LIGNIN AS ALTERNATIVE RENEWABLE FUEL

Lignin fuel technology

Lignin has the combustion heat of 26.6 KJ/g, and holds highest energy among all natural polymeric compounds that contain carbon, hydrogen and oxygen. In energy, lignin is equivalent to ethanol, which also contains carbon, hydrogen and oxygen, and has the combustion heat of 30 KJ/g. However, for a given volume, lignin’s combustion heat is approximately 1.5 times as much as that of ethanol, because of lignin’s higher density. Since no appropriate activiation method had been found until now, fine granular lignin as a flammable high-energy fuel had been unable to serve as engine’s fuel. With its characteristics of high dispersion and fluidity, the fine particulate of lignin, down to nanometers range, through adoption of an innovative activiation technology (detailed in a submitted patent application), can be evenly mixed with diesel oil to form a kind of quasi-liquid fuel of a state in between liquid and solid, and thus become a partial substitute for diesel oil. Obviously, lignin can also be mixed into gasoline and jet fuel. The quasi-liquid fuel can be directly used in the existing diesel engines with no need for any structural alteration of the diesel internal combustion engines, though an independent fuel tank and fuel passage is needed if it can be used in a further user-friendly way and if the amount of lignin to subsititute of fossil fuels is further increased..

fig1

The diesel engine can run without stop in the idle state using the mixed fuel up to 30%w/w lignin. Apart from actual water pumping tests, Brake Specific Fuel Consumption test using a 15HP diesel engine had also been performed. The preliminary test shows that for a quasi-liquid of 9.2%vol. lignin in normal diesel fuel, the Brake Specific Fuel Consumption is 265-288g/kwh against 258-280g/kwh for the correspondent 100% diesel fuel. Details are listed in the following table. Note also that the exhaust temperature of the lignin diesel fuel is about 40oC lower than that of pure diesel fuel, showing that lignin may promote internal combustion as it contains about 30%w/w oxygen.

fig2

table

Economies

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Lignin is the major byproduct and a waste polluting the environment from paper mills. Thus the use of lignin as a fuel substitute leads to a positive revolution for benefitting paper mill industry without foreseeable harmful effects. For comparison, the price of lignin in Chinese market is about 150-200 USD per ton. Converting it into equivalent fossil fuels, it corresponds to about 300-400 USD per ton of fossil fuels, while the actual price of fossil fuel is about 600 USD per ton in current Chinese market. Thus, lignin fuel is also of very high commercial values.

The net removal of CO2

On average, it could be assumed that 15% of the world total consumption of diesel, gasoline and jet fuels can be replaced by lignin. Assuming the world total consumption of diesel, gasoline and jet fuels is 2,500 million tons, the replaced fuels should be 375 million tons. Suppose the fossil fuels contain about 85% carbon, the equivalent carbon dioxide can be replaced is 375x0.85x44/12=1168.75 (million tons). As lignin is derived from atmosphere, combustion of lignin results in zero net carbon dioxide release, thus lignin substitution of fossil fuels will result in a net removal of CO2 about 1000 million tons annually. However, with further possible modifications of this lignin fuel technology, the amount of lignin to substitute fossil fuels can be increased further, say 50%, and the removal of atmosphere carbon dioxide is expected to be much higher.