Steam Generation from Hot Oil 1

[sshep]

One of our units has a considerable amount of waste heat available in a product stream (at 530F+) coming off a column bottoms. It is proposed to generate 350psi steam using this stream. I initially envisioned a kettle type boiler, but have others suggesting that this needs to be a drum & thermosyphon. If anyone has direct experience, what is the recommended equipment to do this?

 

[unclesyd]

Can't you use this stream to preheat the feed to this unit or feed to another unit? This would be a lot simpler that steam generation.

 

[25362]

I think you wouldn't be able to produce more than low pressure (LP) steam in a kettle boiler due to the fact that the oil temperature wouldn't allow you to do anything beyond that.

If you want to exploit the available heat you'd probably consider, at least, a 200^oF drop in temperature. This would bring your hot stream down to 330^oF. The generated saturated steam would then be at say 320^oF which corresponds to about 90 psia, not 350 psia as planned.

I've seen PDA (propane deasphalting) unit designs with the asphalt stream cooled by producing LP steam by a drop in temperature from 500^oF down to 325F in a kettle-type boiler. Of course, the lowest asphalt temperature was dictated by its viscosity and pumpability.

 

[sshep]

A complete energy analysis of the unit has already been completed- this is heat ultimately discharge to air, for which the unit has no good use. The distant location is such that the best way to share this heat is with other units is via existing steam utility. Between 530F and 455F I can boil-up 15kpph+ of steam, with lower level waste heat preheating BFW.

Thanks for all interest. At this point I am soliciting experience about the actual equipment to generate the steam from hot oil such as the PDA description given. My hot oil is essentually kerosene. We generate steam in several of my units via steam drum circulating systems (ethylene cracking furnace effluent, stack gas heat recovery systems, etc.). I want to know if a circulating system is also recommended for hot oil recovery or if a simple kettle is appropriate.

 

[25362]

From what I can recall the PDA kettle boilers I mentioned didn't have a BFW preheat in separate HE. The whole operation was done in single kettle-type units. The asphalt dropped from 260 to about 162^oC, while the incoming BFW entered at 70^oC with LP steam produced at about 160^o.

The steam generation was under pressure control, the BFW fed under LLC. All streams were provided with flow, pressure and temperature recorders. These were units providing 1.5*10⁶ kcal/h, about half the duty you are planning to get.

 

[25362]

Anyhow, it is advisable to provide a dome to the kettle shell with an inclined demister in it to improve quality of steam, even it is meant to be totally used in the same plant for heating or stripping purposes.

Besides, one small point: external level indicators won't show the true boiling water level, because bubbling boiling water may have a density about half of the "static" water inside the level measuring instrument.