Johan Grievink

Process intensification and process systems engineering: A friendly symbiosis

An attempt is presented to define process intensification in relation to the other chemical engineering disciplines, in particular to process systems engineering. It is shown that process intensification is fully in development and, as a consequence, the essential characteristics are subject to debate. The innovative character of process intensification is in nice harmony with the objectives of process systems engineering: a symbiosis between them has high potential.

Designing reactive distillation processes: present and future

The potential benefits of applying reactive distillation (RD) processes are taxed by significant complexities in process development and design. The design problem is formulated in the wider context of process development and engineering. From that perspective design methods for RD units developed over the last decades are classified and described. A fingerprint of the most representative work in the three categories, graphical, optimisation- and heuristic-based, is presented and deficiencies are identified. In response to a need for a more integrated design methodology, a conceptual model is offered which uses a hierarchy of embedded design spaces of increasing refinement and conjugates the strengths of both the graphical- and optimisation-based methods.

Is a monolithic loop reactor a viable option for Fischer-Tropsch synthesis?

A Monolithic Loop Reactor design for Fischer-Tropsch synthesis with a production capacity of 5000 ton middle distillates per day (about 40000 bbl/day) is presented. The required volume, 3350 m 3 , is competitive with conventional reactors, while eliminating disadvantages of existing reactor types such as catalyst attrition and separation, backmixing and large diffusion distances. Although the kinetic expressions used in this study do not allow calculating the selectivity precisely, all important conditions, low temperature rise and constant H 2 /CO ratios, are met to ensure high selectivity towards heavy hydrocarbons.

Integrated optimal reliable design, production, and maintenance planning for multipurpose process plants

In multipurpose process plants, which are characterized by sharing different resources (equipment, manpower etc.) for production, unplanned equipment shutdown could affect the timely production of products and hence process profitability. Many approaches have been proposed to ensure high equipment availability by combining design, production, and scheduling frameworks with a maintenance optimization framework. In these approaches, the initial reliability characteristics of equipment, which also determine equipment availability, are considered fixed by problem definition. In this work, a combined design, production and maintenance planning formulation for multipurpose process plants is extended to incorporate the reliability allocation problem at the design stage. A simultaneous optimization framework is presented that addresses the problem of optimal allocation of reliability among equipment simultaneously with the selection of process configuration, production and maintenance planning for multipurpose process plants at the design stage. This framework provides the designer with the opportunity to select the initial reliability of equipment at the design stage by balancing the associated costs with its impact on the design and the availability in the operational stage. The overall problem is formulated as a mixed integer linear programming (MILP) model, and its applicability is demonstrated using a number of examples.

Process design and control structure screening based on economic and static controllability criteria

Abstract A method is developed that screens process flowsheet and control system configurations, defined in terms of selected controlled and manipulated variables that exhibit poor steady-state behavior under the presence of multiple simultaneous disturbances and model parameter variations. The steady-state disturbance rejection characteristics of the nonlinear process models are considered in conjunction with economic criteria for the elimination from further consideration of poor designs early in the design process. A wide variety of static control objectives for the system is incorporated within an optimization framework that evaluates the required contribution of the selected input variables to alleviate the effects of the imposed disturbances on the control objectives specified in a hierarchical order. Sensitivity information of the optimal solution to the control design problem is utilized to identify the most influential design parameters on static controllability performance, hence providing the guideline for improving the disturbance rejection properties of the flowsheet. The proposed approach allows the study of plants with unequal number of manipulated and controlled variables and the investigation of cases with saturation of manipulated variables and hard bounds on the controlled variables. The method has been applied to a number of different designs for a complex flowsheet that involves multiple reactive and separation steps with recycle. Reactive distillation configuration proved to exhibit superior economic and static controllability performance compared with the conventional reactor–separator scheme for combined reaction kinetic parameter variations.

Integrating reliability optimization into chemical process synthesis

Abstract The growing need to achieve high availability for large integrated chemical process systems demands higher levels of system reliability at the operational stage. In these circumstances, it has become critical to consider the reliability aspects of a system and its components at the design stage. Traditional reliability/availability analysis methods and maintenance optimization frameworks, commonly applied at the design stage, are limited in their application, as in most of these methods the designer is required to specify the process system components, their connectivity and their reliabilities a priori . As a result, these traditional methods do not provide the flexibility to reconfigure a process or select initial reliabilities of equipment in a way that maximizes the inherent plant availability at the design stage. In this paper, we developed an optimization framework by combining the reliability optimization and process synthesis challenges and the combined optimization problem is posed as a mixed integer non-linear programming optimization problem. The proposed optimization framework features an expected profit objective function, which takes into account the trade-off between initial capital investment and the annual operational costs by supporting appropriate estimation of revenues, investment cost, raw material and utilities cost, and maintenance cost as a function of the system and its component availability. The effectiveness and usefulness of the proposed optimization framework is demonstrated for the synthesis of the hydrodealkylation process (HDA) process.

Optimisation of the conceptual design of reactive distillation columns

It is shown that the introduction of a different tray holdup in the stripper and rectifyer section of a continuous kinetically controlled reactive distillation column facilitates the design procedure. It also creates a range of design alternatives, generating the possibility to optimise for both the total number of trays and the total liquid holdup in the column. This allows for minimising investment related costs such as the column height and the amount of catalyst. When investigating the influence of product specifications and process parameters such as the heat of reaction and the stoichiometric sum on column design, the introduced range of design alternatives should be compared rather than single designs.

The placement of two-stream and multi-stream heat ex-changers in an exisiting network through path analysis

Abstract A prescreening and decomposition method is presented to analyse heat exchanger networks for retrofitting. The method, called Path Analysis, selects and analyses fractions from the existing network, either by heuristics or by an algorithm. By comparison of all fractions, the critical parts of the network that should be adapted can be identified. The adaptations can be done independent of the remaining network. Thus Path Analysis enables a considerable reduction of the effort in retrofit design. Meanwhile the simplest network adaptations are favoured. Path Analysis is applied to several cases. The results for an aromatics case are presented. Using the right software tools, the engineering effort can be reduced considerably, compared with existing methods. Solutions tend to be less complex, while the profitability is sometimes higher than was expected from global analysis. With Path Analysis the retrofit design using new multi-stream heat exchangers proved to be straightforward.

Development of a synthesis tool for Gas-To-Liquid complexes

Optimal synthesis of a Gas-To-Liquid complex is complicated due to many degrees of freedom in a highly constrained design space. One can choose between alternative, competing syngas manufacturing technologies, different types of Fischer–Tropsch catalysts and reactors, with numerous connectivity options and a range of operational conditions. On the other hand, the design space is confined by equipment, operational and knowledge constraints. Furthermore, economic performance needs to be aligned with carbon and energy efficiencies. To support GTL process design a computational synthesis tool is under development. Its purpose is to find and analyse the optimum structure and operational conditions for a given market scenario. The process model covers alternative syngas generation units and Fischer–Tropsch reactors with an extensive syngas recycle structure. The process units interact with the utility system, where power can be generated from off-gas and/or excess steam. The units are modelled in a reduced, input–output way by algebraic equations, reflecting mass and energy balances and pressure effects. A superstructure arises when considering multiple stages for Fischer–Tropsch synthesis with parallel reactors. The synthesis tool, implemented in AIMMS®, is applied to a realistic sample problem, showing profit optimisation by varying the distribution of NG to syngas generation units with different efficiencies. A sensitivity analysis is carried out by means of Singular Value Decomposition of sensitivity matrices to find dominant patterns of parametric influence on the optimum.

The application of a task-based concept for the design of innovative industrial crystallizers

A new task-based design approach [Menon, A. R., Pande, A. A., Kramer, H. J. M., Grievink, J., & Jansens, P. J. (2007). A task-based synthesis approach toward the design of industrial crystallization process units. Industrial & Engineering Chemistry Research, 46, 3979] is applied to design a crystallization process unit. Task-based design involves the conceptual built-up of a process (unit) from functional building blocks called tasks, which represent fundamental physical events. The motivation for developing this approach is to get a better control over the physical events governing crystalline product quality. To deliver a proof of concept, two lines of research are followed. First of all, several small scale experiments are designed to demonstrate practical feasibility of the approach. The new equipment allows for isolation and manipulation of individual crystallization tasks. Second, a model based on the experimentally tested tasks is developed for a crystallizer design and used in dynamic optimization of three case studies. The results show that completely different and tight product specifications can be achieved with the same design simply by changing the operational policy of the crystallizer. This remarkable increase in flexibility to achieve a broad range of product qualities is the result of the ability to control the rate at which individual crystallization tasks are executed as well as the material flows between those tasks.