Inflame Desulfurization and Denoxification of High Sulfur Containing Fuels

The present invention relates to a process for the preparation of liquid fuels and the resulting fuel and, more particularly, a process that allows a high sulfur and nitrogen containing fuel to be converted into energy by combustion with a substantial reduction in sulfur oxide emissions and nitrogen oxide emissions.

Low gravity, viscous hydrocarbons found in Canada, The Soviet Union, United States, China and Venezuela are normally liquid with viscosities ranging from 10,000 to 200,000 CP and API gravities of less than 12. These hydrocarbons are currently produced either by mechanical pumping, steam injection or by mining techniques. Wide-spread use of these materials as fuels is precluded for a number of reasons which include difficulty in production, transportation and handling of the material and, more importantly, unfavorable combustion characteristics including high sulfur oxide emissions and unburned solids. To date, there are two commercial processes practiced by power plants to reduce sulfur oxide emissions. The first process is furnace limestone injection wherein limestone injected into the furnace reacts with the sulfur oxides to form solid sulfate particles which are removed from the flue gas by conventional particulate control devices. The cost for burning a typical high sulfur fuel by the limestone injection method is between two to three dollars per barrel and the amount of sulfur oxides removed by the methods is in the neighborhood of 50%. A more effective process for removing sulfur oxides from power plants comprises flue gas desulfurization wherein CaO+H.sub.2 O are mixed with the flue gases from the furnace. In this process 90% of the sulfur oxides are removed; however the cost for burning a barrel of fuel using the process is between four and five Dollars per barrel. Because of the foregoing, the high sulfur content, viscous hydrocarbons have not been successfully used on a commercial basis as fuels due to the high costs associated with their burning.

It is well known in the prior art to form oil in water emulsions for use as a combustible fuel. See for example U.S. Pat. Nos. 4,114,015; 4,378,230 and 4,618,348. In addition to the foregoing, the prior art teaches that oil in water emulsions formed from low gravity, viscous hydrocarbons can likewise be successfully combusted as a fuel. See for example British Patent Specification No. 974,042 and U.S. Pat. No. 4,618,348. The assignee of the instant application has discovered that sulfur-oxide emissions can be controlled when burning viscous high sulfur containing hydrocarbon in water emulsions by the addition of sulfur capturing additives to the emulsion composition. See U.S. Application Ser. Nos. 875,450 and 014,871.

Naturally, it would be highly desirable to develop a process for the preparation of liquid fuels and a resultant liquid fuel which, upon combustion, has a substantial reduction in sulfur oxide and nitrogen oxide emissions.

Accordingly, it is the principal object of the present invention to provide an additive for addition to a hydrocarbon fuel which, upon combustion of the fuel, acts as a sulfur and nitrogen capturing agent so as to substantially reduce the formation and emission of sulfur and nitrogen oxides.

It is a particular object of the present invention to provide a process as set forth above which is useful for hydrocarbon in water emulsions to be burned as fuels.

Further objects and advantages of the present invention will appear hereinbelow.

The present invention relates to a process for the preparation of liquid fuels and the resulting fuel and, more particularly, a process that allows a high sulfur and nitrogen containing fuel to be converted into energy by combustion with a substantial reduction in sulfur oxide emissions and nitrogen oxide emissions.

It is well known in the art to form oil in water emulsions either from naturally occurring bitumens or residual oil in order to facilitate the production and/or transportation of these viscous hydrocarbons. Typical processes are disclosed in U.S. Pat. Nos. 3,380,531; 3,467,195; 3,519,006; 3,943,954; 4,099,537; 4,108,193; 4,239,052 and 4,570,656. In addition to the foregoing, the prior art teaches that oil in water emulsions formed from naturally occurring bitumens and/or residual oils can be used as combustible fuels. See for example U.S. Pat. Nos. 4,144,015; 4,378,230 and 4,618,348.

The present invention is drawn to a process for the preparation of a liquid fuel and the resulting fuel which, upon combustion, exhibits a substantial reduction in sulfur oxide emissions and nitrogen oxide emissions. As noted above, the particular process is useful for fuels in the form of hydrocarbon in water emulsions as disclosed in co-pending Application Ser. Nos. 014,871 and 875,450.

The process of the present invention comprises admixing a sulfur and nitrogen containing hydrocarbon (either hydrocarbon residual, hydrocarbon in water emulsion, or other suitable hydrocarbon) with a water soluble additive which acts as a capturing agent for sulfur and nitrogen upon combustion of the hydrocarbon as a fuel. In accordance with the present invention, the water soluble additive consists essentially of Na.sup.+, Fe.sup.++ and an element X selected from group consisting of Mg.sup.++, Ba.sup.++, Ca.sup.++, Li.sup.+, K.sup.+ and mixtures thereof wherein Na.sup.+ is present in an amount of less than or equal to 40 wt.% based on the total weight of the water soluble additive, Fe.sup.++ is present in an amount of greater than or equal to 0.4 wt.% based on the total weight of the water soluble additive with the balance essentially element X wherein the ratio of Na.sup.+ and Fe.sup.++ is about between 7.5:1.0 to 100:1.0.

It has been found that the Fe.sup.++ addition acts as a nitrogen capturing agent thereby reducing the amount of nitrogen oxide emissions. The Na.sup.+ addition acts as a strong sulfur capturing agent for reducing sulfur oxide emissions; however, as the Na.sup.+ addition tends to be corrosive to boiler apparatuss the amount of Na.sup.+ in the additive should be limited. The remaining element X acts as a sulfur capturing agent and is used as a positive addition to complement the amount of Na.sup.+ in the additive formulation. The overall additive formulation results in an effective sulfur and nitrogen capturing additive which does not result in serious detrimental corrosion of boiler apparatus.

FIG. 1 is a bar graph showing the effect of additives on the reduction of SO.sub.2 emissions.

FIG. 2 is a bar graph showing the effect of additives on the reduction of nitrogen oxide emissions.

In accordance with the present invention, the process of the present invention is drawn to the preparation and burning of a fuel formed from a naturally occurring bitumen or residual fuel oil product. One of the fuels for which the process is suitable is a bitumen crude oil having a high sulfur content such as those crudes typically found in the Orinoco Belt of Venezuela. The bitumen or residual oil has the following chemical and physical properties: C wt.% of 78.2 to 85.5, H wt.% of 9.0 to 10.8, O wt.% of 0.2 to 1.3, N wt.% of 0.50 to 0.70, S wt.% of 2 to 4.5, Ash wt.% of 0.05 to 0.33, Vanadium, ppm of 50 to 1000, Nickel, ppm of 20 to 500, Iron, ppm of 5 to 60, Sodium, ppm of 30 to 200, Gravity, .degree.API of 1.0 to 12.0, Viscosity (CST), 122.degree. F. of 1,000 to 5,100,000, Viscosity (CST), 210.degree. F. of 40 to 16,000, LHV (BTU/lb) of 15,000 to 19,000, and Asphaltenes wt.% of 9.0 to 15.0. In accordance with one feature of the present invention, a mixture comprising water and an emulsifying additive is mixed with a viscous hydrocarbon or residual fuel oil so as to from an oil in water emulsion. The characteristics of the oil in water emulsion and the formation of same are set forth in the above-referenced co-pending applications which are incorporated herein by reference. In accordance with the present invention, an additive which captures sulfur and nitrogen and prohibits the formation and the emission of sulfur oxides and nitrogen oxides during combustion of the hydrocarbon or hydrocarbon in water emulsion fuel is added to the fuel prior to the combustion of same. The water soluble additive for use in the process of the present invention consists essentially of Na.sup.+, Fe.sup.++ and an element X selected from the group consisting of Mg.sup.++, Ba.sup.++, Ca.sup.++, Li.sup.+, K.sup.+ and mixtures thereof. In accordance with the particular feature of the present invention the Na.sup.+ is present in an amount of less than or equal to 40 wt.% based on the total weight of the water soluble additive. The Fe.sup.++ is present in an amount of greater than or equal to 0.4 wt.% based on the total weight of the water soluble additive. The balance of the water soluble additive is made up by the element X. The ratio of Na.sup.+ to Fe.sup.++ in the additive ranges from about between 7.5:1.0 to 100:1.0. The preferred formulation for the additive of the present invention used in the process of the present invention consists essentially of Na.sup.+ in an amount of between 5 to 40 wt.% based on the total weight of the water soluble additive, Fe.sup.++ in an amount of 0.4 to 2.0 wt.% based on the total weight of the water soluble additive with the balance essentially element X. It has been found that in order to obtain the desired emissions levels with respect to sulfur and nitrogen upon combustion of the fuel produced by the process of the present invention, the additive must be present in a molar ratio of additive to sulfur in the fuel of greater than or equal to 0.500 and preferably greater than 0.750.

The advantages of the present invention will be clear from consideration of the following example.

In order to demonstate the effect of the additive of the present invention on the combustion characteristics of hydrocarbon fuels containing sulfur and nitrogen, ten additive formulations were prepared. The composition of the additive formulations are set forth hereinbelow in Table I.

Each of the additives were added to various oil in water emulsions for burning as natural fuels. The fuel characteristics operating conditions and combustion characteristics for the fuels admixed with each additive are set forth below in Tables II-XI.

As can be seen from the foregoing tables, Fe.sup.++ additions to the additive has a marked effect on reducing nitrogen oxide emissions upon combustion of the fuel. The comparative effect of Fe.sup.++ on nitrogen oxide additions compared to the effect obtained from Na.sup.+ and element X (in this case magnesium) is set forth in FIG. 2. Likewise, as can be seen from the foregoing tables II-XI, Na.sup.+ has a marked effect on reducing sulfur oxide emissions when compared to iorn and the element X addition. See FIG. 1.

In addition to the foregoing, it is seen from the foregoing combustion data that the molar ratio of additive to sulfur in the hydrocarbon fuel has an effect on the reduction of SO.sub.2 and nitrogen oxide with reductions of greater than 80% in SO.sub.2 being obtained at molar ratios of additive to sulfur of greater than 0.500 and preferably greater than 0.750.

In addition to the foregoing, the combustion ash characterisitics for Emulsion 5 of Table II and Emulsion 2 of Table IX were analyzed. The compositions are set forth below in Table XII.

The ash composition employing additive 9 (a high sodium additive composition) indicates that the ash is potentially corrosive and therefore undesirable. Accordingly, the ideal additive composition in order to minimize sulfur oxide and nitrogen oxide emissions and reduce the potential for corrosion comprises Na.sup.+ in an amount of about 5 to 40 wt.%, Fe.sup.++ in an amount of between 0.4 to 2.0 wt.% with the balance essentially element X.

This invention may be embodied in other forms or carried out in other ways without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered as in all respects illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency are intended to be embraced therein.