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A fluid dynamic model having at least 5,000,000 cells of the portion of a gas phase reactor from the exit of the condenser to a half a reactor diameter above the bed plate is useful in determining the design of the bottom surface or support structure for a bed plate to minimize liquid pooling below

A fluid dynamic model having at least 5,000,000 cells of the portion of a gas phase reactor from the exit of the condenser to a half a reactor diameter above the bed plate is useful in determining the design of the bottom surface or support structure for a bed plate to minimize liquid pooling below and above the bed plate when operating in condensing mode.

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1. A method of operating a fluidized bed reactor in condensed mode having in cooperating arrangement a bed plate and a grid supporting a circular bed plate for a gas phase polymerization reactor having a fluidized bed of polymeric particles, a discharge port within half the diameter of the bed plate

1. A method of operating a fluidized bed reactor in condensed mode having in cooperating arrangement a bed plate and a grid supporting a circular bed plate for a gas phase polymerization reactor having a fluidized bed of polymeric particles, a discharge port within half the diameter of the bed plate above the bed plate, said grid comprising a series of vertical baffles traversing the underside of the bed plate dividing the area below the bed plate into a series of cells so that from below the grid an upwardly directed jet comprising monomers, ballast gas and from 3 to 40 weight % of dispersed condensed hydrocarbons having a velocity sufficient to fluidize the bed, does not experience a raceway across the bed plate and a gas phase, and a condensed phase are substantially homogeneously distributed over not less than 80% of an area of available flow path through the bed plate,said method comprising on a computer:i. modeling an operation of the reactor including: a) building a three dimensional model of the reactor from an outlet of a heat exchanger to the top of a lowest discharge port, including a deflector plate, the bed plate having descending vertical baffles and a fluid zone representing the fluidized bed of polymer particles between the discharge port and the bed plate (hereinafter the modeled section of the reactor), and modeling a gas and liquid phase using Computational Fluid Dynamics software;b) dividing the model into not less than 5,000,000 cells;c) modeling the flow of a gas at a temperature from 25° C. to 120° C. and a pressure from 1700 kPa (250 psi) to 3445 kPa (500 Psi) comprising monomers, ballast gas and from 3 to 30 wt % of one or more condensed liquids having a density from 0.60 g/cc to 0.70 g/cc and an inlet normal droplet distribution from 25 to 500 microns through the modeled section of the reactor at a flow rate sufficient to fluidize the bed;d) optionally modeling liquid film formation on zones where gas and liquid impinge on mechanical components of the reactor including walls, leading to formation of larger or smaller dropletsii. determining one or more of: e) a flow pattern of gas and liquid below the bed plate;f) a change in the particle size distribution of the liquid phase due to impingement of the gas on mechanical components of the reactor including one or more of: filming formation, film stripping, turbulent breakup of droplets, and droplet coalescence due to flow patterns arising from the vertical baffles;g) a flow pattern above the bed plate of gas, liquid(s) and polymer particles up to a distance of one half the diameter of the bed plate;h) a height above the bed plate at which 80% of the droplets have evaporated;i) a distribution of droplet size above the bed plate;j) a propensity for liquid pooling above the bed plate; andiii. iteratively repeating step ii) for different flow rates but the same composition of inlet gas and liquid loading and recording the results;iv. comparing the results from step iii) to determine operating conditions at which liquid(s) flow through the bed plate without biasing liquids across, and either below or immediately above, the bed plate. 2. The method according to claim 1, further comprising iteratively varying one or more of the composition of the inlet gas, the composition and loading of liquid in the inlet gas, storing the calculated results; andcomparing the stored results to determine one or more of a preferred composition of the gas phase, the composition of the liquid and the loading of the liquid. 3. The method according to claim 1 further comprising iteratively varying the design of the grid, storing the calculated results; andcomparing the stored results to determine one or more of a preferred design for the grid. 4. The method according to claim 1, wherein the monomers comprise not less than 70 wt % ethylene and up to 30 wt % of one or more C4-8 alpha olefins. 5. The method according to claim 1, wherein an induced condensing agent is present in an amount to provide from 3 to 40 wt % of liquids based on the weight of a recycle gas flow at a reactor inlet and comprises a non-polymerizable hydrocarbon or fluorocarbon. 6. The method according to claim 5, wherein the operating conditions in step i c) for the reactor are at a temperature from 75° C. to 110° C. and a pressure from 1800 kPa (260 psi) to 2400 kPa (350 psi).