Reuse of Water in Typical Indian Oil Refinery

Reuse of water in Typical Indian Oil Refinery

Sridebi Basu1 and Bhagu R. Chahar2

1Research Student, Department of Civil Engineering, Indian Institute of Technology Delhi, Huaz Khas, New Delhi-110016 ; email:[email protected]

2Professor, Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India; email: [email protected]

ABSTRACT

The raw water requirement for any oil refinery is very huge which is mainly used as process water, cooling water, fire water, horticultural water and drinking water. The drinking water is supplied after treating the raw water. The desired amount of raw water is stored in the raw water reservoir within the refinery complex. The raw water is taken from nearest raw water source which is mostly a natural river flowing nearest to the complex. The source of waste water in oil refinery is oily sewer, contaminated oily sewer and sanitary sewer. All these waste water are treated and the treated water is discharged to nearest natural drainage. The storm water generated from oil refinery are discharged to nearest natural drainage which not necessary the same source of supply. This paper presents sustainable method so that augmentation of makeup raw water in a typical Indian refinery shall be fulfilled by treated water along with storm water received from the complex. The excess water shall be suitably collected for use in dry days before discharging to the natural source.

INTRODUCTION

Fresh water is one of the limited resources on this earth. Fresh water is required in every field of human life along with natural ecosystem. The excessive withdraw of fresh water or polluting the ground water disturbs the balance of natural ecosystem. The rapid urbanisation and increased population growth of urban areas are experiencing increased demand for fresh water while simultaneously generating more waste water (Basu, Chahar 2012). But the water on earth and beneath the crest is limited. Water, being a restricted resources but essential part of human existence, rational use of water is one of the crucial requirements.

The availability of fresh water and discharging of effluent directly to environment has an impact in sustainability. Thus the management of water is more important in present scenario than the cost of fresh water import and waste water disposal. The better water management will lead enabling expansion, higher output. The better treated water will reduce fouling and corrosion of process equipments and pipes which are exposed to treated water. A better water management give a better image to share holders.

2791World Environmental and Water Resources Congress 2013: Showcasing the Future © ASCE 2013

World Environmental and Water Resources Congress 2013

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https://www.researchgate.net/publication/268588800_Practicable_Water_Management_in_a_Typical_Indian_City?el=1_x_8&enrichId=rgreq-b6a4f29728271d0b0f22d33a62f1ce1f-XXX&enrichSource=Y292ZXJQYWdlOzI2OTA0NjQwNjtBUzoxNzgzMTUzODE5NzcwODhAMTQxOTUyNTEwODIyNw==

Petroleum refineries are complex systems of multiple operations that depend on the type of crude to be refined and the desired products. Due to these reasons, no two refineries are alike. Depending on the size, crude, products and complexity of operations, a petroleum refinery is one of the large consumer of water, relative to other industries and users in a given region.

Oil has been refined for various uses for at least 1000 years. An Arab handbook written by Al-Razi in approximately 865 A.D. describes distillation of “naft” (naphtha) for use in lamps and thus the beginning of oil refining (Forbes, 1958). The main product of early commercial-scale refineries was kerosene, used as a substitute for whale oil. Gasoline and heavier fractions were considered waste disposal problems (Nelson, 1969).

Oil production and oil refinery wastewater streams have caused environmental problems for many years. In the 1950's Soviet refineries were discharging wastewater containing up to 4000 mg/L of oil on a regular basis (Lysogorova, 1961). As late as 1973, German law required only 95% removal of oil. This has the implication that of 100 L of fuel oil entered a refinery separator, 5 L could exit with the outlet water, rendering about 5 million L of water undrinkable (Nöh,1988).

Water is as important as oil in oil industry. Water is required for all major processes in oil refinery including steam generation and power supply. The total water requirement for the plant is quite a huge. The water is transported from nearest natural sources normally by pipeline to the plant reservoir. Extracting of such a huge quantity of fresh water from natural sources disturbs the natural ecosystem of the natural body. To reduce the stress on natural source the refinery must withdraw the least amount of fresh water required for the plant.

The waste water generated within the plant is treated. The treated water along with storm water is discharged to the nearest natural water resources and which is different than the source. If the same natural source is used then in normal practice intake is in the upstream of the discharge. This also leads to stress in natural source for the certain stretch.

The better water management helps to expand the refinery without increasing the fresh water requirement. The reuse of water reduces the recurring cost of water purchase and water pumping.

OVERALL REFINERY WATER BALANCE

Many of the processes in a petroleum refinery use water. However, not each process needs raw or treated water, and water can be reused in many places. A large portion of the water used in a petroleum refinery can be continually recycled with in a refinery. There are losses to the atmosphere, including steam losses and cooling tower evaporation and drift. A smaller amount of water can also leave with the products. Certain processes require a continuous make-up of water to the operation



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https://www.researchgate.net/publication/236500792_Petroleum_Refinery_Engineering?el=1_x_8&enrichId=rgreq-b6a4f29728271d0b0f22d33a62f1ce1f-XXX&enrichSource=Y292ZXJQYWdlOzI2OTA0NjQwNjtBUzoxNzgzMTUzODE5NzcwODhAMTQxOTUyNTEwODIyNw==

such as steam generating systems or cooling water systems. Understanding water balance for a refinery is a key step towards optimizing water usage, recycle and reuse as well as optimizing performance of water and wastewater treatment systems.

Figure 1 shows a typical example of the water balance in a refinery.

Sources of water

For refinery sources of water can be surface water, ground water, municipal water, water in crude, rain and combination of many.

Surface water

The raw water supply to refinery can be from various surface-water sources such as rivers or lakes. In some cases it may be supplied from the sea or from other brackish water sources. Water supply may be from groundwater located in aquifers, if the subsurface water is available and accessible. Ground water supply is mostly the additional to surface water supply. The raw water treatment s required depending upon the uses.

Municipal water

Refinery raw water may be supplied from a municipality. Municipalities generally supply potable water for drinking water purpose but may also be able to supply treated effluent for industrial use or reuse. Potable water required for drinking water and sanitary water is often purchased from a local municipality. If available, potable water may also come from groundwater aquifers or alternative sources. In many cases the raw water is treated to use as drinking and sanitary water.

Refinery/Process Unit

Rain water

Water in product

Stream loss

Storm waterWaste water

Recycle Ground Water

Raw Water

Cooling water evaporation and drift losses



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Water in crude

The crude often carries entrained water that remains from the oil well extraction process and/or pickup during trans shipment. The water is usually removed as storage tank bottom sediment and water or in the desalter which is part of the crude unit in the refinery. It is sent to wastewater treatment for treatment.

Rain water

Another source of water for a refinery is rain which is stochastic in nature. Rain that falls within the refinery battery limits is contaminated rain water and it is treated before discharge. Rain that falls in nonindustrial areas of a refinery, e.g. parking lots, green areas or administrative housing, is discharged without treatment depending on local regulations.

Rain water harvesting is one of the good water management practices to capture uncontaminated storm water. It is not widely used. With proper storage and or treatment this storm water may be used for certain purpose and the excess of requirement shall be used to recharge ground water.

Water leaving the refinery

The amount of water that leaves refineries is waste water or different refinery process water losses.

Wastewater

Refineries generate a significant amount of wastewater which is having hydrocarbons. Wastewater also include water rejected from boiler feed water, cooling tower blowdown stream, or even once-through cooling water that leaves the refinery. Once-through cooling water typically does not receive any treatment before discharge. Cooling tower blowdown water and wastewater from raw water treating may or may not receive treatment at the wastewater treatment plant (WWTP) before discharge. Contaminated wastewater is sent to wastewater treatment plant for further treatment.

Steam losses

Low pressure steam that is produced in the refinery is vented to the atmosphere when it is in excess. Other sources include tracing steam that is vented at some locations in the refinery. Proper monitoring of the steam system in the refinery will help minimize the production of excess steam and minimize/ eliminate the need for venting. Any expected losses should be considered when reviewing the water balance in a refinery.



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Cooling tower losses

As water is cooled in the tower by evaporation, this results in a loss of water in the refinery. Some of the water in the cooling tower is entrained by the large quantities of air passing through the tower and are lost to the atmosphere. These entrainment losses are also referred to as cooling tower drift. Any expected losses from cooling towers should be considered when reviewing the water balance in a refinery. In some cases once-through cooling water is used in the refinery

Raw water treatment

Source water for a refinery are treated before being used in different processes. The type of treatment depends on the quality of the source water and its ultimate use in the refinery. Primary treatment of all raw water entering a plant may include screening and sedimentation to remove suspended solids, but subsequent treatment will depend on the ultimate use for each water system. A typical plant water supply might be separated into process, boiler feed, cooling, potable, fire water and utility water systems.

Process water

In refineries, water used for various purposes is in close contact with the hydrocarbons. Softened water is usually used for these purposes.

Boiler feedwater

In a refinery, the boiler feedwater (BFW) required for the generation of steam needs to be treated prior to use. The higher the steam pressure being generated, the higher the purity of the BFW required.

Cooling water

Water-cooled condensers, product coolers (heat exchangers) and other heat exchangers use a large amount of water in a refinery. Some refineries use air coolers, where the process stream is exchanged with air prior the being sent to a cooling water heat exchanger. This will minimize the use of cooling water in the refinery. Some refineries use a once-through system where the incoming water is exchanged against the process fluid and the warmer cooling water is then returned to the source of the water. However, being water is a limited resource it is preferred to recirculate the water through a cooling tower and then back to the process.

Some water treatment is necessary even for once through cooling systems to prevent scale formation, corrosion, and slime and algae formation. The extent of treatment required for circulating systems is much greater since impurities are concentrated in the system as evaporation losses occur.



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In cooling tower systems, a build-up of salt concentration is unavoidable since water is evaporated in the cooling tower. Make-up water is required to replace these and other losses.

Sea water has been used successfully as cooling water especially in coastal areas with fresh water shortages. Cathodic protection systems employing magnesium anodes located in the floating head and channel of exchangers prevent excessive corrosion.

Deposits are minimized by restricting cooling water temperature increase below the point where the calcium salts begin to precipitate.

Potable water

Potable water is required for use in kitchens, wash areas and bathrooms in refineries as well as in safety showers/eyewash stations. Municipal water or treated raw water or treated groundwater can be used for this purpose. The treated water must be chlorinated to destroy bacteria, and then pumped in an independent system to prevent potential cross-contamination. Potable quality water may also be required in some specialist chemical operations.

Fire water

The requirements for fire water in refineries are sporadic, but can constitute a very large flow. It is preferred to collect storm water from non process areas and store it in a reservoir dedicated to the fire water system in the plant.

Provisions are made for a connection in emergency situations of the fire water system into the largest available reservoir of water. Usually this is the raw water supply since fire water requires no treatment. Sea water or brackish water is often used as fire water by plants located along coastal areas.

Utility water

Utility water is used for miscellaneous washing operations, such as cleaning an operating area. It should be free from sediment but does not require any other treatment.

Wastewater in refineries (other than domestic waste) originates from either process water streams or rainwater, although some coastal refineries will also have ship’s ballast water to treat as well (Kirkup, 1977).

METHODOLOGY

The crude and main extracting process governs the type of treatment required to for waste water treatment. Thus choice of crude and process can play a big role to reduce fresh water demand. But for simplicity of the problem formulation let us assume the process part has no impact on fresh water demand reduction. The treated



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water generated from treatment plant shall be used as boiler feed water, for cooling tower makeup water and for other process requirement.

The waste water generated from sanitary sewer shall be used for inside horticulture first and rest shall be used for process purpose. As the sanitary sewer is free from oil thus it shall be used for such process water where the same shall not get mixed with oil such as cooling water makeup etc.

The storm water generated from the plant is directly discharged to nearest natural sources. This method suggests that the storm water shall be stored in raw water reservoir and as well as drinking water reservoir and fire water reservoir for further use inside the plant. This will reduce the pumping load from raw water source plant.

The storm water is not available throughout the year. Storing of storm water within raw water reservoir, drinking water reservoir and fire water reservoir is not sufficient for maximum use. As the storm water is free from any oil contamination thus the same may be stored in the ground water aquifers for the nearest locality borewell pumping use. This is not direct benefit for the refinery but it will keep alive the aquifer for those who are using the same. It will have an immense community impact. It will also keep the nature healthy for mankind.

The stricter norms shall be imposed to confirm that the water injected to aquifer is free from any sort of impurities and it is not able to pollute the ground water.

Most effective water management needs the following methods

• Less water contamination by bund wall or any other structures

• Separation of contaminated water at source by individual drainage system or piping system

• Better maintenance, monitoring and controls

• Holding ponds for testing

• Control release to treatment plants or direct discharge point

• Effective treatment plants

• Educated operators

• Re-use of non-contaminated storm water

DISCUSSION

Let us assume the followings



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• Total process requirement is 100 units of water per unit time.

• Cooling water requirement 200 units of water per unit time

• Makeup cooling water requirement as 4 units per unit time

• Drinking water requirement 1 unit of water per unit time

• Horticultural water requirement as 2 units of water unit time

• Thus total fresh water requirement is 303 unit of water.

• Fire water requirement is not considered as it intermittent requirement.

• Let us assume after treatment of waster process water 70% can be recovered. Thus the treated water from process is 70 units of water per unit time

• Cooling tower return is 196 units of water per unit time

• Sanitary sewer is 80% of drinking water thus 0.8 units of water per unit time

• Total water generated from treatment is 266.8 units of water per unit time

• The extra raw water required is 36.2 units of water per unit time

• After using of treated water the raw water pumping requirement reduces from 303 units of water per unit time to 36.2 units of water per unit time. The cost of raw water and pumping of cost for 266.8 units of water per unit time has been reduced after using the treated water. This will reduce the initial investment cost also. The diameter of pipeline will be reduced as well as the pumping capacity. This will reduce the cost a lot.

The storm water generation is stochastic in nature thus dependence on storm water to run a plant is not feasible solution. Depending upon the project the water requirement varies. From previous years rainfall the total storm water generation may be calculated for a year. If it is found sufficient to run the plant for a year then the same can be stored in aquifer. Then bore well pumping can be allowed for that plant without disturbing the natural above ground fresh water storage. If the storm water generation is not sufficient then the same shall be injected to aquifer for community use during dry days.

Let us assume a typical refinery is having total area of 750 Ha among which 250 Ha is plant area. Green belt is 200Ha. Thus the rainfall from 500 Ha shall be uncontaminated and same may be used for refinery purpose and excess can be stored in ground water. Assuming design rainfall as of typical Indian conditions as 80mm/hr and surface flow coefficient as 0.7 the total surface runoff from the refinery uncontaminated area shall be 280,000



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cum/hr. This volume shows the potential quantity of storm water generation from any refinery. After using the required amount rest storm water shall be stored in aquifer for future use instead of throwing in some natural stream to reach the sea water.

All the above volumes are assumed based on some realistic value. As every refinery is different from each other so the real water management of each refinery is different than each other. Each case shall be studied thoroughly and best water management shall be imposed. As water is precious thus the cost implication of treatment and injection to ground water after treatment shall be neglected.

Following are few methods which can be easily implemented in Indian refineries as good water management practices for their units.

• Recharging of dry well through storm water runoff and rooftop rain water collection as part of rain water harvesting scheme.

• Stream trap efficient management.

• Adopting Drip irrigation method for water conservation.

• Using of treated water from sewage treatment to green belt area

• Reduction in water consumption

• Monitoring of water consumption

• Construction of oil catcher in strategic location to avoid ground water pollution and surface water pollution

CONCLUSION

In the refining sector, water use is already being reduced and the quality of the water that is discharged is being improved so as to limit the impact that the industry has on the environment. Even almost zero discharge is a realistic target – the technology is already available. The recharge of ground water through uncontaminated storm water is another noble method for zero discharge pragmatic targets. Due to absence of strict law and heavy penalty on discharge the methods are still not in use in case of Indian refinery. Awards, intensives may be imposed to make the water management for fruitful for the investors.

REFERENCE

Forbes, R.J., Studies in Early Petroleum History, Leiden, Netherlands, E.J. Brill Co. (1958).



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Basu, S. and Chahar, B.R., (May 2012) “Practicable Water Management in Typical Indian City”, World Environmental and Water Resources Congress 2012 : Crossing Boundaries, May 20-24, 2012, Albuquerque, New Maxico, 3686-3695.

Kirkup, W.M., "Refinery Oil/Water Separation Equipment and Its Applications," Filtration and Separation, 14, 259-65 (1977).

Lysogorova, I.K., "Purification of the Oil Industry's Waste Water Which Pollutes Bakings Bay", in U.S.S.R. Literature on Water Supply and Pollution Control, ed. Levine, B.S., Washington, D.C., US Public Health Service (1961).

Nelson, W.L., Petroleum Refinery Engineering, 4 ed., New York, NY, McGraw-Hill Book Publishing Company (1969).

Nöh, H., "Separators and Emulsion Separation Systems for Petroleum, Oil, and Lubricants," in proceedings of the Pretreatment in Chemical Water and Waste Water Treatment, 3rd Gothenburg Symposium, New York, NY, Springer-Verlag (1988).



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https://www.researchgate.net/publication/300051481_Separators_and_Emulsion_Separation_Systems_for_Petroleum_Oil_and_Lubricants?el=1_x_8&enrichId=rgreq-b6a4f29728271d0b0f22d33a62f1ce1f-XXX&enrichSource=Y292ZXJQYWdlOzI2OTA0NjQwNjtBUzoxNzgzMTUzODE5NzcwODhAMTQxOTUyNTEwODIyNw==



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Reuse of Water in Typical Indian Oil Refinery