_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 220107, “Significantly Reduce Emissions Using Ammonia-Enriched Fuel Gas for Gas Turbines, ” by R. Téllez-Schmill, SPE, and T. Owodunni, SPE, KBC. The paper has not been peer reviewed. _ Within the dynamic shift toward sustainable energy, gas turbines (GTs) will assume a critical role for power generation. GTs now can operate with fuel-gas blends rich in either hydrogen or ammonia. Based on the results presented in this paper, a recommendation emerges for the refining and petrochemical industries to favor the combustion of ammonia over hydrogen for the purpose of reducing CO2 and NOx emissions. This study suggests that green hydrogen should be used to produce electricity or green chemicals instead of being burned for fuel. Evaluating CO2 and NOx Emissions from GTs While CO2 emissions are determined directly from combustion chemistry, the estimation of NOx emissions requires more-sophisticated methods. Two main paths exist to the formation of NOx in combustion systems—thermal NOx and fuel NOx. Thermal NOx usually is produced by the oxidation of nitrogen, found in air, at high temperatures. The extended Zeldovich mechanism is used widely to determine thermal NOx. Fuel NOX, on the other hand, is generated mainly by the oxidation of NH3. In the literature devoted to fuel NOx, no clear mechanism or correlation for determining fuel NOx exists, although it has been reported that pressure and equivalence ratio play important roles in conversion of fuel nitrogen to NOx. With optimized staged combustion, NOx emissions from burning 100% ammonia fuel can be reduced to as low as 9 ppm by volume. Moreover, several manufacturers are now developing GTs that burn pure ammonia, implementing some of the research findings to reduce issues around ammonia firing. In this paper, the authors focus on thermal NOx because it can be determined with reasonable accuracy and consider fuel NOx as an additive. GT Computer Model for Simulation Approach Creating an effective GT design requires a highly flexible fuel-supply system that can adjust the flow of natural gas automatically to meet changing GT loads based on a fixed hydrogen or ammonia content in the fuel gas. As operators’ aim is to optimize the proportion of GT fuel to set as hydrogen or ammonia upon the turbine’s activation, the goal is to meet site power requirements without compromising regulatory obligations for NOx and CO2 emissions. Achieving this optimization is best accomplished by simulating the GT and reviewing its performance and emissions under diverse mixture ratios. However, GT simulation involves building a GT model within a process simulation environment, which is a tedious task. The process flowsheet must combine three main unit operations: air compressor, combustor, and expander. When conducting GT-sizing sensitivity analyses, several inputs must be meticulously updated and verified. This traditional practice is inefficient and prone to human error. Parametric case studies also are time-consuming and onerous, resulting in a lack of systematic consideration for the full range of options. Even if these complications can be overcome, emission calculations, especially NOx emissions, are rarely attempted because of such difficulties.
C.P. Carpenter (Wed,) studied this question.