This research is focused on producing hydrogen-enriched synthesis gas using steam biomass gasification. Such a gas can be used directly in land based gas turbine engines for electricity generation. Since a large percentage of the synthesis gas produced contains hydrogen, it can be used, with an additional simple step to produce hydrogen. The hydrogen is used in a process that produces jet fuel from bio oils as shown in Figure 1 below. The primary industrial method for hydrogen production is steam reforming of hydrocarbons such as oil, coal, and natural gas, where high-temperature steam reacts with the fuel to produce hydrogen and carbon monoxide. But this method is unattractive for a few reasons: the resulting hydrogen is more expensive than the starting fuel, carbon dioxide is still produced, and it relies on fossil fuel sources. Due to these limitations, we are developing clean and renewable methods of hydrogen production, focusing on solar-based approaches.
Research is currently being performed to create hydrogen through sustainable means. Figure 2 shows how this can be accomplished. Biomass (wood chips, grasses etc.) is chipped and dried and placed into an extremely hot reactor. In this heated environment biomass molecules break apart into synthesis gas (H2, CO, CO2, CH4, Tars and other molecules). Char is moved to a combustor where it is burned. The heat is then recycled in the gasification chamber. The heated synthesis gas is cooled in a heat exchanger and then thoroughly cleaned before separating out the H2. This process uses a great deal of superheated steam for fluidizing the gasfication bed. Saturated steam is sustainably created in a solar thermal field and then superheated by the heat exchanger. In this way the process can be made as efficient as possible.
Small scale (20-250 kWth) downdraft gasifiers are a valuable source of energy for populated rural areas. These units are cheap, easy to use, require minimal maintenance and can drastically improve the lives of rural communities that have no access to electricity or gas for cooking. Knowing the synthesis gas (syngas) composition from various biomass sources yields useful data for gasifier operation and feedstock selection. The goal of this study is to characterize the syngas produced from several feedstocks chosen for their cost and availability. The gasifier in these experiments is an Ankur Scientific WBG-20 rated at 50 kWth. This air fed gasifier is capable of producing syngas at a rate of up to 60 Nm3/hr. It was designed primarily for woody biomass, but can handle many different feedstocks if they are pelletized and have wet-basis moisture content below 25%. Diagrams of the key components of the system are seen in figure 3 below. The pelletized feedstock is loaded in to the hopper. The reaction bed in the hearth is externally lit and the oxygen in the incoming air combusts with some of the biomass in order to generate the heat that is then used by the pyrolysis and gasification reactions. The syngas is cleaned by several filtering mechanisms to be able to run directly into a natural gas engine and generator set to produce electricity.
A gas chromatograph is used for syngas composition analysis. The chromatograph used is the Agilent MicroGC300, which is on-line, and can sample roughly once every 2-3 minutes. The main component syngas composition results from a set of experiments with various feedstocks can be seen in figure 4 below. The measured composition is used to compute the heating values of the syngas produced through gasification of each feedstock, and can be seen in figure 5.