外文翻译---波特兰水泥的原料准备

外文资料翻译 Portland Cement Preparation of Raw Materials 1. Crushing The raw materials as received from the mines are in lump form and have to be crushed before fine grinding. The size of the lumps would depend upon the raw material and the method of mining, so the size of the crushing equipment used would depend primarily upon the size of the lumps received. In a modern cement factory, manufacturing 1000 to 2000 tonnes of cement per day, the limestone is mined by mechanical means and hence the size of individual pieces may be 1 meter or so. In smaller factories, the mining of limestone may be manual and the size of individual pieces may be 200 mm or so. Similarly, clay, shale, bauxite, laterite, sandstone, coal, gypsum, etc. may be received in sizes not larger than 300 mm. (a) Limestone Crushers: The requirement of limestone per day for a 2000 TPD factory may be about 2600 to 3000 TPD, for a 1000 TPD factory 1300 to1500 TPD and for a 300 TPD factory 400 to 450 TPD. As the mining operation has to be carried out in daylight hours only, the crushing operation should also be carried out in the 10 or 12 hours of light per day. The capacity of a limestone crusher for a 2000 TPD factory may be 300 TPH, for a 1000 TPD factory 150 TPH and for a 300 TPD factory 50 TPH. The decision on the type of limestone crusher would depend upon the physical properties of the limestone; however, for smaller factories using manually mined limestone, single stage Hammer Crushers are most suitable; but for larger factories two stage crushing is always more economical and more efficient. The first stage may be a Jaw Crusher, Gyratory Crusher or Impact Crusher and the second stage a Hammer Crusher or Cone Crusher. If possible, a screen of suitable size may be introduced after the secondary crusher to allow only undersize to go for further processing while oversize is returned to the crusher. A typical flowsheet for a limestone crushing plant in a 2000 TPD factory may be. Dumpers-Feed Hopper with Laminated conveyor at the bottom 300 TPH Jaw Crusher (feed size 1000 mm - product size 200 mm ) 300 TPH Hammer Crusher or Impact Crusher or Cone Crusher (feed size 200 mm - product size 20mm 300 THP Vibrating screen accepts minus 20 mm - oversize back to crusher. Proper dedusting arrangements must be made at the crushers, the vibrating screen and the transfer points and a Dust Collector with fan installed. Power consumed for the crushing operation may vary from 3 to 6 Kwh per tonne of limestone. (b) Other Crushers. Crushers required for crushing shale, gypsum, coal, etc. may be of suitable design, preferably Hammer Mills, and of suitable size. For the 2000 TPD factory requiring 10 % addition of shale to the raw mix, using the dry process and using 6 % gypsum for cement grinding, the shale required would be about 3000 TPD, coal 4000 TPD and gypsum 100 TPD. The preferable size of the crushers would be 30 TPH, 50 TPH and 20 TPH respectively. The feed size may be specified minus 300 mm, and product size 20 or 25mm. 2.Storage of Raw Materials Limestone in lump form is generally not stored at the factory, it is crushed as soon as it is received at the factory or even crushed at the mine itself and only crushed limestone is store at the factory. Shale or other corrective materials, coal and gypsum are generally stored in lump form as well as in crushed form. It would, therefore be advisable to have a common covered storage space for all types of crushed materials with proper partitions and proper reclaiming arrangements, Shale, gypsum, coal, etc., received in lump form, should be stored suitably and arrangements made to feed the same to the respective crushers mechanically. Two types of storage for crushed material are common: (a) crane gantry with Electric Overhead Travelling (EOT) cranes and (b) Storage bins with overhead feed belt conveyors and underground reclaiming belt conveyors, the second alternative may be more economical both in first costs and operating costs. The latest development in the storage of crushed raw materials, especially for factories with annual capacities of 0.5 million tonnes or more, is the Bed Blending System in which crushed limestone from different faces of the mines and correctives are spread in predetermined layers at one end and the material reclaimed with the help of cutter blades at the other end, so that a preblended raw mix of approximately the desired chemical composition is fed to the raw mill hoppers.the system can be housed either in the open or under cover, depending upon the climatic conditions of the location. Lump materials are generally stored in the open and reclaimed with the help of Pay Loaders or Scraper Haulers or Bull Dozers. 3.Fine Grinding In the manufacture of Portland Cement types, the calcareous constituent have to combine with the argillaceous constituents are ground and the more intimately they are mixed, the more efficient would be combination. If the limestone is of cement grade composition, the argillaceous constituents are intimately dis-seminated in the calcareous matrix, such a raw material can be ground coarse; but if the calcareous constituent is very pure and considerable amount of clay or shale has to be added, the raw mix must be ground much finer. A few tests carried out in a pilot plant can indicate the optimum degree of grinding required for a particular raw mix. It must be remembered that the raw materials fed to the grinding equipment are generally minus 20 mm and the product size may be 13 7% on 90 micron sieve. Intimate mixing is another important factor; the raw mix has to be brought to a very precise oxide composition, which in the manufacture of cement is generally gauged determining the total carbonates (TC) by simple acid/alkali titration. For example, if at a factory the holding point of TC is 78%, the TC from batch to batch should not vary more than 78 0.1%, and this can be achieved only by thorough mixing. 4.storage of Ground Material In the wet process the ground slurry is stored either in silos or in basins with continuous mixing. The storage capacity should be 2 to 3 days consumption for the factory. In the dry process, tall silos are used for storage of the dry raw meal. It is now the general practice that mixing silos or homogenising silos are placed above the storage silos, so that the ready mixed and corrected raw mix is fed to the storage silos by gravity, result in a saving in power. The various methods of feeding the slurry and the dry raw meal to the burning equipment will be discussed in the next section, dealing with burning operation. 5.Coal Grinding As coal has been considered a raw material, grinding of coal should also considered in this section. Coal has to be ground dry. Raw coal always contains 2% to 10% moisture; during the rainy season the moisture content always goes up, sometimes even up to 15% to 20%. Therefore, coal has to be dried suitably before grinding. In early days rotary driers were used, but some forty years ago, mills were designed in which the coal could be dried and ground simultaneously with the help of hot air, in air swept ball mills. In separate drying and grinding systems the raw is dried in suitable driers with the help of hot air generated in an oil fired or coal fired or coal fired furnace; the spent air is vented to the atmosphere through suitable dust collectors. The dry coal is then ground, either in an open circuit coal mill in which the ground coal is transported to the coal firing hopper with the help of a bucket elevator, other dry coal may be ground in an air swept close circuit mill, and air used to transport the ground coal to the cyclone over the coal firing hopper; the same air is used as primary air in the coal firing pipe. In a simultaneous drying and grinding system, the front portion of the mill; fitted with lifters and chains, acts as the rotary drier and the back portion, filled with steel balls, acts as the closed circuit mill; hot air, either from the rotary kiln or from an auxiliary furnace, is used as air for drying and transporting the coal. The spent air, in this case also, is used as primary air in the coal firing pipe. The power consumption in separate drying and grinding units may work out to 25 to 30 kW h per tonne fine coal and in the simultaneous drying and grinding units to about 20 to 25 kW h per tonne fine coal. 6.Burning A mixture of pure lime and silica in the proportion of 2. 8:1 should give 100% tricalcium silicate on burning, but it will require a very prolonged heating at 1600 or more, to obtain a perfect combination. It is not possible to obtain such prolonged heating conditions in actual plant practice; it is, therefore, necessary to add some fluxing materials to bring about the combination at a lower temperature and in a shorter time. Alumina, iron oxide and, to some extent, magnesia and alkalies present in the raw mix act as the fluxing agents. By judicious inclusion of these oxides in the raw mix it is possible to shorten the reaction time to reasonable limits within the range of temperatures available in actual plant practice. In the process of burning in the manufacture of cement, the raw mix is first heated to about 100 where the moisture present in the dry raw meal or in the semi -dry process nodules or in the wet process slurry is removed. The dry raw mix is further heated and at about 400 to 500 the combined moisture present in the clay matter of the raw mix is dissociated and removed and magnesium carbonate, if present, is dissociated. On further heating to about 900 the calcium carbonate (the main ingredient of the raw mix) is dissociated, carbon dioxide evolved and simultaneously combination between the lime (CaO) and the Silica (SiO2), alumina (Al2O3) and iron-oxide (Fe2O3) starts. Presumably, first all the FezO3 present in the raw mix and a part of Al2O3 combine with lime to form C4AF at about 1200 . This point may be termed as the start of the burning zone of the rotary kiln. The C4AF being the liquid form, the loose powdery mass starts becoming more coherent, and the movement of the material in the rotary kiln becomes more sluggish. At the same time, a part of the SiO2 present starts combining with CaO to form C2S. Then the remaining Al2O3 present combines with lime to form C3A, and now because the material has more liquids proper clinker nodule formation starts. As the mass passes further down the kiln, all the SiO2 present combines with lime (CaO) to form C2S and the remaining lime (CaO) starts combining with C2S to form C3S. This point may be called the beginning of the actual clinkering zone which extends to the point where practically all the lime present combines with C2S to form C3S and very little free lime is left. At this point the clinker leaves the burning zone and cooling of the clinker starts. Clinker burning takes place in the above mentioned sequence in all the processes of burning, viz. , Long Dry Process Kiln, Long Wet Process Kiln, Short Dry Process kiln with suspension preheaters and Short Kilns with great heat exchangers. Lime silicates (C2S and C3S) are the true cementations materials, C3S contributing towards early strength and C2S towards late strength, so the Process Chemist tries to obtain the highest possible C3S and lowest possible free lime in his clinker commensurate with: 波特兰水泥的原料准备 破碎 作为从矿山得到的原料以块状形式（存在），必须在研磨之前被破碎。 块状的大小取决于原料和采矿的方法，因此，所用破碎设备的尺寸（规格）将主要地取决于收到的块状大小。在一个现代化的水泥工厂 ,每天生产（日产） 1000 到 2000吨的水泥，石灰石采用机械的方法（手段）挖掘，因此个别的块大小可能达到 1米左右。在较小的工厂，石灰石的采矿可能是人工的，个别块的大小可能达到200 毫米左右。同样地 ,粘土、页岩、（铝）矾土、红土（铁矾土）、，沙岩、煤、石膏等，其大小一般不超过 300 毫米。 (a)石灰石破碎：一个 2000TPD 的工厂每天石灰石的需求量可能是 2600 到3000TPD；一个 1000TPD 的工厂每天石灰石的需求量可能是 1300 到 1500TPD；一个 300TPD 的工厂每天石灰石的需求量可能是 400 到 450TPD。由于采矿操作必须在白天进行 ,破碎操作也应该在白天的 10 或 12 个小时内进行。一个 2000TPD 的工厂石灰石破碎机的能力可能是 300TPH；一个 1000TPD 的工厂是 150 TPH；一个300TPD 的工厂是 50TPH。石灰石破碎机的选型取决于石灰石的物理性质，然而，对于用人工挖掘石灰石的小型工厂 , 单段锤式破碎机是最适当的，但对于比较大的工厂，二级破碎总是更经济和更有效率，第一个阶段可 以是颚式破碎机、转子破碎机或冲击破碎机，第二个阶段破碎为锤式破碎机或圆锥式破碎机。如果可能，适当尺寸的筛子应该用于二级破碎以便只允许小于（筛孔）尺寸的物料通过而大块物料继续破碎。一个典型的 2000 TPD 石灰石破碎生产线流程应该是： 底部装有薄板传送带的卸料斗； 300TPH 颚式破碎机 (原料大小 1000 毫米、 产品大小 200 毫米 )； 300 TPH 锤式破碎机或冲击破碎机或圆锥破碎机 (原料大小 200 毫米、产品大小 20 mm )； 300THP 振动筛 -允许小于 20 毫米通过 太大的返回破碎机。 破碎机、振动筛和转向点必须安排适当的除尘，收尘器安装有风机。破碎作业的能耗变化很大，从 3 到 6 Kwh/吨石灰石。 （ b）其它的破碎。页岩、石膏和煤等的破碎必需使用破碎设备，使用锤式磨机及适当的大小（规格）可能是适当的设计。对于 2000 TPD 的工厂，原料混合物中需要加入 10%的页岩，使用干法生产（工艺）以及水泥磨中加入 6%石膏，页岩 的需求量大约为 300TPD、煤 400TPD 和石膏 100TPD。破碎机较好的大小（规格）将分别地是 30TPH， 50TPH 和 20TPH，原料粒度规（指）定为小于 300 毫米，产 品粒度为 20 或 25 mm。 2.原料的储藏 块状石灰石通常不在工厂储存 ,一旦进厂就立即被破碎，或者甚至在矿山本身就被破碎，在工厂只是储藏。页岩或其他的校正原料、煤和石膏通常最好以破碎过的块状形式储存，因此，对所有类型的破碎过的原料，最好有公共的带有屋顶的并被适当分割以及适当取料 -页岩、手石膏、煤等的储藏空间（联合堆棚），收到的块状（物料）将被巧妙的储存和排列以使相同的物料去各自的破碎机械。 破碎物料储库的两种类型通常是： (a)带有电动天车 (EOT)的起重机， (b)带有高空物料皮带输送机和地下取料皮带输送机的 储藏箱柜（储库）， 第二种选择可能在第一费用（基建费用）和生产费用更经济。在破碎的原料储藏方面的最新发展-尤其是年产五十万吨或更多的工厂 , 是“混合床系统（预配料均化系统）” -从不同矿区来的破碎过的石灰石和校正原料，从一端以预先确定的层铺开，在另一端借助于刀片取料 , 以便使预混料近似于需要的化学成分被喂到生料磨喂料斗。根据当地气候，该系统既可有厂房，也可露天或搭棚。块状物料通常露天储存并且借助于装载机或铲车或推土机取料。 3.粉磨 在波特兰类型水泥的生产中，石灰质成份必须与粘土质成份联合粉并且更密切地混合，（成分）差别越大越要混合。如果石灰石是水泥主要成分，粘土成分密切地分布在石灰质的点阵中，这样的原料粉磨可能是地粗糙的，但是如果石灰质成份是非常纯的并且相当量的泥土或页岩必须加入 , 混合原料必须充分粉磨。在一个试验工厂进行的一些测试表明了详细的原料混合所需要的最适宜的研磨程度。供应给磨机的原料一般小于 20 毫米、产品细度应该是 90 微米筛子的筛余为 13 7%-这必须被记住。密切的混合是另一个重要因素，原料的混合不得不带进大量氧化物成分，在 水泥的生产中通常通过简单的酸 /碱滴定测量确定总碳酸盐 (TC)。 举例来说，如果在一间工厂把握的 TC 是 78%，每一批的 TC 变化量不应该超过 78 0.1% ，而且这可能只有通过完全的混合来实现。 4.生料储存 在湿法生产（工艺）中，粉磨的生料浆既可储存在生料（料浆）库和带连续混合的料浆池中，储存能力应该是工厂 2 到 3 天的消费量。在干法生产（工艺）中，高大的生料库用于干生料的储存，设置在储存库之上的混合库或“均化库”是目前通常采用的，以便预先混合并得到调整的混合生料通过重力被喂入到储存库，以节省动力。生料浆和干生 料以各种不同的方法喂入到煅烧设备，煅烧过程行为将在下面章节中讨论。