A regulation method for regulating the temperature in a reactor utilized in the polymerization of olefins

Abstract: The invention relates to a regulation method for regulating the temperature in a reactor (10) utilized in the polymerization of olefines. A circulating gas is led to the reactor (10) along a circulating-gas flow line (11) and the circulating gas is cooled by leading part of the circulating gas flowing along a circulating-gas flow line along a by-pass flow line (22) through a cooler (23). A regulating device (21) for the circulating-gas inlet-flow temperature controls the amount of the circulating-gas by-pass flow along a circulating-gas by-pass flow line (22) through the cooler (23) such that the sum of the openings of a valve (24) in the circulating-gas flow line (11) and a valve (25) in the circulating-gas by-pass flow line (22) is maintained essentially constant in the range of 90-120%.

Description: The invention relates to a regulation method for regulating the temperature in a reactor utilized in the polymerization of olefins, in which method a circulating gas is led to the reactor along a circulating-gas flow line and the circulating gas is cooled by leading the circulating gas through a cooler. In the methods known from prior art, the circulating gas is led to the reactor via a straight pipe line provided with a cooler. This known regulation method is extremely slow, due to which the temperature of the circulating gas cannot rapidly be changed. US-A-3229754 relates to the control of the polymerization of olefins in the presence of a solvent and a catalyst at a substantially constant temperature. It discloses a temperature control system to maintain a reactor at a constant and predetermined temperature. The refrigeration of the reactor is done by means of a fluid passing through a cooler. The object of the invention is to provide an improvement in the currently known reactor-temperature regulating methods. The objects of the invention are achieved by means of a regulation method, which is mainly characterized in that a circulating gas is cooled by leading part of the circulating gas flowing along a circulating-gas flow line along a by-pass flow line through a cooler, and that a regulating device for the circulating-gas inlet-flow temperature controls the amount of the circulating-gas by-pass flow along a circulating-gas by-pass flow line through a cooler such that the sum of the openings of a valve in the circulating-gas flow line and a valve in the circulating-gas by-pass flow line is maintained essentially constant in the range of 90-120%. The inventive regulation method provides certain important advantages. The inventive regulation method makes a rapid regulation possible, owing to which the temperature of the circulating gas may be changed sufficiently rapidly. When the valve is controlled according to the inventive method, no detrimental fluctuations occur in the inlet flow of the circulating gas into the reactor. The sum of the openings of the valves is always maintained essentially constant in the range of 90-120%. On the basis of practical experience, a preferable range is 105-115% and the most preferable value is reached in the range of about 110%. The invention is described in detail with reference to a certain preferred inventive embodiment shown in the accompanying drawings, to which embodiment the invention is not intended solely to be limited. Fig. 1 shows as a process flowchart a circulating-gas reactor utilized in the polymerization of olefins. Fig. 2 shows as a block diagram a certain preferred embodiment of an inventive regulation method. In Fig. 1, a circulating-gas reactor utilized in the polymerization of olefins is generally referred to by a reference number 10. A circulating-gas flow line 11 leads to the reactor 10. The circulating gas exits from the reactor 10 along a circulating-gas return flow line 12 to a separator 13, which is preferably a cyclone separator, and further along a line 14 back to a circulating-gas compressor 15. A partial flow may be, when so desired, led from the circulating-gas flow line 11 leading to the reactor 10 as a cyclic flow along a flow line 16 back to the circulating-gas compressor 15. The temperature of the reactor 10 is measured by means of one or more temperature measuring devices. Fig. 1 shows temperature measuring devices 17, 18 and 19. The temperature regulating device of the reactor 10 is referred to by a reference number 20. The temperature regulating device 20 of the reactor 10 controls a circulating-gas inlet-flow-temperature regulating device 21. The circulating gas is cooled by leading part of the circulating gas flowing along the flow line 11 along a by-pass flow line 22 through a cooler 23. The circulating-gas flow line 11 is provided with a valve 24 and the by-pass flow line 22 passing through the circulating-gas cooler 23 is provided with a valve 25. A cooling medium flows along a return line 26 to a pump 27 and further along a flow line 28 to the cooler 23. The heated cooling medium exits from the cooler 23 along a return flow line 29. The return line 29 is provided with a valve 33, and by regulating this valve 33 part of the heated cooling medium may be led along a flow line 34 as a cyclic flow back to the cooling cycle. The inventive regulation method is as follows. The reactor 10 is cooled by means of the circulating-gas cooler 23 for removing the polymerization heat. The temperature regulating device 20 of the reactor 10 provides a set value for the circulating-gas inlet-flow temperature regulating device 21. The circulating-gas inlet-flow temperature regulating device 21 controls the amount of the by-pass flow along the circulating-gas by-pass flow line 22 through the cooler 23. This is achieved by controlling the opening of the valves 24 and 25 such that the sum of the openings of the valves 24 and 25 is always essentially constant, preferably 110%. The temperature of the cooling medium may be adjusted in two alternative ways. The first way is as follows. A set value is provided for the temperature of the heated cooling medium leaving from the cooler 23. A cooling-medium return-flow temperature regulating device 30 regulates the temperature of the heated returning cooling medium by omitting part of the heated medium flow from a cyclic flow 29,34 and 28 and by substituting it for a cold cooling medium. The amount of the cooling medium passing through the circulating-gas cooler 23 is maintained essentially constant. This way is preferable, when the circulating gas contains a substantial amount of heavy components, which tend to condensate, if the temperature of the circulating gas is too low. This way provides for the temperature of the circulating gas a minimum value. The second way is as follows. A set value of the opening of the valve 24 is transmitted to a monitor 35. If the position value of the opening of the valve 24 deviates from the set value of the opening of the valve 24, the set value of a cooling-medium inlet-flow temperature regulating device 36 changes too, whereby the position value of the opening of the valve 24 again returns to its set value. This function is relatively slow, and it does not cause any disturbances for the circulating-gas inlet-flow temperature regulation device 21. The cooling-medium inlet-flow temperature regulating device 36 regulates the temperature of the cooling medium by omitting part of the heated cooling medium leaving the cooler 23 from the cyclic flow 29,34 and 28 and by substituting it for a cold cooling medium. This way is preferable, when there are no limitations to the temperature of the cooling medium. This way allows the valves 24 and 25 to be maintained approximately in their optimal positions during the entire period of time, i.e. the valve 24 is open by 70% and the valve 25 is open by 40%, whereas the valves 24 and 25 may yet be in the range to be regulated, and the valve 25 still is relatively much capable of opening more, which, if needed, thereby increases the cooling capacity of the circulating-gas cooler 23. In Fig. 1, a reference number 32 refers to a switch, which is controlled by the cooling-medium return-flow temperature regulating device 30 and correspondingly a cooling-medium inlet-flow temperature regulating device 36. The switch 32 in turn controls the valve 33 in the return flow line 29. As is apparent from the block diagram of Fig. 2, the temperature of the reactor 10 is measured by means of any of the four temperature measuring devices 17,18,19 and 37. The temperature measuring signals are transmitted via a function means 38 as a measuring value m₁ to the temperature regulating device 20 of the reactor 10. The set value of the temperature regulating device 20 of the reactor 10 is referred to by a letter a₁. The outlet of the temperature regulating device 20 of the reactor 10 is transmitted via a multiplification operator 39 as a set value a₂ to the cooling-medium inlet-flow temperature regulating device 21. A temperature measuring device 40 measures the temperature of the circulating gas flowing in the circulating gas flow line 11 and provides a measuring value m₂ for the circulating-gas inlet-flow temperature regulating device 21. The outlet of the circulating-gas inlet-flow temperature regulating device 21 is transmitted to a function means 41, which controls the position of the valves 24 and 25. The outlet of the circulating-gas inlet-flow temperature measuring device 21 is transmitted to the monitor 35 as a measuring value m₃. The outlet m₃ is thus the current position value of the opening of the valve 24. A set value a₃ of the opening of the valve 24 is transmitted to the monitor 35. The outlet of the monitor is led to the cooling-medium inlet-flow temperature regulating device 36 as a set value a₄. A measuring value m₄ of the inlet flow temperature of the cooling medium is transmitted to the cooling-medium inlet-flow temperature regulating device 36. The outlet of the cooling-medium inlet-flow temperature regulating device 36 controls via the switch 32 the valve 33 in the return flow line 29. A set value a₅ is transmitted to the cooling-medium return-flow temperature regulating device 30, and a set value m₅ of the return-flow temperature of the cooling medium is transmitted to the regulating device 30. The outlet of the cooling-medium return-flow temperature regulating device 30 is transmitted via the switch 32 as a control for the valve 33 in the return flow line 29. The inventive regulation method provides for the reactor 10 more flexibility for producing various polyolefins within a wide operating range of the reactor conditions. The invention relates to a regulation method for regulating the temperature in a reactor (10) utilized in the polymerization of olefins. A circulating gas is led to the reactor (10) along a circulating-gas flow line (11) and the circulating gas is cooled by leading part of the circulating gas flowing along a circulating-gas flow line along a by-pass flow line (22) through a cooler (23). A regulating device (21) for the circulating-gas inlet-flow temperature controls the amount of the circulating-gas by-pass flow along a circulating-gas by-pass flow line (22) through the cooler (23) such that the sum of the openings of a valve (24) in the circulating-gas flow line (11) and a valve (25) in the circulating-gas by-pass flow line (22) is maintained essentially constant in the range of 90-120%.

Claims: A regulation method for regulating the temperature in a reactor (10) utilized in the polymerization of olefins, in which method a circulating gas is led to the reactor (10) along a circulating-gas flow line (11) and the circulating gas is cooled by leading the circulating gas through a cooler (23), characterized in that the circulating gas is cooled by leading part of the circulating gas flowing along a circulating-gas flow line (11) along a by-pass flow line (22) through a cooler (23), and that a regulating device (21) for the circulating-gas inlet-flow temperature controls the amount of the circulating-gas by-pass flow along a circulating-gas by-pass flow line (22) through the cooler (23) such that the sum of the openings of a valve (24) in the circulating-gas flow line (11) and a valve (25) in the circulating-gas by-pass flow line (22) is maintained essentially constant in the range of 90-120%. A regulation method according to Claim 1, characterized in that said range is 105-115%, preferably ca. 110%. A regulation method according to Claim 1 or 2, characterized in that the temperature of a cooling medium to be led to the cooler (23) is regulated by providing for a cooling-medium return-flow temperature regulating device (30) a set value (a₅) and by transmitting a measuring value (m₅) of the cooling-medium return-flow temperature to the cooling-medium return-flow temperature regulating device (30), whereby the cooling-medium return-flow temperature regulating device (30) regulates the temperature of the heated returning cooling medium by omitting part of the heated cooling-medium flow from a cyclic flow (29,34 and 28) and by substituting it for a cold cooling medium. A regulation method according to Claim 1 or 2, characterized in that the temperature of a cooling medium to be led to the cooler (23) is regulated by providing for a cooling-medium inlet-flow temperature regulating device (36) a set value (a₄) and by transmitting a measuring value (m₄) of the cooling-medium inlet-flow temperature to the cooling-medium inlet-flow temperature regulating device (36), whereby the cooling-medium inlet-flow temperature regulating device (36) regulates the inlet-flow temperature of the cooling medium by omitting part of the heated cooling-medium, leaving from the cooler (23), from the cyclic flow (29,34 and 28) and by substituting it for a cold cooling medium. A regulation method according to Claim 4, characterized in that a set value (a₃) of the opening of a valve (24) in the circulating-gas flow line (11) and a position value (m₃) of the current opening of the valve (24) are transmitted to a monitor (35), whereby, when the position value (m₃) of the opening of the valve (24) deviates from the set value (a₃) of the opening of the valve (24), the set value (a₄) of the cooling-medium inlet-flow temperature regulating device (36) changes too, as a result of which the position value (m₃) of the opening of the valve (24) again returns to its set value (a₃). A regulation method according to any of the Claims 1-5, characterized in that the temperature regulating device (20) of the reactor (10) transmits a set value (a₂) to the circulating-gas inlet-flow temperature regulating device (21) and that a measuring value (m₂) of the temperature of the circulating gas flowing in the circulating-gas flow line (11) is transmitted to the circulating-gas inlet-flow temperature regulating device (21), whereby the outlet of the circulating-gas inlet-flow temperature regulating device (21) controls the position of the valves (24,25).

Inventors: PALMROOS ARI, TAKAKARHU JOUNI, PALMROOS, ARI, TAKAKARHU, JOUNI
Applicants: BOREALIS POLYMERS OY
Application year: 1992
Main classification: G05D23
IPC codes: G05D23, C08F2, C08F10, B01J8, B01J19