Performance

 

Inputs for the performance of the Hot-Side SCR NOx control technoloty are entered on the Performance parameter screen. The following parameters are available:

•Actual NOx Removal Efficiency: The actual removal efficiency is dependent on the minimum and maximum removal efficiencies of the SCR and the emission constraint for NOx (set on the  Overall Plant Regulations & Taxes screen). The model assumes a minimum removal of 50%. The actual removal is set to match the constraint, if feasible. It is possible that the SCR may under or over comply with the emission constraint. This input is highlighted in blue.

•Maximum NOx 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 NOx removal efficiency for compliance.

•Particulate Removal Efficiency: The ash in the high dust gas entering the SCR collects on the catalyst layers and causes fouling. Ash removal is not a design goal; rather, it is a reality which is taken into consideration by this parameter.

•Number of SCR Trains: This is the total number of SCR equipment trains. It is used primarily to calculate the capital costs. The value must be an integer.

•Number of Spare SCR Trains: This is the total number of spare SCR equipment trains. It is used primarily to calculate capital costs. The value must be an integer.

•Number of Catalyst Layers: The total number of catalyst layers is a sum of the dummy, initial and spares used. All catalyst layer types are of equal dimensions, geometry, and catalyst formulation. You specify each value; the value must be an integer. The catalyst layer types and quantities are combined with pressure drop information to determine the auxiliary power requirements and the capital cost of the SCR technology. A layer may be interpreted as either a full layer (e.g., typically 1 meter deep), or a half layer (e.g., typically 0.5 meters deep) to represent alternative SCR catalyst replacement schemes. There is a limit of 8 total initial and reserve layers. The following inputs allow you to specify the number of catalyst layers:

•Number of Dummy Catalyst Layers: This is the number of dummy catalyst layers. The value must be an integer. A dummy layer corrects the flow distribution. It is used to calculate the total pressure drop across the SCR and the auxiliary power requirements.

•Number of Initial Catalyst Layers: This is the number of initial active catalyst layers. The value must be an integer. Three layers are installed initially. It is used to calculate the total pressure drop across the SCR and the auxiliary power requirements.

•Number of Reserve Catalyst Layers: This is the number of reserve or extra catalyst layers. These are available for later catalyst additions. The value must be an integer. It is used to calculate the total pressure drop across the SCR and the auxiliary power requirements.

•Catalyst Replacement Interval: This parameter calculates the operating hour interval between catalyst replacements. The interval is determined by the decision to replace all at once or each of them separately after each interval. Currently, the model is not set up to replace two half layers simultaneously.

•Catalyst Space Velocity: The calculated space velocity is determined by several factors, including many of the reference parameters in the next section . The space velocity is used to determine the catalyst volume required.

•Ammonia Stoichiometry: This is the molar stoichiometry ratio of ammonia to NOx entering the SCR device. The calculated quantity is based on an assumed NOx removal reaction stoichiometry of 1:1 for both NO and NO2, and a specified ammonia slip. It affects the amount of ammonia used and the amount of NOx converted to moisture.

•Steam to Ammonia Ratio: The molar ratio of steam to ammonia is used to determine the amount of steam injected to vaporize the ammonia. The value assumes the steam is saturated at 450 degrees Fahrenheit and the ammonia is diluted to 5 volume percent of the injected gas.

•Steam for Soot Ratio: This is the steam required for soot blowing.

•Total Pressure Drop Across SCR: The total is determined from the individual pressure drops due to air preheater deposits, the active catalyst layers, the dummy catalyst layers, the ammonia injection system and the duct work. It is used to calculate the total pressure drop across the SCR and the auxiliary power requirements.

•Oxidation of SO2 to SO3: The oxidation rate is calculated for a high sulfur catalyst and affects the flue gas composition. It uses the space velocity and the inlet temperature. The SO3 produced acts as an ash-conditioning agent if an ESP is used downstream.

•Hot-Side SCR Power Requirement: The default calculation of auxiliary power is based on the additional pressure drop, electricity to operate pumps and compressors, and equivalent energy for steam consumed. It is expressed as a percent of the gross plant capacity.

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