Adding chillers and other equipment can increase output and reduce VOCs.
During summer months, refineries must increase production to meet peak demand for gasoline and leverage the window of opportunity for increased revenue and profits. But oftentimes they hit a roadblock: The built-in rundown cooling system that cools the fuel once it leaves the processing unit — typically a set of aerial cooler fans — can’t handle the increased volume, causing capacity constraints.
That’s where temporary cooling equipment comes in. It can improve processes to speed production rates while also lowering volatile organic compounds (VOCs).
Robert Carpenter, process engineer at United Rentals, explained how the company helped one refinery dramatically improve its processes during peak demand using temporary rundown cooling equipment.
For its summer fuel blend, the refinery uses several hydrocarbon streams. The biggest component is naphtha, which has high vapor pressure and low octane. To quench or sponge the naphtha, they blend in aromatics to the finished product tank.
Aromatics have a higher octane and lower vapor pressure.
“But aromatics are very valuable, so you want to use as small an amount of them as possible to meet the gasoline specifications,” explained Carpenter.
The refinery’s problem: Both the naphtha and the aromatics were too warm coming out of the process. This required the refinery to use more aromatics to get the gasoline blend to the desired vapor pressure.
The plant engineer called in United Rentals for help.
“They knew that they wanted to cool the aromatic stream from the ARU [define] but they weren’t sure of the optimal location in the process,” said Carpenter. “We looked at several places in the unit and came up with the best solution.”
“The higher the temperature of any given fluid when it goes to a tank, the higher the vapor pressure is and the more VOCs it will release."
Once the right place for the temporary rundown cooling system was identified, United Rentals brought in a heat exchanger, a 1,000-ton chiller, pumps and the generators to power them.
“We were able to cool down the stream so the refinery could use less of the valuable, high-octane aromatics to meet the gasoline specifications,” Carpenter added.
By renting the equipment, the refinery was able to keep up production and greatly increase profits during the five months that it used the temporary rundown cooling system. The refinery has already requested that United Rentals reinstall the system in the spring.
The addition of rundown cooling systems is also helping refineries and other types of chemical processing plants meet the more stringent maximum achievable control technology (MACT) standards for VOC emissions, according to Carpenter.
“The higher the temperature of any given fluid when it goes to a tank, the higher the vapor pressure is and the more VOCs it will release,” he explained.
A supplemental rundown cooling system helps ensure that plants don’t exceed the VOC emissions limit specified in their operating permits.
United Rentals’ staff of experienced process engineers work with plants that need additional rundown cooling equipment for any reason. The engineers help customers determine what equipment they’ll need, the optimal placement and the recommended length of time to keep it in place.
Learn more about United Rentals’ industry solutions at www.unitedrentals.com/solutions.
Freelance writer Mary Lou Jay writes about business and technical developments in a variety of industries. She has been covering residential and commercial construction for more than 25 years.