International Journal Advances in Social Science and Humanities
Available Online at: www.ijassh.com
RESEARCH ARTICLE
Bagasse, Straws, Tips and Vinasse: From Sugarcane Waste to a Clean and
Renewable Bioenergy Source
Paulo Sergio Vasconcelos
1*and Lucio Guido Tapia Carpio
21School of Business Administration, Accounting and Economics, Federal University of Grande Dourados,
Brazil, Cidade Universitaria - Rodovia Dourados-Ithaum, km 12. CEP 79804-970 - PO Box 322 – Dourados, MS – Brazil.
2 Energy Planning Program,Federal University of Rio de Janeiro, BrazilCentro de Tecnologia – Bloco C –
Sala 211 – Cidade Universitaria,Ilha do Fundao – CEP 21941-942 – Rio de Janeiro – Brazil.
*Corresponding Author: Paulo Sergio Vasconcelos
Abstract
Bagasse, straw, tips and vinasse generated as waste in sugar and ethanol production from sugarcane became important inputs for electric energy cogeneration, that is, bioenergy. In addition to solving an environmental problem and assisting in electric energy generation during drought periods, cogeneration is now a major profit source for sugarcane industry companies. From 2005 to 2014, cogenerated electric energy dispatch increased from 1.1 TWh to 19.4 TWh, and biomass became the third electric energy generation source in Brazil, after hydro and fossil sources. Technology applied and research conducted to extend the benefits of sugarcane species and to improve the manufacturing and treatment processes. New sugarcane species proved to recover fields degraded by livestock. Sugarcane bagasse, straw, tips, vinasse and ethanol replace petroleum by-products in electric energy generation and in the automotive area, with positive benefits and pollution reduction. An overview of the current situation of the electric energy cogeneration process by the Brazilian sugarcane industry and its positive implications on the economic and environmental results of companies in the sector discussed in this paper.
Keywords: Bioenergy, Cogeneration,Biomass, Bagasse, Sucarcane.
Introduction
The use of bagasse, straw, tips and vinasse, sugarcane wastes from sugar and ethanol productive cycles, has environmental advantages when used as input in electric energy generation if compared to the use of non-renewable sources, such as coal, oil and natural gas. Currently, the main input for boilers of sugar-ethanol industry units is sugarcane bagasse, which once regarded as waste or leftovers in the sugarcane milling process (juice extraction from the solid part) for sugar and ethanol manufacturing.
burn the straw portion accompanying the sugarcane after cutting. In this case, the sugarcane received by the plant goes through a dry cleaning process that replaces the traditional cleaning with water. Straw separated in this operation sent to boilers for burning along with the bagasse.
Rich in mineral nutrients, vinasse, which is a byproduct or waste liquid of ethanol production, has high organic matter content and is traditionally used by the plant itself in the fertirrigation of fields where sugarcane is grown. Vinasse is characterized as a distillery effluent with high fertilizer value [4,5]. However, the harmful effect caused by vinasse in soil and groundwater has been studied in recent years [5,6,7].
During the distillation process, for every liter of ethanol produced in Brazilian sugar-ethanol plants, 10 to 15 liters of vinasse are generally obtained [5, 8, 9, 10, 11]. With the development of high-performance reactors, the prospects for vinasse treatment improved through anaerobic digestion. The resulting biogas, with high methane content produces electric energy [5] in gas turbines or to burn directly in boilers. After biogas separation, vinasse causes less damage to the soil, if used in fertirrigation.
The aim of this paper is to study electric energy generation from inputs previously regarded as waste from ethanol and sugar production in Brazilian sugar-ethanol plants.
Review of Literature
The worldwide electric energy generation capacity by biomass sources reached 80,227 MW in 2014. Brazil was the country with the largest installed capacity, 15.3% of the global total, followed by USA (13.6%), China (11.8%), India (6.2%) and Japan (5%), as shown by IRENA [12]. The biomass source represents 9.73% of the power granted by the National Electric Energy Agency (ANEEL), which places it as the third most important electric energy generation source in Brazil [13].
Table 1 shows the sources of electric energy generation in Brazil.
Table 1:Sources of electricity generation in Brazil (2015). Source: ÚNICA, 2015.
With significant growth in the electric energy supply to the National Interconnected System (SIN), the sugar-ethanol industry generates 7.6% of the bioelectricity power granted in Brazil [13]. Electric energy delivery growth to the SIN in 2014 was of 21% compared to 2013. It is interesting to note that during the sugarcane harvest period, in addition to the electricity used for own consumption, additional electric energy is generated, which is supplied to the SIN. Some plants continue delivering electric energy to the SIN in the off-vintage period.
In this period, as plant production lines stopped (usually in periodic maintenance) all electric energy generated dispatched. In 2014, of the total electric energy generated, the sugarcane industry delivered 60% to the SIN and consumed 40% [13].
Figure 1 shows the evolution of domestic consumption and supply to the SIN of electric energy generated by the sugar-ethanol industry from 2005 to 2014. According to ÚNICA [13], the delivery of 19.4 TWh in 2014 saved 13% of water of reservoirs from the Southeast/Midwest Brazil electric energy submarket.
Source Autorized Power (MW) % Autorized Power
Hydro 92,887.44 65.21
Fossil 27,129.79 19.05
Biomass 13,852.33 9.73
Wind 6,559.11 4.61
Nuclear 1,990.00 1.40
Solar 15.24 0.01
Figure 1: Production of sugarcane bioelectricity in Brazil (TWh) per year. Source: ÚNICA, 2015.
The Brazilian sugar-ethanol industry sells US$ 43.6 billion in by-end products, which represents about 2% of Brazil's GDP. This value is equivalent to the economic output of countries such as Paraguay, North Korea, Afghanistan, Jamaica and Estonia. Plants and agents involved in the economic activity of sugarcane, sugar, ethanol and electric energy production generate gross revenues of more than US$ 100 billion per vintage [14].
Biomass: Bagasse, Straw and Tips
Sugarcane production in Brazil increased from 80 million tons (Mt) in 1970 to 655 Mt in the 2015/2016 vintage [15].
With production increase and widespread crop mechanization, input availability for burning in boilers (bagasse, straw and tips) increased, increasing electric energy and heat generation [2]. Depending on the technology used in the manufacturing of the boiler installed in the plant, straw and tips burned along with the bagasse, in varying proportions. In addition, pellets, briquettes, wood chips and sawdust burned along with the bagasse. In order to increase the straw and tips amount, different sugarcane qualities tested.
Energy Cane
In plants that only produce ethanol, the so-called “energy cane”, a quality genetically modified through crosses between more rustic sugarcane species, with lower sucrose and higher fiber amounts (bagasse, straw and tips), is already being used. “Energy cane” varieties have thinner stems in larger quantity that spread to clumps, besides containing 25% to 30% fiber, which is much more than the amount found in sugarcane for conventional sugar production, which contains 12% fibers. GLOBO RURAL [16] showed this research line in a report about the Bioflex plant, located in São Miguel dos Campos, state of Alagoas.
The Raizen plant in Piracicaba (SP) also uses the straw in its production process, both for cellulosic ethanol and electric energy cogeneration. Energy cane species are more rustic, such as the species developed for Brazil, called "Vertix". “Vertix” sprouts faster and has longer life, as it can support from 7 to 15 crops without replanting. Conventional sugarcane resists five crops, on average. Due to its resistance, energy cane planted even in low fertility soils [16].
Biomass and Electric Energy Generation Processes
Technology alternatives used to generate electric energy from biomass are varied. However, there is a process in all alternatives that converts biomass into an intermediate input, which, when used in a power machine, produces the mechanical energy that activates the electricity generator [17].
Figure 2: Electricity generation from biomass alternatives.
From alternatives shown in Figure 2, direct combustion in the biomass conversion process selected, producing inputs such as steam and fuel gas used in steam and gas turbines as drive force. These two turbine types have significant differences in electric energy generation, investment and operating costs, sophistication, technology domain and commercial availability.
CORREA NETO [17] details the main characteristics of technologies used in Brazil, as well as the technological innovations proposed to expand bagasse energy resources use.
BENEDUZZI et al. [18] conducted thermodynamic analyzes of two electric energy cogeneration thermal plants, considering data from 2003/2004 and 2007/2008 vintages. Their objectives were to verify advantages of modernization and use of more efficient equipment. They concluded that, with use of more efficient technology, it was possible to generate an additional 99 kWh of electric energy per ton of sugarcane processed.
SOUZA DIAS et al. [19] explained that the main cogeneration system currently used in Brazil based on the Rankine cycle. Bagasse burning in the boiler produces steam expanded in turbines with electric energy generators. Exhaust steam turbines used as thermal energy sources to the various operations of sugar and ethanol production. Most installations only use steam back pressure turbines, which limit the bagasse amount that can be burnt to supply the process steam demand [20]. Until the 1990s, cogeneration systems employed in plants designed to meet the thermal energy needs of sugar and ethanol production, burning all the available bagasse and producing little or no electric energy to use in the plant. The regulation of the electric energy sector in Brazil, which started in the 1990s, created conditions for sugar-ethanol industries and other producers to sell excess electric energy, starting the modernization of existing facilities for cogeneration [21]. Modern plants have replaced low pressure/low efficiency boilers by medium- and high- pressure boilers (42-90 bar), according to SEABRA and MACEDO [22]. Systems with condensing-extraction steam turbines allow for electric energy production maximization [23].
Vinasse and the Electricity Generation Process
Vinasse is a by-product or liquid residue obtained in the distillation process for ethanol production from different biomasses, such as sugarcane in South America, sugar beet, grape and fruit in Europe and corn and tequila in North America [5,7,24,25].
feed stock in feed production; use in yeast production; use in construction materials (component for brick manufacturing); and use in anaerobic digestion, producing biogas [4].
With the development of high-performance and low hydraulic retention time reactors, such as the Up flow Anaerobic Sludge Blanket (UASB) reactor, vinasse digestion for biogas generation to be used in electric energy cogeneration became viable [5,28,27]. CHRISTOFOLETTI et al. [5] and MORAES et al. [11] developed a detailed description of the vinasse anaerobic digestion process fundamentals and its integration into the sugar-ethanol plant. A basic station could be as follows: a bio digester, where vinasse deposited and biogas generated; a connection to a compressor; a combustion chamber; a gas turbine; and an electric energy generator, which delivers the energy for internal use or network supply, in cogeneration (Figure 3).
Figure 3: Electricity generation process using vinasse as input.
After biogas generation, vinasse is less aggressive to the environment in this stage, and still be used in sugarcane field fertirrigation. According to PORTAL-RIO [29], a sugar-ethanol industry implanted in the city of Campos dos Goytacazes, north of the state of Rio de Janeiro, begins to generate electricity using vinasse biogas, in experimental stage, in the 2015 vintage. Through a bacterial bio digestion process of vinasse organic content, biogas with 80% methane obtained.
The University of Taubaté and the Sugarcane Technology Center participate in the research, sponsored by BNDES and Canabrava Group investments, totaling R$ 16 million. The biogas feeds an UASB reactor. In 2012, the JB Group from Pernambuco and Cetrel Bioenergy from Bahia, in partnership, inaugurated a vinasse plant of bioenergy generation with total investment of R$ 13 million [30].
Vinasse use for biogas generation has environmental benefits, reducing emissions in relation to vinasse and generated products. The generated product can be used as input in electricity generation, besides being used as fuel for vehicles, replacing fossil gas.
Environment Implications
Bagasse and vinasse use has environmental benefits, such as carbon emission reduction, deforestation reduction and the absence of flooding and land flooding to build hydroelectric reservoirs. In addition, it does not interfere in tropical ecosystems.
This is because bagasse and vinasse are sugarcane by-products generated during ethanol (bagasse and vinasse), and sugar (bagasse) production. Sugarcane crops historically do not cause deforestation, as they occupy areas already deforested and degraded by cattle (old pastures opened in agricultural borders, especially in the Brazilian Midwest region).
Figure 4: Soil losses by erosion in different cultures (Ton/hectare/year).
GALDOS et al. [31] detailed relevant technical aspects of waste management for sugarcane ethanol production.
Regarding retention capacity of rainfall water, which is an important item in agriculture, even for soil protection, sugarcane considered one of the most efficient crops, as it has losses lower than 5% [32]. It also does not interfere with food production, as sugar produced from sugarcane. Compared to traditional thermal power plants that use fossil fuels, electric energy generation by sugarcane industry has other competitive advantages, such as small-sized generating units that allow the decentralization of generation centers and reduce transmission costs.
Sugarcane Burning
Sugarcane field burning was a practice adopted all over Brazil to facilitate the sugarcane harvest by workers. This practice was necessary, as the entire harvest used to be manual and the sugarcane straw hindered the workers’ harvest during cutting. However, burning, besides changing sugarcane yield in plants, also causes environmental pollution through emission of gases and particles that harm the ozone layer, as well as the health and quality of life of nearby town populations. Moreover, burnt sugarcane must go through an extra cleaning process at the beginning of the sugarcane preparation process milled in the plant. Lack of proper control and wind occurrence may cause the fire to reach neighboring properties to the sugarcane fields, destroying crops, industrial and private facilities, besides generating thick smoke clouds that impair traffic on nearby roads and cause accidents. CONAMA issued resolutions No. 382/2006 and 436/2011 about maximum atmospheric pollutant emissions for stationary sources.
In March 2013, the Brazilian Supreme Federal Court (STF), through the Library Documentation/Coordination Department, published "Sugarcane Burnings - Bibliography, Legislation and Jurisprudence", whose aim was to publicize the existing doctrine on the subject in the Virtual Libraries Network (RVBI), in full-texts and specific pages published on the internet.
The São Paulo state government, where the largest area planted with sugarcane is located, providing raw material for the highest concentration of sugar-ethanol industries in Brazil, was the pioneer in legislating about sugarcane field burnings. In 2002, through state law no 11241, São Paulo defined a schedule with gradual plantation burning reductions, whose goal is to eliminate the practice from mechanized agriculture areas by 2021, and to eliminate the practice from non-mechanized agriculture areas by 2031.
Reverse Logistic Policies of Waste and Agricultural Zoning
Federal Decree no 7404/2010 regulates the National Policy on Solid Waste created by federal law no. 12305/2010, and sets standards for selective collection and recovery of solid waste from the productive sector for recycling or other environmentally suitable destination, such as biomass use (bagasse) to produce electric energy.
The state of Mato Grosso do Sul applies the Climate Risk Agricultural Zoning for sugarcane crops through decree no. 93/2011, according to federal decree no. 6961/2009. The affected areas are, as follows: the Amazon and Pantanal biomes and the Upper Paraguay River Basin; lands with declivity above 12%; lands with native or reforestation vegetation cover; remaining forests or protected areas; dunes, mangroves; scarps; rock outcrops; mining areas; urban areas; and indigenous lands.
Electricity Cogeneration Licensing
Regarding electricity cogeneration by sugar-ethanol plants Mato Grosso do Sul state has the following resolutions. SEMA/IMAP no. 004/2004, from the State Environment Institute, citing environmental licensing standards for biomass plants with capacities lower than 30 MW of electric energy generation and for electric energy plants with capacity exceeding 30 MW. SEMAC no 010/2007, for power cogeneration license granting. SEMAC no 020/2007, which unifies licensing procedures for installation, water collection, soil fertilization, gas station, and biomass plant.
Brazilian Electric Energy Market
Law no. 10848/2004 and decree no 5163/2004 regulate electric energy sales by the current model of the Brazilian electric energy sector, with two contracting environments, as follows: the regulated one, called Regulated Contracting Environment (ACR) and the free one, called Free Contracting Environment (ACL). ACR is the market in which electric energy purchasing and sale negotiated between selling agents and distribution agents, through bidding (auction). Contracts signed between sellers, which are generating agents that offered electric energy for the lowest price and won an auction, and electric energy distribution companies, which are the buyers. These contracts called Power Purchase Contracts in the Regulated Environment (CCEAR).
The second market, ACL, is where free negotiations of purchase and sale between generation, marketing, export and import agents and free consumer companies occur. ACL negotiations formalized by commercial contracts containing electric energy and power volumes, prices, terms and guarantees. Generation and marketing agents can sell electric energy in both environments. Rules and trading procedures of the Electric Energy Trading Council (CCEE) consist of the Normative Resolution no 109/2004. Contracts are registered in CCEE and form the basis for their accounting and financial settlement.
Under the current rules, auto producers and cogeneration companies with an installed capacity below 50 MW can participate in CCEE operations, as long as they already interconnected to intake facilities and not dispatched by the National System Operator (ONS). Electric energy auto producers and/or cogenerates may be CCEE agents, or represented by another registered agent, in order to market electric energy in ACR and ACL. Compliance assurance of signed contracts made by the result of their own generation or by other contracts already registered in CCEE.
In order to ensure the complete electric energy supply delivery in their contracts, cogenerators should offer electric energy and power "ballast" as physical guarantee of the maximum electric energy and power amount associated to the self-generation enterprise or third-party purchase agreements, which can also be used to meet the delivery expected in the sales contract.
and/or consumed and the effectively measured volume. Differences determined by CCEE valued by the Differences Settlement Price (PLD). The short-term market known as "spot market" and "spot price", in reference to international trends of free market. PLD is calculated and published weekly for each load level and for each SIN submarket, based on the marginal cost of system operation (CMO), limited by a minimum and a maximum price. OLIVEIRA [33], HOFSETZ and SILVA [34] described in detail the electric energy markets existing in Brazil.
Discussion
The sugarcane vintage takes place between April and November in the Brazilian Southeast/Midwest regions, period in which drought occurs, hindering the water replacement of hydroelectric power plant reservoirs in this region. It is noted that the main hydropower plants with reservoirs are located in this region (about 70% of the hydroelectric reservoir capacity in Brazil is concentrated in the Southeast/Midwest regions). Depending on the sugarcane amount harvested during the vintage, some plants extend the milling period by up to two months. In this case, they produce additional bagasse, and may consequently generate more electricity. Plants located in the Brazilian Northeast region have their vintage between November and April.
Thus, considering all of Brazil, the sum of sugarcane regional vintage periods indicates that electric energy cogeneration happens throughout the year (one part in the Southeast/Midwest regions and another part in the Northeast). Rain shortage occurred in Brazil in 2001/2002, and reservoirs of hydroelectric plants in the Southeast/Midwest regions had their water supplies reduced to critical levels.
This event was the main reason for the electric energy rationing practiced by the government. Government actions taken since then, increasing the share of thermal generation in the Brazilian electric energy matrix. In 2014, which was another period with low rainfall in the same Southeast/Midwest regions, hydroelectric generation reduction and thermal power plants generation increase occurred, taking into account that the thermal energy price is higher [35]. In this new period of rainfall shortage (2014/2015), the National System Operator (ONS) dispatched thermoelectric plants throughout the period, in continuous activity to maintain the electric energy demand supply. It was an opportunity for sugar-ethanol industries to expand their operation in cogeneration, taking advantage of the higher return due to high prices charged by the Brazilian energy market. Thus, during the most recent electric energy crisis, the new market opened in 2004 for the sugar-ethanol industry consolidated. The traditional sugarcane industry solidified as an energy industry with the addition of electricity cogeneration to its product portfolio: a new product and a new market for the traditional Brazilian sugarcane industry. Since 2004, sugarcane biomass has been increasing its participation as input for bioelectricity generation.
According to EPE [36], national policies promoted electric energy generation diversification. A magazine specialized in economics, EXAME [37], published a significant report that shows information obtained from ANEEL in which there was 7.9 GW of electric energy cogeneration installed capacity by the sugar-ethanol industry at the beginning of 2014, and in May 2015 the capacity expanded to 9 GW. SIN received electric energy from 177 sugar-ethanol producing units, according to EPE [36]). As ÚNICA [13] reports that the total number sugar-ethanol industries reaches 355 production units, there is still growth potential in the bioenergy source electric energy supply.
Figure 5:Auctions CAP-price evolution (US$/MWh).
A-3: new energy auction to deliver 3 years ahead – Thermoelectric power plant. A-5: new energy auction to deliver 5 years ahead – Hydroelectric power plant. LFA: special auction for alternative sources –
Wind and Bioelectricity.
In April 2014, the electric energy price on the free market reached of US$ 365.34/MWh [38]. As its generation is concentrated in the dry seasons of the Southeast/Midwest regions, electric energy generation by the sugar-ethanol industry is a very important source of energy to complement hydro generating facilities. It regarded as "winter energy". According to the ONS, each 1,000 MW mean bioelectricity inserted in the interconnected system during the dry season means savings of 4% of Southeast/Midwest subsystem reservoirs [39].
Sugar-ethanol plants participate of electric energy markets as cogenerators, selling, delivering and sometimes even buying power to honor deliveries under sale contracts. In electric energy auctions of regulated environment (ACR) for the supply of electricity generated from biomass source, the sugar-ethanol plants have shown significant results from 2004, as shown in Table 2.
Table 2: Biomass marketed in ACR auctions.
The peak number of projects and mean MW contracted in the ACR happened in 2008. In visits to sugar-ethanol plants located in Mato Grosso do Sul state, the authors of this study were informed that units belonging to business groups negotiate cogeneration electric energy centrally, having specialized management in their structure. Independent sugar-ethanol plants operating in ACR sell electric energy to local distribution companies. Both business group plants and independent power plants also operate in the ACL. It also learned that electricity sale results, especially in the last three years, have been significantly relevant to company revenues. In some of these companies, cogeneration was the factor that enabled operating profit in their financial and accounting balances.
Conclusion
In this paper, the electric energy cogeneration practice through inputs previously considered as waste from ethanol and sugar production in Brazilian sugar-ethanol industries studied. The crisis in low cost electric energy generation created by stored water reduction in reservoirs of major Brazilian hydroelectric plants, which caused by lack of rain, occurred mainly in the Southeast/ Midwest regions, opened a new opportunity for the sugar industry, which already produced electricity for its own consumption. In addition to the electric energy cogeneration opportunity, especially in the dry season, the pressure to reduce the environmental impact by eliminating waste discharged in nature redirected the business industry. With the power generation expansion by bagasse, straw and tips burning, a new business unit of high
Auction year
of sale Average MW
2004 135 19 66,83
2005 64 5 98,72
2006 119 9 85,45
2007 115 11 85,05
2008 541 31 88,47
2009 10 1 78,98
2010 191 12 74,80
2011 102 12 50,50
2013 203 11 59,23
2014 90 6 76,70
2015 52 3 79,74
Total 1622 120
Projects Average Price
profitability caught the attention of entrepreneurs and large international groups. Vinasse use for electricity generation is more recent, implying higher investment, and some practical initiatives in this direction already found. Through futurology exercise, it is not very difficult to see the possibility of a radical change in the sugar-ethanol industry with the growing importance of bioenergy generated from sugarcane, with a positive impact on financial and environmental results.
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