high-efficiency cogeneration plants create cost and environmental benefits

This article originally appeared in the Lamp, 2008 — Number 2

It takes a lot of power to run an energy company the size of ExxonMobil, and cogeneration helps provide that power while saving energy, cutting operational costs and reducing global greenhouse-gas emissions.

The cost of providing energy to ExxonMobil’s worldwide operations is more than $10 billion a year.

That’s a hefty tab, but a process called cogeneration (or simply “cogen”) allows the company to efficiently generate its own electricity to run pumps, compressors, instruments and other equipment. At the same time, cogen produces the steam needed in processes that transform raw materials into consumer products.

Cogeneration works this way: A fuel, usually natural gas, is burned in a large gas turbine that generates electricity. The hot gases emitted from the turbine are typically routed to a unit called a heat-recovery steam generator and used to produce steam for use in the manufacturing process.

Later this year, ExxonMobil will expand the use of cogeneration in refining operations with the startup of new facilities at the Esso refinery in Antwerp, Belgium. With a capacity of 305,000 barrels per day, Antwerp is the company’s second-largest refinery in Europe.

Antwerp’s cogen plant will produce 130 megawatts (MW) of electricity, enough to meet the refinery’s power requirements and also 85 percent of the electricity needed by other ExxonMobil sites in Belgium. Its construction is expected to span 20 months.

“This is a multinational project,” says Project Executive Neil Thomas. “The engineering and procurement work was executed in Italy. Construction workers, project supervision and management came from Belgium, France, Germany, Italy, the Netherlands, Portugal, Australia, the United States and the United Kingdom. The plant construction activity has involved more than 400 workers at peak.”

ExxonMobil and cogen

“Cogeneration offers significant benefits,” says Tom Schiano, power projects manager for ExxonMobil Gas and Power Marketing Company.

“It’s energy-efficient compared with the alternative of buying electricity from a utility and separately burning fuel for steam on-site. In some locations, we actually generate more electricity than we need and are able to profitably sell the balance into the local power grid. With cogeneration, less fuel is needed to provide for the company’s power and steam needs. Although ExxonMobil is a major energy producer, it’s also a large energy consumer. These savings are as important to us as they would be for any business.”

Cogeneration also provides significant environmental benefits. “Since total fuel consumption with cogen is less than with separate facilities for power and steam, fewer greenhouse gases are produced,” says Schiano.

ExxonMobil’s investment in this highly efficient cogeneration technology has helped reduce global greenhouse-gas emissions equivalent to taking 2.5 million cars off the roads. The emissions savings from the company’s global cogeneration plants are also equivalent to expanding 2007 U.S. wind-power generation by about 30 percent in lieu of traditional power plants.

ExxonMobil has interests in approximately 4,500 MW of cogeneration capacity in about 100 individual installations at more than 30 different sites around the world. That’s enough electricity to power more than 2 million households.

The largest cogen plant in the ExxonMobil system, with 500 MW of power capacity, is at the Beaumont Refinery in Texas. With completion of new facilities under construction around the world, capacity will increase to more than 5,000 MW in the next three years.

Cogen development opportunities are routinely evaluated when the company is considering new investments where power and steam are both needed. They are frequently a key element in major new investments.

In Fujian, China, ExxonMobil has partnered with Sinopec, Saudi Aramco and Fujian province in a $5 billion downstream and chemicals venture to help meet China’s robust demand. The project is slated for startup in 2009. A 250 MW cogeneration plant is expected to provide half the facility's power.

In Singapore, ExxonMobil Chemical Company is building a second world-scale petrochemical project. Startup is expected in early 2011. When completed, it will be ExxonMobil’s largest owned and operated petrochemical complex. Cogeneration is expected to provide 100 percent of its electricity needs.

Stepout at Antwerp

The Antwerp facility employs the fundamental principles of cogeneration, but it applies those principles to something new.

“In a typical refinery, cogeneration makes electricity that can be used or sold, as well as heat, in the form of steam, for refinery processes,” says Neil Thomas.

“Antwerp is different. To make our 130-megawatt plant highly efficient, we had to be innovative with the heat-recovery system. Since the cogeneration facility produces more steam than the refinery needs, we use the heat created in the gas-turbine exhaust to heat crude oil – the intial step in the process of converting crude into products. This alternative means of heat recovery is what sets Antwerp apart from other cogeneration units.

“This isn’t new technology,” Thomas adds. “It’s a group of existing technologies that have been carefully engineered into a new configuration.”

Antwerp’s unique cogeneration operation produces important benefits beyond the energy-efficiency advantages of producing steam and electricity simultaneously.

“We realize cost and environmental benefits through efficient use of fuel to generate power and gain process heat recovery,” says Thomas.

“Cogeneration is a good example of how business needs and the market encourage investments to reduce costs, generate income and achieve significant environmental gains,” Tom Schiano concludes. “We do this for sound business reasons: Our shareholders benefit, and so does the environment.”