Sun is the principle source of energy on the earth, which makes the biosphere act as a vast biomass generation facility. There biomass generation facility can also be considered as a large carbon sink. Proper management of these carbon sinks is vital for handling the issue of climate change. Biomass contribute about 12% of today's world primary energy supply, while in many developing countries, its contribution ranges to even 40-50%. India is an agrarian country and biomass is abundantly available resource of the nation. It is observed that processing of agricultural crops during harvesting produces a substantial amount of agricultural residues. However, a large portion of the residues is inefficiently burned, in the field itself, primarily to clear the field from straw and stubble after the harvest of the preceding crop. The issue of open field burning is a widespread phenomenon, especially in northern parts of India (Punjab and Haryana). Given the fact that 23% of rice straw residue produced in India, 48% in Thailand, and around 95% in the Philippines burns in open field, open field burning has become an environmental threat as well as health related issue. Punjab is considered as the food bowl of India and, it is surprising to note that burning of straw is widespread. These statistics suggest a strong need for an effective utilization of the agro residues so that the environmental impact of open field burning can be reduced. At the same time the country is also suffering with frequent power cuts and poor availability of electricity, especially in rural areas. Considering both these factors, an effective solution could be to make the use of the biomass for electricity generation. If agro residue is used for electricity generation, instead of burning it in an open field, it can address not only the issue of emission, but also provide electricity in the rural area.
It is also observed that the Indian grid has high emission numbers and electricity generation is heavily dependent on low cost fuel, e.g. coal. For instance, the specific CO2 emission from the electricity grid reached an alarmingly high level, 0.81 kg of CO2/kWh in 2011. As a result of this the contribution of coal, oil and gas, taken together if high. For instance, 82% of entire electricity generation in 2013 resulted from these sources alone. It appears that the energy security of India may come under heavy stress and emission intensive electricity generation trend would be difficult to reverse in the near future. Under such circumstances there is a strong need to evolve a technology option that is not only environmentally neutral, but that actually absorbs emission from the environment and cut down the environment emission. Biomass is the only energy source which has capacity to absorb carbon in its structure. Emission issues can be handled effectively if, large availability of biomass in the country is made available for achieving dual goal of energy generation as well as carbon sequestration.
In the present work the literature for the open field burning is reviewed first and the technology option of utilizing agro residue is studied in particular. It is inferred that the solution to the issue of open field burning and the shortage of electricity can be addressed by opting for Intermediate Pyrolysis (IP) process. Further, in order to test the IP process using local agro residues an exhaustive experimental program is laid out. Under this, trial runs on IP process are carried out to obtain process parameters. Further, a detailed chemical analysis is undertaken, in which different samples of feedstock, biooil and its blend and biochar is analyzed for different tests. The intermediate Pyrolysis process utilizes the straw from the field and produces biooil and biochar. The biooil can be used for energy generation while biochar can be used in the field as a fertiliser. To investigate and obtain pertinent data for use of biooil blend in the engine an engine trial is carried out in the laboratory. Similarly, to investigate the effect of the use of biochar in the field, a field trial for growing of crops, onion and capsicum, was carried out. The data and the process parameters obtained by conducting these trials are used for the further analysis.
The intermediate Pyrolysis process produces biooil and this biooil can be used for power generation in the blend. Since carbon emission from the biooil is environmentally neutral, power generation from biooil qualifies under renewable energy. Additionally, the use of biochar is considered as a low cost carbon sequestration as biochar could remain in the soil for the years to come. These two emission-reduction advantages of the IP process (products of biooil & boichar) are on different time scales (few hours and several years respectively). Therefore, in order to correctly assess these, the concept of time value of the carbon emission approach is very important. In order to incorporate the effect of the time value of carbon emission a novel emission model is presented. This model can assess the time value of carbon emission from IP process and compare the IP process vice-a-vice other conventional processes. The novelty of the model is that it predicts the effect of emission for a given process in terms of a single value (known as emission discounting number).
Literature suggests that biooil can be used for the power generation in the blend (up to 30%) with biodiesel or with the diesel. In the former case (blend with biodiesel) the emission from the blend will be environmentally neutral, but in the latter case (blend with diesel) the emission from the blend will only be partially environmentally neutral. In case if the emission from the blend is partially environmentally neutral, the energy produced from this blend can be considered as combination of gray and green energy. Referring to the literature, the provision of such mixed combination of energy is not in the present scope of biofuel policy of India. This calls for certain readjustment, correction and modifications in the existing policy and the way economics of such mixed mode of energy is accounted. Present study, therefore proposes an ISCB (Incentive scheme, Sustainability aspect, Carbon credit and Banking facility) model which account for a mixed mode of energy generation option. This model considers the benefits like embedded energy, carbon credit based pricing system, banking facility and other incentive offered by government for promotion of renewable energy.
One of the products of IP process is biochar and literature suggests biochar can be used as a slow-release fertiliser in the field. The use of fertiliser in the field has several implications, it can be used as a tool to bring down the cost of farming and hence, it can lift the social as well as the economic conditions of farmer in particular and society in general. Besides this IP process can also reduce emission to a great extent. Combining all these effects, one can comment that the IP process has positive implications on all fronts of sustainability, i.e. social, economic as well as environment. In order to correctly estimate its implication a triple bottom line (TBL) analysis is carried out in the present study.
Finally, based on the overall results, it is concluded that the IP process prevents open-field burning, and instead produces biooil and can thus generate surplus renewable energy, with very little duration of the engine performance. Further, the use of biochar as a fertiliser can increase the yield of the crop, around 140% and 12% for capsicum and onion respectively. The emission discounting model shows positive effects on emission, up to 10% decrease is estimated. Further, ISCB model can help smooth the implementation of IP process, while triple bottom line analysis shows improvement in performance across all the three pillars of sustainability.
Keywords: Renewable energy; open field burning: intermediate pyrolysis process; biomass; carbon sequestration; policy; triple bottom line; sustainability; biochar; biooil