ENV-17-26 Reality Check: Proof that the New AP-42 Flare VOC Emission Factor has Technical Flaws

Description:

This paper and poster presentation use flare heat and material balance calculations to assess typical petroleum refinery flare VOC emission rates and destruction efficiencies (DEs) when applying the most common calculation methodologies used to estimate flare VOC emissions: Method 1 – Assume Flare 98% VOC DE Method 2 – Assume Flare 99% VOC DE Method 3 – Use existing AP‐42 Flare THC Emission Factor (EF) of 0.14 lb THC/MMBtu‐LHV Basis Method 4 – Use new AP‐42 Flare VOC EF of 0.66 lb VOC/MMBtu‐LHV Basis This paper does not address the proposed June 2017 AP‐42 EF addressing enclosed ground flares, nor does it address the details of the methodology used by EPA to establish the new December 2016 flare VOC EF. Instead, using basic heat and material principles, the primary purpose of this paper is to demonstrate that EPA’s new flare VOC EF, published by EPA in AP‐42 Section 13.5 in December 20161, has inherent technical flaws when applied to estimating VOC emissions from typical refinery fuel gas streams. When compared to calculating hourly VOC emission rates assuming a 98%‐99% DE, the December 2016 EF (Calculation Method 4) tends to significantly overestimate VOC mass emission rates from petroleum refinery flares and underestimates flare VOC DE2. Although in Footnote “b” to AP‐42 Table 13.5‐13 (old THC EF‐Calculation Method 3), it is stated that the “THC emission factor may not be appropriate for reporting VOC emissions when a VOC emissions factor exists”. EPA is not requiring the use of its new VOC EF (Calculation Method 4). In fact, each refinery has the flexibility to develop a site‐specific flare EF that best represents the facility’s understanding of its flare operation. Therefore, depending on the flare gas stream, the original flare THC EF may be an appropriate choice.