Decarbonisation Whisky Distilleries
Biogas
Waste disposal is major global issue. Global yearly waste is expected to rise by 70% between 2018 and 2050 unless dramatic improvements are implemented (1). Waste, according to the rule of conservation of nature, is rather a natural component of the cycle and can be reused optimally. In general, organic biodegradable waste has significant potential for biogas generation, which is one of the clean and sustainable energy resources.
Biogas is a combination of combustible gases, composed majorly of methane and carbon dioxide produced by anaerobic bacterial breakdown of organic substances in the absence of oxygen (1). The equation for combustion of Biogas is:
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The gases released are the by-products of the cellular-respiration of these decomposer microorganisms and the structure of the gases relies upon the material that is being decomposed.
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A leading single malt distillery in Scotland “Glenfiddich” announced that its whisky lorries will run on ‘Green Biogas’ synthesized from their own processing waste. The whole delivery fleet of this organisation said to be run on green biogas created from distillery residues. William Grant and Sons, the business's parent company, created the technology required to transform waste into biofuel and have already installed the fuelling stations (2).
Additionally, William Grant & Sons stated that it intends to make its technology accessible to the Scottish whisky sector in order to "help the decarbonisation of transport in accordance with the UK and Scottish governments' net zero ambitions." To scale-up the decarbonizing benefits, this closed-loop process is applied across the entire transport fleet by the company. Each vehicle is claimed to offset up to 250 tonnes of CO2 every year, the equivalent of planting up to 4,000 trees (2).
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The Process
The entire biological breakdown of organic matter to methane (CH4) and carbon dioxide (CO2) is difficult and involves a number of different bacteria, each of which is responsible for their respective share of the operation. For some bacteria the biomass can be a waste whereas for some it can serve as food making them dependant on each other (1).
There are 2 main kinds of waste that are created in the production of whisky. First is called the “Spent Grain” or “Draff” and the other are called “Pot Ale & Spent lees”. The Draff and the Pot ale containing sugars which are further broken down in the Hydrolysis process and the Spent lees containing organic acids and low alcohols further broken down to acid in the Acidogenesis process.
The comprehensive overview of the complete process is as follows:
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Hydrolysis:
Long-chain atoms “Polymers”” are reduced to “Monomers” during Hydrolysis. Under anaerobic circumstances, proteins, simple carbohydrates, and starch hydrolyze quickly(1)​.
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Acidogenesis - Acetogenesis:
A balanced bacterial mechanism converts around 50% of the monomers and long-chain fatty acids (LCFA) to acetic acid (CH3COOH). 20% is transformed to carbon dioxide and hydrogen, while the remaining 30% is depleted into short-chain volatile fatty acids (VFA).
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Methanogenesis:
The final stage in the generation of methane is carried out by methanogenic bacteria or Methanogens, which are said to be one of the first living species on the planet. Methane generation is caused by two distinct kinds of bacteria. The first group converts acetic acid to methane, whilst the second generates methane from carbon dioxide and hydrogen, as a result, 70% methane comes from the decompostion of acetic acid & 30% comes from the carbon dioxide and hydrogen.
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Why Biogas?
Biogas is a type of biomass that is more sustainable and has more advantages for reducing greenhouse gases (GHG) than solid biomass. Biogas is a mode of biomass energy that emits less CO2 than fossil fuels and solid biomass. (4)
According to European Biogas association, Biogas sector is important and rising factors to achieving climate neutrality by 2050. This technology has the potential to cut global greenhouse gas (GHG) emissions by 10% to 13%. Biogas generation may reduce up to 240% of GHG emissions when compared to EU fossil fuels. Apart from that renewable heat and electricity can also be produced from biogas. (5)
Carbon Emissions
Being the fourth-highest amount of any fuel type and the highest amount of any renewable fuel type, Solid biomass energy releases 230 gm of carbon dioxide equivalent per kWh (gCO2 per kWh). However, contrary to conventional biomass usage, biogas produced on site eliminates transportation emissions, and using whisky waste does not add into deforestation or exploitation of agricultural land. Hence, this reduces the carbon emissions factor for biogas energy to 0.00000022 gCO2e per kWh when used for process heating. (3)
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Source: World Nuclear Association: Average life-cycle CO2 equivalent emissions
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The mechanism which results in the above statistics is called “Short Carbon Cycle”. Biogas, unlike natural gas or oil, is created from fresh organic components, which are straightforwardly derived from biomass. This biomass captures a particular quantity of CO2 from the environment throughout its growth in order to perform photosynthesis. This collected CO2 is released back into the atmosphere via the burning of biogas and is subsequently caught again by freshly growing biomass. Thus, the combustion of biogas does not raise the amount of CO2 in the atmosphere, but rather causes it to circulate in short carbon cycles. (5)​
Problems with Biogas Plant
Although biogas has a strong potential to cut down waste and carbon emissions, it still has a few downsides –
High Capital cost: Along with lack of necessary building area and knowledge to apply it, the capital costs required in buying and installing a biodigester is a very crucial challenge faced while planning the commissioning stage of a Biogas plant (6). Distilleries with smaller capacities might not have the area to integrate an AD plant and this might add to the costs for purchasing more land for this installation.
Emergent technology: There are currently no new technologies to simplify and enhance the biogas generating process, implying that it is not a perfectly efficient system (7). More research is required to develop new technologies and increase manufacturing efficiency. Large-scale production for a larger population is not yet feasible, and government investment in the sector is unpopular, with governments preferring to invest in better mature alternatives such as wind and solar (8).
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Adaptability as a fuel: Even after refining and compression, contaminants remain in biogas, which can make it unfit to use as a biofuel. The engines of the vehicles might need to be retrofitted with compatible engines/systems or it may corrode the metal parts of the engine and increase the need for and cost of maintenance (7).
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Reliant on weather: Biogas production, like other intermittent energy sources (solar, wind), is influenced by the weather. The process anaerobic digestion takes place in a temperature-controlled setting of 37°C (8).
Maintenance & Setup: A comprehensive risk management programme should address not just the safety of its employees, but also visitors, third-party contractors, and potential emergency responders. Along with this, due to the emission of foul odour from the waste processed, Biogas plants should be built distant from residential neighbourhoods and other industrial regions (9).
Calculations
Biogas
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Biomass amount and composition is taken as an input which will be whisky waste feedstock. If the amount of waste is not specified, then it is calculated based on whisky production capacity. For draff, 0.002469 te draff per litre of whisky is used and the amount of pot ale is taken to be 3.3 m3/te of draff (6).
Biomass composition is required on as received basis. Biomass chemical formula CcHhOoNnSs is calculated using as received composition and molecular weights of the atoms involved. When the composition is not specified, following are the values for barley composition (10) –
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2) Using the following overall reaction of biomass (11) :
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This provides amount in kg/hr and composition of Biogas which includes methane, carbon dioxide, hydrogen sulphide and ammonia content of biogas.
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3)The biogas energy is calculated only based on methane content considering the amount of rest of the flammable compounds is negligible:
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where, H(methane) is heat of combustion of methane i.e., 13.9 kWh/kg (12).
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4) The amount of thermal energy produced by the biogas is considered to be equal to the amount of thermal energy natural gas produces as both the biogas and natural gas boiler have been assumed 83% efficient (13).
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5) Density of biogas is calculated at digestor operating conditions i.e., 40°C and 1 atm
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where, component(i) includes CH4, CO2 and NH3 and their densities are taken as 0.6172 kg/m3 (12) and 1.7201 kg/m3 (14) and 0.6593 kg/m3 (15) respectively.
The amount of biogas is converted from mass basis to volume basis by using the density of biogas.
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6) Based on volumetric flowrate, the size of the AD plant is assumed using the following range (16):
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7) Using the values in the above table, capital and operating costs of the AD plants were calculated. To calculate the yearly cash flows, an inflation rate of 2% (17) on the operating costs and natural gas prices was used. To calculate the net present value of the project, 7% discount factor was considered (18).
Using the values in the above table, capital and operating costs of the AD plants were calculated. To calculate the yearly cash flows, an inflation rate of 2% (17) on the operating costs and natural gas prices was used. To calculate the net present value of the project, 7% discount factor was considered (18).
Why Biogas + CHP?
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Combined Heat and Power (CHP) plant is a power plant that produces heat energy and electricity simultaneously. A typical CHP plant can convert up to 70% to 90% of the fuel’s energy content into useful forms of energy. Compared to the CHP plant, the power plants in traditional grid system can only convert up to a third of the fuel’s energy into useful energy(22).
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The CHP plant includes either an engine or a turbine where the fuel is burned. From this electricity is produced and the exhaust gases are sent to the heat recovery unit. This heat can be used to convert water into steam which can be used within the whisky production processes. Therefore, using a CHP results in a more efficient system by recovering the waste heat when compared to direst combustion of fuels.
There are several benefits of adding a CHP unit to a Biogas plant as follows:
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Efficiency improvement: The combination of Biogas with the cogeneration plant enables production of electricity and if required heat. Having a CHP unit in the Biogas plant capitalizes most of the fuel by converting it into electricity with 35% efficiency and heat up to 60% efficiency. (21)
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Environmental benefits: The combination of CHP with AD plant minimises the GHG emissions more since it produces electric energy along with heat energy. This renewable electricity source replaces very carbon-intensive source of emissions i.e., electricity from the grid which has a higher impact on emissions as compared to replacing the heating only. It also avoids transmission and distribution losses, playing a crucial role in decarbonizing energy production. (22)
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Dependability and Resilience: CHP is an on-site generation resource which can be engineered to run self-sufficiently apart from the electric grid to improve facility’s dependability. CHP systems can be built to continue working in the case of a disaster/natural calamity or grid outage to provide power for major components, hence improving facility's resiliency. (22)
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Monetary benefits: Substituting the electricity generated from CHP in place of the electricity from the grid provides a cheaper option and can reduce overall operating costs.
Biogas + CHP
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In addition to Biogas production calculations, the following steps are followed for CHP:
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CHP thermal and electrical energy conversion efficiency is taken to be 45% and 35% respectively (19). It is rated based on the electricity production capacity.
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2.For calculating the capital cost of CHP, 830 pounds/kW of electricity rating is used whereas operating cost is calculated as 4.5% of the capital cost (19).
3.Yearly cash flows include CHP operational costs, savings on natural gas and electricity as well as electricity sold to the grid which is sold at reduced price of 7.46 p/kWh (20).
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References
1. Jorgenson, Peter Jacob. Biogas - green energy. Tjele : Faculty of Agricultural Sciences, Aarhus University, 2009.
2. Scotsman, The. Glenfiddich whisky lorries in Scotland to run on ‘green biogas’ made from distillery leftovers. 27 07 2021.
3. Smoot, Grace. What Is the Carbon Footprint of Biogas? A Life-Cycle Assessment. CLIMATE ACTION. 2022.
4. Arnau, Angela Sainz. European Biogas Association. [Online] [Cited: 11 05 2022.] https://www.europeanbiogas.eu/avoided-emissions-from-biogas-and-biomethane-can-lead-to-a-negative-carbon-footprint/#_ftn2.
5. Association, European Biogas. The contribution of the biogas and biomethane industries to. Belgium : European Biogas Association, 2020.
6. The impact and challenges of sustainable biogas implementation: moving towards a bio-based economy. Ralph Muvhiiwa, Diane Hildebrandt, Ngonidzashe Chimwani, Lwazi Ngubevana & Tonderayi Matambo. s.l. : Energy, Sustainability and Society, 2017.
7. Evans, Scarlett. Power Technology. [Online] 2018. [Cited: 10 05 2022.] https://www.power-technology.com/analysis/biogas-pros-and-cons/.
8. EnergyPedia. Advantages and Disadvantages of Biogas. [Online] [Cited: 11 05 2022.] https://energypedia.info/wiki/Advantages_and_Disadvantages_of_Biogas.
9. Bierl, Aaron Kalisher and Craig. Altenergymag. [Online] [Cited: 12 05 2022.] https://www.altenergymag.com/article/2015/05/biogas-big-opportunities-but-beware-the-risks-/19898/.
10. Microwave dielectric properties of agricultural biomass at high temperature in an inert environment. Farough Motasemi, Arshad Adam Salema, Muhammad T Afzal. s.l. : ASABE (American Society of Agricultural and Biological Engineers), 2015.
11. Serrano, Roger Peris. Biogas Process Simulation using Aspen Plus. s.l. : Universitat Politecnica De Catalunya Barcelonatech, 2010.
12. Methane. NIST Chemistry WebBook, SRD 69. [Online] 2021. [Cited: 12 05 2022.] https://webbook.nist.gov/cgi/cbook.cgi?ID=C74828&Mask=1.
13. Purchasing Energy-Efficient Large Commercial Boilers. Office of Eenrgy Efficiency & Renewable Energy. [Online] [Cited: 12 05 2022.] https://www.energy.gov/eere/femp/purchasing-energy-efficient-large-commercial-boilers.
14. Carbon dioxide. NIST Chemistry WebBook, SRD 69. [Online] 2021. [Cited: 12 05 2022.] https://webbook.nist.gov/cgi/cbook.cgi?ID=C124389.
15. Ammonia. NIST Chemistry WebBook, SRD 69. [Online] 2021. [Cited: 12 05 2022.] https://webbook.nist.gov/cgi/cbook.cgi?Name=Ammonia.
16. Agency, International Energy. Outlook for biogas and biomethane - Prospects for organic growth. s.l. : International Energy Agency, 2020.
17. Why have interest rates gone up? Bank of England. [Online] 05 05 2022. [Cited: 13 05 2022.] https://www.bankofengland.co.uk/knowledgebank/why-are-interest-rates-in-the-uk-going-up.
18. Treasury, HM. THE GREEN BOOK : CENTRAL GOVERNMENT GUIDANCE ON APPRAISAL AND EVALUATION. s.l. : UK Government, 2022.
19. A perspective on decarbonizing whiskey using renewable gaseous biofuel in a circular bioeconomy process. Xihui Kang, Richen Lin, Richard O’Shea, Chen Deng, Lianhua Li, Yongming Sun, Jerry D.Murphy. 2020.
20. Selling electricity back to the grid. Evo Energy. [Online] 09 08 2020. [Cited: 13 05 2022.] https://www.evoenergy.co.uk/news-updates/selling-electricity-back-to-the-grid/.
21. INTEREST IN BIOGAS CHP (COGENERATION). Biogas World. [Online] 12 06 2017. [Cited: 11 05 2022.] https://www.biogasworld.com/news/biogas-chp-discover-technologies/.
22. CHP Benefits. United States Environmental Protection Agency. [Online] [Cited: 11 05 2022.] https://www.epa.gov/chp/chp-benefits#economic.