Question

In an evaporation, the steam consumption is 2000 kg/h for the evaporation of 1500 kg/h of water. The economy of the evaporator is:

• A. 0.75
• B. 1.0
• C. 1.3
• D. 30

Hint:

Evaporator economy is a dimensionless ratio.
For a single-effect evaporator, the economy is always less than \(1.0\) due to energy losses, while multi-effect evaporators can achieve economies greater than \(1.0\) by reusing vapor.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Evaporator economy is a key performance index used to evaluate the steam consumption efficiency of an evaporation system.
It is defined as the mass of water vapor evaporated from the feed per unit mass of steam supplied to the system.
Key Formula or Approach:
The economy of an evaporator is calculated using the formula:
\[ \text{Economy} = \frac{m_v}{m_s} \]
where:
\(m_v\) is the rate of water evaporated (kg/h),
\(m_s\) is the rate of steam consumed (kg/h).

Step 2: Detailed Explanation:
Let us identify the given values from the problem:
Rate of water evaporated, \(m_v = 1500\text{ kg/h}\).
Rate of steam consumed, \(m_s = 2000\text{ kg/h}\).
Substituting these values into the economy formula:
\[ \text{Economy} = \frac{1500}{2000} \]
Simplifying the fraction:
\[ \text{Economy} = \frac{15}{20} = 0.75 \]
An economy of \(0.75\) indicates that for every kilogram of steam supplied, \(0.75\text{ kg}\) of water is evaporated from the product.
This is a typical performance range for a single-effect evaporator, where the economy is always less than \(1.0\) due to heat losses.

Step 3: Final Answer:
The economy of the evaporator is 0.75.