Development of advanced, dry, SO{sub x}/NO{sub x} emission control technologies for high-sulfur coal. Final report, April 1, 1993--December 31, 1994 Page: 64 of 91
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Low T., Operation
The success of the new atomizer and DID allowed trouble-free operation at scrubber and
baghouse approach temperature of 10*F and less. The nature of the deposits that formed on the DID
was found to a function of solids concentration as well as T.. Tests with lime-slurry produced no
significant deposition at a T. of 10 F as long as the solids concentration was greater than about 10%.
The success of this project in attaining very high S02 removal is directly attributable to the ability to
operate the system at low T,.
Droplet Impingement Device (DID)
Most tests were conducted with the B&W patented Droplet Impingement Device (DID)
installed at the scrubber outlet. Its purpose was to prevent deposition downstream of the scrubber by
selectively collecting large, heavy, unevaporated slurry droplets, that may be present at low T..
Smaller, lighter and dry particles have much less momentum and follow the gas stream around the
DID without being collected. Provisions were made to clean the DID by rapping, rotating, or both.
The DID performed well during all test phases. It was found to be needed only when the scrubber
was operated at very low T. with slurries containing less then 10% solids. Under these conditions,
incomplete evaporation and low initial solids concentrations resulted in large, wet, slurry droplets at
the scrubber exit. These droplets impinged the DID and gradually built deposits that had to be
removed by rotating and rapping the DID. In a few cases, the deposits were moist and difficult to
remove. However, even for these cases, the downstream flues and equipment remained deposit-free,
demonstrating that the DID concept is viable during extreme or upset conditions. In tests using
slurries above 10% solids, little material collected on the DID. The success of the DID throughout
this test has lead to a study to develop a commercial system.
Atomizer Deposition
A proprietary atomizer was used throughout the project. Its design minimized deposition on
the atomizer tip, which is a serious drawback to commercial dry scrubber systems. Deposition
eventually affects atomizer performance which leads to reduced scrubbing performance, catastrophic
deposition on scrubber walls, flues, and in the baghouse, and downtime for maintenance. The new
B&W Durajet'" prevented all but very slight deposition that was easily removed by light rapping every
eight hours. It is hoped to incorporate this design on the next commercial dry scrubber or to retrofit
existing scrubbers.
Effect of Moisture
Initial LIDS testing produced SO2 removals of only 54%, compared to 92% in 1991. Sample
analyses showed that the poor performance was likely caused by exceptionally fast evaporation in the
scrubber as evidenced by the low moisture content of the baghouse ash and poor scrubber
performance. At similar conditions, baghouse ash moisture was only 0.1% compared to 2.3% in 1991.
To compensate, small amounts of a deliquescent salt (CaCl2) were added to the slurry to increase the
residual ash moisture in the baghouse. Tests without salt addition produced moisture levels below
0.5% and baghouse SO2 removal below 40%. With the addition of CaCl2, the residual moisture
increased to 1.6% and SO2 removal increased to above 80%. This effect is usually not seen, or is not
as great, with conventional dry scrubbing systems, because it is believed that the chemical makeup of
the solids (i.e. higher Ca(OH)2 content) maintains residual ash moisture above 1.0%. Residual2-48
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Amrhein, G.T. Development of advanced, dry, SO{sub x}/NO{sub x} emission control technologies for high-sulfur coal. Final report, April 1, 1993--December 31, 1994, report, December 23, 1994; United States. (https://digital.library.unt.edu/ark:/67531/metadc783090/m1/64/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.