Torrefaction and partial pyrolysis to produce fuel pellets with counter current flow of tar

Abstract

The present application discloses a continuous process for the preparation of fuel pellets, said process comprising the steps of a) feeding a feedstock to a torrefaction and partial pyrolysis step at a temperature in the range from 250° C. to 500° C., whereby a solid char and volatile fraction are obtained, said volatile fraction comprising a tar fraction; b) directing the evolved volatile fraction as counter current stream relative to the stream of the feedstock, and at least partially condensing the volatile fraction on the incoming feedstock so as to obtain a tar-rich fraction combined with the incoming feedstock; and c) pelletization of the combined solid char / tar-rich fraction so as to obtain said fuel pellets. Novel fuel pellets are also disclosed.

Description

FIELD OF THE INVENTION[0001]The present invention relates to the field of fuel pellets production based on various sources of feedstock, e.g. biomass and waste.BACKGROUND OF THE INVENTION[0002]Bergman and Kiel, “Torrefaction for Biomass Upgrading”, 14th European Biomass Conference & Exhibition, 17-21 October 2005, discloses a process of torrefaction of biomass, separation of the volatiles, and cooling of the torrified biomass. It is suggested that the torrified biomass may undergo size reduction and pelletization.[0003]Bergman et al., “Torrefaction for biomass co-firing in existing coal-fired power stations—“Biocoal””, ECN-C-05-013, Energy research Centre of the Netherlands (ECN), 2005, discloses a process of torrefaction of biomass at a temperature of about 280° C., wherein the torrified biomass is cooled and the torrefaction gas is combusted and used for drying the biomass and as a heat supplement for the torrefaction process.[0004]Bergman, “Combined torrefaction and pelletisation...

AI Technical Summary

Benefits of technology

[0010]The present invention provides a process for providing fuel pellets based on biomass or waste that can be optimized for use in power plant boilers (grate, fluid bed or suspension fired), district heating boilers, small pellet stoves, industrial process furnaces, kilns and boilers, small-scale heating devices, and barbeque grills. The pellets may be utilized as a global trading product. Process steps to control pellet heating value density, pellet milling properties, particle size in pellet and pellet ash properties may be included. From the end-user's point of view, the following pellets properties are attractive, namely i) a high heating value density to minimize transport costs, ii) a high pellet stability and hydrophobic properties of the pellets which make handling simple, minimized dust problems, and thereby reduce the risk of self-ignition and provide the option of out-door storage even in wet climates; iii) the option of easy grinding of the pellets in a mill e.g. a coal mill to obtain a small particle size; and iv) acceptable pellet ash properties so that ash deposition, corrosion and flue gas cleanings equipment interference are minimized and residual product utilization is possible.

Problems solved by technology

It was concluded that torrifaction of grass was not an attractive pre-process as the pellets were very brittle and possessed little mechanical strength and reduced bulk density.

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