Chemical Processing - November 2007 - (Page 40)

>> PROCESS PUZZLER Deter dryer difficulties Readers suggest how to improve reliability and avoid danger advantage is that turbo dryers are continuous; the spray dryer described is a batch dryer. In one turbo dryer application, a urea plant processed 5,000 lb./hr. with an initial moisture of 20% to a final content of 0.2% through a dryer 47-ft. high with a diameter of 15-ft. In another example, 4,200 lb./hr. of catalyst pellets were dried from 45% to 18% in a 23-ft. dryer with a diameter of 19ft. Tray dryers require more space than spray dryers but excel in efficiency, reliability and safety. A turbo dryer can dry any product below the boiling/flash point without the need for high pressure pumps. Installations I have been involved in have operated for years without any down time. Scott E. Crosby, president SKL Process Solutions, Grass Lake, Mich. Change the nozzles Have you ever considered air-atomizing nozzles? Significantly less line pressure is needed to form a spray pattern because the atomization energy is provided by compressed air or nitrogen. Mark Otterson, process engineer Lubrizol, Avon Lake, Ohio Consider four steps Surely there are many aspects to be corrected: 1) change to multiple spray; 2) use polytetrafluoroethylene nozzles with a pattern that will allow working at lower pump pressures; 3) change the oil gaskets on pumps, and bearings materials; and 4) add to the slurry, if possible, a rinsing aid that will allow better wet and dry flow. Emilio Malaguti, technical manager Chemtron, Hialeah, Fla. www.chemicalprocessing.com >> THIS MONTH’S PUZZLER A bulk spray dryer operates between 2,800 psig and 3,200 psig with a bioproduct feed slurry (Figure 1). The dried solid auto-ignites at 430°C, and this has occurred twice in four years. The reliability is poor. The on-stream factor is about 75% for numerous reasons: erosion of the single spray nozzle, which lasts only about three days before pressure drops below 2,800 psig; build-up of solids — knockers were deactivated due to poor maintenance; shaker failure in the baghouse; repeated bearing failure because of dust and poor location of blowers; frequent gas leaks, especially during start-ups; and failure of the oil seals on the high pressure pumps. In addition, we have observed several safety issues, including operating without an inlet filter element, removing the cartridge filters on the pump to achieve a higher atomization pressure, and infrequent tune-ups of the burner. Any suggestions on how we can improve safety and reduce breakdowns? >> Vent A ticking bomb? FIT PI TCV Combustion blower PI Product Product TE Product Product Natural gas Cartridge ﬁlter Slurry Reciprocating pumps Hopper TE Product Exhaust blower Filter Plug Spray nozzle TE PSH PSL PI Product Super sack Figure 1. Spray dryer suffers from poor reliability and poses operating dangers. Replace the spray dryer It almost sounds like this application isn’t well suited for a spray dryer. For harsh applications such as you have described, I would suggest looking into a rotary tray “turbo” dryer. Slurry is added to the top tray of the dryer. After one turn, the material is squeegeed to the next tray below. After several revolutions the product is dry. A unique 40 • November 2007 aspect of the dryer is that material is agitated as it cascades between levels, exposing fresh surfaces for drying. Product is removed at the bottom by a screw conveyor or other means. The air flow is generally counter-flow, not co-current as in the spray dryer. Dry hot air enters the bottom and humid air exits the top. Very little dust accumulates. A baghouse isn’t needed. Another http://www.chemicalprocessing.com

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Chemical Processing - November 2007 Contents From the Editor ChemicalProcessing.com Field Notes In Process Energy Saver Compliance Advisor PAT isn't Standing Pat Pursue the Perfect Plant Eliminate Exchanger Tubing Troubles Portable Conveyor Speeds Paint Production Process Puzzler Plant InSites Equipment & Services Product Spotlight/Classifieds Ad Index End Point

Chemical Processing - November 2007

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