Decarbonisation Whisky Distilleries
Biogas Result
Assumptions:
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The distillery has enough space for a new operation, an anaerobic digestion plant on site to produce biogas which is used in biogas boiler to produce 6 bar steam will be installed.
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The site’s heat demand is 3,627,800 kWh and electricity demand is 225000 kWh.
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Whisky waste consists of draff and pot ale and produced in quantities of 2469 tes and 8148 m3 respectively.
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An anaerobic digestion (AD) plant will be installed onsite, and biogas will be produced by processing whisky waste through AD operated at 40 C [3]. This temperature was considered for biogas properties i.e., density.
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The biogas produced is used in biogas boiler to produce steam in order to meet the process heating requirement.
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Natural gas/biogas boiler efficiency is 83% [4].
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AD plant operational life is typically 25 years [3] , and the distillery operating hours are 8000 each year [5].
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Current gas and electricity prices are 8 p/kWh [6] and 33 p/kWh [7] respectively.
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The feedstock (i.e., barley) composition was taken on as received basis [8] and it was assumed that 16% carbon content remains in the waste biomass [9].
Results
The whisky waste processed through on-site AD plant can produce 65 m3/hr of biogas with 54.3% methane content and energy density of 3.6kWh/m3. It meets 77% of process heating requirement.
Since this biogas plant only operates on whisky waste on-site there are low to no emissions related to this process and can reduce 74% of process heating CO2 emissions.
CAPEX of approximately £2.9 million is required which includes AD plant as well as biogas boiler of the rating. Due to small scale of AD plant (i.e., <250 m3/hr), the CAPEX and OPEX are 1.66 and 1.93 times that of a large-scale plant (i.e. >750 m3/hr). The cash flows include savings on natural gas, operational costs of AD plant. Net present value of the project, however, is -£1.18 million which makes it economically Infeasible unless provided an incentive for decarbonisation.
Sensitivity Analysis
As per the sensitivity analysis between whisky production capacity and the economic feasibility of AD biogas plants are only economically feasible for distilleries with annual capacities over 12 million litres. Only 4 out of 120 distilleries in Scotland [10] operate at this capacity, however, distilleries located nearby such as Islay and Speyside distilleries which has combined whisky production of 22 million and 229 million litres respectively [10], can install a single anaerobic digestion plant with a combine capacity exceeding the minimum requirement.
