A novel pyroformer system for biomass intermediate pyrolysis with in-situ char-promoted reforming (by char re-circulation) of pyrolysis vapours and potential integration of pyroformer with commercial scale fluidised bed gasifier to enable pyrogasification

Abstract

Strong scientific evidence shows that anthropogenic greenhouse gas emissions from usage of fossil fuels are responsible for global warming and climate change.Biomass is a sustainable and reliable resource for replacing fossil fuels to produce energy and chemicals through pyrolysis and gasification routes. Pyrolysis of biomass leads to three products i.e. bio-oil, non-condensable gas and char. Gasification of biomass leads to a syngas which consists of hydrogen, carbonmonoxide, carbon dioxide, ,methane, nitrogen water vapour and some C1-C4 gases.The objectives of this thesis included: to conduct tests on a twin-screw pyrolysisreactor (Pyroformer); to evaluate the effects of char recirculation on products; to characterise the bio-oil and char produced and characterise an in-situ blend of biodiesel/bio-oil; and to review the design of the Pyroformer and its coupling with a bubbling fluidised bed gasifier, thus enabling a novel concept of Pyrogasification.To observe the biomass and char flow characteristics, and to calculate the residence time and char to biomass ratio (C/B), cold flow tests were performed ina transparent model of 20 kg/h Pyroformer. Biomass throughput limitations were identified at different feeding rates and C/B.Pyrolysis tests were conducted in a Pyroformer with up to 10 kg/h feeding rates.It was observed that, during pyrolysis of dry digestate pellets, gas yield increased and liquid yield decreased at optimum C/B of 3.1 at 5 kg/h. The organic phase ofbio-oil for MSW had an HHV of 30.3 MJ/Kg and a very low total acid number of 0.2mgKOH/g.ENPlus certified wood pellets and miscanthus pellets were pyrolysed in a 100 kg/h Pyroformer with in-situ blending of bio-oil with biodiesel. Product yield of 21, 32and 47 wt% for liquid, char and gas fractions were observed for wood pellets; and31, 32 and 37 wt% with miscanthus. Bio-oil content in the blend was 19.75 and11.28 wt% for wood and miscanthus derived feed stocks. The heavy metal content in biochars met voluntary biochar standards for soil remediation. A gasifier commissioning test was done with hydrogen, CO, methane and CO2 yields of 13.3,17.3, 4 and 17 vol% at 818 °C.