# UCC Dry Sorbent Inje c t i on Sy s tem Enhanced In-Line Mill Technology Saves Utilities Millions 

# T e c hnology BR I E F

Coal-fired power plants are being driven by the EPA to assess various technologies and capabilities for enhanced SO 3 removal. Since 2005, United Conveyor Corporation-Dry Sorbent Injection has conducted numerous Dry Sorbent Injection (DSI) tests to demonstrate SO 3 removal performance versus trona particle size. The test described in this technology brief confirms that low SO 3 stack emissions are achievable with dry sorbent injection technology. A key discovery is that milling technology, specifically in-line pneumatic milling systems, provides the only way to achieve very low SO 3 stack emissions when injecting trona. Additionally, results show that a fine milled particle size can reduce sorbent usage by half.
Dry Sorbent Injection Test Overview The DSI test compared SO 3 removal performance of as-delivered unmilled trona, in-line coarse milled trona and in-line fine milled trona. DSI is an economical and effective technology that injects selected sorbents into the flue gas to control SO 2 , SO 3 , mercury and other acid gases. When trona is the appropriate sorbent choice, in-line milling decreases trona usage by increasing surface area per ton injected to enhance reactivity and improve dispersion throughout the flue gas.
The test had three primary objectives:
1. V erify known removal performance of as-delivered unmilled trona and UCC fine milled trona
2. De termine the SO 3 removal performance of in-line coarse-milled

trona
3. Use the SO 3 removal curves to compare the life cycle sorbent costs of each approach
Implementation and System Configuration Trona injection was performed with one positive pressure pneumatic conveying system splitting into eight injection lances located downstream of the air preheaters and upstream of the electrostatic precipitator (ESP) – a common configuration for injection systems. The United Conveyor Corporation (UCC) splitter system was designed to ensure ±10 percent sorbent distribution across each injection lance, and was verified to achieve this performance during laboratory testing. The lance placement was determined using computational fluid dynamics (CFD) modeling. The patent-pending UCC in-line mill system, was used to mill the trona. The UCC in-line mill system operates with the positive pressure pneumatic conveying system and utilizes only the conveying air stream in the milling process. The mill size reduction is adjustable, and was reduced by design during some test runs, intentionally increasing the sorbent particle size to closely match competing mill performance and corresponding SO 3 removal rates.
The median trona particle sizes evaluated:

• As-deliv ered unmilled trona: 30-40 micr ons

• Coar se milled trona: 16-18 micr ons

• UCC fine milled tr ona: 12-14 micr ons Plant Operation The UCC test was performed at a plant with a 700MW unit with the following environmental controls:

■ Selective catalytic reduction (SCR) system for nitrogen oxide (NOx)
removal

■ Cold side ESP for particulate removal

■ Wet flue gas desulfurization (FGD) for SO 2 control
The baseline for the plant SO 3 concentration levels were:

■ The boiler and SCR converting approximately 2 to 2.5 percent total

SO 2 to SO 3
■ ESP outlet SO 3 concentration in the range of 28-33ppm without DSI injection



### Injection PointSampling Methodology and Testing Tools
SO 3 concentration was measured by both a dew point monitor and controlled condensate testing (EPA Method 8A). All testing samples were taken between the ESP and FGD. The dew point monitor provided continuous monitoring of the flue gas dew point which was converted to an approximate SO 3 concentration. SO 3 concentrations calculated indirectly from dew point compared conservatively to SO 3 concentrations determined by EPA Method 8A.

Note: SO 3 concentrations well below 5ppm were measured using interval and event sampling techniques. However, UCC acknowle dges that at concentrations well below 5ppm, the measurement tolerance of current technology and test methods may not provide the accuracy necessary to consistently validate emission limits due to testing tolerance bands exceeding absolute measurements.
As-delivered unmilled, coarse milled and fine milled trona samples wer e taken passively by a pitot tube placed in the center of the conveying stream. This sampling method was validated by taking 100 percent material samples at multiple injection lance sites concurrent with the pitot tube samples. All samples were analyzed using a Beckman Coulter laser analyzer.
Test Results and Analysis The test results showed:

■ Predictable SO 3 removal performance curves for each particle size measured/tested

■ Smaller particle size allows lower SO 3 removal while significantly lowering trona usage

■ Fine milled trona is projected to save $4.5 million and $2 million over

five years compared with as-deliver unmilled trona and coarse milled trona respectively

P roven Return on Investment Figure 1 shows a comparison of the annual trona costs and five year aggregated savings associated with achieving 5ppm SO 3 concentrations at the ESP outlet using as-delivered unmilled, coarse milled (competitive mills) and UCC fine milled trona. The annual trona cost comparison assumes a capacity factor of 90 percent for a mid- to large-sized power plant and a price of $180/ton for as-delivered unmilled trona. Conclusion DSI systems are low capital cost and suitable for retrofit into units with SCRs and/or wet scrubbers. UCC DSI technology delivers effective SO 3 control and is capable of achieving SO 3 emission limits well below 5ppm as a result of in-line milling technology producing sorbent particle size of 12 to 14 micron. This small particle size will reduce sorbent usage up to 50%. Industry leading UCC DSI technology provides the coal-fired power industry the most efficient and economical method to meet current and future SO 3 emission limits and regulations.



## www.unitedconveyor.com

UCC is a registered trademark of United Conveyor Corporation ©2010 U nited Conveyor Corporation TB11-01 Sorbent (Trona) Particle Size (median) Injection Rate (lb/hr) Annual Sorbent Costs 5-Year Sorbent Savings As-delivered Trona 25 - 40 micron 2,300 $1,631,988 n/a

Coarse Milled 16 - 19 micron 1,600 $1,135,296 $2,483,100

UCC Fine

Milled 12 - 14 micron 1,000 $ 709,560 $4,464,000 Figure 1 - Cost Comparison to Achieve <5ppm SO 3

Note: Typically less than 5ppm is necessary to avoid a visible SO 3 Plume Figure 2 - Milled Trona Injection Rate vs. Outlet SO 3 Concentration



### Median Trona Particle Size As-Delivered – 25-40 micron Coarse Milled – 16-19 micron UCC Fine Milled – 12-14 micron

SO 3 (ppm)

Trona Injection Rate (lb/hr)