Mercury emissions from a modified in-situ oil shale retort

Abstract

Gaseous Hg emissions were measured during the processing of a large modified in-situ oil shale retort (4×10 4 m 3) in Colorado. A continuous, on-line, gas monitor based upon the principal of Zeeman atomic absorption spectroscopy was the primary analytical method. The on-line monitor technique was shown to be well suited for this application and compared favorably with an independent reference method which collects gaseous Hg by Au-amalgamation. Forty-two hours of on-line data were obtained over a 35-day period during the latter half of the retort burn. Hg emission rates in g day −1 were calculated from Hg concentration and offgas flow rate data. The predicted total gaseous Hg mass emission for the retort was 4 kg. Extrapolation of the data to a hypothetical modified in-situ oil shale facility with a daily production of 8× 10 61 (5 × 10 4 bbl) of oil results in a projected emission rate of ≈ 8 kg day −1. This estimated value is higher than Hg emission rates recorded for coal fired power plants. Emission rates were found to be highly variable both within and between days. Factors which may limit Hg emissions from a modified in-situ retort are discussed. Adsorption losses to unretorted shale at the bottom of a retort are suggested as a major sink for Hg. Losses of Hg to the extensive offgas plumbing system may also be substantial.