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re-confgured to separate the chemical complex For each HRSG the duct burner confguration
network from the portion of the network under includes two groups, eight burner elements
testing (the new generating units that will deliver for natural gas and eight burner elements for
power to the external grid during the testing and hydrogen, each group having the design duty of
commissioning period). 53.8 MWth. Both groups are installed in between
The tie-in of the COGEN has been designed so the two superheater sections of the HRSG, where
as not to require a major shut-down of process stainless steel baffes are installed in order to
units and has been coordinated with planned achieve the required gas velocity in between the
turnarounds. A minimum period of 6 months’ burner elements
operating transition of new and old facilities is This confguration allows the full fexibility in the
foreseen to resolve new design and commissioning use of the fuels: the natural gas and hydrogen
issues. groups can be operated fully independently
The block diagram in fgure 2 illustrates the future up to the maximum duty and can also be fred
site distribution architecture and the scope of this simultaneously.
project. The only limitation when both fuels are used is
the fue gas temperature downstream of the duct
HRSG postfring with natural burner, which is automatically limited at 870 °C in
order to avoid damage to the HRSG.
gas and hydrogen Another limitation is present at start-up when, for
safety reasons, the hydrogen burner elements can
The Dow Plant generates hydrogen as secondary be started up only when the natural gas burner
product. elements are already in operation.
To avoid faring this valuable product, the post fring
system of the COGEN HRSGs
This confguration and the package boilers burn all Permitting and certifcations
allows the full fexibility the available hydrogen from Dow Overview of the steps followed to obtain the
in the use of the fuels: Plant. authorization to build and operate the plant.
The boilers are able to utilize 6,350
the natural gas and kg/h of hydrogen, nevertheless
hydrogen groups the hydrogen supply to the new Operating permit
can be operated fully COGEN and the package boilers The operating permit application has been
independently up to is not larger than 5,300 kg/h in prepared and submitted to competent authority by
the maximum duty normal operating cases, since Dow according to the Federal Immission Control
there are some consumers in the
Act (BlmSchG).
and can also be fred Dow Plant. The permit was issued in conjunction with the
simultaneously In normal operating conditions the collateral clauses as prerequisites for approval and
two package boilers operate at among these, the main ones affecting the design
minimum steam production level are:
set by the operator, fring hydrogen only. • statutory building regulations and preventative
All the remaining available hydrogen fowrate fre protection;
is burnt in the postfring burner of the HRSGs, • Environmental Impact Assessment.
which uses natural gas as pilot and second The start-up of Plant shall be authorized by third-
supplementary fuel, when it is needed to meet the party authority representatives, namely ZUES
steam demand of Dow Plant. (Zugelassene Überwachungsstelle), who shall
Hydrogen and methane have very different verify the compliance of the project with the permit
volumetric calorifc values, therefore they cannot be supported by the certifcations from various notifed
burnt in the same burner elements. Separate sets bodies (TÜV, DVGW, DMT, Stuerzl, WK, Mueller
of burner elements are installed, one for hydrogen BBM etc.)
and one for methane.
The post fring load is controlled as follows:
• the hydrogen controller sets the hydrogen Building permit
fow to the HRSG burners in order to maintain Every construction in the Lower Saxony Region
the required pressure in the hydrogen header; requires the application by the owner for a Building
• the HP steam pressure controller sets the Permit (Baugenehmigung) to the local authority,
natural gas fow to HRSG burners in order which is the Authority of Stade in the case of the
to maintain the required pressure in the HP Dow Stade COGEN project.
steam header; Typically, the period of time needed from the
• the operator is allowed to override this control application to the release of this permit by the local
for one or more HRSG’s and to operate it/ authority is three months. During this period, only
them at controlled steam production. demolition of existing facilities and site preparation

64 Impiantistica Italiana - Novembre-Dicembre 2013