reactor space comprises evacuation means between the air inlet and the product inlet for capturing and evacuating via a vapour outlet a part of the airflow coming from the air inlet.

The invention involves a microbial conversion process under the influence of micro-organisms. These micro-organisms can only absorb dissolved substrate (monomers) via their cell wall. Solid (polymerized) substrate must for this purpose first be hydrolyzed, i.e. decomposed under the influence of water. The hydrolysis takes place enzymatically and/or thermally. When sufficient oxygen is available, the dissolved substrate is utilized by the biomass for growth and metabolism. These two processes, i.e. growth and metabolism, go hand-in-hand. The quantity of biomass increases due to growth with simultaneous and proportional production of heat. A part of the organic starting substance is eventually converted biologically (combusted) to form carbon dioxide and water.

In a conventional composting process the initial quantity of dissolved substrate is consumed after several days and the process enters an equilibrium phase. From that moment the hydrolysis is the factor determining the speed of the conversion and heat production; that which is hydrolyzed is immediately consumed. The temperature is an important factor in the hydrolysis speed, and thus in the speed of conversion of the biomass.

The present invention is based on a counterflow of air through a moving biomass. Distinct zones hereby develop in the biomass, wherein at an exit particularly a conversion of organic material to carbon dioxide and water takes place with the production of heat, and at an entrance to the reactor a zone in the biomass is particularly characterized by hydrolysis of larger organic molecules (polymers) which serves as preliminary phase for the later conversion.

By guiding the airflow in forced manner in opposing direction through the mass the generated heat is discharged and guided upstream into the biomass where the hydrolysis takes place. This results in a significant increase in temperature of this process, and thereby in a significant increase in the hydrolysis speed. A second aspect of hydrolysis at higher temperature is that substrates which are more difficult to degrade will also be hydrolyzed. In addition to an increase in the hydrolysis speed, more energy thus also becomes available in the later conversion phase. All in all, an exceptionally rapid and efficient hydrolyzation can thus be achieved without the necessity for an external heat source. A balance in the heat production (conversion) and the heat discharge (the amount of air blown through) determines the temperature. This warm airflow will be at least substantially saturated with water vapour produced in the conversion zone and will be extracted from the biomass. Between the air inlet and the product inlet this warm airflow will be partially, and in particular largely, released (laterally) via a vapour outlet provided for the purpose, and thereby separated from the biomass. This extraction of moisture results in the intended drying of the starting material, and thereby in a significant reduction in mass thereof. A remaining part of the supplied air flows through the hydrolysis zone and there provides for sufficient aeration of the biomass. The material supplied at the front of the reactor will heat up quickly through condensation of this hot saturated air and subsequently heat up further through biological activation with a limited air cooling.

Transposed to conventional composting, the present invention provides a thermally enhanced hydrolysis as pretreatment, with a higher energy output as a result, with the same reactor volume and the same reaction time, and so a higher capacity per cubic metre of reactor volume. Owing to the vertical disposition of the conversion reactor the apparatus according to the invention moreover requires a relatively small surface area of space and ingenious use is made of settling of the biomass under the influence of gravitational force. The steady product flow through the reactor space hereby requires only an infeed and an outfeed. This preferably takes a stepwise form.

The hot air saturated with water vapour which is released laterally provides for the actual dewatering, and so drying of the reactor mass. Outside the reactor space the air can be dried relatively easily by causing the water vapour to condense. The heat released here can be utilized to preheat the air carried into the reactor. It has been found in practice that a small part of the total airflow is already sufficient to provide the hydrolysis zone with sufficient oxygen and to establish the intended ambient temperature therein. A particular embodiment of the method according to the invention therefore has the feature that the airflow is for the greater part released, viz. for about 70%-90%, in particular for around 80%, between the air inlet and the product inlet. Just as the branched airflow, the airflow which continues on is also warm and saturated with water vapour which has been absorbed from the conversion zone. In the cooler hydrolysis zone condensation will therefore take place and the heat of condensation released here makes an additional contribution toward the intended relatively high ambient temperature in the hydrolysis zone.

The optimal position of this branching depends to some extent on the starting material but is in most cases about halfway. A particular embodiment of the apparatus according to the invention therefore has the feature that the evacuation means are provided about halfway along the reactor space between the air inlet and the product inlet. The branching-off of the airflow which is hereby realized creates a separation between the conversion zone on the one hand, which is cooled by an airflow which is still undivided, and the hydrolysis zone on the other which, as a consequence of a considerably reduced throughflow of air, is at a considerably higher temperature. A particular embodiment of the apparatus according to the invention hereby has the feature that the reactor space comprises a hydrolysis zone, in which during operation hydrolysis of the starting mass takes place at a relatively high temperature, and a conversion zone in which during operation organic matter is decomposed in microbial molecular manner at a lower temperature, wherein the evacuation means are provided between the hydrolysis zone and the conversion zone.

With a view to an effective aeration of the reactor space, a further particular embodiment of the apparatus according to the invention has the feature that the air inlet comprises an air chamber in which a slat system is provided downstream in the airflow which is able and configured to distribute the airflow at the bottom of the reactor space from the air chamber and over the reactor space. Air holes which provide for the air supply can be arranged below the slats. The material will by contrast slide over the slats, while the air is carried via an initially downward path into the material. Material is in this way prevented from entering the air chamber, while the airflow can nevertheless penetrate into the reactor space with the material therein.

With a view to a minimal ecological footprint, it is preferred that the process takes up as little fresh air as possible, while a quantity of vented air is preferably also low. With this in mind a preferred embodiment of the method according to the invention has the feature that the airflow, after having left the reactor space, is for at least the greater part fed back to the reactor space in an at least substantially closed system. A particular embodiment of the apparatus according to the invention has for this purpose the feature that the vapour outlet is coupled in an at least substantially closed circuit to an inlet of the ventilator means. In a further embodiment the apparatus according to the invention is characterized here in that close to the top of the reactor space a defined air outlet is provided at which a remnant of the airflow is for at least the greater part received, and that the air outlet is coupled in an at least substantially closed circuit to an inlet of the ventilator means.

Both partial airflows through the system can thus be captured. A net air consumption of the system mainly still comprises in this case a further quantity of oxygen consumed by the aerobic decomposition processes within the reactor. This relatively small oxygen requirement can be easily replenished solely by outside air or, if desired, in other manner from outside. The waste gas flow from the system to the surrounding area is hereby also minimal, and a possible waste gas flow is readily manageable and can if necessary be cleaned by means of a small-scale installation.

A high concentration of ammonia will generally be present in the air from the reactor and can rise to several thousand ppm coming from proteins and other nitrogenous compounds involved in the decomposition process. In order to prevent this ammonia dissolving in condensate, which could otherwise cause discharge or disposal problems, a further embodiment of the method according to the invention has the feature that the airflow, after having left the reactor space, is cleaned, in particular has ammonia removed, before being guided over a condenser. A particular

embodiment of the apparatus according to the invention has for this purpose the feature that the vapour outlet is coupled via an ammonia scrubber to a condensation device which is able and configured to extract moisture from an airflow. In a further embodiment the apparatus according to the invention has the feature here that the air outlet is also coupled via an ammonia scrubber to a condensation device which is optionally shared with the vapour outlet and which is able and configured to extract moisture from an airflow.

For optimal processing it is important that the material admitted into the reactor has sufficient structure and can be well aerated in order to admit oxygen and discharge water vapour by means of the forced airflow. Particularly for those cases where the starting material does not have this naturally, a further particular embodiment of the method according to the invention has the feature that the dry, or at least dried matter is mixed with fresh residue before the residue is fed to the reactor space. A particular embodiment of the apparatus according to the invention has for this purpose the feature that supply means are coupled to an outlet of a mixing device, which mixing device comprises a first inlet for the starting mass and a second inlet for dry, or at least partially dried mass.

Through intensive mixing of the fresh material with dried material a homogenous and free- flowing mass can thus be obtained with a sufficient proportion of dry matter which can typically be in the order of about 40-50% after mixing. This mixing step results in a circulation flow of solid matter over the reactor and has various favourable effects. Grains are broken and thereby properly mineralized to optimal starting material for the microbial decomposition process, and possible inhomogeneity in the flow of air and/or solid matter through the reactor is hereby temporarily and/or locally variable. This ensures a constant quality of the product flow.

In a preferred embodiment the method according to the invention is characterized here in that for this purpose dried residue is taken off at the product outlet and mixed as drier matter with fresh residue before the residue is fed to the reactor space. A preferred embodiment of the apparatus according to the invention has for this purpose the feature that the second inlet of the mixing device is coupled to the product outlet of the reactor. A part of the dried product is thus used as additive to the mass for processing in order to impart an optimum composition and consistency thereto.

In addition to the above described advantages, this back mixing of reactor product moreover has the advantage that the starting material is hereby inoculated with microbial biomass. This inoculation provides for a rapid biological activation. Furthermore, the microbial management in the reactor can hereby specialize, and particularly adapt itself to higher reaction temperatures, especially in respect of the hydrolysis step. A further particular embodiment of the method according to the invention is therefore characterized in that the process is performed at a temperature approaching an upper limit of the microbial decomposition process. The microbial management then develops into a hyperthermophilic one. The hereby achievable efficiency gains are found in practice to more than compensate for the quantity of dry or dried product possibly required for the back mixing when desired. A particularly favourable embodiment of the method according to the invention has in this respect the feature that dry, or at least dried matter is mixed in a ratio of about 1 :2 to 1 :4 with fresh residue.

The input material preferably has to be free of coarser solid parts since these can cause blockages in the further processing and the internal transport and by their very nature are moreover less susceptible to microbial decomposition. In order to avoid this, a further particular embodiment of the method according to the invention therefore has the feature that the residue is ground before being fed to the reactor space. A particular embodiment of the apparatus according to the invention has for this purpose the feature that a grinding device is provided, an outlet of which is coupled to the product inlet of the reactor and with an inlet which receives starting mass from a buffer storage. The buffer storage serves to bring about uniform feed to the reactor and make this feed less dependent or not dependent on variations in an external supply.

A supply of air which is too cold to the conversion zone can result in a stagnation in the conversion process and should therefore preferably be avoided. It is therefore preferred to impart a defined air temperature to the airflow before guiding the air into the reactor. The heat produced during the conversion can advantageously be utilized for this purpose. To this end a particular embodiment of the method according to the invention has the feature that the airflow is preheated with heat which has been extracted from the residue before the airflow is guided into the reactor space. Not only does this provide for a more complete control of the whole process, it also results in a quicker and more efficient start-up of the system.

The invention will be further elucidated hereinbelow with reference to an exemplary embodiment and an accompanying drawing. In the drawing:

Figure 1 shows a schematic representation of handling of solid matter in an exemplary embodiment of a method and apparatus according to the invention;

Figure 2 shows a schematic representation of an air treatment in the exemplary embodiment of figure 1 ;

Figure 3 shows a schematic representation of a microbial cycle in the process and the

apparatus according to the invention;

Figure 4 shows a schematic zone division in a reactor space in the process and the apparatus according to the invention;

Figure 5 shows in perspective an exemplary embodiment of an apparatus according to the invention applied in the exemplary embodiment of figures 1 and 2;

Figure 6 shows a first cross-section of the apparatus of figure 5;

Figure 6B shows an enlargement of a circular area B in figure 5;

Figure 7 shows a second cross-section, transversely of the section of figure 6, of the

apparatus of figure 5; and

Figure 7B shows an enlargement of a circular area B in figure 7.

It is otherwise noted here that the figures are purely schematic and not always drawn to (the same) scale. Some dimensions in particular may be exaggerated to greater or lesser extent for the sake of clarity. Corresponding parts are designated in the figures with the same reference numeral.

An exemplary embodiment of a system in which an embodiment of the apparatus according to the invention is applied is shown schematically in figures 1 and 2. The apparatus according to the invention here comprises a conversion reactor 100 having coupled thereto a solid matter system, which is shown schematically in figure 1 on the left-hand side of reactor 100, and an air treatment system which is drawn schematically on the right-hand side of reactor 100 in figure 2. These systems will be described in more detail below.

By way of elucidating the biological action of reactor 100 the aerobic biological conversion process induced in reactor 100 is shown schematically in figures 3 and 4. In the process diagram of figure 3 the rectangles represent quantities, the circles represent processes and the arrows represent material flows. Wet substrate material 50 is introduced into the reactor. This is mainly organic polymerized substrate. Micro-organisms can only absorb released substrate (monomer) via the cell wall. Solid polymerized substrate must for this purpose first be hydrolyzed, i.e.

decomposed under the influence of water. This hydrolysis takes place enzymatically and/or thermally in a first part 52 of the reactor. When sufficient oxygen is present, the dissolved substrate is utilized by the biomass for growth and metabolism 54. The amount of biomass increases through growth with simultaneous proportional production of heat. The organic fraction is combusted (biologically) to form carbon dioxide and water. The organic nitrogen becomes ammonia.

From the moment that the initial quantity of substrate dissolved via hydrolysis is consumed, the process enters an equilibrium phase: that which is hydrolyzed is immediately consumed. The hydrolysis is now the factor determining the speed of the conversion and the heat production. The temperature is an important factor in the hydrolysis speed, and thus in the conversion speed of the decaying mass. The balance of the heat production (conversion) and the heat discharge (the amount of air blown through) determines the temperature. This is influenced halfway along the reactor by here venting a part of the blown-in airflow between a conversion zone and hydrolysis zone 52. ITydrolysis zone 52 is hereby subject to less cooling and the (hydrolysis) temperature can be increased to a maximum acceptable for the micro-organisms. A hyperthermophilic micro culture can thus deve lop/ specialize here. Moisture is also removed from the reactor with the vented air, and drying of material 56 thereby carried out.

Due to the counterflow principle different temperature zones are created in the reactor, these being shown schematically in figure 4. Because of the air separation about halfway along the reactor two specific temperature zones are defined: a hydrolysis zone 52 and a conversion zone 54. A number of other zones which can be distinguished as such are also shown in the diagram.

In practice all the zones are not sharply delimited but transpose gradually into each other.

Following below is a short description of each of the successive zones in the reactor.

HEATING ZONE 50

The material introduced into the top of the reactor will heat quickly due to condensation of the hot saturated air. This creates a heating zone 50 at the top of the reactor.

HYDROLYSIS ZONE 52

Prevailing in hydrolysis zone 52 is a high temperature for a high hydrolysis speed. This high temperature is achieved by the air from the (subsequent underlying) conversion zone 54 already being at high temperature, and by a limited relatively small airflow (20%) through the hydrolysis zone. While this latter provides for sufficient oxygen, it only provides for a low cooling capacity. As a result of condensation even more (condensation) heat can develop in hydrolysis zone 52. The intended temperature is the maximum feasible for the microbial conversion and is in the order of about 80-82°C. This is controlled with control valve 26 which determines the pressure drop, and thereby the airflow over this zone 52.

Hydrolysis zone 52 requires an extra volume where the conversion is limited (about 20% of the conversion zone). The hydrolysis speed is however exponential to the temperature, whereby the condition for more than proportionally accelerated conversion (in the conversion zone) is realized. On balance, the effect is clearly positive. In addition, this solution, in the case of equal bed height and capacity, requires only little electrical energy because the airflow amounts here to only in the order of a fifth of the total and the required pressure drop is correspondingly lower. Because the oxygen content will be very low downstream of hydrolysis zone 52 (expected to be well below 10%), it is possible to preferably discharge this air and to keep the total air consumption extremely low.

CONVERSION ZONE 54

The material enters conversion zone 54 with a high concentration of dissolved substrate. The aeration is high here so that there is heat discharge, whereby the temperature falls. This forms an ideal climate for an (explosive) growth and activity of biomass, which is accompanied by a corresponding production of heat.

EQUILIBRIUM ZONE 56

As the“fuel” for conversion becomes exhausted, the system enters into a condition where the hydrolysis and conversion are in equilibrium. Because it is less efficient, this equilibrium zone 56 is kept small by means of a dimensioning of the reactor.

COOLING ZONE 58

In a cooling zone 58 at a product outlet of the reactor the material is cooled by supplying colder air and by exudation.

An input buffer 10 is present to allow a feed of wet/moist product to the reactor to progress uniformly and continuously and not be dependent on variations in a local or external supply, for instance from dewatering presses. The input material for reactor 100 must be free of coarser solid parts since these can otherwise cause blockages in the draining of the reactor and in transport systems. With this in mind, a pretreatment 12 is present. If there is a risk of coarse parts being present that are larger than typically in the order of 3 centimetres, the whole material flow can then be comminuted by a grinding device provided therein which reduces larger parts to below this size. A screening of coarse, non-processable materials, such as stony material and metals, can also take place herein.

If the input material has little or no structure, the aeratability can hereby be too low to enable biological activation and/or discharge of water vapour. This is obviated with a mixing device 14 which is able to mix the fresh material with dry or dried material. A homogenous and free- flowing mass can be obtained by carrying out this mixing in intensive manner. The required dry matter after mixing will be about 40-50%. In this respect a so-called back mixing is in this case applied by taking off a part, for instance in the order of 15%, of the dried material from outlet 110 of reactor 100 and carrying it to mixing device 14. Mixer 14 is an important component in the overall system. It serves to make the supply to reactor 100 homogenous and aeratable. A reliable way of mixing is found to be a batchwise mixing, wherein the two flows for mixing are loaded by weight. This mixing (back mixing) makes the structureless substance areatable and introduces active biomass into the material (inoculation). There is thus a recirculation flow of solid matter over the reactor. This has positive effects:

-Grains are broken and thereby properly mineralized (similar to conversion in

composting).

-Inhomogeneity in the flow (air and/or solid matter) through the reactor is hereby temporarily and/or locally variable. This ensures a constant quality of the product.

-The input flow is inoculated with product whereby the biomass in the reactor can specialize (adapt to the high temperature).

-The inoculation provides for a rapid biological activation; and

-A specialization of the types of micro-organisms (hyperthermophily) occurs. Depending on the dry matter of the input flow, the back mix flow amounts to about double the feed flow in kilograms. After an (average) residence time the material has thus typically been around five times. In the exemplary embodiment of figures 5-7 the reactor feed 105 lies at a height of about 6 to 7 metres. The mixed material is carried upward by a transport system (not shown) which does not affect the structure. The biomass for driving, mixed with a proportion of dried end product, is introduced into the top of reactor 100 and levelled by a rotating rake so that the throughflow of air is homogenous.

Situated on the underside and upstream of an outlet 110 of reactor 100 is a draining system which provides for a uniform settling of the reactor content. The draining of the dried material from the reactor takes place through a number of parallel dosing sluices 111..113, see also figure 7. The passage of dry matter to screw conveyors 114 can hereby be controlled. Sluices 111..113 cover the full width of the reactor. Thus provided in the shown reactor, with a section of about 3 x 3 metres, are three frequency-controlled rotating sluices 111..113. The material runs via a steep funnel shape to the respective sluice. Rotating sluices 11 1..1 13 periodically change rotation direction so that preferred flows along the funnel sides are discontinued. This process can be monitored by means of inspection hatches 115 provided for the purpose, and possible obstructions in the discharge of material can be cleared.

Lying coaxially under each rotating sluice 111..113 is a screw conveyor 1 14 which carries the drained material to one side of reactor 100. Located here is a transverse screw 116 which collects and carries the material from three sluices l l l.. H3 to a product outlet 110 outside the reactor. Dosing sluices 111..113 are controlled for throughput. Below these sluices the material is carried with screw conveyors 114 and transverse screw 116 via product outlet 110 to mixer 14 and a product buffer 16. Since a reasonable air pressure prevails at the bottom of the reactor, an airtight draining is preferably available, or the pressure is temporarily removed during draining. Feed and draining take place periodically, for instance for five minutes each hour. The entire dry matter system is thus periodically in operation, typically for five minutes per hour. The degree of filling of reactor 100 and of input buffer 10 are used as control parameters in an automation (not shown).

The space under the funnels forms an air chamber 125 to which a blower is connected via an air inlet 20. The blower provides a continuous forced airflow through the reactor counter to the material flow for the purpose of the drying process. Slats 120 are arranged in the funnel walls. Slats 120 run over the full width of the funnels and are configured in respect of number and blow-out height such that, when the material enters, the air velocity is limited to about five times the average vertical air velocity in the reactor. The air will push away the material behind the slats to some extent and keep it in motion so that bridging or clogging is prevented. Concealed under the slats are slots which open toward the reactor space for the purpose of a free air supply to the reactor space. The material slides over slats 120 but the air flows via an initially downward path into the material. This prevents the material being able to enter air chamber 125. The air is thus blown counter to the material flow with only a small pressure drop over slat system 120 at the bottom of reactor 100.

The blown-in air is extracted at two heights from the reactor. Roughly halfway along the height about 80% of the air is captured via evacuation means 130 provided for the purpose and discharged via a vapour outlet 22 with a control valve 26. The height of this air branching 22 depends on the input material to be processed.

The evacuation means comprise a system of elongate gutters 130 disposed transversely of a flow direction of the airflow over at least substantially a full width in the reactor space. Gutters 130 lie in the airflow in order to capture air therein and guide it via pipe conduits 135 to vapour outlet 22. Gutters 130 comprise in this example a number of parallel plates bent in a wedge shape disposed along the width of the reactor. The tip of the wedge points here toward the top of the reactor. The material drops downward around the wedge. Present under the wedge is an air space which is in contact with a pipe 135 connected through the reactor wall. Pipes 135, which can lie on either side of the wedges, run into a collection channel 22 which runs to control valve 26. The number of wedges, the angle and the open width of the wedge shape are adapted for the best compromise between air resistance and good throughflow of the dropping material. The remaining about 20% of the air flows further upward with a very low pressure drop to the top of the reactor. Via an air outlet 24 provided here this air is also captured. The stated percentages for the amount of air relate to dry air. Solid matter and air thus pass in counterflow through reactor 100. The biological process in the reactor needs aeration for the supply of sufficient oxygen and for the discharge of water vapour. This is provided by the air system shown schematically in figure 2. This ensures that the conditions of the in- and outgoing air (temperature, relative humidity, oxygen content) and the airflow velocity are optimal for the process and that as little fresh air as possible is consumed. The waste gas flow is hereby also kept small and a waste gas cleaning can be kept small-scale and easily manageable in order to comply with environmental requirements for the emission of ammonia and odour.

The oxygen supply necessary to maintain the microbial processes in the reactor is not normally an issue. This is because the quantity of air required for an effective discharge of water vapour is in the order of ten times higher than the quantity of air required for the supply of oxygen for the biomass. The air requirements for oxygen and water discharge are hereby separate of each other, whereby the consumption of fresh air and emission of waste gas can be minimized. This separation is made possible by cooling the air from reactor 100 by means of a primary condenser 31. The cooled and dried air can hereby be fed back to reactor 100 and once again absorb water vapour because the temperature rises. The moisture (compensate) extracted from the air, designated in the figure as fbO. can be drained or applied as process water.

The air from the reactor can have a high concentration of ammonia which can rise to several thousand ppm. In order that this ammonia does not dissolve in the condensate fbO and to avoid a drainage or discharge problem, the ammonia (as well as amines) is removed with very high efficiency from the air with an acid scrubber 32 upstream of primary condenser 31. Acid scrubber 32 produces an almost saturated solution of ammonium sulphate, which is recoverable as an accepted fertilizer from the process. The condensate H₂0 may possibly still comprise volatile organic components (VOCs), but these are otherwise harmless in the discharge.

The remainder of the airflow exits air outlet 24 at the top of reactor 100 with a higher temperature and a substantially lower oxygen content than the air from branch 22. This flow is the most favourable for guiding out of the system as displacement air for the necessary fresh air. A separate acid scrubber 33 and a secondary condenser 34 are present for this purpose. This acid scrubber 33 can be wholly integrated with the primary acid scrubber 31 without additional pumps or measurement and control components. The airflow passing through the branch provides for the largest part of the drying capacity. Primary condenser 31 will therefore have to have a higher capacity than secondary condenser 34. The same applies for the acid scrubbers 31,33.

The air which is ultimately exhausted has odour removed to at least below a local permit value. Provided for this purpose is an air filter 38 which filters possible harmful components from the vented air, for instance on the basis of oxidation scrubbing or biofiltration. Fresh air can be normal outside air, although it is advantageous here to draw in odorous air, for instance from storage buffer 10 of input material and/or from product buffer 16, in order to reduce the airflow to an odour treatment provided therefor. It is also possible to introduce oxygen-enriched air into the system. At 40% oxygen the airflow to be treated in the odour removal can be more than halved. The fresh air can be admitted via a control valve 30 and admixed to the recirculating airflow. The air can optionally be preheated with the heat from secondary condenser 33 via a heat exchanger 36 provided for the purpose before admitting the air into the reactor. A partial thermal drying is hereby realized, whereby the end dry matter is improved.

The method and apparatus described here are particularly suitable for the processing of animal manure in addition to other organic residual material flows. The ratio [organic matter content / water content] and the absolute water content of the starting substance here determine to great extent the end dry matter to be obtained. The following rough limits are to be applied here:

Exemplary embodiment

Assuming a throughput in the order of 1 tonne per hour of an organic matter with 25% dry matter (with 70% organic matter, 50 g organic nitrogen/kg dry matter) and an end dry matter of 60%, a practical exemplary embodiment can be realized on the basis of for instance a parallel arrangement of a number of the shown reactors, typically with a combined occupied ground surface area in the order of 10 square metres and a height in the order of 6 metres. This gives the following characteristic values for the overall installation:

All in all, the invention hereby provides an exceptionally efficient biological drying of residue of diverse nature which can be utilized here as starting material. The integrated hydrolysis provides an unrivalled conversion speed and decomposition options of organic matter, which makes possible the biological drying of more substances normally perceived as difficult, for instance material with a low content of dry matter and/or material which is fermented and has little structure.

The air leaving the hydrolysis zone contains very little oxygen. The process can hereby function with an extremely low consumption of fresh air and the waste gas flow is correspondingly small. The system is further suitable for continuous operation, in counterflow, and the process can take a fully closed form. Implementation of the process is hereby also easy to control and automate. The apparatus can hereby be embodied centrally, but also take a decentralized form, with a minimal use of personnel. The biological drying is preferably controlled such that the temperature is close to the upper limit which can generate the micro-organisms. Relatively little air is blown through here, and the energy consumption for maintaining the airflow will be correspondingly low. It becomes attractive and easy to recover heat in addition to the possible recovery of other valuable raw materials. With a vertical arrangement and the compact bed in the reactor the floor area required is small compared to belt driers and solar drying. In addition, the reactor is suitable for outdoor arrangement. For this purpose all structural parts of the reactor are preferably manufactured as far as possible from stainless steel or preserved steel.

Although the invention has been further elucidated above with reference to only a single exemplary embodiment, it will be apparent that the invention is by no means limited thereto. On the contrary, many variations and embodiments are still possible within the scope of the invention for a person with ordinary skill in the art.

Claims

1. Method for biological drying of an organic residue, wherein the residue is carried into a reactor space; the residue is subjected to a microbial decomposition process; water is extracted from the residue; and the residue is removed in an at least partially dried form at a product outlet of the reactor space, characterized in that during the process the residue is moved in a first direction through the reactor space, that a forced airflow is simultaneously carried in a second direction opposite to the first direction through the reactor space, and that the forced airflow is partially, and in particular for the greater part, released from the reactor space between an air inlet of the reactor space and a product inlet of the reactor space.

2. Method as claimed in claim 1, characterized in that the airflow is released for about 70%- 90%, in particular for around 80%, between the air inlet and the product inlet.

3. Method as claimed in one or more of the foregoing claims, characterized in that the airflow, after having left the reactor space, is for at least the greater part fed back to the reactor space in an at least substantially closed system.

4. Method as claimed in one or more of the foregoing claims, characterized in that the airflow, after having left the reactor space, is cleaned, in particular has ammonia removed, before being guided over a condenser.

5. Method as claimed in one or more of the foregoing claims, characterized in that dry, or at least dried matter is mixed with fresh residue before the residue is fed to the reactor space.

6. Method as claimed in claim 5, characterized in that dried residue is taken off at the product outlet and mixed as drier matter with fresh residue before the residue is fed to the reactor space.

7. Method as claimed in claim 5 or 6, characterized in that the dry, or at least dried matter is mixed with fresh residue to form a homogenous, free-flowing mass with 40-50% dry matter therein.

8. Method as claimed in claim 5, 6 or 7, characterized in that dry, or at least dried matter is mixed in a ratio of about 1 :2 to 1 :4 with fresh residue.

9. Method as claimed in one or more of the foregoing claims, characterized in that the residue is ground before being fed to the reactor space.

10. Method as claimed in one or more of the foregoing claims, characterized in that the residue is moved stepwise through the reactor space.

11. Method as claimed in one or more of the foregoing claims, characterized in that the airflow is preheated with heat which has been extracted from the residue before the airflow is guided into the reactor space.

12. Method as claimed in one or more of the foregoing claims, characterized in that the drying is performed at a temperature approaching an upper limit of the microbial decomposition process.

13. Apparatus for biological drying of an organic starting mass, comprising a process reactor with a reactor space and with a product inlet for receiving the starting substance at or close to a top of the reactor space, which reactor space debouches on a bottom side remote from the product inlet into a product outlet where at least partially dried organic mass can be removed,

characterized in that the reactor space comprises an air inlet close to the product outlet at the bottom of the reactor space, that the reactor space is provided with ventilator means for maintaining and guiding a forced airflow into the reactor space via the air inlet, and that the reactor space comprises evacuation means between the air inlet and the product inlet for capturing and evacuating via a vapour outlet a part of the airflow coming from the air inlet.

14. Apparatus as claimed in claim 13, characterized in that the air inlet comprises an air chamber in which a slat system is provided downstream in the airflow which is able and configured to distribute the airflow at the bottom of the reactor space from the air chamber and over the reactor space.

15. Apparatus as claimed in claim 13 or 14, characterized in that the reactor space comprises a hydrolysis zone, in which during operation hydrolysis of the starting mass takes place at a relatively high temperature, and a conversion zone in which during operation starting mass is decomposed in microbial molecular manner at a lower temperature, and that the evacuation means are provided between the hydrolysis zone and the conversion zone.

16. Apparatus as claimed in claim 13, 14 or 15, characterized in that the evacuation means are provided about halfway along the reactor space between the air inlet and the product inlet.

17. Apparatus as claimed in one or more of the claims 13 to 16, characterized in that the evacuation means comprise a system of elongate gutters which are disposed transversely of a flow direction of the airflow over at least substantially a full width in the reactor space, which open counter to the airflow and lead to the vapour outlet.

18. Apparatus as claimed in one or more of the claims 13 to 17, characterized in that the vapour outlet is coupled via an ammonia scrubber to a condensation device which is able and configured to extract moisture from an airflow.

19. Apparatus as claimed in one or more of the claims 13 to 18, characterized in that the vapour outlet is coupled in an at least substantially closed circuit to an inlet of the ventilator means.

20. Apparatus as claimed in one or more of the claims 13 to 19, characterized in that close to the top of the reactor space a defined air outlet is provided at which a remnant of the airflow is for at least the greater part received, and that the air outlet is coupled in an at least substantially closed circuit to an inlet of the ventilator means.

21. Apparatus as claimed in claim 20, characterized in that the air outlet is coupled via an ammonia scrubber to a condensation device which is able and configured to extract moisture from an airflow.

22. Apparatus as claimed in one or more of the claims 13 to 21, characterized in that supply means are coupled to an outlet of a mixing device, which mixing device comprises a first inlet for the starting mass and a second inlet for dry, or at least partially dried mass.

23. Apparatus as claimed in claim 22, characterized in that the second inlet of the mixing device is coupled to the product outlet of the reactor.

24. Apparatus as claimed in one or more of the claims 13 to 23, characterized in that a grinding device is provided, an outlet of which is coupled to the product inlet of the reactor and with an inlet which receives starting mass from a buffer storage.