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through an area currently occupied by a major structural beam requiring major structural
modification of the building support structure.
The other potential loop seal design was an L-valve that would also increase solid circulation
rates over the J-leg and reduce the amount of inert or recycled syngas injected to recirculate the
solids back to the mixing zone. However, this design would probably still require significantly more
gas being injected in this area to move the solids across the horizontal L-valve than would be
required for a Y-leg loop seal. Another advantage would be the increased length on the mixing zone
would add some additional residence time in the mixing zone, and construction would be simplified
because of the use of conventional pipe tees instead of utilizing a specially constructed pipe-Y in
the bottom of the mixing zone.
Other recommendations were to increase the standpipe diameter and dipleg diameter to
minimize the effect of bubble size and friction effects with the wall on solids flowing down either
the standpipe or dipleg. Another recommendation was to add a loop seal to the bottom of the dipleg
so that the standpipe inventory could be operated independently of the level where the dipleg solids
reentered the standpipe. Without a loop seal in the bottom of the dipleg, the standpipe inventory
always had to operated at a level greater than the dipleg solids return height or a significant amount
of gas would bypass up the dipleg, thereby severely spoiling the performance of the primary
cyclone.
In addition, a simple atmospheric-pressure cold-flow system was constructed to determine the
effects of different loop seals and mixing zone sizes on the amount of solids circulation, backmixing,
and residence time in the mixing zone. The sizes investigated were approximately 87% of TRDU-
scale equivalent mixing zone dimensions. Since the unit can only operate under atmospheric
pressure and the same starting bed material was used for the TRDU, the particle-to-gas density ratio
was not matched in these tests. Air and nitrogen flows were adjusted to match the relative
distribution in the TRDU and to match the desired riser velocity (at atmospheric pressure and
temperature). The mixing zone test sizes were selected to be equivalent to the original mixing zone
diameter, a diameter 2 inches larger and another 4 inches larger than the original mixing zone. Cold-
flow tests utilizing a 25-pound batch of red-colored FCC catalyst support material as a tracer were
completed for each mixing zone configuration. The colored sand residence time tests were
conducted using both burner air only and a combination of burner air and combustion air. From
these tests, it was possible to measure residence time distributions passing through the mixing zone.
These residence times were measured at 50, 65, and 75 seconds for the amount of time that the
colored FCC material remained in the mixing zone. Based on these results, a diameter matching the
medium diameter was selected for the TRDU design, and this residence time distribution was
utilized in the calculation of the steam/carbon kinetics shown in Appendix A.
Based on the above recommendations and the results of the cold-flow testing, the L-leg loop
seal design was selected as the best design given the building and budget constraints for the project.
Figures 4 through 6 show the as-designed L-valve modification for the TRDU. The modifications
consisted of constructing three new sections as shown in Figure 4. One section would be for the L-
valve loop seal (Figure 5), and the other two sections would replace the J-leg elbow (also shown in
Figure 6) and the bottom section of the TRDU mixing zone. In addition, as shown in Figure 6,18
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Swanson, Michael L. Advanced High-Temperature, High-Pressure Transport Reactor Gasification, report, August 30, 2005; [Grand Forks, North Dakota]. (https://digital.library.unt.edu/ark:/67531/metadc889538/m1/30/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.