US2332800A - Process for cleaning petroleum refining equipment - Google Patents

Description

Oct. 26, 1943.

w. B. KILLOUGH PROCESS FOR CLEANING PETROLEUM REFINING EQUIPMENT Filed Feb. 12, 1941 L Mug? w mm 6. 'INVENTOR.

BY fl If W ATTORNEY Patented Oct. 26, 1943 PROCESS FOR OFFICE REFINING EQUIPMENT Walton B. Killough, Baytown, Tex., assignor to Standard Oil Development Company, a corporation of Delaware Application February 12, 1941, Serial Nb. 378,608

1 Claim. (01. 196-69) The present invention relates to improvements in the art of treating hydrocarbons, and more particularly it relates to improvements in the art of removing coke and coke-like materials from refinery equipment such as fractionating columns and the like.

Extended heat treatment of petroleum oils in refining operations results in decomposition of the hydrocarbons with the formation of polymerized products of high molecular weight. These polymerized high-molecular weight hydrocarbon compounds and salts naturally occurring in the oil or resulting from the reaction of acidic water with ammonia or other vapors that may be injected in the oil stream to prevent corrosion of metallic surfaces, usually deposit in conduits, on trays or on the walls of the chambers in which the heat treatment is taking place. It is therefore necessary in conventional practice when a particular unit such as a distillation tower becomes fouled with the abovementioned deposits, to remove the tower from the production phase, steam the same and allow it to cool for safe entrance of workmen to remove the coke and polymerized hydrocarbons. In vessels, such as fractionation towers having trays and bubble cap plates or other equipment which efiects an eflicient or intimate gas or liquid contact, the cleaning of the same is a tedious, timeconsuming, expensive operation which must be performed by hand.

The main object of my invention is to provide means for efficiently removing the coke-like polymerized hydrocarbons from a particular vessel such as a fractionating column in an improved manner, by the washing action of a, hydrocarbon oil which is employed after the unit has been takenofi the onstream operation.

It is my belief that during the refining of oils .in a particular vessel, such as a fractionating tower, heavy polymers accumulate on the plates around the bell caps. These heavy hydrocarbons are subjected to heat treatment, since it is believed that the velocity of the ascending vapors is such that these polymerized hydrocarbons are carried up the tower by entraimnent and eventually are held between two or more plates. As time goes on, these compounds become heavier and heavier, that is to say, they increase in molecular weight, but ordinarily remain fluid or in a suspended state until the temperature of the tower is reduced when it is removed from the onstream operation. As the temperature of the tower is reduced and the normally fluid contents are removed, the heavy polymerized hydrocarbon or carbonaceous compounds precipitate and cement in a solid mass eifectively clogging the unit. This caked mass is extremely difficult to remove from a fractionation tower, particularly since the construction of the tower is such that entry by workmen therein is difiicultand the restrict ed area frequentlyhinders use of ordinary cleaning procedures. It is therefore necessary for the workmen to enter the tower after it has been steamed and cooled, to remove the coke-like products by chipping and scraping. This method of removing the caked mass is highly unsatisfactory from an economic standpoint, since valuable operating time is lost and the work constitutes a life hazard. i

As previously indicated, I have devised a process for cleaning petroleum refining equipment of coke-like material and other deposits, and my invention will be best understood by reference to the accompanying drawing which shows diagrammatically apparatus which I have selected to illustrate my invention.

The drawing shows a combination of a pipe still and a fractionating column, together with other accessory equipment, and I will now describe my process as used in cleaning the fractionating tower, with the understanding that the application of the process to this particular type of equipment is purely illustrative and does not impose a limitation on my invention since heat exchangers and the like may also be cleaned by my cleaning process.

Referring in detail to the drawing, I represents a charging line through which a hydrocarbon oil such as a crude petroleum is introduced into the system The charge oil is forced into coil 2 located in furnace 3, and in the furnace it is heated to distillation temperature, say a temperature of from about 525 F. to 685 F. The heated oil is withdrawn from coil 2 in furnace 3 through line 4 and, by means of pump 5 and line 6, is introduced into, fractionating tower 1. Light products are removed overhead from fractionating tower 1 in line 8 and then discharged into condenser 9 where condensable hydrocarbons are liquefied and subsequently recovered by means of line H] connecting with receiving drum ll. Liquefied hydrocarbons are recovered through line l2 while non-condensable hydrocarbons are recovered through line l3. A sidestream fraction consisting of gas oil is removed from fractionating tower 1 through line H may be cooled in cooler 28 and is collected in storage tank I5. Other side-stream fractions may be taken off from the tower, if desired,

guished in furnace 3 and the oil stream has been.

discontinued in line I, the oil remaining in tower l is pumped out through line 16 and a gas oil of 25 to 40 A. P. I. gravity is immediately charged into the top of the said tower through" line I! and pump l8 which is in communication with gas oil storage drum E5. The oil in line ll't y is ordinarily provided at an initial temperature of about 100 to 150 F. as'itenters the tower. Although the oil may be heated to higher temperatures it is preferable to introduce the oil at the relatively low temperatures specified above. While the flushing oil is being introduced in the top of the tower, a sufficient amount of steam is injected into the bottom of tower I. through: line I9 to maintain the temperature. of the flush ing oil at substantially the temperature at which it isintroduced. The flushing. oil, 1.. e., the gas oil, may be introduced. into the. bottom. of the; tower as in the conventional flow of the crude oil during the refining operation, but it is. preferred tointroduce it into the top of'the tower. above the top plate and. permit. it. to circulate. downward. The gas oil. is circulated through the tower at a rate of about 100 t0.2l),000- gallons an hour depending on the size of. the unit1be-- ing cleaned. While it is'preferred, for convenience, to employ a gas oil obtained: duringz'the: onstream operation, I may use gas oilfrom. any source as the flushing oil. Circulationof theoil is maintained for 1 to 24 hours to obtairr effective cleaning. The oil .discharging from; the: tower through line L6 isvisually examined; periodically to determine whetherv or not it; (IODIL tainssuspended bodies and; vwhenthe .oil. no long-- er contains these suspendedbodies. the operat knows that substantially all of the coke-like material has-been removed fromthe-tower; The oil leaving the tower through line It: may b.e.-dfi:-- verted by means of line to a-tank or sump: 2:!1 equipped with suitable baffles tolallow. settling of suspended materials flushed from the tower. After the suspended materiallhas settled, theoi'l may be recirculated by meansof lines 221tar1da 23 through the furnace 3-heated; ifi' necessary; and pumped again to tower Tthroughlinesu'; pump- 5; and'lines 24- and H. Ihe precipitatedapolymerized matter orsalts are removed. from; the: tank or sump by anysuitable means asdredging, and this materialmay be mixed; material obtained through line it during".v the operating cycle to manufacture a low grade fuel. such as bunker C fuel; On completion of the washing cycle as indicated by visual inspectionofthe washing oil, circulation of the n flushing medium through tower his then. discontinued; and the tower is-pumped free of 'gas 'oi l; Steam is again injected-into the tower throughzlinei to remove waxy or other hydrocarbons remaining on or wetting the sides of the tower l or the bubble caps and trays therein. After a final wash with water which is introduced through line 25, the tower may be opened for inspection if such is deemed necessary.

It is important that the sequence of steps and the several operations described be employed since, if the oil-washing operation is not followed by steaming and water washing, it has been found that the cleaning of the tower is not as effective as when all the steps described herein are employed.

In order to further illustrate my invention,

and particularly to disclose the nature of the flushing oil, the following specific example is set forth fully describing gas oils which I have found to be satisfactory in my process. It is understood, of course, that the details enumerated in the following example are purely illustrative, and other oils may be: used in place of those disclosed:

Erample A virgin gas'oil' of the following characteristics was used. in the cleaning of a fractionating tower:

Gravity; a A. P. I. 38.2 Initial boiling point F 400* Final boiling point l=.' 620 Flash F 184- The-fractionating tower was removed from ser-' vice and, before the unit was allowed tocool, it'was' washed with virgin gas oil' at a tempe'ra ture-of about F. for ten hours. The'washin'g was accomplished by pumping the gas oil at a rate of" 250 barrels per hour to the top of the tower and allowing-it to flow downward over the trays. The oil leaving the tower was not re circulated but was drawn' off and employed in another process; The tower was then steamed for safety and opened for inspection; It was found to be" substantially free of coke like' de posits. The small amount, of material remain- 5 ingon" theplat'eswa's readily-removed without the usual scraping and chipping:

Many variations of my invention may be made by those familiarwit'h this particular art with out departing from the spirit of the said inven'-' tion.

.What Iclaimis:

A method for cleanings: fr'actionating column which comprises" introducing into" the column immediately after it has been removed from onstream operation andiwhilef it is still hot, a gasoil' having a gravity inith'e'. range from'about' 25 A. Pl I. to'aboutAO" A. P; I., c'au'sin glsaidigafl oil to flow downwardlyithrough said'column removing. it from theb'ott'om thereofand introducing steam into the bottom of said column? during the downward flow or gas-oil? there"- through. 1

WALTON B. KIEIJOUGHi

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