Glycerol is the main by product for making biodiesel. It is non- toxic liquid, colourless, viscous, odourless, sweet, and has thousands of uses.
Biodiesel industry has expanded the supply of glycerol is expected to reach in excess of 350,000 tons/year in the US and 600,000 tons/year in Europe. Glycerol at the moment produced for biodiesel process production such as during transesterification of triglycerides, saphonification of fats for soap making, catalysts, and alcohol and is therefore costly to refine into higher grade glycerol. For this reason glycerol market prices has drop and the biodiesel industry is challenged with possible option for the excess of glycerol. . For alternative fuel, glycerol combustion could be one of the simplest solutions. Heat recovered from glycerol oxidation could simply be use to reduce the heating cost for biodiesel production.
The environmental advantages using glycerol as a fuel source would reduce fossil fuels. Glycerol burned effectively to biodiesel would give higher demand for biodiesel and reduce the use of fossil fuels. Unlike petroleum based waste oils, glycerol is soluble in water, biodegradable, and its property gives advantages as fuel for transport and stage. Due to its water soluble property, glycerol can be easily washed away. Even the ash burning glycerol is water soluble that is easy task handling equipment and cleaning. However, presence of sodium sulfate will limit its applications, depending on concentration present. Glycerol burner can be provided by vendors supplying waste fuel burners.
Crude glycerol can become a reliable heating fuel and economical if burned properly as it has similar BTU to propane gas. Burning glycerol can create energy which can be used for electrical generation and heating applications. Also burning glycerol would reduce transportation cost as plants could burn their own glycerol on site, reduce energy costs, and act as a useful mode of disposal. The combustion of glycerol will produce 16 MJ of heat per kilogram of glycerol burned which could be provided back to the biodiesel process, another co-located system, or converted into other energy forms like electricity. Due to high cost, safety issues, and technical problems for the combustion of glycerol has been prevented for chosen solution for biodiesel industry.
Glycerol has a high auto ignition temperature of 370oC is the biggest difficulty in burning glycerol. This compared to 210oC for kerosene and 280oC for gasoline use as standard fuel. This is a problem because the glycerol has higher activation energy for the oxidation reaction and glycerol will be difficult to ignite, but kerosene can be ignited with a single spark and hold a flame in ambient air. For glycerol to burn effectively the fuel must be sprayed into a high temperature environment.
Combustion of glycerol would be a good solution, but only if it works. Burning the glycerol in a power station may be an option, but it has inefficient combustion produces pollutants and poor energy conversion. Combustion of glycerol would be difficult due to its thick, high viscous, full of oxygen, high auto ignition temperature, low heating value, and concerns of hazardous emissions. All these reasons mean it is difficult to ignite, hard to flow the product into a burner, and also maintain a flame.
Dangerous aldehyde like corrosive gas acrolein is fear to produce and it's toxic at low concentrations when glycerol is not completely combusted. Acrolein is thermal decpmpostion product of glycerol when it is heated above 280oC which below the auto ignition temperature of glycerol. Acrolein is very dangerous that it was used as a chemical weapon during World War 1, which cause serve damage to the skin. Acrolein is very flammable and unstable at high temperatures, so acrolein gases can be exhausted to the environment. For this reason biodiesel has advise not to burn glycerol. Acrolein will not be produced if it carried out at sufficient high temperature such as excess of 1000 0C and a moderately long mean residence time in the combustion chamber. Market has lack to commercialise an efficient combustion system for crude glycerol and cost benefits. The burners require constant maintain and several safety implications in running continuously. Also getting specific burners for glycerol would be a large capital cost.
Glycerol burner technology
Since burning glycerol has been inefficient, engineers have attempted to design an effective burner for glycerol for biodiesel production. Currently engineers have design a novel spray atomization swirl burner developed by DEC-NCSU that overcomes a safety and technical problems. For glycerol combustion preheating and recirculation are the important factors. Recirculation role in the flame is to increase the time in which each glycerol particle spends in hot combustion environment. Crude glycerol has been tested such as animal fat and waste soybean oil, which has successfully combusted in the burner. In this design crude glycerol does not require blending with another fuel source or pre- treatment. The design has an exceptional approach to maximise heat, preheat the combustion chamber, radical retention, and carefully mix the air and fuel flows. Very few acrolien emissions will be produce in this design which is similar to other fuel source such as kerosene.
MK Glycerin Burner is another design to come in use to burn glycerol effectively. It is the first fully automatic unit to burn 100% crude glycerol and safely. Raw glycerin could be used as a heating fuel without further refining which can be immdeditly produce and avoid transportation costs. MK Glycerin burner can operate at a really high temperature over 1500 OC which above the acrolein formation temperature. The design burner can switch change immediately from glycerin to fuel oil, to synthetic and non synthetic waste oil, to vegetable and waste vegetable oil, or even crude oil.
Balanced chemical reaction of combustion reaction of glycerol - 2 c3h8o3 + 10 o2 ===> 6 co2 + 8 h2o