The coal-fired Electrabel Rodenhuize power station near Ghent is now operating 100% with biomass. With a capacity of 180MW, it is currently the largest biomass power station in Belgium. It also offers the best results of all converted power stations with regard to environmental performance. The conversion results in a 90% reduction of nitrogen oxide (NOx) and particulate matter emissions. This means that 1.2 million tons of CO2 emissions will now be avoided every year. Geldof Metal Constructions developed a new technology to supply, pulverise and inject wood pellets to make this conversion possible. The same process can now also be used to quickly convert other similar power stations too.
The project helps Belgium advance towards achieving European Union climate plan objectives. This plan aims to ensure that at least 20% of energy comes from renewable energy sources by 2020. Electrabel is part of the GDF Suez group, and the conversion fits in with their development plan ‘Samen voor minder CO2’ (Together for less CO2). The objective of the plan is to supply green energy to one million Belgian families by 2015.
Geldof has been involved in the switch from coal to biomass as a fuel ever since the outset. It has taken place in three phases, starting with a pilot installation for co-firing with biomass, and ending with the use of biomass as the only fuel. Electrabel came to Geldof as early as 2005 with the request to enable Rodenhuize coal-fired power station to operate partly using biomass. The switch was partly stimulated by green energy certificates and government subsidies for environment-friendly initiatives.
Electrabel wanted to keep the conversion time to a minimum and have a guarantee for full operation in each phase of this project. Geldof was therefore given a turnkey contract that entrusted them with the design, coordination and full implementation. “All aspects of the project – such as engineering, procurement, construction & commissioning – therefore form part of an integral package. This means all disciplines are taken care of directly by Geldof and can be managed centrally. This working method enables quick business decisions and close monitoring of the proposed project planning. It also allows a shorter turnaround time and means we are responsible for the entire project, so we can keep a very close eye on everything and have direct dialogue with our client about all the critical aspects of the conversion,” explains Gunnar Watthé, project leader at Geldof.
Each phase of the conversion brought with it new challenges which required creative thinking. The basic criteria specifications were used as the starting point which the installation had to satisfy. These specifications included objectives for performance, availability and safety. It was up to Geldof to develop a complete plan to meet these requirements. Using existing expertise in the processing of wood and pellets as a basis, Geldof was able to develop a completely new concept that could be accommodated in an existing power station with a limited amount of space.
Each phase of the conversion took place independently of the next. It was therefore impossible to predict the design of a next step, as the experience gained could always be explored in further detail. Gunnar Watthé: “We had to work out what the best solution would be phase by phase. We also always had to take into account the available space, existing infrastructure, our client’s wishes and the new technology that we had to introduce in order to make what was being asked of us possible.”
Co-firing with wood pellets
In the first phase, the Bio 1 pilot project, Geldof had to come up with a way of co-firing 30% biomass together with the coal as efficiently as possible. Using the requirements specification as a guide, Geldof proposed a concept to Electrabel. It was decided to work with sustainably produced wood pellets which were supplied via a separate transport installation. The pellets were checked upon delivery before being deposited in a new 2,000m³ storage tank, which provides enough stock for one day. The pellets were cleaned and pulverised as they left the storage silo to then be transported pneumatically to the four coal channels linked to the burner. Gunnar Watthé: “In this and all subsequent phases we opted to build constructions off-site as much as possible before transporting them to the site to construct them further. This is safer and means we can work more easily on-site.”
After the first installation was built and working properly, Electrabel wanted to use the experience we had gained in a new installation, Bio 2. This had to enable the power station to use even more biomass in its operation, but still with the co-firing principle. The Geldof engineers installed a second 2,000m³ silo and adapted the installation further so that Electrabel could use twice as much biomass.
Max Green: 100% biomass fuel
Electrabel called on Geldof for a third time in 2010, after the company had successfully completed the previous two phases. They were asked to develop a system with which the power station could operate entirely on blast-furnace gas. Rodenhuize serves as a back-up for Electrabel’s Knippegroen power station, located on the ArcelorMittal site in Ghent, which was formerly SIDMAR. At the same time, Electrabel also took the opportunity to switch Rodenhuize entirely to biomass. This third phase, in which Geldof developed a complete system for 100% operation with biomass, started under the project name Max Green.
A pipe was installed to supply the blast-furnace gas which runs from ArcelorMittal Ghent to Electrabel Rodenhuize, about 15 kilometres away. Electrabel invested in a special extra burner to process this. The switch to biomass brought other challenges with it too. Geldof always met with Electrabel to discuss the action plan and how to achieve the performance set out in the requirements specification. An extensive safety dossier, which included explosion and fire safety guarantees, was drawn up together with the client.
Optimal operation and safety
The conveyor belts were removed for Max Green so that the whole power station could be converted to biomass. Geldof installed a third 2,000m³ silo. The wood pellets now go from the three silos to their respective distribution bunkers which spread them over three sets of four 15 ton hammer mills. The pipes go to two burners from each hammer mill. The twelve hammer mills therefore have 24 pipes which supply wood pulp to the 24 burners, spread over three levels. The distribution to the burners was improved and smaller problems with the splitters were also resolved in this phase of the project. This means that each burner is now supplied directly with the same amount of wood pulp from the hammer mills. Around 120 tons of wood pellets are processed every hour, which amounts to 800,000 tons per year.
Because a non-normalised raw material is used, foreign objects are first removed using ferrous/non-ferrous extraction, sieving installations and similar. In order to achieve the required particle size, Geldof developed an optimal pulverisation unit with hammer mills, which pulverises the pellets to the required granulometry using the appropriate sieving devices. Previously acquired knowledge of processing wood and pellets was used extensively here. Once the required particle size was reached, the wood pulp was blasted straight into the burner. Geldof collaborated with the developer of the new burners for this. Co-engineering was used to set parameters such as the flow, particle size, caloric value, mass-air ratio and correct supply height.
Alongside this technical complexity, the safety aspect also played an important role. It is very important that explosions and fire are completely avoided, or at least very quickly restricted, in installations such as this. The conveyor belts were therefore fitted with a dustproof cover and filtered particle extraction. Sealed systems and spark-, heat- and fire-detection are used as much as possible throughout the process. Geldof also installed various extinguishing systems and the silos were fitted with relief hatches. These hatches break in the event of a possible explosion to ensure that the silo remains intact and the power of the explosion is forced away from the installations. Finally, explosion suppression devices were also installed in various places using compartmentalisation, whereby a chemical powder is injected at the location of the spark, flames or heat, to suppress it and form a chemical barrier to stop the danger from spreading.
Thierry Vannecke, Bruges-Ghent entity manager for Electrabel: “Geldof’s knowledge of these types of installations and their multidisciplinary approach provide the necessary flexibility for adapting the way existing power stations operate to modern standards and client requirements such as ours. Their integrated operation and own engineering department mean they can quickly convert concepts into concrete models. Our power station in Rodenhuize is now unique with regard to the technology it uses and also in terms of its scope and performance. With a peak capacity of 180MW we are currently achieving a world record for power stations like this. It’s also the biggest conversion of it s kind.”
June 25th, 2012