Process and apparatus for the polymerisation of olefins

A process for the gas phase polymerisation of olefins in a fluidised bed reactor, which process comprises:

• a) passing a fluidising gas comprising one or more olefin monomers through a fluidised bed of polymer particles in the presence of a polymerisation catalyst,
• b) withdrawing a first gaseous stream comprising solid particles from the top of the reactor,
• c) passing the first gaseous stream to a gas/solids separator, separating solid particles therefrom, and forming a second gaseous stream comprising residual solid particles,
• d) passing at least a portion of the second gaseous stream to one or more heat exchangers to remove heat of reaction, wherein residual solid particles contact the heat exchanger, and
• e) recycling at least a portion of the cooled stream from step (d) as the fluidising gas in step (a),
• characterised in that the rate of fouling of the one or more heat exchangers is such that
• i) the increase in pressure drop across the heat exchangers is equivalent to less than 5% per year, and/or
• ii) the decrease in heat transfer of the heat exchangers is equivalent to less than 5% per year.

A process for the gas phase polymerisation of olefins in a fluidised bed reactor, which process comprises:

• a) passing a fluidising gas comprising one or more olefin monomers through a fluidised bed of polymer particles in the presence of a polymerisation catalyst to produce polymer at a polymer production rate of C Tonnes/hour,
• b) withdrawing a first gaseous stream comprising solid particles from the top of the reactor,
• c) passing the first gaseous stream to a gas/solids separator, separating solid particles therefrom, and forming a second gaseous stream comprising residual solid particles,
• d) passing at least a portion of the second gaseous stream to one or more heat exchangers to remove heat of reaction, wherein residual solid particles contact the heat exchanger, and
• e) recycling at least a portion of the cooled stream from step (d) as the fluidising gas in step (a),
• characterised in that the one or more heat exchangers have a heat exchange surface area which totals less than 120×C m2.

A process for the gas phase polymerisation of olefins in a fluidised bed reactor, which process comprises:

• a) passing a fluidising gas comprising one or more olefin monomers through a fluidised bed of polymer particles in the presence of a polymerisation catalyst at a first temperature, TR1, to produce a first polymer,
• b) withdrawing a first gaseous stream comprising solid particles from the top of the reactor,
• c) passing the first gaseous stream to a gas/solids separator, separating solid particles therefrom, and forming a second gaseous stream comprising residual solid particles,
• d) passing at least a portion of the second gaseous stream to one or more heat exchangers to remove heat of reaction, wherein residual solid particles contact the heat exchanger, and where at the point of first contact with the one or more heat exchangers the second gaseous stream having a temperature, TH1 and
• e) recycling at least a portion of the cooled stream from step (d) as the fluidising gas in step (a), and
• f) transitioning the reaction in the fluidised bed reactor to one comprising steps (a) to (e) as above except that step (a) is operated at a second temperature, TR2, to produce a second polymer, and that at the point of first contact with the one or more heat exchangers the second gaseous stream has a temperature, TH2, TR2 being higher than TR1 and TH2 being higher than TH1, characterised in that TH2 is above the melting temperature of the first polymer.

An apparatus for the gas phase polymerisation of olefins in a fluidised bed reactor having a maximum designed production capacity of C Tonnes/hour, which apparatus comprises:

• a) a fluidised bed reaction zone,
• b) an outlet located at the top of the reaction zone for withdrawing a first gaseous stream comprising solid particles from the top of the reactor,
• c) a gas/solids separator for separating solid particles from the first gaseous stream to form a second gaseous stream comprising residual solid particles,
• d) one or more heat exchangers to which at least a portion of the second gaseous stream is passed, and where no means, such as filters, which completely remove the solids from the second gaseous stream are present between the gas/solids separator and the one or more heat exchangers, and
• e) a recycle line for recycling at least a portion of the cooled second gaseous stream as the fluidising gas to the fluidised bed reaction zone,
• characterised in that the one or more heat exchangers have a heat exchange surface area which totals less than 120×C m2.