Posted on: 05. 26. 26
Industrial facilities like gas turbines, reciprocating engines, and process heaters need predictable fuel gas supplies to run at maximum thermal efficiency. When incoming fuel gas composition varies unexpectedly, the impact is felt across the entire facility. Most operators will notice performance symptoms before they understand the cause: engines drop load unexpectedly, exhaust gas temperatures spike, or flame stability fluctuates in the combustor. Learn how to recognize these events and react quickly before your equipment suffers prolonged damage.
Fuel composition shifts are seldom obvious. Pipeline quality may appear stable month to month, but fuel assemblies can experience gradual variations of heavy hydrocarbons, water content, or inert gases. When heavy hydrocarbon or water concentration increases (or nitrogen concentrations decrease), these subtle changes affect the BTU value of your gas stream. As the energy density of your system’s fuel supply lowers or becomes inconsistent, components optimized for a single BTU specification struggle to keep up. Learn to recognize these conditions early to protect system reliability and avoid unnecessary downtime.
Unexpected Costs Associated With Fuel Gas Quality Changes
Fluctuations in gas quality quickly impact combustion stability. Whether your system is designed for power generation or as an industrial burner, the combustion process expects a precise mixture of air and fuel. An abrupt decline in fuel gas quality upsets this ratio, leading to incomplete combustion or flame instability. Besides lowering thermal efficiency, this imbalance wreaks havoc on your equipment.
Imagine working on an operational team responsible for a mid-sized industrial burner. For several months, your system operates without interruption, but one day your supplemental fuel source experiences a slow but noticeable change in supply pressure. Your operators never catch the gradual change in your fuel gas makeup until several days later when more natural gas liquids (NGL’s) like ethane and propane travel through your fuel line. Your equipment was tuned to expect a relatively light methane-rich supplemental fuel stream.
Within hours of the NGL increase, your system alerts you to soaring turbine blade temps and a spike in emissions. As heavier hydrocarbons burn, your flame shape lengthens, moving the heat release zone closer to sensitive downstream equipment.
The resulting thermal loading causes components to wear faster, developing cracks or damaged coatings much earlier than expected. Exhaustion of hot section components triggers mandatory outages to replace expensive components long before the end of life. Fuel gas quality issues can also cause burner flame lift-off or flashback. Flame lift-off occurs when fuel/air mixture velocity surpasses flame velocity and literally lifts the flame off the burner. In extreme cases, lift-off can cause flameout of the entire system. Flame flashback occurs when the flame propagates back up into the fuel nozzle. Flame flashback destroys burner tips instantly.
Effects of Low fuel gas quality
The lower heating value of your fuel has immediate impacts on equipment design limits. Engines and burners compensated for low-quality fuel by running a larger volume of gas through the combustion chamber. This added volumetric demand can overwhelm your equipment’s fuel system. Control valves will open further, fuel manifolds will see higher pressure drops, and supply pumps will cycle harder to maintain the mass flow rate.
If you reach the maximum volumetric flow capacity of your equipment, your system goes fuel-limited. Fuel-limited means your equipment can no longer operate at its rated load. If your facility depends on gas turbines or engines to drive compressors or generate electricity, running fuel-limited translates to lost production. In addition to volumetric challenges, low-quality fuel presents higher concentrations of inert gas diluents such as CO2 or nitrogen. These harmless additives eat into your flame temperature and do not contribute to combustion.
Cool flame temperatures result in incomplete combustion, which dramatically increases carbon monoxide output and hydrocarbon release. Within hours, your facility could be exceeding your local environmental permit limits. Ensure you track your exhaust gas emissions and learn to recognize when fuel is the root cause of sudden emission increases.
Pro Tip | Understanding Pressure Drop
Did your fuel gas manifold pressure suddenly increase? Did your output power decrease at the same time? Operating at a low fuel gas quality means your system is forcing more volume through the burner nozzles to compensate. Monitor your valve position trends weekly to identify abnormal conditions before they cause flameout. Monitoring trends aligns with other money-saving operations like preventive maintenance.
4 Steps to Troubleshooting Combustion Problems
Once you suspect a fuel problem based on unit performance, follow these steps in the field to confirm your theory. Guessing will only slow down the troubleshooting process and lead you to replace components that aren’t damaged. This step-by-step guide will take you through the most likely causes of low fuel gas quality.
Step 1 | Reviewing Control Valve Position Trends
First, examine the historical performance of the unit’s fuel control valves. Fuel that has dropped in quality will cause your control valve to drift higher than normal operating ranges. Your operators will open the valve more to attempt to deliver the same mass flow rate of fuel to the turbine or process heater. Cross-reference your valve position with the total power output on your unit. Does your valve say its 90% open, but your system is only generating 70% of the rated load? This is a clear sign that your fuel gas quality has decreased. Proper fuel gas management extends the service life of gas storage systems.
Step 2 | Inspect your Fuel Conditioning Equipment
Before accusing your supplier of selling you poor-quality gas, rule out failures in your onsite fuel conditioning equipment. Take a look at the differential pressure reading across your fuel gas filter separator. An increase in pressure drop indicates liquids, particulates, or aerosols are beginning to plug the filter media. Not only does plugging change your incoming fuel gas composition, but liquid carryover adversely affects burner stability.
Step 3 | Perform Gas Chromatography
The only way to truly know if your fuel gas quality has declined is by analyzing a live fuel sample. If your facility has an online gas chromatograph available, evaluate the latest gas analysis reports. Do you notice a significant shift in the amount of methane, ethane, or nitrogen?
If not, grab a manual sample of your fuel gas supply using a certified sample cylinder. Remember to fill the sample cylinder at system operating pressure and ensure the sample temperature remains above the fuel gas’s hydrocarbon dew point.
Step 4 | Check Exhaust Gas Temperature Variation
Fluctuations in fuel quality often present as uneven temperatures across the exhaust manifold of reciprocating engines or turbines. Take a look at the exhaust gas temperature indicators. Do one cylinder or thermocouple drastically differ from the rest? A high spread can indicate some fuel nozzles are delivering a different fuel mixture, or begin to drift out of calibration due to plugged fuel ports. Clean and inspect your fuel nozzles if your exhaust gas temperature spread exceeds manufacturer recommendations.
Call Us Today | Pro-Gas Can Help Improve Your Operations
Troubleshooting unexpected shifts in fuel gas quality takes vigilance and attention to detail. When you suspect your fuel gas quality is not up to par, taking immediate action can prevent minor efficiency losses from becoming major equipment repairs. At Pro-Gas, we understand the pressure operators are under to maximize asset performance while staying compliant with regulatory requirements.
We provide customized technical expertise and equipment tuning to match your facility’s unique system design. Our experts are available to work alongside your engineering and maintenance teams to install permanent monitoring equipment, perform comprehensive fuel system audits, and design preventive maintenance programs that fit your operation’s budget. Contact us now to learn how Pro-Gas can keep your system burning efficiently and protect your valuable assets.
Frequently Asked Questions
Q. How do I know if fuel gas quality has changed?
- Operators notice the most immediate changes in engine power output, exhaust gas temperature fluctuations, and control valves opening farther to maintain standard loads. Knowing these effects allows you to troubleshoot fuel density problems before your system shuts down.
Q. Why does poor fuel gas quality cause higher emissions?
- Low-quality fuel causes systems to burn inefficiently, leading to higher-than-normal carbon monoxide and hydrocarbon content in your exhaust stream. Both of these byproducts can put you out of compliance with your local emissions permit.
Q. What’s the best way to troubleshoot fuel gas quality in the field?
- Performing gas chromatography on a live fuel gas sample is the only way to confirm your fuel gas makeup. Field technicians should use a certified sample cylinder when obtaining fuel samples from the system. Ensure the sample remains at system operating pressure and above the fuel gas’s hydrocarbon dew point.
