Ruks Engineering Ltd. CT Water Systems

Introduction | Feasibility Study | Specifications | Air as Feed Gas | Drawings | Reference

OZONIZATION OF COOLING TOWER

INTRODUCTION

Water cooled chillers use evaporative cooling towers as the ultimate source of heat rejection. As spray water of the tower re-circulates through condensers of the HVAC machines, it is essential that the following are achieved;

Water in the system does not cause corrosion of the condenser tubes and pipes.
As this water sprays through the tower, air flow causes drift, carrying water droplets to a large area in the vicinity of the tower. Hence, it is absolutely essential to ensure the level of water borne bacteria and viruses in the water is below accepted norms (1000 CFU/ML Colony Forming Units per milli Litre). It is now a well known fact many diseases, including the dreaded Legionnaire's disease, are caused by the fine mist from cooling towers. Importance of this is more pertinent applications, close to high populated areas.
Minimize build up of water borne microbes such as algae, plankton etc.
Keep water clean from dirt, sediments and particulates.
Minimize build up of scales in the condenser tubes. Increased scaling results in increased power consumption of HVAC compressors, a major factor in operating cost of the system.
To comply with laws restricting discharge of chemically treated water.

CONVENTIONAL TREATMENT (MULTI CHEMICAL TREATMENT)
To achieve these, it was customary to use a variety of multi chemical treatments, combined with filtration. Usually, more than one chemical is used, as no one chemical can provide solution to all above problems. The applied chemicals are spent in the water, and therefore, it is necessary to add chemicals continually. As part of the water in the system constantly evaporates, concentration of residual chemicals builds up in water in the sump of the cooling tower. It also increases calcium and magnesium count in tower water, major components contributing to scale formation in condenser tubes. Additionally, it alters PH of water and disables its corrosion inhibition ability. To restore this, it becomes necessary to drain out a large portion of water from the sump of the tower. This is called sump blow down or bleed off water. Blow down water (together with water lost due to evaporation and drift) are made up by continuous injection of fresh water into the sump, called make up water. If adequate quantity of water is not blown down, the result is increased scale formation on condenser tubes, and increased power consumption. The trade off is in favor of blowing down the necessary quantity of water and keep scale formation down.

Blowing down water causes serious concerns due to the high cost of operation of the plant, and environmental problems. Typically, a chemically treated cooling tower operates at cycles of concentration between 1.5 and 5.0. Cycles of Concentration is defined as the number of times a molecule of water is rotated in the condenser system, before it is blown down, or carried away as drift, or boiled through process of evaporation. Analytically, it is the ratio of the sum of water evaporated, water lost due to drift, and water blown down to the sum of water blown down and drift loss. C = {E/(B+D)}+1. E and D are constant and B is the only variable component. Higher the value of C, lower is the volume of water blown down. Drift is also a form of blow down, except it is uncontrolled.

OZONE TREATMENT OF COOLING TOWER WATER
Present trend in the industry is to use the alternate method of treating cooling tower with ozone. This achieves all of the purposes served by multi chemical treatment, and more. Briefly described, it involves production of low concentration of ozone at site, and injecting this into a side stream water taken from the tower basin, and returning the injected water (with ozone) to the basin. Ozonization of tower water:

Disables scale formation tendency on condenser tubes.
Suppresses corrosion of condenser tubes and condenser water pipes.
Eliminates water borne bacteria, viruses, algae, plankton and microbes in the water.
Removes odors and color from condenser water system
Eliminates use of chemicals completely.
Can discharge directly to sewer.
Bleed off water can be used for irrigation by maintaining the total dissolved solid content within 3000ppm.

Cost of operating the plant is very low, because ozone is produced in situ. The best known advantages of this are:

Reduces dramatically blow down or bleed water, and reduces power consumption. Operating the tower at cycles of concentration of 20 is quite easily attainable. This results in incredible reduction in electricity and water consumption or make up water. During mild seasons, it may well be possible to operate with zero blow down. Annualized savings in blow down water is around 80%, a phenomenal reduction. Savings in electricity of 15% is attainable.

Reduces electrical power consumption of HVAC compressor. For a retrofit conversion form chemical to ozone system, we would expect power savings of over 15%.

ADVANTAGES OF TREATMENT WITH OZONE
Advantages of ozone system over chemical system are many: Direct and tangible economic advantages resulting in direct cost savings, consequential and indirect advantages, and environmental benefits. Following is brief summary of these;

DIRECT AND TANGIBLE ECONOMIC ADVANTAGES

Savings in cost of water: Blow down water is reduced dramatically, by over 80%.
Savings in power consumption of HVAC compressor. For retrofit, we would expect power savings in excess of 15%.
Addition of chemicals incurs recurring cost. In ozonized towers, chemicals are totally eliminated.
Although chemical treatment inhibits corrosion, yet corrosion formation is quite high. In chemically treated systems, corrosion of 3 MPY or more for copper is not uncommon. Ozonization reduces corrosion significantly. Typically, in ozonized systems, corrosion of 0.3MPY for copper is attainable. This is a very impressive figure by industry standards.
Scale formation on condenser tubes with chemical treatment is high. Periodic descaling of condenser tubes is necessary, typically once a year. This results in increased power consumption, and adds to cost of maintenance of the plant. In ozonized system, the need to descale condenser is vastly reduced. If operated properly, it can be eliminated altogether. Descaling once in 5 years is a reasonable assessment.
Discharge of chemical laden water is not permitted by law in most countries. It should be treated prior to discharge. Cost of this treatment is very high. This may not yet be legislated in many countries, but it is likely such legislation will come in effect soon, as environment consciousness is on the rise globally. Blow down from ozonized cooling tower does not require any form of treatment because it is totally free from all chemicals.

CONSEQUENTIAL AND INDIRECT ADVANTAGES

Increased Plant Capacity: Due to scale formation in the condenser tubes (with chemically treated towers), discharge pressure of the HVAC compressors always tend to remain high. In an ozonated system, due to elimination or vast reduction of scales on condenser tubes, compressor discharge pressure is lower. This results in savings of electrical energy of the compressors. Besides the power consumption factor, operation of compressor at reduced discharge pressure increases cooling capacity of the installed HVAC system, thus reducing the capital cost of the system, or allowing plant augmentation without additional capital. Operation of compressor at reduced discharge pressure extends life of the compressor, as there is less thermal stress on the system. This prolongs utilization of the invested capital.

Reduction of compressor discharge pressure by 5% results in reduction of power consumption by approximately 7%, and increase of system output capacity by about 3%.
Descaling condenser tubes, typically once a year for chemically treated systems, results in plant down time. Each condenser takes at least 3 days to descale. This is either eliminated or reduced vastly in ozonized system, resulting in better plant and capital utilization.
Frequent descaling reduces life of the condensers, as each descaling results in scrapping metal out of the tubes. Reduction or elimination of descaling results in longer plant life, and better capital depreciation.
Continuous addition of chemicals requires holding of inventory, warehouse space, time of warehouse staff, and upkeep of protocols needed to handle corrosive chemicals. Ozone treatment eliminates all these.
Elimination of bacteria and viruses results in reduced sickness and allergies. This is particularly significant if HVAC fresh air intakes are placed in leeward direction of the tower. Contaminants from cooling tower drift have been recorded several miles away from cooling towers. This is a very important consideration for a public building application.
Condenser tubes and condenser water pipes will always remain clean in an ozonated system. This results in cleaner appearance, hygienic system, reduced maintenance and longer life of the HVAC system. Water in cooling tower basin will be clean and clear, unlike the brown, dirty, mucky water, typically seen in basins of cooling tower working on chemical treatment.

ENVIRONMENTAL BENEFITS

Incredible reduction of water consumption results in water conservation and preserving underground aquifers, our obligation to future generations.
Significant reduction in electrical energy results in reduced use of fossilized fuel, reduction in greenhouse effect, acid rain and global warming.
Draining chemically laden water into municipal drains eventually results in contamination of under ground aquifers. Preservation of national aquifers is of paramount importance for future generations of a countries population. Blow down water from ozonized cooling towers does not impose these problems.
Elimination of bacteria and viruses results in better air quality for the surrounding areas.

Given the prevailing cost of water and electricity, in many countries, we reckon payback period for ozonization of the tower is 2 to 3 years. There after, it is just a profit situation.

FEASIBILITY STUDY

Detailed Feasibility Study and Return and Investment Analysis can be custom provided to suit clients specific requirements, several site specific information is needed to provide the study.

For your specific needs, please contact:

Ruks Engineering Ltd
18 Automatic Rd, Unit 18
Brampton, Ontario
L6S 5N5
Canada

Tel: (905) 789 9652 Fax: (905) 789 0381
email: info@rukseng.com / ozone@rukseng.com

Or Contact Our Distributors

Introduction | Feasibility Study | Specifications | Air as Feed Gas | Drawings | Reference