WATER TREATMENT IN OIL FIELD
Water produced during oil and gas extraction operations constitutes the industry’s most important waste stream on the basis of volume. The treatment of produced water is a necessity before the majority of the conventional produced waters can be applied to other uses.
Hoo Chemtec specializes in water treatment processes and technologies to remove oil, hydrocarbons, heavy metals, solids, toxic materials and other contaminants from your operations wastewater stream.
• Produced water treatment are:
1. De-oiling – Removal of free and dispersed oil and grease present in produced water.
2. Soluble organics removal – Removal of dissolved organics.
3. Disinfection – Removal of bacteria, microorganisms, algae, etc.
4. Suspended solids removal – Removal of suspended particles, sand, turbidity, etc.
5. Dissolved gas removal – Removal of light hydrocarbon gases, carbon dioxide,hydrogen sulfide, etc.
6. Desalination or demineralization – Removal of dissolved salts, sulfates, nitrates,contaminants, scaling agents, etc.
7. Softening – Removal of excess water hardness.
8. Sodium Adsorption Ratio (SAR) adjustment – Addition of calcium or magnesium ions into the produced water to adjust sodicity levels prior to irrigation.
9. Miscellaneous – Naturally occurring radioactive materials (NORM) removal.
• Current Wastewater Treatment - Petrochemical Industry
1. Avoid production of water onto the surface – Using polymer gels that block water contributing fissures or fractures or Downhole Water Separators which separate water from oil or gas streams downhole and reinject it into suitable formations.
2. Inject produced water – Inject the produced water into the same formation or another suitable formation; involves transportation of produced water from the producing to the injection site. Treatment of the injectate to reduce fouling and scaling agents and bacteria might be necessary. While waste water is generated in this option, the waste is emplaced back underground.
3. Discharge produced water – Treat the produced water to meet onshore or offshore discharge regulations. In some cases the treatment of produced water might not be necessary.
4. Reuse in oil and gas operations – Treat the produced water to meet the quality required to use it for drilling, stimulation, and workover operations.
5. Consume in beneficial use – In some cases, significant treatment of produced water is required to meet the quality required for beneficial uses such as irrigation, rangeland restoration, cattle and animal consumption, and drinking water for private use or in public water systems.
The current wastewater treatment steps are :
- Primary treatment (API/CPI/PPI separator, sour water strippers, buffer tanks)
- Secondary treatment (coagulation flocculation-flotation, biological treatment)
- Tertiary treatment (sand-filtration, membrane-filtration, chemical oxidation)
Raw water treatment—Primary treatment
● When lime softening is used for raw water treatment, the sludge generated in this process should be thickened, and optionally dewatered.
The thickener overflow water can be discharged directly without any further treatment, when local regulations allow.
● The use of ion exchange for treatment of raw water creates an alkaline wastewater stream and an acidic wastewater stream as a result of the
regeneration of the ion exchange beds. These streams should be collected in a tank and the pH neutralized prior to being discharged directly to
an outfall (bypassing wastewater treatment) if allowed by local regulation.
● The use of reverse osmosis for raw water treatment results in the creation of a reject stream that is very high in dissolved solids. This reject stream should be discharged directly to an outfall (bypassing wastewater treatment) ;
To assist in the removal of colloidal particles from suspension, chemical coagulation and flocculation are required. These processes, usually done in sequence, Chemicals are mixed with wastewater to promote the aggregation of the suspended solids into particles large enough to settle or be removed.
Biological treatment is the most widely used wastewater treatment technology for removal of dissolved organic compounds in the oil refining industry.
In general, biological treatment can be classified into two categories:
● suspended growth processes; and
● attached growth processes.
Activated sludge treatment with powdered activated carbon (Powdered Activated Carbon Treatment)system is similar to the conventional activated sludge system described above. In this treatment system both biological oxidation and carbon absorption occur simultaneously, thus enhancing the removal of contaminants in the wastewater.
Sand or media filtration can be used to remove the gross solids and suspended solids found in the refinery effluent. Media filtration systems work by pushing the water through a vessel packed with a filter media such as sand or anthracite. Anionic or cationic polymers are often added to the feedwater to improve particle removal efficiency.
The ion exchange process effectively removes arsenic, heavy metals, nitrates, radium,salts, uranium, and other elements from the produced water. Ion exchange is a reversible chemical reaction wherein positively or negatively charged ions present in the water are replaced by similarly charged ions present within the resin. Ion exchangers are regenerated after they are exhausted
Pressure Driven Membrane Separation Technologies
Microfiltration (MF), Ultrafiltration (UF), Nanofiltration (NF) and Reverse Osmosis(RO) utilize high pressure across the membranes to accomplish filtration of contaminants from the produced water.
Removal of calcium and magnesium from water is referred to as softening,and the treatments commonly used include lime-soda, phosphates, ion exchange and reverse osmosis. Reverse osmosis can also be used to soften the water.
Chemical oxidation in a refinery is generally used for reduction of residual COD, non-biodegradable compounds, and trace organic compounds.
The following oxidation reagents are generally used in a chemical oxidation system:
● hydrogen peroxide;
● chlorine dioxide; and
Hoo Chemtec can supply the suitable for treating refinery effluent :
● basic media/sand filtration;
● microfiltration or ultrafiltration;
● microfiltration or ultrafiltration, with reverse osmosis;
●microfiltration or ultrafiltration with nanofiltration;
● ion exchange softening.
●Basic media/sand filtration
The type of treatment depends on the quality of the source water and its ultimate use in the refinery. Turbidity, sediments and hardness;