Performances techniques et environnementales du four de carbonisation Green Mad Retort à Madagascar

Abstract

Des essais de carbonisation d’eucalyptus issus de plantations au nord de Madagascar ont été menés sur le terrain dans des fours de carbonisation à chambre de combustion externe (Green Mad Retort ou GMDR). Les analyses d’une cinquantaine d’essais démontrent que des rendements massiques élevés (34 %) et très stables sont obtenus avec ces fours, même pour des charges à l’humidité élevée. L’étude confirme le lien direct entre augmentation du rendement massique et diminution des émissions de gaz à effet de serre liés à la carbonisation (CO2 et CH4). Il est également démontré, grâce à des mesures réalisées sur deux fours à des stades de développement différents, qu’il est possible et utile d’éliminer la majeure partie des émissions de méthane à la sortie de la chambre de carbonisation. Dans ce cas, les émissions de méthane sont de l’ordre de 4,3 kg par tonne de charbon de bois produite, ce qui est 5 à 17 fois moins élevé que les émissions publiées pour d’autres techniques de carbonisation, à l’exception des fours cornues industriels.

Improving traditional charcoal production system for sustainable charcoal income and environmental benefits in highlands of Ethiopia

“…Previous research on the efficiency of improved charcoal production systems in India and East Africa reported efficiency levels of 30%–42% [ 51 ]. Similar results were observed in northern Madagascar plantation forests [ 52 ], with an efficiency of 34%, and in Kenya with efficiencies ranging from 27% to 35% [ 53 ]. Additionally, a study conducted in Kenya [ 54 ] demonstrated an increase in efficiency from 10% to 40.85% by using metallic clay-insulated kilns instead of traditional earth mound kilns.…”

“…Notably, the longer carbonization time in the Green mad retort kilns can be attributed to extended cooling hours (84 h) and an effective carbonization time of 46 h. Technological advancements, improved insulation, and enhanced control mechanisms in the improved kiln likely contributed to this efficiency. Previous studies also support this explanation, emphasizing the positive impact of improved airflow control on carbonization performance, where the redirection of hot flues back into the kiln enhances efficiency and leads to shorter carbonization times [ 20 , 52 , 53 , 63 ].

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“…Firstly, their enhanced insulation retains heat more efficiently, leading to higher temperatures within the kiln and facilitating a more rapid and complete conversion of wood into charcoal [ 42 , 58 ]. Secondly, these kilns have better airflow management, preventing excessive combustion and ensuring a more efficient conversion process [ 20 , 52 ]. Thirdly, their design focuses on minimizing heat loss, enabling a higher proportion of generated heat to be utilized for charcoal production [ 58 ].…”

“…Moreover, improved kilns maintain a consistent temperature distribution, promoting uniform conditions for all wood pieces and resulting in higher conversion rates [ 59 ]. Additionally, improved kilns often capture and use combustible gases released during the process, further enhancing efficiency [ 52 ]. Research findings support the notion that incorporating a chimney in improved kilns enables efficient gas recirculation and internal combustion of pyrolysis gases; sustaining the pyrolysis process without requiring external heat, leading to superior efficiency and higher charcoal yield output compared to conventional kilns [ 56 , 60 , 61 ].…”

Charcoal Production Systems from Smallholder Plantation implications on Carbon Emission and Sustainable Livelihood Benefits in North Western Ethiopia

“…Thus, improved charcoal kilns will lead to lower emissions allowing countries in Sub-Saharan Africa to play their role in tackling climate change, whilst bene ting from a renewable source of cooking fuel. The values of greenhouse gas emission particularly methane in the present study is higher compared to the study in Madagascar(MichaelTemmerman et al, 2019). This difference in values could be probably the different nature of wood diameter, moisture content, and carbonization process during charcoaling(Kammen & Lew, 2005;Ojelel et al, 2015) Moreover, a 39.2-54.3% emission reduction of carbon monoxide (CO) from the three improved kilns was observed compared to the traditional earth mound kilns.…”