HIGH EFFICIENCY MIST COOLING SYSTEM & INDUCED DRAFT MIST COOLING TOWER

Water Cooling has played an important role in all types of Process industries, Power Plants & Sugar industries, since its inception. Efficiency of a Process plant largely depends on the availability of designed cold water temperature throughout the year, but mainly in summer & monsoon. During these months spray ponds/ cooling towers fail to achieve desired cold-water temperature which results in drop in vacuum at Pan station of a boiling house at a Sugar plant thus increasing batch time and consume higher amount of steam.

Mist creation technology offers a superior alternative, achieving a 1–2°C approach to WBT compared to 5–6°C in conventional systems. This ensures a stable cold-water temperature of around 30°C (at 29°C WBT) year-round in tropical climates, significantly enhancing sugar plant performance. This article will compare cooling systems and highlight the advantages of Mist technology.

In sugar plants, direct contact condensers condense water vapor from vacuum pans and evaporators while maintaining a 25–26 inch Hg vacuum. 

In cogeneration power plants, heat exchangers under vacuum condense turbine steam, allowing condensate recovery for reuse. 

Earlier, vapour/steam condensation was done using river or pond water as a cooling medium. Cold water was pumped through a heat exchanger, and the heated water was discharged back into the source. This open-loop system is known as a Once-Through Cooling System. 

A once-through system is an open-loop system that consumes large amounts of water and contributes to water pollution. With increasing water scarcity and stricter environmental regulations, closed-loop wet cooling systems were developed. These systems recirculate water, reducing both water consumption and pollution. 

In a wet cooling system, water circulates to condense steam or vapor in the condenser. Instead of discharging warm water into a water source, it is cooled using air in a spray pond or cooling tower. Only losses due to evaporation, drift, and blow-down require replenishment, significantly reducing water consumption. 

For direct contact applications, where vapors mix with cooling water, a well-designed system minimizes make-up water requirements. 

TYPES OF WET COOLING SYSTEMS

1. SPRAY SYSTEMS

A spray pond is a reservoir where warm water, typically from power plants, is cooled before reuse by spraying it into the air. Cooling occurs primarily through evaporative cooling (85–90%) and conductive heat transfer. The design ensures maximum contact between water and air for effective heat dissipation. Spray ponds, predecessors to natural draft cooling towers, are less efficient and require 25–50 times more space, though they have lower construction costs.

Nozzles in spray pond:

Spray nozzles in a spray pond are placed 1.5–2.0 m above the water surface, with a spray height of 2.5 m or more, requiring 50–75 kPa pressure. Effective nozzles produce a fine, conical spray (3–6 mm droplets), resist clogging, and allow easy cleaning. Smaller droplets enhance cooling but increase pressure loss and wind-drift.2. Cooling Tower System

Basin size:

Spray pond surface areas range from 1.2 to 1.7 m² per m³/h of water cooled, with 3–4 m drift channels to manage wind effects and prevent water drift. Ponds should be long and narrow, oriented perpendicular to prevailing winds for optimal heat transfer. Depth has little impact on cooling but should be 0.9–1.5 m to accommodate system needs. Drift and evaporative losses typically range from 3–5%.

Thermal performance:

Spray pond thermal efficiency is calculated as (TH – TC) / (TH – TW), where TH and TC are the hot and cold-water temperatures, and TW is the air’s wet bulb temperature. Efficiency typically ranges from 50% to 70%. More details are available in engineering literature.

2. COOLING TOWER SYSTEM

Wet cooling towers cool heated water from surface condensers through evaporation, using either mechanical or natural draft. Most modern towers use mechanical draft with fans to force airflow.

In induced/forced draft towers, fans at the top draw air through side louvers, cooling water as it trickles down. A well-designed induced draft tower achieves a 4°C approach to wet bulb temperature with a 10°C temperature drop. However, efficiency decreases with higher ambient temperature or humidity.

3. MIST COOLING SYSTEM

(TECHNICAL DIFFERENCE BETWEEN SPRAY SYSTEM & OUR REVOLUTIONARY MIST COOLING SYSTEM):

The Mist Cooling System (MCS) by MREPL is a patented technology that maximizes cooling efficiency using evaporative cooling. It creates ultra-fine 5-micron water droplets using water pressure alone, without additional fluids. Mist creator nozzles induce air suction, forming a mist that rises 6–8 meters and cools water close to wet bulb temperature (WBT).

MCS operates at just 1.0–2.5 kg/cm² pressure, ensuring a 1–2°C approach to WBT—far superior to spray systems (6–7°C approach). Unlike spray systems with 5 mm droplets and frequent nozzle clogging, MCS features a choke-free design with a 25 mm nozzle opening. Additionally, MCS requires only one-third the space of spray systems, reducing civil costs significantly.

HOW MCS IS EFFICIENT:

With consideration of Approach to WBT

The cooling tower efficiency can be expressed as

η = [(ti – to) / (ti – WBT)] × 100 

where,

η = cooling tower efficiency

ti = inlet temperature of water to the tower (°C)

to = outlet temperature of water from the tower (°C)

WBT = wet bulb temperature of air (°C)

Let us take an example comparing efficiency of cooling tower & MCS:

MCS achieves 90% efficiency, exceeding conventional cooling towers (69.23%) with a lower WBT approach, thereby enhancing cooling performance and water savings.

VARIOUS MODELS OF MIST COOLING SYSTEM / TOWER TO SUIT SITE CONDITIONS:

MODEL-I: OPEN TYPE MIST COOLING SYSTEM FOR SUGAR PLANT:

Here, MCS ensures an approach of 1ºC to design WBT with a ∆T of 12 to 15ºC Water loss due to drift is 0.1 to 0.25% depending on wind speed.

MODEL-II: LOUVER TYPE MCS FOR SUGAR / CO-GENERATION POWER PLANT (a perfect option for Conventional Induced draft CT):

Here MCS pond is closed from sides, up to a height of 8 to 10 mtrs. by louver type cover sheeting. This reduces the plot size by 60% of open pond design. MCS ensures an approach of 2ºC to WBT with a ∆T of 12 to 15ºC Drift loss comes down to 0.02% and also space requirement reduces considerably.

SALIENT FEATURES OF MIST COOLING SYSTEM (MODEL-I & II):

1. COLD WATER TEMPERATURE: MCS ensures an approach of 1ºC to WBT with a temperature drop of 12 to 15ºC
2. ENERGY SAVINGS: With a greater temperature drop, the process side requires less water. MCS operates at water pressure equal to the cooling tower height, reducing circulation pump energy. Additionally, MCS eliminates the need for fans, further saving significant energy on circulation and cooling.
3. PROCESS BENEFITS: In Sugar Plant: Due to lower cold-water temperature obtained from MCS, MCS ensures better vacuum at pan station with low temperature boiling thus ensuring steam economy. Better quality of sugar and higher exhaustion of Molasses.

In Power Plant: Due to lower cold-water temperature obtained from MCS, higher vacuum can be maintained at the exhaust side of the TG thus ensuring higher pressure drop across the system which in turn results into more energy output or reduced steam input.

HENCE INSTALLATION OF MCS WILL ENSURE LARGE COMMERCIAL BENEFITS TO YOU IN FORM OF ADDITIONAL PRODUCT OBTAINED AT A HIGHER YIELD.

4. MAINTENANCE: MCS has no moving parts and is made of special-grade saran polymer, a highly non-corrosive material with a lifespan of 10-15 years, making it maintenance-free. In contrast, cooling towers require frequent maintenance, including yearly replacement of louvers, fan blades, and clamps.
5. CHOKELESS DESIGN: MCS has a choke-less design with openings larger than 1 inch (25 mm), reducing the risk of clogging.
6. SYSTEM FLEXIBILITY (CAPACITY TURN DOWN RATIO): We offer MCS with individual line isolation valve. MCS is the only system which gives you such high flexibility in operation.
7. CHEMICAL TREATMENT: Chemical dosing requirements are similar to that of cooling tower as same hold up of water is maintained in suction pit due to Tabletop design of basin.
8. MAKE-UP WATER REQUIREMENT: Due to latest Louver Type design, drift loss through MCS is reduced to 0.05% while maintaining an approach of around 2ºC to wet bulb temperature. Hence, Overall make-up water quantity required is approximately same as compared to cooling towers.
9. PAYBACK PERIOD WILL BE OBTAINED IN LESS THAN ONE YEAR ONLY CONSIDERING ALL ABOVE BENIFITS OF THE MCS.

MODEL-III: INDUCED DRAFT MIST COOLING TOWER (IDMCT) (Fill less design):

Model-I & Model-II require higher basin size by 3 to 4 times in comparison to conventional IDCT. To eliminate this drawback, for the first time in the world, we have combined the technology of Mist Creation with induced draft Fan thus cooling the water most efficiently. This uses our Patented Technology of Mist Creator Nozzles. Mist Creator Nozzles break water in micron size, thus giving the highest surface area for heat transfer.

This technology eliminates fills in the cooling tower, making it maintenance-free. The absence of fills reduces air pressure drop, lowering fan power consumption by 30-50% compared to conventional cooling towers.

Models are available from 50 m3/hr to 3000 m3/hr with an approach of 3ºC to design WBT & temperature drop of up to 15ºC.

SALIENT FEATURES OF INDUCED DRAFT MIST COOLING TOWER (MODEL-III):

1. An approach of 3 to 4ºC is ensured to design WBT with a temperature drop up to 15°C.
2. No FILLS used as required surface area is created by Mist Formation.
3. Footprint required is same as compared to Conventional IDCT.
4. Rugged structure with Pultruded FRP/ HDGI MOC and FRP casing with Stainless Steel 304 Nozzles, ensuring a life of 15 + years.
5. Choke less design of our Mist Creator Nozzles ensure a maintenance free operation for lifetime. Guaranteed designed performance even in summer & monsoon.
6. IDMCT requires same make up water in comparison to conventional IDCT.
7. Guaranteed designed performance even in summer & monsoon.

We also refurbish conventional induced draft cooling towers into induced draft mist cooling towers by installing our revolutionary Mist Creation System. The fills are completely removed, as our nozzles perform the fill’s function with higher efficiency.