ANS:A - large scale evaporation of liquor is needed.

Multiple effect evaporation is generally recommended when fuel is cheaply available. Explanation:

1. Multiple Effect Evaporation: In multiple effect evaporation, vapor from one evaporator effect is used to heat the liquid in another effect, thereby creating a series of evaporators (effects) arranged in sequence. This arrangement allows for the reuse of heat energy, resulting in improved energy efficiency compared to single-effect evaporation.
2. Reasons for Recommendation:
   • Cheap Fuel Availability: Multiple effect evaporation is particularly advantageous when fuel is readily available and inexpensive. Since this process relies on heat input to drive evaporation, having access to low-cost fuel sources makes the operation more economically viable.
   • Energy Efficiency: By utilizing the latent heat of vaporization from one effect to heat the liquid in subsequent effects, multiple effect evaporation significantly reduces energy consumption compared to single-effect evaporation. This is especially beneficial when fuel costs are low, as the savings in energy costs outweigh the initial investment in multiple-effect equipment.
   • Scalability: While multiple effect evaporation can indeed handle large-scale evaporation processes efficiently, it is also suitable for smaller-scale operations. However, the economic benefits of multiple effect evaporation are more pronounced at larger scales due to the higher initial capital investment required for multiple-effect equipment.
   • Corrosive Liquids: While multiple effect evaporation can be used to concentrate corrosive liquids, this factor alone does not necessarily dictate the preference for multiple effect evaporation. The primary consideration is the availability and cost of fuel, which significantly impacts the overall operating costs and feasibility of the evaporation process.

In summary, multiple effect evaporation is generally recommended when fuel is cheaply available due to its energy efficiency and cost-effectiveness. However, it can also be utilized for concentrating corrosive liquids and is suitable for both large-scale and smaller-scale evaporation processes.