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
2 www.AndoverTechnology.com

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 addon 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.
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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.
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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
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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

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00

percent at or belo

w

value

HCl, lb/MMBtu

all subbituminous

subbituminous w/ CS ESP

Limit, 0.002 lb/MMBtu
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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

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80

Percent at or belo

w

Cl concentration

Coal Cl Content, lb/MMbtu

Northern Appalachian

Illinois Basin

Powder River Basin

Texas Lignite

Western Bituminous

Montana-ND Lignite

Dry basis
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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.
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Appendices

HCl emissions from Subbituminous Units with CS ESPs
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Hydrogen Chloride

Plant Name state

Unit 

Number

Boiler

type MWe

Fuel_Cl

_lb/MM

Btu 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

Data for HCl emissions from Subbituminous Units with CS ESPs