5 replies to this topic

What kind of heat exchanger can one use for two streams that both contain solids? One stream is a slurry (something that comes pretty close to sewage sludge, is cold, needs to be heated) and one stream containing significantly less solids as the first stream, but fouling is still possible on this side of the heat exchanger. Flows are industrial, and quite large (order of 10 kg/s). Temperatures remain below 100 deg C.

This question is for a preliminary cost estimate in a bio-ethanol factory. Nothing is being built yet.

I've looked at shell and tube heat exchanger with floating head and u-tube shell and tube heat exchanger. They are both able to handle solids on one side of the heat exchanger, but I am not certain how wise it would be to have (less) solids on the tube side too.

Any comments?

Additionally, I'd like some advice for a type of heat exchanger can be used for a reboiler in a stripper of a bioethanol factory. The liquid in the reboiler contains solids (yeast and some junk from the feed, which is partially a solid). I'm assuming that no filter is needed, but I cannot find the name of the right type of reboiler. Thermosiphon is perhaps the most common reboiler, but I concluded that it will not be able to handle any solids at all.

Thanks in advance.

[Zauberberg]

Based on your description, Spiral Heat Exchanger (SHE) seems to be the most appropriate solution. It is capable of handling dirty, highly viscous fluids, with solids present as well. Generally it is used in such applications: crude/vacuum residue exchangers, FCC slurries etc.

Footprint space occupied by SHE is significantly less than the equivalent Shell & Tube exchanger, while heat transfer rate is greatly improved due to true counter-current flow pattern of hot and cold fluids. Once when I got an opportunity to employ this type of heat transfer equipment in dirty, fouling and solids-containing production fluid, I have never regretted. It is perfect for these kinds of services, and the corresponding pressure drop is low.

Disadvantage is low design pressure - only up to 35bar max, if I remember well. Visit AlfaLaval website and ask for a budgetary quotation, and look also at the link provided below:

http://www.canaley.c...Heat_V3_low.pdf

[Zauberberg]

Question about Reboiler:

Thermosyphon is more forgiving than a kettle, if solids are present in the system. Kettle will simply act as a dirt collector and very soon it will not be able to deliver process duty requirements. In general, the presence of solids calls for a special design which is - in most cases - forced circulation.

Do not believe too much to equipment manufacturing vendors, who will claim that other types of exchangers are going to be efficient and long-lasting in service. It's simply not true.

[Qalander (Chem)]

Question about Reboiler:

Thermosyphon is more forgiving than a kettle, if solids are present in the system. Kettle will simply act as a dirt collector and very soon it will not be able to deliver process duty requirements. In general, the presence of solids calls for a special design which is - in most cases - forced circulation.

Do not believe too much to equipment manufacturing vendors, who will claim that other types of exchangers are going to be efficient and long-lasting in service. It's simply not true.

Dear themiller Hello/Good Morning,
Although not usual, but the application of scrapped surface double pipe heat exchangers can be explored if the heat duty is not that great and solids are to be separated-out subsquently in downstream processing equipments.
Hope this helps
Qalander

Thanks for the advice. I must admit that it surprises me a bit... looking at pictures I can imagine that spiral heat exchangers get clogged up just as fast as a bunch of tubes.

What prevents fouling in these things?

[Zauberberg]

The flow pattern is such it promotes turbulence and eliminates stagnant areas, which are the main culprits of fouling and solids deposition. If you take a look at SHE construction you'll observe that "swirling" motion of fluids produces high turbulence at velocities which are lower than corresponding velocities in shell & tube exchangers (for the same pressure drop).

I have looked for references in heavy fouling applications, and SHE has proved itself in few troublesmoe services: crude/residue exchangers in hot preheat train, and in FCC slurry product/pumporaound exchangers as well, where fouling and erosion has always been an issue.