Over 50 Persons listened to Five Speakers discuss Dry Sorbent Injection at the Second Hot Topic Hour on DSI held Thursday June 21st

 

Although Dry Sorbent Injection has been used for more than 40 years, now that EPA has finalized the MATS rule establishing low limits on emissions of Hg, HCl and filterable particulate matter (fPM) for all U.S. coal- and oil-fired power plants greater than 25 MW, DSI is gaining even greater attention. The interest in DSI is so great that we held one session with five speakers on June 7th and a second session again with five speakers yesterday. The speakers addressed the use of dry sorbent injection to meet the new MATS and CSAPR as well as material handling issues and methods to improve the performance of and reduce the usage of sorbents.

 

A common thread of all speakers was that DSI is not as simple as it may appear. The relationship between various acid gases and other controlled gases in the flue gas can be very complex. DSI can also have an impact on the performance of other existing control equipment and vice-versa. Careful study is necessary to select the sorbent and sorbent particle size that will achieve control goals at the lowest operating cost. Study is also necessary to determine how the sorbent will affect or be affected by other emission control equipment installed.

 

Selection of the correct delivery system components is also critical. Dry materials can solidify and plug critical conveying tubes and injection devices. And to obtain the lowest sorbent usage (and usually cost), the sorbent particle size needs to be appropriate to the flue gas conditions and the sorbent needs to be uniformly delivered to the gas stream.

 

If there was one underlining message to be gleaned from these two sessions it was “If you are considering DSI for your power plant, you would be wise to obtain the services of an expert to conduct modeling and field testing to determine the best sorbent, the correct particle size, the best injection location and how to achieve uniform mixing of the sorbent and flue gases.” This will allow you to achieve the regulatory emission limits at the lowest operating cost. Even operators that are currently using DSI might consider a study to optimize the use of sorbent.

 

The speakers at this second session were:

Steve Baloga, P.E. / Vice President – Southern Air Solutions Corporation, presented the results of trona injection for SO2 and HCl reduction for a utility boiler with ESP, an industrial boiler with ESP and a cement kiln with FF baghouse.  He showed considerable data demonstrating how the injection of milled Trona can minimize HCl emissions to achieve compliance while not exceeding the fPM limit. Significant reductions of SO2 can also be accomplished as an added benefit. He also discussed additional considerations that users must consider when evaluating sodium based reagents: impact on PM emissions (including PM2.5/CPM), impact on Hg emissions, impact on flyash quality, removal and potential leaching of volatile HAP metals in trona laden flyash, and cement alkali silica reactivity issues related to sodium sorbents.

 

Tony Licata, Vice President of Babcock Power Environmental Inc., discussed the impact of mixing on the performance of dry sorbent injection systems. The data presented demonstrated that using static mixers to directly inject sorbent or as cross mixers after injection will allow you to achieve optimum mass transfer resulting in maximum pollutant removal with the lowest sorbent use. He also emphasized that physical modeling is faster and more accurately predicts the performance of mixers than CFD.

 

Mike Tate, Technical Manager of Research & Development for Graymont Inc., described the key properties of hydrated lime that impact sorbent performance.  He also discussed how these properties affect the design of sorbent injection systems. He stated that differences in flue gas composition and process characteristics between boilers point to the need for testing to define performance.

 

Curt Biehn, Manager of Technical Sales & Marketing at Mississippi Lime Company, described the performance of hydrated lime when injected at different points in the flue gas train and with different pollution control equipment. One important conclusion was if you are injecting before a baghouse, seasoning is essential. After seasoning, the HCl emissions dropped to well within the MATS limit with less than a third of the sorbent injected. He also discussed injection prior to an ESP, SCR and ahead of the Air Heater.

 

Yougen Kong, P.E., Ph.D., Technical Development Manager at Solvay Chemicals Inc. talked about the effect of milling sodium sorbents on their performance in removing HCl and SO2. He gave a very good overview of the pros and cons of milling and described the performance of pin mills and air classifier mills. The data presented demonstrated that milling trona or sodium bicarbonate could increase the sorbent efficiency or acid gases mitigation rate (SO2, SO3 and HCl). However, to achieve optimum performance and lowest O&M cost, you need to design a milling system instead of purchasing just a mill. You should consider:

 

            Sorbent feedrate

            Downstream pressure drop

            Temperatures at mill inlet and outlet

            Mill cleaning.

 

The Bios, Abstracts and Photos information is linked below.

BIOS, ABSTRACTS, PHOTOS - JUNE 21, 2012.htm