Interlock and process

1. An interlock for use in a process for degassing of a polymer powder in a degassing vessel, which interlock comprises

a. measuring the temperature of the vapour phase resulting from a liquid-vapour separation, which vapour phase is used as a purge gas in a degassing vessel,

b. comparing said measured temperature to a threshold value, and

c. in the event that the measured temperature is above the threshold value then the use of the vapour as purge gas is stopped or reduced.

2. An interlock for use in a process for degassing of a polymer powder in a degassing vessel, which interlock comprises:

a. measuring:

1) the liquid level,

2) the temperature of the vapour phase, and

3) the pressure of the vapour phase,

for a liquid-vapour separation using a liquid-vapour separation vessel from which the resulting vapour phase is removed and used as a purge gas,

b. comparing each of said measured parameters to a corresponding threshold value, and

c. in the event that one or more of the following apply:

i) the measured liquid level is above its defined threshold value,

ii) the measured temperature is above its defined threshold value, or

iii) the measured pressure is below its defined threshold value

then the use of the removed resulting vapour as purge gas is stopped or reduced.

3. An interlock according to claim 1 wherein the liquid-vapour separation vessel is downstream of a condensation/compression system, by which is meant a system in which the purge gas is cooled and compressed in order that hydrocarbons removed from the degassed polymer condense to form the liquid phase in the separation vessel.

4. n interlock according to claim 2 wherein the liquid-vapour separation vessel is downstream of a condensation/compression system, by which is meant a system in which the purge gas is cooled and compressed in order that hydrocarbons removed from the degassed polymer condense to form the liquid phase in the separation vessel.

5. A process for the degassing of a polymer powder in a degassing vessel, which process comprises:

a. passing polymer powder and purge gas to a degassing vessel wherein the purge gas contacts the polymer powder,

b. removing degassed polymer from the degassing vessel

c. removing a stream comprising the purge gas and degassed hydrocarbons from the degassing vessel,

d. passing the removed stream to a liquid-vapour separation vessel wherein there is present a liquid phase comprising at least some of the degassed hydrocarbons and a vapour phase comprising the purge gas, and

e. recycling vapour resulting from the separation vessel as purge gas in step (a)

wherein the temperature of the vapour phase resulting from the liquid-vapour separation is measured, and that in the event that the temperature measurement indicates a loss in separation efficiency in the separation vessel then the recycling of the resulting vapour as purge gas is stopped or reduced.

6. A process for the degassing of a polymer powder in a degassing vessel, which process comprises:

a. passing polymer powder and purge gas to a degassing vessel wherein the purge gas contacts the polymer powder,

b. removing degassed polymer from the degassing vessel

c. removing a stream comprising the purge gas and degassed hydrocarbons from the degassing vessel,

d. passing the removed stream to a liquid-vapour separation vessel wherein there is present a liquid phase comprising at least some of the degassed hydrocarbons and a vapour phase comprising the purge gas, and

e. recycling vapour resulting from the separation vessel as purge gas in step (a)

wherein there are measured

1) the liquid level,

2) the temperature of the vapour phase, and

3) the pressure of the vapour phase,

for the liquid-vapour separation using the liquid-vapour separation vessel, and that in the event that these measurements indicate a loss in separation efficiency in the separation vessel then the recycling of the resulting vapour as purge gas in step (e) is stopped or reduced.

7. A process according to claim 5 wherein the stream comprising the purge gas and degassed hydrocarbons is passed through a condensation/compression system, by which is meant a system in which the purge gas is cooled and compressed in order that hydrocarbons removed from the degassed polymer condense to form the liquid phase in the separation vessel.

8. A process according to claim 6 wherein the stream comprising the purge gas and degassed hydrocarbons is passed through a condensation/compression system, by which is meant a system in which the purge gas is cooled and compressed in order that hydrocarbons removed from the degassed polymer condense to form the liquid phase in the separation vessel.

9. A process according to claim 5 wherein the purge gas comprises nitrogen.

10. A process according to claim 6 wherein the purge gas comprises nitrogen.

11. A process according to claim 5 wherein the reduction in quantity of purge gas from the separation vessel is compensated for by use of an alternative purge gas.

12. A process according to claim 6 wherein the reduction in quantity of purge gas from the separation vessel is compensated for by use of an alternative purge gas.

13. A process according to claim 5 wherein the polymer powder particles to be degassed are obtained from a gas phase polymerisation process or a slurry polymerisation process.

14. A process according to claim 6 wherein the polymer powder particles to be degassed are obtained from a gas phase polymerisation process or a slurry polymerisation process.

15. A process according to claim 5 wherein the polymer powder particles are polyethylene or polypropylene.

16. A process according to claim 6 wherein the polymer powder particles are polyethylene or polypropylene.