Energy. Группа авторов

Чтение книги онлайн.

СКАЧАТЬ lignocellulosic feedstock can lead to cost‐effective biofuel (Lund et al. 2016, pp. 36–38). Pre‐treatment process can be biological, physical and chemical depending upon the source and means of conversion procedure. Among the different methods for pre‐treatment, biological method which is a microbial process consumes less energy compared with the other two processes and moreover, a safe and environment‐friendly process (Potumarthi et al. 2013). Physical pre‐treatment can be done via mechanical comminution, steam explosion, ultrasonic radiation and extrusion process (Gupta et al. 2014, pp. 1–17). Under the chemical pre‐treatment methods, acid hydrolysis, alkaline hydrolysis, ammonia hydrolysis and ozonolysis are different available methods. Use of bioethanol‐blended gasoline in automobiles offers a viable option to cut down the use of petrol. This will also reduce the GHG emission along with contribution in achieving goals of Paris agreement.

Biodiesel is another biofuel that can be produced from oil‐based feedstock, animal fat wastes and waste cooking oils. Animal fat wastes are commonly obtained from chicken, cow, pork lard, fish and other animals. Oil‐based feedstock can be edible (soybean, corn etc.) or non‐edible. But, according to food first principle, use of edible feedstock is not promoted worldwide. However, continuous evolving technologies for converting biomass to fuels have enabled the bioenergy industry to utilize more of lignocellulosic biomass. Technological developments open doors for new types of feedstock for bioenergy production e.g. forest biomass, agricultural residue, perennial grasses and trees and even municipal waste (Lund et al. 2016, pp. 36–38).

      2.3.5.3 Advanced or 2G Biofuels

Currently, biofuels production is based on edible feedstock termed as conventional biofuels or first‐generation (1G) biofuels. In the last 20 years, conventional biofuels were promoted by the policymakers in view of changing climate conditions. However, after 2007, various discussions have started worldwide on the sustainability issues of these biofuels (IRENA 2019b). Biofuel usage was raising concern on food security, price of food and feed, and land use change. Production of 1G biofuels has negative impact on food resources, and there is a high probability of land use change and indirect land use change because of high demand of edible feedstock. Recent advances in production technologies lead to advanced biofuels or second‐generation (2G) biofuels, future of sustainable bioenergy (IRENA 2019b). Advanced biofuels are derived from non‐edible feedstock and other biomass such as agricultural waste, animal fat wastes and municipal wastes etc. On the basis of production method adopted by advanced biofuel industry, they can be classified into four categories which are tabulated in Table 2.1.

      Potential research is going on in search of algae (3G) biofuels which are based on algae consumption for biofuel production. Recent study (www.energy.gov) has found that algae could be richer in biofuel production compared with conventional feedstocks. There are some limitations associated with algae usage such as its mass production can increase the total cost by 40% (Oh et al. 2018). Thus, more inputs are needed from scientific community in future to pave the path for 3G biofuels.

Table 2.1 Categorization of advanced biofuel industry based on production process.

      Source: Based on Ref. IRENA (2019b).

Method	Biomass type	Biofuel
Microbial conversion	Lignocellulosic e.g. stalks, corn stover etc.	Bioethanol or biobutanol
Transesterification	Waste and/or non‐edible vegetable oils or animal fats	Fatty acids and methyl esters (FAME) i.e. biodiesel
Hydro‐treatment followed by alkane isomerization and cracking	Waste and/or non‐edible vegetable oils or animal fats	Drop‐in fuels (HVO/HEFA)*
Thermochemical/ gasification	Waste and/or non‐edible vegetable oils or animal fats	Biocrude/ syngas (converted to renewable gasoline)

      Note1: HVO – hydro‐treated vegetable oils and HEFA – hydro‐processed esters and fatty acids.

      2.3.6 Ocean Energy

      As we know, 70% of the earth's surface is covered by water in different forms. Ocean energy also known as blue energy is present in the form of tidal, current, wave, temperature gradient and salinity gradient energy. Electricity could be generated using energy possessed by all the different types of ocean energy. IRENA 2020 report (IRENA 2020b) states that electricity generation capacity of ocean energy till 2019 was 500 MW, very small contribution compared with capacity of other alternative sources of energy. Approximately 1.7 GW is under development (Wilberforce et al. 2019). Compared with other alternative sources of energy, ocean energy is steady and predictable (especially tidal range technology) making it a right choice for power production in future (Crus 2008, pp. 70–75). Looking at the promising potential of ocean energy, various researches are going worldwide to see the feasibility of how to harness this energy (Wilberforce et al. 2019). Most of researches were aimed to pinpoint best possible locations for ocean energy exploitation, energy conversion efficiency of various technologies used in ocean energy sector and consequences of several technologies on the marine ecosystem as well as on the environment, as this is a raising concern about the usage of ocean energy technologies. This is a clean form of energy, GHGs emissions are negligible and assumed to be environment‐friendly. Despite all these factors, its share in energy sector is very small at present.

      Around the globe, mainly four types of ocean energy are harnessed to generate electricity, namely wave, ocean thermal energy conversion (OTEC), tidal and salinity gradient energy. Out of all these forms, tidal range share with respect to generation capacity is approximately 99%. Currently, contribution of other forms is not significant but many projects are under development based on OTEC, tidal stream and wave energy (Kerr et al. 2015). On completion of various current projects share of OTEC, tidal stream and wave energy will become noticeable. Theoretical maximum capacity of all projects which are under construction will be 15 GW (Wilberforce et al. 2019). Major contributors in the commercialized marine technology are the United States and United Kingdom (UK) along with small share of South Korea, Ireland, The Netherlands and China.

      2.3.6.1 Wave Energy

      Wave energy convertor devices capture the energy possessed by the waves (kinetic and potential) and transform it to electric power. Wave energy convertors are classified into different types of categories based on the deployed location. Onshore devices are of two types ‘Oscillating water column’ (trap air to run a turbine) and ‘Overtopping devices’ which uses height differences of waves to generate electricity. ‘Oscillating wave surge converters’, ‘Point Absorber’ and ‘Submerged Pressure Differential devices’ come under the near‐shore location category. Offshore devices are ‘Attenuator’, ‘Bulge wave devices’ and ‘Rotating mass converters’. Each of these devices has its own characteristics (Wilberforce et al. 2019). Worldwide many companies are involved in research and development (R&D) to exploit wave energy so that this technology can be commercialized (Lorente et al. 2011; www.aquaret.com). Some studies have revealed that theoretical global capacity of wave energy was 32 PWh (petawatt‐hour) per annum (Mørk et al. 2010; Lagoun et al. 2014) which was double of the global electricity provided in the year 2008 (Leonard and Michaelides СКАЧАТЬ