ENV-17-29 Refinery Sector Rule Flare Monitoring

Description:

The Refinery Sector Rule (RSR, a.k.a. Maximum Achievable Control Technology [MACT] Subpart CC) revisions published December 1, 2015 include requirements for refineries to determine the heat content of flare vent gases and possibly purge gases to demonstrate compliance. The regulation requires that heat content data be used to calculate the combustion zone net heating value, the dilution parameter, and the maximum flare tip velocity for each 15-minute block. The calculated values are then compared to established operational standards, or in the case of the maximum flare tip velocity used to establish an operational standard, for ongoing compliance. The revised RSR currently includes options for obtaining the necessary heat content information. Refineries can elect to install a monitoring system capable of continuously measuring component concentrations present in the flare vent gas. Alternatively, refineries can utilize an eight-hour evacuated canister grab sample and subsequent analysis approach as long as one of the listed analytical methods are used to determine the gas composition. Although these monitoring options have become synonymous with gas chromatography, the language may be vague enough to allow for the approval of other methods including mass spectrometry. One of the drawbacks to these monitoring methods is the need to reduce the compositional data to calculate a vent gas heat content for each 15-minute block. Another alternate monitoring option listed in the RSR language is the use of a continuous in-line calorimeter with or without an additional hydrogen analyzer. This monitoring method records heat content data instead of gas component concentrations, eliminating some data reduction. Utilizing the optional hydrogen analyzer does require some data reduction to adjust the recorded heat value to account for hydrogen. The main drawback to this monitoring option is the inability to determine vent gas molecular weight from compositional analysis for flare operational control. This paper will compare the different heat content monitoring options available for RSR compliance. It will address the advantages and disadvantages of each monitoring method and the following data reduction activities to obtain vent gas heat content for each 15-minute block. The paper will also highlight some information from equipment vendors and refineries that have already installed similar monitoring devices for consent decree compliance where applicable. The ultimate goal of the paper is to provide stakeholders an understanding of the heat content monitoring methods available and the pros and cons of each monitoring method.