Thermal Performance Analysis of Premixed Impinging Flames of Low Calorific Value Landfill Gases Blended with Hydrogen

Low calorific value landfill gases (LCV LFG) containing less than 40% CH4 is generally not suitable for industrial applications due to the low energy content, and difficulty in maintaining stable combustion. Therefore, these gases are disposed at the landfill sites by flaring or venting into the atmosphere. The objective of this study is to investigate the use of this wasted renewable energy resource for useful applications by blending with hydrogen to enhance combustion, thermal and emission performance.
The initial numerical investigations revealed that the initial temperature and pressure has a considerable effect on combustion performance of hydrogen enriched low calorific value LFG. Therefore, the combined effect of initial temperature and pressure was analysed in detail. The results showed that the combustion performance of LFG with 30 vol% CH4 enriched with 30 vol% hydrogen (BH30) has comparable performance to biogas with 60 vol% CH4 (BG60) for a range of operating conditions. The overall investigation results show that hydrogen-enriched LCV LFG could be used for industrial heating applications with the use of suitably designed combustion systems operating at low initial pressures and relatively high initial temperatures.
Based on the insight obtained from the investigation of the fundamental combustion characteristics of LCV LFG blended with hydrogen, a further numerical and experimental analysis were performed to investigate the heat transfer characteristics of impinging flames. This investigation is important to evaluate the feasibility of using these low-quality fuel mixtures for industrial heating applications where premixed impinging flames are commonly used. The numerical analysis showed that the local heat fluxes of BH30 is low compared with BG60, but sufficiently high to be used for heating applications. In order to obtain necessary heat power required for applications, the combustion systems operated with LCV gasses need to be operated with rich mixtures and high volume flowrates of premixed gases and hence maintaining stable combustion is a critical challenge. The blending of hydrogen with LCV LFG enhances the flame stability while operating with high volume flowrates because of its high reactivity and laminar burning velocity. However, it reduces the total heat power output slightly due to the low volumetric calorific value of hydrogen compared with CH4. Further experimental investigations are necessary to decide on optimal operating parameters of combustion systems operating with LCV LFG blended with hydrogen.