Master of Science in Sustainable Process Development

Permanent URI for this collectionhttp://192.248.9.226/handle/123/28

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item: Thesis-Abstract
Non-dimensional analysis of mass transfer in a spouted bed dryer for black pepper drying
(2023) Abeysooriya, SH; Amarasinghe, BMPK
Black pepper is an agricultural crop that is extensively used as a spice and as an additive in numerous other applications. Postharvest drying of pepper is an important step to enhance the pepper quality and shelf life. Among many types of dryers spouted bed dryer is suitable for wide range of agricultural products. Knowledge on mass transfer analysis in the drying process is vital for improvements in the drying process and for dryer design. In this study, nondimensional analysis of the mass transfer process of black pepper drying, in a spouted bed dryer was performed. Experimental results of a research conducted on black pepper drying using a conventional spouted bed dryer along with a cyclone separator was used for the analysis. The drying experiments were conducted to study the effect of operating variables; inlet air temperature, bed height and air velocity. Non- dimensional analysis of mass transfer coefficient was employed using the Buckingham pi theorem and the data generated in a series of black pepper drying experiments in a spouted bed dryer were used to develop the model equation. The model consists of dimensionless parameters; Sherwood (Sh) number, Reynolds (Re) number, Schmidt (Sc) number and bed height to particle diameter (H/dp). R software (Version 4.1.2) was employed for the determination of the coefficients of the model using the non-linear regression method and for statistical analysis. The model shows mass transfer coefficient is a function of the inlet air temperature, air velocity, dynamic viscosity of air, moisture diffusivity, bed height and air density. The mass transfer coefficient values predicted from the developed correlation varied between 0.012 m/s and 0.032 m/s. The model predicted results were validated against experimentally determined values of mass transfer coefficients. The experimentally estimated mass transfer coefficients varied between 0.012 and 0.031 m/s and were in good agreement with model predicted values. Further, mass diffusivity values of the drying process varied between 2.87 x 10-5 – 3.6 x 10-5 m2/s. The results show that an increase in inlet air temperature reduces the mass transfer coefficient and the Sh number. However, increase in air velocity increases the mass transfer coefficient, which is in agreement with available relations for other similar products. Furthermore, mass transfer coefficient values decreased while increasing static bed height. This is an acceptable trend because of lower turbulence created by the higher static bed and the spouting of more particles in the higher bed rather than lower static bed heights.
item: Thesis-Full-text
Kinetic modeling of tar formation in an updraft biomass gasifier
(2020) Jayathilake GKM; Gunarathne D
As the depreciation of the fossil fuels in the world, it is obligatory to discover new fuels to the highly industrialized society. With increasing requirements of the energy, it is globally focused on the use of renewable energy. Biomass can be used as an alternative energy source to replace fossil fuels, which contribute to the greenhouse gas emission. Therefore, biomass is a major renewable energy source as of today. Nowadays, converting biomass into biofuel is a major goal. So, the gasification process can be used as such an effective way to convert biomass into syngas. Even if the major goal of the gasification is to produce syngas such as H2, CO, intermittently, many byproducts are generated such as NOx, SO2, fly ash and tar. The formation of tar in the gasifier is a problematic situation. The formation of tar mainly depends on temperature, residence time, type of biomass and gasifying medium. Modeling is an effective method to optimize the gasifier operation. Also, it can be used to determine the relationship between operational parameter limits and explain trends in output products. By using Aspen Plus process simulation tool, a kinetic model was developed to predict the tar formation of updraft gasifier considering the main chemical phenomena biomass pyrolysis, reduction and combustion. The results were compared with the experimental data from the literature to validate the model. According to the developed model, the tar content and the composition could be estimated with respect to the equivalence ratio (ER) and pyrolysis zone bed height. When the ER is increasing the formation of tar is trending to decrease. The pyrolysis zone bed height beyond 1.3 cm does not show a significant impact on the tar content. It is possible to use the developed model to minimize tar content by operating at a suitable temperature (by controlling the ER) and by keeping an applicable residence time (by maintaining a suitable bed height). Further, this model can be used to optimize the tar formation with different biomass types and gasifying mediums when the temperature profile of the gasifier is available.
item: Thesis-Full-text
Process parameter optimization of urban biowaste carbonization
(2020) Perera SMHD; Narayana M
About 75% of Municipal solid waste (MSW) collected around the country is organic biomass which mainly includes food waste, wood, paper, saw dust and paddy husk. Urban councils in Colombo city and nearby suburbs collect biowaste separately which has created a huge potential in converting urban biowaste into value-added component like biochar, thus resolving the problems associated with MSW management and mitigating socio-economic and environmental issues related to MSW. In this study, torrefaction is identified as the most viable technology available for the conversion of organic MSW into biochar and the study mainly focuses on developing a three dimensional computational fluid dynamics (CFD) model of a continuous packed-bed torrefaction reactor for organic MSW and then optimizing the process variables and the geometry. A mathematical model including all heat, mass and energy transfers, and heterogeneous & homogeneous reactions is firstly developed and then converted to a numerical model and simulated using OpenFOAM for an insulated cylindrical reactor in which hot gas at elevated temperatures (473 – 623K) is provided from the bottom while solid at ambient conditions is fed from the top. The torrefaction reactor is optimized for gas inlet temperature and residence time and then the geometry of the reactor is optimized for the optimum gas inlet temperature and residence time. Four reaction zones are identified in the reactor domain; i.e. drying, softening & depolymerization, limited devolatilization & carbonization and extensive devolatilization and carbonization. The optimum inlet gas temperature, residence time and D/L ratio are 573K, 13000s and 0.24 respectively. For the optimum conditions, biochar yield is 55.7% while ash content is 19.1%. Further In dry basis, 95.9% of biomass is decomposed and the total weight loss based on the initial wet biomass is 86.6%.
item: Thesis-Full-text
Investigation of CO2 sequestration possibility via aqueous phase mineral carbonation using industrial waste materials
(2020) Nanayakkara SG; Rathnayake HHMP
Carbon dioxide (CO2) as the most vital greenhouse gas in the earth’s atmosphere plays a major role in maintaining the global temperature. Higher concentrations of CO2 in the atmosphere, increases amounts of heat entrapped in the atmosphere. Thus, the environmental temperature increases when the CO2 concertation increases and results in global warming. The global CO2 emission was approximately 35.3 billion metric tonnes in 2018 and, it is predicted to be increasing up to 43.08 billion metric tonnes by 2050 as per the prevailing trends in statistical analysis. Therefore, maintaining an acceptable concentration of atmospheric CO2 is required. In this situation, anthropogenic CO2 capture and storage technologies have emerged to reduce the atmospheric CO2 concentration. Among the carbon capture methods, post-combustion CO2 capture technologies are the most common as there is the advantage of ability to retrofitting to existing plants. Mineral carbonation is considered as a natural and exothermic process among available post combustion CO2 capture technologies, which gives promising results in CO2 sequestration by storing as mineral carbonates. Suitable materials for mineralization are natural minerals like silicate rocks, serpentine, olivine minerals or else industrial wastes like oil shale ash, steel slag, paper mill waste, fly ash or mine tailing, etc. In this study, the existing literature on CO2 sequestration capabilities through aqueous phase mineral carbonation of industrial waste materials were reviewed and analyzed. Industrial waste materials, such as coal fly ash and steel slag have significant capture capacities and coal fly ash consumes significantly lesser energy and costs to capture one tonne of CO2. In addition, calcium extraction from Lakvijaya Coal Fired Power Plant fly ash was experimentally investigated to identify the potential for indirect carbonation, to sequestrate CO2 from coal flue gas. A maximum calcium extraction efficiency of 9.65% was obtained for coal fly ash obtained from Lakvijaya Coal Fired Power Plant.
item: Thesis-Full-text
Investigation of multicomponent heavy metals adsorption capability using raw coir dust and processed coir pith
(2020) Amarasinghe AMPC; Rathnayake HHMP
Water is the most vital natural resource that sustains all living organisms on the earth and access to safe and clean water has become a crisis due to intense water pollution by anthropogenic activities, over-pumping of groundwater for irrigation purposes, limited water availability due to climate changes, regional conflicts over common water resources, etc. Wastewaters that contain various heavy metals, such as arsenic, chromium, manganese, nickel, lead, cadmium, zinc, and copper are being discharged into natural water bodies annually by many industries. Industrial processes that generate wastewater with significantly high levels of heavy metals use various techniques, such as chemical coagulation, chemical precipitation, membrane separation, extraction, electrodeposition, ion-exchange, and electrochemical techniques in order to remove the heavy metal contents. Nevertheless, most of these techniques use expensive chemicals and require considerable time, and some of them are proven to be less effective and less efficient, especially in removing trace amounts of metals. Besides above methods, adsorption technique is one of the most widely used technique to remove heavy metals from water and studies have revealed that it is much effective in removing heavy metals with high solute loading and even at minute concentrations. In the past decade, significant number of studies have been conducted worldwide on the removal of heavy metals from aqueous solutions by non-living and biologically inactive biomass. This approach of wastewater treatment is known as biosorption, and the non-living biomass used there is defined as bio sorbent. Use of bio sorbents to remove heavy metals from wastewater is a novel and developing technology in the water treatment field. Coir pith is a waste-derived material that can be utilized as a biosorbent for heavy metals removal from wastewater. In this study, directly obtained raw coir dust from coconut husks and processed coir pith were tested for their removal efficiencies of 8 heavy metals, i.e., As, Cd, Cu, Cr, Mn, Ni, Pb, and Zn. Standard heavy metal solutions were prepared for each metal and heavy metal content of standard solutions, coir pith, and coir dust were first measured using the Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES) method. A multicomponent batch adsorption experimental procedure was conducted to determine the removal efficiencies of each metal by both coir dust and coir pith. In experimental procedures, respectively, 1g, 2g, 3g, 4g, and 5g of coir pith and coir dust were added to equal volumes of each metal solution and allow adsorption for 2 hours. Then filtered samples were tested for the heavy metal concentrations using iii the ICP-OES method. Multicomponent heavy metal removal efficiencies of coir pith were tested by varying the adsorption temperatures and the contact time between the heavy metal solution and the coir pith sample. Analytical results show that both raw coir dust and coir pith act as suitable bio sorbents for removal of As, Cd, Cr, Ni, and Pb, and the optimum solid/liquid ratio is 0.1 g/ml at room temperature for 2 hours if contact time for all these five heavy metals. According to the results comparison between the of raw coir dust and processed coir pith, raw coir dust shows higher heavy metals removal capacities Coir pith is the most suitable biosorbent for Cu removal while coir dust is most suitable biosorbent for Mn removal. For raw coir dust metals and bio sorbents 0.08g/ml at room temperature for 2 hours contact period is the optimum solid/liquid ratio. For processed coir pith metals and bio sorbents 0.1g/ml at room temperature for 2 hours contact period is the optimum solid/liquid ratio Anyway both coir pith and coir dust are not suitable for Zn removal from aqueous solutions. For all metals except Zn, contact period of 30 minutes and temperature of 30 °C are the optimum operating conditions. In this experimental we have used multi component heavy metal sample as a result of it both materials adsorption and desorption are happening in the same sample. When we consider heavy metal adsorption with the temperature from 30-70 °C heavy metals adsorption capacity has decreased the reason for this with the increasing of temperature kinetic energy of the metal has increased then desorption is happened inside the sample. As a result of it with increasing of temperature heavy metals adsorption capacity will decrease. When we consider contact time of the heavy metals sample with the absorbent, For Cr, Cu and Pb show similar results. From 30 min to 2 hr material adsorption efficiency has decreased but 2 hr to 4 hr adsorption efficiency has increased the reason is for this, from 30 min to 2 hr desorption appeared in the sample but with the increasing of the contact time from 2 hr to 4 hr again heavy metals adsorption is happened in the sample. But all other heavy metals are showing decreasing trend of heavy metals adsorption capacity with the increasing of contact time.
item: Thesis-Full-text
Process parameter optimization of washing pretreatment for inorganic removal from rice husk
(2020) Peiris DMA; Gunarathne D
Rice husk is particularly known as one of the most common agricultural waste and the usage of rice husk in energy applications is typically via the combustion process. Using agricultural waste for combustion application can lead to slagging, corrosion and fouling of boilers due to some problematic elements such as K and Cl. Water washing removes those problematic elements from rice husk and hot water washing treatment improves the removal efficiency of those alkali oxides, halides and total ash content. Further, hot water washing pretreatment has been identified as an effective method compared to acid treatment and alkali treatment. This study is aimed at optimizing the washing parameters; washing temperature, time and water to biomass ratio. Effectiveness of washing was directly evaluated by conductivity measurements and the removal of inorganic elements. The second order kinetic model was successfully applied for the leaching of K and Cl species and the kinetic parameters were obtained. Washing temperature has significant effect on Si removal, a considerable effect on K removal and a very weak effect of Cl removal. Moreover, water/biomass ratio has an appreciable effect on K removal, a very weak effect on Cl removal whereas almost no effect of Si removal. Washing temperature of 65 ⁰C and water to biomass ratio of 100 was selected as the optimum process conditions. At the selected optimum conditions, about 84% of K and 81% of Cl can be removed while Si removal is insignificant. Within 10 minutes leaching time, 97% of leachable Cl and 81% leachable K can be removed.
item: Thesis-Full-text
Effect of particle size and secondary air for particulate biomass combustion in a bubbling fluidized bed reactor
(2020) Silva GGSN; Narayana M
Biomass combustion is used as basic technology to generate heat by humans for millennia. With the incremental needs of modern man, biomass combustion still plays a major role in heat and power generation. In Sri Lankan context, biomass combustion is extensively used in manufacturing industries for boilers, furnaces, dryers, etc. Even though biomass is abundantly available as an energy source in Sri Lanka, industrial biomass combustion systems are operating under very low efficiencies. Operating these industrial combustion systems in an optimum manner will help in numerous ways to industries, environment and society. In this study, particulate biomass combustion in a bubbling fluidized bed combustor model is used to evaluate optimum secondary air flow rate rates and particle sizes. First Proximity of particulate biomass (saw dust) was conducted to find out moisture and volatile content, then sieve analysis was conducted to segregate and name the particle sizes. Different particle sizes were fluidized using measured primary air flow and combusted under varied secondary air flow rates and obtained maximum temperature achievement in three distinct locations (top, middle and bottom) in the fluidized bed reactor by using installed temperature transducers. Secondary air flow rates and temperature results were tabulated for each particle sizes to analyze temperature variation. Matlab CFTool feature was used to generate surface fits for all three location (top, middle and bottom) temperature variation against particle size and secondary air flow rates. After evaluation results and surface fits, Optimum operating secondary air flow rates and particles sizes were identified for used lab scale bubbling fluidized bed combustor. Recommendations were suggested for industrial scale particulate biomass combustion systems such as boilers, furnaces, etc. for optimum operation based on lab scale system results.
item: Thesis-Full-text
Influence of CO₂ injection on biomass updraft gasification process
Lenagala, IRND; Narayana, M
The utilization of fossil fuels has enabled large-scale industrial development and largely supplanted water-driven mills, as well as the combustion of wood or peat for heat. The burning of fossil fuels by humans is the largest source of emissions of carbon dioxide, which is one of the greenhouse gases that allows radiative forcing and contributes to global warming. This study focuses on to performance analysis of updraft gasifier with the injection of CO2 as gasifying agent. During the study CO2 was fed in to updraft gasifier in different feed ratios and producer gas composition was analyzed. Rubber wood chips were used as the feed stock of gasifier and testings were carried out in input fractions of CO2 to analyze its impact of CO yield.
item: Thesis-Full-text
Modeling of biomass gasification with CO₂ enrich air as gasifying agent
Jayakody, KKR; Narayana, M
The biomass gasification has been carried out using an updraft gasifier. This work focuses on the production of producer gas from biomass (Rubber Wood). Mathematical model for thermo-chemical process of biomass gasification is developed in this research work. ASPEN PLUS simulator and pilot plant gasifier were used to investigate the effect of reactor temperature, equivalence ratio and CO2 to air ratio on composition of producer gas. The gasifier was operated over a temperature range of 500-1000 C, while varying equivalence ratio from 0.2 to 0.36and CO2 to air percentage from 1% to 10% and it was found that the most of trends were similar for both the case. The results showed Carbon monoxide concentration in the product gas increases with increase in temperature and CO2 to biomass ratio but decreases with increasing equivalence ratio.
item: Thesis-Full-text
Analysis and optimization of cyclone separators by using rans
De silva, MSM; Narayana, M
Many types of particulate matter collectors are used in the industry to separate particulate matter from the gaseous streams. Among various type of particulate collectors, cyclone separators are one of the most extensively used gas cleaning equipment because ofthey are inexpensive; easier to fabricate, and could be designed to stand under harsh operating conditions. Due to this extensive usage in the industry, many theoretical and experimental studies have been carried out and empirical models were developed to predict cyclone separator’s most important operational parameters. These models have many limitations of illustrating flow behavior properly due to the complex nature of the cyclone gas-solid flow behavior. Computational Fluid Dynamic (CFD) simulation could be useful to predict cyclone performance as an alternative approach. This work represents a CFD simulation of a Lapple cyclone separator using OpenFOAM software. Cyclone simulations have been carried out using turbulence models associated with the Reynolds Average Navier Stokes (RANS) equations. Multiphase Particle in Cell (MPPIC) method was used for the particle modeling, in which particle interactions with other particles were represented by models. The perditions of simulations have been compared both mutually and to literature in terms of cyclone pressure drop, gas-solid flow pattern and collection efficiency. RANS model fairly predict the gas-solid flow pattern of the cyclone. Pressure drop and collection efficiency of cyclone well fitted to the experimental results in the literature. Optimum values for inlet gas-solid velocity and particulate loading rate for the Lapple cyclone were obtained by RANS analysis. Pressure drop variation with gassolid inlet velocity which has been obtained by this analysis could be useful to minimize the energy requirement while maintaining the required collection efficiency.
item: Thesis-Full-text
Assessment of environmental impact for accidental release of heavy gas
Gunawardena, YN; Gunasekera, MY; Narayan, M
An air dispersion model can be used to mathematically simulate air pollutants dispersion in the ambient atmosphere. These dispersion results can be used to predict their environmental impact, concentrations and movement. Such predicted data of hazardous gases released after a chemical accident are valuable since it can be used to provide timely information to emergency response providers as well as to make decisions on siting chemical plants at safe distances from settlements during plant development stages. Dense gas dispersion is the focus of this research as several pressurized dense gas release accidents have happened during the last few years in this country. These gases form clouds heavier than air when released to the atmospheric environment. In this study a mathematical model for the dispersion of heavy gas due to an accidental release is presented in order to determine the environmental impact. The heavy gas model was then used to simulate the dispersion of negatively buoyant and highly toxic chlorine gas to illustrate the use of heavy gas dispersion modeling in hazard analysis. A worst case scenario study with stability class A, was used for an accidental release of 900kg of chlorine from a location in Kaluthara district in Sri Lanka. To determine the impact of the release probit analysis, safe distance and hazardous time period calculations were done. From the model results, for a 900kg chlorine release, safe Immediately Dangerous to Life or Health (IDLH) distance was above 490m. Within this hazardous zone the safe time period starts after 5.44 minutes from the release. Further, this model can be used to predict information, such as concentration variation of the substance released with time and, cloud dimensions such as height and radius. For validation, experimental data in literature were collected and a sensitivity analysis was done to identify the best values for the model parameters.
item: Thesis-Full-text
One dimensional mathematical model for packed bed biomass combustion using MATLAB
(2018) Priyadarshani, U; Narayana, M
Packed bed biomass combustion is widely used thermal conversion process which contributes major portion of energy fulfillment around the globe. This process is usually involving higher operation cost due to low efficiency and high emissions. Hence there is a huge room for improvements in the process and needs to be optimized as well as modernized. This thesis presents two-phase one-dimensional mathematical model with MATLAB solver which can be used for diagnosis and optimization of packed bed combustion process under low computing resources and less cost. The mathematical model uses the discretized equations to develop the ordinary differential equations which are solved using implicit method. Free-board region is not taken into account. Only the biomass bed is considered here to solve the combustion system by applying conservation equations into gas and solid phase separately. The main model is consisting with different sub models with subjected to four stages of combustion as drying, pyrolysis, Char oxidization and char combustion. The biomass batch is initially ignited by continuous preheated gas inlet and higher gas flow rate. Radiation heat transfer is assumed to be negligible due to high temperature gas flow at the inlet. Combustion is occurred in batch wise. Particle diameter and bed porosity is considered with a mean value for the simplicity of the model. The developed model is used to find the solid temperature profile and generation of CO2 and CO gases. By using walking column approach, industrial moving grate furnace was represented and required optimum grater length for a particular mass flow rate can be calculated with the fixed bed simulation results.
item: Thesis-Full-text
Performance analysis of a cyclone separator using CFD
(2018) Rathnayake, NNW; Narayana, M
Cyclone separator is a well-recognized, cost effective procedure of particle separation which used in many industrial works. As in cement industry, this cyclone separator used in order to separate calcium carbonate (CaCO3) particles from hot gas. Apart from that, it also used to pre heat CaCO3 particles by cyclone riser duct and to produce calcium oxide (CaO) (calcinations). Both of these procedures take place within the cyclone separator simultaneously. The efficiency of the cyclone separator determined by many factors such as cyclone dimensions & geometry, particle diameter & density and gas velocity. In this study, we considered about the effect of following 2 parameters on the efficiency of our fabricated cyclone separator. They are, Air flow velocity (inlet velocity) and Particle diameter. Experimental data were taken from the INSEE cement plant at Puttalam. Our experimental setup was the four stage preheater cyclone zone at the INSEE cement plant. Experimental data were taken from the bottom cyclone of the, Four Stage Pre Heater Cyclone Zone at the INSEE cement plant and figured the optimum values for those parameters to enhance the efficiency of the cyclone separator. CFD (Computational Fluid Dynamics) analysis also involved in to figure the optimum values for same parameters. In CFD analysis, for two phase air & calcium carbonate dust mixture, both multiphase ((k-epsilon, RNG (Re Normalization Group), wall function)) & discrete phase models have been used. Using multiphase model, we could plot contours of velocity, volume fraction and etc, of the individual phases. The Discrete model enabled us to track particles. This helped us to study collection efficiency by changing particle diameters & inlet velocities. It appeared that the final results of the experimental data and the CFD analysis were quite similar.
item: Thesis-Full-text
Modeling of clay roof tiles drying process to minimize warping and cracking
(2018) Kumara, GT; Narayana, M
The main drawback of traditional open rack type natural tile drying process is that in low humid windy seasons the rate of moisture removal will be high and due to formation of high moisture content gradient in side the tile warping/cracking is taking place. On the other hand in high humid rainy season the drying rate becomes very low and the drying time will become very high which is non tollarable within the tile production process. With this background NERDC is in the process of developing a tunneltype drier in which the temperature and RH could be controlled. Then the intention is to control these parameters in side the drier so as to maintain the optimum drying condition i.e the maximum drying rate without warping/cracking. To achieve this objective a model has to be developed to interpret the drying rate related to R.H and Temperature of the drying environment and the moisture content of the tile. Once this model is developed and if the maximum allowable drying rate for not warping/cracking is known RH, Temperature in side the dryer could be maintained to achieve the maximum drying rate. Although a literature survey was done a proper model for clay roof tile drying was not found. So, mathematical model with a few unknown constants was developed by using fundamental concepts. Subsequently laboratory tests were conducted to find out the unknown constants of the developed mathematical model. The model was verified by using the results obtained at the tile drier (tunel) developed by NERDC at Waikkala . These tests were carried by maintaining R.H and Temperature in side the drier for which warping/cracking was not observed. Therefore by using these results although the model was verified the optimum drying conditions cannot be interpreted. For that interpretation maximum possible drying rates for particular moisture contents of the tile has to be foundout by a separate experiment
item: Thesis-Full-text
Effect of particle size on packed bed biomass combustion
(2018) Rajapaksha, GDM; Narayana, M
In this thesis, particle size effect on biomass (rubber-wood) combustion in a packed bed reactor was investigated in experimentally. Mass loss rate, bed shrinkage rate, temperature profile at different bed locations and gas compositions in the out-of-bed flue gases were measured at a constant primary air flow rate. In this study used a fixed batch of biomass. An external heat source was used to ignite the biomass initially and after ignited the biomass, removed the external heat source. Rubber-wood cubes were fired with size ranging 25mm, 38mm, 50mm and 63mm. As time pass, the height of the packed bed is decreasing due to shrinkage of the bed and also the weight of biomass is reducing with time. It is found that at the operating condition of the current study, burning rate of biomass particle is higher with smaller fuel size; and also smaller biomass particles are faster to ignite than the large biomass particles and have unique combustion stages; on the other hand, larger biomass particles produced a higher flame temperature. Larger particles also cause the combustion process becoming more transient where the burning rate varies for the most part of the combustion process. And also biomass combustion time (operational time) is increased with increasing biomass particle size. And here calculate the percentage of excess air, when increased the particle size, amount of excess air release is high. Therefore, need to control the amount of primary air supply when increased particle sizes.
item: Thesis-Full-text
CFD modeling of a centrifuge for oil - water separation
Thilakarathna, HGSM; Narayana, M
Centrifugation is an efficient, economical and environmentally friendly method to remove un-desirable water content from oil and water mixtures and separate out the desired oil content.Moreover, the disc stack centrifuges are widely used for separating liquids of different densi-ties and applied in industrial coconut oil clarification as well.The main focus of this research work is to model the fluid flow inside the Westfalia discstack centrifuge using Ansys Fluent and identify the flow behavior. With the availability of thelimited computer hardware facility, the model has been run without the discs to avoid com-plexities. In the developed 3 dimensional model, the fluid dynamic behavior of the multiphaseflow has been considered and modeled using the VOF multiphase model available in fluent.The step by step procedure of the model development has been discussed such as the veryfirst stage of geometry selection, drawing and importing to the fluent, mesh generation, allsolution set ups and even the two stage simulation procedure.The simulation results of this research work provides an out line of the resulted flow param-eters of velocity and pressure profiles, turbulent effects such as turbulence intensity, turbulentkinetic energy, and specific dissipation rate and also the phase volume fractions which havebeen saved in every critical stage of the simulation process. Despite the phase volume fractionwhich has been experimentally validated, all other results were theoretically validated.CFD modeling of flow behavior inside the centrifuges is not a popular topic among theresearchers due to the complex flow patterns and the requirement of advanced computer hard-ware facility. However this research work provides a platform to model the similar flow be-haviors and even to model the same case including the discs.
item: Thesis-Full-text
Virtual suppports to analyse static floating structures and dynamic systems by static analysis software
Kumarasinghe, HS; Peiris, K; Narayana, M
When an object with high rigidity is subjected to free forces, moments and constrained forces, moments, stresses and strain will be formed in it. A support may be identified as a constrained which supplies forces/moment without any displacement. In some cases although the constrains could balance the free forces/moments by and keep the system under equilibrium, the constraints cannot be keep a unique displacement (field). Therefore in such a case in an elemental analysis the solution for displacements will have many solutions conditions and in a computer where numerical methods (iterative) are used such solution will not be possible. In this study a method is introduced to overcome this problem by the concept of ‘virtual constraints’ without changing the original stress-strain condition of the system. System without adequate constraints will be known as floating system and dynamic systems (with high rigidity) with the application of reversed inertia forces could also be considered as floating system. Therefore such system also could be analyzed for stress-strain by proper introduction of artificial supports with the same software meant to analyses static system.
item: Thesis-Full-text
Investigation of temperature profiles of traditional puta and preparation of chalcopyrite ash for ayurvedic treatment using muffle furnace
Pathiraja, PMYS; Gunawardena, SHP; Herapathdeniya, SKMK
Bhasmas (ashes) are complex compound forms of metals, minerals or gemstones obtained after a series of ayurvedic pharmaceutical preparation processes; purification (shodhana), trituration (bhavana) and incineration (marana) in combination with various herbal extracts and other substances. These three processes play an important role in preparation of ashes. Puta is the specific quantum of heat required to get the desired quality ashes in the process of incineration (marana) and naturally available fuels like cow dung cakes are used to produce heat in the conventional puta. The amount of heat required to produce a specific ash is substance specific and described in terms of fuel burnt. The objectives of this research are to establish temperature profiles for Maha Puta, Gaja Puta and Varaha Puta and to verify temperature profile of Varaha puta using a muffle furnace. Temperature profiles were established using dried cow dung cakes with an average calorific value of 15.44 MJ/kg as the fuel and the maximum temperatures achieved for Maha Puta, Gaja Puta and Varaha Puta were 1380 0C, 1060 0C and 850 0C respectively. Then temperature profile of traditional Varaha Puta was matched with a muffle furnace and Chalcopyrite ash (Swarna Makshika bhasma) was prepared using both traditional method and electric muffle furnace. The ashes produced using both methods showed similar properties and hence the temperature profile obtained for traditional Varaha Puta using the muffle furnace was verified.
item: Thesis-Full-text
Study the effect of chitosan as an emulsifier and as an additive over cationic bitumen emulsion
Mallawarachchi, DR; Amarasinghe, ADUS; Prashantha, MAB
Chitosan has amine and amino groups which have the ability to generate cationic type surfactants when combine with H+ ions. Thus its action as a cationic emulsifier is suitable for negatively charged siliceous aggregates used for road paving in Sri Lanka. This study consisted of two parts. Firstly, water soluble Chitosan was tested for suitability of using as an emulsifier in the production of cationic bituminous emulsions and secondly Chitosan was used as an additive to mix with bitumen emulsion. In the first part, currently using amine emulsifier was replaced at 20% intervals and tested for emulsion properties; emulsion viscosity, storage stability, settlement test, sieve test and breaking of emulsion. In the second part, Chitosan was added to emulsion and viscosity, storage stability and break time were tested. Results of first part indicated that Chitosan replacement was only possible up to 10% replacement for cationic slow setting type of emulsions but rheological properties of rapid setting emulsions could be improved by replacing up to 60% of amine emulsifier with Chitosan. A significant increase in viscosity from 16 SSU (with 0% Chitosan) to 43 SSU (with 60% Chitosan) was observed for rapid setting emulsions. Storage Stability showed the optimum value of zero at 40% replacement and all the values up to 60% replacement were found to be within the ASTM specified level of ±1%. Break time measurements suggested that for slow setting type emulsions Chitosan use as an emulsifier has increased the emulsion breaking rate. Further high viscous and stable rapid setting emulsion could be obtained without hindering the compliance to ASTM standard by replacing the amine emulsifier with Chitosan. Results of second part suggested that Chitosan acts as a viscosity modifier and increases the emulsion viscosity from 26SSU to 92SSU when added at 0.2% of emulsion weight. But this addition has increased the settling tendency of emulsion thus most suited to be mixed at the point of use. In both cases, at a critical amount of added Chitosan was observed. This maximum limit was found to be 0.2% (w/w).
item: Thesis-Abstract
Comparison of suitaility of different binding materials in briquette forming
Shyamalee, AMD; Amarasinhe, ADUS; Senanayake, NS
The process ofmanual saw dust briquette making was tested with different binding agents in the laboratory with 1.5 ton hydraulic jack. Dry cow dung, wheat flour and paper pulp were selected as binding agents. This briquette was designed with size 35mm Diameter x 35mm length and cylindrical shape. Saw dust was sieved through 2mm screen mesh and 6 different samples were prepared with sieved saw dust and each binding agents as 5%, 10%, 20%, 30%, 40%, and 50% dry basis. Cow dung samples were shown difficulties of mould detaching. Wheat flour and paper pulp binder samples with 5%, 10%, and 20% (dry basis) binders also failed onmould detaching due to breaking of briquettes. The minimum requirement of binder percentage was found to be with 30% dry binder of wheat flour and paper pulp to form stable briquette and hence it was selected for comparison of properties. Densities of briquettes with 30% binder of wheat flour and paper pulp were 373.7 kg/m3 and 289.8 kg/m3 respectively. Compression behavior of briquettes with 30% (dry basis) binding agents was examined for cyclic loading applied using the hydraulic jack. Maximum load of 110kg (35.9 kg/cm2 pressure) was maintained for all the experiments. Number of force cycles needed to reach the pre-determined load was recorded; paper and wheat flour binder briquettes were needed five cycles and cow dung briquettes were needed additional two cycles. Natural drying time was evaluated at 86~89% relative humidity and 25~30oC ambient temperature, It was recorded that briquettes came to 25% moisture content (Wet basis) within 33 hours and 20% moisture content (Wet basis) within 35 hours. Compressive strength of the briquettes was tested for binder percentages of 30%, 40% and 50% (dry basis)of wheat flour and paper pulp binders. Results have indicated that compressive strength increased with the increase of binder percentage. Paper binder briquettes have comparatively high compressive strength in the range of 0.124N/mm2 to 0.238N/mm2 while wheat flour briquettes have 0.032N/mm2 to 0.055N/mm2. Calorific values of raw materials and briquettes were tested. Briquettes obtained from 30% paper binder and 30% wheat flour binder has calorific values of 18.14MJ/kg and 20.04MJ/kg respectively.