Deza improves performance with Honeywell’s advanced process control (APC) solution.
Project payback was less than six months, and the controller service factor has been greater than 99% since commissioning.
Based in the Czech Republic, Deza’s business is processing benzol and crude coking tar, both by-products of coke production from coal. The operations include production of basic aromatic commodities, organic intermediates, the purchase and sale of chemical products and R&D and analytical activities in organic chemistry.
The company wanted to improve the performance of its phthalic anhydride (PA) plant and approached Honeywell to conduct an APC benefits study.
Challenge
The Deza PA process consists of seven functional processes and two support processes. In order to improve performance, Deza had several objectives:
* Maintain the reactant concentration in the oxidising reactor below its upper limit.
* Ensure the reactant concentration in the feed section does not reach explosive limits.
* Keep the turbo blower throughput below or at the operation specified upper limit.
* Maintain the oxidation reactor catalyst temperatures within safe limits.
* Make sure controller outputs stay inside specified limits.
* Maximise the crude PA production.
After a detailed survey taking into account all PA reaction sections, Honeywell concluded that the air compressor (which would pose a bottleneck during peak production) together with the feed preparation and reaction sections would benefit most from APC.
Solution
Honeywell’s solution was to install Profit Controller, its multivariable control and optimisation software, covering the air compressor, feed preparation section and oxidising reactor. In addition, the Profit Toolkit application validates the oxidising reactor temperature and continuously updates them in Profit Controller. Honeywell’s Uniformance process historian database (PHD) reports and issues trend forecasts for key data, helping improve process plant analysis. Honeywell’s performance monitoring package provides useful statistics on the controller’s performance in terms of online time, standard deviation from controlled variables (CVs), constraint activity and more.
Profit Controller centres on the patented range control algorithm (RCA), which controls all CVs within their ranges and allows the Profit Controller to explicitly constrain all of the CVs dynamically. RCA keeps Profit Controller online in situations where other multivariable controllers become unstable.
Product value optimisation (PVO) is a dynamic rather than steady-state solution, which lets Profit Controller optimise the entire unit faster and potentially offers a more precise and more profitable final solution. PVO finds not only the steady-state solution, but also the optimal dynamic path leading there. PVO is treated as part of closed-loop control and is unified into the RCA. As a result, optimisation speed can be tuned independently of the speed of CV error correction.
Key to the project’s success was operator acceptance throughout the project schedule and strong management support allowing control engineers to fully participate and take responsibility for all project phases including controller design, basic controller tuning, plant step testing, implementation and commissioning of the multivariable predictive controllers. Rigorous attention and resolution of regulatory control problems before implementation of the advanced controls was a major factor in achieving the high level of robust control.
Benefits
Advanced process control (APC) can be a very useful tool when it comes to improving process performance and increasing capacity. Even small capacity boosts can be worthwhile, especially when they are achieved without major investment and demand for the product is strong.
Honeywell APC has yielded significant economic and operational benefits for Deza. A subsequent performance guarantee audit found that the project payback was less than six months, and that the controller service factor has been greater than 99% since it was commissioned.
Comparing the performance of the PA unit using APC has shown that every ton produced now consumes less utilities and raw materials than before.
For more information contact Debbie Rae, Honeywell Southern Africa, +27 (0)11 695 8000, [email protected], www.honeywell.co.za
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