Comparison between three-effect evaporation and two-effect + single-effect evaporation
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To save steam, we generally use multi-effect evaporation (such as three-effect), but in many cases two-effect + single-effect evaporation is employed, where the two-effect system makes use of secondary steam while the single-effect system uses direct steam. What is the purpose of doing this? Why not use a three-effect system directly? This is the most steam-efficient approach. Although a single-effect system can also achieve the desired results, its energy consumption is high. Could an experienced friend please explain this? Thank you.
The three-effect evaporation process has a long duration and requires a higher temperature level from the heat source.
This is determined by the properties of the material and the material of the equipment; some materials are not suitable for triple-effect evaporation.
First-effect evaporation is quite simple; direct steam makes it easy to control. In triple-effect evaporation, the steam pressure decreases gradually in subsequent effects, and the temperature also drops
This is determined by the thermosensitivity of the material being evaporated, as well as by the crystallization and viscosity of the concentrate. It offers dual-effect energy savings, but the single-effect version provides better control over material concentration and heating time.
The main purpose is to make dual use of secondary steam, with single-effect supplementation or adjustment of the evaporation rate. Moreover, it is simple to operate and control, which is a continuation of the old-fashioned traditions.
Also, the evaporation amount is very low, and the volume to be processed is small; direct evaporation is sufficient, so there’s no need to go any further
Yes, my process involves treating 5 tons of water per day
The more stages there are in this series, the more economical it becomes; energy consumption is lower, but more equipment is required, the failure rate increases, and the frequency of operational adjustments also rises. The choice depends on the operational needs – if the system has excess energy available, then two-stage or three-stage systems can be considered; after all, there’s a lot of heat available. If energy savings are the goal, then two-stage or three-stage systems are preferable. In both cases, the steam generated in the previous stage is used as the heat source, which results in lower energy consumption. To give a simple illustration: to evaporate 1 ton of water, a single-stage system may require 1.1 tons of steam, while a two-stage system needs around 0.55–0.6 tons. A three-stage system is even more economical. I hope this helps, haha
In the viscose production acid station, eleven-effect evaporation is generally used for the coagulation bath; later on, six-effect and four-effect evaporation were introduced. This is primarily determined by the amount of water that needs to be evaporated, as well as by the requirements related to utility consumption. It is also influenced by the equipment investment and the scale of production.
My understanding is that if it’s greater than three efficiencies, it’s not economical. It is necessary to improve the purification in the subsequent stages by enhancing the quality of the raw steam.