Limekiln upgrade exceeds expectation
March 2002
System Integration & Control Systems Design
Honeywell Hi-Spec Solutions has successfully completed an upgrade to the control system managing production activities at Sappi's Ngodwana Mill limekiln.
Sappi's Jeff Hosking says the upgrade has exceeded expectations and the system is working well. Based on this success, Sappi Ngodwana is in the process of considering using the Advanced Lime Kiln Solution (ALKS) for other applications within the mill.
"Although it is early days yet, performance has improved significantly, with a definite upswing in quality and quantity," says Hosking, "we utilise a number of tests to assess lime quality. Previously we were using between 0,6 and 0,8 tons of lime to produce one ton of caustic - and now we are using below 0,6 tons. This means the quality of lime has definitely improved."
He adds that in the wake of improved system performance, gas savings, and an opportunity to sell lime externally are also possible. From an environmental point of view, a significant reduction in the Total Reduced Sulphur (TRS) emissions is also expected.
A vital element in the kraft pulping process, the limekiln's action converts lime mud back into quick lime for re-use in the causticising process.
Honeywell Hi-Spec Solutions' Advanced Lime Kiln Solution controls the entire limekiln with the primary objective of controlling the temperature profile of the lime product to produce consistent, high quality burned lime. ALKS treats the entire kiln as a single control problem, optimising operation through Hi-Spec Solutions' proven Robust Multivariable Predictive Control Technology (RMPCT), in conjunction with continuous monitoring of process conditions.
ALKS facilitates increased stability of lime kiln operation, including improved cold and hot end temperature, better environmental control, more efficient energy usage, decreased lime availability variation, decreased target residual carbonate, increased lime production, smoother production rate changes, reduced kiln maintenance and increased stability of pulping operations.
The Ngodwana Mill project involved the upgrade of an older generation TDC 2000 distributed control system to Honeywell's PlantScape Hybrid Control System with Hi-Spec Solution's ALKS. Honeywell Industrial Control's John Cound says that in order to satisfy Sappi's desire to fully test ALKS prior to removal of the old TDC system, Honeywell devised an innovative and creative solution. To alleviate any concerns over performance, a phased approach to the upgrade was used in which a Hiway bridge was established between the new PlantScape servers and the existing TDC controllers. This created a temporary platform on which Hi-Spec's ALKS' ability to optimally control O2 and CO emission levels could be validated. And, most importantly, with no initial need to shut down the kiln.
Now that ALKS has proved itself, the old TDC controllers have been removed and replaced with PlantScape C200 controllers.
Additional engineering services provided by Honeywell as part of the project have further enabled Sappi's Ngodwana mill to maximise the new solution's advantages. For example, the Sappi team has access to a US-based consultant with considerable experience in advanced limekiln control utilising the ALKS Solution. The mill also has access to local resources from Honeywell Industrial Control, which has gained valuable industry experience through their involvement in similar TDC2000 migration projects at several other sites, including Sappi Usutu, Sasol Secunda, Sapref and Engen.
Roy Botha, Honeywell Southern Africa
011 805 1201
[email protected]
www.honeywell.com
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