Precipitators can be improved to meet MATS and MACT - Hot Topic Conclusion
Yesterday
The speakers yesterday, Bruce Scherer
and Dr. Ralph Altman of
Particulate Control Technology, and Michael (Mike) James Widico,
Vice-President, Business development, APC at KC Cottrell agreed
that even relatively small precipitators can be upgraded to meet the new
standards for 0.03 lbs/MMbtu. Specific details about how this could be
accomplished were provided.
There were a number of interesting discussions on rapper design, SO3
conditioning, and flow. One discussion involved the removal of activated carbon
particles. It is becoming apparent that considerable mercury is being emitted in
the particulate form. The older precipitators are most likely to be the largest
emitters. The magnitude of this problem has been discounted because
1.
There is no need to measure particulate mercury.
2.
The opacity and the outlet emission have not changed. Therefore there cannot be
any activated carbon escaping.
EPA may have missed the boat when it decided to require only measurement of
gaseous mercury. However, this does not mean that a utility will not be held
accountable for particulate mercury emissions. Furthermore with a little bit of
mathematics one sees the fallacy in the opacity change logic.
The particulate emissions may be 10 mg/Nm3. This is a very low
number. However, the mercury requirement translates to 4 micrograms/Nm3. So
a plant emitting 10.004 milligrams of dust of which 4 micrograms is mercury it
will be at the limit. If it emits 10.005 milligrams it will be in violation. If
gaseous emissions are already 3 micrograms then it it only takes 2 micrograms of
particulate mercury to make the difference.
The fact that substantial differences between sorbent trap and mercury CEMS
measurements are being observed is much more meaningful indication of
particulate mercury emissions.
Bruce and Ralph teamed to make the following analysis relative to improvements:
MACT/MATS Compliance
Limit of 0.03 lb/MMbtu for filterable particulate
EPA
excluded condensable fraction
ESP performance at these low emissions levels dependent on a number of factors
ESP
Optimization must approach ideal conditions more closely than for previous
requirements
| Upstream
equipment dictates inlet conditions
Injected
sorbents can have a significant effect
Observed
ESP Performance
Most Effective ESP Upgrades
Installing high frequency power supplies
Increasing
the degree of electrical sectionalization
Optimizing
the gas flow distribution for an ESP
ESP performance insensitive to plate spacing
9 inch rebuilds are producing very
low emissions
16 inch rebuilds are producing
very low emission
The “size” of an ESP needed to meet the new limit keeps getting smaller
SO3/Sorbent Related Issues
Upstream equipment impacts ash layer resistivity
SO3 concentration
a major factor controlling resistivity
Allowable
SO3 “window” dictated by:
SCR catalyst’s SO2 oxidation can produce high SO3
levels
Hg sorbent (ACI) efficiency begins to drop at about 3 ppm of SO3
Depending on moisture, ash type, temperature, 3 ppm of SO3 is
close to the minimum required for ash conditioning
Accurate SO3 control, probably by sorbents, is imperative
Sorbents
incident on ESP a secondary issue
Sorbent particle size generally large, easy to capture
ACI injection rates minimal, generally don’t impact ash resistivity,
re-entrainment from hoppers can be an
issue however
Sodium based sorbents appear to enhance ash conductivity
Calcium sorbents only an issue if SO3 drops too low
Sectionalization
Good sectionalization is a common characteristic of all small, highly efficient
ESPs
For any given SCA, increased efficiency is realized by increasing
sectionalization
This correlation holds for both 60 Hz and HF power supplies
Sectionalizing with respect to gas flow preferred
Allows energization to more closely follow grain loading
Electrically extends the effective length of the ESP
Minimizes rapping losses
Gas Flow Optimization
Non-ideal ESP factors previously tolerated must be optimized
Sneakage above & below collecting electrodes, hopper re-entrainment
Non-uniform velocity profiles across ICAC plane, should be within 10% RMS
Temperature & particulate stratification (mixing)
ESP performance at low emission rates is inherently limited by the worst actor
of the above factors
Summary
ESPs significantly smaller than 300 SCA on a 9” center basis have been
demonstrating sub-MATS emissions
Keeping ash resistivity in the 109ohm-cm range common to most small,
high performers is important
Intermittent energization with HF power supplies is beginning to show promise
with higher resistivity ash
Mike Widico explained that KC Cottrell has supplied more than 4500 units around
the world and has developed a number of solutions to make precipitators capable
of meeting MATS and MACT.
§ Improved gas distribution
§ New Internals –collectors, electrodes
§ Improved Rapping
§ Increased power -more T/R sets, or
§ Hi Frequency TRs & control systems
§ Flue gas conditioning
§ Raise the roof
§ Additional inlet / outlet fields
§ New parallel ESP
§ Full or part baghouse conversion
One of the major options is the use of sorbents. A sorbent which minimizes
resistivity contributes to high collection efficiency. KC Cottrell conducts
laboratory studies of various combinations of coals and sorbents in a dedicated
laboratory. KC Cottrell also has magnetic rapper designs which have
considerable advantage over the tumbling hammer. The force for each rapper can
be adjusted to optimize the cleaning.
Individual presentations follow:
Precipitator Improvements Webinar - Hot
Topic Hour October 2, 2014
Precipitators can be improved to meet MATS and MACT.
Revision Date:
10/2/2014
Tags:
221112 - Fossil Fuel
化石燃料,
KC Cottrell, Particulate Control Technologies, Electrostatic Precipitator,
Rapper, Maintenance, SO3 Conditioning, MACT, MATS
Relatively small precipitators can be upgraded to meet the new standards for
0.03 lbs/MMBtu. Analysis relative to improvements.
Revision Date:
10/2/2014
Tags:
221112 - Fossil Fuel
化石燃料,
Particulate Control Technologies, Electrostatic Precipitator, MACT, MATS,
Rapper, SO3 Conditioning, Maintenance
Relatively small precipitators can be upgraded to meet the new standards for
0.03 lbs/MMBtu.
Revision Date:
10/2/2014
Tags:
221112 - Fossil Fuel
化石燃料,
KC Cottrell, Electrostatic Precipitator, MATS, SO3 Conditioning, Maintenance,
MACT, Rapper