Modeling, simulation and control of the dynamics of a Heptads’ effect evaporator system used in the Kraft recovery processes

This research article attempts to investigate the dynamic behavior of the heptads’ effect evaporator (HEE) used to concentrate the weak black liquor during the Kraft recovery process in a paper industry. In order to fully characterize the HEE unit, a complete understanding of its performance for ste...

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Bibliographic Details
Published in:Transactions of the Institute of Measurement and Control 2018-04, Vol.40 (7), p.2278-2290
Main Authors: Verma, Om Prakash, Mohammed, Toufiq Hazi, Mangal, Shubham, Manik, Gaurav
Format: Article
Language:English
Subjects:
Black liquor
Computer simulation
Deviation
Dynamic response
Evaporators
Flow velocity
Liquor
Mathematical models
Nonlinear differential equations
Nonlinear equations
Proportional integral derivative
Recovery
Unsteady state
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Summary:This research article attempts to investigate the dynamic behavior of the heptads’ effect evaporator (HEE) used to concentrate the weak black liquor during the Kraft recovery process in a paper industry. In order to fully characterize the HEE unit, a complete understanding of its performance for steady state and transient conditions is required. For this purpose, a set of first order nonlinear differential equations have been developed for the backward feed flow configuration (BFFC) for an unsteady state. Further, the developed non-linear model is linearized and linear state space equations obtained. The dynamic response of the system in terms of vapor temperature and liquor concentration changes for different changes in input liquor flow rate has been investigated. The rise, delay and settling times for the temperature deviation from steady state have been found to be significantly less as compared with that for the concentration deviation. The results also indicate that each effect of HEE acts as an individual first order system. The placement of such first order systems in series makes both the liquor concentration and vapor temperatures response more sluggish progressively with each subsequent effect. Finally, a Cascade-PID control strategy has been implemented and shown to exhibit differentiated and improved dynamic performance of the HEE system versus open-loop dynamic response.
ISSN:0142-3312
1477-0369
DOI:10.1177/0142331217700239