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| Home | Emission
Reduction Solutions
Emissions of byproducts to our petroleum industry are
getting a lot of space in the Canadian press. Much has changed and quite a few guidelines
for dealing with these emissions are out. The list of institutions guiding the control of
emissions is long and varied: GRI, EUB, CAPP, CGA, and SEPAC to name a few. Recent developments in environmental regulations are leading the oil and gas industry to consider aromatic hydrocarbons and other volatile emissions as detrimental to our atmosphere. These fugitive emissions from tanks and other equipment include aromatic hydrocarbons such as Benzene, Toluene, Ethyl Benzene, and Xylene (BTEX), and are present along with other volatile organic compounds (VOC’s). Some good sources for relevant guidelines, regulations and their timing, are www.capp.ca and www.eub.gov.ab.ca, each accessible through www.petroassist.com. These VOC and BTEX emissions are produced in many processes, but I will concentrate on A: tank batteries, and B: glycol dehydration units. Tank batteries produce these vapors simply out of necessity of allowing tanks to vent as they get filled and emptied, and as they expand and contract as the tanks heat up and cool down. A thief hatch at the top of the tank may release some emissions in the process. On the other hand, glycol dehydrators circulate glycol through a contactor tower that absorbs water from the gas stream and thus dries the gas up and readies it for sales. Unfortunately, glycol also picks up BTEXes, VOC’s and many other materials produced in the production process. As the glycol is regenerated by boiling the water off, unfortunately some BTEXes and VOC’s are also boiled off, creating some emissions considered detrimental. There are many other sources like instrumentation, controls, and pumps, but the above two are the main sources as is indicated by the amount of attention these systems get from regulators. Tank Batteries Vapors of all kinds from tanks were often vented to atmosphere, but there is more interest in recovering them now. Some producers use different forms of Vapor Recovery Units to take these vapors and send them through a compressor that sends it on for use as fuel gas for burners or motors, or other uses. Together with an intelligent valving setup, such a system can be used to maintain a gas blanket on a tank, or to collect make-up gas for the tanks in a pressure vessel for later use when tanks are emptied. A number of technologies allow operators to use these gases, or casing vent gas, to be used as fuel gas. Often this gas requires drying to bring up its heat value. A small simple dehydrator will accomplish this at a relatively low cost. If the gas is not being used it will often be sent to an incinerator. (More on incinerators below) Glycol Dehydration Units Benzene emissions (the B in BTEX) in particular are getting attention from industry, government and the public. Benzene is known to be harmful at certain levels, and thus is targeted. Together representatives from these three groups adopted a "Best Management Practices" to be implemented in Canada by January, 2001. (Best Management Practices for the Control of Benzene Emissions from Glycol Dehydrators by the Working Group on Benzene Emissions from Glycol Dehydrators, written in 1997, Chaired by Environment Canada) As a producer, an easy way to determine the amount of Benzene and other emissions from your dehydrator is to use GRI GlyCalc™ 3.0. This is a Windows-based program that can easily be obtained from GRI (Gas Research Institute) for under $ 50.- US through Radian International in Austin, TX. (512-419-5719). It requires some specific input data, all of which should be familiar, such as gas composition, temperature, gas flow rate, glycol circulation rate, and a few more. These data can help a producer determine if their emissions are within the above guidelines. Should you suspect you’re not within the above guidelines, common ways of reducing these emissions include:
Optimization Optimization not only saves on emissions, but also on operating expenses so it makes the most sense as a first step. As dealers in dehydrators, we often find contaminants such as asphaltenes in both the reboiler and in the accumulator sections of units that saw service for some time. One easy solution is frequent filter changes in the glycol system. A simple annual maintenance procedure will do wonders for emission reduction. A tip: buy a dehydrator that is built such that it can be opened from the outside of the building. This eliminates having to dismantle the building and half the piping just to flush a reboiler/accumulator. The cost to do this is easily recovered by getting unit on line faster (in both labour as well as downtime) during the first turnaround. Redirecting Emissions to Tanks Still column emissions are simply directed to a tank where they condense and separate into water and hydrocarbons. Remaining gases are typically sent on to incinerators. Controlled Disposal This includes Condensers and Incinerators. Condensers Simple systems include tanks with condensing surfaces added that rely on atmospheric cooling. As they rely on atmospheric conditions to function, they are at the whim of Mother Nature. Such systems are relatively new and are being tested now. At the other end of the spectrum is a variety of elaborate condensation systems using air, water, gas, glycol or even the ground as a heat sink to condense emissions. One such system, powered by fans, which include cooling towers, and use air-cooled condensers, water-cooled condensers, low-pressure separators, is known to work well. These systems tend to cost more than the proverbial "tank with fins", but are more reliable and efficient as well. This design is called the R-BTEX™ process, is field proven, but tends to be economically viable only at higher gas flow rates (30 MMSCF/d+) due to the higher up front expense. These systems are available from companies such as Sivalls, Inc. and Natco, who developed it in conjunction with GRI, and now have the rights to manufacture and sell them. These systems recover hydrocarbon liquids that can be sold that may offset some of the up-front costs over time. Water is disposed of normally. Any remaining gas can be used as fuel gas in the reboiler firetube, or sent on to an incineration system. Incinerators Incinerators help reduce emissions of BTEXes and VOC’s in facilities where it is simply uneconomical to recover these with one of the above methods. Usually incinerators differ from flares in that they are designed to provide 99% + combustion of the products introduced into their streams. The resulting materials exhausting from the stack are completely burned. Some incinerators on the market are externally powered, and others are completely freestanding and require no external source of power. Incinerators rely on some make-up gas to maintain steady combustion. Some incinerators use refractory linings to maintain a high combustion temperature, some modern units achieve this through other innovative means. The lower cost solutions mentioned above such as solution gas recovery systems, incinerators, and simpler condensing devices will likely be the solution of choice for the smaller Canadian operator with smaller amounts of emissions per site. We will see more of the more elaborate systems in place at larger plants and centralized facilities. It will be most interesting to see what industry adopts as a solution for these emission problems by January 1, 2001. |
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