Patent Application
20100146841
This invention relates to a fuel for boilers and fuel oil burners based on vegetable oil.
The invention also relates to the use of this agrofuel in unmodified combustion installations of burners and boilers.
For several years, facing the threat of global warming and the gradual exhaustion of natural resources, numerous studies have been conducted on replacing fossil energy sources with renewable energy. In particular, the search is oriented toward the use of agricultural waste to create new fuels.
However, if the use of vegetable oils in substitution of fuel oil appears to be an ideal solution on the environmental plane, numerous attempts to burn vegetable oil directly or to incorporate a certain amount of it in a standard fuel oil have demonstrated significant problems: stability of the fuel, compatibility with the burners of conventional boilers, clogging of the burners because of poor combustion, or else viscosity, which currently rule out the marketing of such fuels to the general public.
Also, the purpose of this invention is to remedy the drawbacks and problems of the prior art by proposing a fuel that is based on renewable carbon, reducing greenhouse gas emissions and meeting the standards of use of the domestic fuel oils, i.e., not requiring modifications of the existing combustion installations.
For this purpose, the invention has as its object a fuel that comprises at least one vegetable oil that is purified by a process that comprises at least one stage for adsorption of peroxidized molecules, phospholipids, and water molecules on a suitable adsorbent, such as, for example, a solid aluminosilicate, active carbon, a silica, a zeolite, etc.
This purified vegetable oil has in particular the following characteristics:
The invention also relates to the use of such a fuel in a boiler that operates with domestic fuel oil, without modification of this boiler.
The invention is now described in detail.
For the most part, the vegetable oils consist of fatty acid triglycerides that have variable degrees of unsaturation according to the nature of the oleaginous vegetable that is being considered: stearic or saturated fatty acids, oleic or monounsaturated fatty acids, and polyunsaturated fatty acids.
The relative concentrations of each of these compounds impart to the oil its physico-chemical properties: stearic acid is remarkably inert chemically but crystallizes at low temperature: oleic acid remains liquid at low temperature but with a significant viscosity, and the polyunsaturated fatty acids such as linoleic and linolenic acids remain fluid at low temperatures but have a chemical instability, in particular relative to their oxidability in the presence of air.
Compared to these triglycerides, a vegetable oil contains compounds in a small proportion, such as phospholipids, peroxides, water, free fatty acids, and minor compounds such as sterols and tocopherols that have antioxidant properties. In a conventional manner, when an oil is purified, most of these minor compounds are reduced and even eliminated.
According to the invention, only a certain number of the constituent elements of the oils play a decisive role for their use as fuels.
This is the case in particular of the water content, the peroxide content, the phospholipid content, and optionally the content of free fatty acids, which influence in particular the production of soot, and therefore the clogging of the burners, as well as the stability of mixtures in storage.
To prevent any formation of deposits during the storage of the fuel, the purpose of this invention is a fuel that comprises at least one vegetable oil that is purified by a process that comprises at least one stage for adsorption of peroxidized molecules, phospholipids, and water molecules. This oil has a maximum water-in-oil content that is less than 0.3%, and preferably less than 0.1%. Actually, a very significant water-in-oil presence would lead to the formation of deposits during its storage.
Furthermore, the peroxidized compounds whose concentration is defined by the “peroxide number” are responsible for polymerization, during storage, of polyunsaturated or olefinic unsaturated compounds, obtained from vegetable oil and optionally domestic fuel oil if the vegetable oil is combined with another fuel. The peroxidized compounds are also responsible—by radical and/or cationic polymerization at the time of combustion—for the formation of gums being transformed into coal-like deposits at the burner. To prevent these problems, the fuel according to the invention comprises at least one vegetable oil whose peroxide number is less than 2 meq per kg of oil.
The phospholipids lead to phosphoric oxides whose acidity catalyzes the cationic polymerization of the peroxidized compounds, unsaturated compounds, and polyunsaturated compounds at the burner. In addition, these acidic oxides can cause the corrosion of the equipment, such as the burner, the boiler or the pipe for discharging combustion gases. So as to preclude these drawbacks, this invention calls for a fuel that comprises at least one vegetable oil with a phosphorus content that is less than 5 mg per kg of oil.
According to a particular embodiment of the invention, the vegetable oil that is contained in the fuel also has an acidic number that is less than 0.5 mg of KOH/g. Actually, even though the free fatty acids do not have a significant effect on the combustion or the storage, taking into account their natural acidity, this invention recommends a content that prevents any deposit problem during long-term storage.
The fuel according to this invention therefore comprises at least one purified vegetable oil that is characterized in particular by the following properties:
Advantageously, the other components of the raw vegetable oil, such as the tocopherols and other antioxidants, are not eliminated.
According to a preferred embodiment, the vegetable oil that is used is a canola oil. Actually, because of its mean composition (1.5 to 2% stearic acid, 56 to 62% oleic acid, 17 to 23% linoleic acid, and 9 to 12% linolenic acid), this oil offers a very good compromise between fluidity under cold conditions and chemical stability.
According to an even more preferred embodiment, the oil that is used is a purified vegetable oil, for example a purified canola oil.
According to this invention, the vegetable oil is purified by adsorption of the most polar molecules of the oil, namely the peroxidized molecules, the phospholipids and water, on a suitable adsorbent substrate, such as, for example, a solid aluminosilicate, active carbon, a silica, a zeolite, etc. Preferably, the adsorption is carried out on a solid aluminosilicate, for example such as clay, and preferably such as Tonsil, dehydrated in advance.
The process can also comprise in particular:
Advantageously, this process makes it possible to preserve in oil the sterols and the tocopherols whose antioxidant properties ensure good fuel storage properties according to the invention.
According to another aspect of the invention, the vegetable-oil-based fuel also comprises at least one domestic fuel oil that is mixed with vegetable oil.
An optimum formulation of the vegetable oil-domestic fuel oil mixture has a proportion of vegetable oil of between 5% and 50% by weight. Preferably, the vegetable oil-domestic fuel oil mixture comprises about 20% by weight of vegetable oil.
Advantageously, the fuel according to the invention has physico-chemical characteristics that are similar to regulatory characteristics of the domestic fuel oil.
The table below shows the results that are obtained with a fuel oil-oil mixture with 20% purified canola oil according to the invention, compared to the regulatory characteristics of the domestic fuel oil (modified decree of Aug. 29, 1967, January 2007 version):
The fuel according to the invention also has good thermal stability and good storage stability.
Compared stability tests, conducted on a basic domestic fuel oil and on a fuel that comprises 20% of purified vegetable oil according to the invention, both treated by conventional antioxidant additives normally used for domestic fuel oil, have shown:
This is explained in particular by the presence in the fuel according to the invention of sterols and tocopherols that originate from the vegetable oil and that have not been eliminated during the purification of the oil.
Furthermore, combustion tests with analysis of waste, carried out on different fuels according to the invention—vegetable oil-domestic fuel oil mixtures at 10%, 20%, 30% and 50% of oil—show a behavior that is comparable to that obtained with pure fuel oil. Advantageously, a reduction of the sulfur oxide emissions due to the dilution of the fuel oil by the vegetable oil that does not contain sulfur compounds is also noted. The results that are obtained are presented in the table below:
The agrofuel according to the invention can therefore be used in boilers, burners or industrial furnaces that usually operate with domestic fuel oil, without modifying the initial installation. It can be used directly or with conventional additives normally used with pure domestic fuel oil.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0755078 | May 2007 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR08/00679 | 5/15/2008 | WO | 00 | 11/16/2009 |
