Plant models Planning

Next the individual process steps are developed (design, calculations, tests, quality assurance measures). All of these activities enter the piping and instrumentation (P I) diagram, which later forms the basis for preparing the plant model, planning construction work, technical data sheets, and the safety and measurement and control concept. 

In plant operations planning each refinery model produces target operating conditions, stream allocations, and blends across the whole refinery, which determines (a) optimal operating conditions, flows, blend recipes, and inventories and (b) costs, cost limits, and marginal values to the scheduling and real-time optimization (RTO) models. 

Allen, D.H. (1971) Linear programming models for plant operations planning. British Chemical Engineering, 16, 685. 

Hence, to model a chemical plant precisely requires a lot of effort. This effort is typically expended when a new plant is planned. However, such a precise process model is not necessary or useful for other purposes. In short-term control of chemical production plants, so-called prediction control models are used which focus on the measurement of system responses to certain changes of control variables on an empirical basis. These models use basic relations of the theoretical models introduced above. The next subsection outlines a brief overview of such models. 

Piping and instrumentation diagram (PSdD). See P ID Cpiping and instrumentation diagram). Planned release of harmful emissions, 858-859 Plant models, 32, 42 3. See also 3-D diagrams. 

The above applications require plant models at different levels of detail. Long term capacity analysis requires the least detail in recipe representation. Typically, the recipe of a batch process is represented with a small number of activities occupying key equipment that is likely to limit production. Long term planning utilizes models with a detail similar to those of capacity analysis. Short term planning and scheduling require more detailed models that account for the ntihzation of all main equipment and the critical auxiliary equipment (i.e., those with high utilization that... 

Measurement Selection The identification of which measurements to make is an often overlooked aspect of plant-performance analysis. The end use of the data interpretation must be understood (i.e., the purpose for which the data, the parameters, or the resultant model will be used). For example, building a mathematical model of the process to explore other regions of operation is an end use. Another is to use the data to troubleshoot an operating problem. The level of data accuracy, the amount of data, and the sophistication of the interpretation depends upon the accuracy with which the result of the analysis needs to oe known. Daily measurements to a great extent and special plant measurements to a lesser extent are rarelv planned with the end use in mind. The result is typically too little data of too low accuracy or an inordinate amount with the resultant misuse in resources. 

The confluence of sharply rising Operations and Maintenance (O M) costs. NRC requested Individual Plant Examinations (IPEs) and increased personal computer capabilities gave rise to the R R Workstation. Its uses and maintains-current PSA models and databases for individual plants to perform O M planning and scheduling, and uses the PSA in IPE models to identify plant design, procedure and operational vulnerabilities. The Risk and Reliability Workstation Alliance was organized by EPRI to support the R R Workshop in order to achieve O M cost reduction, plant productivity and safety enhancement through risk-based, user-friendly, windowed software louls (Table 3.6 8). The Alliance, initiated in 1992, includes 25 U.S. utilities and four international partners from Spain, France, Korea, and Mexico. SAIC is the prime contractor for the R R Workstation, with participation of five other PSA vendors. 

Kaiser, G. D., 1986, Implications of Reduced Source Terms for Ex-Plant Consequence Modeling and Emergency Planning," Nuclear Safety 27,3, pp 369-384, July-September. 

The dotted lines in the diagram indicate the various feedback paths that exist to enable the individual to identify if a particular stage of the processing chain was executed correctly. Thus, if the operating team had planned a strategy to handle a complex plant problem, they would eventually obtain feedback with regard to whether or not the plan was successful. Similar feedback loops exist at the rule and skill-based levels, and indicate opportunities for error correction. The application of the stepladder model to a process industry example is given in Appendix 2A at the end of this chapter. 

The collection and tabulation of data will provide an opportunity to become familiar with the company and will generate a good understanding of the operation of the plant. Much of the data will be needed to establish the models needed to size the various areas of the plant. For instance, hours worked should be analyzed to identify shift work, direct and indirect effort, and the normal and overtime activity. Outside contractors may be employed, and this contribution will need to be determined, sometimes by visiting the contractor s facilities. When expansions are being planned, it may be necessary to discuss the contributions that outside contractors make to the factory and assess the increase which they can accommodate. 

The recent introduction of inexpensive desktop computers has allowed their extensive use throughout many companies. The standard spreadsheet packages which accompany these machines enables the above data to be laid out in an interactive way, so that what if situations can be explored at the planning stage and the implications of, for example, market trends in the food industry, to be examined over the long term for its effect on the plant layout. The model may include a factor to take into account improvements in technology and working practices in both the office and factory. 

When spills and releases of hazardous gases or liquids occur, the concentration of the hazardous material in the vicinity of the release is often the greatest concern, since potential health effects on those nearby will be determined by the concentration of the substance at the time of the acute exposure. There are many models of routine continuous discharges (e.g., discharges arising from leaky valves in chemical plants), but these carmot be applied to single episodic events. Research on the ambient behavior of short-term environmental releases and the development of models for concentration profiles in episodic releases are cmcial if we are to plan appropriate safety and abatement measures. 

The waste management situation in Austria is presented, and it is explained that Baufeld-Austria GmbH has developed a method and concept, with the eooperation of cement plant experts, to enable some Austrian eement factories to responsibly use plastics waste as an energy source. The conditions used for developing the model, relating to fuel quality, environmental proteetion, and public health, are explained. The Baufeld model for processing of plastics waste is then described. Details of future plans are included. 

Lakshmanan, R., and Stephanopoulos, G Synthesis of operating procedures for complete chemical plants. I. Hierarchical, structured modeling for nonlinear planning. Comput. Chem. Eng. 12, 985 (1988a). 

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