By Rainer Haug, Senior Product Manager – Cooling & Drinking Water Products, Kurita Europe GmbH
Keeping cooling towers and heat exchangers FReE from fouling deposits
Protection of cooling systems requires the use of various specific treatment products to make sure the whole cooling system and the various materials it is being built from are not attacked by corrosion or affected by different types of possible deposits.
The Cooling Labyrinth
In general, a cooling system compromises two types of equipment: A cooling tower that removes the surplus heat through evaporation and one or more heat exchangers which transfer the heat quickly from the process to the cooling water.
The cooling tower again has two main sections: The actual tower with its delicate plastic parts as filling material and the cooling water basin on which the tower is placed and where the cooled water is collected after running through the tower.
In the upper cooling tower, the warm water is distributed through a spraying system onto the filling packages. Here the water enters a kind of labyrinth starting at the top, the only exit being the basin at the bottom. The water itself is flowing down by gravity as a relatively thin layer on the large surface of the plastic filling. In addition, the filling construction is made in a way to allow the cooling water a long contact time with the air, resulting in slow flow velocities of the water on its way down to the basin.
Counter flowing to the water, on its way through the labyrinth, is the air. The airstream ensures partial evaporation of the cooling water, which results in the actual cooling effect. As the heat exchange itself is achieved by partial evaporation of the warm cooling water into the air stream, the evaporation also results in a concentration effect of the minerals and salts which are staying in the downflowing cooling water. In addition to the above, the air itself also contains particles, which are washed out and dispersed in the cooling water as suspended solids.
All the above add together to create quite critical challenges, including the risk of fouling and formation of deposits. Those are especially concerning inside the hard-to-reach cooling tower filling labyrinth, several factors come together in one place: mineral salt concentration increase, availability of fouling material, large surfaces, and low flow velocity. It is therefore essential to keep the fillings FReE of deposits by proper treatment to ensure a smooth tower operation.
The second part of a cooling system is one or even several heat exchangers. Also, the heat exchangers need to be kept clean to ensure a good heat transfer. While the right water flow rate through a heat exchanger in addition to the use of antiscalants like Kurita’s Turbodispin® D – type of polymers suppresses the formation of deposits on the heat transfer surfaces, active corrosion protection is essential to prevent the metal from being corroded.
Depending on the industry heat exchangers can be made from different types of metals. Depending on the metal which had been used for the construction of the heat exchanger different types of corrosion inhibitors need to be applied. Especially for copper and brass heat exchangers Azole based products for a long time have been and still are the current benchmark.
Kurita´s Fouling Removal Efficiency program FReE keeps cooling systems clean of various deposits. Even further it has been specially developed to remove them online, starting from biofouling but also including mineral scales like Al Silicates, Calcium carbonate, and -sulfates.
At the same time, using Kurita´s own film forming technologies FReE protects the cleaned surfaces, and especially those of copper or other yellow metals, with an azole-free product from corrosion.
While it is a common understanding that both deposit prevention and corrosion inhibition are necessary for all systems the specific need for different systems may vary depending on the industry the cooling system is used in. Kurita FReE cleaning and protection technology enables to tailor the program and adjust it to the need of the different industries and heat exchanger construction materials.
Using Kurita´s large know-how on applying film-forming technologies in different kinds of applications Turbodispin® 4363 has been developed to protect cooling systems from biofilms and to apply an active corrosion inhibition for copper and other yellow metal materials.
It can replace traditional biodispersants and copper inhibitors with special filming technologies. The treatment itself is further reinforced by Kurita’s special range of polymers for inorganic deposits and suspended solids, the Turbodispin® D series.
Turbodispin® 4363 is an Azole free three functional product that helps to keep heat exchanger and cooling tower surfaces clean from organic deposits and at the same time provides active corrosion inhibition of yellow metal surfaces.
Applications of FReE in cooling systems, as well as lab data, show that effective and even superior corrosion protection of copper and copper-based alloys as compared to the treatment with azoles. Corrosion rates of copper have been reduced by up to 30% ensuring a longer lifetime of the heat exchanger being in place.
Kurita’s Turbodspin® 4363 technology is based on a filming technology showing several advantages. It is used to remove biofouling and acting as a dispersing agent, which works without modifying the surface tension of the water. The dispersant and bio-dispersant effects are obtained as thermodynamically the active groups of the filmer agent have a higher affinity for the metallic surfaces than the biofouling or corrosion products. Turbodispin® 4363 penetrates the deposits slowly and therefore disperses slowly the deposits themselves or parts of it. The remaining deposits, due to their now porous structure, become fragile and also is removed step by step through the supporting dispersant for the inorganic matter.
Due to the high affinity of the active ingredients towards the metallic surfaces a complete film corrosion protection “barrier” is formed especially on Copper. The barrier effect will minimize the impact of any critical situation as a physical (molecular) layer is created between the metal surface and the water.
As a further advantage, FReE Technology can also be combined with any other Kurita water treatment program.