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Jul-2006

Reducing refinery SOx emissions

Through an extensive study and 18-month trial, a Canadian refinery chose SOx reduction additive technology to reduce its SOx emissions

Eric Butler, Kate Groves and John Hymanyk, Chevron Canada Limited
Michael Maholland, Patrick A Clark and Guido Aru, Intercat (Johnson Matthey)
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Article Summary
As a requirement to approval of an amended air emissions permit for Chevron Canada’s Burnaby refinery, the Greater Vancouver Regional District (GVRD) mandated that Chevron investigate ways to further reduce refinery emissions of sulphur oxides (SOx). The FCCU, which was identified as one of the largest SOx emission sources in the refinery, was targeted for emissions reductions. The Chevron Burnaby refinery project team embarked on a rigorous study to identify and evaluate the various commercially available SOx reduction technology options.

This study analysed the numerous impacts the SOx reduction technologies would have on the refinery and the surrounding community. It evaluated such factors as performance, environmental and community impacts, economic factors and risk/feasibility. In addition, members of the scientific community were asked to conduct a peer review, which provided a non-biased perspective on the list of technologies and on the ranking process. As a result of this evaluation, Chevron Burnaby selected SOx reduction additive technology to reduce SOx emissions in the refinery.

To verify the performance projections of the SOx reduction additive technology under long-term operating conditions, and to assess any operational impacts, the refinery embarked on a controlled 18-month trial to maintain SOx emissions at substantially reduced levels. At the end of this trial, the refinery will propose an air permit amendment to the GVRD that will reflect sustainable emissions reductions. This proposed SOx emissions reduction implementation plan is expected to achieve an annual SOx reduction of approximately 600 tonnes per year.

As part of the Canadian Environmental Protection Act of 1999, the government mandated a reduction in the sulphur content in gasoline sold in Canada. The regulations, which took effect in January 2005, allow for the average sulphur content in gasoline to be 30ppm. The new regulations are a key element in the Canadian government’s clean air strategy. Decreasing the sulphur content in gasoline allows for the increased efficiency of emissions control systems in vehicles and reduced tail-pipe emissions of carbon monoxide (CO), nitrogen oxides (NOx) and volatile organic compounds (VOCs) — the leading contributors to smog.

In order to meet the new gasoline sulphur specifications, the Chevron Burnaby refinery found it necessary to make modifications to its existing facilities. In 2002, Chevron Canada applied to the GVRD for an amendment to the refinery’s existing air emissions permit in order to build and operate a new low-sulphur gasoline hydrotreater. Soon afterwards, the University of British Columbia (UBC) School of Occupational and Environmental Hygiene issued its final report of a commissioned study assessing the potential human health impacts of air emissions from the refinery, tank farm and associated facilities.

The report indicated that ambient concentrations of fine particulate matter, nitrogen dioxide, ozone and CO in the surrounding community were not elevated as compared to other GVRD residential locations. However, ambient concentrations of sulphur dioxide (SO2), averaged over a one-hour period, were periodically detected to be higher at a nearby monitoring station than at any other monitoring site within the GVRD region, even though the 24-hour averaged SO2 concentrations were not significantly elevated compared to other areas in the GVRD. As a result of the UBC study, the GVRD mandated that as a requirement to its approval of an amended air emissions permit, Chevron investigate ways to further reduce refinery emissions of SOx. In summary, the requirements of the amended permit included:
— Review of relevant SOx reduction technology information, including how the technology could apply to the Burnaby refinery
— Development and implementation of a public consultation process, plus the documentation of all feedback solicited as a result of the process
— Development of a model to be used as a predictive tool to assess the influence of potential SOx reduction technologies on ambient air quality
— Development of a SOx reduction implementation plan that includes time frames for implementation.

UBC air emissions review
The UBC review of the Chevron Burnaby refinery emissions was undertaken to address community concerns about possible health impacts of air emissions from the refinery to nearby residents. The UBC team analysed ambient air-monitoring data for a suite of air pollutants measured at monitoring locations adjacent to the refinery as well as several locations in other residential neighbourhoods in the GVRD. Air emissions modelling was not carried out by the UBC project. The locations of the air-monitoring stations surrounding the refinery are shown in Figure 1.

Ambient concentrations of the suite of air pollutants were reviewed for the years 1998–2000. The UBC analysis showed that the North Burnaby ambient concentrations of fine particulates, nitrogen dioxide, ozone and CO were not elevated compared to other GVRD residential locations. For SO2, ambient concentrations averaged over each 24-hour period were not significantly elevated compared to other areas in the GVRD. However, there were more frequent short-term peak SO2 excursions (ie, one-hour and ten-minute average concentrations) at Station T23, near the top of Capitol Hill, versus other GVRD areas. At Station T23, there were also infrequent exceedances of one-hour regulatory standards and ten-minute exposure guidelines (Figure 2). For this reason, the Capitol Hill Station T23 became the focus of further evaluation.

For the protection of human and environmental health, Environment Canada has set desirable and acceptable objectives for one-hour and 24-hour SO2 concentration in the ambient air. Similarly, the World Health Organization (WHO) in Geneva has reviewed international literature and set guidelines for ten-minute, 24-hour, and one-year SO2 concentrations based on exacerbation of respiratory symptoms in sensitive human populations. The US Agency for Toxic Substances and Disease Registry (ATSDR) has also published a minimum risk level that incorporates a ten-fold uncertainty or safety factor. These values are shown in Table 1 and also in Figure 2.
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