i the waste, recover the energy and

i the waste, recover the energy and

i PROCESS SIMULATION OF THERMAL PRETREATMENT OF BIOFUEL PRODUCTION FROM PALM OIL EMPTY FRUIT BUNCH MOHAMMED AHMED OMAR BAHAMAT BACHELOR OF CHEMICAL ENGINEERING UNIVERSITY MALAYSIA PAHANGii ABSTRACT Oil palm is the most important product from Malaysia that has helped to change the scenario of its agriculture and economy. Lignocellulosic biomass which is produced from the oil palm industries include oil palm trunks (OPT), oil palm fronds (OPF), empty fruit bunches (EFB) and palm pressed fibers (PPF), palm shells and palm oil mill effluent palm (POME). However, the presence of these oil palm wastes has created a major disposal problem. The fundamental principles of waste management are to minimize and recycle the waste, recover the energy and finally dispose the waste. Moreover, lignocellulosic biomass is high moisture content, low bulk energy density and therefore difficult to be transported, handled and stored. It can also be easily subjected to fungal attack and biodegradation. The properties of biomass have affect the efficiency of utilization.

An appropriate method of thermal pretreatment which is drying will carry out to improve biofuel properties. Drying operation generally has high values of temperature and air flow, not only for the heating and also for reduction of moisture of the gas phase. Since, high moisture content fuels burn less readily and provide less useful heat per unit mass. Therefore, the aim of this study is to model and simulate the drying process which produces biofuel from oil palm biomass by steady-state simulation with Aspen Plus performed.

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Biomass is represented as lignocellulosic component which is hemicellulose, cellulose and lignin. By applying Aspen Plus different parameter such as temperature, residence time and moisture content are studied. Sensitivity analysis can be carried out to estimate the variation of some parameters that can influence product yield. The process simulation results will be compared with previous research for model validation purpose.

Once the process model is validated, the sensitivity analysis will be conducted to study the effect of several process parameters. The obtained result is expected to be useful in future design, operation, and optimization in drying process.iii ABSTRAK Minyak kelapa sawit merupakan produk penting keluaran Malaysia yang telah melakukan perubahan di dalam bidang agrikultur dan ekonomi. Biomassa lignoselulosa yang dihasilkan daripada industri kelapa sawit termasuk batang kelapa sawit (OPT), daun kelapa sawit (OPF), tandan buah kosong (EFB) dan gentian sawit (PPF), kelapa sawit dan kelapa sawit kelapa sawit (POME).

Walaubagaimanapun, kewujudan minyak kelapa sawit telah membawa kepada satu masalah yang besar. Prinsip asas pengurusan sisa adalah untuk mengitar semula dan mengurangkan sisa, memulihkan sumber tenaga dan akhirnya melupuskan sisa tersebut. Tambahan pula, biojisim lignoselulosa mempunyai kandungan kelembapan yang tinggi, tenaga ketumpataan pukal yang rendah yang membuatkan ia susah untuk diangkut, diuruskan dan disimpan.

. Ia juga senang diserang oleh kulat dan membawa ia ke arah biodegradasi. Ciri-ciri biojisim juga memberi kesan terhadap keberkesanan terhadap pengunaanya. Rawatan awal menggunakan haba seperti kaedah pengeringan dilihat sebagai kaedah yang sesuai dijalankan untuk meningkatkan ciri – ciri bio bahan api. Kebiasaanya, operasi pengeringan mempunyai kadar bacaan suhu dan aliran udara yang tinggi, ia bukan sahaja untuk tujuan penghabaan malah ia juga digunakan untuk mengurangkan kandungan kelembapan ketika di dalam fasa gas. Disebabkan kandungan lembap yang tinggi ia membuat kadar pembakaran adalah kurang dan menghasilkan haba yang tidak digunakan per jisim. Oleh itu, tujuan utama kajian ini adalah untuk mencipta model dan membuat simulasi dengan mengunakan Aspen Plus.

Hemiselulosa, selulosa dan lignin merupakan komponen lignoselulosa yang dianggap sebagai biojisim. Parameter yang berbeza seperti kadar suhu, masa dan kandungan lembap telah dikaji. Analisis telah dilakukan untuk mengenalpasti variasi di dalam parameter yang boleh memberi kesan terhadap produk yang dihasilkan. Bacaan atau keputusan yang diperoleh daripada simulasi yang telah dijalankan akan dibandingkan dengan kajian yang sebelumnya untuk tujuan pengesahan. Kesan untuk beberapa parameter yang lain turut akan dikaji setelah pengesahan telah siap dilakukan. Keputusan yang diperoleh daripada kajian dijangka akan digunakan untuk simulasi, operasi dan optimum dalam proses pengeringan.iv Contents ABSTRACT .

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…………………………………………………….. 1 1.2 Motivation …………………………………………………………………………………………………….. 2 1.3 Problem statement …………………………………………………………………………………………. 3 1.4 Objectives ……………………………………………………………………………………………………… 3 1.5 Scope of study ……………………………………………………………………………………………….. 4 CHAPTER 2……………………………………………………………………………………………………………….. 5 Literate review ……………………………………………………………………………………………………………. 5 2.1 Palm oil industry …………………………………………………………………………………………….. 5 2.1.1 Empty Fruit Bunch as energy potential …………………………………………………………….. 7 2.2 Biomass …………………………………………………………………………………………………………. 8 2.2.1 Woody biomass …………………………………………………………………………………………… 10 2.2.2 Non-woody biomass ………………………………………………………………………………. 10 2.3 Biomass Components ……………………………………………………………………………………. 11 2.3.1 Lignocellulose ……………………………………………………………………………………………… 12 2.3.2 Cellulose …………………………………………………………………………………………………….. 12 2.3.3 Lignin: ………………………………………………………………………………………………………… 13 2.3.4 Hemicellulose ……………………………………………………………………………………………… 14 2.4 Renewable energy ………………………………………………………………………………………… 14 2.4.1 Gasification …………………………………………………………………………………………… 15 2.4.2 Factors affect the performance of energy……………………………………………………….. 16 2.5 Drying………………………………………………………………………………………………………….. 19 2.5.1 Drying technologies ……………………………………………………………………………………… 20 2.6 Combustion …………………………………………………………………………………………………. 23 2.6.1 Combustion mechanism ……………………………………………………………………………….. 23 2.7 Factor affecting drying yield …………………………………………………………………………… 24 2.7.1 Temperature ……………………………………………………………………………………………….. 24 2.7.2 Residence time ……………………………………………………………………………………………. 25 2.7.3 Moisture content …………………………………………………………………………………………. 25 2.8 Biomass gasification reactor using Aspen Plus ………………………………………………….. 26v 2.8.1 The material and Method ……………………………………………………………………………… 26 2.8.2 Thermodynamic equilibrium models ……………………………………………………………… 27 2.8.3 Process description ………………………………………………………………………………………. 28 2.8.4 Stream specification …………………………………………………………………………………….. 29 2.8.5 Results and Discussion ………………………………………………………………………………….. 29 CHAPTER 3……………………………………………………………………………………………………………… 31 Methodology ……………………………………………………………………………………………………………… 31 3.1 Introduction …………………………………………………………………………………………………. 31 3.2 Study Method and Physical Properties ……………………………………………………………. 31 3.3 Case study ……………………………………………………………………………………………………. 32 3.4 Simulation description …………………………………………………………………………………… 35 3.4.1 Construct simulation flowsheet …………………………………………………………………….. 35 3.4.2 Selective components of material ………………………………………………………………….. 36 3.4.3 Chemical reaction ………………………………………………………………………………………… 37 3.4.4 Set the variable and condition ……………………………………………………………………….. 38 3.4.5 Result and analysis ……………………………………………………………………………………… 38 3.5 Assumption ………………………………………………………………………………………………….. 38 REFERENCES ………………………………………………………………………………………………………… 39vi LIST OF TABLES Table Title Page Table 2.3 Chemical composition of oil palm biomass. 12 Table 2.8 Specifications for the inlet streams in Aspen Plus 29 Table 3.3 Mass balance of EFB combustion of 60% moisture content. 34 Table 3.4 Analysis on the composition of EFB 37vii LIST OF FIGURES Figure Title Page Figure 2.1 Palm oil processing flow chart 6 Figure 2.2 Various type of biomass 9 Figure 2.4 Typical range of HHV for some common biomass fuels. 17 Figure 2.5 Process of drying biomass 20 Figure 2.6 Combustion mechanism 23 Figure 2.8 Flowsheet of biomass gasification process 28 Figure 3.3 Schematic of overall process 34 Figure 3.4 Flowsheet of process by Aspen Plus 36viii LIST OF SYMBOLS ?C Degree Celsiusix LIST OF ABBREVIATION EFB Empty Fruit Bunch OPF Oil Palm Found OPT Oil Palm Trunk POME Palm Oil Mill Effluent MC Moisture Content HHV Higher Heating Value LLV Lower Heating Value MIT Massachusetts Institute of Technology HP High Pressure FG Flue Gas BFW Boiler Feed Water SSD Super Steam Dryer HAD Hot Air Dryer1 CHAPTER 1 Introduction 1.1 Background of study Malaysia is the second largest-country producer of palm oil after Indonesia and play a key in the economy of Malaysia. The palm oil industry produces about 90 million tons of lignocellulosic biomass, including empty fruit bunches (EFBs), oil palm trunks (OPT), and oil palm fronds (OPF), as well as palm oil mill effluent (POME). Since Malaysia is agriculture based tropical country, many crops such as palm, rice and sugarcane are cultivated in this region (Hosseini & Wahid, 2014). Annually, a minimum of 168 million tonnes of biomass waste is generated in Malaysia. In general, palm oil waste accounts for 94% of biomass feedstock while the remaining contributors are agricultural and forestry by-products. It has been estimated that 85.5% of available biomass in the Malaysia comes from oil palm agriculture (Umar, Jennings, & Urmee, 2014). The solid oil palm residue is a biomass consisting of, by wet weight, 23.8 million tonnes (54%) of empty fruit bunch EFB, 13.2 million tonnes (30%) of shell, and 7.9 million tonnes (18%) of fiber (Junian, Makmud, & Sahari, 2015). The production of fuels and chemicals from biomass is not a new concept. Cellulose, ethanol, methanol and other biomass-derived chemicals have been in use since 1800 to make paint, glue adhesive, synthetic cloth and solvents (Demirba?, 2001). Biomass as one of the earliest energy sources appears to be the most promising renewable energy source due to its various resources and its environmentally sound properties. Furthermore, renewable and nuclear energy technologies are considered to be long term solutions, but renewable biomass has the ability to generate hydrocarbon- based liquid fuels directly which could approach carbon neutrality. According to the United National Conference on Environment and Development, biomass will potentially supply about half of the world primary2 energy consumption by the year 2050. Therefore, renewable energy, particularly biomass, has been recognized as an important part of any strategy to address the environmental issues related to fossil fuels and is becoming increasingly important for sustainable development (Abdullah, Gerhauser, & Bridgwater, 2007). However, Sources of biomass are quite diffuse and may not be available in sufficient quantities to make a national impact as an energy use (Saidur, Abdelaziz, Demirbas, Hossain, & Mekhilef, 2011). Thus, dependency on fossil fuel and coal as main energy sources is expected to remain in future due to its stability and low cost. Biomass Can be co-fired with conventional fossil fuels to reduce emissions and achieve economic benefit. The biomass wastes from the palm oil industry offer great potential for large-scale energy generation in Malaysia. In general, moisture plays an essential role on the characteristic and behavior of any organism derived material (Yan, Acharjee, Coronella, & Vasquez, 2009). Thermal pretreatment of drying heat process is important to evaporate moisture from biomass and a flow of air is used to carry out the evaporated moisture. 1.2 Motivation Due to the abundance and renewable nature of biomass, it seems to have a major share in future energy production to reduce energy dependence on fossil fuels. Fossil fuels are non-renewable energy and combustion for energy generation of fossil fuel release the most significant amount of greenhouse gas such as gas carbon dioxide (CO2) to atmosphere which contribute extreme changes in global climate (McKendry, 2002). Biomass become a new source since, it can easily be converted from its natural into concentrated high energy fuels such as biogas or a type of gas that is virtually identical to natural gas. These fuels are relatively clean burning when compared with fossil fuel in use today. Moreover, the cost of producing biomass for use as fuels and energy source is relatively cheap compared to the cost of finding and extracting fossil fuels. Development of oil palm industry in Malaysia also become a motivation of this research project, since the demand of energy increased in Malaysia and abundant of palm oil there, many industries3 start being concerned with using all resources from the oil palm in an optimal way, while at the same time reducing the environmental effect of the recycling systems in or outside of the mill (Chiew & Shimada, 2013). The main motivation of this research is to simulate drying process of palm oil empty fruit bunches (EFBs) to improve the quality of its biomass for combustion and gasification. 1.3 Problem statement The problem with combustion of EFB is high cost of thermal conversion since the volume of its biomass is high with high moisture. Thus, this process becoming increasingly expensive, which affected production profits (Chiew & Shimada, 2013). This study is focused on the drying process of EFB to reduce the moisture content, which will be a pre-treatment step to combustion process, EFB contain high moisture content which approximately (30-60%). Therefore, drying is crucial to decrease moisture to (10-15%) and improve the properties in terms of energy use. Moreover, to reduce costs of combustion process while still maintain the benefits of EFB, the pre-treatment is expected to improve the properties of EFB. Biomass with less moisture content will decrease the rates of biological deterioration, which lead to decrease quantities of insect and fungi since they may make a destruction on the biomass. Therefore, a modelling and simulation approach for thermal pre-treatment of EFB will be investigated in this work to gain depth understanding on the drying process. Simulation of drying process approximate a real-life situation using Aspen Plus software will help to study how the system work (Wainer & Giambiasi, 2001), and is easier for changing parameters without damage other real process. By applying Aspen Plus in this study, the percentage of moisture content can be determined and reduced by simulation process. 1.4 Objectives The objective of this research is to study the effect of drying Empty Fruit Bunch on combustion process4 1.5 Scope of study • Simulation of thermal pre-treatment process for reducing moisture content in EFB by using Aspen Plus software. • Vary temperature to evaporate moisture content. • Result validation of simulation result with experimental result. • Sensitivity analysis through case study.5 . CHAPTER 2 LITERATE REVIEW 2.1 Palm oil industry Palm oil was introduced to java by the Dutch in 1848 and Malaysia (then the British colony of Malaysia) in 1910 by Scotsman William Sime. Palm oil is one of the 17 major oils traded in the global edible oils and fats market. It has been consumed as food, from as long as 5000 years ago and today is found in one out of every ten food products worldwide. As one of the world’s largest producers and exporters of palm oil and its products, the Malaysian palm industry is the pride of the country (Basiron, 2002). Malaysia is the largest producer of palm oil in the world and has around 4.3 million hectares of oil palm plantation. The country also produces an average of 81.5 million tonnes of fresh fruit bunches. Among other contributors, palm oil industry represents the highest contributor of solid wastes and generates more residues during harvesting, replanting and milling processes. The residues that come from the milling processes are fruit fibres, shells and empty fruit bunches (EFB) which have good potential as energy resources. Other residues which include trunks and fronds are also abundant at the plantation area. These wastes are currently left on the ground or burned due to the inconvenience of handling and transporting the wastes to a proper site which are causing many environmental problems. For example, open burning is not only causing air pollution and green house effects but also creates other health issues. The Malaysian palm oil industry is basically export-oriented owing to the country’s small population base. The oil palm industry has been the backbone of Malaysia’s social and economic development. Since more than 90% of its production is exported, the industry is one of the top earners for the country, contributing about RM 3.18 billion in foreign exchange in 2006 (Mekhilef, Siga, ; Saidur, 2011).6 Palm oil like other vegetables can be used to create biofuel for internal combustion engines. Biofuel has been promoted as a form of biomass that can used as a renewable energy source to reduce the net emission of carbon dioxide into atmosphere. Therefore, biofuel is seen as a way to decrease the impact of green house and as a way of diversifying energy supplies to assist national energy security plans. Figure 2.1 illustrates the process of collecting fresh fruit bunches and the mills to extract palm oil. The is then transported to a local refinery for refining process. The refining process will further remove unwanted residue from and result in production of Refined Bleached Deodorized Palm oil (RBD) Palm Oil) which is fit for human consumption. After refining of CPO, RBD palm oil is obtained, likewise for palm kernel (the inner shell), RBD palm kernel is obtained. The RBD oils are products of downstream processing. Further blending and packing of these oils produces various types of downstream products. A refiner or manufacturer will then export these products to various users. Malaysia is relatively a small population and is unable to consume all the quantity processed locally, hence resulting in about 90 percent of export of Malaysian palm products. Figure 2.1 palm oil processing flow chart7 2.1.1 Empty Fruit Bunch as energy potential A palm oil plantation yields huge amount of biomass wastes in the form of empty fruit bunches (EFB), palm oil mill effluent (POME) and palm kernel shell (PKS). In a typical palm oil mill, empty fruit bunches are available in abundance as fibrous material of purely biological origin. EFB contains neither chemical nor mineral additives, and depending on proper handling operations at the mill, it is free from foreign elements such as gravel, nails, wood residues, waste etc. However, it is saturated with water due to the biological growth combined with the steam sterilization at the mill. Since the moisture content in EFB is around 67%, pre-processing is necessary before EFB can be considered as a good fuel. Unprocessed EFB is available as very wet whole empty fruit bunches each weighing several kilograms while processed EFB is a fibrous material with fiber length of 10-20 cm and reduced moisture content of 30-50%. Additional processing steps can reduce fiber length to around 5 cm and the material can also be processed into bales, pellets or pulverized form after drying. There is a large potential of transforming EFB into renewable energy resource that could meet the existing energy demand of palm oil mills or other industries. Pre-treatment steps such as shredding/chipping and dewatering (screw pressing or drying) are necessary in order to improve the fuel property of EFB. Pre-processing of EFB will greatly improve its handling properties and reduce the transportation cost to the end user i.e. power plant. Under such scenario, kernel shells and mesocarp fibres which are currently utilized for providing heat for mills can be relieved for other uses off-site with higher economic returns for palm oil millers. The fuel could either be prepared by the mills before sell to the power plants or handled by the end users based on their own requirements. Besides, centralized EFB collection and pre-processing system could be considered as a component in EFB supply chain. It is evident that the mapping of available EFB resources would be useful for EFB resource supply chain improvement. This is particular important as there are many different competitive usages. With proper mapping, assessment of better logistics and EFB resource planning can lead to better cost effectiveness for both supplier and user of the EFB.8 A covered yard is necessary to supply a constant amount of this biomass resource to the energy sector. Storage time should however be short, e.g. 5 days, as the product; even with 45% moisture is vulnerable to natural decay through fungi or bacterial processes. This gives handling and health problems due to fungi spores, but it also contributes through a loss of dry matter trough biological degradation. Transportation of EFB is recommended in open trucks with high sides which can be capable of carrying an acceptable tonnage of this low-density biomass waste. For EFB utilization in power stations, the supply chain is characterized by size reduction, drying and pressing into bales. This may result in significantly higher processing costs but transport costs are reduced. For use in co-firing in power plants this would be the best solution, as equipment for fuel handling in the power plant could operate with very high reliability having eliminated all problems associated with the handling of a moist, fibrous fuel in bulk. 2.2 Biomass Biomass consists primarily of the elements carbon (C), hydrogen (H), and oxygen (O). Additionally, signi?cant amounts of trace elements can be found in some types of biomass (Kaltschmitt, Thrän, ; Smith, 2002). Biomass is any organic matter—wood, crops, seaweed, animal wastes—that can be used as an energy source. Biomass is probably the oldest source of energy after the sun. For thousands of years, people have burned wood to heat their homes and cook their food. Biomass gets its energy from the sun. All organic matter contains stored energy from the sun. Typically, biomass is acclaimed as a ‘carbon neutral’ fuel as biomass is part of the bio-cycle in which the carbon dioxide produced from biomass combustion is consumed by cultivation of new crops. Biomass carry out photosynthesis and absorb sun energy to make cellulose from sugars. The energy will release when combusted and carbon dioxide is released as off gas is approximately equivalent to the amount of carbon monoxide that absorbed during photosynthesis process. In this case, it is show that the use of biomass energy has the potential to greatly reduce greenhouse gas Emissions (Gilbert, Alexander,9 Thornley, ; Brammer, 2014). This is the reason of burning biomass releases about the same amount of carbon dioxide as burning fossil fuels. However, fossil fuels release carbon dioxide captured by photosynthesis millions of years ago, in other words, an essentially “new” greenhouse gas (Joelsson ; Gustavsson, 2010). Therefore, biomass is a low carbon fuel and a form of sustainable fuel that offers significant reduction in net carbon emissions compared with fossil fuels (Chew ; Doshi, 2011). Majority of biomass for bioenergy feedstocks comes from three sources which is forests, agriculture and waste. Regardless of source, biomass materials can be generally classified into two broad categories which are woody and non-woody (Calle?, 2007). While forests provide only woody materials, agriculture sources provide both woody and non-woody biomass for bioenergy production. All of these are known as lignocellulosic biomass. There is also non-lignocellulosic biomass which is municipal solid waste, sewage sludge, and animal waste. Figure 2.2 show the picture of various type of biomass which includes rice straw, rice husk, paper mill waste, bark, sawdust, peat, wood chips and so on. Figure 2.2: Various type of biomass10 2.2.1 Woody biomass Woody biomass comprises mainly of products and by-products derived from the forest, woodland and trees sector. Woody biomass is the accumulated mass, above and below ground, of the roots, wood, bark, and leaves of living and dead woody shrubs and trees which is primarily comprised of carbohydrates and lignin produced through the photosynthetic process (Siccama et al., 2007). However, agriculture, as one might expect, are also a source of woody biomass. For example, fast-growing tree species such as hybrid willow and poplar have been developed for production in agricultural settings. Woody biomass not only can be used for producing biofuels for generating electricity, also can manufacturing biochemical such as adhesives, solvents, plastics, inks, and lubricants. (Hubbard, 2007). Depleting of fossil fuel and rising fuel costs, making woody biomass a great renewable natural energy alternative to replace fossil fuel. 2.2.2 Non-woody biomass Non-woody biomass includes agricultural crops, herbaceous products, animal waste as well as tertiary waste (Chew ; Doshi, 2011). Agriculture residue is one of the source of non-woody materials used to make bioenergy. These are the on-field by-products of the production of food, fiber or feed crops. Straw from cereals and rice, maize residues, stalks and leaves from oil seed crops are included in the category. Herbaceous biomass is considered as especially important since it can be used not only for the direct production of electricity or heat, but also for the production of liquid biofuels which is the one of the few options for a carbon neutral transport sector (Lichtfouse, 2011). Herbaceous biomass is considered as especially important since it can be used not only for the direct production of electricity or heat, but also for the production of liquid biofuels which is the one of the few options for a carbon neutral transport sector (Lichtfouse, 2011). When wood resources are unavailable, non-woody biomass for energy production were much more useful for generate energy.11 Secondary waste such as industrial waste and animal waste also known as non-woody biomass (Calle?, 2007). In recent, there are no full technology about utilization of animal waste and municipal waste for generation energy. However, it is a great improvement if fuel can be produced form these wastes successfully since the management of municipal and animal waste is well known as a global problem. 2.3 Biomass Components Biomass can be lignocellulosic materials or non-lignocellulosic materials. Lignocellulosic biomass is one of the most abundant biomass resources on the earth and can be used as a feed-stock for preparing fuels and chemicals. Lignocellulosic biomass composition plays a very important role in the performance and efficiency of both pre-treatment and biodegradation stages (Haghighi Mood et al., 2013). Lignocellulosic biomass is the fibrous and non-starch of the plant that consists mainly of cellulose, hemicellulose and lignin. Oil palm wastes used in this research project are known as lignocellulosic biomass (Anwar, Gulfraz, ; Irshad, 2014). The lignocellulosic composition of biomass can be seen in Table 2.1. With focusing of EFB, fiber and shell, the table show that the shell have the highest lignin composition which is 50.7% from the other while EFB have the highest cellulose and hemicellulose composition with 38.3% and 35.3% respectively. These compositions will influence the result of drying since different composition produce different product yield.12 Table 0.3: Chemical composition of oil palm biomass. Component Oil palm biomass chemical composition (wt.%) EFB Shell Frond Fiber Trunk Reference Saka,2005 Singh,1999 Khalil et al.,2006 Koba; Ishizaaki, 1990 Punsuvon et al.,2005 Cellulose 38.3 20.8 49.8 34.5 37.14 Hemicellulose 35.3 22.7 83.5 31.8 31.8 Lignin 22.1 50.7 20.5 25.7 22.3 Ash 1.6 1 2.4 3.5 4.3 2.3.1 Lignocellulose Lignocellulosic materials such as agricultural residues (e.g., wheat straw, sugarcane bagasse, corn stover), forest products (hardwood and softwood), and dedicated energy crops (switchgrass, salix) are recognized as renewable sources of energy. Typical wood plants consist of cellulose, hemicellulose, lignin, and some percentages of other substances, including minerals and organic extractives. 2.3.2 Cellulose Cellulose is the major structural components of plants, especially of wood and plant fiber. It is a linear polysaccharide of ?-D- glucose, and all residues are linked in ? (1?4) glycosidic bonds(de Oliveira Garcia, Amann, ; Hartmann, 2018). It is a crystalline material with an extended, flat, 2-fold helical conformation. Cellulose has hydrogen bonds which help maintain and reinforce the linear conformation of the chain. The degree of polymerization of cellulose is13 5 approximately 10,000 to 15,000 glucopyranose monomer units in wood and cotton, respectively. 2.3.3 Lignin: Lignin is a three-dimensional, highly branched, polyphenolic substance. It is an irregular array of variously bonded “hydroxyl-” and “methoxy-” substituted phenylpropane units (Schmer, Vogel, Mitchell, ; Perrin, 2008). It is often associated with the cellulose and hemicellulose to make lignocellulosic biomass. Softwood lignin are formed from coniferyl alcohol. Hardwood lignins have both coniferyl and sinapyl alcohol as monomer units. Grass lignin contains coniferyl, and sinapyl. It is an amorphous cross-linked resin, serving as cement between the wood fibers and a stiffening agent within the fibers.14 2.3.4 Hemicellulose Unlike cellulose, which is a polymer of only glucose, hemicellulose is a polymer of several simple sugars. This complex polysaccharide contains five carbon sugars (usually xylose and arabinose) and six carbon sugars (galactose, glucose, and mannose), all of which are highly substituted with acetic acid. Xylan, a xylose polymer, is the most abundant building block of hemicellulose. Hemicellulose is usually branched with DP ranging from less than 100 to about 200 units. Due to its branched nature, it is amorphous and thus relatively easy to hydrolyze to its monomer compared to cellulose. 2.4 Renewable energy Biomass is a renewable energy source because its supplies are not limited. We can always grow trees and crops, and waste will always exist. Biomass is a waste after pre-processing which provide feedstock for various conversion technologies to supply bioenergy or for other uses. Biomass is an endless resource which grown sustainable and can be converted into energy in the form of bio-gas, liquid fuel or processed solids by thermal, chemical, thermo-chemical and biochemical methods (Demirbas, 2005). Energy from biomass currently contributes 10–12% of gross worldwide energy. Due to geographical, economic, and climatic differences, the share of biomass energy in relation to total consumption differs widely among different countries, ranging from less than 1% in some industrialized countries like the United Kingdom and The Netherlands to signi?cantly more than 50% in some developing countries in Africa and Asia. It is by far the most important renewable15 energy source, being signi?cantly larger in energetic terms than the second largest, hydropower (Johansson ; Burnham, 1993). 2.4.1 Gasification Gasification is a thermal process of converting dry biomass feedstock into a mixture of gases that can be burnt in internal combustion engines and gas turbines. The use of producer gas to run internal combustion engine was first tried in around 1881. It was referred to as ‘suction gas’, because the gas was sucked by the engine from the gasifier. It was also known as ‘town gas’ or ‘coal gas’s. A variation of this gas (using steam or hydrogen instead of oxygen or air) is also known as ‘synthesis gas’ because a variety of chemical compounds can be made from it (Rapagnà, Jand, Kiennemann, ; Foscolo, 2000). The essential chemical species in all these gases are CO (Carbon monoxide) and H2 (Hydrogen), both of which burn to release heat. Town gas was predominantly used for street lighting in early European cities like London. It lost out to natural gas because it is highly poisonous due to the presence of carbon monoxide. Gradually the use of producer gas as a domestic fuel was taken over by cheaply available natural gas. The advent of petroleum further accelerated a decline in the need for producer gas. Gasification is the generic term to describe the technology of conversion of solid fuels into gaseous ones. Thus, there can be coal gasification or biomass gasification. Although both coal and biomass can be burnt directly to get heat energy, gasification of these fuels has certain advantages which cannot be achieved by direct burning. The main advantage of biomass gasification is that the resultant gaseous fuel can be used in an engine directly. Since gas engines are readily available, through biomass gasification one can produce electricity. It is certainly possible to get electricity from directly burning biomass, but that would require, first, a boiler for making steam and then a steam turbine. Environmentally, Biomass Gasification is a clean technology free of CO2 emissions, if well designed. Utilization of renewable energy sources makes it a sustainable energy system. Biomass Gasification has been receiving attention because of reduction of wood consumption up to 50%, environmentally sound16 technology, decentralized electricity generation, good use of domestic resources, savings in foreign currency in importing energy and easy to operate and maintain. The disadvantages can successfully be mitigated both by “good practices” and engineering measures. In developed countries, there is not much interest in small-scale decentralized electricity generation because of its high cost. However, co-firing, i.e. using biomass along with other fuels to reduce fossil fuel consumption is becoming very popular and this practice is responsible for the consumption of vast quantity of biomass. Developed countries like Brazil are more interested in liquid bio-fuels, bio-ethanol and bio-diesel. India is becoming a leading user of the small- scale version of this technology and many new designs are being innovated. Thailand is also experimenting with it. Bangladesh is an agrarian country and there is easy availability of agriculture-based mass, which can be used to generate energy. Burning this biomass directly is the oldest and also the least efficient method of generating energy. On the other hand, gasification of this mass is technologically viable and at the same time has the potential to replace the consumption of fossil fuel to some extent. In this study, the goal is to construct a downdraft biomass gasifier at laboratory scale and to check whether the required composition of producer gas can be achieved successfully. The construction of the gasifier is based on the design proposed by (Bhattacharya et al.2). 2.4.2 Factors affect the performance of energy 2.4.2.1 Heating Value The heating value, in units of MJ/kg or BTU/lb or cal/g, is one of the most important characteristics of a fuel because it indicates the total amount of energy that is available in the fuel. Heating value is mostly a function of a fuel’s chemical composition and can be expressed in two ways: the higher heating value (HHV) or the lower heating value (LHV). HHV is the total amount of heat energy that is available in the fuel, including the energy contained in the water vapor in the exhaust gases. LHV is the same as HHV except that it does not include the energy embodied in the water vapor. Generally, the HHV is the appropriate value to use17 for biomass combustion, although some manufacturers may utilize the LHV instead, which can lead to confusion. The HHV for coal ranges from 20 to 30 MJ/kg (8600-12900 Btu/lb). Nearly all kinds of biomass feedstocks destined for combustion fall in the “as-received” (not oven dry) HHV range of 15-19 MJ/kg (6450-8200 Btu/lb) with 15-17 MJ/kg (6450-7300 Btu/lb) for most agricultural residues and 18-19 MJ/kg (7750-8200 Btu/lb) for most woody materials. Figure 2.4.2.1 shows the typical range of HHV for some common biomass fuels. Note that wood (which has lower ash content) tends to have a slightly higher heating value than field crops. The HHV and LHV of wood fuel are shown in Figure 2.4.2.2 as a function of fuel moisture content Figure 2.4.2.1 Heat content of various fuels18 Figure 2.4.2.2 Typical biomass higher and lower heating value verse moisture content 2.4.2.2 Fuel Size and Density The particle size and density of biomass fuels are also important as they affect the burning characteristics, namely the rate of heating and drying during the combustion process. Fuel particle size also dictates the type of handling equipment required. The wrong size fuel will negatively impact combustion process efficiency and may cause jamming or damage to the handling equipment. Smaller-sized fuel is more common for commercial-scale systems because smaller fuel is easier to use in automatic feed systems and allows for finer control of the burn rate by controlling the rate at which fuel is added to the combustion chamber. Fuel particle size and density are probably the most overlooked factors affecting fuel performance and should be given careful consideration when selecting a fuel type. Bulk density is the mass of a material divided by the volume it occupies. Bulk density of granular materials is dependent on the manner in which it is handled. For example, freely settled material has a lower bulk density than tapped or compacted materials. 2.4.2.3 Composition In addition to heating value and moisture content, three other biomass properties are significant to biomass’ performance as a fuel: (1) ash content, (2) susceptibility to slagging and fouling, and (3) volatiles content. Ash content is the mass fraction of biomass composed of incombustibles mineral material. Grasses, bark, and field crop residues typically have much higher ash contents than wood. Systems that are designed to combust wood can be overwhelmed by the volume of ash if other biofuels are used. Slagging and fouling are problems that occur if ash begins to melt during combustion, forming deposits on combustor surfaces (fouling) or leaving hard chunks of glassy material in the bottom of the combustion chamber (slag, aka “clinkers”). Certain mineral components in biomass fuels, primarily silica, potassium, and chlorine, can cause these problems to occur at lower temperatures19 than normal. Many studies have observed that the high mineral content in grasses and field crops can contribute to fouling and clinkering—a potentially expensive problem for a combustion system. The timing of harvest can affect this property, with late harvested crops having noticeably lower ash content (Adler et al., 2006). Dirt contamination also adds to the mineral content and associated slagging and fouling problems, so it is important that biomass feedstock be as “clean” as possible. Slagging and fouling is minimized by keeping combustion temperatures low. Alternately, some biomass combustion equipment is designed to encourage the formation of clinkers but is able to dispose of the hardened ash in an effective manner. 2.5 Drying This is process in which heat is the dominant mechanism to convert the biomass into another chemical form. In this review, the drying process was presented as a technological-environmental alternative aiming for the thermal treatment of residues from different nature and origins. Drying is one of the unit operations that have the highest energy consumption in the chemical industry for the generation of heat. In order to guarantee a dry final product with the desired final moisture content, drying via air requires that the properties of ambient air, such as moisture and temperature, be altered (Perazzini, Freire, Freire, ; Freire, 2016). Drying operation generally requires high values of temperature and air flow, not only for the heating and reduction of moisture of the gas phase, but also to “carry” the vapor out of the material, which demands significant quantity of energy. Depending on the material to be dried, high temperatures of the drying air and high gas flow need to be used to evaporate the water contained in the biomass. The biomass wastes of organic origin and some inorganic ones have water bonded to their structure, once they are characterized as hygroscopic. Thus, the operational cost of drying may be very elevated for hygroscopic solid wastes, since a higher drying potential is needed, that is, high inlet air temperature and low air relative humidity, demanding greater energy in the system. Typically, raw biomass used20 for biofuel has moisture content of 60 70 wt%. Mechanical drying methods such as shredding, grinding, pressing, ?ltering, centrifuging or a combination of these processes are often applied to remove moisture level to around 50 wt%. Thermal drying methods with direct heating (hot air dryer, HAD) or indirect heating (superheated steam dryer, SSD) are often used to bring the moisture level to a lower level. In Figure 2.5.1 the air pass away through combustion process to increase the temperature of air, the heated flue gas is flow through biomass for drying then the biomass feed into gases process, is a considerable energy densification process, during which chemical energy transfers from the feedstock to the product. Figure 2.5.1 process of drying biomass 2.5.1 Drying technologies From biomass combustion to wood pellet and briquette production, drying your biomass can be a key step in your plant’s processing efficiency. Wood biomass dryers come in a variety of types, temperatures, and configurations. Canadian Biomass provides a comprehensive guide of the biomass drying technology available to help you in considering the best system for your particular application. All information is provided by the manufacturers. A. SWISS COMBI BELT DRYER21 The Swiss Combi belt dryer is a proven low-temperature belt dryer. It can use waste heat from other processes as a heat source. A wide variety of bulky biomass can be dried, such as sawdust, wood chips, and bark. Because of the low drying temperature, no significant volatile organic compounds are emitted. The multi-layer drying process (up to three layers) makes it possible to dry the product to 1% moisture content with excellent efficiency. It also minimizes dust emissions and allows full saturation of the drying air. This is because the lowest layer of material is wettest and acts as a filter. Swiss Combi has re-engineered its low-temperature Kuvo belt dryer. The new Kuvo is stronger, modularized, and can be manufactured more cost effectively. All components can be transported in standard size trucks or 40-foot containers. Module assembly on-site is fast and easy with no welding required. Inspection and maintenance access has been optimized. The lateral sealings have been improved for reduced air leakage and lower dust emissions. Depending on local requirements, various noise reduction concepts are available. B. ANDRITZ DRYING SOLUTIONS Andritz offers a complete range of biomass drying solutions, and technology is selected based on customer requirements, raw material, and available heating media. Belt dryers are the primary choice for low-value heat sources and are easily maintainable and cleanable. They use energy sources such as hot water, steam, hot oil, or flue gas. Pneumatic dryers are typical for lime kiln and boiler firing. Pneumatic dryers offer a high final dryness, exceeding 96%, and a high degree of milling for small particles and clear cut-off. These dryers are generally heated by waste gas flows. Rotary drum dryers are the technology of choice for high-value heat sources. They have very forgiving characteristics and good air circulation, which means low oxygen content. They offer simple operation and a high degree of automation, along with low exhaust gas flow and high energy efficiency. Fluid-bed dryers are suitable for particulate and granulate material. With or without an internal in-bed heat exchanger, the high heat transfer rate makes drying and cooling efficient.22 C. EARTH CARE DRYING SYSTEMS Earth Care Products offers drying equipment supply and engineering along with torrefaction technology. Its drying systems comprise proven state-of-the-art equipment with 38 years of continuous improvement, providing customers with some of the best and most efficient dryer systems available. Earth Care Products’ drying system starts with its patented Z8 dryer. This unit implements a reverse flow, eight-zone drum design for increased materials exposure to hot gas turbulence, increasing drying efficiency. The material passes through a single-pass section and then through a reverse flow, triple-pass section, and then repeats the process. The reverse flow design uses increasing velocity through the drum, creating more uniform drying of different particle sizes without overheating fine particles. This design has been shown to prevent volatile organic compound emissions from drying wood biomass. Earth Care Products provides simple dryer seals, wedged tracks, full tooth sprockets, stainless skin, and heavy-duty trunnions and drives for long service life. The company offers designed biomass burners to complement its Z8 dryer, along with full control packages and material handling equipment. D. BRUKS BED DRYER The Bruks bed dryer is intended for use in drying wood chips, sawdust, hogged fuel, and biofuels. Materials are spread evenly across a wide bed and pulled slowly and gently over a steel plate with small holes (no wire screens). Air is pushed through the holes under pressure, which drives the moisture from the bottom of the mat to the top. As the material moves through the dryer, large volumes of steam escape through the top of the mat, leaving the dried materials behind. An infrared moisture sensor monitors the dryer’s progress and controls the position of the final skimming screw that ensures the output moisture level. Low drying temperatures (120 ?C maximum) keep volatile organic compound and particle emissions to a minimum, making it possible to meet even the most stringent environmental permit limits without having to treat the exhaust air. The interior is fully accessible while the dryer is running.23 2.6 Combustion Biomass combustion simply means burning organic material. For millennia, humans have used this basic technology to create heat and, later, to generate power through steam. While wood is the most commonly used feedstock, a wide range of materials can be burned effectively. These include residuals and byproducts such as straw, bark residuals, sawdust and shavings from sawmills, as well as so-called “energy crops” such as switchgrass, poplar and willow that are grown specifically to create feedstock. Pelletized agricultural and wood residues are also an increasingly popular option because they are very easy to handle Biomass combustion is clearly a proven technology, but design improvements over the past couple of decades have helped to increase its efficiency, reduce emission levels and reduce costs. At the same time, the creation of professional certification programs for installers and inspectors has helped to boost the safety of biomass combustion systems. 2.6.1 Combustion mechanism For solid biomass to be converted into useful heat energy, it has to undergo combustion. Although there are many different combustion systems available, the principle of biomass combustion is essentially the same for each. There are three main stages to the combustion process as shown in Figure 2.6.1.24 Drying – All biomass contains moisture, and this moisture has to be driven off before combustion can take place. The heat for drying is supplied by radiation from flames and from the stored heat in the body of the combustion unit. Pyrolysis – When the temperature of the dry biomass reaches between 200 ºC and 350 ºC, the volatile gases are released. Pyrolysis products include methane carbon monoxide (CO), carbon dioxide (CO2), and too high a liquid molecular if cooled. Weight these compounds gases mix with oxygen from the air and producing a yellow flame. This process is self-sustaining as the heat from the burning gases is used to dry the fresh fuel and release further volatile gases. Oxygen has to be provided to sustain this part of the combustion process. Char is the remaining material after all the volatiles have been burned off. Oxidation – At about 800 ºC, the char oxidizes or burns. Again, oxygen is required, both at the fire bed for the oxidation of the carbon and, secondly, above the fire bed where it mixes with carbon monoxide to form carbon dioxide that is given off to the atmosphere. Long residence time for fuel in a combustor allows the fuel to be completely consumed. It is worth bearing in mind that all the above stages can occur within a fire at the same time. 2.7 Factor affecting drying yield There are several factors affect the drying yield. To construct effective drying process, there are necessary to study these parameters since process optimization depend on them. Several of the major factors affecting yield reported in the literature are described below. 2.7.1 Temperature Compared to all of the factors affecting drying process, the temperature effect of drying temperature was largest, emphasizing the importance of temperature and temperature process control Significant interaction effects between temperature and time were determined for mass yield, energy yield and energy density. Most of the25 literature defines 200 to 300 °C as the range for drying temperature but currently there is no definition of temperature range. According to work of Gucho et al., 2015, drying of beech wood and miscanthus (sinensis) was carried out to study the influence of drying temperature (240– 300 °C). There is an increase in energy density of 14% for beech wood and 18% for drying from 240 ? 300? During heating, the releasing volatile gas and other hydrocarbons. The energy density increases with drying temperature because C/H and C/O ratios increase with rising temperatures. 2.7.2 Residence time Residence time is the average amount of time that a particle spends in a particular system which will affects the yield of drying Basically, residence times reported have generally been relatively long which is between 30 minute and 3 hours. However, in commercial scale, as reactor size increase with increased residence time. From the work of, effect of residence time on the properties of corn stalk was studied. It can be said that when the residence time increase the energy and mass yield decrease (Poudel & Cheon Oh, 2014). This due to removal of the moisture content and volatile matter content of the biomass during drying. At the beginning of the drying, there was a significant mass loss. However, the effect of residence time become not significant after 10 min because more reactive components are decomposing at the beginning of the drying while with a longer drying time, the mass loss can be attributed to the decomposition of the less reactive component (Sadaka & Negi, 2009). The HHV also increase with an increase in the drying time. 2.7.3 Moisture content Moisture content is one of the easier biomass properties to measure and can make the difference between a good and a bad fuel. High moisture fuels burn less readily and provide less useful heat per unit mass; this is because water itself provides no energy value and much of the energy in the fuel is used up to heat and vaporize water (Jenkins, Baxter, Miles Jr, & Miles, 1998; Schmer et al., 2008). On the other hand,26 extremely dry fuel can cause dust problems, leading to equipment fouling and potential explosion hazards. Moisture content can be calculated on two bases: wet or dry. In wet basis calculations, the moisture content is equal to the mass of water in the fuel divided by the total mass of the fuel. In dry basis calculations, the moisture content is equal to the mass of water in the fuel divided by the mass of the dry portion of the fuel. It is important to know which type of calculation is being used, as the two values can be quite different. For example, a 50% wet basis moisture level is the same as a 100% dry basis moisture level. Air-dried biomass typically has about 15-20% moisture, whereas the moisture content for oven-dried biomass is around 0%. Moisture content is also an important characteristic of coals, varying in the range 2-30%. The practical maximum moisture level for combusting fuel is about 60% (wet basis), although most commercial equipment operates with fuels that only have up to about 40 % moisture. 2.8 Biomass gasification reactor using Aspen Plus 2.8.1 The material and Method Aspen Plus is a market-leading comprehensive chemical process modeling tool, used by the world’s leading chemistry organizations and related industries. It originated from a joint project called Advanced System for Process Engineering (ASPEN) which is started by the Massachusetts Institute of Technology (MIT) and the US Department of Energy in the 1970’s and finished in 1981. AspenTech was founded in the same year and the ASPEN project was commercialized by AspenTech called Aspen Plus (Sills et al., 2012). Aspen Plus is used in the industrial chemical process modeling, simulation, optimization, sensitivity analysis and economic evaluation. It provides the comprehensive physical property models and the library of unit operation models, fast and reliable process simulation functions, and advanced calculation method. With the physical property database and the operation models provided by Aspen Plus, engineers are able to simulate actual plant behavior effectively and accurately thereby improve the productivity and reduce the costs. Aspen Plus has been widely used for simulating coal conversion. Literatures like coal gasification simulation,27 coal hydrogasification processes and integrated coal gasification combined cycle (IGCC) power plants have been already published(Nikoo & Mahinpey, 2008). There are also detailed guides about modeling and simulation coal conversion published by AspenTech. However, there are not many researches related to the modeling and simulation of biomass gasification process in a dual fluidized-bed gasifier. 2.8.2 Thermodynamic equilibrium models The basic principle of using thermodynamic equilibrium models is the equilibrium state gives the maximum conversion under certain conditions. In these models, the reactions are considered to be zero-dimensional and they are independent with time. The reaction kinetics and the reactor hydrodynamics are not considered in the thermodynamic equilibrium models. The stoichiometric and nonstoichiometric methods are used to determine the thermodynamic equilibrium. Because biomass gasification involves a series of complex reactions, the stoichiometric model is not suitable for this situation as every reaction should be considered in this model. The nonstoichiometric method is frequently used when simulating gasification process using Aspen Plus. For nonstoichiometric method, the reacting system has minimum Gibbs free energy when the equilibrium is reached. This method is also called Minimization of the Gibbs free energy method. The advantage of minimization of the Gibbs free energy method is no specific reaction mechanism is needed to solve the problem, only the elemental composition of the feed is needed for the input, which can be obtained from its ultimate analysis (Basu, 2013). Therefore, the nonstoichiometric method is particular suitable for biomass gasification simulation as the exact chemical formula of biomass is unknown and the gasification reaction mechanisms are very complicated. Ramzan et al. simulated a fixed-bed gasifier using the minimization of Gibbs free energy method for the modeling (Ramzan, Ashraf, Naveed, & Malik, 2011).28 2.8.3 Process description In Aspen Plus, there is no particular gasifier model ready for use, therefore to model a dual fluidized-bed gasifier, it is necessary to separate the whole process into different blocks that can be simulated with the existing models provided by Aspen Plus. Biomass is fed as a non-conventional component into a decomposition reactor-PYR which converts the biomass into conventional components by calculate its ultimate analysis and proximate analysis. Heat Q1 is supported for the decomposition process. A calculator is used to determine the yield of the components. Then the decomposition mixture goes into a separator-SEP where a portion of char is separated and flows into the combustor. The char is combusted in the combustor-COM with excess air, the heat Q is generated to support the endothermic reactions in the gasifier-GASIFIER. The split fraction of char is varied until the gasification temperature is reached at certain degrees. The rest of char with gases from the separator-SEP are fed in the presence of steam into the gasifier-GASIFIER where the gasification takes place. Therefore, the RGIBBS reactor provided in Aspen Plus was chosen as a gasifier. The outlet stream from the gasifier is expressed as AFT-GAS. Figure 2.8: flowsheet of biomass gasification process29 2.8.4 Stream specification The detailed specifications for biomass, air, steam, and Q1 as feed streams are listed in Table 2.8. Table 2.8: Specifications for the inlet streams Stream Components Temperature Pressure Mass flow rate Biomass Specified as its ultimate, proximate and sulfur analysis 25 ? 1 atm 2000 kg/h Air 21% O2 79% N2 (Volume fraction) 450 ? 1 atm Air to biomass ratio is 1.12 Steam H2O 450 ? 1 atm Steam to biomass ratio (S/B) is 0.6 Q1 – 25 ? – 2.8.5 Results and Discussion Sensitivity analysis of Steam temperature: In this case, steam temperature was varied from 150-1000 ? while other parameters remained unchanged. The syngas composition, gasification efficiency, char split fraction and the LHV of syngas were studied. For all the syngas compositions results, the compositions are given in volume fraction, dry and NH3,H2S,HCl free. As the steam temperature increases from 150-1000 ?, CO rises from 33.69% to 34.56%. Both H2 and CO2 decrease. H2 drops from 57.00% to 56.66% and CO2 from 9.18% to 8.64%. Both CH4 and N2 contents are very low. (0.05% and 0.08%). The effect of the steam temperature on the char split fraction when the steam temperature increases from 150 to 1000 ?, the char split fraction decreases from 0.137 to 0.108. This is because the heat required for the gasification is reduced, the reduced heat is provided by the heated steam. Therefore, less char is needed for the combustion, which means more char is gasified and more syngas is produced.30 Sensitivity analysis of Air temperature: In this case, air temperature was varied from 25-1025 ? while other parameters remained unchanged. The syngas composition, gasification efficiency, char split fraction and the LHV of syngas were studied. the effect of the air temperature on the syngas composition (vol. % dry basis). As the air temperature increases from 25-1025 ?, CO rises from 33.13% to 35.20%. Both H2 and CO2 decrease. H2 drops from 57.21% to 56.41% and CO2 from 9.52% to 8.25%. Both CH4 and N2 contents are very low. (0.05% and 0.08%). The effect of the air temperature on the char split fraction when the air temperature increases from 25-1025 ?, the char split fraction decreases from 0.155 to 0.087. This is because the heated air supplied a part of heat required in the gasifier. Therefore, less char is needed for the combustion, which means more char is gasified and more syngas is produced. The results show that preheating air is more effective than preheating steam. Therefore, preheating the air is more recommended than preheating the steam. If excess heat is available, the air should be preheated. The effect of the air temperature on the LHV of the syngas when the air temperature increases from 25-1025 ?, the LHV of the syngas increases from 10.38 to 10.56 MJ/Nm3 . The effect of the steam temperature on the gasification efficiency is illustrated when the air temperature increases from 25-1025 ?, the gasification efficiency increases from 74.32% to 81.31%. Sensitivity analysis of Steam to biomass ratio (moisture content): In this case, steam to biomass ratio was varied from 0.3-1.0 while other parameters remained unchanged. The syngas composition, gasification efficiency, char split fraction and the LHV of syngas were studied. As the steam to biomass ratio increases from 0.3-1.0, CO drops from 43.25% to 26.33%. Both H2 and CO2 increase. H2 increases from 53.55% to 59.40% and CO2 from 2.79% to 14.17%. Both CH4 and N2 contents are very low. (0.32%-0.02% and 0.08%). The effect of the steam to biomass ratio on the char split fraction demonstrate with the steam to biomass ratio increases from 0.3-1.0, the char split fraction decreases from 0.122 to 0.136. The effect of the steam to biomass ratio on the gasification efficiency is when the steam to biomass ratio increases from 0.3-1.0, the gasification efficiency decreases from 83.65% to 71.31%.31 CHAPTER 3 METHODOLOGY 3.1 Introduction In this work, Aspen Plus V9 will be used to model and simulate the drying process of oil palm waste. Before running simulation, data collection should be done for general understanding of the processes and as input data for Aspen Plus software. This simulation flowsheet will be developed using cause study from previous research published is open literature. The process simulation results will be compared with previous research for model validation purpose. Once the process model is validated, the sensitivity analysis will be conducted to study the effect of several process parameters such as temperature and residence time on the moisture content. Several case studies will be conducted to obtain the optimum process operation. Analysis of the product of dry EFB will be carried out. The obtained result is expected to be useful in future design, operation, and optimization in drying process. 3.2 Study Method and Physical Properties The Aspen plus model for a drying process can be developed for the calculation of mass and energy balance which is very useful in analysis of process. Sensitivity analysis can be carried out to estimate the variation of some parameters that can influence product yield. The Aspen Plus simulation tool is applicable for simulation of the combustion processes. The most common way is to simulate the combustion using gasification technology, which applies Gibbs free energy minimization to calculate equilibrium. The reactions in the gasification process are complex and by using the Gibbs reactor, it is not necessary to specify the stoichiometry or the reaction rates. However, reactions that describe the major conversion rates in a gasifier can be extracted from the literature.32 The PK-BM property method was selected as the global property method for this model. This method uses the Peng Robinson cubic equation of state with the Boston-Mathias alpha function for all the thermodynamic properties, which is suitable for the nonpolar or mildly polar mixtures such as hydrocarbons and light gases. The PK-BM property method is recommended for the gas processing, refinery, and petrochemical applications (Boston & Boys, 2000). Since biomass and ash were defined as nonconventional components, only the density and enthalpy were calculated during the simulation. HCOALGEN was selected as the enthalpy model for both biomass and ash, the density model was DCOALIGT. Different empirical correlations for heat of combustion, heat of formation and heat capacity are included in the HCOALGEN model. 3.3 Case study The base case study it assumed 280,000 tonnes/yr raw EFB with 60 wt% moisture is dried and combusted to drive the steam power plant. the annual operation hour is assumed to be 8000 hours which corresponds to 35,000 kg/h EFB of 60% MC based on the EFB composition, the combustible in dry and ash free basis and the amount of ash were found to be 13,359 kg/h and 641 kg/h respectively(Adler, Sanderson, Boateng, Weimer, & Jung, 2006). The theoretical air to fuel ratio is at 2.3025, with a 20% excess air for the combustion applied to all cases, the actual air to fuel ratio in this study is 2.763 and correspond to 96,719 kg air/h. The dry-air used in this study is assumed to contain oxygen and nitrogen of 21 mol% and 79 mol% respectively. This, at the same time, corresponds to a mass fraction of oxygen of 23.3 wt%. Therefore, Nitrogen and Oxygen are contributing 74,182 kg/h and 22,536 kg/h respectively. In the combustion, CaCO3 is added to remove SO2 and the amount of CaCO3 fed is 77.74 kg/h (Bruce & Sinclair, 1996).33 The moisture content of EFB is 60 % and it will apply mechanical drying to reduce moisture content to 48 % then thermal drying to reduced it to 10 %. EFB is ?rstly dried by mechanical drying from initial moisture content of 60 wt% to 48 wt% and is followed by Hot Air Dryer HAD to further reduce the moisture content to an optimal value of 10 wt %before combustion. After the mechanical drying, the EFB is fed into the HAD at a rate of 26,923 kg/h. The amount of water remaining in the EFB after drying by HAD is 1555.56 kg/h and therefore the mass of water removed through this process is 11,368 kg/h. Based on the speci?c heat capacity of water and EFB and also the known heat of vaporization of water being 2357.62 MJ/kg, a total heat of 8.46 MW is required to dry the moist EFB and preheat it to 28.78 ?C. The mass ?ow rate of hot air consumed for the drying is found to be 465,803 kg/h and the ultimate wet air leaves the dryer at 38.78 ?C. Since the air extracted from atmosphere is at 32 ?C, the heat extracted from low-pressure steam to preheat hot air to 100 ?C is 9.04 MW (ang, Li, Wang, Li, & Jiang, 2007). In this case, 35,000 kg/h EFB with 60 wt% moisture is fed directly to the boiler for combustion. it can be estimated that the wet EFB carries a HHV of 7.55 MJ/kg. Based on the energy balance of the boiler, the total energy ?ow of the fresh EFB is 264,335.99 MJ/h. Therefore, the overall heat generated by the combustion is 73.43 MW. By assuming the stack temperature at 200 C, the stack loss is estimated as 21.462 MW and the rest 47.66 MW are used for HP steam generation at the boiler. An overall schematic diagram of the overall process is given in Fig. 3.3 of which dried EFB is burned in a Boiler producing Flue Gas, High Pressure Steam (HP) and Ash. The results of the individual components were summarized in Table 3.3.34 Figure 3.3: Schematic of overall process Table 3.3: Mass balance of EFB combustion of 60% moisture content. Composition RAW EFB AND AIR FEED (Kg/h) ASH (Kg/h) FLUE GAS (Kg/h) C3657H4810N39S5O2258K9C 13,359 – Ash 641 641 K – 55 Cl – 6 N2 74,182 – 74,182 O2 22,536 – 3,744 CO2 – – 25,053 NO2 – – 279 H2O 21,000 – 27,731 CaCO3 77.74 – CaSO4 – 105.73 Total mass flow (kg/h) 131,797 807 130,98935 3.4 Simulation description Figure 3.4: process flow chart From previous case study we can now apply the methodology to start the simulation by following these descriptions. 3.4.1 Construct simulation flowsheet Fig. 3.4.1 shows the simulated ?owsheet of the steam power plant using Aspen Plus of which the duties of HAD, SSD and the boiler are input. The red and blue colors in indicates HAD and SSD respectively. Selective component of materials Chemical reaction Set the variables and condition Result and analysis Construction simulation flowsheet36 Fig. 3.4.1 Flowsheet of process by Aspen Plus 3.4.2 Selective components of material The feedstock chosen consisted of raw empty fruit bunch (EFB) at 25°C. At the beginning of simulation, all the components were specified properly. Because the uncertainty of exact formulas of biomass and ash, they were defined as nonconventional solid components. For other components is defined as H2, Co2, O2, N2,Co,H2O, CH4 and Ash. For these components, only enthalpy and density were calculated during the simulation. Aspen Plus includes special models for estimating both enthalpy and density for coal-derived materials. These models can be used to estimate biomass properties as well since biomass can be considered as coal-derived material. More details will be discussed in the next section. The analysis on the composition of EFB in weight percentage can be summarized in the Table 3.437 Table 3.4 analysis on the composition of EFB 3.4.3 Chemical reaction Below is the generalized formula for a combustion reaction Equation 3.1: ������+��������?��2+��2�+������� Since biomass fuels are primarily composed of carbon, hydrogen and oxygen, the main products from burning biomass are carbon dioxide and water. Flame temperatures can exceed 200 °C, depending on the heating value and moisture content of the fuel, the amount of air used to burn the fuel and the construction of the furnace. Combustion has three requirements fuel, air and heat. If any of these three are removed, burning stops. When all three are available in the correct proportion, combustion is self-sustaining, because the fuel releases excess heat to initiate further burning. Complete combustion of biomass requires a certain amount of air. Air consists of 21 percent oxygen and about 79 percent nitrogen. Therefore, the product of a stoichiometric combustion of biomass in air will include carbon dioxide, water vapor and nitrogen. reaction will generate heat. ���������+�����?��2+��2�+�2+������t38 3.4.4 Set the variable and condition Difference parameter can be studied such as temperature, residence time and moisture content. The pressure for all unit operations are set at 1 atm, and the temperature will increase from the initial until reach desired moistures content. 3.4.5 Result and analysis The result of simulation may hold some errors in order to ensure the accuracy in process. Thus, the results will be compared and analyzed with previous simulation process. This simulation will modify to get better results and more accurate. 3.5 Assumption The following assumptions were made in order to simplify the model: o The product particles have a fixed geometry and their dimensions remain unchanged for the whole drying process. o The moisture content of the raw material is assumed to be a typically high value of 60%. o The mass flow of air remains constant through the whole dryer. o Perfect mixing and constant temperature are assumed in each block. o For each control volume, the inlet flow rate of product is equal to the outlet flow rate of product from the previous control volume. o There is no constant-rate period, that means that drying happens during the falling-rate only. o Operation at atmospheric pressure, pressure drops are neglected o The system is isothermal and operates under steady state conditions.39 REFERENCES Abdullah, N., Gerhauser, H., & Bridgwater, A. (2007). Bio-oil from fast pyrolysis of oil palm empty fruit bunches. 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