Peter L. Douglas

Performance comparison of Fick’s, dusty-gas and Stefan–Maxwell models to predict the concentration overpotential of a SOFC anode

Models for mass transport inside a porous SOFC anode were developed based on Fick’s model (FM), the dusty-gas model (DGM) and the Stefan–Maxwell model (SMM) to predict the concentration overpotential. All models were validated with experimental data for H2–H2O–Ar and CO–CO2 systems. The effect of pore size on all model predictions was discussed. It was concluded that the dusty-gas model is the most appropriate model to simulate gas transport phenomena inside a SOFC anode. However, this model requires numerical solution, whereas Fick’s and Stefan–Maxwell’s do not. It was found that the SMM, rather than the FM, is a good approximation of the dusty-gas model for H2–H2O system, except in the case of high current density, low H2 concentration and low porosity, where only the DGM is recommended. For the CO–CO2 system, there is no simple rule for selecting an alternate model to DGM. Depending on the CO concentration, porosity and current density, the FM or the SMM could be used. The only restriction is for small porosities where only the DGM should be used. This paper also demonstrated that only the DGM is recommended for a multicomponent system (H2–H2O–CO–CO2).

A multi-period optimization model for energy planning with CO2 emission consideration

A novel deterministic multi-period mixed-integer linear programming (MILP) model for the power generation planning of electric systems is described and evaluated in this paper. The model is developed with the objective of determining the optimal mix of energy supply sources and pollutant mitigation options that meet a specified electricity demand and CO(2) emission targets at minimum cost. Several time-dependent parameters are included in the model formulation; they include forecasted energy demand, fuel price variability, construction lead time, conservation initiatives, and increase in fixed operational and maintenance costs over time. The developed model is applied to two case studies. The objective of the case studies is to examine the economical, structural, and environmental effects that would result if the electricity sector was required to reduce its CO(2) emissions to a specified limit.

Supercritical CO2 extraction of nimbin from neem seeds – an experimental study

Abstract Nimbin is one of the many substances found in neem seeds and is reported to have several medicinal properties and uses. For example, it is an anti-pyretic, can be used to treat arthritis, hypoglycaemia, peptic ulcers, anti-secretory activity, and it can also be used as an antibiotic. In this paper, we present the results of a preliminary experimental study to extract nimbin from neem seeds using CO2 supercritical fluid extraction (SFE). The operating pressure in the extraction was varied from 10 to 26 MPa, the temperature was varied from 308 to 333 K and the flow rate was varied from 0.24 to 1.24 ml/min. An optimum extraction rate was observed at a pressure of 23 MPa when operating at 308 K. Best extraction conditions occurred at 23 MPa, 308 K and a flow rate of 1.24 ml/min for a 2 g sample of neem. The measured extraction rate was found to be about 0.18 mg of nimbin/g neem seed per hour of operation which is equivalent to about 0.35 kg nimbin extracted per kg nimbin present in neem seeds. The future work needs to focus on the interaction between the various operating parameters such as temperature, pressure and flow rate of supercritical carbon dioxide. In addition physical properties i.e., particle size, porosity need to be determined in order that a model can be developed and tested.

Integration of design and control for chemical processes: A review of the literature and some recent results ☆

Abstract This paper presents a literature review on the integration of control and design problem followed by the description of two new methodologies that have been recently applied to achieve this integration. These methods are based on mathematical tools that have been commonly used for the design of robust controllers. Using these tools, the integration of the control and design problem can be formulated as a nonlinear constrained optimization problem that is significantly less computationally demanding than previously proposed dynamic optimization-based optimization methods. A mixing tank process is used to illustrate the proposed methodologies. Part of the material included in this manuscript was presented as a keynote lecture at the DYCOPS 2007 conference ( Ricardez Sandoval et al., 2007 ).

Techno-Economic Study of CO 2 Capture from Natural Gas Based Hydrogen Plants

Abstract Canadian oil sands are considered to be the second largest oil reserves in the world. However, the upgrading of bitumen from oil sands to synthetic crude oil (SCO) requires nearly ten times more hydrogen (H2) than conventional crude oils. The current H2 demand for oil sands operations is met mostly by steam reforming of natural gas (SMR). The future expansion of oil sands operations is likely to quadruple the demand of H2 for oil sand operations in the next decade. This paper presents modified process schemes that capture CO2 at minimum energy penalty in modern SMR plants. The approach is to simulate a base case H2 plant without CO2 capture and then look for the best operating conditions that minimize the energy penalty associated with CO2 capture while maximizing H2 production. The two CO2 capture schemes evaluated in this study include a membrane separation process and the monoethanolamine (MEA) absorption process. A low energy penalty is observed when there is lower CO2 production and higher steam production. The process simulation results show that the H2 plant with CO2 capture has to be operated at lower steam to carbon ratio (S/C), higher inlet temperature of the SMR and lower inlet temperatures for the water gas-shift (WGS) converters to attain lowest energy penalty. Also it is observed that both CO2 capture processes, the membrane process and the MEA absorption process, are comparable in terms of energy penalty and CO2 avoided when both are operated at conditions where lowest energy penalty exists.

A methodology for the simultaneous design and control of large-scale systems under process parameter uncertainty

This work presents a simultaneous design and control methodology for large-scale systems. The approach is based on the identification of an uncertain model from a first-principle process model. Using the identified uncertain model, a Structured Singular Value (SSV) analysis is used to estimate the realizations in the disturbance set that generates the worst-case variability and constraint violations. Then, simulations of the first-principle process model are performed with the critical disturbance profile as input to estimate the actual worst-case output variability and the worst-case variations in the process constraints. Since the proposed methodology is formulated as a nonlinear constrained optimization problem, it avoids the computationally expensive task of solving dynamic optimization problems, making it suitable for application to large-scale systems. The proposed methodology was tested on the Tennessee Eastman process to show that a redesign of the major process units in the process could significantly reduce the costs of this plant.

SIMULATION OF A ROTARY DRYER FOR SUGAR CRYSTALLINE

Dynamic heat and material balances were developed, and residence time, heat and mass transfer rates were calculated using literature correlations. The model equations were solved numerically using the Speedup simulation package and tested against industrial data. Comparison of model predictions with industrial data show that the model is accurate for steady state operation and predicts dynamic trends that are consistent with engineering judgment. Predicted outlet moisture and temperatures differ by about ±10 % from the industrial data.

Design of extractive distillation for the separation of close-boiling mixtures: Solvent selection and column optimization

A practical methodology for the design and optimization of extractive distillation is proposed in this work. The extractive distillation is generally applied to the separation of close-boiling mixtures, which by conventional distillation is difficult to separate. The design and optimization of extractive distillation is more complex than that of the conventional distillation when considering the selection of suitable solvent to enhance the separation. Currently, the solvent selection can be effectively handled by the assistance of the computer-aided molecular design (CAMD) approach. The selection result may however be inconclusive due to the lack of accurate or missing parameters in the property model. In this work, the experimental verification and the property parameter determination were proved to be necessary as an additional step to achieve a successful and reliable design. The overall design methodology was illustrated through an industrial separation of C8-Aromatics mixture.

Techno-Economic Study of CO2 Capture from an Existing Cement Plant Using MEA Scrubbing

Carbon dioxide is the major greenhouse gas responsible for global warming. Man-made CO2 emissions contribute approximately 63% of greenhouse gases and the cement industry is responsible for approximately 5% of CO2 emissions emitting nearly 900 kg of CO2 per 1000 kg of cement. CO2 from a cement plant was captured and purified to 98% using the monoethanolamine (MEA) based absorption process. The capture cost was

The integration of design and control: IMC control and robustness

51 per tonne of CO2 captured, representing approximately 90% of total cost. Steam was the main operating cost representing 39% of the total capture cost. Switching from coal to natural gas reduces CO2 emissions by about 18%. At normal load, about 36 MW of waste heat is available for recovery to satisfy the parasitic heat requirements of MEA process; however, it is very difficult to recover.