US1873136A - Process for preventing corrosion in oil refining equipment - Google Patents

Description

Aug. 23, 1932. i w. G. LAlRD 1,873,136

PROCESS FOR PREVENTING CORROSION IN OIL R EFINING' EQUIPMENT Filed MW. 27, 1926 071 SUPPLY WA TERREMOML SYSTEM TOPP/NG LIME Y M/X/NG CHAMBER 14 REF/N/NG APPARATUS Patented Aug. 23, 1932 pairs stares earner or-rice;

w-ILBon e. LAIRD, or new ORK, N. ,Y., ASSIG-NOR 'ro HEAT 'rnnnrine ooi/rrAivY, or HEW YORK, 1\T. Y., A oonronnrron or DELAWARE Process non PREVENTING CORROSION IN OIL nnrrnrne EQUIPMENT Application filed. November 27, 1926. Serial No. 151,040.

This invention relates to a process for preventing corrosion in oil refining apparatus.

To those familiar with the operation and maintenance of oil refining equipment in modern refinery practice, it is well known that the life of the apparatus, particularly such parts as are exposed to oil vapors, is comparatively short due to the rapid corrosion taking place. Various means and methods have been resorted to in order to ofiset or retard this corrosion but so far nopractical solution of the problem seems to have been found. Some special steel alloys have been proposed for the construction of oil refining equipment but their present cost is almost prohibitive. At the same time the loss in replacing corroded parts and that incident to having a unit shut down for frequent repairs is not a small item on the refiners expense account, without considering the danger to life and property which would result from a fire or explosion caused by a corroded vapor line or furnace tube.

Certain types of petroleum are known to contain as high as 5 per cent sulphur while others contain very little or no sulphur and it is generally understood that certainsulphur compounds formed during the cracking or distilling operation are at least in part responsible for the corrosion referred to above. However it has been found that the combined action of water, free oxygen and the sulphur content of petroleum is responsible for the excessive corrosion of oil refining equipment. All crude petroleums contain varying amounts of water and in many cases the water is a solution of salts such as magnesium chloride which dissociates to give hydrochloric acid. Even the high boiling distillates used in cracking are steam distilled or have been exposed to the atmosphere from which they have absorbed moisture. In addition to water all natural petroleums, as well as the distillates such as gas oil, fuel oil, kerosene, etc, which have been exposed to the atmosphere after distillation, contain free oxygen. Furthermore it has been found that the solubility of oxygen or air in petroleumis about seven timesthat in water and that its absorption is facilitated by theaction ofsunlight or even diffused day light, so the usual. free oxygen content of petroleum. is increasedwhen it is exposed to light and air in storage or transit. The use of air under high" pressures when pumping petroleum according to the fair lift princile and in air-wells in order to increase the oil yield in adjacent pumping wells necessarlly saturates the petroleum with oxygen, thereby rendering oil handled in this manner more corrosive than otherwise would be the case. V

Thecombined action of these constituents (water, sulphur compounds and oxygen) maybe represented as follows: Oxygen 1n the presence of moisture (H O) reacts with by the presence of sulphur which liberates the oxygen foradditional corrosion right at the point of liberation. This is, undoubtedly, the cause of the deep pots found in corroded pipe taken from pipe still furnaces and vapor treating equipment.v

These reactions will take placeat a fairly rapid rate. at ordinary temperatures but under the high temperatures and pressure used in cracking oil their rate is'increased many times.

Accordingly the primary object ofathe present invention is to provide-a processfor by, or naturally present in the oil to be .ods now in use.

cracked or distilled may be removed from the oil before it is subjected to the refining treatment or have their corrosive properties annulled during refining, for example,

during the cracking operation, or to remove certain of said constituents and annul the corrosive action of others.

In order to accomplish these ends the oil to be refined may first be treated "by any known settling or dehydrating process for removing the bulk of its water content, however, if the oil contains only a small amount of water this step may be omitted. The oil freed of most of its water content is next subjectedto a topping. operation in which a current of gas is passed through the oil as it is being heated whereby the last traces of moisture together with the absorbed oxygen and the gasoline fraction are swept out of the oil, the gasoline being recovered in the usual manner. This topping step is carried out in such a manner as to leave the oil entirely dry and free from any trace of free oxygen or other corrosive gas. The oil is then taken while hot or cold, as desired, from the topping plant and passed directly to the refining apparatus,.provided it is ,an oil containing very little or no sulphur, however, if the oil contains any appreciable amount of sulphurit is first passed from the topping plant into a mixing chamber where lime or some 7 alkali-earth metal carbide or oxide is intimatelymixed with the oil andthe mixture then passed into the refining apparatus, for

example, through the cracking tube or tubes of a furnace where the lime (CaO) or calcium carbide(CaC takes up sulphur from the 'oi'l, which togetherwith the absence of water and oxygen prevents the corrosion of the crackingequipment. v

The invention will now be described in detail, reference being had tothe accompanying drawing in which Thefig-ure is a diagrammatic sketch or flow sheet of the process.

vIn accordancewith the invention the, oil which is to "be cracked or distilled and which may be' either an asphaltic or paraffin base crude oil or a distillate thereof is passed from any convenient source of supply 2 by conduit 4 into a suitable apparatus 6 where the greater portion of the water content of the oil is removed by any of the well-known meth- From the Water removal system 6 the oil is conducted by. conduit 8 into topping still 10. If the oil to be treated contains only a small amount of water it may be conducted directly from the supply-2 to the topping still 10 by the conduit 12 without passing-through the water removal sys-' tem.

The topping still 10 may be of any approved type but it is preferred to use a column still in which the oil entering the still is heated through a diaphragm by the va-' pors produced in the still itself so that the p allelnthrough a still on the opposite sides 'of a diaphra-gm wherein the vapors of the oil which have been distilled are being.

fractionally condensed. A sufliciently large volume of gas is used to provide a partial pressure effect to substantially reduce the temperature of the distillation and condensation in thestill below the temperatures of the ordin ary distillation at atmospheric pressures. This low temperature evaporization and condensation avoids the excessive corrosion, and, furthermore, the gas on each side of the diaphragm tends to keep the materials in active agitation or ebulli-tion so that the corrosion isminimized. r a

In the topping'still 10 the oil is preferably heated only to a sufficient temperature to va-.

porize any water or moisture present and also the gasoline fraction in case a crude oil is being used. The vaporized water and gasoline together with the oxygen or other corrosive gasespabsorbed in the oil are swept from the oil in the column bypassing a gas therethrough. The gas used forv thistopping step is preferably natural gas or a purified hydrocarbon gas, for example crackingstill gases freed from sulphur containing gases, oxygen and carbon dioxide. The gas may be heated before being introduced into the column and may even 'bejused' as the sole means for heating the oil or may be passed with the oil into the column as disclosed in the application cited. 7 Y

The gasoline, water and gases removed from the oil are passed through a condenser and the gasoline recovered in the usual manner, while the removed gases may beabsorbed 7 If the oil being treated contains relatively little Mer no-sulphur it is passed while hot, di-

rectly from the column 10 to'the refini ng apparatus 14 by the conduit 16 or if it is not.

desired to refineor crack it immediately, it may be put in storage. But where the oilcon tains appreciable quantities of sulphur it is passed from the column 10 by the conduit 18 into a mixing chamber 20, where itis intimately mixed with dry lime (CaO) or .carbide from the supply 22. Instead of lime or calcium carbide other oxides or carbides of the calcium grouper hydroxides of the alkali metal group may be used. From the chamber 2Q whichmay be a combined grinding and mlxing chamber in which the lime and oil may be intimately mixed by being ground together, the mixture is passed by the conduit 24 into the refining apparatus 14:-

The amount of lime or other compound used in the process should at least be equivalent to the sulphur content of the oil but it is preferred to use two or three equivalents per equivalent of sulphur. The refiningapparatus may comprise any of the well-known systems in which oil is heated to a distilling or cracking temperature inv a heating coil,

tube or tubes mounted in a furnace and then passed to a vaporizer or reaction chamber from which vapors pass through a dephlegmator and so on. If reflux condensate is returned from the dephlegmator to the heating zone, as is done in many cases, it may, if it still contains any appreciable quantity of sulphur or sulphur compounds, be introduced into the mixing chamber 20 Where an additional quantity of lime may be added to fix its sulphur content in the subsequent heating step.

In the operation of the process described above oils which contain large amounts of brine are very corrosive and are treated to remove the brine and in certain cases may be washed with fresh water before the oil is admitted to the topping column where the last traces of water is removed. The removal of the salts contained in the brine eliminates the possibility of corrosive substances being formed therefrom in the heating, nevertheless if small amounts of hydrochloric acid,

7 for example, is formed it quickly unites with the oxide or carbide present in the cracking mixture so that too much care need not be taken to wash out all the salts.

Because of the very corrosive effect of petroleum vapors in the vapor space of ordinary stills and in vapor heat interchangers it is preferred to use the type of column still described in the application referred to above for efiecting the pre-treatment of the petroleum oil. In this type of column still the liquid oil is so completely mingled with the gas and vapor that the metal surfaces are protected to a large extent by the liquid. Furthermore if additional water is mixed with the entering oil along with the gas, the water by being vaporized will aid in the removal of oxygen and have a diluting effect on any corrosive constitutents present in the vapors.

action, the presence of gasoline in the chargtain these constituents and absorb additional 370 7 oxygen on being exposed to the atmosphere, it is important that these constituents be removed. Accordingly the oil is heated to 'a temperature sufficient toevaporate the-water and a dry gas free from corrosive constituents 5 is passed through the oil'to sweep out the water vapor and absorbed oxygen and other gases. The gas in this step of the process acts to reduce the partial pressure of the corrosive gas content of the oil including J moisture and furthermore acts to replace these con stituents in theaoil'and removethem from the system. When oils'which contain a gasoline fraction aresubjected to the treatment the gasoline is also removed along with the water and absorbed oxygen OI'gZLlI. so that a maximum amount. of gasoline willbe formed in cracklng, since according to the law of mass ingstock will hold backthe formation of that much gasoline during the cracking operation w:

"For oils containing little or no sulphur furthertreatment of the oil before crackingwill be unnecessary and evenwith high sulphur oils the removal of water and absorbed oxygen decreases the rate-of corrosion several times. In a five day test with naphtha solutions of sulphur compounds, which included hydrogen sulphide, no action on iron was noted at ordinary temperatures while incases where water was added corrosion resulted. Furthermore it has been found thatrise'in temperature accelerates the rate-of corrosion. Therefore in accordance with the invention the dry and oxygen free oil which contains an appreciable amount of sulphur, is mixed with dry lime. or its equivalent prior to its introduction into the refining apparatussuch as the tube or tubes of a'heating furnace. As sulphur'compounds are formed in the crack ing or distilling apparatus they immediately j react with the highly reactive 0:10 or CaC to-form calcium sulphides and consequently are preventedfrom reacting on the walls of the equipment. An-excess of, lime orother compound, above that required to react with the sulphur in the .oil, is used in order to make sure that all the sulphur which would 2- ordinarily cause corrosion is taken up. When a carbide is used as a sulphur fixing agent in the process the reaction, for example, between calcium carbide and hydrogen sulphide is as follows l r 'CaC d -H S=CaS+C H +heat Besides acting as a fixing agentfor the 5111-, phur, a combustible gas, acetylene is also formedffrom the carbide and serves toaug r30 -ment the supply and B. t. u. value "of thecgas formed from the oil. 7 v

Under certain circumstances it may be necessary to provide storage for the oil leaving the column still 10., for examplefwhere several cracking units are being supplied withnon-corrosive' oil or in case of "a shut- -down. The storagetanks used in this event,

are air-tightand previously deleted of all air,,oxygen or moisture by replacing these gases with purified hydrocarbon or other inert gases so that the oil in storage will have no opportunity to'absor-b anything but non-corrosive gases. I

From the :above description of the invention it. will beseen that the presentp'rocess provides an effective method of preventing corrosion in oil refining equipment and "at the same time provides a novel/oil product free of corrosive'constituents, being adapted for use as a cracking or distilling stock.

' While the invention has been described in tacting the same with cracking still gases substantially freed or free oxygen and sul- Lphur co'nt'aining :g'ases under non crac'kin'g conditions, andthereafter mixingthe treated distillate with lime. I I 4. The process of treating a petroleum oil which comprises intimately-contactingthe oil with cracking' still gases" substantially freed of freeoxyg'en and suliur containing gases under non-cracking conditions, and thereafter mixing the treated 'oil with lime;

in testimony whereof I aflix my signature.

WILBUR 'Gr.v LAIRD.

detail with respect to the means and manner thereof. Obviously the invention is equally applicable to oils and other liquids other than petroleumoil where'it is desired to eliminate corrosion in the equipment in which such oils or liquids are to be'handled, used or treated.

Having thus described my invent-ion, what I'claim is: r j 1 j 1' 1; The method ofpreventing corrosion in oil distilling apparatus, which comprises treating the oil to'be distilled to rem'ove'ex 'cess water, passing the treated oiltogether with a hydrocarbon "gas through a still to distil off the gasoline and to remove absorbed oxygen and remaining water therefrom, mixing the resulting oil While hot with a quantity of dry lime equivalent to at least twice the amount of sulphur in theoil and passing the mixture into the distilling-apparatus.

2. The method of preventing corrosion in oil refining stills, which comprises passing the oil to be cracked into. a topping still, passing a'hydrocarbon gas into intimate contact With the oil in said still whereby gasoline, water and absorbed oxygen are removed from said oil, withdrawingtopped oil fromsaid still and mixing therewith a quantity of lime in excess of the amountof sulphur in said biland passing the mixture to, the refining still. y V

'3. The process of treating a petroleum oil distillate, which comprises intimately con-

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