|
OPERATIONAL EXPERIENCE FROM THE UNITED STATES' FIRST VERTICAL ROLLER MILL FOR CEMENT GRINDING By: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 Simmons Production Manager Salt River Materials Group Phoenix Cement Plant Lee Gorby Manager of Quality Control Salt River Materials Group Phoenix Cement Plant John Terembula Product Manager – Milling FLSmidth, Inc. ABSTRACT For several decades the cement industry has successfully utilized Vertical Roller Mills (VRM) for grinding of raw materials and solid fuels. Most recently, this technology has been employed for the comminution of Portland cement, blended cements and slag cements. The VRM offers several 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 little experience with cement produced from a VRM in the US market. This paper relates the operational experiences from the first VRM for clinker grinding put into operation in the United States in 2002. Included in the discussion are operational data, maintenance discussion and laboratory data focused on product quality. All of the discussion is based on comparison to ball mill operation at the same plant. INTRODUCTION Traditionally, the closed circuit ball mill with high efficiency separator has been the most common system for cement grinding. However, as happened with raw grinding over the last 25 years, the vertical roller mill (VRM) is now successfully being used for many clinker grinding applications and is rapidly becoming the standard for new grinding installations. The first such vertical roller mill installation in the United States was part of a total plant expansion and began operation in August of 2002. Phoenix Cement Company modernized their existing three kiln plant to a state-of-the-art high efficiency operation by incorporating the newest technology available in the cement industry. Spurred by a growing demand for cement, the cement producer increased their clinker capacity from 1700 STPD (1590 MTPD) to a capacity of 3000 STPD (2700 MTPD). For the new VRM cement grinding system, the cement producer contracted with an equipment supplier based in Bethlehem, Pennsylvania for a proven mill design that was originally developed in Japan during the early 1980’s. FIGURE 1 shows the VRM installed in the plant. FIGURE 1: Vertical Cement Mill Near Phoenix, AZ ball mill operation has been established throughout the history of ball mill cement grinding. The deficiencies as well as adequacies of ball mills are well known with regard to quality issues making the effect of each quality issue critical to understanding the VRM’s reliability as a cement mill. QUALITY CONTROL In a cement vertical roller mill grinding is performed in closed circuit and with an integral high efficiency separator. This arrangement will give a good steep PSD. Experience has shown that the overall product particle size distribution is consistent with that obtained from a ball mill grinding plant with a modern high efficiency separator. During the initial VRM optimization period the mill is fine-tuned to match its product to the existing ball mills. This is achieved by making adjustments to operational parameters such as: • Separator rotor speed • Air flow rate • Grinding pressure • Dam ring height Because the VRM has significantly higher grinding efficiency than a ball mill there is much less heat input from the grinding process. This is evident in the almost 50% less installed power, but is further taken into account with a smaller percentage of the energy being absorbed by the material. Compared to ball mills where 75% of installed power may be absorbed a good VRM will take only 50% of the installed motor power as heat. The end result is that the product will not be heated up as much as in a ball mill. This means that a lower degree of gypsum dehydration could occur. A lesser degree of gypsum dehydration is not problematic considering two conditions; the inability to adequately control temperatures in ball mills creates an environment where operation is at the extreme of the gypsum dehydration. Additionally, less dehydration is not an issue if the gypsum is sufficiently reactive to control the setting reactions with a lower degree of dehydration as is normally 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 gypsum Prehydration is not typically problematic in a VRM as it is in ball mill systems where higher temperatures and internal water-cooling systems are common. However, if cement is produced at a relatively high temperature and still has a lot of gypsum that is not dehydrated one must be aware of the potential problem of gypsum dehydration coupled with clinker prehydration that can take place during storage in the cement silos. If a problem of this kind is present it can be coped with 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 anhydrite The actual VRM results achieved in Phoenix are built upon the theoretical rules for quality control presented here. During the initial period of operation, extensive quality data was recorded and analyzed. The results from comparisons between the existing ball mills at the Phoenix plant and the new VRM are presented in an abbreviated form. The data summarized below are based on The 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 the system.  Through the first 2 years of full production the general trend indicates that maintenance costs are on the same level or slightly lower than for ball mills. It is expected that they will actually decrease as experience is gained and best practices are refined by the maintenance crew. Wear The 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 can also 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 been measured 2 times, once through each method described above, roller segment rotation and rewelding of both the table and roller liners. The actual wear rate for both the roller and table liners before hardfacing was 0.30 g/T. The measured wear rate with hardfaced liners was 0.12 g/T. The 50% reduction in wear rate with hardfaced liners was expected as data from other vertical cement mills indicated such a savings could be expected. In either case the wear rate has exceeded expectations and operation has not been detrimentally effected by wear. CONCLUSION Two years of cement vertical roller mill operation have proven the decision to invest in this new grinding application was the right one. The VRM continuously demonstrates the ability to make product equal to or better than existing ball mills with the tendency towards the better. The VRM product meets all market requirements in terms of both output and quality. A higher level of operational flexibility and improved consistency has been maintained. Overall better efficiency allows for lower operating costs. And easy, predictable maintenance add further benefit to the bottom line. The Phoenix based cement producer is completely satisfied with the installation of a VRM for cement grinding. 指导essay REFERENCES Benetatou, Angeliki and Jorgensen, Soren W., “OK Roller Mill for Cement Grinding-Experience from 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 2002 Jorgensen, Soren W., “Vertical Mill For Grinding Cement and Slag-Experience with the OK Roller Mill 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, 2003 Jorgensen, 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, |
 |
|||
| 网站地图 |
