Title of Invention

AN IMPROVED COAL CRUSHING BOWL MILL

Abstract

An improved coal crushing mill consisting of a feed pipe (27), a rotating bowl (11) where coal falls at the centre of the bowl through feed pipe, the. bowl is lined with hard liner called bull ring segment (07), grinding rolls (10) where coal is grinded in between the grinding rolls (10) and bull ring segment (07), wherein a spring system (01) which controls effectively and beneficially, the stresses imparted on the coal during crushing operation.

Full Text

FIELD OF INVENTION The invention relates to a coal crushing Bowl Mill for cashing coal of proper size before transporting to the boiler fox firing, PRIOR ART In a Bowl mill raw coal is fed through center feed pipe. Coal falls at the center of the rotating bowl. Bowl is lined with replaceable hard liners called bull ring segments. Due to centrifugal force, the coal starts moving towards the bowl periphery in a spiraling fashion. In the process, it comes between the grinding roll and the bull ring segments and get crushed. The crushed coal is carried by the hot air under pressure to the classifier section for further transportation to the boiler for firing. For imparting the grinding pressure required, there are three spring assemblies which press down the grinding rolls on the bull ring segments. There are three grinding rolls kept 120 degrees apart. Similarly there are three spring assemblies to press them down. The springs are initially compressed to a value, so as to impart a predetermined pressure on the grinding rolls. The pressure of the springs can be adjusted as required during the process of grinding. The axial movement of the spring is provided for allowing the big size foreign materials like stones, pyrites any other hard foreign matter to pass through without getting ground. Depending on the size i.e. the diameter of bowl there are distinct families or series of pulveriser like 80", 90", 100", 110" and different types of springs are used for different family of pulveriser. The base capacity of the bowl, type of spring used and the initial spring compression imparted are shown below:- The base capacity of these mills is given below: 80" family - 35 / tones / hour (approx.), 90" family - 48 tones / hour (approx.), 100" family - 68 tones / hour (approx.), 110" - family - 90 tones / hour (approx.), The springs used for these mills are listed below, 80" - 25 K spring (25,000 lbs / inch) 90" - 28 K spring (28,000 lbs / inch) 100" - 30,000 k spring (30,000 lbs / inch) 110" - 38,000 K spring (38,000 lbs / inch As per the guidelines the springs are pre-tensioned to 1" springs compression. Initial spring compressions for these mills are given below. SI No. Mill Size Initial Spring Compressions in lbs (kilo Kgs / tons) 1 80" Family 25,000(11.3) 2 90" Family 28,000(12.7) 3 100" Family 30,000 (13.6) 4 110" Family 38,000(17.2) Where K = spring constant The life achieved by grinding rolls of 80" family is about 3000 hours where as the life achieved for mills of family 100" is only about 800 to 1200 hours, when the initial compression used at 13.6 tons. An analysis of stresses induced due to various initial spring compressions for 100" family of coal mills is carried out and is compared with the stresses induced in 80" family of mills. Legends for calculations given in the following pages. Crushing force = Fi+(K*X) Crushing force per unit of contact = (Fi + (K*X) / L Fi = Died Wt of the Journal Assembly acting at its CG + Initial compression K = Spring Constant L = Length of grinding roll X = Spring Movement (Deflection) Forces are found out by taking moments about the trunnion axix. GR-Grinding Roll, 1 ton = 1000 Kgs, POS --- Position TS - Trunnion Shaft PERP - Perpendicular JRL ASLY - Journal Assembly CG - Center of Gravity LOC - Location SPR - spring Stress Analysis for 100" Size Family of mill with 30 K spring and 7 tons initial compression Stress Analysis for 100" Size Family of mill with 30 K spring and 8 tons initial compression Stress Analysis for 100" Size Family -of Bowl Mill with 30000 lbs/inch spring constant and 10 tons of initial compression Stress Analysis for 100" Size Family of Bowl Mill with 30000 lbs/inch spring constant and 11 tons of initial compression Stress Analysis for 100" Size Family of Bowl Mill with 30000 lbs/inch spring constant and 12 tons of initial compression Stress Analysis for 100" Size Family of Bowl Mill with 30000 lbs/inch spring constant and 13.6 tons of initial compression. (As envisaged originally) Stress Analysis for 80" size family of bowl mill with 11.16 tons initial compression and 25000 lbs/inch spring constant The table below shows the percentage decrease in stress due to reduction in initial spring compression from 13.6 tons to the values given in the first row. Table 10 shows that there is reduction in stress due to reduced initial spring compression by about 21.33% (for 7 tons of initial orrrpresson to about 5.17 % for initialising compression of 12 tons). However the reduction becomes much less when the spring deflection (movement) increases due to large size of coal or rejects like stones, pyrites etc. Table 11 shows the increase in stresses per unit length as compared to 80" family of mill. This analysis throws light on. the reported less life of grinding rolls and bull ring segments for" 100" family of mills for the same material of grinding roll and bull ring segments.. From the analysis it is derived that the present system for 100" mills induces lots of stresses on griding media, which is then transferred to critical gear box components like main vertical shaft, thrust bearings, radial bearines and worm pear and worm shaft etc. This leads to reduced life of grinding media. Fromthe-field data collected it is observed that sites have reduced initial spring compression from 30,000 lbs (corresponding to 1" compression) to between 15,000 lbs to 20,000 lbs. This has improved life of grinding rolls and bull ring segments to a where (K*X) it is multiplication ODerator. crushing force = Fi + K multiplied by X. considerable extent. However the life as compared to the life achieved in 80" family of mills is still on the lower side. The analysis shows that it is beneficial to have larger initial, compression with a spring having lower stiffness. And it is not beneficial to have lower initial compression with a higher stiffness spring. Another disadvantages of the existing system, is that it leads to higher fineness than required. This is over came by cutting the venturi collar resulting in higher velocity, consequently leading to higher wear of venturi and valve body. LABORATORY EXPERIMENTS: Laboratory experiments that we conducted, reveal that the crushing force required is about 6 to 7 tons for a coal lump of size 100, which translates into a stress of about 60-70 Kg/mm. OBJECT OF THE INVENTION The main object of the present invention is to develop an improved coal crushing bowl mill particularly a spring system that induces reduced stress on grinding media and critical and costly mill components like vertical gear, worm shaft etc. Another object is to increase the life of wear components and life of critical gear box components liKe Dearings, worm gear, worm shaft etc. Another obiect is to decrease the cost of springs themselves springs with higher stiffness require higher rod diameter. Springs with higher .diameter are difficult to manufacture and hence expensive. There are very few manufactures of these springs in all over the world. Reducing spring stiffness will reduce the spring diameter, thus bringing down the cost of theese springs. It will also make more manufacturers available to procure from. Yet another object of this invention is to reduce the power consumption of the mill. Higher grinding forces require higher power. Reducing spring compression would require lesser power and thus there will be saving in power consumption. Now the invention and the existing mill will be described with references of the accompanying drawings. Figure 1 shows a typical existing vertical spindle Bowl Mill. Figure 2 shows the spring preloading arrangement with Journal assembly and details of spring assembly of the present invention. Figure 3 gives the details of original spring in the existing system. Original spring had a rod diameter of 3.5 inch and spring stiffness of 30, 000 lbs / inch. Figure 4 shows the details of the modified springs of the present invention which induces reduced stresses, where Q indicate diameter. DETAILED DESCRIPTION OF INVENTION: We propose to replace 30 klbs/inch spring with a spring of approve 15 klbs/inch keeping the other component same, so that the present assembly could be used with out much modification. Two other components spring stud adopter & spring stud guide will be suitably modified to accommodate lower dimensions of the spring. Table below shows the stresses induced due to use at this spring . As seen from tables 12 & 13 , with the use of lower stiffness spring, there is considerable reduction in stresses induced at higher deflection ( 100 mm deflection - about 40 % reduction). Also a reduction of about 23% at small movement ( 25 mm deflection). With this spring , if required higher initial compression can be kept such as 10 tons or 12 tons, still achieving lower stresses. Which will give adequate grinding force ,but will reduce higher stresses due to higher size coal, stones, tramp iron etc. thus over all reducing the stresses. WE CLAIM 1. An improved coal crushing bowl mill for crushing coal consisting of a feed pipe (17), a rotating bowl (11) where coal falls at the centre of bowl (11) through feed pipe (17), the bowl is lined with liner called bull ring segment (07), grinding rolls (10) connected with a spring (01) where coal is grinded in between the grinding rolls (10) and bull sign segments (07) Characterised in that the said spring (01) system controls effectively the coal with 40% less stress exertion at higher (100%) deflection and 23% less strength at a 25% movement of spring. 2. The mill as claimed in claim 1, wherein the spring of lesser diameter induces lesser stresses. 3. The mill as claimed in claim 6, wherein there are three spring assemblies to press down the grinding rolls to the bull ring segments. 4. The mill as claimed in claim 7, wherein the spring assembly are initially compressed to a value, so as to impart a predetermined value of pressure. An improved coal crushing mill consisting of a feed pipe (27), a rotating bowl (11) where coal falls at the centre of the bowl through feed pipe, the. bowl is lined with hard liner called bull ring segment (07), grinding rolls (10) where coal is grinded in between the grinding rolls (10) and bull ring segment (07), wherein a spring system (01) which controls effectively and beneficially, the stresses imparted on the coal during crushing operation.

Documents:

228085-FORM 27.pdf

948-KOL-2005-FORM-27-1.1.pdf

948-KOL-2005-FORM-27.pdf

948-kol-2005-granted-abstract.pdf

948-kol-2005-granted-claims.pdf

948-kol-2005-granted-correspondence.pdf

948-kol-2005-granted-description (complete).pdf

948-kol-2005-granted-drawings.pdf

948-kol-2005-granted-examination report.pdf

948-kol-2005-granted-form 1.pdf

948-kol-2005-granted-form 18.pdf

948-kol-2005-granted-form 2.pdf

948-kol-2005-granted-form 3.pdf

948-kol-2005-granted-form 5.pdf

948-kol-2005-granted-gpa.pdf

948-kol-2005-granted-reply to examination report.pdf

948-kol-2005-granted-specification.pdf