Abstract
Biomethane is a renewable energy gas with great potential to contribute to the diversification and greening of the natural gas supply. Ideally, biomethane can directly be injected into the natural gas grid system. For grid injection, specifications such as those in EN 16723-1 shall be met. One of the impurities to be monitored is hydrogen chloride (HCl). To assess conformity with the specification for HCl, accurate and reliable test methods are required. Here, we report the development of three novel test methods, based on a variety of laser absorption spectroscopy techniques (Direct absorption spectroscopy-DAS and wavelength modulation spectroscopy-WMS) and ion-exchange chromatography, for the measurement of HCl in biomethane. Gas mixtures of HCl in biomethane were used to demonstrate the performance of the spectroscopic systems in the nmol mol-1 to low μmol mol-1 ranges, achieving uncertainties in the 4% range, k = 2. For ion-exchange chromatography analysis, HCl was first collected on an alkali-impregnated quartz fiber filter. The analysis was performed according to ISO 21438-2 and validated using synthetic biomethane spiked with HCl. The relative expanded uncertainties for the ion exchange chromatography HCl measurements are in the 10-37% range, k = 2. The results presented for the 3 test methods demonstrate that the respective methods can be used for HCl conformity assessment in biomethane.
Highlights
There is an increased need from the European Union (EU) to diversify its energy supply, thereby targeting renewable sources such as biomethane.[1,2] Biomethane is a renewable energy gas that can be used for equipment and applications designed for natural gas, and can be injected into the natural gas network if certain specifications are met
Permeation-based hydrogen chloride calibration gas mixtures in methane were prepared at low μmol mol−1 levels and consecutively measured using the analytical method based on direct absorption spectroscopy (DAS) and 2f-WMS
The results presented for the 3 test methods, demonstrate that the respective methods can be used for hydrogen chloride (HCl) conformity assessment in biomethane with different uncertainties associated to the results depending on the method used
Summary
We describe dedicated methods for the analysis of HCl in biomethane and biogas, aiming to achieve analytical performance characteristics better than those provided by the methods specified in EN16723-1. DTDLAS is a variant of TDLAS that combines this spectroscopic technique with a special, first principles data evaluation approach to directly extract absolute species amount fraction (concentration) without calibration of the sensor with a calibration gas mixture, under the provision that a metrologically traceable line strength parameter is available.[7,11,15] Ion exchange chromatography on the other hand is an analytical technique that is widely used to measure the concentration of gases with very low limits of quantification,[16,17] and a good candidate to develop a test method for HCl concentration measurements in biomethane. Uncertainty evaluations are presented for the analytical values reported for all measurements
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