LIFE CYCLE ASSESSMENT (LCA) OF AGRICULTURAL RESIDUES (COCOA CORTEX, SUGARCANE BAGASSE AND OIL PALM FIBER) FOR POWER GENERATION IN BOILERS THROUGH FUEL COMBUSTION

Among the renewable energy resources available is biomass from agricultural waste. Herein, we propose 3 agricultural waste products (cocoa cortex, oil palm fiber and sugarcane bagasse. The environmental and energy performance of agricultural waste used as fuel to produce 1 kWh of electricity each in Ivory Coast was studied using the Life Cycle Assessment method. LAM is a method of environmental evaluation. It evaluates the environmental impact of a product over its entire life cycle. the life cycle of each of these 3 agricultural wastes is made up of collection, transport to the electricity production site and combustion of these biomasses in the boilers of the cogeneration units. The results are as follows: In terms of global warming impacts, for these 3 waste products (cocoa cortex, oil palm fiber and sugarcane bagasse) respectively (0.12; 0.16 and 0.19) kg CO2 eq. / kWh. In terms of impacts on the depletion of non-renewable resources for these 3 wastes (cocoa cortex, oil palm fiber and sugarcane bagasse) respectively (0.007; 0.010 and 0.012) MJ / kWh. In terms of eutrophication-related impacts on global warming for these 3 wastes (cocoa cortex, oil palm fiber and sugarcane bagasse) respectively (0.38; 0.4 and 0.91) g PO43-/ kWh. According to the results of the 3 impacts taken into account in this LCA study, it is desirable to use these 3 agricultural wastes to produce electricity with very good energy and environmental performance, instead of fossil fuels (diesel, oil and coal). Finally, the objective of this research will be to provide credible information to decision-makers (governments, private and public companies, national and international organizations and the general public) in order to promote the installation of energy production units (heat and/or electricity) based on the combustion of these 3 agricultural residues in rural and industrial areas.


Introduction
To satisfy the world's growing need for energy (heat or electricity), the combustion of agricultural residues appears to be one of the best solutions for producing large quantities of energy. However, the lack of data on the environmental impact of burning certain types of agricultural waste to produce energy means that cogeneration units using biomass as fuel are not being set up in certain regions of the world. Among the range of methods used to measure a product's environmental performance, Life Cycle Assessment (LCA) appears to be the most suitable for carrying out this study. LCA is a method of assessing environmental impacts and therefore quantifying a product's performance throughout its life. The life cycle begins with the production stage of the raw materials used to manufacture the product and ends at the end of the product's life, passing through the production and use stages. This is known as "cradle-to-grave" assessment [1]. The first known Life Cycle Assessment study was carried out by Coca-Cola in 1969 to determine whether or not it was beneficial to manufacture metal cans from an environmental point of view [2,3]. The beginning of LCA studies therefore dates from the end of the 1960s and the beginning of the 1970s when the concerns were related to the consumption of energy and raw materials, as well as the treatment of waste. The first LCA studies were therefore related to these themes [2,4]. During the 1970s and 1980s, the use of Life Cycle Assessment remained limited due to a lack of knowledge of the method. Its use has remained confined to producers of packaging as well as politicians responsible for waste management. Because of the energy crisis of 1973, energy was the main focus of these studies [2,4]. The environment and the consequences of human actions on it will experience growing interest in the 1980s, following chemical disasters such as the Bhopal accident in 1984 or the nuclear explosion at Chernobyl in 1986. then, the LCA method remained relatively in the shadows until then will arouse renewed interest, especially in the field of packaging [2]. However, LCA leading to different results for the same products is controversial and leads to much debate [2,4]. In the 1990s, the Life Cycle Assessment method experienced a period of harmonization where the different experiences and achievements obtained during the last two decades were pooled. The Society of Toxicology and Environmental Chemistry in Europe (SETAC) takes charge of the organization of conferences and working groups for the improvement of the method. A society was also created in 1992 (SPOLD: Society for the Promotion of Life Cycle Development) for the development of public and accessible databases. A code of conduct was published in 1993 [5] in order to obtain harmonization in the steps necessary for such a study. ISO standards are then developed to show the way to carrying out an LCA (Baumann and Tillman, 2004a). Far from solving all the problems, but giving avenues for improvement, the European standards were created in 1998 and updated in 2006. The ISO 14040 standard (International Standardization Organization, 2006a) defines the principles and framework of the Life Cycle Assessment, while the ISO 14044 standard (International Standardization Organization, 2006b) [6] brings together the technical content necessary for the proper conduct of an LCA. However, these standards remain imprecise on how an LCA should take place. Through the life cycle analysis (LCA) method, this research will study the environmental and energy performance of these 3 ((cocoa cortex, oil palm fibers and sugar cane bagasse) agricultural residues used as a source of energy to produce electricity.From their combustion in boilers where the heat obtained at the exit will make it possible to turn a turbine which by electromagnetic phenomena will then produce electricity.This LCA study will use the conventional LCA method CML 2001 (Center of Environmental Science of Leiden University (Netherlands) widely used which has impact characterization data on approximately 1000 substances [7]. Then compare the environmental impacts of each waste with each other and then with those of diesel.

Materials, techniques and methods used 2.1 The waste investigated
The waste studied are cocoa cortex, oil palm fibers and sugar cane bagasse. These agricultural residues will be dried and then crushed before the char physical and chemical properties [11], figure 1 below:  These results will be important for the study of the LCA of this waste

Chemical analysis of agricultural waste ash
The combustion of 0.5 g of each agricultural residue was carried out in the electric boiler adapted to the laboratory, then the ashes were collected. The chemical analysis of the ash of each agricultural waste was then carried out by SEM (Scanning electronic miscroscope ) and the results are presented in the following table (2):

Determination of the higher Calorific Values PCS of the agricultural waste studied
The calorific values (PCS) of the waste were obtained through our previous studies and their lower calorific values (NCV) were deduced through the following equation (1): With, H which is the mass percentage of hydrogen (H = % H) contained in the waste sample. And determine by calculating H = (%Hu) / 9, where % Hu is the rate humidity of the waste.
Then the quantities of heat deduced in previous works by equation (2) below: ( ) The results are presented in the table (3) according to previous work:

LCA life cycle analysis methodology
Life cycle analysis (LCA) is a standardized assessment method (ISO 14040 and 14044) for carrying out a multicriteria and multi-stage environmental assessment of a system (product, service, company or process) on its entire life cycle. Its purpose is to know and be able to compare the environmental impacts of a system throughout its life cycle, from the extraction of the raw materials necessary for its manufacture to its end-of-life treatment (disposal of waste, recycling, etc.) , through its phases of use, maintenance and transport (from the cradle to the grave) figure (2) below :

Life cycle analysis of the agricultural residues studied
Our life cycle assessment (LCA) study of the biomass from our agricultural residues will enable us to assess 3 environmental impacts, namely : -the impact on global warming ; -the impact on the depletion of non-renewable energy resources (fossil fuels); and -eutrophication. According to the ISO 14040 standard (International Standardization Organization 2006a), we are going to carry out the LCA of our biomasses through the application of 4 fundamental stages: the phase of defining the objectives and scope of the study, the impact inventory phase, the impact assessment phase and the results interpretation phase.

The phase of defining the objectives and scope of the study 2.4.1.1 LCA objective
The aim of our LCA study is to assess the environmental impacts associated with both the production and combustion of each of the agricultural residues studied in small cogeneration units in order to obtain electricity. The environmental performance of the various biomasses studied will then be compared with each other and with that of diesel fuel.

The functional unit (U F)
The functional unit U F is the production of one tonne (1t) of agricultural residues "from the fields to the boiler furnace" and its combustion to produce electricity "from the boiler furnace to the alternator of the cogeneration unit". And our results will be reduced to the production of 1 kWh of electricity from the biomass studied to allow comparison with diesel.

System boundaries
In our LCA study, we consider all the relevant stages in the life cycle of our agricultural residues that are likely to contribute to the consumption of resources and the emission of pollutants into the environment. We therefore consider the following stages: Production of agricultural waste: agricultural waste is collected from the fields and transported by lorry over short distances (50 km) from the fields to the cogeneration unit in the same area. The agricultural waste is then crushed using the cogeneration unit's mechanical crusher. Combustion of the shredded agricultural residues: initially to produce heat which will then be converted into electricity using the alternator of our cogeneration unit [1].

The target audience
This study will enable us to provide more information and arguments to decision-makers in international organisations, private or public companies and the governments of the various countries. In order to promote the installation of small cogeneration units to produce electricity in rural areas from the combustion of agricultural residues.

Inventory analysis
This inventory analysis will consist of quantifying the resources consumed and identifying the pollutant emissions into the environmental atmosphere. To do this, it will be important to quantify, for each stage identified when the system boundaries were drawn up, the flows of incoming and outgoing products, which will then make it possible to assess the resources consumed and identify the discharges into the environment.

Production of agricultural residues (from the fields to the boiler hearth)
One (1 t) tonne of agricultural waste is collected in the fields and then transported 50 km to the boiler hearth by a lorry, which will consume 39.5 MJ of diesel. According to the Gabi LCA software, which shows that transporting 1 tonne of product over a distance of 100 km by lorry consumes 79 MJ of diesel [13].

Combustion of crushed agricultural residues (from the boiler furnace to the alternator of the cogeneration unit)
The combustion of 1 tonne of each crushed agricultural residue in the furnace of our cogeneration unit will produce a certain amount of heat which will then be converted into electricity by turbines through electromagnetic induction phenomena. A number of gases and pollutants will then be released, including CO 2 , CH 4 , N 2 O, CO, COnV, SO 2 , PM 10 and PM 2.5 . a. Quantity of energy produced According to equation (  The quantities of heat resulting from the combustion of 1 tonne of each crushed agricultural residue were deduced. Then, with an efficiency of 50%, the cogeneration unit produces electricity [14] and the results obtained are presented in the table (5) below. The quantities (in ppm and ppb) of certain gases (CO 2 , CH 4 , N 2 O, CO) released into the atmosphere were obtained using MQ sensors connected to Arduino boards via a computer to detect, quantify and record these gases at regular intervals of 1 min, during the combustion of 0.5 g of each of the agricultural wastes studied in the adapted electric boiler. The results obtained represent the average of the various readings recorded for each gas released over a 2-minute period table (6) below. The table (6) above can be used to deduce the quantities of these atmospheric pollutants relative to the combustion of 1 tonne of each of the agricultural residues. And according to the balance equation for the complete combustion of methane, the results obtained are presented in the following table (7). . This is a more widely used methodology and is often considered to be more comprehensive.
-Impacts on global warming I RC The characterisation factor used to translate and express the various impacts on global warming of the substances used in this LCA study is the Global Warming Potential (GWP) over 100 years. Generally speaking, the Global Warming Potential (GWP) is defined by the integration, over a given period of time, of the radiative forcing (increase or decrease in the exchange of energy by radiation) generated by 1 kg of this gas, injected instantaneously into the atmosphere. The GWPi of a gas i is reduced to that of CO 2 and is calculated using the following equation:  -Impacts on the depletion of non-renewable energy resources I ER The impacts on the depletion of non-renewable energy resources used in this LCA study are represented by the Lower Calorific Value (LCV) expressed in (MJ/kg) of the non-renewable resource i consumed during the various stages of the LCA. The main indicator considered for IER will therefore be expressed in MJ.

-Eutrophication I E
This environmental impact is due to the significant presence of N and P type nutrients in the aquatic environment, which results in the development of algae to the detriment of certain less resistant biomass varieties. The CML 2001 method uses eutrophic power (EP) as a characterisation factor, measured with the indicator in PO 4 3equivalent units. This involves converting the N and P atoms contained in the (algal) biomass into equivalents. This impact will be calculated in our LCA study on the basis of the quantities of N and P atoms present in the SEM chemical analysis of the ash from our agricultural waste.

Impact assessment or calculation
To assess the environmental impacts of our LCA study of agricultural residues, we have chosen the OpenLCA LCA software, which is freely available and allows us to integrate the chosen method. We will be using the CML 2001 methodology to model the impacts of interest to us. All its scientific foundations are accessible and transparent [17]. Our OpenLCA LCA software, which incorporates the CML 2001 method, will enable us to identify and classify the resources and then the pollutant discharges identified during the analysis of the inventory into the environmental impacts to which they are linked. The software will then translate these resources and discharges into environmental impacts by multiplying their quantities by the characterisation factors included in the CML methodology, which relate to 3 environmental impacts (impact on global warming, impact on the depletion of non-renewable energy resources and eutrophication).The two pollutant gases used in this LCA study to calculate the impacts on global warming are carbon dioxide (CO 2 ) and methane (CH 4 ).The Table (9) below for the method used to calculate the impact.

Calculating the global warming impact I RC
The global warming impact I RC is calculated using the following formula: I RC = ∑ With, I RC : is the impact on global warming (measured in CO 2 equivalent) ; : is the quantity of substance "i" with a global warming impact (greenhouse gas) identified during the inventory analysis; : is the global warming potential of substance "i", identified during the inventory analysis and having an impact on global warming (measured in CO 2 equivalent). The table ( ) above shows the main substances contributing to global warming and their GWP over 100 years.

Calculation of the impact on the depletion of non-renewable energy resources I ER
The assessment of the impact on the depletion of non-renewable energy resources I ER is obtained by multiplying the quantities of non-renewable energy consumed by their energy content (PCI) according to the following formula: = ∑ With, : is the impact on the depletion of non-renewable resources (measured in MJ) ; : is the quantity of non-renewable resource (fossil fuels) "i" consumed and identified during the inventory analysis (measured in kg) ; : the Lower Calorific Value of the non-renewable resource i consumed and identified during the inventory analysis (measured in MJ/kg).
The table ( ) below shows the main non-renewable energy resources with their Lower Calorific Values (LCV) : : is the quantity of substance "i" released into the environment and contributing to eutrophication : is the eutrophying power of substance "i" contributing to the eutrophication impact (measured in PO 4 3equivalent). Thus table ( ) summarises the eutrophying powers of substances likely to produce N and P atoms that make up algal biomass.

Interpretation of the results
The phase of interpreting the results of the LCA study of our biomasses will enable us to draw conclusions from our study while proposing improvements and prospects for the continuation of our research. This part will be detailed in parts 3-results and discussion, then 4-conclusion and outlook.

Results and discussions about the chemical analysis of the ashes
Despite the low content of mineral matter and alkali or alkaline earth metals, the waste must be dried thoroughly before combustion in the boilers. And clean the hearths of the boilers after several combustions because these inorganic materials and alkali metals contained in the ashes can create problems of corrosion and agglomeration at a certain combustion temperature [20].

The results of the calculations of the environmental impacts during the production of energy from
waste 30% of total CO 2 emissions are used by plants for growth [21]. And the quantity of eutrophication generated by each agricultural waste is deduced by the phosphorus P content of their ash obtained through chemical analysis of the ash with the SEM.  To reduce our calculated impacts to the production of 1 kWh of electricity in order to allow comparison with those of diesel as suggested by the LCA methodology (same functional unit), the results obtained will be divided respectively by 5231,3953 and 3292 because 1 ton of each of agricultural waste (cocoa cortex, oil palm fibers and sugar cane bagasse) used produces 5231 kWh, 3953 kWh and 3292 kWh respectively. And The impacts linked to the production of 1 kWh of electricity from a generator using diesel are given by [22]. Then the results become those of the table (15) below : -in terms of impact on global warming Sugar cane bagasse has the highest value (0.19 (kg CO2 eq. / kWh)) of the 3 wastes. But the waste products (cocoa cortex, oil palm fibre and sugar cane bagasse) have respectively lower impacts (8 times, 6 times and 5 times) than diesel. These 3 agricultural residues are therefore more efficient than diesel.
-impact on the depletion of non-renewable resources Sugar cane bagasse has the highest value (0.012 (MJ/ kWh)) of the 3 wastes. But the waste products (cocoa cortex, oil palm fibre and sugar cane bagasse) have respectively lower impacts (128 times, 90 times and 75 times) than diesel. So these 3 agricultural residues perform better than diesel. This is because diesel is an exhaustible fossil fuel, whereas the 3 biomasses are renewable resources.
-eutrophication-related impacts Sugar cane bagasse has the highest value (0.9 (g PO 4 3-/ kWh)) of the 3 wastes and its impact is even greater than that of diesel (0.6 (g PO 4 3-/ kWh)). But the 2 other wastes (cocoa cortex and oil palm fibre) have considerable impacts of 0.38 and 0.40 (g PO 4 3-/ kWh) respectively. This means that P fertilisers are used to grow the raw materials that generate this waste. We therefore need to reduce the use of P and K fertilisers when growing the raw materials that generate this waste. After analysing the results of the 3 impacts taken into account in this LCA study, it would be advisable to use these 3 agricultural wastes to produce electricity with very good energy and environmental performance instead of fossil fuels (diesel, oil and coal) [1]. But there should be sufficient data to take into account the environmental impacts caused by other pollutants such as N 2 O, CO, COnV, SO 2 , PM 10 and PM 2.5 . And take into account spatio-temporal discernment and integrate determining local specificities in order to increase the environmental analysis performance of Conventional LCA [23].

Conclusion and outlook
This study, using LCA with OpenLCA software, could serve as a basis and a tool to help decision-makers (governments, private or public companies, national and international organisations and the general public) in eco-design for the implementation of energy production units (heat and/or electricity) based on the combustion of agricultural residues. This will encourage the creation of a biomass-based energy sector. This LCA study could in particular allow decision-makers (public and private) to have the necessary information in order to install cogeneration units to produce electricity from these 3 agricultural residues (cocoa cortex, oil palm fiber and sugarcane bagasse) in rural areas which are major producers of raw materials but are often not covered by the electricity grid. Thus, Côte d'Ivoire, the world's largest cocoa producer, could become the first largest producer of electricity from the combustion of cocoa cortex in the boilers of cogeneration units.