Seven Circle Bangladesh Limited (SCBL) produces different grades of cement under the brand name Seven Rings Cement. the company offer both bulk and bag delivery options to our buyers. We pride ourselves in using top quality ingredients, 100% of the raw materials are imported from suppliers in theAsia Pacific region.
Specifications: Composition: IS 1489( Part 1) :1991 Min 80% Cement, Clinker Packed in 50Kg net PP/Paper Bag 15% Fly ash 5 % Gypsum
SCBL operates a cement grinding mill; it grinds together all the necessary raw materials in order to produce cement. Find below the general process to produce cement, each factory differs in the ratio of raw materials used in order to produce their product.
Dear Experts, I want to know about the GM size wise percentage distribution in a 2 chamber close circuit OPC ball mill. Mill dim. 3.4 x 12.5 Media load 128 MT high chrome Also let me know how do the supplier selected 80mm as max. Ball size in this mill? Please share the formula as well. Clinker feed size is 25mm with standard BWI & sp. gravity.
H there, These are just the basics if you want to accurately do it you have to fill it up to 80% BC and then do alongitudinal sieving and then correct the BC based on the results. The biggest ball determination is explained and it is based on material hardness and biggest size. Let me know if you need more info. Regards; FJalali
Thank you very much sir for this help. I was keen to know the media surface area in 1st and 2nd compartment also. You document helped me in knowing that also. Sir, Can you share the grinding balls standard surface area to be kept in raw mill and coal mill (monochamber)?
Dear Sagarhbt, Why are you concerned about surface area? I never hear about basing your ball charge on surface area! In your first compartment the grinding is not related to surface area at all and it is related to weight and number of impacts. In the second compartment the grinding is related to pass of contact or length of circumference (see attachment). But you should figure the ball charge base on how it is grinding along the length of the compartment. As I said before charge 80% of the weight base on one of the recommended ball charges and then take longitudinal samples and adjust based on the results. Let me know if you nedd ant help. Kind regards; FJALALI
Dear Sagarhbt, Why are you concerned about surface area? I never hear about basing your ball charge on surface area! In your first compartment the grinding is not related to surface area at all and it is related to weight and number of impacts. In the second compartment the grinding is related to pass of contact or length of circumference (see attachment).
But you should figure the ball charge base on how it is grinding along the length of the compartment. As I said before charge 80% of the weight base on one of the recommended ball charges and then take longitudinal samples and adjust based on the results.
Highly energy intensive unit operation of size reduction in cement industry is intended to provide a homogeneous and super fine (3000-4000 Blain) cement. Grinding operation is monitored for following parameters to ensure objectivity and economy of operation.
Chemical analysis of cement, generally on hourly basis. Product fineness, Blain surface and 45-micron residue. Cement SO3, % Grinding aid usage, grams/tonne Cement moisture, % Production rate, tonnes/hour Operating hours as run factor in % Specific power consumption (SPC) kWh/tonne.
Grindability and Power Consumption.Among various theories of comminution, most commonly accepted which is relevant to ball /tube mills is Bond's theory, which states that power input in comminution process is proportional to the surface generated in the process and the grindability of the material. To measure grindability, Bond developed 'Bond's Work Index' (BWI), a 'test mill' and a testing procedure for WI. With the help of this we can work out power required to grind a material from a given feed size to a product of given fineness.
Water Spray in Cement Mills.Water spray installed generally in second compartment of ball mill to control cement temperature. Cement discharge temperature should be kept below about 110oC but, the same time should allow some 60% dehydration of gypsum to optimize cement strength without excessive false set. Water spray is controlled with mill outlet gas or material temperature. A hardware interlock is recommended with mill main drive to avoid accidental spray in mill.
Grinding aids are generally added to the ball mill to reduce electrostatic agglomeration of fine particles and to reduce coating formation on grinding media which reduces grinding efficiency. The optimum addition rate should be determined carefully to enhance grinding efficiency. Grinding aids also serve to reduce coating problems in cement storage and enhances cement strengths.
Ball Mill.Ball mills with high efficiency separators have been used for cement grinding in cement plants all these years. Ball mill is a cylinder rotating at about 70-80% of critical speed on two trunnions in white metal bearings or slide shoe bearings for large capacity mills. Closed circuit ball mill with two compartments for coarse and fine grinding are generally found in cement plants for cement grinding. Compartments (filled with grinding media) are divided by a double diaphragm with flow control to utilize maximum mill length for effective grinding.
Grinding media contain balls of different sizes in designed proportions with large sizes in feed end and small sizes in discharge end. About 27 to 35 % volume of mill is filled with grinding media. Equilibrium charge is that charge where compensation for wear can be done by balls of one size only usually the largest size in the compartment. Grinding media could be made of forged steel, cast steel or even cast iron. To economize grinding media consumption, presently grinding media used are high chrome steel balls.
Mill shell is lined with lining plates to protect it from wear, high chrome steel liners are now commonly preferred to give longer life. Lifting liners are used to enhance impact in first compartment, where coarse grinding is dominated by impact. In second compartment which is longer in size (L>1.5D), classifying liners are used to ensure media classification along the length of mill with large size balls near mid partition and smaller balls at mill discharge end.
Ball mills are of 'bucket elevator' type for cement grinding, material is taken by conveyors to a separator where coarse was returned to the mill and fine sent to cyclone separator or bag filter for collection.
Different drive arrangement for ball mills are in existence. Commonly existing arrangement is mill drives with a girth gear and a pinion driven by motor with a gear box. Larger mills have a twin drives of half the ratings on either side of same girth gear. In central drive arrangement both the girth gear and pinion are avoided by connecting gear box output shaft directly to mill.
Closed circuit ball mills are existing with all types of separators () grit, mechanical and high efficiency in cement industries. Presently high efficiency separators are common to achieve maximum energy optimization. Brief description of separators is presented at the end.
Mill drive power or mill differential pressure to control mill feed rate. Mill Sound level to control filling level inside mill with feed rate. Mill outlet gas temperature. Mill outlet material temperature. Cement temperature. Outlet gas flow determined from mill inlet and outlet drafts or flow meters installed.
Vertical Roller Mills.In Vertical Roller mill 2 - 4 rollers (lined with replaceable liners) turning on their axles press on a rotating grinding table (lined with replaceable liners) mounted on the yoke of a gear box. Pressure is exerted hydraulically. This mill also has a built in high efficiency separator above the rollers to reduce circulation loads and consequently reducing differential pressure across the mill.
The mill is started either with the rollers in lifted-up position, or with the hydro-pneumatic system at low pressure. In grinding mode, actual metal to metal contact should be prevented by limit switches or a mechanical stop and by consistent feed. In VRMs the material cycle time is usually less than a minute against several minutes for a ball mill or tube mill. Thus, control response should be accordingly faster. In case mill feed fails action should be taken within no more than 45 seconds or excessive vibration will cause mill shut-down. Moreover, the vertical mills are subject to vibrations if material is too dry to form a stable bed. Therefore, provision is made for controlled spray water inside the mill During mill operation magnetic separator and metal detector should be always functional to ensure to exclude tramp metal which can damage the grinding surfaces.
Roller Press.Roller press consists of two rollers lined with wear resistant material. One roller is fixed and the other one is movable to exert pressure, applied hydraulically. A roller press looks similar to a roll crusher. However, the pressure exerted between rollers is very high - of the order of 400 kg/cm2 as compared to roll crushers. Feed is fed over the total width of the rollers by a central chute. About 30 % material gets pulverized to the required product fineness. Roller press output pre-ground material is fed to a ball mill operating in closed circuit. Ball mill required is smaller in size and larger grinding balls are no more required.
Separators Several types of separator are employed in mill circuits and there are numerous variations of each type: Mechanical separators Mill discharge material is fed onto a rotating dispersion plate whence it is spread off into a rising air stream. Coarse particles either fall directly from the dispersion plate or are rejected between the auxiliary fan blades and the control valve. Fine dust is taken along with main fan flow and is detrained as the gas flows downwards loses momentum (velocity) and diversion through the return vanes. Controlling parameters are the number of auxiliary blades, the clearance between auxiliary blades and control valve, and the radial position of the main fan blades
High efficiency separators, 3rd generation separators were introduced to improve the mechanical separator's fines recovery efficiency. Examples of these separators are O-Sepa (FLSmidth), Sepol (ThyssenKrupp) A simplified process flow these separators is as follows. Material is fed onto a rotating dispersion plate via air slide, whence it is dispersed off into the classifying air stream. Separator loading is recommended to be up to about 2.5kg feed/M3 air flow. Vortex is formed by the rotor which classifies particles between centrifugal force and the inward air flow. The fine fraction exits upwards/downwards with the air sucked by ID fan passes through cyclone separators or a bag filter for product collection, while the coarse fraction falls and is discharged from the bottom and send back to mill for regrinding. Fineness is controlled by rotor speed (increasing speed increases fineness).