The Mercury and Air Toxins (MATS) rule was issued December 21, 2011 by the Environmental Protection Agency (EPA). It was required by a court-ordered Consent Decree which arose from the litigation resulting from its predecessor, the Clean Air Mercury Rule (CAMR), which was vacated in 2008. The rule sets maximum achievable control technology (MACT) standards for coal and oil generating stations for removing mercury, acid gasses, and a variety of toxic metals from the flue gas for coal and oil-fired utility boilers. EPA projects that the MATS rule’s annual incremental compliances cost will be $9.6 billion.
Overall MATS Requirements
For coal-fired units, MATS limits emissions for hydrogen chloride (as a surrogate for acid gas hazardous air pollutants (HAP), filterable particulate matter (PM) (as a surrogate for non-mercury HAP metals), mercury, and organic HAP. The limits vary based on type of coal burned and whether the units are new or were already in operation when the final rule was published. Total non-mercury HAP metals and individual non-mercury HAP metals limits can be used as an alternate to the filterable PM limits. Coal-fired electric utility steam generating units (EGUs) with flue gas desulfurization (FGD) units can use SO2limits as an alternative to the hydrogen chloride limits.
The new MATS rule creates a variety of new work practices standards generally aimed at maximizing the efficiency with which fuel Is burned to minimize hazardous air toxins (such as dioxin or fiurin) not continuously measured with continuous emissions monitoring systems (CEMs). Such work practices include maintaining and inspecting the burners and associated combustion controls (as applicable), tuning the specific burner type to improve combustion, obtaining and recording CO and NOX values before and after the burner adjustments, keeping records of activity and measurements, and submitting a report for each tune-up conducted. Please note that the new work practice standards apply to all units, even those with controlled mercury emissions.
Best Practices and Optimization
In its final regulation, EPA adjusted the language to recognize the value of automated boiler optimization tools such as neural network systems. Under the final rule, the best practices “boiler tune-up” must be conducted at each planned major outage and in no event less frequently than every 36 calendar months, with an exception that if the unit employs a neural-network system for combustion optimization, the required frequency is a minimum of once every 4 years (48 calendar months). Initial compliance with the work practice standard of maintaining burners must occur within 180 days of the compliance date of the rule, now formally set to be January 31, 2016 for existing EGU’s.
The tune-up requires inspection of all burner and combustion controls, and cleaning or replacement of any components of the burner or combustion controls as necessary upon initiation of the work practice program and at least once every required inspection period. Burner or combustion control component parts needing replacement that affect the ability to optimize NOX and CO must be installed within 3 calendar months after the burner inspection. Also required is observation of damper operations as a function of mill and/or cyclone loadings, cyclone and pulverizer coal feeder loadings, or other pulverizer and coal mill performance parameters, making adjustments and any needed repair to dampers, controls, mills, pulverizers, cyclones, and sensors; as well as evaluation of windbox pressures and air proportions.
Systems responsible for controlling air-to-fuel ratios must be calibrated and functioning properly, including calibration of excess O2 probes and/or sensors, adjusting overfire air systems, changing optimization software parameters, and calibrating associated actuators and dampers to ensure that the systems are optimally operated. Any component out of calibration, in or near failure, or in a state that is likely to negate combustion optimization efforts prior to the next tune-up must be corrected or repaired.
Also included in the best practices definition are explicit requirements to “optimize combustion to minimize generation of CO and NOx.” The rule states that “NOx optimization includes burners, overfire air controls, concentric firing system improvements, neural network or combustion efficiency software, control systems calibrations, adjusting combustion zone temperature profiles, and add-on controls such as SCR and SNCR; CO optimization includes burners, overfire air controls, concentric firing system improvements, neural network or combustion efficiency software, control systems calibrations, and adjusting combustion zone temperature profiles.”
The tune-up also requires documentation of the CO and NOx concentrations in the effluent stream in ppm, by volume, and oxygen in volume percent, before and after the tune-up adjustments are made. Boilers employing neural network optimization systems, however “need only provide a single pre- and post-tune-up value rather than continual values before and after each optimization adjustment made by the system.”
Summing Things Up
So what are we to make of these requirements? First a disclaimer: NeuCo did not play any role in having these requirements – which admittedly sound like all the best reasons to invest in combustion optimization – written into the MATS regulations. Since the implicit objective to all these requirements is to improve fuel efficiency (with the tacit assumption that any such effort must necessarily balance NOx and CO to avoid adverse outcomes such as slagging and waterwall corrosion), I can tell you right off that we would have lobbied hard to have the rule address not just combustion, but rather the integrated optimization of combustion and heat transfer including optimal sootblowing that NeuCo offers in our BoilerOpt package. (As has been demonstrated conclusively over the last half-decade, integrating the combustion and soot cleaning processes not only more than doubles fuel efficiency gains (relative to doing only neural combustion optimization), and can further reduce NOx; it also provides a substantial availability benefit through decreasing boiler tube leak outages, which are responsible for 50% of the equivalent forced outage rate for coal-fired boilers.)
But back to the EPA’s definition of combustion optimization. The way the best practices provisions for optimization are laid out indicates that the language in the rule is carefully and deliberately stated. As I mentioned earlier, the explicit requirement that NOx and CO be simultaneously optimized means that the EPA understands the importance of managing this stoichiometric tradeoff to increase boiler efficiency through better fuel and air management. And one might even conclude that by allowing optimization adopters to conduct tune-ups every 48 instead of every 36 months, the EPA was shrewdly recognizing the industry trend toward longer planned outage intervals and trying to offer the best carrot they could muster.
The rule acknowledges many of the additional parameters important to successful combustion optimization efforts, including an understanding of mill loading, proper pulverizer and damper functioning, combustion zone temperature profiles, etc.
Finally, the rule states that – while “continual” before/after measurements of NOx and CO flue gas concentration are required for manual boiler tune-ups – those EGU’s that employ on-line neural network combustion optimizers only have to document average before and after optimization values. Thus not only are the initial boiler tune-up dates deferred by a year and subsequent tune-ups required only every 4 as opposed to every 3 years for boilers with neural network combustion optimizers, but the requirements for documenting the effects on NOx and CO are also substantially relaxed. My read on this is that if burners need to be inspected, the plant needs to be offline. If that is true, then generators seeking to extend outage schedules to every four years will be challenged if they don’t have neural network combustion optimization software installed and running at their units.
To summarize, we believe the objectives of “best practices” boiler operations as expressed in the MATS would be ideally served through the comprehensive and integrated optimization of stoichiometry, boiler cleanliness, and heat transfer provided with our BoilerOpt package. Even with the limited definition of optimization that the EPA has provided in MATS, the rule creates an opportunity for NeuCo to deliver real value to generating units while helping them attain some regulatory relief by using neural network combustion optimization to comply with the rule.
Despite its 800+ pages, the MATS rule fails to make two main issues 100% clear:
1. What will the testing and tuning really cost in the end?
2. Exactly what scope does the EPA require in the neural net combustion optimizer?
A big advantage of having a neural combustion optimizer by the end of 2014 is that you won’t have to be one of the 2015 guinea pigs that struggle to figure out exactly what the EPA is expecting. But in 2016, if the EPA decides that the combustion optimizer you have doesn’t meet its minimum criteria, what are you going to do?
NeuCo has formulated a MATS focused combustion optimizer that we believe will
1. satisfy the EPA,
2. provide the extra year for our customers to see what testing and tuning really involve,
3. provide a risk-limited upgrade path for our customers should the EPA expand its definition of optimization or should customers see the value of NeuCo’s products and decide to invest more.
We think that NeuCo is uniquely positioned to make this offer to the market – we have the most flexible, best protected and most used technology in US power generation and we are committed to customer success in the long term. NeuCo believes that the best practices provisions will help spur industry-wide adoption of the optimization technology we have been working for 15 years to continuously improve and enhance, and the benefits of which our existing customers already enjoy. Exciting times ahead!