A few weeks ago, information and analysis firm IHS declared that oil majors ExxonMobil and Saudi Aramco had individually developed new steam cracking processes that allow petrochemical producers to (more or less) skip the refining process when converting crude oil directly to light olefins. Incredibly, these new, groundbreaking processes have the potential to save operators up to US$200/t of ethylene produced, according to IHS Chemical's ‘Process Economics Program (PEP): Steam Cracking of Crude Oil’ report.
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Lying at the heart of petrochemical complexes, steam crackers have been a technology of choice for decades. It all began in 1891, with Russian engineer Vladimir Shukhov’s development of the world’s first thermal cracking method, the Shukhov cracking process, which marked a significant milestone for the petrochemical industry. Jumping ahead to 1912, William Merriam Burton and Robert E. Humphreys designed a similar thermal cracking process that operated under temperature conditions of 700 - 750°F and an absolute pressure of 90 psi. In this system, both the condenser and the boiler were continuously kept under pressure. Later, in 1921, the Universal Oil Products Company’s C. P. (Carbon Petroleum) Dubbs introduced a more sophisticated method that operated at higher temperatures of 750 - 860°F. The Dubbs process, as it came to be called, dominated the market until the early 1940s – the beginning of the catalytic cracking era.
Following this period of new inventions and innovation, in 1941, the world’s first steam cracker was established at Standard Oil Company of New Jersey’s (now ExxonMobil's) Baton Rouge refinery in Louisiana. In the years and decades to follow, ethylene emerged as a large volume intermediate, replacing acetylene as a prime material for synthesis, and the emergence of steam cracking brought about the replacement of thermal cracking plants. Since then, the technology has been continually optimised to meet the economic and environmental requirements of modern society, and, with this latest announcement, both ExxonMobil and Saudi Aramco have stepped things up a gear.
ExxonMobil commissioned its world scale facility in Singapore in 2014, producing 1 million tpy of ethylene directly from crude oil. Researchers at IHS Chemical believe that this process achieves some US$100 - 200/t more than traditional naphtha cracking, taking advantage of the premium that naphtha commands over crude oil in Southeast Asia. So how does it work? According to the research, the steam cracking process bypasses the refinery and feeds crude oil directly to the cracking furnaces (which have each been modified to include a flash pot between the convective and radiant sections). Then, oil is preheated and flashed, ‘topping’ the lighter components from the crude. The extracted vapour is subsequently fed back into the furnace’s radiant coils and cracked in the typical manner. The heavier liquid that collects at the bottom of the flash pot is transferred to the company’s adjacent refinery, or sold to market.
The Saudi Aramco steam cracking process, on the other hand, operates according to an entirely different concept. Although the process is currently only a proposed project, in June 2016, Aramco announced a joint venture with SABIC for the construction of a crude oil to chemicals complex in Saudi Arabia – according to IHS Chemical, it is possible, at least in part, that the complex will employ the new steam cracking process. It begins by feeding a whole barrel of crude to a hydrocracking unit, which removes sulfur and shifts the boiling point curve toward lighter compounds. The gas-oil and lighter products are sent to a traditional steam cracker, while the heavier products go to a proprietary, Aramco-developed deep fluid catalytic cracking (FCC) unit that maximises olefin output. IHS Chemical estimates the cash cost for the crude to olefins process to be US$200/t cheaper than for a naphtha cracker; however, as the hydrocracking and FCC equipment would result in significant capital costs, the process is estimated to work out as roughly equivalent, cost wise, to naphtha cracking in Saudi Arabia.
Petrochemical producers are certainly set to benefit from breakthrough processes such as these in decades to come. Who will be next to step up their game? Only time will tell.