PROCESSES: BASICS OF PROCESS DESIGN - Biomass as a Sustainable Energy Source for the Future - page 208

duties (e.g., degrees of conversion, selectivity, and separation). This is an outside view
from the perspective of a unit. One also needs an inside view on how to structure each
of the process units such that the functions and targets can be achieved or corrected if
found to be infeasible. Supposing targets for conversion and selectivity have been
established, the question arises as regards the following: what types of reactors should
be chosen, how many, and in which configuration (parallel, sequential staging). The
equipment engineering is part of level 5. Iterations between both views are likely dur-
ing the design. This section deals with the creation of a network of process units (per
subprocess), taking an outside view on the network. The design of the process unit
(the inside view) is part of a lower level.

a. Scope
The goal is to design per chosen subprocess a network of process units that
jointly achieve the conversion targets that were set for the subprocess at the pre-
ceding level of design. Each unit performs specific processing functions.
A network in a subprocess is represented as a functional block diagram. Con-
version targets are set for each of the functions, mass and energy balances are set
up, and SHEET evaluations are made.

b. Knowledge
The processing functions operate on a material stream to affect a change. The
physical state of the material can be characterized by a stream state vector.
Table 7.2 presents the common stream states as well as common processing
functions to change a specific state. The processing functions can be used to
synthesize a network.
Targeting a specific state for a change by means of a processing function
often results in another state being changed to some extent, too. This latter
change may need to be undone by exerting another processing function in par-
allel. An example is keeping the reactor temperature constant by external

TABLE 7.2 Generic state vector of a stream with some common transformation
mechanisms
State of a material stream Processing function to affect a change

1. Thermodynamic phase(s) (G/L/S) Evaporation/condensation, melting/solidifying,

crystallization/dissolving, sublimation

2. Phase ratio Phase change/decanting/drying

3. Temperature Heating/cooling

4. Pressure and velocity (flow rate) Compression/pumping/expansion

5. Chemical identity (species) Reactions

6. Electrical charge Reactions

7. Composition per phase Reactions/mixing/diffusional separation

8. Particle/droplet/bubble size Milling, grinding/dispersion/agglomeration/

coalescing

9. Mass flow Mixing, splitting