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Show 2.0 REACTOR DESIGN (con't) 2.1 General Procedure (con't) Although it is impossible to present generally valid data on the dependence of space velocity on temperature, we can do so if we narrow the discussion to clean flue gases (no S02 or other catalyst poisons) of a composition that is typical for gas turbine of gases. Table 1 presents such data that are based on laboratory tests in which a typical gas turbine offgas was denoxed to a conversion level of about 90%. Knowing the required catalyst volume and the permissible maximum pressure drop, a preliminary reactor design can be made. The major variables in this design procedure are: • the thickness of the catalyst layers • the total surface area of the catalyst layers (these two variables determine the pressure loss over the catalyst layers) • the cross sectional area of the reactor perpendicular to the gas flow (this variable controls the various inlet and outlet pressure losses associated with changes in flow cross section) In principle, this procedure fixes all the major geometrical variables of the design. The space velocity is determined in a laboratory test in which the hyrodynamical variables are considerably different from the commercial LFR situation. In the lab test, the gas is passed at a relatively large linear velocity through a catalyst bed with a large height/diameter (H/D) ratio. In the commercial reactor, the situation is quite the reverse (small linear velocity, small H/D ratio). The flow through a thin catalyst slab in which there could be Significant local variations in bed porosity, is characterized by a spread of gas residence times in the bed which results in loss of NOx conversion. In a practical design this must be compensated by the use of an extra amount of catalyst (over and above the amount calculated on the basis of the lab tests). A proprietary mathematical model was developed in which all the factors which cause a loss of conversion are quantified. Using this model, a correction factor is calculated to compensate for these losses. 5 |