Based on the heat engine framework, a simple scaling theory for dust devils is proposed and compared to observations. This theory provides a simple physical interpretation for many of the observed characteristics of dust devils. In particular, it predicts the potential intensity and the diurnal variation of dust devil occurrence. It also predicts that the intensity of dust devils depends on the product of two thermodynamic efficiencies, corresponding respectively to vertical and horizontal temperature gradients.
Catalytic combustion is an emerging technology in which fuels can be combusted homogeneously supported by a catalyst. The catalyst allows non-flammable mixtures of fuel and air to be oxidized with the resulting heat generated used to initiate thermal or homogeneous combustion. With the proper catalysts the fuel can be combusted with efficiencies so high that unburned CO or HC emissions are less than 10 ppm. Furthermore, because the fuel-air mixtures are relatively lean compared to conventional processes the adiabatic temperatures are below that required for the formation of NOx i.e. > 1500°C. The success of this technology would eliminate the need for expensive after-treatment of emissions from gas fired power plants and boilers.This is a very demanding application, especially for natural gas fueled combustors, since the catalyst will have to initiate reaction between 400 and 500°C, at linear velocities exceeding 50 ft/sec, and retain its activity after experiencing temperatures up to 1400°C. Furthermore, the monolithic ceramic or metallic support upon which the catalyst is deposited must also retain structural integrity after experiencing high temperatures and severe thermal shock.This paper will describe the fundamental concepts of this new technology, the major technical problems being addressed and the progress being made.
A catalytic combustion system for advanced industrial gas turbines is under long tern development employing recent advances in catalyst and materials technologies. Catalytic combustion is a proven means of burning fuel with single digit NOx emissions levels. However, this technology has yet to be considered for production in an industrial gas turbine for a number of reasons including: limited catalyst durability, demonstration of a system that can operate over all loads and ambient conditions, and market and cost factors. The catalytic combustion system will require extensive modifications to production gas turbines including fuel staging and variable geometry. The combustion system is composed of five elements: a preheat combustor, premixer, catalyst bed, part load injector and post-catalyst combustor. The preheat combustor operates in a lean premixed mode and is used to elevate catalyst inlet air and fuel to operating temperature. The premixer combines fuel and air into a uniform mixture before entering the catalyst. The catalyst bed initiates the fuel-air reactions, elevating the mixture temperature and partially oxidizing the fuel. The part load injector is a lean premixed combustor system that provides fuel and air to the post-catalyst combustor. The post-catalyst combustor is the volume downstream of the catalyst bed where the combustion reactions are completed. At part load conditions a conventional flame bums in this zone. Combustion testing is on-going in a subscale rig to optimize the system and define operating limits. Short duration rig testing has been completed to 9 atmospheres pressure with stable catalytic combustion and NOx emissions down to the 5 ppmv level. Testing was intended to prove-out design elements at representative full load engine conditions. Subscale combustion testing is planned to document performance at part-load conditions. Preliminary full-scale engine design studies are underway.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.