Supply of current to the public electricity network
The mode of operation of a gas engine varies in principle according to whether it supplies its own needs and only feeds the surplus into the network. The mode of operation is determined by local conditions, especially the price of electric power. Biogas from Waste and Renewable Resources. An Introduction. Dieter Deublein and Angelika Steinhauser Copyright 2008 WILEY-VCH Verlag GmbH amp Co. KGaA, Weinheim ISBN 978-3-527-31841-4 Figure 5.1 Power generators - survey 1 st row . CHP 2nd row left Gas...
Bigadan process formerly Krger process Figure
The Bigadan process is a one-level mesophilic process with sanitization. It includes an interesting and complex heat recovery system. The installations were manufactured in the mid 1990s in Germany, with converting capacities between 40 000 and128000Mga-1 liquid manure with admixing of bio waste. The heat recovery system is certainly interesting from a technical point of view, but in biogas installations enough heat is normally available anyway therefore, the complicated and difficult to clean...
Sewage sludge digestion tower installation
Sewage sludge fermentation is also known as digestion. It occurs in the so-called digestion towers. Their volume size depends on the number of residents of the cities where the sewage comes from. For settlements from 10 000 to 15 000 residents, sewage water treatment plants with single-stage digestion, where the substrate is mixed a few times per day, are Figure 4.21 Single-stage sewage sludge fermentation plant with internal phase separation. Figure 4.21 Single-stage sewage sludge fermentation...
Heavy metals
Heavy metals, which act as trace elements at low concentrations stimulating the activity of the bacteria, can have toxic effects at higher concentrations Table 2.10 . In particular lead, cadmium, copper, zinc, nickel, and chromium can lead to disturbances in biogas plants, but so also can sodium, potassium, calcium, and magnesium. The content of lead, cadmium, chromium, copper, nickel, mercury, and zinc in the biomass rises during fermentation, but only slightly. The high zinc contents of the...
Generation of electricity in a gas turbine
Biogas can be converted to current via gas turbines of medium and large capacity 20MWel and more at a maximum temperature ofca. 1200 C. The tendency is to go to even higher temperatures and pressures, whereby the electrical capacity and thus the efficiency can be increased. The main parts of a gas turbine are the compressor, the combustion chamber, and the turbine.48 Ambient air is compressed in the compressor and transmitted to the combustion chamber, where biogas is introduced and combustion...
Pump system
Pumps Table 1.6- are in general needed in order to transport substrate to and from the equipment in the plant. Centrifugal pumps are to be found in 50 of all biogas plants. In 25 of all plants, positive-displacement pumps are installed to handle high solid concentrations. Ca. 16 of all biogas plants are operated without pumps, depending on geographical conditions. Other pumps like mono pumps or gear pumps, etc., are seldom used. Cutting pumps are used preferably in the pretreatment tank in...
Abbreviations
Heat transfer coefficient at the wall outside the bioreactor Heat transfer coefficient at the wall inside the bioreactor Heat transfer coefficient at the wall outside the heating pipe Heat transfer coefficient at the wall inside the heating pipe Average temperature difference between heating medium and substrate Maximum temperature difference between substrate and the outside of the reactor Temperature difference between inlet and outlet of the heating medium to the bioreactor Maximum...
Removal of water
Biogas must have a relative humidity of less than 60 to prevent the formation of condensate in the transporting pipelines. This condensate, particularly in combination with other impurities, could corrode the pipe walls. Often the biogas has to be dried before further cleaning, e.g., by means of downstream absorption plants. In order to be allowed to feed biogas into the natural gas network, a fine drying process is categorically required according to many European regulations. Biogas can be...
Financing
Biogas plants are financed from own resources, credit, and public promotion. The basis is a feasibility study which convinces investors and creditors of the technical feasibility, economy, environmental compatibility, and general creditworthiness. Therefore the following questions have to be answered Who will be the general contractor and what relevant experiences has he Will the plant work economically, based on a turnover and a profit preview with cost-benefit calculation Is the risk well...
Gas pipelines
Biogas pipelines are subject to the same regulations as those for natural gas,1' e.g., branches attached to the main biogas pipes must always be smaller in diameter than the main pipes. The flow rate should not exceed 20 m s-1 at pressures above 16 bar in branch pipes or 5 m s-1 at pressures below 16 bar. Under certain conditions, long-distance pipelines have to be heated, or the gas which is to be transported has to be preheated. Otherwise the temperature would fall below the dew point,...
Parameter hydrogen partial pressure
A narrow spatial symbiosis is necessary for an undisturbed process between the H 2-producing acetogenic bacteria and the H2 consuming-methanogenics. If generally a biological reaction is to take place, the reaction must be exergonic i.e., the free energy must be negative. The hydrogen concentration should be well balanced on the one hand methanogenics need enough hydrogen for the methane production. On the other hand the hydrogen partial pressure must be so low that acetogenic bacteria are not...
Absorbents based on glycol and ethanolamines
Even higher loads and selectivities are achieved with chemical absorbents Figure 3.5- . Chemical absorption into alkaline solvents occurs under medium or low partial pressure. Absorbents are mainly amines such as monoethanolamine Figure 3.5 Chemical scrubber plant with glycol. Figure 3.5 Chemical scrubber plant with glycol. MEA , diglycolamine, diethanolamine DEA , triethanolamine and methyldietha-nolamine MDEA or a hot potassium carbonate solution. At present, the best approved and most...
Parameter temperature
The temperature shows two optima for acidifying bacteria a smooth one at abt. 32-42 C for mesophilic microorganisms and a sharp one at 48-55 C for thermophilic microorganisms Figure 2.19 . Most of the methanogenic microorganisms belong to the mesophilics. Only a few are thermophilic. A few others are able to produce methane even at low temperatures 0.6-1.2 C , e.g., on the surface of permafrost soils. In laboratory tests, methane formation could be proven also with temperatures below freezing,...
Thermal processes
The yield of biogas is 30 higher if the substrate is thermally disintegrated before it enters the bioreactor. This process occurs at pressures above 10 bar and temperatures above 150 C. The fermentation only takes half the time of other processes and sanitization is automatically included. The higher the temperature and residence time, the better is the degradation. The optimum temperature is about 135-220 C with a residence time of 2 h.37 Parameters exceeding these settings often yield a...
Organic acids fatty acids and amino acids
Normally, organic acids are present in the substrate. These are decomposed during methanation. They exist partly in the undissociated and partly in the dissociated form Figure 2.24 . Especially undissociated acids have an inhibiting effect, because they penetrate as lipophilics into cells, where they denaturate the cell proteins. If too much organic acid is fed to the bioreactor within a short time and or their degradation is hindered, a too strong acidification takes place. Therefore the load...
Adsorption with pressure swing technology VPSA under vacuum
Vacuum pressure swing adsorption plants Figure 3.6' work in principle like the pressure swing adsorption plants and use the same adsorbents. The special economy of the VPSA technology is derived from the lower operating pressure. The biogas is only slightly compressed lt 1 bar' by a ventilator and does not need to be pretreated or precleaned. Thus, the difficult oil and water separation is avoided. The pressure swing is achieved with a vacuum pump. The substantial advantage of these plants is...
Combined fermentation of sewage sludge and bio waste
Experience92' on the combined fermentation of sewage sludge and bio waste has been obtained in a plant in Germany Figure 5.1 .93' The daily throughputs per inhabitant of processed waste water and bio waste are listed in Table 5.1. The bio waste from different origins is collected separately and dumped together into a flat hopper from where a wheel loader transports it to a screw mill, from where it is then transported to the liquid preparation stage, consisting of two steps dissolving the...
Plasmodiophora brassicae
Plasmodiophora brassicae, an obligate endoparasite, is classified as a fungus and belongs to the group of the plasmodiophoromycota. It causes swellings at the main and side roots of cabbage and cruciferous plants, blocking the uptake of nutrients and water. Permanent endospores are formed which remain infectious in the soil for many years. The heat resistance of the fungi varies widely depending on the origin. In most cases 3 4 tests the fungus is inactivated at temperatures in the range 50-55...
Adsorption at ironcontaining masses
In this procedure, hydrogen sulfide is adsorbed onto iron III hydroxide Fe OH 3 , also known as bog iron ore, and or adsorbed onto iron III oxide FeiO3 . Both procedures run similarly and are dry desulfurization processes. For the preparation of sewage gas and biogas desulfurization by adsorption onto iron III hydroxide, Fe OH 3 is preferred. H2S is converted at the iron III hydroxide surface or iron III oxide surface to iron III sulfide and water Ferric oxide or hydroxide masses are stacked...
Removal of ammonia
When liquid manure and in particular wastes from fish processing or the food industry are used as substrates, ammonia can occur in considerable quantity, depending on the stability of the process of fermentation. Actually, ammonia is formed at high pH values from ammonium, which is formed in the liquid manure. Therefore, the ammonia formation can be avoided by a suitable operation of the plant. The removal of the ammonia should be combined with other biogas cleaning procedures. When ammonia is...
Parameter specific surface of material
To support a biochemical reaction a material surface12 as big as possible is necessary. The material surface often varies proportionally to the square of the particle size. In order to increase the material surface, comminution of the biomass is in many cases recommended before fermentation. Figure 2.8 clearly demonstrates the advantages of comminution in an agitated ball mill RWKM for biogas production. The degradation process is accelerated in the first few days as a result of the mechanical...
Wattless current compensation
Synchronous generators produce wattless current due to a phase shift. The phase shift cos cp of a generator, which is to be connected to the electricity network, should be within the limits of 0.9 capacitively to 0.8 inductively in the case of withdrawal and supply of power. Generators are equipped with an automatical cos cp controller even for varying power generation. Additional compensation is not necessary. With asynchronous generators, compensation capacitors are necessary. These may not...
Reinforced concrete tanks
The reinforced concrete must be free of cracks and resistant under the special conditions during fermentation over the entire period of utilization. With reinforced concrete, the acidic substrate can penetrate to the reinforcement and corrode it if carbon dioxide-containing air also permeates to the Figure 1.1 Reinforced concrete in Europe top left , Heating and agitation devices inside a vertical bioreactor top right , Construction of a basin middle left , Uncovered basin middle right , Thoeni...
Os
Sludge volume index Total investment costs Plant investment costs without CHP Specific investment costs for the biogas plant per volume of the bioreactor Investment costs for concrete works k-factor of the bioreactor wall with insulation Specific price for sold current Investment costs for the CHP k-factor of the heating pipes Amortization per year for the CHP Specific investment costs for CHP per capacity of electrical energy Cost for ignition oil Specific cost for ignition oil Local overhead...
Low pressure biogasholder
Most i.e. 80 of the installed biogasholders are of the low-pressure type. Many consist of a biogas bag of plastic foil. Others are constructed of steel. Biogas from Waste and Renewable Resources. An Introduction. Dieter Deublein and Angelika Steinhauser Copyright 2008 WILEY-VCH Verlag GmbH amp Co. KGaA, Weinheim ISBN 978-3-527-31841-4 Bioreactor cover or biogas bag of foil The plastic foils used are manufactured from plastics resistant to UV, weather, fungus, microbes, and biogas, e.g.,...
Landfill for residual waste
Until the 1990s, residual waste i.e. household waste was discarded on landfills, by default. Biological components of the waste were degraded quite slowly and the fermentation process took about 20-40 years. The landfill gas produced during the process was gathered by using horizontal drainages and gas pits for disposal. About 12-300m3 oflandfill gas was produced in total per Mg ofresidual waste, but it contained quite a high level of toxic and corrosive organic components, so that damage to...
Acidogenic genera
Nearly all acidogenic microorganisms also participate in hydrolysis. The genera Clostridium, Paenibacillus and Ruminococcus appear in all phases of the fermentation process but are dominant in the acidogenic phase. The cluster Cytophaga - Flavobacterium - Bacteroides is the second largest group of microorganisms during the first two phases of decomposition, but represents in the methanogenic phase less than 5 of all microorganisms. This is an indication that species of these groups are mainly...
Utilization of biogas for the generation of electric power and heat
Biogas can be used either for the production of heat only or for the generation of electric power. When current is obtained, normally heat is produced in parallel. Such power generators are called combined heat and power generation plants CHP and are normally furnished with a four-stroke engine or a Diesel engine. A Stirling engine or gas turbine, a micro gas turbine, high- and low-temperature fuel cells, or a combination of a high-temperature fuel cell with a gas turbine are alternatives....
Parameter scum
The foaming and the scum31 formation are interdependent. The flotation of the activated sludge, which leads to the formation of a scum, is effected by the occurence of filamentous bacteria in large quantities. A low Figure 2.28 Scum left , agitated by a RECK-Blizzard right . Figure 2.28 Scum left , agitated by a RECK-Blizzard right . substrate concentration in nutrient-limited plants supports filamentous bacteria more than flake-forming bacteria. Nowadays, approximately 30 different filamentous...
Process engineering and equipment construction 1
Figure 4.41 shows the flow sheet ofa biogas plant for bio waste. The biomass is continuously dehydrated by centrifuges applied during the hydrolysis stage. In this process the liquid phase is transferred into the methane reactor while the solid phase is recirculated for continuous hydrolysis. A series arrangement of several tanks allows the use of cultures of special bacteria and optimization of the degradation of organic substances. Usually about 40-50 of the organic substances dissolve easily...
General aspects of the recovery of biomass in the future
In developed countries it is difficult for an agriculturist to decide how to best use his land. If the object is to use the land in the best ecological way possible, a slow downcycling of the biomass will be recommended in the first place. The agriculturist should decide to do silviculture. For example, wood can be used to build houses. After the house has been deconstructed, the quality of the wood is still good enough to serve as material for wardrobes or rail tracks and then to make boxes or...
Bio waste plants
In Germany, 70 of the biogas plants for bio waste, operate based on wet fermentation with suspension of the wastes, while in 30 of the plants, stacked waste is leached by means of percolation. Most plants work in batch mode Table 5.2 . In all current processes, the bio waste is first accepted and then pretreated and subjected to a single-phase or multi-stage bioreactor plant. The biogas is utilized for power generation and the fermentation residue aerobically decomposed, while waste water is...
Ground basin with plastic foil lining
Ground basins with plastic foil lining are the cheapest bioreactors and tanks in biogas plants. They are usually 3.0 m deep, about 1.5 m deep in the ground and with a 1.5-m high earth wall around the basin, made from the excavated earth. The basins are covered with a gas- tight foil. Ground basins are made of a lining of 2.0-mm thick, welded polyethylene foil. This foil is absolutely resistant to UV light, frost, liquid manure, and seeping silo juices. It has an extensibility of ca. 700 and can...
Cultivation of algae
Cultures of micro-algae are suitable as substrates for fermentation gas production. Test results with micro-algae suggest higher yields than those from energy-affording plants C4 plants or energy forests .38' 39' Chlorella vulgaris proved to be a particularly good choice.40' Micro-algae provide for their need for carbon for photosynthesis through atmospheric CO2 and their need for energy from sunlight. They are easy to rear in simple basins. The basins can be set up extensively and can even be...
Detailed overview of biogas components
Table 1.58 gives an overview ofthe typical gas components and their impacts on the gas quality. The gas components are specific to the plant and substrate and should be checked regularly on a long-term basis, as shown by the evaluations of 10 selected biogas plants 60-110 animal units in Bavaria that use different substrates Figure 1.1 . In plants Nos. 1-5, about 6.5-62.5 offat removal tank flotated material were added, depending on the entire dry weight of the substrate. In plant No. 1 about...
Distribution of the residues
Residues from biogas plants are subject to the German law of fertilizers, including when domestic waste water is fermented or when it is mixed with agricultural substrates. The German law of fertilizers regulates single parameters such as temporary permissions to deploy fertilizer, the determination of fertilizing needs, the upper limits for the deployed amount of fertilizer, techniques to deploy, and a lot more. These regulations are called the principles of the good and professional execution...
Index
ABBR see anaerobic baffled reactors absorbents, based on glycol and - carbon dioxide removal 345-348 - ferric chelate solution 340 access door 252 acetate, methane formation 99 acetic acid - inhibition 122 acetobacter 129 acetogenic bacteria 134-135 acetogenic phase 96-97 acid detergent fiber ADF 213 acid detergent lignin ADL 213 acid value, of the feed and discharge 216 acoustic processes, for degradation 232 - long-chain hydrocarbon compounds 53 - sodium alginate 344 ADF see acid detergent...
Industrial purification of sewage
Many different anaerobic processes have been developed for industrial water treatment. The objectives for these developments were high concentration of biomass in the reactor. optimal contact between sludge and sewage. In Germany, 150 anaerobic plants for the treatment of industrial sewage are operating. The decisive factor for the construction of these plants was mainly that anaero- Figure 4.28 Common anaerobic sewage treatment plants 75' Clarigester left , UASB-reactor right . Figure 4.28...
Plant installations
Contact Process CP Figure 4.36 In the contact process, the bioreactor, a degassing device, and a clarifier with biomass recycling are combined. This process is characterized by a low volume load and a residence time of 0.5-5 days. The procedure can be used for waste water with high concentrations of suspended solids up to 40 without risk of clogging. Clarification of the overflow could be difficult, because the biomass washed out does not have good sedimentation properties. The contact process...
Risk of explosion
To avoid the risk of explosion, the guidelines for explosion prevention, the regulations concerning electrical systems in spaces where there is a high risk of Figure 1.1 Law and norms in Germany regulating the feeding of biogas into natural gas networks.22'-23''24' Figure 1.1 Law and norms in Germany regulating the feeding of biogas into natural gas networks.22'-23''24' explosion, the technical regulations concerning flammable liquids and the advices contained in these regulations, and the...
Process engineering and equipment construction Yxn
Water-soluble metabolites are flushed out with water, which is continuously percolating the bulk goods. The phase separation happens either with cake filtration Hygenisat on one day before discharge Figure 4.45 AN-Biothane process. Hygenisat on one day before discharge Figure 4.45 AN-Biothane process. during the percolation or in a screw press, belt-type press, or centrifuge, often still combined with added precipitating agent. In the two-stage process, the wash water is then transferred into...
Network failure registration
The generator is disconnected when the values stipulated below Low - voltage protection High-voltage protection Decreasing frequency protection Increasing frequency protection values under-run or over-run the limiting 80 of the rated voltage 110 of the rated voltage 49 cycles per second 51 cycles per second. For monitoring the frequency and the voltage, a three-phase relay is used. With synchronous generators, in place of the frequency monitoring a vector jump relay is used, which registers...
Compression
To compress methane from biogas the same compressors can be used as those for compressing natural gas, i.e. reciprocating piston compressors, rotary piston compressors such as sliding vane compressors, liquid ring compressors, rotary screw compressors, and turbo compressors such as radial and axial compressors Table 4.1 . Diaphragm compressors are in principle technically too complex and therefore uneconomic for methane gas compression. The necessary specific compression work wt is calculated...
Parameter pH
The equation below gives the relationship between pH and hydrogen ion concentration in mol mL-1 Water with a hydrogen ion concentration of 10-6molL-1 or 10-4gL-1 has, for instance, a pH value of 6. Because of the hydrogen transportation by NAD, different products of fermentation are developed the H ions isolated from the substrate are carried over to the uncharged NAD. The NAD molecules so charged NADH H regenerate oxidize , by forming H2 molecules NADH H H2 NAD AG 18.07kJmol-1 This reaction...
Passing the biogas through an algae reactor or addition of sodium alginate
The idea of connecting an algae reactor to the discharge pipe of the bioreactor was disclosed to the patent office,21' but was not realized for economic reasons. On the other hand, the addition of sodium alginate22' to the substrate appears very promising. Sodium alginate is won from sea algae and is usually added today to animal feeds. It is recommended to add to the substrate in the bioreactor a quantity at a dilution of 1 10 000 e.g., to inoculate a bioreactor of 650 m3 volume with 65 kg...
Biogas for feeding into the natural gas network
Apart from the local direct conversion of biogas to current and heat, there is the possibility to clean the biogas, to separate methane and carbon dioxide,63' and to feed the methane into the low-pressure natural gas network see also Section 2.1.1. . Carbon dioxide can be compressed and filled in bottles for sale. Before feeding the biogas into the natural gas network, the following features must be adjusted 64' Oxygen and humidity content Sewage gas biogas can be added to natural gas H without...
Generation of electricity in a micro gas turbine
Micro gas turbines are small high-speed gas turbines with low combustion chamber pressures and temperatures. They are designed to deliver up to ca. 200 kWei electrical power. Nearly all micro gas turbine manufacturers offer turbines of radial design with combustion air compressor, combustion chamber, generator, and heat exchanger Figure 5.13 . Micro gas turbines are characterized by a single shaft on which the compressor, the turbine, and the generator are fixed. The turbine propels the...
Parameter cultivation mixing and volume load
The start-up phase ofan anaerobic plant often lasts 2-4 months Figure 2.17 . The start-up of the plant usually has a long-term effect on the biocenosis. The start up even can fail completely i.e., the bioreaction does not work and biogas is not produced. To avoid these problems, the hydrolyzer and the methane reactor 15 Degree of disintegration As decrease in relative to the BOD of untreated sewage BOD due to breakdown of microorganisms sludge are often inoculated with anaerobic sludge from...
Ammonium NH and ammonia NH
Ammonia and ammonium result from the anaerobic biological degradation of nitrogen compounds. Ammonia forms ammonium ions in the substrate, the extent of this depending on the pH value. Ammonia has an inhibiting effect, and with larger concentrations can even be toxic, while ammonium is innocuous. It can only have an inhibiting effect at concentrations NH4 -N gt 1500 mgMg-1, where its inhibiting effect is predominantly due to the species whose concentration depends on the pH value. Ammonium...
Chemical oxygen demand COD
The chemical oxygen demand in the residue in relation to the organic matter COD in the substrate is a measure of the degree of decomposition. For the determination of the COD value, nearly all organic carbon compounds are degraded to CO2 and H2O by a strong oxidizing agent potassium dichromate and the oxygen consumption is measured. Two hours at a temperature of 150 C are sufficient for the complete oxidation and the determination of the COD value. According to the standards, an exactly...