Special Reports

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Special Report No. 17-02: Impact of Wet ESPs on PM2.5/CPM and Non-Particulate Emissions from Industrial Boilers – Literature Review and Summary of Available Data

PDF , Source: Special Reports Published: 09/2017 View Abstract

Abstract: This report conducts a detailed literature review on the ability of wet electrostatic precipitators (WESPs) to capture fine particulate matter (PM2.5 – particulate matter ≤2.5µm), sulfuric acid (H2SO4) mist, mercury (Hg), other trace metals and certain hazardous air pollutants (HAPs). Data on filterable PM (FPM) and condensible PM (CPM) emissions from several boilers equipped with wet ESPs and data available in the 2013 Environmental Protection Agency Boiler MACT (Maximum Achievable Control Technology) database, are also summarized. The literature test data (mainly for utility boilers or slip streams and pilot scale installations) show that upwards of 50% of both PM2.5 and H2SO4 mist could be captured in a wet ESP. However, the capture efficiencies are quite boiler-specific. Limited test data also show fairly high removal efficiencies for phenol, phenolic compounds, and formaldehyde across WESPs. While mercury capture is also significant (>50%), it is unclear whether this capture is hindered in the presence of significant SO2 due to the potential for the captured (oxidized) Hg to be re-emitted as gaseous elemental Hg. For total PM, condensible particulate matter (CPM) and trace metals other than Hg, wet ESPs appear to behave in a similar fashion to dry ESPs. There is also evidence in literature that, in the presence of SO2, a WESP can indeed produce very fine (low nanometer range) H2SO4 aerosols. It is suspected that the reactive species produced in the non-thermal plasma of the corona discharge oxidizes the SO2 to SO3 which forms sulfuric acid in the presence of water vapor. Thus, it appears that the generation of ultrafine H2SO4 aerosols can be avoided only when the flue gas entering the WESP contains very low levels of SO2. Limited industry data and data in EPA’s Boiler MACT database are inconclusive with regards to any additional capture of CPM across WESPs. Much of the evidence in the literature focused on FPM, H2SO4, metals, and other HAPs, and not on CPM.

Special Report No. 17-01: An Overview of Potential Sources and Sinks of Methane in the Forest Products Value Chain

PDF , Source: Special Reports Published: 07/2017 View Abstract

Abstract: This report provides a general overview of methane’s role as an atmospheric greenhouse gas and the potential sources and sinks of methane in the forest products value chain. The information summarized herein indicates that fossil fuel-related methane emissions from the forest products value chain are relatively small compared to biogenic methane emissions and small compared to overall greenhouse gas emissions from the value chain. Biogenic methane emissions and sinks, however, can be important elements of the value chain’s carbon footprint. Current understanding suggests that, within the forest products value chain, the elements most affecting potential biogenic methane are forests and landfills. Unmanaged and managed forests can be net sources or sinks of methane depending on many site-specific conditions. Methane fluxes from forest soils have received more research attention than other processes in the forest. This research documents very large site-to-site variability in soil-related net methane fluxes, with soil moisture being a key determinant of whether soil is a net methane sink (dry soils) or methane source (saturated or wet soils). Factors other than moisture, however, also affect methane flux from forest soils. Soils are not the only potential sources of methane from forests. Recent research has identified the potential for methane to be produced in relatively large quantities within living trees and on the surface of foliage. These sources, however, while potentially large are not well understood. Methane is known to be produced from decomposing forest products in landfills, but significant uncertainties remain about the rates and quantities of methane emissions, especially at the product- and site-specific levels. While the effects of these uncertainties on emission estimates are likely smaller than those currently associated with forest-related methane, the uncertainties should be recognized when developing estimates for use in carbon footprint studies.

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