Particle formation from gas cookers
Sustainable process-product development & green chemistry
Sustainable & Clean Technologies - III: Combustion & Emission (T1-6)
Keywords: particles, gas cookers, natural gas, nanoparticles
The contribution of the home environment and other life style factors in the pathogenesis of allergic disease has attracted much attention, particularly the role of indoor pollution from gas cooking appliances via nitrogen dioxide (NO2) and carbon-monoxide (CO) emissions. A recent hypothesis (1) is that the epidemiological associations between illness and nitrogen dioxide may be the consequence of confounding by particle numbers. When particles are measured as mass the greatest contribution comes from the largest particles, but the greatest number of particles by far are the submicron ones. These ultrafine particles are generated, as is NO, by the combustion process, and therefore the two pollutants (ultrafine particles and NO2) are likely to correlate closely.
It was communicated that like many other phenomena in nature, the presence of carbon nanotubes in blue combustion flames went virtually unrecognized because it was essentially unexpected (2). Observations of carbon nanotubes and related nano-forms in relatively efficient burning, mostly blue combustion flames such as propane and natural gas suggests that the proliferation of so-called clean- burning gaseous fuel sources, particularly methane-series gases (CnH2(n+1); n=1,2,3…etc) may, in fact, make a significant contribution of carbon nanocrystal forms to both the indoor and outdoor air environment. Murr et al (3) reported the presence of aggregated multiwall carbon nanotubes with diameters ranging from 3 to 30 nm and related carbon nanocrystal forms ranging in size from 0.4 to 2 m (average diameter) in the combustion streams for methane/air, natural gas/air, and propane gas/air flames from domestic (kitchen) stoves.
In this PhD study, particle formation during natural gas combustion at domestic appliances are investigated. The work involves determination of particle size distribution and chemical composition of the particles together with the total amount of particles formed. Once the particles have been identified, mechanism of formation of the particles will be studied and a model for particle formation during gas combustion will be developed.
Preliminary experiments were carried out using the gas cooker in its normal procedure - natural gas supplied from the city line and air supplied from the surroundings. There were no pots placed above the cooker. Samples were collected at ~10cm above the burner, by means of a gas ejector probe developed for particle analysis in a research program instigated to study fine particles (4). The particles were classified with a TSI Model 3080 Electrostatic Classifier with a TSI Model 3081 LDMA (Long Differential Mobility Analyzer), and/or a TSI Model 3085 NDMA (Nano Differential Mobility Analyzer). The particle concentrations were measured with a TSI Model 3775 Condensation Particle Counter (CPC). Since particle concentrations in the ambient air were changing over time and there was no experimental control over the gas quality, the repeatability of experiments was not likely. Despite changing conditions in each experiment, CPC and SMPS measurements indicated that particle concentrations increase and size distributions change right after starting the flame. However the elevated particle concentrations did not go beyond sharp peaks observed once in a while, which would indicate a release of high amount of fine particles at some instant during gas combustion. Because of the changing conditions in each experiment, it was not possible to report a trend for the size and frequency of these peaks. Before correlating these peaks directly to the gas combustion, controlled experiments are required. For this reason, a well-controlled experimental set-up is prepared. The main unit in the set-up is a steady-state operating flow reactor, with no mixing. The burner is placed at the bottom of the reactor with the required gas connections and particle free combustion air is supplied from the reactor bottom. The ignition and flow control panel of the burner is kept outside the reactor, leaving the primary air supply nozzle inside the reactor. Sampling ports are placed along the reactor to allow sampling at different locations above the flame. Experiments are carried out using filtered natural gas from the city line and will be repeated using a gas mixture simulating the natural gas in order to observe the affects of different components on particle formation. TEM studies will be carried out for the identification of the particles. In order to assure flame stability, flow velocity through the reactor is kept below 10cm/s (5). The excess air ratio of the system is kept above 10.
Initial experiments are performed as a combination of total particle counts and particle size distribution measurements at the reactor outlet, before, during and after combustion. As soon as the flame is started particle concentrations increase, giving a sharp peak. This initial peak is due to start-up of the flame and it’s outside focus of this study. Once this initial peak disappears, reactor reaches to steady state conditions. Particle, temperature and gas concentration measurements indicate that steady state is reached within ~ 50 minutes after combustion is started. Particles are detected only in the size range 2-12 nm with a nice size distribution curve.
REFERENCES
1. Seaton, A., Dennekamp, M. (2003), Thorax, 58, 1012-1015.
2. Bang, J.J., Guerrero, P.A., Lopez, D.A., Murr, L.E., Esquivel, E.V. (2004), Journal of Nanoscience and Nanotechnology, 4.7, 716- 718.
3. Murr, L.E., Bang, J.J., Esquivel, E.V., Guerrero, P.A., Lopez, D.A. (2004), Journal of Nanoparticle Research 6: 241–251,
4. Johannessen, J.T., Pratsinis, S.E., Livbjerg,H. (2000), Chem. Eng. Sci., 55(1), pp.177-191.
5. Matthews, T. G., Thompson, C. V., Wilson, D. L., Hawthorne, A. R. (1989) Environment International, 15, 545-550.
Presented Tuesday 18, 11:40 to 12:00, in session Sustainable & Clean Technologies - III: Combustion & Emission (T1-6).
