While the convenience and energy density of liquid fuels is an admirable target, if maximizing energy recovery from biomass and wastes is targeted, biogas production is the best choice. Further, even where ethanol and biodiesel production is used, biogas production from their waste products can improve the energy balance of the overall conversion process.
Soil and Water Sciences Department P. University of Florida. Template Image What is Biogas? Is biogas the same as biofuel? Similarly to biomass demand, the biogas demand has a number of end user sectors, which have different characteristics in terms of application, economic value added, customers, social benefits, and environmental impact [ 14 ]. If biogas is conditioned or cleaned, it will be an outstanding solution for a variety of applications commonly known for natural gas with the addition of the versatility of its end uses.
Some examples include: motor fuel, electricity, heat, combined electricity and heat, and recently replace carbon compound into plastic products [ 11 ] and also the generation of by-products that can be used as an organic fertilizer. There is an important environmental advantage of biomass utilization in terms of reduction of natural resource depletion [ 15 ], carbon neutral resource in its life cycle Asian Biomass Handbook , and sustainable energy systems [ 16 ].
Also the fermentation process is an alternative for wet-bases raw residues treatment, and particularly anaerobic digestion because of the cost-effective [ 18 , 19 ]. Since the last century , some Asian countries, like China and India, started their first trials in using biogas [ 21 ], through a stabilization process that allows the use in household and farm-scale applications.
Similarly, England reported using it in the s for lighting streets [ 11 ]. In both cases, the main biomass source to produce biogas was taken from sewage in order provide a fuel for cooking and lighting. In a brief context, the use of biomass to provide energy has been fundamental to the development of societies. Nowadays, the demand on energy and the impact on climate change have led to calls for an increase in the use of biogas in different ways.
In this section, the main process or conversion technologies employed for the biomass are presented with specific regard to biogas production. The biomass conversion technologies are closely related to the type of biomass, quantity, the availability, the cost-effective, and the end user requirement of the biofuel. Conversion technologies of biomass into energy. It is important to note that a pretreatment of the biomass is necessary before applying a conversion technology.
In some cases, biomass has to be harvested, collected, transported, or stored [ 22 ]. Further, resource availability varies from region to region, according to weather conditions, soil type, geography, population density, and productive activities, which makes the choice of technology for processing more complex. One of the oldest uses in which biomass has been utilized for energy in the world is through the burning wood combustion.
This action represents a traditional use of biomass, particularly in rural zones. It is considered an essential resource to the economic development of societies [ 23 ].
Recently, technologies suggest the use of energy efficiency stoves, which not only has a better thermal efficiency but also avoids indoor air pollutions. Other specialized equipment involves furnaces, boilers, steam turbines, and turbogenerator. The combustion of biomass allows the recovery of the chemical energy stored. In general, combustion processes involve direct oxidation of matter in air, that is, ignition or burning of organic matter in an air atmosphere sufficient to react with oxygen fuel.
Thermochemical process, as the direct combustion, has a core axis, the temperature. One of the main differences is an induced atmosphere in which conversion of biomass took place. This oxidation process can occur in the presence or absence of a gasifying medium. The conversion of biomass depends on temperature and pressure variables. For example, if the substrate to transform is in the presence of a gas such as oxygen, water vapor, or hydrogen, producing fuel is performed through gasification.
If, however, material degradation occurs in the absence of oxygen, that is, nitrogen, under controlled pressure and temperature, then the process is called pyrolysis. There are some good experiences in the pyrolysis of certain materials, in which a charcoal, bio-oil, and a fuel gas can be recovered [ 25 ].
Biochemical treatment unlike thermochemical process achieves power generation through biological transformation of organic compounds, employing anaerobic digestion, or fermentation of biomass.
Fermentation is usually used to produce biofuels, as ethanol, from sugar crops, and starch crops [ 22 ]. Nevertheless, there is another route, in which biomass conversion is done, the anaerobic digestion. Among the general background information about conversion technologies, anaerobic digestion is the main focus in this section due to the direct biogas production.
The anaerobic process is analog to ruminant digestion process. The biomass is degraded by a consortium of bacteria within an anaerobic environment, producing a principal product, gas. This gas, called biogas, represents a proven technology and its use is widely spreading through Europe. The anaerobic digestion process generally occurs in reactors or tanks in a single, multistage process or dry digestion. Anaerobic digester can be categorized, designed, and operated by different configurations: batch or continuous, temperature mesophilic or thermophilic , solid content high or low solid content , and complexity single stage or multistage [ 26 ].
Another specific configuration considering the organic rate load, digester, is divided into passive systems covered lagoons , low rate systems complete mix reactor, plug flow, and mixed plug flow , and high rate systems contact stabilization, fixed film, suspended media, and sequencing batch [ 27 ].
All these types of reactors perform the anaerobic digestion, but each one operates for salient features with a variety of applications of the end products.
An experience in the livestock sector in Mexico using covered lagoon anaerobic digestion reactor shows benefits in the use of biogas not only on environmental aspects as improving the quality of wastewater but also economically due to the avoid of penalties for the water discharges and the social acceptance of the livestock activity in the region Table 3.
Source: using data from Ref. In this example, the different benefits of biogas production in livestock sector highlighted the use of biogas in energy generation. Against other energy sources, in this case, the biogas produced is used in the farm for their own consumption by a gas combustion engine. The heat generated by the motors can be used for heating the reactor or drying waste. Biogas has the quality that does not have to be consumed at the moment of production.
The production of this biofuel also impacts in macro- and microeconomic aspects, due to the generation of new sources of employs and access to energy in a remote place. Moreover, the livestock producer is selling an organic fertilizer obtained by high-quality digestate obtained in the biogas production. Furthermore, odor reduction and the removal of pathogenic organism in livestock residues are achieved. The methane emission of the manures is captured, reducing the release of methane to the atmosphere.
Methane CH 4 is considered one of the largest contributors to the GHG emissions by livestock sector, with a global warming potential 25 times more than carbon dioxide CO 2 [ 29 , 30 ]. In general, the biomass conversion technologies mentioned above can be integrated into the concept of biorefinery. Analog to oil process, the different biomass feedstocks offer a wide range of products that can be used as fuel, including gas, oil, or chemical, offering greater possibility of using cogeneration systems and supply facilities in the transport sector.
When the major end product in a biogas plant is methane, similar to natural gas, this upgraded gas is called biomethane. The methane content determines the energetic value in the biogas [ 11 ]. In this respect, one of the main reasons for upgrading biogas to a degree equivalent to natural gas is to inject to the gas distribution network and thus diversify some natural gas sources. Biomethanization process opens new paths to achieve this goal: first, because the gas storage in an extended way allows the injection into a distribution system and second due to the variety use of fuel in transport stations, mainly.
As we see in the sections above, the main biogas uses in development countries are lighting, cooking, and further in gas turbines. In industrial countries biogas is produced in large-scale digester biogas plants with an interest in the concentration of methane from biogas to fulfill natural gas standards.
Depending on the end use, different biogas treatments cleaning or upgrading are necessary. For example, vehicle gas fuel requires a biogas similar to natural gas quality so a biogas upgrading process is needed. In other words, biomethanization allows biogas to be contained, controlled, and distributable. There are some undesirable components in biogas that promote corrosion in many materials and engines: H 2 S, oxygen, nitrogen, water, siloxanes, and particle traces see Table 1.
These impurities can induce or promote corrosion in many parts of the biogas system or equipment in which biogas is used. Overall, these components must be removed in order to allow the concentration of methane in biogas. Water content in biogas can cause corrosion in pipelines due to the formation of carbonic acid in a reaction derived from water and carbon dioxide [ 31 ].
Fortunately, it can be removed by cooling, compression, absorption, or adsorption activated carbon, sieves, or SiO 2. Hydrogen sulfide H 2 S , another unwanted component in biogas, is of corrosive nature, leading the damage of motor engine, pipes, etc.
It is a highly toxic gas that attempts to destroy the human health. The removal of hydrogen sulfide can be done by precipitation, adsorption on active carbon for H 2 S removal US B2 patent [ 32 ].
Siloxanes also constitute an impurity in biogas. Put simply, a biofuel is a fuel that has been derived from living matter — it could come from wood, manure or even algae. When the tree is burnt, this Co2 is release back into the environment in exchange for oxygen to fuel the fire. Due to this process, there has been no net-gain in atmospheric Co2. For as long as humans have been burning wood to heat their food and homes, they have been using biomass fuel. For instance, the biomass fuels we produce at Eco come from wood cuttings created by local foresters, tree surgeons and landscapers.
Biomass can come as a waste product, like ours, or it can be grown with the specific purpose of becoming biomass fuel. Crops such as sugarcane and corn starch can be grown with the intention of the fermenting its sugars to produce bioethanol, an alcohol fuel which can be used directly or as an additive to fossil fuels.
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