UK gas distribution networks have started to inject biomethane into the natural gas grid in order to reduce net CO2 emissions. However, it is important that the biomethane contains low levels of impurities, particularly siloxanes (polymers containing silicon), sulphur and ammonia, which can be present as by-products from biomethane production. Siloxanes can be a problem as burning them in domestic appliances can produce deposits of silica which reduce performance over time.
Following European Commission M/475 Mandate to CEN for standards for biomethane for use in transport and injecting in natural gas pipelines, ‘CEN TC 408 Biomethane’ started writing EN 16723 to provide guidance on biomethane quality specifications.
NPL joined CEN TC 408 to understand and advise the suitable limits of impurities that could be present in the grid and for vehicle use, which have been written as EN 16723. A main concern with regards to performing the analytical measurements required to meet EN 16723 was the limit of total silicon which was eventually set at a challenging level of less than 1 mg m-3.
EN 16723 provides a list of impurities in biomethane at levels that are very challenging to measure. NPL has developed new gas standards and purity analysis methods to support these required measurements. NPL joined as a partner in EMRP Metrology for Biogas to lead two work packages and develop new method and standards for measuring several of the impurities listed in EN 16723 including siloxanes, sulphur, ammonia and BTEX (benzene, toluene, ethylbenzene and xylene). As part of this work, NPL developed a new total silicon method using GC-ICP-MS.
As part of ongoing EMPIR and Innovate UK A4I projects, NPL are supporting instrument manufacturers by validating their new commercial analysers for measuring siloxanes in biogas.
NPL has supported the UK by advising on new quality standards to replace the Gas Safety (Management) Regulations GSMR 1996 which mandates quality of the UK natural gas grid and covers gas composition. Through attendance at standardisation committee meetings and participation in European projects, NPL has developed sufficient knowledge to provide advice on UK uptake of European quality standards.
NPL has raised the issue of siloxanes in the grid with UK government departments, gas distribution networks, and appliance and boiler manufacturers. It is important to introduce a limit of total silicon in the grid in the UK as soon as possible, as currently over 100 biogas plants are already injecting biomethane into the grid which could already be reducing lifetime of home appliances.
NPL is establishing a biomethane purity laboratory (with the aim of obtaining ISO 17025 accreditation) to support the UK gas industry in showing compliance to EN 16723.