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Publication Date: 2013-Oct-25
Document File: 2 page(s) / 85K

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The Prior Art Database

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DESCRIPTION of the innovation related to one of the 4 growth drivers: energy, environment, health, high technology and based on the following criteria:


This innovation addresses the need to reduce OPEX, CAPEX and energy consumption for oxygen production, especially for power plants using oxy-combustion (Environment growth driver).


Prior Art

Oxygen is industrially produced in large-scale air separation units (ASU) by cryogenic technology. Air is compressed, cooled and expanded, then separated from nitrogen by in a distillation column. Electrical power for compressors is the component of OPEX in ASU’s. ASU’s are needed for CO2 capture processes using oxy-combustion, where synthetic air comprising purified oxygen and recycled CO2 is used instead of atmospheric air which requires expensive downstream N2/CO2 separation. In CO2 capture from power plants using oxy-combustion, ASU compressors are the main source of energy penalty.


Novelty and advantages

The proposed process uses liquid oxygen carriers such as a cobalt porphyrin (CoP) solution for oxygen separation. Such liquid oxygen carriers take up oxygen by permeation at moderate pressure (atmospheric oxygen partial pressure is a fraction of a bar), are selective to oxygen, and can be regenerated in moderate conditions. In the proposed process, a liquid oxygen carrier is used as a washing agent for atmospheric air, absorbing oxygen, possibly with, or prior to, a cooling step to remove the heat generated by the absorption process. Oxygen is produced in a regeneration step using waste heat, for example from a power plant flue gas (see figure below).

The typical heat of formation of many oxygen carriers such as CoP or haemoglobin (not proposed due to stability issues) is about 60 kJ/mol O2.1 This corresponds to 520kWh/t O2 which is 2.6 times larger than the specific electrical power consumption of large ASU’s; however the proposed process uses thermal energy at lower temperature. Thermal energy cost, based on US natural gas price is 3 cents/kWh compared to 7 cents/kWh. This brings the energy cost ratio to 1.1. The price of thermal energy from coal amounts to 0.8 cents/kWh, making the energy cost of the proposed process lower than that of ASU’s, by a factor of nearly 3.5. In a power plant there is a considerable amount of low grade heat available in the flue gas, eliminating the need for additional fuel for this oxygen carrier regeneration and the energy penalty for oxygen production for oxy-combustion. A 550 MWe coal power plant can provide ~200 kWh per tonne of required O2 by cooling flue gas from 57°C to 40°C as a result of water condensation. Oxygen sorption on CoP is demonstrated near ambient temperature (45°C) in transport facilitated membranes with a permselectivity of 118 (O2/N2). 2

Another possible scheme is to use such a heat-regenerated liquid oxygen carrier in combination with an ASU, where the hot compressed ai...