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Optimization of Evaporator Vacuum Systems

Many liquor evaporators use two-stage steam jet ejectors to provide a source of vacuum for removal of non-condensable (NCGs) gases. Steam-jet ejectors are inefficient compared to electrically driven liquid ring pumps, but were often used due to their simple operation and low first cost. Liquid ring pumps can be a viable alternative but care must be given for proper selection. Assessment of applications at numerous pulp mills involving replacement of ejectors have offered simple returns in the range of one to two years. It is worth noting that based on discussions with internationally known pulp and paper process engineering firms, the majority of European mills specify liquid ring pumps as a matter of practice, and that North American mills tend to use steam-jets.