MVR Technology
MVR technology is to compress the secondary steam of the evaporator by mechanical method, increase its pressure and temperature, increase its enthalpy, and then send it back to the heating chamber of the evaporator to be used as heating steam, so as to keep the feed liquid in boiling state, while the heating steam itself condenses into water. Compared with the multi effect evaporation technology, MVR technology compresses and recycles all the secondary steam and recovers the latent heat, so it is more energy-saving than the multi effect evaporation technology.
Advantages of MVR Technology:
After start-up, there is no need for fresh steam, or a small amount of fresh steam is consumed, so the operation cost is low.
Simple structure, single effect operation, simplify the pipeline, instrument, electrical system.
Easy to start, simple operation, stable operation, less maintenance.
It occupies a small space and has few utilities. In general, there is no need for condenser and cooling tower.
Falling Film Concentrators are really an adaptation for high solids service of the FF evaporator design discussed above. By nature, FF concentrators, where evaporation takes place from a liquor film within the heating element result in high supersaturation levels being developed within the liquor. This can result in uncontrolled scale formation due to excessive crystal nucleation rather than gentle crystal growth.
Some FF concentrator designs actually do not even attempt to control scale formation on the heating surfaces, but rather provide a mean to remove such scale faster than it forms and before it can negatively impact capacity or lead to plugging. Quick switching designs,commonly used with plate and tubular-element units, rely on this strategy by continuously moving multiple concentrator bodies (or chambers within the same body)between product liquor and washing positions.
Another design approach involves operating the FF concentrator at low heat flux to reduce the amount of supersaturation developed in the liquor during heat transfer. A substantial amount of heat transfer area has to be provided in this case,as well as a commensurate recirculation rate,to reduce both operating AT and specific evaporation per unit of heat transfer area.
Comparison
| item | 5 effect station | combined evaporation process | ||
| MVR pre concentration | 5-effect evaporation station | |||
| Evaporation water (t/h) | 100 | 64.28 | 35.72 | |
| Incoming concentration(%) | 10 | 10 | 20 | |
| Out concentration(%) | 45 | 20 | 45 | |
| Evaporator area(㎡) | 10000 | 8500 | 4000 | |
| Condenser area(㎡) | 800 | / | 300 | |
| Consumption | Steam (t/h) | 25 | / | 9 |
| Electricity(kWh/h) | 500 | 1600 | 180 | |
| Water(t/h) | 900 | / | 350 | |
| Running cost | RMB/hour | 4500 | 960 | 1633 |
| RMB/T water evaporation capacity | 45 | 25.93 | ||
| RMBx10000/Day | 10.8 | 6.2 | ||
| RMBx10000/Year(340days) | 3672 | 2115 | ||
Note:In operation cost estimation:steam 150rmb/t,electricity 0.6 rmb/kWh,water 0.5rmb/t.
The investment of combined evaporation process equipment increased: evaporator (2500 m2) 375x10000 RMB; MVR compressor 400x10000rmb, total 775x10000 RMB
Annual operating cost reduction of combined evaporation process: 3672-2115 = 1557 (10000RMB)
Investment increase payback period of combined evaporation process: 755 ÷ 1557=0.5year
It can be seen that taking the scale of 100t / h as an example, the combined evaporation process can recover the increased investment in half a year, and save 1557 (10000 RMB) every year in the future, with considerable economic benefits.
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