ANS:A - steam economy

Multiple effect evaporation accounts for:

1. Steam economy: By utilizing the vapor generated in one effect to heat the feed in the next effect, multiple effect evaporation significantly reduces the amount of external heating steam required, leading to improved steam economy.
2. Lower operating costs: Due to the reduced steam consumption and energy savings achieved through multiple effect evaporation, operating costs are lower compared to single-effect evaporation systems.
3. Investment economy: Although the initial investment cost for multiple effect evaporation systems may be higher than for single-effect systems, the long-term cost savings in terms of reduced steam consumption and lower operating costs often result in an overall economic benefit, thus contributing to investment economy over time.