Adding gas from biomass to the gas grid - SGC

compressibility data are provided once a month by setting switches connected to the data processor(‘flow computer’).Only at very high gas flows (about above 100,000 m 3 /hour) an on-line signal is provided to the dataprocessor. These data can be supplied by the central control post, or derived from localcompositional measurements.Energy measurementThe energy content of the gas is obtained by on-line calorimeters or calculated from compositionaldata obtained by IR or GC analysis. Since compositional data are already indispensable for theprocess control, calorimeters are becoming obsolete.6.3.4 Standards and regulationsThe measurement methods are described in a large array of national and international standards.All measurements for the custody transfer (e.g. volume flow, calorific value, composition analysis,and calculation methods) are standardised by the International Standard Organisation (ISO). Thedetermination of the other parameters is partly described in ISO standards. Most of the remainingdeterminations are described in DIN or ASTM standards. Table 31 lists the most importantstandards on gas quality control.Particles and impuritiesThe gas that is injected into the grid must be ‘technically free’ from impurities and particles. Theterm ‘technically free’ means that the gas must be upgraded to a quality that does not cause anyoperation problems if it used in certified equipment. It is difficult to set any limits for impurities andparticles since these parameters often are very difficult to measure. Therefore in some cases afiltration of the gas is prescribed and the mesh size of the filter is defined. In the Swedish standardfor biogas as vehicle fuel, a filter with maximum 5 micron mesh size is prescribed and this filter mustbe placed as close as possible to the point of injection.page: 75