71 4.1.3 Prioritizing the Factors The three major site location factors are usually the location of raw materials, location of markets, and transportation. Once these aspects have been determined, otherimportant (but secondary) considerations can be identified and evaluated. However, even if many of the basic requirements for a chemical process are satisfied by a partic ular site, the site still may not be accept able if certain important criteria canno t be fulfilled, e.g. lack of government approval due to adverse public opinion, environmental regulations, availability of labour, etc. Therefore, it is necessary to consider the process ofsite selection as an overall package of essentialrequirements all of which must be satisfied by the preferred site location; primary factors (probably 3 or 4) which are highly desirable; and achievement of as many desirable (but non-essential) requirements as possib le. Final site sele ction (i.e. ob tainin g a listing of site preferen ces) may be helped by listing all the features (required and existing) for each site, and assigning a subjective numerical value (say 1 to 5, or 9) for each feature. Each location can then be given a final point s rating . Some discretion must be exercis ed because serious disadvant ages must not be obscured by this approach. For example, a site that was otherwi se ideal (or top of the list of preferences) but which had no local water available would probably be of little use as a chemical plant complex! Action: Prepare a list ofsuitable sites for the construction ofthe chemical Plant, arranged in descending order ofpreference.List all the merits and disadvantages ofeach site, and explain in detail why the first site is preferred. State any factors that need to be monitored throughout the project, e.g. changes in government policy. References Baasel (1990; Chapter 2) and Peters and Timmerhaus (3rd edn, 1980; Chapter 3). Both chapters include detailed reference lists. 4.2 PLANT LAYOUT Having selected a suitable site for the chemical plant, it is then possible and necessary to make a preliminary decision regarding the layout of the plant equipment. Although the equipment has not been designed in detail, preliminary estimates of the physical size ofeach item should be available in the equipment list (see Section 3.3). Any sizing differences between the initial and final estimates should not be too excessive, and appropriate areas for access, maintenance and safety (and insurance) should be allowed around the plant items when determining the layout. A preliminary determination of the plant layout, also called the plot plan, enables consideration of pipe runs and pressure drops, access for maintenance and repair, access in the event of accidents and spills, and location of the control room and administrative offices. The preliminary plant layout can also help to identify undesirable and unforeseen
