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Title: Model predictive control of a wet limestone flue gas desulfurization pilot plant

Abstract

A model predictive control (MPC) strategy based on a dynamic matrix (DMC) is designed and applied to a wet limestone flue gas desulfurization (WLFGD) pilot plant to evaluate what enhancement in control performance can be achieved with respect to a conventional decentralized feedback control strategy. The results reveal that MPC can significantly improve both reference tracking and disturbance rejection. For disturbance rejection, the main control objective in WLFGD plants, selection of tuning parameters and sample time, is of paramount importance due to the fast effect of the main disturbance (inlet SO{sub 2} load to the absorber) on the most important controlled variable (outlet flue gas SO{sub 2} concentration). The proposed MPC strategy can be easily applied to full-scale WLFGD plants.

Authors:
; ; ;  [1]
  1. University of Seville, Seville (Spain). Dept. of Chemical & Environmental Engineering
Publication Date:
OSTI Identifier:
21212653
Resource Type:
Journal Article
Resource Relation:
Journal Name: Industrial and Engineering Chemistry Research; Journal Volume: 48; Journal Issue: 11
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; LIME-LIMESTONE WET SCRUBBING PROCESSES; PILOT PLANTS; ON-LINE CONTROL SYSTEMS; POLLUTION CONTROL EQUIPMENT

Citation Formats

Perales, A.L.V., Ollero, P., Ortiz, F.J.G., and Gomez-Barea, A.. Model predictive control of a wet limestone flue gas desulfurization pilot plant. United States: N. p., 2009. Web. doi:10.1021/ie801530x.
Perales, A.L.V., Ollero, P., Ortiz, F.J.G., & Gomez-Barea, A.. Model predictive control of a wet limestone flue gas desulfurization pilot plant. United States. doi:10.1021/ie801530x.
Perales, A.L.V., Ollero, P., Ortiz, F.J.G., and Gomez-Barea, A.. 2009. "Model predictive control of a wet limestone flue gas desulfurization pilot plant". United States. doi:10.1021/ie801530x.
@article{osti_21212653,
title = {Model predictive control of a wet limestone flue gas desulfurization pilot plant},
author = {Perales, A.L.V. and Ollero, P. and Ortiz, F.J.G. and Gomez-Barea, A.},
abstractNote = {A model predictive control (MPC) strategy based on a dynamic matrix (DMC) is designed and applied to a wet limestone flue gas desulfurization (WLFGD) pilot plant to evaluate what enhancement in control performance can be achieved with respect to a conventional decentralized feedback control strategy. The results reveal that MPC can significantly improve both reference tracking and disturbance rejection. For disturbance rejection, the main control objective in WLFGD plants, selection of tuning parameters and sample time, is of paramount importance due to the fast effect of the main disturbance (inlet SO{sub 2} load to the absorber) on the most important controlled variable (outlet flue gas SO{sub 2} concentration). The proposed MPC strategy can be easily applied to full-scale WLFGD plants.},
doi = {10.1021/ie801530x},
journal = {Industrial and Engineering Chemistry Research},
number = 11,
volume = 48,
place = {United States},
year = 2009,
month = 6
}
  • An experimental study was performed on a countercurrent pilot-scale packed scrubber for wet flue gas desulfurization (FGD). The flow rate of the treated flue gas was around 300 Nm{sup 3}/h, so the pilot-plant capacity is one of the largest with respect to other published studies on a pilot-plant wet FGD. The tests were carried out at an SO{sub 2} inlet concentration of 2000 ppm by changing the recycle slurry pH to around 4.8 and the L/G ratio to between 7.5 and 15. Three types of limestone were tested, obtaining desulfurization efficiencies from 59 to 99%. We show the importance ofmore » choosing an appropriate limestone in order to get a better performance from the FGD plant. Thus, it is important to know the reactivity (on a laboratory scale) and the sorbent utilization (on a pilot-plant scale) in order to identify if a limestone is reactive enough and to compare it with another type. In addition, by using the transfer-unit concept, a function has been obtained for the desulfurization efficiency, using the L/G ratio and the recycle slurry pH as independent variables. The Ca/S molar ratio is related to these and to the SO{sub 2} removal efficiency. This function, together with a simplified function of the operation variable cost, allows us to determine the pair (L/G ratio and pH) to achieve the desired SO{sub 2} removal with the minimum operation cost. Finally, the variable operation costs between packed towers and spray scrubbers have been compared, using as a basis the pilot packed tower and the industrial spray column at the Compostilla Power Station's FGD plant (in Leon, Spain).« less
  • Presently, decentralized feedback control is the only control strategy used in wet limestone flue gas desulfurization (WLFGD) plants. Proper tuning of this control strategy is becoming an important issue in WLFGD plants because more stringent SO{sub 2} regulations have come into force recently. Controllability analysis is a highly valuable tool for proper design of control systems, but it has not been applied to WLFGD plants so far. In this paper a decentralized control strategy is designed and applied to a WLFGD pilot plant taking into account the conclusions of a controllability analysis. The results reveal that good SO{sub 2} controlmore » in WLFGD plants can be achieved mainly because the main disturbance of the process is well-aligned with the plant and interactions between control loops are beneficial to SO{sub 2} control.« less
  • A model has been developed to predict the dissolution rate of a limestone slurry as a function of particle size distribution and limestone conversion. The model is based on basic mass-transfer theory and includes a factor allowing the flux of calcium ions from the limestone surface to vary with the fraction dissolved. Changes in the flux with the fraction dissolved have been reported to be caused by the presence of sulfite but can also be caused by accumulation of inerts at the liquid-solid interface and/or by changes in the effective mass-transfer area. Calculations show that the decrease in flux reportedmore » for sulfites can have a significant impact on the slurry conditions within the reaction tank, i.e., impact on the limestone conversion and the relationship between liquid and solid alkalinity. In the absence of sulfites, the flux from limestone particles has been assumed to be constant with respect to the degree of dissolution. The modeling results have been found to be in good agreement with the measured values of a continuous stirred tank reactor. The model was able to accurately predict the impact of both the particle size distribution and reaction tank residence time on limestone conversion and dissolution rate.« less