Rationalisation of and mitigation options for proposed EPA-HQ-OAR-2010-0682
Part 2: Impact on FCC units. In May 2014, the EPA issued EPA-HQ-OAR-2010-0682, FRL-9720-4, RIN 2060-AQ75 for review and comment.
Aaron Wright, Robert Ohmes, Joni Lipkowitz
KBC Advanced Technologies
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The rule closes emissions limits under all of the major air emission categories such as NSPS, NESHAP and MACT. In addition, new requirements are added for periods of startup, shutdown, and malfunction.
In Part 2 of this paper, we will expand the discussion to focus on how the regulations will impact the FCC. Options will be based on industry experience and practical thinking, as well as offering novel alternatives.
FCCU - Proposed Rule
The EPA is proposing the following standards and changes in standards, particularly in startup and shutdown:
• HAP emissions from FCCU under Refinery MACT 2 (e.g., wet scrubber, fabric filter, cyclones) would be operating before emissions are routed to them and would be operating during startup and shutdown events in a manner consistent with normal operating periods, such that the monitoring operating limits set during the performance test are maintained and met.1
• The EPA recognises that there are safety concerns associated with operating an ESP (electrostatic precipitator) during startup of the FCCU. Elevated CO levels pose an explosion threat due to the high electric current and potential for sparks within the ESP. Consequently, it is common practice to bypass the ESP during startup of the FCCU. Once torch oil is shut off and the regenerator is fueled by catalyst coke burn-off, the CO levels in the FCCU regenerator flue gas will stabilise and the flue gas can be sent to the ESP safely. While the catalyst is not circulating or is circulating at reduced rates, the PM (particulate matter) and metal HAP emissions are expected to be much lower than during normal operations. Therefore, the EPA proposes specific PM standards for startup of FCCU controlled with an ESP under Refinery MACT 2. The EPA also proposes that an FCCU, using an ESP as the APCD (air pollution control devices), meet a 30-percent opacity limit (on a 6-minute rolling average basis) during the period that torch oil is used during FCCU startup. The EPA notes that Refinery NSPS J includes the exception for one 6-minute average of up to 60-percent opacity in a 1-hour period primarily to accommodate soot blowing events. As no soot blowing should be performed prior to the ESP coming on-line, the EPA is not including this exception to the proposed 30-percent opacity limit during startup for FCCU that are controlled by an ESP.1
• Refinery NSPS J includes an incremental PM emissions allowance for post-combustion devices and relies on a 30-percent opacity limit that is outdated and has been demonstrated to be ineffective at identifying exceedances of the 1.0 g PM/kg of coke burn-off emissions limit. Per Refinery NSPS J, the EPA proposes ongoing compliance with PM emissions limits for an FCCU, using an ESP as the APCD, to meet a 30-percent opacity limit, except for one 6-minute average, not to exceed 60-percent opacity, during the period that torch oil is used during FCCU startup. This opacity limit was selected because it has been used historically to assess compliance with the PM emission limit for FCCU in Refinery NSPS J and because the emission limit can be assessed using manual opacity readings, eliminating the need to install COMS (continuous opacity monitoring system).1
• THE EPA proposes an excess oxygen concentration of 1 volume percent (dry basis) based on a 1-hour average during startup. They consider the 1-hour averaging period for the oxygen concentration in the flue gas from the FCCU to be appropriate during periods of FCCU startup because air blast rates can be directly controlled to ensure adequate oxygen supply on a short-term basis.1
• Under Refinery MACT 2, an initial performance demonstration test is required to show that FCCU is compliant with the emission limits selected by the refiner. The performance test is a one-time requirement; additional performance tests are only required if the refiner elects to establish new operating limits, or to modify the FCCU or control system in such a manner that could affect the control system’s performance. The EPA proposes that it is necessary to require a performance test once every 5 years for all FCCU.1
• For environmental impacts of an HCN (hydrogen cyanide) emission limit beyond that achieved by the CO emission limit as a surrogate for HCN, the EPA is proposing, at this time, that it is not necessary, pursuant to CAA section 112(d)(6), to revise the MACT standard to establish a separate HCN standard.
• The current Refinery MACT 2 includes several different compliance options, some based on PM as a surrogate for total metal HAP and some based on nickel (Ni) as a surrogate for total metal HAP. Refinery NSPS J was the basis of the PM emission limits and the metal HAP MACT floor in Refinery MACT 2. Refinery NSPS J limits PM from FCCU catalyst regeneration vents to 1.0 gram particulate matter per kilogram (g PM/kg) of coke burn-off, with an additional incremental PM allowance for liquid or solid fuel burned in an incinerator, waste heat boiler, or similar device. Refinery NSPS Ja includes a limit of 0.5 g PM/kg of coke burn-off for newly constructed sources.1
• Refinery MACT 2 also includes two emission limit alternatives that use Ni, rather than PM, as the surrogate for metal HAP. The first of these Ni alternatives is a mass emission limit of 13 grams Ni per hour; the second nickel alternative is an emission limit of 1.0 milligrams Ni per kg of coke burn-off. Compliance with the Ni emission limits in Refinery MACT 2 is demonstrated by either a daily average site-specific Ni operating limit (using a COMS and weekly determination of Ni concentration on equilibrium FCCU catalyst), or APCD-specific daily average operating limits using CPMS and monthly average Ni concentration operating limit for the equilibrium FCCU catalyst.1
• The EPA is proposing to incorporate the use of 3-hour averages for the site-specific opacity operating limits in Refinery MACT 2 for both the PM and Ni limits, because this is a cost-effective development in monitoring practice.1
• Refinery NSPS Ja provides a specific monitoring alternative to pressure drop for jet ejector-type wet scrubbers equipped with atomising spray nozzles. The EPA proposes it is necessary to require owners or operators of a jet ejector-type wet scrubber or other type of wet scrubber equipped with atomising spray nozzles to perform daily checks of the air or water pressure to the spray nozzles pursuant to CAA section 112(d)(6).1
• The EPA did not identify any developments in practices, processes, and control technologies to reduce CO or VOC emissions from FCCU as part of the review of Refinery NSPS J, and the EPA has not identified any developments in practices, processes, and control technologies for FCCU that would reduce organic HAP since promulgation of Refinery MACT 2.1
• Refinery MACT 2 uses CO as a surrogate for organic HAP and establishes an emission limit of 500 ppmv CO (dry basis). Although this limit is expressly provided as a limit addressing organic HAP emissions, this emission limit is also expected to limit the emissions of oxidisable inorganic HAP, such as HCN. Thus, the EPA considers that the CO emission limit also acts as a surrogate for the control of oxidisable inorganic HAP, such as HCN. The EPA anticipates that most FCCU would have to install a selective catalytic reduction (SCR) system to meet NOx emission limits, if applicable.1
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