Short Answer:

Make-up water is the fresh water added to a cooling system, boiler, or condenser to replace the water lost through evaporation, leakage, blowdown, or drift. It ensures a continuous and balanced water level in the system for proper operation.

In simple words, make-up water compensates for the loss of water in circulation systems and maintains efficiency. It is usually treated before use to remove impurities, as untreated water can cause scaling, corrosion, or damage to equipment like boilers and cooling towers.

Detailed Explanation :

Make-Up Water

In any system that uses water for cooling, heating, or power generation — such as boilers, condensers, and cooling towers — some water is always lost during operation. This loss occurs due to evaporation, blowdown, leakage, or drift. To maintain the required water level and ensure continuous and efficient operation, fresh water is added to the system. This added water is known as make-up water.

Make-up water plays a vital role in maintaining the overall water balance in thermal power plants and industrial systems. Without make-up water, the system would lose its cooling or heating capacity and may face operational issues such as overheating or reduced efficiency. Therefore, make-up water is necessary to replace the lost water and maintain steady operation.

Need for Make-Up Water

In a closed water circulation system, such as a cooling water system or a boiler feed system, water loss occurs continuously during operation. These losses include:

1. Evaporation Loss:
   A part of the circulating water evaporates while removing heat in cooling towers or condensers. This evaporated water is lost to the atmosphere and cannot be recovered.
2. Blowdown Loss:
   To prevent salt and mineral buildup, a small portion of water is intentionally drained out from the system. This process is called blowdown and helps maintain water purity.
3. Leakage Loss:
   Water may leak through joints, seals, valves, or pipelines during operation.
4. Drift Loss:
   Small droplets of water may escape along with air in cooling towers. These droplets, though small, contribute to total water loss.

All these losses must be compensated by adding make-up water, which restores the normal operating level and maintains system efficiency.

Sources of Make-Up Water

The make-up water can be obtained from various sources depending on the availability and location of the plant. The most common sources include:

1. Fresh Surface Water:
   Water from rivers, lakes, or ponds is commonly used in large power plants and industries.
2. Ground Water:
   Water drawn from wells or boreholes can be used after suitable treatment.
3. Municipal Water Supply:
   In urban areas, treated municipal water is used as a make-up source.
4. Recycled or Treated Wastewater:
   In some industries, wastewater is treated and reused as make-up water to conserve fresh water resources.

Treatment of Make-Up Water

Before make-up water is added to the system, it must be treated to remove impurities that can cause scaling, corrosion, or foaming inside the equipment. The treatment process depends on the source and intended use of the water.

Typical treatment steps include:

1. Filtration:
   Removes suspended solids, dirt, and debris from the water.
2. Softening:
   Removes hardness caused by calcium and magnesium salts to prevent scale formation in boilers and condensers.
3. Deaeration:
   Removes dissolved gases such as oxygen and carbon dioxide that cause corrosion.
4. Demineralization:
   Removes dissolved salts and minerals using ion exchange or reverse osmosis processes.
5. pH Adjustment:
   The water’s pH is adjusted to maintain neutrality and prevent corrosion or scaling.

Proper treatment ensures that make-up water does not harm system components and helps maintain efficient operation.

Make-Up Water in Cooling Systems

In a cooling tower, a significant amount of water is lost due to evaporation and drift. To maintain the required water level, make-up water is continuously added. The quantity of make-up water depends on the evaporation rate, blowdown rate, and drift losses.

Function in Cooling Towers:

• Compensates for evaporated and drift losses.
• Maintains water level in the cold-water basin.
• Ensures consistent cooling performance.

Example:
If a cooling tower loses 2% water due to evaporation, 1% through blowdown, and 0.2% by drift, then total make-up water required is 3.2% of the total circulating water per cycle.

Make-Up Water in Boilers

In boiler systems, make-up water is required to replace water lost during blowdown and steam leakage. Boiler water must be extremely pure to prevent scale, corrosion, and deposits inside boiler tubes. Therefore, boiler make-up water undergoes rigorous treatment before use.

Function in Boilers:

• Replaces water lost during blowdown and steam formation.
• Maintains required boiler water level.
• Provides continuous feed to generate steam.

Treated make-up water helps achieve longer boiler life, fewer breakdowns, and higher thermal efficiency.

Calculation of Make-Up Water

The quantity of make-up water required depends on total system losses and can be estimated using the formula:

For efficient operation, this water must be continuously monitored and automatically regulated using level sensors and control valves.

Importance of Make-Up Water

1. Maintains water level in boilers, condensers, and cooling towers.
2. Ensures continuous and efficient system operation.
3. Prevents overheating of equipment.
4. Reduces the risk of corrosion and scaling by maintaining water quality.
5. Conserves water through reuse and recycling.

Without proper make-up water, the system may overheat, lose vacuum in the condenser, or suffer reduced efficiency due to high salt concentration.

Conclusion

In conclusion, make-up water is the fresh water added to compensate for losses due to evaporation, blowdown, drift, or leakage in a closed water circulation system. It is a critical part of power plants, boilers, and cooling systems, ensuring continuous operation and efficiency. Since the quality of make-up water affects system life and performance, it must be properly treated before use. A well-maintained make-up water system helps in conserving water, maintaining system stability, and improving the overall performance of industrial and power plant operations.