Property Upgrades of Some Raw Nigerian Biomass through Torrefaction Pre-Treatment- A Review

Abstract

Today, agricultural waste is one of the most common resources in Nigeria that could solve environmental, fuel and energy issues. However, it has some limitations such as low bulk densities, loose and irregular sizes, handling and storage problems, low energy density, reduced fixed carbon, low calorific value, high volatile matter and high moisture content etc. making it difficult to be utilized for fuel. One of the viable and promising technologies to upgrade the properties of raw biomass is through torrefaction technique which is capable of upgrading the combustion and fuel characteristics of biomass, demonstrated from behaviours that are similar to coal during combustion. During this process, about 70% of the initial biomass weight and about 90% of the original biomass energy is obtained as torrefied biomass while the remaining 30% biomass weight and 10% biomass energy is given off. In addition, the presence of moisture content in raw biomass that could aid biological degradation is reduced (< 3% w.b.) while combustion efficiency is being enhanced through upgraded fixed carbon and calorific value (15-25% wt) and reduced volatiles. These upgraded properties makes torrefied Nigerian biomass suitable to be used independently or co-fired in power plants and as an upgraded feedstock for domestic and industrial applications in a developing country like Nigeria. Unfortunately, there is scarce research materials on biomass torrefaction in Nigeria which could be attributed to the cost of acquiring torrefaction plant and other resources for torrefaction characterization which are on the high side. This paper therefore explores and reviews the property upgrades of raw biomass through torrefaction technique. The challenges of biomass energy in Nigeria, torrefaction effects on some Nigerian biomass, equipment used for the analysis of torrefied samples, alongside the torrefaction properties, combustibility indices and their products were examined. The review study concluded that torrefaction technology is a promising technique in Nigeria which is capable of improving and upgrading the quality, energy value and other properties of raw Nigerian biomass and could at the same time serve as an alternative source of energy asides hydropower energy if embraced by the concerned bodies.

Quality enhancement of fuel briquette from cornhusk and cassava peel blends for co‐firing in coal thermal plant

“…Biomass has great capability to absolutely replace fossils, for example, coal, for sustainable energy production but its use is limited by its low bulk density, calorific value and energy density, high moisture content and its transportation, handling and storage problem 3,4 . These are major challenges confronting bioenergy production technologies.…”

“…2 Biomass has great capability to absolutely replace fossils, for example, coal, for sustainable energy production but its use is limited by its low bulk density, calorific value and energy density, high moisture content and its transportation, handling and storage problem. 3,4 These are major challenges confronting bioenergy production technologies. These challenges could, however, be improved upon by applying biomass blending 5,6 and a thermochemical process called mild pyrolysis (also known as torrefaction) 3,7 before biomass can be used to co-fire boilers.…”

“…In addition, quite a number of research works usually end at the conversion process of raw biomass to torrefied products. 11,12 Densification of torrefied fuel therefore is a very important process for appropriate utilization and improved logistics of biomass 4,13,14 and to reduced air pollution.…”

Torrefaction of non - oil Jatropha curcas L. (Jatropha) biomass for solid fuel

“…The results in Table 2 , in comparison to the results of raw biomass in Table 1 show that the torrefaction processes reduced the equilibrium moisture content by 56%, 71% and 32% for the fruit husk, stem and seed cake respectively. The reduction in EMC is credited to the devolatisation, depolymerisation and dehydration process which liberated moisture and volatile matter from the biomass [ 46 ]. The reduction in equilibrium moisture content is consistent with the findings by Tumuluru et al.…”

“…The general reduction in the hygroscopicity of the torrefied Jatropha biomass material under investigation could be attributed to the loss of the hydroxyl group (OH) as the hemicellulose and cellulose are decomposed during torrefaction. The loss of the hydroxyl group makes the biomass more hydrophobic thereby reducing the microbial activities which makes it feasible to be stored in a humid environment [ 19 , 46 ]. The overall results show that the ability of the torrefied Jatropha stem to retain moisture is higher than of the torrefied seed cake and the torrefied fruit husk.…”