Abstract: An aircraft comprising at least one propulsion unit configured to propel the aircraft in a first direction and at least one further propulsion unit configured to propel the aircraft in a second direction substantially opposite to the first direction. The aircraft also includes at least one wing, wherein the at least one propulsion unit is mounted in front of the leading edge of the at least one wing, such that the air downstream of the at least one propulsion unit flows around the at least one wing to provide lift and a longitudinal thrust in the first direction. The at least one further propulsion unit is configured to provide a longitudinal thrust in the second direction.

Abstract: A process is provided for increasing the concentration of sulfuric acid in a waste solution of sulfuric acid previously used to produce titanium dioxide. The waste solution of sulfuric acid is fed into a first heat exchanger/evaporator stage that operates at a sulfuric acid concentration of less than 30%. A portion of the solution discharged from the first heat exchanger/evaporator is fed into a heat exchanger/evaporator that uses waste heat and operates at a sulfuric acid concentration that is greater than 40%, while the remainder of the solution discharged from the first heat exchanger/evaporator and the solution discharged from the heat exchanger/evaporator using waste heat is fed into a second heat exchanger/evaporator that operates at a sulfuric acid concentration that is greater than 50%.