ROBERT WILHELM, ERIK ESCHE, GÜNTER WOZNY, JENS-UWE REPKE
ZION GUETTA, HOLGER THIELERT
DEVELOPMENT OF A MOBILE PILOT PLANT FOR THE
EVALUATION OF NOVEL SCRUBBING LIQUIDS FOR THE
ABSORPTION OF CO2 FROM INDUSTRIAL GASES
MOBILNA INSTALACJA PILOTAŻOWA DO OCENY
NOWEGO PŁYNU DO ABSOPRPCJI CO2 Z
PRZEMYSŁOWYCH GAZÓW ODLOTOWYCH
A b s t r a c t
Most available scrubbing liquids suffer from either high heating duties for the regeneration or
vulnerability towards gas components. In order to increase the efficiency of the absorption
process a novel scrubbing liquid has been developed by thyssenkrupp Industrial Solutions
AG. For verifying relevance and feasibility of long-term operation of the new fluid
assumptions for installation were created – conceptual design and detailed simulation of the
process without detailed thermodynamic information.
Keywords: CO2 separation, process engineering, modular construction
S t r e s z c z en i e
Na większość dostępnych cieczy absorpcyjnych oddziaływają wysoka temperatura i są one
wrażliwe na składniki gazów odlotowych. W celu zwiększenia wydajności procesu absorpcji
firma thyssenkrupp Industrial Solutions AG przedstawiła nowy płyn do skruberów. Dla
weryfikacji przydatności i możliwości długoterminowej eksploatacji nowego płynu
przedstawiono założenia dla instalacji – projekt koncepcyjny oraz szczegółową symulację
procesu bez szczegółowych informacji termodynamicznych.
Słowa kluczowe: wydzielanie CO2, projektowanie procesowe, konstrukcja modułowa
DOI:
MSc. Robert Wilhelm, DSc. Eng. Erik Esche, Prof. PhD. DSc. Eng. Günter Wozny, Prof. PhD. DSc.
Eng. Jens-Uwe Repke, Process Dynamics and Operations Group, Faculty of Process Sciences,
Technical University of Berlin.
DSc. Eng. Guetta, DSc. Eng. Holger Thielert, thyssenkrupp Industrial Solutions AG.
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1. Introduction
The importance of the removal of carbon dioxide (CO2) from various industrial gases,
such as coke oven gas, is of great scientific and industrial interest [1]. A common method
for the removal of CO2 is the application of reactive scrubbing fluids in an absorption
process. Chemical absorption is advantageous for the application of gases with low partial
pressures and a high required selectivity regarding the absorption of CO2.
For this purpose, a novel scrubbing liquid has been developed by thyssenkrupp
Industrial solutions AG in order to improve the process efficiency. Therefore, an
application for the separation of CO2 is discussed in this contribution to evaluate the
applicability and the long-term robustness of the novel scrubbing liquid under industrial
conditions.
The objective of the work is the operation of the pilot plant industrial conditions at a
steel mill in Duisburg, Germany. In order to gain experience for the subsequent scale-up, a
flexible, modular, and transportable pilot plant is designed and built at Process Dynamics
and Operations Group at Technische Universität Berlin [4]. The pilot-plant itself mainly
consists of the absorption section and desorption for the regeneration of the amine solution.
Proceeding and following these, pre- and posterior treatment columns are installed to
maintain sustainable operational conditions despite fluctuations in the gas feed.
The main goal of the operation of the plant and experiments is the evaluation of the
novel scrubbing liquid under industrial conditions and the determination of viable operation
conditions. Therefore, the minimal heat required for desorption is determined for each
operating point and the scrubbing liquid is analysed in terms of selectivity, longevity, and
applicability.
1.1. Proposed Workflow for the Plant Engineering
Towards the scaled up industrial application, experimental data is required to examine
the removal of carbon dioxide from industrial gases and to investigate a conceptual design
for a faster process development. For this purpose, the pilot plant is designed to gain
information about the operability and the process itself to compensate for the lack of
operational experience [2]. For this reason, workflow for the plant engineering of a pilot
plant is given in this contribution.
2. Research and Process Concept
The objective of the plant is the evaluation of the scrubbing liquid under industrial
conditions and the optimisation of the operation of the pilot plant to develop an efficient
process concept, independent of the various industrial production sites. Due to the variety
of possible applications, the plant needs to be designed with regard to mobility and
consideration for a modular construction that offers increased flexibility.
The basic engineering of a pilot plant to examine the novel scrubbing liquids without
operational experience or limited thermodynamic knowledge can be attempted by using a
comparable medium. In this contribution, monoethanolamine (MEA) is used as a scrubbing
liquid and considered as a typical representative for the separation of CO2 [5]. Coke oven
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gas from a steel mill is considered as the feed. In the following table, the possible
compositions of the feed gas are shown.
T a b l e 1
Composition of the feed gas with pressure and temperature
N2
H2
O2
CO
CH4
CO2
NH3
H2S
p
[bar]
T
[°C]
Range
[Vol.-%]
5-49
1-4
0-1
10-65
0-1
0-25
0-1
0-1
1-
1.4
30-
150
Regarding the compositions of the gases, a flexible operation of the process is required,
such as a protection against corrosive or acidifying components. The operational pressure
ranges from 1 to 1.4 bar in the absorption section, whereas in the desorption section, the
pressure is increased to reduce the evaporation of water and amine at the required
temperature for desorption (see Fig. 1). In the following section, the aforementioned plant
design is detailed.
3. Plant Design
Fig. 1 Simplified flow diagram for the separation of CO2
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Based on the process concept a simplified flow diagram for the separation of CO2 is
shown in Fig. 1. The feed gas enters the plant in the pre-treatment column at almost
ambient pressure, where cooling takes place and impurities or corrosive components, such
as H2S, are removed by using sodium hydroxide. The suction and transportation of the
gases is realised by using a compressor. Upon entering the absorption section, carbon
dioxide is separated from the gas and chemically dissolved in the scrubbing liquid as
carbonate and carbamate ions. The gas leaving the absorber may contain smaller amounts
of absorbent. Therefore, posterior treatment columns are installed in order to reduce the
quantity of the absorbent and decrease the temperature of the purified gas. The loaded
scrubbing liquid is pumped to the desorber, wherein, the regeneration of the scrubbing
liquid takes place by electrical heating. The carbon dioxide is emitted to the gaseous phase
and leaves the process through the second posterior treatment column. In turn, the
regenerated liquid is reused and pumped to the absorber, thus closing the scrubbing liquid
cycle.
3.1. Process Simulations and Assumptions
After the conceptual design of the process, a preliminary estimation of the operation
conditions and design parameters with further investigations is needed. For this purpose,
the process is modelled and simulated in Aspen Plus®. The rigorous simulation is required
for the following sizing of the equipment and the estimation of the number of theoretical
stages for both the absorption and desorption columns.
Fixed specifications for the estimation of the packing height is the separation of 90
Vol.-% of carbon dioxide. This is set by a design spec within the simulation. In order to
keep the flexibility of the pilot plant, three different gas loads factors are considered, which
are characterised by the F factor and three different gases with varying CO2 concentrations.
For the different values of the F factor, the operation points needed to be determined. Under
the restriction of the separation of 90 n/n % of CO2, the operation point is set by the
minimal required electrical heating. The minimal required heating value is defined by the
following equation:
𝑞𝑠𝑝𝑒𝑧 =𝑄𝐷𝑒𝑠𝑜𝑟𝑏𝑒𝑟
𝑚𝐶𝑂2,𝑠𝑒𝑝𝑒𝑟𝑎𝑡𝑒𝑑 (1)
where
qspez – specific amount of heating for the current operation conditions,
QDesorber – required amount of heating in the desorber,
mseperated – mass flow of separated carbon dioxide in the scrubbing liquid.
The results for the operation points of the pilot plant are shown in the following table:
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T a b l e 2
Operation conditions of the pilot plant for three gas load factors with following composition:
22.7 Vol.-% CO2, 24.6 Vol.-% CO, 4 Vol.-% H2, 48.6 Vol.-% N2
F factor [Pa0.5]
QDesorber [kW]
qspez [MJ/kgCO2]
0.5
5.36
3.37
1.0
11.47
3.61
1.2
14.06
3.72
Changes of the gas load have an influence not only on the absorber, but also on the
loading of the scrubbing liquid. An increasing gas load requires an elevated liquid flow of
scrubbing fluid and additional electrical heating [5]. Fig. 2 represents an operation point
with its conditions for an F factor of 1 Pa0.5.
Fig. 2. Operation conditions for a gas load factor F of 1 Pa0.5
3.2. Technical specifications and equipment planning
Based on the process simulation the equipment is sized and the technical specifications
are determined [3].
Structured packings are employed for the columns with a total height of 6m packing for
the absorption and 2.5m for the desorption. The additional columns for the pre- and
posterior treatment contain 1m of structured packing each. With the height of the packing in
the columns, the technical drawings of the apparatuses are drafted. For safe operation of the
plant, strict safety regulations are required. Therefore, the whole pilot plant is planned,
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constructed, and operated under European explosion protection ATEX/II2G. For safety
reasons, a HAZOP analysis is conducted and the results are transferred to the process
concept. The next step is the design of a three-dimensional (3D) model, which is necessary
for the piping and the positioning of the apparatus in the condensed space of the mobile
modular pilot plant.
Fig. 3 shows a 3D model of the whole pilot plant within the steel framework. This
highlights the main challenge for the design of the plant, namely, the limited space. Each
module has a height of 2.8 m, is 5.3 m wide and 2.3 m deep. The total height including the
handrail on the upper level is 6.7m. Within the framework, which consists of two separate
modules, apparatus need to be affixed. In addition to the pre-treatment columns, the two
post-treatment columns, the two absorption columns, and the desorption column, the plant
contains a compressor, ten pumps, and two liquid tanks. To handle this challenge, a
comprehensive 3D model is developed in AVEVA PDMS® to ensure access for
maintenance and operation. With the sole exception of piping for the pressurised air, the
3D model contains the piping for all utilities, gas, and liquid streams. The positioning of the
gas pipes is of especially great importance due to their comparatively large diameter.
The pipes reaching out of the steel frame are the gas inlet and outlet. In addition, cable
trays are positioned at the top of each module for supplying electricity and controlling all
devices.
A basin below the lower module is installed to catch liquids in case of leaks or
emergencies. Components, such as pumps and electrical heaters are placed at the bottom to
facilitate maintenance work.
Fig. 3 3D model of the plant with apparatuses and the complete piping
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Fig. 4 shows two photographs of the current state of construction work at TU Berlin.
Due to the considerable height of the pilot plant, both the lower and the upper modules are
separated and worked on side by side.
Fig. 4 Photos of the lower module (left) and of the upper module (right)
3.2 Process automation and analytics
The plant is automated using ABB’s Freelance 700F process control systems. More than
30 temperature, 13 pressure, 8 level, and 13 flow indicators provide the required
information for the process control. In addition, control sequences are implemented for the
start-up, shut-down, emergency shut-down, and inertisation procedures.
As mentioned before, the main goal is the separation of CO2 from the feed gas. Hence,
samplings are intended to measure the CO2 concentration within the gas stream by an
infrared photometer of ABB (Multiwave Model 3502). This device enables online
measurements at different positions. The positions are shown in Fig. 2. In total, seven
positions are intendent for accurate measuring. To keep the coefficient of absorption under
surveillance, positions QI1, QI3, and QI5 are of great importance and are equipped with
automated valves. In addition, manual sampling locations are positioned in the liquid pipes
for the analysis of the scrubbing fluid in order to measure the load of carbon dioxide within
the fluid.
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4. Conclusion and Outlook
This contribution tackles the challenge of overcoming the step between lab experiments
and the first industrial application. Therefore, a modular and mobile pilot plant is
constructed to gain experience in the separation of CO2 from industrial gases. Besides
evaluating the novel scrubbing liquid without detailed thermodynamic knowledge or
operation experience, the possibilities of a faster process development are investigated.
For basic engineering, it is necessary to clarify the operating conditions and to provide a
conceptual design. Following the process simulations and the sizing of equipment, a
detailed 3D model is required which puts a larger emphasis on safe operation and
maintenance of the plant.
The goal of this work is to evaluate aspects such as the long-term robustness and the
applicability, and to prove the industrial viability of the scrubbing liquid under real
conditions. For this reason, the continuous operation of the process for more than 500 hours
is planned. Furthermore, a more complex and detailed analysis of the liquid and gas phase
is intended in order to increase the availability of the process.
A b b r e v i a t i o n s
ATEX – European directives on equipment and work in explosive atmospheres,
CO2 – carbon dioxide,
MEA – monoethanolamine,
n/n – mole per mole.
R e f e r e n c e s
[1] Bock C., Gaswäsche – Industrielle CO2-Abtrennung: Miniplant zur schnellen Evaluation
von Waschmitteln, CITplus, vol. 25, 2014.
[2] Stünkel S., Simultaneous Synthesis of the Downstream Process and the Reactor
Concept for the Oxidative Coupling of Methane (OCM), 10th International Symposium
on Process Systems Engineering, PSE 2009.
[3] Esche E., Innovative Product and Process Development with Mobile and Modular Mini-
plant Technologies, Technical Transactions, series Mechanics, vol. 1, 2012.
[4] Müller M., Innovative Produkt- und Prozessentwicklung mittels mobiler und modularer
Mini-plant Technik, Jahrestreffen der Fachgemeinschaft Prozess-, Apparate- und
Anlagentechnik, Fulda 2011.
[5] Shen K.P., Solubility of Carbon Dioxide in Aqueous Mixtures of Monoethanolamine with
Methyldiethanolamine, Chem. Eng., vol. 37, 1992, 96-100.
