Roofing Process Cooling Recommendations
Example Plant
Cooling requirements:
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According to the information furnished (sample plant), your maximum cooling requirement will be approximately 7.0 Million btu/hr. This is what will be required to cool the composite shingle web to 95F under the conditions listed below.
Web width= varies 31" to 39.375"
Max.design line speed= 700 fpm
Max.material wt.= 97.1 lb/100sq.ft.
Max.Cp=0.269 btu/lb-degF
If we were to assume that all the cooling occurred through evaporative methods, you would need to design for 15 gpm of water flow. Although difficult to measure, we know that heat is also lost through cooling rolls, air convection, and radiated to the environment.
Another factor in figuring cooling water demand is the amount of over spray and other sources of depletion.
All in all, I feel it will be safe to set up the evaporative portion of your cooling system to accommodate a flow rate of 15 gpm.
In the recommendations listed below, you must implement the air flow requirements to perform effective evaporative cooling performance.
These recommendations will be limited to methods of cooling administered between the press roll arrangement and the finished product looper.
RECOMMENDATIONS
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ROLL CONFIGURATION:
I recommend that you modify your roll configuration to increase the dwell time in the cooling section. You should have 180 to 210 feet of sheet travel between your first application of cooling water and the end of your effective cooling section. Many plants have changed their cooling rolls to 12" dia. to maximize space.
TOTAL WATER FLOW:
I recommend that you provide a filtered water supply able to provide 15 gpm at 60psig.
NUMBER OF HEADERS:
The number of spray headers should be between 12 and 16 to provide the most flexibility in stage control logic without redundancy.
NOZZLE TYPE:
You must decide which type of nozzle type you prefer; liquid pressure or air atomized. Air atomized nozzles will apply at low flow rates with fewer plugging problems. The air atomized nozzles consume a lot of compressed air. The energy costs associated with compressing that air cost your plant as much as $40,000 per year, not including capital for compressor equipment and maintenance.
Liquid pressure nozzles require more frequent cleaning and upkeep. From my observations, air atomized nozzles are more frequently used throughout the industry, because most plants are unable to administrate effective nozzle maintenance on small orifice nozzles. Many plants use air atomized nozzles in locations requiring lower flow rates and liquid pressure nozzles in all other locations.
NOZZLE SIZE:
If you can successfully filter your spray water to 10 micron Spraying Systems 9501 nozzles will suffice. I recommend Spraying Systems 9502 and 9503 sizes when appropriate filtration can not be achieved. These nozzles will give a 95 deg angle of spray and allow for an overlap of spray pattern while permitting you to locate the headers relatively close to the sheet.
For air atomized nozzles, you may want to use Spraying Systems SU13-SS with a 2850 fluid cap and a 73328 air cap.
NOZZLE SPACING/PROTECTION:
Simple geometry will direct the spacing and nozzle/sheet distance. There are a few guidelines
to follow. Overlap spray patterns approximately 10 to 15% of pattern width. Allow for approx. 25% of the outermost patterns to spray off the edge of the sheet. This will allow for sheet walk and also eliminate the impact of the light edges of the spray pattern. The nozzle tips must be protected from contact by the product web. Guards or shields must be used.
HEADER LOCATION/ACCESSIBILITY:
Header location should be such that water application occurs just after sheet contacts roll surface. This will allow the maximum dwell time between water application and roll contact. This factor may not be as important as operator accessibility. Please fax a copy of your cooling roll layout and I will recommend location.
FILTRATION:
Supply water should be filtered with duplex/cartridge type filter units. I recommend 10 micron accordion type disposable cartridges.
PIPING:
I recommend use of 304SS pipe. High pressure rubber lined flex hoses with quick disconnects will make header removal much more practical. Ball valves should be located upstream from the solenoid and flex hose.
FLOW CONTROL VALVE:
Work is going on now to test the effectiveness of regulating header pressure as a means of reducing the roughness of stage control. You may want to prepare your piping for an additional control valve for future integration into your cooling control package.
SOLENOIDS:
I recommend 12VDC, fail closed solenoid valves. 120VAC solenoid valves may be used, but present a potential for more serious electrical hazards.
TOTAL AIR FLOW:
Air flow is an area needing much improvement in your cooling section. Depending on the method of distribution, you will need 50,000 to 75,000 scfm of dry cool ambient air to effectively evaporate and perform the necessary cooling in the cooling section.
METHOD OF AIR DISTRIBUTION:
Direct impingement will afford the most effective cooling because it breaks up the humid boundary layer at the sheet surface. Air knives provide good boundary layer turbulence but provide it for very short dwell times (only several inches of sheet travel). If full length impingement methods are not practical, you may opt to use another method. Force large amounts of ambient air across the web using cage fans or large scale methods.
AIR KNIVES:
High pressure air knives can be very effective in stripping excess water at the exit of the cooling section.
METHOD OF CONTROL:
I recommend the five loop cooling control package as described in the Roofing Technology product bulletin.
NOZZLE MAINTENANCE:
I recommend written procedures for methods and frequency of nozzle maintenance. Nozzle failures may be the greatest cause of cross web temperature variation. Operators need a good supply of nozzle parts and cleaning tools available at all times.
SPC AND COOLING:
SPC charting of finished product moisture content is a very effective tool in pointing to cooling performance problems.
I hope you have benefited from this information. Please give me a call if you have any questions.
Sincerely,
John E. Youngk
John E Youngk
President
Roofing Technology, Inc.