Retrofit of distillation

Example 5.15 Retrofits of distillation columns by thermodynamic analysis The synthesis of methanol takes place in a tube reactor in section 3 in the methanol plant shown in Figure 5.7. The reactor outlet is flashed at 45°C and 75 bar, and the liquid product (stream 407) containing 73.45 mol% of methanol is fed into the separation section (see Figure 5.8), where the methanol is purified. Stream 407 and the makeup water are the feed streams to the section. Table 5.2 shows the properties and compositions of the streams in section 3. The converged simulations are obtained from the Redlich-Kwong-Soave method to estimate the vapor properties, while the activity coefficient... 

Example 5.9 Retrofits of distillation columns by thermodynamic analysis... 

Demirel, Y., Retrofit of distillation columns using thermodynamic analysis, Sep. Sci. Technol.,41 (2006)791. 

As an example, one very common retrofit situation is the replacement of distillation column internals to improve the performance of the column. The improvement in performance sought is often an increase in the throughput. This calls for existing internals to be removed and then to be replaced with the new internals. Table 2.8 gives typical... 

The retrofit of more complex distillation sequences can also be considered. Within a larger, more complex sequence, any pair of columns that are together in a sequence can be considered as candidates for the same retrofit modifications as those discussed for two-column retrofit. 

The nonlinear nature of these mixed-integer optimization problems may arise from (i) nonlinear relations in the integer domain exclusively (e.g., products of binary variables in the quadratic assignment model), (ii) nonlinear relations in the continuous domain only (e.g., complex nonlinear input-output model in a distillation column or reactor unit), (iii) nonlinear relations in the joint integer-continuous domain (e.g., products of continuous and binary variables in the schedul-ing/planning of batch processes, and retrofit of heat recovery systems). In this chapter, we will focus on nonlinearities due to relations (ii) and (iii). An excellent book that studies mixed-integer linear optimization, and nonlinear integer relationships in combinatorial optimization is the one by Nemhauser and Wolsey (1988). 

The internal modifications to retrofit the distillation system consider the distillation column and its internals. In this level of retrofit, some changes are made in the internals or nozzles of the main column and the side strippers. Moreover, the reboilers and pump around loops are examined and adjusted as required. Therefore, more complex modifications are required at this level that lead to higher investments. The objective of these modifications is to find out the ideal distribution of stages for each section in the main column [4]. This ideal design is applied to the existing column by modilying its internal to the niinimrim extent to reduce the costs. 

The cost of gas from the industrial boiler retrofit is compared to the delivered prices to the industrial sector of distillate and residual oil and natural gas. Comparisons are presented for the Midwest, New England and Northwest regions for 1985 and 1990 under three economic scenarios. The scenarios are based on assumptions regarding escalations in the price of oil and the resultant impacts on the prices of other conventional fuels. Scenarios are classified as low, medium, and high, corresponding to oil prices of 14.50, 15.15, and 19.72 per barrel, respectively, in 1990. The scenarios are part of DOE s current policy and evaluation program.(5)... 

The first commercial DWC in Korea was developed through the retrofit of an SSC and was installed successfully in a plant of LG Chem. Ltd. (Lee et al, 2011b). Their case study reports this industrial implementation of the DWC with particular attention paid to the practical aspects of the retrofit project. Figure 9.16 shows an alcohol-purification unit in a 2-ethylhexanol (2-EH) production plant. This unit consists of three main distillation... 

GadaUa, M., Jobson, M. and Smith, R. (2003) Shortcut models for retrofit design of distillation columns. Chemical Engineering Research and Design, 81, 971-986. 

Liu, Z.Y. and Jobson, M. (2004) Retrofit design for increasing the processing capacity of distillation columns 1. A Hydraulic performance indicator. Chemical Engineering Research and Design, 82,... 

There are two major costs that play an important role in the feasibility of retrofitting a distillation column to HMD. One of them is the capital cost of the membrane module along with compressor, exchangers and associated installation, piping and labor costs (that is, cost of retrofitting). The other is the utility cost, which includes condenser and reboiler... 

For the techno-economic evaluation of retrofitting a distillation column to an HMD system, one important indicator is the net savings (NS %). It is the percentage of difference in the... 

Figure 23. Choosing between structured packing or high performance trays for distillation retrofits. (Reproduced with permission of the American Institute of Chemical Engineers. Copyright 1997 AlChE. All rights reserved.)...

Part 3 of this book presents a number of major developments and applications of MINLP approaches in the area of Process Synthesis. The illustrative examples for MINLP applications, presented next in this section, will focus on different aspects than those described in Part 3. In particular, we will consider the binary distillation design of a single column, the retrofit design of multiproduct batch plants, and the multicommodity facility location/allocation problem. 

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