Grass-roots design

Various criteria were proposed for the optimal selection of the equipment configuration and the number and sizes of units. In grass-root design, the capital cost of equipment is mostly used as the optimization criterion. In retrofit design a more appropriate objective function seems to be the net profit, which has to be maximized. Papageorgaki and Reklaitis (1993) formulated the criterion as follows ... 

An economic evaluation of this alternative process showed that for a grass roots design, the capital costs of the new process would be reduced by about 25%, compared to the current process. 

The relations between energy efficiency and capital cost must be evaluated from the analysis of the overall plant system. At some point, improved energy efficiency will require more investment. However, many of the practical processes of today may well be operating quite far from this point. Further process analysis along these lines may well be fruitful, particularly for grass roots design situations. 

Ever-increasing environmental concerns may make it necessary to evaluate the existing process to reduce emissions, operator exposure, limit waste disposal of filter aid, or reduce wash quantities requiring solvent recovery or wash treatment. Breakdown of an old piece of equipment often provides the opportunity and justification to improve plant conditions. New grass roots designs may have the tendency to revert to industry standards. This is also the opportunity to improve conditions or substantiate the current equipment of choice. 

Moderate operating parameters catalyst can be used as a replacement to other transalkylation units, or in grass roots designs... 

Figure 5 Estimated savings in some DSM technologies, achieved by applying PI principles to process and plant design (grass-roots situation).

On typical grass-roots, chemical processing facilities, as much as 10% of the total capital investment is allocated to process control equipment, design, implementation, and commissioning. Process control is a very broad topic with many distinct aspects. The following possible sub-topics give some idea of the full breadth of this topic ... 

Fully self-supported, stand-alone, grass-roots plant design ... 

The other cost contributions, either as direct or indirect costs, are expressed by means of factors /j relative to the purchasing cost of basic equipment. Table 15.6 presents some mean values, ordered by the type of process fluids, fluids and solids, or solids (Peters Timerhaus, 1991). The reference year is 1990. The factors FI to F9 designate direct costs, while the factors FIO and FI 1 regard indirect costs. The factors F12 and F13 allow the estimation of contractor fees and unforeseen events. The factors F6 to F9 considers only plant extensions and improvement of an existing site, and not grass-root... 

For the depropanizer column, most of the default values are acceptable. Because a single distillation system would be installed normally on an existing plant site, using utilities provided by the site, the Project Type would not be selected as Grass Roots/Clear field. This Project Type would cause new items, already provided at the site, to be included in the design and cost estimates. Typically, these include a new control system and electrical substation components. 

A grass roots facility to produce polyvinyl alcohol (PVOH) is being constructed in a chemical complex on the U S. Gulf Coast. Your design team will complete the process engineering for the unit which produces polyvinyl acetate (PVAC). PVAC is further reacted in another part of the facility to produce the PVOH final product. The polyvinyl acetate unit includes the polymerization reactor system and the downstream recovery process. Your design must be capable of an annual production rate of 100 MMlb of PVAC intermediate. 

It is possible to design a light ends unit to process feeds from several plants, and this is often done, particularly in the case of building a grass roots refinery or in the case of a major expansion involving several new units. In taking this approach, one key rule must be observed. 

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