Difference between revisions of "Biodigesteur domestique/en"

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In France and other industrialized countries, the cost of energy being very low compared to workforce cost, only few small biodigestor units exist. However, many industrial units are present in wastewater treatment plants or around big breeding farms.
 
In France and other industrialized countries, the cost of energy being very low compared to workforce cost, only few small biodigestor units exist. However, many industrial units are present in wastewater treatment plants or around big breeding farms.
  
Different kind if biodigestors exist. They can be continuous or discontinuous, and also have different operation temperatures (psychrophilic : 15-25°C, mesophilic : 25-45°C or thermophilic : 45 – 65°C). In this tutorial, we are studying continuous mesophilic biodigestors à 38°C, which are the most commonly used in temperate regions.
+
Different kinds of biodigestors exist. They can be continuous or discontinuous, and also have different operation temperatures (psychrophilic : 15-25°C, mesophilic : 25-45°C or thermophilic : 45 – 65°C). In this tutorial, we are studying continuous mesophilic biodigestors at 38°C, which are the most commonly used in temperate regions.
  
The main feature of this system is its similarity to a digestive system. It also needs a certain temperature to be efficient, requires bacterias and receives food regularly.
+
The main feature of this system is its similarity to a digestive system, as it also needs a certain temperature to be efficient, requires bacterias and receives food regularly.
  
 
In a compost, under aerobic conditions, decomposition of organic matter produces gas (H2S, H2, NH3) and an important amount of heat. Only decomposition deprived from air produces methane. It is one of the reasons why fermentation happens in a sealed tank.
 
In a compost, under aerobic conditions, decomposition of organic matter produces gas (H2S, H2, NH3) and an important amount of heat. Only decomposition deprived from air produces methane. It is one of the reasons why fermentation happens in a sealed tank.
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In this tutorial, we will present the different components of a biodigestor (matter circuit and gas circuit) and how to use it.
 
In this tutorial, we will present the different components of a biodigestor (matter circuit and gas circuit) and how to use it.
  
This documentation realised with the association Picojoule describes fabrication of one of their micro-methanisation protypes. It does not provide full cooking gas autonomy but is a good introduction to methanisation. Hélie Marchand's half-burried digestor has a greater capacity : [[Biodigesteur]].  
+
This documentation realised with the association Picojoule describes fabrication of one of their micro-methanisation protypes. It does not provide full cooking gas autonomy but is a good introduction to methanisation. Hélie Marchand's half-burried digestor has a greater capacity : [[Biodigesteur]].
  
 
These explanations are largely inspired from the work of Bertrand Lagrange in its books Biométhane 1 and 2, that we strongly recommand !
 
These explanations are largely inspired from the work of Bertrand Lagrange in its books Biométhane 1 and 2, that we strongly recommand !
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}}
 
}}
 
{{Materials
 
{{Materials
 +
|Step_Picture_00=Biodigesteur_domestique_sch_ma_biodigesteur.jpg
 
|Material='''Matter circuit'''
 
|Material='''Matter circuit'''
 
* 1 60 L can  
 
* 1 60 L can  
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|Step_Title=Matter circuit - Digestor
 
|Step_Title=Matter circuit - Digestor
 
|Step_Content===== Sizing ====
 
|Step_Content===== Sizing ====
For a good digestion, at 38°C, the organic matter must stay 30 days in the biodigestor. We will size the digestor volume based on this duration and on regular inputs.
+
 
 +
For a good digestion at 38°C, the organic matter must remain 30 days in the biodigestor. We will size the digestor volume based on this duration and on regular inputs.
  
 
Let's take an example: if the regular input is 2L per day, as the matter must stay at least 30 days, the digestor volume must be at least 60 liters.
 
Let's take an example: if the regular input is 2L per day, as the matter must stay at least 30 days, the digestor volume must be at least 60 liters.
  
 
==== Building ====
 
==== Building ====
 +
 
Degradation by the bacterias takes place in the digestor. The needed bacterias to produce methane are called methanogen bacterias. They grow in an environment deprived from oxygen, called an anaerobic environment. To remove organic matter from oxygen, it needs to be immerged into water.
 
Degradation by the bacterias takes place in the digestor. The needed bacterias to produce methane are called methanogen bacterias. They grow in an environment deprived from oxygen, called an anaerobic environment. To remove organic matter from oxygen, it needs to be immerged into water.
  
 
*Drill two opposite holes in the digestor tank. They should be at one third of the tank height.
 
*Drill two opposite holes in the digestor tank. They should be at one third of the tank height.
  
* Insert a through hole connector (greased beforehand) in each of the two holes.
+
* Insert a through wall connector (greased beforehand) in each of the two holes.
  
 
* Grease the inside of the through wall connectors.
 
* Grease the inside of the through wall connectors.
  
* Place a plate inside if the digestor, as separation between the input and output holes. Letting matter circulate above and below the plaque, it will increase the time spent by the organic matter inside of the digestor.
+
* Place a plate inside if the digestor, as a separation between the input and output holes. Letting matter circulate above and below the plate, it will increase the time spent by the organic matter inside of the digestor.
  
 
* Drill a hole in the tank cover and place there a through wall connector for gas.
 
* Drill a hole in the tank cover and place there a through wall connector for gas.
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}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Circuit matière - Entrée
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|Step_Title=Matter circuit - Input
|Step_Content=C’est par l’entrée du système, sa bouche, que le biodigesteur est nourri. Le montage sera entièrement réalisé à blanc pour s’assurer de ses bonnes dimensions puis démonté et collé.
+
|Step_Content=The entry of the system will be the biodigestor mouth. The installation will first be done to verify dimensions of the system, and then will be dissasembled and definitively glued.
  
*Faire pénétrer un tuyau PVC dans l’une des ouvertures du digesteur, il est inutile qu’il rentre de trop, cela limite la circulation de la matière,
+
* Put a PVC pipe in one of the digestor openings, without putting it too much inside (this would reduce matter circulation).
  
*Faire un angle à 90° en utilisant deux raccords 45°. Sur des petits diamètres de tube il est préférable d’avoir des angles doux. Un raccord à 90° est vite obstrué et bloque le transit,
+
* Create a 90° angle using two 45° bends. On small diameter tubes, it is better to have smooth angles, as a direct 90° angle would get stuck more easily.
  
*Réaliser la bouche à partir de tuyaux de grands diamètres, plus la bouche est large plus il est simple de nourrir proprement le digesteur. Une première fermentation a lieu dans la bouche, un couvercle dévissable ferme le tout,
+
* Build the "mouth" with large diameter pipes. The larger the mouth is, the easier it will be to feed the digestor. A first fermentation process happens in the mouth. An unscrewable lid closes the mouth.
  
*Relier la bouche au digesteur de manière à ce que celle-ci-soit plus haute et que la matière circule par gravité.
+
* Link the mouth to the digestor, placing it higher than the digestor, so that matter can circulate in the system with gravity.
 
|Step_Picture_00=Biodigesteur_domestique_small_bouche.png
 
|Step_Picture_00=Biodigesteur_domestique_small_bouche.png
 
|Step_Picture_01=Biodigesteur_domestique_small_bouche_install_e.png
 
|Step_Picture_01=Biodigesteur_domestique_small_bouche_install_e.png
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}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Circuit matière - Trop-plein
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|Step_Title=Matter circuit - Overflow
|Step_Content=Par analogie, le trop-plein représente le terminus du système digestif. A chaque fois que le système est nourri, un même volume de digestat quitte le biodigesteur. Pour faciliter l’entretien une sortie basse est réalisée. Elle permet de vidanger le digesteur.
+
|Step_Content=The overflow represents the end of the digestive system. Each time the system is fed, the same volume of digestate leaves the digestor. To make maintenance easier, a low exit in created. It allows draining of the digestor.
* Faire pénétrer un tuyau PVC dans la seconde ouverture du digesteur, il est inutile qu’il rentre de trop, cela limite la circulation de la matière,
 
  
* Mettre un raccord Y,
+
* Place a PVC pipe in the second hole of the digestor. It should not be too much inside, as would again limit circulation of the matter.
  
* La partie horizontale est prolongée par un tube puis muni d’un bouchon, c’est la vidange,
+
* Place a Y connector.
  
* Faire remonter la deuxième branche jusqu’au haut du biodigesteur à l’aide de 3 manchons à 45°, toujours pour éviter d’obstruer le système,
+
* The horizontal part will be plugged to a pipe with a cap. This will be the draining pipe.
  
* Un tube PVC part vers l’extérieur, c’est par là que se déverse le digestat,
+
The second part will be continued vertically, until the top of the biodigestor, using 3 45° sleeves, again to prevent blockage of the system.
  
* Le trop-plein est plus bas que le couvercle du digesteur, il permet de maintenir un « ciel gazeux » et de ne pas avoir de matière organique dans le circuit de gaz.
+
* One of the PVC pipe goes outside of the system, where the digestate flows.
 +
 
 +
* The overflow should be lower than the digestor cover. This will allow to maintain a "geaseous roof" and to avoid organic matter in the gas circuit.
 
|Step_Picture_00=Biodigesteur_domestique_small_trop_plein_install_.png
 
|Step_Picture_00=Biodigesteur_domestique_small_trop_plein_install_.png
 
|Step_Picture_01=Biodigesteur_domestique_small_trop_plein.png
 
|Step_Picture_01=Biodigesteur_domestique_small_trop_plein.png
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Circuit matière - Collage et étanchéité
+
|Step_Title=Matter circuit - Bonding and sealing
|Step_Content=Si le système monté à blanc est satisfaisant il faut coller les éléments de PVC entre eux :
+
|Step_Content=If the blank assembly is satisfaying, we will now glue PVC components together :  
* Marquer chacun des raccords en faisant une croix sur la jonction, cela permet de remonter le système en respectant les alignements,
+
* Mark each of the connectors on their junction, so that you can reassemble the system respecting alignements.
* Nettoyer les zones à coller,
+
* Clean areas that will be glued.
  
* Coller à la colle PVC,
+
* Bond with PVC glue.
  
* Laisser sécher,
+
* Let it dry.
Il faut à la suite tester l’étanchéité :
+
Then we will test the sealing :  
* Boucher provisoirement la sortie du trop-plein (ex : chambre à air + collier de serrage), visser le couvercle d’entrée matière, visser le bouchon de vidange,
+
* Block temporarily the overflow outpur (for example with an air chamber and a hose clamp), screw the cap of the matter input part ("the mouth") and the draining plug.
  
* Mettre le système sous pression à l’aide d’un compresseur en soufflant par la vanne gaz,
+
* Put the system under pressure with a compressor flowing in the gas valve.
  
* Asperger les jonctions à l’aide d’un spray d’eau savonneuse, si des bulles se forment le collage n’est pas étanche, il faut le revoir.
+
* Spray soapy water on the junctions. If bubles form, the sealing is not correct and the system has to be rebuild.
 
|Step_Picture_00=Biodigesteur_domestique_collage_pvc.png
 
|Step_Picture_00=Biodigesteur_domestique_collage_pvc.png
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Chaleur et Isolation
+
|Step_Title=Heat and Isolation
|Step_Content===== Chauffage ====
+
|Step_Content=====Heat====
Ce type de biodigesteur est mésophile, c’est-à-dire que les bactéries se développent entre 25°C et 45°C, idéalement à 38°C. Contrairement au compostage, la biodigestion ne génère que très peu de chaleur. Pour atteindre ces températures de travail il faut donc apporter de la chaleur au système. Il est possible de chauffer de nombreuses manières :
 
* par compostage autour du digesteur,
 
  
* par chauffage solaire,
+
This kind of biodigestor is mesophile, which means that bacterias develop between 25°C ans 45°C, ideally at 38°C. Unlike compost, biodigestion create only few heat. To reach these temperatures, heat will have to be provided to the system. It is possible to heat by different means :
 +
* compost around the digestor,
  
* en brulant une partie du méthane produit.
+
* Solar heating,
Dans notre cas, étant donné le petit volume du système, nous utilisons un chauffe-lit positionné sous le digesteur
 
  
==== Isolation ====
+
* By burning part of the produced methane.
Pour éviter que le biodigesteur soit énergétiquement déficitaire, il est important de très bien l’isoler pour lui apporter un minimum d’énergie calorifique. De plus, une bonne isolation permet de limiter les variations de températures auxquelles les bactéries sont très sensibles. Il est possible d’isoler de nombreuses façons. Nous avons isolé l’enceinte avec des plaques de liège. Il est possible d’utiliser de la paille, très bon isolant à bon marché.
+
It our case, given the small volume of the system, we are using a bedwarmer placed below the digestor.
 +
 
 +
====Isolation====
 +
 
 +
<div class="mw-translate-fuzzy">
 +
====Isolation====
 +
To prevent the digestor from loosing energy, it is important to provide a proper isolation, so that only few heat has to be provided. In addition, a good isolation limits temperature variations, to which bacterias are very sensitive. Many differents ways exist for isolation. We chose to use corkboards, but is also possible to use straw for example, which is very cheap and provides good isolation.
 +
</div>
 
|Step_Picture_00=Biodigesteur_domestique_chauffage_et_isolation.png
 
|Step_Picture_00=Biodigesteur_domestique_chauffage_et_isolation.png
 
|Step_Picture_01=Biodigesteur_domestique_isolation.png
 
|Step_Picture_01=Biodigesteur_domestique_isolation.png
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Circuit gaz
+
|Step_Title=Gas circuit
|Step_Content=Nous venons d’étudier le circuit de matière organique, de l’entrée à la production du digestat. Un des grands intérêts du biodigesteur est qu’il produit également du biométhane. Dans cette partie nous étudierons les différents éléments du circuit de gaz pour la bonne production et la purification du combustible.
+
|Step_Content=We have presented the organic matter circuit, from the mouth to the digestate production. One of the main interests of th biodigestor is that it also produces methane. In this part, we will study the different components of the gas circuit, necessary to ensure a good production and purification of the fuel.
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Circuit gaz - Digesteur
+
|Step_Title=Gas circuit - Digestor
|Step_Content=C’est dans le digesteur, en dégradant les matières organiques que les bactéries produisent le biométhane. Il est composé de plusieurs gaz en proportions variables, dont :
+
|Step_Content=In the digestor, bacterias will produce biomethane as they degradate the organic waste. In variable proportions, it is composed of :  
* Méthane                     (CH<sub>4</sub>)        50 à 70%
+
* Methane                    (CH<sub>4</sub>)        50 to 70%
  
* Dioxyde de carbone (CO<sub>2</sub>)        35 à 40%
+
* Carbon dioxyde (CO<sub>2</sub>)        35 to 40%
  
* Hydrogène Sulfuré    (H<sub>2</sub>S)          1 à 3%
+
* Hydrogen sulphide        (H<sub>2</sub>S)          1 à 3%
  
* Vapeur d’eau             (H<sub>2</sub>0)          variable
+
* Water vapor             (H<sub>2</sub>0)          variable
On y trouve également des traces d’hydrogène, d’oxygène, de monoxyde de carbone, d’azote et d’autre gaz présents en très faibles quantités.
+
There can be also traces of hydrogen, oxygen, carbon monoxyde, nitrogen, and other gases in very small quantities.
 
|Step_Picture_00=Biodigesteur_domestique_digesteur_gaz_small.png
 
|Step_Picture_00=Biodigesteur_domestique_digesteur_gaz_small.png
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Le méthane
+
|Step_Title=Methane
|Step_Content=Le méthane, CH<sub>4</sub>, est un carbure d’hydrogène de la famille C<sub>n</sub>H<sub>2n+2</sub> tout comme le propane (C<sub>3</sub>H<sub>8</sub>) ou le butane (C<sub>4</sub>H<sub>10</sub>). Il est très léger (d=0,55), il ne s’accumule donc pas au sol, au contraire du butane et du propane et diminue les dangers d’explosions. Le gaz naturel est composé principalement de méthane.
+
|Step_Content=Methane, CH<sub>4</sub>, belongs to the hydrocarbons family C<sub>n</sub>H<sub>2n+2</sub>, as propane (C<sub>3</sub>H<sub>8</sub>) or (C<sub>4</sub>H<sub>10</sub>). It is very light (d=0,55), and does not accumulate on the ground, unlike butane and propane, which decreases risks of explosion. Natural gas is composed mainly by methane.
  
Pour être liquéfié, en vue d’un transport plus commode, il doit être refroidi à -165°C ou comprimé à 400 bars. Cela n’est possible qu’avec des moyens industriels, on le conserve donc dans notre cas à l’état gazeux.
+
To become liquid, making it easier to transport, methane has to be cooled to -165°C or compressed at a pressure of 400bars. This is only possible with industrial means, so in our case we will keep it at a gaseous state.
  
Par rapport à la masse, c’est le meilleur carburant sur le plan calorifique (12 000 Kcal/kg), mais c’est le plus volumineux.
+
In terms of mass, it is the best fuel for thermic energy (12 000 Kcal/kg), but itis also the most voluminous.
  
Dans cette application, c’est le méthane qui nous intéresse, nous allons voir comment épurer le biométhane des autres composés.
+
Our objective is to separate methane from other gas compounds.
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Le dioxyde de carbone
+
|Step_Title=Carbon dioxyde
|Step_Content=La proportion varie en fonction des réactions bactériennes, de la température et des éléments à digérer. Le CO<sub>2</sub> gène la combustion mais ne l’empêche pas.
+
|Step_Content=Its proportion depends on the bacterian reactions, the temperature and the organic waste. CO<sub>2</sub> disturbs combustion, but does not prevent it.
  
Le plus simple est de procéder à un lavage du gaz à l’eau. Le dioxyde de carbone est très soluble (878 cm<sup>3</sup>/l à 20°C) alors que le méthane l’est très peu (34 cm<sup>3</sup>/l). Cette eau chargée de CO<sub>2</sub> peut être utilisée pour l’irrigation ou pour la culture d’algues comme la spiruline.
+
The easiest is to wash the gas with water. Carbon dioxyde is very soluble (878 cm<sup>3</sup>/l at 20°C), unlike methane (34 cm<sup>3</sup>/l). This water carrying CO2 can be used for agriculture irrigation, or for algeas farming such as spirulina.  
* A la sortie du digesteur, après la vanne, faire passer le gaz dans un réservoir-bulleur,
+
* At the digestor exit, after the valve, create a gas circuit bringing the gas in a bubbler-reservoir.
  
* Le réservoir doit être rempli d’eau,
+
* The reservoir must be filled with water.
  
* Le tube d’arrivée de gaz plonge dans l’eau,
+
* The gas arrival pipe dives into the water.
  
* La sortie de gaz est en haut,
+
* The gas output pipe in on the top of the reservoir.
  
* Un bouchon de vidange sur le bas du réservoir-bulleur permet de collecter l’eau enrichie en CO<sub>2</sub>.
+
* A draining plug at the bottom of the bubbler-reservoir with allow collection of water carrying CO<sub>2</sub>.
 
|Step_Picture_00=Biodigesteur_domestique_bulleur.png
 
|Step_Picture_00=Biodigesteur_domestique_bulleur.png
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=La vapeur d’eau
+
|Step_Title=Water vapour
|Step_Content=Il est souhaitable d’avoir le minimum d’eau à la combustion, celle-ci en dégageant déjà une grande quantité. De plus avec la condensation dans les tuyaux il y a un risque d’obstruction dans les points bas du circuit de gaz :
+
|Step_Content=It is advisable to have a minimum of water when combustion happens, as it already produces a lot. In addition, condensation in pipes risks to block the lower parts of the gas circuit. To remove water vapour :  
* Installer un collecteur d’eau au point le plus bas du système,
+
*Place a waste collector at the lowest point of the system.
  
* Si le circuit gaz est long, installer tous les 5 mètres des collecteurs aux points les plus bas,
+
* If the gas circuit is long, install collectors every 5 meters, at the lowest points of the circuit.
  
* Un bouchon de vidange sur le bas des collecteurs permet de purger l’eau régulièrement.
+
* A draining plug at the bottom the collectors allows for regular removal of water.  
Le réservoir-bulleur peut jouer le rôle de collecteur d’eau s’il est placé en bas du circuit de gaz.
+
The bubbler reservoir can play this role of water collector if it placed at the lowest of the gas circuit.
 
|Step_Picture_00=Biodigesteur_domestique_collecteur_d_eau.png
 
|Step_Picture_00=Biodigesteur_domestique_collecteur_d_eau.png
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=L’hydrogène sulfuré
+
|Step_Title=Hydrogen sulphide
|Step_Content=L’hydrogène sulfuré (H<sub>2</sub>S) est combustible mais fortement corrosif par la production d’acide sulfurique. Sa présence est nuisible et nous l’éviterons au maximum par un bon équilibre du pH du biodigesteur. Pour l’éliminer, on fait passer le biométhane à travers de l’oxyde de fer ou de la paille de fer qui sera régénérée par exposition à l’air libre avec départ de souffre. Le charbon de bois ou les billes d’argile peuvent également servir de matériaux filtrant.
+
|Step_Content=Hydrogen sulphide (H<sub>2</sub>S) is burnable but produces sulfuric acid, which is highly corrosive. A good pH balance in the biodigestor avoids most of hydrogen sulphide production.  
 +
To eliminate it, biomethane will go through iron oxide, or iron straw, that will be regenerated by exposing it to the air (sulfur will leave). Coal or clay balls can also serve as filters for hydrogen sulphide.
 
|Step_Picture_00=Biodigesteur_domestique_filtre_H2S.png
 
|Step_Picture_00=Biodigesteur_domestique_filtre_H2S.png
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Circuit gaz - Stockage
+
|Step_Title=Gas circuit - Storage
|Step_Content=Dans le digesteur, il est préférable d’avoir une fermentation qui se déroule à pression minimum. Pour cela, le gaz devra être évacué à mesure de son dégagement. A moins d’avoir une consommation continuelle et régulière de gaz, on devra disposer d’une réserve fournissant le gaz aux « pointes » de consommation et le stockant le reste du temps.
+
|Step_Content=In the digestor, it is advised that fermentation takes place at a minimum pressure. Gas will therefore has to be evacuate along its production. Unless gas consumption is continuous and regular, it is necessary to have a storage place, supplying gas only when necessary.
  
Les réservoirs souples de type « vessie » sont intéressants. A l’inverse, utiliser un récipient indéformable peut être dangereux : il faut être en mesure de vider l’air contenu à l’intérieur avant d'y introduire du méthane, le mélange des deux gaz peut être explosif.
+
Flexible reservoirs, "bladder" like, are interesting. Using a non-flexible container can be dangerous: because we will need to empty it from air befor introducing methane. Mixing air and methane can be explosive.  
* Monter le ballon de stockage en parallèle du circuit de gaz,
+
* Assemble the storage reservoir simultaneously to the gas circuit.
  
* Installer une soupape de sécurité 100 mbar au plus proche du stockage, elle dégazera s’il y a une surpression potentiellement dangereuse.
+
* Place a 100mbar safety valve as close as possible to the storage. It will remove gas in case of potentially dangerous overpressure.
 
|Step_Picture_00=Biodigesteur_domestique_gazom_tre.png
 
|Step_Picture_00=Biodigesteur_domestique_gazom_tre.png
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Circuit gaz - Retour de flamme
+
|Step_Title=Gas circuit - Flashback
|Step_Content=Partout où on craint un retour de flamme, placer une boule de paille de fer ou de cuivre sur le parcours du gaz qui, par conduction thermique, étouffe la combustion en abaissant la température. Il ne faut cependant pas trop tasser la paille métallique dans les tuyaux au risque de limiter le bon passage du gaz.
+
|Step_Content=In any place where a flashback is feared, place a ball of iron straw or copper straw on the gas circuit. Through thermic conduction, it will decreases temperature and stifle the combustion. Be careful however not to compact too much the metallic straw in the pipes, otherwise it would impede a good circulation of gas.
  
Dans notre cas, pour éviter un retour de flamme vers le digesteur et surtout le ballon de stockage, nous installons de la paille de fer dans le tuyau au plus proche de la gazinière.
+
In our case, to avoid flashbacks to the digestor and above all to the storage reservoir, we place iron straw in the closest pipe to the gas cooker.
 
|Step_Picture_00=Biodigesteur_domestique_retour_de_flamme.png
 
|Step_Picture_00=Biodigesteur_domestique_retour_de_flamme.png
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Circuit gaz - Combustion
+
|Step_Title=Gas circuit - Combustion
|Step_Content===== Réglage des bruleurs ====
+
|Step_Content===== Burners setting ====
Comme il est mélangé à du dioxyde de carbone non combustible, le biométhane a un pouvoir calorifique nettement plus faible que le propane, le butane ou le méthane pour un même volume.
 
  
 Les appareils qui fonctionnent avec ces gaz ont donc une plus grande admission d’air qu’une gazinière au biométhane.
+
As it is mixed with non combustible carbon dioxyde, biomethane has a lower calorific power than propane, butane of pure methane for the same volume.
  
Pour adapter les bruleurs standards à du biométhane :
+
Therefore, devices functionning with these gases have a higher air admission than a gas cooker using biomethane.
* Fermer légèrement l’arrivée d’air primaire, au moyen d’une bague métallique ou de papier aluminium.
 
OU
 
* Démonter le gicleur et utiliser l’éjection directe de gaz.
 
ATTENTION : les flammes de méthane sont moins visibles que celle de propane ou butane, il faut faire attention à ne pas se bruler au contact de la gazinière.
 
  
==== Autres utilisations ====
+
To adapt standard burners to biomethane :
Le biométhane peut également être utilisé dans des lampes à gaz, des chaudières ou des moteurs à explosions : groupes électrogènes, engins agricoles, voitures…
+
* Slightly close primary air arrival, with a metallic ring or with aluminium.
 +
OR
 +
* Disassemble the gas nozzle and use direct gas ejection.
 +
CAUTION: flames from methane are less visible than from propane or butane, be careful not to get burned when using the gas cooker.
  
==== Pression ====
+
====Other uses====
Le biodigesteur et le stockage sont à pression atmosphérique pour ne pas ralentir le travail bactérien. Une gazinière biométhane fonctionne avec un gaz à 10 mbar, pour cela :
+
 
* Installer un compresseur entre le stockage et le bruleur,
+
Biomethane can also be used in gas lamps, heaters, or combustion engines: generators, agricultural machines, cars...
OU
+
 
* Effectuer une pression sur la vessie de stockage (10 cm d’eau), cela réduit d’environ 5% la production de biogaz mais est beaucoup plus économe que l’acquisition d’un compresseur.
+
====Pressure====
 +
 
 +
The biodigestor and the storage are at atmospheric pressure, to ensure correct work of bacterias. The gas cooker will use 10mbar pressure. To provide this pressure:  
 +
* Install a compressor between the storage and the burner,  
 +
OR
 +
* Press the flexible reservoir (10 cm of water). It will reduce methane production by 5% but is less expensive then buying a compressor.
 
|Step_Picture_00=Biodigesteur_domestique_gicleur.png
 
|Step_Picture_00=Biodigesteur_domestique_gicleur.png
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Circuit gaz - étanchéité
+
|Step_Title=Gas circuit - Sealing
|Step_Content=Chaque raccord entre un élément et un tuyau de gaz doit être sécurisé avec un collier de serrage.
+
|Step_Content=Each connector between a component of the circuit and a gas pipe has to be securized with a hose clamp.
  
Une fois l’ensemble du circuit monté, faire un test d’étanchéité, comme pour le circuit matière, en le mettant sous pression et en aspergeant de l’eau savonneuse sur les jonctions. Si des bulles apparaissent, il y a une fuite.
+
Once the whole circuit is assembled, test the sealing, proceeding as for the matter circuit: put the circuit under pressure and spray soapy water on each junction. If fbubbles appear, there is a leak.
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Utilisation du digesteur - Alimentation
+
|Step_Title=Digestor usage - Feed
|Step_Content=Le biodigesteur est un système vivant, composé de millions de bactéries, il faut donc lui porter une attention particulière.
+
|Step_Content=The biodigestor is a living system, composed by billions of bacterias, and needs to be taken care of.
 +
 
 +
====Regular feeding====
 +
 
 +
Ideally, the biodigestor has to be fed every day.  It is possible to reduce it until once a week at the minimum. If the volume of organic matter is too important, it is advised to divide it in different "meals".
  
==== Alimentation régulière ====
+
'''It is important to shred or grind the organic matter (knive, blender...) and to add their weight in water, in order to''' :
Dans l’idéal le biodigesteur est nourri tous les jours. Il est possible de descendre jusqu’à une fois par semaine. Si le volume de matière à transformer est important, il vaut mieux le répartir sur plusieurs « repas ».
+
* Prevent the matter from blocking the system,
  
'''Il est important de broyer les aliments (au couteau, mixeur …) et d’y ajouter leur poids en eau pour''' :
+
* Accelerate degradation and system productivity.
* Faciliter le « transit » des éléments qui ne resteront pas bloqués dans le système,
 
  
* Accélérer la dégradation bactérienne donc la productivité du système 
+
====Balanced diet====
  
==== Alimentation équilibrée ====
+
Biodigestor can be complementary to a compost. Indeed, compost creates humus, and needs a high carbon/nitrogen ratio (20 to 30), with mostly cellulose and lignous compounds. Too much putrescible organic matter will destructurate the compost.
Le biodigesteur est un complément très intéressant au composteur. En effet un compost a pour objectif de créer de l’humus, pour cela il a besoin d’un fort rapport carbone/azote, (entre 20 et 30), avec principalement de la cellulose et des composés ligneux. Un surplus de matière organique putrescible déstructure le compost.
 
  
A l’inverse, les matières humides et putrescibles sont les bienvenues dans un biodigesteur (fruits et légumes en décomposition, épluchures…). Il faut limiter les matières fibreuses, sèches et dures voire les éviter dans un petit digesteur. Ils risquent de boucher la circulation de matière, ils ont également tendance à flotter et à former une écume très difficile à faire disparaitre et, en formant des croutes ou en se déposant au fond, ils utilisent de la place inutilement.
+
Conversely, wet and putrescible matters are welcome in a biodigestor (fruits and vegetables, peelings ...) Fibrous, dry and hard matters need to be limited in the biodigestor. They may be the cause for blockage of the system, and remain in the digestor forming foam or a crust, that is difficult to remove.
  
Une alimentation très azotée est idéale, l’azote n’est que très peu présent dans le biométhane mais il participe fortement à sa synthèse via la stimulation de l’activité bactérienne. De plus il permet d’obtenir un fertilisant très riche avec le digestat.
+
High nitrogen input is ideal in the digestor, as it will stimulate bacterias activity. In addition, the digestate produced will be a rich fertilizer.
  
Il est important d’apporter du « vert » au régime du digesteur, si les épluchures ou diverses fanes ne suffisent pas, de l’herbe tondue et broyée complète bien.
+
It is important to bring "green food" in the digestor diet. If peelings and leafstalks are not enough, it is possible to add grass.
  
Les produits animaliers (viandes, lait, œufs…) doivent être évités dans un biodigesteur, ne montant pas en température comme un compost il ne détruit pas les germes pathogènes.
+
Animal products (meat, milk, eggs...) should be avoided in the digestor, as it does not reaches high temperatures enough to detroy pathogens, unlike compost.
  
Les huiles alimentaires ont un très fort pouvoir méthanogène (780 litres de méthane par kilo d’huile !) mais acidifie le biodigesteur. S’il devient trop acide les bactéries vont mourir. A consommer avec modération.
+
Oils have an important methanogen power (780 liters of methane per kilogram of oil!) but it brings acidity to the digestor, which might kill the bacterias when too important. Oils should be brought to the system sparingly.
  
L’eau de cuisson permet de réchauffer le système tout en fluidifiant le transit. Elle est également chargée en amidon (pommes de terre, céréales, pâtes, riz …) apprécié par les bactéries.
+
Cooking water allows for system heating and fluidifies circulation. It also provides starch (potatoes, cereals, rice ...) that bacterias like.
  
L’urine peut être utilisée régulièrement. Les excréments sont acceptés en petites doses mais ils ont un faible pourvoir méthanogène, une grande partie de leur valeur énergétique a été absorbée pendant la digestion.
+
Urine can be used in a regular basis. Feces are accepted sparingly, but they have a weak methanogen power, as an important part of their energetic value has already been absorbed during digestion.
  
==== pH ====
+
====pH====
En milieu acide, l’activité enzymatique des bactéries est bloquée. Cette acidité est surtout due à l’accumulation d’acides organiques. En milieu basique, les fermentations produisent de l’hydrogène sulfuré (H2S) et de l’hydrogène (H2). La digestion peut s’effectuer entre des pH de 6,6 et 7,6 avec un optimum entre 7 et 7,2.
+
 
 +
In acid medium, the enzymatic activity of the bacterias is inhibited. This acidity is mainly due to organic acids accumulation. In basic medium, fermentation produce hydrogen sulphide (H2S) and hydrogen (H2). Digestion can take place between pH of 6,6 and 7,6, with an optimum between 7 and 7,2.
 
|Step_Picture_00=Biodigesteur_domestique_banane_broy_e.png
 
|Step_Picture_00=Biodigesteur_domestique_banane_broy_e.png
 
}}
 
}}
 
{{Tuto Step
 
{{Tuto Step
|Step_Title=Ensemencement
+
|Step_Title=Inoculation
|Step_Content=Nous avons vu précédemment que les excréments ont un faible pouvoir méthanogène car déjà digérés. Ils restent cependant importants pour lancer l’activité bactérienne dans le digesteur.
+
|Step_Content=We have seen previously that feces have a weak methanogen power because they are already digested. However, they are important to launch bacterial activity in the digestor.
  
Une vache, à travers ses rots, génère à elle seule entre 60 et 200 litres de biogaz par jour. Nous allons donc récupérer une partie de la flore intestinale du ruminant dans … ses excréments.
+
A cow, generates between 60 and 200 liters of biogas a day. We will recover part of its intestinal bacterias in its feces.
  
Pour lancer la fermentation bactérienne dans le digesteur :
+
To launch the bacterial fermentation in the digestor:  
* Mélanger une bouse de vache fraiche à de l’eau et l’insérer à l’entrée du biodigesteur.
+
*Mix fresh cow manure with its weight in water, and insert it at the entrance of the biodigestor.  
Si l’activité du biodigesteur est arrêtée à cause d’une longue période sans alimentation il faut à nouveau l’ensemencer de la même manière.
+
If the activity of the biodigestor is stopped due to a long period without food, it would have to be inoculated again in the same way.
  
La stabilisation de la digestion jusqu’à une production régulière d’un gaz combustible peut durer plusieurs semaines, il est bon de ne pas trop perturber son alimentation.
+
Digestion stabilisation until a regular production of biogas can last several weeks, during which it is advised not to disturb feeding.
 
|Step_Picture_00=Biodigesteur_domestique_collecte_bouse.png
 
|Step_Picture_00=Biodigesteur_domestique_collecte_bouse.png
 
|Step_Picture_01=Biodigesteur_domestique_m_lange_bouse.png
 
|Step_Picture_01=Biodigesteur_domestique_m_lange_bouse.png
Line 336: Line 352:
 
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{{Tuto Step
 
{{Tuto Step
|Step_Title=Digestat
+
|Step_Title=Digestate
|Step_Content=Le digestat issu de biodigesteurs domestiques une fois stabilisé est un fertilisant liquide très riche en azote et minéraux.
+
|Step_Content=The digestate from domestic biodigestor, one stabilized, is a liquid fertilizer rich in minerals and nitrogen.
  
Il peut être appliqué dilué à 10% sur toutes les plantes avec un intervalle d’un mois entre chaque utilisation.
+
You can dilute it at 10% in water, and use it every month for any kind of plants.
  
Si des produits animaliers (viandes, lait, œufs…) font partis du régime du biodigesteur il ne faut pas appliquer de digestat sur les fruits et légumes mangés crus (fraises, salades, carottes…). Il trouvera son utilisation dans les vergers ou sur les plantes non-alimentaires.
+
If animal products (meat, milk, eggs...) are part of the digestor diet, it is better not to use digestate for fruits and vegetables that will be eaten raw (strawberries, lettuce, carots...) It is better to used in orchards or non-food plants.
 
|Step_Picture_00=Biodigesteur_domestique_silece_a_pousse.png
 
|Step_Picture_00=Biodigesteur_domestique_silece_a_pousse.png
 
|Step_Picture_01=Biodigesteur_domestique_fertilisant.png
 
|Step_Picture_01=Biodigesteur_domestique_fertilisant.png
 
}}
 
}}
 
{{Notes
 
{{Notes
|Notes=* La première édition du tutoriel à été réalisée par Clément Chabot lors de l'escale Biodigesteur du Tour de France des Low-tech.
+
|Notes=<div class="mw-translate-fuzzy">
 +
*The first edition of this tutorial has been realised by Clément Chabot, during the Biodigestor stop of the Low-tech Tour in France.
 +
</div>
 +
 
 +
Comme tout le travail du Low-tech Lab, '''ce tutoriel est participatif''', n'hésitez pas à ajouter les modifications qui vous semblent importantes, et à partager vos réalisations en commentaires.
 +
 
 +
<br />
 +
 
 +
*The first edition of this tutorial has been realised by Clément Chabot, during the Biodigestor stop of the Low-tech Tour in France.
 +
 
 +
<div class="mw-translate-fuzzy">
 +
* The documented solution was realised with Pierre and Thomas from the association PicoJoule http://www.picojoule.org/ [http://www.picojoule.org/] https://www.facebook.com/Picojoule/?fref=ts
 +
</div>
 +
 
 +
====References====
  
* La solution documentée a été réalisée avec Pierre et Thomas de l'association PicoJoule http://www.picojoule.org/ [http://www.picojoule.org/] https://www.facebook.com/Picojoule/?fref=ts
 
  
==== Sources ====
 
 
* Bernard LAGRANGE, Biométhane 1. Une alternative crédible ; 2. principes-techniques, utilisations
 
* Bernard LAGRANGE, Biométhane 1. Une alternative crédible ; 2. principes-techniques, utilisations
 
* https://fr.wikipedia.org/wiki/Pouvoir_m%C3%A9thanog%C3%A8ne
 
* https://fr.wikipedia.org/wiki/Pouvoir_m%C3%A9thanog%C3%A8ne
 
* https://fr.wikipedia.org/wiki/Biogaz
 
* https://fr.wikipedia.org/wiki/Biogaz
  
==== Notes ====
+
====Notes====
* tutoriel sur un digesteur semi-enterré d'Hélie Marchand à Madagascar : [[Biodigesteur]]
+
 
 +
* Hélie Marchand's tutorial of a semi-burried digestor in Madagascar : [[Biodigesteur]]
 +
}}
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{{PageLang
 
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{{Tuto Status
 
{{Tuto Status

Revision as of 11:51, 22 May 2020

Prototype de avatarLow-tech Lab | Categories : Housing, Energy

Introduction

A biodigestor is a solution to convert organic waste into fuel gas (biogas) and fertilizer (digestate). The biodigestor particularity is that digestion is done thanks to bacterias in an environment deprived from any oxygen. This situation is called anaerobic fermentation.

Biogas is a mix of different gases, containing mainly methane, which can be used for gas cookers, boilers or as fuel for engines.

Methanogen fermentation also exists in nature. For example, it happens in swamps when organic matter is decomposed underwater.

Biogas domestication happened in the beggining of the XIXth century, and the variety of biodigestors have considerably increased since then. They are particularly present in developing tropical countries, where farmers become autonomous in energy thanks to biogas production based on organic waste. Heat being an important catalyst of this reaction, small units are economically interesting in this area.

In France and other industrialized countries, the cost of energy being very low compared to workforce cost, only few small biodigestor units exist. However, many industrial units are present in wastewater treatment plants or around big breeding farms.

Different kinds of biodigestors exist. They can be continuous or discontinuous, and also have different operation temperatures (psychrophilic : 15-25°C, mesophilic : 25-45°C or thermophilic : 45 – 65°C). In this tutorial, we are studying continuous mesophilic biodigestors at 38°C, which are the most commonly used in temperate regions.

The main feature of this system is its similarity to a digestive system, as it also needs a certain temperature to be efficient, requires bacterias and receives food regularly.

In a compost, under aerobic conditions, decomposition of organic matter produces gas (H2S, H2, NH3) and an important amount of heat. Only decomposition deprived from air produces methane. It is one of the reasons why fermentation happens in a sealed tank.

In this tutorial, we will present the different components of a biodigestor (matter circuit and gas circuit) and how to use it.

This documentation realised with the association Picojoule describes fabrication of one of their micro-methanisation protypes. It does not provide full cooking gas autonomy but is a good introduction to methanisation. Hélie Marchand's half-burried digestor has a greater capacity : Biodigesteur.

These explanations are largely inspired from the work of Bertrand Lagrange in its books Biométhane 1 and 2, that we strongly recommand !

This work is free and open, do not hesitate to clarify and complete it based on your knowledge and experience.

Video overview

Materials

Matter circuit

  • 1 60 L can
  • 1 160 mm plug
  • 1 160-100 mm reducer
  • 1 100-50 mm reducer
  • 1 meter PVC 50 mm tube
  • 4 45° 50 mm PVC MF bends
  • 2 50 mm separable connections
  • 2 50 mm through wall connectors
  • 2 MM 50 mm sleeves
  • 1 50 mm PVC plug
  • PVC glue
  • Etchant
  • Joint compound for plumbing

Gas circuit

  • 2 planar nuts 1/2’ for through wall gas connector
  • 1 batch of planar joints
  • 1 threaded tube of 1/2’
  • 1 brass MF 1/2’ bend
  • 1 connector FF 1/2’ gland nut
  • 1 gas valve 15x21 MM
  • 1 batch of hose clamps
  • 1 gas pin 1/2’ F
  • 5 m gas pipe
  • 1 water filter
  • 1 sulfur filter made of clay balls
  • 2 gas valves
  • 3 T gas pipes
  • 1 compressed air dismountable connector
  • 1 manometer
  • 1 flexible 150L water tank
  • 1 gas compressor
  • 1 gas cooker
  • 1 heat mat

Tools

  • saw
  • drilling machine with cylinder saw
  • screwer
  • cutter
  • compressor

Step 1 - Matter circuit - Digestor

Sizing

For a good digestion at 38°C, the organic matter must remain 30 days in the biodigestor. We will size the digestor volume based on this duration and on regular inputs.

Let's take an example: if the regular input is 2L per day, as the matter must stay at least 30 days, the digestor volume must be at least 60 liters.

Building

Degradation by the bacterias takes place in the digestor. The needed bacterias to produce methane are called methanogen bacterias. They grow in an environment deprived from oxygen, called an anaerobic environment. To remove organic matter from oxygen, it needs to be immerged into water.

  • Drill two opposite holes in the digestor tank. They should be at one third of the tank height.
  • Insert a through wall connector (greased beforehand) in each of the two holes.
  • Grease the inside of the through wall connectors.
  • Place a plate inside if the digestor, as a separation between the input and output holes. Letting matter circulate above and below the plate, it will increase the time spent by the organic matter inside of the digestor.
  • Drill a hole in the tank cover and place there a through wall connector for gas.

Use teflon and planar joints on each side to seal the system.

  • Grease the seal of the tank cover and close it. The grease should ensure the seal, and the cover maintains pressure.
  • Intall a valve after the through wall connector for gas.

Step 2 - Matter circuit - Input

The entry of the system will be the biodigestor mouth. The installation will first be done to verify dimensions of the system, and then will be dissasembled and definitively glued.

  • Put a PVC pipe in one of the digestor openings, without putting it too much inside (this would reduce matter circulation).
  • Create a 90° angle using two 45° bends. On small diameter tubes, it is better to have smooth angles, as a direct 90° angle would get stuck more easily.
  • Build the "mouth" with large diameter pipes. The larger the mouth is, the easier it will be to feed the digestor. A first fermentation process happens in the mouth. An unscrewable lid closes the mouth.
  • Link the mouth to the digestor, placing it higher than the digestor, so that matter can circulate in the system with gravity.


Step 3 - Matter circuit - Overflow

The overflow represents the end of the digestive system. Each time the system is fed, the same volume of digestate leaves the digestor. To make maintenance easier, a low exit in created. It allows draining of the digestor.

  • Place a PVC pipe in the second hole of the digestor. It should not be too much inside, as would again limit circulation of the matter.
  • Place a Y connector.
  • The horizontal part will be plugged to a pipe with a cap. This will be the draining pipe.

The second part will be continued vertically, until the top of the biodigestor, using 3 45° sleeves, again to prevent blockage of the system.

  • One of the PVC pipe goes outside of the system, where the digestate flows.
  • The overflow should be lower than the digestor cover. This will allow to maintain a "geaseous roof" and to avoid organic matter in the gas circuit.


Step 4 - Matter circuit - Bonding and sealing

If the blank assembly is satisfaying, we will now glue PVC components together :

  • Mark each of the connectors on their junction, so that you can reassemble the system respecting alignements.
  • Clean areas that will be glued.
  • Bond with PVC glue.
  • Let it dry.

Then we will test the sealing :

  • Block temporarily the overflow outpur (for example with an air chamber and a hose clamp), screw the cap of the matter input part ("the mouth") and the draining plug.
  • Put the system under pressure with a compressor flowing in the gas valve.
  • Spray soapy water on the junctions. If bubles form, the sealing is not correct and the system has to be rebuild.



Step 5 - Heat and Isolation

Heat

This kind of biodigestor is mesophile, which means that bacterias develop between 25°C ans 45°C, ideally at 38°C. Unlike compost, biodigestion create only few heat. To reach these temperatures, heat will have to be provided to the system. It is possible to heat by different means :

  • compost around the digestor,
  • Solar heating,
  • By burning part of the produced methane.

It our case, given the small volume of the system, we are using a bedwarmer placed below the digestor.

Isolation

Isolation

To prevent the digestor from loosing energy, it is important to provide a proper isolation, so that only few heat has to be provided. In addition, a good isolation limits temperature variations, to which bacterias are very sensitive. Many differents ways exist for isolation. We chose to use corkboards, but is also possible to use straw for example, which is very cheap and provides good isolation.


Step 6 - Gas circuit

We have presented the organic matter circuit, from the mouth to the digestate production. One of the main interests of th biodigestor is that it also produces methane. In this part, we will study the different components of the gas circuit, necessary to ensure a good production and purification of the fuel.

Step 7 - Gas circuit - Digestor

In the digestor, bacterias will produce biomethane as they degradate the organic waste. In variable proportions, it is composed of :

  • Methane (CH4) 50 to 70%
  • Carbon dioxyde (CO2) 35 to 40%
  • Hydrogen sulphide (H2S) 1 à 3%
  • Water vapor (H20) variable

There can be also traces of hydrogen, oxygen, carbon monoxyde, nitrogen, and other gases in very small quantities.



Step 8 - Methane

Methane, CH4, belongs to the hydrocarbons family CnH2n+2, as propane (C3H8) or (C4H10). It is very light (d=0,55), and does not accumulate on the ground, unlike butane and propane, which decreases risks of explosion. Natural gas is composed mainly by methane.

To become liquid, making it easier to transport, methane has to be cooled to -165°C or compressed at a pressure of 400bars. This is only possible with industrial means, so in our case we will keep it at a gaseous state.

In terms of mass, it is the best fuel for thermic energy (12 000 Kcal/kg), but itis also the most voluminous.

Our objective is to separate methane from other gas compounds.

Step 9 - Carbon dioxyde

Its proportion depends on the bacterian reactions, the temperature and the organic waste. CO2 disturbs combustion, but does not prevent it.

The easiest is to wash the gas with water. Carbon dioxyde is very soluble (878 cm3/l at 20°C), unlike methane (34 cm3/l). This water carrying CO2 can be used for agriculture irrigation, or for algeas farming such as spirulina.

  • At the digestor exit, after the valve, create a gas circuit bringing the gas in a bubbler-reservoir.
  • The reservoir must be filled with water.
  • The gas arrival pipe dives into the water.
  • The gas output pipe in on the top of the reservoir.
  • A draining plug at the bottom of the bubbler-reservoir with allow collection of water carrying CO2.



Step 10 - Water vapour

It is advisable to have a minimum of water when combustion happens, as it already produces a lot. In addition, condensation in pipes risks to block the lower parts of the gas circuit. To remove water vapour :

  • Place a waste collector at the lowest point of the system.
  • If the gas circuit is long, install collectors every 5 meters, at the lowest points of the circuit.
  • A draining plug at the bottom the collectors allows for regular removal of water.

The bubbler reservoir can play this role of water collector if it placed at the lowest of the gas circuit.



Step 11 - Hydrogen sulphide

Hydrogen sulphide (H2S) is burnable but produces sulfuric acid, which is highly corrosive. A good pH balance in the biodigestor avoids most of hydrogen sulphide production. To eliminate it, biomethane will go through iron oxide, or iron straw, that will be regenerated by exposing it to the air (sulfur will leave). Coal or clay balls can also serve as filters for hydrogen sulphide.



Step 12 - Gas circuit - Storage

In the digestor, it is advised that fermentation takes place at a minimum pressure. Gas will therefore has to be evacuate along its production. Unless gas consumption is continuous and regular, it is necessary to have a storage place, supplying gas only when necessary.

Flexible reservoirs, "bladder" like, are interesting. Using a non-flexible container can be dangerous: because we will need to empty it from air befor introducing methane. Mixing air and methane can be explosive.

  • Assemble the storage reservoir simultaneously to the gas circuit.
  • Place a 100mbar safety valve as close as possible to the storage. It will remove gas in case of potentially dangerous overpressure.



Step 13 - Gas circuit - Flashback

In any place where a flashback is feared, place a ball of iron straw or copper straw on the gas circuit. Through thermic conduction, it will decreases temperature and stifle the combustion. Be careful however not to compact too much the metallic straw in the pipes, otherwise it would impede a good circulation of gas.

In our case, to avoid flashbacks to the digestor and above all to the storage reservoir, we place iron straw in the closest pipe to the gas cooker.



Step 14 - Gas circuit - Combustion

Burners setting

As it is mixed with non combustible carbon dioxyde, biomethane has a lower calorific power than propane, butane of pure methane for the same volume.

Therefore, devices functionning with these gases have a higher air admission than a gas cooker using biomethane.

To adapt standard burners to biomethane :

  • Slightly close primary air arrival, with a metallic ring or with aluminium.

OR

  • Disassemble the gas nozzle and use direct gas ejection.

CAUTION: flames from methane are less visible than from propane or butane, be careful not to get burned when using the gas cooker.

Other uses

Biomethane can also be used in gas lamps, heaters, or combustion engines: generators, agricultural machines, cars...

Pressure

The biodigestor and the storage are at atmospheric pressure, to ensure correct work of bacterias. The gas cooker will use 10mbar pressure. To provide this pressure:

  • Install a compressor between the storage and the burner,

OR

  • Press the flexible reservoir (10 cm of water). It will reduce methane production by 5% but is less expensive then buying a compressor.



Step 15 - Gas circuit - Sealing

Each connector between a component of the circuit and a gas pipe has to be securized with a hose clamp.

Once the whole circuit is assembled, test the sealing, proceeding as for the matter circuit: put the circuit under pressure and spray soapy water on each junction. If fbubbles appear, there is a leak.

Step 16 - Digestor usage - Feed

The biodigestor is a living system, composed by billions of bacterias, and needs to be taken care of.

Regular feeding

Ideally, the biodigestor has to be fed every day. It is possible to reduce it until once a week at the minimum. If the volume of organic matter is too important, it is advised to divide it in different "meals".

It is important to shred or grind the organic matter (knive, blender...) and to add their weight in water, in order to :

  • Prevent the matter from blocking the system,
  • Accelerate degradation and system productivity.

Balanced diet

Biodigestor can be complementary to a compost. Indeed, compost creates humus, and needs a high carbon/nitrogen ratio (20 to 30), with mostly cellulose and lignous compounds. Too much putrescible organic matter will destructurate the compost.

Conversely, wet and putrescible matters are welcome in a biodigestor (fruits and vegetables, peelings ...) Fibrous, dry and hard matters need to be limited in the biodigestor. They may be the cause for blockage of the system, and remain in the digestor forming foam or a crust, that is difficult to remove.

High nitrogen input is ideal in the digestor, as it will stimulate bacterias activity. In addition, the digestate produced will be a rich fertilizer.

It is important to bring "green food" in the digestor diet. If peelings and leafstalks are not enough, it is possible to add grass.

Animal products (meat, milk, eggs...) should be avoided in the digestor, as it does not reaches high temperatures enough to detroy pathogens, unlike compost.

Oils have an important methanogen power (780 liters of methane per kilogram of oil!) but it brings acidity to the digestor, which might kill the bacterias when too important. Oils should be brought to the system sparingly.

Cooking water allows for system heating and fluidifies circulation. It also provides starch (potatoes, cereals, rice ...) that bacterias like.

Urine can be used in a regular basis. Feces are accepted sparingly, but they have a weak methanogen power, as an important part of their energetic value has already been absorbed during digestion.

pH

In acid medium, the enzymatic activity of the bacterias is inhibited. This acidity is mainly due to organic acids accumulation. In basic medium, fermentation produce hydrogen sulphide (H2S) and hydrogen (H2). Digestion can take place between pH of 6,6 and 7,6, with an optimum between 7 and 7,2.



Step 17 - Inoculation

We have seen previously that feces have a weak methanogen power because they are already digested. However, they are important to launch bacterial activity in the digestor.

A cow, generates between 60 and 200 liters of biogas a day. We will recover part of its intestinal bacterias in its feces.

To launch the bacterial fermentation in the digestor:

  • Mix fresh cow manure with its weight in water, and insert it at the entrance of the biodigestor.

If the activity of the biodigestor is stopped due to a long period without food, it would have to be inoculated again in the same way.

Digestion stabilisation until a regular production of biogas can last several weeks, during which it is advised not to disturb feeding.


Step 18 - Digestate

The digestate from domestic biodigestor, one stabilized, is a liquid fertilizer rich in minerals and nitrogen.

You can dilute it at 10% in water, and use it every month for any kind of plants.

If animal products (meat, milk, eggs...) are part of the digestor diet, it is better not to use digestate for fruits and vegetables that will be eaten raw (strawberries, lettuce, carots...) It is better to used in orchards or non-food plants.


Notes and references

  • The first edition of this tutorial has been realised by Clément Chabot, during the Biodigestor stop of the Low-tech Tour in France.

Comme tout le travail du Low-tech Lab, ce tutoriel est participatif, n'hésitez pas à ajouter les modifications qui vous semblent importantes, et à partager vos réalisations en commentaires.


  • The first edition of this tutorial has been realised by Clément Chabot, during the Biodigestor stop of the Low-tech Tour in France.

References

Notes

  • Hélie Marchand's tutorial of a semi-burried digestor in Madagascar : Biodigesteur

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