The La Spezia Power Plant is equipped with a 1 x 600 MW coal-fired power unit and 2 x 350 MWe gas-fired combined cycle power units for a total of 1300 MWe. The unit normally fires imported coal with < 1% Sulphur. The flue gases are treated sequentially by FGD absorber. It is equipped with a 1 x 100% DeSOx lines with an absorber. The blow down from the absorber, along with other wastewaters, is sent to a new wastewater treatment plant.
Wastewaters from FGD treatment plant can no longer be discharged into the sea due to tough Italian and EU environmental regulations. In order to overcome this major environmental problem, ENEL decided to feed the absorbers with fresh and re-circulated waters and install the Zero Liquid Discharge (ZLD) plant so that no industrial wastewater discharges are allowed by the entire power plant.
Scope of Service
To overcome the challenge, ENEL selected the Softening – Evaporation – Crystallization (SEC) process to treat the wastewaters and reuse/conserve fresh waters. Aquatech supplied, installed, and commissioned the ZLD plant as an EPC contractor with local associates. The SEC plant comprises of three treatment tanks where lime, sodium sulfide, and coagulant are added. A 1 x 100% Softener Clarifier is used for removal of suspended solids, temporary hardness, and precipitated metal hydroxides. Followed by a 1 x 100% softener clarifier (calcium reduction by soda ash dosing) for removal of permanent hardness, a 1 x 100% Falling Film type Brine Concentrator (equipped with Vapor Compressor), 1 x 100% Crystallizer (equipped with a Thermocompressor) and 2 x 50% Belt Filter Presses.
The plant also includes several chemical dosing systems, storage tanks, pumping systems, electrical works (MCC, cable trays, cabling etc), controls & instrumentation.The ZLD plant is a fully integrated automated system. The Brine Concentrators operate in seeded slurry mode. Each Brine Concentrator is equipped with an external mist eliminator for ease in maintenance. The Crystallizer operates in forced circulation method. The industrial grade soft water and high purity distillate produced in the system will be used in the main power plant.
Design FGD Wastewater Analysis
Process Flow Diagram