2022留学researchpaper美国机械英语essay论文
OPERATIONAL EXPERIENCE FROM THE UNITED STATES' FIRST VERTICAL ROLLER MILL FOR CEMENT GRINDINGBy:美国机械英语论文-美国第一个立磨由留学生论文指导中心提供。Mark SimmonsProduction ManagerSalt River Materials GroupPhoenix Cement PlantLee GorbyManager of Quality ControlSalt River Materials GroupPhoenix Cement PlantJohn TerembulaProduct Manager – MillingFLSmidth, Inc.ABSTRACTFor several decades the cement industry has successfully utilized Vertical Roller Mills (VRM) forgrinding of raw materials and solid fuels. Most recently, this technology has been employed forthe comminution of Portland cement, blended cements and slag cements. The VRM offersseveral benefits compared to the ball mill in regards to operating costs and flexibility. However,the quality of the cement produced is extremely important in cement grinding and there is littleexperience with cement produced from a VRM in the US market. This paper relates theoperational experiences from the first VRM for clinker grinding put into operation in the UnitedStates in 2002. Included in the discussion are operational data, maintenance discussion andlaboratory data focused on product quality. All of the discussion is based on comparison to ballmill operation at the same plant.INTRODUCTIONTraditionally, the closed circuit ball mill with high efficiency separator has been the most commonsystem for cement grinding. However, as happened with raw grinding over the last 25 years, thevertical roller mill (VRM) is now successfully being usedfor many clinker grinding applications and is rapidlybecoming the standard for new grinding installations.The first such vertical roller mill installation in the UnitedStates was part of a total plant expansion and beganoperation in August of 2002.Phoenix Cement Company modernized their existingthree kiln plant to a state-of-the-art high efficiencyoperation by incorporating the newest technologyavailable in the cement industry. Spurred by a growingdemand for cement, the cement producer increasedtheir clinker capacity from 1700 STPD (1590 MTPD) toa capacity of 3000 STPD (2700 MTPD).For the new VRM cement grinding system, the cementproducer contracted with an equipment supplier basedin Bethlehem, Pennsylvania for a proven mill designthat was originally developed in Japan during the early1980’s. FIGURE 1 shows the VRM installed in theplant.FIGURE 1: Vertical Cement Mill NearPhoenix, AZball mill operation has been established throughout the history of ball mill cement grinding. Thedeficiencies as well as adequacies of ball mills are well known with regard to quality issuesmaking the effect of each quality issue critical to understanding the VRM’s reliability as a cementmill.QUALITY CONTROLIn a cement vertical roller mill grinding is performed in closed circuit and with an integral highefficiency separator. This arrangement will give a good steep PSD. Experience has shown thatthe overall product particle size distribution is consistent with that obtained from a ball millgrinding plant with a modern high efficiency separator. During the initial VRM optimization periodthe mill is fine-tuned to match its product to the existing ball mills. This is achieved by makingadjustments to operational parameters such as:• Separator rotor speed• Air flow rate• Grinding pressure• Dam ring heightBecause the VRM has significantly higher grinding efficiency than a ball mill there is much lessheat input from the grinding process. This is evident in the almost 50% less installed power, butis further taken into account with a smaller percentage of the energy being absorbed by thematerial. Compared to ball mills where 75% of installed power may be absorbed a good VRM willtake only 50% of the installed motor power as heat. The end result is that the product will not beheated up as much as in a ball mill. This means that a lower degree of gypsum dehydrationcould occur.A lesser degree of gypsum dehydration is not problematic considering two conditions; the inabilityto adequately control temperatures in ball mills creates an environment where operation is at theextreme of the gypsum dehydration. Additionally, less dehydration is not an issue if the gypsumis sufficiently reactive to control the setting reactions with a lower degree of dehydration as isnormally the case.If in special cases this is not the case different options are available to cope with the problem:• Addition of more gypsum (within the SO3 limit)• Increased dehydration of gypsum by adding more heat to the mill system• Addition of a more reactive form of gypsumPrehydration is not typically problematic in a VRM as it is in ball mill systems where highertemperatures and internal water-cooling systems are common. However, if cement is producedat a relatively high temperature and still has a lot of gypsum that is not dehydrated one must beaware of the potential problem of gypsum dehydration coupled with clinker prehydration that cantake place during storage in the cement silos. If a problem of this kind is present it can be copedwith it by one (or more) of the following options:• Ensuring that the cement is cooled to a lower temperature before going into the silo• Provoking a higher gypsum dehydration level in the mill• Replacing part of the gypsum with natural anhydriteThe actual VRM results achieved in Phoenix are built upon the theoretical rules for quality controlpresented here. During the initial period of operation, extensive quality data was recorded andanalyzed. The results from comparisons between the existing ball mills at the Phoenix plant andthe new VRM are presented in an abbreviated form. The data summarized below are based onThe longest continuous period that the mill was stopped was 66 hours during roller maintenance.To date the reliability of the mill gives every indication that this will be the norm for the life of thesystem.Through the first 2 years of full production the general trend indicates that maintenance costs areon the same level or slightly lower than for ball mills. It is expected that they will actuallydecrease as experience is gained and best practices are refined by the maintenance crew.WearThe VRM design allows the option of rotating the roller segments 180 degrees before replacing.They can also be hardfaced in place with a standard rewelding procedure. The table liners canalso be replaced or hardfaced. As of this time both methods have been undertaken.After the mill was in operation for over 10,000 hours the roller and table wear rates have beenmeasured 2 times, once through each method described above, roller segment rotation andrewelding of both the table and roller liners. The actual wear rate for both the roller and tableliners before hardfacing was 0.30 g/T. The measured wear rate with hardfaced liners was 0.12g/T. The 50% reduction in wear rate with hardfaced liners was expected as data from othervertical cement mills indicated such a savings could be expected. In either case the wear ratehas exceeded expectations and operation has not been detrimentally effected by wear.CONCLUSIONTwo years of cement vertical roller mill operation have proven the decision to invest in this newgrinding application was the right one. The VRM continuously demonstrates the ability to makeproduct equal to or better than existing ball mills with the tendency towards the better. The VRMproduct meets all market requirements in terms of both output and quality.A higher level of operational flexibility and improved consistency has been maintained. Overallbetter efficiency allows for lower operating costs. And easy, predictable maintenance add furtherbenefit to the bottom line. The Phoenix based cement producer is completely satisfied with theinstallation of a VRM for cement grinding.指导essay REFERENCESBenetatou, Angeliki and Jorgensen, Soren W., “OK Roller Mill for Cement Grinding-Experiencefrom Operation of Titan Cement’s OK27-4 Mill”. CemTech Conference, 2002.Roy, Gary R., “Increasing Cement Roller Grinding Capacity with vertical Roller Mill Technology”.IEEE-IAS/PCA Cement Industry Technical Conference 2002Jorgensen, Soren W., “Vertical Mill For Grinding Cement and Slag-Experience with the OK RollerMill in the Americas”. Cementos Hormigon, 2002.Terembula, John W., “The Successful Commissioning of the Phoenix Cement OK Mill”.International Cement Review, October 2003.Petersen, Luis, “Experience with the New Generation OK Mill”, NCB International Seminar, 2003Jorgensen, Soren W., “Cement grinding vertical roller mills versus ball mills”, 13th Arab-International Cement Conference and Exhibition, November 2004.Terembula, John W., “Ball Mill .vs. Roller Mill”, International Cement Review, December 2004,
