Navajo Refining Co., a subsidiary of Holly Corp., Dallas, started up a $50 million capacity expansion at its Artesia, N.M., refinery in first quarter 1992. The project produced a 50% increase in the refinery's overall finished-product capacity.
As part of the expansion, Navajo made a major step toward meeting market-growth demand for unleaded gasoline in the Southwest U.S. by starting up a 6,500 b/sd hydrofluoric acid (HF) alkylation unit. Designed and installed under license from Phillips Petroleum Co., the unit is one of the most recent HF alkylation additions in the U.S.
The new alkylation unit was key to Navajo's extensive expansion. Navajo will use the alkylate to boost octane in its regular unleaded and premium unleaded gasolines. In addition to boosting octane, increased use of alkylate in the motor fuel blend reduces olefins and aromatics.
"Our new HF alkylation unit includes a horizontal reactor/settler, plus several innovative acid-release mitigation features," said Virgil Langford, Navajo's vice-president of refining.
"The unit produced its first barrel of alkylate in early 1992.
Major components were moved from another unit, refurbished, and installed in the new unit. Langford said there have been no safety problems through construction, start-up, or operation of the unit.
OPERATING RESULTS
Randall Menefee, project manager for the Artesia HF unit, said the alkylate quality from the unit has been excellent. "When we started the new ... unit, we produced an alkylate with a research octane number of about 96.5... running straight butylenes......
Although the unit is designed to convert a mixture of butylenes and propylenes to alkylate using HF as the catalyst, Menefee said Navajo began by running straight butylenes because there were other economic markets for the refinery's excess propylenes.
Navajo expected alkylate octane to decrease a little-to about 93 RON-when propylenes were added to the feed mixture. The 93-RON octane level is well within Navajo's gasoline blending needs, according to Menefee.
Now that Navajo is running the combined butylenes/propylenes feedstock, the unit is producing about 5,700 b/sd of alkylate at 93.594 RON, said Menefee. This leaves extra capacity to serve any market growth that may occur with Navajo's expanded fluid catalytic cracking (FCC) and alkylation operations.
To date, only a few minor mechanical problems, such as valves and pumps, have needed correction.
"This is an easy unit to start up and shut down," said Menefee. "We can pull the feed out and put it back in and the unit doesn't seem to mind one bit. It doesn't bobble at all."
Operators on the unit have said it is the easiest HF alkylation unit to start up that they have ever worked on.
PROCESS SELECTION
Navajo considered several options, including sulfuric acid alkylation, before selecting Phillips' process.
"HF alkylation has an excellent safety record," said Langford. "Besides, the amount of sulfuric acid we'd have to move in and out of town in tanker trucks or rail cars would ... be too expensive and would add risk to the operation of such a facility."
The refinery's original HF alkylation unit was a UOP-designed, 2,800 b/sd unit in use since the late 1950s. The old unit was shut down and mothballed.
Phillips' alkylation specialists worked closely with Navajo planners during construction and start-up. HF alkylation technical specialists made several visits to the site to help Navajo tailor the proven alkylation unit for its specific requirements.
SAFETY
While installing the horizontal reactor/settler (see front cover), refinery engineers rearranged vessel supports to position a large storage tank below the level of other HF-containing vessels. That storage tank can hold all of the HF in the operating system.
This arrangement means that, in the event of an accidental acid release, the entire system can be drained quickly into the storage tank, reducing the leakable amount of HF to a minimum.
The unit design relies on gravity flow to move HF through the reactor/settler system. This system increases safety by eliminating the trouble-prone pumps and high-pressure systems required by some other alkylation unit designs.
Workers at the Artesia refinery also train regularly in safety drills (Fig 1.), adding to the safety features of the new HF alkylation unit.
EXPANSION PROJECT
The expansion program at Artesia boosted the refinery's capacity from 40,000 b/sd to 60,000 b/sd by reactivating crude and vacuum units at Navajo's refinery in Lovington, N.M., 65 miles east of Artesia.
Downstream processing capacity at Artesia was also added.
Other improvements included a new 12,000 b/sd continuous catalytic regeneration UOP Platformer and a new 20 ton/day sulfur plant. The FCC unit was also modified and naphtha hydrodesulfurization capacity was doubled to 20,000 b/sd.
Navajo's Artesia facility is a high-conversion refinery. Using vacuum distillation, catalytic reforming, FCC, alkylation, desulfurization, and asphalt units, it can process intermediate or sour crudes. Navajo has almost 1.6 million b/d of capacity to store crude oil and intermediate and refined products on site.
PERMITTING
Navajo managers had little problem getting permits to build the unit. The permitting procedure took about 7 months. The process included checks on construction and operating factors, including plant emissions, emissions outside the refinery, and historical weather patterns.
It has been said that HF alkylation units would never again be permitted in the U.S., but Navajo received no negative comments on its plans:
"Permitting agencies require extensive data and impact models of the HF alkylation unit, but we didn't get any negative comments on the proposed unit from neighbors, state agencies, or the federal EPA during the 45-day open comment period," said Matt Clifton, senior vice-president of Holly Corp.
Clifton added that Phillips' experts have done a great deal of development work over the past several years that improved the unit design and contributed to the ease with which Navajo was able to permit, construct, and start up the unit.
Copyright 1993 Oil & Gas Journal. All Rights Reserved.
