Pulp mills are increasingly challenged to optimize productivity and quality while minimizing costs and the overall impact on the environment. Advanced batch digester solutions provide complete scheduling, process control, and optimization:
o To improve digester production through increased blows
o To reduce quality variance by maintaining consistent and stable kappa
o To reduce operational costs

Tight control of the loading and cooking processes provides digester batch operational flexibility and capacity utilization, allowing the digester house to dove tail the dynamic production requirements at the paper machine.

Advanced batch digester solutions are usually a complete, multi-level package designed to stabilize and optimize the batch digester operation. The functions at Level One provide safety interlocking, motor start/stop logic, and sequencing.

Level-Two functions handle automated chip and liquor charging, steam ramping, and cook and blow controls. In a sustained endeavor to improve the profitability, Pulp Mill Managers adopt a two pronged strategy:
o To push down the cost of production
o Increase the production efficiency

The cost of production is reduced by having a supervisory control on the consumption of White Liquor and Steam. The efficiency of the digester is improved by implementing interactive controls which help reduce the cooking cycle time, and also maintain consistent kappa for each blow.

As a first step towards achieving the desired objective one needs to ascertain the current metrics of digester performance. Detailed study of the existing operational philosophy and the type of raw materials used and their properties (ADT / BDT) is required. Current consumption figures of white liquor and steam are gathered from the log books.

The metrics collected are base lined as the current performance. A scientific analysis is done using statistical tools to estimate the mean and the sigma of the current operation. This helps in providing an opportunity to sigmatize the process and push the mean towards optimum profitability of operation.

The Digester House is the most important unit in the Fibreline area - and often a bottleneck for any pulp mill operation. It also offers great opportunity for maximizing the benefits by adopting better controls and APC implementation in this area helps in maximising swiftness, magnitude and sustainability of returns. Besides quantifiable and tangible benefits as described above, APC also offers a range of other soft benefits such as improved and stable downstream operation,less operator intervention, ease and flexibility of operation etc.

Sr. No Operating Parameter Improvement

1. Improvement in Yield 0.5 to 0.75%
2. Reduction in Steam 15%
3. Reduction in 5% WL consumption
4. Increase in Throughput 0.5 Blows / Day

Conclusion
Advanced batch digester solutions are a key element of Pulping Solutions. Results are proven based on the implementation of these solutions in various Paper mills world wide.

- T.Nandakumar