15 November 2021
Wastewater treatment from the Oil & Gas Industry. SIGMA Technology.
1. Oil & Gas industry and its wastewater: a technological challenge
The oil and natural gas industry, commonly known as Oil & Gas, is the industry that generates the energy necessary to carry out human and industrial activities as they are operated today. This means that their actions have a direct impact on the sustainability of resources, the environment and the rest industries and sectors.
The three main activities in this industry are:
- Extraction of crude oil and natural gas.
- Transformation of crude oil into its fractions.
- Obtaining energy from oil derivatives and natural gas.
This industry is one of the most important consumers of fresh surface and underground water.
One of the main objectives today for this industry is the reduction of water demand, which implies proposing the reuse of wastewater as a mandatory practice in order to save resources and raw materials and to meet the principles of economic and environmental sustainability of the industry Oil & Gas.
Wastewater, properly treated, can be reused in many different actions, for example:
- Watering of Green areas
- Anti-fire flow network
- Refrigeration systems
- Water for cleaning cars, trucks, etc.
To guarantee the sustainability of this resource and of the Oil & Gas industry itself, these principles of the circular economy of water must be applied, through which waste water becomes a resource.
Wastewater from the Oil & Gas industry can be very diverse in each plant (oil extraction, cracking, oil and gas utilization, etc.) and fluctuating in itself, but it has basic characteristics such as the following:
- High content in oils, fats and hydrocarbons.
- Dissolved organic matter.
- Traces of crude oil.
- High content in suspended solids.
- High viscosity.
- Dissolved salts.
- Heavy metals.
The components that must be removed more effectively are oils, fats, hydrocarbons, suspended solids and dissolved organic matter.
For the treatment of this wastewater, an engineering is required that can provide integrated, robust but adaptable solutions that combine innovative technologies, with very efficient application and with the possibility of being optimized. These technologies must provide high enough quality treated water to be reused.
The most efficient technologies used in the separation of oils, fats and hydrocarbons are API, CPI and DAF technologies:
API: special tanks in which a natural separation of the heavier sediments takes place. Light, low-density and buoyant substances are collected by API scrapers (designed according to American Petroleum Institute standards) and removed from the water.
the CPI (corrugated plate interceptor) is a coalescing plate separator applied in the separation of oils and hydrocarbons.
API and CPI technologies can be combined within the same tank for process optimization.
DAF: DAF (Dissolved Air Flotation) equipment allows the flotation of suspended solids and colloidal substances for their separation from water, after applying a coagulation-flocculation process for the grouping of these solids and colloids.
Other less common but equally effective technologies are cyclones/hydrocyclons and membrane filtration systems.
Table 1. Applied technologies for the separation of oils, fats and hydrocarbons.
|API separators||Must be designed based on retention time.||Inefficient with emulsified oils|
|CPI separator||Designed based o density, viscosity and flow regimen. Retention times are elevated.||Inefficient with emulsified oils. It is usually combined with API technology.|
|DAF clarifier||Introduction of pressurized water containing dissolved air, forms microbubbles that allow floc to float||Very high efficiency of separation of solids, oils, fats and hydrocarbons with a well-designed coagulation-flocculation system.|
|Hydrociclons||Suitable for high concentration of oils. High maintenance cost.||Efficiency increases with the arrangement in series of several hydrociclons|
|Membrane filtration||Pore size of 0.01µm||It efficiently extracts dispersed oils and aromatic compounds.|
The most effective technologies used to remove dissolved organic compounds are adsorption, extraction and advanced oxidation systems.
Table 2. Technologies applied for the removal of dissolved organic compounds.
|Adsorción||Activated Carbon||Removal of benzene, toluene and traces of crude oil. It applies high retention times and depends on pores size of the AC.||Removal performances between 50 - 75%..|
|Zeolite||Removal of BTEX (benzene, toluene, ethylbenzene and xylene). Compact modules.||Removal between 70 - 80%. High regeneration cost. It depends on the hydrophobicity of the compounds.|
|Nut Shell||Removal of oils and traces of crude oil.||Removal between 60 - 80%. Low cost of raw materials.|
|Nano compounds||Removal of oils and traces of crude oil.||Removal of 50% in reduced contact times.|
|Polymeric||Removal of benzene, toluene and traces of crude oil. Manufactured as PET (polyethylene terephthalate) or polystyrene.||Removals up to 99%.|
Removal of free and dissolved oils.
|Efficient but expensive for solvent regeneration. The solvent has to be treated as waste.|
|Oxidation||Photocatalytic||Removal of TOC, phenols, BTEX and TPH (total petroleum hydrocarbons). High influence of the pH. Applied catalyst: TiO2||Removal of >80% of BTEX, >95% of TOC, >60% of phenols, >75% of TPH.|
|UV/O3||Removal of naphtha acids, ammonia and aromatic hydrocarbons. pH must not be alkaline. Negatively affected by high concentrations of bicarbonate and Cl-.||Removals of >80%.|
In addition to treating the water, the sludge generated must be managed as special waste. For its dehydration and stabilization, high-performance separator technologies are applied: filter presses and centrifuges.
2. SIGMA Case Study: Wastewater treatment from the Thermal Power Plant UPT Ibiza
2.1 General data of the project
PROJECT LOCATION: Thermal Power Plant in Ibiza. Owner: Endesa; Operator: Endesa Generación.
PROJECT YEAR: 2012 – 2013
FUNCTIONING OF THE THERMAL UNIT ENERGY PRODUCTION PLANT: The Ibiza Thermal Power Plant or UPT is a conventional cycle thermoelectric facility located in the municipality of Ibiza. It has 13 active thermal groups that add a power of 270 MW (six motors, four gas turbines and three double gas turbines), and that use natural gas as the main fuel and diesel as an auxiliary fuel:
2 x 216 MW motors
4 x 18,4 MW motors
1 x 25 MW gas turbine
1 x 14 MW gas turbine
2 x 25 MW gas turbines
3 x 25 MW double gas turbines
TREATMENT GOALS: Removal of oils, hydrocarbons and suspended solids of the wastewater from the UPT Ibiza.
WASTEWATER FEATURES: high content in oils and hydrocarbons and suspended solids, with a concentration of 1100 mg/L.
SUMMARY OF THE TREATMENT: Wastewater treatment is divided into the following stages, the main objective of which is the elimination of suspended solids, oils and hydrocarbons contained in the water:
- Coarse separation unit of oil and hydrocarbons with Technology API - CPI
- Solid separation via sieving and sand removal units
- Fine hydrocarbons separation unit
- Reactives dosing process: coagulation-flocculation reactors
Clarification with dissolved air flotation DAF (equipment SIGMADAF FPAC-20-S)
PERFORMANCE: the equipment designed and installed by SIGMA allows reaching, at the DAF equipment outlet, concentrations below 55 mg/L of total suspended solids, oils and fats, which means a removal efficiency of 95%.
2.2 Description of the wastewater treatment plant of the UPT Ibiza.
COARSE SEPARATION UNIT OF OIL AND HYDROCARBONS WITH TECHNOLOGY API - CPI.
The system designed by SIGMA uses CPI separator plate technology for the separation of hydrocarbons within the tank.
It is made up of a rectangular tank with an inclined bottom ending in a screw extracting the settled solids, it includes a skimmer system for the separation of hydrocarbons and oils of API technology.
It has a heating circuit using hot water. Constructed of very high-quality steel.
SOLID SEPARATION VIA SIEVING AND SAND REMOVAL UNITS
Includes inclined SIEVING and W screw for lifting the separated solids. The sandblasting section includes a horizontal sand transport screw.
FINE HYDROCARBONS SEPARATION UNIT
Consisting of a rectangular tank with a trapezoidal bottom, equipped with a set of independent coalescing lamellae for optimum water distribution performance, it contains a skimmer system for the separation of hydrocarbons and oils. It has a heating circuit using hot water.
This equipment is part of the sieving and sand removal train, forming a compact system built in very high-quality steel.
PHYSICAL-CHEMICAL TREATMENT WITH COAGULATION - FLOCCULATION AND CLARIFICATION WITH DAF
The physical-chemical treatment consists of the addition of coagulant and flocculant for the formation of flocs that contain the suspended solids present in the water and that cannot be separated naturally by sedimentation given their low density, it also allows the partial elimination of organic matter associated with these solids and the elimination of oil and hydrocarbon residues that may have remained after the previous treatment.
The addition of coagulant and flocculant is carried out in series tanks provided with stirring and built in very high-quality steel. A dosage system specially adjusted to the necessary doses of these products is supplied. These doses are established by means of previous flocculation tests carried out in the laboratory, later, the dosage is re-adjusted on an industrial scale.
The flocs generated are separated from the water using DAF dissolved air flotation technology. For the treatment plant of the UPT of Ibiza, a SIGMA DAF equipment model FPAC - 20 - S is designed and installed.
The SIGMA DAF FPAC models are a system for clarification with dissolved air flotation to treat wastewater, with a large surface and separation by cross-flow. They are equipment with a low profile and a lot of free surfaces where the floated sludge can accumulate.
SIGMA DAF FPAC equipment works with small to medium flow rates (between 5 and 160 m3/h) and w
ith very high loads of pollutants to be removed (total suspended solids, oils and fats, organic load).
They have application in FBR (Flotation Bio-Reactors), sludge thickeners, rendering industry, meat industries and slaughterhouses, food industry, mining, petrochemical and paper industries, among others.
SIGMA DAF FPAC systems are specially designed to treat currents with very high solid loads (up to 40 kg of solids/m2 of free surface of the system) that need a large surface area for their flotation and separation and that do not have sufficient buoyancy to float. Also, flotation air is necessary to improve flotation when mixing of emulsions, oils and solids affects the specific gravity.
A recirculation pump redirects part of the clarified water leaving the DAF unit to a pressurization-saturation system. The recirculated water is pressurized by the pump to approximately 6 bar and mixed with pressurized air. In this way the pressurized water will be saturated with pressurized air. Under these pressure conditions, the air is dissolved in the water. Inside the DAF unit depressurization occurs, resulting in the generation of air micro-bubbles. The dissolved air micro-bubbles allow the removal of solids, fat particles, oils, hydrocarbons, etc. that do not have enough buoyancy and have been previously flocculated. The bubbles are between 30-50 microns in diameter, essential dimensions for efficient flotation. The bubbles quickly adhere to particles of similar and larger dimensions and rise to the surface. This mixture of water and bubbles is homogeneously distributed in the inlet compartment of the DAF unit under laminar conditions and the floated particles are redirected directly to the dehydration system in the upper part of the unit, where they are eliminated through a system of skimmers specially designed. Sludge, oils, greases and hydrocarbons floating in foam form leave the unit and are collected in a sludge hopper.
The floated flocs leave the unit as foam through a skimmer system and are collected in a sludge hopper.
Settling matter descends into the sediment compartment at the bottom of the DAF unit and is discharged by the worm-drive sludge removal system.
Clarified water leaves the unit through an adjustable supernatant system. Part of this stream of clarified water will be redirected by the recirculation pump to enter the compression and saturation system described above.
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