An Operation Research Approach to the Economic Optimization of Kraft Pulping

The first attempt to apply operations research to the kraft industry came in 1959 by C.W. Carroll at the Institute of Paper Chemistry. Carroll developed a pulping rate expression and incorporated engineering balances to complete his mathematical model. Carroll then developed an optimization technique to optimize kraft mill economic performance. This work develops the mathematical model utilizing a different pulping rate expression and further develops certain areas (e.g. recovery boiler, lime kiln, and washer models) utilizing regression equations obtained from literature and material and energy balances in an approach much like that of Boyle and Tobias. An attempt was made to incorporate automatic step size reduction into Carroll\u27s optimization method (Created Response Surface Technique). A comparison of a three-dimensional optimization output with that of Carroll\u27s user-response program is included. Results of the optimization comparison indicated that it is possible to incorporate automatic step size reduction and obtain better accuracy than Carroll reported. However, results indicate that it may be desirable to use the CRST to get close to the optimum and then use another technique to pinpoint the final optimum. Comments on the Industrial Applicability of this approach are included

Setpoint Tracking Predictive Control in Chemical Processes Based on System Identification

A Kraft recovery boiler in a pulp-paper mill provides a means for recovery of the heat energy in spent liquor and recovery of inorganic chemicals while controlling emissions. These processes are carried out in a combined chemical recovery unit and steam boiler that is fired with concentrated black liquor and which produces molten smelt. Since the recovery boiler is considered to be an essential part of the pulp-paper mill in terms of energy resources, the performance of the recovery boiler has to be controlled to achieve the highest efficiency under unexpected disturbances. This dissertation presents a new approach for combining system identification technique with predictive control strategy. System identification is the process of building mathematical models of dynamical systems based on the available input and output data from the system. Predictive control is a strategy where the current control action is based upon a prediction of the system response at some number of time steps into the future. A new algorithm uses an i-step-ahead predictor integrated with the least-square technique to build the new control law. Based on the receding horizon predictive control approach, the tracking predictive control law is achieved and performs successfully on the recovery boiler of the pulp-paper mill. This predictive controller is designed from ARX coefficients that are computed directly from input and output data. The character of this controller is governed by two parameters. One parameter is the prediction horizon as in traditional predictive control and the other parameter is the order of the ARX model. A recursive version of the developed algorithm can be evolved for real-time implementation. It includes adaptive tuning of these two design parameters for optimal performance. The new predictive control is proven to be a significant improvement compared to a conventional PID controller, especially when the system is subjected to noise and disturbances

Integrated computational fluid dynamics and 1D process modelling for superheater region in recovery boiler

Superheaters are the last heat exchangers on the steam side in recovery boilers. Their performance is accountable for proficient recovery boiler operation. The objective of this work is to obtain thorough knowledge about the superheating process and material temperature distribution for superheater platens. The study includes the effects of 3D flue gas flow field in superheater region and generated steam properties in steam cycle. The detailed analysis for flue gas side and steam side is important for improving recovery boilers' energy efficiency, cost efficiency, safety and contribution for carbon neutral energy production. In this work, for the first time, a comprehensive 1D-process model (1D-PM) for superheated steam cycle is developed and linked with a full-scale 3D-CFD model of the superheater region flue gas flow. The developed 1D-PM is validated using reference data including mass and energy balance calculations, and measurements. The results reveal that first; the geometrical structures of headers, connecting pipes and superheater platens affect platen-wise steam distribution. Second, the integrated solution of the 3D flue gas flow field and platen heat flux distribution with the 1D-PM substantially affect both generated superheated steam properties and material temperature distribution. It is also found that the commonly used uniform heat flux distribution approach for superheating process is not accurate because it does not consider the effect of flue gas flow field in superheater region. This novel integration modelling approach is advantageous for trouble shooting, optimizing the performance of superheaters in recovery boiler and selecting their design margins for the future. It could also be applied for other large scale energy production units including industrial biomass fired boilers

The effect of recovery furnace bullnose designs on upper furnace flow and temperature profiles

"April 1992""Submitted to International Recovery Conference, June 7-11, 1992, Seattle, WA.

Comparison of simulation results and field measurements of an operating recovery boiler

"September 1993.""Submitted to 1993 TAPPI Engineering Conference, September 20-23, 1993, Orlando, Florida.

A Model of the kraft recovery furnace

Ph.D

Black liquor combustion validated recovery boiler modeling, five-year report

The objective of this project was to develop a new computer model of a recovery boiler furnace using a computational fluid dynamics (CFD) code specifically tailored to the requirements for solving recovery boiler flows, and using improved submodels for black liquor combustion based on continued laboratory fundamental studies. The project originated in October 1990 and was scheduled to run for four years. At that time, there was considerable emphasis on developing accurate predictions of the physical carryover of macroscopic particles of partially burnt black liquor and smelt droplets out of the furnace, since this was seen as the main cause of boiler plugging. This placed a major emphasis on gas flow patterns within the furnace and on the mass loss rates and swelling and shrinking rates of burning black liquor drops. As work proceeded on developing the recovery boiler furnace model, it became apparent that some recovery boilers encounter serious plugging problems even when physical carryover was minimal. After the original four-year period was completed, the project was extended to address this issue. The objective of the extended project was to improve the utility of the models by including the black liquor chemistry relevant to air emissions predictions and aerosol formation, and by developing the knowledge base and computational tools to relate furnace model outputs to fouling and plugging of the convective sections of the boilers. The work done to date includes CFD model development and validation, acquisition of information on black liquor combustion fundamentals and development of improved burning models, char bed model development, and model application and simplification