Processing

Biogas is formed as a result of digestion, that want to say biological turnover in completely oxygen-free (anaerobic) environment. The organic end product which is formed is usually called digestate or bio-fertilizer. It is rich in nutrients and its high content of organic matter, that is say mull, it also makes it excellent soil conditioner. This is especially valuable for soils with a low molar content or poor quality structure, for example compact clay soils. The root residue can replace stall manure in animal-free agriculture and thereby reduce the need for fertilizers. This can be particularly important in organic farming where fertilizer does not may be used. The biogas consists to the greatest extent part of methane and carbon dioxide. Methane, like is a very energy-rich association, is also the main component of natural gas. The combustion of methane is mainly formed carbon dioxide and water. When the biogas methane incinerated, this still does not provide a net supplement of the greenhouse gas carbon dioxide to the atmosphere, since the carbon in the biogas originates from the carbon dioxide of the air bound into the plants via photosynthesis. This carbon is already in circulation in the nature above the crust, and the biogas is therefore considered a renewable energy source. Climate change as a result of the global the warming, the so-called greenhouse effect, is now considered a very urgent problem and greenhouse gas emissions should be minimized. The utilization of biogas contributes not to the increasing greenhouse effect on the same as when burning fossils fuels, such as coal, oil and natural gas, which are all extracted from the interior of the earth.

ORGANIC WASTE IS NUTRITION AND ENERGY The biogas process has been used in human service for over 100 years and the technology is constantly being improved to fit into our modern society. This is accelerated not least by the fact that, from 2005, it is not allowed to deposit, ie dump, biodegradable waste. The biogas process here constitutes an interesting alternative, where under controlled conditions it is possible to control the biological degradation, so that all the nutrients and energy found in the material are utilized. The waste can thus be regarded as a resource, which after the biological treatment becomes nutritious fertilizer and renewable, environmentally friendly energy. Even the biogas that is formed in already established landfills, so-called landfills, is nowadays largely collected and can benefit society. It is not only waste that can be digested for the extraction of biogas. Among other things, the digestion of agricultural crops is now being planned as a means of contributing to energy supply in certain regions. Fertilizers from for example pigs and cattle can also be treated in biogas processes for the extraction of methane. The finished product becomes a nutrient-rich fertilizer which is also more manageable and hygienic and smells less than the fresh fertilizer. Emissions of ammonia and methane to the atmosphere decrease if the manure is digested in closed containers instead of being stored and handled in a conventional manner. The most common use for biogas is as an energy source for heat and electricity production. The biogas can also be discharged onto the general gas network after some treatment, which opens up for many new uses. The biogas is classified as our cleanest fuel for vehicles and, like natural gas, can be used as a vehicle fuel. The number of filling stations providing such vehicle gas is now increasing based on southern and western Sweden. A very common use for the biogas is to utilize its energy for heating premises or for the production of cogeneration. The latter means that both electricity and heat are formed. The biogas produced from the waste can also be used as vehicle gas after treatment. The exhaust gases are cleaner than in diesel operation, which is particularly advantageous when driving in urban traffic. In a cycle society, the nutrients in the organic waste can once again come to productive ground. The biogas process is an environmentally friendly alternative for such a return of nutrients to the soil via the bio-fertilizer that is formed.

5 AN IMPORTANT LINK IN THE CIRCUIT The biogas process is an important link between consumption and production in a society where nutrition and energy are to be utilized in a long-term and sustainable manner. One reason for utilizing the nutrients in the waste is that the use of fertilizer can then decrease. In a sustainable and resource-efficient society, waste management is included in a cycle, where organic material and nutrients such as nitrogen, phosphorus and potassium are constantly returned to productive soil. At the same time, biogas is formed as a valuable by-product. The biogas process fits in well with the municipalities' environmental goals, where energy planning, public transport, the disposal of organic residues, the environmental and environmental impact of agriculture and society as well as cooperation between the city and the country constitute important pieces. The biogas process is therefore expected to be of greater importance for the procurement and utilization of nutrition and energy in our future society.

What gives the biogas energy value is its content of methane. The gas is therefore large similarities to natural gas, which means that these fuels can be used in a similar way. However, the biogas must be upgraded, it wants say, purified from carbon dioxide, to reach natural gas quality. When the biogas is used directly for heat and electricity production, the pretreatment of the gas is relatively simple and carbon dioxide need not be removed. PRODUCTION OF HEAT Heat production is by far the simplest and also the most common use for biogas. Normally no one is required other pretreatment than separation of water to utilize the gas for this purpose. Boilers are found on most biogas plants in the country, where gas is most often used for heating nearby premises and housing. Conditions for good finances is achieved if the storage requirement and the distance of the gas can be limited at the same time as oil is replaced during combustion. Biogas is a local fuel that is mainly used where it is produced, but excess heat can be brought to external premises either directly via gas pipeline or indirectly via district heating network. In a larger district heating network can be found the good conditions for being able to use the gas as part of the total heat delivery all year round. In smaller plants, on the other hand, it is common to a certain one part of the biogas must be flared, ie burned off, summer time when the heat demand is limited.

PRODUCTION OF POWER HEAT Biogas can also be used for cogeneration production, ie in plants which produces both heat and electricity. This is an effective way to utilize the energy in gas. As with heat production alone the gas must be drained on water or dried before use. In addition, it must Purified from dust and possibly some corrosive components such as hydrogen sulphide and chlorinated hydrocarbons. In many of the country's biogas plants, electricity is produced in gas engine-driven generators. For this purpose are used in Sweden mainly called Ottomotors, whose principle is that the gas is compressed with using cylinder pistons to then ignite with spark plugs. Distribution between formed electricity and heat depend on the design of the plant, but normal values are about 35% electricity and 65% heat based on a total efficiency, that is, share of useful energy in relation to energy supplied, of about 90%. A CLEAN AND EFFICIENT FUEL Methane burns with a clean and clear flame, which means that boilers and other equipment are not soiled by soot and slag. This entails, in addition to a cleaner work environment even reduced wear on the plant. Its life expectancy increases which in turn means lower operating and maintenance costs. addition are, for example, the environmentally harmful emissions sulfur and heavy metals negligible.Reduced emissions of particles and hydrocarbons It also has positive health effects, as fewer allergy and carcinogens substances come into the air, compared to if coal or oil is burned. The biogas is also an efficient fuel. Because it is in gaseous form At the beginning, one can mix in the combustion into air with greater precision than is possible when burning solid or liquid fuels. This achieves one more complete combustion. Biogas low content of sulfur allows a low exhaust gas temperature, which gives high efficiency. At

combustion of more sulfur-rich fuels, such as coal and oil, the exhaust gas temperature must be kept higher to avoid sulfur precipitation as sulfuric acid and causes damage to the exhaust duct and chimney. The higher temperature does then that part of the energy is lost. ECONOMIC INSTRUMENTS Biogas has since 1995 been generally exempt from energy tax. In addition, the biogas is then April 1, 2004 entitled to electricity certification. This is a proof that the holder of a plant that produces renewable electricity receives from the state for every megawatt hour of electricity produced. The certificate can be sold to the electricity users via electricity suppliers and gives the electricity producer one extra revenue. This gives the biogas a competitive advantage over non-renewable energy sources such as oil, coal and natural gas. Information on electricity certificates can be found on the Swedish Energy Agency's website, www.stem.se.

In a digester a low overpressure prevails and the biogas leaves it without fan help. Thereafter, the gas is usually collected in a low pressure bearing, for example a gas clock. The purpose with the warehouse is to be a buffer for smoothing out differences between current production and consumption of biogas. As previously mentioned, the gas must then be purified and dried to varying degrees depending on the area of use. To be able to use the biogas as vehicle fuel or bring it out an upgrade is also required on the gas network to natural gas quality. UPGRADE Upgrading of biogas means carbon dioxide is separated to raise the energy content of the gas and thus extend the driving distance for vehicle operation for a certain volume of gas. The separation of Carbon dioxide also results in an even gas quality

with respect to heat value, that is the energy released during complete combustion of a normal cubic meter of gas. According to the car manufacturers, this is a prerequisite for minimizing emissions of nitrogen oxides during combustion in the engine. Usual Carbon dioxide separation techniques also remove other harmful components such as can be found in gas from a digester. Despite this is usually advantageous to first pure gas from certain substances, such as particles and hydrogen sulphide at high levels, when these might otherwise cause problems corrosion or mechanical wear in the upgrade plant. There are four today techniques for upgrading biogas represented at various plants in Sweden. Upgraded biogas must, according to government requirements, be added to an odorous substance in order for it to should be detectable during leakage. Since upgraded biogas still has about 10% lower energy content than natural gas must it is first added to a higher hydrocarbon, to example in the form of LPG, before it can be carried out on the gas network. This gives the biogas equivalent properties to natural gas, which makes that it also gets the same uses as this one. QUALITY SPECIFICATIONS In Sweden, a quality-specific - cation regarding biogas for vehicle operation. The standard is divided into two different biogas grades: type A for vehicles without lambda control (for example trucks) and type B for vehicles with lambda control (passenger cars). Something simplified means the classification that cars should be run on biogas a methane content of at least 95% while heavier vehicles require at least 96% methane.The background to the standard is that one wants get consistent quality of gas between different facilities and be able to drive the same vehicle on both biogas and natural gas. DISTRIBUTION When it comes to the distribution of biogas, it is still most commonly used for gas consumption locally in the vicinity of the plant. Often added a lead from the production site to it many times the only consumer. The wires are built in plastic because the gas pressure is low. Upgraded biogas can is also distributed in a mobile container system to the filling stations. When the opportunities are now opened to bring out biogas on it the general gas network facilitates the spread of the biogas significantly. Sweden is then 1985 connected to the European gas grid via a pipeline that generally extends from Malmö up to Stenungsund (2004). From this tribal line there are branches into local and regional distribution networks. The senior management works with the highest pressure, about 80 bar, while the branches distributes the gas with a pressure that is lower than in a regular water pipe. Inflation era Locations along this trunk line are biogas plants that can advantageously be connected to the gas network. RENEWABLE GAS ON THE GAS NETWORK The biogas plants do not always have one production volume corresponding to local demand, which varies greatly below year. One consequence of this is that great amounts of biogas must be flared off annually. One way to increase the demand for biogas is to distribute this in the gas network according to same principle applied for "green electricity". This means that when you think a certain one amount of gas at a fuel station is counted against the amount of biogas that is added to the system. Through the gas network, the biogas can thus reach out to new customers who pay for an increase share of renewable gas in the system.

Upgrading technology

Pressure water absorption (water scrubber) is the most common technique for upgrading of biogas in Sweden. The method is based on that gases such as carbon dioxide, hydrogen sulphide and ammonia dissolve more easily in water than methane makes. The solubility of carbon dioxide in water is increasing with increasing pressure and decreasing temperature. Pressure Swing Adsorption (PSA) is the second most common technology. It separates differently substances on the basis of their molecular size, which is why the technique is also called molecular sieve. With PSA, carbon dioxide, oxygen, nitrogen and hydrogen sulphide on, for example, active carbon at different pressure levels. Absorption with Selexol is based on the dissolution of carbon dioxide, hydrogen sulphide and ammonia Selexol, a form of glycol solution. The method is highly reminiscent of pressurized water absorption, but the Selexol method is more efficient because Selexol absorbs three times as much carbon dioxide as water does. Chemical absorption (chemisorption) uses of a chemical to which carbon dioxide is bound. The advantage of this technique is that the chemical only absorbs carbon dioxide and, where appropriate, hydrogen sulphide, while basically nothing methane is separated. The upgraded gas gets thus very high methane content, about 99%.

The more of the raw material's organic content which is traded, the more biogas you get. However, all organic material rarely goes break down within a reasonable time. A residue is formed which mainly consists of inorganic material as metals and minerals, unreacted organic material and newly formed biomass, that say microorganisms that have grown underneath process. The root residue is very nutritious and also adds new biomass to the soil humus. Disease-generating organisms, heavy metals and harmful organic substances as well as visible pollutants such as for example plastic must not occur if the product is to be be used as fertilizer. Generally It can be said that contaminated raw material gives one contaminated end product. Careful sorting is therefore very important for a successful result.

DIFFERENT TYPES OF RESIDUAL Depending on the material that can be digested the content of the residual product varies considerably and this will be decisive if it fits in agriculture or if it is better suited for incineration in a heating plant. The residues of the biogas plants can be divided in a number of different categories. • Waste water refers to treated industrial wastewater which after a first digestion step is usually further processed in further purification step. The content of the various waste waters vary and they may sometimes need to be passed on to municipal sewage treatment plants. • Sewage sludge from municipal sewage treatment plant is usually dewatered after the digestion. This is made to obtain a slightly drier residue that requires less space at storage and possible disposal. The concentration of phosphorus in the sludge is often high, which is valuable from a nutrient point of view. The sludge's sometimes relatively high content of heavy metals, however, have led to only one less part is used as fertilizer. • Bio-fertilizer is called the product that is formed at biogas plants that fertilize manure, source-sorted organic waste, agricultural products with many relatively clean substrates. The fertilizer is intended for agriculture and reminiscent of flute fertilizer from cattle and pigs with regard to nutrient content and texture. The presence of pollution is generally very limited.

Soil improvers are made from residues with high solids content as mixed with topsoil, sand, peat, fl ice, bark with more. Most digested organic residues can, after any dewatering or composting, that is, biological turnover in the presence of the oxygen of the air in a soil product. Soil conditioners based on bio-fertilizers can be used in the cultivation, possibly after their nutrient content has been optimized by additives. If the raw material is of poorer quality, the product may be better suited as a base for construction of, for example, roadsides or as cover material on landfills. • Landfill products are in most cases permanently left where they were once deposited in the waste warehouse. With newer technology for depositing the material, the residual product can sometimes recycled and used as soil improvers or fillers. A NICE PRODUCT When organic material is converted into a biogas process, all plant nutrients are preserved in the final product. Organically bound nitrogen is released partly during the digestion and transition to ammonium (NH 4 +). This is in most cases positive because water soluble ammonium can be quickly picked up by the plants, while nitrogen in organic form must first be released using the activity of microorganisms in ground before it becomes available to plants. Ammonium, however, easily transitions into the liquid gaseous ammonia (NH 3 ), especially at high pH values. This must be taken into account handling of the residue so that the nitrogen not lost by ammonia departure. Therefore, storage of the digestate in closed containers is recommended, also to minimize the risk of methane leakage into the atmosphere. By spreading the bio-fertilizer directly on the ground or ground it in the soil at the spread one can limit the emissions of ammonia considerably.

CERTIFICATION OF RESIDUAL PRODUCTS

Since 1999, there is a certification system for leftovers and compost. This has been prepared on the initiative of the Swedish Renovation Agency (RVF) together with one Other parties in particular. Certification system means an environmental labeling and quality assurance of organic end products from biological treatment of waste. customer confidence and outlets for the product increases. Certification is voluntary and is based on openness to the customer through careful documentation and free insight regarding the environmental and quality parameters. To get their product approved, samples must be taken and the plant's routines are regularly checked for at least one year, the so-called qualification year. The manufacturer also receives support and advice quality work and get access to available education and information. After the qualification year, certificates can be issued. Then, between one and two plant visits per year are made to ensure continued good handling. Inspection and certification services are performed by SP Sweden Testing and Research Institute. The certification rules (SPCR 120) can be found download from their website, www.sp.se. Where There is also a list of the biogas plants that have received their voting permit approved in accordance with the certification rules.

Anaerobic decomposition of organic waste in one Biogas process is broadly similar to the turnover of plant material and concentrates that take place in rumen of ruminants. It's a complicated one process involving many different groups of microorganisms. These microorganisms are all common in nature, to examples in manure, and follow originally with the raw material into the digester. The degradation of the substrate, that is, it organic matter, takes place stepwise. All steps are important for the process to be able to continue right up to the formation of the end products methane and carbon dioxide. Each microorganism group also has its specific role in this context. degradation DIFFERENT STEPS Very first, large molecules decompose like

such as proteins, fats and carbohydrates to less using enzymes secreted by hydrolytic bacteria. This step is called hydrolysis. They formed the products can be utilized by many different bacteria as ferment, that is, ferment, to them Liquid fatty acids, called volatile fatty acids acids (VFA), in the acid formation. Examples of fatty acids formed are acetic acid, butyric acid, propionic acid, valeric acid and caproic acid. In addition to the acids, hydrogen gas is also formed carbon dioxide, as well as small amounts of mixtures other alcohols. Of the products formed during the acid formation, it is only acetic acid or hydrogen gas and carbon dioxide that can be converted directly to methane. Other acids must first undergo another transformation step, the so-called acetic acid formation. In this step breaks bacteria down the fatty acids to acetic acid and vätgas. Omvandlingen kallas också för anaerob oxidation och kan endast ske om vätgastrycket i processen är mycket lågt. I det sista nedbrytningssteget sker själva metanbildningen. Här omvandlas antingen ättiksyra eller vätgas och koldioxid till slutprodukterna metan och koldioxid. De två nedbrytningsvägarna utförs av två olika typer av metanbildande mikroorganismer. Dessa metanbildare har så speciella egenskaper att de inte räknas till bakterierna utan tillhör en helt egen mikroorganismgrupp, de så kallade arkéerna. METANBILDARNAS ROLL De metanbildare som använder vätgas har en mycket viktig roll i biogasprocessen eftersom de, förutom att bilda metan, hela tiden håller nere vätgastrycket så att nedbrytningen av fettsyror i den anaeroba oxidationen kan fortgå. Detta samarbete mellan två mikroorganismgrupper, i detta fall metanbildare och ättiksyrabildare, kallas för syntrofi . Om metanbildningen störs ökar mängden syror snabbt och pH, som normalt bör vara cirka 7-8, sjunker, vilket kan medföra att hela processen till slut avstannar. Metanbildarna är, förutom att de inte tål syrgas ens i mycket låga koncentrationer, känsliga för till exempel höga halter av fettsyror och ammoniak. De växer dessutom extremt långsamt och har ett mycket specifi kt behov av näringsämnen och vitaminer. För att en anaerob process ska lyckas är det viktigt att miljön anpassas så att alla mikroorganismer, inklusive metanbildarna, får bästa möjliga förutsättningar att bryta ner substratet så fullständigt som möjligt.

TEMPERATURE Optimal treatment temperature may vary, among other things depending on which substrate that is digested. Anaerobic microorganisms are active within a wide temperature range that extends from the psychrophysics area (optimum 15-30 ° C) via mesophyll (optimum) 35-40 ° C) to thermophilic area (optimum 55-65 ° C). Generally, the higher the temperature, the faster the process. The temperature can also be important for example for how rapidly and completely different organic pollutants are broken down. This in turn affects the contents of the root residue. For biogas processes Mesophilia 1 (37 ° C) or thermophilic (55 ° C) temperature is usually applied. In the case of anaerobic degradation, the largest is found part of the substrate's energy and carbon in the final products methane and carbon dioxide, while only minor amounts of heat and biomass are formed. This means among other things that the volume of the raw material decreases during the digestion. This also means a difference compared to aerobic conversion of organic material, since heat and biomass production is considerably larger. Aerobic processes, For example, composts warm up themselves while energy must almost always be added An anaerobic process to keep it warm. Usually a smaller portion is used formed the biogas for this purpose.

HYGIEN

Raw materials such as waste, sludge and manure almost always contain some kind of pathogenic organisms, such as bacteria, viruses and parasites. Because the spread of infection must be prevented great demands are placed on all management lines system design. Several pathogenic organisms, such as Salmonella, are difficult to grow and count in the laboratory. Instead, the number of indicator bacteria is counted, for example, common intestinal bacteria, in the material before and after the digestion. An increased number of these bacteria usually also show in one increased number of pathogens. A method for reducing the number of pathogens is to heat treat (pasteurize) the substrate at 70 ° C for one hour. The number of indicator organisms decreases sharply and Salmonella and other pathogens cannot usually be detected after treatment. Trace-forming bacteria however, some heat-resistant viruses are affected not appreciable. If the facility receives animal by-products, such as slaughterhouse waste, pasteurization is a requirement from the EU. When handling substrates and digestate it is very important that the tankers used for the import and export of material at the biogas plants is cleaned and disinfected that the finished product is not re-contaminated. One way is to have separate compartments in the vehicle for transport of substrate and digestate, respectively.

Anaerobic digestion technology allows control of the biogas process so that the decomposition is optimized and the desired result is achieved. process is designed inter alia depending on the properties of the raw material regarding water content, consistency and more. Sometimes pretreatment of the substrate need to be done to achieve desired properties. Solid waste may, for example, need to be ground and diluted with water so that they can be more easily pumped into the digester or reactor as it airtight The idea is sometimes also called. The process selection may also vary depending on which is the main purpose of the treatment, for example if you want to get it out much biogas as possible, stabilize large quantities of substrate or break down the organic material as completely as possible. Thermophilic processes are generally more effective than mesophilia, but at the same time are more effective sensitive to interference. Today it is mesophilia la the temperature range most common, but the proportion thermophilic plants are increasing as a result you learn to handle them better. The processes can be divided into batch and continuous. One also distinguishes between one-step and two-step processes. In addition, the reactors can designed in different ways. PROCESS TYPES • Batch processes deal with the raw material in the same place throughout the decomposition the process without any material being removed or new substrate is added. Different degrees of Mixing may occur. Batch processes are often used for treatment of solid material, for example in landfill disposal. • Continuous processes are added to new material continuously or in smaller portions with short time intervals, that is, semi-continuous. This technology is often chosen for pumpable substrates and applied inter alia in the treatment of sewage sludge in the treatment plants. The degree of mixing may vary, But the most common is that the process is totally mixed with the aid of rotating agitators. • The one-step process, which is the most common procedure, means that all degradation steps occur in a sequence in the same location, often with some form of mixing. • The two-step process means the process is divided into an acid-forming and one methane-forming moiety, where the various steps can optimized separately, usually in two separate digesters. Biogas is formed in both stages, but the largest amount is available in the other step. The method is particularly suitable for the treatment of wet waste from the food industry. In practice, the two-step process means that the residue or the acid-rich leachate from the first process is separated to then be "fed" into the next digester with fixed time intervals. 

COMMON BIOGAS REACTOR • Continuously stirred tank reactor (CSTR) completely mix the substrate with different kind of stirrer. This is a common type of biogas reactor that is most often used in single-stage processes for the treatment of sludge, household waste and manure. • Anaerobic filters (AF) are suitable for waste water or sludge with low dry matter content. In the filter there is a carrier material, so called fillers that are often in plastic which the active microorganisms can attach and grow. This is beneficial to examples for methane builders that grow very slow and otherwise easy to rinse out of the process. The biogas produced from An anaerobic optimized for methane formation can have high quality, that is, with methane contents up to 85%. • Fluidised / Expanded beds (FB / EB) are used also for substrates with low solids content. Small particles are added for the microorganisms to attach to. By having one Sufficiently strong upward flow is obtained by the particles to "float" and thus the microorganisms come into contact with the substrate. • Upfl ow anaerobic sludge form (UASB) allows microorganisms to accumulate and grow in lumps. Despite the high inflows of subtrate, they can remain in the reactor. New material is pumped in with such force that it provides a sufficient mix for to create contact between microorganisms and substrates. INSTRUCTIONS FOR DESIGN OF BIOGAS PLANTS The Swedish Gas Association (SGF) has prepared general instructions for performing biogas plants, ”Biogas instructions BGA 99 ". These provide a good overview of aspects design, safety equipment, testing, control and more of biogas processes and can be found on SGF's website (Www.gasforeningen.se).

process concepts

Mission means that raw materials are added to a biogas process. Another more everyday expression of this is that substrate is "fed" into the process with fixed time intervals. In order to maintain constant volume in a continuous process, a certain amount of ready-made reactor content is often taken out while at the same time corresponding amount of new material is supplied. The load is usually reported as organic load or organic loading rate (OLR). This describes how much organic material is supplied to a process per unit of time, for example 2 kg of organic substance per m3 digesters and days. Hydraulic residence time or hydraulic retention time (HRT) indicates the average treatment time for the material, usually between 12 and 25 days. Another time concept is the exposure time that indicates how long a material is exposed to a certain temperature before adding new material. The degree of extinction is stated in percent and describes the proportion of the organic raw material that has been converted to biogas below a set time. This term is used among otherwise when estimating how long it is effectively rotate a particular material. The gas yield indicates how much biogas in Nm3 which is formed per unit weight of organic substrate fed into the process.