Hi. I’m Carolyn Snyder and today I’d like to tell you about a simple and elegant solution for measuring CO2 in natural gas, a requirement for most oil and gas companies.
Natural gas mainly consists of methane (CH4 70–90 %). There are a number of other components (ethane, propane, butane, nitrogen, hydrogen sulfide and others) including carbon dioxide (CO2) which may be present in concentrations from several ppm up to 8%. Pipeline transmission legislation sets limits for the CO2 content of natural gas. Therefore, CO2 has to be measured and, if necessary, reduced by technical processes such as amine washers, polymeric membranes, or pressure swing absorbers (PSAs).
Measuring the CO2 content of natural gas can be accomplished by various means including gas chromatography and optical non-dispersive infrared measurement. Often a simpler and more cost-effective solution is the use of a process gas analyzer setup.
Methane, ethane, propane and other hydrocarbons in natural gas influence the CO2 measurement. This cross interference is low for methane (approx. 1:700), but larger for ethane (approx. 1:100) and higher hydrocarbons. If CO2 has to be measured in the percent range, the error from cross interferences by the background gases is negligible. Calibration can be performed with the mean background concentration of the natural gas components. Even calibration in nitrogen might be possible.
For ppm CO2 ranges, calibration with mixed background gases or a nitrogen background is not possible. Varying gas composition in natural gas would lead to varying errors in CO2 measurement, which are too high for ppm measurement ranges. To overcome the problem of varying background in natural gas, a special gas analyzer setup with a CO2 absorbing agent can be used. In an external sample handling system the sample gas stream is split and the CO2 in one stream is removed with a scrubber. This stream is flowing through the reference side. The other stream which still contains the CO2 is applied to the measurement side of the analyzer cell. With this configuration, variations in the background of natural gas will affect both sides of the analysis cell and will therefore be cancelled out. In the external sample handling system, the left vessel contains the CO2 absorbing material, whereas the right vessel is a blank vessel filled with glass beads to equalize the flow.
Figure 1 shows a flow diagram of the recommended analyzer system. When measuring sample gas, V3 is open and the gas stream is divided into unscrubbed and scrubbed (CO2 removed) gas streams. The unscrubbed gas stream is flowing through the de-energized (NO–C) three-way valve (V1) into the measurement side of the analysis cell. The scrubber gas stream is flowing into the reference side of the cell. For zeroing the analyzer, V3 is closed and V4 is opened. Now the unscrubbed gas stream is blocked by the energized (NC–C) threeway valve (V1) and the scrubber gas stream is divided to flow into the measuring and the reference side of the cell. For spanning with a CO2 test gas in N2, V2 is opened and the system is working in the measuring configuration described above.
Whether you’re suffering in a heat wave or slogging through the fog, all minds at this time of year turn to thoughts of holidays. So we’re putting aside the pH and shelving the gas analyzers for a little while to focus on a few of the best places in the world to go on vacation. We’ve chosen from the myriad of destinations based on excellence and to give you a variety.
Paris – U.S. News & World Report calls Paris the number one place in the world to visit and we can’t help but agree. With Neoclassic architectural beauty featuring stately mansions, charming streets, and glowing streetlamps all reflecting in the River Seine, nothing else quite matches. And then there’s the food! A simple stop in a café can be a memorable culinary experience. Visit all the spots you’ve heard about – Notre Dame, Musee D’Orsay, Eiffel Tower, Versailles, the Arc de Triomphe – not one will be disappointing. And plan to use whatever French you command because the Parisians appreciate it.
Napa Valley – The world offers a lot of wonderful wine countries – from France to New Zealand – but the Napa Valley in northern California is certainly one of the friendliest to visitors. With vineyards and wineries clustered in a valley surrounded by tiered hillsides, Napa allows an easy drive from tasting room to tasting room and good hotels plus gourmet cuisine to top it off. The excellence of California wines is the icing on the cake.
Yellowstone – Whether you’re American or coming from an international location, Yellowstone National Park is the ultimate outdoor getaway. Famous for its steaming geysers, Yellowstone also offers hundreds of miles of hiking trails that take you through forests, beside rivers, and up mountains. Make plenty of noise, because Yellowstone is also famous for grizzly bears and you’ll probably spot elk, buffalo, and maybe a shy wolf. Though the park attracts many visitors, its 2,221,766 acre vastness means you can find places with few people. Of course, the famous Old Faithful geyser is where you’ll find the crowds but it’s worth it.
Sydney – Yes, the Sydney Opera House is everything you’ve heard. If you can arrange to approach the building by boat, you’ll be even more amazed. An architectural masterpiece, the Opera House is a contemporary icon, but it’s just one of the many attractions of this livable, cosmopolitan city. The food is great, the transportation is easy, and the beaches are very close. Be sure to visit the zoo or other wildlife attractions to see Australia’s amazing animals up close and personal. And you’ll love the fashionable but laid back locals. Come and say g’day.
Bora Bora – Six miles of paradise. That’s how fans of this island describe it. Lush jungles, huge volcanoes, and, above all, shimmering sands, add up to what James Michener called the “most beautiful island in the world”. Dotted with luxurious resorts, Bora Bora makes its living as a tourist destination and it’s very expensive, but you can save some money by visiting off season or dropping in on a cruise ship. If you decide to go, focus on the beautiful lagoons – they’re something to write home about.
Las Vegas – Read any list of popular vacation spots and you can’t avoid Sin City, Las Vegas. Think of it as a theme park rather than a city, Las Vegas offers never-ending entertainment at reasonable prices. Gamble, go to shows and attractions, gamble, try the cheap and plentiful food, gamble, sit by the pool, and gamble. As long as you remember that the house always wins, you can have a lot of fun. And if the glitz gets too glitzy, sneak off to the Grand Canyon.
Let’s add to this list London, New York City, Walt Disney World, Hong Kong, Rio, Washington, D.C., all those beautiful islands dotting the Caribbean and the South Pacific, Cape Town, New Orleans, and a ridiculous list of other places and we have holidays to take for a hundred years. Here’s wishing you the best summer yet with plenty of fun!