Preservation of Capex Towards Industrial Cooling Towers

Awareness of capex preservation is increasing amongst asset owners. By using the latest developments in Protective Coating technologies, they are avoiding expensive Repair & Rehabilitation expenses, and thereby reducing the Life Cycle Cost of massive assets such as the Industrial Cooling Towers.

Anupam Shil
Anupam Shil, Head – SBU (Protective Coating), STP Limited

Industrial Cooling Towers are used to remove heat through evaporation of water in a moving air stream being carried from various sources such as a machinery or some heated process material. Their main use is to remove the heat absorbed in the circulating cooling water used in large processing units, such as power plants, refineries, petrochemical plants, steel plants, fertilizer and chemicals plants, etc. They serve to dissipate the heat into the atmosphere and air diffusion distributes the heat over a much larger area as compared to what hot water can distribute heat in a larger body of water.

Few coal-fired and nuclear power plants located in coastal areas make use of once-through sea water for cooling. In such a set-up, the discharge water outlet system requires very careful design to avoid environmental problems by causing disturbance in the aquatic life.

Industrial Cooling Towers

Based on the method adopted to circulate the air, cooling towers can be classified as:
  1. Natural Draft Cooling Tower (mostly used in large power plants).
  2. Induced Draft Cooling Tower, which can further be sub-divided into a variety of modified designs based on their intended utility.
The circulation rate of cooling water in a 700 MW coal-based power plant is typically about 71,600 cubic meters an hour and the circulating water requires a supply water make-up rate of approximately 5 percent (i.e., 3,600 cubic meters an hour). Most petroleum refineries also have very large cooling tower systems. A refinery processing 40,000 metric tons of crude oil per day (i.e., 3,00,000 barrels or 48,000 m3 per day) circulates about 80,000 cubic meters of water per hour through its cooling tower system.

In fact, the world's tallest cooling tower 'Kalisindh Super Thermal Power Project' (KATPP) is at Jhalawar, Rajasthan. It is a 600 MW x 2 capacity unit encompassing two 202 meters (663 ft) tall cooling towers.

Such massive water handling requires equally expansive water containing concrete structures. A sizable capital expenditure budget is allocated towards these, as they are an inevitable part of the processing system. As prudent investors, it is important that preservation of these valuable assets is contemplated and effectively planned.

disintegration of concrete
This figure is a concise depiction of various forces which results in disintegration of a concrete structure with time.

In the last few decades, accelerating consumerism and its demands on the construction sector has posed serious questions in terms of availability of high-quality raw materials, which are essential for a structure to have a long and dependable life. The limited natural resources cannot suffice for this rate of growth versus the rate of depreciation that has surfaced due to several nations growing together at a fast pace. Most of the construction materials that are being used today and consumed in enormous quantities, after completion of their service life do not remain by nature, recyclable; the finest example being Concrete. The speed at which depletion of these resources are taking place demands serious attention towards finding ways and techniques to mitigate this threat by implementing proactive solutions that can keep structures healthy and longer-lasting.

While at the time of construction, water is an essential element to initiate the process of hydration, once the construction is over, ingress of water into concrete results in these chemical changes within a structure that eventually results in its ageing.

STP Article

  1. ASR (Alkali Silica Reaction) – One of the most important chemical reactions that take place in an alkaline environment within the concrete with its fine or coarse aggregates is ASR. This results in conversion of the available amorphous silica to a gel form, which not only creates internal stresses within the structure due to volumetric expansion, but also acts as reservoirs due to its inherent tendency to absorb water.
  2. Carbonation – Sometimes also referred to as the corrosion of concrete, it is a chemical reaction occurring between calcium hydroxide present inside the cement (post hydration) with Carbonic acid (formed by reaction of atmospheric carbon with moisture/water). This results in formation of Calcium Carbonate (Chalk) and free water. Even though this transformation forms a compound that has significant compressive strength, it reduces the pH environment (state of passivity) within concrete, making the rebar more corrosion prone, while also transforming the crystalline structure of Ca (OH)2 to amorphous CaCO3.
  3. Acid Attack – Increasing industrial emissions into the atmosphere contains a large reserve of SOx and NOx pollutants. These combine with atmospheric moisture (clouds) to form various acids like Sulphuric/Sulfurous acids, Nitric/ Nitrous acids, etc. During rains, these mild acids come down to start acid-alkali reactions within a cementitious body, thus resulting in breakdown of the crystalline lime within a concrete.
  4. Freeze-Thaw – In colder regions, due to atmospheric temperature dropping to sub-zero levels, water trapped inside concrete expands while it freezes. This causes internal stresses and such repeated cycles cause cracking and eventually spalling of concrete chunks, thus, disintegrating the structure.
  5. Rebar Corrosion – Water ingress into concrete acts as an electrolyte resulting in ionic exchange between Iron rebar and oxygen. This results in corrosion of the rebar, causing reduction in its tensile strength and at the same time generates internal stress due to swelling of the rebar.
A closer look will reveal that all the above five causes are mainly due to ingress of water/moisture through surface cracks and the labyrinth of micro pores and nano-capillaries within a concrete structure. Water, while it sustains life, also acts as the most destructive element that has the power to disintegrate a compound back to its elemental form. Due to this fact, application of Protective Coatings ensure that a civil structure remains waterproofed, has emerged over the years as a proven solution to enhance its useful service life. Thus, more dependable coating technologies are being adopted to protect concrete structures, starting from foundation to the rooftop.

We know that the presence of an electrolyte and potential difference between two connected zones through a metallic pathway causes loss of material at the anodic location, and results in corrosion of metal. Similarly, ingress of water/moisture in cured concrete brings about several chemical changes causing its gradual disintegration. However, when it comes to protection of metals, much more extensive guidelines are being accepted and adopted globally like the ISO:12944 which provides painting system guidelines for corrosion protection of steel structures. Concrete, on the other hand, has been covered with surface preparation standards (by International Concrete Repair Institute); however, the industry yet awaits a universally accepted global standard, providing guidelines for surface coating of concrete structures.

Coating technologies have travelled from age-old bitumen to coal-tar to epoxies to polyurethanes. Coal tar mastic initially superseded in terms of performance against bitumen due to its resistance against soil bacteria and root infiltration, especially for underground applications. Eventually, the hybrid formulations, where coal tar base was used as epoxy resin filler in combination with phenalkamine hardeners, delivered high performance coaltar epoxy coatings at a much affordable price.

Cooling Towers

Then the chemistry of solvent-free formulations gave a new dimension to the protective coating technology by delivering coatings with extremely low micro-porosity. Thin aliphatic polyurethanes augmented well to all grades of epoxies by providing them good UV protection. And with the advent of 100% Solids, High-build, UV resistant PU coatings, preservation of critical concrete structures for decades has been conceptualized.

Last year, a thermal power plant in its expansion project at Tamil Nadu approved to protect the NDCT slanted raker columns with ShaliUrethane PC (2K Zero VOC UV Resistant Polyurethane Protective Tough Coating).

A gas-based power plant in Maharashtra approved to protect its more than a decade-old IDCT basin with ShaliUrethane PC (2K Zero VOC UV Resistant Polyurethane Protective Tough Coating); its concrete structures exposed to moisture and sunlight protected with ShaliPoxy HB (2K Protective Flexible Epoxy Coating); followed by a UV-resistant top coat of ShaliUrethane PU TC 2K (2K Aliphatic Polyurethane UV Resistant Top Coat).

Structural repairs of damaged concrete in such Repair & Rehabilitation projects are carried out using either ShaliFix EM (3K Epoxy Mortar) or ShaliFix FRM (Polymer Modified Fiber Reinforced Mortar) after applying compatible bonding primers like ShaliBond Concrete or ShaliSBRLatex. In case of spalled concrete exposing rebar sections, adequate treatment of rebars with ShaliPrime Zn R (2K Anti-Corrosive Zinc Rich Primer), after neutralizing with ShaliPrime RC (1K Water Based Rust Convertor), and refurbishment of spalled section with ShaliFix MC (High Performance Cementitious Repair Micro Concrete) is carried out.

NBM&CW February 2019

Repair & Rehabilitation of Concrete Structures - A Paradigm Shift

Repair and rehabilitation of rapidly deteriorating structures is a matter of concern for most countries in the world. Deterioration is observed in the form of cracking and corrosion (Riveros et al., 2018). It is very difficult to Read More ...

India's Repair Industry Needs a Responsibility Criteria

In India, the repair industry is not organized, hence, the exact numbers on annual cost to owners/public funding for repair, protection & strengthening are not available. Today, India is placing new concrete to the tune of Read More ...

Rehabilitation of Overstressed Rigid Pavements

Due to shortage of resources like cement as well as finances, hardly any concrete roads were constructed in free India, though, in the long run they are cheaper than bituminous roads, was an established fact. Some internal Read More ...

Concrete Repair: Principles from EN 1504 and Practical Considerations

Many a times, even after taking all the due precautions and all quality control measures, Concrete structures deteriorate. One of the practical reasons is due to the fact, that at the time of planning or at the design table Read More ...

Repair & Rehabilitation to improve life-span of buildings

Across Indian cities, there are millions of old buildings that are in a dilapidated condition. In Mumbai alone, there are 14,375 dilapidated structures across the city and another 10,500 in the suburbs. Such structures pose an Read More ...

Repair/Rehabilitation of Structure

UPV Test in Progress
A structure, when it is constructed, has generally got a service life. The service life is dependent on the quality, workmanship of the construction and various other factors including materials, components, Read More ...

Remedial measures for reinforced concrete structures using cementitious materials

Remedial Measures for Reinforced Concrete Structures
An essential part of a successful repair of concrete structures, is to establish the underlying cause and extent of concrete deficiency, and deterioration mechanism. For a repair to be successfully completed, Read More ...

Latest Techniques for Repair & Rehabilitation- A Perspective

Latest Techniques for Repair Rehabilitation
For a successful repairing work of a structure, the most vital things to be considered are identification of the root cause, selection of the right products & methods, proper repairing of the damage by skilled Read More ...

Durable Repairs State-of-the-art Corrosion Mitigation Techniques

Steel Protected in Carbonated Concrete
Most of today's concrete construction relies on the composite interaction of concrete and steel, which is aided by the near equivalence of their thermal expansion characteristics Read More ...

Concrete Repair: Principles, Guidelines and Practical Considerations

Steps For Repair
India has witnessed a tremendous spurt in construction over the last couple of decades. Residential, Commercial, Industrial and Infrastructure construction and expansion has been progressing Read More ...

Polymers blend for repair applications (Epoxy resins & polymers)

Micrographs of Polymer Blends
Epoxy resins are widely used as highly cross linked materials in various repair applications where special performances such as good mechanical, thermal and electrical properties are required Read More ...

Concrete structures repair & Rehabilitation - Causes of Distress & its Solution

Concrete Degradation
CONCRETE DEGRADATION may have various causes & reasons. It can be damaged by factors like fire, alkali - aggregate reaction expansion, sea water effects, bacterial corrosion, calcium leaching, physical Read More ...

Soil Strengthening – Use of Pressure Injection Grouting as a means of Improving Load Bearing Capacity of Existing Foundations

Ejection of Underground Water
This Paper describes the procedure for improving the Load bearing capacity of the foundations by means of strengthening the soil under and around the foundations. Use of Injection grouting in the Read More ...

Retrofit of R.C. Beams & Columns

Finite Element
During the last week of March a few years ago, author was invited by a certain Company in an Indian city to review and advise upon measures to strengthen the ground floor and basement beams and columns Read More ...

Stainless Steel Rebar: A Necessity for Coastal Regions

Ferritic Stainless Steel
Both stainless steel and carbon steel derive their corrosion resistance from a naturally occurring chromium rich oxide film, which is present on its surface. This invisible film is inert, tightly adherent Read More ...

Rigid Pavement Repair and Maintenance Strategies

Rigid Pavement Repair
The rapid growth in road construction brought about considerable expansion of road infrastructure, which subsequently fell into disrepair through lack of maintenance. The damage is Read More ...

New Building Material & Construction World

New Building Material & Construction World
MGS Architecture

Modern Green Structures & Architecture

Modern Green Structures & Architecture

Lifting & Specialized Transport

Lifting & Specialized Transport

Indian Infrastructure & Tenders Week

Indian Infrastructure & Tenders Week