The system function and the functional unit

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Feedstock for pyrolysis

In the pyrolysis process, a broad variety of biomass feedstocks may be utilized. Bagasse (from sugar cane), rice husk, rice straw, peanut hulls, oat hulls, switchgrass, wheatstraw, sludge, and wood are examples of waste biomass feedstocks [4]. The moisture content of the feedstock, which should be less than 10%, is critical to the pyrolysis process. High quantities of water are generated at greater moisture contents, while reducing too much moisture content could cause the evaporation of volatile matter during drying process thus reducing quantity of bio-oil. Drying is required for high-moisture waste streams, such as sludge and other wastes, before they can be pyrolyzed.
The particle size of feedstock affects the efficiency and nature of the pyrolysis process. Because of the necessity for rapid heat transmission through the particle, most pyrolysis methods can only handle tiny particles up to 2 mm in diameter. The need for tiny particle size necessitates size reduction of the feedstock prior to pyrolysis.

Applications of bio-oil

Bio-oil is a dark brown liquid, and its density is significantly higher than that of woody materials, reducing storage and transportation expenses. Bio-oil cannot be used directly in conventional internal combustion engines. Alternatively, the bio-oil can be converted to a specific engine fuel or a syngas and subsequently bio-diesel through upgrading procedures. Bio-oil is especially appealing for co-firing since it is easier to handle and burn than solid fuel, and it is also less expensive to carry and store. Because of the simplicity of handling, storage, and burning in an existing power plant where additional start-up procedures are not required, bio-oil can offer significant benefits over solid biomass in certain situations. Bio-oil is also an important source of a variety of organic molecules and chemicals.

Importance of biochar

The increased awareness about climate change has thrust biochar into the spotlight. The combustion and breakdown of woody biomass and agricultural leftovers emits a significant quantity of carbon dioxide. Biochar may store CO2 in the soil, reducing greenhouse gas (GHG) emissions and increasing soil fertility. Aside from the potential for carbon sequestration, biochar offers various other advantages, which are outlined below.
• Biochar can improve available nutrients for plant development, retain water, and minimize fertilizer usage by limiting nutrient loss from the soil.
• Biochar lowers methane and nitrous oxide emissions from soil, hence lowering GHG emissions even further.
• Biochar may be used as a substitute for other biomass energy systems in a variety of applications.
• Biochar can be used as a soil amendment to boost the yield of plant growth.

Pyrolysis reactors

The reactor is the most important component of every pyrolysis operation. The heating system is a vital component of the manufacturing facilities. Several reactors have been built over the last two decades to accomplish this aim, depending on the heating system used. Table 1.3 summarizes the characteristics of fast pyrolysis reactors for bio-oil processing.
Researchers have investigated a variety of pyrolysis reactors, including fixed bed, bubbling bed, fluidized bed, cyclone bed, vacuum reactor, etc. [14,15]. Among these reactors, the fluidized bed reactor yields the most bio-oil because it can be used at lower temperature and high heating rate.

Absorption cooling system

The cooling cycle of single effect absorption cooling system is given in Figure 1.7. A heat medium (hot water) ranging from 70°C to 95°C from an industrial process, cogeneration system, solar energy, or other heat source powers the absorption cycle. The nominal thermodynamic performance of absorption chillers is given by the coefficient of performance or EER/Energy efficiency ratio which is the ratio between cooling energy obtained and thermal energy used. This coefficient is 0.7 for a typical absorption chiller. There are different types of refrigerant-absorbent pairs which can be utilized for absorption refrigeration systems. The most familiar pairs that provide acceptable thermodynamic performance and are environment friendly are lithium bromide-water and ammonia-water pair.
In this work, the working fluid of the absorption chiller is a solution of lithium bromide and water. The refrigerant is water, while the absorbent is lithium bromide, a harmless salt.

Modeling of absorption chiller in Aspen Plus

In the past, absorption chillers have been modelled and simulated in a number of programs, such as the one developed by Lazzarin et al [71]. Modern models are commonly developed in one of two softwares: Absorption simulation (ABSIM), developed by Oak Ridge National Laboratory [72] and Engineering Equation Solver (EES), developed at the University of Wisconsin [73–75]. When compared to actual data, EES modeling allows the user to compute thermo-physical parameters of working fluids with high accuracy [76].
Models for single and double effect water/lithium bromide and ammonia/water chillers were developed in Aspen Plus by Somers et. al. [77]. The model was coupled with a gas turbine as a waste heat source, and parametric studies were carried out for a variety of part load circumstances, evaporator temperatures, and ambient temperatures. For the water/lithium bromide solution, the ELECNRTL property technique was employed [78]. It is ideal since it was created exclusively for electrolytes solutions, making it advantageous to other robust but less specialized approaches like Peng-Robinson. The steamNBS property approach was utilized to determine the pure water states [79]. When the simulated results are compared to experimental data, the model shows an excellent agreement of within 5% for water/lithium bromide and 7% for ammonia/water. Finally, among the three models, the best chiller design was chosen, and an annual performance analysis was performed to assess the predicted cooling performance and energy savings. A range of cycle choices were investigated when the model was developed in Aspen Plus. The exhaust from a gas turbine was used as the waste heat resource.
Several other researches have been conducted to model the absorption chiller in Aspen Plus [80,81]. Using the Aspen Plus simulator, Darwish et al. [81] investigated the absorption refrigeration system (water/ammonia). The findings were compared to data generated by manufacturers and published in the open literature. COP (coefficient of performance), heat duties of the evaporator, absorber, and condenser, concentration in the ammonia weak and ammonia strong solutions, and flow rates of the ammonia weak solution and refrigerant vapor exiting the evaporator were all used in the analysis. The model findings and the experimental data were found to be in good agreement. The choice of Aspen Plus over other available programs to simulate the absorption chiller was principally motivated by two factors. First, Aspen chiller models might be immediately incorporated into the pyrolysis process. Second, Aspen Plus features an optimization capacity that will help in the development of a design that maximizes the energy savings.

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Life cycle assessment (LCA)

LCA is a technique for evaluating a product’s environmental performance across its whole life cycle, from raw material extraction to final disposal, including material recycling if necessary. The most common applications for an LCA are as follows:
• Identifying improvement possibilities in a product’s life cycle by identifying environmental hot spots
• Assessment of the contribution of each step of the life cycle to the total environmental load, generally with the goal of prioritizing product or process upgradation.
• For internal or external communication, as well as a foundation for environmental product declarations, product comparisons are useful.
• The foundation for life cycle management and decision reporting in businesses is the use of standardized metrics and the identification of key performance indicators.
Unlike traditional environmental analysis tools, this method has the advantage of focusing on the elementary stages of the life cycle of the product studied. Main approaches are listed below:
− The ‘cradle to grave’ analysis includes all the basic steps from the extraction of raw materials and resources to the disposal or reuse of the product.
− The ‘cradle to gate’ approach deals with the extraction of raw materials to the finished product (ready to be shipped or transported at the factory gate). The use and disposal phase are not included in this study.
− The ‘door to grave’ analysis where only the use and disposal phases are taken into account. Life cycle assessment (LCA) is a well-known technique that examines environmental implications over the whole life cycle of a product or service [82,83]. LCA is a complete monitoring of the energy and materials used in the product chain of items or systems, and is primarily used to compute the emission of each material and stage that finally forms the final product to the environment [84,85]. As a result, LCA assesses the aggregate possible environmental consequences [86]. The primary goal is to establish documentation and ameliorate the overall unfavourable environmental profile of the researched product or service [87].

Table of contents :

CHAPTER 1: LITERATURE REVIEW
1.1 Introduction
1.2 Fundamentals of pyrolysis process
1.2.1 Process Description
1.2.2 Feedstock for pyrolysis
1.2.3 Types of pyrolysis
1.2.4 Applications of bio-oil
1.2.5 Importance of biochar
1.3 Pyrolysis reactors
1.4 Modeling of pyrolysis
1.5 Exergy
1.6 Cost of bio-oil
1.7 Waste heat for Process cooling
1.7.1 Absorption cooling system
1.7.1.1 Process description
1.7.1.2 Generator
1.7.1.3 Condenser
1.7.1.4 Evaporator
1.7.1.5 Absorber
1.7.2 Important Features
1.8 Modeling of absorption chiller in Aspen Plus
1.9 Life cycle assessment (LCA)
1.9.1 Introduction
1.9.2 LCA of biofuel production systems
1.9.3 Previous studies
1.9.4 Methodology
1.9.4.1 The system function and the functional unit
1.9.4.2 Description of the scenarios
1.9.4.3 The limits and boundaries of the system
1.9.4.4 Data and assumptions
1.9.4.5 Life Cycle Inventory Analysis
1.9.4.6 Environmental impact assessment
1.9.4.7 Interpretation and recommendations
CHAPTER 2: METHODOLOGY
2.1 Experimental process overview
2.1.1 Feedstock handling and preparation
2.1.2 Pyrolysis
2.1.3 Solids preparation
2.1.4 Vapor Condensation
2.1.5 Product Yields
2.1.5.1 Bio-oil Composition
2.1.5.2 Non-condensable gases (NCG)
2.2 Lab-scale model development
2.2.1 Feedstock pretreatment
2.2.2 Pyrolysis
2.2.3 Condensers
2.3 Scaling up from lab to industrial scale
2.3.1 Industrial Scale
2.3.2 Industrial scale model development
2.3.2.1 Feedstock preparation (Area 100)
2.3.2.2 Crushing
2.3.2.3 Pyrolysis (Area 200)
2.3.2.4 Solids removal (Area 300)
2.3.2.5 Bio-oil Condensation (Area 400)
2.3.2.6 Refrigeration machine (Area 500)
2.3.2.7 Heat Generation (Area 600)
2.3.2.8 Electricity generation (Area 700)
2.4 Performance parameters
2.5 Economic analysis
2.6 Life cycle assessment
2.6.1 Goal and scope definition
2.6.2 Functional unit
2.6.3 System boundaries
2.6.4 Inventory analysis
CHAPTER 3: RESULTS AND DISCUSSION
3.1 Model validation
3.2 Industrial scale
3.2.1.1 Feedstock drying
3.2.1.2 Grinding
3.2.1.3 Fluidized bed reactor
3.2.1.4 Condensation
3.2.1.5 Heat Generation
3.3 Exergy analysis
3.4 Process performance
3.5 Economic assessment
3.5.1 Total project investment and operating cost
3.5.2 Sensitivity analysis
3.5.3 Monte Carlo sensitivity analysis
3.6 Life cycle assessment

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