IGEM - TD/16
|Publication Date:||1 November 2019|
This Standard covers the requirements for design, construction, installation, testing, commissioning, operation, maintenance, modification and de-commissioning of Grid Entry Units (GEUs) (See Figure 2). Upgrading Plant (UP) are outside the scope of this Standard, however, consideration of the UP and its impact on the design and operation of the GEU may be appropriate.
GEU allows entry of biomethane into a gas network. Although biomethane is largely methane and has properties broadly similar to those of NG, additional steps may be required before it can be admitted into the network. Typically a GEU may be required to perform:
• Enrichment with Liquefied Petroleum Gas (LPG) (typically commercial propane).
This may be required so as to ensure that the biomethane meets the Wobbe Index (WI) and calorific value (CV) requirements of the Gas Transporter (GT), as set out in the Network Entry Agreement (NEA).
• Pressure control.
Biomethane pressures may vary and will require suitable controls to be put in place for entry into the network.
Note: Pressure regulating installations (PRIs) are covered in IGEM/TD/13.
• Flow management.
This may be required if a specified flowrate of biomethane into the network is required, or if blending of biomethane with NG is required in order to satisfy (or partially satisfy) the WI and CV requirements of the GT, as set out in the NEA.
The daily quantity of biomethane injected is required for commercial purposes, Regulatory purposes pertaining to the calculation of area calorific value, and for application of any government incentives.
Note: Metering installations are covered in IGEM/GM/8.
• Gas analysis.
This is required for the determination of calorific value and demonstration of compliance with the gas quality requirements of the GT, as set out in the NEA.
• Odorant injection.
This may be a regulatory requirement and will be stipulated by the GT, as set out in the NEA.
Note: Odorant systems are covered in IGEM/SR/16.
This is required for monitoring GEU operation, and for closure of a Remotely Operated Valve (ROV). In addition, operational data may need to be transferred at the end of the gas day.
• Rejection of off-specification gas.
This typically employs a diverter valve arrangement to redirect off-specification gas to prevent entry into the gas network.
All references to gas pressure are gauge pressure, unless otherwise stated.
Unless stated otherwise all volumes are for the real dry gas at ISO standard reference conditions of 15°C and 1.01325 bar abs.
Unless stated otherwise all energies are calculated using a gross calorific value for the real dry gas at ISO reference conditions of 15°C (combustion) and 15°C and 1.01325 bar abs (metering).
Italicised text is informative and does not represent formal requirements.
Appendices are informative and do not represent formal requirements unless specifically referenced in the main sections via the prescriptive terms "must", "shall" or "should".