Session A – Transition fuels: natural gas and biogas

Session chair: Paul Holland, EffecTech (GB)

The session “Transition fuels: natural gas and biogas” will take place on Tuesday 18 June 2019 with the following lectures:

A.1KEYNOTE: Assessing and validating a new method of knocking characteristic determination for LNG as fuel by Martijn van Essen, DNV GL (NL)

LNG is becoming increasingly relevant and popular as a fuel in marine and road applications, owing to its increasing availability worldwide in combination with its favourable emissions characteristics and lower noise production compared with traditional hydrocarbon-based engine fuels. Gas composition variations in LNG influence the so-called knock resistance of the fuel. This parameter describes the tendency of a given fuel composition to cause ‘knocking’ in the engine during combustion. Too low fuel knock resistance induces engine knock, which can severely compromise engine performance, varying from increased pollutant emissions and reduced fuel efficiency to engine failure. The knock resistance of LNG is characterized by a methane number, which is similar to the octane number used to qualify gasoline. Several empirical methods have been developed and most of them are based on the work performed by AVL in the 1970s. To safeguard that modern engines to be used in LNG-fuels ships and trucks are matched with the expected variations in fuel composition, DNV GL developed together with an industry consortium of suppliers and engine manufacturers a next generation algorithm to calculate the methane number (Propane Knock Index Methane Number) for LNG compositions. This PKI MN is developed and tested for modern engines and shown superior performance as compared to existing methods. The algorithm is a simple polynomial equation and in contrast to existing methods straightforward to integrate in gas composition sensors for real-time methane number calculations. We programmed the PKI MN algorithm in a fast-responding, continuous correlative gas analyser. In this presentation the benefits of the novel gas analyser for monitoring the knocking index of LNG mixtures near real time will be demonstrated. For example, we demonstrate real time monitoring of the changes of the gas composition during bunkering and in the fuel line of a truck. These results are compared to measurements with a Gas chromatograph. Additionally, we will demonstrate the benefit of using a using a real time gas sensor in a feed forward fuel adaptive gas engine control system. The results we will present show that real time fuel adaptive control makes engines suited for a broad range of fuel compositions and substantial fuel savings.

A.2LNG test installation for LNG probe vaporizers by Hans-Peter Visser, ASaP (NL)

LNG is a cryogenic liquid which starts to boil at -162 °C) at atmospheric pressure. So consequently, it is very difficult to test and validate analytical LNG systems. During our daily work we are always exposed to the same standards like ISO 8943, EN 12838, GIIGNL, etc. These standards provide guidance but do not give information on how to test or the test methods they provide are not practical. As an ambitious manufacturer of complete LNG measuring systems, ASaP has developed a unique LNG test unit. This test unit will be discussed during the presentation. Together with the University of Amsterdam we have developed a performance evaluation for the equipment which is tested at our LNG testing facility. This presentation will give an overview of what has been developed.

A.3Characterization of solids in liquefied natural gas by Matthew Hammond, EffecTech (GB)

Freeze-out of certain components in LNG can result in damage to process equipment including cryogenic heat exchangers. Because of this risk, these components are removed from the feed gas, limiting their amount fraction to very low amounts. However, solid formation can still occur which can block narrow tubing within the heat exchanger. Little is known about the freeze-out conditions in multicomponent liquid hydrocarbon mixtures and such systems are complex to model. Generally, the literature contains only computational studies on binary or tertiary systems which do not fully represent real LNG. Additionally, information on the physical properties of the solids themselves is scarce. A bespoke cryostat has been designed in order to study the freeze-out components in LNG. Gas mixtures with a known composition are liquefied in the cryostat and the solids formed can be investigated using a laser imaging system. Properties of interest include particle size, size distribution, morphology and velocity. Windows in the cryostat’s sample cell give a unique look into the behaviour of the solids at typical downstream LNG conditions. Fine control over temperature and pressure, as well as composition, is beneficial in understanding the effect of process conditions on the behaviour of these particles in LNG. The experimental data collected can be compared to previous computational and experimental studies. It is hoped that this research will help to improve understanding and better manage freeze-out in LNG production at import/export facilities.

A.4Implementation of ion mobility spectrometry into micro GC for sulfur analysis in natural gas by Henk Top, DNV GL Oil & Gas (NL)

Since 2014 Agilent Technologies G.A.S. Dortmund, Gasunie and DNV GL Oil & Gas are working together to implement a more sensitive detector for the micro gas chromatograph platform. Micro GC’s are normally equipped with a (micro) thermal conductivity detector (TCD). The detection limit for this type of non-destructive detector is within the ppm range. For sulfur components, a typical detection limit is between 3 ppm and 5 ppm with a TCD. This limit is insufficient for quality control of sulfur components in natural gas or biomethane when using a micro GC. By implementing an additional miniaturized ion mobility spectrometry (IMS) based module, lower detection limits can be achieved in the ppb – ppm range. IMS is an analytical technology to separately detect gaseous compounds in the eluent of the analytical micro GC module. The separation is based on the specific drift times, that ionized compounds need to pass a fixed distance (drift tube) in a defined electric field. The ions travel at atmospheric pressure against a flow of inert drift gas to a Faraday-plate. This presentation gives an overview of the development and results of a miniaturized IMS module for the detection of H2S and COS in natural gas. Until now, multiple units were successfully installed in the field to (online) control sulfur levels in natural gas transmission pipelines.

A.5Quo vadis, biomethane conformity assessment? by Jianrong Li, VSL (NL)

The demand of renewable energy keeps increasing in EU to reduce carbon dioxide emissions and to contribute to the diversification of the European energy supply. Biomethane is a sustainable alternative to natural gas. To facilitate the use of biomethane in existing transmission and distribution infrastructures, CEN/TC 408 developed specifications (EN 16723) for injecting biomethane into the natural gas grids and using it as a transport fuel. Currently, the test methods needed for conformity assessment cited in EN 16723 are neither harmonized nor validated. They lack metrological aspects and are not specifically developed for biomethane. To address this need, ISO/TC 193/SC 1 has created a working group “Biomethane” (WG 25) to work on standardized methods. To assess conformity of biomethane with the specification and to provide essential input to WG 25 “Biomethane”, test methods are being developed for a group of parameters, mainly impurities such as siloxanes, halogenated volatile organic compounds (halo-VOCs), hydrogen chloride (HCl), hydrogen fluoride (HF), ammonia (NH3) and amines. A further objective of this research is to develop fit-for-purpose measurement standards for these parameters, to enable SI-traceable calibration and accurate measurement results. An overview of the progress made with respect to the development of measurement standards and test methods obtained at VSL is presented. These standards include static measurement standards for siloxanes and halo-VOCs, dynamic gas standards for HCl and HF, transfer standards for amines, as well as the corresponding test methods using gas chromatography and spectroscopic techniques. The work presented is pivotal for the further development of processes for conformity assessment, including (standardized) test methods. This research is carried out in close collaboration with the biogas producing and upgrading industry, regulators and biomethane testing laboratories and other end-users to ensure that the developed test methods are robust and efficient and can readily be implemented.

A.6Trace sulphur and organic compounds in biogas from different biomass sources by Serge Biollaz, PSI (CH)

Trace compounds in biogas can be a challenge for the use of biogas in energy converters. Different converters have different tolerances to various biogas contaminants such as siloxane, terpenes or sulphur compounds. In order to design robust systems for gas cleaning and energy conversion, information is needed about which compounds exist in biogas from different sources (wastewater treatment plant, biowaste digester, or agriculture anaerobic digester). Sampling campaigns at several industrial biogas production sites in Switzerland demonstrated that agricultural biogas contains a wider variety of sulphur compounds than wastewater or biowaste digester gas, including several sulphur compounds which were not detected in either the biowaste or wastewater gases. Biowaste digester gas contained more terpenes than the other two gas sources. Siloxanes are measured in wastewater gas and agricultural biogas at levels which are critical for SOFC. All samples have been taken via a liquid quench system and have been analysis offline with GC-SCD/FID or GC-ICP/MS. There is a need for reliable process monitoring in order to protect the downstream process such as fuel cells and other sensitive processes.

A.7Metrology for biomethane project: Development of standardized methods for the analysis of terpenes and ammonia in biomethane by Beatrice Sanz, RICE GRT gaz (FR)

European Commission targets specify that 20 % of the European energy consumption should come from renewable sources by 2020. One of the most promising options to reach this target is gas generation, from biomass, especially biomethane for injection into natural gas grid. EN 16723 (biomethane for injection into gas grid and use for transport fuel) presents specifications for VOCs, corrosive components and compressor oil in biomethane, impurities monitored for health and safety reasons. Currently, it proposes test methods that are neither harmonized nor validated, and usually not dedicated to biomethane. Launched in June 2017, the EMPIR project 16ENG05 Metrology for Biomethane is aimed for specific, robust and standardized analytical methods development, along with novel and improved reference standards. The project is intended for most of the parameters to be monitored when injecting biomethane into the natural gas grid and when using it as a vehicle fuel. Among the thirteen partners of the project, RICE GRTgaz is involved in the development of analytical methods for the quantification of amines, terpenes and ammonia at trace levels in biomethane. These tasks are performed with measurement standards prepared by NPL and VSL. In order to quantify these three classes of compounds in biomethane, complementary analytical methods were developed including: 1) Sampling on sorbent tubes followed by thermodesorption and gas chromatography analysis (TDS-GC-MS): two methods (amines, terpenes); 2) Micro gas chromatography (μGC): two methods (terpenes, ammonia); and 3) Optical Feedback Cavity Enhanced Absorption Spectroscopy (OFCEAS): ammonia. The development of these methods is quite challenging as they will have to reach the specifications listed in the EN 16723: 10 mg/Nm3 for both amines and ammonia. In the field of this presentation, four of the five developed methods (terpenes and ammonia) will be described and compared in terms of limits of quantification, costs and ease of use.

A.8Realization of a traceable laser-based quantification method for HCl in biomethane by Javis Nwaboh, PTB (DE)

For ecological reasons, there is an increased need to diversify EU natural gas supply, targeting renewable energy sources such as biomethane. For quality control, the standard EN 16723-1 for biomethane to be injected into natural gas grids provides limit values (e.g. < 1 mgCl/m3 for chloride compounds; note that 1 ppm hydrogen chloride (HCl) is approx. 1,5 mg/m3 at 25 °C and 1 atm) for impurities in biomethane. A limit value is required for e.g. HCl to minimize the effects due to the potential formation of corrosive hydrochloric acid when it comes into contact with water vapour. In the EMPIR biomethane project, accurate and reliable test methods are being developed for impurities of chloride compounds, such as HCl in biomethane. Laser spectroscopic techniques such as direct tunable diode laser absorption spectroscopy (dTDLAS) can provide a unique option to develop accurate and reliable in-situ HCl test methods for biomethane. dTDLAS is a variant of tunable diode laser absorption spectroscopy (TDLAS) which combines this spectroscopic technique with a special, first principles data evaluation approach to directly extract traceable absolute gas species amount fractions. This is the principle of an optical gas standard (OGS), which comes with no need for calibration with reference gases (an instrument similar to the Ozone standard photometer). Laser spectrometers based on dTDLAS have been tested and metrologically validated in a variety of applications. We present a first lab-based realization of our new dTDLAS HCL sensor, specially designed and developed to realize a traceable test method for HCl amount fraction measurements in biomethane. This sensor can, with some modifications, be operated as an OGS. The sensor is equipped with an interband cascade laser (ICL) emitting at 3,6 µm and targets nmol/mol to µmol/mol HCl amount fractions in biomethane. The design and optimization towards application in biomethane is discussed. HCl amount fraction results are presented to demonstrate the current performance of the sensor. The traceability of the results to the SI is addressed and an uncertainty budget for the dTDLAS amount faction results is presented.

 

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