OA17600A - Rotary kiln for reducing phosphate ore in kiln process for production of phosphoric acid and method for solving ring forming in kiln tail in kiln process for production of phosphoric acid. - Google Patents
Rotary kiln for reducing phosphate ore in kiln process for production of phosphoric acid and method for solving ring forming in kiln tail in kiln process for production of phosphoric acid. Download PDFInfo
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- OA17600A OA17600A OA1201500482 OA17600A OA 17600 A OA17600 A OA 17600A OA 1201500482 OA1201500482 OA 1201500482 OA 17600 A OA17600 A OA 17600A
- Authority
- OA
- OAPI
- Prior art keywords
- kiln
- rotary kiln
- rotary
- tail
- phosphoric acid
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- NBIIXXVUZAFLBC-UHFFFAOYSA-N phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 title claims abstract description 100
- 238000000034 method Methods 0.000 title claims abstract description 63
- NBIIXXVUZAFLBC-UHFFFAOYSA-K [O-]P([O-])([O-])=O Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 title claims abstract description 48
- 239000010452 phosphate Substances 0.000 title claims abstract description 48
- 229910000147 aluminium phosphate Inorganic materials 0.000 title claims abstract description 46
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 37
- 239000000779 smoke Substances 0.000 claims abstract description 33
- 239000000446 fuel Substances 0.000 claims abstract description 18
- 230000036571 hydration Effects 0.000 claims abstract description 14
- 238000006703 hydration reaction Methods 0.000 claims abstract description 14
- UEZVMMHDMIWARA-UHFFFAOYSA-N meta-phosphoric acid Chemical compound OP(=O)=O UEZVMMHDMIWARA-UHFFFAOYSA-N 0.000 claims abstract description 14
- 239000002994 raw material Substances 0.000 claims abstract description 10
- 238000010438 heat treatment Methods 0.000 claims abstract description 6
- 239000008188 pellet Substances 0.000 claims description 84
- 235000011007 phosphoric acid Nutrition 0.000 claims description 46
- 239000000463 material Substances 0.000 claims description 45
- 238000004140 cleaning Methods 0.000 claims description 21
- 125000005341 metaphosphate group Chemical group 0.000 claims description 19
- 239000002131 composite material Substances 0.000 claims description 18
- 239000003638 reducing agent Substances 0.000 claims description 18
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 15
- HBMJWWWQQXIZIP-UHFFFAOYSA-N Silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 claims description 14
- 239000004927 clay Substances 0.000 claims description 14
- 229910052570 clay Inorganic materials 0.000 claims description 14
- 229910010271 silicon carbide Inorganic materials 0.000 claims description 14
- 238000007790 scraping Methods 0.000 claims description 9
- 238000005520 cutting process Methods 0.000 claims description 5
- 238000006748 scratching Methods 0.000 claims description 2
- 230000002393 scratching Effects 0.000 claims description 2
- 238000004062 sedimentation Methods 0.000 abstract 1
- 239000010410 layer Substances 0.000 description 43
- 235000021317 phosphate Nutrition 0.000 description 40
- 239000007789 gas Substances 0.000 description 35
- 239000011343 solid material Substances 0.000 description 22
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 18
- 238000007254 oxidation reaction Methods 0.000 description 16
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium monoxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 14
- OKTJSMMVPCPJKN-UHFFFAOYSA-N carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 13
- 230000003647 oxidation Effects 0.000 description 13
- 229910052799 carbon Inorganic materials 0.000 description 12
- 238000006243 chemical reaction Methods 0.000 description 12
- UGFAIRIUMAVXCW-UHFFFAOYSA-N carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 10
- 229910002091 carbon monoxide Inorganic materials 0.000 description 10
- 239000007787 solid Substances 0.000 description 10
- 239000000377 silicon dioxide Substances 0.000 description 9
- 229910052760 oxygen Inorganic materials 0.000 description 8
- 239000001301 oxygen Substances 0.000 description 8
- MYMOFIZGZYHOMD-UHFFFAOYSA-N oxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 description 8
- OAICVXFJPJFONN-UHFFFAOYSA-N phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 7
- 229910052698 phosphorus Inorganic materials 0.000 description 7
- 239000011574 phosphorus Substances 0.000 description 7
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 6
- 239000011230 binding agent Substances 0.000 description 6
- 230000003247 decreasing Effects 0.000 description 6
- HWKQNAWCHQMZHK-UHFFFAOYSA-N Trolnitrate Chemical compound [O-][N+](=O)OCCN(CCO[N+]([O-])=O)CCO[N+]([O-])=O HWKQNAWCHQMZHK-UHFFFAOYSA-N 0.000 description 5
- 239000000440 bentonite Substances 0.000 description 5
- 229910000278 bentonite Inorganic materials 0.000 description 5
- 230000005540 biological transmission Effects 0.000 description 5
- 239000007788 liquid Substances 0.000 description 5
- DLYUQMMRRRQYAE-UHFFFAOYSA-N Phosphorus pentoxide Chemical compound O1P(O2)(=O)OP3(=O)OP1(=O)OP2(=O)O3 DLYUQMMRRRQYAE-UHFFFAOYSA-N 0.000 description 4
- 238000007792 addition Methods 0.000 description 4
- 238000001035 drying Methods 0.000 description 4
- 239000000428 dust Substances 0.000 description 4
- 238000011049 filling Methods 0.000 description 4
- 239000002006 petroleum coke Substances 0.000 description 4
- 239000002893 slag Substances 0.000 description 4
- 229910001220 stainless steel Inorganic materials 0.000 description 4
- 239000010935 stainless steel Substances 0.000 description 4
- 229910052681 coesite Inorganic materials 0.000 description 3
- 238000002485 combustion reaction Methods 0.000 description 3
- 229910052906 cristobalite Inorganic materials 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 238000002955 isolation Methods 0.000 description 3
- 238000002844 melting Methods 0.000 description 3
- 150000003013 phosphoric acid derivatives Chemical class 0.000 description 3
- 239000000843 powder Substances 0.000 description 3
- 229910052904 quartz Inorganic materials 0.000 description 3
- 239000004449 solid propellant Substances 0.000 description 3
- 229910052682 stishovite Inorganic materials 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- 229910052905 tridymite Inorganic materials 0.000 description 3
- PNEYBMLMFCGWSK-UHFFFAOYSA-N AI2O3 Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-N HF Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- ABTOQLMXBSRXSM-UHFFFAOYSA-N Silicon tetrafluoride Chemical compound F[Si](F)(F)F ABTOQLMXBSRXSM-UHFFFAOYSA-N 0.000 description 2
- PASHVRUKOFIRIK-UHFFFAOYSA-L calcium sulfate dihydrate Chemical compound O.O.[Ca+2].[O-]S([O-])(=O)=O PASHVRUKOFIRIK-UHFFFAOYSA-L 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 239000001569 carbon dioxide Substances 0.000 description 2
- 229910002092 carbon dioxide Inorganic materials 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-M fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 2
- 229910000040 hydrogen fluoride Inorganic materials 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000005453 pelletization Methods 0.000 description 2
- 238000010298 pulverizing process Methods 0.000 description 2
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Inorganic materials [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- ROPDWRCJTIRLTR-UHFFFAOYSA-L Calcium metaphosphate Chemical compound [Ca+2].[O-]P(=O)=O.[O-]P(=O)=O ROPDWRCJTIRLTR-UHFFFAOYSA-L 0.000 description 1
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 1
- 229920001732 Lignosulfonate Polymers 0.000 description 1
- 235000019738 Limestone Nutrition 0.000 description 1
- 239000004115 Sodium Silicate Substances 0.000 description 1
- NTHWMYGWWRZVTN-UHFFFAOYSA-N Sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 235000015450 Tilia cordata Nutrition 0.000 description 1
- 235000011941 Tilia x europaea Nutrition 0.000 description 1
- QORWJWZARLRLPR-UHFFFAOYSA-H Tricalcium phosphate Chemical compound [Ca+2].[Ca+2].[Ca+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O QORWJWZARLRLPR-UHFFFAOYSA-H 0.000 description 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-O ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 1
- -1 and then pelletized Substances 0.000 description 1
- 239000010426 asphalt Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- LSNNMFCWUKXFEE-UHFFFAOYSA-M bisulfite Chemical compound OS([O-])=O LSNNMFCWUKXFEE-UHFFFAOYSA-M 0.000 description 1
- 239000001506 calcium phosphate Substances 0.000 description 1
- 229910000389 calcium phosphate Inorganic materials 0.000 description 1
- 235000011010 calcium phosphates Nutrition 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 239000001913 cellulose Substances 0.000 description 1
- 229920002678 cellulose Polymers 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 239000000571 coke Substances 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 239000003337 fertilizer Substances 0.000 description 1
- 238000005755 formation reaction Methods 0.000 description 1
- 239000003517 fume Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 239000003779 heat-resistant material Substances 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 239000011229 interlayer Substances 0.000 description 1
- 239000004571 lime Substances 0.000 description 1
- 239000006028 limestone Substances 0.000 description 1
- 230000000116 mitigating Effects 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000006011 modification reaction Methods 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 150000003016 phosphoric acids Chemical class 0.000 description 1
- 230000002035 prolonged Effects 0.000 description 1
- NIFIFKQPDTWWGU-UHFFFAOYSA-N pyrite Chemical compound [Fe+2].[S-][S-] NIFIFKQPDTWWGU-UHFFFAOYSA-N 0.000 description 1
- 229910052683 pyrite Inorganic materials 0.000 description 1
- 239000011028 pyrite Substances 0.000 description 1
- 239000011819 refractory material Substances 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- KEAYESYHFKHZAL-UHFFFAOYSA-N sodium Chemical compound [Na] KEAYESYHFKHZAL-UHFFFAOYSA-N 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 229910052911 sodium silicate Inorganic materials 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 239000006188 syrup Substances 0.000 description 1
- 235000020357 syrup Nutrition 0.000 description 1
- OBSZRRSYVTXPNB-UHFFFAOYSA-N tetraphosphorus Chemical compound P12P3P1P32 OBSZRRSYVTXPNB-UHFFFAOYSA-N 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
Abstract
Disclosed is a rotary kiln for reducing phosphate ore in kiln process for production of phosphoric acid, comprising a kiln body, a kiln head box, a kiln tail box and a driving device for driving the rotation of the kiln body, wherein a fuel burner is provided at the kiln head, a feeding pipe and an outlet flue connected to an external hydration tower are provided at the kiln tail box, the upper part of the kiln body is provided with no air pipe, the outlet flue is provided in the radius range of the kiln body with the axis of the rotary kiln as a centre, and the smoke conveying direction in the outlet flue is substantially parallel to the axis direction of the rotary kiln or has an included angle of less than 45°thereto. When using the rotary kiln of the present invention for the kiln process for the production of phosphoric acid, and raw materials enter from the kiln tail box, the fuel burner is ignited for heating, the phosphate ore raw material is reduced under a high-temperature condition to produce a smoke exiting the kiln, and in the present invention, the smoke exiting the kiln is allowed to enter the outlet flue without large shifting, thereby preventing the centrifugal physical sedimentation at the kiln tail such that the metaphosphoric acid in the kiln smoke directly enters the hydration tower along with the kiln smoke. The present invention can effectively mitigate the phenomenon of ring forming in the kiln tail of the rotary kiln.
Description
The présent invention refers to a reaction device for reducing phosphate ore, particularly a rotary kiln for reducing phosphate ore.
BACKGROUND OF THE INVENTION
At présent, there are mainly two methods for industrial production of phosphoric acid in the world. (1) A wet process for production of phosphoric acid. In this process, phosphate ore is decomposed by sulfuric acid to produce dilute phosphoric acid and solid slag (briefly called phosphogypsum) which mainly comprises of CaSO4-nH2O, and the dilute phosphoric acid is then concentrated to a concentration of about 54%. The main shortcomings of this process are as follows: one is considérable consumption of sulfuric acid; and another one is less effective utilization of phosphogypsum which contains sulfuric acid, phosphoric acid and soluble fluoride, soluble in water, which may cause severe environmental pollution once washed by rain water when piled outside; and the third one is the content of impurities in the phosphoric acid produced is so high that the phosphoric acid is normally used as fertilizer; the fourth one is the utilization of high-grade phosphate ore which is necessary for the economy of production. (2) A hot process for production of phosphoric acid. In this process, phosphate ore, silica and carbonaceous solid reductant are directed into a ore furnace which is heated by the energy of erc formed by electric short circuit to a température above 1300FJ, and the phosphorus in phosphate ore is reduced to be P4 and carbonaceous solid reductant is converted to be carbon monoxide (CO) at the same time, and the gas mainly contains P4 and CO is cooled by washing water after discharged from the furnace, and P4 which is cooled to form the yellow phosphorus séparâtes from the gas, and the remaining gas containing CO is discharged into the air after ignited in the chimney outlet; and P4 obtained is then heated to a température of approximately 80 □ to form P4 liquid, and then an oxidation-combustion reaction of the P4 liquid with air in the hydration tower occurs to produce phosphoric anhydride, phosphorus pentoxide (P2O5), which is absorbed by water to be desired phosphoric acid. The main shortcomings of this process are as follows: firstly, it consumes lots of electric energy; secondly, the remaining gas discharged from fumace after being separated from P4 may contaminate the atmosphère environment because it still contains quantifies of fluoride (exists in form of silicon tetrafluoride (S1F4) and hydrogen fluoride (HF)) and a few P4 gas which is not deposited; thirdly, the gas contains huge amounts of CO is directly burnt following by being discharged into the air which causes an energy waste; fourthly, high-grade phosphate ore is also required for the economy of production.
For overcoming the impact on production of phosphoric acid exerted by shortage of electric energy tension, insufficient pyrite resources and graduai décliné in quality of high-grade phosphate ore, Occidental Research Corporation (ORC) in America proposed KPA in the early 80s, namely the rotary kiln process for production of phosphoric acid (briefly as KPA) (see Frédéric Ledar and Won C. Park et al, New Process for Technical-Grade Phosphoric Acid, Ind. Eng. Chem. Process Des. Dev 1985, 24, 688-697), and conducted the pilot test using the kiln of 0.84cm (inner)x9.14cm as a pilot equipment (see the US patent document US4389384). In this process, phosphate ore, silica and carbonaceous reductant are grinded to enable 50 to 85 percent of grinded material to be 325 mesh powder, followed by addition of bentonite with a proportion of 1% for pelletizing, and after being preheated and dried in the chain-type dryer, the pellets obtained are directed into the rotary kiln with natural gas burning at the kiln head and then reduced, and the highest solid température and CaO/SiO? molar ratio of pellets are controlled in the range of 1400Π to 1500Q and 0.26 to 0.55, respectively, to make the melting point of pellets higher than température for réduction of phosphate ore by carbon, and then phosphorus in the pellets is reduced followed by being evaporated from the pellets in form of phosphorus steam which is then oxidized by air in the space of middle part in kiln to form P2O5, and the exothermic heat generated from the oxidation reaction balances the endothermie heat required for the réduction of the phosphate ore, and finally, the smoke containing P2O5 is absorbed by hydration to form phosphoric acid.
The KPA described above exhibits a good prospect for industrial application because of the mechanism thereof which is as follows: the phosphorus in phosphate ore is transferred into the gas in kiln after réduction of phosphate ore to form P4 gas, and thus phosphores is separated from other solid substances in the pellets by taking advantage of gas-solid séparation principle, and the heat generated from the exothermic oxidation reaction of P4 gas with oxygen in the kiln essentially balances the endothermie heat required for réduction of the phosphate ore in the pellets (endothermie reaction), and finally the smoke exiting the kiln which contains P2O5 is absorbed by hydration to form phosphoric acid, and the clean class of phosphoric acid obtained is much higher than that produced in wet process. Additionally, compared with the traditional hot process for production of phosphoric acid, the energy consumption of process described above has been greatly decreased because of the primary energy used in process and the heat generated by the combustion exothermic reaction of the combustible material, such as P4 and CO formed by the réduction of phosphate ore, which is used for energy supply to maintain température required for réduction of phosphate ore.
However, our research shows that KPA described above is difficult to be carried out in large-scale industrial applications and practice for its main defects as follows:
1. A rotary kiln is a device with a kiln body rotating at a certain speed (0.5r/min to 3r/min) which is characterized by the ability thereof to enable the solid materials flipped and mixed with a continuous mode to ensure the solid material heated uniformly, and at the same time, the solid material must subjected to mechanical friction in material movements and the material may be damaged if its mechanical strength is less than the mechanical friction. The basic mechanism of KPA proposed by ORC is as follows: after being grinded to enable 50 to 85 percent of grinded material to be 325 mesh powder, and then pelletized, phosphate ore, silica and carbonaceous reductant (fine coke or coal powder) must be together closely to enable the mixture not to be melted at the température for réduction of phosphate ore by carbon with a CaO/SiO? molar ratio of 0.26 to 0.55 and ensure the réduction of phosphate ore to be carried out successfully. In the process, carbon used as reductant in the pellets may be oxidized rapidly by oxygen in the air to form carbon dioxide when température is higher than 350□, and if the method of consolidation of pellets in chain grate under high-temperature condition (>900 □) in traditional metallurgical industry is adopted, ail of carbon in pellets will be oxidized, and resulting loss of reductant causes the failure of réduction of phosphate ore and the process. The compressive strength and drop strength of the pellets are only approximately lOkN/pellet and not greater than 1 time/m, respectively, if the pellets are dried to be dehydrated at a température below 300 □ only with bentonite as binder; because the function mechanism of bentonite is as follows: the interlayer water in structure of bentonite is used to adjust the release rate of water in pellets in drying process to improve the burst température of pellets, and yet bentonite itself has no signincant effect on the improvement of strength of pellets. The pellets obtained in the process described above could not withstand the mechanical friction produced by the pellets movements in kiln before the température in the kiln reaches 900□, and then the pulverization in large scale of pellets occurs, and séparation of the power of phosphate ore in pellets from the power of silica and carbonaceous reductant results in the failure of réduction of phosphorus. More seriously, the melting point of phosphate ore power déclinés sharply below 1250Π once phosphate ore power has been separated from the silica power, and the phosphate ore power obtained will be converted to be liquid in high-temperature réduction zone in the kiln ( wherein the température of solid material is approximately 1300Π), and the liquid obtained may adhéré to the kiln liner to form a ring which may hinder the normal movement of material and resuit in overflow of the most material added into the kiln from the feeding end, and then the failure of réduction of phosphorus which results in the failure of the process occurs. There is no industrial, large-scale or commercial application of KPA described above for the inhérent defects of the raw materials added into the kiln.
2. In KPA described above, the area of the lower part of solid material layer in the kiln is a réduction zone and the upper part thereof is an gas flow area which belongs to an oxidation zone, and the pellets are fed into the kiln from the kiln tail and discharged from the kiln head relying on their own gravity and friction caused by the rotary motion of the kiln, and a fuel burner is provided at the kiln head, and fume produced by burning is exhausted by a draught fan provided at the kiln tail, and a slight négative pressure is maintained in the kiln and the direction of gas flow and material movement is opposite. Since no mechanical isolation area exists between the réduction zone (the solid material layer région) and oxidation zone (the gas flow région above the solid material layer), therefore, the convective mass transfer between the pellets exposed at the surface of solid material layer région and oxygen and carbon dioxide in the gas flow in the oxidation zone occurs; and it results in the oxidation of a portion of reductant before the pellets are heated by the heat transferred from the gas flow to pellets to a température for réduction of phosphate ore, and thus the pellets cannot get a full réduction in the réduction zone for the lack of carbonaceous reductant; more seriously, a further chemical reaction of the pellets exposed at the surface of solid material layer in high-temperature zone with P2O5 formed by réduction in the smoke occurs to form calcium metaphosphate, calcium phosphate and other metaphosphate and phosphates which resuit in the return of phosphores in the gas to pellets, and a white shell rich in P2O5 is formed on the surface of pellets, and the thickness of the shell is generally 300pm to lOOOpm, and the content of P2O5 in the shell can be high above 30%; and thus a low amount of P2O5 which is not higher than 60% in the gas phase transferred from pellets is obtained which causes a decreased yield of P2O5 in phosphate ore, and then it results in a waste of minerai resources and a big rise of production cost of phosphoric acid and then the loss of commercial applications and industrial promotion values. Some researchers hoped to get the insulation of réduction zone and oxidation zone by a utilization of the gas volatilizing from the solid material layer, however, it is proved to be impracticable by the inévitable phenomenon of white shell forming in the industrial test in a rotary kiln with a inner diameter of 2m.
Considering the technology defects described above, it is difficult for KPA proposed by ORC to be used for large-scale industrial applications and practice.
Joseph A. Megy proposed some improved methods based on KPA (see US patent document US7910080B), namely, with the basic process and method of KPA maintained, a tail ring is provided at the discharging end in the kiln head for a increased filling rate of solid material in the kiln, and the diameter of the kiln is increased for a decreased surface-volume ratio of the solid material layer in the kiln, and a decreased probability of the exposure of material in the solid material layer to the surface of layer, and a shortened time for oxidation of reductant in pellets by oxygen in the smoke in kiln, and a reduced loss of reductant in pellets before the pellets being sent to the réduction zone, and a decreased amount of phosphates or metaphosphates formed at the surface of pellets in high température zone. Additionally, some petroleum coke is added into the solid material in kiln to produce the reducing gas formed by volatilization of the volatile components in petroleum coke, and the reducing gas is desired to exist between solid material layer and gas flow oxidation zone for a further decreased probability of the reaction of oxygen and P2O5 in gas flow in kiln with pellets to ensure the normal operation of process. However, the increased filling rate of solid material in the kiln makes the pellets subjected to a increased mechanical friction in kiln and pulverized with a greater proportion, and more substance with a low melting point which is smaller than the température for réduction of phosphate ore by carbon
is formed, and then the forming of the ring in kiln becomes more rapid and massive and which causes the failure of process appearing much earlier. Addition of a small amount of petroleum coke cannot produce sufficient gas to form an effective isolation région between solid material layer and gas flow area in kiln, however, if the amount of petroleum coke added is too large, the 5 solid material will carry a lot of fuel, and the remaining fuel will encounter with the air for cooling of slag pellets and bum rapidly, and the heat of large scale produce by buming results in the problem of the cooling for slag pellets, and an increased cost of production and no possibility of commercial and scale application of the process.
In view of the above problems, the inventors proposed a solution to solve the above problems 10 (see the Chinese patent documents CN1026403C and CN1040199C) after repeated research, namely, a process for production of phosphoric acid by directly reducing of phosphate ore, wherein the double-layered composite pellets are adopted. The spécifie technology solution is as follows: the phosphate ore is pelletized with added materials and P2O5 in the pellets obtained is reduced to form phosphorus steam which is oxidized above the solid material layer by the air 15 introduced into kiln to form P2O5 gas which is absorbed in the hydration device to form phosphoric acid. The most important feature of said technology solution is the structure of double layers in pellets, wherein the inner layer is formed by phosphate ore, silica (or lime, limestone etc) and carbonaceous reductant after being grinded, mixed and pelletized, and wherein the inner pellets formed is wrapped with a layer of solid fuel with a carbon content of 20 more than 20%, and binder is added into materials prepared for the inner and outer layer, and the pellets are consolidated by drying. The molar ratio of CaO/SiCh in pellets can be less than 0.6 or more than 6.5, and the amount of carbonaceous reductant is selected as 1-3 times the theoretical amount for réduction of phosphate ore, and the amount of solid fuel in outer layer may be 5%-25% of mass of inner pellets; and the binder added into the inner and outer layer may be 25 asphalt, sodium humate, ammonium humate, sodium silicate, sulfite cellulose liquor, syrup, lignosulfonate or the combination thereof, and volume of addition of the binder is 0.2%-15% (dry basis) of the mass of materials added into. The pellets can be consolidated by drying and the consolidation température is selected in the range of 80 0-6000, and the consolidation time is selected in the range of 3min-120min.
In the solution described above, the pellets are wrapped in a heat-resistant material containing carbon solid with the addition of a binder for a good adhesion to inner pellets of the outer wrapping material. The composite pellets with double layers are directed into the kiln after being dried for consolidation, and the réduction of phosphate ore performs very well in high-temperature zone (approximately 1300D to 14000) in the kiln. The wrapping layer containing solid reductant (carbon material) ensures an effective physical isolation between inner pellets and oxidation zone which is gas flow containing oxygen and P2O5 above the solid material layer. The wrapping layer rises to the surface of solid material layer with the rotational movement of kiln and contacts with the oxidation zone described above, and a convective mass transfer occurs with a limited oxidation reaction of carbon in wrapping layer by oxygen in oxidation zone (the reaction is not complété because time for exposure of pellets to surface of solid material layer in industrial large-scale rotary kiln is very short), and thus oxygen in gas flow cannot be delivered to the inner pellets to enable carbon reductant in inner pellets not to be oxidized and réduction of P2O5 in phosphoric ore to be complété, and then a high réduction ratio of P2O5 in this process is obtained. Additionally, it is impossible for reaction between P2O5 in oxidation zone with carbon in wrapping layer which may cause production of phosphates and metaphosphates and forming of white shell rich in P2O5 on composite pellets in original KPA, and then a high yield of P2O5 is obtained. Moreover, in this solution, solid fuel is used for substituting or partially substituting of gas or liquid fuel to further reduce the production cost of phosphoric acid.
Additionally, a organic binder is used in pelletization process in the process described above to make the composite pellets get a compressive strength over 200kN/pellet and a drop strength over 10time/m after being dried (the température for drying is lower than that for oxidation of carbon in pellets), thus the composite pellets can be résistant to mechanical friction without being pulverized to avoid a poor strength of pellets and prématuré oxidation of carbon in the preheating zone in the original KPA, and no pulverization of pellets makes the failure of process caused by forming of ring under high-temperature condition which is resulted in by pulverized materials to ensure the smoothly running of the process under the given condition.
However, in the course of the subséquent study, the inventors discovered a sériés of new technical problems. The combustion air fed into the rotary kiln contains a certain amount of water (the water fed into the rotary kiln because of air humidity), and the water reacts with P2O5 in gas flow in the rotary kiln to form metaphosphoric acid (HPO3), and then metaphosphoric acid generated reacts with the dust m the smoke m the kiln to form complex metaphosphates, and the substance formed inside the cylinder casing in the kiln tail (namely the ring formed in the kiln tail of the rotary kiln) is gradually generated and constantly grown up because of complex metaphosphates; after a period of working of the kiln, the grown up ring formed in the kiln tail seriously hinders the movement of pellets and makes the pellets fed into the rotary kiln to be retumed out of the kiln from the kiln tail, and then the normal working of the process is disrupted and the working of the kiln must be stopped for cleaning of the kiln, and the resulting induced operating rate of the rotary kiln and increased production cost of phosphoric acid make it difficult for the commercial applications of the process.
Therefore, to improve the production efficiency of the current process of producing phosphoric acid with a kiln, reduce the production cost and ensure the stable opertion of the process, the current kiln process of producing phosphoric acid requires continuous modifications and improvements of those skilled in the art.
SUMMARY OF THE INVENTION
To overcome the serious technical defect of failure of long-term production in kiln process for production of phosphoric acid, it is an object of the présent invention to provide a rotary kiln for reducing phosphate ore in kiln process for production of phosphoric acid with a simple structure, low investment, low cost, and an ability of mitigating the phenomenon of ring forming in the kiln tail of the rotary kiln effectively, and another object of the présent invention is to provide a method for solving ring forming in kiln tail in kiln process for production of phosphoric acid with a simple operation, low investment and good effects.
In long-term application and practice of kiln process for production of phosphoric acid, the forming of ring in the kiln tail of the rotary kiln is an important technical problem troubling those skilled in the art because the ring results in the failure of feeding of raw material pellets into the kiln and normal movement of the gas flow. Expérience proves that if the problem of ring forming in the kiln tail is not solved, a shortened process period, decrease process efficiency, significantly increases process cost and even the failure of the process are obtained. After years of intensive research, we finally identified the main reason for the formation of ring in the kiln tail. In kiln process for production of phosphoric acid, metaphosphoric acid in the gas flow is deposited in the kiln tail and then reacts with dust in the kiln to from metaphosphates solid and then the solid ring in the kiln tail. To solve the technical problem described above, after repeated tests, we propose the following technical solution: a rotary kiln for reducing phosphate ore in kiln process for production of phosphoric acid, comprising a kiln body, a kiln box, a kiln tail box and a driving device for driving the rotation of the kiln body, wherein a fuel burner is provided at the kiln head, a feeding pipe and an outlet flue connected to an extemal hydration tower are provided at the kiln tail box, the upper part of the kiln body is provided with no air pipe, the outlet flue is provided in the radius range of the kiln body with the axis of the rotary kiln as a centre, and the smoke conveying direction in the outlet flue is substantially parallel to the axis direction of the rotary kiln or has an included angle of less than 45°thereto.
In the rotary kiln described above, particularly, the kiln body compromises an external cylinder casing and a kiln liner disposed inside the cylinder casing (the kiln liner is constructed of firebricks or refractory castables), and the kiln body is divided into a réduction zone and preheating zone in a lengthwise direction of the rotary kiln, wherein the réduction zone is located near kiln head box and the preheating zone is located near kiln tail box, wherein the length of réduction zone is 1/3 to 3/5 of the length of the kiln body and the length of preheating zone is 2/5 to 2/3 of the length of the kiln body.
In the rotary kiln described above, particularly, the kiln liner is constructed of composite firebricks or refractory castables, and the kiln liner located in réduction zone comprises a clay material layer (with a small thermal conduction coefficient) close to cylinder casing and a high-aluminous material layer (with a high refractoriness and relatively large thermal conduction coefficient) close to the inner cavity of kiln; and the kiln liner located in preheating zone comprises a clay material layer (with a small thermal conduction coefficient) close to the cylinder casing and a silicon carbide material layer (with a low level of reacting with metaphosphate and relatively large thermal conduction coefficient) close to the inner cavity of kiln.
In the rotary kiln described above, particularly, a kiln cleaning machine is disposed extemally the cylinder casing, wherein a scraper (made of heat-resistant stainless steel) is installed which can extend into the kiln tail box progressively and keep scratching relatively to the inner wall of the cavity.
In the rotary kiln described above, particularly, an axis of the rotary kiln forms an angle of 1.7°to 2.9°with a horizontal plane, and a length-diameter ratio of the kiln body (ratio of kiln length to inner diameter of steel cylinder casing) is in the range of 10 to 25:1, and filling rate of kiln is in a range of 7 to 25 percent, and a rotating speed is controlled in a range of 0.6r/min to 3r/min. A thickness of refractory in kiln is preferably in a range of 200mm to 280mm.
In the rotary kiln described above, particularly, a plurality of thermocouples for monitoring the in-kiln température are mounted in the lengthwise direction of the kiln body of the rotary kiln, and the thermocouples are coupled to a température control device and a température display device outside the rotary kiln via an electrically conductive ring or a wireless transmitting and receiving device; the kiln head of the rotary kiln is provided with an industrial télévision for monitoring conditions in the rotary kiln.
In the rotary kiln described above, particularly, an air pump for extracting air sample is mounted on the outlet flue or inside the kiln tail box of the rotary kiln.
As a general technical idea, the présent invention also provides a method for solving ring forming in kiln tail in kiln process for production of phosphoric acid, the rotary kiln described above is used in the kiln process for producing phosphoric acid, and the raw material is fed into the cavity of the rotary kiln through a feeding pipe at the kiln tail of the rotary kiln, and then the fuel burner is ignited to heat the réduction zone in the rotary kiln to a température of 1300Q to 14500, and the phosphate ore raw material in the rotary kiln is reduced by the reducing agent under a high-temperature condition to produce the smoke exiting the kiln, and designed outlet flue according to the présent invention enables the smoke exiting the kiln at the tail of the rotary kiln not to deviate much in the movement direction upon entering the outlet flue, and thus the centrifugal physical settlement of metaphosphoric acid in the smoke existing the kiln is prevented so that the metaphosphoric acid in the kiln gas directly enters a subséquent hydration tower along with the smoke exiting the kiln and is converted to be orthophosphoric acid after meeting water.
As a further improvement of the process described above, the kiln liner located in the preheating zone of the rotary kiln is made of double-layered composite fïrebricks or refractory castables, the kiln liner adjacent to the cylinder casing of the rotary kiln is made into a clay material layer by using the clay material, and the kiln liner adjacent to the inner cavity of the rotary kiln is made into a silicon carbide material layer by using the silicon carbide material, and thus a reduced adhesion of metaphosphate on the kiln liner in the preheating zone of rotary kiln to the kiln liner, and the resulting falling off of metaphosphate on its own can mitigate the phenomenon of ring forming in the kiln tail of the rotary kiln, a low level of reaction of silicon carbide with metaphosphoric acid can significantly reduce the adhesion of metaphosphate to the preheating zone at the kiln tail of the rotary kiln and resuit in the falling off of metaphosphate formed at the kiln tail of the rotary kiln on its own to further ease occurrence of ring forming at the kiln tail.
As a further improvement of the process described above, a matching kiln cleaning machine is disposed externally the kiln tail box, wherein a scraper is installed in the kiln cleaning machine which can extend into the kiln tail box progressively and keep scraping relatively to the inner wall of the cavity; when a retum of pellets outside the kiln from the kiln tail which is caused by the ring-forming at the tail of the rotary kiln occurs, the fuel supply for heating the rotary kiln is stopped first, meanwhile the feeding of pellets into the rotary kiln is stopped, and the pellets in rotary kiln are discharged for emptying of the kiln, and then the scraper in the kiln cleaning machine is used to extend gradually into the rotary kiln, and thus the ring formed at the kiln tail is removed by cutting and scraping with the rotation of the rotary kiln itself.
Compared with the prior art, the advantages of the présent invention are as follows:
(1) In the présent invention, the outlet of the smoke exhausting pipe at the kiln tail of the rotary kiln is disposed in the same direction as the axis of the rotary kiln (a proper déviation may be permitted for convenience of facilitating a pipe to the hydration tower) so that the smoke exiting the kiln at the tail of the rotary kiln does not deviate much in the movement direction upon entering the outlet flue, and thus the centrifugal physical settlement of metaphosphoric acid in the smoke existing the kiln is prevented so that the metaphosphoric acid in the kiln gas directly enters a subséquent hydration tower along with the smoke exiting the kiln and is converted to be orthophosphoric acid after meeting water. A reduced amount of metaphosphoric acid settled in rotary kiln prolongs the forming cycle of ring at the kiln tail and increases the working efficiency of the rotary kiln.
(2) In the preferred solution of the présent invention, the kiln liner located in the preheating zone of the rotary kiln adopts a double-layered composite material structure, and the kiln liner adjacent to the cylinder casing of the rotary kiln adopts a clay material layer, and the kiln liner adjacent to the inner cavity of the rotary kiln adopts a silicon carbide material layer, a low level of reaction of silicon carbide material with metaphosphate enables metaphosphate settled on the preheating zone to fall off on its own.
(3) In the preferred solution of the présent invention, a scraper made of heat-resistant stainless steel is mounted outside the kiln tail box of the rotary kiln; once a return of pellets outside the kiln from the kiln tail which is caused by the ring-forming at the tail of the rotary kiln occurs, the fuel supply for heating the rotary kiln and the feeding of pellets into the rotary kiln are stopped, and meanwhile the scraper is used to extend gradually into the rotary kiln, and thus the ring formed at the kiln tail is removed by cutting and scraping with the rotation of the rotary kiln itself.
(4) In the preferred solution of the présent invention, with the thermocouples being disposed, it can be ensured that a maximum température of the composite pellets with a CaO/SiO2 mole ratio in inner pellets of less than 0.6 does not exceed 1370Π and a maximum température of the composite pellets with a CaO/SiO2 mole ratio in inner pellets of greater than 6.5 does not exceed 1450 □ for a better control of the reaction condition and an ensured product quality .
(5) In the preferred solution of the présent invention, an air pump for extracting air sample is mounted on the outlet flue at the outlet of the kiln tail box or on the kiln tail box of the rotary kiln, and the air samples collected by the air pump, after being washed with water to remove dust, are fed into a gas analyser to monitor the content of CO and O2 in the smoke in the outlet of the rotary kiln for a better control of the content range of CO and O2 in the smoke exiting the kiln (generally is 0 to 5 percent).
In summary, the rotary according to the présent invention has advantages of a simple structure, small investment and low cost etc, and the application of rotary kiln in the method according to the présent invention can be a good solution to the problem of the failure of commercialization of KPA caused by the ring forming at the kiln tail of the rotary kiln, and thus a real commercialization of KPA, and a greatly prolonged producing cycle and a significant économie
effect in energy saving and reducing of the cost of production process are obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a structural schematic view of a rotary kiln according to a spécifie embodiment of the 5 présent invention.
Fig. 2 is an enlarged sectional view taken along A-A in Fig. 1.
Fig. 3 is an enlarged sectional view taken along B-B in Fig. 1.
Fig. 4 is an enlarged sectional view taken along C-C in Fig. 1.
Fig. 5 is a structural schematic view of a kiln cleaning machine according to a spécifie 10 embodiment of the présent invention.
Fig. 6 is an enlarged sectional view taken along D-D of Fig.5.
Fig. 7 is a theoretical view of the kiln cleaning machine according to the spécifie embodiment of the présent invention upon operation.
Fig. 8 is an enlarged sectional view taken along E-E.
The description of the legends:
The reference number 1 dénotés a kiln head box; 2 a supporting wheel device; 3 a kiln body; 4 a transmission pinion; 5 a driving device; 6 a kiln tail box; 7 an outlet flue; 8 a feeding pipe; 9 a kiln tail dynamic seal; 10 a transmission gear; 11 a kiln liner; 12 a cylinder casing; 13 a thermocouple; 14 an air pump; 15 a fuel humer; 16 a silicon carbide material layer; 17 a clay 20 material layer; 18 a high-alumina material layer; 19 a kiln head dynamic seal; 20 a scraper; 21 a platform; 22 a wheel; 23 a travel decelerating motor; 24 a machine frame; 25 a rotation shaft; 26 a supporting truss; 27 a rotary kiln door frame.
• DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The présent invention will be further described in detail with reference to the figures and spécifie preferred embodiments, which is not intended to limit the présent invention.
EMBODIMENTS:
A rotary kiln for reducing phosphate ore in kiln process for production of phosphoric acid shown in figure 1 to 8 comprises a kiln body 3, a kiln head box 1, a kiln tail box 6 and a driving device 5 for driving the rotation of the kiln body, wherein the driving device 5 comprises a motor, a transmission pinion 4 connected with the motor and a transmission gear 10 meshing with the transmission pinion 4, and a supporting wheel device 2 is disposed in the middle of the kiln body 10 3. A kiln head dynamic seal 19 is employed between the kiln head box 1 and the kiln body 3, and a kiln tail dynamic seal 9 is employed between the kiln tail box 6 and the kiln body 3.
The kiln head of the kiln body 3 according to the présent embodiment are provided with a fuel bumer 15 and a high-temperature slag pellets outlet, and the kiln tail box 6 of the kiln body 3 are provided with an outlet flue 7 which is connected to an extemal hydration tower, and an feeding 15 pipe 8 is in communication with an inner cavity of the rotary kiln. The upper part of the kiln body 3 is provided with no air pipe, and the outlet flue 7 is disposed on an axis of the rotary kiln, and a smoke delivery direction in the outlet flue 7 is substantially parallel to the axial direction of the rotary kiln.
The kiln body 3 according to the présent embodiment compromises an external cylinder casing 20 12 and a kiln liner 11 disposed inside the cylinder casing 12, and the kiln body 3 is divided into a réduction zone and preheating zone in a lengthwise direction of the rotary kiln, wherein the réduction zone is located near kiln head box 1 and the preheating zone is located near kiln tail box 6, wherein the length of réduction zone is 1/3 to 3/5 (1/2 in the présent embodiment) of the length of the kiln body and the length of preheating zone is 2/5 to 2/3 (1/2 in the présent 25 embodiment) of the length of the kiln body. The kiln liner 11 is constructed of composite refractory castables (or composite firebricks), as shown in Fig. 3, the kiln liner 11 located in réduction zone comprises a clay material layer 17 close to cylinder casing 12 and a high-aluminous material layer 17 (with an aluminum oxide content not lower than 65 percent) close to the inner cavity of kiln; and as shown in Fig. 4, the kiln liner 11 located in preheating zone comprises a clay material layer 17 close to the cylinder casmg 11 and a silicon carbide material layer 16 close to the inner cavity of kiln.
In the présent embodiment, a matching kiln cleaning machine is disposed externally the kiln tail box 6, as shown in Fig. 5 and Fig. 8, the kiln cleaning machine is placed on a platform 21, and the bottom of the kiln cleaning machine is provided with wheels 22 rolling on the platform 21, and the wheels 22 are driven by a travel decelerating motor 23, the main body of the kiln cleaning machine is a machine frame 24, a rotation shaft 25 driven by a motor is mounted in the upper part of the machine frame 24, the rotation shaft 25 extends in a substantially horizontal direction out of the machine frame 24, and a supporting truss 26 is sleeved around the extended portion, the free end of the extended part of the rotation shaft 25 is provided with a scraper 20 (which is made of heat-resistant stainless steel) which may progressively extend into the kiln tail box 6 (it is easy for the rotating scraper to extend into the kiln tail box) of the rotary kiln and keep scraping relative to the inner wall of the cavity. Once a return of pellets outside the kiln from the kiln tail which is caused by the ring-forming at the tail of the rotary kiln occurs, the fuel supply for heating the rotary kiln and the feeding of pellets into the rotary kiln are stopped, and meanwhile the scraper is used to extend gradually into the rotary kiln, and thus the ring formed at the kiln tail is removed by cutting and scraping with the rotation of the rotary kiln itself.
The problem of ring forming in the kiln tail of the rotary kiln can be solved by using the rotary kiln according to the présent embodiment, and the spécifie operation is as follows: the rotary kiln described above is used in the kiln process for producing phosphoric acid, and the raw material is fed into the cavity of the rotary kiln through a feeding pipe 8 at the kiln tail of the rotary kiln, and then the fuel burner 15 is ignited to heat the réduction zone in the rotary kiln to a température of 1300D to 1450Π, and the phosphate ore raw material in the rotary kiln is reduced by the reducing agent under a high-temperature condition to produce the smoke exiting the kiln, the outlet of outlet flue 7 at the kiln tail is disposed in the same direction with (namely parallel to) an axis of the rotary kiln so that the smoke exiting the kiln at the tail of the rotary kiln dose not deviate much in the movement direction upon entering the outlet flue, and thus the centrifugal physical settlement of metaphosphoric acid in the smoke existing the kiln is prevented so that the metaphosphoric acid in the kiln gas directly enters a subséquent hydration tower along with the smoke exiting the kiln and is converted to be orthophosphoric acid after meeting water.
Furthermore, in the présent embodiment, the kiln liner 11 located in the preheating zone of the rotary kiln is made of double-layered composite refractory castables (or composite firebricks), the kiln liner adjacent to the cylinder casing 12 of the rotary kiln is made into a clay material layer 17 by using the clay material, and the kiln liner adjacent to the inner cavity of the rotary kiln is made into a silicon carbide material layer 16 by using the silicon carbide material, a low level of reaction of silicon carbide material with metaphosphate can significantly reduce the adhesion of metaphosphate settled on the kiln liner 11 in preheating zone to the kiln liner 11 of the rotary kiln, the structure of kiln liner described above can further prevent the metaphosphate reacting with kiln liner 11 and the ring forming and resuit in the falling off of metaphosphate formed on its own to further ease occurrence of ring forming at the kiln tail. Additionally, according to the présent embodiment, a matching kiln cleaning machine is disposed extemally the kiln tail 6, wherein a scraper 20 which is made of heat-resistant stainless steel is installed in the kiln cleaning machine which can extend into the kiln tail box progressively and keep scraping relatively to the inner wall of the cavity; when a return of pellets outside the kiln from the kiln tail which is caused by the ring-forming at the tail of the rotary kiln occurs, the fuel supply for heating the rotary kiln is stopped first, meanwhile the feeding of pellets into the rotary kiln is stopped, and the pellets in rotary kiln are discharged for emptying of the kiln, and then the scraper 20 in the kiln cleaning machine is used to extend gradually into the rotary kiln from a rotary kiln door frame 27, and thus the ring formed at the kiln tail is removed by cutting and scraping with the rotation of the rotary kiln itself (the operational principle of the kiln cleaning machine can be seen in Fig. 7 and Fig. 8). As can be seen from the above, the rotary kiln according to the présent embodiment effectively eases the problem of ring-forming at the tail of the rotary kiln in the kiln process for producing phosphoric acid by adopting multiple measures of safeguard and technical means.
Additionally, in the présent embodiment, a plurality of thermocouples 13 for monitoring the in-kiln température are mounted in the lengthwise direction of the kiln body 3 of the rotary kiln, and the thermocouples 13 are coupled to a température control device and a température display device outside the rotary kiln via an electrically conductive ring or a wireless transmitting and receiving device. with the thermocouples 13 being disposed, it can be ensured that a maximum
température of the composite pellets with a CaO/SiCh mole ratio in inner pellets of less than 0.6 does not exceed 1370Π and a maximum température of the composite pellets with a CaO/SiO2 mole ratio in inner pellets of greater than 6.5 does not exceed 1450□ for a better control of the reaction condition and an ensured product quality. The kiln head of the rotary kiln is provided with an industrial télévision for monitoring conditions in the rotary kiln.
Additionally, in the présent embodiment, an air pump 14 for extracting air sample is mounted on the outlet flue 7 at the outlet of the kiln tail box 6 of the rotary kiln. The air samples collected by the air pump, after being washed with water to remove dust, are fed into a gas analyser to monitor the content of CO and O2 in the smoke in the outlet of the rotary kiln for a better control 10 of the content range of CO and O2 in the smoke exiting the kiln (generally is 0 to 5 percent).
In the présent embodiment, an axis of the rotary kiln forms an angle a in a range of 1.2°-2.9° with a horizontal plane (2.3° in the présent embodiment), a length-diameter ratio of the kiln body 3 is 10 to 25:1 (15:1 in the présent embodiment), a filling rate of the rotary kiln is 7 to 25 percent (13 percent in the présent embodiment), and a rotation speed of the rotary kiln is controlled in a 15 range of 0.6r/min to 3r/min (lr/min in the présent embodiment). A thickness of the refractory material of the rotary kiln is preferably in a range of 200mm to 280mm (220mm in the présent embodiment).
Claims (10)
1. A rotary kiln for reducing phosphate ore in kiln process for production of phosphoric acid, comprising a kiln body (3), a kiln head box (1), a kiln tail box (6) and a driving device (5) for driving the rotation of the kiln body, and a fuel burner (15) is provided at the kiln head of the kiln body (3), a feeding pipe (8) and an outlet flue (7) connected to an external hydration tower are provided at the kiln tail box (6), wherein the upper part of the kiln body (3) is provided with no air pipe, the outlet flue (7) is provided in the radius range of the kiln body with the axis of the rotary kiln as a center, and the smoke conveying direction in the outlet flue (7) is substantially parallel to the axis direction of the rotary kiln or has an included angle of less than 45°thereto.
2. A rotary kiln for reducing phosphate ore in kiln process for production of phosphoric acid according to claim 1, wherein the kiln body (3) compromises an external cylinder casing (12) and a kiln liner (11) disposed inside the cylinder casing (12), and the kiln body (3) is divided into a réduction zone and preheating zone in a lengthwise direction of the rotary kiln, and the réduction zone is located near kiln head box (1) and the preheating zone is located near kiln tail box (6), the length of réduction zone is 1/3 to 3/5 of the length of the kiln body (3) and the length of preheating zone is 2/5 to 2/3 of the length of the kiln body (3).
3. A rotary kiln for reducing phosphate ore in kiln process for production of phosphoric acid according to claim 2, wherein the kiln liner (11) is constructed of composite firebricks or refractory castables, and the kiln liner (11) located in réduction zone comprises a clay material layer (17) close to cylinder casing (12) and a high-aluminous material layer (18) close to the inner cavity of kiln; and the kiln liner (11) located in preheating zone comprises a clay material layer close to the cylinder casing (12) and a silicon carbide material layer (16) close to the inner cavity of kiln.
4. A rotary kiln for reducing phosphate ore in kiln process for production of phosphoric acid according to claim 1, 2 or 3, wherein a matching kiln cleaning machine is disposed externally the kiln tail box (6), and a scraper (20) is installed in the kiln cleaning machine which can extend into the kiln tail box (6) progressively and keep scratching relatively to the inner wall of the cavity.
5. A rotary kiln for reducing phosphate ore in kiln process for production of phosphoric acid according to claim 1, 2 or 3, wherein an axis of the rotary kiln forms an angle of 1.7°to 2.9°with a horizontal plane, and a length-diameter ratio of the kiln body (3) is in the range of 10 to 25:1; and a fîlling rate of kiln is in a range of 7 to 25 percent, and a rotating speed is controlled in a range of 0.6r/min to 3r/min.
6. A rotary kiln for reducing phosphate ore in kiln process for production of phosphoric acid according to claim 1, 2 or 3, wherein a plurality of thermocouples (13) for monitoring the in-kiln température are mounted in the lengthwise direction of the kiln body of the rotary kiln, and the thermocouples (13) are coupled to a température control device and a température display device outside the rotary kiln via an electrically conductive ring or a wireless transmitting and receiving device; the kiln head of the rotary kiln is provided with an industrial télévision for monitoring conditions in the rotary kiln.
7. A rotary kiln for reducing phosphate ore in kiln process for production of phosphoric acid according to claim 1, 2 or 3, wherein an air pump (14) for extracting air sample is mounted on the outlet flue (7) or inside the kiln tail box (6) of the rotary kiln.
8. A method for solving ring forming in kiln tail in kiln process for production of phosphoric acid,wherein the rotary kiln described according to claim 1 is used in the kiln process for producing phosphoric acid, the raw material is fed into the cavity of the rotary kiln through a feeding pipe at the kiln tail of the rotary kiln, and then the fuel burner is ignited to heat the réduction zone in the rotary kiln to a température of 1300Π to 1450Π, and the phosphate ore raw material in the rotary kiln is reduced by the reducing agent under a high-temperature condition to produce the smoke exiting the kiln, and designed outlet flue enables the smoke exiting the kiln at the tail of the rotary kiln not to deviate much in the movement direction upon entering the outlet flue, and thus the centrifugal physical seulement of metaphosphoric acid in the smoke existing the kiln is prevented so that the metaphosphoric acid in the kiln gas directly enters a subséquent hydration tower along with the smoke exiting the kiln and is converted to be orthophosphoric acid after meeting water.
9. The method according to claim 8, wherein the kiln liner located in the preheating zone of the rotary kiln is made of double-layered composite firebricks or reffactory
5 castables, the kiln liner adjacent to the cylinder casing of the rotary kiln is made into a clay material layer by using the clay material, and the kiln liner adjacent to the inner cavity of the rotary kiln is made into a silicon carbide material layer by using the silicon carbide material, and a reduced adhesion of metaphosphate on the kiln liner in the preheating zone of rotary kiln to the kiln liner, and the resulting falling off of 10 metaphosphate on its own mitigates the phenomenon of ring forming in the kiln tail of the rotary kiln.
10. The method according to claim 8 or 9, wherein a matching kiln cleaning machine is disposed externally the kiln tail box, wherein a scraper is installed in the kiln cleaning machine which can extend into the kiln tail box progressively and keep scraping relatively to the inner wall of the cavity; when a return of pellets outside the
5 kiln from the kiln tail which is caused by the ring-forming at the tail of the rotary kiln occurs, the fuel supply for heating the rotary kiln is stopped first, meanwhile the feeding of pellets into the rotary kiln is stopped, and the pellets in rotary kiln are discharged for emptying of the kiln, and then the scraper in the kiln cleaning machine is used to extend gradually into the rotary kiln, and thus the ring formed at the kiln tail 20 is removed by cutting and scraping with the rotation of the rotary kiln itself.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201310218599.1 | 2013-06-04 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| OA17600A true OA17600A (en) | 2017-04-28 |
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