The addition of grinding aids to the clinker in cement production is indeed important for several reasons
The addition of grinding aids to the clinker in cement production is indeed important for several reasons. Firstly, the fineness (Blaine specific surface) of the finished cement is one of the main factors that are affecting the development of early strength. Besides, the addition of grinding aids provides an energy consumption which consumed during cement grinding. In general, the energy consumption is linear up to a fineness of approximately 3000 cm2/g (Hewlett, 1998). Above this level, the energy consumption increases progressively due to agglomeration in the cement mill and a higher amount of energy is lost in heat. This is usually taken care of by the use of grinding aids and also by optimizing the cement mill technology. Reducing energy consumption is, therefore, another main driving force in the field of cement mill technology. Approximately 35-40 kWh/t is required to produce Portland cement with a Blaine in the area of 3000-3400 cm2/g (Hewlett, 1998).
When the grinding agents are used, the energy is reduced or the production rate is increased at the same energy consumption level. Moreover, energy saving is indeed important when producing blended cement. In the production of blast furnace slag cements the pure cement clinker is far more easy to size reduce compared to the slag. Trenkwalder and Ludwig, 2001 estimated the power consumption to be 43 and 68 kWh/t for producing cement and slag meal (separate processes) with a Blaine of 3000 and 4000 cm2/g respectively. Together with optimized mill technology they achieved a reduction in the electric power consumption of 7% without the use of grinding aid. Including a suitable grinding aids in such processes, the possibilities for the further increase in the grinding efficiency are most likely present. In summary, conventional grinding aids are usually used to increase the production rate in the cement mill. If such additions give beneficial chemical effects during hydration of the final cement (e.g. increased strength, improved workability etc.) the grinding aid will be regarded as quality improver or performance enhancer. Several conventional grinding aids today are also claimed to give beneficial chemical effects to a certain extent (Engelsen; C.J., 2008).
The main goals of GAs addition are to reduce the energy required to grind clinker in this subtlety and therefore increase the efficiency of cement mill, furthermore, to increase performance efficiency of the mill. Grinding aids provide some important positive effects on the final stage of grinding, such as cement, cement paste rheology of fresh or enhanced strength development of concrete (Gan, 1997). Milling is carried out at present time mainly in drum-ball mill.
Because of disadvantages: the high specific energy consumption and metal in recent times beginning to apply also other mill types, but for fine grinding of cement clinker, drum mill still indispensable (Shevchenko et al., 2008). It is clear that with increasing dispersion of cement is growing its activity, that allowing reduces specific consumption of cement at manufacturing concrete specified strength (Luginina, 2004). Moreover, the intensification of cement grinding helps save energy and improves the performance of existing equipment (Katsioti, 2009). Also, reducing wear metal grinding bodies and reduces gild expenses. Various grinding aids have different effects on the grind ability of clinker (Bravo, 2003). At present time, it is expedient study the effect of different, complex compositions intensifiers on grind ability and clinker quality of different mineralogical composition (Domone, 2010).
Grinding aids are preventing agglomeration and coating on ball and mill lining, this is due to its nature as organic substances that are strongly adsorbed on the surface of ground particles. Besides their dispersing effect, grinding aids also increase the efficiency of air separators because the finest particles are not carried along with the largest. The result is a reduction of circulating load and an improvement of particle size distribution (Sottili, 2001) (Emeish, S., 2013). The grinding process of cement absorbs 60-70% of the total energy employed. Finish grinding accounts for about 38% of specific electric power consumption. The quantity of energy required by the process to obtain the correct fineness is only partially employed for the creation of new surface: in fact, most of the total energy is lost as heat. Grinding efficiency rapidly decreases as fineness increases, mainly due to the agglomeration between the finest particles (Heren, 1996).
The advantages obtained by the use of grinding aids are significant mill output increase at the same fineness, the increase in production that can be used to reduce production costs or to cover market demand and fineness increase at an equal output, or both effects. In some cases very high fineness may only be obtained by using grinding aids and improved particle size distribution at equal fineness can be observed. It is well known that the particle size fraction between 3 and 30 µm affects the strengths development while the fractions below 3 µm contribute in the early strengths enhancement. The use of grinding aids allows higher mechanical strengths to be obtained and have a positive influence on particle size distribution. Such as higher separator efficiency, improved flow characteristics of the cement during transport, silo storage and during loading/unloading operations (Cella, 2001). In summary, conventional grinding aids are used to increase the production rate in the cement mill. If such additions give beneficial chemical effects during hydration of the final cement (e.g. increased strength, improved workability etc.) the grinding aid is regarded as quality improver or performance enhancer. It is emphasized that several conventional grinding aids today are also claimed to give beneficial chemical effects to a certain extent (Emeish, S., 2013).
In the mid-1930s, cement plants started to use cement additives to increase the production volume of cement. Since then, the use of additives became related to cement production. Until the 1960s, the basic materials used as grinding aids were amines, amino-acetates, phosphate, lingo sulfonate, acetic acid, glycols, and gluconates. Developed countries, such as Japan, United States, Germany, and Russia, conducted intensive research. The application of grinding aids became more diversified; the limitations of research on grinding aids remain an obstacle to the development of grinding aids technology. Most of the studies conducted on the hydration processes, interaction mechanisms of the main cement compounds, and the comparison of the effect between higher dosage (0.1% to 1% of the cement weight) and common dosage (0.02% to 0.05%) of grinding aids did not focus on grinding efficiency (Ramachandran; 1976; Heren and Olmez, 1996; Aggounet et al, 2008). Although China is the world’s largest cement producer, its development of grinding aids was slow and only started by the end of the1950s. Experiments used pulp waste and detergent waste. Results showed poor performance of these aids. At the beginning of the 1970s, the use of amine glycol and glycol base as grinding aids demonstrated better performance. However, the high cost of materials, limited availability, and uncertain quality limited further development. In the last decades, the main focus was to find new and more efficient amines to enhance grind ability and hydration (Lai; F.C.et al 2013).
Sika was the first construction chemicals supplier that launched sustainable construction. The company patented the Sika Grind 800 series, a new technology for green products based on polycarboxylic ether polymers. Sika Grind 800 series shows superior performance in the grind ability, strength enhancement, and flowability compared with the conventional glycol and amine-glycol-based grinding aids. To reduce agglomeration during the grinding of clinker, grinding aids are usually added in the range of 0.02% to 0.1% of the manufactured cement weight. Chemical basis of the grinding aids includes ethanolamines, such as triethanolamine, monoethanolamine, and tri isopropanolamine, as well as glycols, such as ethylene glycol and propylene glycol. The high polarity in their chemical functioning groups of -OH, -NH, etc. causes the tendency to adsorb on electrostatic surfaces from fractured covalent bonds of Ca-O, Al-O, and Si–O, and to resist the rebinding phenomenon, greatly assisting the formation of further cracks in the grinding process (Jeknavorian et al, 1998).
Eventually, better dry powder dispersion of the ground cement increases mill productivity and cement fineness for the same energy consumption, and produces improvement in flow, leading to faster unloading and improved storage volume of bulk cement storage. In a recent study of Teoreanu and Guslicov, (1999), a specific power consumption value of 25 kWh/t to100 kWh/t was used in cement manufacturing plants for conventional amine-glycol and glycol bases. However, no superior performance was observed or no new polymer grinding aids for grind ability and strength enhancement in grinding cement was formulated. Majority of the studies in literature (Teoreanu and Guslicov, 1999 and Joseph and Salim, 2011) are focused on the laboratory-scale milling control system and may not represent the actual production scale results. Therefore, a comparative study was carried out to evaluate the performance of polycarboxylic ether (PCE)-based new polymer grinding aids (SikaGrind 874MY) and the conventional amine-glycol- and glycol-based grinding aids (conventional/existing strength enhancer (SE)). The parameters used were production output, fineness, and mortar compressive strength. There are correspondingly many hypotheses in the scientific literature as well as in industrial practice. Starting from basic physical and chemical background, the laboratory screening process covering several hundred compounds and mixtures as well as extensive computer simulations (molecular modeling) (Mishra; R.K.,2012) provide a better understanding of grinding aids(Mishra; R.K.,2013). This makes it possible to design new, more efficient, customized additives. A wide variety of chemical admixtures (CAs) is added in cement and concrete with some dedicated function to enhance various performances of cement and concrete, such as 1) grinding aids for grinding energy-saving in cement production; 2) superplasticizers for improvement of workability of concrete and reduction of water amount required; 3) thickeners for mitigation of the bleeding problem of fresh concrete; 4) retarders and accelerators for adjustment of the setting behavior of fresh concrete and early strength, and 5) air-entraining agent
