FR2510605A1 - Bio-gas prodn. by fermentation of stable litter, liq. manure etc. - advanced pneumatically through aerobic pre-fermenter and digestion chamber - Google Patents

Abstract

Raw material is first size-reduced by milling etc. to a state in which air can be blown through it. The material, with up to 75% moisture content, is loaded into a down shaft which is then closed with an airtight cover. An aerobic pre-fermentation is promoted in the down shaft by injection of heated, compressed air. The bottom of the down shaft communicates, via a U-tube, with bottom of a digestion chamber in which anaerobic fermentation produces methane etc. The material is advanced pneumatically over a partition in the chamber by air pressure behind material in the down shaft. Backflow of material in the chamber is prevented by hanging chains which flex only in an upstream direction. Fermented material is advance from the base of the chamber beyond the partition, via a U-tube, into the bottom of a riser shaft with discharge overflow trap at the top. The installation is equipped with instruments to measure necessary process characteristics such as gasflow, temp., pressure, pH and rH values and oxygen content. Liq. ferment is pref. recycled from the overflow discharge trap to the digestion chamber. The system is used for producing a fuel gas from stable litter, liq. manure, sewage etc. The fermenting material is advanced pneumatically without conveyors of a mechanical nature. The non-return chains also serve to break surface encrustations and release gas.

Description

 The subject of the invention is a method and an apparatus for carrying out methanogenesis.

 Organic matter of animal and vegetable origin can lead, by successive or simultaneous degradations, in aerobic or anaerobic medium, to gaseous compounds, the most important of which are metnane, carbon dioxide and ammonia.

 Composed of more or less polymerized and nested elements, these organic materials constitute most of the time a solid substrate, fibrous or not; this is the case for urban or agricultural organic waste. However, this substrate can also be liquid, milk serum being a typical example.

 The composition of the substrates remains very variable.

 The vast majority of these substrates are constituted by ternary compounds such as sugars, starches, hemicelluloses, celluloses and lignins, but quaternary bodies such as protides and peptides can also be associated with them.

 the degradation of these substrates with a view to their use involves three essential phases: hydrolysis, solubilization, and, lastly, gasification.

 The progressive decomposition of the initial compounds leads by lignolysis, pectinolysis, hemicellulolysis, cellulolysis, amylolysis, proteolysis and peptolysis to more simplified constituents whose degradation then reveals alcohols, ketones, volatile and semivolatile fatty acids, amines, l 'amnionlac, hydrogen, hydrogen sulphide, carbon dioxide, and ultimately metnane.

The agents participating in these degradations come from habitats of animal, plant and telluric origin. Over one hundred main species have been counted, namely psychroprliles, mesophiles and thermophiles. They evolve in environments with very variable pH and redox potentials, with different ranges depending on the species (variation in pH: 5.5 to 8.5 - variation in rd: + 200 to
the population density is very high at the beginning of the degradations (in total up to 10 to 15 billion protrists, fungi, bacteria and pages per gram of manure for example). These heterogeneous populations tend to simplify gradually degradations, under the action of physical and biological factors and the elimination of certain foods quickly consumed.

the different phases where-these fac
teurs are as follows - a cold and airy phase, mainly urolytic, sac
carolytic and peptolytic; - a mesophilic and semi-aerated phase during which the
rising temperature, intestinal agents participate
to a putrifying phase with production of hydro sulphide
gene, phenolic products, ammonia, dioxide
carbon, and also volatile and semi-volatile fatty acids; - a thermophilic and aerated phase, during which
tloermogenic, fungal and bacterial ferments appear
between 400C and 600 C; their action is lignolytic, hemi
cellulolytic and cellulolytic; celluloses and hemi-
celluloses being nested in deer lignins, the yield
melanic fermentation depends on delignification
initiated by fungal populations; hydrolysis occurs for
also follows in semi-aerobic and anaero environments
mesophilic or thermopail bie with suitable species; - a reducing liquid phase, during which appears
smells of alcohols and fatty acids; the middle must then
be buffered with ammonia-containing organic compounds,
amines, but also alkaline mineral compounds and
alkaline earth metal causing salt formation; - a final methanisation phase, which can be carried out
by very different ferments, sporogenic or not, coc
cus sticks, mesogenic or thermogenic.

 By patent no. 2 305 113, a plant for digestion of organic matter was poured into which the material to be worked is introduced, after having been humidified, in a cylindrical compartment in which it undergoes aerobic fermentation under pressure, then it is pushed by a compacting piston, through an angled siphon, in a small anaerobic fermentation compartment but in a large compartment. In the elbow of the siphon, forks oppose a reflux of the material. the aforementioned patent also provides an extraction well in which the fermented material is entrained by a claw.

the invention allows fermentation to be carried out under better conditions than if the system described above is used. The improvements made are, for example, the
replacement of a mechanical thrust by a pneumatic thrust, a different shape from the tank which allows better circulation, and the presence of a digester with which an integrated gasometer may or may not be associated. the differences between the invention and the aforementioned patent clearly result, for example, from the examination of claims 1, 9 and 12 of this patent.

 The process according to the invention for carrying out methanogenesis is characterized by the succession of the following operations: a) a seeding is carried out from a substrate coming from various media such as earth, liquid manure, manure and sludge d 'sewer or marsh, at the same time as a progressive humidification which can reach 75; b) air is blown through the substrate; c) the substrate is immersed in a medium with a high buffering capacity and then inoculated into a methanogenic population by a leaven consisting of fermentation, diluted, liquid and 50-liquid residues; d) agitation of the medium is carried out to improve the yield and the speed of fermetation; and e) the calorific contribution of the exothermic reactions is used to maintain the fermentation in a mesophilic or thermophilic medium, with the possible use of a thermal insulation to improve the thermal balance.

 The rise in temperatures which results from the air blowing indicated above allows mesophilic and thermophilic germs to develop. In addition, this oxidation makes it possible to eliminate the too quickly acidogenic compounds responsible for the slowing down or premature stopping of the methane fermentation.

 The apparatus according to the invention for carrying out an ithanogenesis comprises a grinder or chopper projector which allows on the one hand the reduction of the solid substrate into filamentous or fragmented masses automissnt a large passage of a stream of pressurized air between the particles, and on the other hand the introduction of the substrate into the feed well of a reactor, and it is characterized in that it comprises in combination: an anaerobic fermentation tank divided vertically by a central partition into two parts connected respectively by a siphon equipped in a known manner with a series of unidirectional folding channels to prevent any return of the substrate, to a supply well in which aerobic pretreatment is carried out in known manner, provided with a hermetic cover and with which a compressor is associated and at least one heat exchanger, and a discharge well; means connected to the evacuation well for separating the fermented solid products from the liquid which must be recycled; and known apparatus for the necessary physicochemical measurements, i.e., gas flow, pressure, temperature, pH, rH, and oxygen content.

 According to a characteristic of the invention, a second series of chains is suspended from the dome of the tank to ensure the degassing of the substrate and the dislocation of the "cap" which tends to form during fermentation; the aforementioned partition leaves at its lower end a passage for the direct circulation of heavy materials towards the evacuation well; and the leaven produced by methanogenesis can be recycled at the bottom of the tank by opening an ad hoc tap.

According to another characteristic of the invention, there are two heat exchangers connected to a purifier; the
supply well has two series of slots located at a certain distance from each other and at a certain distance, respectively, from the cover and from the lower end of the well; the air which comes from the booster via the first of the heat exchangers flows upward through the lower slots then through the upper slots, exits through the top of the well and is sent to the abovementioned purifier with interposition of a tap on each of the pipes connecting to one of the heat exchangers; and the upper slot airway is connected with the interposition of a tap to a circuit for recycling the leaven produced by methanogenesis.

 From the top of the dome of the tank leaves a pipe through which the gases resulting from the methanization arrive at a hydraulic valve, located either outside the tank or in it, and intended to cause oscillations of the mass in fermentation; leaving this valve, these gases are sent to a gasometer which can be either outside the tank or above it. In the latter case, the gases escape through a pipe which passes through the tank and ends in a condensate trap intended to recover the water present in the hot gases originating from fermentation. In both cases, the gases are taken to a scrubber.

 The solid fermented products leaving the evacuation well are poured on a trisportor, while the liquid products are recovered in a tank and can further recycled either in the supply well, or at the bottom of the tank, or at the bottom the evacuation well.

 It is optionally possible to provide in the evacuation system of the fermented products or in the means for separating the solid and liquid products, an injection of air from a booster. This forced ventilation accelerates the transformation process of the substrate for use in compost.

We will now describe in more detail, by way of nonlimiting examples, an embodiment of the invention and a variant, with reference to the appended drawings in which:
The set of figures 1 and 1A is a schematic section of an apparatus according to the invention.

 Figure 2 is a section through Il-Il of Figure 1.

 Figure 3 is a plan of the pipes of the apparatus of Figures 1 and 1A.

 Figure 4 is a section, similar to Figure 1, of a variant.

 Figure 5 is a section through V-V of Figure 4.

 FIG. 6 is a plan similar to FIG. 3 but showing the pipes of the apparatus of FIG. 4.

In Figure 1, we see in 1 a supply well closed by a cover2 perfectly sealed. The substrate, previously ground or chopped, is introduced, after opening the cover 2 which is then closed, into the well 1 which constitutes an aerobic pre-fermentation chamber. A booster 3 (FIG. 3) for carrying out the oxygenation sends air through a pipe 4 fitted with a tap 5 to the lower part of the pretreatment chamber, after filling the supply well, to oxygenate the all of the ground substrate, and during aerobic pretreatment, to homogenize and standardize the temperature resulting from this pretreatment. Through slots 6, the air
crosses, in ascending quran, the substrate column contained in the well 1 and slots 7 located at the upper part of the well, and is brought, by a pipe 8 and after opening a tap 9, to a heat exchanger 10 After passing through the exchanger 10, the air is supplied by the pipe 8 to a purifier il (FIG. 3). However, this air can also be brought, by a tap 12 and a pipe 13, to a heat exchanger 14, the doctor blade of which will be indicated below, and then, by a pipe 15, to the purifier 11.

The heat input brought to the well i maintains the temperature of the mesophilic or thermophilic medium in a methanization tank 16, described below in more detail, to which the substrate is brought as will now be indicated.

 After closing the taps 9 and 12, the air coming from the booster 3 arrives through the pipe 4 and the tap 5 at the well 1, compresses at the top of this well, and pushes the substrate through a siphon 17 in the tank 16, in which the anaerobic fermentation takes place and which is divided into two parts by a central partition 18. Channels 19 with unidirectional folding prevent, in known manner, any return of the substrate during anaerobic fermentation to the pretreatment chamber 1.

 The ventilation of the supply well 1 takes place by opening the taps 5 and 9, the tap 12 being closed as well as a tap 20 located on a pipe 21 connected to the heat exchanger 14 and to a tank 22 which will be described below (Figures 1, 1A and 3).

 Channels 23 suspended from the dome 16a of the tank 16 ensure the degassing of the substrate and the dislocation of the "cap" which tends to form during fermentation, creating chimneys through which the gases are evacuated. the degassed materials increase and descend to the bottom of the tank, before passing through a siphon 24 to a drainage well 25 which is 1800 to the supply well 1 (see Figures 1 and 2), is attached . laterally at the bottom of the tank 16 by the siphon 24, and has at its top a cover 26 an outlet siphon 27 and a weir 28 with adjustable opening 29. the gases accumulated in the upper parts of the evacuation well 25 are brought to the purification system 11 by a removable flexible pipe 30 and the aforementioned pipe 15 (FIG. 3). An air supply can be provided at an appropriate point in the evacuation circuit, starting from the booster 3, by means of a pipe 31 provided with a tap 32 and the point of arrival of which is chosen according to needs and n 'and not shown. Preferably, if the air is injected into the exhaust well 25, it occurs through slots similar to chambers 6 and 7 of the supply well 1. Whether or not there is forced ventilation from the evacuation well 25, the gases accumulated in the upper parts are evacuated by the pipe 30 towards the purifier 11.

 The gases resulting from anaerobic fermentation inside the tank 16 form a pocket at the top of the latter.

This accumulation of gas, by compressing, exerts on the upper level of the substrate in the tank a thrust which lowers the level of ca substrate during fermentation. The gases resulting from anaerobic digestion exit through a pipe 33 provided with a tap 34 and go towards a gasometer 35, by means of a hydraulic valve 36 whose r81e is to cause oscillations of the mass in fermentation which is result in a flow and a reflux between the tank 16, the supply well 1 and the evacuation well 25. The pressure in ID pipe 33 which joins the tank 16 to the gasometer 35 then, by the pipe 8, to the scrubber 11, is the same as that which prevails in the tank.

When this pressure is greater than that exerted by the water height of the valve 36, it is this adjustable water height which determines the trigger threshold and therefore the pulse rate (the higher the water height weak, the more frequent the impulses and vice versa). The air escapes through the valve 36 and goes towards the gasometer 35. There is therefore no more accumulation of gas inside the tank 16, therefore no more pressure on the substrate, and more lowering of the upper level of this substrate, which returns to its initial level.

 There is therefore a lowering of the level of the substrate in the tank 16 before the valve 36 is triggered and a return to the initial level after its triggering.

The vertical partition 18 allows the circulation of the substrate in the tank, as indicated by the arrows. A passage 37 under the partition 18 allows the direct circulation of heavy materials towards the evacuation well 25. The action of the channels 23 comes to combine with the flow and reflux of the substrate provided by the hydraulic valve 36. These chains must have a density higher than that of the substrate
Several daily pulses ensure the evacuation of the fermented products, intermittently, by adjusting the opening 29 of the weir 28. This weir (FIG. 1A) results in a press 38 which separates the fermented solid part from the liquid or sourdough and which may possibly other subject to the air blowing mentioned above. A conveyor belt 39 discharges the solid material, while the liquid is recovered in the bowl 22. This leaven can be used in different ways under the action of a pump 40 located on the pipe 21, after reheating using the heat exchanger 14.

He can :
a) between recycled into the upper part of the supply well 1 by the pipe 2 and the tap 20;
b) be injected into the bottom of the tank 16 through the pipe 20 and a pipe 41 provided with a tap 42;
c) enters sent at the bottom of the evacuation well 25 by a pipe 43 provided with a tap 44
Although it has been indicated previously that the pipe 33 connects the gasometer 35 to the purifier 11 by the pipe 8, it is possible, in a variant not shown, to send the gases resulting from the anaerobic fermentation to another purifier .

 If we now refer to Figures 4 to 6, we see a second embodiment of the invention. The supply 1 and discharge 25 wells are identical to those of FIG. 1, and the substrate is discharged through the weir 28 in the manner indicated above. The tank 16 'resembles the tank 16 and has like it a partition 18', but contains a hydraulic valve 36 'which is identical to the valve 36, and it is surmounted by a gasometer 35'. The valve 36 ′ is located on a pipe 33 ′, one end of which, like the pipe 33 in FIG. 1, leaves from the top 16 ′ a of the tank, and the other end of which opens into the gasometer 35 ′. opens a pipe 45 which ends on the one hand in a condensate trap 46 intended to recuperate the water present in the hot gases coming from the fermentation and which condense in the pipe 45, and on the other hand, like the pipe 33 , in the pipe 8 leading to the purifier 11 with the interposition of a tap 47. However, in a variant not shown, the gases resulting from the anaerobic fermentation in the tank 16 'can be sent to another epu rater.

 Finally, there is provided a set (not shown) of known devices intended for physicochemical measurements, on the ground: the gas flow rate, the pressure, the temperature, the pH, the rH, and the oxygen content. The choice and positioning of these devices are well known to those skilled in the art, and it is therefore not necessary to describe them or indicate their positioning.

Claims (8)

 R3VENDICATI ONS  i - A process for carrying out methanogenesis, characterized by the succession of the following operations: a) seeding is carried out from a substrate coming from various media such as earth, liquid manure, manure and sewage sludge or swamp, at the same time as a progressive humidification which can reach 75 ffi; b) air is blown through the substrate; c) the substrate is immersed in a medium with a high buffering capacity and then sown in methanogenic population with a leaven consisting of remnants of fermentations, diluted, liquid and solid; d) agitation of the medium is carried out to improve the yield and the speed of fermentation; and e) uses the heat input from the exothermic reactions to maintain the fermentation in a mesophilic or thermophilic medium, with the possible use of a heat-insulator to improve the thermal balance.  2 - Apparatus for carrying out methanogenesis, comprising a shredder or chopper projector which allows on the one hand the reduction of the solid substrate into filamentous or fragmented masses allowing a wide passage of a stream of pressurized air between the particles, and on the other hand share the introduction of the substrate into the feed well of a reactor, and characterized in that it comprises in combination: a) an anaerobic fermentation tank (16 or 16 ') divided vertically by a central partition (18 or 18 ') in two parts connected respectively by a siphon (17) equipped in a known manner with a series of channels (19) with unidirectional folding to pocket any return of the substrate, to a supply well (1) where takes place in known manner an aerobic pretreatment, provided with a hermetic cover (2) and with which are associated a booster (3) and at least one heat exchanger (10), and with an evacuation well (25); b) means (22 and 38 to 40) connected to the evacuation well (25) for separating the fermented solid products from the liquid which must be recycled; and c) known apparatus for the necessary physicochemical measurements, i.e., gas flow, pressure, temperature, pH, rH, and oxygen content.  3 - Apparatus according to claim 2, characterized in that: a) a second series of chains (23) is suspended from the dome (16a or 16'a) of the tank to ensure the degassing of the substrate and the dislocation of the * "cap "which tends to form during fermentation; b) the aforementioned partition (18 or 18 ′) leaves a passage (37) at its lower end for direct circulation of the heavy materials towards the evacuation well (25); and c) the leaven produced by methanogenesis can be recycled at the bottom of the tank by opening an ad hoc tap (42).  4 - Apparatus according to claim 2, characterized in that: a) there are two heat exchangers (10, 14) connected to a purifier (11); b) the supply well (13 has two series of slots (6, 7) located at a certain distance from each other and at a certain distance, respectively, from the cover (2) and from the lower end from the well; c) the air which comes from the booster (3) via the first (10) of the heat exchangers flows upward through the lower slots (6) then through the upper slots (7), exits by the top of the well and is sent to the abovementioned purifier (11) with the interposition of a tap (9 or 12) on each of the connecting pipes (8 and 13) to one of the heat exchangers (10 and 14); and d) the upper series (7) of slots is connected with the interposition of a tap (20) to a circuit (21) for recycling the leaven produced by methanogenesis.  5 - Apparatus according to claim 4, characterized in that the substrate contained in the supply well (1) is pushed through the siphon (17) in the tank (16 or 16 ') where fermentation takes place under the action of air from the booster (3) after closing the aforementioned valves (9 and 12).  6 - Apparatus according to claim 2, characterized in that from the top of the dome (16a) of the tank (16) leaves a pipe 433) through which the gases resulting from the methanization arrive at a hydraulic valve (36) intended to cause oscillations of the mass in fermentation and leaving this valve are sent to a gasometer (35) connected to a purifier (11).  7 - Apparatus according to claim 2, characterized in that the solid fermented products leave the evacuation well (25) and are evacuated by a conveyor (39), while the liquid products are recovered in a tank (22) and can be recycled either in the supply well (1), or at the bottom of the tank (16 or 16 '), or at the bottom of the evacuation well (25).  8 - Apparatus according to claim 2, character ized in that the anaerobic fermentation tank (16 ') contains a hydraulic valve 36') intended to cause oscillations of the mass in fermentation and supports a gasometer (35 ') whence the gas can escape by a pipe (45) which passes through the tank (16 ') and ends on the one hand in a condensate trap (46) intended to recover the water present in the hot gases coming from fermentation, and on the other hand to a purifier (11).