Network

W hen the future of the UK gas network looked bleak in the face of a popular move towards the electrification of heat, it was saved in no small part by the UK's attachment to its gas boilers. Now those very same beloved appliances have the potential to limit that hard-won future as they constrain the range of gas sources allowed in the system. Understandably, when gas distribution companies were given innovation funding, SGN grasped the opportunity to ready the networks for future gas sources. Its project, Opening up the Gas Market, is the first gas project to be completed under the Network Innovation Competition. Importantly, it has revealed the amount of neglect prevalent in industry stand- ards, and the amount of work that will be necessary to ready the sector for the future. The proposals in the project's conclusions would represent the biggest change to the gas industry for 40 years. The purpose of the project was to widen the UK specification for gas composition to allow more sources of gas to be used in the system. With increasing imports of LNG, hydrogen and biogas likely to be adopted in the not-too-distant future, this work is a critical link between the networks of today, and those of tomorrow. To deliver this future, the project focused on "widening the Wobbe". The Wobbe Index (WI) is used to compare the rate of combustion energy output of different composition fuel gases. Two gases with the same WI are considered interchangeable. The UK is starting from a conservative point. It has one of the smallest permit- ted WI ranges, significantly smaller than elsewhere in Europe. This small range is detrimental for several reasons. The UK, as a major user of natural gas, should be an attractive market, but its current WI range excludes 90% of global LNG imports. The UK requires gas processing of these imports, adding significant costs. Wobbe Index GB WI vs EASEE-gas 47.2-51.41MJ/m 3 45.7-54.7MJ/m 3 NETWORK / 18 / DECEMBER 2016/JANUARY 2017 One of the project's principal aims was to better align the WI range with a harmonised and wider gas specification called the European Association for the Streamlining of Energy Exchange – gas (EASEE-gas), which European Union member states are currently working towards. The most significant barrier to widening the WI is the fear that using a wider range of WI gases in domestic gas appliances will result in incomplete combustion, and a buildup of carbon monoxide, the silent killer. Such a result is unacceptable, and attempts to widen the WI in the past have been abandoned. SGN planned to test new gas compositions in a representative proportion of households in the UK to track the effects on domestic appliances. Oban, a small town in Scotland, was chosen as the location for the project. SGN supplies gas to 1,104 properties on a closed network directly through vaporised LNG, making it the ideal location for experimentation with different gas compositions. The two-stage approach first involved laboratory testing of representative gas appliances, before three different LNG sources were injected into the network over a period of a year. During that period more than 300 customers' properties were visited to test how the appliances were performing. The results were conclusive: domestic and small commercial appliances, correctly installed, serviced and operated can safely burn gas with WI of up to 54.76MJ/m 3 . SGN FUTURE OF GAS KEy concluSIonS • Changing the WI range in GB would result in £325 million of avoided nitrogen ballasting costs every year • Increasing the range to 53.25MJ/m 3 would make it possible to accept more than 90% of LNG imports, up from only 10% at present • Domestic and small commercial appliances that are correctly installed, serviced and operated can safely burn gas with WI of up to 54.76MJ/m 3 • Increasing the range has negligible impact on the efficiency, performance and life of domestic or small commercial appliances • The proposed upper limit allows sufficient headroom for any deleterious unknows in the field condition of appliances • The cost of maintaining the current limits is grossly disproportionate to the risk involved in increasing the range • Using Oban as a statistical representation, it is estimated about 4% of appliances would be classified as "at risk" • Using the same representation, 2% of appliances would be classified as "immediately dangerous" • Appliance maintenance, servicing and replacement when required produces a seven-fold reduction in the absolute risk • Both the Sooting Index and the Incomplete Combustion Factor are no longer valid • CO campaigns that focus solely on CO alarms are not the most effective means of reducing CO risk • The interchangeability diagram can be simplified and updated to reflect current requirements • The Oban network safely stored, injected, distributed and used gas with WI ranging from 49 to 53.2MJ/m 3 during the trial period WhAt IS thE WoBBE IndEx? The current high WI limit was set by the then British Gas Corporation based on the work of BC Dutton in the 1970s. After privatisation of the gas industry in the early 1990s, the Dutton approach was incorporated into the Gas Safety (Management) Regulations GS(M)R in 1996 as an interchangeability diagram and has remained unchanged since then. It is based on the performance of appliances in use at the time of Dutton's studies. Concerns that incomplete combustion can occur at high WI, resulting in an increased risk of CO poisoning, and that flames can become unstable and unburned gas could be emitted from domestic appliances have maintained the status quo. However all European gas appliances sold since 1993 are tested at a much wider range of gas quality than specified in the GS(M)R. Wobbe Index = Gross calorific value Relative density

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