Paul Stuart

Integrating product portfolio design and supply chain design for the forest biorefinery

Abstract Supply chain (SC) design involves making strategic long-term decisions for a company, e.g. number, location and capacity of facilities, production rates, flow of material between SC nodes, as well as choosing suppliers and markets. The forest biorefinery is emerging as a promising opportunity for improving the business model of forest product companies; however it introduces significant challenges in terms of mitigating technology, economic and financial risks—each of which must be systematically addressed in the SC design. In this regard, product portfolio definition and technology selection are two important decisions that have rarely been considered in a systematic SC evaluation. This paper presents a methodology, in which product/process portfolio design and SC design are linked in order to build a design decision making framework. According to this methodology, design of “manufacturing flexibility” links product/process portfolio design to SC design, through a margins-based SC operating policy. Techno-economic studies along with scenario generation for price and demand changes representing market volatility are employed in the methodology.

Application of steady-state detection method based on wavelet transform

A wavelet-based method is proposed for steady-state detection in continuous processes. In this method, process trends are extracted from the measured raw data via wavelet-based multi-scale processing. The process status is then measured using an index with value ranging from 0 to 1 according to the wavelet transform modulus of the extracted process signal. Finally, a steady state is identified if the computed index is small (close to zero). The determination of a characteristic scale for performing steady-state detection was also studied. Compared with the existing approaches for steady-state detection, this method has better precision for detecting changes in process due to the good localization property of wavelet transform, and is more suitable for on-line applications. In this paper, the method is described in detail, and has then been applied to the crude oil unit of a refinery, and to the recausticizing plant of a chemical pulp mill.

Emerging Biodrying Technology for the Drying of Pulp and Paper Mixed Sludges

Effective sludge management is increasingly critical for pulp and paper mills due to high landfill costs and complex regulatory frameworks for options such as sludge landspreading and composting. Sludge dewatering challenges are exacerbated at many mills due to improved in-plant fiber recovery coupled with increased production of secondary sludge, leading to a mixed sludge with a high proportion of biological matter that is difficult to dewater. Various drying technologies have emerged to address this challenge of sludge management, whose objective is to increase the dryness of mixed sludge to above critical levels (≈42% dryness) for efficient and economic combustion in the boiler for steam generation. The advantages and disadvantages of these technologies are reviewed in this article, and it is found that many have significant technical uncertainties and/or questionable economics. A biodrying process, enhanced by biological heat generation under forced aeration, is introduced that has significant promise. A techno-economic analysis of the batch biodrying process at a case study mill showed an annual operating cost savings of about

Key variables analysis of a novel continuous biodrying process for drying mixed sludge.

2 million, including the elimination of landfilling practices and supplemental fuel requirements in the boiler. It was shown that if a biodrying residence time of less than 4 days can be achieved, payback periods of 2 years or less can result in many mills. The potential for the development of a continuous biodrying reactor and the fundamentals of its mathematical modeling are thus presented. Compared to the batch reactor configuration, it is expected that the continuous process would result in improved process flexibility and controllability, lower investment and operating costs due to shorter residence times, and an improved potential to fit into the crowed pulp and paper mill site.

Development and Experimental Evaluation of a 1D Distributed Model of Transport Phenomena in a Continuous Biodrying Process for Pulp and Paper Mixed Sludge

A novel continuous biodrying process has been developed whose goal is to increase the dry solids content of the sludge to economic levels rendering it suitable for a safe and economic combustion operation in a biomass boiler. The sludge drying rates are enhanced by the metabolic bioheat produced in the matrix of mixed sludge. The goal of this study was to systematically analyze the continuous biodrying reactor. By performing a variable analysis, it was found that the outlet relative humidity profile was the key variable in the biodrying reactor. The influence of different outlet relative humidity profiles was then evaluated using biodrying efficiency index. It was found that by maintaining the air outlet relative humidity profile at 85/85/96/96% in the four compartments of the reactor, the highest biodrying efficiency index can be achieved, while economic dry solids level (>45%w/w) are guaranteed.

Framework for margins-based planning: Forest biorefinery case study

Effective sludge management is increasingly critical for pulp and paper mills due to high landfill costs and complex regulatory frameworks for disposal options such as sludge landspreading and composting. A novel continuous biodrying process has been developed to dry mixed sludge so that it can be combusted efficiently in a biomass boiler for energy recovery. Modeling this process is important in order to better understand the transport phenomena in the biodrying reactor and for design and scale-up of the process. A one-dimensional (1D) distributed model for heat transfer coupled with mass and biological transfer phenomena is introduced in this article that shows that the temperature of the sludge matrix is a critical parameter. The model assumes lumped parameters in the gas flow direction and distributed parameters in the (vertical) solids flow direction. Bioheat as a source term and evaporative heat as a sink term are critical issues. In order to evaluate the parameters and assess the model accuracy, a series of experiments was performed. The matrix temperatures predicted by the model were found to be in reasonable agreement with the experimental results, showing that the main transport phenomena were reflected in the model. Larger discrepancies between the water removal rates predicted by the model and the experimental values were indentified at higher aerobic exothermicity, which can be attributed to the complex mechanisms governing the growth cycle of mesophilic and thermophilic bacteria. A dimensionless analysis was performed to identify key dimensionless groups as well as the most dominant transport phenomena in the biodrying process. The results confirmed that convection processes dominated heat transfer at the top of the reactor, and the exothermic aerobic bioenergy dominated at its bottom.

Metrics for evaluating the forest biorefinery supply chain performance

Abstract The biorefinery concept offers a promising solution to transform the struggling forestry industry. Not only will the implementation of new products and processes help to diversify revenues, it will also offer an opportunity to change the manufacturing culture by better managing the flexibility of assets to react to volatile market conditions. In this paper, an integrated supply-chain planning framework is presented. It is based on optimizing a superstructure to help decision makers identify different supply-chain policies to adapt to different market conditions. It integrates revenue management concepts, activity-based cost accounting principles, manufacturing flexibility and supply-chain flexibility in a tactical model to maximize profit in a price-volatile environment. A case study of a newsprint mill implementing a parallel biomass fractionation line producing several biochemicals is used to illustrate this approach. Results and benefits are presented for the traditional pulp and paper business and for the transformed biorefinery in different market scenarios.

Steady state identification for on-line data reconciliation based on wavelet transform and filtering

Abstract For sustainable decision-making regarding biorefinery strategies, different criteria, i.e. economic, environmental, social, should be considered. However, the economic criteria typically do not consider market volatility, whereas todays market involves price and demand volatilities. Biorefinery strategies must be flexible to be robust to market volatility. Therefore, relevant metrics must be developed to quantify the systems performance against volatility. This paper presents metrics of flexibility and robustness which analyze the performance of the supply chain in a dynamic environment, providing additional information along with economic metrics. In this paper, the link between the two metrics, and how profitability and robustness change with flexibility are discussed. The results reveal that, although profitability does not always increase with more flexibility and there is an optimum level of flexibility, the systems robustness is improved by increasing flexibility. Moreover, a “conditional value-at-risk” parameter is introduced to show what patterns of sale lead to highest profit and robustnestness.

Early warning signs of bulking in an activated sludge system through interpretation of ATP data in a systems analysis context

Abstract In order to derive higher value operational knowledge from raw process measurements, advanced techniques and methodologies need to be exploited. In this paper a methodology for online steady-state detection in continuous processes is presented. It is based on a wavelet multiscale decomposition of the temporal signal of a measured process variable, which simultaneously allows for two important pre-processing tasks: filtering-out the high frequency noise via soft-thresholding and correcting abnormalities by analyzing the maximums of wavelet transform modulus. Wavelet features involved in the pre-processing task are simultaneously exploited in analyzing a process trend of measured variable. The near steady state starting and ending points are identified by using the first and the second order of wavelet transform. Simultaneously a low filter with a probability density function is employed to approximate the duration of a near stationary condition. The method provides an improvement in the quality of steady-state data sets, which will directly improve the outcomes of data reconciliation and manufacturing costs. A comparison with other steady-state detection methods on an example of case study indicates that the proposed methodology is efficient in detecting steady-state and suitable for online implementation.

Applying controllability techniques to analyze a white water network for improved productivity in integrated newsprint mills

A research project was undertaken at an integrated thermomechanical pulp and paper mill in Canada to evaluate the use of adenosine triphosphate (ATP) monitoring methods in order to identify the potential for operational problems related to microbiological aspects of activated sludge. The specific filamentous bulking ATP (fbATP) ratio is an emerging measurement technique that measures the proportion of flocs that have bulking potential by filtering a sample through a 250 µm mesh and measuring the ATP in the retentate. For the host mill in this study, the specific fbATP measurement provides early warning signs of bulking, at 1.0 to 1.5 times the sludge age, before poor settling occurs. A possible bulking scenario was identified in which the initiator was the overflow of an upstream tank containing high BOD whitewater, resulting in spikes of organic acids to the treatment and promoting the proliferation of certain types of filamentous bacteria. A storage response by filamentous bacteria to these high readily biodegradable substrate conditions was monitored with fbATP. By predicting the onset of bulking conditions, this technique can potentially assist operators to make corrective actions proactively.