Heat integration, controllability issues

Now, we want to look at the dynamics of this complex flowsheet. There are three major issues that must be addressed in designing a control system for a heat-integrated column process that is operating under neat conditions. Auxiliary reboUers or auxiliary condensers are not used to balance the vapor boUup needed at the base of the low-pressure column with vapor condensation needed at the top of the high-pressure column. 

Design and synthesis of chemical processes are multi-objective optimisation problems in nature where several objectives are required to be optimised, maximised or minimised, simultaneously within a specified range of constraints. In this section the proposed integrated framework is introduced. The approach formulates the decision maker preferences into mathematical forms and then integrates these goals as a multi-objective optimiser into an overall stepwise procedure to cover all aspects of optimal design considerations, i.e. economical, environmental, heat integration as well as operability/controllability issues. 

A third major effect often encountered with recycle and heat integration is the propagation of disturbances from unit to unit, and their recirculation around internal process flow paths. To understand why this plantwide control issue differs so substantially from single-unit issues, it is worthwhile to review briefly the objectives of single-unit regulation. 

This chapter has provided a brief overview of process integration issues and possible solutions. For a much broader discussion of the topic of heat integration, the reader should consult Douglas (1988) or Seider et al. (2008). For a more extensive development of control system design issues, including a number of simulation case studies, Luyben (2002) should be consulted. 

System integration involves numerous miscellaneous development activities, such as control software to address system start-up, shut-down and transient operation, and thermal sub-systems to accomplish heat recovei y, heat rejection and water recoveiy within the constraints of weight, size, capital and operating costs, reliability, and so on. Depending on the application, there will be additional key issues automotive applications, for example, demand robustness to vibrations, impact, and cold temperatures, since if the water freezes it will halt fuel cell operation. 

At ICI Paints we have been tackling some of those Issues over the past few years. Our approach, whilst keeping in mind the distant unitary goal of a computer-controlled facility, has been to focus on hardware modules which could be developed and used incrementally on route to system Integration. Thus, our work follows the primary split of process parameters into heat-transfer and temperature control, and mass transfer and agitation. 

Another practical limitation in complex applications lies in the fact that, if temperature is used as a control parameter, one needs to worry about the integrity of a system that is heated too much (e.g., water-membrane systems or a protein heated above its denaturation temperature). When issues such as those mentioned above are addressed, parallel tempering can be turned into a powerful and effective means of enhanced conformational sampling for free energies over a range of temperatures for various systems. 

The issue of this kind of control configuration has been investigated using frequency dependent formulations of measures such as the condition number, the Relative Gain Array by Bristol (1966) and the Relative Disturbance Gain by Stanley et al (1985). This paper will focus on discussing the dynamic control structure on the heat pump section and how each dynamic control structure affects on the stability of the integrated distillation column. 

The integrated IHX/pump component is one of the JSFR key technologies to achieve a compact primary coohng system. As is illustrated in Fig. 11.8, it includes a primary pump, IHX tube bundles, and PRACS heat exchange tubes. Major issues of this component are prevention of gas entrainment from the sodium free surface, sodium level control, pump shaft stability, mbe wear due to vibration, temperature distribution control, and fabrication capabihty. 

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