Technical paper on the injection of biogas into the natural gas networks

Transcription

1 FINAL natural gas networks 0 - Introduction This paper presents the technical considerations that ENTSOG believes have to be taken care of regarding requests to inject biogas into natural gas transmission network, as well as the list of responsibilities related to the processing and control of the biogas injection process. The paper does not cover issues such as the responsibilities concerning the inlet pressure, evaluation on the global energy efficiency of the process, convenient way to consume or transport biogas and injection payment rules, which fall within the remit of the various EU member states' competent authorities. 1 Background Biogas production has seen strong growth in Europe; the creation of a lasting biomethanation sector depends on the valorisation of biogas. While the most common valorisation method is the production of heat and/or electricity, valorisation in the form of fuel and the injection of biogas into the natural gas network is also conducted. 2 Definitions Biogas: generic term used to refer to gases produced by anaerobic fermentation or digestion of organic matter. For injection into a gas network it has to be upgraded and purified (see Marcogaz, report D497). (Transmission) gas network: for the purpose of this document, system of pipelines conveying gas from the point of production or delivery (interface with another TSO, SSO or LNG terminal) to the point of use (distribution centre or industrial customer) (Gas) network operator: a European transmission system operator (TSO) 3 - Injecting biogas into the natural gas network in Europe Biogas has been injected into the European natural gas network in The Netherlands, Germany, Austria, Switzerland and Sweden for several years. In these last two countries, the injection of biogas into the natural gas network forms part of a policy to develop biomethane for vehicles. ENTSOG AISBL; Rue Ducale 83, 1000-Brussels; Tel : ; Fax: ; info@entsog.eu

2 Since 2003, European Directive 2003/55/EC has granted the injection of gases from nonconventional sources into the natural gas network when technically possible and when safety is maintained. The European Directive 2009/73/EC concerning common rules for the internal market in natural gas and repealing Directive 2003/55/EC provides supplementary rules. These rules established by this Directive for natural gas, including LNG, shall also apply in a non-discriminatory way 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 1. The application of the directives requires the safety issues surrounding the injection of biogas to be examined both on a technical and a health basis: 1. all gas infrastructure operators and/or legal authorities make the technical specifications, whose purpose is to guarantee the quality of use of the gas delivered and to safeguard the integrity of the infrastructure, public. Certain specifications may be added to those which describe the various kinds of natural gas so that the specificity of the biogas produced and its origin can be taken into consideration 2 2. the evaluation of health risks is generally carried out by competent organisations or bodies under the mandate of the regulatory authorities. The evaluation process must define the types of biogas which may be injected into the networks and, if possible, their health checks (bacteria and micro-organisms). Finally, at the time of the publication of this paper, the following ongoing European projects are covering the technical and safety conditions for biogas injection in : Mandate to CEN for standardization for biomethane for use in transport and injection in natural gas pipelines; CEN TC234 WG9: biogas quality and injection into the natural gas network; In May 2010, GERG project 1.62, on the influence of micro-organisms and trace components in biogas and the influence on gas quality requirements for green gas, was concluded. Its remarks can be used for further research on the issue, as it seems that there still exists lack of knowledge in certain areas. Specific care has to be taken by the biogas producer (or upgrading responsible) in order to protect 1 See Article I Subject matter and scope of DIRECTIVE 2009/73/EC of 13/07/ Specifications for natural gas and biogas: Calorific value, Wobbe index, density Water / Hydrocarbon dew point CO 2 content Sulphur content (total, mercaptans, H 2S + COS) content O 2 content Impurities and odorant (depending on National Regulations) Specifications for biogas not limited to: Cl, F, H 2, NH 3, CO, siloxane contents Page 2 of 9

3 the gas market against possible risks: Risk for the public health: a safe combustion has to be guaranteed for all types of appliances if upgraded and purified biogas substitutes partly or completely natural gas. Risk for the transmission network: purification procedure should secure that biogas does not contain corrosive compounds at levels greater than those foreseen for natural gas. Risk for the storage facilities (through contamination by bacteria for instance) and hence for the security of supply. Interoperability risk: if biogas injection results in gas quality being outside the specifications applied for the network, injection into the network shall be halted to avoid cross-border flows limitations. The above considerations are further analysed in the paragraphs that follow. 4 - Technical conditions for the injection of biogas into the transmission network The conditions for the injection of biogas into the natural gas transmission network are partly covered by the operators' technical specifications (see 4.3). The following paragraphs recall the main technical points which need to be defined before biogas is injected into a transmission network. 4.1 European Transmission gas networks The physical characteristics of the transmission gas networks vary for technical or safety reasons with pipe diameters in most cases from DN80 up to DN1400 and a gas pressure between approximately 16 bars up to the maximum operating pressure. For the purpose of this document, these networks include the compression stations used to pressurize natural gas but not the underground storages. In some countries, the transmission gas network is divided in functional manner in: the principal network for large volume flows that links neighbouring operators (adjacent operators and LNG terminals) and in some cases underground storages and very large industrial plants, the regional network to dispatch gas to public distributions and industrial customers. 4.2 Injection Mixture Only purified and upgraded biogases may be injected into the on the basis of the technical specifications described below ( 4.3). Biogases not fulfilling these specifications (off specs) are not accepted unless TSO accept the Page 3 of 9

4 injection of off specs biogas on a case to case basis. In this instance, the injection into the gas network allows the biogas to be mixed with the passing natural gas Injection conditions Injection into a gas network must be studied on a case by case basis as the injection conditions heavily depend on the following factors: 1. The technical specifications to be applied to the biogas where it is injected including those specifications on the quality of the gas (company technical instructions, regional or national requirements, interconnection contract, etc.), 2. The physical conditions of the natural gas established during the year (flow rate, pressure, temperature and composition) determine: the possibility of undertaking injections - mixtures or not (see 4.2), the maximum quantities of biogas which can be injected 3, the pressure, and possibly, temperature conditions to carry out the injection. Note 1: Some National authorities oblige DSOs to inject biogas into their systems even when their system can t absorb the maximum biogas quantities (network absorption capacity 4.8). This has as a result the DSOs to have to inject the excessive quantities of gas (quantities that are unable to absorb, which means a mixture of network gas plus injected biogas) into TSOs network. 3. The possible presence of "sensitive" installations (chemical companies, gas power plants, etc.) downstream of the injection point, and 4. The configuration of the gas network and its future developments. Important note: the case of biogas injection in pipelines which are connected to underground storages should be treated separately as their operators (SSO) should give their own specifications. However, current knowledge recommends that biogas should not be injected without specific treatment into underground storage facilities and, consequently, into the pipelines which feed them so as to avoid the contamination of water tables and the development of micro organisms. Oxygen can lead to corrosion and formation of elemental sulphur. Micro organisms can produce hydrogen sulphide by sulphur. Biogas injected to the network has to be free from micro organism dangerous to human being or pipeline integrity. 3 Injection should be possible during the whole year to avoid reverse compression into higher pressure stages Page 4 of 9

5 Gas network Principle and functions behind the injection of biogas into the gas network Note: the order of functions is indicative and can be different. The second compression stage to reach the discharge pressure is not shown. * odorisation and mixture of LPG (H-gas), air or nitrogen (both L-gas) are optional and depend on national regulation Health aspects The hazards for health are closely connected to the substrates used for biogas production. The MARCOGAZ recommendation 4 covers the utilisation of non-conventional sources of piped gases and gives relevant information on the potential hazards of these gases. A competent and legitimate authority in the country in which the injection point is located must be able to certify to the producer that the biogas in question does not present any risk (chemical and micro-biological) to public health, the environment or the security of the installations. This point comes from the fact that most network operators are unable to evaluate the health risk and nor can 4 Injection of Gases from Non-Conventional Sources into Gas Networks, MARCOGAZ, D497, 2006 Page 5 of 9

6 they judge whether a biogas complies or not with the types of biogas which are permitted for injection. Furthermore, it must also be possible to check the quality of the elements entering the biogas plants as they impact directly on the quality of the biogas produced. Moreover, the TSO should be informed by the party responsible for the injection of biogas if there are changes in the substrates for biogas production. Note 2: the position of the National authorities is not unanimous as some authorities do not permit biogas from sewage station sludge, town dump, industrial waste or refuse site Processing and control of the quality of the gas Shippers injecting the biogas into the network are responsible for the biogas compliance with the technical specifications and/or lease specifications. The owner of the gas quality control equipment (being the producer) must check the quality of the gas by looking at the purified and upgraded biogas. The mixture of LPG (H-gas), air or nitrogen (both L-gas) with biogas is required by some National authorities, in order to adjust the calorific value or Wobbe Index of the biogas to that of natural gas so that the biogas can be injected. The adjustment of the Wobbe Index and/or gross calorific value must be performed in line with the regulations in force. If borne by the TSOs, the related adjustment costs should be properly recognized and allocated. The gas analyses are carried out by accredited laboratories or with certified material or material which has demonstrated its reliability on the scale of threshold concentration levels which are sought. The type of analysers depends on the measured quantities if they are relevant for billing (type certified analysers) or for contractual issues (approved analysers only). For continuous checks, the time that the analysis takes must be as short as possible without altering the quality of the measurement so as to detect any non-conformity of the injected biogas as quickly as possible. The producer and the shippers have to define by bilateral agreement their roles concerning the respect of biogas quality and the conformity with technical specifications included in the Network Code. The list of contents that must be checked continuously depends on the source of biogas. However, the following content and quantity values shall be checked continuously in all circumstances: combustion parameters (gross calorific value, the Wobbe Index), and density and, the CO2, H2O, H2S and O2 content levels Page 6 of 9

7 The other content and quantity values outlined in the technical specifications may be checked through sampling in a laboratory. These checks must take place at sufficiently short intervals (on a daily or weekly basis) at the time of the biogas plant's start-up so as to detect any anomalies. The checks may take place less frequently if the installation's production meets the relevant quality and stability requirements (monthly or even annual checks). In case checks are carried out by the producer, the information exchange with the TSO must be ensured. 4.6 Odorisation (optional) If the gas network operator is responsible for odorisation, it must take control of the odorisation unit so as to comply with national regulations and the certification obligations. The producer may be required to ensure that the odorisation system is properly functioning. The injection - mixture principle also applies to the odorisation of the biogas produced by small installations (see 4.2). Note 3: Gas delivered on most of the European cross border points is not odorised. Therefore, in cases that is necessary gas from DSOs networks to be injected into TSOs networks (see 4.3 point 2), contained odorants cause a problem of compatibility with the un-odorized gas of the TSOs network Pressure (and temperature) In general, two compression stages are carried out: the compression in the purification procedure but dependant on the purification procedure adopted, then, the compression of the purified biogas (up to a discharge pressure) to carry out the injection in the gas network. A specification concerning the temperature could also be required Network absorption capacity Consumption varies on average from 1 to 10 in the winter and the summer on a gas network which supplies distribution centres. The injection of biogas is only possible if it is done at a flow rate which is below the summer flow rate. Otherwise, a part of biogas production will have to be stored, flared off or injected into networks which can absorb these quantities (as required by some National authorities). As a general rule, injection will therefore have to be carried out on gas networks with enough energy consumption demand Injection and metering station Page 7 of 9

8 A pressure regulation system which operates as a backpressure regulator (regulation of upstream pressure) must be able to modulate the injection of biogas into the natural gas network. In the future, it could be replaced by a flow rate regulator if there is a risk that the gas network's capacity could be exceeded. The gross calorific value metering and measuring equipment 5 and subsequently their data transmission systems must comply with regulations for measurement instruments. The injection station's safety and isolation means are ensured by gas network equipment in application of European standards, competent authority requirements and technical specifications which apply to the network operator. A shut-off device must be installed on the edge of the site so that the gas network operator can isolate the biogas production unit. In compliance with the draft European directive on renewable energy sources, the technical requirements of the injection and metering station is taken care of by the gas network operator. It is operated by the operator or one of its service providers and requires approved bodies to check the equipment Management of alarms and non-conformities An alert procedure must be foreseen in case the quality of the biogas becomes non-compliant. The shipper, based on producer information, must promptly inform the gas network operator (operating or dispatching manager) if he can no longer guarantee the quality of the biogas produced or if its procedure experiences a malfunction. The producer and the operator must work together to establish a procedure to manage these situations. The procedure must include a first level intervention by the producer on the injection station or the shut-off unit upstream of the natural gas network. Any costs incurred by the TSO as a result of the shipper not complying with the quality requirements should be borne by the shipper himself. A buffer capacity to check the conformity of the biogas before it is injected may be required. It is recommended when injection - mixture is not accepted. It must be dimensioned in such a way as to incorporate the measurement time of the analyzers used (see 4.5) as well as the reaction time of the shut-off equipment. 5 Roles and responsibilities The responsibilities linked to the injection of biogas into the natural gas network may be defined on 5 The Gross calorific value measurement device can be a gas chromatograph (as for natural gas) or a correlation technique device. Page 8 of 9

9 a case by case basis for each injection project or at a regional or national level by the regulatory authorities. The rules are different in European countries and responsibilities are attributed to the different actors: regulatory/ legal authorities, energy suppliers, biogas producers, network operators and third parties. The owner or operator shall be clearly defined for the following facilities: biogas processing, compression unit, injection station (regulation and safety), biogas control systems (gas quality, metering, odorisation and LPG / Air / Nitrogen mixture if needed). Finally, this document reminds that the following responsibilities for the main functions should be allocated between the different actors: the biogas production health aspects, the compliance with the technical specifications which correspond to the injection conditions (see 4.3), the quality control of the gas, its odorization (purified or mixed biogas) or deordorization (when it is necessary, note 4), the obligation of informing the adjacent TSO, adjacent SSO and the final customers of the fact that they may be supplied with biogas, and any contractual items described in the agreement between the parties. 6 Conclusions ENTSOG welcomes biogas as an additional and renewable energy source, which promotes indigenous production and supports meeting commitments towards sustainability, diversifies energy sources and contributes to security of supply. In order to further facilitate its usage, biogas is injected to natural gas systems, which requires that it is produced, upgraded and purified to the required quality according to the specifications applied for the relevant transmission system by the responsible TSO. Page 9 of 9