Compositions – Gaseous compositions – Carbon-oxide and hydrogen containing
Reexamination Certificate
1999-10-28
2004-02-17
Silverman, Stanley S. (Department: 1754)
Compositions
Gaseous compositions
Carbon-oxide and hydrogen containing
C423S418200, C423S648100
Reexamination Certificate
active
06692661
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for the partial oxidation of hydrocarbons to produce gaseous mixtures comprising hydrogen and carbon monoxide, such as synthesis gas, and fuel or reducing gas.
In particular, this invention relates to a partial oxidation process which comprises the steps of:
feeding a hydrocarbon-comprising gas flow into a reaction chamber;
feeding a free oxygen-comprising gas flow into said reaction chamber.
Throughout this specification and the appended claims, the term: “hydrocarbon(s)”, is used to denote a light and/or heavy saturated and/or unsaturated hydrocarbon or hydrocarbon mixtures (e.g. C
1
-C
6
); the expression “hydrocarbon-comprising gas flow” is used to either denote a fluid which contains gaseous hydrocarbons, such as methane or natural gas, or a gaseous flow comprising suspended solid combustible (e.g., coal dust or carbon soot), or a gaseous flow comprising dispersed liquid hydrocarbons (e.g., such light or heavy hydrocarbons as naphtha or fuel oils).
In technical language, a gas flow which contains suspended liquid hydrocarbons is usually referred to as a “mist”, while a gas flow which contains dispersed solid hydrocarbons is termed a “smoke”.
The invention also concerns a burner for implementing the above process.
As is known, in the field of hydrocarbon partial oxidation there exists a pressing demand for a high yield process which can be easily implemented, and is both energy and cost efficient.
PRIOR ART
To fill the above demand, processes have been developed wherein the oxidation reaction is carried out at relatively low temperatures, on the order of 1300° C., to significantly reduce oxygen consumption and produce hydrogen and carbon monoxide more economically.
A process of this kind is described in EP-A-0 276 538, for example, wherein a hydrocarbon-comprising gas flow is first mixed with a recovered solution comprising carbon soot and then, following evaporation of the water contained in the solution, mixed with oxygen in a reaction chamber at a temperature in the 927° to 1316° C. range, the combustion to hydrogen and carbon monoxide taking place in that chamber.
While this prior process does afford a reduction in the energy consumption in the reaction chamber, as well as in the amount of oxygen to be fed into the reaction chamber, it has a number of disadvantages, as listed herein below.
First of all, the carbon soot formed from the hydrocarbons pyrolysed in the reaction chamber which, in the proximity of the burner, get in contact with and are admixed to the hot gases circulating within the chamber before they can be suitably mixed with oxygen.
This production of carbon soot is mainly disadvantageous in that a whole series of energy-intensive operations are made necessary for separating the carbon soot from the reaction products and feeding it back into the reaction chamber, that a more complicated plant is needed for implementing the process, and that capital and operating cost is high.
In addition, the carbon soot produced inside the reaction chamber affects the overall yield of the partial oxidation process, lowering the amount of hydrogen and carbon monoxide which can be obtained per unit of burned hydrocarbon, even where all the carbon soot produced and returned to the burner is gasified.
On the other hand, prior processes effective to produce low carbon soot concentrations involve operating the reaction chamber at very high temperatures (on the order of 1400° C.), and therefore, at a high rate of oxygen consumption and low conversion rate, for example as described in EP-A-0 276 538, page 2, lines 6-13.
In addition, the plants for implementing the aforementioned processes have a disadvantage in that they are inflexible in operation, being unable to accommodate the large load variations to which the reactants fed into the reaction chamber can be subjected, with the result that the variations may trigger or boost the formation of carbon soot.
It is on account of such limitations that prior art processes for the partial oxidation of hydrocarbons have involved large investment costs for their practical implementation, thereby significantly penalizing the production costs of such basic materials as hydrogen and carbon monoxide, and this in the face of a growing demand for them. Moreover, a pressing demand in the field for hydrocarbon waste matter as the residues from distillation processes in the oil industry to be burned off cannot be satisfactorily filled by the aforementioned prior processes.
SUMMARY OF THE INVENTION
The underlying technical problem of this invention is to provide an improved process for the partial oxidation of hydrocarbons, at high yield, which allows a high production of hydrogen and carbon monoxide per unit of burned hydrocarbon, while drastically lowering the formation of carbon soot even when operating at low temperatures, and is flexible and easy to implement for a reasonably low energy consumption and operating cost.
According to the present invention, the above problem is solved by a process as indicated above, which is characterized in that it further comprises the steps of:
mixing and reacting a first portion of said free oxygen-comprising gas flow with a first flow comprising reacted gases circulating within said reaction chamber;
mixing a second portion of said free oxygen-comprising gas flow with said hydrocarbon-comprising gas flow in said reaction chamber, obtaining a gas flow comprising both hydrocarbons and free oxygen at least partly mixed together;
mixing and reacting said gas flow comprising both hydrocarbons and free oxygen at least partly mixed together with a second flow comprising reacted gases circulating inside said reaction chamber, obtaining a gas flow comprising hydrogen and carbon monoxide.
Throughout this specification and the appended claims, the expression: “gas flow comprising reacted gases”, is used to denote a gas flow which contains H
2
O, CO
2
, trace hydrocarbons, H
2
S, COS, and possibly N
2
and Ar circulating inside the reaction chamber, additionally to the partial combustion products, i.e. CO and H
2
.
Advantageously, this invention enables the production of hydrogen and carbon monoxide per unit of burned hydrocarbon to be increased substantially relative to the prior art processes.
In fact, thanks to the step of mixing a portion of the free oxygen-comprising gas flow with the hydrocarbon-comprising gas flow within the reaction chamber, before the last-mentioned flow contacts the hot gases circulating inside the chamber, the formation of carbon soot during the following combustion step can be prevented or at least reduced drastically.
In this way, the conversion yield of the hydrocarbons in the reaction chamber will be only marginally—if not at all—affected by the presence of carbon soot, thereby ensuring an optimum production in hydrogen and carbon monoxide.
It should be noted that thanks to the present invention the formation of carbon soot in the reaction chamber can be totally suppressed when the flow being processed comprises gaseous hydrocarbons, and can be held down to a bare minimum even where the gas flow comprises liquid and/or solid hydrocarbons.
This result is advantageously obtainable even when operating at low temperatures, preferably in the 950° to 1300° C. range, and therefore, at a lower rate of oxygen consumption and higher yield (increased production in CO and H
2
) than the prior art.
As an example, for the partial oxidation of natural gas—in a condition of total absence of carbon soot—the oxygen requirement can be kept lower than 210 moles O
2
per kilomole of dry gas produced, which represents quite a surprising achievement compared to the requirements for oxygen of prior art processes.
In other words, the process of this invention prevents a portion of the hydrocarbons flowing through the reaction chamber from becoming mixed, in the absence of oxygen, directly with the high-temperature (e.g., in the 1000° to 1400° C. range) gases circulating within the chamber, causing the hydrocarbons to be pyrolysed and carbon soot form
Casale Chemicals SA
Johnson Edward M.
Silverman Stanley S.
Sughrue & Mion, PLLC
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