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Heat exchangers deliver pasteurisation to New Zealand AD plant
22/2/2023
6 min read
Feature
Anaerobic digestion (AD) to produce biogas and biomethane has huge potential to generate renewable energy, as well as treat a wide range of organic wastes and provide biofertiliser in the form of digestate (the solid, fibrous material left over in the reactor after the AD process is complete). Here, Matt Hale from HRS Heat Exchangers, explains some of the options for pasteurising materials in the digester.
We at HRS have long argued that, if biogas energy is to fulfil its potential, then the benefits of using digestate as part of sustainable farming practices must also be maximised. Only last year the European Biogas Association (EBA) published two papers which highlighted the importance of digestate in the overall sustainability profile of anaerobic digestion (AD) and biogas energy in Europe – particularly since Russia’s invasion of Ukraine has led to renewed interest in AD technologies and new national targets for biogas energy generation.
However, some of the progress involved in AD actually has an energy requirement – such as heating digesters or treating feedstock or digestate to improve handling and hygiene. To maximise the potential of AD as a technology, it is important that energy efficiency is considered at every one of these opportunities.
Digester heating
In terms of temperature regime, AD can be divided into mesophilic or thermophilic systems. Mesophilic digesters are the most common type worldwide, and operate at between 35°C and 40°C, typically around 37°C. In contrast, thermophilic digesters operate at temperatures above 50°C, with shorter retention times but higher operating energy requirements. These are therefore less common.