Evaluation of partial clinker replacement by sugar cane bagasse ash: CO2 emission reductions and potential for carbon credits

Abstracts

Este trabalho apresenta um estudo sobre a viabilidade de possíveis cenários de redução de emissão de CO2 na fabricação de cimento através da implementação de projetos de Mecanismo de Desenvolvimento Limpo (MDL) associados à substituição parcial de cimento por cinza do bagaço de cana de açúcar (CBCA). Estudos sobre o comportamento térmico, químico e mecânico de concretos com 5 a 20% de cinza indicaram que existe melhora no desempenho de todas as propriedades analisadas e que a cinza pode ser usada como aditivo na fabricação de cimento. As emissões de CO2 de dois cenários hipotéticos de implementação de projeto de MDL através desta tecnologia no estado de São Paulo, com base na metodologia oficial aplicável, foram avaliadas. Os resultados demonstram que existem reduções de emissões em ambos os cenários, inclusive para o mais desfavorável, evidenciando a possibilidade de obtenção de créditos de carbono negociáveis.

mecanismos de desenvolvimento limpo; emissão de CO2; cinza do bagaço de cana de açúcar; créditos de carbono

Evaluation of partial clinker replacement by sugar cane bagasse ash: CO₂ emission reductions and potential for carbon credits

E. M. R. Fairbairn^I; T. P. De Paula ^I; G. C. Cordeiro^II; B. B. Americano^III; R. D. Toledo Filho^I

^ICivil Engineering Program, COPPE, Universidade Federal do Rio de Janeiro, [e-mail], [e-mail], CT-Ilha do Fundão, 21945-970, Rio de Janeiro-RJ, Brazil;

^IICivil Engineering Laboratory, Science and Technology Center, Universidade Estadual do Norte Fluminense Darcy Ribeiro, [e-mail], Av. Alberto Lamego, 2000, 28013-602, Campos dos Goytacazes - RJ, Brazil;

^IIIFBDS - Fundação Brasileira para o Desenvolvimento Sustentável, Rio de Janeiro, RJ, [e-mail]

ABSTRACT

This work presents a study about the viability of possible CO₂ emissions reductions scenarios for the cement manufacturing through the implementation of Clean Development Mechanisms (CDM) associated with the partial replacement of cement by sugar cane bagasse ash (SCBA). Studies on the thermal, chemical and mechanical behavior of concretes containing 5 to 20% of ash indicated that there is improvement on the performance of all analyzed properties and that the ash can be used as admixture on the cement manufacturing. The CO₂ emissions of two hypothetical scenarios of CDM Project implementation in the state of São Paulo through this technology were evaluated based on the official and applicable methodology. The results show that there are emission reductions on both scenarios, even for the most unfavorable, evidencing the possibility of obtaining negotiable carbon credits.

Keywords: clean development mechanisms, CO₂ emissions, sugar cane bagasse ash, carbon credits.

1. Introduction

Until the early 70's, most development projects such as dams, roads, buildings and industrial installations which require large quantities of raw materials, such as steel, cement, among others accounted only the economic benefit / cost rate. As a result of this development model it has emerged an increasing environmental degradation caused by impacts from human activities. The production of cement, for example, is an activity that emits large amounts of gas which are capable of enhancing the greenhouse effect, as carbon dioxide (CO₂). The result of these various negative interferences aroused public opinion and led several intearnational organizations to consider an essential paradigm changing, where it should be pursued more environmentally friendly means of development. One can refer to the reports generated by the Club of Rome regarding the various forms of world development, conferences such as the Stockholm Convention in 1972, the creation of UNEP (United Nations Environment Programme) in 1980, the Brundtland Commission, in 1987, where one has coined the concept of sustainable development. The summits of Rio 92 and its subsequent edition in 2002, Rio +10, held in Johannesburg , South Africa, sought to formalize the commitment of countries to put into practice sustainable development.

1.1 Climate change

Some of the main themes discussed in Rio 92 and Rio +10 are the climate change and ways to prevent dangerous anthropogenic interference with the climate system. The main scientific evidences of these phenomena had already been addressed in reports drawn up by the IPCC (Intergovernmental Panel on Climate Change), created in 1988.

Linked to UNEP and WMO (World Meteorological Organization), the IPCC consists of a network of scientists from over 130 countries that aims to transform the scientific knowledge of the international community on recommendations for government policies. In its first report, the IPCC suggested the establishment of a political negotiation instance, the UNFCCC (United Nations Framework Convention on Climate Change), which was then created in 1990. In its second report, in 1995, the IPCC has shown that there is an intensification of global warming (Figure 1) due to excessive emission of greenhouse gases from human activities, such as methane (CH₄), nitrous oxide (N₂O), fluorine gases (HFCs, PFCs, SF₆) and especially carbon dioxide (CO₂).

1.2 The Kyoto protocol and its mechanisms

On the basis of this evidence and within the framework of the UNFCCC, was drawn up in 1997 in the city of Kyoto in Japan, a Protocol whose main guideline would be the establishment of binding targets of greenhouse gases emissions of developed countries, so-called Annex I countries, in 5.2% compared to 1990 emissions, for the period of 2008 to 2012.

The developing countries, or non-Annex I, within which Brazil is classified, have not contributed with significant emissions due to lower industrial activity and consumption over the last 150 years. Therefore they would be exempt from emission reduction commitment, but could contribute with the Protocol in other ways.

In order to create alternatives for emissions reductions to be more flexible, the Protocol provides three mechanisms: Emissions Trading, where developed countries with unused emission quotas can sell their quota for countries that have exceeded their targets for the reduction; Joint Implementation, where countries with reduction targets can buy ERUs (Emission Reduction Units) of other countries with targets that have implemented emission reduction projects and want to sell these credits; and CDM (Clean Development Mechanisms), where a country with targets can invest in emission reduction projects in developing countries, acquiring CER (Certified Emission Reductions), which unit equals 1 ton of CO₂. The investor country may redeem the credits in its emissions in order to fulfill their goals, and the host country, beyond receiving technology, has the financial return generated from the sale of CER. These three mechanisms compose the "carbon market" [1].

The Kyoto Protocol entered into force in 2002, after ratification of Russia, and currently it has been ratified by a total of 184 countries, among which the United States, one of the countries which have historically contributed with most of the world's emissions, are not included.

1.3 The Portland cement, the sugar cane bagasse ash (SCBA) and the clean development mechanism (CDM).

Several initiatives under the Kyoto Protocol and CDM occurred in developing countries, especially Brazil, India and China. Many projects related to reducing emissions as the Nova Iguaçu landfill, state of Rio de Janeiro, where there is conversion of methane from decomposing garbage in CO₂ which greenhouse potential is 21 times smaller; the use of biomass for energy generation; the utilization of the waste incineration energy, as performed the Usina Verde, in the UFRJ campus, also in Rio de Janeiro; the reforestation of degraded areas; the use of alternative fuels; the reduction of the clinker ratio in the cement production, where are emitted about 1 ton of CO₂ per ton of cement [2], among numerous other ways of reducing emissions, are receiving CER. All CDM projects, as exemplified above, must meet, among other requirements, the requirement to use an innovative technology, unknown by the market and the calculation of emission reductions must follow a specific methodology, approved and consolidated by the UNFCCC for that activity.

The method that involves the reduction of clinker in cement by increasing the share of additives represents a promising alternative for Brazil, which in 2010 had a production of 59.1 Mt of cement, having the southeast of the country responsible for about 50% of this amount [3]. Most emissions from cement production occur during the burning of lime for the production of clinker and the burning of fossil fuels. The main additives commonly used are fly ash, gypsum, blast furnace slag and limestone filler.

Like the cement industry, the sugar cane industry, currently under a great expansion process, driven by growing demand for alternative fuels like ethanol, also figures as a strategic sector in the economic and environmental global scenario, having been produced about 730 million tons of sugar cane in the 2010 crop, responding the southeast for about 70% of the total [4]. The sugar cane produced in Brazil serves as raw material for the production of sugar and ethanol, generating about 190 million tons of bagasse. Almost the entire bagasse generated on the sugar cane mills has been burned for biomass energy harnessing through cogeneration power plants, a process in which the final residue is the bagasse residual ash. It is estimated that about 4.5 million tons of SCBA are generated at each crop in Brazil [5].

Within this context, recent researches on the performance of bagasse ash in concrete has been developed in the Laboratory of Structures at COPPE/UFRJ, based on studies of the rheological, thermal and mechanical properties and also associated with durability. The results obtained [5-9] show that there is great potential for use of SCBA as pozzolan in cement production. Additionally, because of the ash biomass origin, which burning does not contribute to the intensification of the greenhouse effect, the replacement of clinker with ash allows the reduction of CO₂ emissions into the atmosphere. One identifies, therefore, a promising scenario for the deployment of CDM, especially in the southeast region of Brazil, through the use of a sugar cane industry residue in the cement industry, both heavily present in this region.

1.4 Objectives

This work aims to quantify the reduction of CO₂ emissions arising from the partial replacement of Portland cement by SCBA and assess the possibility of implementing a CDM.

1.5 Justification

In view of that the cement industry is responsible for approximately 5% [10] of global CO₂ emissions, the search for cleaner production technologies capable of absorbing a residue which is largely generated in another industry and providing financial gains, reveals a quite promising field of research and development. In this sense, the Laboratory of Structures of COPPE/UFRJ has researched the use of cementitious materials with new perspectives on dosage and composition, where the use of SCBA with pozzolanic potential, in the partial replacement of cement, has shown the best mechanical performances and potential for CO₂ emission reductions in the production of cement.

2. Feasibility of SCBA as an additive in cement

The SCBA, for being rich in amorphous silicon dioxide, can be used as pozzolan in cement manufacturing. Silica present in ash comes mainly from the epidermis of plant cells, through the absorption of monosilicic acid (H₄SiO₄) from the soil, and residual sand that sometimes is not entirely removed on the sugar cane washing process and is jointly burned with bagasse in steam boilers [6].

The first studies regarding the behavior of cementitious materials containing bagasse residual ash dating to the late 1990. Studies of Martirena Hernández et al. [11], Singh et al. [12], Ganesan et al. [13] and Morales et al. [14] show that replacing cement by ash (5 to 30% by mass) is able to improve the mechanical properties and durability of concrete.

More recently, through mechanical, rheological, calorimetric and durability tests in concrete samples with 0 to 20% of bagasse ash, Cordeiro et al. [5] concluded that there is considerable improvement in rheological performance and durability and maintenance of long-term compressive strength, as shown in Figure 2. The ash used in this study was collected during the cleaning operation of the bagasse burning boiler and it was ground to improve homogenization and reactivity. This work also indicated that the maximum adiabatic temperature rise of concrete decreased by 11%. In this way, it is possible to infer that the use of residual SCBA as a mineral admixture in cement is technically viable, since it is able to improve several physical and mechanical properties of concretes.

3. Emissions from the cement production

Emissions in cement production are mainly associated with the step of clinkerization and the combustion of fossil fuels such as coal, mineral and diesel oil, both for electricity self-generation and for the power generation on the grid. The clinkerization step consists in the heating of the flour or "the raw" until temperatures around 1450°C. With this, the limestone undergoes a thermal decomposition giving rise to the clinker, according to the calcination reaction shown below:

The first product of the reaction is calcium oxide, the main oxide constituent of clinker. The second product of this reaction is CO₂. The heating of limestone represents more than half of the contributions in greenhouse gases from cement production, having in sight that the carbon emitted is outside the natural carbon cycle.

The clinker is mixed with other admixtures such as gypsum and pozzolans in variable proportion according to the type of cement. This mixture then undergoes a second grinding, giving rise to Portland cement itself, which is bagged and stocked, and which average composition (cement CPII) is of 80% of clinker, 15% of additives and 5% of other materials [15].

It is estimated that one ton of CO₂ is released for every ton of cement produced. This average value for the world production tends to be more or less greater in different countries mainly in function of the national energy matrix to be less or more clean. Countries with large participation of renewable energy such as wind, solar, biomass or hydroelectric power, such as Brazil, tend to show lower emissions associated with the production.

An alternative to reducing emissions from cement production activity is the use of renewable fuels at the expense of mineral fuels, both in the self-generation within the factory and in the grid, and the combustion efficiency improvement of furnaces.

Another possibility is to reduce the share of clinker in cement through mineral additions, such as blast furnace slag and pozzolans, as the bagasse ash. This last alternative is advantageous since it does not require adaptations of engines and furnaces to new fuels avoiding therefore large financial and technological investments. However, for an effective reduction of CO₂ it is necessary to consider all emissions relating to obtaining, transporting and preparation of the additives used, which often undermines the replacing viability of many materials that aim at reducing emissions and gains in carbon credits.

4. The SCBA as "clean" additive

Currently, the sugar cane biomass has served as fuel for steam thermoelectric generation, where the energy generated is sufficient to ensure the self-sufficiency of sugar cane mills and still generate surpluses. The CO₂ emissions from biomass burning does not contribute to the intensification of greenhouse effect, since the carbon from sugar cane already existed in the atmosphere and was absorbed during the vegetal growth.

The main product of bagasse burning is the SCBA. The mass of ash generated corresponds to about 2.5% of the bagasse burned, or 0.6% of the mass of sugar cane harvested.

5. Considerations on the methodology for CDM implementation

In accordance with the UNFCCC guidelines, a CDM project must follow a specific methodology for the activity developed. For the case of this study, the methodology applied is the ACM 0005, entitled Approved and Consolidated Baseline Methodology for Increasing the Blend in Cement Production [16], which defines all the prerequisites, constraints, and equations needed for legitimate determination of emission reductions.

The ACM 0005 methodology is applicable to any project that increases the share of additives in cement, i.e. reduce the share of clinker. In addition, there are prerequisites such as that there is no shortage of additive used, there is no suitable alternative destination for the additive and cement production is geared only to the internal market.

Considering national production of SCBA (2.556 Mt) and cement (46 Mt) in the year 2007, and assuming a replacement of up to 50% permitted by Brazilian standard [17], it is concluded that the amount of additive produced is enough to supply 37% of national production of cement during the project implementation with replacement fraction of 15%, with no shortage of ash.

Currently, the most common destination of the ash produced is the use as soil fertilizer, although its fertilizers properties are not relevant and its degradation is very slow, so that this practice aims at the simple disposition of ash. Searches for new destinations that add value to the ash, as an additive in cement production, are preferable alternatives, and therefore, more suitable than the common practice [6].

According to the SNIC [3], the cement production geared to exportation in 2007 corresponded to 2.7% of total cement produced, so that national cement production is predominantly geared towards the domestic market. Still according to the SNIC, the south/southeast region, responsible for the majority of national production, has not registered cement exportation in the year of 2007, with the exception of the State of Paraná which has exported about 1% of its production [3].

Another important prerequisite for the acceptance of the CDM project is that this presents what is named on the methodology as "additionality". Additionality occurs if emissions arising from the implementation of the project are lower than those that would have occurred in the absence of the project. In addition, it is necessary to prove that the project is only feasible or becomes economically advantageous only if approved as CDM and if carbon credits are obtained. Projects considered more attractive than others when it is evaluated only the financial returns they bring, so that they could be deployed without even the gains of the carbon credit, do not have additionality. Projects resulting from the introduction of unfamiliar technologies and which face market acceptance barriers are examples of projects which may be legitimized as CDM.

The use of SCBA as an additive in cement is a non-existent practice on the market. The use of this agro-industrial waste, which emissions balance is null, is a new technology, consequently being incipiently studied by academia, indicating that the use of ash as additive generates additionality.

5.1 The calculation of emissions

According to the ACM 0005 methodology, the analysis of emissions is not made for all greenhouse gases, but only for CO₂, since reductions in emissions of CH₄ and N₂O by changes in combustion process are not significant.

The methodology requires definition of two distinct realities (scenarios) for the calculation of emissions. The first, so-called Baseline Scenario, reflects the emissions that would occur in a particular future period if the current processes of production were not changed, representing a historical trend in emissions. The other, called Project Scenario, represents the emissions that would occur as a result of project implementation. The Baseline should consider the situation in which occur the lowest possible emissions, so that the calculation of emission reductions is conservative.

The calculation of emissions involves four main steps: Baseline emissions, Leakage, Project emissions and Emissions reduction.

5.1.1. Baseline emissions

The Baseline emission is calculated using the following equation:

where 〖BE〗_BC,y is the Baseline CO₂ emissions per ton of blended cement type; 〖BE〗_clinker the clinker CO₂ emissions per ton of clinker in the baseline in the project activity plant; 〖BE〗_blend the blend Baseline benchmark of share of clinker per ton of blended cement and 〖BE〗_{ele_ADD_BC} the emissions relating to electricity for grinding and preparation of additives in the Baseline, including gypsum, given in tons of CO₂ per ton of cement.

The terms of the above equation are in turn calculated as below:

The term 〖BE〗_calcin refers to emissions arising from the calcination of calcium and magnesium carbonate. The calculation of this term involves the determination of the levels of calcium and magnesium oxide both in raw flour and clinker and the use of emission factors provided by the methodology for both oxides. The term 〖BE〗_{fossil_fuel} refers to emissions from the burning of fossil fuels for the production of clinker. This term is calculated by the sum of the quantity of various types of fuel consumed weighted by their emission factors. The term 〖BE〗_{ele_grid_clnk} refers to emissions arising from the use of grid electricity for the production of clinker. This term involves the total energy used weighted by the grid emission factor. Finally, the term 〖BE〗_{elec_sg_CLNK} refers to emissions arising from the electrical self-generation for clinker production, and is calculated in a similar manner to the term  _{le_grid_clnk}. All terms used for the calculation of the term 〖BE〗_linker are divided by annual production of clinker so that the unit of the terms is ton of CO₂ per ton of clinker.

5.1.2. Leakage

The second step of the calculation of emissions is called Leakage, which corresponds to "fugitive" emissions that occur outside of the process due to burning of fossil fuels for the transport of raw materials, fuels and additives to the plant. However, the methodology quantifies these emissions only for the transportation of the additive used in the project, since these tend to decrease when it is reduced the amounts of clinker in cement. This type of emissions is calculated using the following equation:

being L_y the total leakage emissions relating to the transportation of additives in kt of CO₂; L_{add_trans} the transport-related emissions of additives in tons CO₂ per ton of the additive; A_{blend, y} the fraction of additives in the Baseline cement and P_{blend, y} the fraction of additives for the Project cement, both in tons of additive per ton of cement. The term 〖BC〗_y represents the total production of cement for each year of the project in kt.

The burning of fossil fuels needed to transport the additive used from its origin site to the plant is the main source of emissions of the new scenario. The average distance of transportation, the fuel used and the efficiency of the transport system used also influence this amount. The term L_{add_trans} synthesizes these emissions and is given by:

being 〖TF〗_cons the consumption of the vehicle in kg of fuel per km; D_{add_source} the average distance of transportation in km; TEF the fuel emission factor used in kg of CO₂ per kg of fuel; C₄ a constant conversion factor equal to 0.001 ton per kg; Q_add quantity of additives carried per vehicle in one trip in ton; 〖ELE〗_{conveyor_add} the annual energy consumption for conveyor system for additives in MWh;

〖EF〗_grid the grid emission factor in ton of CO₂ per MWh and

〖ADD〗_y the annual quantity of additive consumed in ton.

5.1.3. Project emissions

The third step is the calculation of emissions of the cement produced in the project or Project emissions. The equations for calculating this step are the same as those used in the Baseline emissions, changing only the nomenclature of BE to PE. It can be concluded beforehand that the terms 〖BE〗_clinker and 〖PE〗_clinker are equal if the clinker used in the project is the same as the currently produced, existing only differences in the amounts of clinker in cement. Additionally, the terms 〖BE〗_{ele_ADD_BC} and 〖PE〗_{ele_ADD_BC} are also equal if there are no emissions associated with the preparation of the new additive. This way, the values calculated in the equation 3 may be used for the determination of the emissions of the project, summarized by the following equation:

The ACM 0005 methodology provides that the grid emission factors used in the calculations shall be determined in accordance with another methodology called Tool to Calculate the Emission Factor for an Electricity System, also authored by the UNFCCC. However, when there are precise and reliable local data, the adoption of these predetermined values is also possible.

5.1.4. Emissions reductions

The calculation of emission reductions is given by:

being 〖ER〗_y the annual reduction of CO₂ emissions in kt; 〖BE〗_BC,y and 〖PE〗_BC,y the total emissions in ton of CO₂ per ton of cement on the Baseline and Project, respectively; 〖BC〗_y the total production of cement for each year of the project in kt; L_y the total leakage emissions relating to the transportation of additives in kt of CO₂ and the term a_y represents an extra emission arising from the diversion of additives from existing uses. That is, if the quantity of additives that are effectively surpluses after application in the existing usage is not sufficient to feed the project, the emissions reductions must be averaged by the a_y factor given by the rate between the quantity of additives not surplus and total quantity of the additives used in the project.

For the case of the use of SCBA there is no current use for this additive, since its use as fertilizer aims more to final disposition of waste than the harnessing of poor fertilizer properties of the ash. This way, if the quantity of ash generated is able to supply the project, the term a_y will be null.

6. Hypothetical scenarios of CDM implementation

The possibilities of application of the SCBA as an additive in the manufacture of cement are numerous for great part of the national territory, in view of the large number of states that gather both sugar cane and cement production. However, the ash transport distance from the sugar cane mills to the cement factories is a decisive factor that can derail some alternatives. Too long distances can decrease the emissions reduction and, in some cases, may increase emissions from cement production due to burning of fossil fuels by transport vehicles which, in Brazil, are predominantly of road type. This way, the southeast region, and especially the state of São Paulo, which concentrates on its territory more than 60% of national sugar cane production [4] and 16% of national cement production [3], has the greatest potential for emissions reductions.

In this study were analyzed, for the base year of 2005, two hypothetical scenarios of CDM project implementation in factories in the state of São Paulo based on manufacture of cements with fraction of 15% of SCBA. For both scenarios it was opted for the use of a residual SCBA collected directly from a boiler and that did not suffer any further treatment besides the grinding. It is clear that for an industrial application the establishment of a protocol for ashes obtaining will be required.

In order to simplify the analysis, the production of ash and cement was concentrated in producer municipalities totaling 35 clusters of ash production [18] and 4 cement manufacturing clusters. The production of these clusters was obtained by the sum of the outputs of the main sugar cane mills and cement factories situated within a radius of 30 km from the base municipality, according to data provided by the National Union of Cement Industry and by the Union of Bioenergy Producers. Then, the road distances of all 140 possible combinations between ash and cement producer clusters were determined [19]. The map shown in Figure 3 illustrates the result of this simplification and displays the main municipalities examined. For the estimation of the ash transport emissions was assumed the use of a diesel truck with load capacity characteristics and specific fuel consumption similar to the best-selling vehicle in the region for this type of transport, according to data from the Association of Motor Vehicles Manufacturers [20]. The loading capacity and specific consumption, required for the emissions calculations, were determined from the vehicle's manual published by the manufacturer.

In the determination of Baseline emissions of each scenario the data used were obtained through average values for each factory weighted by its total production in the year of 2005. The composition adopted for the cement of the Baseline was 80% of clinker, 15% of additives and 5.0% of gypsum [15].

For calculating Project emissions, in both scenarios, the methodology requires that the quantities of additives used in the project are equal to those of the Baseline, being allowed by the Brazilian standard, a fraction of up to 75% of additives [17]. To this end, it was considered, in both scenarios, that half the production of cement factories involved would be of a generic type A with 65% of clinker, 30% of gypsum and 5.0% of additives, and the other half would be a generic cement type B, with 80% of clinker, 15% of SCBA and 5.0% of gypsum. The final composition of the production of both cements for the project in each scenario will therefore be of 72.5% of clinker, 15% additives, 7.5% of SCBA and 5.0% of gypsum.

In the calculation of the emission reductions certain emissions relating to additives and to the gypsum, represented by 〖BE〗_{ele_ADD_BC} and 〖PE〗_{ele_ADD_BC} on equations 2 and 6, were not calculated since these terms are equivalent, in both the Baseline and the Project, and cancel each other out in the calculation of emission reductions, because the amount of additive and gypsum in both situations is equal.

For the first scenario, was simulated the implementation of the project between the municipalities of greater production of bagasse and cement. The municipality identified with the largest concentration of sugar cane production was Jaboticabal, in the northern region of the state, with 31,630 kt of cane produced in 18 mills, and the municipality of greater cement production was Sorocaba, on which lies two cement factories with total production of 2,793 kt. This hypothesis was assumed because it involves the largest quantities of cement and ash in an emission reduction project between two municipalities. However, the rate clinker-cement in the region of Sorocaba was hypothetically assumed as being that of the Brazilian average, since local production varies seasonally.

In a second scenario was analyzed the implementation of CDM to the set of cement/ash municipalities with greater transport distance between themselves, being, apparently, the less favorable scenario for the emissions reduction. The greatest possible distances between the various pairs of cement/sugar cane municipalities in São Paulo occur between Ribeirão Pires, east of the state, with a production of 631 kt of cement and the cane producer municipalities of the west region of São Paulo. Faraway 724 km of Ribeirão Pires, the city of Teodoro Sampaio is the furthest from that town and presented a production of 897.3 kt of sugar cane, followed by Andradina and Pereira Barreto, with distances of 719 km and 711 km and productions of 2,200 and 1,300 kt of sugar cane, respectively.

The determination of the most favorable scenario for CDM deployment within the State of São Paulo would involve all possible combinations of additives producers and receivers as well as the various combinations of quantity of ash transported. The most favorable set of combinations would be one that minimized the final average distance of ash transportation. This analysis has been addressed in recent studies of Fairbairn et al. [21], where the use of computational algorithms for transport distance minimization and for optimization of the ash distribution among the factories was successful.

7. Results

7.1 Scenario 1: municipalities of greater production of ash and cement

For this scenario, the calculation of emission reductions resulting from the implementation of CDM is done between the two municipalities of greater production of the state of São Paulo: Jaboticabal and Sorocaba.

The two cities are separated by a road distance of 318 km. Considering the share of ash on the total cement produced as 7.5% (cement type A with 0% ash and cement type B with 15% ash) and the cement production of Sorocaba, 209.475 kt of ash are required for this scenario, which is easily supplied by the ash production of Jaboticabal, estimated at 790.769 kt. Table 1 summarizes the results obtained by applying the ACM 0005 methodology for emissions calculating in scenario 1.

7.2 Scenario 2: most unfavorable ash transport distances

The scenario 2 estimates the worst-case situation for CDM project implementation regarding emissions from ash transport, the main emission arising from the use of this additive. The cement production of Ribeirão Pires requires, for the proposed ratio of replacement, 47.3 kt of ash. Whereas Teodoro Sampaio produces 22.4 kt of additive, there is a deficit of -24.9 kt of ash to supply the total production of cement. This way, was included the production of 55 kt of ash from Andradina, which presents the second largest transport distance, keeping the analysis conservative and supplying the project with surpluses of ash. It is worth to point out that the economic and financial feasibility of ash transportation is not part of the scope of this analysis, which is restricted to the criteria defined by the ACM 0005 methodology.

For this scenario, the calculation of fugitive emissions for ash transport, called Leakage, and the calculation of emission reductions are separated into two equations: one for the transport of 22.4 kt of ash from Teodoro Sampaio to Ribeirão Pires, and another to 24.9 kt transported from Andradina to the same municipality. The sum of the emission reductions of both alternatives make up the final emission reduction of the scenario 2. The results obtained for this scenario are shown in table 2.

8. Discussion

In both scenarios analyzed was possible to obtain a positive balance of emissions reduction, revealing that there are real perspectives of CDM project implementation. Even for the scenario 2, the most unfavorable due to the largest transport distances, the average CO₂ emissions per ton of ash (L_{add_trans}) is almost 100 times smaller than the CO₂ emissions per ton of clinker (〖BE/PE〗_clinker).

The results obtained for CO₂ emissions per ton of cement on the Baseline of both scenarios are lower than the world average, estimated at 1.0 tons of CO₂ per ton of cement [2]. This low rate of emissions is due to the fact that the energy matrix that underlies the Brazilian power grid is hydroelectric in nature, which emission factors are considerably smaller than those of other energy sources more common in other countries. This fact is demonstrated by the low values of the terms 〖BE〗_{ele_grid_clnk} and 〖PE〗_{ele_grid_clnk}.

Emissions relating to calcination reaction and the burning of fossil fuels represent almost all emissions of Baseline for both scenarios. However, among the factories considered in this study, there is a considerable discrepancy in relation to the use of fossil fuels in the production, denoting sensitive technological differences. Factories in the municipality of Ribeirão Pires did not register emissions relating to the combustion of fuels, unlike factories of Sorocaba.

In both scenarios, the total amount of SCBA generated was able to supply the demand of factories, generating surpluses of ash. It is possible to imagine a series of alternatives for destination of this surplus as: (1) involve more cement factories and sugar cane mills in the project; (2) increase the fraction of ash on cement in the analyzed scenarios through technological improvements in the ash preparation and (3) increase the production of cement in the analyzed scenarios. All these alternatives raised could promote greater emission reductions.

A more detailed study of the feasibility of implementing this type of CDM project should consider a financial and economic analysis, incorporating ash staging and obtaining costs, transport costs, the revenue obtained by selling the CER, besides several variables of the local market, but that are outside of the purposes of this work. However, it is noteworthy that, in the case of a residue to be disposed, the ash has a obtaining cost virtually nil, although its cost tends to increase with the increasing in demand. In relation to the revenue obtained by selling the CER, the amount paid per ton of CO₂ has historically varied between € 15 and € 35.

9. Conclusions

Initiatives to reduce environmental impacts in the industry as the reduction of greenhouse gas emission and re-use of waste generated are strategic, both politically and economically, and configure themselves as issues of great relevance in the current international scenario. In this sense, the use of SCBA as an additive in the manufacture of cement goes towards the global yearning for environmentally correct production technologies. The capacity of improvement in mechanical performance through the use of ash in cementitious compounds has already been proven by several researchers.

Brazil presents a great potential for implementation of CDM projects involving the use of SCBA and the southeastern states, such as the state of São Paulo, concentrate the largest share of both ash and cement productions. The use of the UNFCCC methodology for estimation of emission reductions indicated, for two hypothetical scenarios of CDM implementation within the state of São Paulo, reductions of 182.5 and 19.9 kt of CO₂. The first value refers to the alternative involving the two municipalities of greater production of ash and cement and the second refers to the more disadvantageous alternative, with municipalities of greater transport distance among themselves.

The use of ash as cement additive has met all the prerequisites of the UNFCCC for CDM projects implementation and gains in certified emissions reductions, being able to generate not only technological, but also financial and environmental benefits.

10. Acknowledgements

The authors acknowledge the Brazilian agencies Capes, CNPq and Faperj for the financial support.

11. References

[01] UNFCCC, United Nations Framework Convention on Climate Change. About history of climate change, framework conventions, CDM. Access in July 2009, available in http://unfccc.int.

[02] HEWLETT, P. Lea's Chemistry of Cement and Concrete, 4th ed., New York: J. Wiley, 1988.

[03] SNIC. Statistical Yearbook of the National Union of Cement Industry. Access in June 2011, available in http://www.snic.org.br.

[04] IBGE, Instituto Brasileiro de Geografia e Estatística. National agricultural production. Access in June 2011, available in http://www.ibge.gov.br.

[05] CORDEIRO, G. C., TOLEDO FILHO, R. D., FAIRBAIRN, E. M. R. Ultrafine sugar cane bagasse ash: high potential pozzolanic material for tropical countries. IBRACON Structures and Materials Journal, v. 30, n. 1, 2010, pp. 50-67.

[06] Cordeiro, G. C. Use of sugar cane bagasse ash and rice husk ashes as mineral admixture in concrete, Rio de Janeiro, 2006, Thesis (D. Sc.) COPPE, Universidade Federal do Rio de Janeiro, 445 p.

[07] Cordeiro, G. C., Toledo Filho, R. D., Tavares, L. M., Fairbairn, E. M. R. Pozzolanic activity and filler effect of sugar cane bagasse ash in Portland cement and lime mortars. Cement and Concrete Composites, v.30, n.5, 2008, pp. 410-418.

[08] Cordeiro, G. C., Toledo Filho, R. D., Fairbairn, E. M. R. Ultrafine grinding of sugar cane bagasse ash application as pozzolanic admixture in concrete. Cement and Concrete Research, v. 39, 2009, pp. 110-115.

[09] CORDEIRO, G. C., TOLEDO FILHO, R. D., FAIRBAIRN, E. M. R. Effect of calcination temperature on the pozzolanic activity of sugar cane bagasse ash. Construction & Building Materials, v. 23, 2009, pp. 3301-3303.

[10] WORREL, E., PRICE, L., MARTIN, N., HENDRIKS, C., MEIDA, L. O. Carbon dioxide emissions from the global cement industry. Annual Review of Energy and the Environment, v. 26, 2001, pp. 303-329.

[11] MartiReNa Hernández, J. F. M., Middeendorf, B., Gehrke, M., Budelmann, H. Use of wastes of the sugar industry as pozzolana in lime-pozzolana binders: study of the reaction. Cement and Concrete Research, v.28, n.11, 1998, pp. 1525-1536.

[12] Singh, N. B., Singh, V. D., Rai, S. Hydration of bagasse ash-blended Portland cement. Cement and Concrete Research, v.30, n.9, 2000, pp. 1485-1488.

[13] Ganesan, K., Rajagopal, K., Thangavel, K. Evaluation of bagasse ash as supplementary cementitious material. Cement and Concrete Composites, v.29, n.6, 2007, pp. 515-524.

[14] Morales, E. V., Villar-Cociña, E., Frías, M., Santos, S. F., Savastano Jr., H. Effects of calcining conditions on the microstructure of sugar cane waste ashes (SCWA): Influence in the pozzolanic activation. Cement and Concrete Composites, v.31, n.3, 2009, pp. 22-28.

[15] OECD/IEA . (2000). Organization for Economic Co-operation and Development International Energy Agency - Emission Baselines: estimating the unknown. New York.

[16] UNFCCC, U. N. (2008). "ACM0005 (Version 4) - Consolidated Baseline Methodology for Increasing the Blend in Cement Production". Fonte: http://cdm.unfccc.int/index.html.

[17] ABNT. Brazilian Association for Technical Standards, NBR5732 - Common Portland cement, NBR11578 - Composite Portland cement, NBR5735 - Slag cement, NBR5736 - Pozzolanic cement. Rio de Janeiro, 2001.

[18] UDOP. Statistics of the Union of Bioenergy Producers, 2007. Access in July 2008, available in http://www.udop.com.br.

[19] Secretária de Fazenda do Mato Grosso do Sul. About inter-municipal road distances. Access in June 2010, available in http://www.servicos.ms.gov.br.

[20] ANFAVEA. Access in August 2008, available on the web site of National Association of Automotive Vehicles. Access in June 2010, available in http://www.anfavea.com.br/Index.html.

Publication Dates

• Publication in this collection
  27 Nov 2012
• Date of issue
  Apr 2012