Method for weakening and removing coke and carbonaceous deposits

Abstract

The present invention concerns a method of weakening and removal of coke or carbonaceous material which deposits as a result of thermal cracking of hydrocarbons on the inner walls of coils, piping, tubing, and in general, hydrocarbon processing equipment.

Claims

1. A method for the weakening of coke or other carbonaceous deposits on inside walls of coils, piping, tubing, and other general hydrocarbon processing equipment comprising: exposing said inside walls of coils, piping, tubing, and other general equipment to a pressurized gas, sealing and pressurizing said coils, piping, tubing, and other general hydrocarbon processing equipment, allowing sorption of gas into the coke or other carbonaceous deposit, and then depressurizing the inside walls of coils, piping, tubing, and other general equipment and contents of said gas, wherein said gas includes carbon dioxide in a concentration of 50% and above.

2. The method of claim 1, wherein the pressure of the gas stream is in a range between about 50 and 5,000 psi.

3. The method of claim 1, wherein the gas is a mixture containing carbon dioxide and one or more secondary component gases.

4. The method of claim 3, wherein the secondary component gas is selected from methane or a higher hydrocarbon.

5. The method of claim 3, wherein the secondary component is gas is hydrogen.

6. The method of claim 3, wherein the secondary component gas includes oxygen.

7. The method of claim 3, wherein the secondary component gas includes nitrogen.

8. The method of claim 1, wherein the gas and/or the coke or other carbonaceous deposit is heated above ambient temperature during the treatment.

9. The method of claim 1, wherein depressurization is at sufficient rate to remove loosened deposits from a furnace.

10. The method of claim 1, comprising the additional subsequent step of passing a flow of gas through the equipment to sweep loosened deposits from the equipment.

11. The method of claim 1, comprising the additional subsequent step of performing mechanical cleaning treatment to remove weakened deposits from equipment.

12. The method of claim 11 wherein the mechanical cleaning treatment is completed by flowing an abrasive-laden high velocity gas stream through the equipment.

13. The method of claim 11 wherein the mechanical cleaning treatment is completed by pigging.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The objects and advantages of the invention will be better understood from the following detailed description of the preferred embodiments thereof in connection with the accompanying figures wherein like numbers denote same features throughout and wherein:

(2) FIG. 1 is a graph illustrating the impact on the hardness of anthracite coal from CO.sub.2 exposure at various pressures.

(3) FIG. 2 shows the removal of coke from a coked furnace tube from an atmospheric distillation unit before and after 12 hours of CO.sub.2 exposure at 750 psi.

(4) FIG. 3 is an exemplary embodiment of the process schematic of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) The present invention concerns a method for weakening and removal of carbonaceous material and coke inclusive of a two-step process of pressurization followed by depressurization. The process can be repeated as necessary in order to maximize the result.

(6) The system/equipment must be able to hold gas at a pressure substantially higher than ambient pressure. This may necessitate the installation of pressure isolation valving or various ports capped and plugged in order to retain the integrity of the treatment gas within the target system. The system is then filled with the treatment gas at pressures ranging from about 50 to 5,000 psi, and may be either isolated or continually attached to the treatment gas source in order to maintain system pressure as the gas is sorbed into the coke deposits. After a set period of time, the treatment gas is released, and a subsequent flow of gas or liquid may be used to remove any deposits that have become dislodged from the wall.

(7) An example and resulting impact of such treatment is shown in FIG. 1 using anthracite coal. The treatment gas, in this example, approximately 100% CO.sub.2, was injected into the system in a vapor state. A liquid state can also be used, but economics favor a vapor treatment. The treatment was carried out at ambient temperature (70 F.) generally which eliminates the need for heating and cooling during treatment. The system was filled with CO.sub.2 at pressures of 130, 400, and 750 psi. At 750 psi, this is the pressure which is close to, but below the condensation pressure of CO.sub.2 at ambient temperature. The hardness of the anthracite coal was measured using a durometer before and after exposure with the starting hardness of the coal estimated to be around 80 on the Shore D scale. A reduction in hardness correlates to the highest sorption volumes which is achieved by long soak times at high pressures. Therefore samples exposed to the highest pressures for the longest periods of time resulted in the greatest reduction in hardness and were most easily friable. Although this example has been done in relation to CO.sub.2 and other gases such as methane, higher hydrocarbons, oxygen, nitrogen, and mixtures thereof can be utilized. Preferably, the gas predominantly carbon dioxide in a concentration of anywhere from 1 to 100%, more preferably at a concentration of 50% and above. Where the carbon dioxide is less than 100% it is a mixture with a secondary gas component in a concentration of 0 to 99%, wherein the secondary gas is selected from methane, higher hydrocarbon, hydrogen, nitrogen, and oxygen.

(8) FIG. 2 shows a similar treatment of an 8-inch pipe segment from an atmospheric distillation pre-heater or furnace. The sample was treated at ambient temperature for 12 hours at a pressure of 750 psig. The image on the left depicts the pipe segment before treatment, while the image on the right is the pipe segment after treatment and a significant portion of the coke deposit removed from the pipe segment. No subsequent treatment was used in the removal of the coke layer from the pipe walls. The example treatment was able to remove 84.3% by mass of coke from the tube walls. The remainder of the coke material, which has been weakened at this stage, can be removed by a subsequent step of either pigging, SAD, spalling or SandJet, as mentioned above.

(9) FIG. 3 shows an exemplary embodiment of the method described. The system includes CO.sub.2 and potentially another gas 100 that is used to feed an optional pump 101. The pump 101 is used to bring the gas to treatment pressure if the gas source 100 is not already. Otherwise, the pump may be excluded from treatment. It is assumed that the equipment targeted for treatment 103 is at an already low-pressure state, likely atmospheric pressure. The gas flows from the source 100 to the target equipment 103 via an optional isolation valve 102. Isolation valve 104 is closed to prevent any of the treatment gas from leaving the target equipment 103. Once the target equipment is at treating pressure, the equipment may be isolated from the source using isolation valve 103 or left in fluidic contact with the equipment in order to maintain pressure as gas is sorbed into the coke material. After a set time (generally around 6 to 12 hours) the gas is relieved quickly (generally less than 1 hr) from the target equipment 103 via isolation valve 104. The gas source prior to venting is either isolated using isolation valve 103 or removed from the process. These steps can be repeated as necessary until the desired results are achieved.

(10) Although various embodiments have been shown and described, the present disclosure is not so limited and will be understood to include all such modifications and variations as would be apparent to one skilled in the art.