Calculating Airflow Requirements for Forced Aerated Composting Systems

摘要

The School of Engineering, Cardiff University has operated a large scale composting research facility at the Carmarthenshire Environmental Resources Trust composting site in south west Wales for more than 4 years. In depth analysis of windrow, aerated bay and in-vessel composting systems has been undertaken at the facility, with a view to establishing engineering data to aid the design of composting systems.rnIn response to the Animal By Products Regulations legislation requiring the use of enclosed systems to compost organic waste that contains, or may have come into contact with meat, has led the research facility to examine the design and management of forced aeration that is required for these types of systems. Earlier work on dynamic respiration rate monitoring of commercial scale composting systems has demonstrated the amount of air required to maintain optimal oxygen content in the composting system (>10%). The heat being produced by a composting mass can be calculated once the rate of CO_2 production has been found as it has been demonstrated that for each mole of CO_2 formed there is a heat release of approximately 500 kJ. Knowing the amount of heat produced at a known level of CO_2 production demonstrates the amount of heat that is required to be removed from the system to maintain a specified temperature. Calculating heat removal from a composting system via the aeration system is found from the enthalpy of air entering the system and the enthalpy of gases leaving the system. From these calculations the volume of air required to maintain temperature and oxygen levels can be found. This information can then be used to specify aeration equipment.