A method for waste heat recovery from a plant for polymerising olefins

Abstract

The present invention relates to a method for waste heat recovery from a plant for polymerising olefins. The method comprises transferring heat from a stage of the polymerisation process to a first fluid to provide a heated first fluid; and supplying the heated first fluid to an adsorption or absorption chiller. The method comprises chilling a second fluid using the chiller to provide a chilled second fluid. Chilling the second fluid using the chiller comprises driving a refrigeration cycle of the chiller using the heated first fluid as the heat source such that heat from the stage of the polymerisation process is used in chilling the second fluid.

Description

[0001] A Method for Waste Heat Recovery from a Plant for Polymerising Olefins

[0002] The invention relates generally to a method for waste heat recovery. More particularly, the invention relates to a method for waste heat recovery from a plant for polymerising olefins. The plant may be for the production of polyethylene or polypropylene.

[0003] BACKGROUND

[0004] It is known that in a plant for polymerising olefins, heat is produced during stages of the polymerisation process. This is due, at least in part, to the process for the polymerisation of polymers, such as polyethylene and polypropylene, wherein an exothermic reaction takes place. Unfortunately, the heat generated during manufacturing, is often wasted (i.e. not put to a beneficial purpose) and typically released into the surrounding environment with the help of a cooling system. When heat is wasted, it can increase load on the cooling systems of the plant.

[0005] As such, there is a need to recover waste heat from a plant for polymerising olefins. Recovery of waste heat may help reduce the load on cooling systems of the plant thereby reducing the carbon footprint of the plant, reducing operation costs and improving sustainability. The present invention provides a solution to this need.

[0006] SUMMARY OF THE DISCLOSURE

[0007] According to an aspect of the invention there is provided a method for waste heat recovery from a plant for polymerising olefins, the method comprising:

[0008] (i) transferring heat from a stage of the polymerisation process to a first fluid to provide a heated first fluid;

[0009] (ii) supplying the heated first fluid to an adsorption or absorption chiller; and (iii) chilling a second fluid using the chiller to provide a chilled second fluid, wherein chilling the second fluid using the chiller comprises driving a refrigeration cycle of the chiller using the heated first fluid as a heat sourcesuch that heat from the stage of the polymerisation process is used in chilling the second fluid.

[0010] In the adsorption or absorption chiller, heat from the first fluid will drive the refrigerant around the chiller. An external source of electrical power is not needed to drive the refrigerant around this type of chiller. The method therefore allows waste heat from a plant to act as a power source for the chiller and provide a chilled fluid. As such, energy from the waste heat may be recovered. The chilled fluid may then be used to meet low temperature requirements of various equipment in a plant for manufacturing polyefins. Recovering the waste heat from a plant in in accordance with the invention, may reduce the energy consumption of the plant and the load on cooling water circuit of the plant which may include cooling water towers and / or sea-water coolers. If there is not sufficient chilled fluid to meet the low temperature requirements of various equipment in the plant, cooled water that is dependent on the ambient temperature and geographical location may be used instead to cool the equipment in the plant. This cooled water would have a higher temperature than the chilled water and would lead to more purges to recovery units and, possibly, venting via a flare. As the chilled fluid provided by the method may be used to meet low temperature requirements of various equipment in the plant, the number of gaseous purges from the plant may also be reduced thereby decreasing the carbon footprint. The present method therefore increases the energy recovery from waste-heat from the plant and reduces the environmental impact of the plant making the plant more sustainable.

[0011] The heated first fluid may have a temperature between 40 and 105 degrees C. Throughout the specification, a temperature range between an upper temperature limit and a lower temperature limit is inclusive of the upper temperature limit and the lower temperature limit. In certain embodiments, the heated first fluid may have a temperature between 40 and 80 degrees C, between 50 and 60 degrees C, between 50 and 80 degrees C, between 75 and 100 degrees C or between 95 and 105 degreesC. The temperature of the heated first fluid depends on the stage of the polymerisation process from which the heat is transferred.

[0012] The chilled second fluid may have a temperature between 2 and 30 degrees C.

[0013] The method may comprise using the chilled second fluid for cooling in the plant.

[0014] In one embodiment, the stage of the polymerisation process from which heat is transferred to the first fluid to provide a heated first fluid may comprise polymerising olefin to produce a polyolefin component in a reactor. Preferably, the reactor may be a loop reactor or a gas phase reactor (GPR).

[0015] The method step of transferring heat from the stage of the polymerisation process to the first fluid may comprise directing the first fluid through a cooling system of the reactor. As such, waste heat from the reactor may be used to drive the refrigeration cycle of the chiller.

[0016] When the reactor is a loop reactor, the heated first fluid preferably has a temperature from 50 to 60 degrees C. When the reactor is a GPR, the heated first fluid preferably has a temperature of between 50 to 80 degrees C. The first fluid may comprise water.

[0017] The method may comprise returning the first fluid from the chiller to the cooling system of the reactor. As the heated first fluid is used as heat source in the chiller, the first fluid is cooled in the chiller (i.e. the temperature of the first fluid decreases as is passes through the chiller). Therefore, once the heated first fluid has been used as heat source in the chiller, the cooled first fluid may be directed from the chiller to the cooling system of the reactor so that the method may be repeated.

[0018] In certain embodiments, the polymerisation process may comprise a first stage comprising polymerising olefin to produce a first polyolefin component in a firstreactor, preferably a loop reactor, and a second stage comprising polymerising olefin to produce a second polyolefin component in the presence of the first polyolefin in a gas phase reactor. Heat may be transferred from the first stage and / or second stage to the first fluid to provide a heated first fluid. As such, waste heat from the first and / or second stage may be used to drive the refrigeration cycle of the chiller.

[0019] In another embodiment, the stage of the polymerisation process comprises extruding pellets of the polymer in an underwater pelletizing system. As such, waste heat from the underwater pelletizing system may be used to drive the refrigeration cycle of the chiller.

[0020] The first fluid may comprise water from the underwater pelletizing system.

[0021] In such embodiments, the heated first fluid may have a temperature between 40 and 60 degrees C.

[0022] The method may comprise returning the first fluid from the chiller to the underwater pelletizing system. Therefore, once the heated first fluid has been used as heat source in the chiller, the first fluid may be directed from the chiller to the underwater pelletizing system so that the method may be repeated.

[0023] In another embodiment, the first fluid may comprise circulation gas from a gas phase reactor. The stage of the polymerisation process may comprise polymerising olefin to produce a second polyolefin component in the presence of a first polyolefin component in the gas phase reactor.

[0024] In such embodiments, the heated first fluid may have a temperature of between 75 and 100 degrees C.The method may comprise directing the first fluid from the chiller to a cooler for gas phase reactor circulation gas such that temperature of the circulation gas is reduced in the chiller prior to the circulation gas entering the cooler.

[0025] In an embodiment, the heated first fluid may comprise a steam condensate generated during a stage of the polymerisation process. In such embodiments, the heated first fluid has a temperature between 95 and 105 degrees C.

[0026] Herein is disclosed a reactor assembly for a plant for polymerising olefins, the assembly comprising:

[0027] a reactor for polymerising olefin;

[0028] heat transfer means arranged to transfer heat from the reactor or a component or medium thermally coupled thereto to a first fluid to provide a heated first fluid; and

[0029] an adsorption or absorption chiller arranged to receive the heated first fluid such that the heated first fluid is configured to provide a heat source to drive a refrigeration cycle of the chiller.

[0030] Herein is disclosed a reactor assembly for a plant for polymerising olefins, the assembly comprising:

[0031] a loop reactor for polymerising olefin to produce a first polyolefin component; a cooling system for the loop reactor, the cooling system comprises a first fluid thermally coupled to the loop reactor such that heat is transferable from the loop reactor to the first fluid; and

[0032] an adsorption or absorption chiller fluidly connected to the cooling system such that the first fluid from the cooling system is configured to provide a heat source to drive a refrigeration cycle of the chiller.

[0033] Herein is disclosed a reactor assembly for a plant for polymerising olefins, the assembly comprising:a gas phase reactor for polymerising olefin to produce a second polyolefin component in the presence of a first polyolefin component, said gas phase reactor having a circulation gas inlet and a circulation gas outlet;

[0034] a circulation line for circulating circulation gas, the circulation line fluidly connecting the circulation gas inlet to the circulation gas outlet;

[0035] a cooling system disposed on the circulation line for cooling the circulation gas, the cooling system comprises a first fluid thermally coupled to the circulation line such that heat is transferable from the circulation gas to the first fluid; and

[0036] an adsorption or absorption chiller fluidly connected to the cooling system such that the first fluid from the cooling system is configured to provide a heat source to drive a refrigeration cycle of the chiller.

[0037] Herein is disclosed a reactor assembly for a plant for polymerising olefins, the assembly comprising:

[0038] a gas phase reactor for polymerising olefin to produce a second polyolefin component in the presence of a first polyolefin component, said gas phase reactor having a circulation gas outlet;

[0039] a circulation line for circulating circulation gas, the circulation line fluidly connected to the circulation gas outlet;

[0040] a flush line for fluidly connected to the circulation line, the flush line being configured to receive circulation gas from the circulation line;

[0041] a cooling system disposed on the fluidisation line for cooling circulation gas, the cooling system comprises a first fluid thermally coupled to the flush line such that heat is transferable from the circulation gas to the first fluid; and

[0042] an adsorption or absorption chiller fluidly connected to the cooling system such that the first fluid from the cooling system is configured to provide a heat source to drive a refrigeration cycle of the chiller.

[0043] Herein is disclosed a reactor assembly for a plant for polymerising olefins, the assembly comprising:a gas phase reactor for polymerising olefin to produce a second polyolefin component in the presence of a first polyolefin component, said gas phase reactor having a circulation gas inlet and a circulation gas outlet;

[0044] a circulation line for circulating circulation gas, the circulation line fluidly connecting the circulation gas inlet to the circulation gas outlet;

[0045] a cooling system disposed on the circulation line for cooling the circulation gas; an auxiliary cooling system disposed on the circulation line for cooling the circulation gas, wherein the auxiliary cooling system is upstream of the cooling system; wherein the auxiliary cooling system comprises a first fluid thermally coupled to the circulation line such that heat is transferable from the circulation gas to the first fluid; and

[0046] an adsorption or absorption chiller fluidly connected to the auxiliary cooling system such that the first fluid from the auxiliary cooling system is configured to provide a heat source to drive a refrigeration cycle of the chiller.

[0047] Herein is disclosed a reactor assembly for a plant for polymerising olefins, the assembly comprising:

[0048] a gas phase reactor for polymerising olefin to produce a second polyolefin component in the presence of a first polyolefin component, said gas phase reactor having a circulation gas inlet and a circulation gas outlet;

[0049] a circulation line for circulating circulation gas, the circulation line fluidly connecting the circulation gas inlet to the circulation gas outlet;

[0050] an adsorption or absorption chiller disposed on the circulation line, wherein the chiller is connected to the circulation line such that the circulation gas provides a heat source configured to drive a refrigeration cycle of the chiller; and

[0051] a cooling system disposed on the circulation line for cooling the circulation gas, wherein the cooling system is downstream of the chiller such that, during use, the temperature of the circulation gas is reduced in the chiller prior to the circulation gas entering the cooling system.BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures, in which:

[0053] Figure 1 schematically shows a plant for polymerising olefins;

[0054] Figure 2 shows a flowchart of a method according to an embodiment of the invention;

[0055] Figure 3 schematically shows a chiller for use in the method of Figure 2; Figure 4 schematically shows a reactor assembly for use in the method of Figure 2; and

[0056] Figure 5 schematically shows a reactor assembly for use in the method of Figure 2.

[0057] DETAILED DESCRIPTION

[0058] Figure 1 schematically shows a plant 50 for polymerising olefins. The plant may, for example, be for a plant for the production of polyethylene or polypropylene.

[0059] The plant 50 comprises one or more loop reactors 1. The loop reactors 1 may be for polymerising olefin to produce a first polyolefin component. For example, an olefin monomer, such a propylene, may be polymerised in the loop reactors 1 to produce a first polymer component. Each loop reactor 1 may comprise a cooling system 1a for cooling the reactor 1.

[0060] Downstream of the loop reactors 1 the plant 50 comprises a gas phase reactor 2 for producing a second polymer component. The gas phase reactor 2 is configured to receive reactor effluent from the loop reactors 1. The gas phase reactor 2 may be for polymerising a second polyolefin component in the presence of the first polyolefin in a gas phase reactor 2. For example, a further olefin monomer may be polymerised to form a second polymer component in the presence of the first polymer component inthe gas phase reactor 2. Although only a single gas phase reactor 2 is shown, the plant 50 may comprise a plurality of gas phase reactors connected in series.

[0061] The gas phase reactor 2 may be a fluidised bed reactor. A circulation line 8 for circulating circulation gas may be connected to the gas phase reactor 1. The circulation gas may be fluidisation gas. The circulation line 8 may be configured to direct circulation gas exiting the top of the gas phase reactor 2 to the bottom to the gas phase reactor 2. The gas phase reactor may have a circulation gas inlet and a circulation gas outlet. The circulation line 8 fluidly connects the circulation gas outlet to the circulation gas inlet. The circulation line 8 may comprise inlets 7 for introducing further components in the gas phase reactor 2, e.g. further olefin monomer, optional alpha olefin and optional hydrogen.

[0062] A cooling system 10 of the gas phase reactor 2 is disposed on the circulation line 8 for cooling the circulation gas prior to the circulation gas being reintroduced into the gas phase reactor 2. The cooling system 10 may help regulate the temperature of the gas phase reactor 2. The cooling system 10 may comprise a heat exchanger.

[0063] A compressor 9 is disposed on the circulation line 8 for compressing the circulation gas prior to the circulation gas being reintroduced into the gas phase reactor 2. The compressor 9 is preferably positioned upstream of the cooling system 10.

[0064] A flush line 11 may extend from the circulation line 8. Circulation gas may be directed along the flush line 11 to cause the operating pressure in the gas phase reactor 2 to reduce. The fluid line 11 may comprise a cyclone 12 and a filter 13 to remove solid particles. The solid particles may be returned to the gas phase reactor 2 via lines 14a, 14b. The remaining gas stream may be directed to a distillation unit 6 via line 15 for recovering uncreated monomer. The flush line 11 may comprise a cooling system (not shown) for cooling gas directed along the flush line 11.The plant 50 may comprise a separation zone comprising a gas phase separator 3, a purge bin 4 a recovery unit 5 and the distillation unit 6.

[0065] The product steam from the gas phase reactor 2 is withdrawn and directed to a gas phase separator 3. The gas phase separator 3 allows a gaseous steam to be withdrawn via line 18. The gaseous steam is directed to the distillation unit 6 where it is distilled so recover unreacted monomer. The unreacted monomer may be recycled to, for example, the gas phase reactor 2.

[0066] From the gas phase separator 3, the product stream is directed to a purge bin 4 and may be purged, using for example nitrogen gas, producing a further gaseous steam including unreacted monomer. This gaseous steam is removed from the purge bin 4 and sent to the recovery unit 5 via line 19 to recover the purge gas and separate the purge gas from the unreacted monomer. The recovered purge gas may be returned to the purge bin 4 via line 21. The unreacted monomer may be recovered in the distillation unit 6 and recycled.

[0067] Product (i.e. polymer) may also be removed from the purge bin via line 20 and sent to an extrusion and pelletizing area. The extrusion and pelletizing area comprises an extruder unit 25 which may be used to extrude and homogenise the product. The product may then be sent to an underwater pelletizing system 26 in which the in molten polymer strands are cut and cooled to form pellets. The pellets are transported by a water stream of the system 26 into a drier for further processing.

[0068] The plant 50 shown in Figure 1 may also comprise a cooling water circuit (not shown). The cooling water circuit may comprise one or more cooling water towers (not shown) or sea-water coolers (not shown) and one or more cooling water pumps (not shown) configured to pump cooling water through the system. The cooling water circuit may be fluidly or thermally coupled the cooling system 1a of the loop reactors 1, the cooling system 10 of the gas phase reactor 2 and the underwater pelletizing system 26. Thecooling water circuit may also be configured to cool additional components and processes in the plant 50. For example, whilst not shown in Figure 1, the purge bin 5, the recovery unit 5, distillation unit 6, extruder unit 25 and underwater pelletizing system 26 may be configured to be cooled by one or more cooling systems.

[0069] The skilled person will appreciate that the plant 50 may comprise additional features and components that those shown in Figure 1 and described above. Those shown in and described with reference to Figure 1 are included for understanding the present invention.

[0070] Figure 2 shows a method 100 according to an embodiment of the invention.

[0071] The method 100 is for the recovery of waste heat from a plant for polymerising olefins. Waste heat encompasses heat produced in the plant such as during polymerisation. The plant may, for example, be for a plant for the production of polyethylene or polypropylene. The method may be used with, but is not limited to use with, the plant 50 shown in Figure 2.

[0072] The method 100 comprises transferring heat 102 from a stage of the polymerisation process to a first fluid. This transfer of heat causes the temperature of the first fluid to increase. The step of transferring heat 102 from the stage of the polymerisation process to the first fluid therefore provides a heated first fluid.

[0073] The heated first fluid may have a temperature of from 40 to 105 degrees C. The temperature of the heated first fluid depends on which stage of the polymerisation process is used to transfer the heat to the first fluid as described further below.

[0074] The method 100 comprises supplying 104 the heated first fluid to an adsorption or absorption chiller 200 (shown in Figure 3). The heated first fluid provides a heat source for the chiller 200.Any suitable absorption or adsorption chiller known in the art may be used in the method. For completeness, the principles of operation of absorption or adsorption chillers are described. It is known to provide an absorption chiller comprising a condenser, a generator, an evaporator and an absorber where the generator contains a dilute solution of a refrigerant and an absorption material. The absorption chiller is used to chill a fluid and the fluid to be chilled is directed into the evaporator of the absorption chiller. During operation of the chiller, a heat source causes a refrigerant vapour to be released from the dilute solution in the generator. The absorption material remains in the solution so that the dilute solution becomes a concentrated solution. The heat source drives the refrigeration cycle in the chiller. The heat source may be provided by a heated fluid passing through a pipe within the generator. From the generator, the concentrated solution goes to be absorber whereas the refrigerant vapour goes to the condenser. In the condenser, the refrigerant vapour is cooled and condensed into a liquid refrigerant. The refrigerant may be cooled by a cooling fluid passing through a pipe within the condenser. From the condenser, the liquid refrigerant goes to the evaporator via an expansion valve which causes the temperature and pressure of the liquid refrigerant to decrease. As described above, a fluid to be chilled is directed to the evaporator. The fluid to be chilled may flow through a pipe within the evaporator. In the evaporator, the refrigerant chills the fluid to be chilled to provide a chilled fluid. Heat is transferred to the refrigerant in the evaporator causing the refrigerant to be vapourised. Once vapourised the refrigerant enters the absorber, the concentrated solution in the absorber absorbs the refrigerant to produce the dilute solution which is directed back to the generator so that process can be repeated.

[0075] It is known to provide an adsorption chiller comprising a condenser, an evaporator, a first adsorption chamber and a second adsorption chamber. Each adsorption chamber comprises an adsorption material. The adsorption chiller is used to chill a fluid. The fluid to be chilled is directed into the evaporator of the adsorption chiller. Duringoperation of the chiller, a heat source causes a refrigerant vapour to be released from the adsorption material in the first adsorption chamber. The heat source drives the refrigeration cycle in the chiller. The heat source may be provided by a heated fluid passing through a pipe within the first adsorption chamber. From the first adsorption chamber, the refrigerant vapour goes to the condenser where the refrigerant vapour is cooled and condensed into a liquid refrigerant. The refrigerant may be cooled by a cooling fluid passing through a pipe within the condenser. The adsorption material remains in the first adsorption chamber. From the condenser, the liquid refrigerant goes to the evaporator. As described above, a fluid to be chilled is directed to the evaporator. The fluid to be chilled may flow through a pipe within the evaporator. In the evaporator, the refrigerant chills the fluid to be chilled to provide a chilled fluid. Heat is transferred to the refrigerant in the evaporator causing the refrigerant to be vapourised. Once vapourised the refrigerant is directed from evaporator to the second adsorption chamber where is it adsorbed into the adsorption material present in that chamber. The process can then be repeated with the roles of the first and second adsorption chambers being reversed. That is, the chiller cycles the first and second adsorption chambers between the processes of adsorbing and desorbing.

[0076] Any suitable refrigerant and absorption or adsorption material may be used in the chiller 200. For example, the chiller 200 may utilize absorption chilling with water as the refrigerant and lithium bromide as the absorption material. The chiller 200 may utilize adsorption chilling with water as the refrigerant and silica gel as the absorption material.

[0077] The method 100 comprises chilling 106 a second fluid using the chiller 200 to provide a chilled second fluid. The second fluid may be directed to an evaporator of the chiller 200. For example, the second fluid may be water or a mixture of glycol and water glycol-water. In the method step 106, heat is transferred from the second fluid into the chiller 200 causing the temperature of the second fluid to decrease thereby providingthe chilled second fluid. The method may comprise chilling the second fluid to a temperature of from 2 to 30 degrees C.

[0078] The step of chilling 106 the second fluid using the chiller 200 comprises driving a refrigeration cycle of the chiller using the heated first fluid as the heat source such that heat from the stage of the polymerisation process is used in chilling the second fluid. That is, the heated first fluid is the heat source for the chiller 200. The method therefore advantageously enables energy to be recovered from heat produced during the polymerisation process in the plant. That energy is then used to provide a chilled fluid.

[0079] The method may comprise a step of supplying 108 a third fluid to the chiller 200. The third fluid may be water. The third fluid may be configured to cool the chiller 200. The third fluid may be directed to a condenser of the chiller 200) . Heat may be transferred to the third fluid within the chiller 200. As such, the temperature of the third fluid increases as it travels through the chiller 200. The third fluid supplied to the chiller 200 has a lower temperature than the heated first fluid that is supplied to the chiller 200. After the third fluid has exited the chiller 200, the method may comprise cooling the third fluid. Once cooled, the third fluid may be returned to the chiller 200. The third fluid may be provided by the water cooling circuit of the plant 50. As such, the third fluid may be directed from the chiller 200 to one or more cooling towers or sea-water coolers of the plant 50 for cooling.

[0080] The method steps of supplying 104 the heated first fluid to the chiller 200, chilling 106 the second fluid and supplying 108 a third fluid to the chiller 200 may be performed simultaneously.

[0081] The method may comprise using 110 the chilled second fluid for cooling in the plant. The chilled water may be used for the low temperature cooling requirements of the plant 50. The chilled second fluid may supplement the cooling provided by the water cooling circuit of the plant 50. The chilled second fluid may be used for cooling one ormore of the loop reactors 1, the gas phase reactor 2, the purge bin

[0082]

[0083] the recovery unit 5, distillation unit 6, extruder unit 25 and underwater pelletizing system 26.

[0084] Figure 3 schematically shows an example of an adsorption or absorption chiller 200 that may be used to implement the method 100. The chiller 200 or multiple chillers 200 may be incorporated into the plant 50 shown in Figure 1 to implement the method 100. As shown in Figure 3, chiller 200 may be configured to receive the heated first fluid through a first inlet 201. The first inlet 201 may be configured to deliver the heated first fluid to a chamber 202 of the chiller 200. The first chamber 202 is a generator of the chiller 200 if the chiller 200 is an absorption chiller or a first adsorption chamber if the chiller 200 is an adsorption chiller. Once the heated first fluid has been used to drive the refrigeration cycle of the chiller 200, the first fluid exits the chiller 200 by a first outlet 203.

[0085] The chiller 200 may be configured to receive the second fluid through a second inlet 204. The second inlet 204 may be configured to deliver the second fluid to an evaporator 205 of the chiller 200. Once second fluid has been chilled by the chiller 200, the chilled second fluid exits the evaporator 205 of the chiller 200 by a second outlet 206.

[0086] The chiller 200 may be configured to receive the third fluid for cooling the chiller 200. The chiller 200 may be configured to receive the third fluid through a third inlet 207. The chiller 200 may comprise a third outlet 208 by which the third fluid may exit the chiller 200. The third fluid may be directed from the third inlet 207 through two further chambers 209, 210 of the chiller 200. If the chiller 200 is an absorption chiller, the two further chambers 209, 210, may be an absorber and a condenser of the chiller 200. The absorber of the chiller 200 may be fluidly connected to the third inlet 207. The absorber of the chiller 200 may be fluidly connected to the condenser of the chiller 200 such that the third fluid may be directed from the absorber to the condenser. The condenser may be fluidly connected to the third outlet 208. If the chiller 200 is anadsorption chiller, the two further chambers 209, 210 a second adsorption chamber and a condenser of the chiller 200. The second adsorption chamber of the chiller 200 may be configured to receive the third fluid from the third inlet 207. The second adsorption chamber of the chiller 200 may be fluidly connected to the condenser of the chiller 200 such that the third fluid may be directed from the second adsorption chamber to the condenser. The condenser may be fluidly connected to the third outlet 208. The skilled person will appreciate that third fluid may be directed to the chiller 200 and between the absorber and the condenser or the second adsorption chamber and condenser by alternative means to those described with reference to Figure 3.

[0087] In Figure 3, for illustration only the chiller 200 is shown with the evaporate 205 positioned between chamber 202 (i.e. the generator or first adsorption chamber) and further chambers 209, 210 (i.e. the absorber or second adsorption chamber and condenser). Figure 3 is not intended to limit the structure of the chiller 200.

[0088] Each of the inlets and outlets 201 , 203, 204, 206, 207, 208 of the chiller 200 may be connected to fluid lines, such as a pipe or a conduit, for delivering the respective fluid to and removing the respective fluid from the chiller 200.

[0089] When the chiller 200 of Figure 3 is used to implement the method 100, the method step of chilling 106 the second fluid may comprise delivering the second fluid to an evaporator of the chiller 200. If the chiller 200 is an adsorption chiller, the refrigeration cycle of the chiller may be driven by delivering the heated first fluid to a generator of the chiller 200. If the chiller 200 is an adsorption chiller, the refrigeration cycle of the chiller may be driven by delivering the heated first fluid to a first adsorption chamber of the chiller 200.

[0090] If the chiller is an adsorption chiller, the step of supplying 108 the third fluid to the chiller may comprise supplying the third fluid to the absorber of the chiller and then to the condenser of the chiller. If the chiller is an adsorption chiller, the step of supplying108 a third fluid to the chiller may comprise supplying the third fluid to the second adsorption chamber of the chiller and then to the condenser of the chiller.

[0091] In an embodiment of the method, heat produced in a reactor, such as one of the loop reactor 1 of the plant 50, may be used to drive the refrigeration cycle of the chiller 200. The stage of the polymerisation process (i.e. the stage of the polymerisation process from which heat is transferred to the first fluid to provide a heated first fluid in method step 102) may therefore comprise polymerising olefin to produce a polyolefin component in the loop reactor 1.

[0092] The method step 102 of transferring heat from the stage of the polymerisation process to the first fluid may therefore comprise directing the first fluid through the cooling system 1a of the loop reactor 1. The cooling system 1a the loop reactor 1 may heat the first fluid to provide a heated first fluid having a temperature of from 50 to 60 degrees C. The first fluid may comprise water.

[0093] The step 104 of supplying the heated first fluid to the adsorption or absorption chiller may comprise fluidly connecting an outlet of the cooling system 1a of the loop reactor to the first inlet 201 of the chiller 200. Heat produced during polymerisation in the loop reactor may therefore be used to drive the refrigeration cycle of the chiller 200.

[0094] Once the heated first fluid has been supplied to the adsorption or absorption chiller and used to drive the refrigeration cycle of the chiller, the method may comprise returning the first fluid from the chiller to the cooling system 1 a of the loop reactor 1. The first fluid leaving the chiller may be directed from the first outlet 203 of the chiller 200 to an inlet of the cooling system 1a of the loop reactor 1. Alternatively, the first fluid may be directed first to the cooling water circuit of the plant 50 to be cooled in the water cooling towers or sea water coolers prior to being returned to the cooling system 1 a of the loop reactor 1.The cooling system 1 a of the loop reactor 1 may comprise a cooling jacket. The cooling jacket may at least partially surround the loop reactor 1. The first fluid may be circuited within the cooling jacket for cooling the loop reactor 1 such that heat may be transferred from the loop reactor 1 to the first fluid. The cooling jacket may help regulate the temperature of the loop reactor 1.

[0095] In another embodiment of the method 100, heat from pelletizing the polymer product may be used to drive the refrigeration cycle of the chiller 200. In such embodiments, in method step 102 the stage of the polymerisation process may comprise extruding pellets of the polymer in an underwater pelletizing system.

[0096] The method step 102 of transferring heat from the stage of the polymerisation process to the first fluid may comprise directing the first fluid the underwater pelletizing system 26. The underwater pelletizing system 26 molten may provide a heated first fluid may have a temperature of from 40 to 60 degrees C.

[0097] The step 104 of supplying the heated first fluid to the adsorption or absorption chiller may comprise fluidly connecting a water outlet of the underwater pelletizing system 26 to the first inlet 201 of the chiller 200.

[0098] Once the heated first fluid has been supplied to the adsorption or absorption chiller and used to drive the refrigeration cycle of the chiller, the method may comprise returning the first fluid from the chiller to the underwater pelletizing system 26. The first fluid leaving the chiller 200 may be directed from the first outlet 203 of the chiller 200 to an inlet of the underwater pelletizing system 26. Alternatively, the first fluid may be directly first to the cooling water circuit of the plant 50 to be cooled in the water cooling towers prior to being returned to the underwater pelletizing system 26.In another embodiment of the method 100, the heated first fluid may comprise a steam condensate generated by a stage of the polymerisation process. In such embodiments, the heated first fluid has a temperature from 95 to 105 degrees C.

[0099] In the plant 50, steam may be used in the recovery unit 5 and distillation unit 6. A steam condensate may be formed from the steam once it has been used in the recovery unit 5 and distillation unit 6. The steam condensate may provide the heated first fluid. Additionally, steam may be used in for the loop reactors 1 , gas phase reactor 2 and extrusion and pelletizing area and the resulting steam condensate may be used as the heated first fluid.

[0100] The step 104 of supplying the heated first fluid to the adsorption or absorption chiller may comprise directing the steam condensate to the first inlet 201 of the chiller 200. Waste heat from the steam condensate may therefore be used to drive the refrigeration cycle of the chiller 200.

[0101] In another embodiment of the method 100, heat produced in the gas phase reactor 2 may be used to drive the refrigeration cycle of the chiller 200. The stage of the polymerisation process in method step 102 may therefore comprise polymerising olefin to produce a polyolefin component in the gas phase reactor 2. Or, more specifically, stage of the polymerisation process in method step 102 may comprise polymerising a second polyolefin component in the presence of a first polyolefin from the loop reactor 1.

[0102] The heat produced in the gas phase reactor 2 may be used to drive the refrigeration cycle of the chiller 200 using several different methods.

[0103] In a first method for using heat produced in the gas phase reactor 2 to drive the refrigeration cycle of the chiller 200, the method step 102 of transferring heat from the stage of the polymerisation process to the first fluid may comprise directing the firstfluid through the cooling system 10 of the gas phase reactor 2. The cooling system 10 of the gas phase reactor may heat the first fluid to provide a heated first fluid having a temperature of from 50 to 70 degrees C.

[0104] The step 104 of supplying the heated first fluid to the adsorption or absorption chiller may comprise fluidly connecting an outlet the cooling system 10 of the gas phase reactor 2 to the first inlet 201 of the chiller 200.

[0105] Once the heated first fluid has been supplied to the adsorption or absorption chiller 200 and used to drive the refrigeration cycle of the chiller 200, the method may comprise returning the first fluid from the chiller to the cooling system 10 of the gas phase reactor 2. The first fluid leaving the chiller 200 may be directed from the first outlet 203 of the chiller 200 to an inlet of the cooling system 10 of the gas phase reactor 2. Alternatively, the first fluid may be directed first to the cooling water circuit of the plant 50 to be cooled in the water cooling towers or sea water coolers prior to being returned to the cooling system 10 of the gas phase reactor 2.

[0106] As described above, the cooling system 10 of the gas phase reactor 2 may comprise a heat exchanger. The first fluid may be the working fluid in the heat exchanger. The first fluid may be water. As described above, the cooling system 10 is disposed on the circulation line 8. The first fluid is configured to thermally contact circulation gas in the heat exchanger so that heat can be transferred from the circulation gas to the first fluid to provide the heated first fluid.

[0107] The first method for using heat produced in the gas phase reactor 2 to drive the refrigeration cycle of the chiller 200 may be implemented by an absorption chiller. In an specific, non-limiting example, the first fluid may be heated to a temperature of 70 degrees C by the cooling system 10. The heated first fluid at of 70 degrees C may then be supplied to the chiller 200 through the first inlet 201. The second fluid entering the second inlet chiller 200 through the second inlet 204 may have a temperature of 12degrees C. The heated first fluid may drive the refrigeration cycle to chill the second fluid so that the second fluid exiting the second outlet 206 of the chiller 200 has a temperature of 7 degrees C. The first fluid, when it exits the chiller 200 through the first outlet 203, may have decreased in temperature of a temperature of 60 degrees C. As described above, the third fluid may cool the chiller 200. The third fluid may enter the chiller 200 through the third inlet 207 of the chiller 200 at a temperature of 33 degrees C. Once the third fluid has cooler the chiller 200, the third fluid may exit the chiller 200 through the third outlet 208 at a temperature of 39 degrees C.

[0108] In a second method for using heat produced in the gas phase reactor 2 to drive the refrigeration cycle of the chiller 200, the method step 102 of transferring heat from the stage of the polymerisation process to the first fluid may comprise directing the first fluid through the cooling system on the flush line 11. The cooling system on the flush line 11 may heat the first fluid to provide a heated first fluid having a temperature from 50 to 70 degrees C. The first fluid may comprise water.

[0109] The step 104 of supplying the heated first fluid to the adsorption or absorption chiller 200 may comprise fluidly connecting an outlet the cooling system of the flush line 11 to the first inlet 201 of the chiller 200.

[0110] Once the heated first fluid has been supplied to the adsorption or absorption chiller 200 and used to drive the refrigeration cycle of the chiller 200, the method may comprise returning the first fluid from the chiller 200 to the cooling system of the flush line 11. The first fluid leaving the chiller 200 may be directed from the first outlet 203 of the chiller 200 to an inlet of cooling system of the flush line 11. Alternatively, the first fluid may be directed first to the cooling water circuit of the plant 50 to be cooled in the water cooling towers or sea water coolers prior to being returned to the cooling system of the flush line 11.In the same manner as the cooling system 10 of the gas phase reactor 2, cooling system of the flush line 11 may comprise a heat exchanger. The first fluid may be the working fluid in the heat exchanger. The first fluid may be water.

[0111] In a third method for using heat produced in the gas phase reactor 2 may be used to drive the refrigeration cycle of the chiller 200, the method step 102 of transferring heat from the stage of the polymerisation process to the first fluid may comprise directing the first fluid through an auxiliary cooling system 10a of the gas phase reactor 2. The auxiliary cooling system 10a of the gas phase reactor may heat the first fluid to provide a heated first fluid having a temperature from 60 to 80 degrees C.

[0112] The auxiliary cooling system 10a of the gas phase reactor 2 is shown in Figure 4 and omitted from Figure 1. Figure 4 shows a reactor assembly comprising the gas phase reactor 2, circulation line 8, compressor 9, cooling system 10, the auxiliary cooling system 10a and the chiller 200. For simplicity, the remaining features of the plant 50 are omitted from Figure 4. The auxiliary cooling system 10a is disposed on the circulation line 8 upstream of the cooling system 10. The auxiliary cooling system 10a is disposed on the circulation line 8 downstream of the compressor 9. The auxiliary cooling system 10a may comprise a heat exchanger. The first fluid may be the working fluid in the heat exchanger. The first fluid may be water. The first fluid is configured to thermally contact circulation gas in the heat exchanger so that heat can be transferred from the circulation gas to the first fluid to provide the heated first fluid.

[0113] The auxiliary cooling system 10a may enable the first fluid to be heated to a higher temperature, e.g. 60 to 80 degrees C, compared to using the first fluid as the working fluid in the cooling system 10 which results in a temperature of from 50 to 70 degrees C. As such, heating the first fluid in the auxiliary cooling system 10a may enable greater chilling of the second fluid by the chiller 200.The auxiliary cooling system 10a is used to drive the refrigeration cycle of the chiller rather than regulate the temperature of the circulation gas to a desired temperature. The cooling system 10 may be used in this method to regulate the temperature of the circulation gas and gas phase reactor 2. The temperature of the circulation gas will be reduced by the auxiliary cooling system 10a. Therefore, the cooling required by the cooling system 10 (i.e. the load on the cooling system 10) to regulate the temperature of the circulation gas and gas phase reactor 2 is reduced which may improve the efficiency and operating costs of the plant 50.

[0114] The step 104 of supplying the heated first fluid to the adsorption or absorption chiller may comprise fluidly connecting an outlet the auxiliary cooling system 10a of the gas phase reactor 2 to the first inlet 201 of the chiller 200.

[0115] Once the heated first fluid has been supplied to the adsorption or absorption chiller 200 and used to drive the refrigeration cycle of the chiller 200, the method may comprise returning the first fluid from the chiller 200 to the auxiliary cooling system 10a of the gas phase reactor 2. The first fluid leaving the chiller 200 may be directed from the first outlet 203 of the chiller 200 to an inlet of the auxiliary cooling system 10a of the gas phase reactor 2. Alternatively, the first fluid may be directed first to the cooling water circuit of the plant 50 to be cooled in the water cooling towers or sea water coolers prior to being returned to the auxiliary cooling system 10a of the gas phase reactor 2.

[0116] In a fourth method for using heat produced in the gas phase reactor 2 to drive the refrigeration cycle of the chiller 200, the first fluid may comprise circulation gas from a gas phase reactor 2. As such, the method step 102 of transferring heat from the stage of the polymerisation process may comprise transferring heat to the circulation gas in the gas phase reactor 2. In such embodiments, the heated first fluid may have a temperature of from 75 to 100 degrees C. The chiller 200 may therefore be disposed on the circulation line 8. The chiller 200 is disposed on the circulation line upstream ofthe cooling system 10. The chiller may be disposed on the circulation line either upstream or downstream of the compressor 9.

[0117] The method step 104 of supplying the heated first fluid to the adsorption or absorption chiller may comprise fluidly connecting the inlet 201 of the chiller 200 to the circulation line 8.

[0118] Once the heated first fluid (i.e. circulation gas) has been supplied to the adsorption or absorption chiller and used to drive the refrigeration cycle of the chiller, the method may comprise returning the first fluid to the circulation line 8. The outlet 203 of the chiller 200 may therefore be fluidly connected to the circulation line. The circulation gas may then pass through the cooling system 10 of the gas phase reactor. The cooling system 10 regulates the temperature of the gas phase reactor 2.

[0119] Figure 5 shows a reactor assembly in which the circulation gas is used as the first fluid to drive the refrigeration cycle of the chiller. Figure 5 shows a reactor assembly comprising the gas phase reactor 2, circulation line 8, compressor 9, cooling system 10 and the chiller 200. The chiller 200 is fluidly connected to the circulation line 8 upstream of the cooling system 10. Whilst Figure 5 shows the chiller 200 coupled to the circulation line 8 downstream of the compressor 9, the chiller 200 may alternatively be coupled to the circulation line 8 upstream of the compressor 9.

[0120] Using circulation gas to drive the refrigeration cycle of the chiller 200 may enable greater chilling of the second fluid by the chiller 200 due to the high temperature of the circulation gas. As the circulation gas passes through the chiller 200, the temperature of the circulation gas will be reduced. Therefore, the cooling required by the cooling system 10 to regulate the temperature of the circulation gas and gas phase reactor 2 is reduced which may improve the efficiency and operating costs of the plant 50.The chiller 200 may be incorporated into the plant 50 shown in Figure 1 to implement the method 100. The skilled person will appreciate that more than one chiller 200 may be incorporated into the plant 50 such that heat can be received from multiple stages of the polymerisation process at the same time. For example, multiple chillers 200 may be used to recover waste heat from one or more of the loop reactor 1, gas phase reactor 2, underwater pelletizing system 25 and from steam condensate at the same time. The method may comprise transferring heat from multiple stages of the polymerisation process to a plurality of first fluids to provide a plurality of heated first fluids. Each heated first fluid may be supplied to a separate chiller to a refrigeration cycle. Each heated first fluid may be configured to chill a second fluid.

[0121] The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings). The claims should not be construed to cover merely the foregoing embodiments, but also any embodiments falling within the scope of the claims. Each feature disclosed in this specification (including any accompanying claims and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0122] All of the features disclosed in this specification (including any accompanying claims and drawings) may be combined in any combination, except combinations where at least some of such features are mutually exclusive. The invention is defined by the appended claims.

Claims

26CLAIMS1. A method for waste heat recovery from a plant for polymerising olefins, the method comprising:transferring heat from a stage of the polymerisation process to a first fluid to provide a heated first fluid;supplying the heated first fluid to an adsorption or absorption chiller; and chilling a second fluid using the chiller to provide a chilled second fluid, wherein chilling the second fluid using the chiller comprises driving a refrigeration cycle of the chiller using the heated first fluid as the heat source such that heat from the stage of the polymerisation process is used in chilling the second fluid.

2. A method according to claim 1, wherein the heated first fluid has a temperature from 40 to 105 degrees C.

3. A method according to claim 2, wherein the heated first fluid has a temperature from 40 to 80 degrees C, from 50 to 60 degrees C, from 50 to 80 degrees C from 75 to 100 degrees C or from 95 to 105 degrees C.

4. A method according to any one of claims 1 to 3, wherein the chilled second fluid has a temperature from 2 to 30 degrees C.

5. A method according to any one of the preceding claims, wherein the stage of the polymerisation process from which heat is transferred to the first fluid to provide a heated first fluid comprises polymerising olefin to produce a polyolefin component in a reactor, preferably a loop reactor.

6. A method according to claim 5, wherein transferring heat from the stage of the polymerisation process to the first fluid comprises directing the first fluidthrough a cooling system of the reactor; and wherein, when the reactor is a loop reactor, the heated first fluid has a temperature between 50 to 60 degrees C.

7. A method according to any one of claims 1 to 4, wherein the stage of the polymerisation process from which heat is transferred to the first fluid to provide a heated first fluid comprises polymerising olefin to produce a polyolefin component in a gas phase reactor.

8. A method according to claim 7, wherein transferring heat from the stage of the polymerisation process to the first fluid comprises directing the first fluid through a cooling system for the gas phase reactor; and wherein the heated first fluid has a temperature of from 50 to 80 degrees C.

9. A method according to any one of the preceding claims, wherein the polymerisation process comprises a first stage comprising polymerising olefin to produce a first polyolefin component in a reactor, preferably a loop reactor, and a second stage comprising polymerising olefin to produce a second polyolefin component in the presence of the first polyolefin in a gas phase reactor, and wherein heat is transferred from the first stage and / or second stage to the first fluid to provide a heated first fluid.

10. A method according to any one of claims 1 to 4, wherein the stage of the polymerisation process comprises extruding pellets of the polymer in an underwater pelletizing system; wherein the first fluid comprises water from the underwater pelletizing system; and wherein the heated first fluid has a temperature from 40 to 60 degrees C.

11. A method according to any one of claims 1 to 4, wherein the first fluid comprises circulation gas from a gas phase reactor and the stage of thepolymerisation process comprises polymerising olefin to produce a second polyolefin component in the presence of a first polyolefin component in the gas phase reactor.

12. A method according to claim 11, wherein the heated first fluid has a temperature of from 75 to 100 degrees C.

13. A method according to claim 11 or 12, comprising directing the first fluid from the chiller to a cooler for gas phase reactor circulation gas such that temperature of the circulation gas is reduced in the chiller prior to the circulation gas entering the cooler.

14. A method according to any one of claims 1 to 4, wherein the heated first fluid comprises a steam condensate generated during a stage of the polymerisation process and the heated first fluid has a temperature from 95 to 105 degrees C.

15. A method according to any one of the preceding claims, comprising using the chilled second fluid for cooling in the plant.

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