The Greenbank G-CAM carbon-in-ash analyser is the latest “state of the art” product which has been designed to measure the degree in loss-on-ignition of carbon-in-ash on a coal fired boiler. Loss-on-ignition is a direct measure of the efficiency in combustion and the information provided by this system can be used to help optimize the boiler. Based around the latest military grade microwave technology, the method of measurement is independent of mass of sample and therefore negates the requirement for load cells or density measurement like other similar carbon-in-ash monitors.

The G-CAM utilises the latest microwave techniques, measuring the microwave absorption and phase shift over a range of frequencies. The system is designed to take rapid multiple isokinetic samples across the economizer ducting, directly after the combustion process and it has been designed to collect over 2kg of samples per day for on-line analysis. It. employs stainless steel ash transport lines from ash ducting which are heat traced above the dew point of the ash which prevents blockages to the ash sample lines and keeps the ash free flowing in the system.

The G-CAM has also been designed to provide automated physical samples for lab analysis if so desired.

The benefits of the Greenbank G-CAM carbon in ash monitor

• Accurate and repeatable carbon in ash measurement
• Latest microwave absorption and phase shift measurement techniques
• Suitable for all coal types
• No load cells or density measurement
• Low maintenance
• Rapid iso-kinetic sampling
• Up to 6 multi-point sampling capabilities
• Increased handling rate up to and over 2Kg per hour
• Touch screen control
• Self protecting against boiler oil burning shut down and start up
• Automated, sample segregation for lab analysis
• Reports duct temperature at collection points for analysis of ash behaviour
• Unaffected by change in coal type or colour

Why measure carbon-in-ash on-line?

Residual carbon in ash is the percentage of un-burnt carbon left in the ash when burning coal, and is a measure of the efficiency in combusting the coal particles in the furnace.

Un-burnt carbon particles are a function of an incomplete combustion process, and can be due to a number of reasons:-

• Incorrect coal to air ratio at fuel rich burners due to poor coal distribution to the burners.
• Large size particles and velocity through the burner flame
• When staging the combustion using over fire air some particles do not complete combustion

Stations moving to low NOx burners or implementation of over fire air at the top of the furnace in a program to reduce emissions usually experience increases in carbon levels in the ash due to a combination of the above factors.

How to measure carbon-in-ash and benefits of using microwave

All techniques that determine carbon-in-ash require a measurement of the carbon level for a known fixed amount of ash to give the percentage accurately. The G-CAM, using the latest microwave techniques, measures the microwave absorption and phase shift (the slowing down of microwave when passed through the ash sample compared to a reference signal) over a range of frequencies. Microwave of a few milli- Watts is used which is then highly affected by the dielectric properties of carbon and not the ash. Microwave is unaffected by the colour or shading of the ash that can change with coal type. Microwave also passes through the whole volume of the ash being measured.

Where to collect the ash sample

Many boilers typically have a combustion imbalance between the two sides and this is often seen by variations in small O2 and CO measurement differences. Hence, the G-CAM system is designed to quickly and simultaneously take up to 6 samples from across the economiser outlet but before the air heater. This gives a cross-section allowing the combustion to be investigated across the boiler. It is not just the number of sampling locations that is important, samples must be taken in a timely manner and with sufficient ash.

It is recommended for a small boiler that 2 sample locations are used, a medium size boiler (typically 500 MW) 4 sample locations and larger boiler or customers who would like to investigate combustion imbalances on front and opposed wall fired boilers can have up to 6 sample locations using only one GCAM processor.

The G-CAM process

The G-CAM is designed to operate continuously with only an annual service interval and specifically designed to clear all probes and sampling pipes.

Samples are typically collected in approximately 5 minutes, giving 12 measurements per hour, and typically interrogating 180 g per hour with microwave for accurate carbon determination.

Maintenance