If possible, onsite, the gas is collected directly onto the sorbents to avoid risk of losing the impurities by adsorption onto the walls of intermediate vessels such as a sampling bags or cylinders. The sorbents are then subsequently thermally desorbed step which allows the impurities to be released from the sorbents. According to this method, the first step is to collect the gas onto adequate sorbents on which the siloxanes adsorb while the matrix passes through unretained. A thermal desorption–Gas chromatography–mass spectrometry method (TD–GC–MS, EN ISO 16017-1 7) is the analytical method proposed for the quantification of siloxanes in biomethane in ISO16723-2.
Analytical methods have been developed for many of these impurities 5, 6. Consequently, robust and reliable methods are required to enable conformity assessment. Specifications developed for biomethane ISO16723-1 3 and ISO16723-2 4 set maximum authorized concentrations for some of these impurities. Through the combustion process in engine, sulfur compounds form sulfur dioxide which has an inhibitory and aging impact on catalysts 2. Consequently, a silica layer can be formed and deposited on the spark plug, cylinder, and impeller, causing the wear and damage of the engine parts and shorten the life of the engine 1. Through the combustion process in engine, siloxanes can be transformed into silicon dioxide. Example for these impurities for biomethane are siloxanes and sulphur compounds. Non-conventional gases (biogas, biomethane, hydrogen, syngas and mixtures with natural gas) may contain impurities that can damage existing gas infrastructures and/or vehicles if they are present in too high levels in the gases. For multi-component mixtures, the best results were obtained when using the models of Lucas and Carr. The results of the evaluation of the different models showed that the correction method using the viscosity of the mixtures calculated with the model of Reichenberg and Carr showed the smallest biases for binary mixtures. Five models for the calculation of the viscosity of the gas mixtures were compared and the models were used for ten binary mixtures and four multi-component mixtures. The method has several different possible applications inclusive for the sampling of biogas and biomethane onto sorbent tubes for conformity assessment for the determination of siloxanes, terpenes and VOC in general. The method requires the correction of the flow rate using a factor based on the viscosity of the gas mixtures once the composition is accurately known. The study presents an optimised method to correct flow rates measured with a LFE flowmeter pre-set on methane while used for gas mixtures of unknown composition at the time of the measurement.
0 kommentar(er)
