Page 26 - Industrial Plants 2014

of the advantages of the low temperature represented by membrane separation stages. In
architecture is to require for reforming tubes low this regard, heating and cooling cycles together
cost stainless steel instead of traditional exotic and with feed introduction procedure were carefully
quite expensive material as HP 25/35 chromium/ tuned on membrane requirements. Again, the
nickel. advantages offered by a non integrated approach
To intensificate heat and material transfer properties allows for a better management of both process
and improve fluidynamic regime, innovative and emergency shut down minimizing thermal and
structured catalyst on SiC foam were adopted mechanical stresses and allowing also for short
instead of traditional pellets (figure start up time: the latter may be
2). From catalytic point of view, Detailed start up and performed within three hours while
taking into account the poor Ni shut down procedures only half an hour is required for plant
activity at low temperatures, a noble were developed to shut down. ESD sequences and
metal based formulation has been ensure a trouble free main control loops are demanded to
selected. Reaction is carried out at operation especially for a dedicated PLC and DCS system
10barg and temperatures in the the most critical plant (figure 4) which ensure to performer
range of 500-650 °C while separation section represented test under safety conditions.
stage may work from 300 to 450 °C by membrane Collected data confirmed that
with sweep gas to increase efficiency separation stages. In membrane integration with steam
in hydrogen separation. this regard heating reforming reaction enables to obtain
The modular concept typical of an and cooling cycles a considerable increase in feed
open architecture, allowed to test together with feed conversion by overcoming
different Pd-based membranes thus introduction procedure thermodynamic constraints.
enriching field of investigation. The were carefully tuned Enhancement respect to equilibrium
three installed units (figure 3) on membrane conversion up to ten point per cent
developing a total area over 1 m , requirements were experimentally obtained by
2
were fully characterized in terms of working with two reaction stages
hydrogen permeance flow, selectivity and an intermediate membrane
as well as long time stability. The real industrial separation step performing hydrogen recovery
environment under which membranes stability was factor ranging from 25 to 35% (figure 5). By
tested gives great relevance to this experience extending this concept at higher numbers of
providing very significant experimental data and reaction and separation stages as well as at higher
observations useful for a fully membrane integration installed membrane area, that means higher
into industrial level. hydrogen recovery factors, very high feed
Detailed start up and shut down procedures were conversion may be obtained even working at lower
developed to ensure a trouble free operation temperature than traditional (860-880 °C). Four
especially for the most critical plant section stages architecture for example working at

Fig. 3 - a) ECN
membrane module:
Pd selective layer
having a thickness of
2.5 µm on tubular
ceramic supports;
b) MRT membrane
module: PdAg
selective layer having
a thickness of 25 µm
on flat metallic
supports;
c) NGK membrane
module: PdAg
selective layer having
a thickness of 2.5 µm
on tubular ceramic
supports

IndustrIal Plants - May 2014
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