FGM Applied to Grid Plate Flame Stabilisers for NOx Prediction in Non-Premixed Gas Turbine Combustion

Abstract

The present work investigates one of the lowest NOx design concepts using directly fueled grid plate flame stabilisers [10] termed Grid Mix (GM). The work uses CFD to predict experimental results for the GM low NOx flame stabilisers operated with propane. An additional study was undertaken to analyse their performance on hydrogen, a zero-carbon fuel at the heart of the UK zero-carbon power generation policy. Combustors are in production using similar technology to GM, and at least two manufacturers have low NOx hydrogen combustors using similar flame stabilisers [9, 18, 21–24]. Also, as the tests were at atmospheric pressure, the results are relevant to process burners, and the test condition for the CFD was a 140 kW thermal input process burner. The Grid Mix technique for non-premixed combustion, with fuel injected into the airflow at the periphery of the air holes, allows rapid fuel and air mixing for lean non-premixed ultra-low NOx combustion. The technology has been investigated at high entry temperatures of modern industrial gas turbines with all the combustion air passing through the flame stabiliser at a typical reference Mach number for this condition of M = 0.047, at an overall pressure loss of ΔP/P = 2.4%, for a heat release of 28MW/m2. These conditions are well above most experimental and CFD publications on low NOx gas turbine emissions. The combustion and NOx predictions for hydrogen show that Grid Mix flame stabilisers offer a viable solution to low NOx with hydrogen combustors. In addition, the advantage of adding fuel and air mixing passage downstream of the Grid Mix fuel injector is also demonstrated, as used by Yorke et al. [18].