Air quality management districts, AQMDs, are continually updating their standards for reciprocating engines and the resulting emissions. Although the changes are made with the best intentions (e.g., reducing airborne pollutants), these changing standards often impose large technical challenges and require equipment upgrades or replacements which adds unexpected costs for business and industries.
This is the situation one of our wastewater treatment customers found themselves in when a change in their local AQMD regulations instigated a large change in what was allowed for natural gas combustion.
This wastewater facility had three large CHP systems that used off-gas from the wastewater (produced through a digester process) as the main fuel source and natural gas as a backup fuel source. The CHP system provides electrical power for the plant, electrical power for the utility grid, and heat for the digester. The system had a combined electrical/mechanical efficiency of around 90% while removing GHG emissions from the environment so it was critical that it continue to run!
The challenge that the new AQMD ruling created was that the allowable natural gas consumption in their engines was changing from 100% to only 49%. However, the engines were originally designed with a dual fuel system that could run on either 100% natural gas or 100% digester gas but not a blend of the two fuels.
This change in allowable fuel ratios caused a big issue with the plant operations! (more…)