Minimizing FGD Costs Mr. Bryan D. Hansen, P.E., Burns & McDonnell

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1 Title: Author: Minimizing FGD Costs Mr. Bryan D. Hansen, P.E., Burns & McDonnell With nearly every utility in the United States adding or upgrading their Flue Gas Desulfurization (FGD) system, it is crucial that the utilities understand key issues in reducing the cost of these new systems. At the same time utilities are also facing increased pressure to eliminate wastewater discharge and to move toward a zero emission or near zero emission facility. This paper discusses the water balance impacts of a wet FGD system and ways to minimize the overall project cost of the FGD system and new wastewater treatment facilities. The addition of a wet FGD system can significantly affect the water balance of the facility. In many cases significant new wastewater treatment systems may need to be installed to handle the FGD blowdown. Major topics include: Plant water balance impacts with a new wet FGD system at an existing plant. Impact of producing saleable grade gypsum versus land filling gypsum. Zero liquid discharge technologies applicable for treating FGD blowdown. Minimizing quantity of FGD blowdown by using higher grade materials of construction such as 317LMN, Duplex 2205, Duplex 255, 6% Moly, Hastelloy C, etc. Impact of switching to a higher or lower chloride content fuel. The cost information section of the paper will discuss the trade off between the increased costs of the FGD system materials of construction verses building a larger wastewater treatment facility. Comparative analysis of these costs for bituminous, sub-bituminous, and lignite fuels will be included. FLUE GAS DESULFURIZATION SYSTEM WATER BALANCE IMPACTS When designing a wet FGD system there are many issues to consider. One important issue is trying to determine where to obtain the makeup water supply and how to dispose of the FGD wastewater. The wet FGD process requires a significant quantity of makeup water for reagent preparation, mist eliminator wash, evaporative losses, and dewatering needs. A portion of this makeup water can come from poor quality water such as cooling tower blowdown and other plant wastewater streams. However, there is always a need for some good quality makeup water for lime slaking (if using lime instead of limestone), mist eliminator wash, and to wash the gypsum produced to achieve the desired gypsum quality. The quantity of wastewater produced by the FGD process is directly related to the fuel characteristics and makeup water quality. Chloride concentration is the primary characteristic evaluated when selecting materials of construction for the wet FGD system. The concentration of chlorides in the fuel source contributes the majority of the chlorides present in the FGD wastewater stream. Typically, fuels have chloride contents ranging from 0.01 percent up to 0.28 percent (see Table 1). Page 1 of 9

2 Table 1 - Chloride Maximum Values by Coal Coal 95th Percentile 98th Percentile Average Basis Sub-bituminous Dry Bituminous Dry Lignite Dry Data obtained from EPA s Mercury Information Collection Request Database By comparison, the concentration of chlorides in most makeup water streams is several orders of magnitude smaller. Therefore, small changes in the fuel chloride content can have a major impact on chloride concentration in the FGD system whereas; small changes in the makeup water supply chloride content are hardly even noticeable. For this paper a variety of fuels were modeled to determine what impact that fuel selection has on the overall cost of the FGD system and wastewater treatment equipment. Table 2 lists the characteristics of the fuels examined in this paper. Table 2 - Coal Analysis Basis COAL ULTIMATE ANALYSIS Wyoming Jefferson, No. 6 Illinois Rosebud, MT Lignite, ND (ASTM, as rec d, wt%) PRB OH Moisture Carbon Hydrogen Nitrogen Chlorine Sulfur Ash Oxygen TOTAL Modified Mott Spooner HHV (Btu/lb) 8,227 11,922 10, 8,789 7, Data taken from EPA s Cue Cost program Figure 1 indicates the relative FGD system makeup water requirements using a No. 6 Illinois coal with various chloride concentrations. Appendix A contains similar information for the other fuels in this evaluation. Page 2 of 9

3 Figure 1 - FGD System Makeup Rate versus Unit Size with No. 6 Illinois Coal 1 Makeup Rate (gpm) ,000 ppm Cl 12,000 ppm Cl 20,000 ppm Cl 40,000 ppm Cl 50,000 ppm Cl BASIS OF EVALUATION For this paper we wanted to determine what combination of wet FGD system and wastewater treatment system would result in the most economical combination. Particularly, we want to look at a brine concentrator/crystallizer type wastewater treatment system. The brine concentrator/ crystallizer system produces a high purity distillate that can be reused in the plant to reduce the overall plant makeup water needs. The waste stream from the brine concentrator/crystallizer is a solid, landfillable material. Essentially, any other plant wastewater streams can be disposed of by directing most of the wastewater to the wet FGD system for makeup and directing the FGD system blowdown to the brine concentrator/crystallizer system. So the question we have is for any given fuel, what combination of wet FGD system materials of construction and brine concentrator/crystallizer sizing will result in the lowest overall cost to the utility. MATERIAL LIMITATIONS For the wet FGD system, various materials of construction can be used. The limiting factor of each material is the concentration of chlorides the material can withstand. Table 3 indicates some common materials of construction and their associated design chloride concentrations. Page 3 of 9

4 Table 3 - Chloride Limitations for Various Materials Materials of Construction Design Chloride Limits (ppm) 317LMN Stainless Steel (S31726) 8,000 Duplex 2205 Stainless Steel (S32205) 12,000 Super Duplex 255 Stainless Steel (S32550) 20,000 Super Austenitic 6% Mo Stainless Steel (N08367) 40,000 C-276 (N10276) 50,000 As can be seen from Table 3, the allowable chloride concentration can vary significantly. The primary disadvantage is that as you go down the table, material costs increase dramatically. For this evaluation we only wanted to consider metallic alloy options to simplify the evaluation. Figure 2 shows the impact that materials of construction have on the wastewater blowdown concentration from the FGD system using No. 6 Illinois coal. Appendix A contains similar figures for the other fuels in this evaluation. Figure 2 - FGD System Blowdown Rate versus Unit Size with No. 6 Illinois Coal Blowdown Rate (gpm) EQUIPMENT COSTS 8,000 ppm Cl 12,000 ppm Cl 20,000 ppm Cl 40,000 ppm Cl 50,000 ppm Cl Equipment pricing was obtained for a variety of brine concentrator/crystallizer systems. FGD system pricing was modeled using a modified version of EPA s Cue Cost program. Current material pricing was obtained for the various metals under consideration. Table 4 indicates the material pricing used in this evaluation. Page 4 of 9

5 Table 4 - Construction Material Pricing Materials of Construction Material Costs ($/ft) Erection Costs ($/ft) Installed Costs ($/ft) 317LMN Stainless Steel (S31726) $19 $39 $58 Duplex 2205 Stainless Steel (S32205) $25 $39 $64 Super Duplex 255 Stainless Steel (S2550) $48 $39 $88 Super Austenitic 6% Mo Stainless Steel (N08367) $45 $39 $84 C-276 (N10276) (wallpaper) $70 $47 $117 C-276 (N10276) (solid) $98 $51 $148 Figure 3 shows the relative costs of a brine concentrator/crystallizer system versus wastewater treatment rate. For this evaluation, any treatment rate less than 10 gpm was not included. Typically, with these low flow rates, a spray dryer or evaporation ponds will provide a more economical solution. Figure 3 - Brine Concentrator / Crystallizer Equipment Costs versus Treatment Rate 7.0 Cost (Millions $) Treatment Rate (gpm) Figure 4 shows the relative installed costs of the brine concentrator/crystallizer systems versus treatment rate. Page 5 of 9

6 Figure 4 - Brine Concentrator / Crystallizer Installed Costs versus Treatment Rate Cost (Millions $) Treatment Rate (gpm) Figure 5 shows the relative installed costs of the FGD system for No. 6 Illinois coal versus plant size for various materials of construction. Appendix A contains similar installed cost data for the other fuels in this evaluation. Figure 5 - FGD System Costs versus Unit Size with Various Materials Firing No. 6 Illinois Coal Installed Costs ($) $200,000,000 $150,000,000 $,000,000 $50,000,000 $0 317LMN Duplex 2205 Duplex 255 6% Mo C-276 Wallpaper C-276 Solid Figure 6 shows the relative annual operating and maintenance costs of the FGD system versus plant size for various fuels. Page 6 of 9

7 Figure 6 - FGD System Annual Operating Costs versus Unit Size Operating Costs ($) $18,000,000 $16,000,000 $14,000,000 $12,000,000 $10,000,000 $8,000,000 $6,000,000 $4,000,000 $2,000,000 $0 Wyoming PRB Armstrong, PA Jefferson, OH Logan, WV No. 6 Illinois Rosebud, MT Lignite, ND As we can see from Figure 2, better FGD materials of construction can reduce the amount of FGD blowdown which subsequently reduces the required size of the wastewater treatment equipment. The problem is how to optimize higher FGD equipment costs, due to better materials of construction, versus the size of the brine concentrator/crystallizer equipment. If we look at the total system installed costs of a wet FGD system plus its corresponding brine concentrator/ crystallizer we can compare the incremental costs of installation. Likewise, we can compare the total operating and maintenance costs of the wet FGD system plus its corresponding brine concentrator/crystallizer equipment. Figure 7 shows the incremental installation costs of the total wet FGD system plus brine concentrator/crystallizer for a No. 6 Illinois coal versus plant size with various materials of construction. The base case was for the 317LMN materials. Appendix A contains similar data for the other fuels under consideration. Page 7 of 9

8 Figure 7 - Incremental Installed Costs of FGD System and Brine Concentrator versus Unit Size for No. 6 Illinois Coal Incremental Costs ($) $50,000,000 $40,000,000 $30,000,000 $20,000,000 $10,000,000 $0 Duplex 2205 Duplex 255 6% Mo C-276 Wallpaper C-276 Solid Putting all this data together we can calculate the present worth of each system versus each fuel for a range of plant sizes. Figure 8 shows the present worth of the wet FGD/brine concentrator system versus the various material of construction over a range of plant sizes. Appendix A contains similar data for the other fuels under consideration. Figure 8 - Present Worth of Installed FGD System and Brine Concentrator versus FGD Materials Firing No. 6 Illinois Coal Present Worth (Millions $) $.0 $350.0 $.0 $250.0 $200.0 $150.0 $.0 $50.0 $ LMN Duplex 2205 Duplex 255 6% Mo FGD Materials C-276 Wallpaper C-276 Solid MW 200 MW MW MW MW 600 MW MW 800 MW MW 0 MW Page 8 of 9

9 CONCLUSIONS From the shape of the curves in Figure 8 we can clearly see that the present worth decreases with increasing materials of construction until we get to the 6% Mo materials. At this point, using higher materials of construction results in an increased overall present worth. This is true for all the various coals under consideration and over all the plant sizes under consideration. Therefore, we would conclude that for any given combination of fuels, a wet FGD system with 6% Mo materials of construction followed by a brine concentrator/crystallizer system would result in the lowest life cycle costs for any plant size. Obviously, the scope of this comparison was limited to a very specific case and other alternatives must be considered for each installation to ensure the utility gets the best value for their investment. Page 9 of 9