Drying Of Rubber Research Articles

Energy-efficient crumb rubber drying by heat recovery and solar air heating

Natural rubber is a key agro-industrial product in Asia, Africa, America, and Oceania, with widespread applications (e.g. tires, latex gloves, wet suits). The energy consumption of the traditional rubber drying process is very high and improvements should be investigated to both reduce the energy consumption, and reduce the cost of the rubber processing. The research investigated both heat recovery and solar air heating (SAH) to minimize the energy consumption of the drying process. A complete assessment of an industrial rubber drying plant in China demonstrated that a heat recovery can reduce the energy consumption by 16 to 44%. If moreover SAH is applied, further energy savings can be achieved. A pilot-scale SAH was tested. Its solar transfer efficiency was between 30% and 50%. Experimental data were theoretically validated, and used in a scale-up design strategy, resulting in an overall drying energy saving of 60 to 77%. The corresponding total investment and payback period are 300 and 420 k€ and 2 to 3.3 years respectively. The novel layout of the energy-efficient rubber dryer, and its energy performance are illustrated.

A Review of the Parameters Related to the Rubber Sheets Production: Major Constituents of Rubber Latex, Rubber Particles, Particle Interaction of Rubber Latex, Rubber Porous Structure, Rubber Drying Kinetics and Energy Consumption

Natural rubber (NR) is obtained principally from Para-rubber trees of the species Hevea brasiliensis which grow in tropical regions. Using ultra-centrifugation method, fresh latex (FL) from Para-rubber trees can be mainly divided into four fractions; an upper white layer consists of rubber particles, Frey-Wyssling particles in a yellow or an orange layer, C-serum phase and lutiods particles in the bottom fraction [1-3]. The averages of rubber particles have diameters of 0.02 to 3.0 micron, and they are protected by a complex film containing lipids and proteins [4-8]. The main forces of attraction between neighboring rubber particles in latex system can be divided into five force types; Structural Forces (SF), Van der Waals Interaction (VWI), Electrostatic Force (EF), Exclusion Interaction (EI) and Polymer-Polymer Interaction (PPI) [9]. The porous model of rubber structure used to describe moisture transfer was based on the existence of two different regions referred to as non-hygroscopic region and hygroscopic region. The rubber products drying always produced a considerable shrinkage effect which considered in the physical of the product, such as the diffusion coefficient, mass and heat transfer. An initial moisture content of raw material, the experimental temperature and the drying equipment had affect to the EMC isotherms and the drying kinetics. Finally, discussions on the implications of the results for strategies to reduce the energy consumption in RSS and STR20 block rubber are also presented.

Cleaner Potential for Natural Rubber Drying Process Using Microwave Technology Powered by Solar Energy

To reduce carbon dioxide emissions from traditional drying methods, this research investigated the use of microwave technology for drying Standard Thai Rubber (STR) in Thailand. Commercial microwave ovens were modified and integrated with the microwave emitting power control system to maintain the appropriate temperature levels to evaporate the moisture from rubber. Throughout the drying process, the temperature of the rubber was measured both internally and outside. The results revealed that STR5L and STR20 could be dried satisfactorily and met the requirements for standard Thai rubber properties by utilizing 500 W for 140 and 120 min, respectively. By keeping the temperatures less than 150 °C, rubbers’ molecular structure is not destroyed from internal heat stress. Although utilizing less power for a longer period of time is possible, more energy was used, which is unfavorable. Compared to traditional hot air drying technologies, which take approximately 4–6 h for the drying process, microwave technology potentially reduces the drying time by half or more. If solar energy is used to supply electrical energy, 300,000 tons of Carbon dioxide can potentially be eliminated annually in the STR drying industry in Thailand by promoting approximately 1115 MW of Photovoltaic technology installations with the solar resources in southern Thailand.

Performance of wet scrubbers to remove VOCs from rubber emissions

Poor performance of wet scrubbers in rubber processing plants due to breakthrough of specific volatile organic compounds (VOCs) causes odour impact events. The performance of wet scrubbers in the rubber drying process to remove VOCs was investigated in order to determine the responsible odorants. VOC emissions originating at the inlet and outlet of wet scrubbers were quantified using gas chromatography-mass spectrometry/olfactometry (GC-MS/O). Critical VOCs were identified alongside seasonal and daily variations of those VOCs. Altogether, 80 VOCs were detected in rubber emissions with 16 classified as critical VOCs based on their chemical concentration, high odour activity value (OAV) and unpleasant odour. Volatile fatty acids (VFAs) were the dominant VOCs with seasonal variations affecting emission composition. Results demonstrated the ineffectiveness of the wet scrubbers to mitigate odorous VOCs whereas the removal of some VOCs could be improved based on their polarity and solubility. It was found that there is a correlation between the wet scrubber performance and VFAs concentration in the emissions. The findings demonstrated that combining quantitative and sensory analyses improved accuracy in identifying odorous VOCs, which can cause odour annoyance from rubber processing. A VOC identification framework was proposed using both analyses approaches.

Optimization of operating parameters for rubber sheet fast drying in a forced-convection rubber smoking room

A new design of a rubber smoking room for fast drying based on conventional rubber smoking room was tested. Effects of the operating parameters for the fast drying of rubber in a forced-convection rubber smoking room were investigated. Temperature distribution, moisture content, thermal efficiency, specific fuelwood, electricity and energy consumption were evaluated for drying of 1,500 rubber sheets. The suitable operating condition from the experiment is 60°C and 12 m/s for the temperature and velocity. The rubber sheet moisture content was reduced to 0.4% db within 36 hours, i.e. 36 hours less than conventional smoke drying. The variation temperature inside the rubber smoking room was near uniform with a maximum of 8.0°C. The temperatures ranges were 38.9-64.6°C at the front plane, 40.4-65.0°C at the middle plane, and 36.7-62.9°C at the rear plane. A new rubber smoking room can save up to 49.3% in fuelwood consumption as compared to conventional rubber smoking room. Hence, the new rubber smoke drying system is capable of enhancing thermal efficiency and saving energy compared to existing rubber smoking room.

Applying Programmable Logic Control (PLC) for Control Motors, Blower and Heater in the Rubber Drying Processing

Rubber is the largest commodity in Indonesia. Rubber is traditionally processed and dried using bamboo hangers, manual arrangement of bamboo drying rubber, heat from firewood for drying chambers and large areas. This drying process has disadvantages, namely inconsistent drying time, non-uniform room temperature, unequal product quality, and unfriendly drying process. The solution is to overcome the automatic rubber dryer machine that is made using PLC to get the motor operating system for automatic rubber handling in the drying chamber, fixed drying temperature, small drying area, and fast-drying time. The experimental method is used for the automatic rubber drying process with PLC to control the movement of rubber in/out of the chamber dryer, heater, and blower for distribution temperature and other components. From the test results, it is found that the control system can work well at the voltage of each component of 220V, such as a sensor with a current of 0.21A and a stop time of 0.01s-0.3 seconds. The motor, heater, and blower are active (ON) at 220V with a current of 8.27A. The heater requires a current of 1.99A for active (ON) and an active blower (ON) with a current of 0.75A.

Improving the Safety of Drying and Packaging Section of Isoprene Rubbers

The analysis of main hazards at the section of isolation and drying of isoprene rubber is carried out. Incident causal factors and scenario analysis were studied and existing measures to ensure industrial safety are reviewed.The main initiating event of an emergency in the workshop is loss of containment followed by release of significant quantities of hazardous substances with subsequent negative development of the accident.The measures aimed at reducing the risk of an accident at the facility are: reducing the likelihood of equipment depressurization; minimizing the amount of hazardous substances entering the accident site; localization of the accident site; limitation of time spent by personnel in hazardous areas.In the event of a power outage, it is proposed to install a diesel generator set of the TSS AD-800S-T400-PM5 brand. This measure allows minimizing the amount of hazardous substances entering the accident site, which leads to a significant decrease in environmental and economic damage from the accident.

Assessment of sensible heat storage and fuel utilization efficiency enhancement in rubber sheet drying

A sensible heat storage unit was tested in the conventional method of rubber drying. The heat storage unit gradually releases the heat to the rubber sheet smoke room. This retains temperature in the range (40–60°C) for prolonging storage in the smoke room. Therefore, the frequent supply of wood to the furnace is trimmed down. Effects of the heat storage brick stack height on heat storage characteristics and applications for rubber sheet drying were investigated. The experiments were conducted at three heat storage heights, 50, 100, and 150cm. For all cases, the temperature of the brick stack was found to increase sharply during the initial period and remained constant for a period of time before slowly declining. This is a result of the heat storage system that maintains the high temperature by slightly releasing the generated heat. Thermal efficiencies of heat storage system varied between 33 and 28% for the heights of 50 to 150cm. The drying time of the rubber sheets using 100cm heat storage was 78h, while the thermal efficiency of the drying system was 6.71%. The frequency of wood addition was reduced from about five to six times per day to one time or less per day.

Mathematical modeling and performance investigation of mixed-mode and indirect solar dryers for natural rubber sheet drying

Smallholder rubber producers typically dry rubber in the open air, a process that takes about seven days, allowing the rubber to deteriorate and thus decreasing the price obtained by the producers. Solar dryers decrease the drying time by 2–3days, thereby yielding a higher quality product. In this study, performances of mixed-mode and indirect solar drying systems have been investigated for 30 natural rubber sheets. Drying efficiency of the mixed-mode dyer is 15.4% which is higher than the indirect solar dryer (13.3%). The moisture contents of rubber sheets are reduced from 32.3 to 2.0% and 29.4 to 8.0% on a wet basis for mixed-mode and indirect solar drying, respectively, in 4days. Hii et al. model is the combination of the Page and Two-term drying model. This model is found to best describe the natural rubber sheet drying behavior in both mixed-mode and indirect solar dryers. Coefficient of determination and root mean square error for mixed-mode and indirect solar drying of natural rubber are 0.998 & 0.0096 and 0.996 & 0.0109, respectively. Performance of the mixed-mode dryer is superior to the indirect solar dryer. Therefore, mixed-mode solar dryers are recommended for natural rubber sheet drying to smallholders.

Improvement of a rubber drying greenhouse with a parabolic cover and enhanced panels

Two structures of a greenhouse for rubber drying: (1) parabolic greenhouse (PG) and (2) parabolic greenhouse with the additional area-enhanced panels (PGEP) have been designed and built in this work. The experiment was divided into two parts: (1) a test of the empty greenhouses; and (2) a test of the greenhouses with rubber sheets drying. The results from the first part revealed that the measured air temperature within the PGEP was 5°C higher than PG’s. The new-designed PGEP provides higher thermal efficiency than the PG. Mathematical model was utilized to predict the air temperatures inside the empty greenhouses and the results agreed well with the experimental data. In addition, the test of greenhouses with rubber sheets drying showed that the drying period in PGEP was only 1.5 days while the drying period in PG was up to 5days. The rubber sheets dried with this method were classified as grade 1 (the top quality) and there was no fungal growth found in the sheets. The finite difference was applied in the mathematical model to predict the reduction of moisture content of the rubber sheets. The results from the model agreed well with the results from the experiments. Other significant parameters were also discussed.

Computational fluid dynamic analysis of innovative design of solar-biomass hybrid dryer: An experimental validation

A solar-biomass hybrid dryer is designed and constructed for natural rubber sheet drying. The dryer consists of solar collector cum drying chamber, heat exchanger and biomass furnace. There is indirect heating of rubber sheet instead of direct exposure to smoke in ribbed smoked rubber drying. An attempt has been done to reduce consumption of biomass by introducing solar energy application. Computational fluid dynamics technique is used to simulate the temperature and air flow distributions in an innovative design of drying chamber. The simulation results for temperature are found very close to experimental values in terms of statistical parameters. CFD simulation is done for air flow distribution inside solar-biomass hybrid dryer to ensure the utility of air circulating fans. The solar-biomass hybrid dryer is tested for drying of 100 number of natural rubber sheets. Moisture content of rubber sheet is reduced from 34.26% to 0.34% (db) in only 48 h, a notable reduction in drying time as well as consumption of biomass. The color and texture of the natural rubber sheet were noticed better than the traditional smoke rubber drying.

Drying kinetics of technical specified rubber

This paper reports the study of crumb rubber drying in different experimental designs. It is important to understand the characteristics of crumb rubber drying in order to formulate a better drying strategy that could give higher energy efficiency. Four experiments were carried out with constant heat at maximum 100°C and a stainless steel container was used to hold the sample of crumb rubber under study. The surface temperature profile of the rubber was investigated using two types of drying methods, normal hot air drying and vacuum drying. It was found that when the sample was dried, external surface temperature for drying with hot air dryer was higher than vacuum dryer. The results showed the evolution of temperature profile was not in good agreement with the prediction which revealed that there was no temperature gradient within the drying samples. The energy consumption for vacuum drying was higher compared to hot air drying, where there was a difference of 0.7079MJ/kg H2O evaporated for drying temperature at 100°C. The best fit model generated from the experimental data was the modified Henderson and Pabis model and the highest effective diffusivity obtained was 5.243×10−9m2/s heating by vacuum oven at 90°C under zero atmospheric pressure.

Determination of Isosteric Heat and Entropy of Sorption of Air Dried Sheet Rubber Using Artificial Neural Network Approach

Equilibrium moisture contents (EMC) of air dried sheet (ADS) rubber were determined by commonly gravimetric-static method with saturated salt solution among surrounding temperatures of 40-70°C correlated to water activity (aw) ranges between 0.10 and 0.9. The experimental results was analyzed by 5 commonly EMC model. The results showed that equilibrium moisture content of ADS rubber decreased with increase of surrounding temperature at constant water activity and the simulated data using Chung-Pfost model has a good relation to experimental data with R2, RMSE and χ2 equal 0.9565, 0.0235 and 0.0006, respectively. However some physical property of ADS rubber sample affects to evaluate EMC modeling. Due to avoid this effect, thus the aim of this research work was to determine EMC value by using Artificial neural network (ANN) method and also evaluate the isosteric heat of sorption by following the Clausius-Clapeyron equation. The results showed that simulated results using ANN approach has relatively high accuracy compared to common EMC model. Finally determination of isosteric heat of sorption and entropy of sorption of ADS rubber were carried on. The results stated that the enthalpy and entropy of heat sorption was power function and polynomial function of moisture content respectively. These two parameters of ADS rubber can be used for prediction suitable storage condition and drying condition for ADS rubber drying in the near future work.

Drying Modeling and Energy Consumption of Air Dried Sheet (ADS) Rubber by Solar and Biomass Energy

This research aims were to evaluate drying kinetics model for describing evolution of moisture transfer of air dried sheet (ADS) rubber by using solar and biomass drying, multi-stages solar and biomass drying [2 stages (2S) and 3 stages (3S)] and conventional open-sun (OS) drying. The experiments were carried out under the conditions of ADS rubber drying with temperature of 30-60°C. Initial moisture contents of sample rubber were varied between 20 and 50% dry-basis. The final moisture content for each drying strategies was fixed at 1±0.05% dry-basis. The experimental drying results were mathematical simulated by 7 common non-linear empirical models. The results showed that fresh rubber sheets drying with OS technique took longer drying time than those of solar and biomass drying. And the simulated data using approximation of diffusion model was the best fitting to experimental data of rubber sheet. Effective diffusivity of ADS rubber was also determined using the 2nd Ficks law of diffusion and conclusion was that effectice diffusivity was dependent on drying temperature and was in order of 10-7 m2/s. With various drying strategies, the results showed that specific energy consumption of 3-stages ADS rubber drying had a relatively low compared to the other drying techniques.

Technical Review on Crumb Rubber Drying Process and the Potential of Advanced Drying Technique

Intensive thermal energy and extensive drying period are required in rubber drying process due to its low conductivity and dielectric properties. Thus, selection of advanced drying techniques of crumbs rubber is essential for the sake of efficiency and energy conservation. The integration of advanced dryers ranging from electromagnetic heater, fluidized bed dryer, heat pump and the vacuum environment were discussed in details in paper. In summary, cost and energy efficient dryer is the aim of this research work and it is important that this technology offers a robust and reliable solution to the rubber processing industry.

Modeling the process of drying of rubber by means of the pressure release method in a screw drying machine

A physical analogy between processes of destruction of brittle bodies under the effect of impact action and the production of polymer granules with highly loosened outer layers upon discharge from the spinneret of a screw drying machine as a result of pressure release is used to construct a mathematical model.

Drying Model, Shrinkage and Energy Consumption Evaluation of Air Dried Sheet Rubber Drying System for Small Enterprise

The main objective of this research was to study drying kinetics of air dried sheet (ADS) rubber using hot air and simulated drying kinetics by empirical model compared to experimental results. The 10-15 fresh rubber sheet with initial moisture content ranging of 23-40% dry-basis was dried by temperature of 40-70°C and air flow rate of 0.7 m/s. The fresh rubber sheet samples were dried until the desired final moisture content reached to 0.15% dry-basis. The experimental results showed that the drying rate of ADS rubber dried with hot air convection was faster than conventional natural air convection and drying rate was related to drying temperature. The experimental data was statistical non-linear regression analyzed by using 10 conventional empirical models. The coefficient of determination (R2) and root mean square error (RMSE) values were used as the criteria for selecting the best equation to describe the experimental data The results showed that the calculated results of Verma et al.’ model had a good relation to the experimental results. For specific energy evaluation, the results showed that at high drying temperature specific energy consumption of ADS rubber was relatively low compared to drying with low temperature. Finally, the determination of physical quality showed that.

Determination of Volatile Fatty Acids from Raw Natural Rubber Drying Activity by Thermal Desorption-Gas Chromatography

Malodourous emission from raw natural rubber (NR) processing activities has become a public nuisance since residential and public development areas are gradually expanding near raw NR processing factories. The malodourous vapour mainly consists of volatile fatty acids (VFA) released from the breakdown of non-rubber constituents during drying stage of the raw rubber processing. An improved sampling methodology to characterise and monitor VFA from the drying stage was implemented. This study focused on the drying stage as the major source of malodour in the raw rubber processing. The thermal desorption-gas chromatography technique enabled direct sampling of air pollutants with minimal errors. It was found that acetic acid and propionic acids were present with highest concentrations. In general, concentrations of individual VFA varied throughout the drying stage. The raw NR processing factories were able to eliminate more than 71 % of total VFA using the relevant water scrubber treatment systems. The malodour characterization technique used in this study provides new technical information useful to develop more efficient malodour control systems for the raw NR processing industry.

Study of a new route by which to make fully cured thermoplastic elastomers with plastics and ultrafine powdered rubber

AbstractA series of fully cured thermoplastic elastomers (TPEs) have been developed by mixing plastics and fully cured, ultra‐fine powdered rubbers (UFPRs). The fully cured UFPRs were prepared by the irradiation of rubber latexes and drying of the irradiated rubber latexes. The average particle size of the UFPRs ranged from 50 to 500nm. The influences of the dose rate, absorbed dose and content of cross‐linking agent on the cross‐linking of rubber latexes were studied. It was found that a new type of TPEs with excellent properties can be easily made by blending UFPRs with plastics.

DRYING OF RUBBER BY THE PRESSURE-DROP METHOD IN AN ENDLESS-SCREW MACHINE

Drying of rubber by the pressure-drop method in an endless-screw machine has come into widespread use in the final stage of the water method of separating rubber from the polymerization solution [1, 2]. Investigations indicate that the extent to which the rubber is dewatered increases with decreasing time of the pressure drop in the rubber discharged from an endless-screw drier [3‐6]. The most effective drying process occurs when the material is discharged from the machine under conditions whereby the rubber particles are ejected spontaneously through the draw plates of the discharge apparatus. Here, it is possible to lower the material-processing temperature [5‐9], and also to use traditional discharge apparatus on the dryer, and equip the latter with additional hardware components [7‐9]. Modeling of Rubber-Drying Process by Pressure-Drop Method. Numerical analysis of this process is frequently performed on the basis of the heat-balance equation [2, 10]. To account for the effect of thermomechanical removal of some of the moisture in the liquid state during the material’s drying, a correction factor is introduced to the heat-balance equation [11]. A more common approach to modeling of the drying of materials is based on its description by a system of differential equations that take into account the heat- and mass-exchange processes. Based on theoretical analysis and results of experimental investigations, Lykov [12] and Lykov and Mikhailov [13] derived a system of differential equations, which makes it possible to account for basic characteristic features of the drying of capillary-porous materials. Its use, however, requires a large volume of experimental data on the heat- and mass-exchange characteristics of the material being dewatered. To describe the drying of a capillary-porous material, Ivashov [14] proposes a simplified system of differential equations of heat and mass transfer, which is oriented toward a predominance in the drying process of the molar transport of moisture in the form of vapor as it boils within the mass of material: