Bases Del Diseño

2
Flowsheets
plant design is made up of words, numbers, and
pictures. An engineer thinks naturally in terms of the
sketches and drawings which are his "pictures."
Thus, to solve a material balance problem, he will
start with a block to represent the equipment and then will
show entering and leaving streams with their amounts and
properties. Or ask him to describe a process and he willbegin
to sketch the equipment, show how it is interconnected, and
what the flows and operating conditions are.
Such sketches develop into flow sheets, which are more

A

elaborate diagrammatic representations of the equipment, the
sequence of operations, and the expected performance of a
proposed plant or the actual performance of an already
operating one. For clarity and to meet the needsof the
various persons engaged in design, cost estimating,
purchasing, fabrication, opera tion, maintenance, and
management, several different kinds of flowsheets are
necessary. Four of the main kinds will be described and
illustrated.

2.1. BLOCK FLOWSHEETS

Characteristics of the streams such as temperature, pressure,
enthalpy, volumetric flow rates, etc., sometimes are convenientlyincluded in the tabulation. In the interest of clarity, however, in
some instances it may be preferable to have a separate sheet for a
voluminous material balance and related stream information.
A process flowsheet of the dealkylation of toluene to benzene
is in Figure 2.4; the material and enthalpy flows and temperature
and pressures are tabulated conveniently, and basic instrumentation
isrepresented.

A t an early stage or to provide an overview of a complex process o r
plant, a drawing is made with rectangular blocks to represent
individual processes or groups of operations, together with
quantities and other pertinent properties of key streams between
the blocks and into and from the process as a whole. Such block
flowsheets are made at the beginning of a process designfor
orientation purposes or l ater as a summary of the material balance
of the process. For example, the coal carbonization process of
Figure 2.1 starts with 100,000Ib/hr of coal and some process air,
involves six main process units, and makes the indicated quantities
of ten different products. When it is of particular interest, amounts
of utilities also may be shown; in this example the useof steam is
indicated at one point. The block diagram of Figure 2.2 was
prepared in connection with a study of the modification of a n
existing petroleum refinery. The three feed stocks are separated
into more than 20 products. Another representative petroleum
refinery block diagram, in Figure 13.20, identifies the various
streams but not their amounts or conditions.
2.2. PROCESS FLOWSHEETSProcess flowsheets embody the material and energy balances
between and the sizing of the major equipment of t he plant. They
include all vessels such as reactors, separators, and drums; special
processing equipment, heat exchangers, pumps, and so o n.
Numerical data include flow quantities, compositions, pressures,
temperatures, and so o n. Inclusion of major instrumentation that isessential to process control and to complete understanding of the
flowsheet without reference to other information is required
particularly during the early stages of a job, since the process
flowsheet is drawn first and is for some time the only diagram
representing the process, As the design develops and a mechanical
Rowsheet gets underway, instrumentation may be taken off the
process diagramto reduce the clutter. A checklist of the
information that usually is included o n a process flowsheet is given
in Table 2.1.
Working flowsheets are necessarily elaborate and difficult t o
represent o n t he page of a book. Figure 2.3 originally was 30in.
wide. In this process, ammonia is made from available hydrogen
supplemented by hydrogen from the air oxidation of natural gas in a...