Technologies enabling a hydrogen economy
Test Exam
Univ.-Prof. Dr.-Ing. Andreas Peschel
March 2024
Question:
1
2
3
4
5
6
7
8
9
10
11
12
Total
Points:
41/2
181/2
7
11
5
9
5
7
5
8
3
7
90
1
TEHE
Test Exam
07.03.2024
Exercise 1
After completing your studies, you started a job as a hydrogen expert in a young start-up.
1. Your boss has heard of the different colors of hydrogen and needs a brief overview
from you. Name the type of production associated with the given colors. Also state
one advantage and one disadvantage of each.
Color
Background
Advantage
Disadvantage
[4 1/2]
Green
Grey
Blue
2. Now you should advise your boss on turquoise hydrogen.
(a) Name the reaction equations for the main reactions for turquoise and SMR-based
grey hydrogen production including the water gas shift reaction. Also state
whether the reactions are exothermic or endothermic. Then use the reaction
equation to explain which technology gives a higher hydrogen yield per mole of
methane.
[3 1/2]
(b) Under which conditions in methane pyrolysis does a higher conversion take place
(related to temperature and pressure)?
[2]
(c) An engineering service provider has sent your boss a block flow diagram for a
planned power-driven methane pyrolysis plant including a feed pre-treatment.
Unfortunately, some information is missing. Your boss asks you, to name the
respective blocks and streams (1-10) in the BFD below.
[10]
(d) Where do scope 1 and scope 2 emissions occur in the process shown in part c?
[1]
(e) There are three main types of reactor technologies for methane pyrolysis. Name
two of them.
[2]
2/8
TEHE
Test Exam
07.03.2024
3. Your boss comments that solid carbon is an attractive by-product. However, there
are different types of solid carbon.
(a) Name three different types of solid carbon and three process parameters that
influence which type is produced in the process. Additionally, please indicate for
which carbon product the largest market (in terms of quantity) currently exists.
[4]
(b) The market value for a carbon product is 1.00 e/kgC .You consider whether the
operation of your plant is worthwhile compared to a blue reference technology
with the following LCOH. Justify your answer with the help of a calculation.
LCOHblue = 1.60 e/kgH2
LCOHturquoise = 4.30 e/kgH2
Assumption: Pyrolysis only produces C and H2 . The process produces
0.75 kgC /kgCH4 .
[3]
3/8
TEHE
Test Exam
07.03.2024
Exercise 2
At the Hamburger harbor in Germany there is an LNG Terminal for LNG import.
The LNG is first regasified before being fed into the pipeline. The heat needed for
regasification is supplied by an ammonia plant (more specific by the ammonia condensation and subcooling). The nitrogen required for ammonia synthesis is provided
by an air separation unit (ASU) and the hydrogen by a steam reforming unit (SMR).
Assume the LNG to be 100 % methane.
Key parameters
Parameter
Mass flow ammonia ṁNH3
Molar mass ammonia MNH3
Molar mass nitrogen MN2
Lower heating value ammonia LHVNH3
Lower heating value hydrogen LHVH2
Lower heating value methane LHVCH4
Heat capacity gaseous ammonia (constant) cp,NH3 ,g
Heat capacity liquid ammonia (constant) cp,NH3 ,l
Cold gas efficiency SMR ηcoldgas,SM R
Overall efficiency ammonia plant ηoverall,NH3
Enthalpy of vaporization ammonia ∆Hevap,NH3
Enthalpy of vaporization methane ∆Hevap,CH4
Heat transfer loss ASU LASU
Value
100
17
28
18800
120000
50000
5.38
4.52
80.0
70.0
1284
511
10
Unit
kg/h
kg/kmol
kg/kmol
kJ/kg
kJ/kg
kJ/kg
kJ/(kg K)
kJ/(kg K)
%
%
kJ/kg
kJ/kg
%
4. Name the respective blocks and streams (1-11) in the BFD below for the process
described previously.
4/8
[11]
TEHE
Test Exam
07.03.2024
5. A new colleague is asking you some questions:
(a) At which units is heat recovery normally done? Name three.
[3]
(b) Which type of reactor is most often used in the ammonia synthesis and how is
the heat extracted?
[1]
(c) Why is the ammonia synthesis reactor not water-cooled?
[1]
6. Using the key parameters in the table above, calculate the following:
(a) What is the necessary mass flow of N2 and H2 to produce 100 kg/h of ammonia?
[2]
(b) What mass flow of methane is needed to produce the mass flow of H2 for ammonia
synthesis considering that the cold gas efficiency of the SMR is 80 %?
[2]
(c) What mass flow of evaporating LNG is necessary to provide the cooling and
liquefication of the synthesized ammonia, considering a 10 % heat transfer loss.
This cooling process is simplified as follows:
[4]
• pure ammonia is considered (100 kg/h)
• the gaseous ammonia is cooled down from 100 ◦ C to −5 ◦ C
• the condensation takes place at −5 ◦ C
• the liquid ammonia is cooled down from −5 ◦ C to −33 ◦ C storage temperature
Can the necessary cooling energy be provided by the mass flow that is needed
in the SMR?
(d) Considering the overall energy efficiency for the NH3 -production plant including
SMR of 70 %, what is the amount of energy needed to produce one ton of NH3
(in GJ/t)?
[1]
7. Considering the following operation conditions of the ammonia synthesis:
• T = 400 ◦ C
• p = 100 bar
• iron-based catalyst
(a) Name two of the main catalyst poisons in this process.
[2]
(b) Is a 100 % conversion per pass of N2 to NH3 possible at these conditions? If not,
what is the main limitation?
[1]
(c) How can you change the reaction conditions (p, T ) to increase conversion?
[2]
5/8
TEHE
Test Exam
07.03.2024
Exercise 3
Your client specializes in manufacturing metal sheets through the deformation of steel
sheets using the hard pressing method. The process involves heating the steel sheets
to approximately 900 ◦ C, then pressing, reshaping, and cooling them. The company
owns 10 machines, each equipped with 6 burners using methane. The individual
burner power is assumed to be 1 MW.
Key parameters
Parameter
PEM power consumption PP EM
Molar mass hydrogen MH2
Molar mass water MH2 O
Value Unit
55 kWh/kgH2
2 kg/kmol
18 kg/kmol
8. As part of the transition to environmentally friendly alternatives, the company has
decided to use hydrogen instead of methane in the burners.
(a) Explain (without calculations) why a transition to hydrogen is favored compared
to an electrification. Give two reasons.
[1]
(b) Considering the transition from methane to hydrogen as a fuel, compare the necessary mass and volume flow to operate the burners at the same power qualitatively. Also compare the temperature levels of adiabatic methane and hydrogen
flames. Use < and >.
Mass Flow:
CH4 □ H2
Volume Flow:
CH4 □ H2
Flame Temperature: CH4 □ H2
[3]
(c) What can you do to bring the hydrogen flame temperature to the level of a
methane flame? Name one approach.
[1]
(d) Name two impacts on the composition of the flue gas when transitioning to
hydrogen burners.
[2]
9. The company considers securing its own hydrogen supply through an electrolyzer.
Nearby sources of renewable energy (solar and wind) can provide the company with
cheap power.
(a) Which challenge arises from such an energy source for electrolysis and what is
the impact on the electrolyzer lifetime?
[2]
(b) Considering only the highly dynamic energy source, which electrolyzer technology should be used for operation? Why?
[1]
(c) Write down the partial reactions for the anode and cathode side respectively.
[2]
10. Assume a hydrogen demand of 300 t/a:
(a) Calculate the appropriate size (in MW) of a PEM electrolyzer with an operation equivalent to 4000 full load hours per year and a typical specific power
consumption.
[2]
(b) What is the stoichiometric water demand (t/a) for such an electrolyzer?
[2]
6/8
TEHE
Test Exam
07.03.2024
(c) Explain the term “thermoneutral voltage”. Why is the cell voltage different
than the thermoneutral voltage / what four contributions to the cell voltage are
there?
[4]
11. After four years of production, the hydrogen production rate at a load of 1.5 MW is
23 kgH2 /h.
(a) What is the specific energy consumption of the electrolyzer plant.
[1]
(b) You have concerns regarding the quality of the water used for electrolysis. Name
four effects poor water quality can have on the electrolyzer and its lifetime.
[2]
12. The company has chosen to generate electricity from excess hydrogen production.
One method to achieve this is through the utilization of fuel cells.
(a) What fuel cell types are currently available on the market, and where are they
commonly applied?
[2]
(b) Draw the power density curve for a fuel cell.
[2]
7/8
TEHE
Test Exam
07.03.2024
(c) Name the components (1-4) of a Proton Exchange Membrane Fuell Cell shown
below.
8/8
[3]