Design aspects reboiler

For thermosyphon reboilers, the hydraulic aspects are as important as the heat transfer aspects. The design of thermosyphon reboiler piping is too broad a subject for this handbook. Some good articles on the subject can be found in References 2-14. Reference 3 is particularly good for horizontal thermosyphon reboilers. Table 1 has typical vertical thermosyphon design standards. 

We have designed and implemented a reactive divided wall distillation column for the production of ethyl acetate from acetic acid and ethanol. Important aspects derived from steady state simulation were considered for instance, a side tank was implemented in order to split the liquid to both sides of the wall and a moving wall inside the column that allows to fix the split of the vapor stream. The dynamic simulations indicate that it is possible to control the composition of the top and bottoms products or two temperatures by manipulating the reflux rate and the heat duty supplied to the reboiler, respectively. The implementation of the reactive divided wall distillation columns takes into account important aspects like process intensification, minimum energy consumption and reduction in Carbon Dioxide emission to the atmosphere. 

The next important aspect of tuning a multivariable controller is to determine what happens when different constraint sets become active. Eor example, assume that you have designed a distillation tower controller with constraints on overhead composition, bottom composition, and tower AP. The MVs are reboiler duty and reflux rate. The foUowing are examples of the types of constraint tradeoffs that you need to consider ... 

As in the case of reboilers and condensers, distillation control is too wide a topic to be adequately covered in a handful of chapters. Entire texts (68, 89, 301, 332, 362) deal exclusively with distillation control. Most of these strike a balance between theory, practice, controls design, and controls optimization. In contrast, the coverage here emphasizes operational aspects what various control schemes can and cannot do, how to put together a control system (not necessarily optimum, but one that works), how to recognize and avoid a troublesome system, what are the ill effects of various poor control schemes, and what corrective action can restore trouble-free operation. 

Limitations (i) the Damkohler number is assumed to be invariant on all the reactive stages (ii) the effect of structural aspects of the unit (e.g. feed ratio t e, location of multiple feeds, reflux and reboil ratios) are not considered and (m) the energy balances are left out from the design methodology. 

Conventional heat recovery from paper machine exhaust air streams can be designed optimally with respect to the climate at the mill location and the type of drying process involved. Different heat pump types can be applied, for example absorption heat transformers, to elevate the stream temperatures above the temperature of the excess heat. In an integrated mill with impingement drying the eventual excess low-pressure steam from the TMP-heat recovery, before or after the reboilers, can be utilised in an organic Rankine cycle for production of electrical power. The next step is to study the design and economic aspects of different types of ORC-plants. 

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