Spray Water Cooling System in Rolling Mills

A pressure of 247.385 psig should be about right......

How about a simple distribution pipe above each coil, with a row of holes in the bottom? Then you would need very little pressure and could save on pumping costs, as well as the expense of nozzles.

First- you can likely do this in a lot less time with a lot less water.

I assume that your coiling machine has the strength to "bend" cool steel as well as "hot" steel.

Calculate the amount of steel to be cooled (mass flow per time unit). Let's use a 5 minute cooling period for grins.

You should have the specific heat for the alloy you are using readily available.

By multiplying the mass flow of steel in a 5 minute period, you can easily calculate the total cooling load in BTUs. Let's assume that the mass flow is 1,000 pounds of steel every 5 minutes. Now, let's assume that the specific heat of that steel is, say, about 0.117 BTU /LbM/F.

The hourly heat removal is 1,000 pounds per 5 minutes X 0.117 BTU/LbM/F X (60 minuter per hour / 5 minutes) X (450F - 100F), or 491,400 BTU/Hr.

Water flow is calculated at 491,400 / ((212F - 60F) + 1030) where 212F is the boiling point of water and 60F is the entering temperature of the water and 1030 is the BTUs per pound latent heat of vaporization of water at atmospheric pressure.

When the water is sprayed in a VERY fine mist on the 450F steel, it will be heated from 60F to 212F, then turn into steam. As the metal moves past the initial sprays, it will eventually be cooled below 212F,

A low velocity blast of ambient air from a directed jet "knife" blower will then cause the water to continue to evaporate below 212F as the water spray continues to cool the metal by convection.

Based on these calculations, you will need a total of about 1,182 pounds of water per hour or about (1182 / 8.33) / 60 = 2.36 GPM where 8.33 is the pounds of water per gallon and 60 is the minutes per hour. Multiply this by, say 1.15 for safety factor so design for 2.7 GPM in the sprays.

Design the sprays for a length that the metal will move in 5 minutes- say 120 inches. Install the sprays so that about 40% of the water feed will occur in the first 24 inches, then spread the remaining 60% of the sprays over the remaining 96 inches of metal with blower knives at say, 60", 96" and 120", angled at 45degrees from vertical toward the metal starting point (against the flow). their contact velocity should be about 150-200 FPM.

One more blower knife assembly should be located at about 144" down the line. This final knife should be about 3 times the flow of the other and designed for about 1,000 FPM contact with the metal to keep any stray water droplets off the cooled metal.

I would select nozzles designed for about 150 PSIG with a "flat oval" pattern and an average droplet size of about 0.016 inch ( 1/64" ) diameter and located at about 18" above the metal flow with slightly overlapping sprays (end to end) to start, and about 3 inch "cone" spacing (end to end) down the metal path. Set the sprays on a staggered pattern across the width of the metal, with about 4 inch running length spacing to start (the 40% "drench" in the first 24 niches) and maybe growing up to about 12 inch running spacing at the end- say 4 inch, then 6 inch, then 8 inch, then 10 inch, then 12 inch along the path.

Since the overall flow rate is relatively low, you can use a gear pump feeding into a header connected to a pneumatic pressurized bladder-type expansion tank to maintain the pressure on the nozzles. Install a pressure relief valve on the header, feeding back to the pumps inlet piping, or- even better- to an inlet tank with a make-up water float valve control and a solenoid valve inlet water control. With this system, size the pump for about 3.5 GPM and select the nozzles for a total discharge of about 2.7 GPM.

Obviously, ALL of the flow rates, etc. need to be matched to YOUR specific system operations, but you certainly should get the idea of sizing methodology.

No charge for the design support.

Re: Design the sprays for a length that the metal will move in 5 minutes- say 120 inches.

That is outrageously slow movement (to the coiler) for any rolling mill I've ever been around. I don't really remember any figures, but I'd think 600 feet per minute might be more in the ballpark.

Exactly my thoughts.. thats why I think its homework.. In the mills where I use to work, the slab at the point of exiting the "6 stand" (for finished coil thickness) was timed at OVER 200KPH!!

That is why I stressed that the "answer" depended on the actual operations.

All I was indicating was the methodology of doing the calculation to meet the OP's indicated issue.

Or skip the spray/drip systems altogether, and just dip the HRS coils in an immersion tank?

The real question is why??

I've never seen in a steel mill the requirement for cooling steel as you ask. In the steel mill I grew up in, steel was hot rolled, hot coiled (at a cooler temp than the hot roll due to the cooling water for the mill rollers) and left to cool down under natural conditions.. outside.

Or is this homework??

Natural cooling makes sense to me as well. Why waste power and water?

My point exactly...

Rough rolled steel, comes from a slab or billet of steel and is heated to almost melting point.. bright red to the layman. As it's rolled, it hardens, BUT it can only be rolled and coiled at at a certain temp. If the temp drops to low, you can have the biggest down coiler in the world and you'll not coil it. Cool it too quickly and it will become brittle and almost next to useless, and then if you have managed to coil it you have to annealed it.

To produce finished steel sheet or coil, the steel must be annealed so it can be cold rolled.

A rough rolled coil, is put into large annealing ovens for 48 hours to soften, then cold rolled on super finished rollers to its finished thickness, then cut into sheet steel, for the automotive industry mainly. The sheet or in some cases the "finished coil" is the sent for pressing to make car panels etc, depending on the customers needs and if they have the ability to handle finished coils of 20 tonnes plus or sheet.

why you want to cool the coil? keep in mind the properties of the material may not be uniform (width and length wise) after cooling the hot strip in coil form.

The coil can be dipped in a water tank if not bothered about properties, your target of 8-10 hours can be easily achivable by direct dipping.

Many thanks for your varied replies and suggestions(Tornado, energy god, brich, tony s, vanam, rhkramer), but i would like to point out that the cooling has to be done at the end of the process. Actually an HR coil is produced from a steel slab which is heated to 1250 degrees before rolling, then this slab is rolled on various rouging and finishing mill stands, water is sprayed to remove the scale formation (due to contact with oxygen in air scales tend to form on steel surface and have to be descaled using high pressured descaling water sprays, having p=350 bar so dat while rolling the scales do not get embedded inside the metal) , Down the line a coiler wounds up the coil (slab which started out as 220 mm thick is now around 2 mm(min) thick due to thickness reduction in stands), At the time of coil formation the temperature of coil is round about 450 degrees and its placed on a saddle in coil storage yard. Here is where we want to cool the coils to 100 degrees or lesser because the further downstream application requires it to be less than 100 degrees in temperature, where its thickness will be more reduced and it will be made into an auto grade coil.Earlier the method employed was natural cooling but due to high demand from downstream, this natural cooling needs to be replaced by forced cooling to reduce the cooling time and give downstream a quick feed. As suggested by (Tornado and Brich) , to have an immersion tank. Guys, we need to cool about 77 coils at the same time, and in order to have an immersion tank , we would need a dedicated crane for dipping one coil at a given time ,which is not a possibility, we cant give the headers containing holes at the top because the overhead cranes have to pick up the coils by inserting their hooks into the coil eye, and thus will damage the headers..best we can do is run the headers on the floor level and make a distribution arrangement there for coil cooling. Thus this brings me back to my query. How much pressure of water required to cool a 450 degree celsius to 100 degree celsius?, what should be the size of piping? what size of nozzle, flow rate of nozzle, lets say we take 2 nozzles from one side, total 4 nozzles from both sides, so flow in lpm? Water is being supplied via a cooling tower, pump of how much flow rate should be selected and what would be the corresponding pressure in the water supply pipelines

I thought I saw the weight in tons per coil (or slab) somewhere in this thread, but can't find it at the moment. The other thing I'd like to see are the basic coil dimensions--diameter and width.

I assume that the coiler makes a nice tight coil, and the coils are transported eye horizontal (coil axis horizontal). So, you can spray water on the outside surfaces of the coil and into the center (eye) of the coil.

Somewhere about halfway between the inside and outside wrap of the coil will be the hottest layer, and that will be the hardest to cool, and will only be cooled by conduction of heat to the cooled surfaces (the outside surface and the eye).

I'm not a heat transfer guy, and don't normally make calculations like that. However, I don't think cooling water on the outside surface and the eye of the coil is going to accelerate the cooling a whole lot.

What is the current cooling time, and what would you like the cooling time to be?

Do you have a way of measuring the hot spot temperature of the coil? I guess there really is no way, is there? Maybe a calculation based on surface temperature (with the spray water off)?

I assume you want the entire coil, including the "hot spot", at or below 100 degrees C?

If you have a way of measuring the hot spot (short of running the coil through the cold rolling line), I'd do some experiments--just set up a bunch of sprays on one just coiled coil and see how fast you can cool it.

The hot rolled coil dimensions are o.d: 2100 mm( max), id:750(max) , width round 1500 mm , max coil weight 36 ton, coil after coiling is placed on a v type mettalic saddle on the floor, saddle elevation is around 350 mm. cooling to be done on both sides along the coil eye(along the width)

The expected cooling time is less than 10 hours to bring the temperature down from 450 to less than a 100 degrees. (rhkramer) we can measure the temperature by using a pyrometer, but i have no idea bout the hot spot you are reffering to, generally it is said that the innermost layer of the coil eye is the most hottest and as the coil is wound up, it uniformly distributes heat in its layers, and tends to retain heat even after cooling, Any HMT or metallurgical Guys who can help out..To carry out experimentation i need the pressure and flow data..

Thanks for the expanded description (and statement that temps are in C)-

How tightly are the coils wound prior to cooling effort- essentially direct contact with adjoining ply sheets or "some" (less than 0.5 mm) spacing or "loose" (1 mm or more)?

Based on the temperatures you indicated, the calculations I noted earlier are still valid, perhaps even more so now that virtually ALL of the metal will be above the boiling point of water (100C) so most of the cooling will be from evaporation.

A huge amount of energy is transferred when water turns to steam- MUCH more than using water alone as the cooling medium.

If you truly have up to 10 hours to cool each coil, then an overhead (or close to overhead to allow for cranes, etc.) spray system would still create the steam as discussed earlier- especially if the coils are wound with "some" or "loose" ply spacing. If the coils are "tightly" wound, you can use a core spray or directed jet and several external sprays- it will take more water because of the lost hot surface contact- to still achieve the same evaporation cooling but with more lost (or recycled) water because the core heat will take longer to be transferred to the cooler wet surfaces.

Based on the 10 hour cooling period, just calculate the total heat to be removed (using specific heat and DeltaT of the metal) and compute total water needs based on the formula and a ten hour window, with allowance for safety. As noted earlier, if the coil is "tight", that safety allowance may need to be 3 to 5 times the water required for larger amounts of hot surface contact possible with "some" of "loose" winding.

If you are thinking of using a cooling tower, are you able to recover the excess spray easily for return to the tower? Whether you use the tower or not, your total water usage (evaporated) will be the same. Ultimately, all the heat transfer will be by evaporation- either at the surface of the metal or in the cooling tower. If you do not have a cooling tower NOW to support this operation, the spray and site evaporate will be much less expensive.

You asked about what pressure would be required for the cooling spray. Other than the relatively low pressure that could be used for a coarse spray nozzle, pressure is not relevant to the cooling process, just water volume (mass flow) for heat removal.

You could always consider cooling it with spray as it uncoils to feed the next operation. This would eliminate the overhead crane issues and reduce the total amount of time and water.

Gentlemen one and all.... unless the OP has a particular process in mind and a unusual reason that the WHOLE coil has the be cooled, then no steelworks would entertain the idea, when nature and time will do the job adequately and in a timely manner, with no extra costs.

The diagram of water being sprayed to the sides, while being a good diagram will not do the job, immersing the coil in a bath of water will do the job but after 2 or 3 coils you need to removed the HOT water and replace it with fresh cold water..

No steel works production office needs the cold coil the second it come off the mills, as it has a process to go through, and that has been thought through, planned for and the timing of the finished product is known.. It would seen our OP is trying to shorten the natural process of things.. as to what gain, who knows, he ain't telling.

Dear Sir as i have told in my previous statements as well that for natural cooling it would require about 48-60 hours per coil in a storage yard ,due to heavy downstream demand we cant dedicate so much cooling time for the same, thus it is required to cool the coils by unnatural means, like a pressurized cooling spray as well as some industrial cooling fans by which the same result can be achieved in less than 10 hours. As i have told earlier that this product has to go for further reduction transforming it into a cold rolled coil , the application wants it to be less than 100 degrees when it goes for pickling in crm. I hope this is a satisfactory answer to your query