IWC 12‐57 Chemistry of FGD Blowdown TOM HIGGINS CH2M HILL Chantilly, Virginia KRISTEN JENKINS CH2M HILL Atlanta, Georgia NATARAJAN SEKHAR CH2M HILL Englewood, Colorado KEN MARTINS CH2M HILL Santa Ana, California KRYSTAL PEREZ CH2M HILL Bellevue, Washington LAURA REID CH2M HILL Charlotte, North Carolina IWC 12‐57 KEYWORDS: Zero liquid discharge, ZLD, evaporation, crystallization ABSTRACT As limits for metals are lowered and new parameters regulated, the complexity and cost of treatment to meet these low limits and add on treatment technology has made zero liquid discharge a more viable option for flue gas desulfurization blowdown. Coal and blowdown chemical make-up impacts the water chemistry and treatment technologies. This paper discusses the water chemistry associated with concentrating and crystallizing blowdown and presents a commercial model used in the evaluation. IWC 12‐57 BACKGROUND INTRODUCTION Past applications of zero liquid discharge Due to the complex water chemistry of FGD (ZLD) systems in the power industry have been blowdown, a tool that can predict the impacts of confined typically to cooling tower blowdown in evaporation and crystallization is critical to areas where water was scarce, in terms of either understand potential impacts of the water source waters or discharge locations for waste‐ chemistry. OLI System’s StreamAnalyzer™ has water. The ZLD designs for these wastewaters been effective in evaluating water chemistry in generally considered water chemistries involving evaporation/crystallization processes including the concentration of sodium chloride. Because modeling boiling point rise, solids formed, and sodium chloride can be crystallized at a relatively potential scaling issues. StreamAnalyzer™ is an low temperature, ZLD of cooling tower equilibrium‐based, multi‐phase simulation of blowdown treatment is simpler than ZLD of flue electrolyte systems produced by OLI Systems, gas desulfurization (FGD) blowdown water. This Inc. This software can simulate solutions under is because limestone‐based FGD systems evaporator and crystallizer conditions, including produce waters with high concentrations of temperature, pressure, and ionic strength. calcium and magnesium chloride, which require We have developed an Excel™‐based mass very high temperatures to crystallize. balance tool that we couple with Presently, ZLD is becoming a more viable StreamAnalyzer™ to evaluate alternative water option for discharge of complex industrial chemistries and ZLD alternatives. This model wastewater. Drivers for ZLD include lowering of requires the manual transfer of data between water quality standards for metals; implemen‐ Excel and StreamAnalyzer™. To automate this tation of chloride, sulfate, and total dissolved process, the water chemistry simulation engine solids (TDS) water quality standards; as well as and equilibrium parameters developed by OLI scarcity of water resources. The Environmental was paired with the process simulation Protection Agency (EPA) is looking to ZLD, using capabilities of Aspen Plus™ (developed by Aspen evaporators and crystallizers, as a viable Technology, Inc.) using Aspen OLI™. The addition treatment technology for FGD blowdown, as of process simulation enhances modeling by noted in their report entitled Steam Electric simultaneously accounting for recycle streams, Power Generating Point Source Category: Final complex chemistry, and the heat balance around Detailed Study Report (EPA, 2009). the system. ZLD treatment of FGD blowdown is complex, It is also critical to understand how changes in as the wastewater has high levels of calcium and coal quality impact the composition and volume magnesium chloride and sulfate. Coal quality of FGD blowdown. Coal quality also impacts impacts both the resulting FGD blowdown and gypsum and fly ash production, which is the disposal alternatives for the final brine. The significant because both can be sold resulting FGD blowdown water chemistry drives commercially or used to cost‐effectively dispose the water recovery, solids formation, and of evaporator brine through mixing and applicable ZLD technologies. This paper presents landfilling. We have developed a tool to approaches to evaluating the coal and FGD estimate FGD wastewater volumes, gypsum, and blowdown, and modeling evaporators and fly ash quality. To determine these factors, the crystallizers using the approaches developed by tool uses information collected for typical coal CH2M HILL. It also outlines the effects of weight‐ qualities found in the U.S., along with chloride fractions of inorganic salts (calcium, magnesium, tolerances for the FGD system. chloride, and sulfate) on final brine recovery. IWC 12‐57 APPLICATION TO FGD BLOWDOWN information, in turn, is used to generate estimates for capital expenditures and operating We applied the aforementioned models to expenses. As shown in Figure 2, the equipment evaluate evaporation and crystallization of FGD sizing can be modified based on individual blowdown. StreamAnalyzer™ has been the core preferences for capacity and redundancy. technology used to evaluate the complex nature Determination of evaporation/crystallization of these processes. This software has the equipment is based on the requirements for the capacity to modify variables such as pH, final stream (either a concentrated brine or salt temperature, composition, and pressure; as well cake). If the desired end point is formation of a as the ability to model the vapor, liquid, and salt cake for disposal, the crystallization and solid phases. These features allow it to simulate dewatering equipment are selected based on the conditions of a multitude of processes, the type of solid expected to be formed and including estimating chemical usages and potential scaling or fouling issues. determining the resulting water chemistry. StreamAnalyzer™ also can determine boiling A wastewater profile is first generated using point rise of the stream to evaluate whether water chemistry data collected from the FGD concentration using a vapor compression blowdown at the location being considered for evaporator is feasible. Conventional treatment. StreamAnalyzer™ is used to check compressors are limited to a pressure where the analytical data for charge neutrality, and steam condenses at around 226° F. The practical then balance the charges. The balanced water limit of heat exchangers is about 8°F, which chemistry is input into an Excel‐based mass limits the brine boiling point rise to 5.5 to 6.5°F. balance spreadsheet. Figure 1 shows a portion Vapor compression evaporators are more of the integrated mass balance generated using energy‐efficient than steam evaporators and are our spreadsheet tool. When pretreatment is typically preferred, depending on the water warranted, we have used the software to chemistry. StreamAnalyzer™ is also used to evaluate operating set‐points. Stripping inert determine the type and relative quantity of gases and chemical softening have been solids formed when the water is concentrated. evaluated using this modeling approach to Understanding the relative amounts of solids in identify operational information such as pH, the brine is helpful in evaluating antiscalant temperature, acidification, and neutralization selection, seeding, brine transfer and holding, requirements. This operational information, and equipment selection. Alternatives for ZLD along with flows and solids compositions, is systems and the corresponding water chemistry linked to separate worksheets that size the impacts are discussed further in later sections. equipment for the system (Figure 2). This IWC 12‐57 Figure 1: Portion of Integrated Mass Balance Spreadsheet Tool Figure 2: Portion of Integrated Equipment Sizing from Spreadsheet Tool Partial ZLD: Equipment Sizing User Key Referenced from full mass balance sheet Local Equipment Preferences Universal Equipment Preferences (Default) 5 Adjustable value used for calculations (e.g. pipe length), enter new value if known User Input for Universal Redundance and Capacity Quantity Percent Capacity Quantity Type of Equipment Installed Each Purchased Pump(s) 2 100% 2 Tank(s) 1 100% 1 Evaporator System(s) 2 100% 2 Equipment Sizing Note: Universal preferences in table above are defaut. Leave local equipment quantities and capacities blank to default to universal preferences. Local preferences override universal preferences, if entered. Equipment Item Quantity Value Units Notes ZLD Feed Pump Type Pump Purchased Installed Percent Capacity each Design Flow (Total) 300 gpm Design Flow (each) 300 gpm Pipe Velocity 6.68 feet per second Default value, enter new value if known Pipe Diameter 6 in Default value, enter new value if known Hazen Williams Constant 150 v = flow velocity (ft/s) 3.34 f = friction head loss 0.62 ft/100 ft Pipe Length 500 ft Default value, enter new value if known Minor Losses 1,000 ft Default value, enter new value if known Total Equivalent Length 1,500 ft Head Loss 9.3 ft Elevation Difference 20 ft Default value, enter new value if known Total Head 29.3 ft Water Horsepower 2.2 HPw 1 HP=33,000 ft-lbs/minute Assumed Efficiency 66% Default value, enter new value if known Total HP 3.4 HP Pump HP 5.0 HP IWC 12‐57 In addition, materials of construction must be carefully selected using the water chemistry Coal quality affects gypsum and fly ash characteristics of the concentrated stream to production, in addition to impacting the water evaluate potential corrosion issues. chemistry of FGD blowdown. Fly ash is composed of particles, either incombustible