Two new steam-cracking processes developed by ExxonMobil and Saudi Aramco, respectively, allow petrochemical producers to essentially skip the refining process in converting crude oil directly to light olefins. These new processes could potentially save refiners as much as US$200-per-ton of ethylene produced, according to a comprehensive engineering analysis conducted by consultancy firm IHS.
“In 2014, ExxonMobil commissioned a world-scale facility in Singapore that produces 1 million tons per year of ethylene directly from crude oil,” said Anthony Pavone, director of engineering at IHS Chemical, and one of the authors of the IHS Chemical Process Economics Report; Steam Cracking of Crude Oil. “We at IHS Chemical believe this process nets ExxonMobil about $100 to $200 per metric ton above traditional naphtha cracking.”
“This new crude-to-olefins process is about production cost savings, and takes advantage of the premium that naphtha commands over crude oil in Southeast Asia. It is this ‘feedstock spread’ that contributes most of the cost-savings advantage,” Pavone said.
The ExxonMobil process completely bypasses the traditional naphtha cracking process. Saudi Aramco has its own process for crude oil to olefins, and in June 2016, Aramco announced a joint venture with SABIC to study building a ‘crude oil-to-chemicals’ complex in Saudi Arabia. Though the exact process configuration for the potential joint-venture was not disclosed, it is possible this complex will employ the Aramco process, at least in part.
According to the IHS report, the ExxonMobil process completely bypasses the refinery and feeds crude oil to the cracking furnaces. These have each been modified to include a flash pot between the convective and radiant sections of the furnaces. Next, the crude oil is pre-heated and then flashed, IHS said, essentially ‘topping’ the lighter components from the crude.
This extracted vapor, the IHS report said, is then fed back into the furnace’s radiant coils and cracked in the usual fashion. The heavier liquid that collects at the bottom of the flash pot is either transferred to the adjacent ExxonMobil refinery, or sold into the merchant market.
“This analysis was conducted at a $50 per barrel cost for crude oil,” Pavone said. “As you might expect for Singapore, this process requires the local availability of light, sweet crude.”
The Aramco process, IHS said, works along an entirely different concept from that of the ExxonMobil crude-to-olefins process. As of yet, IHS cautioned, the Aramco process is still only a proposed project; no facility actually has been built to test the process.
The IHS report said the Aramco process begins by feeding the whole barrel of crude to a hydrocracking unit, which removes sulfur and shifts the boiling point curve significantly toward lighter compounds. The gas-oil and lighter products are sent to a traditional steam cracker, while the heavier products are sent to a proprietary, Aramco-developed deep-fluid catalytic cracking unit (FCC) that maximises olefin output.
“We at IHS Chemical estimate the cash-cost for this Aramco crude-to-olefins process would be $200-per-ton cheaper than for a naphtha cracker,” Pavone said. “The hydrocracker and deep-fluid catalytic cracker add significant capital costs, though, so at 15 percent pre-tax return on investment (ROI), we estimate the Aramco process would pencil in at roughly equivalent costs to naphtha cracking in Saudi Arabia.”
The IHS report is based upon a “bottoms-up” Class-3 process design and proprietary steam cracking kinetic reaction software simulation of both the ExxonMobil and Saudi Aramco crude-to-olefins processes.