Energy saving pillow jacket design exchanger for falling film black liquor concentration
Paper Pulp Black water Introduction
Weak Black Liquor (WBL) from the brown stock washers is typically at 13-18%TS. Most of this water content must be evaporated to produce a material with high enough solids to support effective combustion in the recovery boiler, typically between 65% and 80%TS.
During evaporation to this level of solids, various volatile components (sulfur compounds, methanol, etc.) are released from the liquor and must be separated from the condensate to allow reuse in the fiberline and recausticizing. From this point of view, the evaporation plant actually serves as a"water factory"within the mill. Black liquor also contains a substantial fraction of inorganic compounds which, during the evaporation process, reach their solubility limit and can deposit as scale on the evaporator heat transfer surfaces greatly limiting the operating capacity of the evaporation plant and of the entire recovery island.
“Black Liquor” is a by-product of pulp from mills that make products from trees, such as paper. It is currently used to recover cooking chemicals and produce high-pressure steam used in the pulp and paper-making process. It is composed of different ingredients from these processes such as lignin, hemicellulose, sodium hydroxide (NaOH) and sodium sulfide (Na2S). The lignin compound in black liquor can be used to make biofuel but it can be expensive to produce and so fuel made from it is not very common.
However, and according to the International Energy Agency (IEA), the future of using black liquor as fuel is promising and it is seen as the fifth most important fuel on earth!
How to reach 80-85% dry solids?
Due to the high viscosity
MP-steam as heating medium
liquor temperature 175 ℃ in final concentrator
Liquor retention time
evaporator acts also as a LHT-reactor
Duplex construction material
high alkali content may cause Stress Corrosion Cracking (SCC)
Mechanical Vapor Recompression MVR Evaporator consumption compared with traditional evaporation equipment calculated by evaporating 1T water
|Name||Steam||Electric Power||Total Cost (RMB)|
|Evaporation Capacity (kg/h)||Consumption (T)||Cost (RMB)||Consumption (kw)||Cost (RMB)|
|Single Effect Evaporator||1.1||220||3||2.1||222.1|
|Double Effect Evaporator||0.55||110||3||2.1||112.1|
|Three Effect Evaporator||0.4||88||3||2.1||90.1|
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:
1) Excellent turbulence design, high heat transfer coefficient;
2) high welding reliability;
3) small resistance on the external surface, not easy to produce dirt;
4) high temperature and high pressure resistance;
5) wide channel, low pressure drop, easy to clean;
6) flexible shape design, optimization of heat transfer effect.