Following is a very common chain of events that
contributes to wasted energy in distillation:
- Human nature leads many to increase reflux when an
overhead specification isn't met (when a decrease in
reboil might be a more energy-efficient move).
- The increased reflux can cause lights to drift up in
the bottom of the tower, which may cause many to increase
reboil (when a decrease in reflux might be the more
energy-efficient move), which can cause heavies in the
overhead to drift up again.
- Result: One increases reflux, another increases reboil…The
cycle continues until the tower gets "wound up."
- The same chain of events can also start at the bottom of the
tower when lights in the base trend higher and reboil is added rather than cutting reflux.
- Other ways that this suboptimum energy point is reached includes not making a
tower adjustment when feed flow or composition shifts, or if ambient temperatures swing night to day or season-to-season.
Our software examines composition requirements, current performance, and then makes suggestions for decreases in reflux, reboil or operating pressure. Our system continues to unload the
tower until either lights in the base and heavies in the distillate approach maximum or
tower loading reaches minimum. The tower winds down to approach minimum energy.
If desired, the system can automatically adjust operating limits based on commodity or product prices, fuel prices, feed rates, feed compositions or plant steam balance. Engineering is able to enter “trigger” points as well as desired percentage change in targets as each trigger point is met. Alternatively, your equation (if you have completed a process optimization study) can be substituted for the default step function feature.
View our distillation demos, pricing sheet, and frequently asked questions pages on this website for further details.
What if I have Advanced Process Control (APC) in my operation?
If you have an APC system installed in your unit that operates above the DCS system, we may still be able to help you achieve optimum performance. Please contact Enhanced Process Monitoring for information on how we can customize our software for your unique requirements. Consider the following three possible problems and how our system can be used to inexpensively provide solutions:
- In some cases existing APC systems obey composition/operating pressure setpoints that are entered by the board operator and assumes they are optimum when they may not be. The result is that columns may be run over-refluxed when feed rates change, or composition constraints may be suboptimum when raw material, product or fuel prices change.
- Solution: Our system will monitor setpoints for controllers on compositions, temperatures, pressures and ratios, providing suggestions for optimum settings. If desired, the system can automatically adjust operating setpoints based on commodity or product prices, fuel prices, feed rates, feed compositions or plant steam balance. Engineering is able to enter “trigger” points as well as desired percentage change in targets as each trigger point is met. Alternatively, your equation (if you have completed a process optimization study) can be substituted for the default step function feature.
- Some existing APC systems obey reflux flow minimum constraints set by the board operator which may be suboptimum. The result is over-refluxing of the
tower, wasting energy
– Solution: With our system, checks will be made to ensure selected minimum constraints (reflux flows) are set correctly.
- Some existing APC systems do not know if analyzers are reading incorrectly and may make incorrect moves based on false analyzer readings.
– Solution: Selected setpoint targets can be adjusted as our system “calibrates” analyzers using lab results and possibly, other analyzer inputs.