Efficiency key to maximizing wastewater’s biogas potential
The recent news from the American Biogas Council (ABC) that American wastewater treatment plants are capturing 100 billion cubic feet of biogas per year is fantastic1, but it is also important that the utilization of this captured resource – and coproducts such digestate – are not wasted.
The ABC recently revealed that 1,200 wastewater treatment plants across the United States currently capture and use biogas produced from wastewater sludge, enough to power about 1.1 million U.S. homes (212 billion kilowatt-hours of electricity annually).
They rightly point out that, as thousands of other wastewater treatment plants do not currently capture biogas (they estimate around 3,800 more wastewater treatment plants have sufficient wastewater flows biogas capture to be a viable option), the potential energy being wasted (some 72 billion cubic feet) is huge.
Focus on efficiency
The one thing that the ABC report neglects to mention is the importance of efficiency across the whole of the biogas sector. A 1% increase in efficiency across the American wastewater biogas fleet (both those currently capturing gas, and those which have the potential to do so), could provide an additional 1.72 billion cu. ft of biogas per year – enough for an additional 19,000 homes (roughly equivalent to Oak Park, Illinois; Lakewood, California; or Celina, Texas).
Whether it is efficient digester heating using external corrugated tube heat exchangers (like the HRS DTI Series) 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 pasteurization, evaporation and concentration.
HRS offers a number of specific biogas systems to boost production, reliability and value while maximizing 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 Pasteurization System (DPS) is capable of pasteurizing digestate, feedstocks, and similar materials pre-or post-digestion, allowing operators to maximize 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 HRS Digestate Concentration System (DCS) 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 odors, and usually requires no additional energy or water, while lower water content means reduced transport costs.
With HRS equipment installed at some 300 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 ABC has highlighted.