Modeling Analysis of a Polygeneration Plant Using a CeO2/Ce2O3 Chemical Looping

Abstract

In the current context of complexity between climate change, environmental sustainability, resource scarcity, and geopolitical aspects of energy resources, a polygenerative system with a circular approach is considered to generate energy (thermal, electrical, and fuel), contributing to the control of CO₂ emissions. A plant for the multiple productions of electrical energy, thermal heat, DME, syngas, and methanol is discussed and analyzed, integrating a chemical cycle for CO₂/H₂O splitting driven using concentrated solar energy and biomethane. Two-stage chemical looping is the central part of the plant, operating with the CeO₂/Ce₂O₃ redox couple and operating at 1.2 bar and 900 °C. The system is coupled to biomethane reforming. The chemical loop generates fuel for the plant's secondary units: a DME synthesis and distillation unit and a solid oxide fuel cell (SOFC). The DME synthesis and distillation unit are integrated with a biomethane reforming reactor powered by concentrated solar energy to produce syngas at 800 °C. The technical feasibility in terms of performance is presented in this paper, both with and without solar irradiation, with the following results, respectively: overall efficiencies of 62.56% and 59.08%, electricity production of 6.17 MWe and 28.96 MWe, and heat production of 111.97 MWt and 35.82 MWt. The fuel production, which occurs only at high irradiance, is 0.71 kg/s methanol, 6.18 kg/s DME, and 19.68 kg/s for the syngas. The increase in plant productivity is studied by decoupling the operation of the chemical looping with a biomethane reformer from intermittent solar energy using the heat from the SOFC unit.

Keywords: CS; DME; SOFC; biological methane; ceria oxides; chemical looping; polygenerative system.

Figure 1

Generic scheme of a thermochemical splitting cycle fed by concentrated solar energy.

Figure 2

Schematic representation of the ceria chemical looping coupled with biomethane reforming.

Figure 3

Prime mover and secondary devices of the polygeneration plant during a high-irradiance clear sky day.

Figure 4

Active components when the system does not receive adequate solar radiation.

Figure 5

Average temperature profile along the year in the solar concentrated dish placed in Turin [57].

Figure 6

Operating conditions of the reduction reactor, syngas production (orange line), and H₂/CO molar ratio (blue line) varying the operating temperatures and the CH₄/CeO₂ molar ratio. (a) The chosen operating conditions are 900 °C and a CH₄/CeO₂ molar ratio equal to 0.76 to satisfy all three requirements of this reactor; (b) at 850 °C; (c) at 800 °C. CeO₂ reduction is complete only with CH₄/CeO₂ molar ratios higher than 0.912, with a much higher expenditure of biomethane if compared with the other two cases.

Figure 7

DME yield in the DME synthesis reactor varying the H₂/CO molar ratio of the inlet streams.

Figure 8

Chemical looping scheme in Aspen Plus.

Figure 9

SOFC scheme in Aspen Plus when the CL is in ON state.

Figure 10

Pre-treatment of the syngas sent to the DME reactor in Aspen Plus.

Figure 11

Simulation of the DME reactor in Aspen Plus.

Figure 12

Post-combustion unit in Aspen Plus.

Figure 13

Treatment of H2OCO2-1 and reforming unit in Aspen Plus.

Figure 14

Distillation unit in Aspen Plus.