
                                       
                       Evaluation of HCl Emissions from 
                         Boilers Firing Low-Rank Coals
                                       
                                      By
                                       
                             James E. Staudt, PhD
                          Andover Technology Partners
                             112 Tucker Farm Road
                           North Andover, MA  01845
                                (978) 683-9599
                                       
                                                                               
                                                                               
                               November 11, 2011

Background
The US EPA has finalized the Utility Boiler Air Toxics Rule, which establishes emissions limits for filterable PM, mercury, and HCl.  This report will discuss an effort that Andover Technology Partners (ATP) has been involved in to calibrate the assumptions in EPA's analysis of the impacts of the rule.  This effort relates to the HCl emissions from subbituminous and lignite fired units and the potential need for add-on acid gas controls (e.g., DSI) on these units.

ATP has reviewed HCl emissions data to determine if there is reason to expect the need for add-on acid gas controls, such as dry sorbent injection (DSI) or other technologies to reduce HCl emissions at subbituminous- and lignite-fired units.  These low rank coals tend have lower chlorine content than bituminous coals and their fly ash tends to have higher natural alkalinity.  Western subbituminous coal (such as that mined in the Powder River Basin and referred to as PRB coal) and lignite coals contain natural alkalinity in the form of non-glassy calcium oxide (CaO) and other alkaline and alkaline earth oxides. The resulting fly ash (classified as `Class C' fly ash) has a natural pH of 9 and higher and the natural alkalinity can effectively neutralize much of the HCl in the flue gas stream prior to the primary control device.  Eastern bituminous coals, by contrast, tend to produce fly ash with lower natural alkalinity. Though bituminous fly ash (classified as `Class F' fly ash) may contain calcium, it tends to be present in a glassy matrix and unavailable for acid-base neutralization reactions. As a result of the fly ash neutralization, HCl emissions from many of the facilities firing low rank coals are likely to be low, and may be sufficiently low enough to avoid the need for add-on acid gas controls.  The ICR data was reviewed to examine HCl emissions and to evaluate the need for additional add-on controls.

                                       


        Evaluation of HCl Emissions from Boilers Firing Low-Rank Coals
Objectives
This effort was to examine emissions data to characterize the HCl emissions from subbutuminous (mostly PRB) and lignite coals.
Using the data in the March 16, 2011 Excel file MACT floor analysis for acid gas, there are 68 entries for subbituminous coals (this excludes blends of subbituminous and other fuels) and there are six entries for Lignite.
Analysis of All Subbituminous Data
Table 1 shows the summary statistics for the 68 units listed as solely subbituminous fired.  Most reported data was by electronic reporting (ERT) or using Part II protocol.  Inferred fuel HCl is determined by multiplying the reported Fuel Cl by 36/35.  Not every unit provided complete data.  As a result, the sample sizes add up to less than 68 units.  In addition to reflecting standard measures (mean, median, standard deviation, and minimum), data from various sources is organized by quartiles. Representation of the data in quartiles rather than representing it in terms of average and standard deviation is preferred because one or two data points with large measurement errors can throw off the average and the standard deviation so that these statistics become misleading.  Using quartiles gives a clearer picture of what the distribution looks like.  Any result greater than the proposed limit of 0.002 lb/MMBtu is highlighted in red
As shown in the table, the maximum value in the third quartile of each sample is below the proposed limit of 0.002 lb/MMBtu. The median emission levels (also equal to the second quartile) are all below the emission limit.   The reported HCl rates of 0.01 lb/MMBtu, as shown in the fourth quartile, are above the maximum inferred fuel HCl, suggesting measurement errors.  The negative percent reduction also demonstrates that there are measurement errors in the data.  The blue line in Figure 1 graphically represents the full data that is summarized in Table 1.  As shown, 88% of the entries are at or below the limit for the rule.  From this data, it can be reasonably assumed that the majority of subbituminous coal fired units will meet the HCl emission standard without the need for additional controls.
Table 2 shows similar statistics, but only for those units with only CS ESPs (i.e., no flue gas desulfurization technology such as wet scrubber or spray dryer and no fabric filters following a CS ESP).  As shown, up to the third quartile is generally below the proposed limit, except when looking at the ETTS data.  The fourth quartile shows emissions rates above the proposed limit.   When looking at the Hydrogen Chloride  -  min data more closely, only 2 of the 22 data points were above the proposed limit (see unit-specific data in the Appendix and Figure 1).   This data is plotted as a red line in Figure 1.   As a result, there is a chance that some facilities may require additional controls for HCl, but it is likely that the vast majority will not.  The data for the full 22 units is shown in the Appendices.


Table 1.   Fuel Chlorine and HCl Emissions Statistics for All 100% Subbituminous Fueled Boilers
                                 Reporting ICR

                                    Fuel_Cl
                                   lb/MMBtu
                          Inferred fuel HCl_lb/MMBtu
                            Hydrogen Chloride - ERT
                           Hydrogen Chloride - ETTS
                          Hydrogen Chloride - Part II
                            Hydrogen Chloride - min
                                   % red'n
average
                                   9.88E-03
                                   1.02E-02
                                   6.41E-03
                                   2.63E-02
                                   5.90E-04
                                   4.47E-03
                                    60.90%
median
                                   2.47E-03
                                   2.54E-03
                                   4.87E-04
                                   3.92E-04
                                   3.97E-04
                                   4.10E-04
                                    74.17%
standard dev
                                   2.02E-02
                                   2.08E-02
                                   2.33E-02
                                   6.79E-02
                                   6.51E-04
                                   1.91E-02
                                    47.69%
Minimum
                                   6.08E-04
                                   6.25E-04
                                   2.17E-05
                                   1.48E-04
                                   2.60E-05
                                   2.17E-05
                                   -127.61%
Max - 1[st]  quartile
                                   1.14E-03
                                   1.17E-03
                                   1.47E-04
                                   2.30E-04
                                   2.53E-04
                                   1.52E-04
                                    54.52%
Max - 2[nd]  quartile
                                   2.47E-03
                                   2.54E-03
                                   4.87E-04
                                   3.92E-04
                                   3.97E-04
                                   4.10E-04
                                    74.17%
Max - 3[rd]  quartile
                                   8.39E-03
                                   8.63E-03
                                   9.41E-04
                                   1.42E-03
                                   5.88E-04
                                   1.00E-03
                                    91.00%
Max - 4[th] quartile
                                   8.33E-02
                                   8.57E-02
                                   1.02E-01
                                   1.80E-01
                                   2.16E-03
                                   1.02E-01
                                    99.41%
Sample size
                                      32
                                      32
                                      37
                                       7
                                      20
                                      56
                                      56
ERT  -  reported by Electronic Reporting Tool as part of ICR
ETTS  -   Collected with EPA's Emission Tracking System
Part II  -  reported using Part II Reporting Protocol prior to ICR

Table 2.   Fuel Chlorine and HCl Emissions Statistics for Subbituminous Fueled Boilers with CS ESPs Reporting ICR

                                    Fuel_Cl
                                   lb/MMBtu
                          Inferred fuel HCl_lb/MMBtu
                            Hydrogen Chloride - ERT
                           Hydrogen Chloride - ETTS
                          Hydrogen Chloride - Part II
                            Hydrogen Chloride - min
                                    % redn
Average
                                   4.99E-03
                                   5.14E-03
                                   1.40E-03
                                   2.78E-01
                                   6.25E-04
                                   1.06E-03
                                    55.37%
Median
                                   1.90E-03
                                   1.96E-03
                                   6.65E-04
                                   2.78E-01
                                   4.02E-04
                                   6.21E-04
                                    62.74%
standard dev
                                   6.62E-03
                                   6.81E-03
                                   2.09E-03
                                   3.91E-01
                                   5.71E-04
                                   1.61E-03
                                    26.66%
Minimum
                                   8.35E-04
                                   8.59E-04
                                   1.62E-04
                                   1.18E-03
                                   3.00E-04
                                   1.62E-04
                                    -12.67%
1[st] quartile
                                   1.34E-03
                                   1.38E-03
                                   6.16E-04
                                   1.39E-01
                                   3.20E-04
                                   3.98E-04
                                    51.49%
2[nd] quartile
                                   1.90E-03
                                   1.96E-03
                                   6.65E-04
                                   2.78E-01
                                   4.02E-04
                                   6.21E-04
                                    62.74%
3[rd] quartile
                                   6.67E-03
                                   6.86E-03
                                   1.10E-03
                                   4.16E-01
                                   5.75E-04
                                   8.88E-04
                                    67.94%
Max  -  4[th] quartile
                                   2.18E-02
                                   2.24E-02
                                   7.88E-03
                                   5.54E-01
                                   2.16E-03
                                   7.88E-03
                                    82.93%
Sample size
                                      26
                                      26
                                      12
                                       2
                                      10
                                      22
                                      22
ERT  -  reported by Electronic Reporting Tool as part of ICR
ETTS  -   Collected with EPA's Emission Tracking System
Part II  -  reported using Part II Reporting Protocol prior to ICR



 Figure 1.  HCl Emissions for Subbituminous Units with CS ESPs, from ICR data 
                      (see Appendix for raw CS ESP data)
                                       
Analysis of Lignite Data
Because there were so few lignite data points, the data is displayed in Table 3 as in the database.  As shown, generally high levels of HCl reduction are achieved with the lignite units, with all units reporting below the proposed limit.  Every one of the units had a fabric filter, and some were scrubbed.  This is a limited database however.  Significantly, it does not include ND or MT lignite fired units.
         Table 3.  ICR data for HCl emissions from Lignite Fired Units
Plant Name
                                     state
                                  Unit Number
                                  Boiler_type
                                Control summary
                                    Fuel_Cl
                                   _lb/MMBtu
                            Hydrogen Chloride - ERT
                           Hydrogen Chloride - ETTS
                          Hydrogen Chloride - Part II
                            Hydrogen Chloride - min
                                  % reduction
Sandow Station
                                      TX
                                      5A
                             Fluidized bed firing
                           FBC, SNCR, ACI, DFGD, FF
                                       
                                   9.24E-05
                                       
                                   2.12E-05
                                   2.12E-05
                                       
Sandow Station
                                      TX
                                      5B
                             Fluidized bed firing
                           FBC, SNCR, ACI, DFGD, FF
                                       
                                   3.02E-05
                                       
                                   2.55E-05
                                   2.55E-05
                                       
Oak Grove
                                      TX
                                      OG1
                               Tangential firing
                              SCR, ACI, FF, WFGD
                                   1.18E-02
                                   1.20E-04
                                       
                                   2.27E-04
                                   1.20E-04
                                    98.98%
Red Hills Generating Facility
                                      MS
                                      002
                             Fluidized bed firing
                                    FBC, FF
                                   3.38E-02
                                       
                                   3.67E-04
                                       
                                   3.67E-04
                                    98.92%
Red Hills Generating Facility
                                      MS
                                      001
                             Fluidized bed firing
                                    FBC, FF
                                   3.38E-02
                                       
                                   3.67E-04
                                       
                                   3.67E-04
                                    98.92%
Monticello
                                      TX
                                       2
                               Tangential firing
                              SNCR, ACI, FF, ESP
                                       
                                   7.49E-04
                                       
                                       
                                   7.49E-04
                                       
ERT  -  reported by Electronic Reporting Tool as part of ICR
ETTS  -   Collected with EPA's Emission Tracking System
Part II  -  reported using Part II Reporting Protocol prior to ICR

Examination of fuel Database
The possible differences between ND or MT lignite and TX lignite were explored using the reported coal data from the 2001 ICR first quarter, which included over 10,000 coal samples.
Figure 1 shows coal Cl content in lb/MMBtu (dry basis), which was estimated from the reported Cl content in ppm and the reported coal heating value (dry basis) in Btu/lb.  Wet basis values would be somewhat higher, depending upon moisture level.  As expected, the highest Cl contents are in Illinois Basin and Northern Appalachian coals.  Texas lignite showed a median concentration of 0.042 lb/MMBtu, which is in the same range as some of the lignite coals shown in Table 3.  The lowest Cl levels are in PRB, Montana-ND lignite and Western Bituminous coals.  As a result, Montana and North Dakota lignite coal fired boilers would likely have lower HCl emissions rates than units firing Texas Lignite.
           Figure 2.  Distribution of Cl Content for Different Coals
                                   Dry basis

Conclusions regarding HCl emissions from low rank coals
The analysis of the ICR data and the fuel data shows that:
   * The majority of subbituminous fueled units are expected to meet the proposed HCl limit as they are currently operating; however, some may not and therefore may choose to install add-on acid gas controls (such as DSI or other FGD technology) to account for fuel heterogeneity and to provide for fuel flexibility.  So, while most subbituminous fired units equipped with CS ESPs are likely to avoid the installation of add-on acid gas controls, there is some uncertainty about how many would choose to do so.
   * The data suggests that lignite-fired units are expected to comply with the proposed limit without any additional controls; however, no data was available for lignite units with only an ESP and the data that was available was limited in number.  Review of coal Cl data suggests that ND and MT lignite should be more likely than TX lignite to meet the proposed limit without additional controls due to the lower Cl concentration in the coal.



                                  Appendices
              HCl emissions from Subbituminous Units with CS ESPs



                                       

         Data for HCl emissions from Subbituminous Units with CS ESPs
                                       
                                       
                                       
                               Hydrogen Chloride
                                       
                                  Plant Name
                                     state
                                  Unit Number
                                    Boiler
                                     type
                                      MWe
                               Fuel_Cl_lb/MMBtu
                                      ERT
                                    - ETTS
                                    Part II
                                      min
                                  % reduction
Whelan 
                                      NE
                                       1
                                     Tang
                                      84
                                       
                                   1.62E-04
                                       
                                       
                                   1.62E-04
                                       
Montrose
                                      MO
                                       2
                                     Tang
                                      188
                                       
                                       
                                       
                                   3.00E-04
                                   3.00E-04
                                       
Montrose
                                      MO
                                       1
                                     Tang
                                      188
                                       
                                       
                                       
                                   3.00E-04
                                   3.00E-04
                                       
Montrose
                                      MO
                                       3
                                     Tang
                                      188
                                       
                                       
                                       
                                   3.00E-04
                                   3.00E-04
                                       
Quindaro
                                      KS
                                    Unit 1
                                     Cycl
                                      77
                                       
                                       
                                       
                                   3.80E-04
                                   3.80E-04
                                       
Hudson
                                      NJ
                                     HUDU2
                                     Wall
                                      660
                                       
                                       
                                       
                                   3.94E-04
                                   3.94E-04
                                       
Nearman Creek
                                      KS
                                      N1
                                     Wall
                                      257
                                       
                                       
                                       
                                   4.10E-04
                                   4.10E-04
                                       
Newton
                                      IL
                                      002
                                     Tang
                                      620
                                   1.30E-03
                                   4.87E-04
                                       
                                       
                                   4.87E-04
                                    62.52%
Prairie Creek
                                      IA
                                    Unit 2
                                    Stoker
                                      221
                                       
                                       
                                       
                                   5.00E-04
                                   5.00E-04
                                       
Joliet 9
                                      IL
                                       
                                     Cycl
                                      326
                                   1.20E-03
                                   5.41E-04
                                       
                                       
                                   5.41E-04
                                    54.74%
Prairie Creek
                                      IA
                                    Unit 1
                                    Stoker
                                      221
                                       
                                       
                                       
                                   6.00E-04
                                   6.00E-04
                                       
Joppa Steam
                                      IL
                                       1
                                     Tang
                                      183
                                   1.73E-03
                                   6.41E-04
                                       
                                       
                                   6.41E-04
                                    62.97%
Vermilion
                                       
                                      002
                                     Tang
                                      110
                                       
                                   6.41E-04
                                       
                                       
                                   6.41E-04
                                       
Vermilion
                                       
                                      001
                                     Tang
                                      72
                                       
                                   6.41E-04
                                       
                                       
                                   6.41E-04
                                       
Hoot Lake
                                      MN
                                       2
                                     Tang
                                      61
                                   2.24E-03
                                   6.88E-04
                                       
                                       
                                   6.88E-04
                                    69.29%
La Cygne
                                      KS
                                       2
                                     Wall
                                      685
                                   1.47E-03
                                   7.31E-04
                                       
                                   9.00E-04
                                   7.31E-04
                                    50.40%
Waukegan
                                      IL
                                      WK8
                                     Tang
                                      383
                                   8.35E-04
                                   9.41E-04
                                       
                                       
                                   9.41E-04
                                    -12.67%
Pulliam
                                      WI
                                       8
                                     Wall
                                      138
                                   2.07E-03
                                       
                                   1.18E-03
                                       
                                   1.18E-03
                                    42.97%
Gallatin
                                      TN
                                       2
                                     Tang
                                      300
                                   9.13E-03
                                   1.56E-03
                                   5.54E-01
                                       
                                   1.56E-03
                                    82.93%
Bridgeport
                                      CT
                                    BHSEMU3
                                     Tang
                                      403
                                   8.14E-03
                                   1.90E-03
                                       
                                       
                                   1.90E-03
                                    76.68%
Hudson
                                      NJ
                                     HUDU2
                                     Wall
                                      660
                                       
                                       
                                       
                                   2.16E-03
                                   2.16E-03
                                       
R.M. Schahfer
                                      IN
                                   R.M.0014
                                     Cycl
                                      468
                                   2.18E-02
                                   7.88E-03
                                       
                                       
                                   7.88E-03
                                    63.88%
ERT  -  reported by Electronic Reporting Tool as part of ICR
ETTS  -   Collected with EPA's Emission Tracking System
Part II  -  reported using Part II Reporting Protocol prior to ICR



