Black liquor evaporation is an essential part of the chemical recovery process as it significantly concentrates the dry solid matter in black liquor so that the liquor can be effectively combusted in recovery boiler. The water removed from the liquor can be segregated and processed so that it can be reused in the mill – reducing fresh water requirements, effluents, and saving money.
Evaporators and concentrators, with their lamella heating surfaces, are adept at processing the spent cooking liquors or mill effluents using the minimum amount of energy while maximizing product dry solids, plant availability, and condensate quality. The lamella heating surfaces are inherently non-scaling. This allows the use of various heat sources inside the lamella, allowing the mill to select the most energy-efficient process connection.
Heat transfer plate
The heat transfer plate consists of two thin plates, which are completely welded around by laser welding process, and the middle area is full of pillow pattern; after forming process, pillow shaped cavity is formed inside the heat transfer plate. Pillow design creates excellent turbulence and provides self-supporting structure. In practical application, additional welding path is often added in the heat transfer plate to adjust and control the interface position of fluid in and out of the heat transfer plate, the flow velocity and flow rate of fluid in the plate, so as to optimize the heat transfer effect.
Advantages of heat transfer plate technology:
Excellent turbulence design, high heat transfer coefficient;
high welding reliability;
small resistance on the external surface, not easy to produce dirt;
high temperature and high pressure resistance;
wide channel, low pressure drop, easy to clean;
flexible shape design, optimization of heat transfer effect.
Falling Film Concentrator
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.
| Name | Pillow plate series | Shell and tube heat exchanger | Detachable plate heat exchanger | Spiral plate heat exchanger |
| Operating temperature range | <800℃ | <800℃ | <170℃ | <350℃ |
| Maximum pressure | <60 bar | <200 bar | <32 bar | <25 bar |
| Heat transfer coefficient to water[W/m2·℃] | 3500 | 2700 | 5600 | 2000 |
| Application of air and water heat exchange | fit | fit | not fit | Partial fit |
| Immersion in tank or water | fit | Partial fit | not fit | not fit |
| Welding of tank and reactor | Applicable | not applicable | not applicable | not applicable |
| Install into the existing reactor and other equipment | Flexible application | Partial applicable | not applicable | not applicable |
| All welded construction | Applicable | Applicable | not applicable | not applicable |
| Heavily contaminated liquids and other applications | Applicable | Applicable | Partial Applicable | Applicable |
| Weight per unit area | low | high | low | high |
| Falling film, condenser and evaporator | fit | fit | Partial fit | Partial fit |
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.
MVR Technology advantage:
There is no need for fresh steam after start-up, or a small amount of fresh steam is consumed, so the operation cost is low.
Easy to start,Simple structure, single effect operation, simplify the pipeline, instrument, electrical system.
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.
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