Performance

 

Inputs for the performance of the Lime Spray Dryer SO2 control system are entered on the Performance parameter screen.

In a Lime Spray Dryer, an atomized spray of a mixture of lime slurry and recycled solids is brought into contact with the hot flue gas. The water in the slurry evaporates leaving dry reaction products and flyash, which drops out of the scrubber. A particulate control device such as a baghouse is also used to remove the rest of the dry products from the flue gas before releasing it. The SO2 removal efficiency is the total of SO2 removed in the scrubber and the baghouse.

Many lime spray dryer input parameters are similar to those defined for wet lime/limestone systems. Each parameter is described briefly below:

•Actual SO2 Removal Efficiency: This is the annual average SO2 removal efficiency achieved in the absorber. The calculated default value assumes compliance with the SO2 emission limit specified earlier, if possible. The default value reflects other model parameter values, including the sulfur retained in bottom ash. This input is highlighted in blue.

•Maximum SO2 Removal Efficiency: This parameter specifies the maximum efficiency possible for the absorber on an annual average basis. The value is used as a limit in calculating the actual SO2 removal efficiency for compliance.

•Actual SO3 Removal Efficiency: The default value is taken from the removal efficiency reported in the literature (references are below). This efficiency then determines the mass of SO3 removed from the flue gas in the collector. For more information see also:

•Hardman, R; Stacy, R; Dismukes, E "Estimating Sulfuric Acid Aerosol Emissions from Coal-Fired Power Plants", US DoE-FETC Conference on Formation, Distribution, Impact and Fate of Sulfur Trioxide in Utility Flue Gas Streams 1998 (currently available at https://web.archive.org/web/20040307161115/http://www.netl.doe.gov/publications/proceedings/98/98fg/hardman.pdf )

•Rubin, E. S. "The Importance of Sulfur Trioxide for the Toxic Release Inventory", US DoE-FETC Conference on Formation, Distribution, Impact and Fate of Sulfur Trioxide in Utility Flue Gas Streams 1998 (currently available at https://web.archive.org/web/20030416143712/http://www.netl.doe.gov:80/publications/proceedings/98/98fg/rubin.pdf)

•Particulate Removal Efficiency: Ash and particulate matter are assumed to be removed by a separate particulate removal device, such as a fabric filter. However, this parameter is provided for conditions where particulates are removed directly from the scrubber.

•Absorber Capacity: This is the percent of the flue gas treated by each operating absorber. This value is used to determine the number of operating absorbers and the capital costs.

•Number of Operating Absorbers: This is the number of operating scrubber towers. The number is determined by the absorber capacity and is used to calculate the capital costs. The value must be an integer.

•Number of Spare Absorbers: This is the total number of spare absorber vessels. It is used primarily to calculate capital costs. The value must be an integer.

•Reagent Stoichiometry: This is the moles of calcium per mole of sulfur into the absorber. The stoichiometry is calculated as a function of the required SO2 removal efficiency, inlet flue gas temperature, inlet sulfur concentration, and approach to saturation temperature.

•CaO Content of Lime: This is the percent of reagent that is pure lime (CaO). This parameter determines the waste solids produced and the reagent mass requirements, given the stoichiometry needed for SO2 removal.

•H2O Content of Lime: This is the moisture content of the lime (CaO). The remaining reagent impurities are assumed to be inert substances such as silicon dioxide (sand). This parameter is used to determine the waste solids produced.

•Total Pressure Drop Across FGD: This is the total pressure drop across the spray dryer vessel prior to the reheater. This is used in the calculations of the power requirements (or energy penalty) and thermodynamic properties of the flue gas.

•Approach to Saturation Temperature: This defines the gas temperature exiting the absorber. The approach is the increment over the water saturation temperature at the exit pressure. As the approach to saturation temperature increases, the evaporation time decreases thereby decreasing removal efficiency.

•Temperature Rise Across ID Fan: An induced draft (ID) fan is assumed to be located upstream of the FGD system. The fan raises the temperature of the flue gas due to dissipation of electro-mechanical energy.

•Gas Temperature Exiting Reheater: This is the desired temperature of flue gas after the reheater. It determines the reheat energy required.

•Oxidation of CaSO3 to CaSO4: This parameter determines the mixture of the two chemical species in the solid waste stream.

•Slurry Recycle Ratio: An atomized spray of a mixture of lime slurry and recycled solids is brought into contact with the hot flue gas. This parameter specifies the amount of solid waste recycled and lime slurry used. It is calculated from the sulfur content of the coal.

•Spray Dryer Power Requirement: This is the equivalent electrical output of thermal (steam) energy used for reheat, plus the actual electrical output power required for pumps and booster fans.

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