Exx eecc uuttiivve SSu mmmaarryy -...

Oil and Natural Gas Corporation Limited Uran Plant Executive Summary for 20 MLD SWRO Desalination Plant at Uran

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EExxeeccuuttiivvee SSuummmmaarryy

INTRODUCTION

ONGC, intend to set-up a sea water desalination plant of 20 MLD capacity, which will cater process water and drinking water to the tune of 18 MLD and 2 MLD respectively. The proposed plant comprises of sea water intake system, integrated membrane based pre treatment of raw water and RO system, post treatment and reject disposal. The proposed desalination plant is based on the best available, proven reverse osmosis technology reflecting the latest innovation in the design, operation and maintenance of water treatment plants and is conceived with the contribution of multidisciplinary experiences acquired in seawater desalination. While designing the plant due consideration has been given to the intake and outfall systems so that the impact on the marine environment will be bare minimum.

The plant is designed to produce 18 MLD capacity to meet the requirement of service and potable water for the Uran plant in-house consumption. Additionally, the plant also requires 2 MLD of Demineralized Water as a boiler feed water which will be achieved by two pass RO system. The plant production is considered for uninterrupted round the year water supply for the plant.

TYPE OF THE PROJECT

As per MoEF notification dated 14th September 2006, desalination does not fall directly under list of projects or activities requiring prior environmental clearance. However, as per the Coastal Regulation Zone Notification 2011 the proposed project 20 MLD desalination plant at ONGC Uran falls under point No. V (i) (h) of CRZ notification 2011, i.e. Desalination plant attracts State Coastal Zone Management Authority' (SCZMA) approval and CRZ clearance from MoEF. Hence it falls under “A” category project.

NEED OF THE PROJECT

As stated earlier, our country belongs to water stressed zone and by 2025, with growing demand and rising population, it is predicted that the country will fall under water scarce zone. Thus, necessitating means to augment the water resources, for drinking as well as for industries, through seawater desalination, waste water recycle and reuse apart from water conservation and rain water harvesting. Moreover, agriculture and drinking water are presently getting priority over industrial requirement. Industries therefore, have to look elsewhere to meet their water requirements.


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In order to meet the increasing water demand, desalination plants have become the latest trend, to provide alternative fresh water sources. Desalination of seawater is one of the oldest techniques used to make water potable.

It is proposed to adopt integrated membrane system i.e. high efficiency Dissolve Air Floatation (DAF) system followed by automatic washable disc filter & ultra filtration membrane for pre-treatment and Reverse Osmosis process for the pretreated water. The proposed desalination plant will enable ONGC to be self sufficient in meeting its water requirement for various unit operations.

DESCRIPTION OF THE PROJECT SITE

Site location and its access

The project site is located within the existing premises of ONGC gas processing plant at Uran, Raigad district of Maharashtra. The area earmarked for the desalination plant is a rectangular piece of land admeasuring about 8750 m2.

The topographical map of desalination project site is shown in the Fig. 02 - 01. The latitude and longitude of the four corners of the proposed project site are as follows:

Sl. No. Latitude Longitude

1 18o 51’ 24.96’’ N 72o 55’ 37.28’’ E

2 18o 51’ 23.20’’ N 72o 55’ 37.55’’ E

3 18o 51’ 23.22’’ N 72o 55’ 36.23’’ E

4 18o 51’ 25.37’’ N 72o 55’ 35.92’’ E

The site is well connected by road. The Uran town is located at a distance of 2 km in NE direction from the project site. The National Highway NH- 4B is passing in east direction at a distance of 11 km from the project site .The road connectivity map of Raigad district is shown in Fig. 02 - 02.

The nearest railway station is Panvel, which is at a distance of 30 km and nearest airport is at Chatrapathi Shivaji terminus located at about 60 km from Uran. The nearest seaport is Jawaharlal Nehru Port Trust, which is at about 18 km from project site. The satellite map of project site is shown in Fig. 02 - 03.


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Fig. 02 - 01 Topographical map of 10 km radius from 20 MLD desalination plant site


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Fig. 02 - 02 Road connectivity of Raigad district


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Fig. 02 - 03 Satellite imagery of project site

Oil and Natural Gas Corporation Limited Uran Plant EIA/EMP report for 20 MLD SWRO Desalination Plant at Uran

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Site description

The altitude of the site is at safe grade elevation of between 13m to 14m above MSL. The site is flat and ready for construction. The west of the site is covered by Arabian sea and east by Dronagiri hills. Fig. 02 - 04 shows the bird’s eye view of the site as captured by satellite and Fig. 02 - 05 shows the general layout of proposed project. The nearest human settlement is Pirwadi village which is located at about 370m in South West direction. The proposed plant is physically isolated from surroundings by constructing compound wall on all sides and other physical protections as per safety requirements.

Fig. 02 - 04 Bird’s eye view of the site


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Fig. 02 - 05 General layout of the proposed project of 20 MLD desalination plant


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Site selection

As already stated, the plant area for the desalination plant has been earmarked in the existing gas processing plant of ONGC Uran. The land area allocated for the desalination plant is 125x70 (8750m2). The main features of site including environmental considerations that make it suitable for this plant are given below: Readily available industrial land with flat terrain. The rectangular piece of land is under the possession of ONGC. No land acquisition is involved, hence no R&R issues. Nearest settlement is about 0.5 km away from the plant site. Suitable topography and geography for plant construction. Good accessibility through road. Availability of power & raw water sources at convenient distance. Suitable seismic zone. From the toposheet, no reserve forests or forest land is identified in

the vicinity of 9 km radius of project site The proposed site is not falling within the vicinity of any monument

or in an archeologically sensitive area. No declared biodiversity parks/sanctuaries are there in the

surroundings of the site.

The above features make it favorable for the proposed project. Hence, alternate sites have not been explored.

i) Seismic consideration

The site lies in seismic zone III as per seismic zone mapping of India (IS: 1893 - 2005) and has moderate seismic potential. There is no capable fault within the study area. The seismic zone map of India is shown in the Fig. 02 – 06.


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Fig. 02 - 06 Seismic zone map of India

Consumption of chemical and its transportation

The chemicals likely to be consumed by the proposed 20 MLD desalination and its approximate monthly requirements of chemical and its source is provided in Table 02 - 01.

Proposed Project Site


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Table 02 - 01

Consumption of chemicals in 20 MLD desalination plant

Chemicals Source

Quantity per month considering

maximum dose rate(kg)

Sodium hypochlorite (1-2 ppm)

From vendors in Indian market

3193

Acid (30% HCl) (20-30 ppm)


4597

Antiscalant (Sodium hexa metaphosphate)

(5-10 ppm)


175

Coagulant (FeCl3) From vendors in

Indian market 11492

Coagulant aid (Polyelectrolyte)


1912

CO2 From vendors in

Indian market 33087

Sodium meta bisulphite (2-5ppm)


2281

Limestone (for about 20-25 ppm calcium pick-up)


42437

Caustic Soda (1-2 ppm)


3500

The above chemicals are not inflammable and are of generic in nature and commonly used chemicals used in water treatment plants. A chemical storage house will be constructed to store the chemicals required for the desalination plant. Requirement of water and its source Seawater at the rate of 2717 m3/hr will be drawn by constructing seawater intake channel system on the Arabian Sea shore, adjoining to ONGC Helipad at about 850 meters away from the project site. Energy requirement The power requirement per day to produce 20 MLD of desalinated water will be 5.0 MW i.e., about 4 kw/hr per m3 of product water. The indicative power requirement of the proposed plant is as follows: Connected load : 3500kW Operating load : 2500kW


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Manpower requirement The desalination plant will be constructed by the EPC contractor and the operation & maintenance will be taken over by ONGC. The tentative manpower requirement during O&M phase is provided in Table 02 - 02. The estimated manpower requirement is based on 3 shifts and 7 days per week of continuous operation of the proposed plant.

Table 02 - 02 Manpower requirement during O&M phase

Category Number

DCS Operators @ 2 persons per shift and 3 shifts a day 6

Shift In-charge @ 1 person per shift and 3 shifts a day 3

Field & maintenance personnel @ 6 persons (Electrical, Mechanical and Instrumentation) per shift and 3 shifts a day

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Plant managers 2

Plant Head (Operation & Maintenance) 1

Administrative staffs 4

Non technical support staff 8

Total 42

PROCESS DESCRIPTION

Marine Intake System

The plant envisages a seawater intake system using open channel of about 1.3 km length and with a closed RCC channel of about 200m with stop log gates, trash racks and traveling water screen arrangement and intake chamber with pump house located near the sea shore. The water is to be pumped to the pretreatment section using vertical turbine pumps driven by VFD. Two nos. parallel chambers, 1W+1SB are provided before the intake sump each designed for 100 % capacity of the intake flow. Stop log gates, trash racks and traveling water screens are installed in each of the parallel chambers for increased availability and reliability of the feed flow to the desalination plant. The intake pump house is designed with 2 nos. of (1W+1SB) vertical turbine pumps with VFD operation for optimum utilization of power. The pump house includes hoisting facility for pump maintenance and a VFD panel room.


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Pretreatment System

The plant requires a reliable source of water of consistent quality. The feed water salinity, suspended solid loads and organics are the factors that determine the selection of pretreatment system and RO recovery.

i) Dissolved Air Floatation Units

The pretreatment system includes facilities to handle oil content in the feed water. Dissolved Air floatation system has been considered to separate floating and settle able suspended solids present in the sea in order to provide consistent quality to the downstream pretreatment units. 2 nos. of dissolved air floatation units have been considered. The design capacity of the DAF units includes a design margin of 20% over the normal operating capacity of 2717 m3/hr. The recovery of the DAF units will be about 98%. The sludge generated from the DAF units will be collected in sludge tank for onward pumping to reject tank. The DAF units are designed to handle feed total suspended solid (TSS) load of 300 ppm and oil content of 100 ppm.

ii) Disc Filters

Advanced pretreatment system comprising of 11 sets of disc filters (10 W+1SB) with high filtration efficiency has been considered with automatic backwash system. The particle size up to 40 micron will be filtered in the disc filtration units. The individual disc filters outlet is connected to a common product header which will feed the downstream ultra filtration skids. Each disc filter skid comprise of four disc filters with suitable piping, valve, instrumentation and automation arrangement for sequential operation and to ensure maximum flexibility in operation & maintenance and achieve guaranteed production The disc filter backwash water is taken from first pass RO reject water thereby removing the permeate loss for backwashing and achieving 100 % recovery in the disc filtration units.

iii) Ultra Filters

There are eight nos. of ultra-filtration skids (7W+1SB) at the upstream of RO skids have been provided to ensure the required flow to RO units. The provision of a standby ultra filtration unit is to compensate for the production loss during backwashing of any of the working ultra filtration skids.


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Vertical, in to out /out to in, pressurized, cross flow, hydrophilic, hollow fiber ultra filtration (UF) membrane system having MWCO as 1,00,000 Daltons has been considered to take care of the total suspended solids, colloidal particles and microorganisms. The UF system is equipped with backwashing, fast flushing chemical cleaning features. The UF membrane system is designed for constant feed flow and each skid flow is controlled by a flow transmitter and a flow control valve. Automatic back washing of the UF skids can be carried out without interrupting plant operation and to achieve an SDI less than 3 for RO feed. The life of the membrane is assumed to be 5 years and the progressive membrane replacement for each RO skid is planned to be carried out within 5 years without affecting the guaranteed quality and quantity. The backwashing is carried out by UF backwash pumps which are driven by VFD. The ultra-filtration units are designed to handle total suspended solids load of 50 ppm and the net permeate recovery from the UF units excluding backwash water requirements is 83.4%.

iv) Reverse osmosis The plant is envisioned with two pass RO system. The first pass RO system is sea water reverse osmosis membrane which produces desalinated water for post treatment and for feeding to the second pass RO system. The product from the second pass RO unit is sent to the demineralization plant.

v) First pass SWRO The first pass RO system consist of 4 nos. of RO skids (3W+1SB) each complete with feed cartridge filters, VFD controlled high pressure pumping system, VFD controlled booster pumps and an energy recovery devices. The first pass RO system has been designed to meet the feed TDS of 45000 ppm and feed temperature of 24 to 32oC. The minimum product recovery of the RO membranes is considered to be 45.4%. RO permeate suck back tanks have been provided for each RO skid to facilitate automatic flushing of the RO membranes by gravity in the event of power failure. Variable frequency drives have been provided selectively for high pressure & booster pumps & motors so as to keep the energy


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consumption minimum and to take care of the total dissolved solids variations as well as feed water temperature variation. The RO section also comprises of chemical cleaning system which includes chemical preparation tanks and chemical transfer pumps for Cleaning in Place (CIP) of RO membranes.

vi) Second pass RO The second pass RO system consist of 3 no’s of RO skids (2W+1SB) for producing feed water for the Demineralization plant from first pass RO permeate. The second pass RO is designed for a product recovery of minimum 85%. The reject from the second pass RO is utilized into the potable water tank of the post treatment section for permeate blending. Each RO skid is provided with a cartridge filter and a RO high pressure pump.

vii) Post treatment system

The post treatment section comprises of equipment for re-carbonation and re-mineralization of the permeate obtained from the RO section. The re-carbonation and re-mineralization plant processes the permeate so as to get the desired potable water alkalinity & hardness (as CaCO3) and positive Langlier Saturation Index suitable for long distance transportation & distribution. The water after post treatment becomes non aggressive & non corrosive. Limestone (reactive) with a purity of 90%, with the particle size of 2 to 5mm and carbon di-oxide are the main chemicals required for re-carbonation and re-mineralization. (Carbon di-oxide absorption has been envisaged for optimal limestone dissolution. The major portion of the permeate stream from RO has been designed for bypassing the limestone filters and only a portion of the RO permeate is treated in the re-carbonation plant. Finally the re-mineralized & re-carbonized water from RO permeate will be blended with RO permeate. A degasser is also envisaged to ensure the removal of any excess carbon di-oxide. Sodium hypochlorite and sodium hydroxide dosing has also been envisaged for maintaining the required levels of residual chlorine in potable water and pH adjustment.)

viii) Reject system

The reject outfall pumping and pipeline system having 800 mm dia, HDPE pipe has been designed and sized with a diffuser having 6 nos. of ports and it is proposed to be located at 3m depth and at a distance of 2.3 km for efficient and effective brine dispersion. The location of intake & diffuser has been shown in Fig. 02 – 07.


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The process flow diagram & mass flow diagram for the proposed desalination plant is as shown in Fig. 02 – 08 & Fig. 02 – 09 respectively


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Fig. 02 – 07 Location of intake channel and diffuser point


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Fig. 02 - 08 Overall process flow diagram


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Fig. 02 - 09 Overall mass balance diagram of SWRO Plant


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WASTE GENERATION

Brine

The generation of brine from the process is about 1704 m3/hr, which will be pumped back into the sea through a submerged diffuser facility. The TDS in reject brine will be generally in the range of 65000-72000 ppm, however the maximum would be 71722 ppm which is appx.1.6 times of ambient seawater Temperature of reject brine will be near to the ambient temperature of the Arabian seawater which varies between 25.3 to 32.5ОC. All other parameters of reject brine will remain same as in the seawater.

Sewage

The plant will be operated by existing staffs of ONGC,Uran and hence, no additional sewage generation is expected. The sewage generated from the proposed plant will be treated in existing STP and thus, no discharge is expected on land environment.

Gaseous emissions

Operation of desalination plant process does not result in conventional air pollutants like PM10, PM2.5, SO2, NOX & CO etc., and therefore, generation problem does not arise for such pollutants.

Solid wastes

It is expected that about 15-20% of membrane elements will be replaced from 3rd year onwards. Membrane elements are made up of polymers namely polyamide in case of RO & polysulfone in case of UF. Used membrane elements can be disposed of as municipal solid waste since, they do not contain any free liquids or hazardous substances at levels that exceeds regulatory threshold.

MITIGATION MEASURES TO BE INCORPORATED IN THE PROJECT TO MEET ENVIRONMENTAL STANDARDS

The various mitigation measures, to be adopted for the proposed plant are described in detail in respective sections of the individual facilities envisaged. However, the summarized inbuilt mitigation measures to meet environmental standards are as follows:

Gaseous emissions are not expected. The generation of brine from process is about 1704 m3/hr, which

would be pumped back into the sea with a diffuser facility.


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Operation of the proposed desalination plant does not result in discharge of effluents into land environment.

Solid waste (membrane) generated will be handled suitably. Suitable acoustic enclosure will be provided to minimize the noise

level.

ASSESSMENT OF NEW AND UNTESTED TECHNOLOGY FOR RISK OF TECHNOLOGICAL FAILURE

The proposed project is based on the best available proven/tested indigenous reverse osmosis technology reflecting the latest innovation in the design, operation and maintenance of water desalination plants and is conceived with the contribution of multi disciplinary experiences acquired in seawater desalination. Desalination plant based on SWRO have been set along the coastal line of India & other peninsula , the plants thus set up are functioning successfully & are catering to the demands for which it was intended .Risk of technological failure is not anticipated.

SAFETY ANALYSIS

The basic goal of safety for the desalination plant is to,

Adopt proven designs for the plants, processes & equipment Adopt safe and quality construction practices Adopt safe operation and maintenance practices

The safety goal is also to prevent occurrences of accidents and should it occur, detect them early and mitigate their impact by engineered features to contain the limit of the damage within the site itself to safeguard the operating personnel and to public. To achieve the goal, a defense in depth approach having diversity and independence is being adopted in all the systems. The facilities under SWRO are basically related to chemical plants, but handles large quantities of cold water only. Inadvertent criticality events, like chemical explosions, fire involving materials and breach in containment of storage tanks are not likely to occur since they are not involved in the process. The probability of occurrence of such events is almost nil. However, the chemical used for pretreatment and conditioning of the water if not properly handled may result in small accidents. These accidents can be controlled by (i) safe design geometry of tanks and equipments (ii) control of concentration (iii) effective administrative controls for operation of the plant and related systems and (iv) multiple barriers between the source and the environment. The safety aspects of the plant will be reviewed by


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ONGC Design Safety Review Committee (DSRC) before start-up of the plant.

PROJECT SCHEDULE

Infrastructural requirements like site development, civil buildings, electrical works etc., and auxiliary requirements like seawater intake system, reject disposal system, are scheduled to be completed within 24 months.

DETAILS OF CRZ CATEGORY

The details of the proposed pump house and onshore/offshore pipelines falling in CRZ category are shown in Table 02 - 03 below.


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Table 02 - 03 Details of plant entities falling under CRZ category

CRZ category

Description Area/ Length of Pipeline under

CRZ (m)

Dimension / Diameter of Pipe

Area under CRZ (Ha.)

Volume under CRZ (m3)

CRZ III

Pump House 83.2 13 X 6.4 X 10.5 0.00832 873.6

Outfall Pipeline 100 0.8 0.008 50.24

CRZ I B

Intake Channel

125X2

1500X2

0.9625 359.375


CRZ IV B

Intake Channel

1375X2

1500X2

110 35105


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