GASIFICATION

THE BIOGEN ADVANTAGE

The Biogen gasification process is unique and superior because we combine unprecedented temperature control in the reactor with our exclusive closed loop tar recovery process.  We employ specialized systems to clean our synthesis  gas virtually tar-free, and the filtered  tars are recycled as fuel in the reactor.  The result is exceptionally clean synthesis gas that will run a wide variety of genset engines, a closed-loop process free of wastewater emissions, and  the ability to operate with the widest variety of biomass.

A SYNGAS  energy process has:

• Higher efficiency than biomass processes for steam, power or CHP (boiler).
• Significantly less investment in CAPEX and OPEX.
• Scalable process located near the biomass

GASIFICATION BASICS

The gasification process starts with a high temperature reactor, where dried biomass (<15% moisture content) is converted into synthesis gas.  Gasification reactors resemble tube furnaces, with a fuel inlet at the top and a grating at the bottom.  A primary difference between a furnace and a gasifier is the stratification of different layers, or zones inside the reactor.  With a furnace, the combustion is at the bottom; near the grating; fuel is added to the top, with gases and smoke exhausting out the top. 

With a gasifier, there is also a combustion, or oxidation zone, however it is positioned higher up in the tube, and there is another zone below, called the reduction zone, where the synthesis gas is produced.  Basically, in the oxidation zone the fuel is initially burned same as in a furnace, with the hydrocarbons in the fuel converting to carbon dioxide (CO2) and water vapor (H2O).  This reaction is exothermic and produces a large amount of energy as heat; but in the reduction zone below, the CO2 and H2O convert to carbon monoxide gas (CO) and hydrogen gas (H2). 

These reactions are endothermic and need a lot of energy to take place; the oxidation zone directly above supplies the necessary energy to form these gases.  These two gases are the main combustible ingredients of the synthesis gas.  Other combustible hydrocarbon gases like methane (CH4) and others are also present from incomplete combustion.  These are called pyrolysis gases, and they increase the caloric value of the synthesis gas.  There are typically small amounts of other more complex hydrocarbons (tars) also present in the gas due to incomplete combustion, along with the incombustible components; Nitrogen gas (N2), and typically some unreacted CO2  and H2O.  So in a nutshell, a gasifier is a type of furnace arranged so that there is a reduction zone underneath the traditional oxidation zone.  Another major difference between a furnace and a gasifier is that there is no exhaust of gases and smoke; all the volatiles emitted become synthesis gas, with no other exhaust emitted.

One of the most important factors is for the biomass fuel to be the correct dryness.  Ordinary burning can support quite a bit of moisture content in the fuel, as the water vapor escapes upward with the smoke and heat.  With gasification all the combustion products, steam, smoke, heat etc. move downward through the mass of fuel; everything in the fuel gets converted, with only some small amount of ash or charcoal left over.  How much moisture can be tolerated depends on the fuel. 

Some moisture is necessary, especially with coal for fuel, as there is little hydrogen contained in it, and the combustible end products with gasification are carbon monoxide, hydrogen and methane.  So in the case of coal, all the carbon comes from the coal, all the hydrogen comes from water, and oxygen comes either from the air in the original combustion reaction, or from water.

With fresh organic fuel, the feedstock contains both carbon and hydrogen, so the amount of water must be kept low in order for the reaction to convert everything effectively. Too much moisture results in some water ending up unconverted to gas.   This residual water vapor winds up combining with the tars in the hot gas and can plug up the grating and restrict the air intake, as well as foul the mechanical systems used to remove charcoal and ash from the reactor.

With fuel like wood chips, moisture content of 10-15% by weight or less works really well in gasification.  Fresh cut trees are close to 45-50% moisture content.  High moisture content in the biomass fuel also directly and dramatically reduces the calorific value of the fuel per unit weight ( see table below).  The result is that biomass drying is a crucial factor for both the gasification process as well as the efficiency of delivering biomass to the gasification plant.

Moisture Content vs Caloric Value for Wood Chip Biomass Fuel
Moisture Content, % by Weight	Lower Heating Value,BTU/lb.
10	7281
20	6333
30	5429
40	4481
50	3533
60	2628

The use of Biochar as a soil additive draws on ancient agricultural practices put into use by the local population of the Amazonian region thousands of years ago. In this area of the world, soil with very different properties compared to typical forestry soils was discovered.  Soil called “Terra Preta do Indios” with black colour and alkaline pH, give rise to endemic micro organisms and are particularly rich, and nourishing, due to high organic matter content, as well as high cationic exchange capacity.  The main feature of these soils is the high volume of black carbon content, more than seventy times above normal, to a depth of eighty centimetres. The charcoal was introduced into the soil by the native population throughout the ages, the charcoal content further increased from thermo-chemical processes (pyrolysis, or in-complete combustion) of vegetable materials.

In the opinion of many leading researchers, the carbon fraction’s chemical and microbiological stability is due to its complex aromatic structure, which has been able to persist for centuries in the environment. The structure is slowly oxidized over the years producing carboxylic groups able to increase the capacity to retain the nourishing, but at the same time allows carbon storage and immobilization in the soil and reduces atmospheric emissions. These characteristics remain for centuries and still now the black Amazon earths are much more fertile than surrounding areas, long after the native population left the areas.

Soil Biochar addition, if applied in a large scale, seems able to mitigate climate change and could be both an economical and environmentally friendly way to increase agricultural production.

Gasification creates a fine-grained, highly porous, pollutant free charcoal that significantly varies in its chemical and physical properties depending on starting material (woody or herbaceous feedstock, residues).

The Biogen is currently collaborating actively with the scientific community and is involved in experimentation and demonstration activity in order to better understand the soil dynamics and the growing effects of Biochar amendment. The results thus far are very positive and encourage field application.

In this way it will be possible to obtain a threefold benefit without reducing emissions through renewable energy production resulting in carbon sequestration, soil fertility and agriculture production increase.