Method and apparatus for producing biochar

Abstract

It is known to produce biochar from wood by the use of ring kilns and the like. However, they are inefficient and release ‘greenhouse gases’ to the atmosphere. The present invention provides a method of producing biochar from woody biomass comprising the steps of (a) placing feedstock ( 60 ) in a first kiln ( 10 ); (b) burning fuel in an oxidiser ( 70 ) and directing the resultant heated gases from the oxidiser to the feedstock to reduce the moisture content of the feedstock; (c) burning fuel in an oxidiser and directing the resultant heated gases from the oxidiser to the feedstock to pyrolyse the feedstock; (d) removing at least some of the pyrolytic gases, released from the feedstock in step c, to the oxidiser for burning therein; (e) directing at least a portion of the at least partially inert gases resultant from the burning of the pyrolytic gases in step d to the feedstock to regulate the amount of heat and air supplied to the kiln to controllably continue pyrolysis of the feedstock therein.

1 . A method of producing biochar comprising the steps of:
 a. placing feedstock in a first kiln;   b. burning fuel in an oxidiser and directing the resultant heated gases from the oxidiser to the feedstock to reduce the moisture content of the feedstock;   c. burning fuel in an oxidiser and directing the resultant heated gases from the oxidiser to the feedstock to pyrolyse the feedstock;   d. removing at least some of the pyrolytic gases, released from the feedstock in step c, to the oxidiser for burning therein;   e. directing at least a portion of the at least partially inert gases resultant from the burning of the pyrolytic gases in step d to the feedstock to regulate the amount of heat and air supplied to the kiln to controllably continue pyrolysis of the feedstock therein.   
     
     
         2 . The method of  claim 1 , wherein the removal of the at least some of the pyrolytic gases in step d of  claim 1  is effected by directing a portion of the gases resultant from the fuel burning in step c of  claim 1  to the kiln. 
     
     
         3 . The method of either one of  claims 1  and  2 , wherein the amount of air introduced to the oxidiser with the pyrolytic gases in step d of  claim 1  is controlled such that incomplete combustion of the mixture of air and pyrolytic gases occurs in the oxidiser. 
     
     
         4 . The method of  claim 3 , wherein air is controllably introduced into the gases directed from the oxidiser in step e of  claim 1  such that at least a portion of the gases are flared-off before reaching the feedstock. 
     
     
         5 . The method of  claim 4 , wherein the at least portion of gases are flared-off via a chimney. 
     
     
         6 . The method of any preceding claim, wherein at least some of the heated gases resultant from the fuel burning in either, or both, of steps b and c of  claim 1  are directed around the outside of the kiln in an at least partial spiral manner. 
     
     
         7 . The method of any preceding claim, wherein at least some of the resultant heated gases from the fuel burning in step b of  claim 1  are directed through the inside of the kiln from the top to the bottom, some of said gases then being directed to the atmosphere via a chimney, and some of said gases being recirculated to the kiln again. 
     
     
         8 . The method of any preceding claim, wherein the fuel burnt in the oxidiser in step c of  claim 1  is solely formed of the resultant pyrolytic gases resultant from the pyrolysing of the feedstock in step c, and removed in step d, of  claim 1 . 
     
     
         9 . The method of any preceding claim, when directly or indirectly dependent on  claim 6 , wherein at least some of the heated gases resultant from the fuel burning in step c of  claim 1  are directed to the top of the kiln directly and mixed with the heated gases directed around the outside of the kiln in an at least partial spiral manner. 
     
     
         10 . The method of any preceding claim, wherein the heated gases resultant from step d of  claim 1  are directed to a second kiln for drying feedstock therein. 
     
     
         11 . The method of any preceding claim, wherein at least some of the pyrolytic gases removed in step d of  claim 1  to the oxidiser for burning therein are directed into a combustor in a direction tangential to the centre of the combustor. 
     
     
         12 . The method of  claim 11 , wherein the pyrolytic gases are directed into the oxidiser at a point above the inlet of a flue provided at the top of the oxidiser. 
     
     
         13 . A biochar manufacturing apparatus comprising a kiln, arranged to accept feedstock, an oxidiser, a flue leading away from the oxidiser, an arrangement of conduits connecting the kiln, oxidiser and flue together, and a plurality of valves for regulating fluid flow through the conduits, wherein a first of said conduits connects to the kiln at a first position for removing pyrolytic gases, produced in use from feedstock in the kiln, for burning in the oxidiser, and a second of said conduits connects the oxidiser to the kiln at a second position for transferring at least partially inert gases produced by burning said pyrolytic gases in said oxidiser, wherein the first said conduit is arranged to direct the pyrolytic gases into the oxidiser in a direction tangential to the centre of the oxidiser and at a point above the inlet to the flue. 
     
     
         14 . The biochar manufacturing apparatus of  claim 13 , wherein the first said conduit is connected to the kiln beneath a grate positioned at the base of said kiln. 
     
     
         15 . The biochar manufacturing apparatus of either one of  claims 13  and  14 , wherein a third said conduit is arranged in a spiral manner around the outside of the kiln. 
     
     
         16 . The biochar manufacturing apparatus of  claim 13 , wherein the third said conduit is the second said conduit. 
     
     
         17 . The biochar manufacturing apparatus of any one of  claims 13  to  15 , wherein the third said conduit meets the second said conduit at the top of the kiln. 
     
     
         18 . The biochar manufacturing apparatus of any one of  claims 13  to  17 , further comprising a fourth said conduit connectable with the first said conduit for directing at least some of the pyrolytic gases, removed from the kiln, back to the kiln. 
     
     
         19 . A biochar manufacturing apparatus according to any one of  claims 13  to  18 , comprising two kilns and one shared oxidiser, the three being configured and arranged to fit into the same shape and volume as a ‘TEU’ twenty foot equivalent unit ISO shipping container, the conduits being arranged such that heated gases produced during pyrolysis of the feedstock in one kiln is directed to the other kiln for drying of the feedstock within. 
     
     
         20 . A biochar manufacturing apparatus being arranged to operate in accordance with the methods of any one of  claims 1  to  12 . 
     
     
         21 . The biochar manufacturing apparatus of  claim 19  including the features of any one of  claims 13  to  18 .