Preparation method of crude desulfurized hemi-hydrated phosphoric acid in hemi-hydrated wet-process phosphoric acid process

Abstract

The invention provides a preparation method of crude desulfurized semi-hydrated phosphoric acid in a semi-hydrated wet-process phosphoric acid process. According to the invention, CaO in the decomposing tank and SO4 < 2-> in the crystal growing tank are utilized, and slurry in the two tanks is jointly fed into the coarse desulfurization reaction tank for mixed reaction to realize desulfurization, so that the desulfurization slurry filtering step is further simplified. Furthermore, the desulfurized slurry is cooled by adopting vacuum flash evaporation and then enters a vacuum filtering system, so that a large amount of scaling in the system is avoided, and fluorine generated by vacuum flash evaporation and vacuum filtering is recycled. According to the method, the purpose of desulfurization can be achieved without adding a desulfurizing agent, the cost of a crude desulfurization agent can be reduced, the crude desulfurization process flow can be shortened, and P2O5 waste caused by adding phosphate concentrate in a traditional crude desulfurization process is also avoided. The desulfurization process is simple, the cost is low, the cleaning frequency of the slurry vacuum filtration system is reduced, and the starting rate of the system is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of semi-aqueous wet-process phosphoric acid technology, and relates to a method for preparing crude desulfurized semi-aqueous phosphoric acid in the semi-aqueous wet-process phosphoric acid technology, and in particular to a method for crude desulfurization and slurry cooling in the semi-aqueous wet-process phosphoric acid technology. Background Art

[0002] At present, wet phosphoric acid desulfurization mainly adopts the reaction of concentrate and phosphoric acid (calcium desulfurization) + solid-liquid separation. Due to the low reaction temperature of concentrate and phosphoric acid, the reaction activity is affected, resulting in a significant reduction in the concentrate yield. At the same time, a separate filter press system is required. The entire process is relatively long, the operating cost is high, and P2O5 is wasted.

[0003] Due to the high temperature of the semi-aqueous wet phosphoric acid reaction slurry, solid-liquid separation is carried out under vacuum, and the filtrate is prone to flash evaporation, which easily produces a large amount of fluorosilicate (sodium potassium) and calcium sulfate precipitation, causing system blockage. In actual production, such sediments are easy to gather in the pump housing, valves, etc., resulting in reduced pump flow, instrument valve loss of control and other problems, especially affecting the filtration rate of phosphogypsum and reducing the system start-up rate, seriously restricting the production of wet phosphoric acid.

[0004] In the prior art industrial production, the removal of sulfate in wet-process phosphoric acid generally adopts the method of adding phosphate slurry or phosphate rock powder as a desulfurizer to the dilute phosphoric acid obtained after slurry filtration to reduce the sulfate content in the dilute phosphoric acid. 2- The concentration method adopts the method of adding phosphate ore slurry to the dilute phosphoric acid obtained by extraction and filtration in the phosphoric acid extraction tank, and reacts in the desulfurization tank to reduce the free sulfuric acid content in the dilute phosphoric acid. Although the method of adding phosphate ore to dilute phosphoric acid can reduce the sulfate content in the dilute phosphoric acid, it has the disadvantages of long desulfurization time, the need for sedimentation and filtration of phosphoric acid after desulfurization, difficult treatment of sedimentation residue, and high phosphorus residue residue. In addition, the pipeline of the wet phosphoric acid slurry vacuum filtration system is easily blocked by the generated fluorosilicate (sodium potassium) and calcium sulfate. The prior art often adopts the method of adding scale inhibitors, which contain organic phosphonic acid polymers. On the one hand, it increases the operating cost, and on the other hand, the added organic matter is easy to affect the subsequent production.

[0005] Therefore, how to find a more suitable desulfurization method in the semi-aqueous wet-process phosphoric acid process and solve the above-mentioned problems existing in the desulfurization process in the existing semi-aqueous wet-process phosphoric acid process has become one of the urgent problems to be solved by many front-line researchers in the industry. Summary of the invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a method for preparing crude desulfurized semi-aqueous phosphoric acid in a semi-aqueous wet phosphoric acid process, in particular, a method for crude desulfurization and slurry cooling in a semi-aqueous wet phosphoric acid process. The desulfurization process provided by the present invention is simple and low in cost, and reduces the cleaning frequency of the slurry vacuum filtration system and improves the system start-up rate.

[0007] The present invention provides a method for preparing crude desulfurized hemihydrate phosphoric acid in a hemihydrate wet-process phosphoric acid process, comprising the following steps:

[0008] 1) The slurry after crystal growth in the crystal growing tank is returned to the dissolving tank and phosphate concentrate is added for dissolution. The obtained dissolved slurry enters the decomposition tank for decomposition reaction. The obtained decomposed slurry overflows into the crystallization tank and concentrated sulfuric acid is added for reaction and crystallization. The slurry then enters the crystal growing tank for crystal growth to obtain the slurry after crystal growth;

[0009] A portion of the slurry after crystal growth is returned to the dissolution tank;

[0010] 2) The slurry after crystal growth in the crystal growing tank in the above step and the slurry in the decomposition tank are sent to the crude desulfurization reaction tank for mixing, stirring and reaction to obtain a crude desulfurization reaction slurry;

[0011] 3) The crude desulfurization reaction slurry obtained in the above step is cooled by vacuum flash evaporation, and the obtained low-temperature slurry enters a liquid seal tank, and then is vacuum filtered to obtain the crude desulfurized hemihydrate phosphoric acid.

[0012] Preferably, the phosphate concentrate comprises, by mass percentage, P2O5: 30% to 38%, CaO: 45% to 55%, MgO: 0.3% to 1.6%, H2O: 5% to 15%, Fe2O3: 0.3% to 2.3% and Al2O3: 0.4% to 1%.

[0013] Preferably, the ratio of the slurry after crystal growth returned to the dissolution tank to the phosphate concentrate is (15-30) m 3 :1t;

[0014] In the liquid phase of the decomposition tank, the mass content of P2O5 is 40% to 45%;

[0015] In the liquid phase of the decomposition tank, SO4 2- The mass content is 0.2% to 0.6%;

[0016] In the liquid phase of the decomposition tank, the mass content of CaO is 1.0% to 1.6%.

[0017] Preferably, the temperature of the decomposition reaction is 90-105°C;

[0018] The mass ratio of the phosphate concentrate to concentrated sulfuric acid is (0.5-1.0):1;

[0019] The crystallization temperature is 95-105°C.

[0020] Preferably, the mass content of P2O5 in the liquid phase of the crystallization tank is 40% to 45%;

[0021] In the liquid phase of the crystallization tank, SO4 2- The mass content is 1.8% to 2.2%;

[0022] In the liquid phase of the crystallization tank, the mass content of CaO is 0.1% to 0.5%.

[0023] Preferably, the mass content of P2O5 in the liquid phase of the crystal growing tank is 40% to 45%;

[0024] In the liquid phase of the crystal growing tank, SO4 2- The mass content is 1.5% to 2.0%;

[0025] The mass content of CaO in the liquid phase of the crystal growing tank is 0.1% to 0.5%.

[0026] Preferably, the crystal growing temperature is 95-105°C;

[0027] In the step 2), the mass ratio of the slurry after crystal growth to the slurry in the decomposition tank is (1-2): (1-2).

[0028] Preferably, the residence time of the mixing and stirring reaction is 0.15 to 1.5 h;

[0029] The temperature of the mixing and stirring reaction is 70 to 105°C;

[0030] The temperature of the low-temperature slurry is 70-105°C.

[0031] Preferably, a portion of the low-temperature slurry entering the liquid seal tank is returned to the rough desulfurization reaction tank, and another portion of the low-temperature slurry is subsequently vacuum filtered;

[0032] The mass ratio of the one part of low temperature slurry to the other part of low temperature slurry is (3-8):1;

[0033] The preparation method further comprises, during the vacuum flash cooling process, performing multi-stage countercurrent washing on the fluorine-containing secondary steam generated to recover fluorine.

[0034] Preferably, the mass content of P2O5 in the hemihydrate phosphoric acid after crude desulfurization is 40% to 45%;

[0035] In the crude desulfurized hemihydrate phosphoric acid, SO4 2-The mass content is 0.2% to 1.1%;

[0036] The mass content of CaO in the hemihydrate phosphoric acid after crude desulfurization is 0.1% to 0.9%;

[0037] The preparation method further comprises the step of recovering fluorine from tail gas generated after vacuum filtration by tail gas washing.

[0038] The present invention provides a method for preparing crude desulfurized semi-aqueous phosphoric acid in a semi-aqueous wet-process phosphoric acid process, comprising the following steps: first, returning the slurry after crystallization in a crystallization tank to a dissolving tank and adding phosphate concentrate for dissolution, the obtained dissolving slurry enters a decomposition tank for decomposition reaction, the obtained decomposition slurry overflows into a crystallization tank and adds concentrated sulfuric acid for reaction and crystallization, and then the slurry enters a crystallization tank for crystallization to obtain a slurry after crystallization; a portion of the slurry after crystallization is returned to the dissolving tank; then the slurry after crystallization in the crystallization tank in the above step and the slurry in the decomposition tank are jointly sent to a crude desulfurization reaction tank for mixed stirring reaction to obtain a crude desulfurization reaction slurry; finally, the crude desulfurization reaction slurry obtained in the above step is cooled by vacuum flash evaporation, the obtained low-temperature slurry enters a liquid sealing tank, and then is vacuum filtered to obtain a crude desulfurized semi-aqueous phosphoric acid. Compared with the prior art, the present invention aims at the problems of long process flow, high operating cost, large P2O5 loss, and easy clogging of the semi-aqueous slurry filtration system in the existing crude desulfurization technology in the semi-aqueous wet-process phosphoric acid process. The present invention specially designs a crude desulfurization process with specific steps, using CaO in the decomposition tank and SO4 in the crystal growing tank 2- The slurries in the two tanks are sent to the coarse desulfurization reaction tank for mixed reaction to achieve desulfurization, which simplifies the desulfurization slurry filtration step. The desulfurized slurry is further cooled by vacuum flash evaporation before entering the vacuum filtration system to avoid a large amount of scaling in the system. The fluorine generated by vacuum flash evaporation and vacuum filtration is recovered.

[0039] The present invention can achieve the purpose of desulfurization without adding an external desulfurizer, and utilizes the excess CaO in the decomposition tank and the excess SO4 in the crystal growing tank to produce a desulfurized product. 2- , mix the slurry in a certain proportion to react and remove the SO4 2-Remove to 0.5%, and achieve a rough desulfurization effect. The technical solution of the present invention can reduce the cost of rough desulfurization agents and shorten the rough desulfurization process, and also avoid the waste of P2O5 caused by adding phosphate concentrate in the traditional rough desulfurization process. The present invention also uses vacuum flash evaporation to cool the slurry after rough desulfurization, and then pumps it to the vacuum filtration system. Because the temperature of the reaction slurry is relatively low, the filtrate is not easy to flash when the solid-liquid separation is carried out under a vacuum state, thereby avoiding the generation of a large amount of fluorosilicate (sodium potassium) and calcium sulfate in the pipeline to cause system blockage, thereby improving the start-up rate. In addition, the fluorine-containing secondary steam obtained by vacuum flash evaporation and the fluorine-containing tail gas generated by vacuum filtration are respectively recovered by multi-stage countercurrent washing, thereby improving the recovery rate of fluorine. The preparation method of crude desulfurized semi-aqueous phosphoric acid in the semi-aqueous wet phosphoric acid process provided by the present invention has a simple desulfurization process, low cost, and a method for reducing the cleaning frequency of the slurry vacuum filtration system and improving the system start-up rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention provides a schematic diagram of the process flow for preparing crude desulfurized hemihydrate phosphoric acid in the hemihydrate wet-process phosphoric acid process. DETAILED DESCRIPTION

[0041] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention.

[0042] All raw materials of the present invention are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0043] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses industrial pure or conventional purity used in semi-aqueous wet phosphoric acid process.

[0044] The present invention provides a method for preparing crude desulfurized hemihydrate phosphoric acid in a hemihydrate wet-process phosphoric acid process, comprising the following steps:

[0045] 1) The slurry after crystal growth in the crystal growing tank is returned to the dissolving tank and phosphate concentrate is added for dissolution. The obtained dissolved slurry enters the decomposition tank for decomposition reaction. The obtained decomposed slurry overflows into the crystallization tank and concentrated sulfuric acid is added for reaction and crystallization. The slurry then enters the crystal growing tank for crystal growth to obtain the slurry after crystal growth;

[0046] A portion of the slurry after crystal growth is returned to the dissolution tank;

[0047] 2) The slurry after crystal growth in the crystal growing tank in the above step and the slurry in the decomposition tank are sent to the crude desulfurization reaction tank for mixing, stirring and reaction to obtain a crude desulfurization reaction slurry;

[0048] 3) The crude desulfurization reaction slurry obtained in the above step is cooled by vacuum flash evaporation, and the obtained low-temperature slurry enters a liquid seal tank, and then is vacuum filtered to obtain the crude desulfurized hemihydrate phosphoric acid.

[0049] The present invention first returns the slurry after crystal growth in the crystal growing tank to the dissolving tank and adds phosphate concentrate to dissolve it. The obtained dissolved slurry enters the decomposition tank for decomposition reaction. The obtained decomposed slurry overflows into the crystallization tank and adds concentrated sulfuric acid for reaction and crystallization. The slurry then enters the crystal growing tank for crystal growth to obtain the slurry after crystal growth.

[0050] A portion of the slurry after crystal growth is returned to the dissolution tank.

[0051] In the present invention, the phosphate concentrate preferably comprises, by mass percentage, 30% to 38% P2O5, 45% to 55% CaO, 0.3% to 1.6% MgO, 5% to 15% H2O, 0.3% to 2.3% Fe2O3 and 0.4% to 1% Al2O3, more preferably 31% to 37% P2O5, 47% to 53% CaO, 0.3% to 2.3% MgO and 0.4% to 1% Al2O3. .6%~1.3%, H2O: 7%~13%, Fe2O3: 0.7%~2.0% and Al2O3: 0.5%~0.9%, more preferably P2O5: 32%~35%, CaO: 49%~51%, MgO: 0.9%~1.0%, H2O: 9%~11%, Fe2O3: 1.0%~1.6% and Al2O3: 0.6%~0.8%.

[0052] In the present invention, the ratio of the slurry after crystal growth returned to the dissolution tank to the phosphate concentrate is preferably (15-30) m 3 : 1t, more preferably (18 to 27)m 3 : 1t, more preferably (21 to 24)m 3 :1t. Specifically, in the present invention, the circulation flow rate Q / concentrate amount = 15-30m 3 / t concentrate.

[0053] In the present invention, the mass content of P2O5 in the liquid phase of the decomposition tank is preferably 40% to 45%, more preferably 41% to 44%, and more preferably 42% to 43%.

[0054] In the present invention, in the liquid phase of the decomposition tank, SO4 2- The mass content of is preferably 0.2% to 0.6%, more preferably 0.25% to 0.55%, more preferably 0.3% to 0.5%, more preferably 0.35% to 0.45%.

[0055] In the present invention, the mass content of CaO in the liquid phase of the decomposition tank is preferably 1.0% to 1.6%, more preferably 1.1% to 1.5%, and more preferably 1.2% to 1.4%.

[0056] In the present invention, the solid content in the crystallization tank is preferably 25% to 35%, more preferably 25% to 32%, and more preferably 25% to 28%.

[0057] In the present invention, the temperature of the decomposition reaction is preferably 90 to 105°C, more preferably 93 to 102°C, and even more preferably 96 to 99°C.

[0058] In the present invention, the mass ratio of the phosphate concentrate to concentrated sulfuric acid is preferably (0.5-1.0):1, more preferably (0.6-0.9):1, and more preferably (0.7-0.8):1.

[0059] In the present invention, the crystallization temperature is preferably 95 to 105°C, more preferably 97 to 103°C, and even more preferably 99 to 101°C.

[0060] In the present invention, the mass content of P2O5 in the liquid phase of the crystallization tank is preferably 40% to 45%, more preferably 41% to 44%, and more preferably 42% to 43%.

[0061] In the present invention, in the liquid phase of the crystallization tank, SO4 2- The mass content of is preferably 1.8% to 2.2%, more preferably 1.85% to 2.15%, more preferably 1.9% to 2.1%, and more preferably 1.95% to 2.05%.

[0062] In the present invention, the mass content of CaO in the liquid phase of the crystallization tank is preferably 0.1% to 0.5%, more preferably 0.15% to 0.45%, more preferably 0.2% to 0.4%, and more preferably 0.25% to 0.35%.

[0063] In the present invention, the solid content in the crystallization tank is preferably 25% to 35%, more preferably 25% to 32%, and more preferably 25% to 28%.

[0064] In the present invention, the mass content of P2O5 in the liquid phase of the crystal growing tank is preferably 40% to 45%, more preferably 41% to 44%, and more preferably 42% to 43%.

[0065] In the present invention, in the liquid phase of the crystal growing tank, SO4 2- The mass content of is preferably 1.5% to 2.0%, more preferably 1.6% to 1.9%, and more preferably 1.7% to 1.8%.

[0066] In the present invention, the mass content of CaO in the liquid phase of the crystal growing tank is preferably 0.1% to 0.5%, more preferably 0.15% to 0.45%, more preferably 0.2% to 0.4%, more preferably 0.25% to 0.35%.

[0067] In the present invention, the solid content in the crystal growing tank is preferably 25% to 35%, more preferably 25% to 32%, and more preferably 25% to 28%.

[0068] In the present invention, the crystal growing temperature is preferably 90 to 105°C, more preferably 93 to 102°C, and even more preferably 96 to 99°C.

[0069] In the present invention, in the step 2), the mass ratio of the slurry after crystal growth to the slurry in the decomposition tank is preferably (1-2): (1-2), more preferably (1.2-1.8): (1-2), more preferably (1.4-1.6): (1-2), or (1-2): (1.2-1.8), more preferably (1-2): (1.4-1.6). Specifically, it can be 1:1.

[0070] In the present invention, the slurry after crystal growth in the crystal growing tank in the above step and the slurry in the decomposition tank are sent to the rough desulfurization reaction tank for mixed stirring reaction to obtain the rough desulfurization reaction slurry.

[0071] In the present invention, the residence time of the mixed stirring reaction is preferably 0.15 to 1.5 h, more preferably 0.25 to 1.0 h, more preferably 0.25 to 0.5 h, and can be 15 min.

[0072] In the present invention, the temperature of the mixing and stirring reaction is preferably 70 to 105°C, more preferably 75 to 100°C, more preferably 80 to 95°C, and more preferably 85 to 90°C.

[0073] In the present invention, the crude desulfurization reaction slurry obtained in the above steps is finally cooled by vacuum flash evaporation, and the obtained low-temperature slurry enters a liquid sealing tank, and is then vacuum filtered to obtain the crude desulfurized hemihydrate phosphoric acid.

[0074] In the present invention, the temperature of the low-temperature slurry is preferably 70-105° C., more preferably 75-100° C., more preferably 80-95° C., and more preferably 85-90° C. Specifically, the preparation method provided by the present invention is a continuous production process. During the continuous production process, the crude desulfurization reaction slurry after the mixed stirring reaction will continue to heat up, and the subsequent vacuum flash cooling process will cool down to keep the temperature stable. Usually, the temperature of the low-temperature slurry after cooling will be lower than that of the crude desulfurization reaction slurry.

[0075] In the present invention, a portion of the low-temperature slurry entering the liquid seal tank is preferably returned to the rough desulfurization reaction tank, and the other portion of the low-temperature slurry is subsequently subjected to vacuum filtration.

[0076] In the present invention, the mass ratio of the part of low-temperature slurry to the other part of low-temperature slurry is preferably (3-8): 1, more preferably (4-7): 1, and more preferably (5-6): 1. Specifically, the ratio of the circulation amount of the part of low-temperature slurry, i.e., the cooling slurry, to the inlet (outlet) material amount is k=3-8.

[0077] In the present invention, the preparation method preferably further comprises, during the vacuum flash cooling process, the fluorine-containing secondary steam generated is subjected to multi-stage countercurrent washing to recover fluorine.

[0078] In the present invention, the mass content of P2O5 in the hemihydrate phosphoric acid after crude desulfurization is preferably 40% to 45%, more preferably 41% to 44%, and more preferably 42% to 43%.

[0079] In the present invention, in the semi-aqueous phosphoric acid after crude desulfurization, SO4 2- The mass content of is preferably 0.2% to 1.1%, more preferably 0.4% to 0.9%, and more preferably 0.6% to 0.7%.

[0080] In the present invention, the mass content of CaO in the hemihydrate phosphoric acid after crude desulfurization is preferably 0.1% to 0.9%, more preferably 0.2% to 0.8%, more preferably 0.3% to 0.7%, more preferably 0.4% to 0.6%.

[0081] In the present invention, the preparation method preferably further comprises: recovering fluorine from the tail gas generated after vacuum filtration by tail gas washing.

[0082] The present invention is a complete and detailed overall technical solution, which can better improve the desulfurization effect in the preparation process of crude desulfurized semi-aqueous phosphoric acid in the semi-aqueous wet-process phosphoric acid process. The method for crude desulfurization and slurry cooling in the semi-aqueous wet-process phosphoric acid process can specifically include the following contents:

[0083] The present invention utilizes the characteristics of semi-aqueous wet-process phosphoric acid: the CaO content in the decomposition tank in the semi-aqueous reaction tank is relatively high, and the SO4 2- The content is relatively high, and the desulfurization effect can be achieved by mixing the slurries in the two tanks in a certain proportion.

[0084] In the semi-aqueous wet phosphoric acid process provided by the present invention, the dissolving tank, the decomposition tank, the crystallization tank and the crystal growing tank are connected in series step by step, the slurry in the dissolving tank flows through the decomposition tank, the crystallization tank and the crystal growing tank in sequence, a part of the slurry in the crystal growing tank is returned to the dissolving tank to dissolve the phosphate ore, and a part of the slurry is sent to the rough desulfurization process in proportion with the slurry in the decomposition tank. The crystallization tank is equivalent to the buffer tank before the crystal growing tank.

[0085] (1) The slurries in the decomposition tank and the crystal growing tank are respectively transported to the rough desulfurization reaction tank by a delivery pump in a ratio of 1:1 for mixed stirring reaction. The reaction time is 15 minutes and the temperature is 95-105° C. to obtain a rough desulfurization reaction slurry.

[0086] (2) The reaction slurry is then transported to the vacuum flash chamber for cooling through a flash circulation pump. The cooled slurry enters the liquid seal tank. Part of the slurry in the liquid seal tank flows back to the desulfurization reaction tank, and the other part is transported to the vacuum filtration system for filtration through a slurry transport pump. The fluorine-containing secondary steam coming out of the vacuum flash chamber undergoes multi-stage countercurrent washing to recover fluorine, and the tail gas is discharged in compliance with the emission standards.

[0087] (3) After filtration by a vacuum filtration system, semi-hydrated phosphoric acid and semi-hydrated gypsum (semi-hydrated phosphogypsum) are obtained after crude desulfurization. The generated tail gas is filtered through a tail gas washing system to recover fluorine and then discharged in compliance with the emission standards.

[0088] See also Figure 1 , Figure 1 The present invention provides a schematic diagram of the process flow for preparing crude desulfurized hemihydrate phosphoric acid in the hemihydrate wet-process phosphoric acid process.

[0089] The present invention provides a method for coarse desulfurization and slurry cooling in a semi-aqueous wet phosphoric acid process. The coarse desulfurization process designed by the present invention utilizes CaO in the decomposition tank and SO4 in the crystal growing tank. 2- The slurries in the two tanks are sent to the coarse desulfurization reaction tank for mixed reaction to achieve desulfurization, which simplifies the desulfurization slurry filtration step. The desulfurized slurry is further cooled by vacuum flash evaporation before entering the vacuum filtration system to avoid a large amount of scaling in the system. The fluorine generated by vacuum flash evaporation and vacuum filtration is recovered.

[0090] The present invention can achieve the purpose of desulfurization without adding an external desulfurizer, and utilizes the excess CaO in the decomposition tank and the excess SO4 in the crystal growing tank to produce a desulfurized product. 2- , mix the slurry in a certain proportion to react and remove the SO4 2-Remove to 0.5%, and achieve a rough desulfurization effect. The technical solution of the present invention can reduce the cost of rough desulfurization agents and shorten the rough desulfurization process, and also avoid the waste of P2O5 caused by adding phosphate concentrate in the traditional rough desulfurization process. The present invention also uses vacuum flash evaporation to cool the slurry after rough desulfurization, and then pumps it to the vacuum filtration system. Because the temperature of the reaction slurry is relatively low, the filtrate is not easy to flash when the solid-liquid separation is carried out under a vacuum state, thereby avoiding the generation of a large amount of fluorosilicate (sodium potassium) and calcium sulfate in the pipeline to cause system blockage, thereby improving the start-up rate. In addition, the fluorine-containing secondary steam obtained by vacuum flash evaporation and the fluorine-containing tail gas generated by vacuum filtration are respectively recovered by multi-stage countercurrent washing, thereby improving the recovery rate of fluorine. The preparation method of crude desulfurized semi-aqueous phosphoric acid in the semi-aqueous wet phosphoric acid process provided by the present invention has a simple desulfurization process, low cost, and a method for reducing the cleaning frequency of the slurry vacuum filtration system and improving the system start-up rate.

[0091] In order to further illustrate the present invention, the preparation method of crude desulfurized hemihydrate phosphoric acid in a hemihydrate wet-process phosphoric acid process provided by the present invention is described in detail below in combination with examples. However, it should be understood that these examples are implemented on the premise of the technical scheme of the present invention, and detailed implementation methods and specific operating procedures are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention, and the protection scope of the present invention is not limited to the following examples.

[0092] Example 1

[0093] 1) A portion of the slurry after crystal growth in the crystal growing tank is returned to the dissolving tank and added with phosphate concentrate for dissolution. The ratio of the slurry after crystal growth returned to the dissolving tank to the phosphate concentrate is 15m 3 :1t, the obtained dissolved slurry enters the decomposition tank, after decomposition reaction at 90℃, the obtained decomposition slurry overflows into the crystallization tank and adds concentrated sulfuric acid to react and crystallize at 95℃, the mass ratio of phosphate concentrate to concentrated sulfuric acid is 0.5t:1m 3 The slurry then enters a crystal growing tank for crystal growing at 95°C to obtain the slurry after crystal growing.

[0094] See Table 1, which shows the composition of the phosphate concentrate in Example 1 of the present invention.

[0095] Table 1

[0096] <![CDATA[P2O5]]> CaO MgO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> <![CDATA[H2O]]> 30％ 45％ 0.3％ 0.3％ 0.4％ 5％

[0097] See Table 2, which shows the concentrations of P2O5, CaO and SO4 in different reaction tanks in Example 1 of the present invention. 2- Quality content.

[0098] Table 2

[0099] Reactor name <![CDATA[P2O5 / %]]> <![CDATA[SO4 2- / %]]> CaO / % Decomposition tank 40 0.2 1.0 Crystallization tank 40 1.8 0.1 Crystal Growing Tank 40 1.5 0.1

[0100] 2) The slurry after crystal growth in the crystal growing tank in the above step and the slurry in the decomposition tank are sent to the crude desulfurization reaction tank at a mass ratio of 1:2 for mixed stirring reaction. The reaction residence time is 0.15h and the reaction temperature is 70°C. After the reaction, a crude desulfurization reaction slurry is obtained.

[0101] 3) After the crude desulfurization reaction slurry obtained in the above step is cooled by vacuum flash evaporation, the obtained low-temperature slurry enters the liquid seal tank, a part of the low-temperature slurry is refluxed to the crude desulfurization reaction tank, the reflux ratio is 3:1, and the other part of the low-temperature slurry is subsequently vacuum filtered to obtain the semi-aqueous phosphoric acid after crude desulfurization.

[0102] The mass content of P2O5 in hemihydrate phosphoric acid is 40%, the mass content of CaO is 0.6%, and the mass content of SO4 2- The mass content is 0.5%.

[0103] 4) During the vacuum flash cooling process, the fluorine-containing secondary steam generated is subjected to multi-stage countercurrent washing to recover the fluorine; the tail gas generated after vacuum filtration is subjected to tail gas washing to recover the fluorine.

[0104] Example 2

[0105] 1) A portion of the slurry after crystal growth in the crystal growing tank is returned to the dissolving tank and added with phosphate concentrate for dissolution. The ratio of the slurry after crystal growth returned to the dissolving tank to the phosphate concentrate is 20m 3 : 1t, the obtained dissolved slurry enters the decomposition tank, after decomposition reaction at 96℃, the obtained decomposition slurry overflows into the crystallization tank and adds concentrated sulfuric acid to react and crystallize at 99℃. The mass ratio of phosphate concentrate to concentrated sulfuric acid is 0.8t: 1m 3 The slurry then enters the crystal growing tank for crystal growing at 99°C to obtain the slurry after crystal growing.

[0106] See Table 3, which shows the composition of the phosphate concentrate in Example 2 of the present invention.

[0107] Table 3

[0108] <![CDATA[P2O5]]> CaO MgO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> <![CDATA[H2O]]> 35％ 50％ 1.2％ 1.0％ 0.8％ 12％

[0109] See Table 4, which shows the P2O5, CaO and SO4 in different reaction tanks in Example 2 of the present invention. 2- Quality content.

[0110] Table 4

[0111] Reactor name <![CDATA[P2O5 / %]]> <![CDATA[SO4 2- / %]]> CaO / % Decomposition tank 42 0.5 1.2 Crystallization tank 42 2.0 0.2 Crystal Growing Tank 42 1.6 0.2

[0112] 2) The slurry after crystal growth in the crystal growing tank in the above step and the slurry in the decomposition tank are sent to the crude desulfurization reaction tank in a mass ratio of 1:1 for mixed stirring reaction. The reaction residence time is 0.5h and the reaction temperature is 85°C. After the reaction, a crude desulfurization reaction slurry is obtained.

[0113] 3) After the crude desulfurization reaction slurry obtained in the above steps is cooled by vacuum flash evaporation, the obtained low-temperature slurry enters the liquid seal tank, a part of the low-temperature slurry is refluxed to the crude desulfurization reaction tank, and the reflux ratio is 5:1, and the other part of the low-temperature slurry is subsequently vacuum filtered to obtain the semi-aqueous phosphoric acid after crude desulfurization.

[0114] The mass content of P2O5 in hemihydrate phosphoric acid is 42%, the mass content of CaO is 0.5%, and the mass content of SO4 2- The mass content is 0.2%.

[0115] 4) During the vacuum flash cooling process, the fluorine-containing secondary steam generated is subjected to multi-stage countercurrent washing to recover the fluorine; the tail gas generated after vacuum filtration is subjected to tail gas washing to recover the fluorine.

[0116] Example 3

[0117] 1) A portion of the slurry after crystal growth in the crystal growing tank is returned to the dissolving tank and added with phosphate concentrate for dissolution. The ratio of the slurry after crystal growth returned to the dissolving tank to the phosphate concentrate is 30m 3 :1t, the obtained dissolved slurry enters the decomposition tank, after decomposition reaction at 105℃, the obtained decomposition slurry overflows into the crystallization tank and adds concentrated sulfuric acid to react and crystallize at 105℃, the mass ratio of phosphate concentrate to concentrated sulfuric acid is 1.0t:1m 3 The slurry then enters a crystal growing tank for crystal growing at 105°C to obtain the slurry after crystal growing.

[0118] See Table 5, which shows the composition of the phosphate concentrate in Example 3 of the present invention.

[0119] Table 5

[0120] <![CDATA[P2O5]]> CaO MgO <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> <![CDATA[H2O]]> 38％ 55％ 1.6％ 2.3％ 1％ 15％

[0121] See Table 6, which shows the P2O5, CaO and SO4 in different reaction tanks in Example 3 of the present invention. 2- Quality content.

[0122] Table 6

[0123] Reactor name <![CDATA[P2O5 / %]]> <![CDATA[SO4 2- / %]]> CaO / % Decomposition tank 45 0.6 1.6 Crystallization tank 45 2.2 0.5 Crystal Growing Tank 45 2.0 0.5

[0124] 2) The slurry after crystal growth in the crystal growing tank in the above step and the slurry in the decomposition tank are sent to the crude desulfurization reaction tank at a mass ratio of 2:1 for mixed stirring reaction. The reaction residence time is 1.5 hours and the reaction temperature is 105°C. After the reaction, a crude desulfurization reaction slurry is obtained.

[0125] 3) After the crude desulfurization reaction slurry obtained in the above steps is cooled by vacuum flash evaporation, the obtained low-temperature slurry enters the liquid seal tank, a part of the low-temperature slurry is refluxed to the crude desulfurization reaction tank, the reflux ratio is 8:1, and the other part of the low-temperature slurry is subsequently vacuum filtered to obtain the semi-hydrated phosphoric acid after crude desulfurization.

[0126] The mass content of P2O5 in hemihydrate phosphoric acid is 45%, the mass content of CaO is 0.2%, and the mass content of SO4 2- The mass content is 0.8%.

[0127] 4) During the vacuum flash cooling process, the fluorine-containing secondary steam generated is subjected to multi-stage countercurrent washing to recover the fluorine; the tail gas generated after vacuum filtration is subjected to tail gas washing to recover the fluorine.

[0128] The technical solutions adopted by the present invention are statistically analyzed, and the results show that:

[0129] The original desulfurization process used phosphate concentrate desulfurization. After the phosphate concentrate entered the rough desulfurization reaction tank, part of the phosphate concentrate was wrapped, the slurry solid content was 5%, the system was seriously blocked, and the start-up rate was about 85%; through the implementation of this technical solution, the slurry solid content was reduced to 2%, the system blockage was improved, and the start-up rate was increased to 92%. Compared with the phosphate concentrate desulfurization route, this technical solution reduces phosphate concentrate by 7,200t / year (dry basis), and based on phosphate concentrate of 1,300 yuan / t, the annual cost is reduced by 9.63 million yuan; due to the increase in the start-up rate, 14,000 tons of desulfurized phosphoric acid are produced annually.

[0130] The above is a detailed introduction to the method for crude desulfurization and slurry cooling in a semi-aqueous wet phosphoric acid process provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and its core ideas of the present invention, including the best mode, and also enables any technician in the field to practice the present invention, including the manufacture and use of any device or system, and the implementation of any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in a number of ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements that are not different from the text of the claims, or if they include equivalent structural elements that are not substantially different from the text of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A method for preparing crude desulfurized hemihydrate phosphoric acid in a hemihydrate wet-process phosphoric acid process, characterized in that: The following steps are involved: 1) The slurry after crystal growth in the crystal growing tank is returned to the dissolving tank and phosphate concentrate is added for dissolution. The obtained dissolved slurry enters the decomposition tank for decomposition reaction. The obtained decomposed slurry overflows into the crystallization tank and concentrated sulfuric acid is added for reaction and crystallization. The slurry then enters the crystal growing tank for crystal growth to obtain the slurry after crystal growth; A portion of the slurry after crystal growth is returned to the dissolution tank; 2) The slurry after crystal growth in the crystal growing tank in the above step and the slurry in the decomposition tank are sent to the crude desulfurization reaction tank for mixing and stirring to obtain a crude desulfurization reaction slurry; 3) The crude desulfurization reaction slurry obtained in the above step is cooled by vacuum flash evaporation, and the obtained low-temperature slurry enters a liquid seal tank, and then is vacuum filtered to obtain the crude desulfurized hemihydrate phosphoric acid.

2. The preparation method according to claim 1, characterized in that: The phosphate concentrate includes, by mass percentage, 30% to 38% P2O5, 45% to 55% CaO, 0.3% to 1.6% MgO, 5% to 15% H2O, 0.3% to 2.3% Fe2O3 and 0.4% to 1% Al2O3.

3. The preparation method according to claim 1, characterized in that: The ratio of the slurry after crystal growth returned to the dissolution tank to the phosphate concentrate is (15-30) m 3 :1t; In the liquid phase of the decomposition tank, the mass content of P2O5 is 40% to 45%; In the liquid phase of the decomposition tank, SO4 2- The mass content is 0.2% to 0.6%; In the liquid phase of the decomposition tank, the mass content of CaO is 1.0% to 1.6%.

4. The preparation method according to claim 1, characterized in that: The temperature of the decomposition reaction is 90-105°C; The mass ratio of the phosphate concentrate to concentrated sulfuric acid is (0.5-1.0):1; The crystallization temperature is 95-105°C.

5. The preparation method according to claim 1, characterized in that: In the liquid phase of the crystallization tank, the mass content of P2O5 is 40% to 45%; In the liquid phase of the crystallization tank, SO4 2- The mass content is 1.8% to 2.2%; In the liquid phase of the crystallization tank, the mass content of CaO is 0.1% to 0.5%.

6. The preparation method according to claim 1, characterized in that: In the liquid phase of the crystal growing tank, the mass content of P2O5 is 40% to 45%; In the liquid phase of the crystal growing tank, SO4 2- The mass content is 1.5% to 2.0%; The mass content of CaO in the liquid phase of the crystal growing tank is 0.1% to 0.5%.

7. The preparation method according to claim 1, characterized in that: The crystal growing temperature is 95-105°C; In the step 2), the mass ratio of the slurry after crystal growth to the slurry in the decomposition tank is (1-2): (1-2).

8. The preparation method according to claim 1, characterized in that: The residence time of the mixing and stirring reaction is 0.15 to 1.5 hours; The temperature of the mixing and stirring reaction is 70 to 105°C; The temperature of the low-temperature slurry is 70-105°C.

9. The preparation method according to claim 1, characterized in that: The low-temperature slurry entering the liquid seal tank, a part of the low-temperature slurry is returned to the rough desulfurization reaction tank, and the other part of the low-temperature slurry is subsequently vacuum filtered; The mass ratio of the one part of low temperature slurry to the other part of low temperature slurry is (3-8):1; The preparation method further comprises, during the vacuum flash cooling process, performing multi-stage countercurrent washing on the fluorine-containing secondary steam generated to recover the fluorine.

10. The preparation method according to claim 1, characterized in that: The mass content of P2O5 in the semi-aqueous phosphoric acid after the crude desulfurization is 40% to 45%; In the crude desulfurized hemihydrate phosphoric acid, SO4 2- The mass content is 0.2% to 1.1%; The mass content of CaO in the hemihydrate phosphoric acid after crude desulfurization is 0.1% to 0.9%; The preparation method further comprises the step of recovering fluorine from tail gas generated after vacuum filtration by tail gas washing.

Images