Pneumatic drying of cassava starch: Numerical analysis and guidelines for the design of efficient small-scale dryers

In a number of tropical countries, the expansion of cassava processing is tied to the development of small-scale, energy-efficient pneumatic dryers used to dry flour and starch. To facilitate this development, in this study a model of the pneumatic drying of starch particles was developed, to be fitted to measurements taken from large cassava processing factories. After that, numerical simulations were performed to analyze the effects of geometry and operating conditions on the energy efficiency and pipe length required to dry the product. The results clarified the influence of processing capacity, air inlet conditions, and starch particle size, emphasizing that air velocity as well as the dilution of the starch should be minimized. In light of the findings described here, we offer guidelines for the design of efficient small-capacity flash dryers

Optimal physicochemical properties of dried litchis for Thai consumers

The litchi is a fruit essential for the economies of several Southeast Asian countries, but markets regularly reject it, mainly due to spoilage. Drying extends the shelf-life of litchis, but in Thailand the optimal characteristics of the dried product have not yet been determined. The purpose of this study was to determine the optimum physicochemical properties of dried litchis – those suitable for Thai consumers. The dried fruits were submitted to physicochemical measurement and consumer evaluation, with datasets subsequently integrated using circular ideal-point regression analysis. Response surface methodology was then used to predict the optimum physicochemical properties of the fruits. It was found that Thai consumer preferences with regard to dried litchis are for the fruits to be of golden-yellow color (L* ranging around 54; H ranging around 79°), to have a soft flesh (SMF ranging between 13 and 14 kN/100 g) and to have a sweet taste (TSS:TA ranging between 25 and 28). The results may be used in the future to prescribe pretreatments and drying conditions

Development and trials of a small-capacity pilot flash dryer for cassava-derived products

The ultimate operation in the production process of cassava starch and flour, consists in drying the product from about 40% down to 13% moisture content, to ensure a long shelf-life. In small processing units, the starch is, in most cases, dried in the sun, which proves to be impractical when increasing the processing capacity. It requires large concrete surfaces and the quality is difficult to control due to the variations of weather conditions, outside contamination and the long drying time. Thus, the lack of efficient small-scale dryers is a barrier to the growth of rural processing units. To address this issue, we conducted a series of works to downscale the flash drying technology commonly employed by industrial starch plants to suits the need of rural processors. Based on the modelling of the flash drying process and on field experience, we designed and built a pilot flash dryer that was started up at CIAT, Cali, Colombia in 2017. It was conceived as a research, development and training tool to facilitate the development of low-cost, efficient small-scale dryers by stakeholders in the cassava sector. First, we will present the design method and the implementation of the adopted technical solutions, then we will present the results from the first drying experimental trials conducted with native cassava starch. The objective was essentially to evaluate the drying efficiency and to investigate the effects of drying air temperature and pipe length. The specific energy consumption is as low as 3500-4000 kJ/kg of water evaporated (1400-1500 kJ/kg of dried product), which may enable cost-effective drying of cassava flours and starch at small-scale. Indeed, demands for implementing the technology have already arisen from various countries including Colombia, Brazil and Uganda

Roller press construction guide

Cassava (Manihot esculenta Crantz) is a perennial root crop native to South America and the main source of calories for many people living in sub-Saharan Africa. However, two days after harvest, the cassava roots become unsuitable for human consumption. To extend its shelf-life, the roots need to be processed into flour; a dried product that is used as the basis for many dishes. To process cassava into flour, the roots are peeled, grated, pressed, pulverized, dried, and milled. From those steps, drying is the most energy-intensive one. Therefore, dewatering before drying is an important step that results in significant energy savings. Dewatering is the step where water is removed by mechanical means instead of by evaporation. Cassava dewatering can be considered as an expression operation, a separation process where the water is expelled from the wet cassava mash by pressure. In sub-Saharan African countries cassava dewatering is done using presses. Those presses usually have a perforated cage and a top piston. The mash, obtained by grating the roots, are placed in bags, and those bags are piled inside the cage one on top of the other. When the press is full, the piston is slowly lowered, squeezing the material, and forcing the water out, through the bags and the perforations in the cage. After pressing, the piston is raised and the bags containing the press cake are removed to be pulverized. This kind of presses are popular because of their simplicity and low cost, but it has three major drawbacks: work drudgery, inconsistent reduction in moisture, and low throughput. Those drawbacks are associated with the fact that those presses operate in batches, instead of continuously. Continuous presses are used widely for the expression of fruit juices and oils from various oilseeds. They require less labour than batch operated presses, have higher throughput and their operation is more consistent. However, continuously operated dewatering equipment suitable to cassava processing centres in sub-Saharan Africa is not available. Therefore, the objective of this working paper is to provide instructions on how to build a simple and low-cost continuously operated cassava dewatering equipment

Pellet machine construction guide

Fish farming has long been seen as a promising solution to combat food insecurity in low-income countries. However, the lack of local fish feed production has been a major obstacle to its success. Despite various initiatives launched over the years to promote fish farming, the lack of access to fish feed has hindered their intended impact, as insufficient feed results in underdeveloped fish stocks, poor harvests, and limited income. Simulation-driven Participatory Technology Development was used to develop a Pellet Machine needed for on-site fish feed production. The machinery produces high-quality fish feed and empowered the rural communities to produce their own fish feed using locally available resources

Improved energy efficiency of farmers' cooperative litchi drying operation in Northern Thailand

In 2007, Hmong farmers growing litchi in the mountainous region of Northern Thailand started to dry the fruit in response to its declining market price. However, the locally available dryer, although affordable and of a size appropriate for smallholder farmers' cooperatives, showed excessive gas consumption, and this, along with rising fuel costs, imposed a threat to the drying operation. The objective of this study was to test low-cost, easy-to-implement modifications to a locally available convection dryer, to improve its energy efficiency. Experiments were conducted in cooperation with a Hmong farmers' cooperative in Northern Thailand. Insulation of the air ducts and control of the air recirculation rate led to energy cost savings of US$2.45 per dryer-load. With the modifications required being simple, the investment needed was recovered after only approximately 20 loads, while the energy efficiency of the dryer increased from 33% to 39%

Training Course Report: determining energy efficiency of dryers

Training Course Report - No abstract available

Solar-powered multipurpose hammermill (Part 2)

This guide is part of the project entitled Design and development of direct-coupled photovoltaic powered agri-processing machinery, funded by Agri-Tech Catalyst (Innovate UK). It was prepared to instruct Mr Emmanuel K. Duah (First Products Enterprise’s Managing Director) on how to build a novel solar-powered multipurpose hammermill to be used for cassava processing. The Construction Guide is separate in 2 parts. Part 1 instructs the construction of the hammermill itself. Part 2 instructs the construction of the cyclone separator and its filter bags

Multipurpose hammermill: construction guide

Efforts to promote fish farming in low-income countries aim to improve food security for rural communities living in poverty. However, many initiatives have fallen short due to the lack of local fish feed production, resulting in underdeveloped fish stocks and poor harvests. To address this challenge, Simulation-driven Participatory Technology Development was used to create machinery for on-site fish feed production

Tunnel dryer and pneumatic dryer performance evaluation to improve small-scale cassava processing in Tanzania

In sub-Saharan Africa, cassava is grown by smallholder farmers and is the principal source of calories for the local population. However, the short shelf life of cassava associated with poor infrastructure in the region results in significant postharvest losses. The expansion of small-scale cassava processing could reduce these losses, but the availability of drying equipment suitable for use in such operations is limited. The objective of this research was to contribute to the development of cassava dryers suitable for use by smallholder farmers. A tunnel dryer and a pneumatic dryer being operated in Tanzania were evaluated using mass and energy balance analysis. It was found that the energy efficiency of the tunnel dryer was 29% and of the pneumatic dryer 46%. For the tunnel dryer, most of the heat losses were through unsaturated exhaust air, while for the pneumatic dryer, most losses were through radiation and convection. Practical Applications: In this study, a tunnel dryer and a pneumatic dryer suitable for use by smallholder farmers were evaluated during processing centers' usual cassava drying operations. The sources and extent of heat losses were identified, and then guidelines developed on how to reduce such losses. For both dryer types, improvements to the thermal insulation used could reduce heat losses to the ambient. For the tunnel dryer, decreasing the air mass flow rate by 57% would help to minimize exhaust heat losses without producing condensation inside the unit. For the pneumatic dryer, air mass flow rate could be reduced by 9%, improving energy performance without having a negative impact on the pneumatic conveying of the product. Those two modifications would be easy to implement and represent a significant contribution to the development of small-scale cassava drying technology