Evaluation of, and improvements to, mechanical de-watering prior to small scale, high temperature casava drying systems
Marchant Andrew1*and Idowu Adeoyu2
1) NRI, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK,
2) Nobex Technical Company Ltd, 15 Vic Morak St, Ikotun, Lagos, Nigeria.
*Email:, Registrant ID# 4694
Mechanical removal of free water is almost universally employed as a means of rapidly reducing the moisture content of various products. It is a normal constituent of cassava processing in Africa, occurring prior to high temperature drying in order to reduce fuel costs. The aim is to reduce the moisture content (m.c.) of the peeled and grated cassava meal from around 85% to around 40 - 45% m.c. For simple sun drying often farmers use twisted rope presses, and this developed to metal presses with manual hydraulic jacks. In Nigeria the use of small scale flash driers is common for the high temperature drying systems. In such cases they will typically utilise small mechanical presses or centrifuges at the smaller sites, and filter presses at larger ones. This paper reviews in field assessments of actual practice and the results of a trials of various adaptations of the basic mechanical press.
Samples were analysed across a three dimensional grid of the press, and assumed symmetry, to assess the spatial variation in the different internal regions. Test protocols included pulsed hydraulic system, internal drain plate with applied vacuum, and a combination of pulsed hydraulic pressure and internal vacuum. Pulse and sequence times were controlled by a laptop running a SCADA system with remote outstation for solenoid valves to enable a varied timing programme to be employed in a straight-forward manner. Moisture content was measured using a proprietary infra-red device with internal weigh cell and continuous difference monitoring. The results of this test programme are discussed.
A model demonstrating the impact of these various components was developed and is presented, showing the cost benefits of achieving maximum de-watering based on fuel savings and increased system throughput. To illustrate the importance of this the difference between best performers and average in Nigeria was 5% (of absolute), and from this to what can be achieved using improved equipment is a further 2%. This equates to 15% of operating costs, and 25% increase in throughput. In environmental terms, based on standardised CO2 emissions for diesel fuel this equates to 1.5 tonnes of CO2 p.a. for an SME producing 50 tonnes of dry cassava p.a.. This can represent the difference between viability or otherwise for many SMEs.