Plant-wide Design Research Articles

Valorizing the Steel Industry Off-Gases: Proof of Concept and Plantwide Design of an Electrified and Catalyst-Free Reverse Water-Gas-Shift-Based Route to Methanol.

Conversion of steel industry off-gases to value-added chemicals enabled by renewable electricity can significantly reduce the environmental burden of the steelmaking process. Herein, we demonstrate that CO2 reduction by H2, both contained in steel mill off-gases, to form syngas via the reverse water-gas-shift reaction is effectively performed by nanosecond pulsed discharges at atmospheric pressure. The experimental results suggest the following: (i) An optimum interelectrode distance exists, maximizing CO2 conversion. (ii) CO2 conversion at constant SEI follows a nonmonotonic trend with H2 excess. CO2 conversion increases with H2 excess up to H2:CO2 = 3:1 upon shifting the chemical equilibrium. At larger H2:CO2, both gas cooling, promoted by the high H2 content, and hindered CO2 collisions in a highly diluted stream hamper CO2 conversion. (iii) SEI enhances CO2 conversion, but the effect decreases with increasing SEI due to equilibrium limitations. A stoichiometric H2:CO2 feed ratio in the plasma reactor is recommended for higher energy efficiency. Intensifying MeOH productivity via SEI elevation is not advised as a 2-fold SEI increase results only in 17% higher MeOH throughput.

Plantwide design for high-purity formic acid reactive distillation process with dividing wall column and external heat integration arrangements

We assessed eight configurations by implementing a dividing wall column (DWC) arrangement and an external heat integration (HI) arrangement for the reduction of energy consumption in the high-purity formic acid (FA) production process. At first, a patented high-purity FA production configuration was adopted and several main process variables were optimized. The optimal configuration was considered the base case for further investigation. The DWC arrangement was applied in the base case configuration to overcome the remixing phenomenon. Next, the external HI arrangement was implemented in those configurations. The simulation results showed that the non-reactive upper DWC between columns C2 and C3 with the HI configuration was the best configuration that provided 46.9% energy saving compared to base case configuration.

Plantwide design and economic evaluation of two Continuous Pharmaceutical Manufacturing (CPM) cases: Ibuprofen and artemisinin

Abstract Increasing Research and Development (R&D) costs, growing competition from generic manufacturers and dwindling market introduction rates for novel drug products bolster the efforts of pharmaceutical firms to secure competitiveness by investigating Continuous Pharmaceutical Manufacturing (CPM). The present paper explores the CPM of two key Active Pharmaceutical Ingredients (APIs), ibuprofen and artemisinin: cost savings and material efficiency benefits are evaluated for CPM vs. batch processing, with two continuous options for each API. Capital Expenditure (CapEx) savings of up to 57.0% and 19.6% and corresponding Operating Expenditure (OpEx) savings of up to 51.6% and 29.3% have been determined for ibuprofen and artemisinin, respectively. Total projected cost savings for a 20-year plant lifetime can reach 54.5% and 20.1%, respectively. Environmental (E)-factors (mass of waste generated per unit mass of product) of 43.4 (for ibuprofen) and 12.2 (for artemisinin) have been computed, indicating environmental and material efficiency advantages for these conceptual continuous pharmaceutical processes.

Design and control of a biodiesel production process using sugar catalyst for oil feedstock with different free fatty acid concentrations

This manuscript reports on the plant-wide design and control of a biodiesel process using a sugar catalyst. This catalyst is less expensive and more environmentally friendly than the conventional catalyst because it does not have to be neutralized and there is no resulting waste salt. Also, the acid catalyst can be used for simultaneous esterification of free fatty acids (FFA) and transesterification of triglyceride because there is no concern about the formation of soap, which is a problem with the conventional base catalyst. Two issues are addressed in this work. The first one is to find the effect of FFA content in oil feed to the optimal design of this process. The second one is to investigate the operability of the proposed process. The results show that total annual cost of the plant-wide process is not significantly changed when the FFA content greater than 15wt%. As compared to a two-step process in literature, the energy consumption per tons of biodiesel production of our proposed process gives significant 65.8% saving for an oil feed with 5wt% FFA. Dynamic simulations demonstrate that the proposed process can accommodate production rate and feed composition changes using a decentralized plant-wide control structure.

Plantwide Design of Ideal Reactive Distillation Processes with Thermal Coupling

Process intensification is aimed to integrate different processes in design to reduce energy consumption and capital investment, as well as to achieve environmental and safety benefits. Reactive di...

Plantwide Design of Transesterification Reactive Distillation to Co-Generate Ethyl Acetate and n-Butanol

Reactive distillation (RD) in the face of azeotrope(s) in the separation of a mixture from an RD column might need debottlenecking design and more columns to obtain high-purity products. Under such circumstances, the integration of heat with the process becomes an effective consideration for reducing costs. In this study, an RD process to produce ethyl acetate and n-butanol from ethanol and n-butyl acetate by conducting a transesterification reaction is presented. The products from the RD column include n-butanol and an ethanol/ethyl acetate mixture. Designs with alternative configurations are used to illustrate plantwide designs of the process with heat integration/coupling. Among these alternatives are two with three columns and one with two columns. In the three-column configurations, separation of ethanol/ethyl-acetate mixtures from the top product of the RD column is conducted by extractive distillation or pressure-swing distillation. The other configuration consists of an RD column followed by a conventional distillation column operated at high pressure. Systematic design procedures are used to optimize the flowsheets of different configurations by minimizing the total annual cost. Heat integration and thermal coupling technologies are used in these three configurations to attempt to provide more economical designs. The results show that the selection of separation system depends on whether heat integration/coupling is considered. In this case, the two-column reactive distillation process with heat integration yields high-purity products and the lowest total annual cost.

Design and Control of the Monoisopropylamine Process

The monoisopropylamine (MIPA) process provides an interesting example of plantwide economic design optimization and plantwide control. The process consists of a tubular reactor and three distillation columns. There are both gas and liquid recycles. Fresh feed streams of isopropyl alcohol and ammonia are introduced into the process. The desired products are MIPA and water. An undesirable byproduct of di-isopropylamine (DIPA) is also produced and is recycled to extinction since its formation reaction is reversible. An excess of ammonia in the reactor inhibits the DIPA reaction, so ammonia is also recycled. The purpose of this paper is to present the details of the process for use by other workers as a test case for use in plantwide design and control studies. A heuristic economic optimum design and a control structure are developed. The process illustrates the classical design trade-off between reactor costs versus separation costs. In addition, the process has two recycles, which are both distillate products from different distillation columns, and this leads to another trade-off. Using more ammonia recycle produces less DIPA recycle. So the optimum design must balance the separation costs of the two recycles. Two of the distillation columns can be effectively controlled using a single temperature and a reflux-to-feed ratio control structure. The third column requires a dual control structure ratio (one temperature and one composition).

Plant-wide design and control of DMC synthesis process via reactive distillation and thermally coupled extractive distillation

In the study, reactive distillation is designed to produce dimethyl carbonate and ethylene glycol by the transesterification of ethylene carbonate and methanol. The products of the reactive distillation column include ethylene glycol and a dimethyl carbonate/methanol mixture, close to azeotropic composition. The azeotrope is separated in the study by pressure-swing distillation and extractive distillation using phenol as an extractive agent. The extractive distillation is found to be much more economical than the pressure-swing distillation. Thermal coupling technology is also implemented between the two columns of the extractive distillation. Thermally coupled extractive distillation provides the best energy efficiency. Proper selection and pairing of controlled and manipulated variables are determined by using steady-state analysis. A simple temperature control scheme is sufficient to maintain stoichiometric balance between the reactant feeds and product purities at or around their designed values for the plant-wide process of reactive distillation + thermally coupled extractive distillation.

Effect of Entrainer Loss on Plant-Wide Design and Control of an Isopropanol Dehydration Process

Azeotropic distillation is an important technology for separating azeotropes or minimizing the energy expenditure of separating close boiling mixtures. In heterogeneous azeotropic distillation, an entrainer is usually added, which is recovered and reused in the subsequent stripping process. Depending on the design, there may be various degrees of entrainer loss. In this work, the plant-wide design and control of an isopropanol dehydration system using cyclohexane as an entrainer via heterogeneous azeotropic distillation is conducted. When there is negligible entrainer loss, a special case of input multiplicity is found, in which a set of design specifications can be achieved by an infinite but bounded set of operating conditions. The optimal condition with the minimum reboiler duty in this bounded set is achieved when the organic recycle flow is the smallest. Due to the existence of these multiple steady states, the entrainer inventory control is self-regulatory over long time operations if a PI control is used for the level of the organic phase in the decanter. If large offsets are allowed in the entrainer inventory control, the system may exhibit a long period of pseudosteady state followed by catastrophic failure. Alternatively, one can allow a small amount of entrainer loss to the bottom of the heterogeneous azeotropic distillation column, and provide a small amount of entrainer makeup. In this case, a control loop is added to guard against process drift due to loss of entrainer. However, because continuous maintenance of entrainer inventory is difficult, an on-off control scheme of entrainer makeup feed is used.

Plant-wide design and control of acetic acid dehydration system via heterogeneous azeotropic distillation and divided wall distillation

Energy-saving plant-wide design and plant-wide control of an acetic acid dehydration system with the feed containing methyl acetate and p-xylene are investigated in the study. A heterogeneous azeotropic distillation using isobutyl acetate as an entrainer is designed to obtain high-purity acetic acid at the column bottom and to keep a small acetic acid loss through the top aqueous draw. The accumulation of p-xylene in the column is avoided by adding a side product stream. The mixture in the aqueous phase of decanter, containing mostly water, methyl acetate, and isobutyl acetate is separated using a divided wall distillation column. The whole acetic acid dehydration system includes a heterogeneous azeotropic distillation column and a divided wall distillation column. The control strategies using temperature loops are proposed for this acetic acid dehydration system. For the heterogeneous azeotropic distillation column, the requirements for acetic acid compositions in both the aqueous phase of the decanter and the column bottom can be satisfied by designing entrainer inventory temperature control and cascade temperature control simultaneously. The stages of controlled temperatures are chosen by singular value decomposition and closed-loop analysis methods based on the criteria of minimum entrainer makeup. For the divided wall distillation column, steady-state analysis methods are used for the selection of proper controlled and manipulated variables and the determination of their pairings. Dynamic simulation results demonstrate that the proposed plant-wide control strategy can maintain product purities and reject external disturbances in feed flow and composition changes as well as internal disturbances such as changes in liquid and vapor splits.

Application of a plant-wide control design to the HDA process

With the increasing interest in and the need for plant-wide design and control, it is desirable to develop rigorous models for realistic and large-scale processes with recycle streams, energy integration and non-ideal systems, and use them for evaluating plant-wide control schemes. In this study, a rigorous model for the hydrodealkylation of toluene (HDA) process is developed using the commercial software, hysys.plant. After reviewing the reported methods for plant-wide control, a systematic method, namely, Control Configuration Design (CCD) method, is selected for application to the HDA process. The resulting control structures from the application of this method are evaluated and compared through rigorous dynamic simulation. The results show that the CCD method successfully yields workable base-level regulatory control structures for the HDA process. The control structures obtained by the CCD method are also compared with that reported by Luyben et al. (Plant-wide Process Control, McGraw-Hill, 1998) using their nine-step method.

Plantwide Design and Control of Processes with Inerts. 1. Light Inerts

Plantwide Design and Control of Processes with Inerts. 1. Light Inerts

Plantwide Design and Control of Processes with Inerts. 3. Intermediate Inerts

In this final paper of a series that explores the design and control of processes containing inert components we study five strategies for the removal of intermediate inerts. It is shown that the best structure for the case of intermediate inerts uses a direct distillation sequence where the reactant is separated first (and recycled) and then the inert is separated from the product.

Plantwide Design and Control of Processes with Inerts. 2. Heavy Inerts

This is the second paper of a series that explores the design and control of processes containing inert components. Three strategies for removal of heavy inerts from a process are compared both from the standpoint of steady-state economics as well as from the standpoint of dynamic controllability. These processes are essentially the “inverses” of the processes discussed in the first paper of the series. It is shown that the best structure for the case of heavy inerts is the inverse of the best light inert structure (the reader is referred back to the first paper of the series). A reactor and full column with side draw is used. The heavy inert is removed as the bottoms product, the sidestream is recycled back to the reactor, and the overhead is the plant product.

Design and Control of a Complex Process Involving Two Reaction Steps, Three Distillation Columns, and Two Recycle Streams

The work examines the plantwide design and control of a complex process typical of many industrial chemical operations. The plant contains two reaction steps, three distillation columns, two recycle streams, and six chemical components. Two methods, a heuristic design procedure and a nonlinear optimization, have been used to determine an approximate economically optimal steady-state design. The designs differ substantially in terms of the purities and flow rates of the recycle streams. The total annual cost of the nonlinear optimization design is about 20% less than the cost of the heuristic design. An analysis has also been done to examine the sensitivity to design parameters and specifications. Two effective control strategies have been developed using guidelines from previous plantwide control studies; both require reactor composition control as well as flow control of a stream somewhere in each recycle loop. Several alternative control strategies that might initially have seemed obvious do not work. This process has important features that fundamentally determine its operability, including the balance of the two reaction steps and the inventory regulation of intermediate species