A Report on

Effluent Treatment Plant

Prepared By-

Nishith Shekhar Tripathi

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ACKNOWLEDGEMENTAn activity can be termed as an accomplishment only when the purpose is fulfilled. The accomplishment of any activity involves a continuous unflinching effort, motivation and support from its mentor. I would like to extend my heartfelt gratitude to my Project Guide Mr. Sumit Kumar for having constant faith in me throughout the project and directing me and supporting me in every possible way at each step. I extend my thanks to Mr. Akhilesh Kumar for helping me and being very supportive. I would like to thank each and every one of those who have been instrumental in the successful accomplishment of project.

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TABLE OF CONTENTS

Title.........................................................................Page no.

Effluent Treatment Plant..........................................................................3

Design Criteria for Effluent Treatment Plant............................................4

Design parameters....................................................................................5

Performance Guarantee Parameters........................................................5

Process Description

• Inlet Launder...................................................................................6

• Distribution Chamber......................................................................6

• Flash Mixer......................................................................................6

• Thickener.........................................................................................9

• Sludge Tank....................................................................................10

• Filter Press.....................................................................................10

General Diagram of ETP of RSP...............................................................13

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EFFLUENT TREATMENT PLANT

Effluent TreatmentWater as we all know is crucial for life cannot be wasted; if water is being used in an industrial plant there should be some methods to recycle it. But water once get used gets contaminated so it should be well treated so it can satisfy the proper prerequisites of usage in the plant. Thus a water treatment or effluent treatment plant is always laid down in any industrial plant. Considering this an effluent treatment plant (ETP) is also being established in Rourkela Steel Plant. Effluent treatment is the process that removes the majority of the contaminants from the effluent of GCP and produces both a liquid effluent suitable for circulation into the blast furnace. To be effective, effluent must be conveyed to a treatment plant by appropriate pipes and infrastructure and the process itself must be subject to regulation and controls. Other wastewaters require often different and sometimes specialised treatment methods. At the simplest level treatment of effluent and most wastewaters is through separation of solids from liquids, usually by settlement. By progressively converting dissolved material into solid and settling this out, an effluent stream of increasing purity is produced. A general flow chart is as follows:-

Process Block DiagramRAW EFFLUENT

EFFLUENT LINE

SLUDGE LINE

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LAUNDER

DISTRIBUTION CHAMBER

FLASH MIXER

THICKENER

SLUDGE TANK

FILTER PRESS

Alum (COAGULANT)

Lime (pH REGUGATOR)

Polyelctrolytes (FLOCCULANT)

DEWATERED SLUDGE

CLEAN EFFLUENT TOWARDS

COOLING TOWER

Design Criteria for Effluent Treatment PlantThe contaminated water from the gas cleaning plant shall be treated in the Effluent Treatment Plant (ETP) comprising primarily the thickener units using alum as coagulant, polyelectrolyte as flocculent and lime for pH correction. Hydraulics of the system shall be so designed that the clarified water from the thickener will be gravitated to the cooling tower top. The underflow sludge from the thickener shall be pumped to two .sludge storage tanks a separate group of pumps shall be provided for disposal of slurry from the storage tanks. The slurry pumps along with the facilities for chemical storage and coagulant/ flocculent dosing and pH correction shall be housed in the sludge pump house-cum-chemical house to be located near the thickeners. The whole unit of Effluent Treatment Plant (ETP) consists of:

Sl.No. Unit Qty

1. Inlet Launder 1set

2. Distribution Chamber 1 No

3. Flash Mixer Tank 2 Nos.

4. Thickener Unit 2Nos.

5. Sludge Tank 2No.

6. Filter Press Building 1 no.

7. Chemical House 1 no.

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Design Parameter:

We have considered the following design parameter to design the proposed Effluent Treatment Plant.

SLURRY FEED CHARACTERSTICS

1) Type of Slurry Gas Cleaning Plant of Blast Furnace.2) Flow Rate 1140 m3/hr3) Suspended Matter 6000 ppm(Av of 4000-8000)4) pH 4.5 – 6.55) Temperature 60-70oC.

Analysis of suspended solids

a. Fe2O3 71.42%b. SiO2 5%c. Al2O3 0 .4%d. CaO 6%e. MgO 3.2%f. P 0.016%g. S 0.483%

Approx. particle size distribution

< 10 micron: 30%10 to 40 micron: 35%40 to 60 micron: 15%>60 micron: 20%

Performance Guarantee Parameters:Performance guarantee are a set of guidelines must be followed by a manufacturer as a demand of the customer. If these demands are not fulfilled then either the unit is updated or rejected. There are about four performance guarantee to be followed by TPL as issued by RSP/Mecon ltd.

1. Concentration of suspended solids in the overflow from the Thickener must not be more than 100 ppm.

2. Cake from Filter Press Chute must have moisture content under 20%.3. Energy consumed as measured at motor control centre of the ETP shall not exceed the

values quoted during the tender stage.

4. No negative tolerance shall be permissible on capacity and quality of the treated effluent from the ETP. Further, no positive tolerance shall be permissible for power consumption of the plant.

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Process Description:

Inlet Launder

The water system for the DCW system is at an elevation of 11.0M. The launder from the converter scrubber leads the dirty hot water from the scrubber to the Distribution chamber. Inlet channel designed for a surge flow of 1950m3/hr with 1.5m/s velocity (self cleaning velocity) to avoid the settlement of solids. Slope in the launder should be 2%.

Distribution Chamber

The water, entering the RCC elevated distribution chamber, have suspended solids from Gas scrubber. The distribution chamber is so designed to lead the water evenly to the two flash mixers, downstream through channels by gravity. For equal distribution of flow to two flash mixers, 2 no’s of isolating gates have been provided in the distribution chamber. In case one of the clarifier or flash mixer is not working then no distribution takes place. Walkway will be provided from Chemical house to distribution chamber for access to the unit for operation of gates. Dimensions of the chamber should be such that it can withstand the surge overflow of 1950m3/hr.

Flash Mixer

This unit is provided for chemical reaction with effluent. Here the effluent is treated with alum as coagulant, polyelctrolytes as flocculants and lime which increases the pH of the slurry. The retention time for each flash mixer is 60 seconds. pH is measured both at inlet and outlet. For a flow of 1140m3/hr (the emergency case in which one of the thickeners is down), volume of the mixing chamber should not be less than 19m3. The treated slurry flows to thickener by gravity. Mild steel or stainless steel can be used for construction.Steps in water treatment-

Stable colloidal suspension

Primary coagulantOrganic and/or mineral

Coagulation stageUnstable colloid

Microfloc formation

Flocculation stageLarge flocs

Settling of suspension

LIME

Calcium Oxide (CaO) is commercially known as lime. It is used in water treatment to reduce acidity, to harden as a flocculant and to remove other impurities such as phosphates. Lime is added in an amount of 2 to 40% by weight according to the weight of sludge. Mixing and reacting steps have duration of 30 seconds.

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ALUM

Alums are useful for a range of industrial processes. They are soluble in water; have an astringent, acid, and sweetish taste; react acid to litmus; and crystallize in regular octahedral geometry. When heated they liquefy; and if the heating is continued, the water of crystallization is driven off, the salt froths and swells, and at last an amorphous powder remains. Potassium alum is the common alum of commerce, although soda alum, ferric alum, and ammonium alum are manufactured.

Chemical action of Alum and Lime-

Al2 (SO4)3.12H2O 2Al3+ + 3SO42- + 12H2O

SO42- + H2O HSO4- + OH- (Cause pH change)

Ca (OH) 2 Ca2+ + 2OH- (Cause pH change)

The basic water causes Al(OH) 3 to precipitate bringing small particles with them and then making water clear. Fe2O3 is removed mainly by coagulation.

POLYELECTROLYTES

Polyelctrolytes are polymers whose repeating units bear an electrolyte group. These groups will dissociate in aqueous solutions (water), making the polymers charged. Polyelectrolyte properties are thus similar to both electrolytes (salts) and polymers (high molecular weight compounds), and are sometimes called polysalts. Like salts, their solutions are electrically conductive. Like polymers, their solutions are often viscous. Types of polyelctrolytes-

1. Non-ionic polymers Non-ionic polymers are Acrylamide homopolymers. Anionic polymers are differentiated by a Functional group. Two monomers are used: Acrylamide and Acrylic acid. These polymers are manufactured by polymerization of acrylamide monomer 12.

During the coagulation/flocculation process, the organic or mineral coagulant quantity is limited to the necessary quantity for destabilization of colloids and does not require excessive amounts to produce a suspension which will settle. Molecular weight from 5 to 15 million

2. Anionic polymers These polymers are manufactured by copolymerisation of acrylamide and sodium acrylate. Polymer characteristics:- Molecular weight from 5 to 22 million- Easily absorbed by mineral matter

3. Cationic polymers Cationic polymers are manufactured by copolymerization of acrylamide and trimethyl ammonium ethyl acrylate chloride (methyl chloride ADAM).Polymer characteristics:- Molecular weight from 3 to 15 million- Easily absorbed by organic matter (humid and folic acids) and some mineral matter (silica)

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After colloidal suspensions have been destabilized by coagulants, flocculant polymers are frequently used to enhance the performance of clarification processes. Because of their very high molecular weights (very long chain of monomers), and of their ionic charge, flocculants will bridge destabilized particles together. This results in the formation of large particles suspended in water. This formation of flocs is called flocculation. The forces involved in this bridging between particle and polymer are mainly ionic and hydrogen bonding. The addition of a flocculant after coagulation may be necessary if the settling time available (linked to the size of the installation and the flow rate) is short. The use of flocculant would allow increased flow throughput to be achieved while still maintaining satisfactory settlement.

The dosage of flocculant to be added is very small, 0.01 ppm to 0.5 ppm.

Thickener/Clarifier

The treated slurry will flow to the Thickener units installed downstream by gravity. Solids shall be separated in the Thickener units. Automatic Hydraulic lifting device for maximum 300 mm lift for rotating rake arm is provided on the drive that will be operated by worm gear arrangement. The arrangement works on the principle of Torque sensing. In case the scrapper stops because of any reason then the assembly will automatically lift up and scrapper regains its movement. Underflow Sludge of each thickener will pump through 2nos sludge pump (1W + 1S) to sludge Tank.

The thickeners being established in RSP are such that if one of them stops working then the other one can take the full load. The design of thickener and selection of pumps has been made on this criterion.The clarified water coming from the thickener must have a concentration below 100 ppm as being asked in performance guarantee. This water is cooled in cooling tower and recycled. The settled sludge is pumped to sludge tank. Two underflow sludge pumps (1W +1S) per thickener are used for this purpose. So number of pumps are 4 (2W+2S).On the basis of design calculations volume flow rate of underflow sludge is found to be 28m3/hr so the pumps used for this purpose must have volume flow rate greater than 28m3/hr.

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Sludge Tank

Two no's of sludge tank will be provided to hold the under flow of thickener. Main purpose of sludge tank is to hold the underflow sludge and transfer it to filter press for dewatering. Each tank has holding capacity of 8hrs. Therefore volume of the tank should be around 224m3. Each tank will be provided with mechanical agitator which will constantly agitate the sludge in order to prevent sludge settlement in the tank. The filter press feed pump along with compaction pump will be used for pumping and compacting the sludge into the filter press for dewatering & concentrating the sludge into cake form.

Filter Press

Sludge from the sludge tank will be pumped to the Filter Press equipments for dewatering purpose. According to performance guarantee the cake moisture should not be more than 20%.

A final treatment is also done on the sludge by dewatering it so to retain as much water as possible. For this purpose different types of filters are used namely-gravity setters, gravity belt filters, centrifuges, vacuum or pressure belt filters and filter press. But among these filter press is most efficient and economical. The filter press has been utilized for many years to separate liquids from solids. In many cases the liquid is saved, while in other cases, the solids are the desired product. The filter press is an efficient system which provides high pressure filtration and/or compaction and ease of operation. Other filtration systems offer high pressure filtration, but only the filter press has both high pressure capability and efficient filter cake removal. The filter elements are constructed of lightweight polypropylene. They are extremely corrosion resistant and virtually eliminate plate breakage.

Effluent treatment managers should consider two types of presses:• The conventional press has a fixed volume which removes moisture by adding more solids.

• The diaphragm press is a variable volume press in which sturdy hollow rubber diaphragm or membrane is positioned behind each filter cloth. Water is pumped to the interior of the diaphragms when the maximum feed pump pressure is reached, expanding the diaphragm reducing the volume of cake solids.

The diaphragm filter press operates like a recessed plate press, at pressures between 690-1,040 kPa (100-225psi). However, higher pressure is achieved by expanding the diaphragms, reducing the volume of the chamber by squeezing out more water.

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Operation of Recessed Plate Filter press

Dewatering is accomplished by pumping a slurry or sludge into chambers (A) surrounded by filter membranes (B). As pumping pressure is increased the filtrate is forced through the accumulated filter cake (C) and membrane until the chamber is full of solid filter cake. The chambers are formed by two recessed plates held together under hydraulic pressure. The hydraulic ram (D) moves the follower (E) against the stack of filter plates (F) closing the press. The ram continues to apply sealing pressure of sufficient force to counteract the high internal compaction pressures. The head stock (G) and tail stock (H) are held in place by specially engineered side rail support bars (I). The filtrate passes through the membrane and is directed by channels in the plates and drain ports (J) to the head stock for discharge. The filtrate typically contains less than 15 PPM suspended solids. The filter cake is easily removed by simply reversing the hydraulic ram, thus opening the press. The lightweight plates may then be moved apart, permitting the compacted cake to fall from the chambers. Higher the internal pressure, the greater the solids compaction. The standard press is constructed to withstand 100 PSI compaction pressure producing a hard dry cake. The special high pressure press can withstand 225 PSI for sludge more difficult to dewater. Air diaphragm type pumps provide very efficient compaction of the sludge. The maximum pressure can be set with the air supply regulator and the pumping rate set with the volume of air flow. The pump will run rapidly during the initial phase of the cycle, slowing steadily as back pressure increases due to cake formation. Low initial back pressure induces rapid pumping and shortens the overall cycle time.

When the pump attains the desired pressure and the flow rate slows, the compaction cycle is complete. An air blow down manifold allows influent to be purged from piping before the press is opened. Overall cycle time is dependent upon the concentration of the influent sludge. Higher concentrations dramatically reduce cycle time. Typical cycle time is two to four hours. Typical cleaning time is less than 30 seconds per plate.

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Maintenance of a Recessed Plate Filter PressThe degree of operator activity associated with filter presses is similar to that of belt presses. Although the press operates unattended during filtration, the system uses a batch process that requires regular operator attention to fill and unload the press .When filtration is complete, compressed air should be used to blow out the core since it is filled with partially dewatered cake at the end of the filtration cycle.Facilities with multiple presses need a fully automatic system for efficient operation. Maintain proper chemical dosages, open and close the press, and blow out the core at the end of the cycle. Even in an automated system, the plate-shifting step must be initiated manually so the facility can prepare to receive the cake drop.Filter cloths require periodic washing. Larger presses have automatic washers that require a high-pressure pumping system to supply spray water. In some installations, the press can be filled with an acid cleaning solution to remove scale deposits when lime is used for conditioning. Acid washing may reduce filter cloth life and replacing filter cloths is labour-intensive. Filter cloth life depends on the material, solids type, conditioning, and washing frequency.

Advantages and Disadvantages of Using Recessed Plate Filter Press Advantages

Recessed-plate filter presses offer several advantages compared to other mechanical dewatering methods, as follows:• High cake solids concentration with associated low cake storage, hauling, and disposal costs.• Little or no operator attention during dewatering phase of cycle (one to three hours).• Cake solids concentration is relatively independent of feed solids concentration.• Use of lime as a conditioner stabilizes and disinfects the final product.

DisadvantagesThere are also several disadvantages to using recessed-plate filter presses compared with other mechanical dewatering methods, as follows:• Batch operation produces more heterogeneous influent.• Process is mechanically complex.• Capital costs are relatively high.• Requires special support.• Requires relatively large area.• Filter cloth preparation, cleaning, and cake removal may be operator intensive.• Cannot be totally enclosed, leaving operators exposed to odours, gaseous and vaporous sulphur compounds, and ammonia during the cake release phase.• When lime and ferric chloride are used in conditioning, and then account for a significant portion (15 to 40 percent) of the cake solids offsetting the weight reduction of high water removal efficiency.• May require polymers for optimum performance.

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General Diagram for Effluent Treatment Plant for Rourkela Steel Plant:

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