Equipment and technology improvements can be sound investments.
by Dave DePasquale, Siemens Industry, Inc.

A refinery operated by one of the largest integrated energy companies in the U.S. has become an example of efficiency, cost savings and streamlined operation.

Located in the Midwest, the refinery is a vital component to the company’s operations, with a gross crude oil processing capacity of 306 million barrels per day (MBD). The refinery processes a mix of light, low-sulfur and heavy, high-sulfur crude oil. It receives domestic and foreign crude oil by pipelines and produces a high percentage of transportation fuels—such as gasoline, diesel fuel and jet fuel—in addition to other products, such as petrochemical feedstocks and asphalt.

The 2,200-acre site has been in continuous operation since it was constructed in the early 1900s. In 2007, the company announced a $1 billion investment to upgrade production operations at the refinery. 

Upon completion of the upgrades in 2015, the plant will become one of the top-five largest refineries in the U.S. The refinery will also produce natural gas and sulfur-rich coke, which will be used as an energy source for area power plants.

“The refinery has become central to our North American operations, as our downstream partnerships will bring crude oil from the fields northeast of Alberta, Canada, to our operations for refining,” says the company’s global electrical team leader. 

The heavy crude found in the oil sands takes longer to refine using a repeated process of heating and cooling to separate its parts for different uses.

“As a 24/7 operation, the refinery must maintain a high level of reliability, productivity and safety to ensure that we maximize efficiencies,” the team leader says.

Catalytic Cracking Unit Upgrade

With 30-year-old equipment nearing the end of its life-cycle, upgrading the four existing 4,500-horsepower motors that power dual catalytic cracking units (CCUs) was necessary to increase reliability, lower maintenance costs, and most important, provide uninterrupted service for 5 years. 

As part of the refining process, the CCUs accept chains of hydrocarbons and break each into smaller ones in a chemical process called cracking. This allows the facility to make more products, such as gasoline, asphalt and aviation fuel. 

As crude oil contains a variety of hydrocarbons, the CCUs are able to separate these chains of hydrocarbons using an extremely hot catalyst such as Zeolite, bauxite, silica-alumina or aluminum hydrosilicate. Both oil and catalyst in the CCU are then moved to another distillation column where the catalyst will be reused.

High-speed motors with active magnetic bearing systems bring operational benefits—such as wide speed range, multiple start-stops, fast ramp-up, unmanned or remote operations and monitoring, and lower the environmental footprint.

Answering the CCU Challenge

The solution was a combination of technology, an in-depth understanding of the products and situation and expertise to deliver one of the first solutions of its kind to the refinery. 

Each CCU would be supported by two 4,500-horsepower, 4.5-kV, 78- to 105-hertz (4,700- to 6,300-rpm) totally enclosed, water-to-air cooled, high-speed motors with complete active magnetic bearing (AMB) systems. These were the first of their kind installed in the U.S. and used in a refinery.

These high-voltage motors featured a unique rotor design. The rotor was made from a special, single-piece forging. The rotor slots were then machined. Once this process was complete, a proprietary fusion process shaped and bonded the copper bars into the slot. The result was a solid rotor that could withstand the centrifugal forces associated with high-speed operation. The overall process led to reproducible vibration behavior under all conditions and throughout the life cycle of the product. 

Ensuring Continued Operation

“One of our key requirements was reliability, as an unscheduled shutdown of our CCUs is unacceptable, and has a significant impact on our production levels and operating costs,” says the refinery engineer. “We had a high confidence level in the motors and drives to help us deliver uninterrupted service of our compressor train for 5 years, but these products had to operate in tough conditions as well.”

The AMB system brought several other operational benefits, including operating at high speeds, a wide speed range (API 617 and API 546), multiple start-stops, fast ramp-up, unmanned or remote operations and monitoring, reduced life-cycle costs, controllable rotor dynamics, no lubrication system and an oil-free string (including compressor) that reduced the environmental footprint.

The motors levitated the shaft and permitted motion without friction or wear, unlike traditional oil-lubricated or grease-lubricated motor bearings. The AMB consisted of an electromagnet assembly, a set of power amplifiers that supplied current to the electromagnets, a controller and gap sensor with associated electronics to provide the feedback required to control the position of the rotor within the gap. Each AMB was equipped with a backup bearing for emergency coast-down in the event of a power failure to the AMB system.