SAINT JOHN, New Brunswick — A proposed overhaul at Irving’s pulp mill on the west side of Saint John could boost output by two-thirds by replacing the mill’s oil-fired boiler and adding a turbine, the company says. Irving Pulp & Paper says it’s submitted its preliminary application for a $1.1 billion capital improvement plan titled NextGen. The project, which could be in construction for four to six years, involves replacing the recovery boiler at the mill, which Irving says is an oil-fired boiler installed in the 1970s. Irving says the new recovery boiler can increase production by approximately 66% and would “facilitate” other environmental upgrades, including a new steam turbine and “green energy generator” as well as improvements to re-use water at the mill. Switching from heavy fuel oil to steam power and natural gas is expected to also reduce greenhouse gases, Irving says. …The assessment calls it the biggest investment in Canada’s forest products industry since 1993.