Like other big industries, the oil industry is facing serious economic and social problems regarding its use of water.
Refineries, which themselves are getting bigger and bigger, have a great thirst for water. This water is absolutely indispensable due to its various different applications. Around 24 m3 of water is necessary for each cubic meter of crude processed. In the United States water consumption in the petrochemical industry is second only to that of the steel industry, and on its own represents 20% of total industrial water consumption.
The petrochemical industry requires water for the following applications:
- Cooling water is the most important in terms of general water requirements. It must be on constant supply, without interruption, for safety reasons besides any economic considerations. For this reason water that has been used is normally recovered via cooling towers except where the refinery is located near the coast, where it is obviously more economic to use seawater for cooling. Although it shouldn’t be forgotten that in this case corrosion and incrustation formation represent serious problems.
- Water for processing must have, depending on its usage, particular levels of purity (unlike that used for cooling) because it is this water that absorbs toxic substances during working. If a notable amount of inferior quality water is used it could lead to serious problems with the refinery’s final effluent.
- Water for general services and safety, should be available in huge amounts at any time in case of a fire.
- Water for drinking and sanitary use is required by a widespread distribution system due to the fact most modern refineries now cover an extremely large area. In the petrochemical industry the separation of the different discharges must be carried out totally and scrupulously. With the huge amounts of water used in refineries some kind of rigorous effluent reuse program should be in place, which means some kind of water treatment system is necessary.
Types of treatment
There are three types of purification treatments for refinery water: primary treatment (carried out on site); mechanical treatment to separate water and oil; and secondary treatment:
- Primary treatment: As previously mentioned, this kind of treatment is part of the petroliferous processing and cannot be considered as a true and proper purification of residual industrial water. The treatment involves the following: degassing of processing water; oxidation of the caustic solution by-product containing sulphurs; and neutralisation of the caustic solution by-products containing phenols.
- Mechanical treatments for water/oil separation: Designing the perfect tank for oil and water separation, based on the specific weight of the two liquids, has been the subject of much research and experimentation.
- Secondary treatment: The aim of secondary treatment is to treat the effluent coming from API separators making it possible to discharge it into the environment.