Lower Total Annual Cost Research Articles

Economic optimization of heat pump-assisted distillation columns in methanol-water separation

Finding efficient alternative to CDiC (Conventional Distillation Column) for methanol-water separation has been an attractive field of study in literature. In this work, five heat pump-assisted schemes are proposed and compared to each other to find the optimal one; (1) VRC (Vapor Recompression Column), (2) external HIDiC (Heat-Integrated Distillation Column), (3) intensified HIDiC with feed preheater, (4) double compressor intensified HIDiC-1, and (5) double compressor intensified HIDiC-2. GA (Genetic Algorithm) is then implemented for optimization of the schemes when TAC (Total Annual Cost) is its objective function. During optimization, two new variables are added for using only appropriate amount of the overhead stream in VRC and double compressor intensified HIDiCs, and another new binary variable is also used for considering feed preheating. Although TAC of the intensified HIDiC with feed preheater is found higher than CDiC by 25.0%, all optimal VRC, external HIDiC, double compressor intensified HIDiCs schemes are reached lower optimal TAC by 3.1%, 27.2%, 24.4%, and 34.2%. Introduced for the first time, the optimal scheme is the double compressor intensified HIDiC-2 with 34.2% TAC saving, 70.4% TEC (Total Energy Consumption) reduction with payback period of 3.30 years.

Design and Control of Thermally-Coupled Reactive Distillation System for Esterification of an Alcohol Mixture Containing n-Amyl Alcohol and n-Hexanol

Semiconductor and pharmaceutical industries often produce waste alcohol mixtures. This study discusses a reactive distillation process of a mixed alcohol feed containing n-amyl alcohol and n-hexanol to react with acetic acid to produce useful esters. In an earlier paper (Lee et al. Ind. Eng. Chem. Res. 2009 48, 7186–7204), optimal design of the same Type-III mixed-alcohol reactive distillation process containing n-butanol and n-amyl alcohol was developed. In that paper, the indirect sequence containing a reactive distillation column with heavier amyl acetate bottom product and a second column to produce butyl acetate gives the lowest total annual cost. In this study, with different mixed alcohol feed (although of the same reaction type), it is found that an alternative direct sequence design is much more economically favorable with 34% reduction in total annual cost as compared to the indirect sequence. The reason for the seemingly contradictory results can be explained by differences in relative volatilities of binary pairs in the stripping sections of the reactive distillation towers. Process intensification technology is also attempted to devise a thermally coupled reactive distillation configuration to further save 13% of the operating energy. The overall control strategy using tray temperatures is also proposed to maintain high-purity products despite various disturbances.

Design, optimization and controllability of an alternative process based on extractive distillation for an ethane–carbon dioxide mixture

Alternative configurations based on cryogenic extractive distillation were proposed and simulated by using Aspen Plus 7.0® coupled to a multi-objective stochastic optimization procedure (differential evolution, DE). The evaluation of the performances of the proposed configurations was focused on the ethane–carbon dioxide azeotrope separation considering different liquefied hydrocarbon fractions as entrainers. The design alternatives were compared to the conventional chemical absorption system.The proposed sequences were simultaneously Pareto optimized by minimizing the total annual cost (TAC) and maximizing the acid gas removal. Complementary studies regarding the theoretical control properties, the thermodynamic efficiency and the greenhouse gases generation were conducted for several representative operating conditions obtained from the Pareto optimized fronts. The proposed cryogenic extractive distillation sequences realized the higher carbon dioxide removal together with the lower TAC compared to the conventional chemical absorption system.

PDB14 - Clinical Outcomes and Health Care Costs Evaluation of Sulfonamides and Thiazolidinediones Compared with Dipeptidyl Peptidase 4 Inhibitors for the Treatment of Uncontrolled Diabetes

To compare clinical outcomes and the health care costs across two cohorts of uncontrolled diabetic patients who initiated treatment with Sulfonamides or Thiazolidinediones (SU/TZD) or Dipeptidyl Peptidase 4 (DPP-4) Inhibitors in a clinical practice setting. A retrospective analysis using a large administrative database and a clinical registry containing laboratory results of three Italian Local Health Units was performed. The index-period ranged from July, 2008 and June, 2010. Patients were treatment naïve to SU/TZD or to DPP-4, but already treated with other oral antidiabetic agents. Demographics, concomitant therapies, Charlson comorbidity index, glycemic and lipid control level and previous hospitalizations were assessed at baseline. Adherence was measured by Medication Possession Ratio (MPR). We calculated unadjusted rates and used a Poisson regression model to estimate risk ratios for diabetes-related hospitalizations occurred during the 18-months follow-up period. Total annual costs included all the pharmacological treatments and the direct costs due to hospitalizations and outpatient services. We identified 1384 patients treated with SU/TZD and 199 treated with DPP-4. DPP-4 patients were significantly younger (mean age 59.2 years and 65.0 years; p<0.001) and with less previous hospital discharges for diabetes-related diseases. Baseline mean HbA1c was 8.1% for SU/TZD and 8.2% for DPP-4 patients. DPP-4 naïve resulted more adherent (MPR≥80%) than SU/TZD naïve (70.9% and 55.8%; p<0.001). The SU/TZD group showed a significant increased risk of diabetes-related hospitalizations (unadjusted rate was 9,17 vs 3,47 per 100 person-years, p=0.002; adjusted incidence rate ratio 1.83; p=0.028). The higher hospitalization rate resulted in higher total annual direct costs per patient (€2.719 vs €2.462 of those treated with DPP-4). Results indicate that uncontrolled diabetic patients who initiated treatment with DPP-4, compared with those initiating with SU/TZD, are associated with a reduced risk of diabetes-related hospitalizations and consequently with a lower overall total annual cost per patient.

Analysis of Dynamic Performance for Multiple Dividing Wall Distillation Columns

Dividing wall columns are intensified process equipment with the capacity of reducing both capital and operational costs for a given vapor–liquid separation, when compared with conventional distillation sequences. For some kinds of mixtures, distillation systems with two dividing walls have been theoretically proved to present lower energy requirements and lower total annual costs than systems with a single dividing wall. Nevertheless, the use of an additional wall may lead to operational issues on the column, because of the more complex arrangement of the walls on the trays of the columns, where additional split of the vapor and liquid streams is expected. Thus, in this work the open-loop properties (minimum singular value and condition number) for the double dividing wall column are studied and compared with those of the dividing wall column for a wide range of frequencies, in order to determinate if the use of additional dividing walls may lead to potential control problems. It has been found that both systems show similar dynamic performance, with advantages for the double dividing wall column for mixtures with low composition of the middle-boiling component.

Simultaneous synthesis of process water and heat exchanger networks

This paper presents a novel superstructure and optimization model for the simultaneous synthesis of process water and heat exchanger networks. This superstructure combines the water network and heat exchanger network using interconnecting hot and cold streams. The water network has been extended for both direct and indirect heat exchanges. In addition, opportunities for heat integration between hot and cold streams, splitting and mixing of the freshwater and wastewater streams are incorporated within the superstructure. The proposed model is formulated as a non-convex MINLP (mixed-integer non-linear program), where the objective is to minimize the total annual costs of the network. A new convex hull formulation is presented for identifying the streams' roles within the network. Three examples involving single and multiple contaminant problems are presented in order to illustrate the applicability and capabilities of the proposed superstructure and model. In all cases the resultant networks exhibit lower total annual costs, whilst the freshwater and utilities consumption are the same as reported in the literature. In addition, novel designs for heat-integrated process water networks with smaller or same number of heat exchangers are presented.

Design and control of a reactive-distillation process for esterification of an alcohol mixture containing ethanol and n-butanol

This paper presents an economical design flowsheet and overall control strategy for simultaneous esterifications of ethanol and n-butanol mixtures with acetic acid. In this work, a difficult-to-design reactive-distillation (RD) process, classified as mixed Type-II/Type-III system, has been studied. After comparing three alternative design flowsheets, an indirect-sequence design containing a RD column, a top decanter, and a stripper gives significantly lower total annual cost and energy consumption than the other two designs. In the control strategy development, conventional inventory control with RD bottom level controlled by manipulating RD bottom flow shows that this process would exhibit multiple steady-states. An improved inventory control strategy with a rather unusual pairing by controlling this level using reboiler duty is proposed to alleviate this complex dynamic behavior. The dynamic results show that the proposed plant-wide control strategy is capable of holding product specifications despite disturbances from throughput and feed composition changes.

Robust Optimal Design of an Glycerol Etherification Process

AbstractGlycerol ethers are valuable fuel additives produced by reaction of glycerol with isobutene. The processes presented in the literature use high‐purity isobutene and are designed assuming accurate knowledge of reaction kinetics and physical properties. The optimal design of a plant processing 2.25 kmol h–1 glycerol, using isobutene of 90 % purity, is addressed considering the uncertainty of the design data. Plants with small reactors have the lowest total annual cost, but the recycle flow rates greatly increase when uncertain variables affect the process, constraining the operation feasibility. The optimal design, fulfilling the constraints despite uncertainty, is found by constructive nonlinear dynamics. The robustness of the optimal design is proved by dynamic simulation.

Design and Control of the Glycerol Tertiary Butyl Ethers Process for the Utilization of a Renewable Resource

In this paper, the design and control of an improved process for the manufacture of a fuel additive (glycerol tertiary butyl ethers, GTBE) from glycerol and isobutylene is developed. The improved process redirects one recycle stream, uses a stripping column instead of a flash tank to recover isobutylene, and uses a rectifying column instead of a distillation column to purify the product. Economic analysis shows that the improved process has a 22% lower total annual cost (TAC) than the best known process published in the literature. Significant increases in the selectivity of the overall process from 84.7% to 99.3% can also be realized by comparing the optimized improved design versus the original design. Dynamic simulations were also conducted and indicated that stringent product specification can be met with a simple decentralized feedback control structure despite impurities in the feed streams and also changes in the throughput.

Implementation of Ethanol Dehydration Using Dividing-Wall Heterogeneous Azeotropic Distillation Column

In this article, the design and optimization procedures of a dividing-wall column for heterogeneous azeotropic distillation (DWC-A) using cyclohexane as an entrainer for ethanol dehydration are investigated. The proposed procedures can detect the optimal values of the design variables and thereby guarantee the minimum energy requirements, which is related to the minimum CO2 emissions and the lowest total annual cost (TAC). Since ethanol and water form an azeotrope under atmosphere pressure, a conventional heterogeneous azeotropic distillation sequence (CHADS), including an azeotropic column and a recovery column, is usually used to perform the ethanol dehydration process. However, due to high energy requirements and equipment investments of CHADS, the TAC is at a relatively high level. DWC-A can be used to eliminate the condenser of the second column and decrease the degree of back-mixing. Both CHADS and DWC-A are simulated with Aspen Plus®, and the results show that DWC-A has an energy saving of 42.17% and the TAC reduction of 35.18% along with higher thermodynamic efficiency and reduction in greenhouse gas emissions.

Bioeconomic modeling of lactational antimicrobial treatment of new bovine subclinical intramammary infections caused by contagious pathogens

This study determined the direct and indirect epidemiologic and economic effects of lactational treatment of new bovine subclinical intramammary infections (IMI) caused by contagious pathogens using an existing bioeconomic model. The dynamic and stochastic model simulated the dynamics of Staphylococcus aureus, Streptococcus uberis, Streptococcus dysgalactiae, and Escherichia coli during lactation and the dry period in a 100-cow dairy herd during 1 quota year. Input parameters on cure were obtained from recent Dutch field data. The costs of clinical IMI, subclinical IMI, and intervention were calculated into the combined total annual net costs of IMI per herd. The cost effectiveness of 4 scenarios with lactational intervention was determined; scenarios included no intervention, treatment after 1 mo of infection, treatment after 2 mo of infection, and treatment after 1 mo of infection and culling of uncured cows after 2 mo of infection. Model behavior was observed for variation in parameter input values. Compared with no lactational intervention, lactational intervention of new subclinical IMI resulted in fewer clinical flare ups, less transmission within the herd, and much lower combined total annual net costs of IMI in dairy herds. Antimicrobial treatment of IMI after 1 mo of infection and culling of uncured cows after 2 mo of infection resulted in the lowest costs, whereas treatment after 2 mo of infection was associated with the highest costs between the scenarios with intervention. Changing the probability of cure resulted in a nonlinear change in the cumulative incidence of IMI cases and associated costs. Lactational treatment was able to prevent IMI epidemics in dairy herds at high transmission rates of Strep. uberis, Strep. dysgalactiae, and E. coli. Lactational treatment did not limit the spread of Staph. aureus at high transmission rates, although the associated costs were lower compared with no intervention. To improve udder health in a dairy herd, lactational treatment of contagious subclinical IMI must therefore be preceded by management measures that lower the transmission rate. Lactational treatment of environmental subclinical IMI seemed less cost effective. Detection of subclinical IMI needs improvement to be able to most effectively treat subclinical IMI caused by contagious pathogens during lactation.

Cost analysis of flavocoxid compared to naproxen for management of mild to moderate OA

Objective:Flavocoxid is a medical food used for the clinical dietary management of osteoarthritis (OA). The acquisition cost of flavocoxid is higher than most traditional, generic NSAIDs. However, flavocoxid may have more favorable gastrointestinal (GI) toxicity resulting in lower overall costs. These costs have not been previously examined. This study provides a decision analytic model to assess the net costs of using flavocoxid for OA from a Medicare perspective.Research design and methods:A decision model was developed to estimate the total costs associated with flavocoxid versus naproxen for the management of Medicare patients with mild to moderate OA. Probabilities were obtained from literature and expert opinion, and costs were obtained from Medicare. Sensitivity analyses were conducted by varying probabilities and costs within clinically relevant ranges.Results:The base case resulted in flavocoxid having lower total annual costs ($1482 per patient) compared to naproxen ($1592). Flavocoxid remained the lowest cost option when the cost inputs were varied by 25% (above and below the base case), and when the probability of GI events with flavocoxid were varied by 25%. However, when GI rates from the literature and implied relative risks from the expert panel were used, or if the cost of PPIs was $0, then naproxen was the less costly alternative, though saving less than the annual cost of flavocoxid. Key limitations were the limited outcomes in the model (only GI events), lack of consideration of adherence or combination therapy, and the reliance on expert opinion due to a lack of data for flavocoxid.Conclusions:In patients over 65 years of age who suffer from mild to moderate OA, flavocoxid may result in lower overall costs, despite a higher acquisition cost. Managed care organizations should consider total health care costs in the decision to include flavocoxid as a covered benefit.

Reducing Energy Consumption and CO2 Emissions in Thermally Coupled Azeotropic Distillation

AbstractThe design and optimization procedures of a heterogeneous thermally coupled azeotropic distillation sequence with a side stripper (TCADS‐SS) for the purification of isopropanol has been investigated. The proposed procedures can detect the optimal values of the design variables and thereby guarantee the minimum energy consumption, which is related to the minimum CO2 emissions and the lowest total annual cost (TAC). The procedures are applied to the study of the separation of azeotropic mixtures using the two distillation sequences. In the TCADS‐SS, the top end of the side stripper has both liquid and vapor exchange with the main column, which eliminates a condenser in contrast with the conventional heterogeneous azeotropic distillation sequence (CHADS). The results show that not only reductions in energy consumption and CO2 emissions but also higher thermodynamic efficiency can be obtained for the TCADS‐SS.

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.

Comparison of Extractive Distillation and Pressure-Swing Distillation for Acetone−Methanol Separation

Two of the most common methods for separating a binary homogeneous azeotrope are pressure-swing distillation and extractive distillation. The former is effective if the composition of the azeotrope changes significantly with pressure. The latter method is effective if a suitable solvent can be found. This paper compares the steady-state design and the dynamic control of these two methods when applied to the acetone-methanol binary system. The minimum-boiling azeotrope at 1 atm contains 77.6 mol % acetone at 328 K. At 10 atm the azeotropic composition is 37.5 mol % acetone at 408 K, so pressure-swing separation is feasible. Extractive distillation is also feasible using water as the solvent. Both systems require two distillation columns. Purities of the two products are set at 99.5 mol %. Results show that the extractive distillation system has a 15% lower total annual cost. However, a third component (water) is introduced that appears as trace impurities in both the acetone and methanol products. It is also much more difficult to attain higher purities in the extractive distillation system than in the pressure-swing system because of ternary vapor-liquid equilibrium constraints. The dynamic controllabilities of the two alternative processes are quite similar. Steady-state designs and control structures are also developed for the two methods when the columns are heat integrated. Heat integration is straightforward in the pressure-swing system because the condenser temperature in the high-pressure column is 60 K higher than the base temperature in the low-pressure column. In the extractive distillation system, the pressure in the second solvent recovery column must be increased from 1 to 5 atm to provide the necessary temperature differential driving force.

Selección tecnico-economica de emisores

El presente trabajo tuvo como objetivo estudiar los factores que intervienen en la selección técnico económico de goteros. En el estudio fueron utilizados emisores autocompensados y no autocompensados, considerando a los aspectos técnicos como porcentaje de suelo humedecido, número de emisores por planta y coeficiente de uniformidad y precio y la presión de operación del emisor como aspectos económicos. Los resultados muestran que la presión de operación de los emisores es el factor más importante a considerar en la selección, ya que para valores más bajos de presión de operación se obtuvieron menores valores de costo total anualizado, independiente del tipo de gotero. En general, los goteros no autocompesados presentaron valores de costo anualizado menores, para un rango de presión similar. Finalmente el análisis tecnico-económico en la selección de emisores es un procedimiento importante.

Outcomes associated with introduction of thiazolidinedione therapy in Medicaid enrolled patients with type 2 diabetes: an updated and expanded retrospective analysis

ABSTRACTObjectives: In an earlier analysis, differences in healthcare costs, medication adherence, and persistence were examined between patients with type 2 diabetes, enrolled in the North Carolina Medicaid, who had newly started thiazolidinedione (TZD) therapy and those starting other oral antidiabetic agents. In this analysis, the size of the cohort was increased by including 18 months of additional Medicaid data (until December 2004) and sought to: (1) replicate the results of the original study in a larger cohort; and (2) extend the original analysis by providing an additional 18 months of observational follow-up.Methods: A total of 2660 patients newly starting TZD therapy between July 2001 and December 2003 were compared to 2050 patients starting other oral antidiabetic medication for health-care costs and outcomes in the post-medication start year. In addition, the initial cohort was followed for an additional 18 months to examine if there were any differences in outcomes, such as hospitalization and total health-care costs, that could be associated with the type of therapy. Multivariate regression techniques, incorporating health-care utilization in the year prior to start of new therapy, were used to determine the net cost impact of one therapy versus the other.Results: Multiple regression analyses found that patients starting TZD have better treatment persistence in the post-medication start year compared to patients starting other oral antidiabetic agents (4% increase in therapy persistence index, p < 0.001). In addition, patients starting TZDs had 18.9% lower total annual health-care costs ( p < 0.01) compared to patients starting other oral antidiabetic agents.Examination of the original cohort of 3191 patients, for up to an additional 18 months, showed TZD's association with improved adherence rates but not with persistence. Importantly, treatment adherence remained the strongest independent predictor of decreased hospitalization risk and health-care cost reduction in this population.Conclusions: Introduction of thiazolidinedione therapy in a Medicaid-enrolled type 2 diabetic population was associated with significantly greater treatment adherence, in the post-start year, compared to patients starting other oral antidiabetic agents.

Design and Control of Conventional and Reactive Distillation Processes for the Production of Butyl Acetate

Jimenez and Costa-Lopez (Ind. Eng. Chem. Res. 2002, 41, 6735) recently discussed a reactive distillation process for the production of butyl acetate in which an extractive agent is used. Their process requires four distillation columns. No details of their plantwide control structure are given. This paper presents a quantitative comparison of two alternative processes for the production of butyl acetate in which no extractive agent is employed. The first is a conventional reactor/separation process with a reactor, three distillation columns, and two recycles. The second uses a reactive distillation column with two other conventional columns and two recycles. Each process is economically optimized, and the reactive distillation process has a 20% lower total annual cost. Plantwide control structures are developed for each process, and their effectiveness in the face of very large disturbances is demonstrated by dynamic simulation.

Healthcare costs and prescription adherence with introduction of thiazolidinedione therapy in Medicaid type 2 diabetic patients: a retrospective data analysis

SUMMARYObjectives: Outcomes in patients with type 2 diabetes may vary depending on the antidiabetic medication used. Observational studies of outcomes of diabetes pharmacotherapy are needed to understand the implications of choice of controller in different populations. This study compared differences in total health care costs, medication adherence, and persistence in patients with type 2 diabetes enrolled in the North Carolina Medicaid Program that were newly started on thiazolidinedione (TZD) therapy with patients starting other oral antidiabetics during the same period. In addition differences among the TZDs with respect to these outcomes were examined.Methods: A total of 1774 patients newly starting TZD therapy between July 2001 and June 2002 were compared to 1709 patients starting other oral antidiabetic medication (metformin or sulfonylureas) for health care costs and outcomes in the post-medication start year. In addition, a sub-group analysis of health care costs in patients starting either TZD (pioglitazone [n = 1086] versus rosiglitazone [N = 688]) was compared. All included patients had complete enrollment for the 24 months of follow-up. Multivariate techniques incorporating health care utilization in the year prior to start of new therapy were utilized to determine the cost impact of one therapy versus another.Results: Results of multiple regression analyses suggest that patients starting TZD have better treatment adherence and persistence in the post-medication start year compared to patients starting other oral antidiabetics (13% increase in Medication Possession Ratios, and 10% increase in therapy persistence index, both p < 0.001). In addition, patients starting TZDs had 16.1% lower total annual health care costs ( p < 0.01) compared to patients starting other oral antidiabetics. There were no differences in adherence and cost outcomes between the 2 TZDs.Conclusions: Introduction of thiazolidinedione therapy in a Medicaid-enrolled type 2 diabetic population was associated with significantly improved treatment adherence, persistence, and lower annual health care costs in the post-start year compared to patients starting other oral antidiabetics.

On Extending Russell and Krajewski's Algorithm for Economic Purchase Order Quantities*

ABSTRACTRussell and Krajewski presented an optimal purchase order quantity algorithm that considered the effect of the transportation rate structure for less‐than‐truckload (LTL) shipments. The authors applied the Russell and Krajewski algorithm to a variety of freight classes and lengths‐of‐haul. Anomalous cases were found in which the freight rate schedule, when used with the suggested algorithm, resulted in incorrect order size decisions. In this comment, the authors consider the impact of these anomalies on the optimal order quantity and associated total costs. A procedure is presented to adjust the Russell and Krajewski algorithm to arrive at the optimal purchase order quantity and the lowest total annual cost.