ZGM type Medium-speed Rolling coal mill

ZGM medium speed roller mill

 

1. Introduction

1.1. Purpose

ZGM type medium speed roller mill is widely used in coal powder preparation system of electric power, metallurgy, cement, chemical industry and other industries, as well as coal pulverizing system of cement, chemical industry, mining and other industries. It can be used to mill bituminous coal, inferior bituminous coal, lean coal, anthracite and lignite.

1.2. Model meaning

ZGM *** ##

ZGM -- medium speed roller mill

***----Nominal radius dimension of roller table of coal mill (CM)

##----There are three kinds of product specifications, and their codes are represented by letters K,N,G: N for standard output type; K for low output type; G for high output type

1.3. Basic structure and characteristics

1.3.1. The base wood structure of ZGM medium speed roller coal mill is shown in Figure 21-1. The body of ZGM medium speed roller coal mill is composed of reducer, grinding device (grinding disc and three grinding wheels), loading device, sealing device, foundation plate, base, casing, separator, pulverized coal distribution box, steam explosion-proof device, footpath, etc. The necessary supporting devices include thin oil station, high pressure oil station, slag discharge device, sealing fan, motor and electrical control cabinet.

1.3.2. Structural features of ZGM medium speed mixed coal mill

1.3.2.1. The three mills of the coal mill are respectively fixed by hinge shaft and press frame, and rotate under the drive of disc rotation and friction force (only self rotation, no revolution). Therefore, the grinding stroke of grinding roller is equal to that of grinding plate, which makes the grinding efficiency high and the rotation speed of grinding plate low, which not only improves the stability of rotation, but also improves the grinding effect.

1.3.2.2. The three grinding rollers of the coal mill are arranged at 120° to each other, and the three points are stressed. Therefore, the grinding force and driving parts are evenly stressed (for example, the plane thrust pad of the reducer is not prone to eccentric load), so as to reduce the damage of transmission components.

1.3.2.3. The roller has three degrees of freedom: the overall up and down movement of the three kilns and the press frame is used to compensate the wear of the roller and liner; the rotation of each roller is used to roll materials; the free swing of each roller in the horizontal plane is used to compensate the profile distortion of the roller and liner after local wear, so as to keep the mill output basically unchanged (about 5%) in the later stage of wear.

1.3.2.4. The cross-section shape of grinding roller and grinding ring (lining plate) is matched, coal is always in contact with grinding ring and grinding roller, and the coal seam thickness at each roller position is the same, so the grinding roller can be worn evenly, run stably and have a long service life, thus maintaining good grinding effect.

1.3.2.5. The diameter of grinding wheel is large, rolling resistance is small, coal block is easy to bite in, which is conducive to increase the output of coal mill, reduce the unit power consumption of coal mill and improve the service life of roller sleeve

1.3.2.6. The loading device loads the vertical direction of the three grinding rollers, and the loading force is automatically adjusted with the output of the coal mill, and the reaction is directly transmitted to the foundation through the loading device (see Fig. 21-2; the shell and frame do not bear the loading force, so it is not easy to cause the vibration of the mill and improve the stability of the mill.

1.3.2.7. Under the same disc diameter, the roller diameter of ZGM medium speed coal mill is large, the width is large, and the speed is low. Therefore, the machine runs stably, vibrates little, and has strong resistance to "three pieces" (stone, wood and iron).

1.3.2.8. It adopts high starting torque motor and high precision planetary gear transmission, with low noise, stable transmission, safe and reliable

These characteristics make ZGM medium speed coal mill have the advantages of stable operation, small vibration, low noise, long life of grinding parts, strong adaptability to "three blocks" in coal, small slag discharge, uniform fineness of pulverized coal, low power consumption, compact overall layout, and no reduction of output in the later stage of wear.

1.4. Working principle

The working principle of ZGM medium speed roller mill is shown in figure 21-3

ZGM medium speed roller mill is a kind of auxiliary disc coal mill. Its grinding part consists of a rotating ring and three fixed and self rotating rollers rolling along the ring. The raw coal to be grinded falls onto the grinding ring from the central coal dropping pipe of the coal mill, and the rotating grinding ring moves the raw coal to the grinding roller with the help of centrifugal force, and then grinds through the grinding roller. The three rollers are evenly distributed on the disc raceway along the circumference direction, and the grinding force is generated by the hydraulic loading system. Through the static three-point system, the grinding force evenly acts on the three grinding rolls, and is transmitted to the foundation through the grinding ring, grinding wheel, press frame, pull rod, drive plate, reducer and hydraulic cylinder. The grinding and drying of raw coal are carried out at the same time. The primary air evenly enters the surrounding area of the grinding ring through the nozzle ring, dries the pulverized coal mixture which is thrown out from the grinding ring tangentially, and delivers it to the separator on the upper part of the coal mill for separation. The coarse powder is separated and returned to the grinding ring for regrinding, and the qualified fine powder is taken out of the separator by the primary air.

The heavy stone coal, pyrite and iron block which are difficult to be crushed and cannot be blown by the primary air are dropped into the primary air chamber through the nozzle ring, and finally blown into the slag discharge box by the scraper, which is cleaned manually (or discharged by the automatic slag discharge device). The slag removal process can also be carried out during the operation of the coal mill (see Fig. 21-4).

 

2. Main technical parameters

The performance parameters of ZGM medium speed roller mill  are shown in table 21-1,

Performance parameters		ZGM65			ZGM80			ZGM95			ZGM113			ZGM123		ZGM133		ZGM145
		K	N	G	K	N	G	K	N	G	K	N	G	N	G	N	G	N	G
Basic capacity	HGI=80, Mt=4%, R90=16%(t/h)	16.3	20	24	28.5	33.5	39	45	51.5	58.5	67.7	78.7	87.7	97.3	107.6	118.4	129.9	148.3	168.3
	HGI=50, Mt=10%, R90=20%(t/h)	10.5	12.9	15.5	18.4	21.7	25.2	29.1	33.3	38.1	43.8	50.9	56.8	63	69.6	76.6	84.1	96	108.9
	HGI=55, Mt=10%, R90=23%(t/h)	12.1	14.9	17.9	21.2	25	29.1	33.5	38.4	42.2	50.5	58.6	65.3	72.5	80.2	88.2	96.8	110.5	125.4
Primary air volume of base point (kg/s)		5.21	6.39	7.67	9.1	10.7	12.46	14.38	16.45	18.69	21.63	25.14	28.02	31.08	34.37	37.82	41.5	47.37	53.76
Ventilation resistance (including separator) (KPa)		4.11	4.38	4.65	4.88	5.13	5.38	5.55	5.74	5.91	6.04	6.22	6.34	6.44	6.58	6.65	6.84	7.18	7.45
Mill shaft power (kW)		106	130	156	185	218	254	293	335	380	440	512	570	632	699	770	844	964	1094
Motor power (kW)		125	160	185	220	250	280	355	400	450	500	560	670	710	800	900	1000	1120	1250
Grinding roll working diameter (mm)		1300			1600			1900			2250			2450		2650		2900
Grinding roll speed(r/min)		31.9			28.7			26.4			24.2			23.2		22.3		21.3
Grinding roll quantity (pcs)		3			3			3			3			3		3		3
Max. enforce of each milling roll (kN)		101			154			217			304			360		421		505
Mill equipment weight (tons)		67			81			100			144			200		247		297

 

3. Equipment shape and structure dimensions

The outline and structure dimensions of ZGM medium speed roller mill are show in Fig. 21-5 and table 21-2,

Table 21-1   Outline dimensions of ZGM medium speed roller mill  (in mm)

Specification Dimensions code	ZGM65			ZGM80			ZGM95			ZGM113			ZGM123		ZGM133		ZGM1I45
	K	N	G	K	N	G	K	N	G	K	N	G	N	G	N	G	N	G
H1	5095			5730			6705			7580			8270		8975		9750
H2	3700			4020			4520			5200			5620		6020		6400
H3	1.780			1.930			2.150			2.550			2.800		2.910		3.000
D1	2750			3300			3885			4570			4995		5420		5960
D2	1050			1150			1250			1350			1450		1550		1700
D3	2350			2770			3244			3800			4140		4454		4760
R1	1345			1555			1775			2040			2215		2370		2540
R2	1500			1750			1945			2230			2410		2570		2730

 

4. Selection method

According to the coal quality and working conditions provided by users, the type selection calculation of Beijing electric power equipment plant is mainly based on DL/T5145-2002 "Technical specification for design and calculation of coal pulverizing system in thermal power plant" and DL/T 436-2004 "Guide for type selection of coal pulverizer and pulverizing system in power plant", which is authoritative and reliable, and can meet the requirements of users to the maximum extent.

4.1. Performance parameters of required fans

If the user chooses ZGM medium speed mixed coal mill, the following data shall be provided (provided by the user and the Design Institute)

4.1.1. Unit capacity.

4.1.2. Altitude (m)

4.1.3. Ambient temperature (℃)

4.1.4. Origin and type of raw coal.

4.1.5. Coal, ash and chemical analysis (design coal and check coal).

4.1.6. Grindability index HGI.

4.1.7. Erosion wear index Ke

4.1.8. Fineness of pulverized coal R₉₀ (%).

4.1.9. Moisture content of pulverized coal M_mf (%).

4.1.10. Boiler operation data (under different load conditions)

4.1.10.1. Coal consumption (t/h) (design coal and check coal).

4.1.10.2. Quantity of operating mills

4.1.10.3. Outlet temperature of coal mill (separator) (℃)

4.1.10.4. Primary air rate (kg/s).

4.1.10.5. Hot air temperature at preheater outlet (℃).

4.1.10.6. Total air volume (kg/s) is required for boiler combustion

4.1.10.7. Excess air coefficient at furnace outlet.

4.2. Actual output calculation example (See table 21-3, just for reference)

Table 21-3 output calculation of medium speed pulverizer for boilers in typical thermal power plants

File name	FUZHOU power plant 2x000MW Capacity calculation of medium-speed coal mill	MG63.JS.01--2008
Product name	ZGM133N type medium-speed coal mill	Page 1         Total 1 Page
No.	Name	Design coal	Check coal 1	Check coal 2
Raw data
1	Productivity Bg  (t/h)	361.04	338.41	424.02
2	HGI	60.5	42	60
3	Fineness of pulverized coal R90  (%)	18.4	18.4	18.4
4	Total moisture Mt  (%)	7.7	9.5	7.87
5	Ash content of raw coal Aar (%)	18.29	11.04	23.68
6	Separator type (rotation 1; static 0)	0	0	0
7	Operation mode N	5	5	5
8	Base point output of coal mill B0 (t/h)	87.3	87.3	87.3
Correction data
1	Influence coefficient of raw coal grindability  ƒH	1.115	0.905	1.110
2	Influence coefficient of pulverized coal fineness ƒR	0.976	0.976	0.976
3	Influence system of raw coal moisture ƒM	1.026	1.006	1.024
4	Ash influence system of raw coal ƒA	1.000	1.000	0.982
5	Influence coefficient of raw coal particle size ƒg	1.0	1.0	1.0
6	Separator affects system ƒC	1.0	1.0	1.0
7	Output reduction factor in later period ƒe	0.95	0.95	0.95
Calculation result for the mill
1	Calculated capacity Bj (t/h)	72.21	67.68	84.8
	Bj = Bg / N
2	Maximum output of raw coal Bm  (t/h)	97.48	77.59	95.06
	Bm=B0ƒHƒRƒMƒAƒgƒC
3	Maximum output of coal mill at later stage Bms  (t/h)	92.61	73.71	90.31
	Bms = Bmƒe
4	Output margin at later stage Yd (%)	28.25	8.91	6.5
	Yd = (Bms - Bj) / Bj
conclusion
Based on DL/T5145--2002 calculation，ZGM133N mill can be right for the requirement in capacity

 

The specific steps of output calculation are as follows:

4.2.1. Firstly, according to the production capacity required by the user, the formula for calculating the output is obtained: the calculated output B_j = B_g/ N, and then according to the calculated output, after considering a certain margin, combining with the output conditions (mainly pulverized coal fineness, moisture, HGD) and referring to table 21-1, the basic point output is determined.

4.2.2 according to the base point output, the maximum output B of raw coal can be calculated, B_m=B₀ƒ_Hƒ_Rƒ_Mƒ_Aƒ_gƒ_c. The correction coefficients in the formula can be found in the relevant table of DL/T 5145-2002, or calculated according to the following formula, i.e.

ƒ_H = （HGI/50)^0.57

ƒ_{R =} （R₉₀/20)^0.29

ƒ_{M =  1.0+(10-Mt) × 0.0114}

ƒ_{A  =  1.0+(20-Aar) × 0.005}

Therefore, when a ≤20%, ƒ_A =  1.0   

                                        ƒ_g =  1.0            

4.2.3. According to the calculation results, if the requirements can be met, the software can be used to calculate the heat balance (omitted) to further determine the detailed parameters and size of the coal mill.

4.2.4. According to the user's requirements or coal quality, the model of coal mill can also be determined by Babcock's selection calculation method or by grinding sample coal with small-scale experimental pulverizer

 

5. Scope of supply and ordering instructions

5.1. Scope of supply (typical scope, which can be increased or decreased according to user's demand)

5.1.1. Pulverizer body (including separator)

5.1.2. Main motor.

5.1.3. Reducer.

5.1.4. Coupling device and protective cover.

5.1.5. Coal mill and motor foundation mounting plate, embedded parts and candle anchor bolts.

5.1.6. Lubricating oil system.

5.1.7. Hydraulic oil system.

5.1.8. The slag discharge box is equipped with inlet and outlet shut-off plates and movable pebble coal scuttle.

5.1.9. Self use maintenance platform and ladder.

5.1.10. Connected maintenance steel frame platform ladder.

5.1.11. Pneumatic seeding plate quick closing valve at the outlet of coal mill.

5.1.12. Slow turning gear.

5.1.13. Coal mill instrument and control equipment (oil station control box).

5.1.14. Sealing fan.

5.1.15. Commissioning oil (including hydraulic oil, lubricating oil and grinding oil).

5.1.16. Special tools.

5.1.7. Random spare parts.

The scope of supply also includes the drawings, operation and maintenance manuals required for installation and commissioning.

5.2. Order requirements

According to the characteristics of ZGM medium speed roller coal mill, such as wide adaptability of coal, high grinding efficiency, low power consumption, long service life, safety and reliability, convenient operation and maintenance, it can meet the needs of domestic electric power, coal, chemical industry, steel, building materials and other industries, users should provide the following information when selecting ZGM Medium Speed Roller Coal Mill:

5.2.1. A variety of coal quality data, including as received basis element composition, dry ash free basis volatile matter (%), low calorific value and deviation value (MJ / kg), Hardgrove grindability index, wear index, maximum moisture content of raw coal (%), particle size range of raw coal, chemical composition of coal ash (%), quartz sand content in coal (%), pyrite content in coal (%), etc.

5.2.2. Boiler system parameter requirements of the coal pulverizer used, including the coal consumption (t/h) of the rated output of the boiler, the number of pulverizers and the number of standby coal mills required during the operation of one boiler, the fineness of pulverized coal R₉₀ (%) The temperature of gas powder mixture at the outlet of the coal mill (℃), the moisture content of pulverized coal (%), the temperature of the hot air before mixing at the inlet of the pulverizer (℃), the temperature of the cold air (℃), the air volume of the primary air at the inlet of the pulverizer (standard condition) and the air temperature (m³/s, ℃) and the resistance of the pulverized coal system from the outlet of the coal mill to the boiler (kPa), so as to determine the parameters of the pulverizer system through the heat balance calculation, and check whether the grinding type matches.

5.2.3. Equipment layout location and form.

5.2.4. Separator type.

5.2.5. Voltage, phase and frequency of the power supply provided.

5.2.6. Pressure, temperature and composition of cooling water provided.

5.2.7. Others: including altitude, atmospheric conditions, auxiliary medium conditions (cooling water, fire steam, primary air, sealing air, etc.) and output control range of coal feeder, etc.

5.2.8. Fully consider the production cycle and define the delivery time.