Process and apparatus for the polymerisation of olefins

1. 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),

wherein the one or more heat exchangers have a heat exchange surface area which totals less than 120×C m 2 .

2. A process according to claim 1 wherein the linear velocity of the second gaseous stream through the one or more heat exchangers is at least 3 m/s.

3. A process according to claim 2 wherein the linear velocity of the second gaseous stream through the one or more heat exchangers is in the range 5 to 20 m/s.

4. A process according to claim 1 wherein the cut size of the gas/solids separator is 20 microns.

5. A process according to claim 1 wherein the fluidised bed reactor comprises a vertically orientated cylindrical reaction zone, above which is located a disengagement zone, and the disengagement zone has a maximum horizontal cross-sectional area, A2, which is between 3.2 and 6 times the cross-sectional area, A1, of the cylindrical reaction zone.

6. A process according to claim 1 the rate of fouling of a fluidisation grid located at the base of the fluidised bed in the reactor is such that increase in pressure drop across the grid is equivalent to less than 5% per year.

7. A process according to claim 1 wherein the rate of fouling of a compressor located in the recycle loop, as measured by the increase in temperature differential across the compressor is such that the increase is equivalent to less than 5% per year.

8. 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 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,

wherein the one or more heat exchangers have a heat exchange surface area which totals less than 120×C m 2 .

9. A process according to claim 2 wherein the linear velocity of the second gaseous stream through the one or more heat exchangers is at least 5 m/s.