ITBO20120134A1 - PROCEDURE AND PLANT OF ANAEROBIC DIGESTION WITH SEPARATE PHASES WITH AEROBIC / ANAEROBIC HYDROOLIS AND ACIDOSIS COMBINED IN PROCESS FOR CONTACT WITH RECYCLING OF DIGESTATE AND MICROBICA BIOMASS FOR GREATER METHANEOUS RANGE FROM ORGANIC FRACTION TO ELEV - Google Patents

Description

DESCRIPTION

"STEPS ANAEROBIC DIGESTION PROCESS AND PLANT

SEPARATE WITH AEROBIC / ANAEROBIC AND ACIDOSE HYDROLYSIS COMBINED IN THE PROCESS BY CONTACT WITH RECIRCULATION OF THE DIGESTATE AND MICROBIAL BIOMASS FOR THE GREATER YIELD OF METHANE FROM ORGANIC FRACTION WITH A HIGH CONTENT OF DRY SUBSTANCE "

FIELD OF TECHNIQUE

The present invention refers to the technological field of anaerobic digestion processes and plants for the production of biogas falling within the international classification C 12 m.

STATE OF THE TECHNIQUE

In the panorama of prior technology, the patents listed below stand out:

FR 818 680

EP O 131 319

EP 0 192900

WO 93/16169

IT 01245395

BO 07 / A000 787

From the known patent literature, the fact emerges that numerous problems have not yet been resolved such as:

- The solids content in the liquid phase cannot exceed ten percent of the mixture being fed

- Avoid the loss of anaerobic microbial biomass

- Recover the anaerobic biomass in the form of high density flakes to reduce the food / population ratio in the digestive phases

- Raise the demolition of volatile solids to eighty-five percent with an increase in the contact surface between the organic fraction and bacteria

- Optimize hydrolysis by first developing it in aerobiosis at particular temperature and humidity conditions and then in anaerobiosis together with acidosis

- To develop multipurpose reactors capable of satisfying different digestive needs in small volumes

- Eliminate the mechanical mixing and heating devices inside the digesters

- Reduce the energy required in the digestive process for thermostating and mixing operations.

The present invention consists of a process and plant for the anaerobic digestion of biomass and / or organic fraction of waste in separate phases consisting of five reactors connected in series and in parallel with particular biochemical and operating conditions controlled, each necessary and indispensable phase of the process digestion, extremely ductile with particular regard to organic fractions with a high content of solids.

The plant is characterized by having an initial pre-treatment of shredding for the volumetric reduction of the masses to be digested, to one or two millimeters, followed by an aerobic hydrolysis reactor capable of developing a considerable optional anaerobic microbial mass capable of starting the structural demolition of organic matter.

The hydrolysis started with aerobic activated sludge ends in two tanks operating in parallel in which, due to the particular operating conditions, the aerobic bacteria become facultative anaerobes with the total structural demolition of proteins, fats, fibers, sugars and carbon hydrates.

The plant consists of:

- A hammer shredder mill capable of reducing the size of the organic mass to particles with a diameter between 1 and 2 mm without causing cell water to escape. The mill is fed through special augers and a device introduces the shredded mass into the tank for aerobic hydrolysis.

- An aerobic hydrolysis reactor, consisting of a tank in which the biomasses are mixed with process water and / or livestock slurry in order to bring the dry matter concentration to 15%. A mixing and homogenization pump, with recirculation through nozzles, causes a strong oxidation of the biomass with an exothermic reaction, with the development of considerable quantities of aerobic bacteria capable of starting the demolition of complex molecular structures of proteins, oils and fats, carbon hydrates , fibers. The aerobic hydrolysis reactor works with a very high volumetric load at a temperature between 30 and 35 ° C with hydraulic residence times of 24 - 48 hours, the diameter-height ratio of the reactor is between 0.5 and 0.7 .

Anaerobic hydrolysis reactors. In these reactors the structural demolition of biomass is completed, essential for obtaining a high efficiency in the production of biogas. The demolition started in the feeding tank is completed, with the formation of simpler molecules and volatile fatty acids such as formic, acetic, propionic, butyric, valeric, et al. These reactions take place due to a combined physical action, thanks to a temperature / pressure and biological ratio and to the work of extracellular enzymes secreted by the aerobic bacteria initially developed in the loading tank transformed, for the operating conditions, into facultative anaerobes. The whole process is favored by the particular mixing system adopted, which brings the solid particles into intimate contact with the extracellular enzymes of the bacteria. The mixing system, supported by special paddle mixers, recirculates the entire contents of the reactor in a time of 2 and a half hours, without forming any surface crust.

The ratio between diameter and height is between 1 and 0.7.

- Real anaerobic digestion reactor. It is a completely mixed anaerobic digester with a particular shape with a diameter / height ratio between 1 and 0.7 in which the volatile fatty acids produced during the hydrolysis phase are transformed into methane and carbon dioxide. The particular mixing and control system adopted provides for the recirculation and mixing of the biomasses inside the reactor and for a further biochemical demolition of the organic fraction, further reducing the size of the solid particles by biological action, increasing the attackable contact surface of the bacteria. . The reactor operates at a carefully controlled and regulated temperature, pH and redox potential, so as to ensure the right volatile fatty acids / alkalinity ratio and therefore a generation time of the methanogenic bacteria of less than four days.

Secondary digester with sedimentation function with gasometric bell for the accumulation of the biogas produced in the hydrolysis and primary reactors. Unmixed reactor, operating at controlled temperature and pressure thanks to which the separation of the phases in the sewage leaving the anaerobic reactor is obtained. The shape of the reactor, together with technical measures, allows to separate the liquid phase, the solid phase and to stop the microbial activity allowing the formation of a phase containing flocculated bacteria. The liquid phase is partly sent to the head of the plant as process water and the portion remains in the digestate storage tank while the solid phase is sent back to the primary digester so as to obtain the doubling of the solids retention time compared to that hydraulic. The flocculated bacteria are carefully recovered and sent for digestion, thus increasing the concentration of methanogenic bacteria per unit volume of the digester. In the secondary digester there will therefore be three distinct phases:

or gas phase, represented by the biogas collected under a dome capable of equalizing flow rate and pressure

or liquid phase, under the first gas phase. Contains bioflocculated bacterial sludge

o liquid / solid phase, represented by the process liquid containing undigested solid residues and larger floccules of bacteria.

The three-level sampling system combined with a compensation tank with partial recirculation inside the same reactors combined with the hydraulic guard guarantee a simple and effective extraction of the mass from inside the digesters and its forwarding to the next phase of the process. The system is extremely safe, does not require maintenance and can be calibrated based on the operation of the reactors.

All reactors have biogas pressure regulation systems in addition to the hydraulic guard with gas sampling dome as well as an internal tor placed on the roof for Γ foam abatement.

Hydraulic guard of the secondary digester is combined with a compensation ton. The dip tubes are designed in such a way as to allow the extraction of floccules of bacteria and the extraction of liquid more or less rich in solid substances, consequently allowing to regulate the residence time and the degree of demolition of the solids.

GENERAL PROCESS LINE

The biomass and / or digestible waste are weighed after being taken from the storage trenches and then shredded with a special hammer mill and placed in the loading tank, the first hydrolytic aerobic reactor, and here added with water and recirculated digestate in order to bring the total solids at the concentration suitable for the best digestion.

The feed tank is characterized by having a special grinding pump and a mixing system with a volumetric pump with variable flow rate regulated by an inverter supported by external mixer-type paddle mixers. A pump uses a thermostat to send the mixture to the heat exchanger to maintain a reactor temperature, at the best operating conditions, between 35 - 37 ° C.

From here the mixture passes to the two anaerobic hydrolytic reactors in which the demolition of the organic molecular structures is completed in perfect anaerobiosis. The two reactors are two tanks that work in parallel and are characterized by having a mixing system with two volumetric pumps capable of working independently on a single reactor or coupled to double the flow rate in the event of particular operating conditions. The pump outlets are connected to particular nozzles suitable for handling the material inside the tanks, which therefore takes place without the presence of mechanical moving parts.

A careful temperature control is implemented on the reactors, in order to guarantee low generation times (Tg) for the bacteria involved in the different processes (Tg less than twenty minutes for facultative anaerobic bacteria and less than four days for methanogenic bacteria)

A particular device guarantees a constant and proportional extraction of the internal mass of the different tanks. Said device includes a hydraulic guard and a three-level pump withdrawal controlled by two pressure gauges operating in parallel and connected in such a way as to obtain the extraction of liquid more or less rich in solid substances, consequently allowing the regulation of the residence time of the solids and therefore their degree of demolition.

DESCRIPTION

The present invention is part of the technological sector concerning the digestion of biomasses.

Through the use of a series of appropriately managed reactors, a high efficiency is guaranteed in terms of biogas production, with a methane percentage higher than seventy percent starting from a wide range of both animal and vegetable biomasses as well as organic waste.

It is known that the production of biogas from organic substances is obtained through reactors consisting of oxygen-free watertight vessels, by facultative anaerobic and / narrow anaerobic bacteria.

These reactors, called digesters, consist of an inlet system for the organic substances to be fermented, a mixing system, a system for controlling the operating parameters (in particular the temperature) and a system for the output of the product gas. and digestion residues. In these digesters there are particular needs, different depending on the phase in which the digestive process is found.

The anaerobic digestion of organic matter is composed of distinct phases, characterized by the activity of different microbial strains.

PHASE OF HYDROLYSIS

This phase is of crucial importance in order to guarantee optimal returns in the subsequent phases.

The organic substance is initially hydrolyzed, i.e. the compounds are solubilized and brought to an aqueous solution.

Not all organic substances can undergo this process, some in fact, such as lignin, require more than one hundred and eighty days to be demolished. Others, such as the fiber of plant tissues, can only be demolished through an attack by hydrolyzing acid-forming bacteria.

Fats and oils hydrolyze easily, releasing glycerin and fatty acids, in the same way proteins release ammonia and amines, which are subsequently transformed into acids.

The hydrolysis takes place thanks to the attack of aerobic and facultative anaerobic bacteria the present invention technologically develops the hydrolysis in two stages the first part the aerobic one in the loading tank developing a considerable bacterial mass which from aerobic will turn into optional anaerobic in the second hydrolysis that developed in the two reactors working in parallel. In the hydrolysis phase, the particular conditions of pH and temperature allow the generation of bacteria (optional anaerobes initially developed in the loading tank) to be less than twenty minutes.

DEMOLITION PHASE

The second phase is that of structural demolition of the organic molecules released after hydrolysis, with the production of volatile fatty acids (Formic, Acetic, Propionic, Butyric, Valeric and others). All the hydrolyzed compounds in the first phase of the process are transformed into volatile fatty acids (AGV), this phase takes place in anaerobic hydrolysis reactors or acidogenesis reactors.

AGVs represent the growth substrate of methanogenic bacteria which, using them, produce energy, cell protoplasm, carbon dioxide and methane.

The methane content depends on the composition of volatile fatty acids: with acids with four and five carbon atoms, the methane content increases by more than twenty percent compared to that obtainable with acids with two or three carbon atoms. The yield of biogas production is strictly linked to the degree of demolition of the organic substance and the latter is a function of the food substrate / bacterial population ratio (organic substance / bacteria) and the intimate contact between the two components of the system. To achieve maximum biogas production, the following conditions must be met:

complete hydrolysis of the substance placed in the system,

total formation of volatile fatty acids;

formation of acids with a high number of carbon atoms;

minimum ratio between fed substrate and population;

maximum bacterial load SSVKg / mc reactor;

maximum contact time between the substance to be gasified and bacteria;

redox potential value less than 500 milliVolts;

pH higher than 6.5 in the methanization step;

right ionic energy ratio between AGV and Alkalinity within the system.

The known technology provides for the realization of one or more reactors operating in series or in parallel, in which the phases of hydrolysis, acidification, hydrogenation and methanogenesis take place simultaneously, with very high reactor volumes in order to guarantee a suitable residence time of the biomass to be ferment and reduced escape through the effluent of the fermenting microbial biomass.

The known mixing is obtained through mechanical mixers placed

inside the reactors; they require high power but guarantee low mixing power. In some cases the mixing is obtained by means of lances immersed in the liquid phase through the recirculation of the biogas, after compression through different devices.

temperature control, normally maintained at values of about 36 degrees, is obtained through internal heat exchangers consisting of tubes placed on the walls where the heating liquid flows. The transfer of heat is obtained thanks to the circulation of the liquid contained in the reactor. The effectiveness of this system is doubtful and does not guarantee the maintenance of the temperature at the desired values given the reduced circulation of the sewage inside the reactor and since the thermometer in charge of the control is very often affected by the influence of the heating system.

MICROBIAL FLORA RECOVERY

In all types of existing reactors, the microbial flora is contained inside the digester through various artifices, such as the use of traps or the recirculation of biomasses through the draft of the digested and recovered material, after degassing.

These recirculation systems, in addition to recovering the microbial flora, also recover a large part of the digestate due to the dispersion of the biomasses, making it impossible to effectively maintain the microbial load per unit volume of the digester.

The indiscriminate withdrawal of the liquid phase means that in the liquid to be recirculated there are present undigested organic fraction and microbial mass with composition and percentages equal to those normally found inside the digester, effectively nullifying the effect of the increase in the microbial load in the digestion phase.

Various types of devices are known for extracting fermented substances, operating according to different techniques. These extraction devices usually have withdrawal members arranged vertically and / or horizontally on the wall or on the bottom of the collection container, inside pipes open at the top and in communication with the hydraulic seal so as to regulate the level of the liquid inside. of the digester. At the bottom of the tank the collection of the microbial culture and the digestate takes place without any regulation, in a ratio that is always a function of the concentration of the two components; this makes it impossible to enrich the microbial mass at the expense of the biomass to be digested. Currently known solutions allow to extract accumulated substances in a uniform manner in the whole cross section of the tank, without distinction between the various components of the system due to the presence of substances positioned in a completely random way inside the container.

The solution proposed by the present invention, due to the effect of the bioflocculation which favors the formation of flakes and the floatation of the microbial mass on the heavier digestate, allows to achieve different falling speeds so that these substances can descend in a significantly regular way along the container itself, creating quite distinct areas of accumulation and withdrawal. Thus there is a surface area free of solids, an intermediate area rich in bioflocculated microbial cultures and an area on the bottom of the digester rich in undigested material.

A three-level pump-based sampling system placed outside and / or inside, in combination with the hydraulic guard, allows for the sampling at different levels, allowing the separate recovery of the liquid phase, containing the microbial cultures and of the phase containing the digestate.

This plant is characterized by some details:

use of a loading tank where the hydrolysis process starts thanks to the formation and development of a considerable quantity per loading unit of specific microbial culture;

- use of two biolytic reactors in parallel for the completion of hydrolysis and acidification, with the production of hydrogen and volatile fatty acids, through biological processes supported by a significant load of optional anaerobic SSVs with particular fermentation technology;

mixing system combined with a fine grinding of the solids, by a specific first mill and a high capacity and head grinding pump. A volumetric pump controlled by an inverter also provides for the recirculation of the mass inside the reactor through special nozzles placed inside it. The entire content of the reactor is recirculated in less than two and a half hours anaerobic digestion carried out in separate mesophilic-thermophilic phases, with the exploitation of volatile fatty acids with four and five carbon atoms capable of ensuring a higher percentage of methane in the biogas;

bioflocculation obtained in the secondary digester. The formation of consistent flakes of bacteria is obtained thanks to the introduction of reduced quantities of predigested sewage and hydrolyzed raw biomass;

the use of a particular selective device for the collection of the digestate, to be removed and from the microbial culture to be recirculated in digestion;

concentrations of bacteria in the sludge (Kg of bacteria per cubic meter of reactor) about three to five times higher than that usually used;

a sludge load capable of guaranteeing a gasification yield that is at least thirty percent higher than those currently obtained;

content of dry matter entering the plant higher than fifteen percent. This concentration is fifty percent higher than that normally used in wet anaerobic digestion.

SYSTEM OPERATION

The biomass, represented by vegetated and / or animal organic matter at a concentration of thirty-five percent of dry matter, is fed to the grinder mill and then to the loading tank, an aerobic biolytic reactor, together with the process water and a portion of rich digestate. of microbial cultures.

The biomass is prepared in the loading tank and a special grinding pump feeds the two anaerobic hydrolysis and acidification biolytic reactors directly on the suction of the mixing pumps serving the anaerobic biolytic hydrolysis reactors, bringing the concentration of the dry substance of the mixture to fifteen percent, due to the dilution obtained inside the pump itself by the liquid withdrawn from the reactors. BIOLITHIC REACTOR

The biolithic reactor consists of two insulated cylinders with a diameter equal to the height and with a truncated cone as a cover and as a base, operating in parallel, with constant mixing of the mass inside them. They work at a temperature between forty and fifty degrees, the temperature correction takes place through thermostats, which regulate a recirculation in the demolition phase through a tube bundle heat exchanger and a hot / cold mixer, the heating system is external and uses one or more heat exchangers, together with hot / cold mixers against the thermal shock of microbial cultures.

The material leaving the hydrolysis reactor contains hydrogen and volatile fatty acids as well as a modest quantity of organic substance not yet demolished.

The relative pressure of the formed gas, containing hydrogen, methane and carbon dioxide, is less than four hundred millimeters of water column.

METHANIZATION REACTOR

The sewage from the two biolytic reactors passes to the anaerobic reactor where, thanks to the hydrogen ionic and methanogenic bacteria, the production of biogas with methane contents higher than seventy per center is completed.

The digester consists of an insulated cylinder, with a height equal to the diameter with a truncated cone as a cover and as a base.

In the anaerobic digester the mass is kept stirred by one

Volumetric mixing pump controlled by inverter, able to homogenize the organic fraction thanks to the use of special Venturi nozzles suitably positioned both on the bottom and on the top of the reactor. On the roof there is an anti-foaming tor which is always fed by the mixing pump.

The reactor has a temperature between forty and forty-five degrees centigrade, redox potential equal to about -500 millivoltamperes, pH higher than 6.5% and sludge load (kg of organic substance / kg of bacterial mass) lower than 0.07 .

The heating apparatus is external and uses one or more heat exchangers together with hot / cold mixers against the thermal shock of microbial cultures.The system is able to regulate the ionic balance between AGV and alkalinity of the liquid phase with the development of gaseous metabolites, ensuring maximum methane production. The carbon dioxide present in the system has a buffering effect on the pH regulation, in this way the kinetic energy possessed by the electrolytes is used to the maximum, favoring gasification for the best operating conditions and for the continuous removal from the process of the metabolites that have an inhibiting action on the kineti.

These reactors, taken as a whole and / or individually, can be used not only for anaerobic digestion processes but also for other types of fermentations, constituting

tanks which in practice are rather advantageous.

In circular or polygonal reactors the use of particular essential structures for the extraction of the digestate is known, but all the devices applied up to now do not allow a differentiated extraction between the liquid phase

containing biological sludge and digestate.

To obtain a good separation it is necessary to resort to external systems, able to separate the various phases by centrifugation or sedimentation with thickening.

These devices provide good results in terms of operation, but have a complex structure and are burdensome in conduction and lead to the loss of part of the bacterial activity when they are not developed after degassing and in a strictly anaerobic environment.

The purpose of the present invention is to realize a plant and a technology which

allows the digestion of biomass with a high solids content, obtaining the maximum possible energy yield in the form of methane. All this will take place in particular reactors for the anaerobic fermentation of even very complex organic substances, ensuring

continuity of production processes.

A further object of the present invention is to propose a series of reactors with technical and functional characteristics optimized for the anaerobic digestion process, but made by means of simple technical solutions, of sure functionality and reliability as well as characterized by a versatility of use.

The characteristics of the invention, not emerging from what is specified above, are highlighted below with particular reference to the figures of the attached drawings by way of non-limiting example

Fig. 1 Anaerobic digestion plant line

Fig. 2 Feed tank

Fig. 3 Recirculation of the slurry to the heat exchanger

Fig. 4 Recirculation of the digestate from the secondary digester to the primary digester

In the figures, every single detail is marked how it performs.

1. Shredder mill

2. aerobic hydrolysis reactor feeding tank

3. two reservoirs of hydrolysis and acidogenesis

4. primary digester

5. heat exchanger

6. secondary digester with gasometric bell

7. bleed tank

8. mixing pump

9. pump feeds of the various phases

10. hydrolysis-exchanger recirculation pump; primary digester recirculation pump exchanger

11. digestate recirculation pump from secondary to hydrolysis and primary

12. mixing nozzles

13. tor break down foam

14. three-level picking system

15. compensation tower.

Claims (1)

CLAIMS 1) Separate phase anaerobic digestion process and plant for the production of biogas starting from biomass with both high and low dry matter content, CHARACTERIZED BY INCLUDING: a shredder mill (1) with special operating characteristics equipped with a feeding system to the loading tank loading tank (2) with particular technical characteristics with mixing system by means, pump (8) thermostated by pump (10) and heat exchanger (5) and feeding by pump (9) to the subsequent hydrolysis and acid genesis tank ( 3) two strictly anaerobic hydrolysis and acid genesis reactors (3) equipped with mixing pumps (8) with nozzles (12), a recirculation pump (10) for temperature control via heat exchanger (5) and sampling on three levels (14) equipped with recirculation pump (9) for feeding to the next primary digester (4) with antifoam tor (13) a primary digester (4) equipped with a mixing pump (8) with nozzles (12) as well as a recirculation pump (10) for temperature control via heat exchanger (5) a secondary digester (6) with overlying gasometer, equipped with a special sampling system at different levels combined with a compensation tank (3) capable of recovering the different sedimented phases of the digester. It is equipped with a recirculation pump (11) to feed the sludge and / or digestate to the primary digester (4). on the gas line, purge vessels, filters (7) such as flame traps and condensate separators.