NGL ’15: Executives advise on NGL treating, plant design in volatile market

Managing Editor

HOUSTON -- Doug Coleman, vice president of new ventures at Prism Midstream, spoke at the NGL Recovery Optimization and Cryoplant Facilities Design 2015 conference and discussed how to treat off-specification NGL from refrigeration and Joule-Thomson (JT) processing plants to maximize yields.

Prism Gas Systems was founded in 2000. The company operates a 320-MMscfd gas processing plant in East Texas, 14.5 Mbpd of fractionation capacity, 700 miles of pipeline, and rail- and truck-loading facilities.

Causes of off-spec NGL. Typical NGL specifications measure carbon dioxide (CO2), methane, ethane, aromatics, olefins and free water content, as well as vapor pressure (VP). NGL pipeline specifications include those specifications along with tests for olefins, distillation endpoint, halides and fluorides, and maximum pipeline temperature.

Off-spec NGL may be caused by high CO2 content, which can occur when CO2 spikes in the inlet gas production, or when the unit is run too cold to increase production. A high C1/C2 ratio can also cause off-spec NGL, Coleman said. The ratio imbalance can occur when the unit is run too cold, or when no NGL stabilizer is installed with refrigeration in a JT plant.

Off-color NGL can occur when rust from the internals of a new pipeline or previously used storage facility is carried into the NGL stream, or with crude carryover from field production facilities. Water contamination and associated dyes may also cause off-color NGL.

High hydrogen sulfide (H2S) content is another cause of off-spec NGL. This typically occurs due to failure of an upstream H2S scavenger injection facility or condensate/crude carryover from field production.

Solutions for specification problems. For high-CO2 NGL, Coleman recommends warming up the unit if it is running too cold. An NGL stabilizer can also be installed to remove CO2 and ethane. A charcoal filter can be installed to remove heavier hydrocarbons and dyes from off-color NGL.

An H2S scavenger can be used to treat sour NGL, although they can be expensive. Coleman touted caustic treating as a cost-effective solution to treat sour NGL, although he cautioned that the spent caustic will need to be replenished. An amine unit treater can also be used, although it is a capital-intensive solution.

Prism Midstream is developing a liquid handling facility to help process off-spec NGL and condensate, providing liquids handling services for the growing volume of Permian Basin production. The processing service includes onsite truck loading, transport and offloading of NGL at the injection point; caustic treatment; and NGL and condensate stabilization.

Optimizing NGL recovery. After his presentation, Coleman participated in a panel moderated by Trae Miller, vice president of technical services for American Midstream. The panel examined design strategies to optimize C2–C5 recovery in response to volatile NGL market dynamics. Speakers included Tom Webb, process engineer at Martin Midstream; and Dennis Williams and Ignacio Bincaz, both in business development at CB&I.

Coleman noted that NGL contracts are susceptible to change. For this reason, plant operational flexibility is recommended so that optionality can be implemented later, if needed.

Webb believes that gas processors should strive for high ethane recovery and rejection capacities, if they are affordable to implement. As new gas sources come online that may be higher in H2S or CO2 content, plant flexibility is needed to accommodate changing ethane rejection/recovery needs.

NGL recovery design. Miller then asked the panelists how they would design an NGL recovery system in the current market. Coleman, who has experience with brownfield facilities, advised attendees to look for a gas separation plant that is flexible and oversized to accommodate inlet gas. He also cited the turboexpander as a key piece of equipment, noting that there are pros and cons for each type of turboexpander.

Webb, who has experience with plants that cannot reject ethane, said, "When the time comes where you need to reject ethane, if there's nowhere for the ethane to go, then you lose propane, butane, and half of your product, and that's really difficult."

Webb also advised attendees to pay close attention to CO2: "Ensure that CO2 doesn't creep up and cause hydrate formation in your tower ... This is one of the major operational expenses, and if you want to be able to reject ethane, it can save you quite a bit of money."

The engineer also advised the audience to consider where product treating for CO2 will be located on the tower. This is an important consideration, as a product treater will usually be required, Webb said.

Williams said that the design process will change if ethane rejection is desired. In that case, "...listen to your customers and make design tweaks to make their lives easier once the plant is up and running," the business developer advised.

Bincaz noted that, if a plant will be in ethane-rejection mode for the foreseeable future and if CO2 will be rejected along with the ethane, then the investment can often be justified because of the future ethane-rejection capability.

Williams added: "We get as much feedback from the client on the front end—as much as they're willing to tell us—so that we give them the best product we can."

Maximizing NGL profits. Miller then posed the question: How can maximum returns be achieved? Coleman noted that gas processing plants are long-term operations. "More sophisticated plants are what customers want," he said.

Ethane recovery is also very important. "In the long term, if you want to be successful, you must have a well-designed plant to compete," Coleman said. He also advised gas processors to make the investment on the front end. "If you only do half the upgrade, then you lose volume, you lose money, and you lost your competitive edge," he cautioned.

Williams offered a financial perspective. "You have to look at who's funding the project. A lot of the midstream players are now funded by venture capital. The private equity firms look very hard at the investment, and so we take that into account and we try to give them an economical plant."

"Many of those companies are in it for the short term, not the long-term, because their investors want a quick return," Williams said. "Other companies are in it for the long term, for 30–40 years, so they couldn't care less about a few million dollars more of investment."

Plant flexibility vs. high yields. Miller also asked the panelists to share their views on the importance of increased flexibility vs. higher NGL yields.

Picking up on Williams' earlier remarks, Coleman said, "Having worked for one of those private equity companies, I wouldn't say we're only in it for the short term. You want the plant to have long-term value, but the capital returns are very important. To be competitive, you have to reduce capital and make a cheaper process."

Webb recommends an open dialogue with the engineering contractor. "Contractors work all over the world and bring a lot of experience," he said. "You'll end up with a better facility if you maintain an open discussion with the engineering contractor and figure out ways to reduce costs. If you can't reduce costs, then you'll lose out to the competition."

Williams rounded out the discussion by noting that increased plant flexibility means greater yields of both desirable products and undesirable products/byproducts. "Plants with enhanced recovery capabilities give a lot of flexibility, and increased flexibility means higher yields, both on the upside and on the downside," the executive noted.

The NGL Recovery Optimization and Cryoplant Facilities Design 2015 conference took place on February 17–18 at the Crowne Plaza Houston Downtown in Houston, Texas.

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