Air Fuel Balancing

The Electric Charge Transfer technology (ECT) is an innovative electrostatic technique for coal flow measurement. It is a patented approach for obtaining coal mass flow (absolute and relative) and transport gas velocity in each conduit. The ECT can also monitor coal fineness for UBC or mill maintenance purposes. Foster Wheeler is the worldwide distributor of this technology, developed by TR-Tech International Oy of Finland.

ECT is an online system that measures the electric field created by electrostatic charges present in any two-phase flow application. The ECT system works in accordance with Coulomb's law in which a point charge creates an electric field around itself. To measure the charges several probes are placed into the coal stream. Electrostatic charging occurs when two materials come in contact with each other and then separate. For example, when coal particles impact the conduit wall in transportation, electrons will be transferred from one material to the other. Both materials end up with a net charge, one positive and one negative. Due to this methodology, the measured charge is not dependent on the dispersion of particles and accounts for random coal roping. The ECT system does not need a direct contact between the probe and coal particles.

The ECT system itself consists of tungsten carbide probes, which are connected to signal conditioning electronics by standard coaxial cables. The signal is then processed utilizing patented software installed in a standard personal computer (PC) with an analog to digital card.

The probes are easily installed through the horizontal or vertical wall of the existing conduit and inserted into the coal stream. Three probes in each conduit are needed for coal flow balance measurement and six for absolute coal flow and velocity measurement. The installation is very simple and requires only a mill taken out of service for several hours, which minimizes lost generating capacity. After installation, the ECT measurement is verified by Rotorprobe sampling and the system is then ready to be used.

ECT calculates the coal flow in the conduits of each mill and displays this information on the computer screen. Compared to other systems that display readings every minute or so, the ECT takes hundreds of readings every second to provide a continuous flow of uninterrupted information on coal flow or particle sizing. The information displayed can be forwarded to the plant DCS system or any computer system on site via network connection. The transfer of the ECT signals via network connection is a very powerful and cost effective way to transfer the measured information. Since 1998 ECT has been installed in 18 utility power plants.

The ECT system offers several distinct advantages:

• All information is continuous and on-line, which is essential for control applications.
• The ECT measurement is not affected by coal type, moisture, ash content or coal roping.
• The electronics can be located up to 1,200 feet from the conduits. No electronic cabinets are needed on the burner decks. The probes are passive and require no power.
• The abrasion-resistant probes in the coal conduit are passive and need no power supply.
• The installation is easy and is also possible in situations where space is limited.

1. Determine the coal flow in conduits.
2. Measure the particle velocity in the pipes.
3. Monitor unsteady phenomena in coal conduits (layout, surging, etc.)
4. Monitor particle size changes of the coal.

• UBC level reduction, reduced unburned carbon losses and increased heat rate
• Reduced standard deviation of fly ash LOI, more consistent fly ash for sale.
• Even left/right fly ash LOI in the precipitator.
• Even boiler oxygen profile, potential to reduce excess air level.
• More even superheater and reheater steam temperature profiles.
• NOx and CO minimization due to well balanced burners.
• Potential for reduced auxiliary power and increased fineness by minimizing primary air flow through the mill.
• On-line mill performance monitoring for LOI minimization.
• Quick identification of mill problems and how to resolve them.
• Potential to detect layout problems early, before they cause damage to piping, burners or windbox.
• Identify riffle distributor pluggage.
• Reduced firing system tuning time due to knowledgeable approach.