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Trona Injection Tests

Mirant Potomac River Station

Unit 1

November 12 to December 23, 2005

Summary Report

Mirant Corporation

January 17, 2006
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1. INTRODUCTION

Trona injection tests were conducted at Mirant’s Potomac River Station on Unit 1 

between November 12 and December 23, 2005. The purpose of these tests was 

to determine the capability of dry injection of trona to achieve substantial SO2 

removal from the stack discharge, and the determination of other operating 

impacts from the trona injection, if any.

Temporary trona injection equipment was installed on Unit 1, to inject dry trona in 

the duct between the boiler economizer outlet and the hot precipitator inlet.

Trona was obtained with rail car delivery directly from the mine in Green River, 

Wyoming.

Temporary test instrumentation was set up to measure SO2 concentration before 

and after trona injection, and compared with the permanent continuous 

emissions monitoring system (CEMS) installed in the Unit 1 stack.

A total of 32 test runs are described in this report covering various unit loads, 

using both Central Appalachian and Colombian coals, and variations in trona 

particle size.
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2. EXECUTIVE SUMMARY

The primary objectives of this series of tests were to determine if substantial SO2 

removal could be achieved with trona injection, and if there were any adverse 

unforeseen impacts from trona injection, primarily with unfavorable opacity or 

particulate emissions.

SO2 Removal

A series of 32 tests were conducted at various unit loads, with several different 

sizes of trona particles, and on both Central Appalachian and Colombian coals 

(representing two different coal sulfur levels). For all these tests 80% SO2 

removal could be achieved. The trona consumption was higher than initially 

predicted, but was reasonably consistent across the range of coals and operating 

variables. The consistency of the data provides the ability to accurately predict 

the trona feed rate required to achieve a given SO2 removal on a controlled 

basis.

Particulate / Opacity Performance

Opacity was continuously monitored during the entire test period. There were no 

instances in any of the tests where opacity increased during trona injection. 

Opacity remained consistently below 4% with no spikes of any kind. The 

precipitator particulate collection improvement experienced with high sodium ash 

(trona) at AEP’s Gavin Station, described in PowerGen 2004 technical paper 

“Successful SO3 Mitigation While Enhancing the ESP Performance at AEP’s 

Gavin Plant by Dry Injection of Trona Upstream of the ESP”, was demonstrated 

in these tests at the Potomac River station.

EPA method 201A and 202 stack tests were also conducted both with and 

without trona injection. The summary conclusions from these tests are included 

later in this report. 

In summary, high SO2 removal from trona injection was demonstrated across the 

load range, and across various operational parameters. No adverse effects were 

seen from the trona injection. Stack opacity and particulate emissions were 

excellent and were not impacted by the trona injection. Trona consumption was 

higher than originally predicted however, and follow up tests are recommended 

to investigate the cause, optimize trona feed rates, and assure consistent 

performance at anticipated levels of SO2 removal.
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Chart 1

Potomac River Trona Injection Nov - Dec 2005

Composite Data All Tests

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

110%

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0

Trona Feed Stoichiometry

SO2 Removal %

High Load

Low Load

Mid Load

Poly. (High Load)

Poly. (Low Load)

Chart 1 shows that even with the variation of all the operational parameters, the 

SO2 removal performance is reasonably consistent across the range of trona 

feed rates and SO2 removal rates. Further testing will be required to identify the 

key operational parameters that could potentially reduce the trona consumption 

required for a given SO2 removal rate.
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3. TEST CONCLUSIONS

1. SO2 removal with trona injection up to 80% was consistently demonstrated 

over the load range with different coal constituencies, trona particle size, 

gas temperatures, and other operating parameters.

2. Trona consumption was higher than expected for a given SO2 removal. 

Follow up characterization tests are recommended in order to optimize the 

trona consumed as a function of unit operating parameters.

3. The precipitator performance was not impacted in any way due to trona 

injection, regardless of trona injection rate. Stack particulate test results 

indicate precipitator performance actually improves with trona present, 

even with the increase in particulate to be collected by the precipitator 

when trona is injected. 

4. The test accuracy was very good, with excellent correlation between the 

test instrumentation and the stack CEMS for SO2 emissions, and with 

accurate scales for trona consumptions.

5. The test results are consistent between tests, and the resultant data is 

suitable to allow predictable and respectable control of the outlet SO2 

emissions rate.