Purocide 325
2-chloro-4,6-dialkylamino-s-triazine
Manufacturer Name: Bellacide® 325
Manufacturer: FMC Corporation

Case Studies: Applications of Bellacide^® 325 in different cooling systems

Abstract
Bellacide® 325 is a 4% aqueous dispersion of terbuthylazine (TBZ) and is widely used to control the growth of algae in recirculating cooling systems.

Two case histories are discussed. The first describes how Bellacide® 325 was used to clean up the cooling system of a metal sections plant in West Germany and to prevent regrowth of algae. In the second trial at a fertiliser plant, Bellacide® 325 was used to control algae following unsuccessful trials with a variety of biocides. In both cases Bellacide® 325 was used in conjunction with low level halogenation.

Conclusions
Both case histories demonstrate the excellent properties of terbuthylazine. Plant performance was greatly improved owing to the reduction of microbiological fouling. Furthermore, chlorine usage in the system was substantially reduced.

The system
A manufacturer of metal sections in West Germany has a cooling system with the following parameters:

This system operates under high heat load with water distributed from one hot water reservoir to five separate cooling towers, below which are situated five cold water reservoirs. All the reservoirs are exposed to light.

The make-up and recirculating water analysis is as follows:

The problem
Before the introduction of Bellacide® 325 the cooling water was treated with sodium hypochionte (NaOCl) to control microbiological growth, but the algal growth was not controlled, even though the circulating water was regularly dosed with up to 10 mg/l free chlorine. The circulating water was green due to suspended algal cells, and there were algal deposits on the walls of the reservoirs and cooling towers. Analysis of the algae showed that they consisted mainly of Chlorella vulgaris, Chlorella pyrenoidosa and various slime-forming strains. Chlorination successfully controlled the bacteria in the circulating water, and the bacterial count was reduced from 10⁸/ml to 10³/ml.

In an attempt to control the algal growth, the chlorine treatment was supplemented by the addition of a quaternary ammonium compound. The dose level of the free chlorine was reduced from 10 mg/l to 2 mg/l and up to 25 mg/l (solids) of a quaternary ammonium compound was added to the system water twice a week. Again, the bacterial levels were reduced, but the algal growth was unaffected. As well as being ineffective, the quaternary ammonium compound caused serious foaming problems in the system water.

The foam and algal growth circulating around the system blocked the heat exchangers and fouled the pump impellers, which led to overheating of the heat transfer surfaces in the forming equipment and the compressors, with consequent loss of production.

To minimise the problems caused by algal deposition in the system a filter was placed in the outlet from the cooling pond, but this required regular cleaning, and an operator was employed from January to November to keep it free from algal deposits. It was decided that this measure was not satisfactory and could only be considered as a short-term solution to the problem.

The treatment
The trial with Bellacide® 325 was carried out in two stages

Cleaning stage (2 weeks)
Day 1: 60 mg/l of Bellacide® 325 (product) was added to the system water and allowed to disperse completely before sodium hypochlorite was added to give 3 mg/l free chlorine in the system water.

Day 3: Sodium hypochlorite was added to give 3 mg/l free chlorine in the system water

Day 5: Sodium hypochlorite was added to give 3 mg/l free chlorine in the system water

Day 7: 30 mg/l of Bellacide® 325 was added to the system water and allowed to disperse completely before sodium hypochlorite was added to give 3 mg/l free chlorine in the system water

This procedure was repeated for a second week. Throughout the cleaning period the purge from the system was increased to remove the dead algae from the circulating water. The addition of Bellacide® 325 at first caused a slight turbidity in the system water but this cleared immediately after the Bellacide® 325 had been thoroughly dispersed and circulated round the system. After four days' treatment the water became clearer and the bright green color in the circulating water was not as intense. At the end of the cleaning program almost all the algal deposits on the walls of the ponds and the cooling tower sections had been removed.

Routine treatment
Routine treatment was started immediately after the completion of the cleaning program. Bellacide® 325 (20 mg/l product) was added to the system once a week and sodium hypochlorite was dosed to the circulating water to maintain 1 mg/l free chlorine. Figure 1 shows the concentration of Bellacide® 325 (HPLC method) maintained in the system water using this treatment program.



Results
The conditions in the cooling system improved and at the normal maintenance dose level the system was kept free from biological fouling. Manual cleaning of the filter in the pond outlet was no longer necessary and production losses due to overheating and machine failure were reduced to an acceptable level.

The use of Bellacide® 325 and chlorine was a complete success in controlling the biological fouling in the cooling system of this aluminium plant.

Bellacide® 325 and chlorine were particularly effective in removing persistent algal strains which could not be cleared with other algicides. Lower doses of Bellacide® 325 and chlorine then maintained the system in a clean condition. Apart from the cost savings resulting from the reduction in plant downtime the savings in labor costs alone more than paid for the cost of the treatment.

Following the successful trial, the combination of Bellacide® 325 and chlorine was adopted as the routine treatment and it has given excellent results ever since.

Treatment of cooling systems in a major chemical plant

The system
The plant is a major site for the production of ammonia, sulphuric acid, urea, acrylonitrile and related products. There are nine major cooling systems with a daily make-up rate of 6.6 m gallons of river water. The subtropical climate (summer temperatures 47-113°F; winter temperatures 50-72°) and prolonged sunshine result in algal growth throughout the whole year.

The problem
Problems due to algal growth were minimised by continuous bromination to maintain a 'free bromine' level of 0.5 mg/l. Despite this treatment the systems still experienced algal growth sufficient to cause operational difficulties. Various algicide treatments were tried including:

Quats: These were unsuccessful and gave foaming problems

Quats + TBTO: These were unsuccessful and solubility problems were encountered with TBTO

High level Cl₂ and biodispersant: These were partially successful

Isothiazolone: These were partially successful

The treatment
In an effort to rectify operational difficulties, Bellacide® 325 was selected for trial.

The biocide treatment in these systems (systems 1 and 2) was replaced with Bellacide® 325 in conjunction with the previous bromination regime, dosed to maintain 30-40 mg/l product for the first 4 weeks of the trial and then reduced to maintain only 10 mg/l product. Prior to the trial, some areas of the top decks were manually cleaned.

Results
The addition of Bellacide® 325 resulted in no algal growth, either on the areas manually cleaned or on areas with existing deposits. Furthermore, laboratory tests on water samples taken from the system confirmed no algal growth, even when incubated under ideal growth conditions. In contrast, all other systems on this site not using Bellacide® 325, experienced algal growth. The existing algal deposits in the systems treated with Bellacide® 325 were also slowly reduced in area and thickness over the course of the treatment.

No operational difficulties due to foaming, incompatibility with other water treatment products, handling problems, blockage of pipework by sudden release of algal deposits etc. occurred during the course of the trial. This confirmed the excellent algal control properties of Bellacide® 325 used in conjunction with low level bromination.

Conclusion
These two case histories have shown the excellent properties of Bellacide® 325 in preventing any new algal growth and in removing existing algal deposits in systems treated with a low level of free halogen.

The information contained herein, is, to our knowledge, true and accurate. Because conditions of use are beyond our control, we make no warranty or representation, express or implied, except that the products discussed herein conform to the chemical descriptions shown on the labels, Nothing contained herein should be construed as permission or recommendations to infringe any patent. No agent, representative or employee of this company is authorised to vary any terms of this notice.

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Bellacide® 325 is a registered pesticide and therefore local labelling restrictions should be strictly adhered to.
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