Benefits of Outsourcing O&M for Water Management
Case Study at Tata Steel CRM Complex
By
Abhijeet Goswami, Ion Exchange (India) Ltd.
Worldwide there has been a dramatic switch from a product oriented to a service driven approach. Consumers have shifted from products to services that deliver end benefit conveniently and economically. Industry too is progressively outsourcing O&M services for equipment to the specialist suppliers.
This 360° solutions-with-service trend is also been increasingly adopted with respect to water management. Total water management capability enables value addition across the customer’s entire process cycle, while comprehensive service support ensures high performance continuity, translating into significant competitive advantage and bottom line benefit to the customer. The resultant single-point responsibility enables greater customer focus on core business, assures consistent, continuous supply and quality with superior price performance ratios and production efficiencies, lower cost and more effective use of capital employed. Outsourcing specialist O&M services also leaves the plant key personnel time to concentrate on overall plant management.
This case study features several of the substantial benefits to Tata Steel Ltd. as a result of outsourcing O&M services for the complete water and waste water complex of their cold rolling mill (CRM) at Jamshedpur.
Background
In 2000, Tata Steel commissioned a 1.5 million tones per annum cold rolling mill (CRM) at its complex at Jamshedpur. The total water management for the entire CRM was awarded to Ion Exchange (India) Ltd. who supplied, installed and commissioned the water and waste water treatment plants. The water treatment section consists of main filtration 3 x 160 m3/h, demineralisation 2 x 40 m3/h, softening 2 x 20 m3/h and side stream filtration 4 x 147 m3/h. The waste water treatment plant treats chrome, alkaline, oily and acidic wastes, as well as 25 m3/h backwash waste from the filtration plant and 25 m3/h DM plant waste. Since 2000, the customer has also outsourced the comprehensive water management of the CRM complex to Ion Exchange (India) Ltd. including operation and maintenance of the water and waste water treatment plants, besides the management of the cooling tower and cooling water treatment programme.
The scope of O&M service involves 24 x 7 operation of the plant, maintenance of the mechanical/ electrical/ instrumentation equipment of the plant (water treatment, waste water treatment, recirculation pump house), supply and monitoring of the cooling tower chemical system, laboratory analysis at plant site and submission of consumables consumption report.
Awarding the entire water management and services to a water management specialist has enabled the customer to focus on its core strength: making steel. In addition, there has been tremendous value addition through savings in consumption of chemicals, improved plant efficiency, consistent quality and quantity of treated water, and recycle of water.
Chemical Savings in Water System
A monthly saving of Rs. 16,66,900 /- in chemical consumption in all the three plants of the water system while maintaining the target Key Performance Indicators (KPI) within limit.
· Introduction of PID control system for effective control of supplied demineralised water, led to reduced consumption of Mono Ethanol Amine (MEA).
· Modification of acid dosing line led to effective pH control and reduced consumption of acid (HCl).
· Modification of alum dosing lines resulted in reduced consumption of alum.
· Utilisation of 48% w/w caustic lye in place of flakes in the water treatment plant reduced chemical cost and avoids preparation of hazardous caustic solution from flakes.
· Implementation of a new treatment programme has reduced cooling tower blow down, system loss, and cold water sump level to save chemicals.
· Optimum utilisation of ion exchangers in water treatment plant to obtain maximum throughput with reduced quantity of chemicals like HCl and NaOH.
Enhancement of chrome waste treatment capacity & cost saving in treatment.
Treatment procedure: The chromic acid waste from the continuous galvanizing lines (CGL#1 & CGL#2) are first collected and homogenised in the chrome waste collection tank. It is then transferred to the chrome reaction tank where hexavalent chromium is converted to trivalent by dosing fresh HCl & SMBS (sodium metabisulfite). Later alkali (NaOH) is added to precipitate the sludge.
After proper settling ,the supernatant liquid containing traces of non-toxic Cr+3 along with Fe & Zn is transferred to the supernatant collection tank and then to the alkali waste water collection tank for further treatment. The sludge is drained to the sludge sump and then dewatered through the filter press. The filtrate collected while dewatering is taken back to supernatant tank and the cake is collected in separate bins and dumped into the hazardous waste pit by the Material Handling Section (MHS).
Problem faced: As per the design the supernatant water used to mix with the incoming waste. Since it contains 5 to 10 ppm hexavelent chromium, treatment volume continuously increases and the chemicals consumption also increases.
Rectification : After a number of analyses and plant studies it was observed that the inlet acidic waste contained FeCl2 and FeCl3 and FeCl2 works as a reducing agent also to convert the Cr+6 to Cr +3 .That is why the supernatant line was modified to connect to the alkaline waste collection tank. Because during the treatment of the alkaline waste it is mixed with the acidic waste and the hexavelent chromium converts to the low LD value trivalent chromium.
Saving: Saving in SMBS consumption: Rs 210000/- per month .
Chrome Waste Treatment
Installation of PID controller to maintain the DM water supply pH
Previous process: From the time the plant was commissioned, the pH in the DM water was maintained by the on-off controller by dosing of Mono Ethanol Amine (MEA).
Problem: Due to the on-off controller, the control and sensing lag time is high, and there was a small pH variation range in the DM water supply. (In the on-off controller the pH variation is 6 to 8.5). But the roll coolant shop and electrolytic cleaning line (ECL) require pH to be between 7 to 7.5.
Rectification/process modification: To maintain the pH in the DM water supply within the range of 7 to 7.5 one PID controller with pH transmitter and an MEA (mono ethanol amine) dosing system were installed, which gave the desired output. It also increased the CRM produce sheet quality and reduced the coolant consumption (because previously, due to low pH <4 and high pH >10, emulsion quality deteriorated).
On-off controller pH range variation:
After installing the PID controller pH variation:
Recycling of Filter Backwash Water
Backwash Waste Treatment: The water treatment plant backwash water from the multi grade filters and TSS laden waste water are collected in two waste water collection tanks from where it is transferred to the high rate solids contact clarifier (HRSCC). In this clarifier all the three steps of flash mixing, flocculation and clarification are carried out in a single step by dosing alum & polymer. After that clear water is stored in the final effluent storage tank from where it is reused for gardening purposes. Sludge from HRSCC is drained into sludge collection tank and then transferred to the filter press. After filtration the cake is collected in bins and disposed by the Material Handling Section.
Outlet quality: pH: 7 - 8 and TSS 10 to 15 mg/l.
Process modification: After the above process the outlet quality of the HRSCC water is suitable for the fire water makeup only the TSS was slightly high. One multi grade filter (capacity 35 m3/h) as installed after the HRSCC and the filter water sent directly to the fire well as makeup.
Introduction of New Bacterial Cultures in Aeration Tank
Brief Description of Oily Waste Section of Waste Water Treatment Plant, CRM: Oily wastes from the Pickling Live Tandem Casting Mill (PLTCM) roll coolant & continuous galvanizing line CGL#2 are collected in the collection tanks. These are then mixed with de-oiling polyelectrolyte (DOP) and alum maintaining the pH 7.0. The oil is removed as sludge. After mixing by cavitation air flotation (CAF) the waste water is sent for biological treatment in the aeration tank following bio-oxidation of biodegradable organic material, it is filtered through a multi-grade filter (MGF) and then through an activated carbon filter (ACF). After filtration, part of the filtered water is used as make-up water in the industrial cooling water circuit or as gardening water. The process layout is shown in Fig-1.
1. Oily waste from CGL#2 SPM – Collection tank-1
2. Oily waste from PLTCM– Collection tank-2
3. Continuous Tank –1
4. Continuous Tank –2
5. Feed Pump
6. CAF – 1
7. CAF – 2
8. Aeration Tank
9. Surface Aerators
10. Clarifier
11. MGF/ACF Feed Tank
12. MGF
13. ACF
14. Final Effluent Tank
Problems Faced & Root Cause Analysis: The problems faced during operation in the oily waste section of CRM waste water systems were as follows: -
· The colour of the ATL started changing to black from normal brown.
· Intense smell of rotten egg (i.e. H2S) was polluting the surrounding area.
· Sludge bulking (huge sludge formation) was found in secondary clarifier, which led to high turbidity of the final effluent. The colour of clarifier effluent was blackish. Both these were unacceptable environmental conditions.
· Sludge volume index, which is an indication of the settling characteristic of the sludge, of the secondary clarifier was calculated to be 90.5 i.e. high normal (normal range is 40 to 100).
· The O2 uptake test (Fig.2) conducted showed a flat response, signifying that the bacteria were no longer active.
Corrective & Preventive Action Taken: Various tests & measures were carried out for arriving at an effective solution.
(i) Accessibility to aeration tank top was improved for observation and two extra circular air spurges were provided to reduce H2S exposure.
(ii) Extra nutrients were tried and the aeration tank was also loaded with a wide range of micro-organisms from cow dung as well as the BOD plant. Draining out the aeration tank to develop new bacteria was not considered due to environmental concerns of 400 cu.m of liquor from the aeration tank.
(iii) Since procurement of a pure culture of thiobacillus ferro-oxidan is time-consuming, it was decided to carry out the treatment of oily waste in laboratory scale with different soil samples collected from the premises of Tata Steel works.
Lab studies on the use of soil samples in the treatment of oily waste had encouraging results. The intermittent enhancement of dissolved oxygen (DO) was taken as a positive indication of growth of the micro organism. The dip in DO may be interpreted as consumption of O2 not only for biochemical reaction but also for some other consumption by other interfering radicals i.e. chemical oxidation. However no tangible colour change was observed at the time of performing the O2 uptake test. The experiment could not be continued beyond D-2 (second day) due to stoppage of airing on D-2 night for some unavoidable reasons.
Conclusion: It was the first time soil has been used directly in running any biological treatment process, creating a medium required for micro organism growth. Normally in activated sludge process, bacteria culture is made by addition of cow-dung or sludge brought from other BOD removal plant. However it was established in this study that soil micro organisms could have a vital role in biological treatment process because they serve as biochemical agents for the conversion of complex organic compounds into simple inorganic compounds or into their constituent elements. Consequently one could use this material as an inexpensive source of desirable micro organisms in biological treatment processes.
Troubleshooting
Apart from the benefits that have accrued to Tata Steel as detailed above, having a fully experienced team at site specialised in water management has helped Tata Steel maximize uptime of their plants. The team’s involvement in trouble shooting in various areas is illustrated below:
Water Treatment Plant
PROBLEMS / REMEDIAL ACTIONSlime gel deposition was detected in DM water supply line. / a) A sample of slime gel was sent for lab analysis. It was found that slime gel formation took place due to micro-biological growth
b) DM water supply line flushing was done during annual shutdown.
DM water supply pumps often tripped due to high consumption of DM water. / PLC logic was developed which allowed both pumps to be started in manual-remote mode so that desired flow and pressure could be maintained effectively.
Throughput of SAC and SBA reduced. / Acid soaking was done for SAC. Alkali brine treatment was done for SBA.
Low pH in DM water supply circuit. / Mono Ethanol Amine dosing prohibition was provided with PID control for maintaining pH of DM water supply effectively.
Waste Water Treatment Plant
Frequent choking of alum dosing pump strainer / Powder alum was replaced by liquid alum.Oily waste from SPM used to contain high COD load (10000-12000 mg/l) which was beyond our design (600 mg/l). As a result, aeration system was frequently disturbed. / Practice has been developed to mix SPM waste with PLTCM waste before treatment supply.
Due to increased load and higher volume of oily waste received, sludge generation increased considerably which created disposal problems. / A spare filter press for section 500 was reinstalled in section 300, which considerably reduced the volume of sludge generation.
Oily waste from SPM contained foaming like surfactants, which caused a lot of foam in the aeration tank resulting in reduction of dissolved oxygen content. / Proper sprinkling system was developed which reduced the foam and thus helped in maintaining the dissolved oxygen content.
Removal of oil scum from continuous tank / Permanent arrangement (by rotor pump) was made for removal of oil scum.
Higher incoming alkaline waste from continuous galvanizing line than its design, which affects the final effluent quality. / Treatment flow was increased from 14m3/h to 20 m3/h
Polymer 441 dosing line made to T- 203 & alum dosing is done through directly from the tank.
Underground pipe line leakage from alkaline waste pipe line from CGL # 1 & CGL # 2. / Overhead line provided for incoming alkaline waste from CGL #2 and CGL #1 to avoid frequent leakages
Section 500 filter press not able to form cake. / Scrape the deposit mud & continuous airing in sludge sump of section 500.
TSS of final effluent high due to section 300. / Complete overhauling was done in multi
grade and activated carbon filters.
Recirculation Pump House (RCPH)