paperpulse-chlorination

7/31/2019 PaperPulse-Chlorination

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H.A. Jenner et al. Four years experience with a new chlorine dosing regime

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Four years experience with a new chlorine dosing regime

against macrofouling

H.A. Jenner 1, H.J.G. Polman 1 & R. van Wijck 2

1) KEMA Power Generation & Sustainables, P.O. 9035, NL-6800 ET Arnhem, Netherlands

2) E.ON Benelux, Coloradoweg 10, NL-3199 LA Maasvlakte (Rdam), Netherlands

Abstract A new method of chlorination called Pulse-Chlorination was developed by KEMA in 1998. Pulse-

Chlorination is based on the principle that mussels and clams, in general have a recovery period

before full opening and start filtering after exposure to a chlorination period. The chlorination

method takes advantage of this recovery time by using short successive periods of chlorination,

alternating with periods without chlorine. The full scale tests on site, among others at E.ON power

station Maasvlakte between 1999 and 2003 resulted in extremely clean condensers. The overall

result is better performance of the cooling water system (K-value) and therefore less maintenance

is necessary. This in turn allows longer intervals between planned outages and brings down the

running costs on the basis of circa 50.000 per day spread out over three years rather than two

years.

1 Introduction

The majority of the Dutch (power) industry use chlorination for anti fouling treatment in their cooling

water systems. This is due to proven efficacy, wide experience, moderate costs, opportunities tooptimisation of the chlorination procedure, and by the fact that low-level chlorination has not proven

to have a major ecological impact [2] [3] [4]. The method described here is called Pulse-

Chlorination which has been declared as a BAT (Best Available Technique) under the terms of

the EU Integrated Pollution Prevention and Control (IPPC) for macro fouling mitigation in once-

through cooling water systems using chlorine [1].

In The Netherlands, the majority of the macro fouling problems in industrial cooling water systems

are caused by three mussel species; the marine mussel Mytilus edulis , the brackish water musselMytilopsis leucophaeata , and the fresh water mussel Dreissena polymorpha , known as Zebra

mussel. Of these species the edible mussel Mytilus is the most troublesome one.


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Pulse-Chlorination is based on the principle that in general mussels and clams have a recovery

period before they open fully and restart filtration, for oxygen and food uptake after exposure to a

chlorination period. Pulse-Chlorination takes advantage of this recovery time by using short suc-

cessive periods of chlorination, alternating with periods without chlorine. During continuous chlori-

nation the mussels close and switch from aerobic to anaerobic metabolism. By applying Pulse-

Chlorination the mussels have to switch continuously their metabolism from aerobic to anaerobic

leading to physiologically exhaustion. This will result in a more rapid effect compared to the con-

ventional continuous chlorination. To determine exactly the behaviour of the mussel, i.e. recovery

period, the valve movements are monitored in a special device, the MusselMonitor.

The E.ON power station is situated on the coast of the Maasvlakte, an industrial area west of Rot-

terdam. The station is coal fired and consists of 2 units with a total of 1040 MWe. The cooling wa-

ter system for both units is an on-shore intake system with trash racks in front of the 8 intake pits

followed by 4 rotating drum screens with water jet cleaning. Four cooling water pumps (2x 18 m 3/s)

are installed and at the end of the two (600 m long) intake culverts each of the in total 4 condens-

ers are protected by self cleaning mussel sieves in front of the water boxes. Without counter

measures fouling is sever and is caused mainly by the seawater mussel Mytilus edulis . However,the first oysters ( Crassostera gigas ) are now found at the station. In the past chlorination was

achieved by a regime of 4 hours on and 4 hours off with a short continuous dosing period during

spatfall. This regime was acceptable but never resulted in real clean condensers. At the

Maasvlakte power station the first tests were done at full scale in 1999.

Aim of the research is to introduce a more environmentally friendly regime with better antifouling

results, with efficiency improvement and enabling an operation period of 2 - 3 years now leading to

considerable cost savings.

2 Materials and methods

2.1 Mobile laboratory

All tests have been carried out in the KEMA mobile laboratory on location. This laboratory is a re-

built 20ft sea container consisting of a wet laboratory part and a dry part for the electronic

equipment. In the laboratory the cooling water system conditions, which are unique for each plant

location, are applied so that results are directly applicable to the station. The tested cooling water


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system conditions, which differ for each of the plant sites and which are crucial for the desired re-

gimes are: ambient water composition, residence time of the cooling water (pumps to condensers)

and water velocity. The organisms used for the MusselMonitor, are collected near the test loca-

tion. For the chlorination experiments, sodium-hypochlorite was used from that plant site. Water is

usually obtained near the cooling water intake. In the laboratory, the water is collected in a 1m3

buffer tank with a water flow of about 500 L/min. With submersible pumps, the water is directed

from the buffer tank through hard PVC tubing system to test tanks. In this system, the water flow is

regulated and measured on-line with magnoflow meters. Continuous on-line measurement is made

of the following water parameters: temperature, turbidity, dissolved oxygen, pH and salinity.

Free Oxidant (FO) and Total Residual Oxidant (TRO) concentration is measured with a single spot

spectrophotometric measurement using DPD reagent (HACH DR/2000) and is used for checking

and calibration of the semie continuous chlorine monitor HACH CL-17. All recorded data from

MusselMonitors and water parameters are stored in a computer and transferred by (cellular)

phone to KEMA in Arnhem. The data acquisition and presentation program developed by KEMA

called Tele Diagnostic System (TDS), enables on-line graphical data presentation of the valve

movement patterns and all measured water parameters and data acquisition is in one database.

2.2 MusselMonitor

At present, the MusselMonitor is one of the most validated Biological Early Warning Systems

(BEWS) for surface waters using valve movement response of bivalves (e.g. mussels or oysters)

[5]. In "clean" water, bivalves show a characteristic valve movement pattern in which they are most

of the time open, showing filtering activity. Bivalves exposed to contaminated water show strikingly

different behaviour, in most cases more frequent opening and closing activity resulting in long

closed periods.

Eight mussels are placed on top of the MusselMonitor. Each mussel is provided with two sen-

sors, fixed one on each of the valves, see Photo 2. The principle is based on the measurement of

the inductive distance between the two sensors at 250 kHz, determined by the degree of opening

and closing of the valves. By using a microprocessor to continuously register action of the valve

movement pattern of eight bivalves, a sensitive, fast reacting, BEWS is obtained. With this monitor

changes in valve movement of


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2.3 General reaction patterns of mussels

Mussels in clean water (uncontaminated) show a characteristic valve movement pattern in which

they are open for more that 90% of the time, showing filtering activity for oxygen and food, see

Figure 1. A mussel exposed to hypochlorite shows a different behaviour pattern, in most cases

closing up within seconds (Figure 2). To reduce mussel settlement and growth in a cooling water

system, it is important that the hypochlorite-dosing regime prevents the mussels opening fully. A

mussel when closed switches from aerobic to anaerobic metabolism. Closed mussels live on their

own reserves and can survive for up to 10 weeks, depending on their condition and water tem-

perature.

After closure, mussels will frequently open a little bit to get rid of metabolic waste products and to

taste if the chlorine is still present. The mussel will repeat this tasting as long as dosing contin-

ues. When the hypochlorite dosing is stopped, and the TRO concentration has fallen below 0,1 mg

Cl2/L, the mussel will open gradually to regain filtering activity. The time it takes a mussel to open

fully and restart filtering activity is called the recovery period. The recovery period depends on the

chlorine concentration the mussel was exposed to, the length of the dosing period, the number of

previous dosing periods and on water temperature. Mussels are more active and more sensitive to

chlorine at higher temperatures.

2.4 KEMA Biofouling Monitor

The KEMA Biofouling Monitor (KBM) is developed for sampling of fouling species in general.

Water flow is up-welling through four PVC tubes, via a sedimentation chamber, and a central out-

let. The settlement of fouling organisms occurs on four plates hanging in the four tubes, being rep-

resentative for the fouling by mussels, oysters, barnacles and hydroids. No interruption of the water

supply is necessary during sampling action and the KBM functions without sedimentation and

flooding problems. The monitor is connected to the cooling water system as a by-pass loop and

needs a water flow of about 50 l/min. to ensure trouble free operation. The KBM enables fouling

settlement registration during the seasons, which allows detection of bivalve settlement in an early

stage, and forms an adequate check on the efficacy of the Pulse-Chlorination regime.

3 Results

In 1998 KEMA has determined the optimum Pulse-Chlorination regime for E.ON power station

Maasvlakte as 10 minutes on and 10 minutes off with an FO concentration of 0.3 mg Cl 2/l. In


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practise it turned out that the 10 minutes on period could not be achieved at the concentration

needed. So the final regime is slightly different 12 minutes on and 8 minutes off. The regime

starts in spring at the first day the water temperature is 10 C and stops at the first day in autumn as

the temperature drops below the 10 C. The Maasvlakte power station is generally exposed to quite

severe mussel and barnacle fouling and in 2002 also oysters appear on the scene. Without mitiga-

tion measures the station will foul in high speed mode.

The most sensitive fouling spot is found to be the return water boxes of the condensers were the

water temperature is already elevated with 4 to 5 K. These boxes were always fouled by large

bunches of hydroids with mussel mattress like fouling over the bottom and in the corners. End of

August the water boxes were inspected and showed to be completely clean. This cleanliness is

found also the following years.

Figure 1: Valve movement of Mytilus edulis, control behaviour

Figure 2: Valve movement of Mytilus edulis; Chlorination from 0:00 to 12:00 continuous dosing

regime TRO = 0.45 mg Cl2/L. from 12:00 to 0:00 Pulse-Chlorination 10 min on / 10 min off TRO= 0.45 mg Cl2/L


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In Figure 1 the mussels show a characteristic valve movement pattern in non chlorinated control

water in which they are open for more that 90% of the time, showing filtering activity for oxygen

and food (control).

In Figure 2 the valve movement of the mussels in chlorinated water is presented. In this figure the

mussels are first exposed to a continuous dosing regime with a concentration of 0.45 mg Cl2/L and

are most of the time fully closed and sometimes open a little bit to taste if the chlorine is still pres-

ent. After this they are exposed to a Pulse-Chlorination dosing regime of 10 minutes on / 10 min-

utes off with a TRO concentration of 0.45 mg Cl2/L. During this period the mussels try to open

during every short time period without dosing to open themselves fully to start filtering activity. Themussels continuously have to switch their metabolism from aerobic to anaerobic leading to

physiologically exhaustion. As a result an optimal effect on mussels will be achieved resulting in a

reduction of mussel settlement and growth in a cooling water system.

The results have shown that there is no optimum Pulse-Chlorination regime efficient for all water

types and fouling species. Even at locations close to each other, different optimal dosing regimes

were needed. The sensitivity depends largely on water type and quality in which the organism

lives, as this influence the reactions and its chlorination by-products (CBPs). Therefore, dosing

regimes cannot be used without being tested at specific locations to determine the minimum con-

centration FO/TRO to produce sufficient effect on mussels. Results show that the time (recupera-

tion) interval is more decisive for the wanted anti fouling effects compare to changes in (higher)

chlorine concentrations. Both KBMs installed in front of the condenser are used as detection de-

vices for the efficacy of the treatment.

An important remark has to be made as Pulse-Chlorination leaves no room for variation or anyaction contrary to the applied regime. Mussels are capable to recuperate completely in two days

without chlorine. The time intervals and FO/TRO concentration have to be established at a critical

point in the cooling water system, e.g. just before the condenser. This means that a reliable on-line

measurement of the FO/TRO concentration is essential for the proper implementation of the Pulse-

Chlorination regime.


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4 ConclusionsPulse-Chlorination should be cost saving due to less chlorine dosing compared to continuous

chlorination. However, Maasvlakte power station already used a 50% reduction regime of 4 hours

on and 4 hours off the use of hypochlorite. A further reduction was not possible on the contrary, the

amount of dosed hypochlorite slightly increased but also the overall performance of both units in-

creased due to the clean condensers. The item cooling water gained more attention resulting in

less fouling problems and longer interval periods between outages, also substantial less labour

was needed for cleaning the culverts and condensers.

It appeared that Pulse-Chlorination leads to an improved anti fouling treatment. This was con-cluded after comparing the analyses of mussel settlement and growth using the KEMA Biofouling

Monitor (KBM) before and after Pulse-Chlorination was applied.

The Dutch water authorities stimulate industries to reduce the usage of biocides (e.g. chlorine) to

reduce the impact on the environment. By applying Pulse-Chlorination the companies show their

commitment to endeavour chlorine reduction. At present, Pulse-Chlorination is entitled as BAT

for chlorination in once-through cooling water systems using chlorine. The regulating authorities

now use this to stimulate companies to reduce their chlorine use.

References

1 BAT-cooling: European IPPC bureau Sevilla, Document on the application of Best Available

Techniques to Industrial Cooling Systems, November 2000 (http://eippcb.jrc.es). BREF (11.00)

Cooling systems.

2 Jenner H.A., Taylor C.J.L., Van Donk M. & Khalanski M., 1997. Chlorination By-Products in

Chlorinated Cooling Water of Some European Coastal Power Stations. Marine EnvironmentalResearch, vol. 43, No 4, pp. 279-293.

3 Jenner H.A., Whitehouse J.W., Taylor C.J.T. & Khalanski M., 1998. Cooling Water Management

in European Power Stations: Biology and Control of Fouling. Hydrocologie Applique. Tome

10, Vol 1-2, 225pp.

4 Paping L.L.M.J., Jenner H.A., Polman H.J.G., Te Winkel B.H. & De Potter M.R., 1999. Ecologi-

cal Conditioning and Optimisation of a Once-Through Cooling Water System. Paper presented

on 13 April 1999 at the Watersymposium 99 at Breda, The Netherlands.

5 Kramer K.J.M., Jenner H.A., de Zwart D., 1989. The Valve Movement Response of Mussels: a

Tool in Biological Monitoring, Hydrobiologia 188/189 :433-443.

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