Water and wastewater treatment in power generation

Most companies in the power generation sector, both conventional and renewable, need to produce and utilize large amounts of vapor, leading to extremely high water consumption. That is why they frequently have water and wastewater treatment plants (combined in different ways).

Water treatment plants are designed to transform the collected water for vapor production (raw water) into high-quality purified water (inflow water) to be used in production processes (mainly vapor boilers).

These treatment plants utilize different technologies, which are combined depending on the quality of the collected water, the most prominent being the following:

•    Physicochemical purification
•    Reverse osmosis
•    Resins or electro-deionization (CEDI)

Reverse osmosis and resins produce effluents as a result of water distillation, which makes it frequently compulsory for companies to also have a wastewater treatment plant.

Wastewater treatment plants can also be used to treat wastewater generated in the cooling towers, which are designed to cool down residual vapor from boilers for reuse, as well as to treat wastewater from spills and water rejections that occur accidentally.

All of these effluents are usually sent to a container for further management in the wastewater treatment plant.

Once the effluents have been treated, two options can be considered:

1.  Discharging the resulting water, which is not the best option except when the quality of the water obtained is not suitable for reuse in production processes.
2.  Not discharging the resulting effluent, so that water can be reused in production processes.

The decision to be made relies on the company, but irrespective of the chosen option, wastewater are required to be treated to satisfy zero liquid discharge requirements.

Zero discharge processes involve several stages, depending on the quality of the wastewater to be treated, among which the following can be noted:

• Chemical pretreatment to remove contents that may cause fouling in later stages.
• First concentration by membrane filtration. Since the salt concentrate will still be too liquid it will be required to be sent to a vacuum evaporator.
• Second concentration by vacuum evaporation. Although the salt content in the resulting effluent is in higher concentration, it needs to be sent to a crystallizer since it is still liquid.
• Crystallization to treat the salt concentrate obtained after evaporation, which is then ready to be sent to the waste management unit, before which a drying process may be conducted.