US 3003857 A
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3,003,857 Patented Oct; '10, 1961 Free 3,003,857 FUEL OIL ADDITIVE William H. Carls, Jr., Chicago, Ill., assignor to The Perolin Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Nov. 4, 1957, Ser. No. 694,099
12 Claims. (Cl. 44-58) economic drawback is the tendency for rapid deposition of ash from the hot combustion gases, resulting in loss of efliciency and power output in such apparatus. This drawback is particularly serious in the case of gas turbines where ash deposition on the turbine blades so changes or alters the blade contours as to produced a rapid drop-off in efiiciency and power output of such turbines. The rate of ash accumulation on turbine blades or on boiler tubes, or other parts exposed to hot combustion gases, varies to a considerable extent from one oil to the other, depending upon ash content thereof, but with the more inexpensive residual fuel oils in which the ash content is always high, the rate of ash deposition normally encountered is likewise always rapid.
By way of illustration, it is frequently found that when using residual fuel oils in a gas turbine, the turbine can only be operated for limited periods between intermittent shutdowns for removal of ash deposits on the blades. Such shutdowns are imperative due to the rapid drop-off in efliciency and power output, and may occur as frequently as every fifty hours of operation. It is quite apparent that a power generating turbine which must be taken out of operation and cleaned as frequently as every third day becomes impractical, notwithstanding the inherent efficiency of such turbine in its initial operation and prior to ash accumulation therein. At the same time, it will be recognized that the added cost and often limited availability of distillate fuel oils of low ash content makes the use of residual fuel oils desirable for the operation of gas turbines.
Various efforts have been made in the past to add to fuel oils materials which might prevent or reduce ash deposition on gas turbine blades from hot combustion gases. To date, however, no really practical and effective solution to this gas turbine problem has been found. Some of the additives reported in the literature to be effective in minimizing such ash deposits are silicon compounds such as silicon dioxide powder, and oil soluble organic silicates such as ethyl silicate, but the observation concerning effectiveness is accompanied with the notation that such oil soluble materials are too expensive for practical purposes. In this connection, it must be borne in mind that practicability of a fuel oil additive for reducing ash deposition in gas turbines and the like, can only be evaluated in terms of an overall consideration of performance and economics of performance under actual or contemplated operating conditions. For example, the cost differential between distillate fuel oil and residual fuel oil places a very real limit on the expense that can be justified in providing an additive for residual fuel oils which will effectively control the problem of ash deposition.
I have now discovered a fuel oil additive composition which when combined with residual fuel oils in economically practical amounts will materially modify and reduce ash deposition on gas turbine blades and the like. Regarded in certain of its broader aspects, the new oil additive composition, in accordance with the present invention, comprises a mixture of an oil soluble organic silicate with an aromatic hydrocarbon or substituted hydrocarbon solvent which has the capacity to actively disperse fuel oil sludge. In such compositions the amount of aromatic solvent can be varied to a considerable extent, with suitable results being obtained when the organic solvent and silicate are present in approximately equivalent parts by weight. It should be understood, however, that the amount of solvent may vary from a minimum amount required to form a homogeneous solution with the or ganic silicate to a maximum amount which may be 4 to 5 times the amount of silicate, as for example when excess solvent is desired for its sludge dispersant action, or the like.
Various oil soluble organic silicates can be employed in the composition, including in particular the lower alkyl silicates such as the tetra-lower-alkyl orthosilicates. From the standpoint of availability and cost, tetraethyl orthosilicate, containing about 28% available SiO is particularly suitable for use in the composition. This material is commercially available from a number of sources. Another effective and commercially available organic silicate is mixed ethyl polysilicates with an average of five silicon atoms per molecule and containing about 40% available SiO The aromatic solvent employed in the composition should be a relatively high boiling, liquid, substituted naphthalene or di-substituted benzene compound, and must further be a substance which will actively disperse petroleum sludge. This physical phenomenon of actively dispersing petroleum sludge can readily be ascertained and demonstrated by bringing a small amount of heavy petroleum sludge into contact with a quantity of the solvent. A solvent which actively disperses the sludge appears to undergo violent inner agitation, and dispersion of the sludge proceeds rapidly without anyapplication of external force or agitation.
Particular types of aromatic solvents suitable for use in my new additive compositions which are commercially available include (1) aromatic solvents which contain methyl naphthalene or naphthalene fractions regardless of origin, that is, whether from coal tar such as creosote oil or from petroleum sources, (2) methylated naphthalene such as alpha methyl naphthalene, beta-methyl naphthalene, mixtures of these and derivatives thereof, and (3) chlorinated solvents such as orthodichlorobenzone.
In preparing the new fuel oil additive compositions the oil soluble silicate and aromatic solvent are blended together in the desired proportion, forming a homogeneous liquid which can be readily added to fuel oil in ap-, propriate amounts while in storage to exert its full beneficial effect when the oil is consumed. V
The amount of the additive composition to be used is based on the ash content of the particular oil being treated, and the SiO equivalent of the additive composition. In general, the amount of additive composition should be such as to provide in the treated oil about I part by weight of SiO- equivalent to each 2 to 4 parts by weight of ash as determined by analysis prior to treatment of the oil.
By way of illustration, an oil additive composition is prepared by combining equal parts by weight of tetra-1 gallon per 4000 gallons of oil for each 100 p.p.m. of ash in the untreated oil. Thus, if the ash content of a particular oil is found by analysis to be 125 ppm, the composition would be added to the oil at the rate of 1.25 gallons in each 4000 gallons of oil. At this concentration, the amount of additive composition employed provides approximately one part of SiO equivalent to each 2.85 parts of ash in the untreated oil.
Additive compositions as above described have been found by extensive testing to be generally effective as additives to residual fuel oils to retard and reduce ash deposition from combustion products thereof. Testing has included both pilot scale testing and full scale testing with a gas turbine having a power output of approximately 25,000 kilowatts.
Two comparative runs were conducted with this 25,000 kilowatt gas turbine, using the same supply of residual fuel oil with one run having no additive and the other run having additive incorporated in the fuel oil at the rate of 1 gallon per 4000 gallons of oil for each 100 ppm. of ash. The additive employed was a homogeneous solution of equal parts by weight of tetraethyl orthosilicate and a mixed methyl naphthalene fraction of petroleum origin, having a boiling range of 400 to 760 F. and also exhibiting the physical phenomenon of actively dispersing petroleum sludge. In the run using untreated oil operation was discontinued after 150 hours in view of the very substantial drop-off of thermal efficiency and power output. In the run using the additive operational data was collected for a period of 240 hours, with the turbine continuing to demonstrate highly efficient operation.
In the following tabulation there are listed comparative values, when using untreated oil (control) and treated oil (with additive), for percent of thermal efliciency and output in percent of rated load at the same time intervals:
Control run discontinued after 150 hours.
:In considering the performance demonstrated in the foregoing table, it should be borne in mind that a drop of thermal efliciency to 90% so increases cost of operation of a gas turbine as to render further operation prohibitively expensive. In the control run this point was reached somewhere between 50 and 70 hours of operation and continuation of the run to 150 hours represented a purely experimental operation which would not take place in the normal use of the turbine. The superiority of the run using treated oil is quite apparent when it is realized that even after 240 hours the turbine is operating at a thermal efficiency of 99%.
As previously noted, the amount of additive composition to be used with a particular fuel oil is basically expressed in terms of the amount of Si equivalent in the additive with reference to the amount of ash in the oil. Thus it requires a smaller amount of an organic silicate such as mixed ethyl polysilicate having an SiO equivalent of about 40% to provide the same control of ash deposition than a given amount of tetraethyl orthosilicate which has an SiO equivalent of about 28%. Expressed another way, on a weight basis an amount of additive containing higher percentage of SiO equivalent can effectively treat a larger quantity of oil. Thus, for example, with an additive composition containing equal parts by weight of a methyl naphthalene solvent and mixed ethyl polysilicate with a 40% SiO equivalent, such composition would be added to oil at the rate of about 1 gallon to 5700 gallons of oil for each ppm, of ash in the oil.
The new oil additive compositions, in accordance with the present invention, appear to act in various ways. The melting point of the ash products is considerably higher than is the case when the additive is not present, with the result that the ash has less of a tendency to fuse or sinter on turbine blades or the like. By reducing the tendency to fuse or sinter a greater proportion of ash products remain suspended in the combustion products as fine particles or dust and are discharge from the apparatus. Of the ash that does accumulate on turbine blades or the like the deposit is of a relatively loose or mechanically weak structure which is readily removed (by water wash or other means) from turbine blades or the like during periods of shutdown. In this connection, it should be noted that the ash deposits which do form when using my additive compositions are no less water soluble than the ash deposits from oils containing no additive.
The use of the new additive compositions to provide about 1 part by Weight of SiO equivalent to each 2 to 4 parts by Weight of ash is in considerable contrast to previously described efforts to use ethyl silicate alone for the reduction of ash deposition. The indication has been that ethyl silicate in the amount to provide at least 2 parts of SiO per part by weight of ash was necessary to have a beneficial effect on ash deposition. Such a proportion means using an amount of ethyl silicate at least four times greater than the amount employed with my new compositions.
The reason for this unique advantage in the new compositions, although not thoroughly understood, appears to be due in part to the dispersant action of the aromatic solvent. This view is substantiated by a carbon black dispersion test involving the following procedure:
A l-gram sample of carbon black should be added to a 200 ml. sample of diesel oil. A number of such sarnples are prepared in 8 oz. Boston Round bottles fitted with metal caps. One of these samples is used as a control and this sample will be untreated. This test permits the comparison of a number of additives, one part of each additive being added to an individual sample per 4000 parts of oil. The samples are then thoroughly shaken for two minutes and set aside for observation. The samples are observed periodically to determine whether separation and settling of the dispersed carbon particles has taken place. The number of hours before complete settling of the dispersed carbon black is re corded and is a measure of the dispersant property of the additive.
When carbon black is added according to the foregoing procedure to samples of diesel oil, diesel oil containing only tetraethyl orthosilicate as additive, and diesel oil containing a mixture of equal parts of tetraethyl orthosilicate and the bcta-methylnaphthalene as an additive, it is found that from the untreated oil and the oil containing ethyl silicate alone the carbon black completely separates in less than two hours. In the sample containing as additive the mixture of tetraethyl orthosilicate and beta-methylnaphthalene the carbon black remains suspended even after a period of twenty-four hours. It is postulated that this activity of the new additive compositions in holding carbon black in suspension is indicative of a special dispersant effect on the tetraethyl orthosilicate whereby the latter is more uniformly or homogeneously mixed with the oil as it is burned so that the silicate is in turn more uniformly mixed and reacted with ash components in the combustion gases.
The fact that my additive compositions are oil soluble and have the dispersive action above described is of real practical advantage in the use of these compositions since they can simply be added to a quantity of oil in the required amount; within a short period of time the dispersive action of the additive provides a homogeneous mixture of additive in the oil. -In contrast to this the use of a solid or slowly dissolving material would require complicated apparatus, such as mixing and metering apparatus in order to obtain a homogeneous treated oil.
Various changes and modifications in the oil additive compositions and oil treating method as herein disclosed will occur to those skilled in the art, and to the extent that such changes and modifications are embraced by the appended claims, it is understod that they constitute part of my invention.
1. A liquid additive composition for residual fuel oils for retarding ash deposition in the combustion of such oils, said composition being self-dispersing in residual fuel oil and being a homogeneous solution of an oil soluble organic silicate in an approximately equivalent amount by weight of an aromatic solvent consisting essentially of methylnaphthalene and which, apart from said solution, has as a characterizing physical property the capacity to actively disperse petroleum sludge.
2. A liquid additive composition for residual fuel oils as defined in claim 1 wherein the organic silicate is a tetra-lower alkyl-orthosilicate.
3. A liquid additive composition for residual fuel oils as defined in claim 1 wherein the organic silicate is tetraethyl orthosilicate.
4. A liquid additive composition for residual fuel oils as defined in claim 1 wherein the organic silicate is a mixed ethyl polysilicate providing about 40% Si0 equivalent.
5. A liquid additive composition for residual fuel oils as defined in claim 1 wherein the aromatic solvent is a methyl naphthalene fraction.
6. A liquid additive composition for residual fuel oils as defined in claim 1 wherein the aromatic solvent is a refined methyl naphthalene solvent.
7. A liquid additive composition for residual fuel oils as defined in claim 1 wherein the aromatic solvent is a beta methylnaphthalene fraction.
8. A liquid additive composition for residual fuel oils as defined in claim 1 wherein the aromatic solvent is an alpha methylnaphthalene fraction.
9. An improved fuel oil particularly adapted for use in gas turbines consisting essentially of a homogeneous mixture of a quantity of residual fuel oil and an amount of a liquid additive composition as defined in claim 1 to provide about one part by weight of SiO equivalent to" each 2 to 4 parts by weight of ash in said oil.
10. A liquid additive composition for residual fuel oils for retarding ash deposition in the combustion of said oils, said composition being self-dispersing in residual fuel oil and consisting essentially of a homogeneous solution of tetraethyl orthosilicate in approximately an equivalent amount by weight of a methyl naphthalene fraction.
11. A liquid additive composition for residual fuel oils for retarding ash deposition in the combustion of said oils, said composition being self-dispersing in residual fuel oil and consisting essentially of a homogeneous solution of tetraethyl orthosilicate in approximately an equivalent amount by weight of a beta methylnaphthalene fraction.
12. A liquid additive composition for residual fuel oils for retarding ash deposition in the combustion of said oils, said composition being self-dispersing in residual fuel oil and consisting essentially of a homogeneous solution of tetraethyl orthosilicate in approximately an equivalent amount by weight of an alpha methylnaphthalene fraction.
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