The production of biochar and byproducts. Tony Bridgwater Bioenergy Research Group Aston University, Birmingham B4 7ET, UK

Transcription

1 The production of biochar and byproducts Tony Bridgwater Bioenergy Research Group Aston University, Birmingham B4 7ET, UK Aston University Bioenergy Research Group IBI2010 Rio de Janeiro September 2010

2 What is pyrolysis? Biomass is heated in the absence of air or oxygen to decompose or devolatilise the biomass into: Solid char Liquid as bio-oil, tar or pyroligneous liquor Gas Three products are always produced Product yields depend on biomass, vapour and solids residence time, and temperature There are several modes of pyrolysis... 2

3 Pyrolysis modes Mode Conditions Wt % products Liquid Char Gas Fast ~ 500ºC; very short hot vapour residence time (RT) ~1 s; short solids RT 75% 12% 13% Inter- ~ 500ºC; short HVRT ~10-50% in 2 25% 25% mediate 30 s; moderate solids RT phases Slow ~ 400ºC; long HVRT; very long solids RT 35% 35% 30% Torrefaction Gasification ~ 300ºC; long HVRT; long solids RT ~ ºC; short HVRT; short solids RT Vapours 85% solid 1-5% 0% (all burned) 15% vapours 95-99%

4 Char or solid yields (all pyrolysis types) Char yield wt.% Temperature ºC

5 Char or solid yields (all pyrolysis types) Char yield wt.% Torrefaction Slow pyrolysis Intermediate pyrolysis Fast pyrolysis Gasification Temperature ºC

6 Gas and liquid yields Non-char or gas and liquid yield wt.% Temperature ºC

7 Gas and liquid yields Non-char or gas and liquid yield wt.% There are 40 challenges for disposal and 20 opportunities for valorisation such 0 as power and chemicals Temperature ºC As char yield falls, other products increase. These must be managed.

8 Fast pyrolysis technology Processes include fluid beds and circulating fluid beds Fast pyrolysis aims to maximise liquids. This is achieved with very high heating rates usually requiring very small particle sizes of generally <3mm in size and < 10% moisture Total liquid yields are up to 75 wt.% on dry biomass feed. The charcoal forms about wt.% of the products. It retains all the alkali metals. It is often used to provide process heat for which about wt.% of the char is required. Some processes consume all the char. Char is captured in enclosed vessels and can be handled in enclosed vessels 8

9 Fast pyrolysis char Pyrophoric spontaneously ignites when fresh Small particle size from maximum 3 mm from fluid beds down to fine dust Availability If process heat is provided by charcoal there is no char product.

10 Fast pyrolysis char spreading trials

11 Intermediate pyrolysis technology Processes include rotary kiln, screw, auger, moving bed, fixed bed Intermediate pyrolysis can process more difficult materials with handling and/or feeding and/or transport problems. The charcoal forms about 25 wt.% of the products. It retains all the alkali metals. Due to the mechanical and abrasive action of the reactor, the charcoal will tend to be small particle size. The liquid is 2 phases aqueous and organic The gas can produce power

12 Slow pyrolysis Processes include batch kilns and retorts, continuous retorts e.g. Lambiotte and Lurgi Feed size and shape is important Heating can be direct (air addition) or indirect Charcoal is mostly lump with smaller particles and dust Gases, vapours and liquids are seldom collected or processed. Exceptions include Usine Lambiotte (now shut own) and profagus (Chemviron, Degussa) in Germany (still operating) 12

13 Batch kilns and charcoal handling Abandoned charcoal kilns in Namibia Charcoal sorting and packaging in Namibia shows dust problem

14 Continuous retorts & chemical recovery Usine Lambiotte primary distillation column Usine Lambiotte carbonisers and liquid distribution

15 Usine Lambiotte outputs & revenues from ~100,000 t/y wood t/year /t k /y % Charcoal 25,000 *100 2, Total pyroligneous liquid 40,000 Water 30,000 Organics 10,000 Acids and alcohols 3, ,732 Oils 310 1, Fine chemicals 56 49,732 2, Fuel 5, Total organics 10, , Total income 7,929

16 Opportunity t/year /t k /y % Charcoal 25,000 *100 2, Total pyroligneous liquid 40,000 Water 30,000 Organics 10,000 Acids and alcohols 3, , Oils 310 1, Fine chemicals 56 49,732 2, Fuel 5, Total organics 10, , Total income 7,929

17 Opportunity t/year /t k /y % Charcoal 25,000 *100 2, Total pyroligneous liquid 40,000 Water 30,000 Organics 10,000 Acids and alcohols 3, , Oils 310 1, Fine chemicals 56 49,732 2, Fuel 5, Total organics 10, , Total income 7,929

18 Chemicals from pyrolysis liquids Acetic acid Acetone Aldehydes Anhydrosugars Butyl acetate Food flavourings Furaneol Furfural Hydroxyacetaldehyde Ketones Lactones Levoglucosan Levoglucosenone Liquid smoke Maltol Methanol Pharmaceuticals Phenolics Preservatives Propionic acid Pyroligneous acid Syringol Tars Taxol Terpenes Wood oils 18

19 Challenge management of byproducts What is not recovered for sale has to be disposed of. High income from chemicals recovery can support good practice waste disposal t/year /t k /y % Charcoal 25,000 est.100 2, Total pyroligneous liquid 40,000 Water 30,000 Organics 10,000 Acids and alcohols 3, ,732 Oils 310 1, Fine chemicals 56 49,732 2, Fuel 5, Total organics 10, , Total income 7,929

20 Torrefaction This is very low temperature pyrolysis. It enhances the properties of the biomass by: removing water, reducing hemicellulose, Improving heating value, Improving the friability of the product for subsequent processing e.g. grinding Vapours can either be: Burned to provide some process heat or waste disposal Collected to yield potentially valuable chemicals The role of torrefied biomass for carbon sequestration is not well understood: questions arise concerning high yield (85 wt.%) versus unknown life in soil 20

21 Questions What is the minimum pyrolysis temperature to give relatively permanent carbon sequestration? (This will tend to maximise solid/charcoal yields). What is the maximum level of volatiles in charcoal compatible with acceptable health and safety and biotoxicity levels? (This will also tend to maximise charcoal yields). What is the best method of applying charcoal to land? What chemicals can be economically recovered from co-products? What is the optimum byproduct or waste disposal solution? What steps are needed to improve charcoal production processes 21

22 Conclusions and recommendations Conclusions Pyrolysis is flexible in the process and products. Chemicals can be produced from the liquids with considerable economic potential Non-products are wastes and must be effectively and acceptably disposed of Recommendations for char production and use Technologies needs to be improved to improve char quality Technologies need to satisfy emissions and health and safety requirements Technologies need to be optimised for valuable products and waste disposal Charcoal needs to be applied acceptably 22

23 Thank you 23