DK142290B - Method of Removing Coke Deposits from Hydrocarbon Vapor Wires. - Google Patents

Description

(11) PRESENTATION 142290

DENMARK «" * "« * Il «, j ;; S

'(21) Application No 2508/75 (22) filed on 4 Jun 1975 (24) Race day 4 jUTl. 1975 (44) The application submitted and - the writ petition published on o · oct. 1980

DIRECTORATE OF

PATENT AND TRADE MARKET (30) Priority requested from it

June 5 1974, 476725, US

(7i) TOSCO CORPORATION, 10100 Santa Monica Boulevard, Los AngeleB, "California $ 0067, OS.

(72) Inventor: John H. Walker, 5800 Stockdale Highway - Apt. 42 Bakers = field, California "93509, US.

(74) Plenipotentiary in the proceedings:

Hofman-Bang & Boutard Engineering Company.

(54) Procedure for removing coke of le jr Inger from hydrocarbon = steam conducting wires.

The invention relates to a method for removing coke deposits from hydrocarbon vapor conduits while still passing hydrocarbon vapor through the conduit.

In the performance of hydrocarbon cracking operations, such as those involved in "fluid coking" operations, coke or carbon is gradually deposited in the steam line leading from the reaction equipment. Ultimately, these coke deposits severely curtail the flow of hydrocarbon vapors from the reaction zone and cause the pressure in the reaction zone to increase to dangerous levels.

As a result, the reactor must be stopped when a dangerous pressure level is reached and the coke deposition is removed from the conduit.

2 142290

Coir deposition on the inner liners of exit lines from the product steam cyclone in "fluid coking" reactors has been a problem for some time. In a hydrocarbon cracking operation, such as "fluid coking" or pyrolysis, the product vapors are usually removed from above through a cyclone located in the upper part of the reactor.

Since these vapors leaving the reaction zone are at or near their dew point or condensation point, they will condense on any cooler surface. This usually applies to the surfaces of steam lines which carry the vapors from the reaction zone to extras such as a fractionator. This condensation and subsequent coke deposition is particularly severe on surfaces with temperatures of from about 370 to about 540 ° 0. The continuous deposition of coke in these product transfer lines causes the pressure drop to increase to unacceptable levels requiring closure and purification as noted above.

In "fluid coking" systems, a suggested solution has been to inject finely divided hot coke particles into the dispersed phase to prevent coke deposition and condensation by heating the vapors and scraping off of stored cocks from the cyclone. This method has been widely used. However, it has proved difficult to implement and has not been able to completely remove coke deposition in the cyclone exit nozzle. Other methods have been proposed to remove coke deposition in the effluent nozzle and steam transfer lines during operation. In the disclosure of U.S. Patent No. 2,934,489, it is proposed to inject a controlled small amount of oxygen-containing gas into the cyclone to burn a portion of the product vapors for the purpose of raising the temperature of the interior surfaces of the discharge lines so as to prevent coke deposition. This procedure is not desirable as combustion products enter the hydrocarbon stream. In U.S. Pat. No. 2,326,525, it is proposed to positively prevent the build-up of coke deposits in steam pipes by periodically forcing a cartridge plunger provided with rotary spray nozzles through the deposition of material in the steam pipe while spraying oil of the order of 105-140. kp / cm in an amount of from about 284 to about 568 liters per liter. per minute through each of four nozzles. The cartridge piston or "bumper" is used to push through tar-like materials or break hardened coke. By applying the oil under such pressures and in such quantities, it is possible to wash the tar-like or soft deposits from the steam riser and scrub the walls free of coke deposits which may have been baked therefrom. The operation is performed once or twice a day for 2 - 3 minutes. This method would not be satisfactory for large-scale commercial "fluid coking" or pyrolysis operations because such amounts of spray oil when injected into the cyclone effluent nozzle would seriously interfere with coking or pyrolysis operations by distilling large quantities of vapor into the steam line. This, in turn, would seriously interfere with the coking operation by producing a substantial increase in pressure in the reactor and fractionation equipment. Such pressure increase could cause the reactor to shut down and damage to the fractionation equipment. To avoid this situation, the feed rate to the reactor had to be substantially reduced to compensate for the vapor volume supplied to the fractionator. Having to perform such a cyclic operation at a frequency of once or twice every 24 hours would be highly undesirable from a service point of view. Such severe fluctuations would not only damage the reactor but also all refining equipment thereafter.

The object of the present invention is therefore to provide a method of removal during operation of coke deposits from steam cyclone effluent nozzles and hydrocarbon vapor pipes without detrimental effect on the fluid coking or pyrolysis reaction, reactor and additional equipment and subsequent refining equipment.

This is achieved by the method according to the invention, which is characterized by the characterizing part of claim 1 *.

It has been found, according to the invention, that for a 834 m 2 / d fluid coking plant a relatively small amount of cold water, preferably between 113 and 152 liters per per minute, applied at a pressure exceeding about 350 kp / cm, give the coke deposit a thermal shock, break it, and blow the pieces out of the nozzle without detrimental effect on the coking or pyrolysis operation. The amount of water will vary somewhat depending on the size of the plant, but the amount of water must be sufficient to produce a sudden, rapid change in the boiling temperature. It is desirable to reduce the amount of steam supply to the "fluid coking" plant during the injection period by an amount approximately equal to the volume of water which will evaporate during the injection operation. The above procedure has been successfully performed on a large scale on an 834 m 2 / d fluid coking plant which had hitherto had to be stopped to manually remove coke deposits from the cyclone outflow nozzle. Experiments conducted at this plant are carried out by the coking operation during operation of from about 30 to about 6 minutes at 4-6 month intervals.

The process according to the invention will be described in the following in connection with a conventional 834 m 2 / d fluid coking plant. Such a plant includes a reactor with a cyclone separator through which the cracked hydrocarbon vapors are passed to remove tar particles before the vapors enter a fractionator. "Fluid coking" reactors generally operate at pressures of less than 3.5 kp / cm. This particular reactor is usually operated at a pressure of less than 1.4 kp / cm, with the maximum reactor pressure Λ being about 1.75 kp / cm. The pressure drop through a clean cyclone is normally from about 0.07 to about 0.28 kp / cm. As coke deposition occurs in the cyclone effluent nozzle, this pressure drop is allowed to increase to about 0.7 - 0.84 kp / cm, at which point the coke deposition must be removed to avoid excessive pressure in the reactor. Thus, when the pressure drop is increased to about 0.70 - 0.84 kp / cm, a lance is inserted through a nozzle into the side of the reactor wall and into the steam cyclone outflow nozzle. the lance contains two small opposite holes through which the jet of water is directed to the coke deposit on the inner surfaces of the outflow nozzle. These holes are preferably inclined towards the end of the lance at an angle of about 5 ° so that the coke pieces are blown out of the nozzle in the direction of the normal hydrocarbon vapor stream. Prior to the injection of water, the feed rate to the reactor is reduced by about 119 m 2 d and the vapor volumes are somewhat reduced to compensate for the volume of evaporated water to be fed above the fractionator. Water at a temperature of from about 10 to about 21 ° C is applied to the lance under pressure. The volume of water and the pressure is increased until a volume of 113 - 152 liters per liter is reached. per minute and a pressure of from about 420 to about 490 kp / cm, at which time the coke deposition will break up and blow out from the nozzle. As soon as the coke deposition is removed, a rapid decrease in the cyclone pressure loss will be noticed and the pressure loss will return to its normal operating range of the order of 0.07 - 0.28 kp / cm. The lance is then pulled out and the coking operation is brought back to normal. The following examples serve to better illustrate the process of the invention applied to an 834 noVd fluid coking plant.

EXAMPLE 1 The "fluid coking" plant was run at a feed rate of about 754 m 2 / d with a cyclone pressure drop of 0.636 kp / cm 2. The step sequence given in the following table was used to successfully reduce the pressure drop to 0.274 kp / cm 2:

TABLE I

Time Unit conditions and procedures 9.00 Unit conditions:

Input 518 m ^ / d

Lower agitation steam 1195 kg / h

Distillation steam 1020 kg / h Lift steam for hot coke 946 kg / h

Cyclone Δ P 0.432 kp / cm2

Reactor pressure 0.844 kp / cm2 9.13 The lance is inserted with a flow of 22.7 liters / min.

9.15 5-7.5 cm inside the cyclone exit nozzle, 113 liters / min. at 316 kp / cm2, 1.05 kp / cm2 reactor pressure, 0.457 kp / cm2 cyclone Δ P.

9.20 10 cm inside the nozzle, the lance is rotated, 133 liters / min. at 457 kp / cm2.

9.53 7.5 cm inside the nozzle, rotated, 133 liters / min. at 457 p kp / cm.

10.06 23 cm in and out, the lance is rotated, 133 liters / min. at 457 kp / cm2.

2 10.14 18 cm inside the nozzle, 133 liters / min. at 457 kp / cm.

2 10.56 23 cm inside the nozzle, 133 liters / min. at 457 kp / cm.

6 142290

Time Unit conditions and procedures 10.59 28 cm inside the nozzle, the lance is rotated.

11.06 An obstacle was felt to disappear.

11.09 33 cm, something gave in, the rotating lance felt for obstruction 35.5 cm inside the nozzle.

11.12 41 cm inside the nozzle, something yielded.

11.16 35.5 cm inside the nozzle, lots of bits hit the lance.

11.20 0.176 kp / cm ^ in cyclone 4 P, now in Ϊ tah. 0.218 kp / cm ^, large chunks hit the wall of the cooling tower.

11.35 Moves 28 - 43 cm rotating with the lance in the down position.

11.40 51 cm inside.

11.49 Out at idle.

o 12.02 135 liters / min. Yed 457 kp / cm 35.5-41 cm lance rotation and probing.

12.17 Moves out as the lance is rotated.

12.18 Out and idle.

6.00 Input: 747 m 2 / d, cyclone & P: 0.274 kp / cm 2.

From the above data, it is clear that the coke could not be removed successfully until the water flow reached about 133 liters per liter.

per minute at 457 kp / cm.

EXAMPLE 2

This example provides a time table of another coking operation performed approximately 4 months after the previous coking operation.

TABLE · 2

Time Unit conditions and procedure 10.00 The unit runs at full speed with the following readings: 7 142290

Time Aggregate conditions and procedure

Beg 787 m5 / d

Stirring steam 1762 kg / h

Distillation steam 1258 kg / h Lift steam for hot coke 1793 kg / h

Cyclone δ E 0.598 kp / cm 2

ISLAND

Reactor pressure 1,407 kp / cm 10.02 The hedge feed and steam volumes were reduced to achieve a reactor pressure of 1,195 kp / cm.

2 11.45 The unit stabilized at 1,195 kp / cm reactor pressure; Readings:

Beg 685 m ^ / d

Stirring steam 1566 kg / h

Distillation steam 1057 kg / h Lift steam for hot coke 1537 kg / h

Steam through conduit for large coke- 363 kg / h to 0 pieces, reduced

Cyclone δ P 0.520 kp / cm2 13.20 Started removing plug for insertion of lance.

13.48 lance in place ready to open the hot water valve.

13.53 The lance inside the valve, water started at 18.9 liters / min. Cyclone δ E briefly decreased 0.07 kp / cm and returned to 0.520 kp / cm2.

13.55 45.4 liters / min, 35> 2 kp / cm2. Now at the tip of the nozzle.

13.56 Now about 5.1 cm inside the nozzle. Cyclone δ E increases to 0.556 kp / cm 2.

13.57 Water flow increased to 56.8 liters / min. and 70.3 kp / cm 2.

p

Reactor pressure now 1,407 kp / cm. The lance is rotated 5.1 cm inside the nozzle.

2 14.00 The water flow increases to 90.8 liters / min. and 176 kp / cm about 5.1 cm inside the nozzle. Sudden decrease in cyclone Δ P to 0.354 kp / cm2. Reactor pressure now down to 1,267 kp / cm. The operators closest to the cooling tower report that they have heard no sounds.

2 14.02 The flow of water is increased to 117 liters / min. and 246 kp / cm.

Rotated at the entrance.

8 142290

Time Unit conditions and procedure 14.03 125 liters / min. and 317 kp / cm 2.

14.Ο6 133 liters / min. and 387 kp / cm2 still the Ted entrance.

14.07 Moves 10.2 cm in. The ladder drum level is very high. Beginning is reduced to 608 m 2 / d to correct the level.

14.08 Operators report hearing blasts hit the wall, but no change in Δ P.

14.09 Moves into the nozzle a total of 15.3 cm. Hear another · blunt

ISLAND

hit the wall. Sudden drop in ^ P to 0.204 kp / cm. The reactor pressure is now 1.054 kp / cm. Operators make corrections to increase reactor pressure.

p 14.11 136 liters / min. and 422 kp / cm of water. Moves in a total of 19.1 cm. 22.9 cm to the back wall.

14.15 Met coke 5.1 cm from the metal. Heard several snippets and achieved a further reduction in & P of 0.014 kp / cm. Setting the steam rates back to normal.

2 14.17 Still at 136 liters / min. and 422 kp / cm of water. The lance is moved out of the nozzle. The lance is rotated.

14.24 fat valve 45.4 liters / min.

14.26 The tooth is stopped.

14.46 δ P 0.176 kp / cm, the measurement is satisfactory.

15.10 The supply is increased to normal.

16.15 The unit is returned to the quantities it ran at. 10.00, cyclone P = 0.169 kp / cm 2.

From the above timetable, it is clear that a smaller decoction occurred at about 176 kp / cm, but the coke mixture did not start successfully until a water flow of 133 liters / min was reached, at a pressure of about 387 kp / cm cm.