Biomass Energy

Biomass energy. It refers to that coming from plants , animals and microorganisms . Its final origin is in solar energy , fixed by plants through photosynthesis , and stored in the form of biochemical energy .

Summary

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• 1 Historical Review
• 2 Ways to use biomass
• 3 Use of biomass in Cuban sugar factories
• 4 Comparison between RACs and the combustion process
• 5 Employment prospects for RACs as fuels in Cuba
• 6 Environmental impact. CO2 emissions
  • 1 CO2 emissions
  • 2 CO2 emissions at harvest
  • 3 CO2 emissions during the process
  • 4 CO2 and energy balance
• 7 Characteristics of obtaining energy from sugar cane
• 8 Biomass formation in sugar cane
• 9 See also
• 10 External Link
• 11 Sources

Historical review

Plants transform solar energy into chemical potential energy and store it in carbohydrates through photosynthesis . Biomass was the first source of energy used by humans . With the discovery of fire , our ancestors took a great step forward in harnessing energy . But with this, they also started in parallel the destruction of the forest masses that covered a large part of the planet’s surface , a phenomenon that continues today with the indiscriminate burning and cutting of forests and jungles .

In recent decades, the use of biomass as an energy source has been present on the international scene, as an attractive and promising way to produce power with minimal environmental impact. Undoubtedly, great biomass potentials are concentrated in agro-industrial residues from cane sugar productions ; This has motivated the interest of prestigious scientific institutions that today invest large sums of money in the development of ambitious energy projects dedicated to gasification and combined cycles. Currently several leading companies in the field of energy They show extraordinary results in demonstration facilities of combined cycles with biomass gasification.

However, international forecasts on the subject project growth in the use of biomass direct combustion systems for countries with developing infrastructure. Hence the importance for the aforementioned industry, at this stage of transition, to be able to have technologies that allow achieving high yields in the direct combustion of agro-industrial waste destined for the production of power in the sugar factories.

Sugarcane biomass is the most widespread form in Cuba to get electricity from the sun . Globally, biomass is responsible for 6% of electricity generation. By 2020 , biomass is expected to cover up to 20% of global electricity demand .

The Biofuels are combustible liquids from different transformations of biomass utilization and represent a great future projection. They can be used to power vehicles to replace those derived from fossil fuels currently used. The ethanol obtained from fermentation alcohol of the monosaccharides contained in the sugar juices of sugar cane or beet , it is widely used in Brazil for automotive transportation.

Ways of using biomass

Biomass can be used in various ways, through the so-called conversion processes, and in general it is burned directly in traditional power plants with steam cycles, as has been the case in sugar mills for a long time ; or in more advanced and efficient systems that use gasification in combined cycles, in which the exhaust gases from gas turbines are used , which feeds an ordinary type generator. The latter is the most efficient way to use biomass and the one with the most promising future.

Another way to obtain fuel from biomass is through fermentation, such as biogas and obtaining fuels such as ethanol by fermentation and methanol by hydrolysis, as well as Biodiesel from the extraction of vegetable oils . In countries like Brazil there is vast experience in the production of ethanol for use in internal combustion engines.

Possible sources of biomass include agricultural residues; energy crops, such as energy cane and eucalyptus forests; wood industry wastes, such as sawdust ; the bagasse ; urban waste, such as packaging boxes , cardboard , broken furniture and paper ; construction wood waste; and urban wastewater .

Common disadvantages of biomass are its lack of uniformity and low density, hence it must be produced near its place of use, since the use of long-distance transport would minimize its advantages. Both difficulties can be eliminated by pelletizing or the construction of briquettes, but this would imply an increase in the operating cost. Another disadvantage is its low caloric value compared to other fuels. Two concrete examples are verified in the sugar industry, where seventy million tons of cane are converted into seven million tons of sugar and seventeen and a half million tons of bagasse; and in the wood industry it is possible that up to 75% of the original tree ends up being turned into waste. Fast-growing trees such as willows and eucalyptus are grown in energy forests.

With the use of biomass, as well as any type of renewable energy, we must make a total analysis of the “life cycle”, that is, the entire chain, because if in the process there are contaminating intermediate steps in the manufacture and transportation of equipment and necessary components, or non-renewable energy is used in some stages, this must be evaluated to really know how clean this form of energy is. A good example of this is the hydroelectric energy that requires the construction of large reservoirs that completely transform the ecosystem, with the disorders that this creates.

The biomass residues of the sugar agribusiness are bagasse with its marrow and sugarcane agricultural residues (RAC).

Bagasse is the fibrous lignocellulosic residue obtained by grinding sugar cane, and it is made up of a heterogeneous mass of particles with an average size of 20 mm. The parenchymal tissue that surrounds the vascular bundles where the juice is found is called marrow; In the industry, the mixture of particles of this tissue with short fibers, earth and other foreign matter is called marrow . When the bagasse fiber is used for the production of pulps and artificial wood, it is necessary to enrich the fibrous fraction by extracting as much marrow as possible.

The sugarcane agriculture residues (RAC) are mainly made up of straw and bud, and can be used in the production of direct animal feed, or for energy purposes. According to some specialists, the available amounts of RAC worldwide exceed fifty million tons per year, which represents an oil equivalent that exceeds seventeen million tons.

The difficulties in achieving the exploitation of this potential reserve are fundamentally related to harvesting, mechanical and chemical treatments, transportation, handling and conservation.

It can be exploited by combustion or by thermal conversion:

• Direct combustion energy: itis a very old process and refers to the combustion of firewood , forest residues and organic residues (dung, cellulose and others) to obtain heat , especially at the household level. In rural areas, firewood plays a very important role as energy for the home, that is, for cooking food, because the inhabitants have little access to gas and kerosene .
• Energy by thermal conversion:Refers essentially to the pyrolysis or distillation of wood in secondary products: charcoal , tar , metallic alcohol or methanol and poor gas, among others.
• Energy by alcoholic fermentation:Consists of producing alcohol from organic materials and residues through alcoholic fermentation. There are techniques to produce alcohol from sugar cane, cassava , wood and cellulose remains. Alcohol is considered one of the possibilities of substitution of fossil fuels . In the country it is produced with molasses from sugar cane .
• Energy by anaerobic fermentation:Consists of the production of gas in closed chambers through the fermentation of organic waste (excrement, organic waste, etc.) without the participation of oxygen and with anaerobic bacteria. The closed facilities are called biogas digesters or biodigesters or biogas plants. The gas obtained is an economical source for lighting homes , cooking gas , heating , etc.
• Animal energy:It is the use of pack animals to plow the fields, as well as to move mills and mills. Its use is quite widespread in rural areas ( cattle , horses , donkeys , mules )

Use of biomass in Cuban sugar factories

The feasibility of using sugarcane agricultural residues (RAC), a renewable energy source that until now has been little used, instead of the usually used fuel oil, in the production of energy for the operation of sugar power plants, in the process of obtaining of sugar , as well as in refining and production of other derivatives. These resources, specifically RAC, allow the production of electrical energy, which in addition to supplying the industry also contributes significantly to the national energy grid . In addition, an analysis is made of the cost of transporting these resources. To all this is added the positive effect on the environment that all these fuels exert, which will make Cuba one of the most important tourist destinations in the Caribbean and the world.

The environmental impact of fossil fuels on sugar production, as well as the main characteristics of sugar biomass and sugar cane agricultural residues (RAC), with a view to its potential use as a source of renewable energy that does not contaminate the environment, which allows reserve of scarce fossil and natural fuels, in addition to maintaining a stable sugar production, which can continue to be carried out, since it brings profits to the Cuban economy if all the collateral products of this process are used to the maximum, in addition to maintaining the Cuban sugar culture, historically characterized and is a symbol of Cuba.

Starting from the hypothesis that it is possible to use the RACs as a renewable energy source, non-polluting to the environment, with a level of efficiency capable of allowing the energy supply of the sugar plants during most of the year in Cuba, because sugarcane It has possibilities to replace the fossil fuels that cause acid rains , the greenhouse effect , among other harmful consequences for humanity., and bearing in mind that Cuba has the potential to produce a large part of its energy from sugarcane, provided that systematic knowledge and control of all aspects that affect the efficient use of these resources is achieved, making the Cuban people and the tourism that visits the Island breathe a cleaner atmosphere from a renewable raw material.

Taking into account the previously defined circumstantial framework, some of the benefits of RACs in replacement of fuel oil will be shown .

The sugar cane harvesting system in Cuba imposes very important characteristics on the RACs. The cane is cut more than 70% mechanically and the machines used have a cane cleaning efficiency of just over 55%. This means that more than half of the RACs remain in the field and that less than 50% goes to the pneumatic cleaning stations (EL).

In these facilities, the RACs are separated from the cane and accumulate in large areas, where they are incinerated to the atmosphere without any use. On the other hand, the part of the cane that is cut manually, almost entirely, is sent to the collection centers (CA), which are facilities where the cane is chopped into small pieces, is pneumatically cleaned and transferred to rail cars . In these installations, the RAC separated from the cane are also accumulated in large areas and the majority of them are incinerated without practical use.

The CA and EL process around 680 t / day of cane and produce 35-40 t / day of RAC. Throughout the country there are some 915 stations of this type. Based on these technical characteristics, it is easy to reason, then, that between 4,000 and 6,000 t of RAC are concentrated and incinerated in each harvest in the small square of each CA and EL.

Comparison between RACs and the combustion process

Below are some comparative criteria for the two fibrous residues of the sugar agribusiness, bagasse and RACs:

• Bagasse has a higher heat of combustion (for humidity = 0%), given above all because the RAC has a higher ash content; however, since bagasse burns with about 50% humidity and RACs have a natural drying process (up to approximately 20%), RACs deliver more energy per unit mass burned.
• The RACs introduce more ash into the furnace, this increases the waste to be extracted and shortens the cleaning periods, recharges the volatile solids separation systems and increases the environmental contamination by particulate matter.
• In general, the properties of RACs are very similar to those of bagasse and many other biomasses. Another very important characteristic of RACs is their density, since it decides extraordinarily on their transportation cost. In original conditions on the CA and EL platforms, the RACs have a density of 30 – 40 Kg / m3, with approximately 40% humidity.

Employment prospects for RACs as fuels in Cuba

The prospects for the sustained increase of RACs as fuel in Cuba are broad and based on several factors, including:

• The need to reduce fuel oil consumption in sugar refineries and alcohol distilleries attached to sugar mills, using RACs as complementary fuel. The economic feasibility has been amply demonstrated and the different technical variants to be used have been mastered.
• The interest of many plants to generate electricity after the end of the harvest, for which they need not only the bagasse they can save as fuel, but all the RACs they can store.
• The decision in the country to mount adjoining thermoelectric plants to sugar plants that would need a complementary fuel, which alternatively could be the RACs.
• The diversification of sugar production, proposed as a master strategy of the sugar industry for the next decades, will demand additional fuel for the operation of different productions and the RACs can indisputably be a good alternative. Within this diversification, conceiving the sugar industry as a sucro-energy industry is very attractive.

Another element, which if not immediately in the future will promote the use of RACs as fuel, is their condition as annual renewable biomass, which means that their combustion does not increase the greenhouse effect or acid rains and in fact contributes to the preservation of the environment.

In Cuba and the small tropical islands this is forced by:

• The end of fossil fuels.
• Price increases as part of that process.
• Incentives or fines for the Kyoto protocol or similar.
• The need for a clean atmosphere in countries that depend on tourism .

Renewable energy is the only way to guarantee a promising future, since it creates total independence from fossil fuels by guaranteeing the production of electricity (cogeneration) and thereby replacing oil, or otherwise, obtaining alcohol to mix it. with diesel and gasoline to minimize the import of these inputs; keep in mind that a ton of cane is equivalent to 1.2 barrels of oil.

Environmental impact. CO2 emissions

An aspect inextricably associated with energy is the environmental pollution it causes, which constitutes one of the causes of greenhouse gas emissions ( CO2 , CH4 , N2O , NOx , CO ), which come largely from the wide variety of activities associated with obtaining, transforming and using energy.

On the other hand, the oil crisis of 1973 contributed to fostering concern on the international level for the use of energy, which leads, among others, to the following proposals:

• Need to increase the productivity of resources, developing goods in a sustainable way or eco-efficient products.
• Using industrial innovation as part of sustainable development.
• Reduction in the intensity of use of resources, taking into account the large reserve potential that is still available.
• Search for new sources of energy to expand their number and the use of biomass fuels and solar cells.
• More efficient use of energy carriers for transportation.

Within this panorama of indispensable increase in the efficiency in the use of energy carriers and in the search for alternative energy sources, one of the branches of agriculture that is attractive for this purpose is the agro-industry of sugar cane, taking into account that This crop offers various alternatives for obtaining renewable energy and the high efficiency of this grass in the production of biomass from solar energy.

CO2 emissions

The operations of the selected sugar production process that cause CO2 emissions into the environment can be grouped into the following impact categories: those that represent a net contribution to the level of CO2 in the atmosphere from the use of fossil fuels, such as the harvesting, transportation, fertilization and use of pesticides and herbicides, and those associated with the sugar manufacturing process, where the energy source is bagasse and CO2 emissions are offset by its fixation by the crop.

CO2 emissions at harvest

One way to quantify the contribution to the level of CO2 from this cause is to determine the amount of equivalent oil required by these activities, which is shown in Table 2, and calculate how much combustion of oil represents, in terms of CO2 emissions, the approximate composition is: C: 85.7%; H: 10.5%; O: 0.92% and S: 2.8%. If the previous percentage indices are divided by the respective atomic weight (C: 12; H: 1; O: 16; S: ​​32), the empirical composition of the latter is obtained, from which the following reaction equation can be established , where it is appreciated that for each kilogram of oil 7.14 kg of CO2 are emitted. This can be expressed according to equation (1)

C 7.14H10.5O0.06S0.09 + 9.9O2 → 7.14CO2 + 5.25H2O + 0.09SO3 (1)

CO2 emissions during the process

The process that emits CO2 in the selected sugar production scheme is the combustion of bagasse in the boiler. Using a procedure analogous to the calculation of oil combustion, the following equation is obtained for bagasse:

C4.025H602.7 + 4,175O2 → 4,025CO2 + 3H2O (2)

From the above it is obtained that the amount of CO2 emitted during the burning of the bagasse is 0.885 kg of CO2 / kg of bagasse with 50% humidity.

CO2 and energy balance

Once the amounts of CO2 emitted and fixed by each of the activities of the selected scheme have been determined, it is appropriate to evaluate the environmental impact of this alternative for obtaining renewable energy . For this, a combined production and electrical energy scheme was selected whose productive results, energy balance and CO2 are:

• Final products: sugar 48 kg / tci and electricity 9.8 kWh / tci.
• A certain amount of liquid fuel (alcohol) can be obtained renewable.
• The residuals are used as organic fertilizer, which eliminates waste from the process.
• There is a surplus of 240 kg of RAC / tci, which can be used for the generation of electrical energy or for animal feed. This last variant has the additional advantage that animal nutrition does not compete with human nutrition.
• The CO2 balance is markedly advantageous: net fixation of 183.5 Nm3.
• The energy balance of this scheme is favorable.
• It is possible to obtain for each ton of integral cane a small amount of cogenerated electrical energy.

Characteristics of obtaining energy from sugar cane

To assess the environmental impact of obtaining renewable energy from sugar cane , the following set of conditions can be used:

• Σ residuals = 0
• Σ energy ≈ 0
• Σ CO2 <0
• Σ fossil fuels ≈ 0

Biomass formation in sugar cane

The level of total CO2 fixation during the formation of the cane biomass is given by two contributions: aerial parts (stems, buds, leaves) and roots, as their magnitude depends on the composition and the contribution to the total biomass of the plant of each of the parts. However, considering the complexity of the photosynthesis process, a first approximation model can be proposed to estimate CO2 fixation, the hypotheses of which are:

• The vegetative composition of the cane in terms of dry matter is: 70% ground cane, 19% bud and straw and 11% roots.
• The composition of the different parts of the plant is considered homogeneous.

According to the reported research work, the RAC collected in Cuba present around four million tons available each year as fuel of adequate properties that could be processed, profitably, in various types of facilities that exist in the country.

The model to estimate the amount of CO2 fixed by sugarcane during the biomass process allows us to obtain this index in the selected production scheme, which illustrates how the use of sugarcane to obtain renewable energy is very attractive, taking into account It is possible to achieve this objective with a favorable balance in terms of reducing CO2 emissions to the environment.

It can be pointed out that the use of biomass as a renewable energy source is a viable alternative in third world countries .