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OAR Box 1828 

Prepped by Ollie Stewart 

Document Number: 

320) IV-B-24 

Docket Number: 

A-83-27 

Printed 11/12/2008 11:12:59 AM Sheet 320 of 325 
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i - 4 A-83-27 

CORPORATION IV-B-24 

MEMORANDUM 

DATE: June 22, 1987 

TO: Walt Stevenson, EPA/OAQPS/ESED 

FROM: David White, Radian Corporation 

SUBJECT: SO- Reduction in Advanced Combustion Systems 

This memo reviews information provided by representatives from TAS, Inc. 

and TRW, Inc. regarding the ability of advanced burner systems to remove SOduring combustion of coal. The objective of these discussions was to 

determine 1) whether significant SO- reductions are possible and 2) the 

commercial status of these technologies. 

TAS Micronized Coal System 

Information on the TAS micronized coal mill and burner was provided by 

Mr. Douglas Hunt, Eastern Sales Manager for TAS. TAS is a small engineering 

design and equipment fabrication company located in Magna, Utah. Work on the 

TAS micronized coal system began in 1978. A copy of the TAS literature 

describing the system is in the Industrial Boiler S02 docket. 

The principle parts of the TAS system are 1) a low-horsepower rotary 

attrition mill reportedly capable of micronizing coal to 80 percent through 

325 mesh (equal to roughly 44 micron [0.0017 inches]) in a single pass (versus 

70 percent through 200 mesh [74 micron; 0.0029 inches] for a conventional 

pulverized coal system) and 2) a staged combustion burner. Micronizing the 

coal increases particle surface area per unit of fuel by 3 to 5 times relative 

to pulverized coal. The increased surface area and smaller particle size 

results in higher fuel reactivity and increased availability of alkali 

sorbents in the coal which are important to in-situ capture of sulfur. 

Another benefit of micronizing is that the small particles of ash formed 

during combustion flow aerodynamically around heat exchange tubes, thus 

avioding problems with ash deposition, reduced heat transfer, and tube 

erosion. TAS claims that because of the increased reactivity of the fuel, 

Progress Center/3200 E. Chapel Hill Rd./Nelson Hwy./P.O. Box 13000/Research Triangle Park. N.C. 27709/(919)541-9100 
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they can operate the primary zone of the burner under strong reducing 

conditions (approximately 60 percent of stoichiometric air requirements) and 

still achieve rapid and complete burnout of the fuel in the secondary 

combustion zone. 

Under these conditions, sulfur in the coal may react with alkalis in the 

coal ash or with injected limestone to form sulfides (e.g., CaS) rather than 

sulfates (CaSO-J as would occur in a more oxygen-rich atmosphere. Similarly, 

nitrogen in the coal may convert to N« rather than NO . TAS reports that 

substantial sulfur capture (near 90 percent) and low NO levels have been 

obtained without addition of lime or limestone during pilot-scale tests. The 

existing data, however, although very interesting, are too limited to draw 

clear conclusions. 

Most of the existing TAS systems are being used on kilns and asphalt 

plants, rather than boilers. The first large coal-fired boiler was recently 

constructed at St. Louis University Hospital in St. Louis, Missouri; start-up 

of the system on natural gas occurred this past winter. As of late April, 

testing with coal had been very limited, due in part to high surface moisture 

in the coal shipped to the hospital and resulting problems with the coal 

handling system upstream of TAS's equipment. The hospital is scheduled to 

perform an EPA compliance test for the local air agency in June during which 

S02 emissions with coal were to be measured. These data could then be used to 

estimate percent S02 capture by alkalis in the coal ash as well as added 

limestone or lime. I talked to Mr. Hunt in early May and he promised to send 

me a copy of the compliance test results as soon as it is available. I have 

not received anything to date, however. 

Based on the available data, the TAS system appears to be a promising 

method for reducing emissions from industrial boilers, but too little data are 

currently available to document its actual performance. 

TRW Slagging Combustor 

The TRW slagging combustor uses conventional pulverized coal combined 

with a staged combustor. TRW is a major technology development company in the 

U. S. A description of the TRW system is in the Industrial Boiler S0? 

2 

docket. 
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The combustor's first stage operates as a small-scale gasifier in which 

the coal is converted to carbon monoxide and hydrogen. The TRW system is 

similar to the TAS system in that both operate the first stage under strong 

reducing conditions. Temperatures in this section are sufficient to convert 

most of the ash to slag. A strong swirl caused by addition of air and fuel 

tangential to the combustor axis imparts centrifugal force on the slag. As a 

result, roughly 90 percent of the slag deposits on the combustor walls and 

flows down to a tap hole. The "de-ashed" combustion gases then flow to a 

second stage where additional air is added to complete combustion. 

TRW has established a target for sulfur capture of 60 to 90 percent with 

addition of lime, but has declined to discuss how or where the lime is fed to 

the system. Actual test data from test with Ohio, Pensylvania, and Wyoming 

coals have reportedly achieved 50 to 90 percent capture at Ca/S ratios of 

between 3 and 4. By staging combustion, reduced levels of NO can also be 

achieved. 

The combustor was developed at a TRW pilot plant in California and is 

being tested in an industrial boiler owned by TRW in Cleveland, Ohio. No 

commercial sales of the combustor are known. Actual test data on SO- removal 

performance have not been published. 

Comparison of SO,. Capture 

While certain simimlarities exist between the TAS and TRW systems, they 

differ in how they handle ash in the coal, which in turn influences the 

addition of lime for SO- control. Specifically, the TAS system maximizes the 

number of ash particles in the furnace (by minimizing their size); this 

approach creates ash particles that are small enough to follow aerodynamic 

streamlines around heat exchanger tubes while maximizing surface area for 

rapid particle burnout and sulfur capture. Additional sulfur capture can be 

accomplished by adding lime or limestone to the micronizing mill along with 

the coal without significantly affecting boiler heat transfer. By contrast, 

the TRW process protects heat exchange surfaces by removing ash as a slag in 

the first stage of the combustor. However, this approach also reduces the 

coal alkali surface area needed for removal of sulfur. 
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Actual test data measuring sulfur capture with either system are limited. 

TAS claims to have achieved 90 percent capture without sorbent addition during 

short-term pilot-scale tests with several coals. However, data collected 

during these tests are insufficient to evaluate the chemistry of the process 

(e.g., percent removal versus Ca/S ratio), its performance on other coals, or 

its scale-up to full-size industrial boilers. The first significant data are 

expected to come from the boiler recently installed at St. Louis University 

Hospital. Short-term pilot-scale tests at the TRW pilot plant have 

demonstrated 50 to 90 percent sulfur capture, but as with the TAS system, 

full-scale data are not available. 

References 

1. TAS Systems Description. TAS-COAL, P. 0. Box 68, Magna, Utah. 

September 4, 1986. 

2. Comments on EPA's Proposed SO- Standard for Industrial Boilers. TRW 

Combustion Business Unit, Redondo Beach, California. December 1986.