(395f) Annular Moving Bed Adsorber for Upgrading Natural Gas

Authors: 
Thakur, R. S., GGV, Bilaspur
Gupta, R. K., National University of Singapore
Rao, D. P., Process Intensification Consultants
Kaistha, N., IIT Kanpur



In the conventional fixed bed Pressure Swing Adsorption, most of the bed is inactive as the length of the mass transfer zone is many times smaller than the bed length. Further, the attainable driving force is small as the gas is in equilibrium with the adsorbent on either side of the mass transfer zone. Therefore the productivity and recoveries are low. However, these limitations can be overcome by using a ‘simulated’ moving bed (SMB) that ensures full utilization of the bed due to the countercurrent contact of the solids and the gas. Thermal swing offers an advantage over pressure swing as the thermal energy can be partially recovered by using heat regenerators that significantly reduce the cost of regeneration. Sivakumar and Rao (2012) proposed a thermal swing SMB with thermal regeneration using two fixed adsorbent beds and an inert bed for the recovery of thermal energy [1]. In this scheme too a large portion of the beds are inactive leading to low productivity.

We propose here an Annular Moving Bed adsorber (AMB) in which the inactive zones are eliminated altogether. The AMB is similar in construction to the rotary hearth furnace used in metallurgical industries. In addition, another concentric annular bed of inert solids, divided into two zones, is provided above the annular adsorption bed to facilitate the heating and cooling for the regeneration.

Simulation studies have been carried out to assess the efficacy of the AMB for upgrading lean natural gas over activated carbon. A non-isothermal model for the annular moving bed has been employed. The simulation studies show that for an operation at a pressure of 1 bar, the energy required for circulation of the gas for regeneration is more than that required for conventional PSA. However, if the operation is carried out above 10 bar, the cost of energy requirements is much smaller than conventional PSA and the productivity is several times higher than SMB and PSA. The AMB appears to be suitable for upgrading large volume of natural gas available at pressure above 10 bar.