(321e) Dish-STARS™ Solar Thermochemical Production of Hydrogen

Dish-STARS™ Solar Thermochemical Production of
Hydrogen

Richard
F. Zheng ¹, Robert S. Wegeng ², Paul H. Humble, Johnny
Saavedra-Lopez ¹, Timothy G. Veldman ¹

¹ Pacific Northwest National
Laboratory, Richland, WA, United States

² STARS Technology Corporation, Richland,
WA, United States

The present paper describes the recent advances in
solar thermochemical processing and reactor engineering to achieve greater than
70% solar-to-chemical energy efficiency, based on PNNL’s Dish-STARS™
technology.  In a Dish-STARS™ module, a Solar Thermochemical Advanced Reaction
System (STARS) is coupled to a parabolic dish solar concentrator to convert
solar energy into storable/useful chemical energy.  The dish concentrator has
been previously developed for electrical power generation.  The STARS unit is a
compact, process-intensive chemical reaction system based on micro- and
meso-channel process technology (MMPT).  Dish-STARS™ steam methane reforming has
been demonstrated on-sun to produce syngas at over 70% solar-to-chemical energy
efficiency, while analyses indicating a potential for values greater than 80%.

The combined Dish-STARS™ system provides a solar
augment to a methane stream such as natural gas, landfill gas and biogas,
increasing its chemical energy content by 20-30% while decreasing its carbon
intensity.  If the syngas product is further reacted to produce valuable
chemical products, such as hydrogen, the reduction in carbon emissions is
retained and reduced carbon intensities can be attained for the chemical
products.  In a co-production mode, low-carbon hydrogen or electricity plus
various hydrocarbons (for example, methanol, olefins or plastics) can be
produced.  Currently, the Dish-STARS™ technology is under commercial
development for the efficient use of concentrated solar energy in near-term
applications for electrical power generation and the production of chemicals,
including hydrogen (see Figure 1).

Figure 1. Level-1
block diagram of general Dish-STARS™ hydrogen production concept.

Over the course of a previous SunShot project, the
STARS concept has been advanced to a technology readiness level (TRL) of 6. 
Reactor design was focused on improving exergetic efficiency of the SMR reactor
and reducing thermomechanical stress through CFD modeling and on-sun
experimental validation.   A high degree of heat integration was achieved by
using a number of carefully designed MMPT heat exchangers to recuperate high
grade heat from the hot syngas stream.  The new reactor and heat exchanger
assembly was tested on-sun under high flux conditions (see Figure 2) and showed
improved efficiency over previous version [1]. 

Figure 1. TRL-6 STARS reactor (left), reactor
and heat exchanger assembly (middle), and the Dish-STARS™ module operated on-sun
(right).

In this paper, details of the STARS reactor design to promote
thermal spreading and reduce thermomechanical stress will be discussed.  On-sun
steam methane reforming performance data and system exergy analysis results
will also be presented.  Preliminary results from a manufacturing investigation
will be included.

References

[1] Zheng, R.F. et al., Energy
Procedia 69 (2015) 1192.