Innovative Combustion Technologies - Optimum combustion

Innovative Combustion Technologies provides combustion-side technical expertise to power plants, enabling them to resolve operational and maintenance challenges, optimise combustion, improve unit capacities and reduce emissions. Drawing on its 20-plus-years' experience, the company develops methods and guidelines to address the challenges that face the power industry.

Optimum combustion can contribute to significant improvements in heat rates and emissions. It occurs when combustion is completed in the lower furnace, while achieving emissions standards and reducing slagging propensity.

Optimum combustion results in the following:

• full load is attainable, while meeting all
• environmental constraints
• combustion is completed within the furnace (no secondary combustion)
• flames are stable and flame scanners are satisfied
• water-wall wastage and dry gas losses are minimised
• spray flows are minimised, while maintaining design steam temperatures
• fly-ash unburned carbon is satisfactory
• no furnace slagging or convection-pass fouling is experienced
• popcorn ash is minimised
• opacity is minimised.

ICT employs the following services to optimise combustion:

• pulveriser inspections
• 'clean' air balancing
• isokinetic fuel sampling
• primary airflow calibrations
• secondary airflow measurement/calibration
• furnace-gas species and temperature (HVT) traverses
• economiser exit-gas species and temperature traverses.

Reducing NOx emissions

The primary contributors to elevated NOx emissions are inadequate pulveriser performance, improper airflow management and an unclean furnace. ICT takes a methodical approach to optimising combustion and reducing NOx emissions by optimising airflow management and improving pulveriser performance, and through burner tuning. To optimise airflow management, ICT offers calibration/design of airflow measurement devices. It improves pulveriser performance through recommendations that include adjustments to mechanical variables/tolerances (inside the pulveriser) to enhance fuel fineness and burner-line air/fuel balances. Burner tuning is performed as a part of an iterative process consisting of burner adjustments and furnace exit HVT (high-velocity thermocouple) traverses, until an optimal condition is obtained.

Preventing furnace slagging

ICT has found that slag prevention is more effective than managing slag incidents. Combustion should be completed lower in the furnace, allowing water walls to absorb more heat, which reduces furnace exit-gas temperatures to below ash-softening temperatures. Slag prevention can also be achieved by maintaining an oxidising furnace atmosphere, since ash-fusion temperatures are lower in a reducing atmosphere. Managing raw coal size, fineness and air-to-fuel ratios assists with the self-cleaning of pendant and platens.

To aid slag prevention, ICT performs pulveriser performance optimisation, verification testing of plant instrumentation (O2 probes, pressure transmitters and coal feeder rate) and evaluation of operating practices when slagging occurs.

Prerequisites of optimum combustion

ICT has developed a list of prerequisites imperative to optimum combustion:

• fuel lines 'clean-air' velocities balanced to ±2%
• fuel lines fuel flow balanced to ±10%
• fuel lines 'dirty-air' velocities balanced to ±5%
• fuel line minimum velocities at 3,300fpm
• fuel line fineness >75% passing a 75µm screen; 300µm particles <0.3%
• primary air/fuel ratio accurately controlled
• primary airflow accurately measured and controlled to ±3%
• over-fire air accurately measured and controlled to ±3%
• uniform furnace exit O2 at an average of 3%
• secondary air distribution to burners within ±10%
• tolerances of burners and dampers within ±5mm
• pulveriser fuel feed smooth, measured and
• controlled accurately
• fuel feed quality and size consistent.