Roller Press FL Smidth PDF [PDF]

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THE ROLLER PRESS The High Pressure Grinding Rolls are used for crushing industrial minerals. In the Cement Industry, the roller presses are used in crushing of clinker, limestone, slag and trass minerals. These crushed minerals are easily ground, reduce the energy consumtion of the grinding mills, extends the working life of mills and all their components.



Grinding Principle The crushing and the grinding occurs between two cylinders under high pressure, rotating in opposite directions and having a gap between them. The feed mineral takes the form of a thin band when passing between the rollers. One of the counter-rotating cylinders is fixed and the other moves horizontally under high pressure. The final product is called the mineral cake slab or only the cake or only the slab. The pressure force of the movable cylinder is provided by a spring . Nowadays, instead of the spring, the hydraulic pressure cylinders are used which securely supply pressure.



Figure 1. Grinding Principle



General Features and Information for Users The manufacturers and suppliers will design the roller presses according to given mineral sample and desired technical specifications. They have slightly different design calculations, but they are generally very similar. The Users can also choose the roller press that is suitable from Manufacturer’s Guide. Here is a roller press example used in the cement plants which is similar to the working mechanisms and hydraulic systems. The Users can adapt this example to their own roller presses. The most important for the users is the calculation of the crushing capacity ( the press throuhput ), the pressure force, the power , the energy consumption, the energy - saving. I hope these information about the roller press will be useful to the users.



Figure 2. Figure 3.



General Design and Main Elements



The symbols can be given differently in different catalogs and guide books. Q = Press Throughput Capacity ( t/h ) =The throughput is calculated by the dimensions of the press and the dencity of the cake slab. ( The Users request from the supplier It’s the throughput, the press force, the absorbed motor power and the specific energy consiption for clinker. The Users also demand optimal operating conditions and layout configuration.) ( The project, the sizing criteria and the sizing are done by the supplier or by the contract manufacturer of the supplier. ) Gz = Initial Gap or Zero Gap ( mm ) = It is determined by the supplier depending on other operating parameters. The most efficient working point must be during commissioning by trials (absorbed power, hard or soft spring effect, initial nitrogen pressure, hyraulic pressure, feeding material size etc.). it is usually between 10 mm. and 15 mm. for clinker. The Users should set this zero gap. Sc = Gap Opening or Operating Gap ( mm ) = Cake Slab Thickness ( mm ) = The gap opening is a function of the material, roller diameter and roller surface. It is varies between 15 mm.and 45 mm. Guide value for Sc are ; for Clinker 30-32 mm., for Limestone 28-30 mm., for Trass and Slap 26-28 mm. Gm = Maximum Gap = Maximum clearance between rolls when there is no operational work. Maximum size of feed mineral x 2 or Operating Gap (Sc) x2 = 60 mm ( for clinker ) Vc = Roller Circumferential Speed ( m/s ) = There is a risk of vibrations at speeds above 1,8 m / s. ( The Critical Speed is 1,8 m/s. If it is higher than this speed, regular operational work is not possible. An optimum speed between 1 and 1.6 is calculated and selected. ) D = Roller Diamater ( mm ) = Each supplier designs the roller presses in specific standard diameters and widths to suit the customer's desired capacity. w = Roller Width = Cake Slab Width ( mm ) = Each supplier designs the roller presses in specific standard diameters and widths to suit the customer's desired capacity. Df = Dencity of feed mineral ( t/m3 ) = The user and the supplier determine in the laboratory. Dc = Dencity of cake slab ( t/m3 ) = The user and the supplier determine in the laboratory.



a = Nip Angle ( 0 ) = Guide value of this angle ( for Clinker 6,9-9,2( 0 ), for Raw Material 9,2-12,6( 0 ), for Trass and Slap 5,7-7,5( 0 ) ) b = Attack angle or Compression Angle ( 0 ) = This angle depends on the roller diamater, the gap opening and the type of mineral ( the mineral granulation, the mineral hardness, the mineral humudity ratio, etc. ). Guide value of this angle ( for Clinker 2,3-2,85( 0 ), for Raw Material 2,85-4( 0 ), for Trass and Slap 1,7-2,3( 0 ) ) g = Feed Angle ( 0 ) = This angle used by the supplier or the manufacturer and is determined at optimum. It is always bigger than the attack angle and It is an angle that gives a minumum load on to the rollers. F = Press Force ( kN ) = It is calculated from the optimal specific surface load and the optimal specific press force. d = Diamater of hydraulıc cylinders ( mm ) = It is calculated and manufactured according to the desired pressing force. z = Number of hydraulic cylinders ( . ) = According to the press size, 2 or 4 pieces are mounted. Ph = Hydraulic Pressure ( bar ) = The hydraulic system pressure setpoints are issued by the supplier. Fs = Specific Press Force ( kN/m2 ) = The specific press force is the press force divided by the projected roller area. The most suppliers allow a specific press force of ~ 8500 ( kN/m2 ). The most important point is to protect the roller from overstress. Overstress increases the roll wear rate and causes the roller bearing failures, further mechanical, electrical and hydraulical failures.( It can be subjected to further discussion ) = It generally recommended ~ 6500 ( kN/m2 ). ( It must be max. 8500 kN/m2 ). Ls = Specific Surface Load ( N/mm2 ) = The specific surface load is the pressure force coming to the unit area of the cylinder surface under pressure. This load shall not exceed 250 (N / mm2). ( It can be subjected to further discussion ). It must be maximum 250 ( N/mm2). ( protection from mechanical failures and wearing, for long service life etc. ) P = Absorbed Motor Power ( kW ) = The absorbed motor power can be calculated by means of the press force, the circumferential speed of the rollers and the attack angle. The drive motor is selected by adding tolerance power.



Es = Specific Energy Consumtion ( kWh/t ) = The specific energy consumption Es is based on the througput capacity. ( for Clinker ~ 2,8 , for Limestone ~ 2,3 , for Trass and Slap ~ 3 are selected ). u =Circulation Factor ( . ) = ( If the press is in closed circuit with a separator or a slab recirculation ) Ec = Specific Energy Consumption ( kWh/t ) = (If a press closed circuit with a seperator or a has a cake slab recirculation, the specific energy consumption is multiplied by the circulation factor u. The specific energy consumption Ec is then based on the material leaving the press circuit.( Final Grinding Product )).



Symbols, Formulas and Definitions with an example Q = Press Throughput Capacity ( t/h ) = 320 t/h ( for clinker ) Gz = Zero Gap ( mm ) = 12 mm ( for clinker ) Sc = Operating Gap ( mm ) = Cake Slab Thickness ( mm ) = 30 mm ( for clinker ) Gm = Maximum Gap (mm ) = 60 mm ( for all minerals ) Vc = Roller Circumferential Speed ( m/s ) = 1,52 m/s ( for all minerals ) D = Roller Diamater ( mm ) = 1450 mm w = Roller Width ( mm ) = Cake Slab Width ( mm ) = 780 mm Dc = Dencity of cake slab ( t/m3 ) = ~2,5 t/m3.clinker ( Limestone ~2,4 t/m3, slap and trass ~2,2 t/m3 ) Ph1 = Initial Hydraulic Pressure ( bar ) = 85 bar ( for clinker setpoint ) = 65 bar (for trass setpoint ) Pn = Initial Nitrogen Charge Pressure ( bar ) = 40 bar ( for all minerals ) Ph = Operating Hydraulic Pressure ( bar ) = ~ 180 bar ( for clinker ) = ~ 160 bar ( for trass ) (Hydraulic safety valve opens at 220 bar pressure. Care must be taken that the operational hydraulic pressure does not exceed 200 bar.) Pmax. = Max. Motor Power ( kW ) = 700 kW x 2, Electric Motor rpm = 1400 1/min. ( constant ) Max. Skewing = 12 mm , Limited Skewing with the sensors < 5 mm , ( Automatic stop at 5 mm ) Hydraulic oil temperature should be kept between 20 and 70 degrees centigrade, ( 20 < Toil < 70 ) C0



Other Formulas



F = (d/1000)2.π.z.Ph.(100/4)



P = (2.F. b radians.Vc)/µ



( kN )



( kW )



Fs = F.106/D.w



( kN/m2 )



Ls = 2.F.103/D.w.αradians



( N/mm2 )



Es = P/Q



( kWh/t )



Ec = P.u/Q



( kWh/t )



µ is efficiency gearbox and motor



Press Force and Operational Pressure Graph



Process Configuration - Installation of The Roller Press



1–2



3



4



The Roller Press can be installed in various combinations 1 - The Roller Press as a pregrinding unit 2 - The Roller Press as a pregrinding unit with slab recirculation 3 - The Roller Press as two stage grinding component ( semi finish grinding ) 4 - The Roller Press as the finish grinding system ( the roller press is in closed circuit with a desagglomerator or a seperator ) The Users choose the most appropriate process configuration. The detailed decription for its optimal installation type, advantages and disadvantages are given by the suppliers.



Effective and Efficient Operational Situations



Figure 5



Adjustable Feed Gate



The Adjustable Feed Gates are very important in press operation. The all manufacturers design and install the adjustable feed gates. For our sample press, the feed gates openings and positions are the average for clinker and a different cake thickness is obtained for the other minerals. The cake thickness is a function of feed gate opening, crushed mineral hardness and granulation, zero gap and applied force. Adjusting to leave more space on the fixed roll side of the feed gates gives the most efficient operation. The best results are found with trials during commissioning. Adjust the values given by your roller press supplier.



Figure 6



Operating Parameters



Figure 7 The degree of comminution of minerals into small grains depends on the energy transmitted to it. It varies in proportion to the applied force. The amount of force applied is also a function of the hydraulic pressure. The working pressure depends on 3 parameters. - Initial Nitrogen Charge, Nitrogen Pressure setting - Initial Hydraulic Pressure set point, Hydraulic System - The initial gap, zero setting of gap Relations between parameters and their effects. Initial Nitrogen Pressure < Initial Hydraulic Pressure set point < Operating Pressure - If the difference between Nitrogen Pressure and Hydraulic Pressure set point is large, Hydraulic Accumulators will work like hard springs. For hard minerals such as clinker, this pressure difference should be adjusted. Set the values given by your supplier taking into account the mechanical deformation and wear rate. - If the difference between Nitrogen Pressure and Hydraulic Pressure set point is small, Hydraulic Accumulators will work like soft springs. This pressure difference must be adjusted for soft minerals. Your supplier will give you the value to work with the highest efficiency.



If the following parameters are set for our example, the data results are approximated as follows. If set to Gm = 60 mm = Constant, Gz = 12 mm = Constant, Gf = 160 mm ( from figure 6 ), Pn = 40 bar, Ph1 = 85 bar ( for clinker ), P Motor Power = 220 x 2 kW ( in idle work ) Output data results, Sc = 30 mm, Q clinker = 320 t/h , P Motor Power = 600 x 2 kW , Pn = Ph = 180 bar ( during operation ) As you can see, some output depends on parameter settings, which are functions of each other. With different parameter settings the Roller Press force ( F ) can be increased or decreased. - Without changing the initial hydraulic pressure setpoint ( Ph1 ) and the zero gap ( Gz ), if the nitrogen initial pressure is reduced, the F force is increased and if the nitrogen initial pressure is increased, the F force is reduced. - The initial nitrogen pressure and the zero gap kept constant , if the initial hydraulic pressure set point is reduced, the F force is decreased and if the initial hydraulic pressure set point is increased, the F force is increased. - The initial nitrogen pressure and the initial hydraulic pressure set point kept constant, if the zero gap is degreased, the F force is increased, if the zero gap is degreased, the F force is degreased. The most effective points must be found during commissioning by trials or The most optimized operation parameters are given to you by your supplier. The same material hardness and granulation may be different in each manufacturing company. Even this hardness difference may require different parameter settings.



Operational Conditions and Hydraulic Cycles



Hydraulic System Installation and Automation Program



Mechanical Condition and Protection



The most important mechanical conditions for the roller presses



The wear in a roller press often occurs on the feed chute, cheek plates and roller surfaces. The wear rate depends on the steel type, the abrasiveness of the feed material, the moisture percentage, surface pressure and other operating parameters. The most important of the wearing parts are rolls. The wear rate on the roll surfaces is approximately 1 - 2 gr / ton.Clinker. This wear rate is not very high. However, if grinding balls, metal parts, concrete pieces and wood pieces pass through the rolls, the roller surfaces will deform before expected. As you can see in Figure 8, apply whatever protective, renewal and repair advice your supplier has given you. It must be repaired according to the procedure given by your supplier when the rolls fall in capacity or when the normal wear time is exceeded. The function of the cheek plates is to prevent material from escaping from the sides. These plates made of high-wear-resistant steel can be easily replaced. The hard coating material can be used for feeding chute wearing. The Periodical Check of the Metal Detector and Magnetic Separator will also prevent major mechanical failures, such as extending the working life of the roller surfaces. References ( Catalogues - Brochures – Websites – Other Documents ) - Krupp Polysius AG – POLYCOM high-pressure grinding roll - Germany - KHD Humboldt Wedag International AG - Roller Presses – Germany - FLSmidth - HRP Hydraulic Roller Press – Denmark - Hoven Hydraulik - Wilhelm Hoven Maschinenfabrik GmbH & Co. – Germany - Bosch Rexroth AG – Industrial Hydraulics - Germany Ertekin İç ve Dış Ticaret Suadiye Mah. Yazanlar Sok. Has Apt. No: 4/16 Kadıköy 34740 İstanbul - TÜRKİYE



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by Ergun Konca – Technical Advisor ( [email protected] )