Difference between revisions of "Parts of a Biogas Plant"

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[[Portal:Biogas|►Back to Biogas Portal]]<br/>
  
 
= Overview =
 
= Overview =
  
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The feed material is mixed with water in the influent collecting tank The fermentation slurry flows through the inlet into the digester. The bacteria from the fermentation slurry are intended to produce biogas in the digester. For this purpose, they need time. Time to multiply and to spread throughout the slurry. The digester must be designed in a way that only fully digested slurry can leave it. The bacteria are distributed in the slurry by stirring (with a stick or stirring facilities). The fully digested slurry leaves the digester through the outlet into the slurry storage.The biogas is collected and stored until the time of consumption in the gasholder. The gas pipe carries the biogas to the place where it is consumed by gas appliances. Condensation collecting in the gas pipe is removed by a water trap.
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The feed material is mixed with water in the influent collecting tank The fermentation slurry flows through the inlet into the digester. The bacteria from the fermentation slurry are intended to produce biogas in the digester. For this purpose, they need time. Time to multiply and to spread throughout the slurry. The digester must be designed in a way that only fully digested slurry can leave it. The bacteria are distributed in the slurry by stirring (with a stick or stirring facilities). The fully digested slurry leaves the digester through the outlet into the slurry storage.The biogas is collected and stored until the time of consumption in the gasholder. The gas pipe carries the biogas to the place where it is consumed by gas appliances. Condensation collecting in the gas pipe is removed by a water trap. Depending on the available building material and type of plant under construction, different variants of the individual components are possible. The following (optional) components of a biogas plant can also play an important role and are described seperatly: Heating systems, pumps, weak ring.<br/>
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Depending on the available building material and type of plant under construction, different variants of the individual components are possible. The following (optional) components of a biogas plant can also play an important role and are described seperatly: Heating systems, pumps, weak ring.
 
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= Influent Collecting Tank<br/> =
 
= Influent Collecting Tank<br/> =
  
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{| cellpadding="10" border="0" align="right" style="width: 220px" class="IMGright"
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{| cellpadding="10" border="0" align="right" class="IMGright" style="width: 220px"
 
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[[File:Bgfixeddomeinst.jpg|200px|RTENOTITLE]]
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[[File:Bgfixeddomeinst.jpg|thumb|right|200px|Bgfixeddomeinst.jpg]]<br/><br/>
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<small class="IMGLEGEND">'''Installation of a fixed-dome plant in Thailand: The influent collecting tank is in front of the photo, the digester and the outlet are located behind it.'''</small><ref name="Photo: Kossmann (gtz/GATE)">Photo: Kossmann (gtz/GATE)</ref><br/>
 
  
 
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<u>Size and Homogenization</u><br/>
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'''<u>Size and Homogenization</u>'''<br/>Fresh substrate is usually gathered in an influent collecting tank prior to being fed into the digester. Depending on the type of system, the tank should hold one to two days' substrate. An influent collecting tank can also be used to homogenize the various substrates and to set up the required consistency, e.g. by adding water to dilute the mixture of vegetable solids (straw, grass, etc.), or by adding more solids in order to increase the bio-mass. The fibrous material is raked off the surface, if necessary, and any stones or sand settling at the bottom are cleaned out after the slurry is admitted to the digester. The desired degree of homogenization and solids content can be achieved with the aid of an agitator, [[Pumps_for_Biogas_Plants|pump]]&nbsp;or chopper. A rock or wooden plug can be used to close off the inlet pipe during the mixing process.<br/>
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Fresh substrate is usually gathered in an influent collecting tank prior to being fed into the digester. Depending on the type of system, the tank should hold one to two days' substrate. An influent collecting tank can also be used to homogenize the various substrates and to set up the required consistency, e.g. by adding water to dilute the mixture of vegetable solids (straw, grass, etc.), or by adding more solids in order to increase the bio-mass. The fibrous material is raked off the surface, if necessary, and any stones or sand settling at the bottom are cleaned out after the slurry is admitted to the digester. The desired degree of homogenization and solids content can be achieved with the aid of an agitator, [[Parts of a Biogas Plant#Pumps|pump]] or chopper. A rock or wooden plug can be used to close off the inlet pipe during the mixing process.
 
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<u>Location</u>
 
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A sunny location can help to warm the contents before they are fed into the digester in order to avoid thermal shock due to the cold mixing water. In the case of a biogas plant that is directly connected to the stable, it is advisable to install the mixing pit deep enough to allow installation of a floating gutter leading directly into the pit. Care must also be taken to ensure that the low position of the mixing pit does not result in premature digestion. For reasons of hygiene, toilets should have a direct connection to the inlet pipe.
 
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<u>Inlet and Outlet</u>
 
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The inlet (feed) and outlet (discharge) pipes lead straight into the digester at a steep angle. For liquid substrate, the pipe diameter should be 10-15 cm, while fibrous substrate requires a diameter of 20-30 cm. The inlet and the outlet pipe mostly consist of plastic or concrete.
 
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<u>Position</u><br/>
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<br/>'''<u>Location</u>'''<br/>
  
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Both the inlet and the outlet pipe must be freely accessible and straight, so that a rod can be pushed through to eliminate obstructions and agitate the digester contents. The pipes should penetrate the digester wall at a point below the lowest slurry level (i.e. not through the gas storage). The points of penetration should be sealed and reinforced with mortar.
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A sunny location can help to warm the contents before they are fed into the digester in order to avoid thermal shock due to the cold mixing water. In the case of a biogas plant that is directly connected to the stable, it is advisable to install the mixing pit deep enough to allow installation of a floating gutter leading directly into the pit. Care must also be taken to ensure that the low position of the mixing pit does not result in premature digestion. For reasons of hygiene, toilets should have a direct connection to the inlet pipe.<br/>
  
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The inlet pipe ends higher in the digester than the outlet pipe in order to promote more uniform flow of the substrate. In a [[Types of Biogas Digesters and Plants#Fixed-dome Plants|fixed-dome plant]], the inlet pipe defines the bottom line of the gas-holder, acting like a security valve to release over-pressure. In a [[Types of Biogas Digesters and Plants#Floating-drum Plants|floating-drum plant]], the end of the outlet pipe determines the digester's (constant) slurry level.
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<br/>'''<u>Inlet and Outlet</u>'''<br/>
  
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Inlet and outlet pipe must be placed in connection with brick-laying. It is not advisable to break holes into the spherical shell afterwards, this would weaken the masonry structure.
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The inlet (feed) and outlet (discharge) pipes lead straight into the digester at a steep angle. For liquid substrate, the pipe diameter should be 10-15 cm, while fibrous substrate requires a diameter of 20-30 cm. The inlet and the outlet pipe mostly consist of plastic or concrete.<br/>
  
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<br/>'''<u>Position</u>'''<br/>Both the inlet and the outlet pipe must be freely accessible and straight, so that a rod can be pushed through to eliminate obstructions and agitate the digester contents. The pipes should penetrate the digester wall at a point below the lowest slurry level (i.e. not through the gas storage). The points of penetration should be sealed and reinforced with mortar. The inlet pipe ends higher in the digester than the outlet pipe in order to promote more uniform flow of the substrate. In a [[Types_of_Biogas_Digesters_and_Plants#Fixed_Dome_Biogas_Plants|fixed-dome plant]], the inlet pipe defines the bottom line of the gas-holder, acting like a security valve to release over-pressure. In a [[Types_of_Biogas_Digesters_and_Plants#Floating_Drum_Plants|floating-drum plant]], the end of the outlet pipe determines the digester's (constant) slurry level. Inlet and outlet pipe must be placed in connection with brick-laying. It is not advisable to break holes into the spherical shell afterwards, this would weaken the masonry structure.<br/>
  
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<u>Toilet Connection at the Inlet</u><br/>
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<br/>'''<u>Toilet Connection at the Inlet</u>'''<br/>► [[Connection_of_a_Toilet_to_a_Biogas_Digester|Household Toilets can be connected to a Biogas Digester.]]<br/>
  
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--> [[Connection of a toilet to a biogas digester|Household Toilets can be connected to a Biogas Digester.]]
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= Digester =
  
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In general terms, digesters consist of the digestion tank as such, which is thermally insulated, plus a heating system, mixer systems and discharge systems for sediments and the spent substrate.<br/><br/>
  
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= [[Types of Biogas Digesters and Plants|Digester]] =
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== Raw Material for Biogas Digesters<br/> ==
  
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In general terms, digesters consist of the digestion tank as such, which is thermally insulated, plus a heating system, mixer systems and discharge systems for sediments and the spent substrate
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►[[Material_for_Biogas_Digesters|Read more here .....]]<br/><br/>
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== Raw Material for Biogas Digesters ==
 
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►[[Material for Biogas Digesters|Read more here .....]]
 
  
 
== Types of Biogas Digesters ==
 
== Types of Biogas Digesters ==
  
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►[[Types of Biogas Digesters and Plants|Read more here .....]]
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►[[Types_of_Biogas_Digesters_and_Plants|Read more here .....]]<br/><br/>
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== Types of Gasholders for Biogas Plants ==
 
== Types of Gasholders for Biogas Plants ==
  
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►[[Types of Gasholders for Biogas Plants|Read more here .....]]
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► [[Types_of_Gasholders_for_Biogas_Plants|Read more here .....]]<br/><br/>
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= Gas Pipe, Valves and Accessories<br/> =
 
= Gas Pipe, Valves and Accessories<br/> =
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== Biogas Piping<br/> ==
 
== Biogas Piping<br/> ==
  
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{| cellpadding="10" border="0" align="right" style="width: 348px" class="IMGright"
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[[File:Bgstirrer.jpg|348px|RTENOTITLE]]
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[[File:Bgstirrer.jpg|thumb|right|248px]]<br/><br/>
  
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<small class="IMGLEGEND">'''Stirring device for a european biodigester'''</small><ref name="Photo: Krieg">Photo: Krieg</ref>
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At least 60% of all non-functional biogas units are attributable to defect gas piping. Utmost care has to be taken, therefore, for proper installation. For the sake of standardization, it is advisable to select a single size for all pipes, valves and accessories. The requirements for [[Piping_Systems_for_Biogas_Plants|biogas piping]], valves and accessories are essentially the same as for other gas installations. However, biogas is 100% saturated with water vapor and contains hydrogen-sulfide. Consequently, no piping, valves or accessories that contain any amounts of ferrous metals may be used for biogas piping, because they would be destroyed by corrosion within a short time. The gas lines may consist of standard galvanized steel pipes. Also suitable (and inexpensive) is plastic tubing made of rigid PVC or rigid PE. Flexible gas pipes laid in the open must be UV-resistant.<br/>
  
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At least 60% of all non-functional biogas units are attributable to defect gas piping. Utmost care has to be taken, therefore, for proper installation. For the sake of standardization, it is advisable to select a single size for all pipes, valves and accessories.
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<br/>[[Biogas_Gas_Pipe,_Valves_and_Accessories#Gas_Pipe|► Read More here...]]<br/><br/>
  
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The requirements for [[Piping Systems for Biogas Plants|biogas piping]], valves and accessories are essentially the same as for other gas installations. However, biogas is 100% saturated with water vapor and contains hydrogen-sulfide. Consequently, no piping, valves or accessories that contain any amounts of ferrous metals may be used for biogas piping, because they would be destroyed by corrosion within a short time. The gas lines may consist of standard galvanized steel pipes. Also suitable (and inexpensive) is plastic tubing made of rigid PVC or rigid PE. Flexible gas pipes laid in the open must be UV-resistant.
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== Water Traps ==
  
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[[Biogas_Gas_Pipe,_Valves_and_Accessories#Water_Traps|► Read more here....]]<br/><br/>
  
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<u>Steel Pipes</u><br/>
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== Valves ==
  
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Galvanized steel water supply pipes are used most frequently, because the entire piping system (gas pipe, valves and accessories) can be made of universally applicable English/U.S. Customary system components, i.e. with all dimensions in inches. Pipes with nominal dimensions of 1/2" or 3/4" are adequate for small-to-midsize plants of simple design and pipe lengths of less than 30 m. For larger plants, longer gas pipes or low system pressure, a detailed pressure-loss (pipe-sizing) calculation must be performed.
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[[Biogas_Gas_Pipe,_Valves_and_Accessories#Valves|► Read more here...]]<br/><br/>
  
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When installing a gas pipe, special attention must be paid to:
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== Gas Analysis Equipment ==
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*gas-tight, friction-type joints
 
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*line drainage, i.e. with a [[Piping Systems for Biogas Plants#Water traps|water trap]] at the lowest point of the sloping pipe in order to empty water accumulation
 
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*protection against mechanical impact
 
  
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[[Biogas_Gas_Pipe,_Valves_and_Accessories#Gas_Analysis_Equipment|►Read more here...]]<br/><br/>
  
 
= Stirring Facilities<br/> =
 
= Stirring Facilities<br/> =
  
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{| cellpadding="10" border="0" align="right" style="width: 400px" class="IMGleft"
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{| cellpadding="10" border="0" align="right" class="IMGleft" style="width: 269px;"
 
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[[File:Bgstirring.gif|200px|RTENOTITLE]]<br/>
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[[File:Bgstirring.gif|thumb|right|200px]]<br/><br/>
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<small class="IMGLEGEND">'''Stirring facilities in the digester'''</small><ref name="Source: OEKOTOP">Source: OEKOTOP</ref><br/>
 
  
 
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Optimum stirring substantially reduces the retention time. If [[Agitation of Digesters|agitation]] is excessive, the bacteria have "no time to eat". The ideal is gentle but intensive stirring about every four hours. Of similar importance is the breaking up of a scum layer which has lost contact with the main volume of substrate and is, therefore, not further digested. This top layer can form an impermeable barrier for biogas to move up from the digester to the gas holder.
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Optimum stirring substantially reduces the retention time. If [[Agitation_of_Digesters|agitation]] is excessive, the bacteria have "no time to eat". The ideal is gentle but intensive stirring about every four hours. Of similar importance is the breaking up of a scum layer which has lost contact with the main volume of substrate and is, therefore, not further digested. This top layer can form an impermeable barrier for biogas to move up from the digester to the gas holder.As a rule of thumb it can be stated that stirring facilities are more important in larger plants than in small scale farm plants.<br/><u>Types of Stirring Facilities</u>:<br/>
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As a rule of thumb it can be stated that stirring facilities are more important in larger plants than in small scale farm plants.
 
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== Types of Stirring Facilities<br/> ==
 
  
 
#The '''''impeller stirrer''''' has given good results especially in sewage treatment plants.
 
#The '''''impeller stirrer''''' has given good results especially in sewage treatment plants.
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= Heating Systems<br/> =
 
= Heating Systems<br/> =
  
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Normally, because of the rather high involved costs, small-scale biogas plants are built without [[Digester Heating|heating systems]]. But even for small scale plants, it is of advantage for the bio-methanation process to warm up the influent substrate to its proper process temperature before it is fed into the digester. If possible, cold zones in the digester should be avoided (see also [[Parameters and Process Optimisation for Biogas#Substrate temperature|substrate temperature]]).
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Normally, because of the rather high involved costs, small-scale biogas plants are built without [[Digester_Heating|heating systems]]. But even for small scale plants, it is of advantage for the bio-methanation process to warm up the influent substrate to its proper process temperature before it is fed into the digester. If possible, cold zones in the digester should be avoided (see also [[Parameters_and_Process_Optimisation_for_Biogas#Substrate_temperature|substrate temperature]]). There are a number of different ways to get the required amount of thermal energy into the substrate are described. <u>In principle, one can differentiate between:</u>
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In the following, a number of different ways to get the required amount of thermal energy into the substrate are described.
 
  
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<u>In principle, one can differentiate between:</u>
 
 
*'''direct heating''' in the form of steam or hot water, and
 
*'''direct heating''' in the form of steam or hot water, and
 
*'''indirect heating''' via heat exchanger, whereby the heating medium, usually hot water, imparts heat while not mixing with the substrate.
 
*'''indirect heating''' via heat exchanger, whereby the heating medium, usually hot water, imparts heat while not mixing with the substrate.
  
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<br/>[[Digester_Heating|►]][[Digester_Heating|More information here...]].
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[[Digester_Heating|►]][[Digester_Heating|More information here...]].
 
  
 
= Pumps =
 
= Pumps =
  
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[[Pumps for Biogas Plants|Pumps]] become necessary parts of a biogas unit, when the amounts of substrate require fast movement and when gravity cannot be used for reasons of topography or substrate characteristics. Pumps transport the substrate from the point of delivery through all the stages of fermentation. Therefore, several pumps and types of pumps may be needed. Pumps are usually found in large scale biogas units.
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Pumps become necessary parts of a biogas unit, when the amounts of substrate require fast movement and when gravity cannot be used for reasons of topography or substrate characteristics. Pumps transport the substrate from the point of delivery through all the stages of fermentation. Therefore, several pumps and types of pumps may be needed. Pumps are usually found in large scale biogas units.
  
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There are two predominant types of pump for fresh substrate: '''centrifugal pumps''' and '''positive-displacement pumps''' (reciprocating pumps). Centrifugal pumps operate on the principle of a rapidly rotating impeller located in the liquid flow. They provide high delivery rates and are very robust, i.e. the internals are exposed to little mechanical stress. They do, however, require a free-flowing intake arrangement, because they are not self-priming (regenerative).
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== Types of Pumps ==
  
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Practically all centrifugal pump characteristics are geared to water. They show the delivery rates for various heads, the achievable efficiency levels, and the power requirement for the pump motor. Consequently, such data cannot be directly applied to biogas systems, since the overall performance and efficiency level of a pump for re-circulating slurry may suffer a serious drop-off as compared to its standard "water" rating (roughly 5-10%).
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► [[Pumps_for_Biogas_Plants|Read more here....]]
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== Rotary Pump ==
 
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Rotary pumps are commonplace in liquid-manure pumping. They are eminently suitable for runny substrates.<br/>A rotary pump has an impeller turning inside a fixed body. The impeller accelerates the medium, and the resulting increase in flow velocity is converted into head or pressure at the rotary pump's discharge nozzle. The shape and size of the impeller can<br/>vary, depending on requirements. The cutter-impeller pump is a special kind of rotary pump. The impeller has hardened cutting edges designed to comminute the substrate.
 
  
 
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<br/><u>Limitation of a Centrifugal Pump</u>
 
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Sometimes, namely when the substrate is excessively viscous, a centrifugal pump will no longer do the job, because the condition of the substrate surpasses the pump's physical delivery capacity. In such cases, one must turn to a so-called positive-displacement or reciprocating type of pump in the form of a piston pump, gear pump or eccentric spiral pump, all of which operate on the principle of displacing action to provide positive delivery via one or more enclosed chambers.
 
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== Positive Displacement Pumps<br/> ==
 
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Positive displacement pumps offer multiple advantages. Even for highly viscous substrate, they provide high delivery and high efficiency at a relatively low rate of power consumption. Their characteristics - once again for water - demonstrate how little the delivery rate depends on the delivery head. Consequently, most of the characteristics show the delivery rate as a function of pump speed.
 
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The main disadvantage as compared to a centrifugal pump is the greater amount of wear and tear on the internal occasioned by the necessity of providing an effective seal between each two adjacent chambers.
 
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The speed of a positive-displacement pump can be varied to control delivery rate. This matches pump control more closely to precision metering of the substrate.The pressure stability of these self-priming pumps is better than that of rotary pumps, which means that delivery rate is much less dependent on head. Positive- displacement pumps are relatively susceptible to interfering substances, so it makes sense to install comminutors and foreign-matter separators to protect the pumps against coarse and fibrous constituents in the substrate<ref name="guide">FNR, 2012: Guide to biogas</ref>.
 
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'''Rotary-displacement pumps and eccentric singlerotor screw pumps''' are the most commonly used. Eccentric single-rotor screw pumps have a rotor shaped like a corkscrew running inside a stator made of an elastically resilient material. The action of the rotor produces an advancing space in which the substrate is transported.
 
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[[File:Eccentric single-rotor screw pump.jpg|thumb|center|180px|alt=Eccentric single-rotor screw pump.jpg]]<br/>
 
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Rotary displacement pumps have two counter-rotating rotary pistons with between two and six lobes in an oval body. The two pistons counter-rotate and counterroll with low axial and radial clearance, touching neither each other nor the body of the pump. Their geometry is such that in every position a seal is maintained between the suction side and the discharge side of the pump. The medium is drawn in to fill the spaces on the suction side and is transported to the discharge side<ref name="guide">FNR, 2012: Guide to biogas</ref>.
 
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[[File:Rotary displacement pump.JPG|frame|center|180px|Rotary displacement pump.JPG]]
 
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== Pump Delivery Lines<br/> ==
 
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Pump delivery lines can be made of steel, PVC (rigid) or PE (rigid or flexible), as well as appropriate flexible pressure tubing made of reinforced plastic or rubber. Solid substrate, e.g. dung, can also be handled via conveyor belt, worm conveyor or sliding-bar system, though none of these could be used for liquid manure. When liquid manure is conducted through an open gutter, small weirs or barrages should be installed at intervals of 20-30 m as a means of breaking up the scum layer.
 
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Each such barrier should cause the scum to fall at least 20-30 cm on the downstream side. All changes of direction should be executed at right angles (90°). Depending on the overall length, the cross gutter should be laid some 30-50 cm deeper than the main gutter. Transitions between a rectangular channel and a round pipe must be gradual. An inclination of about 14% yields optimum flow conditions. The channel bottom must be laid level, since any slope in the direction of flow would only cause the liquid manure to run off prematurely. All wall surfaces should be as smooth as possible.
 
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== Industrial transport of Substrate ==
 
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The transport of stackable substrates is a feature of wet digestion plants through to material infeed or to the stage of wetting down to mash with make-up liquid. Most of the work can be done with loaders of conventional design. It is only when automated feeding takes over that scraper-floor feeders, overhead pushers and screw conveyors are used. Scraper-floor feeders and overhead pushers are able to move virtually all stackable substrates horizontally or up slightly inclined planes. They cannot be used for metering, however. They permit very large holding tanks to be used. Screw conveyors can transport stackable substrates in virtually any direction. The only prerequisites are the absence of large stones and comminution of the substrate to the extent that it can be gripped by the worm and fits inside the turns of the worm's conveyor mechanism. Automatic feeder systems for stackable substrates are often combined with the loading equipment to form a single unit in the biogas plant<sup id="cite_ref-guide_0-6" class="reference">[http://giz.energypedia.info/wiki/Substrate_management#cite_note-guide-0 [1]]</sup>.
 
  
 
= Weak Ring<br/> =
 
= Weak Ring<br/> =
  
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The weak/strong ring improves the gas-tightness of [[Types of Biogas Digesters and Plants#Fixed-dome plants|fixed-dome plants]] It was first introduced in Tanzania and showed promising results. The weak ring separates the lower part of the hemispherical digester, (filled with digesting substrate), from the upper part (where the gas is stored). Vertical cracks, moving upwards from the bottom of the digester, are diverted in this ring of lean mortar into horizontal cracks. These cracks remain in the slurry area where they are of no harm to the gas-tightness. The strong ring is a reinforcement of the bottom of the gas-holder, it could also be seen as a foundation of the gas-holder. It is an additional device to prevent cracks from entering the gas-holder. Weak and strong ring have been successfully combined in the [[Types of Biogas Digesters and Plants#Fixed-dome plants|CAMARTEC design]]
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| style="width: 276px" | [[File:Weakstrongring.jpg|thumb|right|280px]]<br/>
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| [[File:Weakstrongring.jpg|thumb|center|352px|RTENOTITLE]]<small class="IMGLEGEND">'''Photo<ref name="Kellner (TBW)">Kellner (TBW)</ref>: Construction of the weak/strong ring of a 16 m<sup>3</sup>, Tanzania'''</small><br/>
 
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<!-- weakring.gif Sasse, Kellner, Kimaro, GATE, 1991 -->
 
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<u>Materials and Construction</u><br/>
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The weak ring consists of mortar of a mixture of sand, lime and cement (15:3:1). The top of the weak ring restores the horizontal level. It is interrupted only by the inlet pipe passing through. The strong ring rests on the weak ring and is the first layer of the upper part of the hemispherical shell. It consists of a row of header bricks with a concrete package at the outside. In case of soft or uncertain ground soil one may place a ring reinforcement bar in the concrete of the strong ring. The brick of the strong ring should be about three times wider than the brickwork of the upper wall. A detailed description of the weak/strong ring construction can be found in Sasse, Kellner, Kimaro (1991).
 
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= Pre-digestion pit for storage of substrates =
+
The weak/strong ring improves the gas-tightness of [[Fixed-dome_Biogas_Plants|fixed-dome plants]] It was first introduced in Tanzania and showed promising results. The weak ring separates the lower part of the hemispherical digester, (filled with digesting substrate), from the upper part (where the gas is stored). Vertical cracks, moving upwards from the bottom of the digester, are diverted in this ring of lean mortar into horizontal cracks. These cracks remain in the slurry area where they are of no harm to the gas-tightness. The strong ring is a reinforcement of the bottom of the gas-holder, it could also be seen as a foundation of the gas-holder. It is an additional device to prevent cracks from entering the gas-holder. Weak and strong ring have been successfully combined in the CAMARTEC design<br/><u>Materials and Construction</u><br/>The weak ring consists of mortar of a mixture of sand, lime and cement (15:3:1). The top of the weak ring restores the horizontal level. It is interrupted only by the inlet pipe passing through. The strong ring rests on the weak ring and is the first layer of the upper part of the hemispherical shell. It consists of a row of header bricks with a concrete package at the outside. In case of soft or uncertain ground soil one may place a ring reinforcement bar in the concrete of the strong ring. The brick of the strong ring should be about three times wider than the brickwork of the upper wall. A detailed description of the weak/strong ring construction can be found in Sasse, Kellner, Kimaro (1991).<br/>
  
−
Sizing depends on:
+
= Pre-digestion Pit for Storage of Substrates =
  
−
substrate arisings, digester capacity, length of time to be bridged between successive deliveries, land-use specifics and yield of co-substrates, supply contracts for substrates from off-site sources, possible disruptions in operation
+
<u>Sizing depends on:</u> substrate arisings, digester capacity, length of time to be bridged between successive deliveries, land-use specifics and yield of co-substrates, supply contracts for substrates from off-site sources, possible disruptions in operation<br/><u>Special considerations:</u>
  
−
<br/>
 
−
 
−
Special considerations:
 
 
*Avoid the possibility of storage plant freezing, for example by siting storage tanks indoors, heating storage containers or locating the plant for pits below grade level
 
*Avoid the possibility of storage plant freezing, for example by siting storage tanks indoors, heating storage containers or locating the plant for pits below grade level
 
*Avoid biodegradation processes that reduce gas yield
 
*Avoid biodegradation processes that reduce gas yield
Line 246: Line 129:
 
*Avoid material emissions to soil and to the surface and underground water system
 
*Avoid material emissions to soil and to the surface and underground water system
  
−
<br/>
+
<br/><u>Designs</u> Containers for storing solid substrates in widespread use in agriculture, such as mobile silos, upright silos, plastic-tunnel silos and round-bale silos and open or roofed storage areas (e.g. solid-manure deposits) and pits/hoppers Containers for storing liquid substrates in widespread use in agriculture, such as tanks and predigester pits<br/><u>Costs</u> Storage facilities are generally in place; when new builds are needed the price has to be calculated on<br/>a case-to-case basis factoring in the multiplicity of influencing variables indicated above<br/>
−
 
 
−
Designs
 
−
 
 
−
Containers for storing solid substrates in widespread use in agriculture, such as mobile silos, upright silos, plastic-tunnel silos and round-bale silos and open or roofed storage areas (e.g. solid-manure deposits) and pits/hoppers
 
−
 
 
−
Containers for storing liquid substrates in widespread use in agriculture, such as tanks and predigester pits
 
  
−
<br/>Costs
+
= Measurement Instruments<br/> =
  
−
Storage facilities are generally in place; when new builds are needed the price has to be calculated on<br/>a case-to-case basis factoring in the multiplicity of influencing variables indicated above
+
Flow-measuring devices (in the pipes) Ultrasonically (pre pits) Radar (pre-pits)<br/>Wheel loader scales
  
 
<br/>
 
<br/>
  
−
= <br/> =
+
= Further Information =
−
 
 
−
== <span style="font-size: 19px; line-height: 23.799999237060547px;">Agitators</span> ==
 
  
−
== Heat Transport<br/> ==
+
*[[Portal:Biogas|Biogas Portal on energypedia]]
−
 
 
−
= Engines<br/> =
 
−
 
 
−
== CHP<br/> ==
 
−
 
 
−
[[File:CHPs.jpg|frame|right|180px|CHPs.jpg]]Combined heat and power (CHP), or cogeneration, refers to the simultaneous generation of both heat and electricity. Depending on the circumstances, a distinction can be drawn between power-led and heat-led CHP plants. The heat-led type should normally be<br/>chosen, because of its higher efficiency. In almost all cases this means using small-scale packaged CHP units with internal combustion engines coupled to a generator. The engines run at a constant speed so that the directly coupled generator can provide electrical energy that is compatible with system frequency. Looking into the future, for driving the generator it will also be possible to use gas microturbines, Stirling engines or fuel cells as alternatives to the conventional pilot ignition gas engines and gas spark ignition engines.
 
  
 
<br/>
 
<br/>
  
−
[http://de.slideshare.net/CENERGY/chp-biogas-cogeneration-the-2-g-difference Have a look at this presentation on CHP engines.]
+
'''<u>Information on materials and devices used in the construction of biogas plants:</u>'''
  
−
<br/>
+
*[[Checklist_for_the_Construction_of_a_Biogas_Plant|Checklist for the Construction of a Biogas Plant]]
 +
*[[Agitation_of_Digesters|Agitation of Digesters]]
 +
*[[Digester_Heating|Digester Heating]]
 +
*[[Piping_Systems_for_Biogas_Plants|Piping Systems for Biogas Plants]]
 +
*[[Plasters_and_Coats_for_Biogas_Digesters_and_Gas-holder|Plasters and Coats for Biogas Digesters and Gas-holder]]
 +
*[[Pumps_for_Biogas_Plants|Pumps for Biogas Plants]]
 +
*[[Slurry-Use_Equipment|Slurry-Use Equipment]]
 +
*[[Biogas_Implementation_-_Groundwater_Management|Biogas Implementation - Groundwater Management]]
  
−
= Flare systems<br/> =
+
<br/><u>'''Web based sources'''</u>
  
−
[[File:Flare system.jpg|thumb|right|180px|Flare system.jpg]]
+
*[http://biogas.ifas.ufl.edu/ad_development/documents/biogasplants.pdf biogas.ifas - biogasplants (pdf])
−
 
+
*[[Checklist_for_the_Construction_of_a_Biogas_Plant|Checklist for the Construction of a Biogas Plant]]
−
<br/>
+
*[http://www.haase-energietechnik.de/en/Products_and_Services/24-e_BiogasBrochure_Feb2011_1.pdf haase-energietechnik - BiogasBrochure (pdf)]
−
 
 
−
In case the storage tanks are unable to take more biogas and/or the gas cannot be used on account of maintenance work or extremely poor quality, the excess has to be disposed of in a safe manner. In Germany, the regulations relating to the operating permit vary from state to state, but installation of an alternative to the CHP unit as ultimate sink is required if the gas flow rate is 20 m3/h or higher. This can take the form of a second cogeneration unit (for example two small CHP units instead of one large one). A margin of safety can be established by installing an emergency flare, as a means of ensuring that the gas can be disposed of in an adequate way. In most cases the authorities stipulate that a provision of this nature be made.
 
−
 
 
−
<br/>
 
−
 
 
−
High Temperature Flares have to be obligatory not only for CDM projects to destroy surplus biogas which cant be utilised due to technical problems or overproduction. Investment costs about 1% of the total investment. (Mang).
 
−
 
 
−
<br/>
 
−
 
 
−
<br/>
 
−
 
 
−
= <br/>Measurement instruments<br/> =
 
−
 
 
−
Flow-measuring devices (in the pipes)
 
−
 
 
−
Ultrasonically (pre pits)
 
−
 
 
−
Radar (pre-pits)<br/>Wheel loader scales
 
−
 
 
−
<br/>
 
−
 
 
−
= Volume flow<br/> =
 
−
 
 
−
= Loading systems<br/> =
 
−
 
 
−
== Feeding pumps<br/> ==
 
−
 
 
−
Pumps are required to bridge differences in height between the levels of slurry-flow through the biogas unit. They can also be required to mix the substrate or to speed up slow flowing substrates. If substrates have a high solids content and do not flow at all, but cannot be diluted, pumps or transport belts are essential.
 
−
 
 
−
Pumps are driven by engines, are exposed to wear and tear and can be damaged. They are costly, consume energy and can disrupt the filling process. For these reasons, pumps should be avoided where possible and methods of dilution and use of the natural gradient be utilized instead.
 
−
 
 
−
If pumps cannot be avoided, they can be installed in two ways:
 
−
*Dry installation: the pump is connected in line with the pipe. The substrate flows freely up to the pump and is accelerated while passing through the pump.
 
−
*Wet installation: the pump is installed with an electric engine inside the substrate. The electric engine is sealed in a watertight container. Alternatively, the pump in the substrate is driven by a shaft, the engine is outside the substrate.
 
−
 
 
−
== <span style="font-size: 17px;">Eccentric spiral pump</span> ==
 
−
 
 
−
This pump has a stainless steel rotor, similar to a cork screw, which turns in an elastic casing. Eccentric spiral pumps can suck from a depth of up to 8.5m and can produce a pressure of up to 24 bar. The are, however, more susceptible to obstructive, alien elements than rotary pumps. Of disadvantage is further the danger of fibrous material wrapping round the spiral.
 
−
 
 
−
=== Rotary piston pump<br/> ===
 
−
 
 
−
Rotary piston pumps operate on counter-rotating winged pistons in an oval casing. They can pump and suck as well and achieve pressures of up to 10 bar. The potential quantity conveyed ranges from 0.5 to 4 m<sup>3</sup>/min. The allow for larger alien objects and more fibrous material than eccentric spiral pumps.
 
−
 
 
−
{| cellpadding="5" border="1" style="width: 100%;"
 
−
|-
 
−
|
 
−
! rotary pumps
 
−
! chopper pumps
 
−
! eccentric spiral pump
 
−
! rotary piston pump
 
−
|-
 
−
! solids content
 
−
| style="text-align: center;" | < 8 %
 
−
| style="text-align: center;" | < 8 %
 
−
| style="text-align: center;" | < 15 %
 
−
| style="text-align: center;" | < 15 %
 
−
|-
 
−
! energy input
 
−
| style="text-align: center;" | 3 - 15 kW
 
−
| style="text-align: center;" | 3 - 15 kW
 
−
| style="text-align: center;" | 3 - 22 kW
 
−
| style="text-align: center;" | 3 - 20 kW
 
−
|-
 
−
! quantity conveyed
 
−
| style="text-align: center;" | 2 - 6 m<sup>3</sup>/min
 
−
| style="text-align: center;" | 2 - 6 m<sup>3</sup>/min
 
−
| style="text-align: center;" | 0,3 - 3,5 m<sup>3</sup>/min
 
−
| style="text-align: center;" | 0,5 - 4 m<sup>3</sup>/min
 
−
|-
 
−
! pressure
 
−
| style="text-align: center;" | 0,8 - 3,5 bar
 
−
| style="text-align: center;" | 0,8 - 3,5 bar
 
−
| style="text-align: center;" | < 25 bar
 
−
| style="text-align: center;" | < 10 bar
 
−
|-
 
−
! structure of substrate
 
−
| style="text-align: center;" | medium long fibers
 
−
| style="text-align: center;" | long fibers
 
−
| style="text-align: center;" | short fibers
 
−
| style="text-align: center;" | medium long fibers
 
−
|-
 
−
! max. size of obstructive elements
 
−
| style="text-align: center;" | approx. 5 cm
 
−
| style="text-align: center;" | depending on choppers
 
−
| style="text-align: center;" | approx. 4 cm
 
−
| style="text-align: center;" | approx. 6 cm
 
−
|-
 
−
! intake
 
−
| style="text-align: center;" | '''not''' sucking
 
−
| style="text-align: center;" | '''not''' sucking
 
−
| style="text-align: center;" | sucking
 
−
| style="text-align: center;" | sucking
 
−
|-
 
−
! suitability
 
−
| suitable for large quantities; simple and robust built
 
−
| suitable for long-fiber substrates which need to be chopped up.
 
−
| Suitable for high pressures, but susceptible to obstructive bodies
 
−
| higher pressures than rotary pumps, but higher wear and tear
 
−
|-
 
−
! price comparison
 
−
| cheaper than positive displacement pumps
 
−
| depending on choppers
 
−
| similar to rotary piston pump
 
−
| similar to eccentric spiral pump
 
−
|}
 
−
 
 
−
<br/>
 
−
 
 
−
<br/>
 
−
 
 
−
== Piping<br/> ==
 
−
 
 
−
The piping system connects the biogas plant with the biogas appliances. It has to be safe, economic and should allow the required gas-flow for the specific gas appliance. '''Galvanized steel (G.I.)''' pipes or '''Polyvinyl chloride (PVC) '''pipes are most commonly used for this purpose. Most prominently, the piping system has to be reliably gas-tight during the life-span of the biogas unit. In the past, faulty piping systems were the most frequent reason for gas losses in biogas units.
 
−
 
 
−
<br/>
 
−
 
 
−
=== Polyvinyl chloride (PVC) piping<br/> ===
 
−
 
 
−
'''Polyvinyl chloride <span style="font-weight: bold">(</span>PVC)''' pipes and fittings have a relatively low price and can be easily installed. They are available in different qualities with adhesive joints or screw couplings (pressure water pipes). PVC pipes are susceptible to UV radiation and can easily be damaged by playing children. Wherever possible, PVC pipes should be placed underground.
 
−
 
 
−
<br/>
 
−
 
 
−
=== Galvanized Steel Piping<br/> ===
 
−
 
 
−
'''Galvanized steel (G.I.) '''pipes are reliable and durable alternatives to PVC pipes. They can be disconnected and reused if necessary. They resist shocks and other mechanical impacts. However, galvanized steel pipes are costly and the installation is labor intensive, therefore they are only suitable for places where PVC is unavailable or should not be used.
 
−
 
 
−
<br/>
 
−
 
 
−
=== Pipe Diameters<br/> ===
 
−
 
 
−
The necessary pipe diameter depends on the required flow-rate of biogas through the pipe and the distance between biogas digester and gas appliances. Long distances and high flow-rates lead to a decrease of the gas pressure. The longer the distance and the higher the flow rate, the higher the pressure drops due to friction. Bends and fittings increase the pressure losses. G.I. pipes show higher pressure losses than PVC pipes. Table 1 gives some values for appropriate pipe diameters. Using these pipe diameters for the specified length and flow rate, the pressure losses will not exceed 5 mbar.
 
−
 
 
−
<br/>
 
−
 
 
−
{| cellpadding="5" border="1" style="width: 100%;"
 
−
|-
 
−
!
 
−
! colspan="3" | Galvanized steel pipe
 
−
! colspan="3" | PVC pipe<br/>
 
−
|-
 
−
! Length [m]:
 
−
| style="text-align: center;" | 20
 
−
| style="text-align: center;" | 60
 
−
| style="text-align: center;" | 100
 
−
| style="text-align: center;" | 20
 
−
| style="text-align: center;" | 60
 
−
| style="text-align: center;" | 100
 
−
|-
 
−
! Flow-rate [m<sup>3</sup>/h]
 
−
|
 
−
|
 
−
|
 
−
|
 
−
|
 
−
|
 
−
|-
 
−
| style="text-align: center;" | 0.1
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
|-
 
−
| style="text-align: center;" | 0.2<br/>
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
|-
 
−
| style="text-align: center;" | 0.3
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
|-
 
−
| style="text-align: center;" | 0.4
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
|-
 
−
| style="text-align: center;" | 0.5
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 3/4"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 1/2"
 
−
|-
 
−
| style="text-align: center;" | 1.0
 
−
| style="text-align: center;" | 3/4"
 
−
| style="text-align: center;" | 3/4"
 
−
| style="text-align: center;" | 3/4"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 3/4"
 
−
| style="text-align: center;" | 3/4"
 
−
|-
 
−
| style="text-align: center;" | 1.5
 
−
| style="text-align: center;" | 3/4"
 
−
| style="text-align: center;" | 3/4"
 
−
| style="text-align: center;" | 1"
 
−
| style="text-align: center;" | 1/2"
 
−
| style="text-align: center;" | 3/4"
 
−
| style="text-align: center;" | 3/4"
 
−
|-
 
−
| style="text-align: center;" | 2.0<br/>
 
−
| style="text-align: center;" | 3/4"
 
−
| style="text-align: center;" | 1"
 
−
| style="text-align: center;" | 1"
 
−
| style="text-align: center;" | 3/4"
 
−
| style="text-align: center;" | 3/4"
 
−
| style="text-align: center;" | 1"
 
−
|}
 
−
 
 
−
<br/>
 
−
 
 
−
The values in table 1 show that a pipe diameter of 3/4" is suitable for flow rates up to 1.5 m<sup>3</sup>/h and distances up to 100 m (PVC pipe). Therefore one could select the diameter of 3/4" as single size for the hole piping system of small biogas plants. Another option is to select the diameter of l" for the main gas pipe and 1/2" for all distribution pipes to the gas appliances.
 
−
 
 
−
<br/>
 
−
 
 
−
=== Lay-out of the Piping System<br/> ===
 
−
 
 
−
PVC can be used for all underground pipes or pipes that are protected against sun light and out of the reach of children. For all parts of the piping system that are above ground one should install galvanized steel pipes. Therefore it is recommended to use l" G.I. steel pipes for the visible part of the piping system around the biogas digester. For the main pipe one uses l" PVC pipe placed underground. The distribution pipes should be 1/2" G.I. steel pipes or PVC pipes, depending whether they are installed above or under the wall plastering. But even though G.I. pipes are less susceptible to damage, placing them underground should always be the preferred solution.
 
−
 
 
−
PVC pipes have to be laid at least 25 cm deep underground. They should be placed in a sand bed and be covered with sand or fine earth. One should carefully back-fill the ditches in order to avoid stones lying directly above the pipe.
 
−
 
 
−
When the piping is installed - and before refilling the ditches - it has to be tested for possible gas leakage. This can be done by pumping air into the closed piping system up to a pressure that is 2.5 times the maximum gas pressure of the biogas plant. If pressure loss occurs within few hours, every joint of the piping system has to be checked with soap water. Soap-bubbles indicate any leakage of gas <ref>www.energypedia.info</ref>.
 
−
 
 
−
<br/>
 
−
 
 
−
The valves, fittings and piping must be mediumproof and corrosion-resistant. Valves and fittings such as couplers, shut-off gate valves, flap traps, cleaning ports and pressure gauges must be readily accessible and operable and they must also be installed<br/>in such a way as to be safe from frost damage. The 'Sicherheitsregeln für Biogasanlagen' (Safety Rules for Biogas Systems) issued by the Bundesverband der landwirtschaftlichen Berufsgenossenschaften (German Agricultural Occupational Health and<br/>Safety Agency) contain information about the regulations for piping, valves and fittings and can be of assistance in achieving compliance with the laws and engineering codes with regard to material properties, safety precautions and leak tests for safe operation of the biogas plant [3-18]. One factor that has proved extremely important is the necessity of providing suitable<br/>means of removing condensate from all piping runs, without exception, or of running the pipes with enough fall to ensure that slight settling or sag cannot produce unintended high points along the runs. On account of the low pressures in the system, very small<br/>quantities of condensate can suffice to cause a complete blockage <ref>FNR, 2012: Guide to Biogas</ref>.
 
−
 
 
−
<br/>
 
−
 
 
−
<br/>
 
−
 
 
−
== Water traps<br/> ==
 
−
 
 
−
Due to temperature changes, the moisture-saturated biogas will form inevitably condensation water in the piping system. Ideally, the piping system should be laid out in a way that allows a free flow of condensation water back into the digester. If depressions in the piping system can not be avoided, one or several water traps have to be installed at the lowest point of the depressions. Inclination should not be less than 1%.
 
−
 
 
−
<br/>Often, water traps cannot be avoided. One has to decide then, if an 'automatic' trap or a manually operated trap is more suitable. Automatic traps have the advantage that emptying - which is easily forgotten - is not necessary. But if they dry up or blow empty, they may cause heavy and extended gas losses. In addition, they are not easily understood. Manual traps are simple and easy to understand, but if they are not emptied regularly, the accumulated condensation water will eventually block the piping system. Both kinds of traps have to be installed in a solid chamber, covered by a lid to prevent an eventual filling up by soil <ref>www.energypedia.info</ref>.
 
−
 
 
−
<br/>
 
−
 
 
−
<br/>
 
−
 
 
−
== Valves<br/> ==
 
−
 
 
−
To the extent possible, ball valves or cock valves suitable for gas installations should be used as shutoff and isolating elements. The most reliable valves are chrome-plated ball valves. Gate valves of the type normally used for water pipes are not suitable. Any water valves exceptionally used must first be checked for gas-tightness. They have to be greased regularly. A U-tube pressure gauge is quick and easy to make and can normally be expected to meet the requirements of a biogas plant.
 
−
 
 
−
The main gas valve has to be installed close to the biogas digester. Sealed T-joints should be connected before and after the main valve. With these T-joints it is possible to test the digester and the piping system separately for their gas-tightness. Ball valves as shutoff devices should be installed at all gas appliances. With shutoff valves, cleaning and maintenance work can be carried out without closing the main gas valve.
 
−
 
 
−
<br/>
 
−
 
 
−
== Gas Analysis Equipment<br/> ==
 
−
 
 
−
=== Sensors<br/> ===
 
−
 
 
−
Sensors in the gas space must satisfy explosion protection requirements and should be resistant to corrosion and high levels of moisture.
 
−
*'''Infrared sensors'''
 
−
*'''Thermal conductivity sensors'''
 
−
 
 
−
The sensors used to measure the temperature should be installed at various heights so that stratification and inadequate mixing can be detected. Care should also be taken that the sensors are not installed in dead zones or too close to the temperature stabilisation equipment. Resistance sensors (e.g. PT 1000 or PT 100) or thermocouples are suitable for measuring the temperature.
 
−
*'''Electrochemical sensors'''<br/>
 
−
*'''Paramagnetic sensors'''
 
−
*'''Inductive and capacitive sensors'''
 
−
 
 
−
<br/>
 
−
 
 
−
[https://energypedia.info/Biogas -> Back to "Biogas Portal"]
 
−
<div><br/></div>
 
−
= BiogasBox =
 
−
 
 
−
[https://dms.gtz.de/livelink-ger/livelink.exe?sort=name&func=ll&objid=72833125&objAction=browse&viewType=390 Documents on the contruction of biogas plants.]
 
−
 
 
−
= Web =
 
−
 
 
−
[http://biogas.ifas.ufl.edu/ad_development/documents/biogasplants.pdf http://biogas.ifas.ufl.edu/ad_development/documents/biogasplants.pdf]
 
−
 
 
−
[https://energypedia.info/index.php/Construction_of_a_Biogas_Plant https://energypedia.info/index.php/Construction_of_a_Biogas_Plant]
 
−
 
 
−
[http://www.haase-energietechnik.de/en/Products_and_Services/24-e_BiogasBrochure_Feb2011_1.pdf http://www.haase-energietechnik.de/en/Products_and_Services/24-e_BiogasBrochure_Feb2011_1.pdf]
 
  
 
<br/>
 
<br/>
Line 578: Line 165:
  
 
<references />
 
<references />
 +
 
*'''Ringkamp, M.; Tentscher, W.; Schiller, H.''': Preliminary results on: statical optimization of family-sized fixed-dome digesters. Tilche, A.; Rozzi, A. (ed.): Poster Papers. Fifth International Symposium on Anaerobic Digestion, Bologna 1988, pp. 321-324
 
*'''Ringkamp, M.; Tentscher, W.; Schiller, H.''': Preliminary results on: statical optimization of family-sized fixed-dome digesters. Tilche, A.; Rozzi, A. (ed.): Poster Papers. Fifth International Symposium on Anaerobic Digestion, Bologna 1988, pp. 321-324
 
*'''Sasse, L.; Kellner, Ch.; Kimaro, A.''': Improved Biogas Unit for Developing Countries. Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH, Vieweg & Sohn Verlagsgesellschaft Braunschweig, 1991
 
*'''Sasse, L.; Kellner, Ch.; Kimaro, A.''': Improved Biogas Unit for Developing Countries. Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH, Vieweg & Sohn Verlagsgesellschaft Braunschweig, 1991
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*<span style="line-height: 1.5em; font-size: 0.85em;">J.; Sasse, L. (Deutsche Gesellschaft für Technische Zusammenarbeit): Production and utilization of biogas in rural areas of industrialized and developing countries. TZ-Verlagsgesellschaft mbH, Roßdorf, 1986, 278 S.&lt;/span&gt;</span>
+
*J.; Sasse, L. (Deutsche Gesellschaft für Technische Zusammenarbeit): Production and utilization of biogas in rural areas of industrialized and developing countries. TZ-Verlagsgesellschaft mbH, Roßdorf, 1986, 278 S.&lt;/span&gt;
  
 
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<u>This section provides detailed information on materials and devices used in the construction of biogas plants:</u>
 
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*[[Checklist for the Construction of a Biogas Plant|Checklist for the Construction of a Biogas Plant]]
 
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*[[Agitation of Digesters|Agitation of Digesters]]
 
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*[[Digester Heating|Digester Heating]]
 
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*[[Piping Systems for Biogas Plants|Piping Systems for Biogas Plants]]
 
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*[[Plasters and coats for digesters and gas-holder|Plasters and coats for digesters and gas-holder]]
 
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*[[Pumps for Biogas Plants|Pumps for Biogas Plants]]
 
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*[[Slurry-Use Equipment|Slurry-Use Equipment]]
 
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*[[Dealing with Underground Water during and after construction|Dealing with Underground Water during and after construction]]
 
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*<br/>
 
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[[Biogas|-> Back to "Biogas Portal"]]
 
  
 
[[Category:Biogas]]
 
[[Category:Biogas]]

Latest revision as of 09:01, 8 April 2015

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Overview

The feed material is mixed with water in the influent collecting tank The fermentation slurry flows through the inlet into the digester. The bacteria from the fermentation slurry are intended to produce biogas in the digester. For this purpose, they need time. Time to multiply and to spread throughout the slurry. The digester must be designed in a way that only fully digested slurry can leave it. The bacteria are distributed in the slurry by stirring (with a stick or stirring facilities). The fully digested slurry leaves the digester through the outlet into the slurry storage.The biogas is collected and stored until the time of consumption in the gasholder. The gas pipe carries the biogas to the place where it is consumed by gas appliances. Condensation collecting in the gas pipe is removed by a water trap. Depending on the available building material and type of plant under construction, different variants of the individual components are possible. The following (optional) components of a biogas plant can also play an important role and are described seperatly: Heating systems, pumps, weak ring.

Influent Collecting Tank

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Size and Homogenization
Fresh substrate is usually gathered in an influent collecting tank prior to being fed into the digester. Depending on the type of system, the tank should hold one to two days' substrate. An influent collecting tank can also be used to homogenize the various substrates and to set up the required consistency, e.g. by adding water to dilute the mixture of vegetable solids (straw, grass, etc.), or by adding more solids in order to increase the bio-mass. The fibrous material is raked off the surface, if necessary, and any stones or sand settling at the bottom are cleaned out after the slurry is admitted to the digester. The desired degree of homogenization and solids content can be achieved with the aid of an agitator, pump or chopper. A rock or wooden plug can be used to close off the inlet pipe during the mixing process.


Location

A sunny location can help to warm the contents before they are fed into the digester in order to avoid thermal shock due to the cold mixing water. In the case of a biogas plant that is directly connected to the stable, it is advisable to install the mixing pit deep enough to allow installation of a floating gutter leading directly into the pit. Care must also be taken to ensure that the low position of the mixing pit does not result in premature digestion. For reasons of hygiene, toilets should have a direct connection to the inlet pipe.


Inlet and Outlet

The inlet (feed) and outlet (discharge) pipes lead straight into the digester at a steep angle. For liquid substrate, the pipe diameter should be 10-15 cm, while fibrous substrate requires a diameter of 20-30 cm. The inlet and the outlet pipe mostly consist of plastic or concrete.


Position
Both the inlet and the outlet pipe must be freely accessible and straight, so that a rod can be pushed through to eliminate obstructions and agitate the digester contents. The pipes should penetrate the digester wall at a point below the lowest slurry level (i.e. not through the gas storage). The points of penetration should be sealed and reinforced with mortar. The inlet pipe ends higher in the digester than the outlet pipe in order to promote more uniform flow of the substrate. In a fixed-dome plant, the inlet pipe defines the bottom line of the gas-holder, acting like a security valve to release over-pressure. In a floating-drum plant, the end of the outlet pipe determines the digester's (constant) slurry level. Inlet and outlet pipe must be placed in connection with brick-laying. It is not advisable to break holes into the spherical shell afterwards, this would weaken the masonry structure.


Toilet Connection at the Inlet
► Household Toilets can be connected to a Biogas Digester.

Digester

In general terms, digesters consist of the digestion tank as such, which is thermally insulated, plus a heating system, mixer systems and discharge systems for sediments and the spent substrate.

Raw Material for Biogas Digesters

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Types of Biogas Digesters

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Types of Gasholders for Biogas Plants

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Gas Pipe, Valves and Accessories

Biogas Piping

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At least 60% of all non-functional biogas units are attributable to defect gas piping. Utmost care has to be taken, therefore, for proper installation. For the sake of standardization, it is advisable to select a single size for all pipes, valves and accessories. The requirements for biogas piping, valves and accessories are essentially the same as for other gas installations. However, biogas is 100% saturated with water vapor and contains hydrogen-sulfide. Consequently, no piping, valves or accessories that contain any amounts of ferrous metals may be used for biogas piping, because they would be destroyed by corrosion within a short time. The gas lines may consist of standard galvanized steel pipes. Also suitable (and inexpensive) is plastic tubing made of rigid PVC or rigid PE. Flexible gas pipes laid in the open must be UV-resistant.


► Read More here...

Water Traps

► Read more here....

Valves

► Read more here...

Gas Analysis Equipment

►Read more here...

Stirring Facilities

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Optimum stirring substantially reduces the retention time. If agitation is excessive, the bacteria have "no time to eat". The ideal is gentle but intensive stirring about every four hours. Of similar importance is the breaking up of a scum layer which has lost contact with the main volume of substrate and is, therefore, not further digested. This top layer can form an impermeable barrier for biogas to move up from the digester to the gas holder.As a rule of thumb it can be stated that stirring facilities are more important in larger plants than in small scale farm plants.
Types of Stirring Facilities:

  1. The impeller stirrer has given good results especially in sewage treatment plants.
  2. The horizontal shaft stirs the fermentation channel without mixing up the phases. Both schemes originate from large-scale plant practice.
  3. For simple household plants, poking with a stick is the simplest and safest stirring method.


Heating Systems

Normally, because of the rather high involved costs, small-scale biogas plants are built without heating systems. But even for small scale plants, it is of advantage for the bio-methanation process to warm up the influent substrate to its proper process temperature before it is fed into the digester. If possible, cold zones in the digester should be avoided (see also substrate temperature). There are a number of different ways to get the required amount of thermal energy into the substrate are described. In principle, one can differentiate between:

  • direct heating in the form of steam or hot water, and
  • indirect heating via heat exchanger, whereby the heating medium, usually hot water, imparts heat while not mixing with the substrate.


►More information here....

Pumps

Pumps become necessary parts of a biogas unit, when the amounts of substrate require fast movement and when gravity cannot be used for reasons of topography or substrate characteristics. Pumps transport the substrate from the point of delivery through all the stages of fermentation. Therefore, several pumps and types of pumps may be needed. Pumps are usually found in large scale biogas units.

Types of Pumps

► Read more here....


Weak Ring

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The weak/strong ring improves the gas-tightness of fixed-dome plants It was first introduced in Tanzania and showed promising results. The weak ring separates the lower part of the hemispherical digester, (filled with digesting substrate), from the upper part (where the gas is stored). Vertical cracks, moving upwards from the bottom of the digester, are diverted in this ring of lean mortar into horizontal cracks. These cracks remain in the slurry area where they are of no harm to the gas-tightness. The strong ring is a reinforcement of the bottom of the gas-holder, it could also be seen as a foundation of the gas-holder. It is an additional device to prevent cracks from entering the gas-holder. Weak and strong ring have been successfully combined in the CAMARTEC design
Materials and Construction
The weak ring consists of mortar of a mixture of sand, lime and cement (15:3:1). The top of the weak ring restores the horizontal level. It is interrupted only by the inlet pipe passing through. The strong ring rests on the weak ring and is the first layer of the upper part of the hemispherical shell. It consists of a row of header bricks with a concrete package at the outside. In case of soft or uncertain ground soil one may place a ring reinforcement bar in the concrete of the strong ring. The brick of the strong ring should be about three times wider than the brickwork of the upper wall. A detailed description of the weak/strong ring construction can be found in Sasse, Kellner, Kimaro (1991).

Pre-digestion Pit for Storage of Substrates

Sizing depends on: substrate arisings, digester capacity, length of time to be bridged between successive deliveries, land-use specifics and yield of co-substrates, supply contracts for substrates from off-site sources, possible disruptions in operation
Special considerations:

  • Avoid the possibility of storage plant freezing, for example by siting storage tanks indoors, heating storage containers or locating the plant for pits below grade level
  • Avoid biodegradation processes that reduce gas yield
  • Do not permit intermingling of hygienically problematic and hygienically acceptable substrates
  • Implement suitable structural measures to minimise odours
  • Avoid material emissions to soil and to the surface and underground water system


Designs Containers for storing solid substrates in widespread use in agriculture, such as mobile silos, upright silos, plastic-tunnel silos and round-bale silos and open or roofed storage areas (e.g. solid-manure deposits) and pits/hoppers Containers for storing liquid substrates in widespread use in agriculture, such as tanks and predigester pits
Costs Storage facilities are generally in place; when new builds are needed the price has to be calculated on
a case-to-case basis factoring in the multiplicity of influencing variables indicated above

Measurement Instruments

Flow-measuring devices (in the pipes) Ultrasonically (pre pits) Radar (pre-pits)
Wheel loader scales


Further Information


Information on materials and devices used in the construction of biogas plants:


Web based sources


References


  • Ringkamp, M.; Tentscher, W.; Schiller, H.: Preliminary results on: statical optimization of family-sized fixed-dome digesters. Tilche, A.; Rozzi, A. (ed.): Poster Papers. Fifth International Symposium on Anaerobic Digestion, Bologna 1988, pp. 321-324
  • Sasse, L.; Kellner, Ch.; Kimaro, A.: Improved Biogas Unit for Developing Countries. Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH, Vieweg & Sohn Verlagsgesellschaft Braunschweig, 1991
  • J.; Sasse, L. (Deutsche Gesellschaft für Technische Zusammenarbeit): Production and utilization of biogas in rural areas of industrialized and developing countries. TZ-Verlagsgesellschaft mbH, Roßdorf, 1986, 278 S.</span>


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