The reasons for the changes in heat balance caused by different bauxite treatments and different process conditions are analyzed. The heat balance of the entire containment system and the effect of adding lime milk at different temperatures on the load of the molten salt furnace and the dissipation heat consumption are discussed. Practice provides technical basis u: pipelined dissolution; diaspore; heat balance; energy dissolution is the key process of Bayer process to produce alumina. Due to the high silicon, low iron, and insoluble properties of diaspore in China, it determines the harsh conditions of its dissolution process: when the dissolution temperature is 245 ~ 250C, high alkali concentration (Na2k> 275g) and longer dissolution are required Time (1.5 ~ 2.0 hours). The flashing stage of the dissolution slurry is low, the preheating temperature of the raw ore slurry is low (~ 150C) and the direct heating steam dissolution process avoids the shortcomings of equipment manufacturing, difficult maintenance and pipeline scarring and wear, but its outstanding features High energy consumption. One is reflected in the low heat recovery utilization rate of the exhaust steam in the dissolution process, and the new steam consumption in the dissolution process is large; the second is that the direct heating of the steam has a large dilution of the slurry (Na2k concentration is reduced by 30-50g), which is required in the evaporation process Concentrating the Na2k concentration of the circulating mother liquor to above 275g results in increased evaporation burden and increased heat consumption. The total heat consumption of the dissolution and evaporation process is about 19G / tAh3, which is about twice that of the same industry abroad. 1. Overview of pipeline dissolution In order to reduce the energy consumption of alumina production, Changal Aluminum Company researched and designed itself in the early 1990s and introduced some equipment from Germany, and built China ’s first set of diaspore with a raw pulp processing capacity of 300m3 / h The pipelined dissolution production line has brought the Bayer process dissolution technology and equipment of alumina production in China to a new level. 1.1 Process flow When developing the technical solution of diaspore diaspore pipeline dissolution, in view of the poor grindability of Henan diaspore bauxite, the complex structure of silicon minerals, insoluble, etc., the grinding, ash, The process of pre-desilication of raw pulp, pipelined dissolution, molten salt heating, and pickling make it a pipelined dissolution system suitable for diaspore in China. The dissolution process is shown in the figure. 1.2 Main process technical parameters 1.3 Main features (1) The high dissolution temperature and the large degree of slurry turbulence strengthen the dissolution process. The dissolution time is short and the effect is good, which can save investment in the staying section. ⑵ Low energy consumption. Achieve low alkali concentration, multi-stage flash secondary steam and molten salt indirect and high-temperature enhanced dissolution, system heat consumption is greatly reduced, dissolution and evaporation heat consumption can be reduced by more than 8.0G / tlk3. (3) After adding lime, it can effectively prevent scar formation at high temperature, which can extend the cleaning cycle and improve the operation rate of the equipment. (4> Compared with the autoclave, the pipelined heating device covers a large area. (5 There are scarring and wear problems of the heating pipe. ⑹ The working pressure and temperature of the system are high, and there are special requirements for the material of the feeding pump and the pipeline heating device. 2 Thermal balance of pipelined dissolution system 2.1 Thermal balance composition The pipelined dissolution body consists of ore slurry heat exchange section, spent steam preheating section, molten salt heating section and staying dissolution reaction section. The design value of the pipelined dissolution temperature is 270 ~ 280. The high-temperature molten salt heating method is used. Two molten salt furnaces with a heating capacity of 11630kW provide heat for the dissolution, and the pre-heated pulp of about 220 ~ 230C is heated to 280C the above. The fuel of the molten salt furnace is heavy oil, and the designed fuel consumption is 100kg / tU2O3. The heat generated by the evaporation of the slurry heats the slurry to 220 ~ 230. The mixed slurry of the final flash discharge and the washing liquid preheats the slurry to 110 ° C. Heat level of pipelined dissolution system ⑷ Dissolution temperature (temperature after heating by molten salt and adding lime milk (6 levels of discharge temperature and pressure from evaporator: as shown in Table 1. Table 1 Discharge temperature and pressure of self-evaporator at all levels Discharge temperature of 260 pressure 2 Bu In the trial production of pipeline, the heat balance has changed, mainly reflected by the pressure increase of the final self-evaporator (E8 is 40X105Pa) Steam's waste heat recovery utilization rate is low. As a result, the discharge temperature is high, and the washing liquid cannot be added. The E8 discharge pump operates at high temperature and its seal leaks and blade wear occurs. 2.3 Analysis of heat balance change and its causes According to the original design requirements, under the premise of the device's feed volume of 300m3 / h, the addition of lime milk is 20m3 / h, and the dissolution temperature is 270 ~ 280. Molten salt up to 220 ~ 400C heats the ore pulp to dissolution temperature income: Q revenue = Q + Q melting + Q stone + Q washing salt, lime milk and washing liquid bring heat and dissolution reaction absorption and device heat loss. c Specific heat of raw pulp; m pulp flow; t2 and t3 are the pulp temperature at the outlet of the preheating section and the outlet of the heating section; heat exchange, spent steam preheating, molten salt heating, dissolution reaction and local heat loss of the slurry self-evaporation system . 2.2 Heat balance parameters Due to the lack of practical experience in pipeline dissolution of diaspore bauxite, the process operating parameters related to heat balance are based on the results of industrial tests conducted in Germany with Chinese ores. degree. No matter what the preheating temperature is, in order to ensure the dissolution effect, the dissolution temperature should reach the specified value, that is, the dissolution temperature should be relatively stable. In this way, the temperature of the dissolving slurry entering the first-level self-evaporator is also basically constant, and the heat generated during the self-evaporation process is also basically unchanged, and the slurry can be preheated to the required value of the index. Since the pipelined spent steam heat exchange section all adopts indirect heating, the temperature of the pipeline inlet slurry, the heat exchange area of ​​the preheater and the change of heat transfer coefficient will affect the heat transfer, which will affect the heat balance of the entire system. situation. Therefore, adjusting the operating parameters of the self-evaporator to an appropriate value can maximize the preheating temperature of the spent steam and reduce the heat consumption of dissolution. In the preliminary test run of pipeline dissolution, a pre-desiliconization device was used to avoid scarring of the heating pipeline: that is, the seed mother liquor was heated and mixed with the high-solid raw ore, and the temperature was 92 ~ 95 for 8 ~ 10. Hours of pre-desiliconization, because the diaphragm of the diaphragm pump can not work under the condition of more than 85, so the pre-desiliconization slurry is added to the cold mother to cool down to the time when the device is used to dissolve gibbsite, the feed temperature is only about 70, long When the aluminum company is used to dissolve diaspore, the heat of the original pulp brought into the system is increased; Q increase = cmAt = 15cm. After the pulp heat exchange section, the temperature of the pulp increases by about 15 accordingly. For zone 11 (self-steaming and exhaust steam preheating), at the dissolution temperature (solution) (1) the temperature of the slurry pump into the diaphragm pump EleetoniePuBl, the heat input by the feed slurry from the evaporator is constant, and the heat of the exhaust steam generated by evaporation In the preheated mine school chimney evaporation = cm? = Cm (t2ti) Because ti increases by about 15C, to ensure the thermal balance of the area, t2 must also be increased accordingly 15 ie Qpre = Qevaporation = kAAt According to theoretical analysis, t2 follows After t rises, Q melting decreases accordingly, which creates favorable conditions for reducing the load of molten salt furnace and reducing energy consumption. However, in the actual production, as t2 and ti increase, At decreases, and the actual heat transfer is less than Q steaming, so t2 cannot increase accordingly. The amount of exhaust steam generated by the evaporator naturally decreases, and the heat taken away by the discharge increases the pressure of the entire self-evaporation system. The E8 rise is particularly obvious, forming a new balance between the discharge temperature and the high pressure of the evaporator. The phenomenon of taking off. In order to solve the above problems, the following measures are taken: on the one hand, the pre-desiliconization process has been modified, the mother liquor is no longer heated, and the temperature of the slurry entering the pipeline system can be reduced to 75 ~ 80 ° C, which plays a role in protecting the diaphragm and adjusting The effect of the pressure of the self-evaporation system, but the shortcoming is that the pre-desiliconization temperature decreases and affects the pre-desiliconization efficiency, the scarring speed of the heating pipe is increased, and the operation cycle of the device is shortened. On the other hand, a lime milk heating device using steam preheating is added. 2.4 The optimal heat balance parameters of pipeline dissolution must satisfy the dissolution temperature in order to meet the technological production requirements and obtain good indexes. If the self-evaporation system is improperly adjusted, the preheating temperature of the original pulp will not meet the design requirements, which will inevitably lead to increased load of the molten salt furnace and increased energy consumption, and the corrosion of the pipe in the molten salt heating section at high temperature will follow. . 2.4.1 Heating temperature of molten salt (after adding lime milk). Because no measures were taken to heat the lime milk, because the outlet temperature of the molten salt heating section must be higher than 270 ~ 280C. The lime milk heating device was installed in the trial production, and the SWT4 outlet temperature was reduced accordingly. Table 2 shows the temperature that the molten salt heating section should reach within the dissolution temperature range of 270 ~ 280C when adding lime milk at different temperatures. Table 2 Effect of different dissolution temperature and lime milk temperature on molten salt heating temperature (C) Dissolution temperature lime milk temperature leg C) As can be seen from the above table, properly increasing the temperature of lime milk can reduce the temperature of the molten salt heating section accordingly Temperature, to avoid the molten salt section running at high temperature, is conducive to the safe and stable operation of the device. From the heat balance of the whole system, the self-evaporating spent steam is used to preheat the lime milk, the heat of the preheating section of the slurry is reduced, and the preheating temperature t2 will introduce steam outside the system to heat the lime milk, which can reduce the heating load of the molten salt furnace. 2.4.2 Self-evaporation and preheating Due to the heat absorption and heat loss of the alumina dissolution reaction, the temperature of the slurry entering the self-evaporator is lower than the dissolution temperature of about 7C. The temperature of the slurry entering the I self is calculated by heating the lime milk to 160C and the dissolution temperature of 275C. It is 268C. 17MPa) The heat generated during the self-evaporation process is: 320 ore flow m3 / h. 3.53 and 3.31 are the density of lime milk and original ore pulp 1370 original ore pulp density, kg / m3. , Using the mixed slurry discharged from the evaporator and the diluent, the original slurry can be heated to about 108C (the original slurry feed can reach 98C when the feed is 70C). The temperature of the slurry after preheating with exhaust steam is: tpre = 108 + 117. 3 Heat consumption The heat consumption of the Bayer method system is mainly composed of evaporation and dissolution. After the concentration of semen and alkali concentration of circulating mother liquor are determined, the heat consumption of the evaporation process is basically constant. For the pipelined dissolution process, under the condition of ensuring the dissolution temperature is 270 ~ 280C, the level of the exhaust steam preheating temperature determines the level of heat consumption in the dissolution process. The heat dissipated by the pipeline is provided by two 11630kW molten salt furnaces. When the dissolution temperature is 275C lime milk is heated to 160C, the outlet temperature of the dissolved salt heating section must reach 281.9C. The heat absorbed by the slurry in the heating process is: Plus = cmAt has decreased. It is of little significance to reduce the thermal negative load of the melting furnace. If it is from 0310, it needs to be explored and confirmed in actual production. (2 The energy consumption of pipelined dissolution depends on the consumption of mineral oil in the heat exchange section of spent steam: 89.5% of the thermal efficiency of molten salt furnace; the thermal efficiency of 095 heating device. When the feeding amount of the device is 300m3 / h, the production of alumina is 24t, which is converted into alumina. The unit consumption is: the load rate of molten salt furnace: 91% ~ 74%. 4 Conclusion (〗 Improve domestic use of pipeline dissolution equipment The heat balance parameters of diaspore-type bauxite have changed to varying degrees, and the preheating temperature of the slurry is high. The actual operation should strengthen the operation control of the self-evaporation of the slurry and the self-evaporation system of the condensate to ensure that the preheating temperature of the slurry is 220 Between ~ 225C, it can reduce energy consumption and load of molten salt furnace, and play a positive role in protecting molten salt furnace. (3 Preheating lime milk with exhaust steam can effectively reduce the temperature of the molten salt heating section, reduce corrosion, wear and scarring of this section, and extend its service life. If the lime milk is heated to 220 from external steam, in addition to the above advantages , Can further reduce the load of molten salt furnace. Water Bottle,Glass Water Bottle,Steel Water Bottle,Thermos Water Bottle YONGKANG SONGDAO ELECTRICAL CO., LTD , https://www.sodobottles.com