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AET’s boiler concept is based on 25 years of experience in steam generation and biomass combustion. This experience has come from a large number of plants with the following characteristics:
- Very high availability
- Steam data and steam quality suitable for turbine operation
- High boiler efficiency
- Fulfilment of strict emission requirements
- Flexibility
- Continuous operation at minimum 100% load
- Low maintenance costs
- Long operating time (>8000 hours) between shutdown for manual cleaning of heating surfaces - applies also to demolition wood.
These characteristics are based on the following:
- Gas tight and fully welded water tube boiler
- Top suspended boiler in order to avoid friction forces during heating and cooling.
- No refractory in furnace
- Tall furnace with long residence time
- Empty radiation pass for cooling the flue gas before superheater
- Vertical flue gas pass for collection of ash
- Un-heated downcomers
- Good natural circulation even under extreme operating conditions
- Effective steam separation in the drum
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The boiler pressure parts are designed in accordance with accepted European norms and standards. This applies to the choice of materials, calculations of wall thicknesses, production, certification of welders as well as quality assurance of the finished product.
The furnace is tall and slim in order to obtain a long residence time and good turbulence, resulting in good mixing of unburnt gases and combustion air. This ensures good combustion with low emissions.
A tall furnace also ensures good circulation of water and steam in the panel walls.
Minimal refractory is used in the furnace in order to prevent ash deposits and slag formation.
From the furnace the flue gas flows into the upper part of the radiation pass and continues down wards. In the bottom hopper the flue gas turns 180 degrees and flows vertically up through the superheater pass. In this way coarse ash particles are separated from the flue gas. The collected particles are reinjedted into the furnace.
The superheater is arranged in the third pass. This will give the flue gas and ash particles a long time to be cooled below the ash melting point before inlet to superheater. Here the flue gas flows vertically upwards and the warmest superheaters with the great pipe distance are therefore placed at the bottom. The ash particles can then fall freely down through the heating surfaces. Both parts contribute to ensure a long operating time without shutdown for manual cleaning of the heating surfaces.
The economiser is placed as a separate unit and is provided with heating surfaces consisting of plain tubes.
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