The challenge
High-pressure plastics production needs reactors that heat evenly and fast. Each of the plant’s three double-jacketed reactors is heated through a U-tube heat exchanger on saturated steam at 66 bar (abs). Low-pressure steam is left at the exchanger outlet; vented or throttled, it is wasted, and a low steam velocity in the tubes gives an uneven temperature.
The solution
Each reactor’s exchanger got a controllable steam ejector Jetomat® (Baelz 590, DN 50, PN 160) with a pneumatic actuator:
- The 66 bar steam is the motive steam of the Jetomat.
- The Jetomat sucks the remaining low-pressure steam from the exchanger outlet and returns it to the exchanger, mixed with the motive steam: a recirculation loop.
- The actuator moves the nozzle spindle, so the steam flow follows the reactor’s heating demand.
The results
- Much higher steam mass flow through the tubes, for a more uniform temperature and stable heat transfer
- Reactors run at 100% capacity, for faster production
- No heat lost from the remaining low-pressure steam
- In service since 2000 and running without problems
Why it works
A steam ejector turns the pressure of the motive steam into suction: it draws in the low-pressure steam and recompresses the mixture in the diffuser. In a recirculation loop this raises the flow through the heat exchanger without a circulation pump.
Takeaway
Where a reactor or an exchanger needs an even temperature at high load, a Jetomat recirculation loop raises the steam flow through the heating surface and uses the steam left at the outlet, on one variable nozzle.
