# Presentation: 693639

## EMISSION CONTROL TECHNOLOGIES FOR COAL-FIRED POWER PLANTS

**Ravi K. Srivastava and Frank Princiotta**
**Air Pollution Prevention and Control Division**
**National Risk Management Research Laboratory**
**Office of Research & Development**
**U.S. Environmental Protection Agency**
**January 16, 2004**

## What We’ll Cover Today . . .

**Electric power industry**
**Pollutant emissions**
**Control technologies**

## Electric Power Industry

- $250 billion in annual electricity sales in 2002; likely to have annual sales between $250 and $270 billion in 2010 to 2015
- Industry operates 16,500 units and 5,700 plants
- There are 3,100 electric utilities, 2,800 IPPs, 230 IOUs, and 2,000 publicly owned utilities
- The industry employs 362,000 people

- In the last five years, we have seen industry spend $88 billion in new power plant investments

## Electricity Generation

**Electricity Generation**

***Electric Generation in 2002***

***Historical & Projected Electric Generation***

- Source: 2002 and historical generation is from EIA’s Annual Energy Review.  Projected generation is from EPA’s Integrated Planning Model.

***Total Generation = 3,858 billion kWhs***

*Coal*

*Oil/Gas*

*Nuclear*

*Hydro*

*Other*

## Source: EEI

## Coal-Fired Power Plants

- There are about 530 power plants with 305 GW of capacity that consist of about 1,300 units.
- Coal plants generate the vast majority of power sector emissions:
- 100% Hg
- 95% SO2
- 90% of NOx

## Emissions of SO2 & NOx

**Emissions of SO****2**** & NO****x**

- Source: EPA

**Million Tons**

**Million Tons**

**Power Sector**

**Power Sector**

**Power Sector**

**Power Sector**

**All Other Sources**

**All Other Sources**

## Emissions of Mercury

- Source: EPA

## Emissions reductions possible through:
Emissions control technologies
Advanced power generation technologies
Power plant upgrading options
Fuel switching

Focus on emissions control technologies

- Emissions control technologies
- Advanced power generation technologies
- Power plant upgrading options
- Fuel switching
- Focus on emissions control technologies

**Pollutant Reduction**

## NOx Control Technologies

- Primary – reduce the NOx produced in the primary combustion zone.
- Widely used - low NOx burners (LNBs) and overfire air (OFA)
- Secondary - reduce the NOx already present in the flue gas
- Widely used - reburning, selective non-catalytic reduction (SNCR), and selective catalytic reduction (SCR)

## Low NOx Burners

- Limit NOx formation by delaying complete mixing of fuel and air
- Reduced oxygen in primary flame zone
- Reduced flame temperature
- Reduced residence time at peak temperature
- Can provide reductions in excess of 50%

## Overfire Air

- 5 to 20% of the total combustion air is injected through ports located downstream of the top burner level
- Burners operate at lower than normal air-to-fuel ratio resulting in NOx control, OFA added to achieve complete combustion
- Can be used with LNB to increase NOx reduction by 10 to 25%

## Reburning

- Reburn fuel (natural gas, coal, other fuels) is injected to provide 15-25% of total heat input
- _>_50% NOx reduction, mercury and SO2 reduction
- Low capital costs
- Fuels costs, availability of adequate residence time
- Applications: cyclone, wall, tangential; 33-600 MWe

- Main fuel and air

## SNCR

- Urea or NH3 injection, generally between 980 to 1150 oC
- 30 to 60 % NOx reduction
- Low capital costs
- Load following, NH3 slip, performance on larger boilers
- Applications: cyclone, wall, tangential; 50-620 MW

## SCR

- NH3 injection, generally between 350-400 oC
- More than 90 % reduction is possible, especially with LNB
- Capital intensive, space requirements, NH**3** slip, SO**3** emissions, catalyst deactivation
- Applications:
- More than 75 boilers; cyclone, wall, tangential; 122 - 1300 MW

## SO2 Control Technologies

## Wet Scrubbers

**Wet Scrubbers**

*FGD at Centralia Power Plant*

- State-of-the-art is 95% SO2 removal
- 98 GW (33%) of coal-fired units have scrubbers
- We project 115 GW to have scrubbers by 2010 for Title IV and State regs

## Lime Spray Drying

**Lime Spray Drying**

- State of the art is 90% removal
- More than 14 GW of installation

## Performance

- 50

- 60

- 70

- 100

- 90

- 80

- Wet Limestone

- Spray Drying

- 1970s

- 1980s

- 1990s

- Median

- Design SO2

-   Removal Efficiency, %

- 0

## Mercury in Coal-fired Boilers

**Mercury in Coal-fired Boilers**

## Mercury Speciation

- In general, speciation depends on:
- Coal properties (mercury, chlorine, and ash contents)
- Time/temperature profile
- Flue gas composition and fly ash characteristics (carbon, calcium, iron, porosity)
- Flue gas cleaning conditions

## Mercury Capture in Existing Equipment

- _Removal in PM Controls_
- Mercury can be adsorbed onto fly ash surfaces; Hg2+ is more readily adsorbed than Hg0
- Mercury can be physically adsorbed at relatively lower temperatures (hot-side ESP vs. cold-side ESP)
- _Capture in Wet Scrubbers_
- Hg2+ capture depends on solubility of each compound; Hg0 is insoluble and cannot be captured
- Capture enhanced by SCR

## ICR Data

-   **Bituminous vs**
**   ****subbituminous**
**  ****Hg capture for different**
**   ****coal-control technology**
**   ****combinations correlate**
**   ****with coal chlorine content**

## Chlorine vs. Mercury Speciation 

- ICR data for Hg0 at ESP & FF inlet
- Hg0 oxidation appears to be independent of chlorine above 100 μg/g
- Other important factors
**Temperature**
**Fly ash carbon**

## Speciation influences emissions control
Ionic Hg2+ is removed easily by wet scrubbers
Volatile elemental Hg0 is difficult to capture
SCR units are being used extensively to meet current NOx regulations
SCR can convert elemental mercury in coal combustion flue gas into the ionic form
field data in Europe and U.S. reflects increase in Hg2+ across SCR reactor

- Speciation influences emissions control
- Ionic Hg2+ is removed easily by wet scrubbers
- Volatile elemental Hg0 is difficult to capture
- SCR units are being used extensively to meet current NOx regulations
- SCR can convert elemental mercury in coal combustion flue gas into the ionic form
- field data in Europe and U.S. reflects increase in Hg2+ across SCR reactor

**SCR and Mercury Interactions**

## SCR-Mercury R&D

- Tested 4 utility plants in the 2001 and 2 in 2002; retested 2 plants in 2002; total of 8 data points
- Oxidized mercury increase across SCR: bit. - up to 71%; subbit. - 10% (one data point only)
- Removal in PM control and FGD (5 data points) - ~ 85% - 90%
- Results from repeated tests were consistent with previous data; impacts of SCR catalyst aging not apparent
- SCR systems with relatively lower catalyst volumes (space velocity greater than 3500 hr-1) also showed significant oxidation increases
- Data gaps: PRB, blends
- Ongoing EPA bench- and pilot-scale research:** **HCl provides critical chlorine source for Hg0 oxidation; NOx has a significant promotional effect; SOx has little effect under the conditions of this study

## PM Control Technologiesfor Power Plants

- Electrostatic precipitators (ESPs)
- 72% of U.S. coal-fired boilers, total PM up to 99.9%, fine PM 80-95%
- Baghouses
- 14% of U.S. coal-fired boilers, total PM up to 99.9%, fine PM 99-99.8%

## Sometimes a picture is worth a ...

## How Does an ESP Work?

**Corona (Negative polarity)**

**Particulate Matter (PM)**

**Discharge Electrode**
**(High Voltage Wire)**

**Collection Plate (Positive Polarity)**

**Particle Flow**

**Charged Particles**

**Collected Particles**
**Dust Layer**

## Emerging Technologies

## Sorbent Injection

**The extent of capture depends on:**
**Sorbent characteristics (particle size distribution, porosity, capacity at  different gas temperatures)**
**Residence time in the flue gas**
**Type of PM control (FF vs. ESP) **
**Concentrations of SO****3**** and other contaminants**

**Flue Gas**

## Activated Carbon Injection (ACI)

*Activated carbon injection system*

*Activated carbon storage and feed system*

- ACI successfully used to reduce mercury emissions from waste-to-energy facilities. Effort underway to transfer to coal-fired power plants.
- Not currently installed at any power plant, but short-term testing suggests it may eventually be able to achieve 90% control for all coal types.

## Carbon Injection Projects

**Alabama Power E.C. Gaston: unit 3, 270-MW, low-sulfur eastern bit. coals (0.14 ppm Hg and 160 ppm Cl); hot-side ESP, COHPAC baghouse; testing on one-half of the gas stream, nominally 135 MW; wet ash to pond**
**WEPCO Pleasant Prairie: unit 2, 600-MW, PRB coal (0.11 ppm Hg and 8 ppm Cl); ESP (468 ft****2****/kacfm), spray cooling, SO****3 ****conditioning; testing on one ESP chamber (1/4 of the unit); fly ash sold for use in concrete**
**PG&E Brayton Point: unit 1, 245-MW, low-S bit. coal (0.03 ppm Hg and 2000-4000 ppm Cl); SO****3 ****conditioning system; 2 ESPs in series (550 ft****2****/kacfm); PAC injection between the ESPs**
**PG&E Salem Harbor: 85-MW, low-S bit. coal (0.03-0.08 ppm Hg and 206 ppm Cl); ESP (474 ft****2****/kacfm); SNCR**

## Mercury Removal Trends with ACI

*Source: ADA Environmental Solutions (2003)*

**Notes:**
Alamaba Power E.C, Gaston: Up to 90% mercury control with Darco FGD PAC; about 78% mercury removal during 2-week testing; significant increase in COHPAC cleaning frequency

WEPCO Pleasant Prairie: removal 60 - 70%  at 10 lb/106 acf and reaches a limit; impact on fly ash sale; no impact on ESP performance; below 300 oF, additional cooling did not improve capture of mercury

PG&E Brayton Point: removal 70% at 10 lb/106 acf and 90% at 20 lb/106 acf; unlike PPPP results, no limit to removal

## PG&E Salem Harbor(w/o PAC Injection)

**85-MW, low-S bit. coal (0.03-0.08 ppm Hg and 206 ppm Cl); ESP (474 ft****2****/kacfm); SNCR**
**High baseline removal due to high levels of LOI; minimal impact on reducing LOI from 30-35% to 15-20% at 300 ****o****F**
**Temperature has greater effect than LOI**
**SNCR has no impact on Hg removal**

- Source: ADA-ES

**Hg Removal (%)**

**Temperature (****o****F)**

## PG&E Salem Harbor(w/ PAC Injection)

**At lower temperatures, removal by PAC affected by high baseline removal**
**At higher temperatures, linear behavior (similar to that at Brayton Point**

- 0

- 10

- 20

- 30

- 40

- 50

- 60

- 70

- 80

- 90

- 0

- 5

- 10

- 15

- 20

- 25

- 280-290 F

- 298-306 F

- 322-327 F

- 343-347 F

- Source: ADA-ES

**Hg Removal (%)**

**Injection Concentration (lb/10****6**** acf)**

## A few more things . . . 

## Wet FGD Modification

- Capable of removing SO2 in excess of 95 %
- Can remove oxidized Hg
- Three routes for NO removal:
- gas phase oxidation to N2O5
- oxidation to NO2 and reduction to N2 in the scrubber via sulfate and bisulfate ions
- Investigate SO2, Hg, NOx removal and SO2 to SO3 conversion

## ESFF

**Electrostatically Stimulated Fabric Filtration (ESFF)--developed by EPA**
**Pulsejet fabric filter with high voltage electrodes centered between groups of four bags**
**Pilot-scale performance data:**
**PM2.5 with ESFF=0.14 mg/m3**
**PM2.5 without ESFF=0.51 mg/m3**
**PM1 with ESFF=0.05 mg/m3**
**PM1 without ESFF=0.17 mg/m3**
**BHA Group, Inc. licensee has developed preliminary commercial design          **

## Development of Multipollutant Sorbents

**Sorbent Development**
**Synthesis, Characterization, Evaluation & Optimization**
**Relate  structure and chemical nature to adsorption characteristics**

**Types of Sorbents Being Studied**
**Sorbents synthesized using industrial by-products**
**Modified carbon-type sorbents**
**Surface modified Calcium Silicate Hydrate (C-S-H)**
**Multipollutant sorbents that also have adsorptive capacity for CO****2**