Hydrocarbon Processing - December 2021 - 44

Process Optimization
1.1
0.4
0.5
0.6
0.7
0.8
0.9
1
2
17
Increasing relative size
FIG. 3. Impact of scale on process yield.
high-fines Group A powder process. The data is masked,
as it is proprietary, and is reported relative to the smallest
unit tested. Constant pressure, temperature and gas
contact time were maintained. FIG. 3 shows that yield
remains essentially constant as size is increased, except
at one scale, due to hydrodynamics caused by bubbles.
Not all Group A powder processes show this behavior.
* Address issues immediately, rather than ignoring them
or wishing them away.
* Take a total engineering approach to the design of the
pilot plant and the first commercial plant. The new
reactor always receives the most attention in the design
phase, but it cannot operate if the front or back end of
the process is designed or built poorly and is incapable
of reliable operation.
* Engineering should collaborate with the research team
as soon as the viability of the process is validated in the
lab, and adequate and repeatable yield data is obtained
to start the first-pass concept plant design. This exercise
often leads to the discovery of gaps in research that can
then be addressed before committing to the pilot plant.
These gaps will eventually be discovered and will need
to be addressed. Unfortunately, this discovery tends to
happen after the engineering firm is hired and staffed up
to design the pilot plant. Engineers charging hours will
end up working at a less-than-optimal pace while waiting
for the missing information, thereby increasing the
project cost and schedule.
* Select the correct engineer for the pilot plant design. The
local full-service or boutique firm may be a lower-cost
option for the design and construction phase, but it may
not be the correct choice. Remember, this is fluidization
and solids processing. Despite the advancements in
the field, it is still somewhat of a " black art. " If the
technology developer is forced to spend money to fix
problems before steady-state pilot testing can begin,
then any perceived cost savings during the design and
construction phase may be spent multiple times over.
In addition, by this time, the process owner will have
operating staff on the payroll just waiting around, which
becomes expensive. Not every company has deep pockets
to ride through such an unfortunate event or reassign idle
operators to other activities.
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* Correct process and mechanical engineering should be
carried out for the pilot and the first commercial plant
reactor, other fluidized vessels and their internals.
* Not spending the correct amount of money is another
caution. There are reasons why the cost for 2-in. metalseated
full-port ball valves and an actuator range from
$3,000-$25,000 (U.S. suppliers' data only).
Common operational issues in chemical synthesis reactors.
Common issues related to the operation in chemical
synthesis reactors include:
* Poor yield/selectivity, caused by:
° Reaction chemistry not studied correctly/insufficiently
° Incorrect catalyst size distribution (too coarse/too fine)
° Incorrect reactor velocity (too low)
° Poor gas distributor design or damaged distributor
* Reactor instability, caused by:
° Reactor velocity too high (high velocity can mean
low bed density and runaway reactions)
° Coil layout too restrictive (solid motion must be
reasonably free to dissipate the heat generated)
° Incorrect distribution of coils within reactor
(coils must cover an adequate portion of the reactor)
* Catalyst attrition, caused by:
° Catalyst is too soft
° Incorrect gas distributor design (jet velocity too high)
° Incorrect cyclone design (cyclone velocity too high)
° Incorrect gas distributor fabrication/installation or
insufficient quality check (either new or repaired)
* Catalyst deactivation, caused by incorrect grid plate design
* Erosion of internals, caused by incorrect placement of
internals relative to gas jets
* Filter operation, caused by:
° Design solid loading to filter too low
° Design filter face velocity too high
° Design filter cake density too high
° Design gas inlet pipe layout incorrect
° Blowback gas temperature too low, causing
pore plugging.
Recommendations. Commercializing a new Group A fluid
bed process requires extensive research to support catalyst development
and prove reaction chemistry, but its commercial
success ultimately relies on the capabilities of the engineers that
scale up and design the first commercial unit for the process. As
such, engineering provides a critical and complementary function
to research in the development of any new multiphase process,
of which fluidization is one of the more important types.
LITERATURE CITED
1
Jazayeri, B., Handbook of Fluidization and Fluid-Particle Systems, Chapter 16, Yang,
W.-C., Ed., Marcel Dekker Inc., 2003.
BEHZAD JAZAYERI is a subject matter expert with more than
40 yr of experience in process engineering, technology
development, process scaleup, and applications of fluidized
beds and gas-solids systems. He has performed more than
50 techno-economic analyses and has designed 30 pilot plants
and first commercial plants using fluid beds, 15 of which were
built and operated. His background includes bio-conversion,
coal gasification, chemical synthesis and polysilicon.
Relative yield
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