MARTINEZ -- The Shell Martinez petroleum refinery, saying it wants to strike a blow against global warming while improving efficiency, seeks approval to process a lighter mix of crude oils and permanently shut down one of two coker units.

On June 3, the county board of supervisors is expected to discuss the kickoff of the environmental review process for the project.

Starting in 2015, and continuing in phases over several years, Shell would construct a variety of processing equipment, including new heat exchangers to reduce energy use, and thus emit less pollution and greenhouse gases, according to a land use permit application on file with Contra Costa County.

Switching from the current mix of heavy and intermediate crude oils to a lighter mix would allow the refinery to permanently shut down a flexicoker unit, which converts the heaviest crudes into lighter oils, according to the application.

"Obviously and hopefully, the Environmental Impact Report will reveal more detail on the feedstocks involved and monitoring requirements," said Jim Neu, a Martinez resident and member of Martinez Environmental Group.

Expressing concern about the cumulative impacts of several pending Bay Area refinery projects, Neu said he also wants information about pollution monitoring, the mode of transport and routing of crude oil as well as products such as propane and butane, and measures to prevent accidents, among other concerns.

The applicant is Equilon Enterprises LLC of Delaware, D.B.A. Shell Oil Products U.S. The Shell Greenhouse Gas Reduction Project would occur entirely on the part of the refinery that is located on county land outside of city limits. About one-fifth of the 850-acre refinery is located within the city of Martinez.

Shell Martinez spokesman Steve Lesher said the Greenhouse Gas Reduction Project is not a matter of expansion but of replacing equipment. There will be no change to the refinery's processing capacity of around 160,000 barrels a day, he said, adding that the refinery already produces propane and butane and ships it out by rail.

Referring to concerns over transport of crude oil and oil products by rail, Lesher said, "There is no rail component to our project," and that no facility for offloading crude from railroad cars is planned. The refinery gets its crude feedstock by ship at its marine terminal on the Carquinez Strait and by pipeline from the Central Valley, he said.

Environmentalists also have voiced concerns over possible delivery to the area of large quantities Bakken crude, a highly flammable variety named after a shale oil patch centered in North Dakota.

A May 21 Bloomberg News story quotes a Shell spokeswoman, Destin Singleton, saying the Martinez refinery "already processes some lighter crudes, like Bakken oil, along with heavier feedstock from California's Central Valley."

Lesher said Tuesday the Shell Martinez project does not depend on Bakken oil.

"We have processed a small amount of Bakken as part of our overall mix, and only a handful of times," Lesher said, adding, "Our current diet is primarily heavy crude," mostly San Joaquin crude from the Bakersfield area.

Contact Tom Lochner at 510-262-2760. Follow him at Twitter.com/tomlochner.