Glycerol combustion and emissions Myles D. Bohon a,⇑ , Brian A. Metzger a , William P. Linak b , Charly J. King c , William L. Roberts a a Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695, USA b Air Pollution Prevention and Control Division, National Risk Management Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, USA c ARCADIS Geraghty and Miller Inc., Durham, NC 27709, USA Available online 25 September 2010 Abstract With the growing capacity in biodiesel production and the resulting glut of the glycerol by-product, there is increasing interest in finding alternative uses for crude glycerol. One option may be to burn it locally for combined process heat and power, replacing fossil fuels and improving the economics of biodie- sel production. However, due to its low energy density, high viscosity, and high auto-ignition temperature, glycerol is difficult to burn. Additionally, the composition of the glycerol by-product can change dramat- ically depending upon the biodiesel feedstock (e.g., vegetable oils or rendered animal fats), the catalyst used, and the degree of post-reaction cleanup (e.g., acidulation and demethylization). This paper reports the results of experiments to (1) develop a prototype high-swirl refractory burner designed for retrofit applications in commercial-scale fire-tube package boilers, and (2) provide an initial characterization of emissions generated during combustion of crude glycerol in a laboratory-scale moderate-swirl refrac- tory-lined furnace. We report a range of emissions measurements, including nitrogen oxides, total hydro- carbons, and particle mass for two grades of crude glycerol (methylated and demethylated) and compare these to No. 2 fuel oil and propane. We also present preliminary data on the emissions of select carbonyls (by cartridge DNPH). Results indicate that a properly designed refractory burner can provide the thermal environment to effectively combust glycerol, but that high particulate emissions due to residual catalysts are likely to be an issue for crude glycerol combustion. Ó 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Keywords: Glycerol combustion; Emission characterization; Bio-fuels; Burner development; Waste fuels 1. Introduction Biodiesel fuels are produced through the transesterification of triglycerides (fats, oils, or lip- ids) into fatty acid methyl esters (FAME). During this process, the triglyceride raw material reacts with an alcohol (almost always methanol) and a base catalyst (typically sodium or potassium hydroxide) to produce FAME (biodiesel) and glycerol (propane-1,2,3-triol) by-product. On a molar basis, one mole of glycerol is produced for every three moles of FAME, and volumetri- cally, approximately 10% of the initial reactants are converted to glycerol. Depending upon the feedstock and the process specifics, the glycerol 1540-7489/$ - see front matter Ó 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.proci.2010.06.154 ⇑ Corresponding author. Address: Engineering Bldg 3, Campus Box 7910, 911 Oval Drive, Raleigh, NC 27695, USA. E-mail address: mdbohon@ncsu.edu (M.D. Bohon). Available online at www.sciencedirect.com Proceedings of the Combustion Institute 33 (2011) 2717–2724 www.elsevier.com/locate/proci Proceedings of the Combustion Institute