H2Tech - Q1 2022 - 25

SPECIAL FOCUS: ADVANCES IN HYDROGEN TECHNOLOGY
Monitoring hydrogen plant performance
K. R. RAMAKUMAR, Johnson Matthey, United Arab Emirates
Process monitoring is an indispensable practice to keep
) plant. A good system of process monitoring not only entrack
of key performance indicators (KPIs) of the hydrogen
(H2
sures safe and reliable plant operations, but also helps in making
strategic decisions such as catalyst changeout schedules. If
KPIs are not monitored closely, there can be situations where
the expected yields are not achieved. This affects the economics
of the H2
plant and that of the entire refinery complex, since
the downstream hydrotreated/hydrocracked product yields
are affected, as well. This will have a direct implication on the
overall refinery margin.
For better monitoring and control, it is imperative to know
the fundamentals of performance indicators. Performance
monitoring requires operating data inputs from the plant,
which are normally accessible from the intranet servers or from
the distributed control system. It also requires stream analyses
from the laboratory (or from online analyzers) to understand
how each reactor is performing with respect to conversion/
yield. The laboratory testing frequency of such streams is normally
decided by the process engineering department in conjunction
with the laboratory section.
The main objective of this article is to guide H2
plant process
engineers in:
* Performing a detailed mass balance across the H2
flowsheet by using available information, such as dry
analysis of outlet streams. Doing so will help identify
bottlenecks across each reactor. The focus would be
to see how much H2
is being made before the final
stream enters the pressure swing adsorption (PSA)
unit. This mass balance will also help estimate the
outlet stream's composition on a wet basis, thereby
facilitating the estimation of equilibrium constants
(Keq
values) for steam methane reforming (SMR)
and water gas shift (WGS) reactions, which will help
calculate the approach to equilibrium (ATE) values.
These values, which are important in understanding
the catalyst activity, can then be compared with the
kinetic model values provided by the catalyst supplier.
* Monitoring other critical parameters and KPIs across
each reactor in the H2
flow sheet.
Feed definition and characterization. Two types of feed
are considered for studying plant performance: Case 1 is a
natural gas (NG) feed, and Case 2 is a naphtha feed. Note:
The flow, composition and operating conditions are purely
The molecular weight is calculated using Eq. 3:
1.6607 x 10-4
(specific gravity)-1.0164
(328.03)2.1962
× (MeABP)2.1962
× (0.716)-1.0164
×
= 1.6607 × 10-4
×
= 78.2 kg/kmol
(3)
H2Tech | Q1 2022 25
assumptions based on the author's experience and do not correspond
to any specific plant.
For Case 1, feed comprising 1,000 kmol/hr of (NG + recycled
H2) is assumed to have the following composition:
* Hydrogen (H2
* Nitrogen (N2
* Methane (CH4
* Ethane (C2
* Propane (C3
) = 2%
H6
) = 5%
) = 2%
H8
) = 90%
) = 1%.
This combined stream of NG and recycled H2
10 ppmv of hydrogen sulfide (H2
recycle H2
contains
S) and 5 ppmv each of methyl
mercaptan and dimethyl disulfide (DMDS).
For Case 2, 80 kmol/hr of naphtha, with 20 kmol/hr of
, is assumed. The most common laboratory information
for naphtha is the ASTM D86 standard covering distillation
and specific gravity. The ASTM D86 cut points of the
assumed naphtha feed are:
* T10%
* T30%
* T50%
* T70%
* T90%
= 110°F
= 128°F
= 135°F
= 145°F
= 155°F.
The reported specific gravity is 0.716. Naphtha must be characterized
further based on the above information. Degrees Fahrenheit
and Kelvin will be used only for the following estimations.
Naphtha characterization. Eq. 1 is used to find the volume
average boiling point (VABP):
(T10%
+ T30%
+ T50%
+ T70%
The correction factor is:
* Slope = (T90%
* ∆ = 3.825°F.
The mean average boiling point (MeABP) is shown in Eq. 2:
MeABP = VABP - Δ = 134.6 - 3.825 =
130.8°F = 328.03°K
(2)
- T10%
+ T90%
)/ 5 = 134.6°F
* Ln ∆ = [-0.94402 - 0.00865 (VABP - 32)0.6667
(2.99791 x slope0.333
)/ 80 = 0.563
)]
+
(1)
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