Designing Combustion Systems for the Use of Hydrogen in Domestic Fires
Session chaired By Pr. Aimee Morgans
Decarbonising the provision of heat in domestic properties is one of the biggest challenges posed by the need to transition to net zero CO2. Currently within the UK, most properties are heated by natural gas (NG) through a combination of central heating boilers and domestic gas fires that provide secondary heat in main living spaces. The fires provide a focal point to a room through the use of a living flame concept, and hence are designed to mimic coal or wood fires with radiating flames giving a colourful visual effect. The replacement of NG with 100 % hydrogen within the gas network is currently under discussion, and this poses many challenges for domestic appliances such as boilers, fires and cookers. When operating on hydrogen, the appliances must pass safety tests, must provide a visible and attractive flame where necessary (e.g. for fires and hobs) and they must at least match the emissions levels for NOx met by the current NG versions. Since hydrogen has a higher flame speed and flame temperature than NG and is of lower visibility, the current designs for appliances cannot be used with hydrogen. New design principles need to be developed that i) avoid the possibility of flame flash back, ii) lower flame temperatures in order to meet NOx emission requirements iii) provide sufficient flame visibility to make the fire as attractive as the NG equivalent appliance, iv) provide adequate shutdown and explosion venting procedures for the use of hydrogen given its flammability limits. A key question is also whether new designs could be developed that allow the use of either NG or hydrogen within the same design (a dual fuel design). Should this be possible, such appliances could be brought to market very quickly, thus easing the transition to hydrogen when the gas network becomes ready. This however poses additional challenges since the same strategies used for reducing NOx, may lead to CO quenching when using NG. The presentation will use a case study based on domestic gas fires to show how such a dual fuel design can be met using non-premixed burners for both fuels. The design must consider important properties such as quench distance, flame temperature and heat transfer mechanisms, NOx and CO emissions, flame visibility and appearance, ignition and shut-down procedures. The project is an excellent example of using combustion theory and design in meeting the societal challenge of transitioning to low carbon fuels. It is funded through the BEIS Hy4Heat programme that is currently exploring the feasibility of transitioning the domestic gas network to hydrogen. The presentation will cover general design principles for prototype fire designs and will discuss how these affect operational, flame visibility and emissions properties for each fuel.
-
Téléchargements
-
-
Liens