Anaerobic digestion is a proven technology, increasingly deployed worldwide. Its slurry by-product, known as digestate, is commonly spread on farmland, but this practice has become un-economical, due to low nutrient density, storage, transportation costs. Digestate gasification, coupled with combined heat and power production is a promising solution to the challenge. However, its environmental benefits have not yet been fully investigated. The plant analysed is based on downdraft gasification technology, and it would be suitable for the average farm in Northern Ireland. The solution would be of particular interest for the area, due to its intensive livestock farming, and new legislation liming the spread of digestate on land. The process analysed includes digestate separation, drying, gasification, syngas conditioning and combustion in a combined heat and power unit. The results of the analysis show that digestate gasification is superior to land spreading in all damage categories considered: Human Health, Ecosystems and Resources. The avoided production of heat and electricity accounts for most of the negative emissions. By assuming gasification ash and char can be utilized as soil amendment and that the ammonium sulphate produced in the ammonia scrubbing unit can be marketed as fertilizer, this scenario is further improved, although only marginally.
|Title of host publication||SEEP21 Conference Proceedings|
|Number of pages||6|
|Publication status||Published (in print/issue) - 15 Sept 2021|
- Life cycle assessment
- small scale gasification
- anaerobic digestion
- combined heat and power