consequence of trimming and smoothing of wood. In general, processing of wood in the furniture industries will lead to waste generation of almost half (45 %) of wood. Similarly, when processing wood in a sawmill, the waste will amount to more than half (52 %) of the wood.
Industrial wastes are generated by the food industry which produces a large number of residues and by-products that can be used as biomass energy sources. These waste materials are generated from all sectors of the food industry with everything from meat production to confectionery producing waste that can be utilized as an energy source. Solid wastes include peelings and scraps from fruit and vegetables, food that does not meet quality control standards, pulp and fiber from sugar and starch extraction, filter sludge, and coffee grounds. These wastes are usually disposed of in landfill dumps.
Liquid wastes are generated by washing meat, fruit and vegetables, blanching fruit and vegetables, pre-cooking meats, poultry and fish, cleaning and processing operations, as well as wine making. These wastewaters contain sugars, starches, and other dissolved and solid organic matter. The potential exists for these industrial wastes to be anaerobically digested to produce biogas, or fermented to produce ethanol, and several commercial examples of waste-to-energy conversion already exist. The pulp and paper industry is considered to be one of the highly polluting industries and consumes a large amount of energy and water in various unit operations. The wastewater discharged by this industry is highly heterogeneous as it contains compounds from wood or other raw materials, processed chemicals, as well as compound formed during processing. Black liquor can be judiciously utilized for production of biogas using anaerobic digestion technology.
Municipal solid wastes are produced and collected each year with the vast majority being disposed of in open fields. The biomass resource in municipal solid waste comprises the putrescible materials, paper, and plastic and averages 80% of the total municipal solid waste collected. Municipal solid waste can be converted into energy by direct combustion, or by natural anaerobic digestion in the engineered landfill. At the landfill sites, the gas produced by the natural decomposition of municipal solid waste (approximately 50% methane and 50% carbon dioxide) is collected from the stored material and scrubbed and cleaned before feeding into internal combustion engines or gas turbines to generate heat and power. The organic fraction of municipal solid waste can be anaerobically stabilized in a high-rate digester to obtain biogas for electricity or steam generation.
Sewage is a source of biomass energy that is similar to the other animal wastes. Energy can be extracted from sewage using anaerobic digestion to produce biogas. The sewage sludge that remains can be incinerated or undergo pyrolysis to produce more biogas.
See also: Biogas, Biomass, Municipal Solid Waste, Waste.
Bio-oil
Bio-oil (sometimes called bio-crude) is the liquid condensate produced from biomass (forestry residues, crop residues, waste paper, and organic waste) by means of processes such as pyrolysis (thermal and catalytic). Depending on the feedstock, the bio-oil could be compatible with existing refinery technology and can be converted into fuels, such as gasoline, diesel fuel, and jet fuel.
The product can vary from a light tarry material to a free-flowing liquid that is produced by the thermal decomposition (destructive distillation) of biomass at temperatures on the order of 400°C (750°F) (Table B-25).
Table B-25 Examples of the yield of bio-oil by pyrolysis from agricultural residues at different temperatures (oC).
| Sample | 400 | 450 | 500 | 550 | 600 | 650 | 700 | 775 |
| Hazelnut shell | 38.0 | 39.5 | 40.4 | 41.9 | 42.2 | 41.0 | 39.2 | 38.5 |
| Tea waste | 34.9 | 35.8 | 36.0 | 36.2 | 38.0 | 37.0 | 35.5 | 33.4 |
| Tobacco stalk | 41.0 | 41.8 | 43.0 | 40.2 | 40.0 | 40.6 | 37.3 | 36.8 |
Also, the product is of interest as a possible complement (eventually a substitute) to crude oil to produce specification-grade fuels (Table B-26).
Table B-26 Representation of the conversion of biomass into fuels.
| Process | Product | Process | Refinery |
|---|---|---|---|
| Pyrolysis | |||
| Bio-oil | Deoxygenation | ||
| Gasoline | |||
| Diesel | |||
| Jet fuel |
Bio-oil is not a product of thermodynamic equilibrium during pyrolysis but is produced with short reactor times and rapid cooling or quenching from the pyrolysis temperatures. Bio-oils are multi-component mixtures of different size molecules derived from depolymerization and fragmentation of cellulose, hemicellulose, and lignin. Bio-oil is a liquid mixture of oxygenated compounds containing carbonyl, carboxyl, and phenolic functional groups. One of the main drawbacks of the bio-oil is that the composition of the pyrolytic oils is similar to that of the original biomass and is different from crude oil-derived fuels and chemicals (Maher and Bressler, 2007).
Hydrocarbon moieties are predominant in the product, but the presence of varying levels of oxygen (depending upon the character of the feedstock) requires testament (using for example, hydrotreating) during refining. On the other hand, the bio-oil can be used as a feedstock to the Fischer-Tropsch process for the production of lower-boiling products, as is the case when naphtha and gas oil are used as feedstocks for the Fischer-Tropsch process. In summary, the Fischer-Tropsch process produces hydrocarbon products of different molecular weight from a gas mixture of carbon monoxide and hydrogen (synthesis gas) all of which can find use in various energy scenarios.
In the hydrothermal upgrading process (HTU process), biomass is treated with water at high temperature