Status and Future Thrusts of Sugarcane Processing Waste to Energy Conversion
14.2 Current Status of Sugar Mills Wastes to Energy Conversion
India contributes significantly to the global sugar market by producing about 15% and 25% of the world’s sugar and sugarcane, respectively [6]. Each year, India produces 370–400 million tonnes (MT) of cane, 27–30 MT of white sugar, 6–8 MT of jaggery and khandsari. 3.2 billion litres of alcohol, 4700 MW of electricity, and other chem- icals are also produced. Around 3500 MW of power export capacity by the industry to the national grid [7].
The sugar business consumes a lot of energy. With sugarcane as a raw material, steam and power is required to run the mill [8]. Largely the sugar industries have co-generation facility for the generation of steam and electricity [9]. As the low- pressure steam is used for heating, the cogeneration plant’s efficiency is increased to 75 and 90%, compared with the traditional plant’s efficiency of 35% [10]. During the sugar-making process, cane typically recovers 12% of its sugar content. The remaining sugar is present in the process’s by-product, i.e. molasses [11].
Different types of spirit which include rectified, extra neutral, impure alcohol and ethanol can be produced in distillery [12]. The distillery having made up of several stages of fermentation chambers that are distilled in stagged manner with separation columns for distillation of different grades of alcohol [13]. Spent wash which is by-product of distillation process and has high fructose can be used for the biogas plants as feedstock [11]. Compost fertiliser can be produced by using press mud and spent wash by addition of microbial culture. Mixing and aeration machine is used to reduce the composting time [14]. A flow diagram of sugar mill process is shown in Fig. 14.1.
Fig. 14.1 Flow diagram of sugar mill process [15]
14.2.1 Alcohol Form Molasses
Molasses is a precious by-product of sugarcane, about 1 tonne of sugarcane produces 4% by weight of molasses by the sugar processing industry in every single run.
Molasses is used for making alcohol. Brewer’s yeast (Saccharomyces cerevisiae) is used to ferment the molasses, which has sugar and minerals as constituents, and can be used to produce beer that contains 6–10% ethanol [16]. Alcohol is used for making Extra Neutral Alcohol and Ethyl alcohol [17]. From 1 MT of molasses, 270 L of alcohol is produced [18]. A flow diagram of production of ethyl alcohol from cane molasses is shown in Fig. 14.2.
India presently has over 70 lakh tonnes of extra sugar, so there is plenty of room to shift extra sugarcane toward ethanol production without compromising the quantity of sugar needed to satisfy domestic demand [20]. One tonne of sugarcane produces 70 lit. of ethanol, as is well known [21]. The Ethanol Blended Petrol (EBP) initiative was started by the Indian government in 2003 with the goal of promoting environmentally
Fig. 14.2 Production of ethyl alcohol from cane molasses [19]
Fig. 14.3 Diversion of sugar for ethanol production (LMT)
friendly fuels by increasing the use of ethanol and lowering energy imports [22]. The EBP programme provides consistent ethanol demand, which injects money into the sugarcane industry [23]. This facilitates prompt payment to cane growers and reduces accumulated arrears for them. The National Policy on Biofuels 2018 expands the parameters for obtaining the raw materials needed to produce ethanol. The strategy planned to achieve a 20% mixing proportion by 2029–2030, [24]. The EBP initiative,
by the Ministry of Petroleum and Natural Gas is now implementing, aims to attain a 10% ethanol mix ratio in petrol by 2021–2022 [25]. The target of blending of 10%
ethanol by 2021–22 and the 20% by 2029–30, a mid-term target of 15% blending could be explored for 2024–25 [23]. In order to facilitate sugar mills to pay the cane dues of farmers on schedule and to be in a better financial position to continue their operations, the government is consistently pushing mills to divert sugar to ethanol production and to export excess sugar. The sugar industry has gained profit by production of ethanol as a biofuel over the past five years since sugar’s usage in ethanol has improved sugar mills financial standing through quicker payments, lower working capital needs and less blockage of cash due to less surplus sugar with mills.
The sale of ethanol generated revenue for sugar mills and distilleries in 2021–2022 of around 18,000 crore, which also contributed to the early payment of farmers’ cane debts. In accordance with the Ethanol Blending with Petrol (EBP) Programme, the annual ethanol production capacity of molasses/sugar-based distilleries has expanded to 605 crore litres, and progress is still being made toward the 2025 objective of 20%
blending. From 35 to 50 LMT of sugar is anticipated to be diverted to ethanol in the next season, bringing in roughly 25,000 crores in revenue for sugar mills [5].
14.2.2 Cogeneration from Bagasse
Bagasse is the fibres of sugarcane obtained after the extraction of juice from sugar- cane crushing [16, 21]. Three tonnes of wet bagasse is generated for every ten tonnes of sugarcane crushed [26]. Wet bagasse contains moisture in the range of 48–52%
[27]. In terms of net calorific value, dried bagasse is more valuable to the economy and industry. The task force on sugarcane suggests offering incentives to sugar- cane mills so they can recycle bagasse [23]. Bagasse serves a variety of different purposes besides being a biofuel. Currently, it is used in the production of construction materials, pulp and paper products, and as a biofuel [28].
Initially bagasse often contains 40–50% moisture, which makes it impossible to utilize as fuel [29]. Bagasse is often kept before being processed further. It is maintained damp, where the modest exothermic process gently breaks down any remaining sugars and dries the bagasse pile, which is then used to produce power [30]. It is often stored moist for paper and pulp manufacture for the removal of the small pith fibres, which obstruct the paper making process, and to remove any leftover sugar. Bagasse is typically used as a fuel source in sugar mills. It can be burnt in big enough amounts to provide all the thermal energy required by a typical sugar mill [31].
Bagasse cogeneration uses the fibrous sugarcane waste, bagasse to cogenerate heat and electricity at higher efficiency in sugar mills. Electricity is produced by burning bagasse as fuel in the crushing season and from surplus bagasse or another biomass during off-season [32] (Fig. 14.4).
An average sugar and ethanol plant consumes 30 kWh of electricity per tonne of crushed sugarcane. Several electric motors and the machines both utilize this energy.
Fig. 14.4 Sugarcane bagasse cogeneration plant [33]
About 300 kWh/tonne of crushed cane (300 kWh/tc) of thermal energy is consumed during manufacture, which is 10 times more than the amount of electrical energy used. Sugarcane mills mostly employ cogeneration because it produces more thermal energy (TE) in the form of steam than electric power (EP) [34].
14.2.3 Press Mud
Press mud is a type of industrial waste produced by sugar mills. About 12 million tonnes of press mud (filter cake) are produced by sugar mills in India as a by-product of the twofold sulphitation process [35]. The proximate analysis of crude press mud showed the presence of moisture (67.95–76.53), nitrogen (1.63–2.29), ash (19.28–
30.76), sugar (12.10–13.29) and crude wax (6.70–11.01) [36]. As a by-product, around 3 tonnes of press mud cake are left behind for every 100 tonnes of sugarcane crushed [37]. Bio earth is produced by composting press mud, and it is a biological oxidation process in which sugar industrial solid waste is mixed with microbial culture in warm, humid and aerobic conditions for decomposition [38]. Degradable organic substrate is transformed physically and chemically during the process to create a stable humidified product. The substance is useful in agriculture as a soil enhancer and an organic fertiliser. Recycling organic waste is becoming increasingly important. By adding early nitrogen, improving nutrient availability, boosting water
Table 14.1 Composition of
bio earth [39] Nutrients Bio earth (%)
Nitrogen 2.0–2.5
Phosphorus 1.8–2.2
Potassium 3.0–4.0
retention, and adding colloidal nitrogen, phosphorous, potassium, calcium, sulphur, and micronutrients, Bio Earth boosts the soil’s microorganism population [39]. The application of sugarcane press mud treatments boosted soil fertility, according to the study [40]. The composition of Bio Earth is shown in Table 14.1.