US2517504A - Water purge to waste heat exchangers - Google Patents

Description

1950 L. G. MOLIQUE WATER PURGE TO WASTE HEAT EXCHANGERS Filed Dec. 8, 1947 INVENTOR. L.G. MOLIQUE BY j/ .1

A TTORNEVS Patented Aug. 1, 1950 UNITED STATES PATENT OFFICE WATER PURGE T WASTE HEAT EXCHANGERS Delaware Application December 8, 1947, Serial No. 790,409

The present invention relates to improvements in the conversion of hydrocarbons and more particularly. to a novel method of preventing decontposition and deposition of carbonaceous materials in the equipment by heat quenching purge streams following conversion periods.

In the prior art, the cracking of hydrocarbons in the presence of a solid catalyst has been practiced by employing various forms of cyclic processes involving several steps such as a hydrocarbon conversion step, a catalyst purging step and a catalyst regeneration step. One of the problems encountered in the practice of such cyclic processes has been to prevent excessive carbon or other coke-like materialsfrom plugging or unduly restricting the transfer lines and other equipment through which the cracked hydrocarbon efiiuent is passed and thereby to avoid unduly frequent shutdown cleaning periods. Based on the belief that this coking occurs during the hydrocarbon conversion step, it has been common practice in the art to quench the cracked products just prior to their eilluence from the cracking zone. According to another belief that coking occurs as well during the regeneration step, it has been suggested that the number of cycles which a unit can be operated between shutdown cleaning periods can be increased by adsorbing cokeforming materials from the hot effluent regeneration gases. Thus, the prior art seems to have sought to solve the coking of equipment problem by quenching the ciiluent cracked hydrocarbon products from conversion. zone or by adsorbing coke-forming materials from efiluent regeneration gases. Notwithstanding the foregoing expediencies, coking of equipment still has been found to occur at such a rate as to necessitate shutdowns for cleanup at undesirably frequent intervals.

Any solution or even any partial solution of the coking problem, which is still constantly present and which is even now the object of the eiforts of a great many workers in the art, has been considered a highly desirable and beneficial advancein the art. Accordingly, the art has continually sought to further retard or minimize the coking of apparatus in cyclic catalytic hydrocarbon conversion processes.

The present inventor has found that a substantial proportion of coking of equipment actually has been occurring during the catalyst purging step which follows the hydrocarbon conversion step but which precedes the catalyst re generation step. Thus it has been found that heavy oils which might remain in the equipment after cessation of the hydrocarbon conversion 4 Claims. (Cl. 196-52) step or which might have been removed during the purge step tend to distill to coke in the pres ence of the hot efiiuent purge gases. This discovery is contrary to the teachings which can be derived from prior art as it exists today. According to this invention, it has been found that by drastically quenching the efiiuent purge materials from the catalyst zone the coking of equipment problem is substantially solved. Further more, it has been found in some instances when quenching of the effluent purge stream was practiced that the coking problem was solved to a considerable extent even in the utter absence of quenching during the hydrocarbon conversion step.

It is, therefore, an object of this invention to provide a process for preventing deposition of coke and heavy oils in catalytic conversion processes. It is a further object of this invention to provide a process for quenching the purge efiiuent following a catalytic conversion process to prevent the deposition of coke and heavy oils. Another object of this invention is to provide a process for quenching a steam purge effluent following a catalytic conversion process to prevent the deposition of coke and heavy oils on and to clean the surfaces of equipment following conversion chambers of catalytic processes. Other objects will be apparent to those familiar with theart from the accompanying discussion and figure.

In the usual manner of operation a body of catalyst may be used satisfactorily for hyclrocar bon conversion for a period from several minutes to several hours before it is deactivated to such an extent that it requires regeneration. Conventionally two or more catalyst chambers are employed so that one or more may be used for conversion while the others are being regenerated and thus continuous conversion maybe maintained. Either continuously or intermittently during the cycle of conversion and regeneration carbonaceous deposits are laid down on the transfer lines and equipment following the conversion zone and must be removed periodically. Ordinarily, a relatively short period of time, such as from six to ten minutes, is employed to purge the catalyst chamber of any residual reactant vapors following the catalytic conversion of hydrocarbons before regenerating the catalyst and I have now found that quenching the purge efiiuent during this brief period and cooling the purge eiiluent to a temperature at which any hydrocarbon vapor or fluid will not be substantially further cracked 0r vaporized is sufficient to eliminate any sub stantial deposition of carbon or heavy oils on:

the surfaces of the transfer lines, heat exchangers, and other equipment following the conversion chambers. This quench may be either conventional oil or water fluid but, preferably, is water. Preferably, a sufficient amount of water is injected to furnish the required cooling of the purge effluent so that any oil trapped in the exchanger will not be vaporized to dryness by the hot purge fiuid, thereby leaving residual carbon and tars on the exchanger tubes, and to provide a washing action on the surface of the lines and tubes of the heat exchanger. Although the exact function of the quench is not known, it is believed that in addition to cooling and liquefying the hydrocarbon vapors which are present in the purge, the quench also washes the surfaces of the lines and tubes of any heavy oils which may be adhering thereon from the product eflluent during the process cycle. Another advantage and function of the quench is to provide a temperature shock by the sudden cooling of the lines and heat exchange tubes and, thereby, to loosen any coke that may be deposited thereon. The quench is then preferably present in sufiicient quantity to decoke and to wash the lines and tubes clean of this loosened coke as well as any heavy oils adhering thereto. However, regardless of the action of the quench on the purge efiiuent, it has been found that an effective elimination of the presence of coke and carbonaceous deposition has been realized by quenching only the purge eiliuent. This is particularly advantageous and preferable to the conventional continuous quench of the product efiiuent in that a smaller amount of quenching material is required with a consequent 1 smaller amount of equipment and also, since there is a diminution of the load on the fractionating system, a fractionating system of smaller operating capacity is required. The supplemen tal extraneous load on the fractionator is lessened when the amount of quench material is reduced and furthermore the quench material is only added to the purge efliuent. It may be desirable to dispense entirely with the fractionation of the quenched purge eiiiuent when the content of valuable hydrocarbons therein is negligible, or fractionation of the purge effluent may be practiced to recover the quenching medium for recycle. Thus, the quenching is conducted for a shorter and more effective period and consequently requires less attention and regulation. Furthermore the use of quenching on the purge efliuent is more efiective and economical than the usual method of employing a quench continuously on the conversion efiiuent.

A better understanding of the invention may be had by reference to the drawing in which feed to a conversion process is introduced through lines l and H into a reactor 12. Conversion products are withdrawn through a line l4 into a heat exchanger I5 and by a line [6 into a. fractionator l8. Lighter products are removed overhead from the fractienator through a line 19 and heavier products are removed through a line 28. Heat may be supplied to the fractionator from a heating coil 2'2, as required. At the end of a conversion period when it is desirable to regenerate the catalyst or to stop the conversion proc ess, catalyst in the reactor may be purged of residual reactants and products by superheated vapors, such as steam, introduced by lines 25 and l I. Water or oil for quenching the purge efiiuent to a temperature to terminate reaction and to wash the walls of the equipment may be introduced through a line 2t into the purge efliuent immediately after the reactor and/0r into the lower part of the reactor by a line 21 and dispersing means 28. The quenched purge efliuent may be removed from the system by a line 3| after passing through the heat exchanger or may be introduced through line It into the fractionator for separation. In the preferred embodiment in which water is employed as the quenching medium, it is desirable to allow a separation of the water and hydrocarbon products as in a separator 30 from which the water is withdrawn from a lower layer through line 31 and an upper hydrocarbon layer is withdrawn through line IE to the fractionator.

During tests of the present invention, it was found that this method of operation is highly efiicient and effective. In comparative runs with and without employing the quench in a hydrocarbon cracking conversion process, it was found that without the quench on the purge it was possible to operate satisfactorily for an average of only about 20 days before it was necessary to dissemble and to decoke a waste heat exchanger following the reactor as compared with an average satisfactory continuous operation period of 60 days when quenching was practiced on the purge efiiuent alone. Thus it is shown that, although the body of catalyst was purged many times during each continuous period of use, it was possible to operate at least three times as long before it became necessary to dissemble and decoke the equipment following the conversion chamber when quenching is employed on the purge effluent alone.

Reasonable variation and modification are possible within the scope of the foregoing disclosure and the appended claims to the invention the essence of which is that coke deposition in equipment contacting fluid effluents from a hydrocarbon conversion zone can be substantially prevented by quenching only the purge gas efiiuent which flows for only a short period of time from said zone whereby it is not necessary to treat in any manner the converted hydrocarbon eiiiuent products or the effluent regeneration gases both of which flow for a long period of time from said zone in order to prevent coke deposition in the said equipment.

I claim:

1. In a catalytic hydrocarbon conversion process wherein carbonaceous material deposited on a catalyst during a conversion step is removed by burning with oxygen-containing gas in a subsequent regeneration step and wherein after the conversion step but prior to the regeneration step there is a purging step employing an oxygen-free purging medium to remove residual hydrocarbons, the improvement which comprises quenching the effluent purge products resulting from said purge step with a quenching medium in an amount sufficient to substantially lower the temperature of said purge effluent thus to prevent substantially the coking and concomitant plugging of equipment in which the purge eflluent is handled.

2. In a catalytic hydrocarbon conversion process wherein carbonaceous material deposited on a catalyst during a conversion step is removed by burning with oxygen-containing gas in a subsequent regeneration step and wherein after the conversion step but prior to the regeneration step there is a purging step employing an oxygen-free purging medium to remove residual hydrocarbons, the improvement which comprises quenching the efiluent purge products resulting from said purge step with a quenching medium in an amount 5 sufficient to substantially lower the temperature of said purge effluent and to wash free of carbonaceous deposits and heavy oils the walls of equipment contacting said purge effluent thus to prevent substantially the cokirn and concomitant plugging of said equipment.

3. In a catalytic hydrocarbon conversion proeess wherein carbonaceous material deposited on a catalyst during a conversion step is removed by burning with oxygen-containing gas in a subsequent regeneration step and wherein after the conversion step but prior to the regeneration stop there is a purging step employing an oxygen-free purging medium to remove residual hydrocarbons, the improvement which comprises quenching the effluent purge products resulting from said purge step with water in an amount sufficient to substantially lower the temperature of said purge effluent thus to prevent substantially the coking and concomitant plugging of equip ment in which the purge efliuent is handled.

4. In a catalytic hydrocarbon conversion process wherein carbonaceous material deposited on a catalyst during a conversion step is removed by 6 a burning with oxygen-containing gas in a subse quent regeneration step and wherein after the conversion step but prior to the regeneration step there is a purging step employing an oxygemfree purging medium to remove residual hydrocarbons, the improvement which comprises quenching the efiluent purge products resulting from said purge step with a liquid hydrocarbon oil in an amount sufficient to substantially lower the temperature of said purge efiiuent thus to prevent substantially the coking and concomitant plugging of equipment in which the purge effiuent is handled.

LAWRENCE G. MOLIQUE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 20 Number Name Date 2,292,699 Kassel Aug. 11, 1942 2,326,525 Diwoky Aug. 10, 1943 2,340,814 Lidov Feb. 1, 1944

Claims (1)

1. IN A CATALYTIC HYDROCARBON CONVERSION PROCESS WHEREIN CARBONACEOUS MATERIAL DEPOSITED ON A CATALYST DURING A CONVERSION STEP IS REMOVED BY BURNING WITH OXYGEN-CONTAINING GAS IN A SUBSEQUENT REGENEATION STEP AND WHEREIN AFTER THE CONVERSION STEP BUT PRIOR TO THE REGENERATION STEP THERE IS A PURGING STEP EMPLOYING AN OXYGEN-FREE PURGING MEDIUM TO REMOVE RESIDUAL HYDROCARBONS, THE IMPROVEMENT WHICH COMPRISES QUENCHING THE EFFLUENT PURGE PRODUCTS RESULTING FROM SAID PRUGE STEP WITH A QUENCHING MEDIUM IN AN AMONT SUFFICIENT TO SUBSTANTIALLY LOWER THE TEMPERATURE OF SAID PURGE EFFLUENT, THUS TO PREVENT SUBSTANTIALLY THE COKING ANC CONCOMITANT PLUGGING OF EQUIPMENT IN WHICH THE PRUGE IS EFFLUENT IS HANDLED.

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