Reduced carbon steel corrosion in CO2-O2 amine environment

Abstract

A structural low carbon steel in combination with and in contact with an aqueous MDEA solvent that includes as an amine-based chemical additive. When mixed with MDEA solvent to form a MDEA solution, the MDEA-based solution in contact with carbon steel reduces the corrosion rate of low carbon structural carbon steels having a carbon content greater than about 0.18% by weight is significantly reduced when the concentrations of CO 2 , O 2 and heat stable salts (HSS) are controlled below critical amounts. The MDEA solution, when controlling the concentrations of CO 2 , O 2 and HSS below critical amounts, suppresses the corrosion of carbon steel having a carbon content greater than about 0.18%. A smooth surface finish further suppresses the corrosion of the low carbon structural steel. When the CO 2 , O 2 and HSS are maintained below critical values, a low carbon structural steel having a micropolished surface finish displayed improved corrosion resistance.

The invention claimed is:  
     
       1. A gas treating system for a coal-fired plant, comprising:
 an aqueous amine solvent;  
 an amine-based chemical added to the amine solvent to form an amine solution;  
 up to about 6% O 2  by weight in the solution;  
 up to about 12% CO 2  by weight in the solution;  
 up to about 1.5% heat stable salts;  
 an alkanoamine treating unit wherein at least some components of the treating unit comprise a structural carbon steel;  
 wherein the structural carbon steel includes at least about 0.18% by weight carbon, and  
 wherein a surface of the carbon steel is in direct contact with the amine solution.  
 
     
     
       2. The gas treating system of  claim 1  wherein the heat stable salts further comprise bicene, formic acid and sulfuric acid. 
     
     
       3. The gas treating system of  claim 1  wherein the surface of the carbon steel in direct contact with the amine solution is micropolished to have a surface finish of 32 Ra and smoother. 
     
     
       4. The gas treating system of  claim 1  wherein the carbon steel has a carbon content of at least about 0.23% by weight. 
     
     
       5. The gas treating system of  claim 1  wherein the carbon steel has a silicon content of at least 0.04%. 
     
     
       6. The gas treating system of  claim 1  wherein the carbon steel is A36 having a carbon content of at least about 0.18% by weight. 
     
     
       7. The gas treating system of  claim 1  wherein the carbon steel in contact with an amine solution is treated to have a carbon content of at least 0.18% by weight. 
     
     
       8. The gas treating system of  claim 1  wherein the carbon steel in contact with an amine solution is treated to have a carbon content of at least 0.23% by weight. 
     
     
       9. The gas treating system of  claim 1  wherein a surface of the carbon steel in contact with the amine solution is carburized to increase the carbon content of the surface to at least 0.18% by weight. 
     
     
       10. The gas treating system of  claim 1  wherein the carbon steel in contact with the amine solution is carburized to increase the carbon content of the surface to at least 0.23% by weight. 
     
     
       11. A gas treating system fora coal-fired plant, comprising:
 an aqueous amine solvent;  
 an amine-based chemical added to the amine solvent to form an amine solution;  
 up to about 6% O 2  by weight in the solution;  
 up to about 12% CO 2  by weight in the solution; up to about 1.5% heat stable salts;  
 an alkanoamine treating unit wherein at least some of the components comprise a structural carbon steel, wherein the structural carbon steel includes at least about 0.18% by weight carbon and wherein a surface of the carbon steel is in direct contact with the amine solution; and  
 wherein the structural carbon steel in contact with the amine solution is characterized by spontaneous passivation whereby the corrosion behavior is passive.