Techno-economic Evaluation of Cost of Methanation

Introduction

As part of the SuperP2G project, the DVGW Research Center at the Engler-Bunte Institute (DVGW-EBI) has evaluated various methanation and CO2 capture technologies from a technically and economically point of view. Therefore, the DVGW’s own tool EcoMeth was enhanced. Additional technologies were integrated e.g. cooled fixed bed methanation and three-phase-methanation. Different methanation plants were modelled in ASPEN. Based on flow diagrams and the ASPEN models, the CAPEX was calculated using the factor method implemented in EcoMeth. Subsequently, the levelised cost for SNG production can be calculated by connecting different plants together. Also, an energetic evaluation of a process chain can be performed.

Hereby, the internal heat integration within the system is mandatory. In addition, by integrating PtG-plants into existing energy systems higher overall efficiencies can be achieved and local resources can be used.

Objectives

The objective of the DVGW-EBI was to identify the bottlenecks from a process engineering perspective in the implementation of PtG technologies. To support local stakeholder in the realization of future PtG technologies, the tool EcoMeth for technical and economic evaluation of PtG plants was developed at the DVGW-EBI. In this way, solutions adapted to the site for the production of renewable gases can be identified and evaluated. Thereby, the focus is on the support in process engineering issues.

Methology

For the CAPEX calculation, the factor method is used, shown in Figure 1. Based on a process flow diagram the costs for the main equipment is calculated. On the main equipment cost, cost factors are added. By the cost factors the cost for e.g. installation, instrumentation and engineering are included. Also, a scale-up of the calculated CAPEX is performed. Due to scaling effects, a decrease of the CAPEX with increasing plant size can be observed.

Figure 1: Method of the cost estimation reproduced from “modulare Kostenschätzung in der chemischen Industrie” by Uwe Strauch

Beside the CAPEX of different PtG technologies, the levelised cost are calculated using the annuity method:

\[ cost = \frac{I_A + \sum_{t=1}^{n}{\frac{C_t-R_t}{(1+r)^t}}} {\sum_{t=1}^n \frac{E_t}{(1+r)^t}} \]

\(I_A\) : Initial investment in €
\(C_t\) : Costs in period t in €/a
\(R_t\) : Revenues of by-products in period t in €/a
\(E_t\) : Energy output in period t in MWh/a
\(r\) : Interest rate in %
\(n\) : Calculatory operating life of the plant in years

Analysis

Within the SuperP2G project the DVGW-EBI analysed different methanation technologies in terms of investment costs. For example, a three-phase methanation was modelled and evaluated. The three-phase methanation is an innovating reactor concept, which is tested in a demo plant at the KIT in Karlsruhe. The reactor is filled with a heat transfer medium in which the nickel catalyst is suspended. The feed gas CO2 and H2 is injected into the bottom of the reactor. While the educts rises through the liquid phase, these react at the catalyst particles to methane and water. After the reactor, the product gas is cooled, so that the water condensed. In a second reactor stage the required gas quality is reached. After the gas is dried, the produced methane can be injected into the gas grid.

Figure 2: Demo plant Three-Phase-Methanation of the KIT in Karlsruhe

Based on the demo plant, a process flow diagram for a plant with the capacity of 10 MW (synthetic natural gas (SNG) output, low heating value (LHV)) was created for the evaluation of the CAPEX. With help of an ASPEN model, mass and energy balances were calculated for a 10 MW (SNG output, LHV). Based on the model and the process flow diagram, the main equipment was determined and the cost were calculated depending on the size. In Figure 1 the total investment cost of a 10 MW plant are shown in the diagram. It can be seen that the main equipment cost plus the catalyst cost have only a share of about 20 % on the total costs. The main part of the cost have the factors, which presents the cost for piping, instrumentation, engineering etc.

Figure 3: Total investment cost of the Three-Phase-Methanation with a capacity of 10 MW (SNG output, LHV) and the distribution of the main equipment cost

Results

After the calculation of the CAPEX of a 10 MW (SNG output, LHV) Three-Phase-Methanation, a scale-up of the plant size was performed. Due to scaling effects the costs are expected to decrease. In Figure 2 the diagram shows the CAPEX of the Three-Phase-Methanation depending on the capacity. It can be seen that with increasing capacity the CAPEX decreases. For a 100 MW plant, a CAPEX of 160 €/kW (SNG output, LHV) is expected. Evaluations of further methanation technologies also showed investment costs in similar ranges.

Figure 4: Scale-up of the CAPEX of the three-phase-methanation

Beside a detailed CAPEX analysis of methanation technologies, an overall PtG process chains can be evaluated. Thereby, the overall efficiency of the process chain is be concentrating on. The efficiency can be calculated by:

\[ \eta_{overall} = \frac{ \sum{\dot{E}_{chem,P}} + \sum{\dot{Q}_{use}}}{ \sum{\dot{E}_{chem,E} + \sum{\dot{Q}_{supply}} + \sum{P_{el,in}} }} \]

\(P\) : Product
\(E\) : Educt

Conclusion

Within the SuperP2G project the DVGW-EBI improved the existing tool EcoMeth for technical and economic analysis of PtG processes. The tool could be extended with additional PtG technologies. Detailed analyses of different methanation plants were carried out and cost drivers were identified. The process engineering as well as the economic perspective were brought together in the tool EcoMeth. Obstacles to implementation of PtG plants at a local level can be addressed directly and individual concepts can be developed.

In order to implement efficient and economical PtG concepts in the future, it is necessary to perform site-specific analyses. On-site resources must be taken into account and included in the process engineering design. To reach high efficiencies of PtG systems, a global heat management system must also be developed. Heat sources and sinks must be included. In addition, due to fluctuating renewables, dynamic operation will become important for PtG-plants. Buffer and storage concepts as well as load changes must be taken into account in the design of the plant.

References

[1] Sauerschell, S.; Bajohr, S.; Kolb, T.; Methanation Pilot Plant a Slurry Bubble Column Reactor: Setup and First Experimental Results, 2022. Energy & Fuels, 36 (13), 7166–7176, doi:10.1021/acs.energyfuels.2c00655

[2] Buffer and storage concepts as well as the load change must be taken into account in the design of the plantSchlautmann, R; Böhm, H.; Zaune, A.; Mörs, F.; Tichler, R.; Graf, F.; Kolb, T.; Renewable Power-to-Gas: A Technical and Economic Evaluation of Three Demo Sites Within the STORE&GO Project, 2021, Chemie Ingenieur Technik, doi:10.1002/cite.202000187