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Cooling Towers: Efficiency. Energy Saving. Cost Effectiveness.

by V.B.Ivanov, Engineer, OOO ENERGOKHRAN, Smolensk, Russia; E.A.Svidersky, Patent Agent № 020, Minsk, Belorussia

In our previous article “Energy Saving and New Fluid Cooling Technologies Applied in Spray-Filled Cooling Towers with Dynamic Cooling” published in early September 2008 at www.energospace.ru, www.gradirnia.ru and other web-sites, we reviewed the principles, advantages and disadvantages of filled and spray-filled cooling towers.

In this article, we will talk about performance efficiency, energy saving and cost effectiveness potential of cooling towers.

The cooling towers that we have inherited were designed and built to a leftover principle which in those times predetermined the selection of so-called support equipment. Low cost was the key consideration in the design, construction and commissioning of support equipment. It was a bad practice and we now need to correct its consequences.

The authors believe that a cooling tower is an independent and complex heat engineering plant. It would appear unwise to spend money on a high-tech, super-efficient manufacturing process without providing certain engineered necessities to support the process. We think that it is a wrong approach to divide equipment into main and auxiliary plants and it should be abandoned.

In most manufacturing organizations, cooling towers were the responsibility of the power supply department. It used to be a typical situation when there would be a shortage of cooling capacity causing an ever-lasting conflict of interests between the company’s power supply department and process divisions. The conflict would heat up as the warm season would begin and cool off the next autumn until the next spring.

As time changed and new owners came to manufacturing enterprises, most far-sighted owners let cooling towers be run by the operations department. In many instances that helped mitigate the cooling capacity problem. Companies started to use new materials and equipment to cool water, mainly, new fills, new jacketing materials, controlled-capacity fans. Today, there is a tendency to exceed design capacities of manufacturing plants through improved, upgraded and intensified production processes, so modern water cooling technologies have become important in implementing the new approach.

Capacity growth has appeared mostly tangible at column-type equipment (distillation, rectification etc.), reactors, multi-case vacuum evaporators, coolers and compressors, in ferrous and non-ferrous metallurgy.

The history of cooling towers has always been a struggle for greater heat and mass surface areas. It was over the life time of just one generation that water cooling intensity grew by 10 to 15 percent. New highly efficient fills and controlled-capacity fans have found their way to the market. However, no more growth of heat and mass surface areas is expected in filled cooling towers as the apparent limit of the fill surface area has been reached. If more fill cells were to be added, air drag would increase entailing increased fan motor power. Plus more fills would become even more expensive.

What we need is new approaches toward highly developed cooling surfaces in cooling towers, preferably dynamic surfaces. We need a qualitative leap similar to internal combustion engines breakthrough from carburetors to direct fuel injection. This may be a far-fetched but a descriptive analogy.

The most effective means of creating a highly developed dynamic surface of heat and mass exchange in the cooling tower would seem to be a uniform flow of fast-moving droplets whereby the motion vectors of droplets and cooling air should not coincide with each other. Long run tests have led to the development of centrifugal jet nozzles ensuring a highly efficient spraying of water with preset water droplet fractional sizes in what has become known as a spray-filled fan-induced draft cooling tower (Russian Patent №2228501 “Cooling of Fluids in Cooling Towers”, Patent №2144439 “Centrifugal Jet Nozzle”, Eurasian Patent № 6902 “Cooling Tower”, Eurasian Patent № 7724 “Fan-Induced Draft Cooling Towers”).

This new cooling method helps us meet three key requirements which are responsible for a cooling tower’s efficiency:

1. Uniform water distribution.

2. Uniform air supply and distribution.

3. Maximum filling of the cooling tower’s interior volume.

What are the specific advantages an owner would have should he abandon the fill material and install a water spray system in the plane of air intake windows? A major operating expense item for cooling towers is the pumps’ electric power demand to lift water to the height of 7 to 12 meters. Ejection spray nozzles installed at the height of 1.0 to 2.0 m would save up to 50% power. To lift an ex-amount of water to the said height, this much power must be consumed:

E=mgh

where ‘m’ is the mass of water in kg, ‘g’ is the free fall acceleration and ‘h’ is the height in meters.

As we can see, a 10 m height reduction would decrease work and, hence, electric power consumption. Experience has shown that in this case the existing pump motors can be substituted with less powerful motors. However, clients are willing to boost cooling towers capacity without having to sacrifice cooling quality. As we saw in our earlier presentations, a 50 to 100 percent increase in the heat and mass surface area would ensure a higher cooling capacity. Also, some depression occurs in the plane of air intake windows owing to air being ejected by sprayed water. This, in its turn, allows to increase cool air flow into the exchange area and reduce power consumption by the fans. With more cooled recycle water and less costs to cool it, the recycle water becomes cheaper and so does the cost of production of the end product. That equipment gets positively cooled by the recycle water helps avoid end product quantity and quality losses. The above considerations can be supplemented by that spray-filled cooling towers also help forget about equipment shutdowns due to clogging with fill destruction and biofouling products.

According to ESCO (see “Environmental Systems” e-magazine, book 6, June 2005), improperly operated cooling towers can be responsible for more than a 50 percent increase in company’s current expenses. Thus, we can estimate that effective cooling costs could be reduced by 30 to 60 percent, taking account of commercial production output growth. On top of the said fixed savings, we can also mention the following single savings:

1. Fill cost.

2. Fill mounting costs (material and mechanical completion costs are approximately worth the fill cost).

3. Water distribution system cost. (The offered water distribution system will cost 20 to 40 percent of the standard water distribution system.)

All in all, after the cost of cooling tower upgrade has been deducted, the client would save anywhere from 40 to 60 percent of the total cost of the three items above.

In winter, 50 to 70 percent of water enters the tower via winterized channels and fans are not required as the nozzles easily manage ejection cooling. The risk of frosting in winter is eliminated. A two to five 0C higher cooling capacity in spray-filled cooling towers will allow two to three percent fuel savings at heat power stations.

One of the key issues of cooling towers operation is droplets entrainment. According to SNiP 2.04.02-84* paragraph 11.49, water and droplets carryover shall not exceed 0.1 to 0.2 percent of the recycle water flow. The no-fill option would see higher air velocities through the tower which would result in increased droplet entrainment. However, this can be avoided by installing a water catchment device at a distance exceeding 0.5 diameter of the fan. This solution will take you out of the area of high air velocities and high depression created by the fan. If needed, a second water catchment device would not cost you much.

So, efficiency, energy saving and cost effectiveness challenges are all closely connected and can be met through a proper water cooling technology. History tells us that new technologies always provide for quantitative and qualitative performance growth for less or same money.

When supplemented with varying capacity fans, water correction system, flame-proof tower jacket, this ideal cooling tower solution would bring confidence and peace of mind to companies’ operations personnel and cost accountants.

All of our inventions are patented in Russia, Belarus and the Ukraine and protected by Eurasian patents as follows:

Russian Patent №2144439 - “Centrifugal Jet Nozzle”

Russian Patent №2166163 - “Ejection Cooling Tower”

Russian Patent №2228501 - “Cooling of Fluids in Cooling Towers”

Russian Patent №31639 - “Cooling Tower"

Eurasian patent № 6902 - “Cooling Tower"

Eurasian patent № 7724 - “Fan-Induced Draft Cooling Tower”

Belarus Patent № 3450 - “Cooling Tower"

Belarus Patent № 5604 - “Centrifugal Jet Nozzle”

Ukrainian Patent № 42892 - “Ejection Cooling Tower”

Please visit http://gradirnia.ru for cooling tower drawings, reports and our patents.