The technologies used to obtain energy (biopower) from different types of biomass are different and the resulting energy products are different too. Biopower technologies convert renewable fuels of biomass into heat and electricity by using equipment, which is similar to the one used for fossil fuels. An advantageous characteristic of biomass is its availability, as it is able to keep its energy intact until it is used.
Thermo-chemical conversion processes of biomass are based on the action of heat that activates the chemical reactions needed to transform the matter into energy and can be used for those cellulose and wood residues whose C/N ratio is over 30 and the humidity content is lower than 30%.
The biomass that is more suitable to be subject to thermo-chemical conversion are wood and all its derivates (sawdust, wood shavings, etc), the most common wood-cellulose by-products (cereal straw, grapevine pruning residues, fruit trees pruning residues, etc) and some processing waste (husks, chaff, stones, etc).
Bio-chemical processes: bio-chemical conversion processes allow to obtain energy throughout a chemical reaction that takes place thanks to the contribution of enzymes, mushrooms and micro-organisms, that form in the biomass under particular conditions, and are used for that biomass whose carbon/nitrogen ratio is lower than 30 and humidity at collection is higher than 30%. The following products are appropriate for chemical conversion: aquatic breeding, some cultivation by-products (leaves, sugar-beet stems, vegetables, potatoes, etc.), liquid residues of zoo-technical industry and some processing waste (residues of alcohol processing made of grains, vegetation water, etc.), and some types of urban and industrial waste water.
The technologies that are currently used in the biopower sector are: cofiring, pyrolisis, gasification, combustion, “small modular” systems, aerobic digestion, anaerobic digestion, and carbonization.
At present, in terms of biomass, “gasification”, which is a thermo-chemical process, is considered as one of the best and most promising technologies to produce electric energy: both as far as efficiency and environmental impact are concerned.
In order to optimise coal plants, it is possible to use biomass as complementary to coal. This is surely one of the cheapest solutions among the energy options offered by renewable sources.
Pyrolysis is the thermo-chemical decomposition of organic materials that is obtained through heat application, at a temperature between 400 and 800°C, in complete absence of any oxidizing agents, or with a very reduced quantity of oxygen.
The combustion of products and agricultural residues has good results if substances rich in structured glucides (cellulose and lignin) and with a water content of less than 35% are used as fuels.
Carbonization is a thermo-chemical process that allows to transform structured molecules of wood and cellulose products into coal (wood coal or vegetal coal).
It is a biochemical conversion process that occurs in the absence of oxygen and consists of the demolition, by micro-organisms, of complex organic substances (lipids, proteins, glucides) contained in vegetal and animal by-products.
It is the metabolization of organic substances through micro-organisms, whose development depends on the presence of oxygen.
Use of biomasses as fuel is advantageous for a number of reasons. First of all, it does not increase the global amount of carbon dioxide in the atmosphere. In fact, the biomasses combustion process frees the same amount of CO2 as the amount absorbed by the plants during their entire life.
Furthermore, use of biomasses such as forest residues, agricultural residues and wood-work residues, contributes to keeping the woods and land clean and creates new work opportunities. It therefore has a favourable effect on employment which, particularly in the rural areas, can lead to a minor dependence on energy from countries producing fossil fuels. Other advantages are its abundance, and the easy way to extract energy, the low sulphur content and as a consequence they do not contribute to the formation of acid rain, and the fact that at the end of the cycle they produce a potential fertilizer.
The different technologies to obtain energy from biomasses are very interesting also due to the fact that to obtain energy from this source means exploiting raw materials that currently are a cause of pollution (waste dumps, septic tanks, forests and land that are not cultivated and/or abandoned, etc.). Furthermore, it encourages an effort to plant a rotation of new forests in the areas that have been left bare, with a consequent advantage for the hydrogeological resistance to landslides. And, by controlling the forests and carrying out any activities related to the forests, makes it less easy for the pyromaniacs to carry out their activities.
However, it must be pointed out that also exploitation of biomasses has an impact on the environment. In some cases, use of wood as fuel, if it is not carried out according to the principle of sustainability (i.e. taking care to replace the heritage of trees that have been cut) can lead to a progressive deforestation.
At present in some areas that do not have many alternative energy resources, this impact is reported. At present, most of the energy coming from biomasses derives from firewood. There are some countries in the Third World, especially in Africa where over 70% of the energy requirement is obtained from fire-wood combustion, a resource that , due to excessive exploitation in some areas can no longer be considered renewable.
Furthermore, intensive cultivation of some plants, in view of a future production of energy (the so-called energy crops) require vast areas of the territory in order to obtain significant quantities of fuel (land that is subtracted from agricultural activities for the production of food), and can involve use of fertilizers and other substances that pollute the land and the water.
A district heating system consists of a transport network and a heat production plant, which serves more than one building at the same time. The district heating plant can use co-generation technologies and/or renewable sources.
An excellent solution
The excellent solution to exploit biomass, as well as the use of individual heating in pellet boilers (wooden balls) or nipper boilers, is the district heating with small-sized biomasses (10 megawatts), that supplies heat to households and/or business activities, and is located close to the biomass production site (wood, farm land, sawmill, etc).