Getting fired up about algae-derived fuel in PC burners1 August 2010
Siemens Energy says it has successfully completed the first firing in a pulverised-coal burner of PetroAlgae Inc’s algae-derived solid biomass fuel.
The PetroAlgae fuel was milled and combined with pulverised coal in a pilot-scale burner with a thermal capacity of approximately 4 MBtu/h. The testing was performed in a test facility installed at the University of Utah in Salt Lake City, USA.
The co-firing tests showed that the biomass/coal fuel mixture burned well, and produced lower NOx emissions than coal alone, as would be generally expected.
In the pilot-scale test, which was conducted in a scaled-down version of Siemens’ current pulverised coal burner design, the biomass fuel was blown into the fuel injector separately from the pulverised coal. Some mixing of the pulverised coal and biomass fuel took place within the fuel injector prior to combustion of the mixture.
Up to 10% of the total heating value was provided by the biomass in these tests.
The tests showed that the PetroAlgae material was easy to handle and inject into the burner, unlike some other biomass fuels.
The fuel burned well and emissions testing showed that the biomass/coal fuel mixture produced NOx emissions around 20% lower than coal alone.
Tests were conducted with and without external air staging and it was found that the biomass and coal mixture produced lower emissions with staging than without, again as would be expected.
Siemens says it intends to conduct further tests of the pilot-scale burner with increased quantities of PetroAlgae’s biomass fuel in the near future.
“This testing has demonstrated that our burners are exceptionally well suited to burn biomass fuel in combination with pulverised coal, providing utility and industrial customers a more sustainable and cleaner alternative to traditional fossil fuels,” said Tony DoVale, president of Siemens Environmental Systems & Services.
Prior to the pilot plant-scale testing with Siemens, PetroAlgae conducted combustion testing at the University of Utah in a bench-scale burner with the biomass providing up to 100 percent of the heating value. These tests were performed with and without external air staging, and they showed similar positive results in terms of handling, injection and burning. Firing the biomass fuel alone produced lower NOx emissions than the coal alone, and the NOx reduction was more pronounced under staging conditions.
The PetroAlgae process
PetroAlgae’s technology aims to increase the productivity of micro-cropping in large-scale, open-pond bioreactors, thereby increasing the commercial attractiveness of biofuel. The process yields 30.6 g/m2/day of biomass, equivalent to 90 t/y. PetroAlgae’s commercial unit (5000 hectares) yields 450 000 t/y of dried biomass, 350 000 t of fuel or power feedstock/ year plus 100 000 t of protein/y.
The algae micro-crops absorb approximately twice their weight in CO2 (sequestering about 190 t CO2 per ha per year), and are harvested every few hours producing two products: the carbohydrate-rich biomass material that can be used for both co-firing in coal-fired power plants and as a “drop-in” replacement for petroleum-based fossil fuels; and a high-protein material.
The PetroAlgae micro-cropping process has been under development for about 20 years by NREL and the University of Arizona.
It achieves up three times the productivity of natural processes by what PetroAlgae has described as “the physics of light management combined with biochemistry.” It does not require arable land and does not compete with the food chain, indeed PetroAlgae sees the protein generated by the process as potentially contributing to the food chain as meal. The system can make use of grey or brackish water and 98% of the water is recycled.
Researchers from Siemens Corporate Technology have come up with an interesting new possibility for facilitating the harvesting of the algae. They have demonstrated in the lab that particularly fast-growing species of algae will accumulate on magnetic particles. The algae can then be harvested “as easily as a magnet collects iron filings,” according to Siemens.