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| Home | Get
your treater to treat you right
Treating systems have long been one of the most expensive and troublesome of all lease surface equipment. Also, there has been little data available for accurately sizing treating equipment, and as a result, treating equipment is frequently over or undersized." According to C. Richard Sivalls. Little has changed since then. Treaters are some of the least understood and yet most common equipment in oil batteries. One reason is that there are many designs of treaters. For the purposes of this article I will define a treater as a heated, lower-pressure (50-100 psi) vessel that treats mostly oil (70 per cent or more), and some (30 per cent or less) entrained water. It’s hard to see what’s inside a welded vessel (vertical or horizontal examples exist ranging in size from 4’ - 14’ diameter x 15’ – 80’ long), but picture your average bottle of "Newman’s Own" salad dressing at Safeway. No, don’t shake it…. If you leave it alone for a while, you’ll notice that it settles out in distinct layers according to the weight of the ingredients. The same thing happens inside a treater. It separates oil, water and gas instead of oil, vinegar and air. The only difference is that the treater speeds up separation by adding heat, pressure, chemicals and (sometimes) electrical mechanisms. Exiting the treater are separate streams of gas, pipeline specification oil, and water clean enough to inject back into the ground. In cases where large amounts of water are produced, a free water knockout can help reduce the treater size requirements by disposing of all of the non-entrained water from the emulsion, and greatly reduces the fuel requirements of the treater. A free water knockout can look similar to treaters, but is designed to handle more water than oil. Typically the firetube (if any) is higher up in the vessel, so as to only heat the lighter emulsion and oil, not the heavier water residing below. Treaters come in many designs, with manufacturers providing their own spin on how to best handle emulsions. Differences are often associated with the types of emulsion, which range from loose to moderate to tight. A lab test will determine which you have. If the emulsion is tight, usually more involvement (heat, residence time, electrostatic grids, or coalescing packs, or a combination of each) is required. Vertical treaters lend themselves better to looser emulsions, whereas horizontals can handle tougher emulsions better. These designs are often seen in heavy oil treaters, where oil and water can often weigh about the same, and thus don’t separate easily. In these situations, specialized controls may also be required, as floats often cannot "see" the difference between the oil and the water. Corrosion is a major factor in the design of the treater. Corrosion is dealt with using coatings to protect against harmful chemicals such as H2S, and CO2. Cathodic protection using anodes offers further protection against galvanic corrosion. Anodes are sacrificed in lieu of the metal of which the treater or firetube are made. Another form of corrosion protection is to make the shell thicker by adding a corrosion allowance. This can provide some degree of comfort, but significantly increase costs. A corrosion allowance’s effectiveness is debatable as typical corrosion does not limit itself to a small amount over a large area. Instead, it tends to be focused on a relatively small area. Therefore 1/16" or 1/8" may have bought you some time, but not as much as a good coating job or good cathodic protection might have provided. Two months old, uncoated treaters have come back with fist-sized holes in them after being exposed to particularly nasty corrosion. Backing up the coating job with anodes is one of the best ways to protect your treater’s internals. This gives some protection against those areas that get damaged during opening and closing of the vessel during annual turnarounds. Some companies also coat their firetubes, but this is only good if you can ensure the coating does not get damaged during insertion and extraction from the vessel. If it does, you now give corrosion a place to concentrate all its efforts. It is important to note then that one should ensure that the design of the internals of the treater lends itself to a perfect coating job. To get your treater to treat you right, get vendors involved with the sizing. They typically know the performance limits of their equipment, and should be able to provide performance guarantees. If you’re buying used equipment, buy from a vendor experienced in selling treaters. Cut back on unpleasant surprises by using a chemical lab to run tests to determine residence time and temperatures required to "break" your specific emulsion. Competent advice and testing will go a long way towards determining suitability, and a good start to an early payout of your oil battery. |
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