Co-firing coal with refined wood pellets is one of the most cost-effective ways to reduce fossil CO2 emissions.
Refined wood pellets, sometimes referred to as black pellets, consist of a woody biomass that is processed under heat and high pressure. The result is a biomass fuel with features resembling hard coal – low moisture content, water-resistant and it can be ground in hard-coal mills.
The tests, the first of their kind anywhere in the world, where initiated in November last year in Reuter West, a 600MW coal power plant in Berlin. Tests were performed at different co-firing rates – 20, 35 and 50 per cent – without any modifications.
Besides the co-firing, several other important aspects of the bio fuel are evaluated.
“We have opened and looked into every box in the process, from the ship unloader to the chimney,” Stefan Dusan, Project Leader, says. “We knew that co-firing refined wood pellets would work well, but not this well. “Reaching these co-firing rates with conventional biomass would require significant investment.”
There are many advantages with wood pellets. It gives flexibility: as the plant does not need major modifications to burn wood pellets. The minimal need for modification also makes the start-up time short. Using refined pellets also reduces the costs of CO2 fees.
The project started in November last year and after having fine-tuned the technology in the laboratory as well as in small-scale experiments, co-firing tests in Reuter West Unit E were conducted over three weeks in June and July.
The main bottleneck in this process is the mills. The mill motor requires slightly higher energy consumption for co-firing rates higher than 20 per cent. This, and other issues, will be subject to further research and development.
“We have shown that co-firing refined wood pellets is possible with minor modifications,” Dusan says. “Now we will transfer the knowledge to our other plants, so they can follow up on our tests.”