Wastewater, water and air emissions treatment in CSP plantsWater and wastewater treatment

CSP plants consume a large amount of water, which is usually drawn from rivers and wells to generate vapor. The vapor is generated by turbines which require ultra-pure water in order for them to generate high quality vapor. For this reason, the incoming water to the power plant  needs to be treated at a water treatment plant (WTP) before use.

As a general rule, such treatment plant applies a reverse osmosis pre-treatment followed by a post-treatment by means of resins or continuous electrodeionization (CEDI)  treatment.

Once ultra-pure water is obtained, it is sent, by and large, to the steam generator turbine, a small amount of which is set aside to clean solar panels.

On the other hand, the generated effluents containing water treatment plant rejects (soil and sand, bacteria and different types of salt) will have to be treated at a wastewatert treatment plant (WWTP) to make them appropriate for discharge.

Wastewater is treated at WWTP’s by means of different technologies for salt crystallization.  The processes used to treat wastewater are mainly  chemical pre-treatment, membranes, vacuum evaporation and crystallization.

Air emissions treatment

The heat captured by solar collectors used in solar thermal power plants is pumped to the power block by means of an organic heat transfer fluid,  which contains  benzene-derived molecules. This fluid undergoes degradation, which poses a considerable security risk, since some of the degradation by-products are potentially hazardous.

Typical heat transfer fluid degradation mechanisms are contamination from water pipe residues and water from the water-vapor cycle; oxidation caused by the reaction of oil with oxygen in the air; and cracking that occurs inside absorber tubes and the auxiliary boiler, when the  heat transfer fluid reaches very high peak temperatures.

Three  are the products resulting from degradation:

1. Solid wastes, mainly carboxylic acids, carbon and carbon deposits, which are highly flammable and corrosive, due to their acidic properties.

2. Short-chain hydrocarbons produced by the breaking apart of bybiphenyl and diphenyl ether molecules.  This type of hydrocarbons have a very low boiling point and alter the viscosity and flash point.

3. Long-chain hydrocarbons produced by several short-chain residues joining together. This type of hydrocarbons have a very low boiling point and alter the viscosity and thermal properties.

In order to remove them, solar thermal power plants  are equipped with three technologies:  the primary filter and the reclamation and ullage systems.

It can therefore be noted at this point that  vapors vented from the ullage system contain benzene, which must be removed,  as it is carcinogenic and its emissions limits are very  strict.

The most appropriate technology for benzene emissions reduction is the use of activated carbon filters, since they contain inert material, which helps to retain volatile organic compounds and  return purified air.