Tennent’s – 2023
Tennent’s became more energy efficient through the re-use of waste heat from their anaerobic digestion plant and chimney stack.
The process of anaerobic digestion at Tennents has to occur at 35oC for biological reasons. The effluent must be heated to this temperature as part of brewing, and this is done through natural gas boilers heating water into steam. Before the heat recovery project, treated effluent would be sent to drain at around process temperature (~35oC), and all that heat would then be lost. Now, the heat recovery process takes the treated effluent going to drain at 35oC and uses it to heat ambient untreated influent coming into the anaerobic digestion plant via a new heat exchanger.
The new heat exchanger is designed to take ~10oC of heat from the treated effluent meaning the untreated effluent is going into the process at ~10oC higher temperature. This means that the heating demand as part of the AD process is reduced significantly. This in turn reduces the steam used for the process and therefore natural gas and carbon emissions.
Heat in the form of steam is a requirement around site for the brewing process. This is produced by combustion of natural gas in the boiler house. Flue gases at high temperatures are produced as a by-product of this combustion, previously these flue gases were immediately exhausted to atmosphere.
The addition of a boiler economiser fitted to the flue exhaust allows us to re-direct the flue gasses through an economiser to pre-heat the boiler feed water while also cooling down the flue exhausts. This reduces the required temperature uplift in boiler feedwater to produce steam, reducing the natural gas volume required and therefore carbon emissions. As part of this project the boiler hot well and chimney were also replaced-representing efficiencies through replacement of ageing equipment.
AD heat recovery has resulted in a significant reduction in steam use and, as a result, natural gas. The carbon reduction associated with this project is ~400tCO2/annum. Chimney Economisers are expected to reduce steam use by ~500tCO2/annum. In addition, the new hot well with new insulation represents an improvement in efficiency.