Patent ID: 8728246
Filing Date: 2014-05-20
Classification: C02F

Abstract:
1. A method of conditioning and removing deposits including mixtures of inorganic compounds comprising, in sequence, the steps of: a) taking a heat exchange system of a nuclear power plant out of service, the heat exchange system including a steam generator having thereon scale comprising a mixture of anhydrous or hydrated oxides of iron and deposits of anhydrous and/or hydrated oxides and/or hydroxides of aluminum and/or silicon; b) introducing into the steam generator an aqueous cleaning solution comprising a treatment concentration of a quaternary ammonium hydroxide, wherein a room-temperature pH of the aqueous cleaning solution is at least 7; c) dissolving the deposits of anhydrous and/or hydrated oxides and/or hydroxides of aluminum and/or silicon through a chemical reaction between the quaternary ammonium hydroxide and the deposits of anhydrous and/or hydrated oxides and/or hydroxides of aluminum and/or silicon by contacting the deposits of anhydrous and/or hydrated oxides and/or hydroxides of aluminum and/or silicon with the aqueous cleaning solution for a treatment period; d) maintaining the aqueous cleaning solution within a treatment temperature range during the treatment period; e) removing the dissolved deposits and substantially all of the aqueous cleaning solution from the steam generator after the treatment period; and f) returning the heat exchange system to service, wherein the method further comprises: estimating a total deposit load of the deposits of anhydrous and/or hydrated oxides and/or hydroxides of aluminum and/or silicon; and adjusting the quantity of quaternary ammonium hydroxide in the aqueous cleaning solution to achieve a target molar ratio relative to the total deposit load.