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2007 Award Winner

Power Base Automation Upgrade Award

WINNER: Athenry Electical Limited

PROJECT: Biomass Fired Unattended 3MW Fire Tube Boiler

Project Overview

• Biomass Fired Unattended 3MW Fire Tube Steam Boiler
• Project design commenced June 2003 and the control cabinet commenced construction August 2003
• Scope was to develop a Standard Unattended Boiler Control System for a 3MW fire tube boiler and couple it to the 1.7MW Biomass Combustion System.
• Athenry Electrical ltd utilised off the shelf Burner Control which was recognised by applicable standards. The Durag burner controller provided flexibility with flame intensity, Infra-red and or Ultra Violet lighting bandwidth options. The Durag is used at the Huntley power Station.
• Project Value: Approximately $98,000.00
• The boiler and gasifier have been installed upon CHH wood panels manufacturing site, Mt Maunganui. They have provided Bryce Coulter of Page Macrae Engineering a small area located to the rear of site in which they can develop and design the boiler control. CHH provide the combustion fuel when ever it’s needed from their waste woodchips.
• The boiler has now been connected to process and can provide steam on a consistent basis.

The Story in Brief

• In March 2003, Bryce Coulter, a design engineer from Page Macrae Engineering in Mt Maunganui approached Kevin Malpas from Adavance Boiler Services and Dave Harris from Athenry Electrical ltd to assist him in designing a boiler control system which would integrate to his newly designed Biomas Gasification Combustion System.
• The object of our control integration was to allow the boiler to utilise this combustion design process and meet all the prerequisites of Unattended Boiler guidelines as set out in the code (The design, safe operation, Maintenance and servicing of Boilers: Part 5 Unattended Boilers). This meant that a form of combustion utilising waste would be capable of generating thermal energy to a designed rating of 1.7MW. This has provided NZ with its first Biomass fired unattended industrial steam boiler of this rating.
• Bryce Coulter and Keith Johnson (Page Macrae's Electrical Engineer) worked together on the design of their Biomass Combustion system. They employed the services of Walter Flanagan of Impact Automation, to design the PLC control for the system.
• Dave Harris of Athenry Electrical ltd initially met with Bryce, Keith and Walter to formulate a method of design integration. There needed to be a mutual understanding from both Walter and David's of how the 2 were going to be integrated. This also would evolve.

Achievements

• The Gasifier out put exceeded its design intention and consistently produced 2 to 3MW of energy. The project was a success due to the broad skill base of the engineers, both mechanical and electrical brought to work on this project.
• The final effect for CHH when steam is being produced consistently is that the system uses its waste and produces steam at minimal fuel costs, the only being oil for the pilot ignition and divert ignition. When the boiler is supplying steam it means that CHH can turn off their natural gas fired boilers costing 100s of thousands of dollars / year to run. They also save on waste disposal as removal of waste can cost 10s of thousands / year.
• The success of the project has allowed Page Macrae to begin research into the viability of building a 6MW thermal plant, this is due to commence this year once the field trials have been completed and funding obtained.
• Feedback from within the market place has been very positive with several clients interested once the 6MW unit has been built and commissioned.

Quality and Technical Innovation

• Components and design aspects to the project: The utilisation of standard boiler control components to provide the safe operation of the boiler as per the Code was the key. This would provide simplicity for verification purposes. We didn't want to reinvent the wheel. There existed 2 controls, 1 x Gasification and 1 x Boiler. In the event of a boiler fault the boiler control needed to remove the heat source and it needed to be failsafe. We achieved this by having hard wired control of the combustion divert system. The basic firing rate control was simply communications between PLC's.
• The difficulties where mainly flame stability when steam demand was required, a need to increase the firing rate. The Factors which effected this where; Fuel supply, Grate rotation and fuel level, Removal of spent fuel, Primary air flow, Gasifier Combustion chamber pressure, Boiler combustion chamber air pressure, Oxygen and after burner airflow, and finally Induced draft air flow. This created a complex number of variables to which we needed to work through, both mechanically and electrically.
• One step to solving the problem was by utilising the Durag controller with UV/IR flame detection capability and its degree of intelligence around this area. The other was continual trial and error with regard to PID loop control. As with normal combustion process, Air and Fuel mix are the 2 most critical of the process. We finally discovered that once we had consistent and reliable fuel supply then by controlling the primary air flow through the grate in response to Steam Demand, After Burner air flow in response to Oxygen level and I.D Fan in response to Furnace inlet air pressure provided us with the stability of flame intensity we required to successfully run the boiler unattended.

Management, Commercial and training

• As this project was of a Research and Development nature, the site facilities and material usage was of a reusable nature. The power supply in the beginning was a diesel 60kva genset. The control room consisted of an old transportable building located under the Boiler. The Gasifier itself is housed within a 40ft sea container which also provided a workshop area.
• The Boiler itself was an old Coal fired boiler which Bryce converted for this project. It also needed to be modified to fit all the devices and instrumentation within the confines of the old boiler.
• There was minimal interface with CHH during this project.
• Training - The services of our final year ETCO trainee was utilised to order, build and wire control panel in our East Tamaki workshop prior to shipment to site in Mt Maunganui.

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