The Kyoto Protocol on greenhouse gas emissions promotes the development of the use of biofuels in the fight against climate change, to the detriment of other fossil fuels, whose emission factors of greenhouse gases and air pollutants in general, are significantly higher.
In this sense, biodiesel is a product obtained by a process of transesterification (formation of methyl esters) of the fatty acids existing in vegetable oils (soy, sunflower, rapeseed...). Its characteristics are similar to that of diesel fuel, although it should be noted that biodiesel has a flash point considerably higher than that of diesel, which makes it much less dangerous. The percentage of sulfur is also a factor to review, since it prevents the emission of this component into the atmosphere with its corresponding environmental improvement.
From the chemical point of view, biodiesel is a mixture of methyl esters of fatty acids. The raw material, fats and oils, are mainly triglycerides of fatty acids. In Europe, the rapeseed is the main raw material, since it is the most economically available oilseed, and other vegetable oils can be used, such as: sunflower, palm, soy, etc. Other possibilities are to use low-
The transesterification reaction is a characteristic reaction of the esters, and consequently of the lipids, in which the oil or the fat reacts with fatty acids, alcohols or other esters with the exchange of the acyl groups. To promote the reaction a catalyst is used, mainly sodium methylate, soda or potash, as can be seen in the following reaction:
Glycerin is a product of the transesterification reaction and therefore its formation in the biodiesel production process cannot be avoided. The amount of glycerin that is generated is very important, representing approximately 10% of the biodiesel produced. Depending on the treatments to which the heavy current originating in the transesterification reaction is subjected, crude glycerin will be obtained, with a glycerol percentage of around 80%, or pharmaceutical grade glycerin, with a percentage of glycerol of the 99.7%. The substances that accompany glycerin are, mainly, water, salts and MONG (non-
Due to the exponential increase in biodiesel production, the crude glycerin generated in the transesterification reaction of vegetable oils is reaching large quantities. Regardless of the wide range of applications of pure glycerol in food, the pharmaceutical sector, cosmetics and many other industries, it is very expensive to refine crude glycerin to a high purity, especially for small and medium producers of biodiesel. For every 9 kg of biodiesel produced, 1 kg of crude glycerin is generated, and different ways of using crude glycerin generated by biodiesel producers are being investigated and analyzed. Due to this large amount generated, the conversion of crude glycerin into specific products that would help to reduce the production costs of biodiesel is being investigated.
An area that shows an appreciable potential to consume high amounts of glycerin is the use of glycerin for energy production. Glycerin burns well, but it has to be burned at high temperatures so that no toxic fumes of acrolein are produced, which is formed mainly between 200ºC and 300ºC.
The direct use of crude glycerin as a liquid fuel assimilable to waste oils has some drawbacks:
It has a low calorific value (between 2,800 and 3,500 kcal / kg), which makes it unable to maintain the flame in a conventional burner. This is aggravated by the presence of water in the mixture.
Its high viscosity makes it difficult to spray.
The presence of salts can cause corrosion problems in the burner nozzles and in the combustion installation itself.
The salts are flame inhibitors, which makes the combustion of glycerin difficult without using an auxiliary fuel.
BLUER has developed a glycerin incineration system consisting of causing its combustion and keeping the gases generated at a sufficiently high temperature in the presence of an excess of oxygen so that the organic compounds are completely oxidized. This oxidation needs a sufficient time to complete, so the reaction chamber is designed to allow a sufficiently long stay of the gases. For this application, it has been worked at a temperature of 1100 °C and a residence time of 2 seconds.
The combustion system developed by BLUER consists of an adequate spraying system combined with a design of the combustion chamber in order to achieve a perfect mixture of glycerin with combustion air, essential to ensure low carbon monoxide and organic compounds emisions. With this system, we are able to maintain combustion and work at temperatures of 1100 ºC using only glycerin as fuel, without the need of using any auxiliary fuel.
In the pilot glycerin incineration plant that BLUER has developed and built, we have been able to determine such important parameters as:
Minimum working temperature in the oxidation chamber.
Optimum air / glycerin ratio.
Possible intervals in the different work parameters.
Maximum achievable temperature in the oxidation chamber.
The values of gaseous emissions that have been obtained working at 1100 ºC in the combustion chamber have been:
Carbon Monoxide (CO): less than 40 ppm
Nitrogen oxides (NOx): less than 13 ppm
Sulfur dioxide (SO2): less than 1 ppm
Volatile organic compounds (VOCs): Not detected
In this pilot plant has also been able to study the problem of combustion products (emission of salts).
Pilot plant for the combustion of glicerine