The production process of slag powder and trial production of high fine open circuit tube mill with three chambers produced by Jiagnsu Pengei Group Co., Ltd Ф3.2×13m

 

In order to adequately utilize large quantity slag resources of granulating blast furnace to implement energy saving and exhaustion reduction, development circular economy and build a 200, 000tpy micro slag powder production line. Main equipment utilizes high efficient boiler Ф2.4×18m rotary dryer（drying capacity≥50t/h）and Ф3.2×13m high fine open circuit tube mill with three chambers to produce the S95 level micro slag powder with Blaine ≥430m²/kg. Utilizing high fine tube mill to produce micro slag powder, the process is mature and reliable which belong to the primary status of slag grinding and has become the main guilding direction of micro slag powder producing equipment choosen.

According to grain size of mill inlet slag is small (max. grain size＜20mm）, focus on considering the slag grinding capacity of grinder when designing grinder level, choosing to utilize smaller grinder, improve total blaine per unit grinder, enlarge contacting and grinding efficiency of slag particle group, grind slag into fine powder in reasonable time to make the Blaine of mill outlet micro slag powder reach the control target of ≥430m2/kg.

To ensure that the Bline of slag powder could reach ≥ 430m2/kg design specifications, ensure the slag activity index achieve the S95 class. All the chambers of mill, especially the grinder of the fine grinding chamber used micro-forging with the type less than Ф16mm, active liner inside of chamber activate the grinding function of micro grinder during the mill operation process which eliminated the disadvantages of the restort of fine powder material and falling of micro-grinder and high & low grinding degree, changed the moving tracking of the grinder during the traditional grinding process, effectively prevented the anti-leaping of micro-grinder, eliminate the restorting area of material and strengthened the grinding capacity of fine chamber. Activate the micro-grinder to make the fine powder material be cut and the grinding capacity be strengthened meanwhile the Blaine of material is obvious improved. Since the inlet & outlet of slag, stop time inside of mill normally is about 20-25 mins.

As there is black block slag and coke in the mill inlet powder, in order for improve the crushing capacity of rough crushing chamber, allocated the 6t steel ball in percent of Ф70mm & Ф60mm；two solutions for grinder of transition chamber: one is ball or forging mix in the whole or partly; the 2^nd is small steel forging, mainly considers the transition inherits the pase and usher in the future serve as a link between past and future, its location is very important which actually creates the condition for grinding of fine grinding chamber, thus the grinding capacity of 2^nd chamber (transition chamber) should be updated. If choose to utilizes ball and forging mix in the whole which though has a spefic void ratio compared to utilization of small forging individually and could enlarge the passing capacity of slag, however it aggravated the grinding burden of 3^rd chamber (fine grinding chamber), meanwhile as it utilizes open-circuit grinding process, it may cause the rough running of micro slag, Blaine is on the low side. For grinding fine powder material (the slag Blaine between 1^st chamber and 2^nd chamber is 100～130m²/kg), the contacting between ball and material is point contacting and its grinding efficiency is not as good as the contacting method for small steel forging and material. Finally utilizes Ф20mm、Ф18mm、Ф16mm three kinds steel forging in 2^nd chamber (transition chamber) according to 2^nd solution to strengthen the grinding capacity of incoming rough slag powder which laid a good foundation for further fine grinding of slag powder on micron grinder of 3^rd chamber (fine grinding chamber)。Meanwhile, Setting the high efficient screening diaphragm inside of mill could make the adequate exertion on function of all chambers of mill, ensure the mandatory screening of rough powder of slag after 1^st chamber grinding, transited to 2^nd chamber and make the rough & medium grinding inside of 2^nd chamber, under a spefic size of screening hole, slag powder less than size of screening hold inside of 1^st chamber could successfully pass the screening device, or they will be furtherly crushed inside of 1^st chamber. After grinding inside 2^nd chamber of rough & medium powder slag, after 2^nd mandortary screening device, the screening holes size of 2^nd screening device is less than that of first line of screening hole which creates good condition for fine slag powder successfully entering into 3^rd chamber (fine grinding chamber).

The mandoratory screening of high efficient screening diaphragm to slag powder is the adequate condition for fine grinding of slag, while the length of 3^rd chamber (fine grinding chamber) of mill is long; the application of micro-grinder is necessary condition of high fine griding of micro-slag powder. High efficient screening diaphragm inside of mill adequately indicate the special screening mechanism of the technology of high fine mill – small sew grate and large circulation, it seems that the screening seam is small, the qty of total screening holes is a lot, passing area is large and smooth, while passing quantity of materiao in unit time will not decrease, the material powder which meet the requirements on grinding material of last chamber could pass the screening. Setting the high efficient obviously improve the production efficiency of the entire grinding system.  

The actual design load of grinder inside of mill is 131t which is 6t more than reated load 125t, considering the power of main motor is 1600kw, the driving power will have large remain, meanwhile start operation system with static phase advancer, when the operating current of main motor is located in rated range which could drive 140-150t grinder while the actual load is 131t, under load commissioning, grinder will count in percent as regulation, grinder material quality in inside of chambers of mill utilizes white iron of chromium alloy.

Commissioning process of machinery installation  

　　① Unload commissioning. on the premise of unload of grinder of slag mill, unload commissioning is 24h, mainly inspects the heating condition of inlet & outlet globe bush, temperature increasing & vibrating of motor and reducer and meshing between main driving gear, etc., due to erection & debugging of specialists, the process of unload commissioning is normal.
　　② Load commissioning. After 24h unload commissioning, if the meshing between bull gear and pinion of mill is normal, operating current is reliable, thus it shall be decided to have load commissioning and the load commissioning shall divide into 5 steps.

During the process of above mentioned load commissioning, no abnormal condition of driving section of mill is discoved, the meshing between bull gear and pinion is normal and the operating current of main equipment in each segment is reliable. When loading is in full load of 131t, operating current of main equipment is 102A, Blaine of outlet slag powder is 450±20m2/kg which could control index requirement.

   The debugging of the output per unit under commissioning of mill: we design as the 30tph capacity; the percent between discharge quantity and loading of grinder for each segment is synchronize, means loading 30% grinder, according to 30% tph discharging then calculate according to this. Meanwhile utilizes the automatical Blaine to inspect the outlet micro slag powder each half hour, when the grinder of mill is counted 100% loading, the output is 30t/h, Blaine of slag powder decrease to 395m2/kg, then the capacity decrease to 28t/h for instant, Blaine of slag powder increase to 435m²/kg. It could discover: the relevant physical and chemical properties of Ф3.2×13m high fine open-circuit mill producing micro-slag powder could reach national standard of GB/T18046-2000 of 《slag powder of cement and concrete》 and the output of mill per unit is 28t/h。

　　Note：

　　① Do the screening of wet slag well. After grinding by micron slag powder system to gain granulated blast furnace slag, and it includes slight coke and black block heavy slag, not only activity but also abrasivness is bad, directly affect the output and quality of mill system, thus it should be left out. Set up steel rough screen net with 70mm diagonal at slag incoming port, primarily filters and eliminates black heavy slag and coke. Set fine screen net with 30mm diagonal before wet slag enters into dryer via belt conveyor to ensure the dryed slag without large block impurity, in order for stable continuous mill, creates good precondition for the output and quality of slag micro-powder.

② Pay attention to iron separtor before mill. Granuated blast furnace slag is the product gained during the iron meal smelting of blast furnace, including a specific metal iron, if it doesn’t eliminate in time, it not only affect the output of mill and quality of micro-slag power, but also cause the disorder of grinder graduation and worsen the grinding environment inside of mill. Thus, set up multi-ways iron separating process (the efficiency of single way iron separating process is low) to eliminate the damange on metal iron particle during the slag grinding process. Normally it could set three ways: 1^st way configures on above of feed belt conveyer of dryer, 2^nd way configures at discharge port of slag drying, 3^rd way is on above of feed belt conveyor of mill. Above mentioned iron spearting process, the efficiency of iron separating could reach over 99% to ensure the reliable grinding process.  

③ Seriously control the moisture content of inlet slag. The grinding process of high fine open-circuit slag tube mill is different from vertical mill and roller press, during actual production process, high moisture content of inlet slag moisture content will affect the Blaine index of micro-slag powder and grinding efficiency of the system, thus it should be seriously controlled. Utilizes high efficient boiler to improve the rotary dryer, the max. moisture content of outlet slag is 1.20%, normally it is 0.8%～1.0% and during the operation, adjusting inlet slag flow rate or the temperature of boiler properly could control the moisture content of outlet slag.

④ Compensate grinder inside of mill in a period of time. The microhardness (HV650) of gruanlated blast furnace is higher than that of cement cliner (about HV550), toughness is good and the abrasiveness is bad, the grinder consumption per ton slag powder is two times than that of cement mill. In order for gaining stable Blaine of micro-slag powder, compensate grinder into chambers inside of mill in a period of time. We ensure that we shall compensate once each half month (primary accumulate as 250g/t slag mill), means compensate two times each month to keep the long-term, reliable and high grinding efficiency and Blaine of outlet micro slag powder. 

⑤ Make the good collocation between new slag and old slag. The slag discharged from the same blast furnace, some old slag after a specific time heaping (2-3 months) will be more abrasive than that of slag discharged from the furnace recently, the output will be 2-3t higher per equipment, the abrasivness of new slag is lower than that of old one, as a specific time heaping, vitreous body of it will embrittlement, the stress inside micro-structure will be released and the abrasiveness will be obviously improved. But after long time storage, though the Blaine between old slag and new one is same, but its activity is lower than that of new one. Proved by test, with the same Blaine (≥440m2/kg)，the activity of 7d and 28d new slag is 1%-3% and 2%-4% higher than that of old slag. While when the new discharged slag and old slag is collocated in the percent of 1:1, then they will be grinded, after checking, the activity of micro slag powder is better and more reliable. Via taking relevant measures, if mill grinder load is 131t, output of S95 slag powder（≥430m²/kg） is 28t per equipment. In order for furtherly improve the output and reduce grinding power consumption, compensates Ф8×8mm micro-forging 9t into 3^rd chamber and total load will be 140t. After adjustment, the operating current of main motor is 108～110A, which don’t exceed the rated current (≤112A) according to design requirements, mill operation is stable and working is normal.  

                                                                                          Jiangsu Pengfei Group Co., Ltd

                                                                                                        2009.3