Session: 03-01 Advanced Combustion Dynamics and Emission Control in Ammonia and Hydrogen Systems

Paper Number: 151612

The Effects of Secondary Air Staging Location, Pressure and Humidification on NOx Emissions for a High Ammonia Blend in Premixed Swirl Combustion 

Ammonia (NH₃) is a zero-carbon fuel which can be produced renewably, so has been gaining significant research interest in recent years. It is also found in the waste streams of all industries handling material of organic origin (e.g. agriculture, sewage, oil refining, coal coking, etc.). As ammonia is toxic, it is often destroyed rather than recovered. The Phosam process enables recovery of high purity anhydrous ammonia from industrial waste streams and has been used commercially in the steel industry.

Ammonia combustion challenges include low reactivity and a high propensity for NO_x emissions. Low reactivity can be overcome by blending with more reactive gases (e.g. hydrogen) and NO_x emissions can be reduced via staged combustion. Fortunately, hydrogen rich process gases are often a byproduct of the same industries.

This work progresses previous work that successfully combusted a 15 %_vol hydrogen rich industrial process gas (coke oven gas) with both anhydrous ammonia and humidified (30 %_vol H₂O) ammonia using a premixed swirl burner in a model GT combustor under fuel rich conditions and ambient pressure. This campaign introduces secondary air at two different locations (15 and 25 cm from the burner exit) and at two pressures (1.1 and 1.3 bara), to demonstrate relative chemical kinetic effects on emissions formation with complete combustion of these relatively complex, multicomponent fuel blends.

The equivalence ratio (Φ) was varied, both in the primary zone and globally, to evaluate the relative parametric effects on exhaust emissions. The global Φ was manipulated by substitution of a portion of the air with nitrogen of equivalent thermal capacity.

When secondary air-staging, the anhydrous blend achieved consistently lower minimised NO than the humidified blend, despite the blends having equivalent minimised emissions in the absence of secondary air. Modest pressure elevation of ~17% reduced NO entering the second stage by ~25%. Staging further downstream produced ~24 % lower NO, when operating at near atmospheric pressure.

Observations of OH* and NH₂* flame chemiluminescence indicated that flame structure was modestly influenced as the secondary staging moved upstream. Both staging locations enabled adequate secondary air mixing prior to gas sampling (CO reduced from ~6000 to <5 ppm). Increases in global Φ (above 0.7) had no measured effect on NO production.

Presenting Author: Daniel Pugh Cardiff University

Presenting Author Biography: Daniel Pugh is a senior lecturer in Engineering at Cardiff University, and director of the School’s Gas Turbine Research Centre. His research interests include fundamental and applied combustion for the development of alternative fuels.

Authors:

Sally Hewlett Cardiff University
Daniel Pugh Cardiff University
Agustin Valera-Medina Cardiff University
Burak Goktepe Cardiff University
Jon Runyon Cardiff University
Anthony Giles Cardiff University
Steve Morris Cardiff University