The Greenbank Group is a leader in the design and manufacture of pioneering cleaner coal technologies (CCT). CCT is widely acknowledged as one of the most effective methods for improving efficiency and thereby reducing emissions in coal fired power plants. The company’s success has been largely due to its commitment to research and development on its portfolio of boiler optimization products. The strides in innovation that Greenbank has made has positioned the group at the forefront of CCT.
Greenbank has been awarded two Rushlight Awards for Power Technology: the Rushlight Fossil Fuel Award for a technological advancement or innovation that has made a significant contribution to the reduction in environmental impact of fossil fuel usage; and the prestigious Rushlight Power Generation & Transmission Award for the most significant engineering development that has improved the efficiency of energy conversion and transmission from fuel source to consumer in the electricity sector.
Crowning Greenbank’s industry achievements came the Queen’s Award for Enterprise in the Innovation category for 2008.
Charles Conroy, Greenbank managing director said: “We are extremely encouraged by the response we’ve had from the power industry regarding our products and believe that by continuing to invest in research and development we can ensure that coal fired power stations become greener, cleaner, and more efficient.”
The CCT products
Key developments for the company have included the introduction of groundbreaking CCT products such as the Variable Area Rope Breaker (VARB), the G-CAM Carbon-in-Ash Analyser, and the particle size analyser (PSA) together with the application of the PfMaster Coal Flow On-Line Monitoring System. These products have been instrumental in delivering major efficiency improvements and benefits in the optimization of coal fired power generation plant in many countries.
Cleaner coal technologies offer both economic and environmental benefits
Providing balanced and equal distribution from mills to boiler burners has been a challenge to operating and performance engineers alike for many years. In particular, where splits in direction occur in the puliverized fuel (PF) piping system or on multi-outlet mills, successful monitoring and controlling of the PF flow can be highly beneficial to efficiency and emissions. And this is a useful place to begin closer examination of Greenbank’s technology.
Its family of boiler optimization products, when combined, offer impressive results in equalizing PF distribution and can therefore maximize balanced air and coal flow into the boiler. This leads to improved burn, use of less coal to generate heat at the same amount of power together with a reduction in carbon-in-ash.
After milling, as coal particles are transported along PF pipes by air, the coal dust concentrates within the pipe and results in a tight formation called a ‘rope’. This formation means that the particles cannot be evenly distributed to boiler burners particularly where PF pipe runs split in multiple directions to carry the PF to the burners. Consequently, these inefficiencies can lead to increases in emission levels of nitrous oxides (NOx) or unburnt coal (carbon-in-ash) resulting in wasted energy.
Greenbank’s VARB technology breaks up the rope effect created by pneumatic transport of fine particulate and provides a homogenous mix of the coal and air to deliver proper and equal distribution to the boiler.
A Greenbank engineer installs the PfMaster Coal Flow Online Monitoring System
The secret behind the success of the VARB PF Diffuser is Greenbank’s relationship with its wholly owned R&D company, Greenbank Advanced Instrumentation and Measurement (GAIM). GAIM was originally formed in collaboration with the University of Nottingham.
Utilizing both academic and industrial expertise GAIM has developed the family of VARB PF Diffusers. It employs specialists in particulate analysis and control who have a deep understanding of the characteristics of particles being transported in air. GAIM offers both computational fluid dynamics (CFD) analysis and a one-third scale test rig where concepts can be brought to life and tested prior to delivery to the customer.
The methodology rigorously applied for each and every VARB design consists of the following steps:
- Acquisition of customer existing PF distribution data.
- Creation of a computational model (CFD) and the numerical simulation of the existing distribution.
- Prediction of the PF rope position.
- Introduction of the VARB design within the computational model.
- Optimization of the VARB design and location within the numerical model.
- Verification of the rope position by survey.
- Installation and optimization of VARB (and Control Gate).
Greenbank’s Variable Area Rope Breaker (VARB) on wagon ready for delivery
Greenbank’s VARB is already making significant in-roads on improving balanced PF diffusion in coal fired power plants. One 2000 MW UK plant has reported a significant 50 per cent reduction in the carbon-in-ash produced since installing VARB technology. The implementation of VARB at another UK plant has been quoted as achieving savings of 45-48 tonnes of coal per day on one 600 MW boiler. It is expected to replicate these savings on each of the remaining three boiler installations. In Canada, one plant is using VARB technology to provide flame stability which alleviates the need for oil supported combustion at half load.
Coal Flow Monitoring System
Another step forward has been the introduction of the PfMaster Coal Flow Monitoring System which enables continuous on-line measurement as well as monitoring and balancing PF being distributed to each burner. Up until now, coal flow transport behaviour and distribution has proved difficult to gauge. One common way of checking fuel distribution has been to use probe sampling devices; however, this has proved very time-consuming and does not always provide accurate results.
The PfMaster sensor monitors for poor distribution of coal to the burners. Electrostatic sensor rings around the whole internal circumference of the pipe identify coal roping and twisting of the PF travelling through the pipe. Signal-sensing utilizes 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. This ensures the longest possible interval between service inspections. PfMaster sensor electronics attached 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. It then determines individual pipe coal velocities from the time of flight of material passing an exact distance inside each PfMaster sensor.
The percentage concentration measurement can be used to ensure the correct air to fuel ratio is being delivered to the burners. In conjunction with a gravimetric feeder the system is able to accurately report on the mass flow of coal being delivered down each pipeline. The velocity measurement can then be used to trim or adjust the rate of primary air and as such help assist in accurately controlling the delivery speed of PF to the burners.
PfMaster 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 optimized 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, which led to appropriate CE and ATEX approvals for the PfMaster sensor. 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.
The G-CAM Carbon-in-Ash Monitor is a state of the art analyzer which measures on-line the amount of unburnt coal using the most current technology in microwave technology.
All techniques that determine carbon-in-ash rely on a measurement of the carbon level for a known fixed amount of ash to give the percentage accurately. Using the latest military grade microwave technology the G-CAM monitor measures the microwave absorption and phase shift (the slowing down of the microwave when passed through the ash sample compared to a reference signal) over a range of frequencies. A microwave of a few milliwatts is used which is then highly affected by the di-electric properties of carbon and not the ash. Microwave technology is unaffected by the colour or shading of the ash that can change with coal type. It also passes through the whole volume of the ash being measured.
A Greenbank welder in action at Woodville, Derbyshire, UK
The G-CAM monitor is designed to operate continuously with only annual service intervals and is specifically designed to self-clear all probes and sampling pipes.
It extracts samples of fly-ash from the economizer and typically takes samples every 6-10 minutes. The system is fully automatic and can decant samples into an external vessel for further analysis or calibration requirements which can be used to verify its high accuracy in performance.
The ability to do this provides the station engineer with real-time information about the combustion efficiency and performance of the coal fired boiler. This allows coal fired energy producers to have the ability to monitor and optimize boiler performance.
Particle size analyser
Greenbank has also developed the particle size analyser (PSA) technology for on-line, non-intrusive measurement of particulate in lean phase flows. The technology has been developed from a dual need to measure particle size distribution for applications such as PF and flue gas analysis. The principal of measurement uses a flat laser sheet, which illuminates small dust particles passing through the sheet at velocity. A digital imaging system then captures images that are used in conjunction with customized software. The software synchronizes the laser and camera to take rapid images of the particles illuminated by the laser sheet and stores them to hard disk as greyscale images.
The images are then analyzed for the range of greyscales and the extent of how in-focus the image is by means of analysis of the sharpness of the particles. The out-of-focus items which represent particulates not exactly in the laser sheet illumination are removed to leave only the particulates properly illuminated. These are then analyzed using algorithms developed especially for this purpose. Once the noise is removed from the image, the software can take the size of each particle. This again uses algorithms that take into account the greyscale and number of pixels.
VARBs break up the rope effect created by pneumatic transport of fine particulates
The development of this technology was customer driven with a requirement for an improvement over optical type opacity and manual style measurements. The PSA captures multiple images per second and rapidly determines the number and size of particles then calculates particulate size distribution.
In the flue gas application, the system can rapidly calculate the mg/m3 from the number of particles measured, their size and the known volume of interrogation from the laser and CCD alignment. The particle size outputs as a percentage and mg/m3 measurement is outputted as a value of between 4-20 mA. The system then repeats the process. A 4-20 mA signal of MW load is taken from the plant so that the system shuts down when not in use.
The Greenbank Group is working to further strengthen its research capabilities by teaming up with the cream of the UK’s brightest academic researchers at a number of leading universities.
In 2002 Greenbank Advance Instrumentation & Measurement (GAIM) was set-up as a joint-venture company with the University of Nottingham. It specializes in the development of new and unique equipment that can be used to characterize, measure and control two-phase fluid flows in the power generation, fossil fuel, cement and steel sectors.
Finance Director Martin Killberry receives the Queen’s Award
GAIM has established facilities to study and measure the characteristics of two-phase flow using the latest laser technology. Techniques also used to study two-phase flows are complimented by a unique test rig and computational fluid dynamics (CFD) engineering capabilities. It also has access to experimental facilities, now based at the University of Leicester.
GAIM is now wholly owned by the management team and is independent of an individual academic partner. This enables the business to link with various universities on a project by project basis. Currently projects or concepts are in hand with Nottingham, Leicester and Cambridge universities.
GAIM works hand-in-hand with Greenbank Terotech’s Systems Division to provide engineering solutions to the power generation industry. As well as having the ongoing role of investigating, characterizing and provide solutions for two-phase flow problems, it has an ongoing policy to improve existing and develop new optimization products.
Charles Conroy, Greenbank managing director said: “Our team is demonstrating time and time again that innovation is the best way forward in reducing the negative impact of generating energy.”
It is evident from the recent industry acknowledgment and awards bestowed on The Greenbank Group that CCT is seen as a crucial step in helping provide the ability for coal fired plants to satisfy the requirements of increasingly demanding environmental legislation.
Coal’s continuing role as a source of power generation has also highlighted the significance of supporting research and development programmes into clean technologies for both economic and environmental reasons.