Technical Concept
In May 2010, EFT and Dongfang Electric Corporation signed the EPC (Engineering, Procurement and Construction) contract to build the 300 MW thermal power plant in the vicinity of the Stanari mine. Key parameters of the TPP Stanari technical concept are:
- Single unit design
- Gross power capacity 300 MW
- Circulating fluidised bed boiler with subcritical steam parameters
- Single reheat steam turbine
- Air Cooled Condenser
- 400 kV grid connection.
There are two technical aspects of TPP Stanari that distinguish it from similar coal fired power plants in the region: Circuating Flluidised Bed (CFB) Boiler and Air Cooled Condenser (ACC).
CFB Boiler
As a clean coal combustion technology, CFB technology has been successfully used on boilers since 1960′s over the world.
The CFB process offers the means for efficient combustion of a wide variety of fuels while maintaining low emissions.
Fuel Flexibility – The relatively low furnace temperatures are below the ash softening temperature for most types of coal. As a result, the furnace design is independent of ash characteristics, which allows it to handle a wide range of fuels.
Low SO2 Emissions – Limestone is effective sulfur sorbent in the temperature range of 815°C to 925°C. SO2 removal efficiency of 95% and higher has been demonstrated along with good sorbent utilization.
Low NOX Emissions – Low furnace temperatures of 850°C to 890°C plus staging of air feed to the furnace produces very low NOX emissions.
High Combustion Efficiency – The long solids residence time in the furnace resulting from the collection/recirculation of solids via the cyclone, plus the vigorous solids/gas contact in the furnace caused by the fluidization airflow, results in high combustion efficiency.
Ash
The boiler combustion process in TPP Stanari applies the circulating fluidized bed technology. The coal is burned in the presence of significant quantity of inert material at the temperature of ~850°C that is much lower temperature comparing to the temperature for ash melting performed in several phases (from initial deformation to diffusion).
The coal as received contains a mixture of various nonvolatile mineral matters. Upon the completion of combustion process the ash actually becomes the nonvolatile matter.
In TPP Stanari, the ash is being inserted from the boiler bottom and from below the second boiler draft and bag filters plant. The boiler bottom ash is evacuated by rotational ash coolers with the waste ash heat used for regenerative heating of the basic condensate flow. The ash is then taken via two bucket conveyors (horizontal and vertical) to the silos for boiler bottom ash. The fly ash is mostly found in the bag filter (the exit concentration of powdery matters is less than 30mg/Nm3) and then transported via feeders to the silos.
Two separate systems adjusted for further ash management are located exactly under the silos for boiler bottom and two silos for fly ash: dry transportation by trucks-cisterns used for commercial purposes to the final customer location and ash damping (with water) and transportation to the disposal area.
Permanent disposal of combustion solid residues is foreseen to be carried out in the mine area with completed coal excavation activities. The cassettes coated with water-resistant folia are specially made for these purposes fully applying contemporary principles and ecologically acceptable technologies.
The ash management at the disposal area is conducted by excavation shovel KOMATSU (“WA-320”). The ash is previously sprinkled with water to prevent the ash blowing from the site. Soon after the completion of ash disposal, the cassettes are covered with folia and surface layer subject to the reclamation process.
ACC
Output steam from three stage single reheat steam turbine will be condensed in the Air Cooled Condenser.
Air-cooled condenser is of external type with forced draft, mounted on a steel structure, consisting of multiple modules. Overall dimensions of the ACC system are 70x59 m. Height of the base of the fan is 32 m, total of 30 pieces, with a power output of 90 kW each.
Main advantages of this system are low environmental impact, shorter construction period, easier operation and control of the overall system.
