Guiding Principles for Mercury Control Strategies



In planning for compliance with EPA’s Mercury and Air Toxics Standard (MATS), there are many options and implications to consider.  Comparison between technologies is best achieved through field testing.  The multitude of testing programs and field data available today have led to improved strategic thinking and planning.

Several key philosophies are synthesized in a few Guiding Principles that enable a clearer path to compliance planning and execution.  As one of the Principles, getting a handle on balance-of-plant and multi-pollutant interactions is critical to success.

One example is ash utilization, which has been improved from recent developments in powdered activated carbons (PACs) and lower injection rates.  Past testing has also shown that mercury control performance degrades in the presence of SO3, whether through injection or native high sulfur coal.  Field tests using newly developed Generation 2 and 3 PACs have shown significantly improved mercury capture performance over conventional PACs and that dry sorbent injection (DSI) for acid gas control impacts this.  In certain applications, a marked effect is seen with interactions between DSI and ACI, which are both necessary for successful MATS compliance.  These correlations are presented, and the implications for compliance planning are discussed.  MATS solutions are very unit-specific.

GUIDING PRINCIPLES FOR MERCURY CONTROL STRATEGIES
Adopt a Science-based Approach
Use science, not hearsay, to understand your mercury capture and other effects.  Successful mercury control requires Contact, Conversion and Capture to occur to remove mercury from the system.  Each of these mechanisms must have a high degree of efficiency.  All three mechanisms must occur in as little as half a second up to a few seconds to achieve rapid and effective mercury control. Go back to the fundamentals to understand what is happening in your system and to interpret test data.

Activated Carbon Injection (ACI) with ADA Carbon Solutions’ Generation 2 and 3 sorbents, FastPAC Premium™ and FastPAC Premium-80™, is designed to achieve these three mechanisms in a highly efficient manner.

Move Mercury Removal "Upstream" to a Single Control Point
Capture of mercury in an engineered, controlled manner upstream of a particulate collector contains the conversion, contact and capture in a specific location and predominantly in one phase (flue gas).  This accomplishes secure capture from the flue gas directly to the solid phase, where it can be removed from the system by an ESP or baghouse.  If this does not occur and the mercury continues on to a downstream wet scrubber, the competing scrubber chemistries and multiple phase partitioning of mercury add complexity to the plant’s mercury control management.  Capture is not necessarily secure in the wet scrubber.

Active Control, Not Passive
Power plant operators are well-served by having an engineering control within their APC processes that they can “dial up” rapidly to obtain increased mercury control or “back off” when over-controlling.  Devices that provide passive contributions to mercury control, such as an SCR to provide conversion/oxidation, may degrade over time or may operate only under higher-load conditions.

Retain the Original Purpose of Equipment
The compliance method must be very reliable and minimize downstream impacts, retaining the primary purpose of the equipment.  Additives or changes to operations can have collateral effects that adversely impact equipment life, reliability, or emissions control.

Minimize Balance-of-Plant Impacts
Balance-of-Plant impacts are a major consideration in MATS planning.  It is essential to examine the current plan for ash, gypsum, equipment changes, coal flexibility, and multi-pollutant control.

TWO KEY POTENTIAL IMPACTS TO ADDRESS:
1. Ash Utilization
Key attributes for successful ash use in cement applications include foam stability over time, batch consistency, and minimal impact on air entraining agent (AEA) consumption.  The combination of unique characteristics of our Generation 2 PACs and the lower, more consistent injection rates required for good mercury control mean improved  ash utilization options.

2. Dry Sorbent Injection/Activated Carbon Interactions
DSI is needed for many reasons, but can have cross-media impacts on ash utilization, particulate collection and ash sluice water.  Minimizing DSI helps to reduce these effects.  When DSI use is driven by high levels of SO3 in the flue gas, FastPAC Premium-80™ can enable reduction in the amount of lime or sodium-based sorbent required.  This optimization results in more cost-effective compliance.

For more information click the DOWNLOAD icon for a complete paper on ADA Carbon Solution Guiding Principles for Mercury Control Strategies.

Or Contact ADA Carbon Solutions to discuss a MATS solution tailored to your process operations.

 

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