New Learnings on Composting Technological Deployment
Michael Bryan-Brown
President / Chief Engineer
Green Mountain Technologies
Bainbridge Island, Washington
One of the advantages of aeratedpilecomposting systems(ASP)is the reduction in energy consumption required for turning andhandling.However, delivering pressurized air for the purpose of cooling compost requires a significant amount of energy. Large ASP systems can have multiple blowers of 100 hp or more running continuously and power bills can exceed $10,000 per month. Additional blowers for biofilters and building ventilation can add to the overall power consumption. All this energy consumption diminishes the benefits of green house gas reductions typically associated with composting.
Several strategies have been employed by the author and others to reduce the energy demand and improve efficiencies. The most common strategy is variable frequency drives (VFD) coupled with system sensor feedback to deliver only the amount of air required. Also, programming controllers to reduce energy consumption during peak demand charges helps lower bills and minimize impacts on the grid. Some facilities have employed landfill gas to run the blowers using direct drive CNG motorswhile others have used duct misters to lower the air temperature and improve cooling.
Operationally siteshave utilized a courser grind to maximize porosity while reducing diesel consumption by the grinder. Pile height is another factor that influences the power required for coolingcost due to pressure losses when higher pilescompact and loose porosity. The author will provide energy data from several operating facilities and make a comparison of energy inputs vs composting time to offer the most efficient design.