Predictive Flare Vent Gas Net Heating Value Through Determination of Average Molecular Weight

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Title Predictive Flare Vent Gas Net Heating Value Through Determination of Average Molecular Weight
Creator Boley, Troy
Contributor Stuck, Derek, and Patel, Nisarg
Date 2013-09-25
Spatial Coverage Kauai, Hawaii
Subject AFRC 2013 Industrial Combustion Symposium
Description Paper from the AFRC 2013 conference titled Predictive Flare Vent Gas Net Heating Value Through Determination of Average Molecular Weight by Troy Boley
Abstract The research community is well aware of the recent investigations and results of industrial flare operations and the demonstrated severe impact on decreased flare combustion efficiency resulting from over-assisting (via steam or air) flare tip combustion zones.1 The petroleum and petrochemical industries use flare systems to safely combust excess process gas and emergency releases. In order to comply with current United States Environmental Protection Agency (USEPA) regulations as promulgated under New Source Performance Standard for petroleum refineries, 77 Fed. Reg. 56,422, September 12, 2012 (NSPS Subpart Ja) and in voluntary consideration of certain aspects of integrated flare control practices noted within recent flare Consent Decrees2, many refineries and chemical facilities have installed an ultrasonic flow meter to measure the total vent gas flow rate. Several facilities have also installed analytical instrumentation, such as in-line gas chromatographs (GC), to periodically measure the composition of the vent gas. The purpose of the compositional analysis was originally to quantify and assess flare emissions rates. However, in the Consent Decrees, these analytical devices are also being utilized to monitor and calculate the combustion zone Net Heating Value (NHV). The flare flow meters selected often contain a proprietary algorithm that utilizes the speed of sound in a gas to determine the gas density, and thus the average molecular weight (MW) of the vent gas. Anecdotally, those facilities with in-line compositional analysis of the vent gas have frequently reported that "similarities" and "commonalities" exist between the flow meter's MW algorithms and the MW determined analytically through calculations based on molar fractions measured by the in-line GC. When considering combustion efficiency and the need for accurate NHV calculations, the usefulness of the means by which one obtains NHV measurements are currently limited by the analytical lag time of the GC instrument, which prevents rapid, real-time monitoring of the net heating value, delays accurate and timely steam or assist air adjustments, and delays the facility's response time to smoking flare events. This paper will seek to explore the theoretical and practical connection between the average molecular weight as measured by state-of-the-art ultrasonic flare gas flow meters and the net heating value as measured by an in-line composition analyzer. Already, it is possible to voluntarily integrate the flow meter MW algorithm into a viable Steam to Vent Gas ratio (mass basis) for a continuous steam-assist control scheme. The ultimate objective is the potential demonstration that the ultrasonic flow meter's MW algorithm might be suitable as a predictor of NHV in the combustion zone, thus allowing automatic supplemental gas addition using a Predictive Emissions Monitoring System3 (PEMS) potentially negating the need for a continuous in-line GC or compositional analyzer during normal operations. Furthermore, the paper will look to incorporate this connection into the Automatic Flare Control Scheme to allow real-time adjustments to the net heating value.
Type Event
Format application/pdf
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ARK ark:/87278/s6vm79d7
Setname uu_afrc
Date Created 2014-10-14
Date Modified 2014-10-14
ID 14368
Reference URL