Process intensification: SEWGS case

Friday November 20, 2015 11:09

In process intensification, several unit operations are combined aiming at specific cost reduction. A typical example is combining an equilibrium limited conversion reaction with the downstream separation into a single unit operation. Cost reductions can thus result from an increase in production rate, a decrease in total energy consumption and/or a decrease of recycle streams.

In this context, ECN is developing the Sorption Enhanced Water-Gas Shift process (SEWGS). In the equilibrium limited Water-Gas Shift reaction, CO is reacted with steam to produce H2 and CO2. In the SEWGS process, a solid adsorbent is used that is reactive for the WGS reaction and simultaneously binds the produced CO2, eliminating the equilibrium limitation and consequently shifting the conversion towards CO2+H2 according to the principle of Le Chatelier. Full CO conversion for the WGS reaction is effectively combined with the H2/CO2 separation in a single unit operation.

The SEWGS process operates at increased temperature and pressure, typically 350-500°C and 10-50 bar. The moment the sorbent is saturated with adsorbed CO2, regeneration is performed via a combination of a pressure release and a purge. Because of the increased temperature, a steam purge can be used. A CO2-rich product is then obtained by condensing out the steam. Following sorbent regeneration, it is again ready for CO2 adsorption.

By combining multiple columns, this batch process is transformed into a continuous process. Each column sequentially performs each step of the process. SEWGS is a reactive hot CO2/H2 separation process, according to the Pressure Swing Adsorption principles. Effectively, the CO conversion is combined with separation, producing a H2-rich and a CO2-rich product stream. The main difference with the industrially widespread applied H2-PSA process is that the SEWGS adsorbent has excellent hydrothermal behaviour, allowing steam to be used to drive the CO2/H2 separation. In contrast to the conventional H2-PSA, a high H2 recovery is combined with a CO2 recovery. Additionally, the H2-rich product is at high pressure and hot, which can be beneficial for downstream processing.

SEWGS is a platform technology, typical applications being H2 production for the chemical industry and CO2 capture in CCS applications. System analysis analyses, based on experimentally verified models, indicate a lower energy consumption for the CO2 separation compared to alternative separation technologies, such as physical or chemical solvent systems. Moreover, SEWGS generally has a higher CO2 removal rate.

The SEWGS process has been demonstrated extensively at lab-scale, for which ECN operates a two development units having 2 kg and 50 kg shaped sorbent, respectively. The next step is a pilot at location. In the Stepwise project, a pilot located next to the SSAB steel plant in Luleå, Sweden, will be build. The capture rate of the pilot is 14tCO2/day.

Relevant literature:

1)        CO2 adsorbent development and demonstration:

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2)        Model development:

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3)        SEWGS system analysis:

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Category: Corporate, Energy efficiency