1,721,009 research outputs found
Interaction of separation and reactive stages on ETBE reactive distillation columns
No full textReactive distillation is a favorable alternative to conventional series of reactor-distillation processes for ether productions. However, the design of such columns is complicated due to the interaction between vapor-liquid equilibrium and reaction rates. There are conflicting reports on whether adding excessive separation stages degrade the column performance. A comparison is made of several designs of single and double feed reactive distillation columns for ETBE production to investigate the effects of separation and reaction stages on the overall performance. The explanations are presented using simulation results, whose mathematical models are written in the Aspen Plus environment. The results confirm that a conservative approach by adding extra separation and reaction stages can be applied to reactive distillation design. However, output multiplicity may be observed for longer column and should be considered in the early design phase
Model gain scheduling control of an ethyl tert-butyl ether reactive distillation column
No full textReactive distillation (RD) is a favorable alternative to the conventional series of reaction-separation processes. However, the control of RD is challenging because of its complex dynamics resulting from the integrated functionality of reaction and separation. A linear proportional-integral-derivative algorithm with fixed parameters has been shown not to be satisfactory to handle the high directionality of the process gain. It needs to be retuned adequately over a wide range of operating conditions. In this work, model gain scheduling is investigated for an ethyl tert-butyl ether reactive distillation column. It employs a set of simple local models, which cover relevant operating conditions and cope with the nonlinear characteristics of the process. The simple models are then integrated by using a proper switching scheme. Simulation results have shown that the proposed control strategy outperforms the standard proportional-integral control in both set-point tracking and disturbance rejection
Application of side reactors on ETBE reactive distillation
No full textReactive distillation (RD) has demonstrated potential reduction in capital investment and operating costs. However, industrial RD is still limited for etherification, esterification and cumene systems. Expensive hardware requirement has reduced the benefits of the simpler RD flowsheet. Side reactors are introduced in this work to reduce the requirement of specific hardware design by shortening the reactive section of the RD column. Using the ethyl tert-butyl ether (ETBE) system as the case study, simulation results show that a shorter RD column with side reactors produced comparable performance to that of a longer RD column. This may lead to a further reduction of the cost of the column if smaller amount of the catalyst result in a decrease in the diameter or height of the column. Therefore, RD with side reactors is a promising configuration that should be investigated during the conceptual design phase
Measurement structure design for multicomponent distillation column with specific estimation objective
No full textIn this work, the problem of designing the estimation structure to infer some of the effluent compositions in a multicomponent distillation column is addressed, with the aim to determine the structure that yields the best estimator functioning in the sense of a suitable compromise between performance versus complexity, regardless of the particular estimation algorithm employed. The structure design involves the selection of (i) the number of modeled components, (ii) the innovated components, and (iii) the number and locations of sensors. The consideration of the problem within the adjustable-structure geometric estimation framework in the light of the column characteristics leads to a methodology with an analysis stage, where structures are screened and candidate ones are selected, followed by a synthesis stage which yields the structure with the best estimator functioning. The proposed approach is applied through simulations to an industrial-type hexacomponent distillation column, finding that the estimation task can be adequately performed with an algorithm whose number of ODEs (77) is considerably smaller than the one (2849) that results from the direct application of the standard EKF
An Assessment of Tarong Bottom Ash for Use on Agricultural Soils
Get PDFCoal combustion by-products (CCBs), including fly ash and bottom ash, present a waste disposal problem in Australia due to a continuing demand for coal fired power. Pozzolanic Enterprises handle ash produced by the Tarong Energy coalfired power station in SouthWest Queensland, which produces approximately 1,200,000 tonnes per annum of CCBs. This comprises roughly 1,100,000 tonnes of fly ash and 100,000 tonnes of furnace bottom ash. The volume and unique properties of the Tarong bottom ash present a significant opportunity for agronomic use. Of particular interest is the ability of Tarong bottom ash to markedly improve the water holding capacity of soils. Given Australia's rural environment is currently enduring a 'one-in-one- hundred-year' drought a study of the ability of Tarong bottom ash to improve water holding capacity is timely. This paper details physical and chemical properties relevant to agronomic use and water holding capacity of ash/soil blends along with some results from initial field trials
Accelerated computation of cyclic steady state for simulated-moving-bed processes
Get PDFIndustrial applications of the simulated-moving-bed (SMB) chromatographic technology have brought an emergent demand to improve the SMB process operation for higher efficiency and better robustness. Improved process modelling and more-efficient model computation will pave a path to meet this\ud
demand. However, the SMB unit operation exhibits complex dynamics, leading to challenges in SMB process modelling and model computation. One of the significant problems is how to quickly obtain the steady state of an SMB process model, as process metrics at the steady state are critical for process design and real-time control. The conventional computation method, which solves the process model cycle by cycle and takes the solution only when a cyclic steady state is reached after a certain number of switching, is computationally expensive. Adopting the concept of quasi-envelope (QE), this work treats the SMB operation as a pseudo-oscillatory process because of its large number of continuous switching. Then, an innovative QE computation scheme is developed to quickly obtain the steady state solution of an SMB model for any arbitrary initial condition. The QE computation scheme allows larger steps to be taken for predicting the slow change of the starting state within each switching. Incorporating with the\ud
wavelet-based technique, this scheme is demonstrated to be effective and efficient for an SMB sugar separation process. Moreover, investigations are also carried out on when the computation scheme should be activated and how the convergence of the scheme is affected by a variable stepsize
Wavelet-based collocation method for stiff systems in process engineering
No full textAbrupt phenomena in modelling real-world systems such as chemical processes indicate the importance of investigating stiff systems. However, it is difficult to get the solution of a stiff system analytically or numerically. Two such types of stiff systems describing chemical reactions were modelled in this paper. A numerical method was proposed for solving these stiff systems, which have general nonlinear terms such as exponential function. The technique of dealing with the nonlinearity was based on the Wavelet-Collocation method, which converts differential equations into a set of algebraic\ud
equations. Accurate and convergent numerical solutions to the stiff systems were\ud
obtained. We also compared the new results to those obtained by the Euler method and 4th order Runge-Kutta method
Limit cycles for the Kukles system
No full textThis paper investigates the number and distributions of limit\ud
cycles for the Kukles system, which also can be regarded as a\ud
class of reduced Kukles system under cubic perturbation. Using\ud
the techniques of bifurcation theory and qualitative analysis, we\ud
have obtained three different distributions of five limit cycles\ud
for the considered systems. In the first two distributions, the\ud
five limit cycles are all non-small amplitude, which is very\ud
different from the previous work
High-resolution method for numerically solving PDEs in process engineering
No full textAbrupt phenomena in modelling real-world systems indicate the\ud
importance of investigating systems with deep gradients. However,\ud
it is difficult to solve such systems either analytically or\ud
numerically. In 1993, Koren developed a high-resolution numerical\ud
computing scheme to deal with compressible fluid dynamics with\ud
Dirichlet boundary condition. Recently, Qamar adapted this scheme\ud
to numerically solve population balance equations without\ud
diffusion terms. This paper extends Koren's scheme for partial\ud
differential equations (PDEs) that describe both nonlinear\ud
propagation and diffusive effects, and for PDEs with Cauchy\ud
boundary condition. Accurate and convergent numerical solutions to\ud
the test problems have been obtained. The new results are also\ud
compared to those obtained by wavelet-based methods. It is shown that \ud
the method developed method in this paper is more efficient
Using wavelets for solving SMB separation process models
No full textWith the expanding applications of the simulated moving bed (SMB) chromatography technology in various industries, it becomes increasingly significant to systematically investigate SMB process modelling, simulation, and model-based control design. How to control an SMB process effectively is a significant and challenging problem at the frontier of process systems engineering research as well as industrial operation. Addressing the challenges in this area, this paper reviews recent advances in modelling and simulation of SMB separation processes, and also clearly identifies the limitation of the existing modelling techniques in industrial applications. To facilitate SMB process modelling, the paper analyses the structure of the existing models for a better understanding of the functionality and suitability of each model. It is our belief that the effort on model development for process control can be made in two aspects: obtaining the sufficiently accurate model with simple representation and good robustness, and development of computationally efficient algorithms for solving the model equations which ultimately capture the process dynamics. Case studies are carried out to demonstrate the key concepts of process modelling and numerical solution of the models. The Wavelet based methods that we recently investigated are highlighted
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