**4. Global biofuel and bioenergy scenarios**

The potential for bioenergy generation from agricultural residues is being studied intensively and many studies have been conducted on both a regional and a global scale. In most cases, the outcomes of these studies vary considerably because of factors, such as the residue to product ratio and the sustainable removable amount of residues, used to calculate potentials range substantially.

So far, a lot of studies in different countries have been conducted for the assessment of availability of residual biomass. Scarlat et al. [51] assessed the availability of residual biomass of agricultural and forest crops suitable for bioenergy synthesis in Romania. Crop yield, variation multi-annual yield, environmental and economic constraints, and competitive uses were the various measures utilized to estimate agricultural residues. A comparable work was developed by Shonhiwa [52] who explored the magnitude of biomass available for energy production using thermochemical conversion technologies in Zimbabwe. Besides, Iye and Bilsborrow [53] evaluated the propensity of agricultural residues in Nigeria based in six areas; three situations were considered subject to the collection and availability of biomass proportion.

Moreover, in Argentina energy potential of residual biomass derived from herbaceous and horticultural crops was studied by Roberts et al. [54]. In Colombia, several studies were carried out to determine the features of residues from agriculture, animal, forestry, and municipal solid waste in order to evaluate its energy potential [11, 55]. Subject to the geographical location of Colombia tropics, Colombia has comparative advantages in the production of agricultural and forest biomass and its potential is sufficient to satisfy the energy demands [56].

As an example, Hiloidhari assumes a RPR of 2 for maize [57], whereas the IEA considers a RPR of 1.5 [58] while Kim et al. adopted a ratio of 1 [59]. Similarly, the fraction of the produced residues that can be detached in a sustainable manner is in the range of 20 [60] to 50% [61] although 70% is recorded in some studies [62]. Apparently, this has a huge impact on the resulting propensity for bioenergy production.

Furthermore, numerous works have assessed the technical feasibility of crop residue production in China. Jiang et al. [63] used a GIS-based approach to examine the availability of crop residues in China. A number of cereal crop were considered and the findings demostrated China potential to provide about 506 million dry biomass metric tons of the residues annually. In another study, Qiu et al. [64] adopted remote sensing data and reported about 729 million MT crop residues in 2010, of which about 20–45% of this amount could substitute coal subject to regional utilization and customary needs of crop residues. Liu et al. [65] discovered that about 630 million MT of crop residues was harvested annually over a decade between 1995 and 2005. The observable dicotomy is as a result of the several factors such as considered crops, assumptions relative to crop-to-residue ration, and residue collection methodology, which is evidence in the estimated technical availability of crop residues available in the results.

Pyrolysis of biomass and their direct liquefaction method with water are often used mistaking to mean the same thing; however, there exist a striking difference between the two processes. Although they are both thermochemical conversion methods that involve the alteration of various components of biomass into liquid products. Whence liquefaction involves decomposition of macro-molecule feedstock into smaller fragments of light molecules where an appropriate catalyst is employed in the conversion. Subsequently, the unstable smaller fragments are re-polymerized into oily constituent with comparable molecular weights with fossil equivalent. Whereas in pyrolysis, the generated fragments are instantaneously merged to an oily compound and the use of catalyst is predominantly may be subject to

The potential for bioenergy generation from agricultural residues is being studied intensively and many studies have been conducted on both a regional and a global scale. In most cases, the outcomes of these studies vary considerably because of factors, such as the residue to product ratio and the sustainable removable amount of residues, used to calculate potentials

So far, a lot of studies in different countries have been conducted for the assessment of availability of residual biomass. Scarlat et al. [51] assessed the availability of residual biomass of agricultural and forest crops suitable for bioenergy synthesis in Romania. Crop yield, variation multi-annual yield, environmental and economic constraints, and competitive uses were the various measures utilized to estimate agricultural residues. A comparable work was developed by Shonhiwa [52] who explored the magnitude of biomass available for energy production using thermochemical conversion technologies in Zimbabwe. Besides, Iye and Bilsborrow [53] evaluated the propensity of agricultural residues in Nigeria based in six areas; three situations were considered subject to the collection and availability of biomass

Moreover, in Argentina energy potential of residual biomass derived from herbaceous and horticultural crops was studied by Roberts et al. [54]. In Colombia, several studies were carried out to determine the features of residues from agriculture, animal, forestry, and municipal solid waste in order to evaluate its energy potential [11, 55]. Subject to the geographical location of Colombia tropics, Colombia has comparative advantages in the production of agricultural and forest biomass and its potential is sufficient to satisfy the energy demands [56]. As an example, Hiloidhari assumes a RPR of 2 for maize [57], whereas the IEA considers a RPR of 1.5 [58] while Kim et al. adopted a ratio of 1 [59]. Similarly, the fraction of the produced residues that can be detached in a sustainable manner is in the range of 20 [60] to 50% [61] although 70% is recorded in some studies [62]. Apparently, this has a huge impact on the

necessity [43].

80 Agricultural Waste and Residues

range substantially.

proportion.

**4. Global biofuel and bioenergy scenarios**

resulting propensity for bioenergy production.

In estimation of the technical potential of crop residues production, production cost of the residues and the cost of feedstock were never considered in past reports. In certainty, farmers' preparedness to collect crop residues rely significantly on the yields and production costs of crop residues as well as on the biomass prices provided in the market. Specifically, the biomass prices offered must cover the costs of collecting crop residues. In this regard, Chen [66] examined the potential yield of each type of crop residue in China at various prices and subsequently, estimated the collective supply of crop residues at these prices. As regards the crop residues, different residues were considered as potential residues and due to the inherent yield and cost uncertainty, they derived the supply curves of the crop residues using alternative assumptions about the production costs of crop residues and residue collection technology.

In Tanzania, the major commercially sourced after agricultural crops include sugar, cotton, tea, cashew nut, tobacco, coffee, and sisal. Significant amounts of residues from these crops have been utilized for the cogeneration of electricity in the sugar sector. Convesely, only a small amount of sisal residues had been utilized as substrate in a pilot biogas plant to generate electricity since 2008. Moreover, almost all biomass can be converted into energy; crop residues are not an exception. The types of residues available for energy generation in the commercial crop sector in Tanzania were bagasse, coffee husks, cashew nut shells, tobacco stems and sisal pulp [67].

The energetically available share of these residues was determined by the termed non-energy applications, whence the energy content of residues is influenced by the plant structure and the moisture content of the residue. Considering the account of these different parameters, the heating value for every tonne of dry matter had been reported. Although they submitted to probability of the estimation due to expedient losses during collection and transportation, the upper bound demonstrated that all residue types contain a incredible energy propensities. The combined potential of 6053 TJ is equivalent to 1680 Gigawatt hours (GWh). This estimated maximum potential is equivalent to over 37% of the country's electricity generation of 4553 GWh in 2008 [68].
