The city of Birmingham will provide $20 million in incentives for a project to expand Children's Hospital. Hospital officials say the $450 million project is the single largest healthcare expansion in the state, creating as many as 500 hospital jobs. The incentive plan involves rebating some of the occupational taxes generated by the expansion for the next 20 years, up to $20 million. The new hospital should open in about four years, said hospital CEO Mike Warren.