Elucidation of the Corrosion Mechanism in Concentrated NH 4 HS Environments With the Aid of the Mixed-solvent Electrolyte Model

Transcription

1 OLI User Conference 2005 October 5, 2005 Elucidation of the Corrosion Mechanism in Concentrated NH 4 HS Environments With the Aid of the Mixed-solvent Electrolyte Model Hirohito Iwawaki, TOYO ENGINEERING Co. Kazuhiro Toba, IDEMITSU ENGINEERING CO., LTD.

2 Contents 1. NH 4 HS Corrosion 2. Simulation Analysis of Concentrated NH 4 HS Environments 3. NH 4 HS Corrosion Test Corrosion Rates Corrosion Products 4. Conclusion

3 NH 4 HS Corrosion Equipment to be concerned Air Cooler Fluid : HC, H 2 S, NH 3, H 2 O Deoxygenated ph : weak alkaline Temp. : 40 to 150 degc Reactor Water dosing OH Condenser High Press. Separator Stripper Oil Refining / Hydrotreating Process

4 Environment NH 4 HS Corrosion Wet H 2 S-NH 3 service (non-acidic environments) Materials Carbon steel Corrosion Rate Max. 3 to 10mm/y Corrosion factors NH 4 HS concentration, temp., flow rate, etc. Severe corrosivity in concentrated NH 4 HS environments Corrosion mechanism unknown Corrosion tests were conducted in in concentrated NH 4 HS solutions.

5 Simulation of Concentrated NH 4 HS Purpose To understand the characteristics of conc.nh 4 HS sol n Problems Target concentrations are approx. 30 to 45wt% NH 4 HS (Over 35mol%) under high pressure at around 90degC. Actual test pressures are unclear considering molecular and ionic interactions. Analysis of test solutions are difficult in autoclave cell during the tests. Solutions MSE* enable to estimate operating pressures and chemical compositions in concentrated NH 4 HS test solutions.

6 Simulation of Concentrated NH 4 HS Dissolved H 2 S vs. total pressures based on bubble point calculations Total Pressure (atm) Aqueous model MSE model as 45wt%NH 4 HS H2S(g) H 2 S(g) Total Pressure (atm) as 45wt%NH 4 HS H2S(g) H 2 S(g ) In NH 4 OH solution based on 45wt%NH 4 HS

7 Simulation of Concentrated NH 4 HS Verification of MSE model by experimental data Approx. 30wt%NH 4 HS Calculated data Experimental data Total Pressure (atm) H 2 S(g) H 2 S vs Total Pressure (30wt%NH 4 HS)

8 Simulation of Concentrated NH 4 HS Verification of MSE results by experimental data. Approx. 45wt%NH 4 HS Calculated Data Experimental Data Total Pressure (atm) H 2 S(g) H 2 S vs Total Pressure (45wt%NH 4 HS)

9 NH 4 HS Corrosion Test Corrosion Rates Corrosion rates in NH 4 HS test solutions 20 Carbon Steel 316L Stainless Steel Corrosion Rate (mm/y) NH 4 HS Concentration (wt%) NH 4 HS concentrations 30, 39, 42wt% Temperatures 90degC Deoxygenated by hydrazine

10 Corrosion Rates NH 4 HS Corrosion Test Comparison with published data Measured corrosion rates have good correspondence with with published data data except for for 30wt%. : Carbon Steel : 316L Stainless Steel (Ref. : Damin, Corrosion/78, 131)

11 Corrosion Products NH 4 HS Corrosion Test Film analysis on carbon steel by diffracted X-ray Detective elements : S Fe O Compositions : FeS FeS 2 Fe 2 S 2 Fe 3 S 3 Fe 3 S 4 Fe 3 O 4 S Solution analysis by X-ray Absorption Fine Structure (XAFS) [Fe(NH 3 ) 4 ] 2+ [Fe(NH 3 ) 5 ] 2+ [Fe(NH 3 ) 6 ] 2+ FeS Fe 2 3 O 4 Ammine iron complexes, Iron Sulfides and Iron oxides were detected.

12 NH 4 HS Corrosion Test Corrosion Products Thermodynamic Simulation by Corrosion Analyzer (Ammine iron complex)

13 NH 4 HS Corrosion Test Corrosion Products Thermodynamic Simulation by CSP excluding complexes formations (Iron sulfide) FeHS(ion) FeS(Amorphous) Fe 9 S 8 FeS, FeS 2 FeHS - FeS 2

14 Corrosion Products NH 4 HS Corrosion Test Simulation by Corrosion Analyzer in non-acidic deoxygenated environment (Iron oxide) Anode :: Fe=Fe e +2e - - Cathode :: 2H 2H 2 O+2e 2 - =H - =H 2 +2OH 2 - -

15 Corrosion Products NH 4 HS Corrosion Test Thermodynamic Simulation by Corrosion Analyzer in non-acidic deoxygenated environment (Iron oxide) Fe 3 O 4 Anode :: Fe=Fe e +2e - - Cathode :: 2H 2H 2 O+2e 2 - =H - =H 2 +2OH (Fe (Fe )+(OH - ) - ) Fe Fe 3 O 3 4 (Fe(OH) 4 2 ) 2 )

16 NH 4 HS Corrosion Test Estimated Corrosion Mechanism NH 4 HS NH HS - Anodic/Cathodic Reactions Fe = Fe e - 2HS - + 2e - = H 2 + 2S 2-2H 2 O + 2e - = H 2 + 2OH - Corrosion Products In Concentrated NH 3 : Fe 2+ + x(nh 3 ) Fe(NH 3 ) x 2+ In H 2 S(HS - ) : Fe + SH + = FeS 1-x + xhs - + (1-x)H + FeS 2 (*) In alkaline deoxygenated : Fe 2+ + (OH - ) Fe 3 O 4 (Fe(OH) 2 ) (*)Shoesmith, J.Electrochem.Soc,127,5,1980)

17 Conclusion MSE model can estimate concentrated NH 4 HS environments. Increases of corrosion rates were confirmed in concentrated NH 4 HS environments. Ammine iron complexes, iron sulfides and iron oxides were detected and simulated by corrosion analyzer as corrosion products. Electrochemical approaches considering the complex formations should be discussed to precisely elucidate the mechanism of NH 4 HS corrosion.

18 These achievements were obtained from a research and development project conducted by Japan Petroleum Energy Center with a subsidy from the Ministry of Economy, Trade, and Industry JAPAN