Quantification of multiple methane emission sources at landfills using a double tracer technique

A double tracer technique was used successfully to quantify whole-site methane (CH(4)) emissions from Fakse Landfill. Emissions from different sections of the landfill were quantified by using two different tracers. A scaled-down version of the tracer technique measuring close-by to localized sources having limited areal extent was also used to quantify emissions from on-site sources at the landfill facility, including a composting area and a sewage sludge storage pit. Three field campaigns were performed. At all three field campaigns an overall leak search showed that the CH(4) emissions from the old landfill section were localized to the leachate collection wells and slope areas. The average CH(4) emissions from the old landfill section were quantified to be 32.6 +/- 7.4 kg CH(4) h(-1), whereas the source at the new section was quantified to be 10.3 +/- 5.3 kg CH(4) h(-1). The CH(4) emission from the compost area was 0.5 +/- 0.25 kg CH(4) h(-1), whereas the carbon dioxide (CO(2)) and nitrous oxide (N(2)O) flux was quantified to be in the order of 332 +/- 166 kg CO(2) h(-1) and 0.06 +/- 0.03 kg N(2)O h(-1), respectively. The sludge pit located west of the compost material was quantified to have an emission of 2.4 +/- 0.63 kg h(-1) CH(4), and 0.03 +/- 0.01 kg h(-1) N(2)O. (C) 2011 Elsevier Ltd. All rights reserved

Simulations of droplet combustion under gas turbine conditions

© 2017 The Combustion Institute In various applications with recirculation, liquid droplets can be immersed in gases that may have a wide range of possible compositions, from pure air to hot combustion products. In order to gain fundamental understanding of the behaviour of individual droplets in vitiated air, numerical simulations of kerosene single droplet evaporation, autoignition, and combustion in conditions relevant to gas turbines have been performed. The droplet autoignition behaviour has been analysed in both physical and mixture fraction space for a wide range of vitiated air compositions and initial droplet diameters. Results show that the autoignition time delay decreases with increasing level of dilution with hot combustion products and decreasing initial droplet diameter. Chemistry is confined up to a radius of almost 10 initial droplet diameters and the location of autoignition is influenced by both the initial droplet diameter and the level of dilution. The time evolution of species in the gaseous phase after autoignition shows similar trends for all the diameters and dilution levels investigated here with the peak of temperature and OH mass fraction moving towards the droplet surface as a consequence of the balance between fuel production and consumption. In mixture fraction space, the location of the peaks of temperature and OH mass fraction after autoignition do not change in time whereas other intermediate species such as CH 2 O and pyrolysis products still exhibit a quite variable behaviour. The long-time flame structure has been compared with gaseous laminar counterflow simulations and, although qualitatively similar, the flame structure in the two configurations has differences with implications for flamelet combustion models used in spray combustion. The droplet evaporation, autoignition, and combustion behaviour has been summarized through a regime diagram showing the evaporation and autoignition time delays as a function of both initial droplet diameter and vitiated air dilution. This allows the identification of different states in the droplet combustion scenario and the introduction of critical values of dilution and initial droplet diameter beyond which single droplet rather than cloud combustion can occur, which can be exploited in the design of lean burn gas turbine combustion systems. The approach presented here can be easily extended to other conditions and fuels allowing the generation of regime diagrams for various operating conditions