Amer #9, Essent, Geertruidenberg, the Netherlands

The AMER9 unit uses biomass both directly and indirectly. The boiler is a forced once-through supercritical type with 4 burners per layer, 6 burner layers for pulverized fuel, 1 burner layer for synthetic gas (from biomass gasification). The plant has a permit to cofire up to 1200 kton (including Amercentrale 8 + 9).

Biomass pellets are cofired up to a level of 27% by heat through 2 modified coal mills up. Only wood based fuel is used since 2006, due to reduced subsidies for agro restproducts.

For indirect cofiring, the Amergas project was initiated. The idea was to gasify about 150 kton/y of low quality demolition wood that cannot be recycled by the chipboard industry. The fuel is pre-treated (size reduction up to 50 mm, moisture content < 20%) and then gasified in a CFB gasifier (atmospheric pressure, 850°C). In its original setup, the raw fuel gas was cleaned extensively in a low-temperature (LT) gas clean-up section (baghouse filter, scrubber), after which the clean fuel gas ( 5 –6 MJ.Nm-3) should be combusted in the coal boiler via specially designed low calorific gas burners. This substitutes 5% of the total energetic plant input or 70,000 t/a coal, resulting in a CO₂ emission reduction of 170,000 t/a. An advantage of this concept is that the main part of the fuel-based contaminants are separated from the fuel gas before entering the coal-fired boiler. This means that a wide range of fuels can be co-fired in this concept, without causing applicable emission constraints and ash quality requirement problems. Disadvantages were the relatively stringent fuel constraints that had to be met and the relatively high specific additional investment costs.

Figure 1: The cofiring system at AMER 9 before modification

During commissioning of the Amer 9 wood gasifier it appeared that the syngas cooler suffered from severe fouling, which hampered normal operations. Finally, it was decided to change the process configuration drastically, see figure 2. In the original design the fuel gas was cooled to 200 °C, dedusted via a bag filter and wetly scrubbed to remove halogens and ammonia plus tars. In the new design the gas is cooled to 500 °C, it is partially dedusted by a hot cyclone and combusted as such in the boiler of the Amer 9 unit. This greatly simplifies the gas cooling and the cleaning system, but, on the other hand, reduces the fuel flexibility of the Amer project.

Figure 2: The cofiring system at AMER 9 after modification

The modified installation has been in operation since December 2002. Results up to now are satisfactory.

Contact person(s) dr. W. Willeboer, tel +31 73 8538624, email W.Willeboer@essent.nl