ATR-based compact reactor system for the distributed hydrogen production
Vincenzo Palma1, Antonio Ricca1*, Biagio Addeo1, Maurizio Rea2, Gaetano Paolillo2, Paolo Ciambelli1
1*Dep. of Industrial Engineering, University of Salerno, via Giovanni Paolo II 132, 84084 Fisciano, ITALY, firstname.lastname@example.org
2R&D - SOL s.p.a, Via Borgazzi 27, 20900 Monza (MB), ITALY
The well-known problems linked to the depletion of fossil fuels and to the growing energy demand address the industrial research toward the development of effective innovative routes for alternative energy resources. If in one hand hydrogen is pointed as the best clean energy vector (to employ in fuel cell systems), in the other hand its production through hydrocarbon reforming still appears as the most viable solution in a transition period towards a hydrogen based economy. One of the main limitation connected to the hydrogen employment diffusion is linked to economic issues related to the H2 transport and storage. In this aim, distributed hydrogen production appeared an optimal solution, both for the stationary and mobile installations. From this point of view, hydrocarbons catalytic Auto-Thermal Reforming (ATR) appears the best candidate process1: it combines the partial oxidation and the steam reforming processes, since hydrocarbons react with both oxygen and steam to obtain a self-sustained and very fast process. Anyway the high carbon monoxide content of the produced stream require a further catalytic stage, the Water-Gas Shift (WGS) in which CO reacts with steam to produce further hydrogen. Anyway, the very different operating temperature of ATR and WGS stages resulted in the necessity of a heat exchange system, with a consequent increasing in plant size and operating costs.
Aim of this work was to design and test a thermally integrated fuel processor based on natural gas ATR, aimed to the hydrogen production intensification and to the external duty minimization.
A compact fuel processor based on Auto-Thermal Reforming process for natural gas conversion was designed and configured to produce up to 10 Nm3/h of hydrogen. Water and air were delivered to the system, together with the hydrocarbon. The system was provided to 2 catalytic stage: in the ATR module, the hydrocarbons conversion to syngas was obtained, in the WGS module the CO present in the syngas was converted increasing hydrogen content. In the ATR module a 0.5 L commercial (Johnson Matthey) honeycomb catalyst noble metals based was loaded, while in the WGS 2 L of commercial (JM) pellets catalysts were employed. Due to the very different temperature in the two stages, a compact and optimized heat exchange module were designed and placed between the two reaction volumes. In this way, sensible heat of effluent gas from ATR volume was exploited to pre-heat reactants before feeding to it; moreover, effluent gas were cooled to a temperature consistent to the WGS stage. Such configuration allowed to feed all reactants at room temperature, without external heat exchangers; moreover, the thermal integration was able to reduce system start-up transient times. Preliminary studies were carried out in order to evaluate the reactants rate and the feed ratios effect on system performances.
RESULTS AND DISCUSSION
Preliminary tests confirmed that the designed system was characterized by very short start-up times, being able to produce up to 5 Nm3/h of hydrogen (27%vol) in less than 3 minutes. The transitory phases were strictly related to the overall gas rate, since higher stream rate resulted in faster system response. Despite thermodynamic predictions, due to the thermal integration the system seemed not to be greatly affected by steam content, since too high steam-to-carbon ratio resulted in a decreasing in system temperature. In Fig. 1, the system performances are summarized in a selected operating condition. As reported, the ATR module well approached the thermodynamic equilibrium, reaching a total methane conversion. On the other hand, WGS module was able to convert only the 51% of CO, mainly due to the thermodynamic limitations, so also affecting the thermal efficiency that anyway reached very promising values.
Fig. 1 System performances (H2O:O2:CH4 = 0.65:0.65:1)
An ATR-based fuel processor thermally integrated was designed and realized. Preliminary tests evidenced the quick start-up and response of the system, that showed very good performances by producing up to 7.4 Nm3/h of H2. WGS module seemed to suffer for thermodynamic limitation, suggesting to feed more steam to the system, as well as to modify catalytic formulation. As a future enhancement, a heat recovery module may be placed downstream the WGS module for a further heat recovery.