The Conical Bottom Reactor Challenge
A stirred reactor with a conical bottom and a lower impeller presents a complex heating geometry. The cone concentrates the solids toward the bottom discharge. The lower impeller provides the mixing in the cone. The heat exchanger must heat the cone contents without interfering with the impeller or the solids flow.
A uniform tube grid cannot follow the cone slope. The tubes must be customized-the different lengths to match the varying depth from the cone surface to the reactor wall. The design distributes the tube lengths to provide the uniform heating across the cone.
The Tube Length Distribution Design
The conical bottom has a slope of 45° from the horizontal, a top diameter of 1,800mm, and a bottom discharge diameter of 200mm. The cone depth is 800mm. The heat exchanger tubes run vertically along the cone wall, extending from the support ring at the top of the cone down toward the discharge.
The tube length varies with the position on the cone: the tubes near the discharge are short-200-300mm-because the cone is narrow at the bottom. The tubes near the top of the cone are long-800-1,000mm-because the cone is wide. The distribution matches the cone geometry.
The lower impeller is positioned in the cone center. The tubes are arranged around the impeller with a clearance of 150mm from the blade tips. The clearance prevents the interference and allows the impeller to create the flow that circulates the fluid past the tubes.
| Design Parameter | Specification |
|---|---|
| Cone top diameter | 1,800mm |
| Cone bottom diameter | 200mm |
| Cone depth | 800mm |
| Cone angle | 45° |
| Impeller diameter | 600mm |
| Tube clearance from impeller | 150mm |
| Tube OD × wall | 10mm × 1.0mm |
| Number of tubes | 36 |
| Tube length range | 200-1,000mm |
| Total surface area | 2.8 m² |
| Heating duty at 3 barg steam | 22 kW |
The Impeller Flow Interaction
The lower impeller creates the downward flow in the cone center and the upward flow along the cone wall. The heat exchanger tubes are positioned in the upward flow zone along the wall. The flow passes over the tubes, carrying the heated fluid upward. The circulation pattern ensures the heat is distributed from the wall zone to the cone center.
The tube spacing is adjusted to match the flow: the closer spacing near the impeller where the velocity is higher, the wider spacing near the top where the velocity drops. The adjustment optimizes the heat transfer coefficient across the cone.
The Drainage and Support
The vertically oriented tubes drain the condensate downward to the condensate header at the cone bottom. The steam supply enters at the top header. The vertical orientation with the co-current downflow provides the stable drainage-the condensate and the steam flow in the same direction, avoiding the instability of the counter-current flow.
The tubes are supported at the intermediate points by the PTFE guide rings that follow the cone contour. The rings hold the tubes at the correct distance from the cone wall. The support prevents the vibration from the impeller flow.
Summary
A custom PTFE heat exchanger for the conical-bottom reactor uses the varying tube lengths to match the cone geometry. The tubes run vertically along the cone wall in the upward flow zone created by the lower impeller. The distribution provides the uniform heating across the cone. The vertical orientation ensures the stable condensate drainage. The design integrates the heating with the impeller hydraulics and the solids flow.
Engineering support for the conical reactor PTFE heat exchanger design is available upon submission of the cone dimensions, the impeller specifications, the heating duty, and the process fluid properties.
