Implementing UF for Water Reuse By Sachin Malekar

Transcription

1 Implementing UF for Water Reuse By Sachin Malekar Everything About Water July 28 The New Zero Discharge Plant for 3 million metric tonnes per annum Expansion at Chennai Petroleum Corporation Limited (CPCL) A Case Study M/s Chennai Petroleum Corporation Limited (CPCL) expanded its crude refining capacity at Manali by 3 million tonnes per annum.as part of the 3. MMTA Expansion Project,a new Effluent Treatment Plant (ETP-III) was constructed to treat effluents generated from it for meeting MINAS standard. With a view of conserving water a new zero discharge plant was installed comprising of Ultrafiltration and Reverse Osmosis membrane processes. This plant treats the treated water from the above effluent treatment plant so as to make use of the treated water as make up to DM plant. The capacity of the Zero Discharge facility (ZDP) is 2 m3/h.the plant was commissioned in the year 25. The unit includes pre-treatment section followed by Ultra filtration and Reverse Osmosis process. The characteristics of the treated effluent from ETP-III are as follows: Sr.No. Parameter Unit Value 1 ph 6 to 8.5 (6.5 normal) 2 Oil and Grease mg/l 1 3 Suspended Solids mg/l 2 4 Particulate size of mg/l Shall pass 85 microns IS sieve suspended solids 5 BOD5 mg/l 15 6 COD mg/l 25 7 Conductivity micromhos/cm 36 8 Total Dissolved mg/l 186 Solids 9 Chlorides mg/l 85 1 Calcium mg/l Magnesium mg/l 7 12 Phosphates mg/l 5 13 Silica mg/l Phenols mg/l 1.

2 15 Sulphides mg/l Total residual mg/l 1. chlorine 17 Ammonical mg/l 5 nitrogen (as N) 18 Total kjeldahl mg/l 1 (Nitrogen (as N)) 19 Free Ammonia (as mg/l 5 NH3) 2 Arsenic (as As) mg/l.2 21 Mercury (as Hg) mg/l.1 22 Lead ( as Pb) mg/l.1 23 Cadmium (as Cd) mg/l 2 24 Total chromium (as mg/l 2 Cr) 25 Hexavalent mg/l.1 Chromium (as Cr) 26 Copper (as Cu) mg/l 3 27 Zinc (as Zn) mg/l 5 28 Nickel (as Ni) mg/l 3 29 Selenium (as Se) mg/l.5 3 Cyanide (as CN) mg/l.2 31 Fluoride (as F) 2 32 Manganese (as 2 Mn) 33 Iron (as Fe) 3 34 Vanadium (as V).2 35 Nitrate Nitrogen 1 36 Radioactive metals a) Alpha emitters µ Curie,max b) Beta emitters µ Curie,max In order to recycle as much water as possible, it is necessary that the water at the inlet of membrane process meet the desired water quality. Therefore an elaborate treatment process was needed.

3 The treatment scheme for the ZDP is as follows: FeCl 3 + Polyelectrolyte Treated Effluent Equalization Pond (Existing) Coagulation Tank Pressure Sand Filter (PSF) Feed Tank PSF Ultrafiltration (UF) Feed Tank Ultrafiltration System Reverse Osmosis (RO) Feed Tank Cartridge Filter RO System Permeate to DM Plant Reject to drain Process Description: 1) Guard Pond: The treated water on MINAS quality is stored in Guard pond of the 3 MMTA project. The water from the guard pond is pumped to existing equalization pond located near the earlier zero discharge plant. 1) Equalization Pond (Existing): The equalization pond is used to damp flow variations from the existing ETP in order to achieve a constant flowrate. 2) Coagulation Tank /Coagulator: The effluent from the equalization tank is pumped to the coagulation tank. Coagulation and flocculation are employed to remove suspended solids from the effluent. The process is carried out by adding a coagulant (in this case FeCl 3 ) which forms large flocs of ferric hydroxide to which the suspended solids adhere and settle at the bottom of the tank. A polyelectrolyte is also added in order to enhance the process of floc formation and agglomeration. The tank is provided with an agitator to disperse the coagulant and the polyelectrolyte uniformly.

4 3) Pressure Sand Filter: The effluent from the coagulation tank flows into the pressure sand filter feed tank from where it is pumped to the two up-flow pressure sand filters. Pressure sand filter (PSF) provides an effluent with turbidity less than 5 NTU. 4) Ultrafiltration System: The treated effluent from the PSF flows to the UF feed tank. From here the effluent is pumped to the UF membranes. UF is a low pressure (5-15 psig) process for separating larger size solutes from aqueous solutions by means of a semi-permeable membrane.uf retains oils, particulate matter, bacteria and suspended solids in order to provide a permeate void of these impurities so as to make it suitable for RO.The differential pressure between the feed and permeate increases during filtration. Hence, periodic back flushing is done to control this increase in pressure. 5) RO system: The effluent from the UF system flows to the RO feed tank.ro is a moderate to high pressure (8-12 psig) driven process for separating larger size solutes from aqueous solutions by means of a semipermeable membrane. This process is carried out by flowing a process solution along a membrane surface under pressure. RO membranes reject dissolved and suspended materials including monovalent salts to give pure water. Three banks of each 11 m3/h capacity (Two working and one standby) have been installed in order to have common spare philosophy. 6) The permeate from the RO system is collected in existing 1.5 MG reservoir for cooling tower make up and 2.5 MG closed reservoir for DM water make up.. Design criteria and performance of each unit: 1) Pre-Treatment Section: The pre-treatment section comprises of the coagulator and the pressure sand filter. The coagulator has been designed with a detention time of 2 minutes while the pressure sand filters have been designed with a service velocity of 12 m/h for a service cycle of 24 hours. There are three filters (2 working +1 standby) with 34 mm Ø 135 mm HOS. The consistent performance of the pretreatment section is given below :

5 Turbidity PSF Feed PSF Outlet NTU micromhos/cm Conductivity PSF Inlet PSF Outlet

6 2) Ultra filtration: There are three UF skids each consisting of seven trains. There are 4 membranes in each train. The membranes are NORIT X-FLOW hollow fiber single layered (insert type) membranes having a molecular weight cut off of 1 kda.each membrane has an area of 4 m 2.The product recovery of UF is 9 %. The product specification at the outlet of UF and the present performance of UF is given below: Sr.No. Parameter Unit Value 141 ph 6 to Oil and Grease mg/l Nil 3 Suspended Solids mg/l Nil 4 Turbidity NTU <1 5 Ammonia mg/l 1 6 COD mg/l BDL 7 Conductivity micromhos/cm 36 8 Total Dissolved Solids mg/l Chlorides mg/l 85 1 Calcium mg/l Magnesium mg/l 7 12 M-alkalinity mg/l Nitrate mg/l 2 14 Phosphates mg/l 5 15 Silica mg/l 2 to 4 16 Sulphates mg/l 3 17 Sodium mg/l Potassium mg/l 4 19 Silt Density Index (SDI) mg/l Less than 2. 2 Others mg/l BDL Performance of the UF system: The performance of the UF system can be easily gauged on the parameters like SDI and the turbidity.

7 Turbidity UF-Oulet UF Desired Outlet.95 NTU UF Performance - SDI SDI Outlet Desired Days 3) Reverse Osmosis (RO): The reverse osmosis unit comprises of 3 skids of 11 m 3 /h capacity each. The arrangement is 2 working + 1 standby. Each skid has three banks with each bank having 12, 6 and 3 vessels respectively. There are 6 membranes in each vessel. Membranes are of TORAY make, model no. TML 2-4.The system recovery is 85 %.The design product specification at the outlet of RO and the present consistent performance of RO is given in the table below: Design product specification:

8 Sr.No. Parameter Unit Value 1 ph Oil and Grease mg/l Nil 3 Conductivity micromhos/cm 1 4 Turbidity NTU Nil 5 Total Dissolved Solids mg/l 35 6 Total Suspended Solids mg/l Nil 7 Calcium mg/l Magnesium mg/l M-alkalinity mg/l Chlorides mg/l Sulphates mg/l 6 12 Silica mg/l COD mg/l BDL 14 Phosphates mg/l.1 15 Ammonia mg/l Nil Performance of the RO section: The performance of the RO section is shown graphically in terms of the key parameters like Chloride and hardness: Chlorides RO Outlet RO Desired 4 3 ppm

9 Calcium Hardness RO Outlet RO Design ppm Magnesium Hardness RO Outlet RO Desired 2 ppm Observation and Conclusion: From the above results it is seen that the plant is performing well with each section giving the desired output in terms of quality and quantity. The ZDP has helped CPCL in reduction of fresh water intake and its dependency on Metro water availability. The author, Sachin Malekar is the Divisional Manager-Technology, Ion Exchange(India) Ltd. For further information on the author, write to us at content@eawater.com