The Baiji refinery, which was once Iraq’s single largest source of fuel, appears to have been almost entirely destroyed.Militants from the so-called Islamic State (IS) group have detonated explosives and set fire to key infrastructure, including control rooms and processing units, as pro-government forces launched a fresh offensive over the weekend to regain control of the facility, Iraqi security and oil officials said.”The damage to the refinery is huge,” said a senior engineer who use…