REDUBAR WP06 D19/M. A LIST of the EU-WIDE EXISTING BEST PRACTICES for the BIOGAS TRANSPORT in the NATURAL GAS GRIDS

Transcription

1 Edited by: Hungarian Scientific Society of Energy Economics ETE, Hungary A LIST of the EU-WIDE EXISTING BEST PRACTICES for the BIOGAS TRANSPORT in the NATURAL GAS GRIDS REDUBAR WP06 D19/M

2 Contents 1. Introduction 3 2. European normative referring to the biogas injection into the natural gas grids 4 3. The system of condition for operating of injection process Technical requirements The actors of the biogas feeding into the NG grids 9 4. The technical points of views of the biogas injection s process Upgrading of biogas for injection Carbon dioxide removal Hydrogen sulphide removal Removal of oxygen and nitrogen Halogenated hydrocarbon removal Siloxane removal Removal of trace gases Increasing of the heating value of the biogas Biomethane producing and injecting practice at the European countries Austria France Germany Sweden Switzerland The Netherlands Denmark Injection into the natural gas grids Quality control Requirements at delivery point The aspects of market at the access to the NG grids Evaluation of the situation of the biogas feeding process in Europe Technical points of views Non technical points of views 37 References 38 2

3 1. Introduction Biomass is considered as the one of the most important contributors to the growth in renewable energy sources. European Commission is targeting 15 million toe of biogas production in Actual biogas production is achieving about 15% of the target. Table 1 shows the European characteristically biogas data [1] Primary production of biogas (ktoe) Landfill gas 2,007 2,905 Sewage sludge gas Other biogas 1,331 2,108 Total 4,899 5,901 Gross heat production from biogas (ktoe) Heat plants only CHP plants Total heat Electricity production from biogas (GWh) Electricity only plants 7,590 8,298 CHP plants ,640 Total electricity 16,973 19,937 Table 1. European Union biogas data for 2004 and 2005 The table indicates the dynamic increasing of biogas production. Comparing the data with the ones of previous years the significant growing of the rate of other biogas can be learned. It is originated from the increasing of anaerobic digestion of agricultural products. Referring to the consumption the intensive growing of electricity production and decreasing of using at heating plants can be observed. The significance of biogas can be seen in figure 1. It introduces the growth of renewable electricity and its projections by 2020 [2]. As can be seen, a capacity of 80 TWh electricity is expected coming from biogas in Figure 1. Renewable growth: electricity projections by

4 It has to be emphasized, that biogas is the only type of regenerative energies, which can be applied at equipments operating by hydrocarbon as fuel without significant modification. In case of substitution of natural gas is its role extremely distinguished. The dynamic increasing of biogas utilization has been prompted by transmission and distribution via the natural gas grid. When locally produced biogas can be injected in the existing natural gas grid, biogas can thus be used in far more energy efficient way without local low tech restrictions, on the same markets as natural gas. Natural gas has a wide and growing range of highly energy efficient applications. Also, biogas is easier to transport and store than electricity or hot water, and can be distributed via the grid to the consumers. In generally the feeding the biogas into NG grids requires at the first step an upgrading process to convert the raw biogas to Green Gas. It is a gaseous form of energy from renewable materials with a quality equal to that of the natural gas in the public network [3]. The upgrading stage is followed by the injections phase. Green Gas can be produced, after cleaning and upgrading of landfill gases or of fermentation products, originating from Sewage or waste water treatment; Composting installations; Manure fermentation, possibly combined with co-substrates Further possibility of Green Gas production is the methanising of synthesis gas. The different input materials result a diversity of the composition of the biogas. On the other side the requirements regarding to the feeding are depending from the technical properties of natural gas of the supplying net. The legislative and structural condition of the members of supplying system are various among each countries too. All of these effects result difference of the required technical parameters at the feeding resp. diverse non-technical condition at the realization of biogas injection process. The points of views of the market and of the technical cooperation need to hand it on the basis of the same principle on European level. 2. European normative referring to the biogas injection into the natural gas grids One of the greatest obstacle of spreading the injection process of biogas is the lack of standards concerning -gas quality requirements, -measurement procedures and -regulations concerning the injection of biogas into the natural gas grid. In order to promote investments in biogas upgrading plants there is a need to establish clear guidelines and regulations for the rights and obligations for the involved organizations, including the owners of the upgrading plants, grid owners, customers (who buy the upgraded gas) etc. These measures can be regarded as parallel to the similar regulation for introduction of green electricity to the power grid. 4

5 The European directive 2003/55/EC aims to open the existing natural gas grid for gas from other sources than natural gas, including gas from renewable. This directive states inter alia that Member states should ensure that, taking into account the necessary quality requirements; biogas and gas from biomass or other types of gas are granted non-discriminatory access to the gas-system, provided that such access is permanently compatible with the relevant technical rules and safety standards. These rules and standards should ensure, that these gases can technically and safely be injected into, and transported through the natural gas system and should also address the chemical characteristics of these gases. The rules established by this Directive for natural gas, including liquefied natural gas (LNG), shall also apply to biogas and gas from biomass or other types of gas in so far as such gases can technically and safely be injected into, and transported through the natural gas system. The directive in generally encourages the biogas injection processes, but at present there is no technical European standard for this process yet. No other directive includes any reference either about the regulation on security of supply or the technical standards. The BIOCOMM study [14] summarizes the deficiency and the requirements of the regulation. The most significant establishments are summarized as follows. International (EU) level There are no existing directives or papers except the EU gas directive (2003/55/EC), mentioned biogas in the internal market of gas. Through the gas directive biogas just received equal treatment, but no priority as renewable energy at the international gas grid, comparable to the priority of renewable electricity at the electrical grid. The biofuels directive (2003/30/EC) mentioned biogas under definition of biofuels. Biogas was not discussed within the topic of security of supply. There is no parallel normative to the EU renewable electricity directive EC/2001/77, benefiting the combined heat and power (CHP)-sector, the heat sector and the fuel sector. Upgraded biogas needs to be measured before injection into the gas grid. International directives need to be applied to small producers of about m 3 /h. There is necessary to modify the set aside norm for making it even more influential in the development of agricultural renewable energy. The legislation concerning biological and technical characteristics of agricultural residues for energy production is missing. Upgraded biogas is currently produced at biogas plants treating biowaste, sewage and organic food waste. It seems as probable, that farmers from manures and energy crops will produce in the future most of the gas. These landfill gases need some separate evaluating process because of in some cases their nitrogen content exceeds the tolerable range. The evaluating of the 5

6 landfill gases within the Member States is different. There would be necessary to elaborate the uniform norms considering the properties of landfill gas of different chemical content. Level of the Member States Heat technologies based on renewable energy have a substantial potential for growth, with a high potential share of the EU s gross energy consumption. Therefore, coherent targets and policies at EU level and in each Member State are important. Normative on compatibility for biogas and gas from biomass with natural gas, with hygienic standards for gas from anaerobic digestion as a key issue, are missing in many Member States. Member States should ensure that, taking into account the necessary quality requirements; biogas and gas from biomass or other types of gas are granted non-discriminatory access Despite the lack of uniform European regulation, some countries have special official technical regulations concerning first of all on the requirements of the quality of biogas injected into the NG network. Some recommendations have been made, among others, on the following measures: -promotion of biogas as an alternative fuel to fossil fuel -R&D programmes, developing biogas technologies linked to industry and domestic use; -increase the available information to the citizens about biogas. Similarly, national frameworks govern the tax system, the subsidies, and the availability of gas and heat grids. The major driver defining the way of biogas utilization is the compensation of the energy, i.e. electricity or (upgraded) biogas. In reality several European countries (Germany, The Netherlands, Switzerland, Sweden, Spain Slovenian) apply legislative measurements for the promotion of direct utilization of biogas or electricity originated from biogas. At the moment in 7 European countries are found biogas upgrading and injecting systems. There had been elaborated technical requirements and operating condition. Against the similarities there include several divergent elements. At the same time at the majority of the Members countries is the feeding process wasn t put into practice yet, and both the technical requirements and non-technical regulation are missing. The uniform European norm and regulation system could incentive the creating of detailed and harmonized standards at each of the Member States. 3. The system of condition for operating of injection process 3.1. Technical requirements From point of view of utilization has to be distinguished three types of biogases; raw gases before treatment gases, which are after treatment suitable for direct delivery into transmission or distribution networks gases, which are after treatment suitable for delivery into gas networks only by blending with other gases. 6

7 In the following are there discussed the gases suitable for injection both directly or after blending process. The relevant norms are in most cases based on the NG standards, but with corrections concerning properties relevant for biogas. The general demands of NG, stated at national legislation (Wobbe index, sulphur content heating value etc.) are in most cases achievable. The upgraded biogas is generally injected into the low-pressure gas grid of the local energy distribution companies, for which no national biogas quality requirements is available yet. Table 2. Physical properties of the upgraded biogas at different EU countries 7

8 The available green gas qualities for injection into the natural gas grids has been summarized at the table 2 [4]. The data are compiled from the relevant prescriptions of six countries applying biogas upgrading and feeding process. At some parameters can be seen significant difference among the values referring to the studied states. In the following there are summarized some country-specific condition. Austria Austria has the directive OVGW G31 in which the quality standards have been given. In Austrian the present quality requirements for gas feed-in are due to historical reasons oriented at the quality of natural gas. The specialities of fermentation gas, in particular the lower energy content of fermentation gas, are not taken into account. France In 2004 Gaz de France the national transporters and distributor has developed a standard for gas injection into the gas grid in France, with more strict limits on oxygen than the other standards (for example the Swedish and the Swiss standards), and also comprises a number of limits for heavy metals and halogens. Gaz de France has established technical directives. In the north of France, gas of low heating value gas (L-gas) is delivered, and in the rest of France high heating value gas (H-gas). The planned biogas injection in Lille concerns L-gas. The limit of 2.5% CO2 places a high demand on the gas processing installation Germany The DVGW standard G-260 contents the technical requirements of gases originating from renewable energies. The expectation concerning about the feeding into the NG grids are formulated at the DVGW standard G-262. It prohibits the injection of landfill gas into the NG grids due to the presence of halogens. There are two types of injecting. In contrary with the gas supplementing technologies. The biogas feeding process has been considered as exchange gas having more exacting requirements. DVGW-Arbitsblatt G includes them detailed Sweden The quality requirements for biogas are listed in the standard The addition of LPG is normal practice in Sweden to raise the gas to the correct calorific value. Landfill gas is not really forbidden in Sweden, but due to the high requirements of the methane content, the processing of landfill gas to the required quality would be difficult. In the Swedish biogas plants, the methane and CO2 levels, as well as the water dew point are continuously monitored. Sweden is the only country having limit referring to the water content. Natural gas used in Sweden - coming from the North see - has a fairly high calorific value since it contains higher hydrocarbons. To reach the same heating value as for natural gas, propane is added to the biogas before it is being injected into the national gas grid. In these cases is the water limit somewhat higher. The correct calorific value is needed in the gas since customers are charged in terms of energy consumption but at each customer only flow is measured, meaning that the energy content needs to be known at all times. Switzerland The Swiss is the only country where is it possible to inject biogas, which isn t, conform for itself to the specifications for the calorific value. However, this is only applicable to the 8

9 transport network and under the condition that there is sufficient mixing with the fossil natural gas. The limit of 6% CO 2 is giving more possibilities to the biogas injectors regarding the separation of methane/co2 mixtures. Two different qualities are allowed in the Swiss regulations: gas for limited injection (CH 4 >50%) and gas for unlimited injection (CH 4 >96%). The Netherlands The Netherlands has the most items mentioned in its directives. This is due to the fact, that the already existing regulations for gas quality, which apply to the national network controllers, have been followed as much as possible. Limits are also set for the components, which are typically present in landfill gas (siloxanes, halogens, etc). The detailed regulation results, that Green Gas can be transported, stored or marketed in the Netherlands without incurring additional costs for quality adjustment, hence is of a quality that will not cause damage to either transmission system or consumer applications. The permitted values for hydrogen, chlorine and fluorine in the Netherlands are higher than in the other countries. The real values appearing at the biogas are much lower The actors of the biogas feeding into the NG grids The Supplier of the Biomass has to contract with the biogas producer for the price and quality. An example of this could be the owner of a sewage treatment plant or a cooperative of farmers, which delivers manure for a fermentation installation. The Producer of Green Gas supplies cleaned biogas to the supplier of Green Gas. Here, a difference can be made between the fermentation installation and the processing and cleaning installation. The Supplier of Green Gas markets the biogas directly to a number of clients, or sells it on to another supplier. The party, which supplies Green Gas to clients, must have negotiated a contract with the network controller. The Network Controller is responsible for the quality of the gas that they distribute. It must therefore guarantee via a contract that the incoming gas is of a good quality. The network controller must check the quality and control the procedures of the supplier. Its further obligation to control if is there sufficient delivery capacity and consumption in their network to be able to distribute Green Gas. The operating system and the responsibilities referring to the biogas injection and distribution chain is based on the cooperation of the natural gas supplying companies and the partners producing biogas. The role and responsibility of the actors are different at each country. That is, why the best practice of feeding is concentrated on the technical condition. The legislative and financial background of the process includes country specific characteristic. At some cases - in order to achieve the best practice of biomethane producing and injecting processes - the role of the actors could be changed or modified. It depends on the actual condition of the realized system and the interest of the members participating at the supply chain. There was analysed by DENA [5] from point of view of the farmers and of the energy suppliers. The basic and most frequently applied form of the participation of farmers is supplying the biogas plant by raw material. Their activity can be completed by some provision (transport). In order to ensure the continuous supply establishment of a cooperative is beneficial. There is 9

10 another way, where the farmers contribute at the establishment of the plants, sharing from the profit too. At finally they can install biogas (biomethane) plants by themselves as well, contracting directly with the gas supplier. The energy suppliers have more possibilities too. According to the basic conception they buy the biomethane of standard quality and their activity is focused on the transport and on the selling only. They could buy raw biogas perhaps from more plants of small capacities and operate the own upgrading plant. It could be more economic. At the third version they are the owner of the biogas plant too, undertaking the higher part of own capital at the installation and the additional technical tasks and duties. 4. The technical points of views of the biogas injection s process The first step of the feeding process is the purification of the input (raw) material. Its physical properties are depending on the producing technology. The mean components of the most common types of non-conventional (NC) gases and of natural gas are shown at the table 3/a. The average values of the same types of gases can be seen on the table 3/b. Table 3/a. The components of different raw gases from NC sources and of natural gas 10

11 Table 3/b Physical properties of different types of NC gases compared with natural gas Table 4 Gas quality parameters currently considered in proposed harmonised EU specification For (partial) reducing of this effect EU proposed some harmonisation referring to the mean parameters. The table 4 shows these values. At the evaluation of the data has to be considered, that the Russian and more the Dutch natural gas have lower caloric value than the typical North Sea H gas indicated at the table. The differences of the data are considerable even within the biogas category. Either the density or the range of the chemical components is distinguished. The last one influences the condition of combustion technological utilization by the modification of heat transfer and UV radiation properties. It is independent from keeping the Wobbe number as constant. 11

12 4.1. Upgrading of biogas for injection The majority of the biogas production is rising from anaerobic digestion (AD) and natural decomposition of agricultural products (landfill gas). Generally, the raw gas has to be upgraded before the injecting process. AD method has been successfully applied in industrial wastewater treatment, stabilisation of sewage sludge, landfill management and recycling of biowaste and agricultural wastes as organic fertilisers. Increasingly the AD-process is applied for degrading heavy organic pollutants such as chlorinated organic compounds or materials resistant to aerobic treatment. The product of anaerobic digestion is a mixed gas primarily composed of methane and carbon dioxide. It contents in smaller amounts of hydrogen sulphide and ammonia Trace amounts of hydrogen, nitrogen, carbon monoxide, saturated or halogenated carbohydrates and oxygen are occasionally present in the biogas. The landfill gases include basically methane and carbondioxid. There are similar contaminating components as AD gas, but charged with a significant quantity of chlorine and fluorine. In small-scale installations the gas is primarily utilised for heating and cooking. In larger units CHP s are fuelled with raw biogas. Nevertheless for many applications the quality of biogas has to be improved. The requirements are rather different. The different types of heat technological equipment (boilers, engines, gas turbines, heat consuming units of thermo technologies) require different rate of purification of biogas. In order to satisfy the technical requirement, carbon dioxide, hydrogen sulphide, ammonia, particles and water (eventually trace elements) have to be removed. Apart from the above components both types of biogas (landfill and AD gas) content hazardous components; siloxanes; bacteria fluorohydrocarbons; chlorohydrocarbons and ammonia. In the landfill gas is the oxygen content occasionally high when too much air is sucked in during the collection phase. They have to be removed too. The contaminating components and the risk character of the biogas is depending on the producing technology was studied by Marcogas. Their list and the effects on the health, the damaging impacts and the countermeasures proposed are summarized at the table 5 [6]. 12

13 Table 5 Potential hazards of biogases and countermeasures applied to raw gases Considering the numerical rates the main parameter that may require removal in an upgrading systems are H 2 S, water, CO 2 and halogenated compounds: The process of desulphurisation is necessary to prevent corrosion and avoid toxic H 2 S concentrations (the maximal workplace concentration is 5 ppm). When biogas is burned, SO 2 /SO 3 is emitted which is even more poisonous than H 2 S. At the same time SO 2 lowers the dew point in the stack gas. The sulphurous acid formed (H 2 SO 3 ) is highly corrosive. The removal of water prevents the accumulation of condensate in the gas line, the formation of a corrosive acidic solution when hydrogen sulphide is dissolved or to achieve low dew points when biogas is stored under elevated pressures in order to avoid condensation and freezing. 13

14 Removal of CO 2 will be required if the biogas needs to be upgraded to natural gas standards or vehicle fuel use. It dilutes the energy content of the biogas but doesn t exert significant environmental impact on. Depending on the required quality of the product, the cleaning-upgrading technology covers the filtering, drying, desulphurisation, CO 2 separation and hydrocarbon addition processes. In the practice the method of CO 2 removal is used as characteristically technology for classification the whole upgrading process. In the following the most usual cleaning processes has been enlisted Carbon dioxide removal At present four different methods are used commercially for removal of carbon dioxide from biogas either to reach vehicle fuel standard or to reach natural gas quality for injection to the natural gas grid. Absorption This technology is applied most often. Its advantages are the high gas quality numerous experiences for the operation favourable pay back period of investment The technology is based on the different ability of gases for solution in the solvents. CO 2 and H 2 S are more soluble than methane. As solvent can be used pressurized water, polyethylene glycol (trade name selexol) or monoethanolamine (MEA). In the case of the last two a pre treatment phase is necessary for removing of H 2 S. The selexol process requires the previous separation of water vapour too. The application of MEA allows the using of atmospheric pressure. The solvent is regenerated by heating (over 100Cº). The methane loss can be kept under 0,1%. The other solvent needs a pressure level of 7-10 bar. The absorption process is purely physical. Usually the biogas is pressurised and fed to the bottom of a packed column where water is fed on the top. The process is running at counter flow system. The method can also be used for selective removal halogenated hydrocarbons hydrogen sulphide as well. In case of water solvent the last one can cause corrosion or plugging of pipe work, hence is it recommended exceptionally - to apply some kind of the pre-treatment phase for H 2 S removing (see ). Further problem of water scrubbing is the amount of methane containing the water leaving the absorptions column. This waste can be reduced by application flashing tanks of lower pressure for desorption of CH 4. It can be led back to the process. The disposal of the wastewater needs some additional investment too. In spite of all these, is the water scrubbing a relatively cheap process. The specific cost is about 0,13 /m 3. The achievable purity is 98%. The application of chemical absorption can result the same purity by somewhat more expenses (0,17 /m 3 ) [7], [8]. The scheme of the high-pressure water scrubbing technology can be seen on the figure 2. 14

15 Figure 2 Scheme of water scrubbing technology Conventional techniques for separating carbon dioxide from biogas demand a lot of process equipment and the methods are usually suited for large plants in order to reach a sufficient economy. In-situ methane enrichment is a new technology under development in pilot-scale, which promises a better economy also for smaller plants. Sludge from the digestion chamber is led to a column where it meets a counter flow of air. Carbon dioxide that is dissolved in the sludge is desorbed. The sludge is led back to the digestion chamber. More carbon dioxide can now dissolve into the sludge resulting in methane-enriched gas in the chamber. The results from lab-scale tests in Sweden indicate that it is technically possible to construct a system that increases the methane content of the gas to 95% and still keep the methane losses below 2%. Adsorption There is about a proven technology too. Their advantages can be summarized as follows: high gas quality dry process, without using of water or chemicals applicability for partial removal of oxygen and nitrogen. The process is generally based on the application of molecular sieves. Their adsorptions ability is different, depends on the size of the molecules of the gaseous compounds in biogas. The adsorptions phase requires high pressure. The saturated adsorbent can be regenerated by low pressure or by thermic desorption. The CO 2 or other adsorbed components are collected and removed. The first phase of the process results a significant amounts of CH 4 at the vent, hence is it led back to the process in order to reduce the methane losses. The widespread applied technology of bed regeneration is based on changing of the pressure level. The process is therefore often called pressure swing adsorption (PSA). The pressure level of the adsorptions phase is about 4-7 bar. The desorptions phase has been carried out in vacuum. Instead of molecular sieves activated carbon can be applied too. The figure 3 introduces the scheme of the PSA system 15

16 Figure 3 Scheme of the PSA system The disadvantages of the technology are the high investment cost and that the CH 4 level are less stabile - compared with other CO 2 removing processes. The achievable purity is about 98% methane, the specific total cost amounts 0,25 /m 3. Membranes The membrane separation technology has much less references. The method is based on the permeability of special membranes. Depending on their size certain molecules can flow through the membrane, the others not. There are two basic systems of gas purification with membranes: a high-pressure gas separation with gas phases on both sides of the membrane, and a low-pressure gas liquid absorption separation where a liquid absorbs the molecules diffusing through the membrane. The high-pressure method is dry technology. It hasn t to apply water or chemical. It needs a pre-treatment phase for removing of the water vapour and H 2 S. The methane loss is extremely high (exceeds 10%), which can be reduced by using more membranes in line and by sending back the vent of the first stages to the process. It results higher costs. The low-pressure process was developed for biogas upgrading only recently. The process can be operated at approximately atmospheric pressure (1 bar), which allows low-cost construction. The removal of gaseous components is very efficient. At a temperature of 25 to 35 C the H 2 S concentration in the raw gas of 2 % is reduced to less than 250 ppm. Membrane separation technology can be combined with the active carbon adsorptions process as well. Pressurised gas (36 bar) is first cleaned over for example an activated carbon bed to remove (halogenated) hydrocarbons and hydrogen sulphide from the raw gas as well as oil vapour from the compressors. A particle filter and a heater follow the carbon bed. The membranes made of acetate-cellulose separate small polar molecules such as carbon dioxide, moisture and the remaining hydrogen sulphide. These membranes are not effective in separating nitrogen from methane. The one stage process can result the purity about 90% only. The specific cost is low as well (0,12 /m 3 ). If the raw gas is upgraded in 3 stages, it can be achieved 96 % methane or more. Naturally the costs will be higher too. 16

17 Because of low operational costs at reduced quality requirements of and small requirement of place the technology could be applied economically at plants for biogas upgrading of small capacities. The technology can be seen on the figure 4 CO 2 (+ H 2 S) + 10 ~15 % CH 4 Biogas Compressor Membrane separator > 78 % CH 4 CO 2 (+ H 2 S) H2S Removal > 90 % CH 4 Internally staged Cryogenic separation Figure 4 Scheme of the membrane separation technology Cryogenic method is the newest separating technology. It is base on the different condensation temperature of components of raw biogases. This difference is at the defining element significant. At normal state carbondioxid on 78Cº, methane on 161Cº and nitrogen on 196Cº are becoming liquid. Advantages: -Extremely high rate of the achievable yield -The most effective technology for full removing the components N 2 and O 2. -Water and chemical free technology The process as upgrading technology is applied mostly at the temperature of about 80Cº. It results cleaned biogas free of water, hydrogen sulphide, siloxane, carbondioxid and other impurities of small amount. The upgraded gas contains oxygen and nitrogen. By decreasing the temperature under 160Cº, the methane condensates and the gas became free from the both components above mentioned. The liquid biogas (LBG) could be used advantageously for the vehicles of running frequently as bottled fuel (damage of vaporisation). There was developed a technology, for a four-stage purification (Scandinavian GtS). At the first phase (+6Cº) the water, the solid impurities and some other components of liquid state has been removed. The next step (-25Cº) makes possible to remove H 2 S, siloxan and other liquid components. The CO 2 removal will be carried out ain the 3rd stages at 80Cº. The biogas is at gaseous phase; the achievable purity is about 91%. If the 4th stage is operating too ( 190Cº), the methane is staying at disposal in liquid phase (LBG). Its purity can achieve the value of 99%. The liquid CO 2 as by-product can be stored and used for other technologies improving the economy of the process. Some other technologies are combining the cryogenic process with the traditional ones. These methods are concentrating to produce LBG, and the purification is carried out by water washing or by membrane separating processes (Acrion technologies). Another process uses traditional processes too, combined by cryogenic separation of CO 2. 17

18 The technology needs high investment costs and the energy demand is high too. The specific cost of the biomethane upgraded by cryogenic technology exceeds the value of 0,40 /m 3. At present are there few references only. Figure 5 shows the scheme of the cryogenic process. Figure 5 Technological scheme of the cryogenic separation The specific prices of the upgraded biogas of each technology are strongly depending on the capacity of the plant. Compared the investment costs of 250m 3 /h and 2,000m 3 /h capacities, the specific cost of the last one decreases on about one third. The total specific costs are reduced on cca 60%. Considering the technical condition of the cryogenic technology, at high capacities is the above mentioned difference higher, giving chance for more installations of the process. The selection among the technologies is very difficult. Similarly to create some priority list or to define the best practice could be arbitrary. It depend on the source and on the quality of the raw gas, on the circumstances of consumption, on the locale standards, on the financial condition and on other factors referring to the actors of the biogas injections chain. In spite of these all it can be established some general conclusions. The cheapest technology is the high-pressured water scrubbing. At the PSA system can be the wastes easily treated. The other technologies need more advanced instrument and process. The operational condition of the water scrubbing and of the membrane separation technologies is the most favourable. Apart from the high specific prices the cryogenic technology needs additional safety measurements and operating staff. This requirement confirms, that the growing rate of its application could be expected at the range of high capacities only Hydrogen sulphide removal The different methods of the CO 2 separation need often an applying of the pre treatment technology concentrated on the hydrogen sulphide removal. Its most common solutions applied directly to the H 2 S purification are summarized as follows 18

19 Biological desulphurisation Desulphurisation of biogas can be performed by microorganismus. For the microbiological oxidation of sulphide it is essential to add stochiometric amounts of oxygen to the biogas. Depending on the temperature, the reaction time, the amount and place of the air added the hydrogen sulphide concentration could be reduced by 95 % to less than 50 ppm. Biological filters In large digesters there is often a combined procedure of water scrubbing (absorption) and biological desulphurisation applied. Either raw wastewater or press-separated liquor from digestate is dispensed over a filter bed. In the bed, liquor and biogas meet in counter flow manner. In the biogas 4% to 6 % air is added before entering the filter bed. The system is applied in several installations for industrial wastewater treatment. Iron chloride dosing to digester slurry Iron chloride can be added directly to the digester slurry or to the feed substrate in a prestorage tank. Iron chloride then reacts with produced hydrogen sulphide and form iron sulphide salt (particles). The method needs to be complemented with a final removal down to about 10 ppm. Iron oxide Hydrogen sulphide reacts easily with iron hydroxides or oxides to iron sulphide. The reaction requires additional energy supplying and needs water. The reaction is optimal between 25Cº and 50 C and the biogas should not be to dry. The iron sulphides formed can be oxidised with air. The product is again iron oxide or hydroxide and elementary sulphur. Iron oxide wood chips Wood chips covered with iron oxide have a somewhat larger surface to volume ratio than plain steel. Their surface to weight ratio is excellent thanks to the low density of wood. Roughly 20 grams of hydrogen sulphide can be bound per 100 grams of iron oxide chips. Iron oxide pellets The technology is based on the red mud, a waste product from aluminium production. Most of the German and Swiss sewage treatment plants without dosing of iron chloride are equipped with an iron oxide pellet installation. Impregnated activated carbon With PSA systems H 2 S usually is removed by activated carbon doted with potassium iodide. Like in biological filters in presence of air, which is added to the biogas, the hydrogen sulphide is catalytically converted to elementary sulphur and water. The sulphur is adsorbed by the activated carbon. Sodium hydroxide scrubbing Applied water solution of sodium hydroxide (NaOH) the absorption capacity of the water has been enhanced. Chemical absorption process can be carried out. Sodium hydroxide reacts with hydrogen sulphide to form sodium sulphide or sodium hydrogen sulphide. The hindrance of the process, that the created salts are insoluble and the method is not regenerative. 19

20 Removal of oxygen and nitrogen Biogas with a methane content of 60 % is explosive in concentrations between 6% and 12 % in air (supposed, that the dominant part of the rest is carbon dioxide). Membranes or low temperature PSA can remove oxygen and nitrogen. N 2 and O 2 pass through, while larger molecules are adsorbed. The method is expensive. In order to avoid the sucking in of the air is it more beneficial to check the oxygen concentration regularly. The applying of the cryogenic process results oxygen and nitrogen free gas of high quality Halogenated hydrocarbon removal Halogenated hydrocarbons (FHC), particularly chloro- and fluoro-compounds are predominantly found in landfill gas. They cause corrosion in CHP engines, in the combustion chamber, at spark plugs, valves, cylinder heads, etc. The compounds can be removed with the same methods used to remove carbon dioxide Siloxane removal Organic silicon compounds are occasionally present in biogas, which can cause severe damage to CHP engines. It is known that the organic silicon compounds in biogas are in the form of linear and cyclic methyl siloxanes. Siloxanes can be removed by absorption in a liquid medium, a mixture of hydrocarbons with a special ability to absorb the silicon compounds. Activated carbon can be used as well to separate organic silicon compounds from biogas. This last one is very effective but at the same time expensive too. The carbon becoming saturated can t be regenerated and it has to be replaced continuously Removal of trace gases There are a number of trace gases in the biogas that can harm the gas distributing system or the gas utilities: Damage can be caused e.g. through corrosion, deposits or mechanical wear. Contaminants can also cause unwanted exhaust products like SOx, HCl, HF, dioxins or furans. There are more methods to remove these types of contamination. Except of the economical and technological points of views, their evaluating needs the considering of the methane losses too. Analyzed the realized biogas purification processes can be established, that their majority uses the water scrubbing, PSA or activated carbon methods Increasing and adjusting of the heating value of the biogas The required heating value can be achieved at more cases through the purification processes. It is especially valid at removing of the CO 2 component. If is it not enough, or the heating value (Wobbe index) is fluctuating, the adjustment happens by propane dosing. Its character at the combustion process is harmonising with the ones of methane. Considering the significant role of the shape, size and structure (UV radiation ability) of the flame, from point of view of the consumers is it very important to keep these properties as stable. Adding propane to the biogas could increase the heating value. To keep this parameter as stable, its volume is adjusted. There are operating other solution (Danish example), where biogas- 20

21 natural gas-air mixture is supplied into a separate pipeline resulting a gas of lower heating value. The adjusting of air volume flow ensures its stability Biomethane producing and injecting practice at European countries There are introduced some selected biomethane producing examples and their features at the relevant EU member countries Austria The total biogas production in Austria was 139 ktoe/year (2007). As first step of biogas injection there was built in the town Pucking an upgrading plant, and a quantity of 6 m 3 /h of Green Gas is supplied into the NG distribution network since June From 10 m 3 /h of raw gas, about 6m 3 /h of purified biogas is produced and distributed. This equates to an annual energy production of 400,000 kwh, equivalent to the average annual requirement of 40 household apartments. The refined biogas fulfils the quality requirements of the ÖVGW directive G31. Refined biogas can also be used as fuel for vehicles or for cogeneration (for example stationary fuel cells) and is not dependent on the location of gas injection. Austria s first biogas feeding-plant injects purified biogas into the existing gas grid. After desulphurisation, CO 2 separation and drying, the purified biogas from the existing biogas-plant is injected into the gas grid via a transfer station. This project is a demonstration plant. During this time heaters of selected customers in nearby housing areas are checked regularly and the economic feasibility of further locations is tested. The other biogas upgrading plant is running since 2007 at Bruck/Leitha [9]. It operates by membrane separation system. The capacity is 180m 3 /h raw biogas resulting 100 m 3 /h biomethane. The plant is mounted inside a standard size container. The biomethane is utilised on the site at gas engines France France has high biogas potential (about 3,250 ktoe) and in 2007 more than 230 plants produced 330 ktoe raw gases at Upgrading technology was applied at the district of the city Lille using absorptions method by water scrubbing. There is processed tonnes of organic waste annually. 4 million m 3 /a Green Gas is produced and injected into the 16 bar separated network. The gas consisting about 97% of methane is used as vehicle fuel at the city buses of Lille. Referring to the biogas supply through the existing NG grids aren t experiences yet. The application of the process was allowed in October Germany At 2007 the 27 states of the EU produces about 5,900 ktoe i.e. 12 billion cubic metres biogas. Germany is accounting for more, than 40% (2,383 ktoe) Two gas quality groups are differentiated: Group L with low Wobbe index. The index is used to characterise the quality of fuel gases and has a fluctuation range from 10.5 to 13 kilowatt- 21

22 hours per standard cubic metre. The H group with the higher Wobbe index has a range from 12.8 to 15.7 kilowatt-hours per standard cubic metre. The H-gas group has the biggest proportion in the German natural gas grid. The first upgrading plants were put into operation at 2006 only. Further five ones were installed at The process is growing very dynamically and in the mid of 2009 are 25 upgrading plants operating injected biomethane into the NG grids. The most characteristic data of 15 upgrading plants are summarized at the table 6. It reflects the state at The volume flow of the gas injected into the NG grids achieves the value of 7,500m 3 /h corresponding the energy consumption of 30,000 households with four persons. 22

23 Table 6 Upgrading plants and realized feeding in applications at Germany 23

24 Sweden At Sweden the total biogas production in 2007 amounted to 1,14 PJ, [1] from which 12% was used as vehicle fuel. This biogas was produced in 233 plants, consisting of 139 sewage treatment plants, 13 co digestion plants that digested manure, 70 landfills, 4 industry sewage, and 7 farm plants Sweden had 35 upgrading plants in The majority of them (23) are operating by water wash technology. [10]. PSA system is used at 9 plants. At Göteborg and at Falkenberg is applied chemical absorption (amine) process and one plant is working by selexol technology. The majority of the upgraded gas has been utilized on the site. There are six cities in Sweden where the upgraded biogas is injected into the national gas grid representing about 5000m 3 /h capacity in total. The gas then needs the same upgrading treatment as for vehicle fuel. The difference is that it then can be somewhat lower restrictions concerning water content. There is more type of rough material for producing biogas (biomethane). At Sweden can be find the most of them, similarly, the used upgrading technologies several cover all version of the wide-spreading applied systems. Some characteristic plant has been introduced as follows. Green gas obtained by co-digestion of manure and organic matter has been produced in Laholm since the year 2000 [9]. The processed gas is upgraded to the proper specifications with propane before injection into the 4 bar network. The capacity of the plant is 500 nm 3 /h. The plant handles 28,000 tonnes/year animal manure and 20,000 tonnes/year of other waste materials, mainly waste from 15 different food industries). The annual production of biofertiliser is around 43,000 tonnes. The gas production from the plant is approximately GWh/year with methane content of about 75%. An upgrading plant was erected in 2000, performing in three steps of sulphur removal, carbon dioxide removal, followed by adjustment of the gas Wobbe number to the same as for natural gas by adding 5-10% propane to the gas. The gas is then introduced into the same gas line that earlier was used to distribute the raw biogas to the district heating plant. Figure 6. Biogas upgrading plant at Laholm Sweden In Helsingborg, green gas has been produced by the fermentation of waste from the food industry since Just as in Laholm, the bio-waste is first pasteurised to kill pathogenic bacteria. LPG is then added to the processed gas. The quantity of 350 m 3 /h of gas is injected into the 4 bar network. Since 2007 from two new locations had been biogas injected into the 4 24

25 bar network in Helsingborg. The two new plants have a capacity of 650 and 250 nm 3 of Green Gas per hour. The upgrading is based on PSA technology. In the town Kristianstad in the south east of Sweden biogas is produced at a co-digestion plant with a continuously stirred tank reactor. About tonnes of waste is treated annually. About 50 % of the organic material comes from liquid manure, 45 % are waste products from the food industry and 5 % comes from household waste. The raw biogas is transported in a 4 km long pipeline to the upgrading plant. Carbon dioxide is removed in a water scrubber without regeneration. Upgraded biogas leaving the system has methane content of approx. 97 % as demanded by the Swedish standard. In the same upgrading plant biogas from the sewage treatment plant, located nearby, is also treated. In 2006 a second upgrading plant was put into operation. Also this plant is based on absorption of carbon dioxide in water, but this system has regeneration of the water. Two biogas plants and two upgrading facilities give good redundancy in the system, which is very important since the Swedish natural gas grid does not serve Kristianstad. The Henriksdal sewage treatment plant processes sewage water from the inner city and of southern parts of Stockholm, resulting in an annual production of about 9 million m3 of raw biogas of around 65% methane content. In 2001 an upgrading plant was built. The upgraded gas is used as a vehicle fuel and for cooking and heating at an apartment complex, Hammarby Sjöstad, close to the sewage plant. The upgrading plant is adapted for treatment of about 1,400m3 raw gas per hour, which gives a possibility to produce around 6 million nm3 of upgraded biogas per year. The gas cleaning is carried out by water scrubbing with regeneration, where carbon dioxide and H 2 S are absorbed in water. After cleaning the water is cooled and used again while the carbon dioxide and the H 2 S are routed through the ventilation system and to the chimney of the plant. Finally, an odour additive is added to the gas to make it possible to detect leaks. The final product, the upgraded and cleaned gas, is stored at a pressure of about 350 bar. The total storage capacity is 7000 nm 3. Henriksdal also has an LNG storage (liquefied natural gas) with a capacity of nm 3 as a backup during maintenance or shut down in production or upgrading. The Bromma sewage treatment plant produces biogas from the anaerobic digestion of municipal sewage sludge. Its methane content is about 65%. From 1996 there has been a continuous project at the plant with the purpose of upgrading the biogas to vehicle fuel quality and to increase the upgrading capacity. At the sewage plant the biogas is upgraded in two parallel gas treatment lines with a total capacity of about 3.0 million m 3 cleaned gas per year (600 m 3 upgraded raw gas per hour). In the upgrading process water is first removed from the biogas by condensation to a specified dew point (<-35 Cº at 260 bar). The pressure of the gas is then increased to 5 bar pressure and H 2 S is separated in a pre-filter. Carbon dioxide is removed in the PSA process; The PSA plant has four separate synchronised adsorption columns that work in a cyclic mode changing between adsorption and regeneration. Finally, the gas is compressed to a pressure of 260 bar and is transferred to storage with a total capacity of 5000 m 3. In Gothenburg, green gas is obtained from the fermentation of sewage treatment sludge. Before this, untreated low calorific gas was distributed in the local city network. Since 2007 the gas has been upgraded to natural gas quality, and injected into the 4 bar network at a rate of 1500 m 3 per hour. From 2007 in Bjuv, 500 m 3 of green gas, obtained by co-digestion of manure and organic waste, has been injected into the gas network every hour. 25