Thermochemistry: The Key to Minerals Separation from Biomass for Fuel Use in High Performance Systems

Biomass use in high efficiency thermal electricity generation is limited not by the properties of the organic component of biomass, but by the behavior of the associated mineral matter at high temperatures. On a moisture and ash free basis biomass has a relatively low heat value of 18.6GJ/t. However, this would not limit its use in high efficiency combustion systems because adequate hightemperatures could be reached to achieve high carnot cycle efficiencies. These high temperatures cannot be reached because of the fouling and slagging propensities of the minerals in biomass. The mineral composition is a function of soils and the growth habit of the biomass, however, the most important element is potassium, which either alone or in combination with silica forms the basis offouling and slagging behaviors. Recent work has demonstrated the phenomenology of ash fouling, mainly by the potassium component of biomass, as well as identifying the key species and sulphates involved in potassium transport at temperatures <800 deg. C. Techniques that separate the mineral matter from the fuel components (carbon and hydrogen) at low temperatures reduce or limit the alkali metaltransport phenomena and result in very high efficiency combustion applications in combustors, gas turbines, and diesel engines. Gasification and various types of clean up systems as well as pyrolysis techniques are able to separate the minerals from the fuel component. The performance of these systems under investigation are discussed in this document.