Organic Clays for Treating Gas and Oil Pipelines
(Special Shared Content with Biomin Inc.)

Study results based on onsite usage of organically modified clays, also known as organoclays, have been proven efficient and
cost-effective in cleaning up water devoted to pipe line cleaning and hydrostatic testing.

Organoclays have been used successfully on a variety of pipe line projects where contaminated water required treatment before disposal, as well as site treatment where spills have taken place in environmentally sensitive locations.

For the most part, pipe line operators have used the technique to treat water used to hydro-test crude oil and natural gas pipe lines, and fuel storage tanks when switching from one fuel to another. In such cases, the crude is removed from the pump station and pipe line. The line is then cleaned, first by flooding with a light solvent such as toluene, followed by water. The solvent removes the oil film from the line (or tank) wall.

This process minimizes the contamination of hydro-test water that is then pumped through the line. Further, it reduces hydrocarbon vapors present in the line during subsequent repairs, replacements and modifications to the pipe line. On occasion, lines connected to compressor and measurement stations are also hydrostatically tested, usually at several times the design pressure.

Even with these precautions, the process results in contaminated water that has to be treated before it can be disposed. The water can be treated in either a nearby municipal treatment plant, or hauled off to a treatment facility. Both approaches are expensive. Another method is to inject this water into disposal wells. This method carries a high cost, because the oil coats the pores in the downhole formations, which necessitates frequent costly clean-up using acid injection.

Lab results
Based on laboratory column tests, organoclay has proven to be much more effective in removing oil than activated carbon.

Emulsified oil
Since hydrostatic testing and pipe line clean-up waters contain emulsified oil, the emulsions are broken by the following process:

1. Heating the water
2. Adding a metal salt such as polyaluminum chloride
3. Lowering the pH and possibly adding a coagulant and flocculent.

The water is then passed through a coalescing plate separator and discharged. The water quality must pass National Pollution Discharge Elimination Standard (NPDS) permits, and local discharge limits, before it can be discharged into a river or a sanitary sewer system.

In many states, the discharge limits for oil and grease are already 10 parts per million (ppm). These standards are likely to be lowered over the next few years, and states that currently do not have these standards will almost certainly adopt them in the near future.

Oil/water separators cannot consistently achieve such low levels of oil and grease content. The traditional method of using activated carbon alone is far too expensive due to quick coating of the carbon's pores by the oil, resulting in frequent changeouts.

Deposits
Another problem often encountered when cleaning crude oil pipe lines is paraffin deposits on the pipe wall. Paraffin can be removed with light hydrocarbons such as toluene, which in turn must be removed from hydro-test water, requiring constant cycling.

Similar problems are found in fuel storage tanks, where chemicals such as polynuclear aromatics and benzene are found. Benzene, in particular, is considered hazardous, and usually requires special treatment.

In the past, operators have used activated carbon, both onsite and offsite, to treat these waters, using carbon as the final polishing step.  Activated carbon, however, removes only 5-10% of its weight in oil and other large hydrophobic low-solubility hydrocarbons. Therefore, the economics of using carbon alone are clearly unacceptable.

Organically modified clays
A granular filter media, organically modified clay, has found acceptance as a pre-polisher to activated carbon, and as a post-polisher to oil/ water separators and batch treatment systems that use emulsion breakers.   This modified clay also is called organoclay.

The clays are being used with great success in groundwater remediation and industrial wastewater treatment by trendsetting corporations in the industry. They can remove oil and other hydrophobic non-polar compounds at 50% their weight or more, 700% more than activated carbon.

Organoclays consist of bentonite, modified with cationic quaternary amines.  The modification results in a non-ionic surfactant with a solid base that allows oils, PNAHs and other hydrophobic, chlorinated hydrocarbons to partition onto the clay surface, where they are strongly held by Coulombic forces.

The organoclay granules are blended with anthracite to prevent early plugging.  Anthracite, which has the same bulk density as the organoclay (56 lbs/ft³), prevents early plugging of the interstitial pores.

It also removes larger droplets of heavy oils, such as Bunker C oil, in the same manner as walnut shells, which are often used to remove large oil droplets from pipe lines, when the oil is in a coagulated sate with comparatively large particles.  This method only works well with particles down to the 10-15 ppm level.

However, the organoclay is far more effective at low levels, frequently achieving non-detect levels.  The organoclay is placed into activated carbon vessels, requiring only the addition of a pressure relief valve on top of the vessel (air builds up more easily due to its higher bulk density).   In a number of recent cases, organoclays were used effectively as part of the treatment train.

Case history 1
In 1995, at a compressor station in Mississippi, a combination of oil leakage and pipe flushing contaminated the washdown water.

To solve the problem, a water treatment system was installed.  It consisted of a wastewater holding tank with an oil drain-off valve, a coalescing oil/water separator fitted with an oil-skimming weir and an effluent holding tank, along with two tertiary polishing filters.

The first filter included organoclay, while the second and last filter contained activated carbon to remove the light-end hydrocarbons from the water before it was discharged.  The effluent quality resulted in non-detect levels, and the media is changed out only once a year.

Case history 2 
In 1996, an oil field produced water at a site in central Michigan containing 500 ppm residual oil.  The water was injected into an injection well at a rate of 3500 bpd.  Injection rates were reduced constantly because the pores in the downhole formation were plugging.

This meant that every three months, the operator had to engage a workover rig to inject hydrochloric acid and xylene-based solvents into the formation to partially restore its permeability.  The cost was $7,500 for each injection, plus downtime for the drilling crew and equipment.

It became obvious a more expedient and less expensive solution was needed.   An oil/water separator was set up at the well head, along with a carbon vessel filled with 1,200 lbs of organoclay.

For a one-time installation cost of $5,900, the effluent water had an oil content of 5 ppm.  Subsequently, the organoclay is changed out at a cost of $1,500 every three months, plus a disposal fee for the spent clay of $40, plus freight-a cost savings of $6,000 every three months, or $24,000 per year.

Case history 3
In 1997, a major natural gas company converted a crude oil pipe line system to natural gas service.  The 900 mile system runs from Wyoming to Missouri. The pipe line had to be flushed out and cleaned out with a solvent-based solution and water.

Approximately 3.5 million gallons of water containing toluene was used, resulting in a free oil and grease (FOG) content of 50 mg/l.  This had to be reduced to 10 mg/l to meet NPDS permit standards.  Volatile organic carbons (VOCs) were detected in amounts of 700 mg/l. BNC Environmental Services of Houston, Texas, set up the following treatment train:   the water was first pumped into a flotation tank and through several sand filters with frequent backwashing at 1,500 gpm.  Then, it was pumped into a slop tank, and subsequently through two carbon absorbers, each filled with 8,000 lbs of organoclay.

At this point, the FOG limits were met.  This was followed by six absorber vessels filled with 56,000 lbs of actiated carbon, which removed 9% of the VOCs, namely toluene and benzene.  A final polish was added by passing the water through an air stripper.  The off gas was passed through a thermal oxidizer at 4,000 cfm, at which point VOC content was non-detect.   Both the organoclay and carbon were changed out twice and frequently backwashed.

The per-gallon cost of cleaning the 3.5 million gallons of water was $0.15-0.20/gallon or $700,000.  This cost is in sharp contract to the cost of hauling it away for treatment at $0.70/gallon (it would be considered hazardous due to the presence of benzene), which would have amounted to $2.45 million, a cost savings of about $1.6 million. Had activated carbon alone been used, without the organoclay, it would have required 784,000 lbs, rather than 112,000 lbs, a cost increase of some $4 million, clearly an inefficient and unacceptable solution.

Case history 4
In 1997, an oil pipe line leak in a marsh near San Francisco Bay required the pipe line operator to contain the spill, repair the pipe line, con- duct hydrostatic testing, and mitigate any environ- mental damage.

The containment and site cleanup were to be per- formed in the usual manner with vacuum trucks. *Ioweler, the California Department of Fish and Game required that contaminated water from the spill site, both surface and groundwater, be drinking water quality before discharge.

This required removing high levels of solids, VOCs and free and emulsified oil. The cleanup contractor placed a treatment system alongside the spill area to eliminate the need for vacuum trucks, which could not have been moved into the marsh.

Excavation required de-watering a sufficient contaminated area to allow exposure and pipe line repair. The water was pumped at about 200 gpm.  Approximately 3.2 million gallons of water were treated.

The treatment train, as designed by Clear Creek Systems of Bakersfield, California, included 25-gal weir tanks with three baffles, two 5-micron bag filters, two vessels of organoclay in parallel, and four vessels filled with activated carbon. The organoclay was changed out three times.  Costs per gallon were a fraction of vacuuming and hauling the water, by barge, to a treatment site.

Conclusion
The case histories illustrate that organoclay is a filter media that can be of great economic benefit to operators in a variety of applications where the presence of small amounts of oil in water drive up treatment costs.

As long as the spent clay is non-hazardous and passes the liquid paint filter test, most states allow disposal in a roll-off dumpster into the local landfill. Otherwise, thermal desorption, or burning as fuel in cement kilns, or inclusion as a component of asphalt are reasonably economical disposal methods.

A side benefit of the organoclay is that it also removes small amounts of heavy metals, both anionic and cationic, particularly in the presence of ferric iron, where co-precipitation is the mechanism. PCB removal due to the organoclay's affinity for both PCB and transformer oil are also frequent applications.

By: George Alther, Guest Author
Biomin@aol.com