Page 52 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Process Planning, Scheduling and Flowsheet Design 37

Table 1- 7 Table 1-8
Time Study Time Study

Percentage
Percent of Time Activity of Engineers of Time
I
Single Avg.
Activity of Englneers Study I Range Consulting outside of scheduled jobs. . . . . . . . . . . . . . . . . . 4.4
Section supervision duties. . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. 7
Process design caiculations 34.69 3fr-52
Conferences, consultation, unscheduled urgent Meetings related to scheduled jobs. . . . . . . . . . . . . . . . . . . . 13. 7
assignments, information assembly 28.98 13-29 Discussions with vendors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6
Supervision and administrative, including time
schedules, discussions with salesmen, prepa- Special technical assignments......................... 2.4
ration of outside correspondence 4.45 4-15 Communications within section....................... 5.9
Preparation of charts, forms, methods for bene-
fit of over-all group 1.95 1-3 Process design calculations (original) . . . . . . . . . . . . . . . . . 51.0
Marking, checking, and reviewing flow sheets Process design calculations {checking)................. 3.7
( no drafting) 10.94 9-12
Group meetings, training periods, over-all de- Equipment schedules, line schedules, etc. . . . . . . . . . . . . . . . 3.1
partment and company development 1.80 1-3 Flow sheet development, checking, revising (no drafting). 2.5
Literature review (current magazines, etc.) 1.80 0.5--2
Coffee breaks, etc. 5.55 4-6 Coffee breaks, miscellaneous activity. . . . . . . . . . . . . . . . . . • 6.0
Unaccounted, including vacation 9.84 5--10 100

This does not include total project coordination or pro- be utilized, sometimes to generate a value and sometimes
ject engineering. (For expanded reference also see [51].) to check a questionable literature value.
It should be recognized that the data in these tables Therefore, when developing an estimate of process
may not necessarily fit other situations; however, it can engineering time required, it is important to recognize
serve as a guide. Since it is based upon engineers associ- the amount of effort that may be necessary to collect phys-
ated. with an engineering department located at an oper- ical property data before any real work can commence.
ating company plant site, there is a basic difference in This same concern exists when evaluating K values and
contacts, availability of production experience, and per- activity data for systems.
haps even philosophy between this type of group and one
centered at an engineering office remote from plant con-
tacts. The interruptions and requirements for data and Estimated Equipment Calculation Man-Hours
results although similar in many respects are certainly dif-
ferent in other respects. The use of this type of activity The required man-hours for a specific calculation vary
information will be combined with detailed calculation with the process system, availability of physical data, and
data and discussed later. the relative familiarity of the process design engineer.
Records collected over a period of years on a wide cross-
section of organic and inorganic process equipment. cal-
Collection and Assembly of Physical Property Data
culations are summarized in Table 1-9. It is impossible to
accurately define the limits of the calculations represent-
An important but time-consuming factor in practically
every design situation and in development offlowsheets is ed, but on an average, they have been found to be helpful
in establishing the order of magnitude of the calculation
the collection and assembly of physical property data for lime, as well as the basis for approximating the over-all
the components of the system in question. Often it is not
sufficient tc obtain single data points from various tables, extent of the process engineering of the project.
since many designs cover rather wide ranges of tempera- Electronic computers, both digital and analog, can be
ture and pressure and the effects of these on the proper- used to great advantage in design studies and calcula-
ties must be taken into account. tions. In evaluating reactor designs it is extremely helpful
Data may be located in many useful handbooks as well to develop a family of performance curves for variables
as published technical papers and company compilations. involved in the system. Usually this type of calculation
However, experience indicates that extensive literature becomes too time consuming with the desk electronic
searches may be necessary to locate specific data on a par- calculator, and is a good problem for the computer.
ticular compound. It is surprising to find so many com- After investing time and talent into a program for the
mon compounds for which the data is incomplete and computer, it is usually only a matter cf minutes or hours
sometimes inaccurate. Empirical correlations must often before a complete series of results can be calculated.