22 RESPONSIBLE CANADIAN ENERGY : Progress Report

BONAVISTA/CONOCOPHILLIPS: ELIMINATING BENZENE EMISSIONS

Two Canadian companies are getting creative in tackling the issue of benzene. They have reduced their plants’ emissions of the known carcinogen to well below regulatory requirements. “We were trying to think outside the box,” says Harold Gold, a regulatory and compliance technologist at Bonavista Energy, whose company has found a way to el iminate more than 99 per cent of the benzene emissions created during the glycol dehydration process.

In Alberta, the main source of benzene is motor vehicle exhaust, followed by industrial emissions and other combustion sources. Significant reductions in benzene concentrations have come mainly as the result of government regulations lowering its concentration in gasoline and improving vehicle emission performance. But natural gas producers have taken on the challenge of reducing emissions from their processes, over and above regulatory requirements.

Glycol dehydration is a common, economical method to remove water from natural gas. As glycol absorbs water in the dehydration process, it also absorbs heavy hydrocarbons, along with some of the benzene occurring in natural gas. The glycol is re-boiled, which allows it to be recycled through the system. As the glycol is heated, water and benzene are vaporized and emitted. Benzene emission reductions can be achieved using various types of condensing tanks, flares or incinerators.

Requirements set by the Energy Resources Conservation Board (ERCB), Alberta’s regulatory body for energy, place benzene emission limits on industry, which vary depending on when the dehydrator was built and how close it is to a public facility or permanent resident. Dehydrators installed after January 1, 2007 have a limit of one tonne per year of benzene emissions.

With the goal of reducing emissions without affecting operating costs, Bonavista Energy retrofitted one of its dehydrators east of Rocky Mountain House in March 2010. The operation now nearly eliminates benzene emissions, while also reducing fuel consumption.

Bonavista Energy already had a condensing unit in place to capture vapors created during the re-boiler stage and condense out the water and hydrocarbon liquids. “We knew we were halfway there,” Gold says.

The remaining vapors in the condenser tank are now piped back to the re-boiler system for use as the primary fuel source. Testing has demonstrated more than 99 per cent of the benzene emissions are used and destroyed in this fuel combustion process.

Bonavista Energy is looking at applying the same technology in its other locations, Gold says. Bonavista wants to be proactive in its approach to benzene emissions, rather than reacting when emission levels approach or exceed the regulatory limits.

ConocoPhillips Canada began applying a similar approach in May 2010 with a JATCO BTEX Eliminator at its site near Three Hil ls, Alberta. The company also now removes more than 99 per cent of benzene emissions, without using additional fuel.

Vapors collected from the re-boiler are routed through a shell and tube heat exchanger, where the glycol flowing toward the re-boiler acts as a coolant. This heat exchanger condenses most of the benzene and hydrocarbons, which are deposited in a storage tank. Remaining vapours are routed back to the re-boiler where they serve as fuel when the burner is firing, reducing fuel costs. When the burner isn’t firing, the vapors are sent to a platinum glow plug, installed in the burner exhaust stack, which stays hot long enough to combust the benzene emissions.

In addition, the new process decreases the load on the re-boiler because the glycol, arriving rich with water and hydrocarbons, is 20 to 30 per cent warmer after acting as a coolant within the heat exchanger. “We are currently evaluating some more potential sites to install the JATCO unit on,” says Andrea Zabloski, an operations engineer in ConocoPhil l ips’ energy eff iciencies group. “It’s running well. It’s just a great project.”