A Chinese research team has combined pressurized CO2 for renewable energy storage with a combined heat and power (CHP) unit. The overall efficiency of the system is 35.96% and the energy storage density is 1.54 kWh/m3.
The proposed solution is a closed loop system with a 600 MW CHP unit and carbon dioxide energy storage (CCES). It utilizes the heat coming from the backwater of the heating network and operates in two compression and expansion stages using water and carbon dioxide as working fluids without exchanging mass with the external environment.
“Off-peak, the s-CO2 released from the low-pressure tank (LPT) is compressed in the compressor, driven by the overproduction capacity of the CHP,” the researchers explained.
The compressed CO2 then passes through an intercooler to store the heat of compression in the water leaving the chilled water tank (CWT).
“After two compression steps, the s-CO2 is stored in a high pressure tank (HPT) and the cooling water is pressurized by a pump to a hot water tank (HWT) for storage,” the researchers said. “The cooling water in the improved system absorbs additional heat from the mid-suction steam before it goes to the HWT.”
The researchers presented the system in a recently published paper, “Thermodynamic Analysis and Optimization of a Compressed Carbon Dioxide Energy Storage System Combined with a Combined Heating and Power Unit.” Energy conversion and management.
“The performance and thermoelectric switching characteristics of the proposed combined system under varying operating conditions need to be analyzed in the future to determine its ability to consume renewable energy,” they said.