ELECTRIC POWER 2007

Conference and Exhibition

EP-07 Session 12E

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RESULTS OF FGD UPGRADE PROJECTS ON LOW-RANK COALS

Paul Farber, Bill Siegfriedt, Steve Katzberger

Sargent & Lundy, L.L.C.

Don Caverly Joseph G. Eutizi Tommy J. Slater

Tucson Electric Power San Miguel Electric Cooperative AEP/SWEPCO

ABSTRACT

This paper describes the approaches used to successfully implement flue gas desulfurization

(FGD) upgrade projects at three power generating stations. Specifically, the FGD projects

consisted of:

• Upgrades of the wet scrubber at American Electric Power/Southwestern Electric

Power Company’s (AEP/SWEPCO) Pirkey Unit 1.

• Upgrades of the wet scrubber at San Miguel Electric Cooperative, Inc.’s (SMEC) San

Miguel Unit 1.

• Increase of dry scrubber capacity at Tucson Electric Power’s (TEP) Springerville

Units 1 and 2.

Impetus for these upgrades was the following, either singly or in combination:

• Tightening of emission regulations

• Increase in SO2 emission allowance prices

• Degradation of coal quality over time.

• Need to reduce emissions to allow expansion

• Desire for improved reliability

The design alternatives and the challenges encountered on each of these projects, as well as their

results, are presented below.
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SPRINGERVILLE GENERATING STATION

TEP’s Springerville Unit 1 commenced operation in 1985, with Unit 2 following in 1990 (on the

right in Figure 9). These are replicate units, each with gross capacity of 425 MW and firing a

New Mexico (Lee Ranch) sub-bituminous coal (analysis summarized in Table 1). Both units are

equipped with Combustion Engineering (now Alstom Power) tangentially fired boilers and with

Joy Manufacturing-Niro (now B&W) spray dryers with reverse air fabric filters (dry FGD

system).

The planned construction of the new Springerville Units 3 and 4 units (approximately equivalent

in size to Units 1 and 2) required an offset in the emissions by reducing the NOX and SO2

emissions from Units 1 and 2. The original and revised emissions limits are noted in Table 3.

Table 3. Springerville Units 1 and 2 Emission Rates

Parameter Prior to Unit 3 Operation Post-Unit 3 Operation

SO2, lb/mmBtu 0.60 0.24

NOX, lb/mmBtu 0.45 0.20
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RESULTS OF FGD UPGRADE PROJECTS ON LOW-RANK COALS Conference and Exhibition

EP-07 Session 12E

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Figure 9. Springerville Generating Station

The dry FGD system for each unit comprises three spray dryer absorbers (SDA) with rotary

atomizers and a reverse-air fabric filter. The Springerville Station receives high-calcium pebble

lime via rail, and a pneumatic system transports the lime to a day bin located at each unit.

Horizontal ball mill slakers convert the pebble lime to lime slurry, which is combined with a

slurry of recycled material from the fabric filter just prior to being fed to the rotary atomizer.

When the units were constructed, the dry FGD systems were built with a partial bypass, the result

of which is that 75% of the flue gas is treated in the spray dryers and the bypassed flue gas is

recombined with the scrubbed stream before entering the fabric filter.

TEP, with S&L as Owner’s Engineer, implemented the following modifications to reduce NOX

and SO2 emissions:

• Installation of low-NOX burners and overfire air (NOX).

• Installation of a fourth spray dryer and elimination of the flue gas bypass (SO2).

Based on an evaluation of proposals received, B&W was selected as the turnkey contractor for

the FGD upgrade.

To complete the upgrade, two infrastructure upgrades were necessary:

• Relocation of the cooling tower water blowdown tank for each unit (cooling tower

blowdown is used to make up the recycle slurry for the dry FGD system).

• Installation of a new 10-ton/hour lime slaker to accommodate the increased lime

usage.
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RESULTS OF FGD UPGRADE PROJECTS ON LOW-RANK COALS Conference and Exhibition

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Both upgrades were successfully completed and the gas path tie-ins coordinated with the

scheduled unit outages. The new spray dryers were installed just outside the building housing the

existing spray dryers (Figure 10 and Figure 11) with access to the new spray dryer penthouses at

the existing SDA penthouse level.

Figure 10. Springerville Unit 1 Spray Dryer

The performance testing of the upgraded Springerville Unit 1 FGD system was done during

April 29, 2005 through May 3, 2005, and consisted of tests at low-load (140 MW gross),

medium-load (250 MW gross), and high-load (420 MW gross).
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RESULTS OF FGD UPGRADE PROJECTS ON LOW-RANK COALS Conference and Exhibition

EP-07 Session 12E

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Figure 11. Springerville Unit 2 Spray Dryer Installation

For the low-load testing, the entire flue gas flow was directed through the new spray dryer

chamber (Module D). Consequently, approximately 33% of the total design flue gas flow rate

was channeled through 25% of the total spray dryer capacity.

During the medium-load testing, approximately 65% of the total design flue gas flow rate was

directed through 50% of the operating spray dryer modules.

In the high-load testing, the entire flue gas flow was sent through all four spray dryer modules.

The purpose of the high-load testing was not only to confirm that the SO2 emission rate was in

accordance with the contract between TEP and B&W, but also that the flue gas flows were

properly balanced between modules. The full-load testing on May 2 also had the purpose of

acquiring data on the lime slurry feed to the FGD system, pressure drop across the modules, and

electrical power consumption by the new module to determine contract compliance with these

values.

The objective of the performance testing was to validate the guarantees provided by B&W in the

contract with TEP. Flue gas flow and SO2 measurements were performed by a third-party testing

company, METCO, out of Dallas, Texas. These measurements were taken at the inlets of each

module’s central gas disperser (CGD) and roof gas disperser (RGD). Similar measurements were

taken in the exit duct of each spray dryer module. Summaries of the Springerville Unit 1 test

results are provided in Table 4 and Table 5.

Flow measurements were taken in accordance with U.S. EPA Methods 1 and 2. SO2 and oxygen

measurements were taken in accordance with U.S. EPA Methods 1, 6c, and 3a, respectively. All
ELECTRIC POWER 2007

RESULTS OF FGD UPGRADE PROJECTS ON LOW-RANK COALS Conference and Exhibition

EP-07 Session 12E

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concentrations determined by METCO were source-gas-sampled, with the moisture removed, and

therefore measured on a dry basis. The design coal for the upgrade project had a calculated SO2

emission of 2.6 lb SO2/mmBtu. The SO2 emissions from the coal being fired at Springerville

during the performance tests were lower than would have been measured if the design coal had

been available. TEP expressed concern that if a coal with an SO2 content equal to the design coal

is fired in the boilers at the Springerville, there might be difficulty in achieving an emissions rate

of 0.24 lb SO2/mmBtu. Consequently, TEP requested that the testing demonstrate the capability

of the system to achieve a minimum of 91% SO2 removal (the removal required to meet the

required emissions rate while firing the design coal) during the full-load tests. The results of the

testing demonstrated that indeed the system was capable of achieving the desired 91% removal

requested by TEP.

Table 4. Springerville Unit 1 SO2 Removal

Run

SO2 Inlet

(lb/mmBtu)

SO2 Outlet

(lb/mmBtu)

Percent

Removal

Low-load 1.870 0.206 89

Medium-load 1.887 0.196 89.6

High-load, May 5, 2005 (Note 1) 2.086 0.113 94.6

High-load, May 3, 2005 (Note 1) 1.792 0.145 91.9

Note:

1. Based on inlet SO2 measurements taken by METCO.

Similar to the concentration measurements, the flow measurements at the inlets to the spray dryer

modules were analyzed. It was determined that the distribution, calculated from the measured

inlet flows to the modules, was balanced to within approximately 5% of the average module gas

flow. Consequently, based on the flow and emissions measurements, TEP and S&L concluded

that the upgrade of the FGD system at Springerville Unit 1 had met all of its requirements.

Table 5. Springerville Unit 1 Flow Distribution (Note 1)

Run Module A Module B Module C Module D

Medium-load -- 45% -- 55%

High-load 24.3% 23.3% 26.3% 26.1%

Note:

1. Distribution percentages are based on total flow to the module at the time of the test.

The performance testing of the upgraded Springerville Unit 2 FGD system was done during

June 9 through June 10, 2005, and consisted of tests at high-load (420 MW gross). Similar to the

Unit 1 testing, the purpose of the high-load testing was not only to confirm that the SO2 emission

rate was in accordance with the contract between TEP and B&W, but also that the flue gas flows

were properly balanced between modules.

Due to operating problems on June 9, SDA Module A was isolated and the entire flue gas flow

was directed through Modules B, C, and the new SDA Module D. On June 10, Module A was

returned to service and a series of gas flow measurements performed to determine flue gas
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RESULTS OF FGD UPGRADE PROJECTS ON LOW-RANK COALS Conference and Exhibition

EP-07 Session 12E

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distribution. Consequently, and with B&W’s concurrence, the official performance test for

Unit 2, with regard to SO2 removal and lime consumption, was performed on June 9. As

indicated in Table 6, the system achieved emissions well below the 0.24 lb SO2/mmBtu permit

value and nearly achieved the 91% removal efficiency attained by Unit 1 during its performance

testing. Since, during the SO2 removal tests, Springerville Unit 2 was operating at 100% MCR

with all of the flue gas being sent through 75% of the modules, it was concluded that this

demonstrated satisfactory operation of the upgraded FGD system. The testing on June 10 was

used to determine the flue gas distribution within the four Unit 2 SDA modules. Both in the

three-module and four-module cases, the flow distribution was within 3.5% of the average gas

flow through each module.

Table 6. Springerville Unit 2 SO2 Removal

Inlet Measurement SO2 Inlet (lb/mmBtu) SO2 Outlet (lb/mmBtu) Percent Removal

SO2 inlet monitor 1.90 0.195 89.7

Coal analysis 2.105 0.195 90.7

Table 7. Springerville Unit 2 Flow Distribution (Note 1)

Run Module A Module B Module C Module D

June 9, 2005 Offline 32% 32% 36%

June 10, 2005 28.4% 23.9% 22.1% 25.6%

Note:

1. Distribution percentages are based on total flow to the module at the time of the test.

CONCLUSIONS

Many of the FGD systems installed in the 1980s were designed for SO2 collection efficiencies of

between 75% and 90% to meet the then current emission limits (typically 1.2 lb SO2/mmBtu).

Upgrading these FGD systems to achieve 95% or more SO2 removal presents an opportunity to

generate SO2 allowances for sale or to offset the emissions of new units. Upgrades to the existing

equipment of that vintage, i.e., 20 years old, also is typically required to restore the original

design function, improve operability and maintainability and ensure unit availability.

The three FGD upgrade projects described in this paper posed unique requirements and

challenges, and all were successfully upgraded to meet the Owners’ needs.