Even though a large potential of energy is associated with straw of sugarcane, so far, very minute efforts have been made in order to establish a suitable route from collec­tion to harness such potential. Similar to the corn stover in the USA (Atchison and Hettenhaus 2004), for sugarcane straw to become an energy source for large biore­fineries, innovations are required between the field and delivery to the processors in the areas of collection, storage, and transportation. As the attention is directed toward the cane harvesting mostly, it is not very clear which way to opt for the collection of straw for energy applications on industrial level. A set of field tests were performed in 1990s by the former Copersucar Technology Center (CTC) in order to evaluate some unburned cane harvesting routes proposed in the recovery of straw. Initially, five routes for collection purposes were evaluated with main intent of use of straw for generation of electricity (Hassuani et al. 2005). As a result of the poor harvester per­formance, when dealing with yield higher than 70 mg ha-1, the routes that were based on whole harvesting of stalks were thrown away and discarded and the other three were subjected to further analyses which are briefly explained below:

Route 1: harvesting of unburned chopped cane with removal of straw in the harvester. This is the conventional cleaning—harvester’s primary and extractor fans on. Chopped cane is transported to the mill of sugarcane. Straw is baled and transported.

Route 2: harvesting of unburned chopped cane without removal of straw in the har­vester (harvester’s extractor fans turned off). Cane stalks along with the straw are transferred to trucks and then transported to the mill. In the dry cleaning station of the mill, stalks and straw are separated.

Route 3: harvesting of unburned chopped cane with partial cleaning (harvester’s primary extractor fan operates at reduced speed and secondary extractor is turned off). A certain amount of straw is left on the ground, while the remaining is transported to the mill with cane stalks. At the mill, stalks and straw are separated in a dry cleaning station (Leal et al. 2013).

The main reason behind the dry cleaning station is to allow and enhance the sepa­ration of mineral (soil) impurities and vegetal (straw) from stalks of cane at the mill. Once these are separated, straw can act as a complementary fuel to bagasse or as feedstock in other applications. These collection routes investigated by CTC led to extremely different percentages of recovery efficiencies. For instance, in Route 2, 95 % of the total available straw can be collected, but, instead, only 66 % can undergo separation in the mill, whereas the rest of the 29 % would be squelched and crushed with the stalks to eventually compose the bagasse. Even though the efficiencies of Routes 1 and 3 are lower, in accordance with the analysis performed by CTC, both of these present lower cost. The cost is dependent upon the impact in the field of sugarcane caused by straw removal such as loss of productivity in agricultural sector due to compaction of soil and the loss of herbicide to the blanket of straw, among others (Leal et al. 2013).

In another study, the six different recovery routes were assessed (Michelazzo 2005). A model was generated to estimate the recovery cost of straw stimulating the capacity of field, consumption of fuel, repair and maintenance, depreciation, and required labor for the operation in field and transport. Results revealed the lowest recovery costs while handling together, cane billets and straw, followed by handling of chopped straw in bulk, the round bale, the giant bale, and lastly the pellet and briquette system.

The routes indicated by these studies are based on the combined stalk handling of the straw from the cane. This is an effective alternative in which mills may even­tually find more than one appropriate route, along with the knowledge of recovery level of straw may not be uniform over cane field (Braunbeck and Neto 2010). CGEE presented an analysis report after investigating three conditions of storage. It concluded that “the densification method was one of the leading factors for final cost of biomass.” Based on the recovery costs identified by CTC, the cost of final biomass including straw storing operations was calculated to be in the range between 17.9 and 39.2 $/mg, depending on the route of recovery and storage methods (Braunbeck and Neto 2010). Even though it is indicated in these studies that the route that is based on the handling of stalks of cane and straw combined should turn out to be an alternative toward cost-effectiveness, mills may eventually find appro­priate to utilize more than one route, also keeping in mind that the level of recovery of straw may not be uniform all over the field of cane. Improvements in the technologies used for straw recovery and incorporation of other biomass aspects can result in the expected reduction in costs. According to a research, for instance,

estimation was made that the total cost on delivery of switch grass was estimated to be 80.46 mg. This was calculated using balancing technology. Nearly 8.5 % of energy input of the feedstock is required (Atchison and Hettenhaus 2004). Mature technology reduces the total delivery. Cost would be reduced to 71.16 $/mg with input of required feedstock to be 7.8 % for corn stover. Investigations have also been done on finding innovative methods for collection. Hess et al. (2009) described designs showing advanced uniform format that would enable lignocellulosic biomass trading and supply to biorefineries in a market of commodity type similar to that of grain. Apart from cost, the methods of recovery and storage must also consider its impacts on quality of biomass for its intended use. Studies estimate that nearly 40-50 % of straw is available in the field to be utilized as an additional fuel to bagasse. Estimation showed that the total electricity surplus from mills of sugar­cane can reach up to 468-670 MJ mg-1 of cane (Seabra and Macedo 2011; Dias et al.

2011) . Certain challenges with the combustion and handling of straw in large amounts in boilers of bagasse at industrial level are being faced and are still sub­jected to investigation. Alternative technologies are based on the straw conversion into biofuels and chemicals via biochemical and thermochemical ways. For the longer term, they are expected to become available on commercial scale. In BIG/GT-CC (biomass integrated gasification/gas turbine-combined cycles), systems may also get adapted to substantial generation of power at the mills. According to a study, surplus of electricity would reach up to 1,048 MJ mg-1 of cane. This analysis was made when 103 kg of straw (dry mass) per milligram of cane was used along with the bagasse in sugarcane mills with installed BIG/GT-CC system. Regarding bio­fuel production, the biochemical conversion of residues of sugarcane could affect the yield possibly by increasing it from 124 to 132 L mg-1 in case of ethanol. Further assumption is made that recovery is almost 40-50 % of straw (Dias et al. 2011; Seabra et al. 2010). If thermochemical state conversion is considered, a reduc­tion to 116 L mg-1 value can be observed for ethanol and 115 MJ mg-1 canes for production of electricity. These rates result in 4 L of more production of higher alcohols per mg of cane (Seabra and Macedo 2011). These yields are characteristics of biomass so that the industrial performance may be affected by recovery route of straw (Seabra et al. 2010). A compromise is therefore required to be considered between the methods of collection and use of biomass of straw.