A Quick Guide to Opportunities for Co-Benefits from Plant Optimization and Existing Pollutants Control Measures

Minamata Convention on Mercury (COP3)

25 to 29 November 2019

Geneva, Switzerland

Carlos E. RomeroEnergy Research Center

Lehigh University

Coal-Boiler Boiler and Air Pollution Control Devices

BOILER

SCR

APH

MILLSCOAL

FGD

PRECIP.

❑Coal • Mercury and sulfur content

• Halogen content

• Coal cleaning processes

❑Boiler Operation• Combustion conditions

• Flue gas conditions

• Other operating conditions

❑Boiler Design/Other Emissions Control Systems• Back-pass arrangement

• Air pollution control devices (APCDs)

Factors Affecting Mercury Emissions

Hg0

Hg2+

Hg(p)

Fate of Mercury in Coal-Fired Boilers

Metal-oxide catalysts can oxidize a significant portion of Hg0 and catalyst systems can reduce elemental mercury.

Oxidized Hg is water-soluble and conventional acid gas scrubbers can dispose oxidized Hg.

Coal Hg can sometimes be selectively removed in the coal cleaning and milling processes.

Oxidized Hg adsorbed by particulate matter in the flue gas can be collected in the particulate control device.

Boiler operating conditions can be adjusted to promote Hg oxidation and sorption onto the fly ash.

$275/kW$1.9/MWh

$530/kW$11.5/MWh

❑Co-Benefit Methods of Control

• Selective Catalytic Reduction (SCR) Systems –Increase mercury oxidation.

• Electrostatic Precipitators (ESP) and Baghouse Systems – Capture particle-bound mercury

• Wet Flue Gas Desulfurization (WFGD) Systems – Capture oxidized Hg. Mercury re-entrainment needs to be minimized.

• Dry Sorbent Injection Systems – Improves mercury capture by sorbent acting on SO3removal.

Co-Benefit of Existing Pollutants Control Measures

❑Direct Methods of Control

• Activated Carbon Injection (ACI) – Uses Powdered Activated Carbon (PAC). Particulate control needed. Can be used in the WFGD.

• Halogen Addition – Injected with the coal. Promotes mercury oxidation for fly ash and WFGD capture.

• WFGD Additive – Proprietary and sulfide based reagents prevent mercury re-entraintment.

Direct Methods of Mercury Removal

Mercury Optimization in Boilers

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❑ Boiler controllable parameters impact combustion in the furnace

❑ Those parameters impact gas temperatures and fly ash characteristics

❑ Fly ash with higher unburned carbon, smaller size and larger porosity works better for mercury reduction

❑ Mercury can be reduced 50% in average by boiler tuning. Heat rate trade-off?

Mercury Optimization in Wet FGDs

Hg0

Hg2+

Hg0

Hg2+

S2-

Re-emission

❑ Wet FGD’s in combination with SCR control devices can achieve mercury removals up to 95%.

❑ Hg2+ is absorbed in the FGD liquid slurry and reacts with sulfides from the flue gas.

❑ More sulfides reduce Hg2+ to Hg0 (re-emission).

❑ ORP is used as an indicator of mercury control in Wet FGD.

Direct Methods of Mercury Removal

Halogen Treatment of Coal

HalogenInjection

Activated Carbon / Dry

Sorbent Injection

Re-Emission Additives

BOILER

SCR

APH

MILLSCOAL

FGD

PRECIP.

Example of Optimized Operation

Hg approaching environmental limit

Optimized Operation of Boiler and Auxiliaries

Optimized Wet FGD Additive Injection to Prevent Re-

emission

A Holistic Approach to Mercury Emissions Control Can Result in

$ Millions Annual Savings

❑ Optimization of Current Boiler Operation❑ Installation of Co-Benefit Equipment*❑ Optimization of APCD Operation❑ Installation of Mercury Control Technology❑ Optimization of Mercury Control System

*As required by regulation on other pollutants

Thank You!!!