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Pollution Control Techniques in Refinery and Downstream Petrochemical Plants
Pollution is a universal problem that intensifies with each passing day due to growing population and pollution of surface & ground water sources.
Indiscriminate industrial development and exploitation of limited water sources are compelling every industry to seriously address this problem. Besides this, availability of water has become a serious issue. Therefore, industries are considering various options to reduce their water usage and to recycle water to the extent possible along with adopting manufacturing technologies that require less water, produce minimum waste water as well as other solid & liquid waste. Increasing cost of water and stringent regulations have helped make water recycle a viable option. This article deliberates on the topics of recycle, zero liquid discharge and solid waste management and explores their various technologies.

Prevention is better than cure. This also applies to pollution. Prevention or minimisation of pollution at source is the best control method. Hence, before going into the methods of effluent treatment, we should look at the possibilities of preventing or minimising effluent generation. Pollution prevention is defined as the use of materials, processes or practices that reduce or eliminate the generation of pollutants or wastes at the source. Also known as reduction at source, pollution prevention includes practices that reduce the use of hazardous and non-hazardous materials, energy, water or other natural resources. Pollution prevention in the manufacturing industry can be achieved by changing production processes to reduce or eliminate the generation of waste at the source. As it applies to industry, the environmental management hierarchy stipulates that when possible:
  • Pollution should be reduced at the source
  • Pollution products that cannot be reduced should be recycled in an environmentally safe manner
  • Disposal into the environment should be used only as a last resort and should be conducted in an environmentally safe manner
Recycle of Waste Water and Study of its Application in Various Industries
Waste water recycle should take shape at the drawing board stage in contrast to the conventional treatment approach of designing the raw water and waste water treatment plants (end of pipe solutions) separately. This will enable planning for water recycle at the design stage itself. The benefits are many.

Firstly, because water is recycled, raw water consumption reduces. The designer can therefore plan for a raw water treatment plant of lower capacity and cost. Secondly, the effluent treatment plant’s capacity is also reduced as we are treating the effluent which is not being recycled and hence the quantity of waste disposed is less, leading to further cost reduction.

Investment is certainly required for product recovery, water recycle plants and advanced technologies to handle even higher concentrations of contaminants.

However, the life cycle and return on investment is quite attractive.

Pollution is not just abated but prevented; pollutants are separated not destroyed; energy is saved and the total cost of water and waste water treatment is reduced.

Hence, we can use this experience of on/ offsite recycle and integrated solutions for water and waste water treatment in large industries to achieve the goal of 'Total Water Management' at the design stage.

We need to only apply these approaches in a complex industry in multiple ways.

Figure 1: Conventional Treatment

Guidelines for Selection of Recycle Scheme
1. Study the manufacturing process thoroughly and identify areas where reduction of water consumption is possible.
2. Identify the process where reduction of pollution load is possible by changing raw material or adopting cleaner manufacturing process.
3. Proper analysis of various streams especially targeting the contaminants which are process specific.

Figure 2: Modern Integrated Solution

4. Identify streams that can be segregated and treated economically. For example, in electroplating, the rinsed water can be segregated and treated for recovery of plating metal. This not only reduces the overall cost of recycle but also facilitates the recovery of valuable products from the waste water stream.
5. Identify effluents which are relatively clean and can be treated with simple processes so that they can be recycled internally without letting the water out into an effluent treatment plant.
6. Identify the quality of water required at various manufacturing stages.v For instance, steam generation may require high quality water and washing or cooling water make up may not require high quality water. It is always economical to design a recycle system to produce water suitable for lower end usage.
7. Select a technology that is easy to implement, operate, maintain & service.
8. Look for the availability of spare parts that may be needed in the future.
9. Reliability of performance in the long run is extremely important.
10. Low in operating cost.
11. Good service network of the plant supplier.

Recycle Technologies
Any waste water recycling plant requires four stages of treatment as follows:
1. Effluent treatment
2. Tertiary treatment
3. Advanced tertiary treatment
4. Zero liquid discharge

Effluent Treatment
For a good effluent recycle system, a good effluent treatment is a pre-requisite. Unless we remove the easily removable pollutants with cost-effective methods, it would be difficult to recycle the effluents economically. Usually effluent treatment plants (ETPs) are designed to meet statutory requirements for disposal. When recycling is considered, the ETP should also be designed considering overall requirements of treatment. For example, in India, disposal standards do not require complete removal of nutrients and dissolved salts. But, when we are installing a downstream reverse osmosis system, it is better to remove nutrients and dissolved salts in the biological system of the ETP. This will help reduce fouling of the reverse osmosis system.

There are different technologies available for effluent treatment to remove different pollutants. Table 1 lists some generic technologies applied in effluent treatment.

Tertiary Treatment
Treatment beyond disposal norms for reusing effluents for low end usages is called tertiary treatment. It acts as pretreatment to advanced treatment for complete recycle of effluents. Table 2 enlists some generic technologies applied in tertiary treatment.

Advanced Tertiary Treatment
Further treatment of secondary treated effluents is required for conforming to the requirements of high end usages (boiler feed, process, etc.) of treated water. Table 3 enlists some of the technologies available to remove various pollutants in advanced treatment:

There are various other technologies which are contaminant and end use specific such as fluoride removal.

Zero Liquid Discharge Treatment
(Evaporation and recovery of waste water containing highly soluble salts)

The highly concentrated reject from the process is further treated in multi effect evaporator (MEE) system generally after reducing dissolved salts by RO processes and the advanced tertiary treatment.

The MEE process uses either mechanical or thermal vapour compression using forced circulation evaporators, falling film evaporators or in combination. Thus, evaporation is increasingly considered for the treatment of refinery and downstream petrochemical waste water to recover more than 95% of water, or as a part of the zero liquid discharge (ZLD) process.

Water Management in Refinery - Case Studies
1. Reliance Industries Limited
Reliance Industries Limited (RIL) has enhanced the capacity of the Jamnagar Refinery to 12,00,000 barrels per stream per day (1200 K BPSD) with the commissioning of the Jamnagar Export Refinery Project (JERP) in Gujarat.
Waste water treatment is carried out in a dedicated state-of-the-art completely automated and PLC – operated effluent treatment plant supplied by Ion Exchange. The effluent treatment area is designed to contain and treat all internal process/utility waste water and storm/fire water, with the objective of zero discharge from the new refinery complex. The treated water is recycled back as cooling tower make-up and partially used as process water after reverse osmosis treatment to the high total dissolved solids treatment train or guard tanks, as required.
Effluents are segregated into four identical waste water streams designed for a treatment capacity of 500 m3/h each and maximisation of reuse.
The scope of treatment also includes three by-product streams generated during the treatment of refinery waste water (skimmed or slop oils, oily sludge and biological sludge). Skimmed oil is chemical and heat treated, with recovered oils transferred back to the refinery for reprocessing.

Effluent Treatment Plant at Reliance Industries Ltd., Jamnagar, Gujarat

Each of the above streams employs identical equipment for treating effluents, namely:
  • Free oil removal facilities including pre-deoiler and API separators with continuous oil skimming and sludge removal facilities
  • Dissolved air Flotation (DAF) unit
  • Two stage biological treatment
  • Clarification
  • Dual media filtration
  • Activated carbon adsorption
  • Disinfection – with chlorine and chlorine dioxide
The effluent treatment plant is treating 100 per cent effluent generated by the refinery since its commissioning in December 2008 and consistently produces treated effluent (pH 6 - 8.5, sulphide < 0.5 ppm, COD < 50 ppm, oil and grease < 5 ppm, phenol < 0.35 ppm) meeting guaranteed parameters for reuse for various applications mentioned earlier.

2. Chennai Petroleum Corporation Limited
The ZLD plant for the expansion at Chennai Petroleum Corporation Limited (CPCL) uses advanced membrane processes to reuse water for its process requirement.

CPCL, during its expansion, increased the crude refining capacity at Manali by 3 million metric tonnes per annum. As part of this 3 MMTA expansion project, a new effluent treatment plant (ETP-III) treats effluents generated from the refinery project to meet the MINAS standard. With a view to conserving water, a new zero discharge plant (ZDP) was designed and constructed by Ion Exchange. This plant treats the treated water from ETP-III to enable use of the treated water as make - up to the demineralisation plant. The capacity of the ZDP is 200 m3/h. The plant was commissioned in 2005 and is operated and maintained by Ion Exchange.

3. Indian Synthetic Rubber Limited

ISRL- Downsteam Petrochemical

Another such example of ZLD is for Indian Synthetic Rubber Limited (ISRL). Three streams containing 3000 m3/d process effluent along with 360 m3/d cooling tower blow down and 240 m3/d DM plant effluent are being treated through primary, secondary, tertiary and advanced tertiary treatments. The final reject (from RO) is being treated in thermal MEE, thereby achieving the objective of > 95 per cent water recovery and ZLD.

Waste water recycle and ZLD is mandatory for many industries because of water scarcity, legislation, rising water costs, unreliable water supplies, environmental requirements from buyers in case of exporters, etc. ZLD also gives enormous importance to sludge management (which is not discussed in this paper and which needs separate attention). Apart from these reasons, industries now identify recycle and ZLD as their social responsibility for environmental friendly manufacturing of goods.

Many technologies are now available for managing industrial waste water and other waste. It is of utmost importance to involve environment management specialists right from the planning stage of the project so that the best optimum solutions can be developed. Priority should always be given to source reduction and product recovery rather than end of pipe waste water treatment and expensive methods of ZLD. Right technologies should be adopted for recovery and recycle of water from waste water. Final effluents which cannot be recycled should be treated and disposed of in an environmental friendly way