Fuel Oil Systems & Combustion Testing

From the food and beverage processing industry to hospitals, industrial boiler systems are an integral part of society. However, as highly pressurized units involving combustible, hazardous gasses, it is crucial to ensure safe, efficient operation. This post discusses common boiler types, how to perform key tests, and why these aspects are so important. 

Types of Boilers

The two most common boiler types of industrial boilers are fire tube and water tube boilers. In fire tube boilers, internal tubes contain the flame and heat gasses. Water circulates around these hot tubes, and when it becomes steam, it exits through a steam header at the top. Fire tube boilers are popular for small to medium-sized industrial applications. 

Water tube boilers, as the name suggests, have water within the tubes while the flame and hot combustion gasses move along the outside of the tubes. In this model, fuel combustion occurs within a furnace, and water tubes can form the walls of the furnace. Water tube boilers are popular in large manufacturing or electrical utilities sites, where high capacity or highly pressurized steam is required. 

Commercial Gas Boiler vs Oil-Fueled Boiler

Boilers are also categorized by the fuel type they use to generate heat. The boiler must create heat in order to transfer that heat to water or steam. In gas-fired boilers, the boiler uses gas as fuel to generate heat, and in oil-fired boilers, oil is used to create heat. 

Common in critical industries, like healthcare facility boilers, that require reliable fuel supplies

When a reliable fuel supply is necessary under all conditions, many industrial boilers are gas-fired; however, they can use fuel oil as a backup source. This backup fuel source is critical in cases where the main fuel supply is curtailed or otherwise unavailable. These boiler setups are common in critical industries, such as healthcare facilities. 

In both cases, gas or oil is ignited with a burner inside the boiler’s combustion chamber. The resulting heat energy is transferred to the heat exchanger, after which it then converts to steam or heats the water. The final product—steam or hot water—is then ready for distribution and application. 

Why Backup Fuel Oil Systems Fail – And How to Prevent It

Fuel oil systems used as a backup source often go long stretches without being used. When inactive for extended periods, these parts can degrade or fail.

Don’t render your system’s backup unavailable when you need it most. Perform this regular maintenance to ensure your fuel oil system is ready to takeover:

Routine Fuel Oil System Testing Checklist

• Running all transfer pumps for extended durations
  • Operate long enough to trigger the main pumps from the day tank
• Testing fuel flow from main tanks to day tanks, and day tanks to the boiler
• Firing the boiler on fuel oil to verify functionality
• Performing safety checks, combustion testing, and tuning

Testing Boiler Safeties and Controls

Part of any Boiler Inspection or Tuning Service should involve testing the system’s safeties. Tests should confirm functionality in 4 ways:

• Operational Testing – Do the controls work as they should?
• Operating – When secured, can the boiler restart automatically?
• Safety Shut-off – If a safety limit is exceeded, is the boiler secure to manually reset?
• Annunciation/ Alarms – Does the system inform operators when an issue arises?

For all boiler systems, testing should include:

• Operating and limit controls
• Water level controls
• Alarms and cut-offs
• Burner combustion safety devices

For gas-fired systems, additional components include:

• Gas pressure switches and regulators
• Control and vent valves
• Main and auxiliary fuel valves (with leak testing)

For oil-fired systems, testing should cover:

• Main and auxiliary oil valves
• Oil pressure regulators and switches
• Atomizing air pressure switches and controls
• Onboard air compressor and oil system (if equipped)

The Importance of Combustion Analysis 

Performing combustion analysis is important to maintain a safe and efficient boiler system. Combustion is when fuel like gas or oil reacts with oxygen in the air, producing heat. The products of combustion, however, include other elements in addition to just heat, such as carbon dioxide. 

If the combustion process is not regulated, high concentrations of byproducts like soot, carbon monoxide, or nitrogen oxides are released. Regulating emissions like carbon monoxide and nitrogen oxides is important because these products harm the environment—causing effects like acid rain and smog. Combustion analysis ensures your boiler is operating within the limits set by the Environmental Protection Agency (EPA), state regulations, and local regulations. 

In addition to environmental harm, an incorrect combustion system can cause a quick rise in carbon monoxide and other explosive gasses, making the system hazardous and less efficient. 

Combustion Test Procedures 

For the reasons listed above, combustion analysis is essential. Commonly measured aspects include gas concentrations, temperature, and pressure. The combustion testing procedure requires measuring stack temperature, ambient air temperature, carbon dioxide, and stack oxygen simultaneously. 

To do so, a sample point is selected. The sample should be taken from a location before any external gasses can enter and dilute the stack’s gas composition. This is typically taken from a test port at the very base of the stack, as close to the boiler as possible.  These readings are then used to tune the boiler for optimum efficiency across all firing rates.

Air Fuel Ratio Tuning

To maximize efficiency, the right amount of air relative to the amount of fuel is needed for combustion. This amount is termed the air to fuel ratio, and discerning the value is called tuning. 

Too little air creates a fuel-rich mixture which can cause soot buildup on heat transfer surfaces, create Carbon Monoxide (a poisonous gas and an indicator of incomplete combustion), or in extreme cases lead to a backfire or furnace explosion. 

Too much air and energy is lost out of the stack as the unused Oxygen and inert Nitrogen (and other components of air) absorb and carry heat out of the boiler.

Complete and efficient combustion is indicated by the CO2 present in the flue gas (for Carbon-based fuels).  For each type of fuel, depending on its makeup, there is a peak percentage of CO2 present.  For Natural Gas this is ~11.8: 1, light (#2) fuel oil is ~15.6: 1.

Conclusion

Routine testing and tuning of your boiler is critical to ensure safe, reliable, and efficient operation.  For boilers operating backup fuel systems, routine testing will avoid surprises and ensure that your backup fuel system is available when you need it most. WC Rouse can improve your boiler’s safety, reliability, and efficiency, contact us today!