issues on continuos process plant operated intermitently

[JCma7212]

Could someone give me his/ her opinion about to operate a hydrocarbon distillation plant in an intermittent way, 5 days in operation and 15 days out of operation; I know this sounds a little strange, but this is because there is no enough load available. from process point of view, it could be assumed as frequent start up and shutdown of the complete unit, including critical equipment as the direct fire heater and distillation column. For sure it will not be the most efficient operation, and probably other issues related maintenance and excessive wearing on dynamic equipment happen. What other issue you can anticipate? any of them could it make this option no feasible?

 

[TiCl4]

With fired equipment, you may want to step up inspection frequency for hot spots in refractory-lined pipe/equipment. That many thermal cycles will take a toll on the refractory.

 

[mk3223]

Is it possible to run the unit in a bypass or re-circulation mode to maintain a minimum stream flow condition in order to skip the shutdown and startup procedures?

 

[horacio Torres]

This intermittently operation will lead the process to.

Leaks will increased be thermal cycling.
Corrosion's rates will be up, startup and shot downs process always produced more corrosion into the equipment internals.
Near miss/operational troubles be more frequency, my view is that star/shutdowns a plant is like the raise and land a plane, is a risk process.
maintenance cost will increased.

Best regards

Horacio

 

[pierreick]

Hi,
A few pointers :
Out of spec products to recycle or destroy ,
higher risk to damage equipment due to frequent start up ( internal of columns as an example) ,
high risk to plug the lines due to poor flushing during shut down . Remember a good start up is always due to a good shut down !
Higher cost of maintenance ( more curative, less preventive )

Based on experience .

Pierre

 

[JCma7212]

Thank you very much for all the replies, important issues I haven´t identified.

 

[don1980]

Consider not shutting down the distillation train, and instead, keep it running by false-loading with reflux. The downside is wasted energy, but that cost may be less than (or close to) the energy cost of re-running the off-spec material generated during the start-ups and shut-downs. Plus, from the perspective of product quality it'll be easier to control by keeping the columns running at a steady-state (min-rate) condition, using additional reflux to keep the trays/packing loaded at the minimum rate.

Consider how long it's going to take to get the columns started and lined out each time you re-start. If it's quick and easy, then shutting down may be the right answer. But if these are large columns with tight product quality specs, the keeping them running may be better.

 

[quadtracker]

I would consider producing enough extra finished product and off spec product into a rerun tank that could be used to recirculate, to blend with new feed stock so that a more continuous operation could be made. Increase your operation cycle and decrease your downtime. This might reduce the other issues mentioned in operating in too many cycles.