Pilot Projects Developed With Selected ESTs

Transcription

1 Project on Converting Waste Agricultural Biomass to an Energy / Material Resource Report VI Pilot Projects Developed With Selected ESTs Prepared by National Cleaner Production Center Sri Lanka February 2010

2 CONTENT 1. INTRODUCTION Background Sustainable Assessment of Technology (SAT) Methodology Ranking of Technology Options SELECTION OF THE TECHNOLOGY FOR PILOT IMPLEMENTATION PROJECT BASIC SYSTEM CONFIGURATION AND OPERATION System Configuration Basic Operation DESIGN PARAMETERS AND SYSTEM SIZING Basic Design Parameters Paddy Husk Stove Heat Exchanger and Exhaust System Drying Chamber Blower and Process Air Distribution System FINANCIAL ANALYSIS 22 References 24 Appendix 25

3 1. INTRODUCTION 1.1 Background Today, the concept of sustainability has become a necessity in the development process of a country due to various issues emerged in the past, especially with relation to the adverse effects on environment and depletion of natural resources. One of the key aspects considered under sustainable development is in relation to the waste management where the concept of 3R Reduce, Reuse and Recycle is introduced. In line with this concept, the project on Converting Waste Agricultural Biomass to a Fuel / Resources implemented in the Moneragala District, Sri Lanka has been initiated, especially targeting to develop a pilot demonstration project in which a local waste material is converted into a value added product or material. It is expected that the relevant technology intervention would minimize the social and environmental issues arisen due to present waste management practice while generating additional income to the local community. The following project activities have been developed for the implementation of the project: Activity 1: Formation and manage a project team, Activity 2: Characterize qualitatively and quantitatively the agro-residues available, Activity 3: Identify potential applications/users of agro-residues including market potentials, Activity 4: Identify, assess and characterize environmentally sustainable technologies (ESTs) related to conversion of agro-residues, Activity 5: Select a set of most viable resource-technology combinations and rank them based on potential of implementation and social & environmental impacts, Activity 6: Develop a pilot project based on a selected resource-technology combination. The first five activities have been completed and the relevant details and results are presented in the first and second progress reports [1], [2]. The study is confined to two divisional secretariats in Moneragala district: Moneragala DS division and Buttala DS division. The agricultural residues and other biomass wastes identified as potential resources in the selected regions include paddy husk, paddy straw, sawdust, banana waste, market waste and wild guinea grass. Both present utilization pattern/availability and future generation potentials are predicted. The technologies available for converting the agro-residues and other wastes for different applications (both conversion to energy and material) are highlighted. Finally, waste 2

4 conversion technology options are selected and ranked with the objective of identifying the most appropriate technology option(s) for the pilot implementation project. The technology evaluation and ranking methodology and process are presented in the next section. 1.2 Sustainable Assessment of Technology (SAT) Methodology As there are several type of biomass residues as well as number of technology options are available for each type of application, selection of the most appropriate resource-technology combination is not an easy task. In fact, as the project is implemented under the concept of sustainable development, the choice of technology too should follow the same philosophy of addressing the economic, environmental and social factors with due emphasis on each. The methodology selected for the present project, the Sustainable Assessment of Technology (SAT), is fundamentally the integration of sustainable development in technology assessment, i.e. integration of three important aspects: environmental soundness, social/ cultural acceptability and economic feasibility. This methodology is built on existing technology assessment framework and could be adapted to local conditions, parameters and constraints. It uses a progressive assessment procedure through tiers on screening, scoping and detailed assessment allowing entry points for diverse stakeholders and optimizing information requirements. Another important characteristic of SAT methodology is that it operates both strategic and operational levels, addressing thereby choices to be made on a more robust basis. It is also a quantitative procedure that allows more objective assessment, sensitivity analyses and incorporation of scenarios. Further, SAT methodology comprises of Plan-Do-Check-Assessment milestones that incorporate feedbacks and learning encouraging continuous improvement [3], [4]. In the present study, the SAT methodology is applied to evaluate different technology options and finally rank then based on their scores under several criteria, as briefed in the next section. 1.3 Ranking of Technology Options The technology options identified through preliminary analysis were undergone a screening process in order to select for more detailed analysis at the scoping level. Table 1 presents the basic information of fourteen technologies selected for the scoping analysis (among thirty six technologies identified for screening), including the waste type, application, technology and equipment. 3

5 Table 1.1: Technologies Selected for Scoping Analysis Residue Application Technology Equipment Paddy Value addition to (A) Briquette making Briquetting machine Husk 1 residue as a fuel Domestic cooking (B) Direct combustion Paddy husk cook stove (C) Gasification Paddy husk gas stove Process heat for lime smoking (D) Direct combustion / Direct heating Paddy husk stove cum cabinet dryer Process heat for fruit and vegetable drying (E) Direct combustion / Indirect heating Paddy husk stove cum tray dryer Process heat for tobacco curing (F) Direct combustion / Indirect heating Tobacco barn Conversion to (G) Carbonization Basket burner cement extender Saw Value addition to (H) Briquette making Briquetting machine dust residue as a fuel Domestic cooking (I) Direct combustion for cooking Improved saw dust cook stove with multi-fuel capability Manufacture of Particle boards (J) Pressing Series of equipment including chipper/press Manufacture of Medium density (K) Pressing Series of equipment including chipper, boiler, press, etc. fibre board(mdf) Market waste Cooking and lighting (L) Biogas generation Biogas digester Continuous type Fertilizer (M) Composting Only hand tools for the Banana Rejects Off-grid electricity generation (N) Biogas generation handling of waste Biogas digester Continuous type and IC Engine Note that, being field based residues, technology options related to paddy straw and wild guinea grass were not able to qualify for the assessment at scoping level. Above technology options were subjected to detailed assessment at scoping level. The criteria selected for the analysis are categorized as technical, financial, social and environment. There were altogether twenty nine criteria, among which eleven are technical, seven are financial, five are social and six are environmental. A weight for each criterion was given on a scale of 10 and each technology was evaluated against each criterion using four different levels of importance as (i) None, (ii) Low, (iii) Medium and (iv) High with scores 0, 1, 2, and 3, respectively. The scores were calculated as weighted sum. In the present study, the four different categories of criteria were also given priority values based on feedback from stakeholders (actors), for which the Analytical Hierarchy Process (AHP) was used [5]. Finally, based on the priority 1 Paddy husk generated in Buttala D.S. Division is used by brick kilns in the area. Therefore the paddy husk considered in the above matrix is for Monaragala D.S. Division only. 4

6 values for the four criteria, weighted average score of each of the technology was calculated and ranked them according to the total score. The criteria used and the final scores of the technology options are presented in Appendix A. The technology options according to the ranks obtained through the above analysis are presented in Table 1.2. Table 1.2: Ranks of technological options Rank Technology/Application Equipment Capacity Residue 1 t/day of waste Biogas digester Biogas generation for off-grid Capacity 4 kwe Banana 1 Continuous type & electricity generation-(n) Biogas yield 95 Rejects IC Engine m 3 /day Direct combustion / Indirect heating for fruit and vegetable drying- (E) Direct combustion / Direct heating for lime smoking-(d) Biogas generation for cooking and lighting - (L) Composting for Fertilizer - (M) Direct combustion / Indirect heating for tobacco curing-(f) Gasification for domestic Cooking - (C) Briquette making for value addition to waste as a fuel-(h) Paddy husk stove cum tray dryer Paddy husk stove cum cabinet dryer Biogas digester Continuous type Only hand tools for the handling of waste Tobacco barn Paddy husk gas stove Briquetting machine Product kg/batch Capacity-8 kwth 54 kg/load of waste Product kg/batch Capacity-5 kwth 72 kg/load of waste 500 kg/day of waste Tank volume 60 m 3 Biogas yield 47 m 3 /day Paddy husk Paddy husk Market waste Market 1 t/day of waste waste Capacity kwth Paddy 36 kg/load of waste Husk Capacity-5.5 kwth Paddy 1.3 kg/load of waste husk Capacity: 200 kg/hr Saw Electricity need - dust 175 kwh/t. Direct combustion for Paddy husk cook Capacity-4.0 kwth Paddy domestic cooking (B) stove 1.0 kg/load of waste husk Improved saw dust Direct combustion for Capacity-3.5 kwth Saw cook stove with domestic cooking (I) 1.0 kg/load of waste dust multi-fuel capability Capacity: 200 kg/hr Briquette making for value addition to waste as a fuel (A) Briquetting machine Paddy Electricity need - husk 205 kwh/t. Pressing for manufacture of Series of equipment Capacity Range: Saw particle boards (J) including press >40 m 3 /day output dust Carbonization for conversion 20 kg/load of waste Paddy Basket burner to cement extender (G) 4 kg ash /load husk Pressing for manufacture of Medium density fibre board (MDF) (K) Series of equipment including chipper, boiler, press, etc Capacity Range: 120 to 1000 m 3 /day output Saw dust 5

7 The sub-total scores under each category of criteria and the total score of each technology option is presented graphically in Figure Total Score EC SC FC TC 0 A B C D E F G H I J K L M N Technology Figure 1.1: Final scores of technologies. At the assessment at detailed level, scenario analysis was carried out based on different priority values for the four categories of criteria. The results of all the scenario analysis indicate the insensitivity of the top ranking technologies to the relative priority values of the criteria. Further, in order to have a deeper insight into the meaning of the score distributions, the data was represented in star-diagrams and comparative study was carried out. For example, the scores of the highest rank technology (N) and lowest rank technology (K) are presented in Figure 1.2. EC5 EC6 EC4 EC3 TC TC2 TC3 TC4 TC5 EC2 15 TC6 EC1 SC5 SC TC7 TC8 TC9 Rank 1 Rank 14 SC3 TC10 SC2 TC11 SC1 FC7 FC6 FC5 FC4 FC3 FC1 FC2 Figure 1.1: Star diagram for highest rank and lowest rank technologies. 6

8 2. SELECTION OF THE TECHNOLOGY FOR PILOT IMPLEMENTATION PROJECT The most appropriate and effective technology option or options could be selected based on scores or ranks presented above. Another aspect that could influence the selection procedure of the technology option is the future scenarios, for example with reference to the generation / availability of waste, change in policies, etc. The scenario analysis carried out earlier indicates that the order of raking didn t change significantly, particularly the first eight technology options. Therefore situations of the first few technology options are briefed in this section to facilitate the selection of appropriate technology option(s) for the pilot implementation project. Rank 1 - Technology (N) Residue/Waste: Banana rejects Application: Off-grid Electricity Generation Process / Technology: Anaerobic digestion of waste / Biogas generation Equipment: Biogas digester (Continuous type) / Internal combustion engine Capacity: 1 t/day of waste input; Plant capacity 4 kwe Biogas yield 95 m 3 /day, Electricity generation kwh/day, Performances: Energy conversion efficiency ; Digester 13.5%, Engine 20% Installation Cost: In the range of Rs 2.5 Million This represents a technology with relatively high resource requirement, though the overall benefits are the maximum. It is evident that the technology option will not be able to implement under the present project due to limitation in finances and the available time frame. However, it is recommended to develop a more detailed project proposal, such that the company could implement with their own resources. Rank 2 - Technology (E) Residue/Waste: Paddy husk Application: Process Heat Generation for vegetable / fruit drying Process / Technology: Direct combustion / Indirect heating Equipment: Paddy husk stove coupled to tray dryer 7

9 Capacity: Product Input kg/batch, Drying time 12 to 18 hr Fuel input- 54 kg/load, Fuel input rate 3 kg/hr; Stove capacity 8kWth Performances: Energy conversion efficiency; Drying 40%, Stove 65% Installation Cost: In the range of Rs. 400,000 This is a very viable technology option for the pilot implementation project. There is a high potential for replication of this technology, not only within the selected region but also throughout the country. Since the technology is a small scale one, the sustainable supply of paddy husk is guaranteed. The technology could be applied to drying of wide variety of products including other food products as well as non-food items. The technology suppliers are also available and could be fabricated locally and therefore the technology transfer and adaptation are possible. Therefore selection of this technology as the pilot implementation project is highly recommended. Rank 3 - Technology (D) Residue/Waste: Paddy husk Application: Process Heat Generation for lime smoking Process / Technology: Direct combustion / Direct heating Equipment: Paddy husk stove coupled to tray dryer Capacity: Product Input kg/batch, Drying time 36 hr Fuel input- 72 kg/load, Fuel input rate- 2 kg/hr, Stove capacity 5 kwth Performances: Energy conversion efficiency; Drying 60%, Stove 65% Installation Cost: In the range of Rs. 600,000 This is a very similar technology option as the previous one and has the same viability and benefits. As the technology represents smoking of a food product, the application to other products is limited. Yet, lime is one of the most common agricultural products grown in the area, dissemination of the technology will have many benefits to the local community, while achieving other objectives related to waste management. In this case too, the technology suppliers are available and local fabrication is possible. Therefore selection of this technology option for the pilot implementation project is recommended. 8

10 Rank 4 - Technology (L) Residue/Waste: Market waste Application: Cooking and lighting Process / Technology: Anaerobic digestion of waste / Biogas Generation Equipment: Biogas digester (Continuous type) Capacity: 500 kg/day of waste input; Tank volume - 60 m 3 Biogas yield 47 m 3 /day Performances: Sufficient for cooking and lighting for 15 families Installation Cost: In the range of Rs. 900,000 This technology intervention is one of the proven concepts for the management of market waste, open dumping of which is becoming a growing problem in many part of the country, especially in the urban sectors. The technology is available locally and the local authorities are keen on implementing such waste management programme. Therefore, implementation of this technology intervention is highly required as a solution to waste management activity, though the previous two technology options are preferred over this one as the pilot implementation project. As in the case of rank 1 technology, it is recommended to develop a detailed project proposal to be submitted to the local authority for further actions. Other Technologies The above four technologies represent use of three types of residues/waste: banana rejects, paddy husk and market waste. Therefore, in selecting the other potential technology options management of other residue types has to be given a due consideration. This will ensure the maximum outcome of an overall waste management programme in the Moneragala district. Therefore the technologies in the next ranks such as composting of market waste (M), process heat generation from paddy husk for tobacco curing (F), and paddy husk gas stove for domestic cooking (C), with ranks 5, 6 and 7, respectively will not be considered as potential candidate technology options for the pilot implementation project. However, the importance of these technology options in an overall waste management programme should be duly recognized. The next ranked (8 th ) technology is sawdust briquetting (H), which represents a residue and a technology that are not covered in the earlier selections. Therefore, it is recommended to 9

11 analyse further the possibility of selecting this technology option, particularly to mitigate adverse issues associated with lack of proper management practices of sawdust in Moneragala district. The details of this technology option are given below: Residue/Waste: Sawdust Application: Briquette making for the process heat generation in industry Process / Technology: Densification / Briquetting Equipment: Screw type briquetting machine, including dryer and vibrating screening machine Capacity: 200 kg/hr of sawdust Performances: Briquette density: t/m3; Energy requirement: 200 kwh/t. Installation Cost: In the range of Rs. 3.5 Million Although the initial investment is quite high compared with the earlier technology options considered, it has the highest value addition to the waste material. As there is a growing market for biomass based energy generation in industry, the future market for biomass briquettes is guaranteed. Therefore, although the limitations in financial resource may not support the selection of this option for the pilot implementation, promotion of the technology is highly recommended. Based on the discussion above, the 2 nd rank technology representing paddy husk fired stove and indirect heating dryer for drying of vegetables / fruits is selected as the technology option for the pilot implementation project. 3. BASIC SYSTEM CONFIGURATION AND OPERATION 3.1 System Configuration The proposed equipment for the drying of vegetables and fruits consists of the following subsystems: - Paddy husk stoves (two) - Heat Exchanger and Exhaust System - Blower and Process Air Distribution System - Drying Chamber 10

12 Figure 2.1 illustrate the basic configuration of the system. Hot Air Outlets Air Distribution System Chimney Blower Fresh Air Inlets Heat Exchanger Loading Doors Dryer Stoves Figure 3.1: Schematic diagram of the paddy husk fired indirect heating dryer (not to scale). Paddy husk stove Paddy husk stove comprised of two concentric cylindrical containers and ash chamber. The outer cylinder is made out of GI sheet (no. 20) and the inner cylinder is made out of stainless steel (no. 18) and the space between the two cylinders are filled with paddy husk ash cement mixture that acts as a heat insulation liner. The inner cylindrical container acts as the fuel chamber, and capable of handling about 13 kg of paddy husk. Ash chamber is fixed at the bottom of the containers, with a door to facilitate the removal of ash. A removable lid is introduced at the top of the stove to direct the combustion products (or flue gas) into the heat exchanger. In the system, there are two such stoves connected in parallel for simultaneous operation. Heat Exchanger and Exhaust System A shell and tube type heat exchanger is used to transfers heat from the flue gas from the paddy husk stoves to the drying air entering from surrounding atmosphere, which is fitted above the outlets level of the stoves. The heat exchanger is of cross-flow type with process 11

13 air flowing through horizontal steel tubes and hot flue gas flowing up across these tubes. The tube bank is arranged in a staggered manner and is placed inside mild steel shell. After passing through the tube bank, the process air is also directed to pass through an annular tube encompassing the exhaust chimney to recover further heat from the flue gas. The exhaust system consists of a metal chimney for allowing the hot flue gas to discharge into atmosphere at a sufficiently high elevation, while generating induced draft for the adequate flow of flue gases. Blower and Process Air Distribution System The blower, installed prior to the drying chamber, draws the ambient air through the stoveheat exchanger unit, and supplies hot air to the drying chamber via a duct system. The duct system divides into two equal branches and connected to the drying chamber (that consists of two compartments) through two inlet headers with guide vanes for proper distribution of hot air. There are four process air outlets from the drying chamber, two each connected to a single short chimney. Drying chamber The drying chamber is mounted on six legs and comprised of two equal compartments. Each compartment has a double door. The walls (including the doors) are made of two layers of galvanized iron (GI) sheet with insulation in between to reduce heat losses, framed together by angular steel bars. Small transparent area is fixed to each door for the purpose of viewing of the products from outside during the drying process. Each compartment contains series of racks or shelves that could support trays containing products (two trays in each rack). The trays are made of polyethylene plastic mesh reinforced with aluminium bars. In order to enhance the drying rate, internal air circulation system is introduced, in which a fraction of the drying air is circulated through an axial flow fan in each compartment. 3.2 Basic Operation The basic steps of the operation of the dryer could be summarized as follows: - In each stove, insert two cylindrical tubes, one at the centre vertically and other at the bottom along a radius horizontally. Then the stove is filled with paddy husk and is well compacted leaving a cylindrical opening at the centre (vertical) extending it 12

14 horizontally at the bottom. Once the packing is completed the two tubes are taken out to creating two tunnel-shaped openings. - The stoves are ignited by a piece of coconut husk, paper or a piece of wood dipped in kerosene oil, inserted through the bottom opening. - Before firing, the lid of each of the stove is closed and connected to the heat exchanger shell. The stoves can supply heat to the dryer for about 6-8 hrs. For longer period of drying, another set of stoves could be connected after complete burning of the first two. - There are several trays in the dryer. Once the trays are in position, the door of the dryer is closed. - Every 2 to 3 hrs, the drying quality of the product could be checked and unloading/loading could be done. - One the completion of burning, the stove is disconnected from the system. The ash removal plate could be moved allowing the ash to drop into the bottom chamber. After removing ash, the stove could be reloaded for the next operation. 4. DESIGN PARAMETERS AND SYSTEM SIZING 4.1 Basic Design Parameters The main requirement of the system is to dry/dehydrate vegetable or fruit products. The initial and final properties of the product vary from type to type, but for the system sizing, following design parameters are selected: - Capacity: 100 kg of fresh product/load - Initial Moisture Content: 85% on wet basis - Final Moisture Content: 10% on wet basis - Efficiency of Drying: 40% - Efficiency of Heat generation: 65% - Drying Time: 18 hrs - Calorific value of Paddy husk: 14 MJ/kg (@ 10% moisture level) Based on the above data, following parameters could be estimated: - Heat Rate into the drying chamber: 7.5 kwth - Fuel consumption: 3.0 kg/hr - Total Fuel Requirement: 54 kg/load 13

15 During the drying period of 18 hrs, it is assumed that two stoves operate simultaneously for 9 hrs and recharge once. Therefore the fuel load per charge per stove is 13 kg. 4.2 Paddy Husk Stove The main components of the paddy husk stove, including the fuel chamber, insulation liner, stove lid, ash chamber with ash removal plate, are presented in Figure 4.1. Stove Lid Stove Lid Rest Air Passage Fuel Chamber Insulation liner Ash removal plate Ash Chamber Figure 4.1: Schematic diagram of the paddy husk stove (drawn to scale). Basic design details/parameters of a paddy husk stove are estimated through the following steps: - Fuel weight per load: 13 kg of paddy husk - Average Density of compacted paddy husk: 270 kg/m 3 (assumed) - Required volume of the fuel chamber: m 3 - Selected height of the fuel chamber: 600 mm - Diameter of the fuel chamber: 325 mm - Insulation thickness: 20 mm 14

16 - Outside diameter of the cylindrical chamber: 367 mm - Size of the ash chamber: 450mm 450mm 60mm - Size of the ash removal plate: 440mm 445mm 1mm The stove lid is mounted on the top of the stove to connect it with the chamber of the heat exchange. An allowance is made to move it in vertical direction to facilitate the fuel loading/unloading process. A stove lid rest is placed on top of the cylindrical shell to introduce a passage of air (between the outer cylinder and the lid) to facilitate the combustion of volatiles (secondary air). 2 cm thick insulation liner made of glass wool is added to the outer cylinder to minimize the heat loss. The materials selected for the above components are as follows: - Internal cylindrical container (fuel chamber): Galvanize Iron (gauge 18) - External cylindrical container: Mild steel (gauge 20) - Ahs chamber / removal plate: Mild steel (gauge 20) 4.3 Heat Exchanger and Exhaust System Heat exchange comprised of thirteen number of 2-inch diameter cast iron tubes, that are arranged in a staggered manner, as shown in Figure 4.2. The tube bank is placed inside GI shell of length: 1.12 m, width: 0.33 m and height: 0.33 m. The length of the tubes is 1.0 m. The shell of the heat exchanger is reinforced by a metal framework with 2.5cm 2.5cm square section. The shell is also covered with 2.0 cm glass wool insulation. Allowance for thermal expansion is introduced at the inside end of the tube arrays. Figure 4.2: Schematic diagram of the heat exchanger 15

17 Main design details of the heat exchanger used in the estimation could be described through the following steps: - Fuel rate (52 kg per 18 hrs): 2.89 kg of paddy husk/hr - Heating value of paddy husk: 14 MJ/kg - Temp of flue gas: 900 deg C - Mass flow rate of flue gas: kg/s - Heat load: 7.18 kwth - Flue gas temperature at the outlet: 150 deg C - Overall Efficiency: 64% - Mass flow rate of dry air: 550 kg/hr - Overall heat transfer coefficient: 6 W/m 2 /K - Mean temperature rise of air: 40 deg C - Total heat transfer area required: 2.15 m 2 - Dimensions of a tube: 1.0 m length, 50.8 mm diameter - Number of tubes required: 13 The configuration of the heat exchanger together with the stoves, the exhaust system and the duct layout is shown in Figure 4.3. Exhaust Chimney Hot air to the dryer Heat Recovery System Air ducting Blower Fresh air in Heat Exchanger Stoves Figure 4.3: Schematic diagram of the heat exchanger 16

18 The flue gas exhaust system comprised of a 15 cm diameter chimney with damper to control the induced draft (and thus the temperature inside the heat exchanger). Further heat is recovered by directing the hot air generated in the heat exchanger thorough annular duct of 40 cm length, and 25 cm diameter, encompassing the chimney. It is important to highlight here that, in this design, stoves are not physically fixed to the heat exchanger unit. This makes the possibility of using other fuels / stoves with appropriate connecting systems. 4.4 Drying Chamber The overall dimensions of the drying chamber are 1.2 m wide, 1.25 m tall and 2.0 m long, mounted on six legs at a height of 0.6 m. It contains two equal compartments of size 1.2 m wide, 1.25 m tall and 1.0 m long each. Each compartment could accommodate 16 trays of size 1.1 m 0.8 m. Thickness of a tray is 3 cm and the gap between two trays is 3 cm. Three air circulation fans are mounted between the two compartments to introduce air circulation within as well as between the two compartments and also to enhance the moisture evaporation process (see Figure 4.4). Capacity of a fan is approximately 0.3 m 3 /s. Figure 4.4: Schematic diagram of the drying chamber 17

19 Basic sizing of the drying chamber could be summarized as follows: - Total moisture to be removed: 83.3kg (4.63 kg/hr) - Ambient air temperature: 30 deg C - Initial RH: 60% - Moisture Content of ambient air: kg H 2 O/kg dry air - Initial Enthalpy: 75 kj/kg - Hot air temperature: 70 deg C - Enthalpy of hot air: 103 kj/kg - Equilibrium relative humidity: 51.4% - Moisture content of hot air: kg H 2 O/kg dry air - Mass flow rate of dry air: 550 kg/hr - Latent heat of evaporation (at 70 deg C): 2335 kj/kg - Heat needed to evaporate water: MJ - Useful heat rate: 3.00 kw-th - Pressure develop by the fans: 113 Pa - Air circulation flow rate: 0.97 m 3 /s - Power consumption for circulation (@ 60% efficiency): 182 W-e - Total efficiency of the dryer: 39% 4.5 Blower and Process Air Distribution System The hot air distribution system comprised of a duct line, which supply air from the heat exchanger outlet to the drying chamber via the main blower. The cross sectional shape of the duct is taken as rectangular shape of 15 cm 10 cm, and the total flow rate through the duct system is m 3 /s. The basic configuration of the duct system is illustrated in Figure 3.1. The pressure loss through the duct line is estimated as follows: - Volume flow rate: m 3 /s - Velocity: 9.6 m/s - Total effective length: 3.5 m - Frictional loss coefficient (K-friction): Total fitting loss coefficient (K-local): Fan duct loss coefficient (K-fan): Total loss coefficient of the duct line: Pressure loss: Pa 18

20 The hot air exit from the drying chamber comprised of two outlets, one each from the two compartments. The sectional shape of these two lines is identical to the main duct line. Further pressure loss occurs at these lines, as presented below: - Velocity: 4.8 m/s - Total effective length: 0.5 m - Frictional loss coefficient (K-friction): Total fitting loss coefficient (K-local): Total loss coefficient of the duct line: Pressure loss: 6.55 Pa The main fan should also overcome the pressure drop in the heat exchanger unit. The pressure loss estimation of this unit is presented here. - No of tubes: 13 - Length: 1.0 m - Diameter: 5.1 cm - Average air velocity: 5.32 m/s - Frictional loss coefficient (K-friction): Total fitting loss coefficient (K-local): Total loss coefficient of the duct line: Pressure loss: Pa Therefore the total pressure loss in the entire duct line becomes Pa. With an efficiency of 60%, the electrical power requirement for the main air supply system becomes 156 W (i.e. the total electricity requirement for the plant is 338 W). The overall dimensions of the entire system are presented in Figure 4.4, which is drawn to a scale of approximately 1:

21 990 mm 500 mm 1000 mm 1200 mm 300 mm 350 mm 560 mm 565 mm 200 mm 560 mm 330 mm 200 mm 870 mm 600 mm 1200 mm 700 mm 1150 mm Figure 4.5: Schematic diagram of the vegetable dryer (drawn to scale)

22 5. FINANCIAL ANALYSIS The fabrication and construction costs for the paddy husk fired vegetable and fruit dryer is estimated to be about Rs. 450,000/= (based on the information provided by a local manufacturer of similar type of dryers). The variable costs incurred in the project include labour cost, maintenance and repair costs and fuel cost (both paddy husk and electricity) and cost for the fresh vegetables and fruits. The income is through selling of dried products. The cost of fresh vegetables and fruits depends on the types as well as the season. Usually, during the peak season the prices of the fresh products become quite low and selection of these products for drying is the general practice. Therefore, during a year, different products will be processed. The financial analysis is based on assuming some average value for the buying and selling prices. Further, it is assumed that the running cost as well as the selling prices will increase yearly, and some assumed values are used in the present analysis. The data used in the financial analysis is as follows: - Fresh product processed: 100 kg/batch (i.e. 18 hrs of drying) - Number of batches processed annually: 180 batch/yr - Dried product: 16.7 kg/batch - Labour cost: 750 Rs/batch - Annual maintenance cost: 5% of the installation cost - Fuel cost - paddy husk (collection, transport, handling): 4.5 Rs / kg - Paddy husk consumption: 52 kg/batch - Fuel cost electricity: 10 Rs/kWh - Electricity consumption: 6.12 kwh/batch - Average price of fresh vegetables/fruits: 20 Rs/kg - Average selling price of dried products: 250 Rs/kg Based on the above data total annual variable cost could be estimated as Rs 570,636.00, and the annual income becomes Rs.751, In the financial analysis, following parameters are also considered: - Project duration / life time of the dryer: 10 years - Cost of capital: 18% - Annual selling price increment: 5% - Annual cost increment: 7%

23 Based on the above figures, financial performance parameters including net present value (NPV), discount payback period and internal rate of return (IRR) are calculated. The results are summarized in Figure Table 5.1. Table 5.1: Financial analysis Year No. Cash Flow ( 000 Rs) Net Cash Present Cumulative Fixed Variable Cost Variable Income Flow ( 000 Rs) Value Present Value Net Present Value The above analysis shows that the NPV of the project is Rs 293,830.00, indicating its financial viability. Further, the discounted payback period is estimated as three years and nine months and the IRR becomes 36% which is twice the cost of capital. Sensitivity analyses could be carried out on the various parameters. For example, 10% increase in installation cost results about 20% decrease in NPV. Further 50% increase in paddy husk cost (from 4.5 to 6.75 Rs/kg) shows 40% decrease in NPV. The result is more critically depends on the cost of fresh vegetables/fruits as well as selling price of the dried product. For example, even a 10% increase in cost of fresh products results in 70 % decrease in NPV, while 10% increase in the price of dried products results in 135% increase in NPV. Therefore it is apparent that careful selection of products at the most suitable time during the year is a very important aspect for the success of the project. 22

24 References [1] Sugathapala, A.G.T. (2009). Converting Waste Agricultural Biomass to a Fuel/ Resources in Moneragala District, Sri Lanka - 1 st Progress Report on Characterization and Quantification of Waste Agricultural Biomass submitted to NCPC. Project funded by UNEP and coordinated by NCPC, October [2] Sugathapala, A.G.T. (2010). Converting Waste Agricultural Biomass to a Fuel/ Resources in Moneragala District, Sri Lanka 2 nd Progress Report on Sustainable Assessment of Technology submitted to NCPC. Project funded by UNEP and coordinated by NCPC, February [3] Chandak, S.P. (2009). Sustainable Assessment of Technologies: Making the Right Choices. International Environmental Technology Centre DTIE, UNEP. Presented at the 1 st Stakeholder Consultative Workshop / Training Programme of the Project on Converting Waste Agricultural Biomass to a Fuel/Resources in Moneragala District, Sri Lanka funded byunep and coordinated by NCPC, 21 st August [4] DTIE-UNEP. EST Assessment Methodology and Implementation - Training Kit prepared for the support of the project on Environmental Management of the Iraqi Marshlands. Funded by International Environmental Technology Centre (IETC) DTIE, UNEP. [5] Saaty T.L. (1999). Decision making for leaders. RWS Publications, Pittsburgh.

25 APPENDIX A: RANKING OF TECHNOLOGIES A1: Criteria used for Evaluation The set of criteria under four different aspects, as (i) Technical, (ii) Financial, (iii) Social and (iv) Environment, used in the present study are presented in Table A1. There were altogether twenty nine criteria, of which eleven are technical, seven are financial, five are social and six are environmental. Table A1: Criteria Selected for Scoping Analysis Category Criterion Notation Technical Suitability to characteristics of waste stream TC1 Availability of adequate amount of waste TC2 Compliance with prevailing local environmental laws, regulations and standards TC3 Accessibility of technologies TC4 Availability of local expertise/capacity building requirement for design, operation and maintenance TC5 Level of use of local material and resources for fabrication and operation TC6 Availability of in country technical assistance during commissioning and operation TC7 Level of similar usages and performance records in Sri Lanka TC8 Adaptability - Ability to fit into local (project area) conditions TC9 Adaptability to future situations (scale-up/expansions) TC10 Ability to replicate TC11 Financial Capital investment FC1 Operational and maintenance costs FC2 Payback period FC3 Value addition to WAB FC4 Investor attractiveness FC5 Availability of co-financing FC6 Co-benefits FC7 Social Job creation SC1 Acceptability to local culture SC2 Improvement of quality of life SC3 Occupational safety and health conditions SC4 Improvement of local technical skills and knowledge base SC5 Environmental Additional support services/utilities (Water/Energy) EC1 Environmental emissions EC2 Noise, vibration and odour EC3 Space and infrastructure requirement EC4 Contribution to WAB management EC5 Net carbon emissions EC6 24

26 A2: Overall Scores and Ranks Based on the priority values for the four categories criteria, weighted average score of each of the technology were calculated and the final overall results of the analysis are presented in Table A2. Table A2: Ranks of technological options based on pair-wise comparison of criteria Criterion (Priorities) Weighted Technology Technical (0.266) Financial (0.105) Social (0.188) Environmental (0.441) Average based on pair-wise comparison Total % Total % Total % Total % Score % Rank A B C D E F G H I J K L M N