Fuel and related compositions – Liquid fuels – Emulsion fuel
Reexamination Certificate
2001-02-15
2002-04-23
Howard, Jacqueline V. (Department: 1764)
Fuel and related compositions
Liquid fuels
Emulsion fuel
C516S053000, C516S924000
Reexamination Certificate
active
06375689
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for producing stable emulsions of at least two substantially immiscible fluids, particularly emulsions of a liquid fuel with water, and to the apparatus used in the process.
In the present description and in the claims, the expression “emulsion of two substantially immiscible fluids” designates a heterogeneous system comprising a continuous phase, constituted by a first fluid (referenced to hereinafter as “primary fluid”), and a dispersed phase, constituted by a second fluid (referenced to hereinafter as “secondary fluid”) which is substantially immiscible with the first fluid; said dispersed phase is in the form of particles (microdroplets) with an average size of less than 5 &mgr;m. This system can optionally be stabilized by adding a suitable surfactant or mixture of surfactants. The term “emulsion” is used here to also include the above heterogeneous systems in which the dispersed phase occurs in the form of particles having very small average dimensions, generally around 1.5 &mgr;m or less, for which the term “microemulsion” can also be used. The above definition also includes emulsions constituted by a plurality of primary fluids and/or by a plurality of secondary fluids, i.e., emulsions in which the dispersed phase and/or the continuous phase are constituted by mixtures of different products.
Emulsions or microemulsions of petroleum products and water, in which particular surfactants or mixtures of surfactants are used, are known in the art.
For example, U.S. Pat. No. 3,876,391 discloses water-in-petroleum type microemulsions which use a surfactant mixture constituted by a first surfactant which is soluble in the petroleum phase and a second surfactant which is soluble in the water phase, whereto a further water-soluble additive, for example an amide, an alkanolamine, a polyamine or an aldehyde, is added. U.S. Pat. No. 4,465,494 discloses microemulsions of liquid fuels with water which contain an alcohol or an amine and use a salt of an alkylphenoxyalkanoic acid as surfactant. A fuel emulsified with water is disclosed in EP-630 398 and is obtained by mixing the components in a static mixer in particular pressure and temperature conditions in the presence of a mixture of surfactants constituted by sorbitan oleate, a polyalkylene glycol, and an alkylphenoletoxylate.
In general, the use of surfactants or other additives such as those mentioned above can entail problems because they can be inherently toxic and/or corrosive with respect to the metals with which they make contact and because toxic byproducts can form during combustion. These drawbacks are particularly evident if nitrogen-containing and/or aromatic products are used. Moreover, on the basis of the Applicant's experience, emulsions of liquid fuels and water prepared according to conventional methods by adding suitable surfactants generally entail stability problems also in optimum storage conditions; accordingly, after some time an at least partial phase separation occurs which entails many drawbacks during the combustion process due to the nonhomogeneous condition of the fuel being fed.
EP-124 061 in the name of this same Applicant discloses an apparatus and a process for forming emulsions of fluid fuels with other immiscible fluids, particularly water. The described apparatus is constituted by a turbotransducer comprising an emulsification chamber in which the fluid fuel and the water are subjected to a combined mechanical and electromagnetic action which generates, inside said chamber, a collimated corridor through which the mixed fuel and water flow. The fluids enter the emulsification chamber through an injector which imparts a turbulent motion, with a predominantly axial orientation, to the fluids. This apparatus produces a fuel for feeding burners or the like which has high energy efficiency combined with a significant decrease in polluting emissions both in terms of particulate matter and of carbon monoxide.
EP-372 353 in the name of this same Applicant discloses a process for producing stabilized emulsions of a fuel, particularly a fuel for Diesel engines, and water, with the addition of a product acting as lubricant and antifreeze, for example sorbitol monoleate. This process entails premixing the fuel, the water and the additive and then passing the resulting mixture through a turbotransducer which is similar to the one disclosed in the above-cited EP-124 061. The resulting emulsion is stable and is suitable for storage in tanks; during combustion, it has high energy efficiency and reduced toxic emissions, particularly as regards nitrogen oxides, carbon monoxide and particulate matter.
The Applicant has observed that in some cases, particularly if low-density fuels are used, the process disclosed in EP-124 061 and EP-372 353 requires a plurality of passes of the emulsion through the apparatus or the use of a plurality of apparata in series in order to transfer to the system constituted by the two immiscible liquids an amount of energy that is sufficient to break the dispersed phase, i.e. usually the water phase, into particles having dimensions which ensure high performance in terms of emulsion stability and combustion uniformity. This fact entails relatively high energy consumption and decreases the productivity of the system.
Moreover, the Applicant has observed that poor efficiency in converting the energy associated with passage through the emulsion apparatus into surface energy of the particles of the dispersed phase, and therefore in forming very fine particles, entails an overheating of the resulting emulsion (for example to temperatures above 60° C.) which causes, in some conditions, evaporation of the lighter fractions of the fuel, with consequent loss of the fluid-dynamics stability of the system and possible irregularities or interruptions in the stream entering the turbotransducer due to cavitation in the pumping system.
The Applicant has now observed that a considerable increase in the efficiency of the emulsion-forming process can be achieved by injecting the fluids to be emulsified into an emulsification chamber provided with an injection system that imparts to the fluids a motion in a direction which is substantially perpendicular to the general direction of transit of said fluids through the emulsification chamber. This injection system can be provided by means of a diffuser provided with an inlet hole, through which a stream of liquid is fed in a substantially axial direction, and at least one outlet hole, which leads into the chamber and whose axis lies on a plane which is substantially perpendicular to the direction of the inlet stream. In this manner, the stream strikes the walls of the emulsification chamber, producing a turbulent motion of the fluids which has a predominantly helical orientation and is capable of providing efficient dispersion of one fluid in the other, forming particles of the dispersed phase having an average diameter on the order of one micron or even less.
In a first aspect, the present invention accordingly relates to a process for producing an emulsion of at least one primary fluid with at least one secondary fluid, said fluids being substantially mutually immiscible, which comprises feeding a stream of said fluids into an emulsification chamber provided with an inlet for said fluids and with an outlet for said emulsion, said inlet and said outlet being arranged along a main axis of said emulsification chamber, obtaining a stream of the emulsified fluids at the outlet;
characterized in that said process comprises imparting to the stream of said fluids that enter the emulsification chamber a motion in a direction which is substantially perpendicular to said main axis of the emulsification chamber.
In a preferred embodiment of the present invention, said process comprises imparting to the stream of said fluids entering the emulsification chamber initially a motion in a direction which is substantially parallel to the main axis and then a motion in a direction which is substantially
Finnegan Henderson Farabow Garrett & Dunner
Howard Jacqueline V.
Marelli Ernesto
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