|
Can trans-Alaska pipeline transport GTL products? Alyeska considers 2 options for moving gas-to-liquids products to market: blending with crude oil, batching Patricia Jones PNA Contributing Writer
One aspect cited by those advocating conversion of natural gas to liquid fuels is that such a North Slope project could utilize the existing trans-Alaska crude oil pipeline to move GTL products to market.
But it’s not quite that simple, according to Mike Malvick, system engineering lead at Alyeska Pipeline Service Co., the business entity that operates the 800-mile crude oil transportation network for its six corporate owners.
Each with its distinct advantages and disadvantages, Malvick described two possible options for using the trans-Alaska pipeline to transport GTL products from a yet-to-be built conversion plant on the North Slope to Valdez, the shipping terminal for existing crude oil exports from Alaska.
“We’ve got an asset that cost billions to construct in the 1970s. It’s in place and able to move any quantity of oil up to the capacity it was designed for,” Malvick said.
Shipping GTL is “…one very interesting option for maintaining the viability of a very valuable Alaskan asset,” he said. “The real key is to come up with additional liquids to transport in the pipeline.”
Researchers at the University of Alaska Fairbanks, in coordination with Alyeska and with funding from the U.S. Department of Energy, have looked at various issues surrounding the concept of shipping GTL through the existing pipeline system. Mixing GTL with existing crude During his presentation at an energy workshop held at UAF in early April, Malvick described the process of mixing GTL products with the existing crude oil flowing through the trans-Alaska pipeline.
Using a mixture would keep the start-up capital costs for transporting GTL at a minimum, Malvick said, as separate product tanks and other infrastructure would not be necessary.
Mixing the two products could also be beneficial, he said, in terms of viscosity, gel strength and solids deposition and precipitation.
“That’s particularly interesting if heavy oil becomes a significant portion of the TAPS stream. Then there might be some synergy there where you blend the two and get something mutually better and easier to transport,” Malvick said.
The main drawback for mixing GTL with crude oil, he said, is that gas-based product loses its environmental value as a low sulfur fuel.
“EPA is rolling out new sulfur regulations on fuels and this GTL product, especially when tailor-made, fits right in there. It has virtually no sulfur, so you don’t have to go through a desulfurization process to have fuel that meets the new EPA specifications,” he said. “If you blend that product with crude oil, you lose it … you have to re-refine it.” Shipping GTL in batches Another option for transporting GTL that UAF researchers and Alyeska personnel have considered is called batching. Under that scenario, batches of GTL would be shipped through TAPS. Each batch would be followed by a pig or other type of barrier within the pipe, then by a shipment of crude oil.
“You would have higher initial capital costs, because you would need to add tankage … and changes within the pump stations to assure separation of the two streams,” Malvick said.
While in theory, shipping GTL in batches would maintain the integrity of the higher value liquid, there could be some contamination from pipeline wall residuals, he said. Additionally, there could be significant interface losses. “Over 800 miles, the interface gets to be quite long, so you get significant lengths of cross contamination occurring,” Malvick said.
Finally, there are some unknowns regarding the flow of pure GTL product through the trans-Alaska pipeline, he said. Pipeline designed for oil, not batching Malvick noted during his presentation that the current design criteria for the trans-Alaska pipeline does not include provisions for shipping separate batches of liquids through the 800-mile pipe. Nor do the current permit restrictions allow for pumping and storing liquids with high vapor pressure, which may or may not be applicable for GTL products.
“We’re in the process of applying to extend our right-of-way agreement, which was originally issued for 30 years,” Malvick said.
Work to renew that agreement, which expires in 2004, is currently being completed with operations remaining under the original pipeline design basis, Malvick said.
“Ultimately UAF, along with Alyeska and DOE, must determine the most economical mode of operation, considering initial capital expense, ongoing operating expense and the product and crude oil valuations at take-off points,” he said.
| 