PF Coal Flow Balancing & Measurement System

Greenbank Terotech Ltd is the official partner and sole distributor of the ABB PfMaster coal flow balancing and measurement monitoring system. The PfMaster system is designed for use on pulverised-coal feeds into boilers. In the coal flow balancing and measurement monitoring system, a single cabinet can connect up to 32 sensors to measure coal distribution and velocity in pulverised-fuel (PF) burner feeds. Poor fuel distribution causes combustion inefficiency. Coal-flow transport behaviour and distribution to boiler burners has, up until now, proved difficult to meter. The dynamics of the coal flow are dependent on factors such as particle size, roping and the physical plant configuration, in particular the layout of the PF pipe-work from individual mills to the burners.

The common way of checking the condition of the fuel distribution has been to use probe-sampling devices. Whilst these do provide an indication of the flow in a given pipe at a given moment, the accuracy is a function of the probe type and procedure used. In addition, the time taken to sample up to eight PF burner feeds across one mill can take several hours using the most accurate single point sampling techniques, and so making controlled changes and checking distribution after improvements over a range of mill throughputs a very labour intensive task.

The PfMaster enables continuous ‘on-line’ measurement, balancing and monitoring of performance of the flow of Pf delivering benefits that include:

Low-maintenance, an essential quality for modern practices in power generation.
Factory calibrated. There is no need for expensive and time consuming manual sampling techniques.
ATEX and CE approval for safety. The device is passive and is designed so that no energy can enter the fuel pipes.
The real time use of velocity information for trimming of primary mill air! The application data shows that reducing the Mill Primary Air for a given load can improve both classification & distribution.
Mills that have multiple coal pipes exiting the classifier can use control valves to balance the fuel distribution.
Used in conjunction with other Greenbank Terotech Limited technology partnership with the University of Nottingham (GAIM), such as the HVARB anti rope breaking equipment and trim control device, the PfMaster allows real time feedback to allow fine tuning of coal flow distribution.
An alternative combustion improvement option is to use the PfMaster to give real time feedback to plant control of secondary air at the burners to balance the combustion at individual burners.

PfMaster Sensor
The sensor monitors poor distribution of coal to the burners, and consists of electrostatic sensor rings around the whole circumference of the pipe with applied technology to account for coal roping and twisting in the pipe. Signal-sensing utilises the detection of electrostatic energy, which is naturally present on the pf particles.

Each sensor features a completely smooth internal bore, making the design relatively immune to wear due to coal impact, and it is unaffected by high pressure excursions from the mill (Pressure Equipment Directive certificates on request). This ensures the longest possible interval between service inspections.

Sensor electronics attached to the sensor act as an amplifier to send the measurements to the control cabinet where coal velocity and concentration are derived. The central cabinet calculates the coal distribution and flow from all the sensors of a particular mill, and determines individual pipe coal velocities from the time of flight of material passing an exact distance inside each PfMaster sensor.

Sensor connection to the central signal-processing cabinet is by a single low-voltage multi-core cable. The sensor electronics design and input modules at the central cabinet have been optimised to provide the highest rejection of possible interference signals generated on the plant.

The sensor electronics incorporate, as standard, barrier circuits to prevent any possibility, under fault conditions, of hazardous voltages igniting the explosive atmosphere present in the pipe-bore. No energy is transmitted into the pipe. As such the PfMaster has appropriate CE and ATEX approvals.

This passive sensing therefore eliminates any dangers which might be present with systems based on active measurement techniques, such as microwave and other Electromagnetic radiation techniques

PfMaster - Signal Processor and Display
At the heart of the system is the signal processor which can handle up to 24 or 32 sensors, sufficient to meet the requirements of a number of Mills. Many user-facilities are available which offer flexible I/O configuration.

The VDU display presents, graphically, the status of all 24 or 32 meters. Any measurement which is in an alarm condition changes colour to indicate the fault. A number of ‘Function’ keys at the foot of the display allow the user to switch between other facilities, which include:

Setup in which the ranging and output control is set
Trend shows the system’s measured value over the past 60 minutes
Log sets the file and logging interval for the internal data-logging facility
Mass Enables relative or absolute mass details to be configured and displayed
In the event of power failure all the remote current outputs are frozen. The processor system automatically restarts on power resumption.

On-Line Velocity Meters
Many low NOx burner designs have been designed for very low PF velocities, some as low as 16 m/s for optimum combustion. It is also well understood that mill classification is improved both on Dynamic and static classifiers with reduced PF velocity through the mill. The on-line velocity meter works on the same principle as the PfMaster, non-intrusive with the same quality sensor electronics & cabinet.

For coal velocity measurement only it is not necessary to utilise the whole pipe circumference as with the PfMaster sensor, and as such the design screws into the pipe via 4 inch BSP fitting, as it determines velocity from the time of flight of material past its two sensors in the same way as the PfMaster sensor. Use the on-line velocity meter to
minimise primary air through the mill for optimum classification, improved distribution and burner combustion.

The PfMaster product has been the result of practical experience and knowledge gained over many years in the process control and flow metering industries. The patented principles on which PfMaster operates culminate from a clear understanding of the technical and application requirements working in the process of delivering Pf to the boiler. Intensive instrument development and long term field trial activities, in the most demanding installations, have verified the durability of PfMaster. Wear of any intrusion into the pipe is a function of the coal type and its velocity. The PfMaster is non-intrusive. Greenbank can guarantee a minimum life of sensor spool pieces. All sensors are factory calibrated before shipping with a certificate of conformity. To date no PfMaster system has ever failed or suffered down-time and required maintenance.