PowerPoint Presentation

Modeling and Simulation of a Heat Exchanger Network For Maximum Energy Efficiency and Minimum CostRathnayake H.H.M.P & Charith Malinga R.M Department of Chemical & Process Engineering, University of Moratuwa, Sri LankaINTRODUCTIONDistillation has turned into the most energy-intensive separation process expansively used in many industries.Literature proves that distillation columns expend more than 95% of the total energy used in separations in chemical process industries all over the world.There is a heating duty (Reboiler) and a cooling duty (Condenser) for the particular distillation column application.Since, the condenser and the reboiler are two heat exchangers, even a basic distillation column can be simplified to a heat exchanger network comprised of at least two heat exchangers.SCOPE OF STUDY This study is devoted towards the separation of Methanol/Water/Sodium Chloride/Sodium Glycolate mixture by continuous distillation at high methanol recovery of 90% by mass.The reason for this application is, in almost all the bio-chemical applications related to the processing of natural polysaccharides such as starches involve in recovering methanol from such a by-product mixture.According to such industrial applications, the feed composition of methanol impure mixture can be taken as Methanol 70%, Water 22.5%, Sodium Chloride 5% and Sodium Glycolate 2.5% mixture at atmospheric pressure of 1 atm, at room temperature of 30oC. Total flow rate of feed solution for this study was taken as 100 kg/hr.The aim of this study is to investigate the energy saving potential of this distillation scheme by process integration via pinch technology. METHODOLOGYFirst, this distillation column scheme was modeled in ASPEN PLUS software to solve all shortcut distillation equations where the input data are feed composition, feed flow rate, feed temperature and feed, top and bottom pressures. The number of stages taken in initial simulation was an assumption of 10 stages. After modeling and simulation with shortcut methods in ASPEN PLUS, a table of the reflux ratio over corresponding number of stages was obtained where the exact reflux ratio was determined and rigorous modeling and simulation was executed in ASPEN PLUS using rigorous distillation column equipment model.Then, the simulation results were exported to Microsoft Excel where the final cost calculations for optimizing the economic number of stages for the distillation column was executed. Thereafter, pinch analysis was done by utilizing ASPEN HX NET software.

Shortcut SIMULATION Results

Optimization of Distillation column

For the Rigorous simulation, the optimum number of stages was determined as 15 because the reflux ratio has become approximately a plateau after 15 number of stages. Rigorous simulation results

These simulation results helped to extract the optimized thermal data for hot and cold utility streams in the process as to perform the pinch analysis for the heat exchanger network in the distillation column. Pinch AnalysisA hot stream is not be able to cooled down below the cold stream supply temperature as well as the cold stream is impossible to be heated above the hot stream supply temperature. (no temperature crossovers )

Practically, the hot stream can be cooled down only to a certain temperature value defined by the temperature approach of a heat exchanger which is the minimum allowable temperature difference (DTmin) in the stream temperature profiles of a heat exchanger unit.

The temperature level where this minimum allowable temperature difference can be observed in a process is called as the Pinch point or Pinch condition. stepwise procedure for Pinch Analysis

pinch analysis carried out with ASPEN HX-NET software

After the extraction of thermal data of process and utility streams, the initial DTmin value was taken as 10 oC and composite curves and grand composite curve were plotted with the help of ASPEN HX-NET software.

The plot of range targets reveals that the optimum DT min value is 20oC.

Optimized HEN Design

According to the pinch analysis simulation acted upon by means of ASPEN HX-NET energy optimizing tool, a total cost of 92.16% of the total cost target has been achieved with 3 numbers of units which had initially targeted for 4 units. As well, a cross pinch load of 229 kW has been achieved by meeting the optimum DTmin value in this heat exchanger network. Ultimate resultsThe process of methanol recovery from sodium minerals by way of distillation was successfully applied with pinch technology to improve the process heat exchanger network reducing the utilities requirements making the process more energy efficient.Some future research work is needed for further validation of these simulation results.

ConclusionFuture workAs a future research work, it is worth of studying how the energy savings would be when the feed conditions are varying.The validation and optimization of simulation results utilizing experimental investigation is needed.

THANK YOU!!!text

Identification of Hot, Cold and Utility streams in the process

Extraction of thermal data for process and utility streams

Selection of initial Dtmin value

`

Construction of Composite Curves and Grand Composite Curve

Estimation of minimum energy cost and capital cost targets

Estimation of optimum Dtmin value

Estimation of practical targets and Heat Exchanger Network Design