US 3689238 A
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United States Patent 3,689,238 INHIBITOR INJECTION Russell F. Stedman, Des Plaines, Ill., assignor to Universal Oil Products Company, Des Plaines, Ill. No Drawing. Filed Oct. 16, 1970, Ser. No. 81,511 Int. Cl. C23f 11/02; F17d 1/02 U.S. Cl. 48-190 7 Claims ABSTRACT OF THE DISCLOSURE Injecting an inhibitor into a vapor stream by dissolving the inhibitor in a liquefied petroleum gas and thereafter dispersing the same as an aerosol into the vapor stream.
tors is that the inhibitors are usel in small amounts as,
for example, in parts per million, and extreme care is necessary to properly introduce the small quantities in a manner that the inhibitor will be uniformly dispersed in the stream in order to satisfactorily serve the desired purpose.
These difficulties are further complicated when the inhibitor is utilized in a vapor stream. Generally there is a minor liquid phase in which the inhibitor becomes dissolved. Accordingly, the inhibitor does not become distributed uniformly throughout the stream and does not adequately serve to inhibit corrosion.
DESCRIPTION OF THE INVENTION The present invention proposes a novel method of injecting an inhibitor into a vapor stream. This is accomplished by introducing the inhibitor as an aerosol and thereby uniformly dispersing the inhibitor in the vapor stream. Thus, the inhibitor is completely dispersed and effectively serves the desired purpose. As mentioned above, the inhibitor is required only in minute quantities and, in the novel method of the present invention, is utilized efiiciently for maximum protection.
In one embodiment, the novel method of the present invention is utilized to inject a corrosion inhibitor into the vapor stream withdrawn from a fractionating zone. For example, a crude oil distillation zone is utilized to distill light products overhead and these light products then are sent to a fractionating column. The vapor stream removed overhead from the fractionating column generally is cooled, first in an indirect heat exchanger and later by a water condenser. The stream passing through the heat exchanger will comprise principally a hydrocarbon vapor phase and a minor liquid phase. The vapor phase also will contain HCl and NH vapor in equilibrium with NH Cl at the prevailing temperature. The ammonium chloride will condense on the inner surfaces of the heat exchanger tubes. The ammonium chloride serves as an electrolyte in the presence of water vapor and is very corrosive. Since the area is substantially vaporous, no inhibitor is present to inhibit the corrosion. This illustrates one example of a vaporous atmosphere in which inhibitor protection is difiicult to obtain. Many other vaporous streams Patented Sept. 5, 1972 containing acidic corrodents occur in the petroleum, petrochemical and other industries.
In another embodiment, the novel method of the present invention is utilized to inject the inhibitor into the suction side of a compressor. For example, in a petroleum refinery the overhead vapor stream from one or more fractionators is sent to a compressor and then to subsequent recovery of the valuable components in the stream. The light overhead streams are compressed and sent to a series of fractionation and recovery steps, referred to in the industry as the gas concentration system. The internals of the compressor are vulnerable to corrosion caused by the acidic corrodents contained in the vaporous charge thereto. Here again, the environment is in vaporous state and inhibitor protection is not available. In addition to corrosion, compressor operation is affected by gum formation which results in sticking of the valve stems, etc. As another advantage to the present invention, the particular inhibitor Will be selected to also serve to dissolve the gum and to avoid maloperation of the compressor.
In still another embodiment the novel method of the present invention may be used to inject inhibitor into pipelines carrying gases and/or vapors. The inhibitor is injected at one and preferably at a plurality of points.
The above are illustrative examples in which the novel method of the present invention may be utilized to advantage. It is understood that the present invention also may be used in other applications where substantially vaporous streams are being passed to piping, tubes, exchangers, vessels, compressors, pumps, etc.
As herein'before set forth, the inhibitor is dissolved in a liquefied petroleum gas. Any suitable inhibitor may be used, with the only requirement being that the inhibitor is soluble in the liquid petroleum gas at the concentration desired. The inhibitors generally are use in very small amounts, which usually are below p.p.m. (parts per million) and more particularly in the range of from about 5 to about 50 p.p.m. based on the vapor stream. A particularly preferred corrosion inhibitor for use in the present invention is an alkyl acid phosphate salt of a N-alkyl-diaminoalkane. In general, the ester portion of the alkyl acid phosphate contains from about 4 to about 12 carbon atoms and the alkyl group attached to the nitrogen atom contains from 6 to 20 or more carbon atoms. A specific corrosion inhibitor in this embodiment is the mixed monoand dioctyl acid orthophosphate salts of N-tallow-1,3-diaminopropane. This inhibitor is readily soluble in liquid petroleum gas and thus is particularly preferred. Also, this inhibitor serves to dissolve gummy deposits and, as hereinbefore set forth, serves to prolong compressor operation. Another corrosion inhibitor comprises a salt of a diearboxylic acid having at least 10 carbon atoms and a N-alkyl-diaminoalkane having an alkyl group of at least 12 carbon atoms. Other corrosion inhibitors comprise salts or reaction products of fatty amines and carboxylic acids. Still other corrosion inhibitors comprise acids, amines or mixtures of these with salts or other reaction products as described above. It is understood that any suitable corrosion inhibitor may be used in accordance with the present invention, with the only provision being that the inhibitor is soluble to the extent desired in the liquefied petroleum gas.
Any suitable liquefied petroleum gas may be used in the present invention and conveniently comprises the LPG (liquefied petroleum gas) available at the refinery. In most cases the LPG will comprise principally propane and may also contain ethane and/or butane. It is understood that liquefied propane may be used as such. Also, when it is desired to inject the inhibitor at a higher pressure, liquefied enhance gas may be employed.
The inhibitor may be dissolved in the LPG in any suitable manner. In one method the desired amount of 3 inhibitor is supplied to a mixing tank and the LPG is charged thereto. In order to insure complete saturation of the LPG, a portion of the LPG may be bled 01f, with the resultant autogenous refrigeration to lower the temperature in the mixing zone. The charge of more LPG under pressure and bleeding off may be repeated as necessary. The LPG solution then may be pressured with additional LPG under pressure and passed, usually through a suitable filter such as plastic impregnated treated cellulose or the like, into the vapor stream. In another method, the inhibitor may be pumped ito a stream of LPG and the solution then injected into the vapor stream. It is understood that any suitable method of dissolving the inhibitor in the LPG may be employed.
The solution of inhibitor in LPG is injected as an aerosol into the vapor stream in any suitable manner. In one method, this is accomplished by passing the solution through a retrievable orifice assembly inserted tangentially into the pipe carrying the vapor stream. The retrievable orifice assembly may comprise a nipple or short piece of piping having an orifice at the outlet. The assembly is firmly inserted at a tangent into the pipe carrying the vapor stream but preferably is arranged so that the assembly maybe removed for periodic cleaning of the orifice when required because of plugging of the opening.
As hereinbefore set forth, the solution of inhibitor in LPG will be injected as an aerosol and will be uniformly distributed in the vapor phase, thus serving to effectively inhibit corrosion, as well as, with certain inhibitors, serving to dissolve gummy deposits formed on the metal surfaces.
As hereinbefore set forth, the inhibitor generally is used in small concentration. In one embodiment, this may comprise from about to about 50 p.p.m. of inhibitor based on the vapor stream, although smaller or larger concentrations, which generally will not exceed 500 p.p.m., may be utilized when desired. The concentration of corrosion inhibitor normally will be correlated with the concentration of acidic corrodents in the vapor stream.
The following examples are introduced to illustrate further the novelty and utility of the present invention but not with the intention of unduly limiting the same.
EXAMPLE I In this example it is desired to inject one quart per day of a corrosion inhibitor comprising the monoand dioctyl acid orthophosphate salts of N-tallow-1,3-diaminopropane into the vapor overhead stream from a fractionating zone. The vapor stream contains HCl and NH vapor in equilibrium with NH Cl. As hereinbefore set forth, the ammonium chloride will condense on the inner surfaces of the heat exchanger tubes through which the vapor stream is passed. The inhibitor is dissolved in LPG as follows. One quart of the inhibitor as a 50% weight solution in heavy naphtha is charged into a 100 gallon capacity mixing vessel. LPG is available at a temperature of about 70 F. and a pressure of 110 p.s.i. LPG is charged into the lower portion of the mixing vessel. The flow of LPG is stopped and a portion bled 01f the top of the mixing vessel, with the resultant drop in temperature to about 20 F. and pressure of about 55 p.s.i. The outlet valve then is closed and more LPG charged, with the bleeding off and charging of LPG repeated as necessary to obtain the desired concentration of LPG with the inhibitor. The LPG under normal vapor pressure then is charged into the upper portion of the mixing zone and the LPG solution therein pressured out of the mixing zone, through a filter and then through a retrievable orifice assembly inserted tangentially into the vapor outlet line. In this manner the inhibitor is introduced into the vapor stream in a concentration of about 10 ppm. of inhibitor based upon the vapor stream. It is readily apparent that larger or smaller concentrations may be injected in this manner by initially charging the desired amount of the inhibitor into the mixing zone and utilizing as much LPG as necessary to obtain the desired concentration, which then is pressured through the orifice into the vapor stream.
EXAMPLE II In this example the inhibitor is pumped by a means of a proportioning pump into a stream of LPG at the prevailing temperature and pressure. The inhibitor is supplied at a concentration to form a solution of 0.25 volume percent of inhibitor in the LPG. The solution then is passed tangentially through an orifice assembly into a gas stream entering a gas compresser. As hereinbefore set forth, the gas stream will be compressed for subsequent charge to a gas concentration system for recovery of the hydrocarbon components thereof.
I claim as my invention:
1. The method of injecting an inhibitor into a vapor stream which comprises dissolving said inhibitor in a liquefied petroleum gas under pressure and thereafter dispersing the pressurized solution as an aerosol in said vapor stream.
2. The method of claim 1 in which the solution of inhibitor in the liquefied petroleum gas is injected through a nozzle tangentially inserted in the pipe carrying said vapor stream.
3. The method of claim 2 in which said vapor stream comprises an overhead stream withdrawn from a fractionating zone.
4. The method of claim 2 in which said vapor stream comprises a vapor stream being charged to a compressor for subsequent recovery of condensable liquids.
5. The method of claim 1 in which said inhibitor is an alkyl acid phosphate salt of N-alkyl-diaminoalkane.
6. The method of claim 5 in which said inhibitor is the mixed monoand dioctyl acid orthophosphate salts of N- tallow-1,3-diaminopropane.
'l. The method of claim 1 in which said inhibitor is a salt of a dicarboxylic acid and an alkyl diaminoalkane.
References Cited UNITED STATES PATENTS 2,081,130 5/1937 Atwell 48-190 2,857,334 10/ 1958 Thompson 21-2.7 3,025,313 3/1962 Gunderson 21-2.7 X 3,063,790 11/ 1962 Pollitzer 21-2.7 3,113,113 12/1963 Marsh et a1. 21-2.7 3,294,705 12/1966 Kautsky 252-390 3,458,453 7/ 1969 Kautsky 203-7 X MORRIS O. WOLK, Primary Examiner R. E. SERWIN, Assistant Examiner US. Cl. X.R.