Systems for recovering nitric acid from pickling solutions

Abstract

In one embodiment, a system for treating a gas stream comprising NO x produced from a used or spent acid pickling solution includes a pickling apparatus, a first chamber, and a second chamber. The pickling apparatus includes an inlet adapted for introducing a reducing agent into contact with the acid pickling solution, wherein the reducing agent reacts with free nitric acid in the acid pickling solution to form NO x ; and a headspace in which gas comprising NO x collects. The first chamber includes a first inlet communicating with the headspace, a second inlet communicating with a source of ozone, and an interior volume adapted to contact the NO x gas and the ozone. The second chamber may include a third inlet communicating with a source of water vapor, an interior volume adapted to contact the gaseous effluent from the first chamber with the water vapor introduced through the third inlet, and an outlet for collecting solubilized nitric acid from the interior volume of the second chamber.

1 . A system for treating a gas stream comprising NO x  produced from a used or spent acid pickling solution generated by treating a material selected from a metal and a metal alloy, the system comprising:
 a) a pickling apparatus selected from a pickling bath, a pickling tank, and a pickling spray device, the pickling apparatus including an acid pickling solution, the pickling apparatus comprising
 an inlet adapted for introducing a reducing agent into contact with the acid pickling solution, whereby the reducing agent reacts with free nitric acid in the acid pickling solution to form NO x , and 
 a headspace in which gas comprising NO x  collects; 
   b) a first chamber including
 an interior volume 
 a first inlet communicating with the headspace of the pickling apparatus and adapted to convey at least a portion of the gas comprising NO x  from the headspace to the interior volume, 
 a second inlet communicating with a source of ozone, and 
 wherein the interior volume is adapted to contact the gas comprising NO x  with the ozone, thereby producing oxidation products including nitrogen sesquioxide and nitrogen pentoxide, wherein at least a portion of the nitrogen sesquioxide and nitrogen pentoxide react with water in the first chamber to form nitric acid; and 
   c) a second chamber directly fluidly communicating with the first chamber and receiving gaseous effluent from the first chamber, the second chamber including
 a third inlet communicating with a source of water vapor, 
 an interior volume adapted to contact gases from the first chamber with the water vapor, thereby solubilizing nitric acid in the gaseous effluent from the first chamber with the water vapor, and 
 an outlet for collecting solubilized nitric acid from the interior volume of the second chamber. 
   
     
     
         2 . The system of  claim 1 , wherein the pickling apparatus includes an acid pickling solution comprising nitric acid. 
     
     
         3 . The system of  claim 2 , wherein the pickling apparatus is used to treat surfaces of materials selected from stainless steel, titanium, and titanium alloys. 
     
     
         4 . The system of  claim 1 , wherein the first chamber includes a static mixer adapted to mix the gas stream comprising NO x  and the ozone in the interior volume of the first chamber. 
     
     
         5 . The system of  claim 1 , wherein the first chamber further comprises a third inlet that communicates with a source of water vapor. 
     
     
         6 . The system of  claim 1 , wherein the source of ozone is an ozone generator. 
     
     
         7 . The system of  claim 1 , wherein the second inlet is located adjacent the first inlet. 
     
     
         8 . The system of  claim 1 , wherein a diameter of the first chamber is at least 24 inches. 
     
     
         9 . The system of  claim 1 , wherein the second chamber is a mist eliminator. 
     
     
         10 . The system of  claim 1 , wherein the inlet adapted for introducing treating material into contact with the acid pickling solution introduces the treating materials into the tank, bath, or spray device. 
     
     
         11 . The system of  claim 1 , wherein the pickling apparatus further comprises a treating compartment in which the acid pickling solution is contacted with the treating material. 
     
     
         12 . The system of  claim 1 , wherein the outlet of the second chamber fluidly communicates with the pickling apparatus so that solubilized nitric acid from the interior volume of the second chamber is conveyed to the pickling apparatus. 
     
     
         13 . A system for treating a gas stream comprising NO x  produced from a used or spent acid pickling solution generated by treating one of titanium and a titanium alloy, the system comprising:
 a) a pickling apparatus selected from a pickling bath, a pickling tank, and a pickling spray device, the pickling apparatus including an acid pickling solution, the pickling apparatus comprising
 an inlet adapted for introducing a reducing agent into contact with the acid pickling solution, whereby the reducing agent reacts with free nitric acid in the acid pickling solution to form NO x , and 
 a headspace in which gas comprising NO x  collects; 
   b) a first chamber including
 an interior volume comprising a static mixer, 
 a first inlet communicating with the headspace of the pickling apparatus and adapted to convey at least a portion of the gas comprising NO x  from the headspace to the interior volume, 
 a second inlet communicating with an ozone generator, and 
 a third inlet communicating with a source of water vapor, 
 wherein the interior volume is adapted so that the static mixer mixes the gas stream comprising NO x  and the ozone, thereby producing oxidation products including nitrogen sesquioxide and nitrogen pentoxide, wherein at least a portion of the nitrogen sesquioxide and nitrogen pentoxide react with water in the first chamber to form nitric acid; and 
   c) a second chamber directly fluidly communicating with the first chamber and receiving gaseous effluent from the first chamber, the second chamber including
 a third inlet communicating with a source of water vapor, 
 an interior volume adapted to contact gases from the first chamber with the water vapor, thereby solubilizing nitric acid in the gaseous effluent from the first chamber with the water vapor, and 
 an outlet for collecting solubilized nitric acid from the interior volume of the second chamber. 
   
     
     
         14 . The system of  claim 13 , wherein the pickling apparatus includes an acid pickling solution comprising nitric acid. 
     
     
         15 . The system of  claim 13 , wherein the pickling apparatus is used to treat surfaces of materials selected from stainless steel, titanium, and titanium alloys. 
     
     
         16 . The system of  claim 13 , wherein the second inlet is located adjacent the first inlet. 
     
     
         17 . The system of  claim 13 , wherein a diameter of the first chamber is at least 24 inches. 
     
     
         18 . The system of  claim 13 , wherein the second chamber is a mist eliminator.