Multi-biofuel district heating plant parallels 2022 emission targets, and delivers world-class 125% fuel utilisation performance
06/10/2014 Danfoss Drives
The future is nowThe world-class 30 MW multi-biofuel plant in Hjørring, northern Jutland, Denmark achieves exceptionally low emission levels, and at the same time is one of the most effi cient plants of its kind in the world.
Its competitive status as one of the most internationally efficient biofuel plants ever built is achieved by high demands placed on all equipment. These demands include maximal implementation of the newest IE4 synchronous reluctance (SynRM) motor technology, driving the numerous pumps and fans throughout the plant. Performance of each SynRM motor is enabled by Danfoss frequency converters.
The plant has the capacity to drive a future geothermic plant on the same site.
Despite heavy investment in new technologies, the plant has a payback period of only seven years. The result for the consumer is a planned reduction of heating rates by 5.5% for the coming financial year, 2014-2015.
Investment 16 M EUR
2 years payback on IE4 SynRM motors operating at partial load
7 years payback on entire new plant
Visionary aims
The goals set by Operations Manager Niels-Peter Heje at tender phase in 2011 specifi ed the newest technologies:
1. Flexible fuel utilisation The primary fuel is wood chips, readily available in the local area. However the boiler must be able to burn many diff erent
non-explosive fuels such as straw, tree roots or tree trunks in the form of wood chips.
"It's a major economic advantage for us that the plant can use all types of biofuels", explains director Per Sorensen. "We have a surplus of wood chips in the local area, so we also save on transportation costs because fuel is so close. Furthermore, it's an advantage in CO2 accounting".
To achieve multi-fuel operation, the plant tolerates a range of 35 - 55% moisture in the fuel. The optimum is 45%. Therefore if the fuel is too wet,the combustion air is preheated. If it's too dry, the fuel is dampened by spraying with water. Water spraying is one of the several novel technologies used in this plant. The alternative is energy-costly fl ue gas recirculation. For loading and blending purposes there are two wood chip loading areas, connected to a common conveyer feeder. Wood chip storage and blending is computer managed by creating multiple virtual stocks, keeping track of wood chips based on type, moisture, and a number of other properties.
2. Vertical boiler for optimal efficiency.
3. An electrostatic precipitator, instead of traditional multicyclones, removes
particles from flue gas.
4. Synchronous reluctance (SynRM) motors and IE4 induction (IM) motors.
All motors over 0.75 kW were specified as synchronous reluctance type (SynRM), 1500 RPM 4 pole motors, rated IE3 - or IE4 if available. Niels-Peter prefers SynRM over permanent magnet (PM) motors, due to PM being difficult and expensive to repair. The construction of the SynRM motor is very simple by comparison, and he therefore expects lower maintenance, and greater motor uptime. SynRM motors have superior efficiency over IM motors. For ratings above
75 kW, IE4 SynRM surpasses IE4 IM for partial speed and load effi ciency performance. For ratings below 75 kW, IM motors only meet IE3. SynRM losses are substantially lower for partial load - this is where SynRM has a distinct advantage over IM motors.
At the time of ordering in April 2013, the project paid a 20% higher price to
obtain IE4 motor rating, by comparison with IE3. This is no longer the case. Prices are decreasing, and in Denmark an IE4 SynRM motor is now available for the same price as IM motors rated IE3.
5. Radial flow pumps, no inline pumps.
6. High efficiency ventilation fans.
7. Transformer located closer to plant to minimise cable losses.
8. ABB 800 XA control system, set up for PROFIBUS communication to frequency converters, control valves and instrumentation. An OPC system for communication with the cranes, absorber and emergency generator. Operators control the plant
using iPads, a new solution for district heating, although already well-known
in other fields.
Outstanding performance parameters
The absorber enables optimum energy utilisation. The absorber heat pump cools flue gas down to a record low 9.5° C, far exceeding the initial target of 12° C.
The low temperature expresses the extremely high utilisation of energy transferred from the boiler output. The absorber consumes extra power compared to a traditional biofuel plant without absorber, around 1 kW electricity for 20 kW extra heat.
However, due to the use of modern IE4 motors, energy consumption is still
competitive with a traditional biofuel plant.
The entire power consumption of the Hjørring plant, including district heating pumps, is 12 kW per 1 MW heat produced. Traditional power ratio for a boiler alone is 10 kW per 1 MW heat produced.
Flue gas emission levels are extraordinarily low. Levels of gas and dust emission are a fraction of the current permissible limits, and parallel the planned compliance levels for the year 2022.
SynRM motor compatibility now standard
As a dedicated frequency converter supplier, Danfoss is committed to manufacturing frequency converters compatible with all motor types. Software development is always ongoing, to include algorithms to comply with the emerging motor types. In this case, the control algorithm was customized to the
SynRM motors at Hjørring District Heating.
Danfoss laboratories tested two motors, a 55 kW and a 22 kW, to prove SynRM
compatibility and confi rm IE4 efficiency levels. Triggered by the development performed for this project, SynRM compatibility is now implemented as standard feature for VLT® AutomationDrive. During commissioning, the electrician sets four motor parameters: current, RPM, frequency and torque, and enables the new automatic motor adaptation (AMA). The AMA for the SynRM motor takes 2.7 seconds, measuring the remaining required motor parameters for optimal performance and energy efficiency.
Danfoss solution
The project chose a Danfoss customised frequency converter development solution over an off -the-shelf drive-motor package from a competing supplier. This Danfoss solution is now available as standard for VLT® AutomationDrive.
Some of the reasons:
*ï® Danfoss off ered extensive application support.
*ï® Danfoss frequency converters are compatible with all the diff erent motor
types installed in the plant.
*ï® Hjørring District Heating already had long experience using Danfoss frequency converters.
The contractor Weiss is convinced this is the right solution and that the result is the ultimative multi-biofuel plant. Gorm Gade Knudsen from Weiss explains, "We like Danfoss products and were not hesitant about committing to a development process. At the beginning of the project, it was quite difficult to find an IE4 motor. However nowadays, it's already realistic to specify IE4 motors."
Based on required performance, Danfoss dimensioned the frequency converters to
match the specifi ed motors. Each frequency converter was selected for the
individual load and application - pump or fan.
For more information, please contact:
Danfoss VLT Drives
Capswood
Oxford Road
Denham
Buckinghamshire
UB9 4LH
UK
Tel: +44 1270 757 584
Email: sara.bernard@danfoss.com
Web: www.danfoss.co.uk/vlt
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