Page 81 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

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Encyclopedia of Physical Science and Technology EN002E-49 May 17, 2001 20:13

Batch Processing 45

The goal is to use common equipment in the manufacture When construction is completed, design, plant opera-
of various products needed by the market via production tions, and the construction group proceed to start up the
planning and scheduling. An individual route may be se- new plant. Technical service takes over to operate the plant
lected for each batch of product, depending on the avail- to the best economic advantage. Any design errors are
ability of the various pieces of equipment. The products overcome with production planning strategies and short-
may have low production requirements or may be at the term production scheduling of the various products that
beginning of their commercial life. These plants are rare, will be produced in the new plant. The time invested in the
since when they are constituted, they are likely to be re- development and construction of the new process is nearly
defined as single-product plants for economic reasons. four years. Throughout all this time, the opportunity for
formal optimization is minor because the new process is
not fully defined. In the course of chemical business, the
D. Batch Process Development
next step for the plant is debottlenecking and production
Conception is the most critical step in the development expansion planning.
of a new process. Though still done largely on the basis
of experience and intuition, it may be implemented with
process synthesis. Computerized algorithms may provide V. ECONOMICS OF BATCH OPERATIONS
for a large number of possible routes to a product. This
method, combined with the analysis of raw material costs Batch plant economics are similar to those ruling contin-
and DS-51 ASTM tests for process hazardousness, are the uous plants: They are set by the revenue collected and the
best options to speed up the bench-scale development of total cost of running the plant at a certain production rate.
new chemical processes. Thus, one or a reduced number The analysis of the cost of manufacturing one or more
of routes to the desired product can be identified for pre- products is often based on the F.O.B. cost of the process
liminary process development. and storage equipment required; the control equipment
Specification of a chemical route and processing steps needed to run the plant; the cost of additional materi-
rarely defines the process completely. The process de- als and labor needed to construct the plant; the indirect
signer is still free to choose appropriate design variables. costs, including supervision as well as engineering and
Further difficulties are encountered due to the lack of com- construction fees; and additional costs due to freight, in-
mercial or engineering data needed for the design. surance, and taxes. A list of the process and storage equip-
Preliminary design, assisted by material and energy bal- ment results from a preliminary design of the plant, which
ances, contributes to flow-sheet development and to es- also yields a process flow diagram (Fig. 2). The equip-
tablishing process operating conditions. Also, it serves ment list is used to make a capital investment estimate of
the purpose of equipment sizing and generating a list of the plant, which includes the total F.O.B. cost and all the
equipment for preliminary process evaluation. The first other expenses of constructing a plant. When real cost data
capital investment estimate of the process is based on this are missing, one can approximate values using Guthrie’s
study. Then, a pilot plant test of the new process can be standard procedures and extensions for batch plants. This
scheduled. Product samples are made for customer anal- analysis yields the total capital costs for the process at the
ysis to set product specifications. Physicochemical and production rate at which the plant can operate. In defini-
engineering parameters are measured in the pilot plant to tive cost analysis a list of control equipment is produced
verify preliminary educated guesses of physical properties with the completion of a definitive design package, which
and transport parameters which need to be firmed for the leads to a mechanical flow diagram. The total book manu-
definitive design. facturing cost of the product is a composite of four costs:
Economic evaluation analyzes the process on the ba- (1) raw materials and utilities, which are proportional to
sis of production costs and the rate of return on capital production rate; (2) direct production costs, which include
investment. If the process is economically attractive, the (a) operation labor and overhead (supervision and cleri-
construction of a commercial plant is recommended to top cal work), (b) operating supplies, which are proportional
management. A definitive design package is generated for to operating labor, (c) maintenance and repair, which in-
construction engineering. A definitive mechanical flow di- clude labor and materials (these costs are proportional
agram is included, with all the electrical, instrumentation, to fixed capital costs), and (d) laboratory labor; (3) plant
and safety needs of the process. The waste disposal and overhead, proportional to operating plus maintenance and
utilitiessectionsarecompleted.Thedesignengineersmust repair labor; (4) fixed charges, which include depreciation
ensure that the process will run safely and it will be en- proportional to total capital costs, as well as local taxes
vironmentally clean. Several process and plant permits, and insurance proportional to fixed capital costs.
without which plant construction cannot proceed, need to Total product cost is obtained by adding to the book
be requested at this time. manufacturing costs the following costs: (1) general