149 Cooling Water treatment-a csae study_Chembond_149.pdf

7/30/2019 149 Cooling Water treatment-a csae study_Chembond_149.pdf

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IMPORTANCE OF COOLING WATER TREATMENT WITH RESPECT TO WATERCONSERVATION THROUGH VARIOUS TREATMENT ALTERNATIVES AVAILABLE FORLOW AND HIGHER COC(CYCLES OF CONCENTRATION) WITH COST EFFCTIVE

PERFORMANCE,MONITORING AND CONTROLS.

Looking into the present scenario of increasing demand of water and the

depleting water tables we as a prudent human being really need to workextensively so that we take care of our present demand and the progenies in

the future. As the water is the necessity of all the industries spec ially the Power

industry. We can use water in a more cost effective manner means of output

with lesser inputs. The higher Cycles of operation in the c irculating water which

not only saves water but also reduces the effective cost of cooling water

treatment and in turn water usages. A few case studies are being given

hereunder discussing various problems and their solutions regarding the water

chemistry with successful implementation.

With the latest developments in the field we can operate the cooling water atvery high cycles of concentrations without any impact on performance.

1. CASE STUDIES ON A BRACKISH WATER SYSTEM OF STATE ELECTRICITY BOARD WITH

EFFECTIVE CONDENSER PERFORMANCE BY HIGH STRESS POLYMER TECHNOLOGY

AND LATEST OXIDATIVE ALTERNATIVES FOR THOROUGH MICROBIOLOGICAL

CONTROL.

High TDS load in brackish water cooling system is a major concern in all

industrial cooling water system, particularly in power plants where the

condenser utilizes large quantities of such water. The performance of the

condenser is affected by the fouling /deposition in the cooling water tubescausing reduced heat transfer rates and drop in vacuum, leading to plant

load limitation. This has an adverse impact on the overall operating costs apart

from adding to the damage caused by an already precarious power situation

in the country. Appropriate mechanical design and application of advanced

high performance polymer treatment minimizes the deposition and improves

the condenser performance, there by reducing the cost of operation. This

case study in a 75x3MW power plant in Western India where proper program

selection as well as effective application, monitoring and control, helped in

improving the condenser performance restoring power generation.

Background

Deposition and fouling in the condenser were major problems faced by the

75x3MW power plant using brackish water for condenser cooling. Each unit is

catered to by a dedicated cooling tower ie, three cooling towers for the three

units. Improper water treatment had caused deposition in the condenser,

leading to a drop in the vacuum and eventually affecting the plant load. This

necessitated the use of two cooling towers with an additional pump to run one

unit, there by increasing the cost of operation. In this arrangement, condenser


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vacuum in a single running unit was around 0.78 kg /cm2 and the plant load

was about 68MW.

After evaluating the water quality, Ashland Drews computer aided program

evaluation software On Guard TM model was used to identify the limiting

factors and select the proper chemistry required to address the issue.

Chembond Drewtreat Limited, a joint venture between Chembond Chemicals

Limited (India) and Ashland Spec iality Chemicals, USA, was entrusted withpackage treatment program to improve the condenser performance and

monitor the treatment program.

Effectively Controlling Deposition Chemical Treatment Methods

The traditional method of using a regular Phosphonate- compound with

chlorine to control the deposition was found to be ineffective for the brackish

water quality as make up to the cooling water system. Awareness about the

importance of using advanced high- performance polymer in a total

treatment package becomes necessary as:

Traditional polymers with phosphate are unable to restrict the

precipitation of dissolved solids on the heat transfer surfaces, in spite of

the noble- metallurgies employed.

Chlorine on its own in unable to prevent the formation of biofilm in the

absence of a biodispersant. This results in fouling in the system and

affects heat transfer

Proper control and monitoring of the water parameters enhances

system cleanliness

Consequently, Chembond Drewtreat Limited utilized Ashlands computer

aided program evaluation software On Guard TM to identify the limiting

factors and select a proper treatment program to overcome them. The On

Guard TM results indicated that the brackish water quality being used as

make up to the cooling tower required the use of advanced high-

performance polymers to address prec ipitation of dissolved solids, espec ially

iron and CaC O3.

The results are as follows:

The formation of carbonate alkalinity leads to the deposition of calciumand magnesium carbonate in the cooling water system. This is more

predominant in brackish water where the concentration of calcium and

magnesium is very high. Hence, it is desirable to control the pH of the

circulating water in the range where potential for carbonate alkalinity is

minimized, which in this case is less than 7.8pH

Based on the modelling, the On Guard TM, which recommends the use of

spec ific technologies for selected water chemistry, the program identified the


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use of advanced organophosphonate in combination with high-performance

polymers to be used for the brackish water treatment.

The program selected consisted of:

Antiscalant: advanced organophosphonate based product to

maintain residual as per the computer modelling of 0.3ppm to control

calcium carbonate scale. High performance polymer 1: the high performance co-polymer residual

requirement for calcium phosphate and C aSO4 dispersion/Scale

control, as per the computerized modelling when used alone is around

0.7.

High performance polymer-2: the high-performance Ter-polymer residual

requirement to control deposition of silica and iron fouling, as per the

computerized modeling when used alone is around 0.2.

Copper inhibitor oxidant-stable Azole- based product to maintain a

residual of 0.7ppm is used to control copper corrosion.

Enhancing the efficiency of chlorineA biodispersant should be added in combination with high performance

polymer program to assist in penetrating the exoploymer protective coating of

the biofilms. This allows efficient diffusion of micro bioc ides like chlorine in to the

biomass.

Monitoring and control parametersThe monitoring of circulation water parameters on a regular basis and control

within the parameters guidelines generated through the On Guard TM

modeling is important. for the c irculating water were finalized based on the

brackish water quality being used as make up.

ResultA baseline date was generated for monitoring the effectiveness of treatment

performance it was decided that the plant performance in the period before

the initial cleaning and start up would be used as the baseline.

Parameter Unit Range

Ph - 7.2-7.6

Conductivity Micromhos


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Status before implementation of treatment

Of the three units, two units were under shutdown (R& M) and only one was

under operation. The initial status of the unit running before implementing the

treatment program was:

Average vacuum = -0.78kg/ cm2

Average load = 68MW

Average exhaust steam temperature = 68*C Number of cooling water pumps in operation =3

Number of cooling towers in operation =2

Remarks

In spite of operating an additional cooling tower and cooling water

pump, the condenser vacuum was low and the plant was forced to

operate at a reduced load.

The system had adopted organophosphonate treatment and

chlorination. However, condenser scaling was frequent and had to be

cleaned with acid and high-pressure hydro jetting regularly. The condenser cleaning frequency was once in two months.

Implementation of the advanced treatment programSpecially formulated dispersants were used for initial cleaning of the system

under controlled conditions. Immediate improvement was observed in the

plant operation after the initial cleanup. The plant performance improved and

the key operating parameters of the running unit were as under:

Sl.

No.

Before CW Treatment in

Aug 2005

After CW Treatment in

Aug 2005

Remarks

1 Avg. Vacuum= 0.78

kg/cm2

Avg. vacuum= 0.84

kg/cm2

Improvement in

vacuum by 0.06 kg/cm2

2 Total unit gen = 44000 MW Total unit gen = 50000

MW

Improvement in gen =

6000 MW

3 Avg. Generation=1500MW

/day

Avg. Generation = 1700

MW/day

Improvement in gen

=200 MW/day

4 Aux power consumption =

1572 MW

Aux power

consumption= 1073 MW

Reduction in power

consumption = 499 MW

5 Aux power consumption in

Rs. 3442000/-

Aux power consumption

in Rs. 2349000/-

Aux power reduction in

Rs. 1093000/-

6 Heat rate =3474 Kcal/Kg. Heat rate= 3175

kcal/Kg.

Reduction in heat

rate=299 Kcal/Kg.7 Lignite consumption=

1.17MT/MW

Lignite consumption =

1.05 MT/ MW

Reduction in lignite

consumed 0.12 MT/MW

8 Turbine efficiency =24.755% Turbine efficiency

=27.086%

Improvement in Turbine

Efficiency =2.33 %

a)Vacuum = 0.84kg/cm2

b) Load =75MW

c) Exhaust steam temp.=

61*C

d) Number of cooling towers

in operation = 1


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These parameters were maintained with the continuous treatment program.

After the other two units were brought online they operated at their rated

output with optimum vacuum in the condenser generating rated power on a

continuous basis.

2. CASE STUDY FOR IMPROVEMENT ON PERFORMANCE OF COOLING TOWERFILLS THROUGH CHLORINE-DI-OXIDE TECHNOLOGY IN A NORTH INDIA

POWER PLANT.

Background

In one of the power plant in North India the tower fills were getting chocked and

hence causing difficulty in the cooling tower operations be way of low cooling effect

and causing fills to fall due to weight.

Cause and the sequence of choking

This was due to the reason that the tower was induced counter flow type and fills

were used to enhance the cooling by increasing the surface area of the droplets

dripping down. Various steps of the development of chocking were observed to be:

1. Sucking air, dirt and dust from the bottom

2. Water was traveling from the top to bottom through the fills.

3. The thin tubular structures of fills were causing the dust /dust ac cumulation.

4. This was giving rise to bacterial muck/sludge causing fills to be heavy.

5. Water was getting dried up on the upper portion of these fills

causing CaC O3 deposition.

Based on the detailes of the analysis of the deposit and thickness on the upper layer

the cause for this was attributed to no treatment in the cooling towers and

concluded that this accumulation was there since the period of no treatment in the

system.


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Non functioning of Oxidizing biocide

The cooling water treatment was implemented in the tower in a later stage but still the

chocking in the tower was the cause of worry, however the condenser performance

improved.

Chlorine was not working well due to its limitation on the Biofilm penetration and

efficiency reduction in the high pH operation.

Hence Chlorine Di-Oxide was used alongwith the biodispersant to enhance the

efficacy of the microbiological control programme. As analysis for the C hlorine di-

Oxide measurement on hourly basis was not feasible alternate method of ORP

(Oxidation and reduction potential) measurement was selected.

1. HOCl- + H++2e- - Cl- +H2O with 1.48 volts53.5 gms

2. HOBr- + H++2e- - Br- +H2O with 1.48 volts97 gms3. 2Cl2 +2e- - 2ClO2 with 0.95 volts135 Gms.

By successful implementation of C hlorine Di-Oxide and the biodispersant really

worked and an improvement in the tower efficiency was visible.

Case studies by

ChembondDrewtreat Limited

EL 71, MIDC Mahape

Navi Mumbai

706050403020100--

K

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Refinery Fouling versus ORP

300.00

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500.00

550.00

600.00

650.00

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Time

ORP

-200

-150

-100

-50

0

50

100

150

200

ORP

FOULING

149 Cooling Water treatment-a csae study_Chembond_149.pdf

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