US 2972235 A
Description (OCR text may contain errors)
United States Patent PURIFICATION or REFRIGERANT Buford Don Smith, West Lafayette, Ind., assignor, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N.J., a corporation of Delaware Filed Dec. 5, 1958, Ser. N 778,524
6 Claims. (CI. 62-84) The present invention is directed to a method of purifying a refrigerant. More particularly, the invention is concerned with purifying a fouled refrigerant containing lubricating oil and water. In its more specific aspects, the invention is directed to purifying fouled ethylene which is used as a refrigerant.
The present invention may be briefly described as a method for purifying a fouled refrigerant containing lubricating oil and water in which the fouled refrigerant is chilled to its dew point. Thereafter, a portion of the chilled fouled refrigerant is formed into a liquid body and then another portion of the chilled fouled refrigerant in vaporous form is contacted with the liquid body to purify the chilled fouled refrigerant by removing water and lubricating oil therefrom. Thereafter, there is recovered from the liquid body the purified refrigerant in a vaporous form. From time to time the liquid body is discarded and then reformed periodically.
The present invention is applicable to refrigerated low temperature polymerization operations such as those employed in forming butyl rubber and other types of synthetic elastomers. The present invention is also applicable to chilling aromatic hydrocarbon-containing feeds for the recovery of crystallizable hydrocarbons such as paraxylene and the like from the chilled aromatic hydrocarbons. Other applications of the present invention are to refrigerating the lubricating oil fractions and the like.
The present invention will be further described by reference to the drawing in which:
Fig. 1 is a flow diagram of a preferred mode, and
Fig. 2 is a flow diagram in detail of the mode of Fig. 1.
Referring now to the drawing, numeral 11 designates a charge line by way' of which ethylene which may contain water is introduced into the system and particularly into an ethylene drum 1 2. Ethylene from drum 12 is withdrawn by line 13 into compressor 14 where it is compressed and then discharged by line 15 into a knockout drum 16. In compressor 14 the ethylene which contains water as an impurity picks up lubricating oil which is used to lubricate the compressor. In knockout drum 16 a substantial amount of the lubricating oil is withdrawn by line 17 controlled by valve 18, but the vapor pressure of the lubricating oil is such that a substantial amount over a period of time will remain in the ethylene by virtue of the vapor pressure. The ethylene from drum 16 containing both water and traces of lubricating oil is discharged by line 19 into acooler 20 where it is cooled by means of water introduced by line 21 and withdrawn by line 22. The cooled ethylene stream is then discharged by line 23 into a heat exchanger 24 containing a tube bundle 25 through which the ethylene passes and containing a body of propane 26 which is being flashed by reduction of pressure through line 27 connecting into a compressor 28 which compresses the propane and discharges it through line 29 into a knockout drum (not shown) and thence through condenser 29a cooled with water inn-o duced by line 29b and finally into propane drum 30. The ethylene is chilled to its dew point in heat exchanger 24 and the vaporous ethylene is then discharged by line 31 into a storage drum 32. By regulating the flashing of the propane in heat exchanger 24 a body 33 of ethylene at its dew point may be formed in the drum 32. By maintaining the body 33 the vaporous ethylene is caused to How through the body 33 and is contacted therewith by introducing the ethylene through branch lines 34 into the body 33. Thus, drum 32 serves as a scrubbing and condensing zone. This contact of the vaporous ethylene with the body 33 causes the removal of water and traces of lubricating oil thereform allowing a purified vaporous ethylene to be withdrawn by line 35 and condensed in condenser 36 and then routed by line 37 through a surge drum (not shown) into a chilling zone 38 where the purified ethylene is employed to refrigerate a paraxylene feed stream introduced by line 39 with the chilled paraxylene stream being discharged by line 40 into a paraxylene recovery zone. The ethylene from chiller 38 is then withdrawn by line 41 and introduced thereby into line 11 and then into drum 12.
From time to time it will be desirable to withdraw the body 33 of liquid ethylene and this may be done conveniently by opening valve 42 in line 43 and discharging the ethylene containing oil and water and replenishing the body 33 with ethylene from line 31.
Any liquid overflow from the heat exchanger 24 is withdrawn therefrom by line 44, discharged and flashed across a valve 44a, and the flashed vapors are then passed through condenser 36 to condense the ethylene in line 35, the propane then discharging by line 45 to a suction knockout drum (not shown) into line 27 to the suction of compressor 28. Any makeup propane may be introduced by opening valve 47 in line 46. Propane for use in heat exchanger 24 is withdrawn by line 48 from drum 30 and introduced thereby into heat exchanger 24.
Referring now to Fig. 2 where identical numerals designate identical parts, it will be seen that fouled ethylene vapor is introducd into heat exchanger 24 by line 23 and passes through the tube bundle 25 containing a plurality of tubes 25a.
The body of liquid propane 26 in the heat exchanger 24 is used to regulate the body of liquid ethylene 33 in the scrubber drum or surge drum 32. In order to accomplish this end, a liquid level controller 49 is arranged in line 50 which connects into the vapor space of drum 32 and into liquid body 33 and is connected by the pneumatic line 51 to a liquid level controller 52 arranged in line 53 which connects into the vapor space of heat exchanger 24 and with the liquid body 26. The liquid level controller 52 operates through pneumatic line 54, a dia phragm valve 55 in line 48 through which liquid propane is introduced into the heat exchanger 24 as has been described with respect to Fig. 1.
The present invention is quite advantageous and useful in that heat transfer equipment which utilizes a flashing refrigerant as the cooling medium is subject to fouling due to the small amount of compressor lubricating oil and water contained in the entering liquid refrigerant. The lubricating oil and water remain on the exchanger tubes when the refrigerant flashes and thus reduces heat transfer capacity of the heat exchanger. Water enters the refrigeration system with the make up refrigerant and the lubricating oil is introduced from the compressors and passes through knockout drums as a vapor or in the form of very fine droplets. To illustrate the mag nitude of the problem a usual compressor lubricating oil may have a boiling range of about 750 to about 950 F. The vapor pressure of such a material is shown in the following table.
3 Table I Lube Vapor Pressure,
. Microns' of Hg As a unit recovering paraxylene from a paraxylene containing feed approximately 5.3 l standard cubic feet per day of ethylene is circulated with a compressor discharge temperature of about 265 F. The high pressure knockout drum operates at approximately 265 F, also. With liquid lubricating oil being removed from the knockout drum, the ethylene vapor therefrom will still cont ain-a substantial amount of oil corresponding tothe vapor pressure of the oil at this temperature of about 1.4 microns of mercury. The oil may have a molecular weight of about 400 and from this it is determined that approximately 10.3 lbs. per day of oil may be deposited on the heat exchanger tubes. Over a period of several days or weeks the accumulation of oil becomes substantial. At a particular unit, it is customary to remove the major portion of the accumulation every two or three days when the heat exchangers are deiced to remove paraxylene crystals which may foul the inside of the heat exchanger tubes, then every two or three months, the outside of theheat exchanger tubes are washed with xylenes to remove the adhering oil film. It is immediately apparent that such operations to remove adhering oil which besides reducing the heat exchange capacity, results in a substantial loss in operating time.
In accordance with the present invention, substantially all of the oil from the liquid refrigerant is removed. This is done by cooling the refrigerant to its dew point and condensing a small portion of it to form a liquid seal or body into which the remainder of the refrigerant vapor is bubbled. The liquid refrigerant effectively scrubs out'oil and water from the vapors and then the fouled liquid is discarded and replaced with fresh liquid. For Example, the fouled liquid may be discarded after 4 or 5 ays. v
The invention will be illustrated further by the following example taken with Fig. 2. Fouled ethylene vapor at about 100 F. may be introducedby line 23 at about 335 lbs. per square inch gauge pressure into heatexchanger 24. The liquid propane in heat exchanger 24 is at a temperature of about -28 F. and about 6 lbs. per square inch gauge. By introducing liquid propane at 95f F. at 180 lbs. per square inch gauge the liquid propane 26 in heat exchanger 24 is flashed to reduce the temperature of the fouled ethylene vapors passing through tube bundle 25. As a result, the ethylene vapor is at its dew point of about 8 F. and by controlling the level of propane 26 it is possible to maintain a body of liquid ethylene 33 at about 8 F. and 330 lbs. per square inch gauge in drum 32. Once the body of liquid ethylene is formed, the fouled ethylene vapor bubbles through it and there 1t is recovered through line 35 purified ethylene vapor at 8 F. and about 330 lbs. per square inch gauge. The purified ethylene vapor is then condensed in 36 and the liquid ethylene is then used in chilling paraxylene stream to a temperature of about 85" F.
While the present invention has been described and illustrated by reference to use of ethylene as the refrig- .erant, other refrigerants may be used; as examples of other refrigerants may be mentioned: propane, carbon dioxide, and the like. The refrigerants may have dew points as follows:
Propane at 190 p.s.i.g. Dew point 120 F. Carbon dioxide at 272 p.s.i.g Dev/point F,
As stated, the present inventio maybe employed in of this nature low temperature polymerization operations, chilling op:
erations for the recovery of crystallizable hydrocarbons such as cyclohexane, durene, paraxylenc, metaxylene, and the like. The invention is also applicable to other chilling operations such as dewaxing operations.
The present invention provides a purified refrigerant which is substantially free of oil and water. Therefore, it is quite useful in eliminating heat transfer dilficulties in low temperature operations requiring use of a refrigerant.
The nature and. objects of the present invention having been completely described and illustrated what I wish to claim as new and useful and secure by Letters Patent is:
l. A method for purifying a fouled refrigerant'containing lubricating oiland water which comprises chilling the fouled refrigerant to its dew point, flowing a vaporous stream of said chilled fouled refrigerant into a scrubbing and condensing zone under conditions to form a liquid body of said chilled fouled refrigerant and simult'aneously,'contacting said vaporous stream with said liquid body and thereby purifying 'saidchilled fouled refrigerant by scrubbing lubricating oil and water there-. from, recovering purified vapors of said refrigerant from said liquid body, and discarding and reforming periodically said liquid body.
2. A method for purifying fouled ethylene containing lubricating oil and water which comprises chilling the fouled ethylene to its dew point, flowing a vaporous stream of said chilled fouled ethylene into a scrubbing and condensing zone under conditions to form a liquid body of said chilled fouled ethylene and simultaneously contacting said'vaporous stream with said liquid body and thereby purifying said chilled fouled ethylene by scrubbing lubricating oil and waterv therefrom, recovering purified vapors of said ethylene from said liquid body, and discarding and reforming periodically said liquid body.
3. A method for purifying fouled ethylene containing lubricating oil and water which comprises chilling the 4. A method forpurifying a fouled refrigerant .con-.
taining water which comprises compressing'said fouled refrigerant whereby lubricating oil is contained therewith, separating a major portion of said lubricating 'oil from said fouled refrigerant, chilling the fouled refrigerant to. its dew point, flowing a vaporous stream of chilled fouled refrigerant int'o scrubbing and condensing zone under conditions to form a liquid body of said chilled fouled refrigerant and simultaneouslycontacting said vaporous stream with said liquid body and thereby purifying said chilled fouled refrigerant by scrubbing unseparated lubricating oil and water therefrom, recovering purified vapors of said refrigerant from said liquid body, and discarding and reforming periodically said liquid body.
5. A method for purifying a fouled refrigerant containing lubricating oil and water which comprises separating a major portion of lubricating oil from said fouled refrigerant, chilling the fouled refrigerant to its dew point, flowing a vaporous stream of said chilled fouled refrigerant into scrubbing and condensing zone under conditions to form a liquid body of said chilled fouled refrigerant and simultaneously contacting said vaporous stream with said liquid body and thereby purifying said chilled fouled refrigerant by scrubbing traces of lubricat ing oil and water therefrom, recovering purified vapors 5 of said refrigerant from said liquid body, and discarding and reforming periodically said liquid body.
6. A method for purifying fouled ethylene at a temperature of approximately 265 F. and containing luliquid body and thereby purifying said chilled fouled ethylene by scrubbing traces of lubricating oil and water therefrom, recovering purified vapors of said ethylene from said liquid body, and discarding and reform bricating oil and Water which comprises separating a 5 ing Periodically Said liquid ymajor portion of said lubricating oil at said temperature, chilling the fouled ethylene to its dew point, flowing a vaporous stream or said chilled fouled ethylene into scrubbing and condensing zone under conditions to form a liquid body of said chilled fouled ethylene and simultaneously contacting said vaporous stream with said References Cited in the file of this patent UNITED STATES PATENTS