Industrial Burner Selection and Tuning: Gas, Diesel, Dual-Fuel

Industrial burner selection is one of those decisions that gets less attention than it deserves. The boiler, oven, dryer or thermal oil heater gets the scrutiny, and the burner is often whatever came in the package. Yet the burner decides how cleanly and efficiently fuel turns into heat, how well the plant follows its load, and how much trouble you have when the gas supply drops or the diesel price moves. This guide covers industrial burner selection for gas, diesel and dual-fuel firing, and then explains how burners are tuned and kept in tune.

What an industrial burner package includes

When people say “the burner”, they usually mean a complete system made up of several parts that have to work together:

• Burner head and combustion head assembly: where fuel and air are mixed and the flame is shaped to suit the combustion chamber.
• Combustion air fan: supplies air against the resistance of the appliance and flue. Its motor may be fixed speed or driven by a variable speed drive.
• Fuel train: for gas, the isolating valves, filter, pressure regulator, safety shut-off valves and pressure switches; for oil, the pump, filter, nozzle(s) and solenoid valves.
• Flame safeguard or burner management system (BMS): enforces the purge, ignition and start-up sequence and shuts the burner down quickly on flame failure or any unsafe condition.
• Combustion controls: the mechanism that keeps fuel and air in the right proportion as the firing rate changes, from a simple linkage to electronic parallel positioning with oxygen trim.

Selection is about getting all of these right for your appliance, your fuel and your load, not just picking a burner with the right kilowatt rating.

Industrial burner selection: the questions to answer first

Before comparing brands or prices, gather the facts the burner supplier will need. A burner chosen without them is a guess.

1. Heat input required. Work from the appliance’s rated output and efficiency, not from the old burner’s nameplate, which may have been oversized or derated over the years.
2. The appliance and its combustion chamber. Furnace length and diameter, and the resistance (back pressure) of the appliance and flue, determine which burner heads and fans will fit and produce a stable flame without impinging on the tubes or refractory.
3. Fuels available now and in future. Pipeline natural gas, CNG, LPG, diesel (AGO) or heavier fuel oils each need different equipment.
4. Load profile. Does the plant run steadily at high fire, or swing between full load and near idle across shifts? This drives the choice of on/off, staged or modulating control, and the turndown you need.
5. Emission limits. If there are NOx or CO limits, choose a burner with verified low-emission performance across the whole firing range, not just at one point.
6. Site conditions. Ambient temperature, the space around the appliance, the electrical supply and its stability all affect fan sizing and control choices.

Gas, diesel and dual-fuel burners compared

Gas burners

Gas burners are simple at the head and demanding in the fuel train. The train must be designed for the supply pressure and flow available at the burner, and every component must suit the gas type. The safety shut-off valves, pressure switches and, on larger burners, valve proving systems are not optional extras. If you are moving from diesel to gas, budget for the gas train, the gas supply pipework and the regulator station, not just the burner.

Diesel and oil burners

Oil burners depend on good atomisation. Nozzle condition, pump pressure and fuel cleanliness all affect flame quality, and a worn nozzle can quietly push up fuel use and soot formation long before anyone sees smoke. Diesel quality varies in Nigeria, so filtration and water separation upstream of the burner are worth getting right. Heavier fuel oils need heating to reach the viscosity the burner needs, which adds equipment and maintenance.

Dual-fuel burners

Many Nigerian plants that have gas still keep diesel as a backup, because gas supply interruptions do happen and production cannot always wait. A dual-fuel burner allows a changeover without swapping equipment. As one burner buyer’s guide puts it, if you need dual-fuel or a backup fuel, “ensure the burner and fuel train are designed for it”. In practice that means:

• Each fuel has its own complete, compliant fuel train and safety interlocks.
• The combustion curve is set up and recorded separately for each fuel, because the right air setting for gas is not right for diesel.
• The standby fuel is fired regularly so that the nozzles, pump and valves are known to work when you need them.
• Operators are trained on the changeover procedure.

Turndown and modulation

Turndown is the ratio between a burner’s maximum and minimum firing rates. A burner with good turndown can follow a varying load without switching off and on repeatedly. Each off-on cycle includes a purge, which blows cool air through the hot appliance and carries heat up the chimney, and frequent cycling also wears components.

• On/off burners suit small, steady loads.
• Two-stage or three-stage burners offer a step between low and high fire.
• Fully modulating burners vary the firing rate continuously and suit most process plants with changing demand.

More turndown is not always better. One buyer’s guide warns that “overly high turndown can compromise combustion stability or increase cost and complexity”. Match the turndown to your actual load range, and remember that an oversized burner effectively loses turndown because it spends its life near minimum fire.

Combustion controls: linkage, parallel positioning and oxygen trim

Older burners use a mechanical linkage (often a jackshaft) that moves the fuel valve and air damper together. The fuel-air relationship depends on cams and linkages that wear and slip over time, so these burners need regular retuning at high fire, low fire and points in between.

Modern burners increasingly use electronic parallel positioning (sometimes called linkageless control), where separate servo motors drive the fuel valve and air damper to programmed positions at each firing rate. This allows a more precise combustion curve and better repeatability.

Oxygen trim goes a step further. A sensor measures oxygen in the flue gas and the control system adjusts the air to keep it near a target. The US Department of Energy’s steam tip sheet on combustion efficiency recommends an online oxygen analyser where fuel composition or steam flow varies widely, noting that the trim system “provides feedback to the burner controls to automatically minimize excess combustion air”. Whether it pays depends on your fuel use and load pattern, so ask for a site-specific estimate rather than a brochure figure.

Burner tuning: what it involves

Tuning means setting the fuel-air ratio across the whole firing range so the burner burns its fuel completely with as little excess air as is safe. The DOE describes periodically checking and resetting burner air-fuel ratios as “one of the simplest ways to get maximum efficiency” from fired equipment.

Why excess air matters

All burners need some air beyond the theoretical minimum to make sure every bit of fuel finds oxygen. Too little and you get carbon monoxide, soot and wasted fuel. Too much and you heat air that goes straight up the chimney. DOE guidance gives useful reference points:

• Boilers and high-temperature furnaces typically run with about 10% to 20% excess air at high fire.
• For most systems, about 2% to 3% oxygen in the flue gas with very low combustibles indicates ideal operation.
• The DOE steam tip sheet gives a rule of thumb that boiler efficiency can be increased by 1% for each 15% reduction in excess air.

Oil burners usually need a little more excess air than gas burners. The US EPA’s boiler tune-up guide lists typical flue gas oxygen ranges by fuel and control type, summarised below. These are indicative ranges only; the burner manufacturer’s settings take precedence.

A sensible tuning procedure

1. Check the instruments. Use a calibrated flue gas analyser and confirm the sampling point is representative.
2. Record the as-found condition. Measure oxygen, carbon monoxide and flue gas temperature at several firing rates, and note the flame shape and colour.
3. Inspect the burner. Look at the combustion head, ignition electrodes, flame sensor, nozzles (on oil) and air inlet. Fix defects before adjusting anything, because tuning a dirty or damaged burner just hides the problem.
4. Adjust across the range. Set the fuel-air relationship at each point on the curve, from low fire to high fire, aiming for the lowest stable excess air with carbon monoxide within the manufacturer’s limit.
5. Test the safety functions. Confirm flame failure response, low and high gas pressure switches, air pressure proving and any limit controls.
6. Document everything. Record before and after readings, settings and any parts replaced. The record is your baseline for the next service.

Tuning should only be carried out by people trained on the specific burner and its control system. The EPA guide makes the same point: the person doing the work “should be skilled in the evaluation and adjustment of the specific boiler and burner equipment in use”.

Signs your burner needs attention

• Flue gas temperature has crept up since the last service.
• Visible smoke, soot on the tubes, or a smell of unburnt fuel.
• Rumbling, pulsing or a noisy flame, especially at start-up.
• Frequent lockouts or failed ignitions.
• The burner cycles on and off often instead of modulating.
• Fuel consumption has risen without a matching rise in production.

Installing or replacing a burner

A burner change is a good moment to correct problems that have built up around the old one. Check that the boiler house has enough combustion air, that the flue is sound and correctly sized, that the fuel supply can deliver the pressure and flow the new burner needs, and that the controls integrate properly with the appliance’s limit and water-level safety devices. Commissioning should finish with a full combustion setup on every fuel, safety function testing and a handover record that your maintenance team can follow.

FAQ

Can we convert our diesel burner to gas?

Sometimes the burner model has a gas or dual-fuel version that fits the same appliance, but in most cases a conversion means a new burner head, a complete gas train and new controls. The gas supply pipework and regulating station are separate pieces of work. Ask for a survey before you budget.

How often should a burner be tuned?

Follow the manufacturer’s service schedule as a minimum. Mechanical linkage burners drift and generally need more frequent checks than parallel positioning systems. Recheck after any repair, fuel change or noticeable change in performance.

Is a dual-fuel burner worth the extra cost?

It depends on how reliable your primary fuel is and what an outage costs you. If a gas interruption would stop production, a properly set up dual-fuel burner is often cheaper than the lost output. It only helps if the standby fuel is maintained and fired regularly.

Speak to Maven about industrial burner selection

Maven Technical Services installs, services and commissions boilers, burners, fuel systems and gas piping for industrial plants. If you are choosing a new burner, converting fuels or want an existing burner checked and tuned, speak to Maven’s engineers.