Tea Drying Research Articles

Assessing the Applicability of Solar Thermal Technologies for Industrial Tea Drying

Most process heat being used for various industrial applications is supplied from fossil fuels. Coal, gas, and wood fuel are the most used heat resources which usually power steam boilers for production of heat used in a wide range of industrial processes. Since economic growth is largely linked to industrial production, it implies that, a shift towards use of clean energy technologies in industries is crucial to meet the rising demand of process heat while, cutting down carbon emissions to mitigate climate change. Solar thermal systems have over the past years shown potential as a practical alternative to fossil fuels for production of heat for several applications including, water and space heating, industrial process heating and electricity generation in thermal power plants. This study seeks to assess the feasibility of employing solar thermal technologies for drying purposes at Tingamira-Tanganda Tea estate in Zimbabwe. Systems advisor model (SAM) was applied to simulate performance of linear Fresnel (LF) and parabolic trough (PT) solar thermal technologies for industrial tea drying. Information on daily heat demand, required process temperatures and current heat sources was obtained to inform the design process of the proposed solar thermal systems. LF system exhibited better techno-economic performance. It requires a smaller collector area (360 m2) with a lower initial capital cost which is about 8% cheaper. Moreover, it produces higher annual energy at lower levelized cost of heat for solar multiples higher than 1. Carbon footprint of the factory would be reduced by about 114 tonnes CO2 annually. Sensible thermal energy storage technology can be considered for back up heat and heat recovery.

Analysis of drying characteristic, effective moisture diffusivity and energy, exergy and environment performance indicators during thin layer drying of tea in a convective-hot air dryer

The objective of this study is mainly to analyze the drying kinetic parameters, effective diffusivity, and thermodynamic performance indicators (energy, exergy, heat, and mass transfer coefficients) of tea under different drying conditions of different drying temperatures (DT) and thin layer thicknesses (TT). Experimental drying was conducted at drying temperatures of 70°C, 80°C, and 90°C with thin layer thicknesses of 10 mm, 15 mm, and 20 mm. The results show that a higher drying temperature and a lower thin layer thickness can increase evaporation moisture content and shorten drying time. By evaluating and comparing the fitting of five drying models adopted by the coefficient of determination (R2) and chi-square (χ2), it can be found that the logarithmic model is the best to describe drying behavior. The effective moisture diffusivity shows a positively correlated trend with the increase in DT and TT, with the value of activation energy ranging from 14.030 to 22.344 kJ mol−1 K−1. The specific moisture evaporation rate (SMER), energy efficiency, exergy efficiency, and sustainability index (SI) descend as the TT increases at all DT; the specific energy consumption (SEC) and improvement potential (IP) rate perform in an opposite manner, but the TT remains unchange. The conclusion drawn from the thermodynamic parameters is opposite to the aforementioned. As the TT increases, the heat and mass transfer coefficients show a significant decrease trend. In addition, the heat and mass transfer coefficients are given as functions of DT and TT, and further knowledge shows that the mass transfer coefficient is positively correlated with DT but the heat transfer coefficient is negatively correlated. In conclusion, this article provides new insights into the effects of drying characteristics, energy consumption characteristics and heat and mass transfer characteristics in the process of tea drying under different drying conditions, and provides certain theoretical reference bases for promoting the optimization of industrialized tea drying production machinery design and drying process optimization.

Potential for Solar Industrial Process Heat Systems for Tea Drying Applications – A Case Study

Abstract An increase in energy consumption especially for industrial applications enhances the uptake of fossil fuels since, they are currently the major sources of industrial process heat and electricity. The need for clean energy technologies is therefore critical, in order to meet the rising energy demand using sustainable energy sources. Solar thermal energy technologies have attracted much attention in terms of research and developmental activities worldwide. The present study seeks to explore the viability of adopting solar thermal technologies at Tingamira - Tanganda Tea estate, Zimbabwe. Data on current sources of heat, daily consumption of process heat and required process temperatures was gathered. Systems advisor model (SAM, version-2021.12.2) was applied to analyse feasibility of linear Fresnel (LF) and Parabolic trough (PT) solar thermal technologies for industrial tea drying. LF system is potentially a better option for producing process heat for low temperature applications. It requires smaller aperture area (360 m2) and a lower initial capital cost of $ 112 860 which is about 8 % cheaper. Also, it yields more energy at lower levelized cost of heat as compared to PT technology when solar multiple is increased up to 2. Replacing wood fuel would reduce the factory carbon footprint by 114 tonnes CO2 annually. Also, potential for sensible rock-bed heat storage systems in the tea factory was assessed. Rock bed sensible TES using natural rocks can avail a viable option for heat storage and about 16 m3 of storage volume would be needed to meet a daily heat demand of 1 MWh.

Application of Optimum Adaptive Generalized Predictive Control to Green Tea Drying

Application of Optimum Adaptive Generalized Predictive Control to Green Tea Drying

Design of Green Tea Drying System Using Smoke and Temperature Sensors Based on Microcontroller

The green tea drying process still uses wood as its fuel because it can reduce production costs. However, the smoke produced by the bottom firewood enters the drying chamber, thus affecting the quality of the green tea produced. Therefore, it is necessary to have a drying system that can detect and control the smoke entering the drying chamber and control the temperature during the drying process. The tea drying system is designed using a smoke sensor and a temperature sensor based on a microcontroller. This system is also equipped with an RH sensor that can monitor the RH value during the drying process. From the device performance test results, it was found that the system designed can control the smoke and temperature in the drying chamber to be applied to the green tea drying process in tea factories.

Development and testing of novel photovoltaic-thermal collector-based solar dryer for green tea drying application

A sustainable solar based PVT tea drying system has been developed to minimize the dependency on the non-renewable commercial tea drying system. In this work, the effect of operating conditions on the performance of a photovoltaic-thermal (PVT) collector-based solar dryer is investigated under sunny and cloudy weather conditions for three different cases- Case-I (natural convection), Case-II (forced convection with an air velocity of 0.096 m/s), and Case-III (forced convection with an air velocity of 0.014 m/s). Firstly, energy performance of the PVT system has been evaluated for all the three cases under sunny and cloudy days, which show that the energy performance has been enhanced to a maximum value of 58.71% and 53.95% for sunny days and cloudy days, respectively, and these are obtained in case of case-III. Then the drying of green tea under mixed-mode drying (MMD) and indirect mode drying (IMD) are presented under sunny days for each of the three cases and compared with open sun drying (OSD) and shade drying (SD). The moisture content has been reduced from 2.95 (d.b.) to 0.14 (d.b.) in all the cases of drying modes. Further, the drying kinetics of green tea leaves is compared using existing models, and a new drying model is proposed, which is found to predict the moisture ratio better. The maximum PVT dryer efficiency, moisture effective diffusivity, and specific moisture extraction rate (SMER) are 26.37%, 4.97 × 10−9 m2/s, and 0.6125 kg/kWh, respectively, for MMD process.

A Study on Performance Evaluation of Tea Dryers

HighlightsThis study used data normalization, radar chart and weighting difference analysis to compare the performances of four types of tea dryers in terms of drying efficiency, energy, costs, qualities, and total efficiency.The electro-thermal dryers were more energy-saving and environment friendly.The vacuum drum dryer has the potential for useful application in high quality tea drying. Abstract. Tea dryers are essential equipment for tea manufacturers whereby, the hot-air tea drying machines, such as multiple-layer conveyor dryer (MLD), electric hot-air dryer (HAD), and low-humidity dryer (LHD), are commonly used. The vacuum drum dryer (VDD), a new type of tea dryer, has the potential to improve the drying quality and efficiency. Hence, it is necessary to assess its performance in comparison with the other three dryers to facilitate its application in the tea industry. This study used data normalization, radar chart, and weighting difference analysis to compare the performance of these four dryers in terms of drying efficiency, energy, costs, qualities, and total efficiency. The evaluation results indicated that the investment cost of the HAD was the lowest among all, followed by LHD and MLD, while the VDD was the highest. In terms of the drying quality, the opposite trend was observed in which the VDD gave the best performance, and followed by LHD, MLD, and HAD. For the rating of total efficiency, HAD outperformed VDD and LHD, where the lowest total efficiency was attained by the MLD. Considering the equal weighting of cost and quality, it can be concluded that HAD showed the best performance while MLD was the worst. Different requirements for cost and qualities affect the final evaluation of tea dryers. The electro-thermal dryers were more energy-saving and environment friendly than the fuel dryer. The VDD has better performance in terms of drying rate and qualities. Despite its energy consumption and equipment costs are higher, it still has the potential for useful application in high-quality tea drying. The continuous effort of researchers and dryer manufacturers in reducing the input costs and enhancing the benefits can improve the energy consumption and machinery cost of VDD. Keywords: Dryer, Performance evaluation, Radar chart, Tea.

TOWARDS THE IMPLEMENTATION OF E-MANUFACTURING: DESIGN OF AN AUTOMATIC TEA DRYING CONTROL SYSTEM

Normal 0 false false false EN-ZW X-NONE X-NONE Many of the production costs for producing tea are attributable to the process of drying the tea. E-manufacturing can assist companies to reduce these production costs by making crucial information available to decision-makers so that they can make informed decisions. This paper presents an application of e-manufacturing to the design of an automatic tea drying control system. This control system will ensure that the multiple drying parameters such as temperature, dryer-exit tea moisture content, and fuel consumption are maintained at optimal states during the course of the drying of tea. The additional aim of this system is to balance the cost of production and the quality of the final product. Using the Guggenheim-Anderson-De Boer (GAB) model, the optimum drying temperature was found to be 100-110°C, while maintaining a dryer-exit tea moisture content of 3 to 3.12 per cent, at a drying rate of 3 per cent per minute. A Barix control application to control the system’s activities, using the web user interface (WUI), was also developed. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0mm 5.4pt 0mm 5.4pt; mso-para-margin:0mm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;}

Models and experiments for energy consumption and quality of green tea drying

AbstractAn experimental apparatus has been developed to evaluate the drying process of green tea leaves. Tea drying is an energy‐intensive process which results in the removal of leaf moisture; it is essential to the quality of the final product. In order to more efficiently use process energy, a prototype drying system has been built and tested. The prototype incorporates a rotating perforated drum which helps speed the drying process. Experiments were carried out with multiple temperatures, airflow rates, and drum rotation rates; a subset of those results is shown here. In particular, the impact of airflow rate on the process was studied. It was found that as the airflow increased, the drying rate increased, as expected. However, the efficiency of energy use, which was quantified by the Specific Energy Consumption rate, varied considerably with flow. While higher flows led to faster drying, it resulted in a lower energy efficiency. Also, a two parameter predictive model was developed that was able to accurately match the moisture removal rates for a very wide range of flows. This predictive model, which is based on thermal‐fluid fundamentals, can be used to extrapolate the presented results to cases which were not considered.

GIS based assessment of rice (Oryza sativa) straw biomass as an alternative fuel for tea (Camellia sinensis L.) drying in Sonitpur district of Assam, India

This paper presents a study on spatial distribution of rice (Oryza sativa) straw and its potential demand as a renewable energy fuel for tea (Camellia sinensis L.) drying. Rice straw availability and its demand in tea gardens are estimated using IRS-P6 LISS III remote sensing data in GIS environment. Shortest road transportation network is designed to ascertain that rice straw is delivered in the tea gardens with minimum transportation cost. Costs of production and harvesting of rice straw are also assessed and incorporated in the overall procurement cost of rice straw biomass. It is observed that the degree of fulfilment of thermal energy demand for tea drying through rice straw is spatially varying. It is also found that straw biomass can economically compete with coal as a source of thermal energy in tea drying and contribute to the farmers earning from otherwise waste straw, if coal equivalent price is fixed for straw. The coal equivalent cost of straw could be raised up to 37.04 $ t−1 which would enhance farmers profit upto 18.26 $ t−1.

MICROWAVE DRYING CHARACTERISTICS OF ASSAM CTC TEA (CAMELLIA ASSAMICA)

ABSTRACT Microwave drying characteristics of Assam crush, tear, curl (CTC) tea were determined at five different microwave power of 180, 360, 540, 720 and 900 W respectively. The effect of power level on moisture content and drying rate (d.b.) of 50 g CTC tea sample were investigated. The time required to reduce the moisture content to any given level in microwave drying was dependent on the power level. Four mathematical models (Henderson and Pabis, Lewis, Page and logarithmic) were used for fitting experimental data. The estimated empirical parameters together with the corresponding sum of square error from nonlinear regression analysis for all the models were tested. The Page model was found to have the better suitability for describing drying characteristics of Assam CTC tea. PRACTICAL APPLICATIONS Assam crush, tear, curl tea is an important process food commodity involving substantial commercial activities at national as well as international levels. Appropriate processing of this commercially important commodity is a critical issue to be addressed to fetch higher prices at competitive tea markets. The major disadvantages of present conventional dryers used in tea drying are low-energy efficiency and long drying time. But reduction in time and energy consumption by using microwave in tea drying could make a significant contribution to tea industry. This study may successfully used for design, analysis and performance evolution of microwave tea drying.

A Microcontroller-Based Monitoring System for Batch Tea Dryer

This paper presents an automated tea dryer system based on programmable controller which controls moisture content of the tea leaves and temperature of the chamber in different stages of drying. Several techniques were used for tea drying systems according to the tea genres. The batch tea dryer is designed with 6 to 8 trays. The temperature above the trays is controlled between 50oC and 100oC. Moreover, the moisture content of the tea leaves declined from around 68% to approximately under 3%. In addition, the temperature of the leaves increased from a little less than 30oC to 80oC. A microcontroller as the main processor was deployed to process received data from sensors and also it provides control signals. Thus, this system equipped a data logger memory to record data during drying process. The analyses of dryer products shown the feasibility of using propose system for batch tea drying.

Adequacy of Crop Residue Biomass as Renewable Energy Source for Tea Drying in Assam: A Spatial Assessment Debendra Chandra Baruah

Assarn is the largest tea producing state with an annual contribution of about 51% of nation's production. Coal, TD 011, and natural gas are used in tea drying as a source of thermal energy. Crop residue biomass is considered as a potential substitute of fossil energy. Availability of sufficient biomass in the vicinity of user location, avoiding costly transportation, is one of the major considerations. The present investigation makes a spatial analysis of paddy crop residue biomass availability vis-A-vis energy demand in tea drying in ten spatial units representing all the dismcts of Assam. Paddy is a major crop in Assarn and grown in all the districts. Energy availability from paddy crop residue biomass was compared with the thermal energy demand for tea drying. Husk fuelled gasification and straw fired combustion technologies were considered with assumed levels of energy conversion efficiencies. The analysis indicated that tea drying in Assam required 12.43 PJ of thermal energy annually. Total annual available bio-energy was estimated as 5.09 PJ and 23.37 PJ from paddy husk and paddy straw, respectively. Overall, bio-energy availability from paddy husk would be sufficient to fulfil only 40.97% of the demand of the state. However, entire thermal energy demand for tea drying in Goalpara, Kamrup, Lakhimpur, Nagaon and Karbi-Anglong could be fulfilled through husk generated bio-energy in these districts. For the state as a whole as well as in seven spatial units (baring Dibrugarh, Sivasagar and North Cachar), bio-energy available from paddy straw would be adequate to fulfil the thermal energy demand for tea drying. Dibrugarh and Sivasagar were deficient in paddy residue biomass. An index is defined to test the adequacy of crop residue biomass to support energy demand in tea processing as ratio of growing areas of paddy and tea. The districts with ratio more than 3.58 were found to meet the resource adequacy criteria

04/01069 Computer simulation of a downdraft wood gasifier for tea drying: Jayah, T. H. et al. Biomass and Bioenergy, 2003, 25, (4), 459–469

04/01069 Computer simulation of a downdraft wood gasifier for tea drying: Jayah, T. H. et al. Biomass and Bioenergy, 2003, 25, (4), 459–469

Thin-layer modelling of black tea drying process

An experimental dryer was developed for determining the kinetics of black tea drying. Drying characteristics of tea were examined using heated ambient air for the temperature range 80–120°C and air flow velocity range 0.25–0.65 m/s. The data of sample weight, dry- and wet-bulb temperatures and air velocity of the drying air were recorded continuously during each test. The drying data were then fitted to the different semi-theoretical models such as Lewis, Page, modified Page, two-term and Henderson and Pabis models, based on the ratios of the difference between the initial and final moisture contents and the equilibrium moisture content. The Lewis model gave better predictions than other models, and satisfactorily described the thin-layer drying characteristics of black tea particles. The effective diffusivity varied from 1.14×10 −11 to 2.98×10 −11 m 2/s over the temperature range. The temperature dependence of the diffusivity coefficient was described by the Arrhenius-type relationship. The activation energy for moisture diffusion was found to be 406.02 kJ/mol. Temperature and air velocity dependence on drying constant was described by the Arrhenius-type and Power-type relationships. The coefficients of determination were above 0.996 for both relationships. The Arrhenius-type model was used to predict the acceptable moisture ratios at the experimental drying conditions and to understand better the influence of drying variables on drying rate constant. The results illustrate that in spite of high initial moisture content, the drying of tea particles takes place only in the falling rate period. This single-layer drying equation can be used for the simulation of deep-bed drying of black tea.

PH—Postharvest Technology: A Comparison of Dryer Types used for Tea Drying

The objective of this work was to determine how various types of tea dryer would perform with different levels of inputs. Three dryer types were commonly found in practice, two others are not generally used and one type is unknown in practice. Simulation models for each type were constructed from a thin-layer drying model. The information gained from the simulations showed which type of dryer was more efficient at heat and air utilization. Graphs of the moisture content of the product discharged from the dryer show which variables need to be controlled most tightly in practice, and which variables might be successfully manipulated by a control system. This study has implications not only for the control of various dryer types, but for the physical design of the dryers. The multi-stage fluid bed dryer with re-circulation is found to have the best combination of characteristics, and is the type increasingly used in industry.

Control of fluid bed tea dryers: controller performance under varying operating conditions

A study was made of the robustness of controllers for fluidized bed tea drying. Several controller configurations have been designed and studied in previous work. Tuning of these controllers is possible using a transfer function estimated from the frequency behaviour of a validated simulation model under normal operating conditions. In this work a range of operating conditions deviating from the standard conditions was studied. Controller tuning determined by the Cohen & Coon or Ziegler–Nichols methods was not found to be robust over the range of conditions tested. A different method was developed, based on dryer modelling, to establish a range of controller settings giving minimal Integral Squared Error while maintaining adequate gain and phase margins. These settings were found to be suitable for the whole range of conditions tested. A simplification to the inferential controller, using gains only rather than complete transfer functions in the inferential estimator, was shown to be justified.

The state of renewable energy harnessing in Tanzania

This paper details the state of renewable energy development in Tanzania and biomass energy supply and consumption. It also highlights the various levels of renewable energy programmes in the country and the Government strategy to improve renewable energy production and utilization technologies. A number of problems hindering the development of renewable energy technologies have been identified and discussed. Biomass accounts for 92% of final energy consumption in Tanzania and will continue to dominate the national energy balance. For example, fuelwood and agricultural residues used to meet domestic energy needs account for 80% of the domestic energy requirements, while commercial energy such as kerosene, electricity and liquefied petroleum gas account for 1%. Total biomass resources for 1990 was 27 million tonnes of oil equivalent (TOE) from the natural forests. Other major industrial biomass energy sources include sawmill industry, sugarcane plantations, sugar industry by-products, cashew nut industry, coffee industry and sisal industry. The major biomass consumers include woodfuel for domestic use, tobacco production, brick making, tea drying and fish smoking. While there are efforts to develop other renewable sources of energy such as solar, wind and minihydros, there are also problems hindering their development. They include the lack of adequate data on the actual energy potential of these sources as well as the lack of local capability to design and manufacture energy related equipment and spare parts.

Monitoring and control of fluid-bed drying of tea

Tea processing requires new technology for improving quality management and process control. A data logging system was developed to monitor and control tea processing lines. The quality of the manual control of the drying operation is limited because of the time taken to reach stability. A model for fluidized-bed tea drying is used for the development of a new control strategy. The fluidization requirements and the drying kinetics for this model are established in experimental studies. The model is simulated in MATLAB and allows various control strategies to be studied before being implemented in practice.

Thin Layer Drying of Black Tea

This paper describes the experiments used to determine the kinetics of tea drying. New thin layer drying apparatus was designed and built to measure the very high rates of drying found at the start of drying, and the results show that the Lewis equation satisfies. The drying rate constant proved to be a linear function of temperature and airflow rate, indicating that tea drying is not only diffusion limited but also a function of convection. The results were validated on independent experiments.