Question:
In Seven-effect evaporator with a thermo-compressor, which of the following is possible to evaporate?
In Seven-effect evaporator with a thermo-compressor, which of the following is possible to evaporate?
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The steam economy of an $N$-effect evaporator is roughly $N$. Adding a thermocompressor (TVR) increases this economy by about 1.5 to 2 units, bringing a 7-effect system's economy to approximately 9.
Updated On: Aug 7, 2026
- 2 kg water with 1 kg steam
- 12 kg water with 1 kg steam
- 8 kg water with 1 kg steam
- 9 kg water with 1 kg steam
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The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
In dairy plants, evaporators are used to concentrate milk before spray drying.
To reduce energy consumption, multiple-effect evaporators are used, where the vapor produced in one effect is used as the heating medium in the subsequent effect.
The efficiency of an evaporator is measured by its steam economy, which is defined as the mass of water evaporated per kilogram of live steam supplied.
Key Formula or Approach:
For a basic multiple-effect evaporator, the theoretical steam economy is approximately proportional to the number of effects ($N$):
\[ \text{Steam Economy} \approx N \text{ kg water / kg steam} \]
Adding a thermal vapor recompressor (thermocompressor) recirculates a portion of the waste vapor by mixing it with high-pressure live steam, which increases the overall economy of the system.
Step 2: Detailed Explanation:
In a basic seven-effect evaporator, 1 kg of live steam can theoretically evaporate approximately 7 kg of water.
When a thermal vapor recompressor (TVR) is added to the system, it entrains a portion of the water vapor produced in the first effect and compresses it back into the heating chest using high-pressure steam.
This thermal recompression increases the steam economy of the system by approximately 1.5 to 2.0 times the equivalent of a single effect.
Therefore, a seven-effect evaporator with a thermocompressor can achieve a steam economy of:
\[ \text{Economy} \approx 7 + (1.5 \text{ to } 2) \approx 8.5 \text{ to } 9 \text{ kg water / kg steam} \]
This means that using 1 kg of live steam, it is possible to evaporate approximately 9 kg of water from the milk.
Thus, option D is the correct choice.
Step 3: Final Answer
In a seven-effect evaporator with a thermocompressor, it is possible to evaporate 9 kg of water using 1 kg of steam.
In dairy plants, evaporators are used to concentrate milk before spray drying.
To reduce energy consumption, multiple-effect evaporators are used, where the vapor produced in one effect is used as the heating medium in the subsequent effect.
The efficiency of an evaporator is measured by its steam economy, which is defined as the mass of water evaporated per kilogram of live steam supplied.
Key Formula or Approach:
For a basic multiple-effect evaporator, the theoretical steam economy is approximately proportional to the number of effects ($N$):
\[ \text{Steam Economy} \approx N \text{ kg water / kg steam} \]
Adding a thermal vapor recompressor (thermocompressor) recirculates a portion of the waste vapor by mixing it with high-pressure live steam, which increases the overall economy of the system.
Step 2: Detailed Explanation:
In a basic seven-effect evaporator, 1 kg of live steam can theoretically evaporate approximately 7 kg of water.
When a thermal vapor recompressor (TVR) is added to the system, it entrains a portion of the water vapor produced in the first effect and compresses it back into the heating chest using high-pressure steam.
This thermal recompression increases the steam economy of the system by approximately 1.5 to 2.0 times the equivalent of a single effect.
Therefore, a seven-effect evaporator with a thermocompressor can achieve a steam economy of:
\[ \text{Economy} \approx 7 + (1.5 \text{ to } 2) \approx 8.5 \text{ to } 9 \text{ kg water / kg steam} \]
This means that using 1 kg of live steam, it is possible to evaporate approximately 9 kg of water from the milk.
Thus, option D is the correct choice.
Step 3: Final Answer
In a seven-effect evaporator with a thermocompressor, it is possible to evaporate 9 kg of water using 1 kg of steam.
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