A polymerization system comprising: a tubular polymerization reactor; and a separation system comprising: a substantially cylindrical vessel defined about a central vertical axis and comprising a vessel inner surface, at least two fluid inlets (110, 112) including a first fluid inlet and a second fluid inlet, a fluid outlet, and a reservoir configured to contain a coolant at a variable level, wherein the first fluid inlet is positioned higher in the vessel than the second fluid inlet and the second fluid inlet is positioned higher in the vessel than the level of coolant contained in the reservoir; wherein the fluid inlets (110, 112) are connected to the polymerization reactor and each fluid inlet (110, 112) is configured to deliver fluid to the vessel from a different zone of the polymerization reactor; wherein the polymerization reactor comprises zones including an upstream end, a downstream end, and a midstream zone located between the upstream end and downstream end; wherein the first fluid inlet is configured to deliver fluid to the vessel from the midstream zone and the second fluid inlet is configured to deliver fluid to the vessel from the downstream end; wherein the first fluid inlet is configured to deliver a higher mass flux of fluid to the vessel than the second fluid inlet; and wherein the fluid inlets (110, 112) are configured to introduce fluid into the vessel substantially tangentially to the vessel inner surface. a tubular polymerization reactor; and a separation system comprising: a substantially cylindrical vessel defined about a central vertical axis and comprising a vessel inner surface, at least two fluid inlets (110, 112) including a first fluid inlet and a second fluid inlet, a fluid outlet, and a reservoir configured to contain a coolant at a variable level, wherein the first fluid inlet is positioned higher in the vessel than the second fluid inlet and the second fluid inlet is positioned higher in the vessel than the level of coolant contained in the reservoir; wherein the fluid inlets (110, 112) are connected to the polymerization reactor and each fluid inlet (110, 112) is configured to deliver fluid to the vessel from a different zone of the polymerization reactor; wherein the polymerization reactor comprises zones including an upstream end, a downstream end, and a midstream zone located between the upstream end and downstream end; wherein the first fluid inlet is configured to deliver fluid to the vessel from the midstream zone and the second fluid inlet is configured to deliver fluid to the vessel from the downstream end; wherein the first fluid inlet is configured to deliver a higher mass flux of fluid to the vessel than the second fluid inlet; and wherein the fluid inlets (110, 112) are configured to introduce fluid into the vessel substantially tangentially to the vessel inner surface. a substantially cylindrical vessel defined about a central vertical axis and comprising a vessel inner surface, at least two fluid inlets (110, 112) including a first fluid inlet and a second fluid inlet, a fluid outlet, and a reservoir configured to contain a coolant at a variable level, wherein the first fluid inlet is positioned higher in the vessel than the second fluid inlet and the second fluid inlet is positioned higher in the vessel than the level of coolant contained in the reservoir; wherein the fluid inlets (110, 112) are connected to the polymerization reactor and each fluid inlet (110, 112) is configured to deliver fluid to the vessel from a different zone of the polymerization reactor; wherein the polymerization reactor comprises zones including an upstream end, a downstream end, and a midstream zone located between the upstream end and downstream end; wherein the first fluid inlet is configured to deliver fluid to the vessel from the midstream zone and the second fluid inlet is configured to deliver fluid to the vessel from the downstream end; wherein the first fluid inlet is configured to deliver a higher mass flux of fluid to the vessel than the second fluid inlet; and wherein the fluid inlets (110, 112) are configured to introduce fluid into the vessel substantially tangentially to the vessel inner surface.