2nd International Conference on Renewable Energy Gas TechnologyBarcelona, Spain 2015
Towards a measurement infrastructure for the conformity assessment of biomethane and upgraded biogas
Adriaan M.H. van der Veen1 and Jianrong Li1
1Chemistry Group,Van Swinden Laboratorium, Thijsseweg 11, 2629 JA, Delft, the Netherlands
1. Introduction
The Renewable Energy Directive 2009/28/EC [1] establishes a framework for the promotion of energy from renewable sources, thus reducing CO2 emissions and securing the supply of energy in the European Union. In its clause (2) [1], the use of renewable energy in the transport sector is referred to as a means to reduce the EU's dependence on fossil fuels. Furthermore, in clause (57) [1] the need to integrate renewable energy into existing transmission and distribution grids is stated. The use of agricultural material [1, clause (12)] is identified as having a high potential for greenhouse gas emission reduction and for having significant environmental advantages at the same time.
To promote the use of biomethane as required by 2003/55/EC [4], the properties of biomethane / biogas need to be specified. Through mandate M/475 [3], the European Commission has mandated CEN, the European Organisation for Standardisation, to draw up such specifications for biomethane for injection into the natural gas transport and distribution grids and for use as transport fuels. Access to the natural gas grids is essential for the promotion of biomethane and shall not be discriminatory [1, article 16]. In this respect, the Renewable Energy Directive supplements the requirements in directive 2003/55/EC [4].
2. Specifications
The feed stocks used for producing biogas differ substantially, as do the processes for producing the biogas and upgrading it to biomethane. The diversity of the feed stocks used to produce biogas means that a larger number of parameters than for natural gas need to be specified, in particular with respect to critical impurities. Draft specifications for biomethane for injection into natural gas grids [5] and as automotive fuel [6] are underway. Meeting these specifications is crucial for the integrity of piping networks, metering equipment, and of the end-users’ appliances.
Once finalised, these specifications need to be implemented. The producers of biomethane and upgraded biogas are responsible for demonstrating that their product meets the specifications. On the other hand, the natural gas grid owners as well as the operators of refuelling stations should accept this green gas.
3. Measurement methods and reference materials
Demonstrating that biomethane and upgraded biogas meets the specifications [5,6] requires, among others, reliable measurement and test methods of known performance. As a first step towards developing these methods, reference methods are developed in the project “Metrology for Biogas” in the European Metrology Research Programme (EMRP). These methods are in turn used to develop measurement standards which enable the production and dissemination of calibration gas mixtures (CGMs) and certified reference materials (CRMs) for calibrating instruments used in monitoring the biogas specifications.
The objectives of the project areaims to develop and validate methods for determining key impurities, moisture, particulates, calorific value, and density:
‒novel traceable methods for the measurement of the contents of key trace-level impuritiesin biogas and biomethane namely: total silicon and siloxanes, sulphur-containing compounds, aromatic hydrocarbons, halogenated hydrocarbons, ammonia, hydrogen cyanide, hydrogen chloride and carbon monoxide.
‒robust analytical capabilities for the measurement of the particulate content and water content / dew point of biogas and biomethane.
‒methods for the measurement of the calorific value, heat capacity, and density of biogas and biomethane.
‒a traceable method for determining the concentration of biomethane in samples of blended biomethane and natural gas.
‒robust methods for sampling biogas and biomethane in the field, and to enable the biogas industry to perform robust and traceable quality assessment measurements.
The project consortium is formed by 12 European National Metrology Institutes and 3 European Universities. It covers vast array of expertise and competences, necessary for carrying out the work in a 3years’ time frame. The project started on 1June2014.
4. Conformity assessment
For conformity assessment, some steps beyond the scope of the aforementioned project are needed. One of these is to develop and draft harmonised methods that enable onsite or offsite measurement of relevant properties. The frequency with which such measurements need to take place is subject to agreement between the biogas producer and receiver.
In the conformity assessment, the measurement uncertainty plays an important role. Measurement uncertainty is a parameter that informs about the accuracy (quality) of a measurement result. It is closely related to the reproducibility of a method. Measurement uncertainty is evaluated in accordance with the GUM [7]. It is, together with the specification limit and the measured value, an input necessary to do the conformity assessment [8].
Another important aspect concerns the use of appropriate CRMs and CGMs to ensure that the equipment is duly calibrated and periodically checked. In doing so, the equipment provides results that are free from significant biases, thus ensuring that the results are metrologically traceable. In the natural gas area, all results used for custody transfer and conformity assessment are metrologically traceable to ensure that they are fit for purpose.
A further issue concerns the sampling of biogas, in particular for the determination of the contents of impurities. Many of these impurities have a tendency to react or adsorb on surfaces of samplers, sampling lines, and sample collection vessels. The activities in the above mentioned project focus on assessing the compatibility and suitability of widely used means for biogas sampling, such as sampling bags and adsorption tubes. Effects such as losses, and the repeatability and reproducibility of results as a function of the storage time are studied and a good practice guide will be developed in due course.
5. Concluding remarks
The project “Metrology for Biogas” is one of the key steps in implementing the specifications EN 16723 for biogas and biomethane. It broadens the array of measurement methods used in natural gas custody transfer to address the specific issues related to the injection of biomethane and upgraded biogas into natural gas grids and for use as transport fuel.
The project serves as a step-up towards the development of European harmonised standard test methods for the parameters in biogas, not covered so far. In this development, other parties need to have their say, as the methods developed in the project “Metrology for Biogas” are developed for a different purpose and are optimised for accuracy rather than for routine conformity assessment of biomethane and upgraded biogas.
6. References
[1]Directive 2009/28/EC of the European Parliament and of the Council on the promotion of the use of energy from renewable sources, Brussels, 23 April 2009
[2]COM (2010) 639, Energy 2020, A strategy for competitive, sustainable and secure energy
[3]European Commission, Directorate-general for energy, M/475 EN, Mandate to CEN for standards for biomethane for use in transport and injection in natural gas pipelines, Brussels, 8 November 2010
[4]Directive 2003/55/EC of the European Parliament and of the Council concerning the common rules for the internal market in natural gas, Brussels, 26 June 2003
[5]European Organization for Standardization, prEN 16723-1 -- Natural gas and biomethane for use in transport and biomethane for injection in the natural gas network — Part 1: Specifications for biomethane for injection in the natural gas network, 2014
[6]European Organization for Standardization, prEN 16723-2 -- Natural gas and biomethane for use in transport and biomethane for injection in the natural gas network — Part 2: Automotive fuel specifications, 2014
[7]BIPM, IEC, IFCC, ILAC, ISO, IUPAC, IUPAP, OIML, ``Guide to the Expression of Uncertainty in Measurement, JCGM 100:2008, GUM 1995 with minor corrections'', JCGM 100:2008
[8]BIPM, IEC, IFCC, ILAC, ISO, IUPAC, IUPAP, OIML, ``Evaluation of measurement data -- The role of measurement uncertainty in conformity assessment'', JCGM 106:2012