Emission Factor Development for Mechanical Evaporators

The United States Environmental Protection Agency (USEPA) has developed and published emission factors for various industries and sources. These emission factors are heavily documented in the USEPA publication AP-42 and also in the USEPA Clearinghouse for Inventories and Emission Factors.

However, over the years since the inception of AP-42, emission factors have not remained up-to-date with all the variations and improvements in the technology which generate the emissions. Stack testing methods provide supporting data in conventional stacks but are often limited when sampling conditions are not ideal, or the source is not an enclosed stack. Theoretical calculations are sometimes possible for particular sources but often provide exceedingly conservative results as the specific situation is overly simplified. 

One such example of this is the emissions associated with mechanical evaporators, or more commonly known as turbo-misters or water cannons. These units are typically located on the banks of, or floating on, an evaporative pond. The mechanical evaporator and pond system produce emissions of particulate matter (PM) as solution droplets are drawn through the mechanical evaporators and are sprayed over the pond and allowed to evaporate and crystallize solid particles depending on the ambient conditions. Due to both the location of the sources and the change in phase of the emissions from liquid solution droplets to solid PM, quantification of the emissions from these sources is very difficult to characterize. 

In the past both the New Mexico Environment Department (NMED) and Arizona Department of Environmental Quality (ADEQ) have requested emission estimates of PM generated from mechanical evaporators for use in air quality permitting. Trinity Consultants has conducted a number of emission factor development studies in the southwestern United States. In all of the studies conducted so far the measured PM concentrations and subsequent emission factors have all been significantly lower and more representative than the theoretical estimates. Therefore the use of site specific emissions factors provides a more characteristic emission factor for the mechanical evaporators and allows facilities to comply with ambient air quality standards as they become more restrictive. Air permit applications using this technique have been submitted to the NMED and ADEQ for review and received approval to be used in future permitting actions as a method of quantifying emissions from on-site mechanical evaporators.

For more information, contact Andrew Glen, PhD at (505) 266-6611.