Successful reconfiguration options for rate increase in evaporator sets

The B side evaporator set at Victoria Mill was reconfigured to increase rate by rerouting vapour and juice lines. It is well known that quadruple evaporator sets are generally of higher throughput capacity but are less steam efficient than quintuple sets, given the same total heating surface. Modified sets, equivalent to 4.5 and 5.5 effects, were investigated at Victoria Mill by simulation and trial work. These unusual configurations are possible at Victoria because the set consists of more than five vessels, some connected in parallel. The incentive to try these configurations came from the need to maximise throughput. The basic reason behind the improvement is an increase in the total heat flux as a result of better heat transfer coefficients in individual vessels. Two cases were investigated. In the first case, the fifth effect, consisting of three vessels, was split so that the juice flowed through one, then was split to the other two (effectively a sextuple for juice). The vapour flow path, however, remained in the quintuple configuration; all three vessel vapour spaces were at final vacuum. Experimental data contirmed model simulations which predicted a 4% increase in rate. The second case involved the partial bypassing of a seriously fouled number 4 vessel. The juice circuit was to remain in the quintuple configuration but some of the vapour supply from the third vessel was to be fed forward to the number five vessels. If all the vapour is fed forward then the set becomes a quadruple effect. Improvement in throughput of around 10% was predicted. Experimental measurements were not made this season due to other mill priorities. The concept is expected to be proved next season.