7 replies to this topic

[vinay1999]

How Do I go about designing a direct contact heat exchanger for cooling cement clinker with Nitrogen gas (Dry quenching). Is there any design software for such an application. If not what design equations are to be considered while designing one.

The design of the cooler/quencher is required for a preliminary estimate to carry out pilot studies.

The cement clinker is of varying sizes. I can give the particle size distribution if required. I need help regarding the calculation of the heat transfer coefficient (HTC) for the system and thereby the requirement of N2 gas for a given clinker flow rate inside the cooler. Are there any correlations for calculating HTC for such systems.

Edited by vinay1999, 03 September 2011 - 03:28 AM.

[kkala]

I had made measurements on existing "fluidized bed coolers" in a fertilizer plant (1979), which cooled granulated ammoniun nitrate product, trying to assess whether these could be also used for granulated phosphoric fertilizers. The adopted terminology "fluidized bed cooler" was rather misleading; the solids were not completely fluidized on air, but rather jumping and moving along an inclined perforated steel sheet, receiving air from down upwards. "Walking floor cooler" would be a more precise term, as seen now in Web.
Flow pattern of solids looked rather complicated in mentioned coolers. Air (N2 in your case) pressure drop through the bed was depending on bed thickness, which was also depending on sheet inclination. More air flow rate would shift more product to cyclones, less would result in insufficient cooling (or even plugging) - at the same time air could promote or delay movement of product (granulated solids). Extent of sheet perforation played also a role. After few measurements, I wrote a report and quitted. But all these points, plus heat transfer, can make a good challenge for a complete thesis (or similar), supported by a pilot plant.
Googling "walking floor cooler" in web, you can find interesting material, including the attached reprint from KHD. It does not specify heat transfer rates, but it contains a heat balance and could be useful in the first steps (if you have not read it already). Hopefully some other member can offer specific help.
I wish good success in your patient (yet rather exciting) task.

Attached Files

•  introducing-PYROFLOOR-The-Great-Cooler.pdf   1.36MB   68 downloads

Edited by kkala, 03 September 2011 - 10:42 AM.

[vinay1999]

Thank you for your advice.I would like to add that , in the existing plant quenching is being done in a rotary cooler with water and the generated steam is further being used to dry the clinker. The client would like to go for a new system where the water quenching is replaced with nitrogen system.So any information on gas cooled rotary coolers would be of immense help.

[kkala]

So the case concerns modification on an existing rotary clinker cooler (see http://www.google.gr...=2&ved=0CDIQsAQ, photo of caribcement). This is different to walking floor cooler (photos on same web reference). But what is the object of "pilot studies"? It seems they do not involve a pilot plant, as I had assumed.

Edited by kkala, 05 September 2011 - 12:30 AM.

[vinay1999]

Forgive me for the ambiguity. By " new system " , I meant a new rotary cooler itself with N₂ quenching. I got some relevant information from this source -" Introduction to Process Engineering and Design By Thakore/bhatt pg nos. - 312 ,317 -319. ( preview of the pages is available in google books) Though this source doesn't speak about the relation of HTC with the speed of rotation or the inclination of the cooler.

Edited by vinay1999, 05 September 2011 - 05:02 AM.

[kkala]

..By " new system " , I meant a new rotary cooler itself with N₂ quenching. I got some relevant information from this source -" Introduction to Process Engineering and Design By Thakore/bhatt pg nos. - 312 ,317 -319. ( preview of the pages is available in google books) Though this source doesn't speak about the relation of HTC with the speed of rotation or the inclination of the cooler.

Speed of rotation and inclination of the rotary cooler mainly affect movement of solids, that is their residence time in it. For a rotary fertilizer drier or a small lime kiln (length ~ 1.5 m), the residence time correlation by US bureau of Mines (Tech. Paper 384, 1925) was found rather precise, despite its simplicity. It can be found in Perry (7th edition, 1999, Solids drying equipment / Rotary Driers). Perry also reports other drier data about solid transport and heat transfer. It also writes that "In most cases, direct-heat rotary driers are still sized on the basis of pilot plant tests". Reported heat transfer formula for commercial driers does not involve inclination or rotational speed, indicating that these have a minor effect on heat transfer coefficient. But they do affect heat transfer because they affect velocity of solid transport (residence time).

Note: Solid transport in a rotary cooler is of course different to that in a walking floor cooler.

Edited by kkala, 05 September 2011 - 08:53 AM.

[vinay1999]

Sir , could you throw some light upon the pressure drop of gas through such contactors

[kkala]

Assumingly you mean rotary coolers, and unfortunately I have no data available on ΔP, even for rotary driers or kilns. In the field we measured (as mentioned in previous post) gas flow rates & temperatures to elaborate balances, but not gas pressures (even though these could be measured).
Pressure downstream fertilizer drier was probably ~ 200 mm H2O (we checked ΔP of bag filters), but this has no value, since there were two fans on the line, forced & induced draft (and much air ingression).
Searching available litterature (Perry, Idelcik - Memento de Pertes de Charge) was not fruitful either.