Energy Recovery From Effluents Of Supercritical Water Oxidation Reactors

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Supercritical Water Oxidation (SCWO) reactors can process waste effluents achieving high conversions without producing pollutants –apart from carbon dioxide-, but the required extreme pressure and temperature operational conditions entail high-energy operational expenditure. Because of this, it is necessary to study reasonable solutions which are able to solve this part of the process with a viable efficiency. One solution could be the integration of supercritical processes with energy production in Combined Heat and Power (CHP) cycles, which are often joined to the use of gas turbines (GT).

Furthermore, the SCWO process produces a high pressure and temperature reactor outlet stream. It is possible to use the excess heat of this stream to implement a steam injection in the gas turbine, which will improve the efficiency of the global process.

Performance of simulation studies necessary for the integration of the SCWO Pilot Plant placed in University of Valladolid, it was found that the integration of this process with the power generation from gas turbines with steam injection showed to be a promising alternative for improving the energy balance of this operation.

Other additional studies was carried out, where the high pressure was used to increase energy production (Figure 1). An ejector is elected for this aim. The core idea underlying this choice is to use the pressure component of enthalpy in the effluent to rise the pressure of a part of the atmospheric air that goes to the GT compressor and then to the combustor, thus reducing the mass flow rate through the compressor and consequently the power spent.

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Figure 1. Heat integration (flow chart)

It’s worth noting that the design of ejectors and assessment of its efficiency is highly dependent on the fluid dynamics, spatial form and flow fields inside the device, being in addition the thermodynamic aspects of these super-sonic to stagnant flow at high pressures and temperatures very complex to describe. For this reason, at present we are performing detailed ejector simulation (using CFD) leading a design proposal.

Yoana García Rodríguez

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