阅读说明：本技术 一种连续化制备过磷酸的方法 (Method for continuously preparing superphosphoric acid ) 是由 马航 曾波 匡家灵 杨东 于 2019-09-05 设计创作，主要内容包括：本发明涉及一种连续化制备过磷酸的方法,在换热器的局部位置使温度达到聚合温度,保持体系中磷酸整体温度不超过200℃,采用常压下循环蒸发,制备得到合格过磷酸。由于体系磷酸温度的降低,一方面提高了设备防腐能力,增加了设备运行周期；另一方面也扩大了设备材质的选择范围,从而降低了设备成本。(The invention relates to a method for continuously preparing superphosphoric acid, which is characterized in that the temperature reaches the polymerization temperature at the local position of a heat exchanger, the overall temperature of phosphoric acid in a maintaining system is not more than 200 ℃, and the qualified superphosphoric acid is prepared by adopting the circulation evaporation under normal pressure. Due to the reduction of the temperature of the phosphoric acid in the system, on one hand, the corrosion resistance of the equipment is improved, and the operation period of the equipment is prolonged; on the other hand, the selection range of equipment materials is also expanded, so that the equipment cost is reduced.)

1. A method for continuously preparing superphosphoric acid is characterized by comprising the following steps:

(1) Introducing the circulating phosphoric acid continuously supplementing the concentrated phosphoric acid into a circulating acid pump, and conveying the circulating phosphoric acid to a tube type heat exchanger (a) for heat exchange;

(2) After heat exchange in the tubular heat exchanger (a), the heat exchange liquid flows into a liquid distributor of the inner tubular heat exchanger (b) by virtue of gravity and is uniformly distributed in the tubes of the inner tubular heat exchanger (b) for secondary heat exchange;

(3) And (c) circulating acid subjected to secondary heat exchange in the inner tube type heat exchanger (b) flows into the flash tank, gas is led out from the tail gas system, and the circulating acid in the flash tank flows into the circulating acid tank and enters the next circulation.

2. A continuous process for the preparation of superphosphoric acid as claimed in claim 1, wherein: in the concentrated phosphoric acid in the step (1), the phosphorus pentoxide phosphate has the mass concentration of 40-54% and the temperature of 10-90 ℃; the mass concentration of the circulating phosphoric acid phosphorus pentoxide in the step (1) is 65-70%, and the temperature is 160-200 ℃.

3. A continuous process for the preparation of superphosphoric acid as claimed in claim 1, wherein: the tubes of the tube type heat exchanger (a) in the step (1) and the tube type heat exchanger (b) in the step (2) comprise austenitic stainless steel, such as: 316, 316L, 904, 904L, hastelloy alloys, stainless steel metals such as hasc and hag G, and non-metallic materials such as graphite and silicon carbide, preferably silicon carbide.

4. A continuous process for the preparation of superphosphoric acid as claimed in claim 1, wherein: the circulating acid pump in the step (1) comprises austenitic stainless steel, such as: 316, 316L, 904, 904L, hastelloy alloys, stainless steel such as hasb, hasc, and hag, and non-metallic materials such as silicon carbide, PEEK, PTFE, PVDF, PCTFE, and PFA, with PFA being preferred.

5. A continuous process for the preparation of superphosphoric acid as claimed in claim 1, wherein: the shell and tube heat exchanger (a) in the step (1) and the inner shell and tube heat exchanger (b) in the step (2) heat the circulating phosphoric acid through heat transfer oil or steam heat exchange; when the silicon carbide is preferably adopted, the circulating phosphoric acid can be directly heated through the tube nest by external microwave equipment.

6. A continuous process for the preparation of superphosphoric acid as claimed in claim 1, wherein: and (3) after the heat exchange of the heat conduction oil or the steam or the direct heating by external microwaves is carried out on the inner tube type heat exchanger (b) in the step (2), the temperature of the circulating phosphoric acid is not more than 200 ℃.

7. A continuous process for the preparation of superphosphoric acid as claimed in claim 1, wherein: and (3) obtaining the circulating phosphoric acid in the step (1) on the evaporation tank or at any pipe fitting position from the evaporation tank to the circulating acid tank in the step (3).

8. A continuous process for the preparation of superphosphoric acid as claimed in claim 1, wherein: and (3) adding the concentrated phosphoric acid in the step (1) to the circulating acid tank.

Technical Field

the invention belongs to the technical field of concentration polymerization of wet-process concentrated phosphoric acid, and particularly relates to a method for continuously obtaining wet-process superphosphoric acid by circularly and continuously polymerizing concentrated wet-process phosphoric acid at a temperature lower than the theoretical polymerization temperature.

Background

Usually according to phosphoric acid or phosphorus pentoxide in phosphoric acid solution (chemical expression P)₂O₅) Mass concentration of (1) m (P)₂O₅) The different kinds of phosphoric acid are defined, and the specific concept is as follows: m (P)₂O₅)<53% of diluted phosphoric acid, m (P)₂O₅) More than or equal to 53 percent of concentrated phosphoric acid, m (P)₂O₅) More than or equal to 68 percent of phosphoric acid, m (P)₂O₅) More than or equal to 76.1 percent of polyphosphoric acid m (P)₂O₅) Greater than or equal to 83.4 percent of the total phosphoric acid is called as superphosphoric acid; concentrating dilute phosphoric acidWater or dissolved phosphorus pentoxide to obtain high-concentration phosphoric acid.

According to different chemical structural formulas, the method is divided into the following steps: orthophosphoric acid H₃PO₄Pyrophosphoric acid H₄P₂O₇Trimeric phosphoric acid H₅P₃O₁₀Tetrapolyphosphoric acid H₆P₄O₁₃Polyphosphoric acid Hn +2PnO3n + 1; the orthophosphoric acid is dehydrated by heating or is reacted with P₂O₅Hydration reaction to obtain polyphosphoric acid.

Removing impurities in the phosphoric acid to obtain the corresponding m (P2O5) fertilizer-grade, industrial-grade, feed-grade, food-grade and electronic-grade phosphoric acid.

The superphosphoric acid SPA is orthophosphoric acid H₃PO₄Pyrophosphoric acid H₄P₂O₇Phosphoric acid, triphosphoric acid H₅P₃O₁₀Tetrapolyphosphoric acid H₆P₄O₁₃polyphosphoric acid H_n+2P_nO_3n+1With m (P)₂O₅) The ratio of polyphosphoric acid increases accordingly.

Production of phosphoric acid from phosphate ore (chemical expression H)₃PO₄) There are three industrial methods of (1):

1. Melting phosphate rock in an electric furnace, and carrying out reduction reaction with carbon to release phosphorus (chemical expression P)₄) And carbon monoxide (chemical expression CO), condensing P therein₄Absorbing phosphorus pentoxide generated by combustion of yellow phosphorus by water to obtain phosphoric acid with high purity, namely thermal phosphoric acid;

2. Decomposing phosphorite with strong acid such as sulfuric acid, nitric acid, hydrochloric acid and the like to obtain crude phosphoric acid containing a large amount of impurities, namely wet-process phosphoric acid;

3. Heating the uniform mixture of phosphorite and carbon powder in the anaerobic environment of the front section of the rotary kiln or tunnel kiln to release P₄Steam and CO, post combustion P₄Steam and CO, absorbing P in the absorbing tower outside the kiln by water₂O₅Obtaining phosphoric acid, namely the kiln phosphoric acid.

Two methods, namely, the first method and the second method are widely adopted in industry to produce the phosphoric acid. Because of obtaining the initial product or through forced circulation vacuumM (P) after concentration in the evaporation process₂O₅) Less than or equal to 48 percent and contains a large amount of impurities, namely m (SO) of wet-process phosphoric acid after defluorination treatment₄ ^2-) Still high, so the corrosiveness is larger at high temperature.

The commercial wet-process phosphoric acid is generally transported by a dangerous chemical liquid tank truck, and is limited by transportation cost, so that the high-concentration phosphoric acid is more likely to become fertilizer-grade commercial phosphoric acid. SPA is commercial fertilizer grade phosphoric acid with the largest market demand and high concentration, and SPA usually reacts with anhydrous ammonia to produce neutral ammonium polyphosphate solutions (10-34-0, 11-37-0 and the like) and can also be used for preparing suspended fertilizers. In comparison with m (P)₂O₅) 46% phosphoric acid, m (P)₂O₅) SPA of 68% can save land transportation cost.

The traditional method for producing the superphosphoric acid generally adopts higher temperature of about 220 ℃ to carry out evaporation concentration so as to achieve the aim of partial polymerization, and researchers also reduce the polymerization temperature concentration by reducing the vacuum degree, but the corrosion is aggravated under the high vacuum degree, and the product loss is larger, so that the energy consumption is overhigh. The evaporation and concentration mode mostly adopts electricity, coal and the like to heat liquid or heat-conducting oil, and the liquid is directly evaporated or is evaporated after heat exchange with the heat-conducting oil. Its main advantages are low cost and convenient operation. Phosphoric acid is heated to 220 ℃ by adopting electricity or coal heating, so that the phosphoric acid can be evaporated and polymerized to become the superphosphoric acid, but the phosphoric acid, especially the wet-process phosphoric acid, has complex components and forms of phosphoric acid, phosphate, sulfuric acid, sulfate, hydrofluoric acid, fluosilicic acid, fluosilicate and the like, so the phosphoric acid has stronger corrosivity in a high-temperature state, no metal material can run for a long time under the condition, and non-metal materials cannot run for a long time under the condition of 220 ℃, so the selection of the high temperature and the equipment material becomes a great obstacle for upgrading the wet-process phosphoric acid into the industrialized production of the wet-process superphosphoric acid.

Disclosure of Invention

The present patent is directed to addressing one or more of the problems set forth above.

Provides a method for continuously preparing superphosphoric acid.

In order to solve the technical problems, the following technical scheme is adopted for realizing the purpose:

1. A method for continuously preparing superphosphoric acid comprises the following steps.

(1) Introducing the circulating phosphoric acid continuously supplemented with the concentrated phosphoric acid into a circulating acid pump, and conveying the circulating phosphoric acid into a heat exchanger (a) for heat exchange;

(2) After heat exchange in the heat exchanger (a), the water flows into a liquid distributor of the tube type heat exchanger (b) by virtue of gravity and is uniformly distributed in tubes of the tube type heat exchanger (b) for secondary heat exchange;

(3) circulating acid of secondary heat exchange flows into a flash tank, gas is led out from a tail gas system, and acid of the flash tank flows into a circulating acid tank and enters next circulation;

The mass concentration of the concentrated phosphoric acid, phosphoric acid and phosphorus pentoxide is 40-54%, and the temperature is 10-90 ℃; the mass concentration of the circulating phosphoric acid phosphorus pentoxide in the step (1) is 65-70%, and the temperature is 140-200 ℃. The tubes in the tube type heat exchanger (a) and the inner tube type heat exchanger (b) comprise 316, 316L, 904 and 904L, Hastelloy and other stainless steel metals, graphite, silicon carbide and other non-metallic materials, and preferably silicon carbide.

The shell and tube heat exchanger (a) and the inner shell and tube heat exchanger (b) heat the concentrated phosphoric acid through heat transfer oil or steam heat exchange.

When the tubes in the tube type heat exchanger (a) and the inner tube type heat exchanger (b) adopt silicon carbide, the circulating phosphoric acid can be heated by external microwave equipment through the tubes directly.

And the circulating phosphoric acid is heated by the tube type heat exchangers (a) and (b), enters the flash evaporation chamber, and enters the circulating acid tank after gas and part of acid liquid are separated from the flash evaporation chamber.

and (b) outputting the phosphoric acid in the circulating acid tank to the tubular heat exchanger (a) and (b) through a circulating pump, and carrying out internal circulating heating, evaporation and concentration until the mass concentration of the phosphoric acid is more than 95%, taking out the product through a product discharge hole, synchronously adding a specific amount of concentrated phosphoric acid, and carrying out synchronous and continuous concentration and evaporation.

the temperature of the circulating acid in the step 3 is not more than 200 ℃, is lower than 220 ℃ required by phosphoric acid polymerization, can locally reach 220 during heat exchange or heating of the heat exchanger (b) so as to generate polymerization, but then enters a flash tank to be mixed with most of the circulating acid, and the temperature is reduced to be below 200 ℃. The corrosivity of phosphoric acid is greatly reduced below 200 ℃, and the selection surface and the durability of non-metallic materials are also greatly improved. Therefore, the method greatly improves the equipment corrosion resistance and the equipment maintenance period of the phosphoric acid for preparing the superphosphoric acid, and greatly expands the material selection.

And the tail gas system in the step 3 is positive pressure or micro negative pressure, the pressure is more than or equal to-0.004 MPa, and separated gas and liquid are brought out with lower loss.

The invention provides the method for circularly concentrating under normal pressure or micro negative pressure at the temperature lower than the theoretical polymerization temperature, which is characterized in that the viscosity of the superphosphoric acid, particularly the wet-process superphosphoric acid is high, the gas and the liquid are not easy to be classified, the phosphoric acid is concentrated and polymerized on heat exchange equipment under normal pressure through the multiple contact of a heat exchange pipe and materials, the gas and the liquid are separated only in the movement of a tube array in a heat exchanger (b), and the phosphoric acid is guided away by a tail gas system and does not need to enter a flash tank for re-separation, so that the separation efficiency is improved, the temperature of the phosphoric acid in the whole system is reduced, the energy consumption of the system is.

Drawings

FIG. 1 is a schematic view of the process of the present invention.

The specific implementation mode is as follows:

The present invention will be further described with reference to the following embodiments.