Enhancing Efficiency and Protecting Equipment with On-Line Total Sulfur Monitoring in Combined Cycle Power Plants

Combined cycle gas power plants are leading the global transition to higher energy efficiency. By using both gas and steam turbines, these facilities extract maximum value from fuel, achieving superior thermal performance compared to simple-cycle plants. However, one major threat to this efficiency is sulfur contamination in the fuel gas supply. Continuous, on-line monitoring of total sulfur has therefore become essential to protect key components, minimize downtime, and maintain compliance with environmental regulations.

Why Sulfur Monitoring Matters

Gaseous fuels such as natural gas, LNG, and LPG can vary widely in composition depending on their source. Even trace amounts of sulfur can lead to severe operational challenges:

Corrosion in heat recovery systems – Sulfur compounds oxidize to form sulfuric acid during combustion. When exhaust gas temperatures fall below the acid dew point, this acid condenses in the Heat Recovery Steam Generator (HRSG), causing corrosion in evaporators, economizers, and stacks.
Fouling of catalytic systems – Plants that use ammonia injection for NOx control can experience deposition of ammonium sulfate and bisulfate on HRSG surfaces. These acidic deposits degrade performance, increase backpressure, and reduce turbine efficiency.
Environmental concerns – Sulfur dioxide (SO₂) emissions contribute to acid rain, underscoring the importance of strict sulfur control for sustainability and regulatory compliance.

Principles of On-Line Total Sulfur Measurement

Modern on-line sulfur analyzers employ pulsed UV fluorescence technology to continuously measure total sulfur in liquid and gaseous hydrocarbons. In this process:

All sulfur species are oxidized to SO₂.
The analyzer quantifies the SO₂ concentration with high precision.
Real-time sulfur readings are transmitted to plant control systems for monitoring and intervention.

This approach complies with ASTM and ISO standards, ensuring accurate and repeatable measurement performance across a wide range of sulfur concentrations — from 1 ppm up to 100% sulfur. Analyzer systems are available with low-maintenance design and self-diagnostic capabilities allowing for seamless operation in demanding industrial environments.

Application in Combined Cycle Power Plants

In a combined cycle configuration, the gas turbine burns compressed air mixed with fuel, driving a generator to produce electricity. Exhaust heat is then recovered by the HRSG, generating steam that powers a steam turbine for additional electrical output.

Sulfur monitoring becomes critical here. If the sulfur content in the fuel exceeds acceptable limits, acid formation can damage the HRSG, leading to costly maintenance and reduced efficiency. By implementing continuous on-line monitoring:

Operators can verify actual sulfur levels in real time.
Accurate sulfur data allows precise calculation of the acid dew point of the fuel gases.
Plant engineers can adjust process parameters—such as stack exit temperature and boiler feedwater temperature—to prevent condensation and corrosion inside the HRSG and stack.

Operational Benefits of Continuous Sulfur Analysis

On-line sulfur monitoring delivers measurable operational advantages:

Corrosion Prevention – Maintaining temperatures above the acid dew point prevents acid condensation and extends equipment lifespan.
Maintenance Optimization – Early detection of sulfur-related issues reduces unplanned shutdowns.
Performance Assurance – Protecting HRSG and turbine efficiency maintains power output and revenue.
Environmental Compliance – Real-time sulfur control supports regulatory adherence for emissions limits.

Together, these benefits help ensure that combined cycle plants operate safely, sustainably, and profitably.

Complementary Gas Monitoring Technologies

In addition to sulfur analyzers, on-line process mass spectrometers can monitor complete fuel gas composition as well as physical properties such as calorific value, Wobbe Index, and combustion air requirements. This combination of technologies enables comprehensive insight into fuel quality and combustion efficiency, allowing plants to optimize both performance and environmental footprint in real time.

Conclusion

Implementing continuous total sulfur analysis at combined cycle gas power plants provides vital protection for critical equipment and ensures high operational efficiency. By accurately identifying and managing sulfur contaminants, operators can mitigate corrosion, extend component life, and maintain stable, efficient power generation.

Reliable sulfur monitoring is not just an analytical function—it is a strategic element of asset protection and process optimization in modern energy systems.

Quick FAQs

1. Why is sulfur a problem in gas turbine systems?
Sulfur in fuel converts to sulfur oxides during combustion, which can form acidic condensates that corrode HRSG components and reduce turbine life.

2. What is the acid dew point, and why is it important?
The acid dew point is the temperature at which sulfuric acid vapor condenses. Keeping process temperatures above this point prevents corrosion and equipment damage.

3. How does on-line sulfur monitoring work?
The analyzer converts all sulfur compounds into SO₂ and measures its concentration using UV fluorescence, providing accurate real-time data.

4. What are the advantages of on-line analysis versus laboratory testing?
On-line systems deliver continuous, real-time sulfur data, enabling immediate corrective action and preventing unplanned downtime.

5. Can analyzers handle both gas and liquid fuels?
Yes, modern on-line sulfur analyzers are compatible with both liquid and gaseous hydrocarbons, covering wide concentration ranges.