COLUMN-Benefits remain elusive from Delta's U.S. oil refinery: Kemp

By John Kemp LONDON, Jan 22 (Reuters) - When Delta Air Lines announced it was buying the Trainer oil refinery from Phillips 66, in April 2012, the U.S. carrier hailed the transaction as "an innovative approach to managing our largest expense". Since then, the company says vertical integration has lowered jet fuel prices in the U.S. Northeast, its home region, and will eventually provide company-specific benefits as the refinery processes more cheap domestic crudes and returns to profitab