By Matt Hale, Global Key Account Director, HRS Heat Exchangers
The recent special report from the International Energy Agency (IEA) confirms that globally, the development of anaerobic digestion (AD) and biogas is accelerating, and that this valuable renewable energy source could provide the equivalent of nearly one trillion cubic metres of natural gas.
The report, Outlook for Biogas and Biomethane1, and the accompanying interactive map2, highlights not only the overall momentum of policy development in the sector (over 50 new policies have been introduced to support biogases since 2020 as countries increasingly recognise their benefits), but it also stresses the importance of valuing the co-benefits of AD. These include waste management (and offsetting fugitive emissions from the unregulated decomposition of organic wastes), and the use of digestate – which can improve soil health and offset emissions associated with the production and use of synthetic fertilisers.
HRS has long argued that in order for biogas to reach its full global potential, then both the efficiency of the AD process and the benefits of using digestate as part of sustainable farming practices must also be maximised. It is therefore good to see the IEA state, ‘A relatively small share of the untapped potential for biogases is cost-competitive, but more can be unlocked if co-benefits are valued.’
The report confirms our own conviction that, ‘There is significant potential and political will to increase biogas production and use in many parts of the world. However, a challenging economic outlook means that plants will need to operate at maximum levels of efficiency in order to deliver for developers, policy makers, energy consumers, and the environment.’3
This means that energy efficiency and production need to be maximized, for example, though efficient digester heating using external corrugated tube heat exchangers compared to traditional inefficient internal heating coils, or the adoption of exhaust gas and digestate heat recovery. Plant performance and longevity can be extended through the use of biogas dehumidification systems to remove water and sulfur from biogas, and the economic and nutritional value of digestate can be increased through pasteurisation, evaporation and concentration.
Maximising process efficiency and digestate value
As well as heat exchangers for digester heating and heat recovery, which can improve digester efficiency and reliability and reduce downtime and cleaning requirements, HRS offers a number of specific biogas systems to boost production, reliability and value while maximising energy efficiency in various stages of the entire AD process.
The HRS Biogas Dehumidification System (BDS) removes water from biogas to protect boilers and CHP engines from corrosion and cavitation. It includes heat recovery as standard, increasing overall AD plant energy efficiency.
The HRS Digestate Pasteurisation System (DPS) is capable of pasteurising digestate, feedstocks, and similar materials pre-or post-digestion, allowing operators to maximise the efficiency of their overall process while meeting regulatory and customer requirements. Its continuous process is simpler than single tank options and provides up to 70% heat regeneration, making it extremely energy efficient.
The DPS uses a double-tube heat exchanger to heat the digestate to 75 °C above the required pasteurisation temperature. This allows for variation in the sludge consistency and its incoming temperature, making sure that the digestate is always properly pasteurised, while the tanks can also be used individually, for example to allow for routine maintenance.
The HRS Digestate Concentration System (BCS) reduces the volume of digestate while increasing its value, often using surplus heat from the CHP engine or biogas boiler. Not only does the DCS remove up to 80% of the water content, but it also increases the nutrient content, reduces odours, and usually requires no additional energy or water.
Lower water content means reduced transport costs and field traffic, bringing further benefits in terms of reduced compaction caused by the application of the digestate to land. At the same time, the use of acid dosing for odour and ammonia control helps increase the nutrient content of the digestate.
With HRS equipment installed at more than 200 biogas plants worldwide, whether you are looking for a heat exchanger for digester heating, or a complete turnkey digestate treatment system, HRS Heat Exchangers have the systems and experience to help deliver the huge biogas potential which the IEA has highlighted.
1 https://www.iea.org/reports/outlook-for-biogas-and-biomethane
