Modeling a Geothermal Fluid Corrosion Simulation in OLI Software

Table of Contents

1. Overview
2. Importance of Modeling Geothermal Fluid Corrosion
3. Step-by-Step Guide to Setting Up in OLI Studio
   • Defining a Geothermal Stream
   • Saturating the Gas with Water
   • Calculating the Corrosion Rate
4. Conclusion

Overview

Geothermal energy is a sustainable and powerful resource, but geothermal fluids are often chemically aggressive, leading to significant corrosion challenges for infrastructure. Modeling these corrosion processes is critical to designing materials and systems that withstand the harsh conditions typical of geothermal environments. This article explains how to set up a typical geothermal fluid corrosion model in OLI Studio: Stream Analyzer and OLI Studio: Corrosion Analyzer. Note: This example is based on version 12.0.0.11 of OLI Studio. Screens and options may vary in other versions.

Importance of Modeling Geothermal Fluid Corrosion

Corrosion in geothermal systems can result in costly damage to equipment, unexpected downtime, and reduced system efficiency. By simulating corrosion rates, engineers and operators can:

• Select suitable materials for pipelines, heat exchangers, and other equipment.
• Optimize system designs to mitigate corrosion risks.
• Predict maintenance schedules to ensure operational reliability.
• Improve the longevity and safety of geothermal systems.

OLI Studio’s robust simulation capabilities enable users to accurately assess corrosion risks under specific geothermal fluid conditions, ensuring informed decision-making.

Step-by-Step Guide to Setting Up in OLI Studio

1. Defining a Geothermal Stream

1. Launch OLI Studio and create a new case.
2. Add a stream by navigating to the Streams tab and double-clicking Add Stream in the Actions pane.
   
3. Define the chemical composition of the geothermal fluid:
   • Input concentrations for common geothermal components.
   • Include dissolved gases like CO₂ and H₂S, as they play a significant role in corrosion processes.
   • This example uses the following composition:
     

     Inflows (lb)
     H2O	0
     H2	25.7
     N2	26.1
     Ar	0.3
     H2S	133.9
     CO2	1268.6
     NH3	58.3
     CH4	68
     HCl	3.4
     B(OH)3	9.1

     
4. Specify a temperature and pressure. This example uses 25 °C and 1 atm. (The geothermal conditions will be specified in a Mixer).
5. Add another stream for the H₂O Steam. This example uses 3000 lb H₂O (enough to saturate our gas stream) at 25 °C and 1 atm. Again, the geothermal conditions will be specified in the Mixer.
   

2. Saturating the Gas with Water via the Mixer Object

1. Add a Mixer object to the process.
   
2. Select the defined geothermal gas stream and steam stream to the Mixer so they appear in the "Selected" column of the Mixer.
   
3. In the Mixer settings:
   • Specify the geothermal conditions. This example uses 390.2 °F and 124.4 psia.
   • The Mixing Method will be the default "Single Point Mix" and the "Type of calculation" will be the default "Isothermal."
     
4. Run the Mixer to create a fully saturated geothermal gas-water mixture. This will be the "1 of 1" stream created by the Mixer.
   
5. Add the aqueous (liquid 1) stream as a new stream by right-clicking "1 of 1" and selecting "Add As Stream" and checking only "Aqueous." Then press OK.
   
   
6. This adds our saturated aqueous stream so we can run the corrosion rate calculations.
   
7. Note: The streams can also be set up in OLI Flowsheet: ESP. Attached to this article are OLI Studio and OLI Flowsheet: ESP examples. 

3. Calculating the Corrosion Rate

Note: Corrosion rate calculations for carbon steel require the AQ Thermodynamic Framework. The MSE Thermodynamic Framework currently supports only duplex stainless 2205 and duplex stainless 2507 in version 12.0.0.11.

1. To run the corrosion rate calculation, highlight the "1 of 1-Liq1" stream. In the "Actions" pane, double-click "Add Corrosion Rates" to add the corrosion rate option.
   
2. Define additional parameters:
   • Operating temperature and pressure. This example uses 199 °C (390.2 °F) and 124.4 psia.
   • For Calculation Type, we're interested in "Set pH" with a target pH of 3.83.
     • For our example, the other properties (Use Single Titrant, pH Acid Titrant, pH Base Titrant, Flow Type, Effects of FeCO3/FeS Scales) can be left as their default. 
   • Choose the contact surface for which you wish to assess corrosion (e.g., carbon steel, stainless steel). For our example, we'll use carbon steel.
     
3. Run the calculation. OLI Studio will provide:
   • General Corrosion Rate
     
   • Localized Corrosion Potential
     
   • Polarization Curve
     

Conclusion

Modeling geothermal fluid corrosion in OLI Studio provides actionable insights that help engineers and operators design resilient systems and choose suitable materials for challenging geothermal environments. By accurately predicting corrosion rates, organizations can mitigate risks, reduce costs, and extend the lifespan of geothermal infrastructure.

For more information about OLI Studio: Corrosion Analyzer, check these articles:

• Introduction to OLI Studio: Corrosion Analyzer for First-Time Users
• Corrosion Rate Calculation FAQs - Advanced
• Localized Corrosion: Theory and Application in OLI Studio: Corrosion Analyzer
• OLI Studio: Corrosion Analyzer Reference Guide
• Corrosion Model Development
• Corrosion Papers

If you have further questions or need support, consult OLI Systems' detailed manuals or reach out to our technical support team for assistance.