ANS:D - all (a), (b) and(c)

1. Low Hardness: Hardness in water refers to the concentration of minerals, primarily calcium and magnesium ions. Water with high hardness can lead to scale formation in boilers, reducing efficiency and potentially causing damage to equipment. Steam condensate typically has low hardness because it originates from pure steam, which contains minimal minerals. Using steam condensate as boiler feed water helps minimize the risk of scale buildup.
2. Low Dissolved Solids Content: Dissolved solids refer to minerals, salts, and other substances that are dissolved in water. These solids can include various ions such as calcium, magnesium, sodium, and chloride. High levels of dissolved solids can contribute to scale formation, corrosion, and other issues in boiler systems. Steam condensate has low dissolved solids content because it originates from pure steam, which does not contain significant amounts of dissolved substances. Recycling steam condensate for use as boiler feed water helps maintain water purity and minimize the risk of scale formation and corrosion.
3. Suspended Solids Content: Suspended solids refer to particles or matter that are present in water but are not dissolved. These solids can include dirt, sediment, rust, and other debris. High levels of suspended solids can cause fouling, blockages, and damage to boiler equipment. Steam condensate is typically free from suspended solids because it is produced from the condensation of pure steam, which is free from particulate matter. Using steam condensate as boiler feed water helps ensure the absence of suspended solids, thereby reducing the risk of fouling and damage to boiler components.

In summary, steam condensate is recovered and recycled for use as boiler feed water primarily because of its low levels of hardness, dissolved solids, and suspended solids. This helps maintain water purity, prevent scale formation and corrosion, and ensure the efficient and reliable operation of boiler systems.