Precombustion CO2 capture

In addition, the ability to work in a wide range of operative conditions is another key aspect for the development of advanced membranes. Chemical stability is of particular importance when the membrane interfaces are exposed to aggressive solvents, such as in several organic solvent nanofiltration (OSN) applications [21]. Resistance to fouling is also important in water filtration because this phenomenon can threaten the continuous operability of the membrane module [22]. In high-temperature (eg, precombustion CO2 capture from syngas [23] or polymer electrolyte membranes for fuel cells [24]) and high-pressure (eg, reverse osmosis and nanofiltration membranes for... 

The treatment process significantly differs from the one previously described in case precombustion CO2 capture is included in a power generation IGCC or the gasification plant is designed for H2 production. In both of these cases, CO included in syngas has to be oxidized to CO2 by a water gas shift (WGS) reaction to promote H2 production. Being moderately exothermic (standard reaction enthalpy AHo = —41.1 MJ/kmol at 25 °C), the WGS reaction... 

In plants featuring CO2 capture, a H2-rich fuel stream is burned in the gas turbine combustor instead of syngas. Burning H2-rich fuel does not pose significantly different issues from syngas, and so the same strategy is followed in the IGCC plant with precombustion CO2 capture. 

CO2 avoidance by membrane separation is approximately 85%, a value shghtly lower than that achievable by conventional precombustion CO2 capture with solvents (Table 13.4). 

Simplified versions of several energy conversion processes that use solvent-based H2S or CO2 capture, with optional design pathways shown, (a) IGCC [3] (b) GTL [11] (c) CTL [11,12] (d) PC Power [3] (e) NGCC with postcombustion capture [3] (f) NGCC with precombustion capture,or H2 production [13,14]. 

Schematically, CO2 capture can be achieved following three main strategies (Figure 39.1) [12] (1) oxy-combustion (or oxy-fuel combustion) where the fuel combustion is performed with pure or enriched O2 instead of air, so that a CO2/ H2O mixture is produced (2) pre-combustion, where the carbon from the fuel is removed prior to combustion (decarbonization) either as CO2, as coke, or in other forms, and whereby the primary fuel heating value is transformed into H2 through partial oxidation, steam reforming, or autothermal reforming with subsequent water-gas shift (WGS) reaction and (3) post-combustion, where CO2 recovery is performed at the end of pipe from a wet exhaust flue gas, usually at 10-30% (v/v) CO2 concentration. The target separations to achieve in these processes to make them feasible are O2/N2 for oxy-combustion, CO2/H2 for precombustion, and CO2/N2 for post-combustion CO2 capture.

A number of promising new materials exist for CO2 capture from precombustion, post-combustion, and oxyfuel processes [17]. Examples of new materials include ionic liquids (ILs), metal-organic frameworks (MOFs), membranes, and fibrous and nanofibrous sorbents (Fig. 10.1). 

The German COORETEC CO2 Reduction Technologies) concept favours coal gasification with precombustion capture to introduce COj capture into coal fired power plants. The same capture process is suited to produce hydrogen from coal in an environmentally-friendly way. This technical option is outlined in the recently drawn up national vision on hydrogen technologies. The first projects in this area are to be funded in the near future. 

Precombustion capture. This solution is developed in two phases (1) the conversion of the fuel in a mixture of H2 and CO (syngas mixture) through, for example, partial oxidation, steam reforming, or autothermal reforming of hydrocarbons, followed by water-gas shift (WGS), and (2) the separation of CO2 (at 30%-35%) from the H2 that is then fed as clean fuel to turbines. In these cases, the CO2 separation could happen at very high pressures (up to 80 bar of pressure difference) and high temperatures (300°C-700°C).42... 

The selection of the liquid absorbents in membrane contactors is critical. The commonly used absorbents for CO2 removal are amine based (i.e., MEA, DEA, and TEA) [160-163], Recently, membrane contactors using ILs as alternative absorbents for the capture of acid gases have been reported [166-170], The unique properties of ILs (nonvolatile with a high affinity for the acid gas component, thermally and chemically stable [171]) make it very promising as CO2 absorbents in membrane contactors, especially for applications in harsh conditions, such as CO2 separation from precombustion flue gas at elevated temperatures and pressures [169,170]. 

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