(139a) Advanced Process Control in a Mobile Pilot Plant for the Evaluation of Long-Term Dynamic Performance of a CO2 Capture Process Under Industrial Conditions

The removal of carbon dioxide (CO₂) from industrial gases is of great interest and is an important technology for the reduction of greenhouse gas emissions. One common method is the application of reactive solutions in absorption/desorption processes. This technology is well-established and has commercially been implemented in industry [1]. However, most processes suffer from unstable operation conditions, such as fluctuations in feed gas compositions or changes in the required load [2]. In addition, non-optimal operation conditions for regeneration lead to increased costs for the whole process. The flexible operation of plants for carbon capture is of great interest and is essential for future applications. The investigation of the dynamic performance of CO₂capture processes by dynamic test campaigns provides information to compensate changes in the operation conditions. For this purpose two scenarios are considered. Firstly, fluctuations in the gas feed, such as changes in the flow rate or gas compositions, are observed. Due to the coupling of the process to power plants, daily changes of the load in a power plant require the flexible operation of the carbon capture process.

Therefore, a modular and transportable pilot plant is designed and constructed by the Process Dynamics and Operations Group at Technische Universität Berlin[3]. Regarding varying compositions of the gases and the operation of the pilot plant a flexible and reliable design of the process is required. In addition to that, the plant is operated under real conditions at a steel mill in Duisburg, which highlights the importance of a flexible implementation.

These aspects need to be considered for the conceptual design, the construction of the pilot plant, and the process control design. For this reason, the concept of the pilot plant contains two absorption columns with a total height of 3 m of structured packing and a diameter of 0.11 m each. The desorption column for the regeneration contains 2.5 m packing with the same diameter. Preceding pretreatment columns are installed to maintain stable operation conditions at the inlet of the absorber and the removal of acidic components. Following the absorption and desorption columns posterior treatment columns are implemented to ensure sustainable process conditions at the gas outlet and to reduce the loss of the amine solution. The pretreatment and posterior treatment columns contain 1 m of structured packing each. The pilot plant is automated using ABB´s Freelance 700F process control system. To ensure reliable operation conditions and to provide the required information for the process control more than 30 temperature, 13 pressure, 8 level, and 13 flow indicators are installed.

For the studies of the dynamic responses of the carbon capture process advanced process control loops are applied by the implementation of soft sensors. Thus, the CO₂ removal is controlled by the feed flow rate of the amine solution to the absorption. Another issue is the change in the gas load. Due to the coupling of the process to power plants, the operation of the CO₂capture process is adjusted to the load of the power plant. For this reason, a switch in operation modes is considered, which compensates partial gas loads and leads to reduced heating duty for the desorption.

The main purpose of this contribution is the systematic evaluation of dynamic responses of the pilot plant towards unstable operation conditions, such as fluctuations in the gas flow or changings gas loads. Therefore, advanced process control loops are introduced by the implementation of soft sensors. These aspects are considered and implemented in a pilot plant.

[1] S. Ziaii, T. F: Edgas, G. Rochelle „Dynamic Modeling to Minimize Energy Use for CO₂Capture in Power Plants by Aqueous Monoethanolamine”, Ind. Eng. Chem. Res. 2009, Vol. 48, 6105-6111

[2] P. Tait, B. Buschle, I. Ausner, P. Valluri, M. Wehrli, M. Lucquiaud “A pilot-scale study of dynamic response scenarios for the flexible operation of post-combustion CO₂capture”, International Journal of Greenhouse Gas Control, Vol. 48, 2016, 216-233

[3] M. Müller, G. Wozny, H. Thielert „Innovative Produkt- und Prozessentwicklung mittels mobiler und modularer Mini-plant Technik“, Jahrestreffen der Fachgemeinschaft Prozess-, Apparate- und Anlagentechnik, Fulda 2011