US2076847A - Cleaning furnace tube - Google Patents

Description

April 13, 1937- c. L. JOHNSTON CLEANING FURNACE TUBE Filed July 10, I954 INVENTOR CHAR S JOHNSTON BY ATTORNEY Patented Apr. 13, 1937 UNITED STATES. PATENT OFFICE CLEANING FURNACE TUBE Charles L. Johnston, Long Beach, Calif., assignor to Universal Oil Products Company, Chicago, 111., a corporation of Delaware Application July 10, 1934, Serial No. 734,523 teams. (01. 196-69) This invention particularly refers to an improved method for removing carbonaceous deposits from the interior surface of tubular elements in oil heaters which is particularly well adapted to use in furnaces for the distillation or pyrolytic conversion of hydrocarbon oils.

In all processes (either distillation or conver-' sion) wherein hydrocarbon oils of a relatively heavy nature are heated to high temperatures in a fluid conduit there is a tendency for the coke to accumulate upon the inner surface of the fluid conduit. This greatly hinders the transmission of heat to the oil and may result in eventual stoppage or failure of the fluid 'conduit- 16 It is the purpose 'of the-present invention to keep the fluid conduits of oil heaters free from any excessive coke accumulation by periodically removing the accumulated coke from the fluid conduit before there has been a sufficient quan- 20 tity accumulated to greatly hinder the operation of the process, or to damage the conduit tubes due to overheating resulting from the excessive carbon deposits. If renewal or replacement of. damaged tubes is not made, eventually 25 a flre hazard will be created. This purpose is accomplished by controlled alternate cooling and I heating of the fluid conduit by passing through the fluid conduit, or through that portion of the conduit wherein the coke accumulates, in the 30 order named, a mixture of water and steam,

water, hot oil and cold oil, whereby to loosen the deposited coke from the walls of the fluid conduit and flush the loosened coke from the system.

While I have determined, within fairly close limits, the conditions most suitable for removing coke from the tubular elements of the fluid conduit following the processing of certain types of oils under specific conditions of treatment and will later outline these preferred conditions in more detail, I do not wish to be limited thereby since I believe the best conditions of temperature, time of treatment, etc., will vary depending 45 upon the nature of the coke deposit which, in turn, is related to the type of oil treated and theconditions of treatment to which it is subjected. The success of the improved method of the present invention is dependent, I believe, at

50 least in part, upon the provisions for cooling, heating and again cooling the tubes. I attribute this to the difference of the coeflicient of expansion between the metal Walls of the tube and the'carbonaceous deposit accumulated therein, 55 the alternate contraction and expansion of the tubes serving to loosen the coke deposit so that it may be flushed from the tubes.

The invention is, therefore, in its broadest aspect, limited only to alternate cooling and. heating of the fluid conduit followed by flushing of 5 the carbonaceous material from the tubes. However, considerable importance is attached to the particular steps employed in the present invention and their sequence, namely, the use of water and steam followed by the use of water 10 and then by the introduction of hot oil and finally by flushing of the tubes with cold oil, although due to the possibility of obtaining fair results by slight modifications and departures from the preferred conditions, it is not intended to limit the invention to the use of specific materials nor to a specific sequence of steps nor to the specific temperature conditions hereinafter mentioned.

The accompanying diagrammaticdrawing illustrates one specific form of oil heating furnace with provisions for employing the features of the present invention and the following description of the drawing will serve to more clearly illustrate one adaptation of the process of the present invention.

Referring to the drawing, the furnace l comprises, in the case illustrated, a combustion zone 2 and a heating zone 3. A combustible fuel-air mixture is supplied to combustion zone 2 through suitable firing ports 4 by means of any suitable form of burners, the tips of which are indicated at 5. Combustion of the fuel is substantially completed in zone Z'of the furnace and the hot combustion gases pass through perforations B in the central wall I of the furnace 'into heating zone 3, flowing downward therethrough over the tubular elements 8 of fluid conduit 9, located within this zone, and passing thence through flue ill to a suitablestack, not shown. 40

Fluid conduit 9, in the case here illustrated, comprises a plurality of superimposed horizontally parallel rows of horizontally disposed tubes 8 extending between the end walls of the furnace and connected, as indicated, in series by means of suitable return bends i I. The return bends on only the near end of the furnace are shown in the drawing. In the case here illustrated, the inlet to the heating coil is at the bottom of the tube bank on the near end of the furnace and the outlet is at the top of the tube bank on the far end of the furnace.

During normal operation of the process, oil may be supplied from any suitable source through line l2 and valve 13 to pump M by means of which it is fed through line l5 and valve Hi to the fluid conduit, flowing therethrough in a general upward direction and being heated to the desired temperature by the hot combustion 6 gases passing through heating zone 3, the stream of heated oil being discharged from the upper portion of the tube bank through line I! and valve l8 to subsequent portions of the-oil treating process not pertinent to the present invention 10 and therefore not illustrated.

After an appreciable amount of coke has been i deposited upon the inner walls of tubes 8 of the fluid conduit but before a sufilcient quantity of coke has accumulated thereon to greatly hinder l5 smooth operation of the process or to create a fire hazard, the supply of fuel to the combustion zone of the furnace is discontinued so that the fires are extinguished and by opening valve is in drop-out line the oil is permitted to drain from 20 the heating coil, pump I 4 having, of course, been stopped and valve I6 closed in order to discontinue the supply of charging stock to the heating coil.

Simultaneous with or following the opening of valve IS in line 20, valve It, in line H, is closed and valves 22 and 24 in the respective lines 2| and 23 are opened, admitting steam and water,

through the respective lines and through lines 25 and I! to heating coil 9, forcing out the oil through line 20 and reducing the temperature in the heating coil. The quantity of steam admitted through line 2| is gradually diminished and the quantity of water admitted through line 23 gradually increased until the temperature of the material leaving the heating coil has reached approximately 200 F., as measured, for example, at a point indicated by pyrometer 26 in line IS. The supply of steam to the heating coil is then stopped by closing valve 22 and the flow of water through the heating coil is continued until the temperature of the water leaving the heating coil is approximately 100 F., or less.

The supply of water is then shut off by closing valve 24, valve I9 is closed and hot oil is charged 4 to the heating coil from any suitable source such as, for example, by diverting a portion of the stream of heated oil from a similar furnace, not illustrated, through line 21 and valve 28 and through line I! into heating coil 9, the temperature of the oil being preferably in the neighborhood of 500 E, or thereabouts. The water may be allowed to drain from the heating coil through valve l0 and line 22, prior to the introduction of the heated oil, or the stream of heated oil may be employed to force the water out of the heating coil, for example, through line 29 and valve 3. into tank 3|.

When desired, any or all of the materials above mentioned (water, steam and heated oil) may be supplied to the heating coil from the opposite direction to that illustrated and above described by well known means, not illustrated. Also, when desired, any or all of the various materials may be supplied to and/or withdrawn from the heat-' ing coil at any desired intermediate point or plurality of points therein. This may be accomplished by connecting the supply lines to any one or more of the various return bends H and by discharging materials thus supplied to the heating coil from either the inlet or outlet end of the heating coil or from a suitable intermediate point beyond the point of introduction of the materials. This method of operation is particularly desirable in case an appreciable deposit of carbonaceous material occurs in only a portion of the heating coil, in which event it is not necessary to apply the cleaning method provided by the present invention to the relatively clean portion of the heating coil.

After the heating coil has been charged with heated oil at a temperature of about 500 F., pump it may be again started to supply relatively cold charging stock to the heating coil, in the manner previously described. The flow of relatively cool oil to the heating coil is continued at a rapid rate for a period of time (10 minutes, for example) in order to flush out the carbon in the tubes, the stream of oil and coke passing from the heating coil, for example, through line 29 and valve 30 into tank 3| wherein the coke may be allowed to -.settle out.

Following this operation the fires may be relighted in combustion zone 2 and the normal operation of the process continued.

The conditions of operation above given in connection with the description of the drawing are those which have been found satisfactory for the removal of coke from the furnace tubes of a topping plant operating on California crude from the Los Angeles basin. The whole procedure above outlined takes on the average about 1 hours, from the time the fires are extinguished until the plant is again under normal operating conditions, whereas, by the former method of cleaning thetubes (by use of a turbine-driven cleaning'device) about five hours is required for cooling before the heating coll can be opened for cleaning and about six hours is required for the actual cleaning operation so that, on the average, the heater is out of service for about eleven hours.

By employing the present method of cleaning at regular intervals of ten days to two weeks, the damaging or burning of tubes from overheating, due to carbon deposits, has been entirely eliminated and practically continuous smooth operation of the process has resulted over periods as long as three months. Without employing the periodic method of cleaning provided by the present invention, it was necessary to shut down the furnace and turbine the tubes at least once a month. It is estimated that the method of the present invention has decreased the maintenance and cleaning costs on this particular furnace installation by at least 50% and it is now in regular use in a large number of such furnaces. This 50% decrease in maintenance cost does not take into consideration the increase in productive operating time obtained when employing the process of the present invention, due to the decreased time required for cleanouts, not to mention, from an operation standpoint, the loss in time of this particular furnace while being turbined.

I claim as my invention:

1. In a process for heating hydrocarbon oils by passing the same continuously through a fluid conduit within a furnace, the method of preventing the excessive accumulation of coke within the conduit which comprises periodically discontinuing the supply of heat to the fluid conduit from the furnace and discontinuing the supply of oil to the fluid conduit, removing the oil from the fluid conduit and introducing thereto a mixture of water and steam, continuing the supply of water and steam to the fluid conduit until the temperature of the materials discharged therefrom is below the temperature of saturated steam, further cooling the fluid conduit by the continued passage of water therethrough, then charging the fluid conduit with hot oil at a temperature of at least 400 to 600 F., then rapidly passing a stream or. relatively cold oil through the heating coil to flush out the carbonaceous material and subsequently 5 lighting the fires and continuing normal operation of the process.

2. A process 'for removing carbonaceous deposits from the fluid conduit of an oil heater embodying the steps which comprise cooling the 10 fluid conduit by passing aqueous fluid therethrough, reheating the fluid conduit by charging the same with hot oil and flushing the fluid conduit with relatively cold oil.

3. A process for removing carbonaceous de 15 posit from the fluid conduit of an oil heater which comprises passing water and then hot oil through the conduit to'loosen the carbonaceous material by resulting contraction and expansion of the conduit, and then flushing the latter 20 out of the conduit.

4. A process for removing carbonaceous deposit from the fluid conduit of an oil heater which comprises passing steam, water and hot oil through the conduit in the order named,

thereby loosening the deposit, and then flushing the loosened material out of the conduit.

5. A process for removing carbonaceous deposit from the fluid conduit of an oil heater which comprises passing steam, water, hot oil and relatively cold oil through the conduit in the order named.

6. A process for removing carbonaceous deposits from the fluid conduit of an oil heater which comprises alternately contracting and expanding the conduit by alternately passing relatively cold and relatively hot fluids therethrough in the absence of combustion whereby the deposits are loosened and finally flushing the fluid conduit.

7. A process for removing carbonaceous deposits from the fluid conduit of an oil heater which comprises alternately contracting and expanding the conduit by alternately passing relatively cold and relatively hot liquids therethrough whereby the deposits are loosened and finally flushing the fluid conduit.

CHARLES L. JOHNSTON.

Images