METHOD TO REMOVE EXPLOSIVE AND TOXIC GASES AND CLEAN METAL SURFACES IN HYDROCARBON EQUIPMENT

Abstract

The present invention relates to a method of rapidly decontaminating and making safe for entry, hydrocarbon contaminated equipment by sequencing a cleaning mist or foam, an encapsulating mist or foam and a dry carrier gas.

Claims

1. A method for removing hydrocarbon contaminants and toxic gases from a system, comprising the steps of: (i) providing a dry carrier gas source; (ii) providing an encapsulating agent source; (iii) providing a surfactant source (iv) providing a cleaning agent with a high solubility index from a cleaning agent source; (iv) mixing the cleaning agent and the dry carrier gas in a high shear mixing device to create a liquid mist/foam which is introduced into the system so as to solubilize the heavy organic residues on metal surfaces; (v) mixing the encapsulating agent and the dry carrier gas in a high shear mixing device to create a liquid mist/foam which is introduced into the system to cap generation of toxic gases from remaining organic residue; (vi) delivering dry carrier gas from the dry carrier gas source to the system to remove all liquid and gaseous hydrocarbon contaminants out of said system (viii) sequencing or cycling of at least two of the following steps (iv), (v) and (vi) until concentration of explosive gases (LEL's) reaches acceptable limits.

2. A method for removing hydrocarbon contaminants and toxic gases from a system, comprising the steps of: (i) providing a dry carrier gas source; (ii) providing an encapsulating agent source; (iii) providing a surfactant source; (iv) mixing the encapsulating agent and the dry carrier gas in a high shear mixing device to create a liquid mist/foam which is introduced into the process system to cap generation of toxic gases from remaining organic residue; (v) delivering dry carrier gas from the dry carrier gas source to the system to remove all liquid and gaseous hydrocarbon contaminants out of said process equipment (vi) sequencing or cycling of steps (iv) and (v) until concentration of explosive gases (LEL's) reach acceptable limits.

3. A method for removing hydrocarbon contaminants and toxic gases from a process system, comprising the steps of: (i) providing a dry carrier gas source; (ii) providing a surfactant source; (iii) providing a cleaning agent with a high solubility index from a cleaning agent source; (iv) mixing the cleaning agent and the dry carrier gas in a high shear mixing device to create a liquid mist which is introduced into the process system so as to solubilize the heavy organic residues on metal surfaces; (v) delivering dry carrier gas from the dry carrier gas source to the process equipment to remove all liquid and gaseous hydrocarbon contaminants out of said process equipment (vi) sequencing or cycling of steps (iv) and (v) until concentration of explosive gases (LEL's) reach acceptable limits.

4. The method of claim 1, further comprising: providing the carrier gas at a flow rate ranging from 10 scfm to 10,000 scfm, and wherein said carrier gas is nitrogen.

5. The method of claim 1, wherein the carrier gas is selected from the group consisting of carbon dioxide or a hydrocarbon gas selected from the group consisting of methane, fuel gas, natural gas, ethane, propane, butane and a combination thereof.

6. The method of claim 1, wherein the encapsulating agent comprises a foaming agent and a cleaning a surfactant.

7. The method of claim 4, wherein the encapsulating agent further comprises an amine compound, a methyl ester and a foaming agent.

8. The method of claim 1, wherein the mixing nozzle is an eductor.

9. The method of claim 1, wherein the mixing nozzle is a t-fitting.

10. The method of claim 1, wherein the pressure differential across the mixing device is in the range of 60-150 psig.

11. The method of claim 1, wherein the expansion ratio across the mixing device has a foaming expansion ratio in the range of 200-1000.

12. The method of claim 1, where the LEL is reduced to a lower explosive limit of less than 10 percent.

13. The method of claim 1, where the H.sub.2S concentration is reduced to less than 2 ppm.

14. The method of claim 1, wherein the cleaning agent is selected from the group consisting of terpene, naphtha, distillates, xylene, toluene, turpentine, paint thinner, and methyl ester.

15. The method of claim 1, wherein the cleaning agent is injected into the process equipment at a temperature range of 60-250° F.

16. The method of claim 1, wherein the cleaning agent is d-limonene.

17. The method of claim 1, wherein the cleaning agent is an organic hydrocarbon compound with a carbon number in the range of C.sub.8-C.sub.40.

Description

BRIEF DESCRIPTION OF TABLES AND FIGURES

[0029] The objects and advantages of the invention is better understood from the detailed description with the following accompanying tables and figures:

[0030] Table 1 describes commercial time savings in a 3-phase separator drum and piping conduit at a SAGD facility;

[0031] Table 2 illustrates effectiveness of cleaning chemistries; and

[0032] Table 3 illustrates temperature effectiveness on cleaning chemistries;

[0033] FIG. 1 illustrates the typical layout of the equipment; and

[0034] FIG. 2 illustrates commercial application of the invention in heavy oil storage tanks.

DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention describes a method for rapidly decontaminating equipment or series of equipment in hydrocarbon processing industries, providing producers and refiners significant time savings. For the purposes of this invention, decontamination is defined as removal of oil and organic residues deposited on metal surfaces of equipment including any hydrocarbon that registers an LEL reading on an LEL detector. Types of compounds that register an LEL reading are typically light hydrocarbons e.g. C.sub.1-C.sub.8, preferably C.sub.8-C.sub.40. Given this enhanced time savings, producers not only reduce cost on additional cleaning steps required but are able to reach environmental and safety limits faster for atmospheric venting and personnel entry and alleviate FGRU capacity constraints. Additionally, this method also provides the benefit of reducing the probability of post-purge LEL spikes, a common safety issue seen in the heavy oil industry. This is a result of the requirement to keep sludge warm for transport and sludge's ability to off gas LELs.

[0036] The process involves sequencing the injection of a cleaning agent, an encapsulating or absorbing agent and a dry carrier gas (e.g., nitrogen) as described herein. The equipment footprint comprises of a series of fittings, hoses, a high shear mixer and high expansion foaming system. Prior to injection, the target equipment must be prepared for decontamination. This preparation involves ensuring that the target equipment is drained, injection or tie-in points are above any heavy residues or sludge levels, and vent streams are appropriately routed or treated (example scrubbed with a vapor scrubber or routed to the flare gas recovery unit). The method does not require operation at pressure, in fact the current treatment has proven very effective in storage tanks with a maximum allowable working pressure (MAWP) of 0.5 psig.

[0037] Once the desired equipment has been made ready for decontamination, a cleaning agent with a high solubility index and optionally, high aromatic content is suctioned or pumped at a controlled rate from the cleaning agent source [200]. Nitrogen [100] is heated and an accurate volumetric or mass flowrate and delivered to the high shear mixer (i.e., misting nozzle) [102] where the gas mixes with the cleaning agent to form a highly effective cleaning mist of cleaning agent liquid in nitrogen gas. The misting nozzle can be of different types spray heads, laval nozzle, an eductor or a t-fitting. In an exemplary embodiment, an eductor is used as the high shear misting nozzle. The misting nozzle is optionally coupled with a high expansion foaming nozzle [103] before entering the target equipment [104]. The foam nozzle [103] is designed to expand the foaming solution into bubbles of nitrogen in liquid chemical. This is achieved by delivering the mist of the foaming solution form the high shear mixer onto a stainless-steel screen and forcing the motive dry gas constantly through the screen. This continuous flow of both foaming solution and dry gas through the screen generates a large volume of foam. Based on the design parameters of the process equipment (e.g. size, vent stream processing, baffles, riser spouts, aeration nozzles, mixing nozzles etc.) the method of application (mist or a foam) is chosen. This mist or foam of the cleaning chemical is delivered to the entire volumetric space of the target equipment. When delivered as a mist, the liquid droplets traverse through the volumetric totality of the equipment like a fog. In a preferred embodiment, the misting nozzle is directly connected to the process equipment.

[0038] The nitrogen source [100] could be a nitrogen pumper, onsite pressure swing adsorption (PSA) system, onsite nitrogen storage with a vaporizer, or high-pressure nitrogen source (e.g., series of packs of cylinders or a tube trailer). The flowrate of carrier gas depends on the size and volume of the target equipment and can range from 10 scfm (˜0.3 m3/min) to 10,000 scfm (˜280 m.sup.3/min), and preferably in the range of 20-7300 scfm. In a preferred embodiment the nitrogen purity is 99.999% or greater. The liquid concentration during delivery is in the range of 0.01-0.2% on a volumetric basis to the carrier gas and preferably in the 0.03-0.1% range. CO.sub.2 or light hydrocarbon gases like methane, fuel gas, natural gas, ethane, propane and butane or a combination could be used as a carrier gas, although not inert.

[0039] When the cleaning agent enters the process equipment, it solubilizes or mobilizes any heavy organic residues stuck to metal surfaces. The typical volume of cleaning chemical injected is dependent on the estimated amount of contaminant in the equipment to be cleaned and the total metallic surface area that needs coverage. The cleaning agent may be applied at ambient temperature (70° F.) but is preferentially applied at higher temperatures, specifically 90-250° F. After injection of cleaning chemistry, it is preferred that drain points are opened to drain all dislodged organic material.

[0040] After the injection of the cleaning chemistry, an encapsulating (or absorbing) agent is delivered from the encapsulating agent source [201]. The encapsulation agent is suctioned or pumped [202] to the high shear mixer [102] where it mixes with the carrier gas and is delivered as a mist or foam into the target equipment. A mist allows for rapid dispersion of encapsulating chemical to all parts of the equipment. A foam on the other hand allows for good contact with all parts of the surfaces. The purpose of the encapsulating agent is two-fold: i) to neutralize the hydrogen sulfide (H.sub.2S) present and ii) cap the generation of noxious gases from the sludge. As the encapsulating mist settles, it forms a skim layer over hydrocarbon residues or sludge. This skim layer prevents any further off-gassing which might otherwise result in a post purge LEL spike.

[0041] One of the active agents in the encapsulating agent is the surfactant. Typically, surfactants have a hydrophobic tail and hydrophilic head. The hydrophilic head is electrically charged. Based on the charge, surfactants are broadly classified anionic, nonionic, cationic or amphoteric. Anionic surfactants have a negative charge and are foaming surfactants. They are used in frequently in soaps and detergents but create a lot of foam when mixed with gas. Nonionic surfactants on the other hand are neutral and do not have any charge on the hydrophilic end. Nonionic surfactants are typically very good at removing oils. They are low foaming or non-foaming and are typically used for cleaning purposes and used in conjunction with anionic surfactants. In a preferred embodiment, the encapsulation agent consists of amine compounds, a foaming and a cleaning surfactant. In another preferred embodiment, the expansion ratios of foam are in the range of 200-1000. The pressure drop (ΔP) across the high shear mixer is monitored and can affect the particle size of mist delivered. It is preferred that the ΔP is in 60-150 psig range. This allows for generation of fine mist or fog, enables good gas lift and dispersion throughout the volume of the tank. In the case where a foam is used as a method of application, it is preferred that the equipment is foam filled from the bottom up. This is to ensure that the total displacement of explosive gases is directed towards the vent hatch preventing any channeling or bypassing of LEL pockets.

[0042] After injection of the encapsulating agent, the vessel is treated with a sequence of treatment steps of carrier gas only and encapsulating agent mist/foam. This sequencing results in a dramatic reduction in time required to bring the noxious gas levels to acceptable limits. After the first hour of injection, vent or recycle stream gas sampling are done periodically until the equipment reaches target LEL limits.

[0043] The invention is further explained through the following examples, based on various embodiments of the invention, which are not to be construed as limiting the present invention.

Comparative Example 1

[0044] An example and resulting impact of such a treatment is shown in FIG. 1. Three tanks (T1, T2, T3) 1-million-gallon capacity skim tanks (approximately 60 ft in diameter and 50 ft in height) were scheduled for roof repairs and internal inspection at a steam assisted gravity drainage (SAGD) heavy oil site in northern Alberta, Canada. All three skim tanks had internals present. Also, the sludge content in the tanks was about 4 feet high and at 120° F. From prior operational data and backed by a purge model, the time taken to reach <10% LEL for maintenance work with nitrogen only purging was almost 20 hours. Given the internals, a mist was chosen as method of delivery. Encapsulating mist in nitrogen and nitrogen only was sequenced through a high shear mixer and delivered to the tanks. The ratio of volumetric flowrates of carrier gas in tanks T1, T2 and T3 was 1:2, 2:1 and 2.2:1, respectively. The results show a 50-70% reduction in time (FIG. 2) to render each tank safe for entry compared to historical data. All vapor exhaust measurements were taken using an industrial scientific MX-6 LEL detector.

Comparative Example 2

[0045] A large, 250 m.sup.3 3-phase separator process vessel containing slop (heavy oil, BTEX, H.sub.2S, sand, coke) needed to be emptied and cleaned for inspection and valve repairs during a turnaround. The vessel had tortuous internals, was laden with 2-3 feet of sludge and coke and continuously needed to remain above 200° F. to keep the sludge fluidized. The time taken to reach safe limits on the last turnaround was around 16 hours with nitrogen purging the method of choice. Two injection points were identified on the vessel given the vessels internals (specifically impingement baffles and splash baffles). The flow was split, and a sequence of encapsulating mist and nitrogen treatment was applied to the 3-phase separator vessel. Per Table-2, within 3.5 hours of sequencing encapsulating mist and nitrogen, the LELs including H.sub.2S was down to acceptable limits, an 80%-time savings for the customer. Additionally, LELs stayed suppressed (at close to 0%) for 7 days following treatment.

TABLE-US-00001 TABLE 1 Time savings in a 3-phase separator drum using novel treatment method At 3.5 hrs Component Initial Reading Target of treatment LEL % 100% 10% max 0 H.sub.2S 8 ppm 2 ppm max 0 O.sub.2  17% 2% <2%

Comparative Example 3

[0046] A 300-meter long diluted bitumen carrying piping conduit was selected to be cleaned for a valving change and an internal inspection. After the piping section was drained, the atmosphere was measured and read 100% LEL and 87 ppm H.sub.2S. The operator preferred the use of an organic chemical with no surfactant. Previously, by using nitrogen purging only, the same conduit took 12 hours to bring down LELs to acceptable limits. By sequencing an organic encapsulating/absorbing agent with nitrogen, the equipment was rendered safe within 4 hours, a 65%-time savings to the user.

Example 4

[0047] Metal coupons were coated with 1 gram of Canadian bitumen and a comparative analyses of solvency strength was tested by spraying 10 ml of highly aromatic and natural solvents. Solvency strength was analyzed by quantification of the residues dislodged and from the coupon as a percentage of the total initial weight. Results are tabulated in Table 2. Additional tests were conducted to quantify the influence of elevated temperature Table 3, clearly indicating increased solubility of the organic residue at higher temperature. Although there were 14 solvents tested, any C.sub.5-C.sub.45 hydrocarbon may be used as the cleaning agent.

TABLE-US-00002 TABLE 2 Solubilization of Bitumen using organic solvents % Bit. Removed No. Chemical (ambient) 1 Friction reducing agent <5 2 Heavy reformate 39.5 3 Toluene/Xylene mix 41 4 Reformed Naphtha 38 5 Xylene 73 6 Toluene 52 7 Gas oil <5 8 Distillates (I) 26.4 9 Distillates (II) <5 10 Heavy aromatic 5 naphtha 11 Terpene 60 12 Turpentine 13 13 Paint Thinner 26.1 14 Methyl Ester −10.6

TABLE-US-00003 TABLE 3 Effect of Temperature on solubility of cleaning chemistries % bitumen % bitumen solubilized solubilized No. Chemical 90 F. 135 F. 2 Heavy reformate 62.5 98.4 4 Reformed Naphtha 61.5 97.9 8 Distillates (I) 32 89.6 11 Terpene 74.2 96.8 7 Gas Oil 46.4 77.4 9 Distillates (II) 57.4 89.2

[0048] 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.