Combustion – Process of combustion or burner operation – Feeding flame modifying additive
Reexamination Certificate
2000-04-25
2003-02-18
Price, Carl D. (Department: 3743)
Combustion
Process of combustion or burner operation
Feeding flame modifying additive
C431S011000, C431S354000, C239S427000, C239S432000, C239S553300, C239S590500, C239S008000
Reexamination Certificate
active
06520767
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the combustion of fuels and more particularly to the efficient combustion of compressible fluid fuel.
BACKGROUND OF THE INVENTION
Efficient combustion of liquid fuels usually involves creating fine liquid droplets or vaporizing the liquid to the gaseous state and thereafter mixing the fuel with air or oxygen in order to initiate and sustain combustion. As disclosed and claimed in our co-pending United States Patent Application Serial No. 08/992,983, now U.S. Pat. No. 6,010,544, the contents of which are incorporated herein by reference, an alternative approach involves forming a supercritical water/hydrocarbon fuel mixture. As taught in that patent, a water/hydrocarbon fuel mixture is heated and pressurized to a level at or above the critical point of the mixture. At critical conditions, the mixture is a homogeneous single phase that can be combusted in a more efficient manner and with considerably reduced undesirable emissions. As further taught therein, the critical temperature of the mixture is at or above approximately 363° C. and the critical pressure is at or above 3000 psi. Optimal conditions are considered to be 390° C. and 4000 psi.
As disclosed and claimed in our co-pending U.S. patent application Ser. No. 09/359,509, now U.S. Pat. No. 6,240,893, the contents of which are incorporated herein by reference, another alternative approach involves forming a sub-critical water/hydrocarbon fuel mixture which is at a pressure that is below the critical pressure charactistic of the mixture and is at a temperature that is at least the greater of about 250° C. and the boiling point of water at the mixture pressure. As taught in that application, a water/hydrocarbon fuel mixture is pressurized to a level below the critical point of the mixture and heated to a temperature that is at least the greater of about 250° C. and the boiling point of water at the mixture pressure. The specified sub-critical mixture provides a local environment of water molecules, tending to limit hydrocarbon polymerization and other undesrable side reactions and keeping the hydrocarbon from precipitating from the mixture. At these specified sub-critical conditions, combustion of the mixture provides a “cleaner” combustion with considerably reduced particulate matter and oxides of nitrogen emissions compared with that which results from the combustion of otherwise comparable water-hydrocarbon mixtures at temperatures below the boiling point of water at the sub-critical pressure employed.
In some applications, the high pressure and temperature of the supercritical mixture or the above-specified subcritical mixtures are directly suitable for injection into a combustion chamber. In other applications, the high pressure of these water/hydrocarbon fuel mixtures result in subsequent fuel/air flow velocities higher than the flame speed of the combustible mixture. Flow velocities which far exceed the flame speed lead to difficulties with ignition and flame stabilization. Thus, for applications such as nearly atmospheric pressure oil burners the fuel/air mixture flow velocity must be reduced by lowering both the pressure and velocity.
A valve could be used to lower the flow velocity since it provides for a variable size orifice, but some of total pressure ahead of the valve is recovered in the velocity downstream of the valve and a valve also introduces increased thermal mass and dwell time. Furthermore, after the fluid passes through the valve its temperature and pressure change dramatically and the fluid's metastable condition can be adversely affected by these changes in the length between the valve and the combustion process. Other solutions to for lowering flow velocity are thus needed.
SUMMARY OF THE INVENTION
In one aspect, the fuel system of the invention includes structure containing a mixture of water and hydrocarbon fuel in which the mixture is at or above its critical temperature and pressure such that the mixture is a homogeneous single phase. Apparatus is provided for rapidly reducing the total pressure of the mixture prior to delivery to a combustion chamber. In another aspect, the invention is a process for combusting a hydrocarbon/water mixture including the steps of producing a mixture of water and hydrocarbon fuel at or above its critical point such that the mixture is a homogeneous single phase and rapidly reducing the pressure of the mixture without an excessive change in the velocity. Thereafter, the reduced pressure mixture is delivered into a combustion chamber. In this aspect, it is preferred that the mixture be maintained at a temperature above 363° C. and at a pressure above 3000 psi before reduction. It is preferred that the pressure reduction occur within a time period less than 1 millisecond prior to being delivered to the combustion chamber and that the pressure be reduced to below 200 psi for atmospheric combustion. The temperature of the supercritical mixture may be in the range of 363° C.-450° C. and in a pressure range of 3000 psi 4500 psi. It is also preferred that the pressure reduction take place within a time period in the range of 0.1-2 milliseconds prior to being delivered to a combustion chamber and that the total pressure be reduced to a range of 2 to 10 times the pressure in the combustion chamber.
In another aspect, the fuel system of the invention includes structure containing a sub-critical water/hydrocarbon fuel mixture which is at a pressure that is below the critical pressure characteristic of the mixture and is at a temperature that is at least the greater of about 250° C. and the boiling point of water at the mixture pressure. Apparatus is provided for rapidly reducing the pressure of the mixture prior to delivery to a combustion chamber. In another aspect, the invention is a process for combustion of a sub-critical hydrocarbon/water mixture of the above-specified characteristics and rapidly reducing the pressure of the mixture. Thereafter, the reduced pressure mixture is delivered into a combustion chamber. In this aspect, it is preferred that the mixture be maintained at a temperature that is between about 25° C. and about 100° C. greater than the boiling point of water at the mixture pressure. It is preferred that the pressure reduction occur within a time period less than 1 millisecond prior to being delivered to the combustion chamber and that the pressure be reduced to below 200 psi for combustion at up to 10 atmospheres of pressure. It is also preferred that the pressure reduction take place within a time period in the range of 0.1-2 milliseconds prior to being delivered to a combustion chamber and that the pressure be reduced to a range of 200-500 psi. for combustion at 10 to 20 atmospheres
Apparatus is provided for rapidly reducing the total pressure of the mixture prior to delivery to a combustion chamber. In another aspect, the invention is a process for combusting a hydrocarbon/water mixture including the steps of producing a supercritical or specified sub-critical mixture of water and hydrocarbon fuel and rapidly reducing the pressure of the mixture. Thereafter, the reduced pressure mixture is delivered into a combustion chamber. In this aspect, it is preferred that a supercritical mixture be maintained at a temperature above 363° C. and at a pressure above 3000 psi. It is preferred that the pressure reduction occur within a time period less than 1 millisecond prior to being delivered to the combustion chamber and that the pressure be reduced to below 200 psi for combustion at 1 to 10 atmospheres. The temperature of the supercritical mixture may be in the range of 363° C.-450° C. and in a pressure range of 3000 psi-4500 psi. It is also preferred that the pressure reduction take place within a time period in the range of 0.1-2 milliseconds prior to being delivered to a combustion chamber and that the pressure be reduced to a range of 200-500 psi for combustion at 10 to 20 atmospheres.
In another aspect, the apparatus for reducing the total pressure of the supercritical or specified sub-critical mix
Ahern Brian S.
Haldeman Charles W.
Choate Hall & Stewart
Nugent Elizabeth E.
Price Carl D.
Supercritical Combusion Corporation
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