We have set up the largest white cement production line with most complicated process flow – Anqing White Cement Plant which has two old small white cement production lines and the total annual capacity is 120,000ton white cement, meanwhile Denmark Maierbo Portland Group purchased and then set up Aalborg Portland (Anqing) Co., Ltd in Nov. of 2004. This company signed the turnkey contract with Tianjin Cement Industrial Design Institute Co., Ltd in Apr. of 2008 to set up a new modern white cement production line whose max. capacity could reach 465,000ton white cement clinker and 600,000ton white cement. The address of new plant located in Southern part of Bailushan, Yangqiao – northeast of Anqing.
Aalborg Portland (Anqing) Co., Ltd is the largest white cement manufacturer in the world whose production base located in Denmark, America, Egypt, Malaysia and China, meanwhile its sales net spread all over the world. After the production line of Aalborg Portland (Anqing) Co., Ltd is put into production, it produced PW42.5, PW32.5 and white cement for external wall decoration, while the sales is mainly in China, and radiate to Russia, Japan, Korea, Australia and far east marketing.
The annual production of Aalborg Anqing White Cement Project is 400,000ton white cement clinker according to turnkey contract, means daily production is 1300ton but the requested daily production could reach 1500ton, means max. white cement clinker production could reach 465,000ton which has become the max. white cement production line with most complicated process flow.
White Silicate cement is white cement which still belongs to silicate type cement. As the special requirements on white cement process has large discrepancy with normal silicate cement, the content of white cement clinker of MgO, SO3 and Fe2O3, thus the requirements on raw material is higher, outlet clinker need to utilize water to quick cooling & bleaching process to improve the white content of clinker. After clinker discharged from kiln (＞1300℃), make Fe2O3 to reduce FeO via quick water cooling, iron aluminate will turn up in the form of C6AF2 to reduce the C4AF content which affect the white content, as it speeds up clinker cooling speed and produce large quantity of glass phase content which is hard to paint, thus compared to normal silicate cement, white cement production line has large difference on limestone mineral dressing, raw meal manufacturing and clinker cooling and white cement packing which open a new design area from the designing site of cement plant.
The process characters of Anqing White Cement Production:
1. Two segment crushing, three times screening and washing of limestone
1st limestone crushing is jaw crusher, 2nd crushing chooses to utilize hammer crusher. After a specific crushing and three times screening of limestone, 1st and 3rd screening is liner vibrating screen, 2nd screening is rotary screening and washing and add hammer crusher into 3rd screening. This could ensure that no limestone with impurity enters into factory. After precipitation, washwater will separate the impurity and then re-cycle. The process of limestone crushing, screening and washing is complicated; the height difference of process distribution exceeds 50m.
2. Raw meal manufacturing should be a combination of dry and wet process.
White cement utilizing silicate raw material to produce quartz sand and pyrophillite, in order to reduce the pollution due to silicate powder, pyrophillite enters into wet process mill for single grinding with two pieces parallel connection after crushing of jaw crusher and roller press. Inside of wet process mill utilizes rubber liner and scree grinder, besides this, utilizes alloy material for roller and disc of raw vertical mill and reduce the metal iron for the grinding process. Limestone and other raw material utilizes vertical mill for grinding, pyrophillite slurry will mix with other raw material and then they will be dried inside of vertical mill, outlet raw meal vertical mill should ensure the qualification of content and moisture. Due to utilizing dry and wet process grinding for raw meal processing process, the most difficult design point for control and drying of material inside of vertical mill.
3. Clinker cooling system is very complicated
Clinker in outlet of kiln will go through one high temperature roller crusher, and then they will be quickly cooled to 100 centi degree via poaching engine, after that, the clinker will be transported by conveying equipment, as during water quenching process, white cement clinker is hot, thus water has become the steam thus it can’t be recovered which cause the much higher heat consumption for white cement calcination compared to that of normal Portland cement. In this project, control clinker temperature after the water quenching inside of poaching engine to be 550-600 centi degree, meanwhile second-cool the clinker to less than 100 centi degree by grate cooler after poaching engine which could recover the waste heat of exhausted waste gas of grate cooler and the waste gas exhausted from grate cooler with 180-200 centi degree could be used as 2nd air for rotary kiln head or 3rd air for calciner.
The control on design and manufacturing of above mentioned poaching machine is very difficult, water spraying inside of poaching machine should be adequate pulverization, the spraying should be limited to a specific range, means it could only spray to the discharged clinker and try to not spray to the inner bricks of poaching machine, steam temperature out of poaching engine should be controlled inside of 350-400 centi degree and the clinker temperature out of poaching engine should be controlled inside of 550-600 centi degree.
As the process flow of the kiln head section of white cement calcination system, thus the bracket of burning system at kiln head, rotary kiln and burning system at kiln tail is higher than that of normal Portland cement burning system and compared to the same type rotary kiln, all of them are about 9m higher.
Others in order for adequate utilizing the waste heat, it configures one heat pipe heat exchanger. 350-400 centi degree steam out of poaching will heat the cooling air up to 200 centi degree after heat exchanging which could be dried via coal grinding (vertical mill).
4. Preheating decomposition of burning system at kiln tail utilizes single series five-stage cyclone preheater and TTF three sprayed calciner meanwhile feeding could implement the toggle between 4 & 5 stages.
Waste gas after preheater should be used to dry raw meal for vertical mill, according to theoretic calculation, the drying requirements for raw meal with inlet moisture ≤15%; When the moisture fluctuation of raw meal grinding is large, moisture of raw meal is inside 15-16.5%, it should control to feed material from the connecting pipes of C3-C2 cyclone (means 4 stage preheating), and now the discharged waste gas of C2 stage could reach 420 centi degree which couldn’t meet the requirements for raw meal drying. Waste gas of raw meal vertical mill will enter into large-scale dust filter via 1st stage cyclone filter, then it will be exhausted, when raw meal vertical stop operation, waste gas discharged from C1 stage cyclone should enter into the large air pipes between C1 stage cyclone and high temperature fan to be sprayed for cooling, then it could enter into bag filter.
5. Cement packing section
Besides one 1t large bag packing for finished cement, add one 1t large bag packing equipment for clinker; cement packer could implement 4.0kg and 25kg paper bag for bag filter besides 50kg paper bags according to the demand of white cement sales.
Debugging and commissioning of white cement production line
As too much key points of process and complicated process flow of white cement production line, meanwhile the rotary ire washer, poaching machine, 1300tpd grate cooler, wet process mill, 1t large paper clinker packer, 3rd air pipes, heat exchanger at kiln head, etc. are designed specially for 1300tpd white cement production line and they are put into operation for first time, thus debugging and commissioning is harder than expected. From the recent half years commissioning, the choice on process, equipments and process flow of Anqing White Cement Production Line is reasonable, however some individual equipment is not proper for white cement production and they has been adjusted during the commissioning, at present white cement has implemented continuous production, since this year, all main equipments has been proved and accepted part by part according to the requirements of contract.
During commissioning, maximum output of burning system during commissioning has exceeded 1500tpd, it still has some updating space.
The commissioning of Anqing White Cement Production Line has gradually been normal, white cement production line has stepped out into white cement area from designing angle and has some breakup in process and technology, accumulate some experiences, especially in the sides of raw meal producing & wet process grinding section, material slurry conveying, mill stop for cleaning, material slurry storage and measuring, moisture control of material slurry, at least from design side, there are 30 years no concern about this and the key point of white cement production process is that how to ensure the qualification of content & moisture of outlet raw meal of raw vertical mill. Look back to the whole design process of white cement production line, there is some lacking and inconsiderate points, for example the abrasive function of pyrophillite and its high grinding consumption, after quenching of poaching machine, seeding of white cement clinker is small and becomes harder and more abrasive, via commissioning, these problems has been solved out by adjustment, at present Anqing white cement production condition has reached or exceed the contract target. At present white cement produced by Anqing white cement plant has reliable performance and high quality, each index of that has exceed that of international extra class, sales market is quite good and white cement clinker has been exported to Australia.
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