Influence of Degree of Unsaturation on Combustion Efficiency and Flue Gas Emissions of Burning Five Refined Vegetable Oils in an Emulsion Burner

Abstract

This work presents experimental studies performed on a low-pressure auxiliary air fluid pulverization burner fueled with refined vegetable oils to research the impact of the fatty acid profile on combustion and regulated emissions. The vegetable oils used were coconut, palm, rapeseed, sunflower, and soya. First, the fatty acid profile and the degree of unsaturation of these vegetable oils were determined by high-resolution nuclear magnetic resonance spectroscopy. The physicochemical properties (density, kinematic viscosity, heating value, and elemental analysis) were also determined and correlated with the degree of unsaturation. It was found that the higher heating value of vegetable oils increases as the degree of unsaturation also increases. In this experimental study, the influence of varying fuel flow rate at three input air flows on combustion efficiency and flue gas emissions was investigated. The nitric oxide and carbon oxide emissions obtained in all the tests performed are well below the permitted minimum levels. Combustion efficiencies equal to or above 80% were achieved for soya, sunflower, and rapeseed oils. A comparison between the degree of unsaturation of the vegetable oils and some combustion parameters is also established. In most of the experiments carried out, it was found that carbon oxide emissions decrease and combustion efficiency increases as the degree of unsaturation of vegetable oils increases.

Statistical Study of Combustion Characteristics and Optimal Operation Factor Determination in an Emulsion Burner Fueled with Vegetable Oils

“…VOs are triacylglycerols whose fatty acids profile displays different substitution patterns with regard to length, degree of unsaturation and chain geometry of the hydrocarbon chains. The fatty acid composition of each VO is unique, affects the state of aggregation, and impacts the physical properties such as density, viscosity and heating value [23,[25][26][27][28]. As a result, fatty acid composition determines the VO's behaviour during the combustion process, as recently shown by [28]…”

“…First, a descriptive study of the variables involved in the combustion process was Furthermore, high viscosity values give rise to poor fuel atomization, incomplete combustion and unburned hydrocarbon formation, which could explain the positive correlation between CxHy and viscosity. As regards the negative correlation between viscosity and the lower heating value (LHV), San José et al [23] observed that the LHV of several VOs, rich and poor in unsaturated fatty acids, increased as the DU (Table 2) increased, contrary to viscosity. In contrast, direct correlation between LHV and viscosity in FAMEs (biodiesel) has been established by some researchers [25][26][27][28] Due to the significance of most of the interaction effects, it is essential to analyse interaction plots (Figures 2-6).…”

“…San José et al [21] showed that the use of a low-pressure auxiliary air fluid pulverization burner is the best option for burning liquid fuels, such as VOs, with a kinematic viscosity between 26 and 112 mm 2 •s -1 (at 50 ºC). Using this burner, which operates with an injection pressure of 1x10 5 Pa, the authors carried out the combustion of VOs, rich in unsaturated fatty acids (SfO, RpO, SyO) as well as CnO and PlO with a high content of saturated fatty acids [22,23]. A relationship between the VOs' degree of unsaturation and certain combustion parameters was established in these works, which found that CO emissions decreased and that combustion efficiencies increased as the degree of VO unsaturation rises [23].…”

Descriptive Statistical Analysis of Vegetable Oil Combustion in a Commercial Burner to Establish Optimal Operating Conditions

“…where, Cp g means specific heat of flue gases at constant pressure for flue gas temperature (kJ/kg fuel • • C), m 1 g mass of non-stoichiometric flue gas per kg of combustible. Both parameters were calculated as procedure described in [24,26]. t a and t g are combustion air temperature and flue gas temperature at output, in ( • C), respectively.…”

“…Both variables were measured directly in gas analyzer. In an effort to ensure the experimental results were obtained in the same facility operating conditions, a test method previously described by our research group was used [24]. Once the facility was put into a steady state with diesel, the burner operation parameters were established (fuel and air flow rates) and the facility was run with the VO pre-heated to 40 • C for about two minutes until steady state was reached.…”