Pro-Plan's Optimization of the Liquor/Lime Circuit
The principal benefits of the Pro-Plan Pulp Mill and Recovery Optimization System result from considering optimization of the total pulp and recovery area and not just isolated area optimizations. Optimization of evaporators, recovery boilers, causticizers and kilns definitely provide benefits, but the most significant benefit arises from coordinating these areas to satisfy the requirements of the total mill.
As on the pulp side, Pro-Plan optimizes liquor storages and production rates in the liquor and lime circuits:
Maintaining levels at their optimum will reduce the 'domino effect' when unplanned events occur.
Bottlenecks occur whenever maximum throughput limits production rates. This may be due to physical limitations, or a limited resource such as steam or liquor. Thus, the occurrence of bottlenecks can vary from day to day, but Pro-Plan adapts to the situation.
Maximizing the throughput of bottlenecks in the liquor circuit will allow pulp production to be maximized also. Optimization of the liquor cycle must start from its source. The optimization of pulp washer dilution factors in Pro-Plan will also maximize production and reduce costs.
Pulp Washer Optimization
Optimizing washer dilution factors based on the cost of evaporator steam, the cost of bleaching chemicals and the cost of lost soda provides a cost benefit to the mill. Pro-Plan also considers the cost of lost production due to evaporator / recovery bottlenecks, and uses that as an additional component of the optimization.
Thus Pro-Plan considers the wider implications of dilution factor on mill production. Minimum and maximum dilution factors will constrain the dilution factor if required by other process considerations.
Evaporator throughput depends on:
As well as optimizing this area in the short to mid term, Pro-Plan also monitors evaporator performance degradation over the longer term. It optimizes evaporator wash scheduling based on degradation rates indicated by evaporator economy, temperatures, pressures and/or maximum throughput.
It recommends when an evaporator wash should take place to maximize throughput over the longer term.
If the mill has the facility to recycle strong black liquor back to the weak black liquor storages, Pro-Plan will also manage this to balance the liquor cycle.
Pro-Plan also considers the addition of spill liquor to the weak black liquor storages and the effect of washer dilution factors on the weak black liquor storages.
The amount of steam available depends on:
The demand for steam depends on demand from:
which are related to production rates. If steam is a constraint, Pro-Plan considers this constraint in determining the optimal operating strategy and matches steam supply with steam demand. Where there are degrees of freedom, Pro-Plan optimizes steam generation by allocating boiler loading according to economics.
The rates of mud extraction, washing, lime chip addition and lime kiln production rates are all recommended to ensure that causticizers are supplied and all storages in the lime circuit are driven to their optimal levels.
The effect of planned and unplanned shutdowns are also considered by Pro-Plan.
Pro-Plan monitors current production rates in relation to the recommended rates. Significant deviations are highlighted.
The costs of steam, power and gas for all production units are calculated and displayed.
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