Wastewater Treatment

Wastewater Treatment 

Considering the vast amounts of water used in a refinery, wastewater treatment constitutes a very significant supporting process for safe operation. Figure 10.9 lists the different types of wastewater, pollutants involved in wastewater streams, and the major refinery units that generate significant amounts of wastewater. The four types of refinery wastewater include cooling water, process water and steam, storm water, and sanitary sewage water. Among these, the most heavily polluted wastewater stream that requires serious treatment is the process water and steam that come into direct contact with petroleum fractions. Storm water may be contaminated because of incidental exposure to pollutant sources on refinery surfaces and accidental spills. Cooling water and sanitary sewage water may not require much treatment before they are sent to public water treatment facilities. One rule of thumb is to avoid mixing different types of wastewater streams to reduce the load on the treatment units.

Pollutants found in the wastewater streams include hydrocarbons with particular concern for toxic aromatic compounds, such as benzene; heteroatom compounds, such as mercaptans, amines, phenols, and cyanides; dissolved gases such as H₂S and NH₃, and acids, such as H₂SO₄ and HF; and suspended and dissolved solids. The refinery units that generate the most significant amount of wastewater are desalting, distillation, thermal and catalytic cracking, coking, as well as heat exchangers and storage tanks [5].

Figure 10.9.  Refinery wastewater, water pollutants, and refinery units.

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Types of wastewater

a. Cooling water

b. Process water and steam

-heavily polluted

c. Stormwater

d. Sanitary sewage water

Pollutants involved

a. Liquid hydrocarbons

b. Suspended solids, dissolved solids

c. Mercaptans (RSH)

d. Phenols (RC6H5O), amines (-NH2)

e. H2S, NH3, cyanides (-CN)

f. H2SO4, HF

Refinery units involved

Desalter, distillation, thermal cracking, visbreaking, coking, catalytic cracking, heat exchangers, storage tank drainage

Credit: Dr. Semih Eser © Penn State is licensed under CC BY-NC-SA 4.0