Biomass-to-energy combustion method

Abstract

A solid biomass-to-energy combustion method includes introducing an oxygen containing gas into a combustion chamber of a suspension furnace to form a flow of gas through the combustion chamber; injecting a particulate solid biomass fuel into the combustion chamber through a port in the furnace wall and into the gas flow, and combusting the particulate solid biomass fuel in the gas flow to form a flame in the gas flow.

1 . A method of preparing solid biomass fuel for a solid biomass-to-energy combustion system, comprising:
 providing solid biomass fuel;   reducing the solid biomass fuel into solid biomass particles having a particle size distribution such that substantially 100% by weight of the solid biomass particles pass through a sieve having 0.125 inch diameter holes.   
     
     
         2 . The method of  claim 1 , wherein reducing the solid biomass fuel comprises
 a first screening step including screening the solid biomass fuel to separate solid biomass fuel particles having a maximum dimension equal to and less than 1.0 inch from first remaining solid biomass fuel particles having a maximum dimension greater than 1.0 inch;   a first size reduction step including size reducing the first remaining solid biomass fuel particles in a high speed rotating hammermill shredder to produce solid biomass fuel particles having a maximum dimension equal to and less than 1.0 inch;   a second size reduction step including size reducing all the equal to and less than 1.0 inch solid biomass fuel particles in a mill to reduce the solid biomass fuel particles to solid biomass fuel particles having a maximum dimension less than 0.125 inch.   
     
     
         3 . The method of  claim 2 , further comprising:
 separating the solid biomass fuel particles into primarily solid biomass fuel particles and primarily solid non-biomass fuel particles; and   magnetically separating ferrous metal particles from the primarily solid biomass fuel particles,   wherein both separating steps being conducted at least one of before and between the first size reduction step and the first screening step.   
     
     
         4 . The method of  claim 2 , further comprising:
 feeding the solid biomass fuel particles having a maximum dimension less than 1.0 inch through a rotary dryer and drying the solid biomass fuel particles having a maximum dimension less than 1.0 inch to a moisture content of less than 5% water by weight.   
     
     
         5 . The method of  claim 4 , further comprising:
 combusting the solid biomass fuel particles;   creating waste heat from combusting the solid biomass fuel particles;   introducing the waste heat from combustion into the rotary dryer; and   using the waste heat to dry the solid biomass fuel particles having a maximum dimension less than 1.0 inch to a moisture content of less than 5% water by weight.   
     
     
         6 . The method of  claim 5 , wherein drying includes drying at a low temperature of 300-500 degrees F. the solid biomass fuel particles having a maximum dimension less than 1.0 inch to a moisture content of less than 5% water by weight. 
     
     
         7 . The method of  claim 1 , wherein the solid biomass fuel is a particulate wood and diverse biomass fuel. 
     
     
         8 . A solid biomass fuel for a solid biomass-to-energy combustion system, comprising: particles of wood and diverse biomass with less than 5% water by weight, the particles of wood and diverse biomass having a particle size distribution such that substantially 100% by weight of the wood and diverse biomass particles pass through a sieve having 0.125 inch diameter holes. 
     
     
         9 . A solid biomass-to-energy combustion method, comprising:
 introducing an oxygen containing gas into a combustion chamber of a suspension furnace to form a flow of gas through the combustion chamber, the combustion chamber being defined by a furnace wall;   injecting a particulate solid biomass fuel into the combustion chamber through a port in the furnace wall and into the gas flow; and   combusting the particulate solid biomass fuel in the gas flow to form a flame in the gas flow, the particulate solid biomass fuel comprising less than 5% water by weight and having a particle size distribution such that substantially 100% by weight of the particulate solid biomass fuel pass through a sieve having 0.125 in diameter holes, so that the particulate solid biomass fuel particles are substantially completely combusted within the combustion chamber while suspended in the gas flow and are not combusted at the furnace wall.   
     
     
         10 . The method of  claim 9 , wherein the furnace is a wall-fired fossil fuel suspension furnace. 
     
     
         11 . The method of  claim 9 , further comprising the step of pneumatically conveying the particulate solid biomass fuel through a conduit to the second port. 
     
     
         12 . The method of  claim 11 , further comprising the step of conveying the particulate solid biomass fuel to the conduit with an auger. 
     
     
         13 . The method of  claim 9 , wherein the particulate solid biomass fuel is injected in an amount such that the particulate solid biomass fuel contributes 100% of the energy produced by the furnace. 
     
     
         14 . The method of  claim 9 , wherein the method produces emissions of 0.025 to 0.040 lbNO x /MMBtu. 
     
     
         15 . The method of  claim 9 , wherein the furnace wall includes an additional port, and the method further comprising the steps of injecting flue gas into the combustion chamber through the additional port in the furnace and into the gas flow. 
     
     
         16 . The method of  claim 15 , further including recirculating to the combustion chamber more than 0% and no more than 35% of the flue gas from the combustion chamber. 
     
     
         17 . The method of  claim 9 , further comprising precisely balancing the particulate solid biomass fuel with the oxygen containing gas such that excess air is 10-40%. 
     
     
         18 . The method of  claim 9 , wherein the furnace wall includes a first port and a second port, and
 further including injecting a fossil fuel into the combustion chamber through the first port in the furnace wall and into the gas flow;   injecting the particulate solid biomass fuel includes injecting the particulate solid biomass fuel into the combustion chamber through the second port in the furnace wall and into the gas flow, the second port being separate from the first port such that the particulate solid biomass fuel is injected into the combustion chamber separately from the fossil fuel; and   combusting the particulate solid biomass fuel includes combusting the fossil fuel and the particulate solid biomass fuel in the gas flow to form a flame in the gas flow.   
     
     
         19 . The method of  claim 18 , wherein:
 the furnace is a tangentially-fired fossil fuel suspension furnace;   introducing the oxygen containing gas includes introducing the oxygen-containing gas tangentially into the combustion chamber so that the gas flow through the furnace has a vortex;   injecting the fossil fuel includes injecting the fossil fuel tangentially into the combustion chamber and into the vortex of the gas flow;   injecting the particulate solid biomass fuel includes injecting the particulate solid biomass fuel tangentially into the combustion chamber and into the vortex of the gas flow; and   combusting the fossil fuel and the particulate solid biomass fuel includes substantially completely combusting the fossil fuel and the particulate solid biomass fuel within the combustion chamber while suspended in the vortex of the gas flow.   
     
     
         20 . The method of  claim 19 , wherein the furnace is a tangentially-fired pulverized coal suspension furnace and the fossil fuel is pulverized coal. 
     
     
         21 . The method of  claim 19 , wherein the furnace wall includes a third port, and the method further comprising the steps of tangentially injecting natural gas into the combustion chamber through the third port in the furnace and into the vortex of the gas flow, and combusting the natural gas in the vortex of the gas flow. 
     
     
         22 . The method of  claim 18 , wherein the furnace is a wall-fired pulverized coal suspension furnace and the fossil fuel is pulverized coal. 
     
     
         23 . The method of  claim 18 , wherein the furnace is a pulverized coal suspension furnace and the fossil fuel is pulverized coal. 
     
     
         24 . The method of  claim 18 , wherein the fossil fuel is atomized oil or distillate. 
     
     
         25 . The method of  claim 18 , wherein the furnace forms part of a boiler and the furnace wall includes boiler tubes. 
     
     
         26 . The method of  claim 18 , wherein the boiler is a utility grade boiler. 
     
     
         27 . The method of  claim 18 , wherein the furnace wall includes a third port, and the method further comprising the steps of injecting natural gas into the combustion chamber through the third port in the furnace and into the gas flow, and combusting the natural gas in the gas flow. 
     
     
         28 . The method of  claim 27 , wherein the first port is upstream of the third port and the second port is between the first port and the third port. 
     
     
         29 . The method of  claim 27 , wherein the second port is upstream of the third port and the first port is between the second port and the third port. 
     
     
         30 . The method of  claim 18 , wherein the first port is upstream of the second port. 
     
     
         31 . The method of  claim 18 , wherein the second port is upstream of the first port. 
     
     
         32 . A solid biomass-to-energy combustion method, comprising:
 introducing an oxygen containing gas into a combustion chamber of a fossil fuel suspension furnace to form a flow of gas through the combustion chamber, the combustion chamber being defined by a furnace wall;   injecting a particulate solid biomass fuel into the combustion chamber through a set of ports in the furnace wall and into the gas flow, the set of ports also being spaced about the combustion chamber; and   combusting the particulate solid biomass fuel in the gas flow to form a flame in the gas flow, the particulate solid biomass fuel comprising less than 5% water by weight and having a particle size distribution such that substantially 100% by weight of the particulate solid biomass fuel particles pass through a sieve having 0.125 inch diameter holes, so that the particulate solid biomass fuel particles are substantially completely combusted within the combustion chamber while suspended in the gas flow and are not combusted at the furnace wall.   
     
     
         33 . The method of  claim 32 , wherein the furnace is a wall-fired fossil fuel suspension furnace. 
     
     
         34 . The method of  claim 32 , wherein:
 the furnace is a tangentially-fired fossil fuel suspension furnace;   the oxygen-containing gas is introduced tangentially into the combustion chamber so that the gas flow through the furnace has a vortex;   the fossil fuel is introduced tangentially into the combustion chamber and into the vortex of the gas flow:   the particulate solid biomass fuel is introduced tangentially into the combustion chamber and into the vortex of the gas flow; and   the particulate solid biomass fuel particles are substantially completely combusted within the combustion chamber while suspended in the vortex of the gas flow.