Comprehensive treatment solutions for stripped sour water containing ammonia, phenols, and reduced sulphur compounds from refinery amine and sulphur recovery units.
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Sour water and desalter effluent treatment for petroleum refineries.
Sour water is generated throughout petroleum refining operations from process units that use steam injection or water washes under conditions where hydrogen sulphide and ammonia are present.
Sour water stripper (SWS) units are essential components of refinery wastewater management systems, designed to remove hydrogen sulphide (H2S) and ammonia (NH3) from process wastewater streams before they can be safely discharged or sent to downstream advanced biological treatment facilities. However, the effluent from sour water strippers still contains significant concentrations of contaminants that require further treatment to meet stringent environmental discharge standards.
The stripped sour water typically originates from multiple refinery process units including crude distillation, fluid catalytic cracking (FCC), hydrocracking, hydrotreating, coking, and amine regeneration units. Each source contributes a unique contaminant profile, resulting in wastewater with highly variable characteristics in terms of ammonia concentration, phenol content, sulphide residuals, and organic loading.
Reynolds & Bauhm is involved in designing integrated treatment processes that address the specific challenges of SWS effluent, combining physical, chemical, and biological processes to achieve consistent compliance with local discharge limits while maximising water reuse potential within the refinery complex.
Amine regeneration units, sulphur recovery plants, hydrotreaters, FCC units, cokers, and crude desalters
Ammonia (50–5,000 mg/L), phenols (20–500 mg/L), sulphides (1–50 mg/L), COD (1,000–10,000 mg/L)
High temperatures (80–120°C), variable pH (8–10), elevated TDS from chemical addition
EU IPPC BREF, EPA effluent guidelines, local discharge permits for ammonia (typically <10 mg/L)
Effective treatment requires understanding the specific chemical and biological challenges posed by each contaminant class.
Ammonia is the primary nitrogenous contaminant in sour water stripper effluent, present as free NH3 or ammonium ions (NH4+) depending on pH. Concentrations can range from 50 mg/L in well-stripped streams to over 5,000 mg/L in weak acid effluents. High ammonia is toxic to aquatic life, contributes to eutrophication, and exerts a significant oxygen demand. Biological nitrification requires careful process design to handle inhibitory phenol concentrations and high salinity typical of refinery wastewater.
Phenol and substituted phenols (cresols, xylenols) enter sour water from FCC main fractionators, coker fractionators, and lube oil extraction units. Phenols are toxic to advanced biological treatment systems at concentrations above 100 mg/L, inhibit nitrification, and can cause effluent toxicity failures. The hydroxyl group makes phenols highly soluble in water, complicating physical solid-liquid separation. Advanced biological acclimation or chemical oxidation is required for effective removal.
Residual sulphides (S²-), mercaptans (R-SH), and thiosulfate (S2O3²-) persist in stripped sour water when stripping efficiency is compromised or when these compounds are generated in downstream units. Sulphides cause odour problems, corrode concrete and metal infrastructure, exert chemical oxygen demand, and are highly toxic. Mercaptans are particularly difficult to remove due to their partial solubility and low biodegradability under standard conditions.
The organic loading in SWS effluent comes from dissolved hydrocarbons, organic acids, phenols, and complex refinery intermediates. COD concentrations range from 1,000 to 10,000 mg/L, with BOD5 representing 30–60% of total COD. The slowly biodegradable fraction requires extended biological contact times. High COD loads can overwhelm conventional activated sludge systems if not balanced with nutrient addition and proper hydraulic retention time.
Our five-stage treatment process is engineered to sequentially remove contaminants from the most concentrated and toxic to the trace residuals requiring polishing.
Hot stripped sour water is cooled via heat exchangers to 35–40°C and equalized in a surge tank to dampen flow and concentration fluctuations. pH adjustment with acid or caustic prepares the wastewater for downstream biological stages.
Where ammonia concentrations exceed 500 mg/L, a secondary ammonia stripping column recovers NH3 as ammonium sulphate or aqueous ammonia for reuse. This reduces biological nitrogen loading and recovers a valuable by-product.
Ammonia is biologically oxidised to nitrate via autotrophic nitrification in an activated sludge or MBBR system. Anoxic zones enable denitrification to nitrogen gas when total nitrogen removal is required by the discharge permit.
Acclimated heterotrophic biomass degrades phenols and organic compounds in aerobic bioreactors with extended detention times (18–36 hours). Nutrient supplementation (N, P) is precisely controlled to maintain optimal COD:N:P ratios.
Clarification or DAF separates biomass, followed by granular activated carbon (GAC) filtration, ozonation, or multimedia filtration to remove residual organics, suspended solids, and trace contaminants to meet discharge limits.
Engineering data for typical sour water stripper effluent treatment systems designed and supplied by Reynolds & Bauhm.
| Parameter | Influent Range | Treated Effluent | Removal Efficiency | Process Unit |
|---|---|---|---|---|
| Flow Rate | 5 – 500 m³/h | – | – | Complete plant |
| COD | 1,000 – 10,000 mg/L | < 125 mg/L | 85 – 98% | Biological + polishing |
| BOD5 | 300 – 4,000 mg/L | < 25 mg/L | 90 – 99% | Aerobic biological |
| Ammonia-N | 50 – 5,000 mg/L | < 10 mg/L | 95 – 99.8% | Stripping + nitrification |
| Phenol | 20 – 500 mg/L | < 0.5 mg/L | 95 – 99.9% | Acclimated biological |
| Sulphide | 1 – 50 mg/L | < 0.1 mg/L | 90 – 99% | Chemical oxidation |
| Oil & Grease | 10 – 200 mg/L | < 5 mg/L | 85 – 98% | DAF unit |
| TSS | 50 – 500 mg/L | < 20 mg/L | 80 – 95% | Clarifier / DAF |
| Temperature | 80 – 120 °C | 20 – 35 °C | – | Heat recovery exchangers |
| pH | 8.0 – 10.5 | 6.5 – 8.5 | – | pH neutralisation |
| HRT (Biological) | – | – | – | 18 – 48 hours |
| Sludge Production | – | – | – | 0.4 – 0.8 kg DS/kg COD |
Reynolds & Bauhm systems are engineered to handle sour water effluent from all major refinery process units.
Amine wash systems used for acid gas removal produce rich amine that is regenerated by steam stripping. The condensate from the regenerator overhead contains ammonia, heat-stable salts, and degradation products. Reynolds & Bauhm systems handle the variable loading associated with upstream process upset conditions.
Explore Oilgas RefineryClaus sulphur recovery and tail gas treatment units generate process condensate with high sulphide and ammonia concentrations. Quench tower blowdown and seal drum drains require pre-treatment before integration with the main refinery wastewater treatment plant.
Explore Oilgas RefineryHydrodesulfurization and hydrocracking units inject hydrogen at high pressure, generating sour water from high-pressure separators and fractionator overhead accumulators. These streams often contain the highest ammonia and organic nitrogen loads in the refinery.
Explore Oilgas RefineryFluid catalytic cracking (FCC) and steam cracking units produce sour water from main fractionator overhead systems and petrol recovery sections. These streams contain elevated phenol concentrations and light hydrocarbons requiring specialised biological acclimation.
Explore Oilgas RefineryDelayed coking and fluid coking operations generate sour water from fractionator overheads and coke handling areas. Coker sour water typically contains high levels of H2S, NH3, and cyanide, requiring specialised treatment protocols for cyanide destruction prior to advanced biological treatment.
Explore Oilgas RefineryCrude desalters use wash water to remove salts and solids from incoming crude oil. When sour crudes are processed, the desalter brine contains H2S and ammonia. Although typically lower in organics than other sour water sources, the high salinity and solids content present unique treatment challenges.
Explore Oilgas RefineryReynolds & Bauhm systems deliver measurable operational, environmental, and economic advantages for refinery operators.
Consistently achieve discharge limits for ammonia (<10 mg/L), phenol (<0.5 mg/L), and COD across fluctuating inlet conditions. Reynolds & Bauhm systems are designed to meet EU IPPC BREF, EPA effluent guidelines, and site-specific permit requirements.
Treated effluent can be polished for cooling tower makeup, boiler feed pre-treatment, or crude desalter wash water, reducing freshwater consumption by up to 60% and lowering the refinery's overall water footprint.
Equalization, advanced process control, and redundant treatment stages ensure that upstream process upsets or maintenance shutdowns do not result in environmental non-compliance events. Systems handle 2:1 flow variation and 3:1 concentration variation.
Enclosed tanks, vapour recovery systems, and biological odour control scrubbers prevent the release of H2S, mercaptans, and volatile organic compounds, protecting worker safety and community relations.
Heat exchangers recover thermal energy from hot sour water, reducing the plant's overall energy demand. Biogas generated from anaerobic pre-treatment can be used for process heating or power generation.
From process design and pilot testing through fabrication, installation, commissioning, and operator training, Reynolds & Bauhm is involved in delivering fully integrated systems with single-point accountability and long-term service support.
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View PageA two-stage stripper recovers ammonia and sulphide at near-atmospheric pressure with steam injection.
Single-column atmospheric stripper: 15–25 trays. Live steam injection at 0.15–0.30 kg steam/kg sour water. Top temperature 100–110°C; bottom 130–140°C.
For ammonia recovery: first column at pH 6 strips H₂S; second at pH 10 strips NH₃. Yields salable ammonia stream + sulphur-rich vapour to Claus.
Stripped water typically: H₂S <5 ppm, NH₃ <30 ppm. Residual phenols 30–200 ppm (not stripped). Direct to biological treatment unit (BTU).
Column shell: 316L (cyanide-bearing service requires CS-clad). Trays: 410 SS. Reboiler tubes: 316L or duplex. Carbonate stress corrosion cracking is the dominant failure mode.
HCN forms NH₄-SCN under stripper conditions, contributing to ammonium thiocyanate accumulation. Specify Cu addition or polysulphide injection to control.
Stripped water is the preferred desalter wash water source (it is hot and salt-free). Closes the water loop and minimises fresh water demand.
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