Oil & Gas Production Downstream Processes

Downstream Processes: Wastewaters from Oil Refineries

Oil refineries generate wastewater containing hydrocarbons, heavy metals, salts, acids, and other contaminants. These wastewaters must be treated before disposal or reuse to prevent environmental pollution.

Environmental challenges

Spent caustic wastewater → Requires special chemical treatment. Oil & grease → Clogs pipes & harms aquatic life. Sour water (H₂S, NH₃, cyanides) → Requires stripping & neutralization.
High salinity & heavy metals → Corrosion & toxicity issues.

Best Available and Cost-Effective Solutions for Downstream Processes

With over 25 years of experience, we specialize in designing and engineering bespoke process technology for treating downstream effluents. Our expertise in spent caustic applications ensures effective treatment solutions.

Our R&D facilities are unmatched, offering the best available and emerging technologies. We design integrated solutions tailored to each application, ensuring robust and automated treatment with minimal plant footprint.

Spent Caustic in Downstream Processes

Spent caustic forms primarily from refining and petrochemical processes where operators use caustic (usually sodium hydroxide, NaOH) to treat hydrocarbon streams. Spent caustic is highly alkaline and corrosive, making it challenging to treat. It has a high Chemical Oxygen Demand (COD) and contains complex contaminants. We treat it using advanced oxidation, wet air oxidation (WAO), catalytic wet air oxidation (CWAO), neutralization, or biological treatment before disposal or reuse.

While, merox and caustic washing units are common in hydrocarbon sweetening, where they remove hydrogen sulphide (H₂S), mercaptans, and other sulphur compounds from LPG, petrol, and jet fuel. These processes generate spent caustic that contains sodium mercaptides, sulphides, and disulphides.

Similarly, fluid catalytic cracking (FCC) in petrol treatment uses caustic to remove sulphur compounds, creating spent caustic with organic sulphides, thiophenes, and phenolics. Ethylene and petrochemical plants also use caustic to quench and wash processes that remove acid gases like CO₂ and H₂S, resulting in phenolic, sulphidic, and naphthenic spent caustic. Additionally, amine regeneration and sour water stripping use caustic for gas treating, producing spent caustic with sulphides and ammonia.

Caustic washing also applies to coker and visbreaker units to remove contaminants from heavy products, generating spent caustic with complex hydrocarbons, sulphides, and ammonium salts. Moreover, in the desalting process, crude oil producers wash crude oil with caustic to remove inorganic salts before distillation, producing spent caustic with chlorides, sulphides, and hydrocarbons.

Other Refinery Wastewaters Include

Process Wastewaters

Process Wastewater from crude oil separation, distillation, cracking, and reforming contains dissolved and emulsified hydrocarbons (oil, grease, benzene, toluene, xylene, PAHs), phenols, organic acids, surfactants, detergents, and heavy metals (lead, nickel, vanadium, chromium, mercury, arsenic). This wastewater is toxic to aquatic life and can bioaccumulate. We manage it through oil-water separators (API separators), membrane processes, and other wastewater treatment plants.

Sour Water

Wastewater from units like hydrotreating, hydrocracking, coking, and sulphur recovery contains hydrogen sulphide, ammonia, and cyanides. If untreated, it can cause air pollution (H₂S release) and water toxicity, contributing to acid rain and groundwater contamination. We treat it through sour water strippers and hydrothermal processes, such as catalytic wet air oxidation (CWAO).

Desalter Effluent

Wastewater from salt removal in crude oil contains chlorides, sulphates, oil, grease, suspended solids, and heavy metals. If not treated, it can corrode refinery equipment and pollute surface water. We manage effluent treatment with membrane filtration processes.

Stormwater Runoff & Accidental Spills

This wastewater contains oil, grease, hydrocarbons, heavy metals, and sediments from spills or leaks. It can contaminate groundwater and cause oil slicks in rivers and lakes. We treat it using membrane filtration and other processes.

Catalytic Wet Air Oxidation (CWAO) has been successfully employed at one of the largest oil refineries in Europe to treat spent caustic effluents from fluidized catalytic cracker and direct coking plants. This process enables the spent caustic to be passed to the site’s wastewater treatment plant. The COD levels are reduced from 150,000 mg/l to less than 500 mg/l, and total sulphide (including polysulphides) from up to 20,000 mg/l to less than 2 mg/l.