This project was done with Altum Technologies’ local partner in Japan, Nippon Steel Engineering Co., Ltd
Pulp & Paper
Case:
FOULING PREVENTION IN BLACK LIQUOR EVAPORATORS:
RESULTS FROM MITSUBISHI PAPER
MITSUBISHI PAPER | JAPAN
By preventing fouling in black liquor evaporators, operation cycle was increased by 300% and acid use was no longer needed.
ISSUE
This Mitsubishi Paper mill had been experiencing issues with scaling in black liquor evaporators, mainly caused by calcium carbonate. The scale formed in this process is very hard in texture and difficult to remove. As a potential solution, the mill tried chemical injections, but this just led to the scale shifting downstream and becoming a problem at the second effect evaporator. The scale itself not only reduced the efficiency of the heat transfer surface, but also prevented the black liquor from contacting with the heated surface below the area where it is deposited, making it impossible to secure enough heat transfer area. This resulted in both reduced heat transfer efficiency and evaporation efficiency.
Due to these scaling issues, it became difficult to maintain the process, especially for the intended four-month period during the winter. In the worst case, the process had to be stopped every month for a cleaning break. On top of this, the chemical this mill used to try and clean the scaling is regulated and can be harmful to the equipment due to its corrosive tendencies. Thus, this mill wanted to try out Altum’s ZPD Ultrasound solution to prevent the scaling altogether.
SOLUTION
Altum’s multichannel ZPD (Zero Process Downtime) solution was installed on the inlet pipe to the evaporators. When preventing scaling in black liquor evaporators, Altum’s solution works by inducing a crystallization effect. By sonicating black liquor before it goes through the heated elements in an evaporator, ultrasound can induce nucleation and create a crystallization effect so that the black liquor will not adhere to heated surfaces as scale.
With Altum’s solution, the intensity of the ultrasonic waves is powerful enough so that the crystallization effect occurs even in viscous liquids such as black liquor. Our solution is installed externally, so there is no need to dismantle equipment or stop production.
RESULTS
The results from this installation were measured both by monitoring the difference in temperature between the heating steam and the black liquor and by visually inspecting the evaporator when opened. The difference in temperature forms an important metric, as once it exceeds 20 °C the operation is seen as no longer operational and is shut down for cleaning.
Before ultrasonic treatment, the temperature difference reached 20°C within approximately a month. However, with ultrasonic treatment, it remained constant, enabling stable, continuous operation for four months. Additionally, upon opening the evaporator after sonication, it was visibly cleaner (see pictures for comparison). Scaling was prevented to the extent that hydrochloric acid cleaning, which was previously required during regular maintenance breaks, was no longer necessary. Furthermore, no chemical injections were needed during the long winter operation cycle.
BENEFITS OF ALTUM'S SOLUTION