CN101774558A - Method for improving yield of concentrated phosphoric acid - Google Patents

Abstract

The invention discloses a method for improving the yield of concentrated phosphoric acid, which is characterized by concentrating the phosphoric acid in the concentrating step in the method for producing the phosphoric acid, wherein in the concentrating step, the speed of an axial-flow pump is 500-510r/min; scale inhibitors are added into a graphite heat exchanger; the steam admission pressure of the heat exchanger is 100-110KPa, the temperature of the steam is 120-122 DEG C, the absolute pressure of a flash chamber is 10-16KPa and the acid feeding temperature of the heat exchanger is 75-80 DEG C. By the method provided by the invention, the cycle of concentrating operation reaches over 30 days, the yield of the phosphoric acid is substantially improved and completely meets the requirement of downstream production, and the method has high application value in the field of phosphoric acid production.

Description

Improve the method for yield of concentrated phosphoric acid

Technical field

The present invention relates to phosphoric acid production technology, particularly relate to a kind of method that improves yield of concentrated phosphoric acid.

Background technology

In the production process of phosphoric acid,, will make a big impact, so in the field of business have " concentrated bottleneck " said to the whole production flow process if the enrichment process production capacity can't reach designed capacity.Producer and designing unit all do not have good solution both at home and abroad, are a big industry difficult problem always.It is higher, practical that this improves the technical scheme technology content in the multiple fertile industry of phosphorus that concentrates output, can solve the problem of phosphoric acid production, significant to improving the business economic benefit.

Big 200,000 tons of P of exit of valley phosphoric acid plant year designed productive capacity ₂O ₅, enrichment process is the productions in parallel of two systems, and main production equipments graphite heat exchanger tubulation number is 649, and heat interchanging area is 579m ², be domestic phosphoric acid plant mainstream configuration equipment.Because in the Phosphoric Acid Concentration production process, impurity such as calcium salt, silicofluoride reach hypersaturated state, constantly have crystallization to separate out attached to the graphite heat exchanger tube wall, cause the heat exchange deleterious, overall heat transfer coefficient can be from 1400W/ (m ²℃) drop to 930W/ (m ²℃), so need regular infusion to clean, the production cycle was generally about 15 days, production driving rate and rate of load condensate are all lower.So domestic phosphoric acid plant monosystem concentrates throughput and does not generally all arrive 100,000 tons of P of annual output ₂O ₅, reach reluctantly about 8.5 ten thousand tons.The concentrated production of big exit of valley phosphoric acid plant faces this difficulty equally, produces concentrated acid P per year ₂O ₅About about 160,000 tons.In order to improve concentrated output, the solution of some producers is enhanced production capacities for increasing concentrated production series, has increased the 4th Concentration Production Line in July, 08 as 300,000 tons of phosphoric acid plants should changing operation in 07 year.

Summary of the invention

The purpose of this invention is to provide a kind of method that improves yield of concentrated phosphoric acid.

The method of raising yield of concentrated phosphoric acid provided by the invention is in the enrichment step of phosphoric acid production method phosphoric acid to be concentrated, and wherein, in the described enrichment step, the rotating speed of propeller pump (as the axial-flow type recycle pump) is 500-510 rev/min; Add Scale inhibitors in the graphite heat exchanger; The admission pressure of interchanger is 100KPa-110KPa, and vapor temperature is 120-122 ℃, and the flashing chamber absolute pressure is 10-16KPa, and the sour temperature of advancing of interchanger is 75-80 ℃.

In this method, the rotating speed of described propeller pump is preferably 500 rev/mins; The admission pressure of described interchanger is preferably 105KPa, described vapor temperature is preferably 121 ℃, above-mentioned flashing chamber absolute pressure specifically can be 10KPa-14KPa, 11KPa-14KPa, 11KPa-15KPa, 12KPa-15KPa or 12KPa-14KPa, be preferably 13KPa, the sour temperature of advancing of described interchanger specifically can be 75-79 ℃, 75-77.3 ℃, 75-78 ℃, 76-77.3 ℃, 76-78 ℃, 77-78 ℃, 77.3-79 ℃ or 77-79 ℃, is preferably 77.3 ℃.Used Scale inhibitors is selected from least a among phosphono-carboxylic acids polymkeric substance (POCA), PAA, AA, HPA and the HPMA, preferred phosphono-carboxylic acids polymkeric substance (POCA).Above-mentioned various Scale inhibitors is conventional Scale inhibitors, can obtain from openly selling the approach purchase.

The method of raising yield of concentrated phosphoric acid provided by the invention, the concentrated cycle of operation reached more than 30 days, and phosphoric acid output has had and has increased substantially, and satisfies downstream production demand fully, has very high using value in the phosphoric acid production field.

Embodiment

The method of raising yield of concentrated phosphoric acid provided by the invention is from extending manufacture cycle and improving and produce load two aspects raising yield of concentrated phosphoric acid.

One, the propeller pump rotating speed is to improving the influence of yield of concentrated phosphoric acid

According to " phosphoric acid, phosphate fertilizer and composite fertilizer " (the 363rd page of Chemical Industry Press's in March, 99 first version) data introduction, phosphoric acid can not be low excessively at the graphite heat exchanger velocity in pipes, otherwise serious fouling can appear, thereby the raising flow velocity can suppress tube wall incrustation and help improving heat transfer coefficient, optimum flow rate is about 3.5m/s, the too high abrasion that then can cause the graphite tube wall.Therefore, under the existing appointed condition of concentration systems, improving the systemic circulation amount then is to improve the effective means of phosphoric acid flow velocity in the graphite heat exchanger pipe.

According to the correlation parameter of producing 100000 tons of general large-scale WPA concentration unit per year, adjust flow velocity by graphite heat exchanger phosphoric acid, known:

Establish 649 of tubulations in the graphite heat exchanger, the internal diameter of every tubulation is Φ 38.1mm, and external diameter is Φ 50.8mm; The flow Q of phosphoric acid is 7315m in the propeller pump ³/ h, lift H are 4.6m; The power P of motor is 260Kw, and rated current I is 30.4A, and power factor (PF) cos Φ is 0.9, and running current I is 20A;

Calculate described graphite heat exchanger internal diameter circulation area A=649 * 0.785 * 38.1 ²=7.395 * 10 ⁵Mm ², the flow velocity of phosphoric acid is in the then described graphite heat exchanger tubulation

$u=\frac{7315\×{10}^6}{7.395\×{10}^5\×3600}=2.747m/s$

Calculating gained phosphoric acid flow velocity as can be known is 2.747m/s, recommends optimum flow rate 3.5m/s that big gap is arranged with data, and the space of improving flow velocity is arranged.

Running current calculating motor real output according to motor is:

Above calculation result shows that power of motor still has big surplus capacity, can satisfy the speed-raising requirement.According to above data, plan the propeller pump rotating speed by n ₁Bring up to n for 450 rev/mins ₂500 rev/mins.

In order to ensure security of system steady running, adjust corresponding data again:

Similarity rule according to the Principles of Chemical Engineering pump:

$\frac{Q_2}{Q_1}=\frac{n_2}{n_1}$

$Q_2=\frac{500}{450}\×7315=8128m^3/h,$

Calculating velocity in pipes once more with this flux values is 3.05m/s, within safety range;

$\frac{N_2}{N_1}={\left(\frac{n_2}{n_1}\right)}^3$

$N_2={\left(\frac{500}{450}\right)}^3\×165.98=228.68\mathrm{Kw},$

The theoretical running current that calculates the axial flow pump motor with this performance number is 27.72A, within rated value.(the belt pulley external diameter of motor is increased to 485mm by 460mm, other parameter constants, propeller pump motor actual motion electric current is 27.86A, with the calculation result basically identical).

In sum, by changing transmitting ratio, with the propeller pump rotating speed by n ₁450 rev/mins are increased to n ₂500 rev/mins, can make the flow velocity of phosphoric acid in the graphite heat exchanger be increased to 3.05m/s by 2.74m/s, improved the heat-exchange capacity of interchanger greatly, the production cycle of concentrated phosphoric acid also increases.

Two, add the influence of Scale inhibitors to yield of concentrated phosphoric acid

Add before the Scale inhibitors, occur all weekly on average that entrainment trap stops up and the situation of separating effect variation, cause in the concentration process P in the byproduct silicofluoric acid ₂O ₅Content be up to 12000PPm, far surpass the normal required value of 200PPm, both caused the loss of phosphorus, also influenced the quality of silicofluoric acid.In addition, the cycle of operation of system is 15 days, and the temperature difference is 3.3 ℃, and the graphite heat exchanger shell side pressure is driving promptly to reach 80kpa in the week, and shell side pressure rises comparatively fast thereafter, and shell side pressure is 95kpa before stopping.

And after the interpolation Scale inhibitors, operation condition improves obviously, does not almost occur stopping state again, and silicofluoric acid output and phosphorous qualification rate thereof all can normalizings.This is because the adding of Scale inhibitors can slow down fouling and reduce the sticking power of fouling to tube wall, make the fouling easy to clean that loosens, improve the pigging working efficiency, after can extend manufacture cycle owing to concentrate to produce the fouling of graphite heat exchanger heat transfer is had the greatest impact, alleviate the output that fouling can improve spissated driving rate and increase concentrated phosphoric acid.

In two months behind the use Scale inhibitors, the temperature difference of system is on average at 2.8～3.1 ℃, and the highest shell side pressure was respectively 86.9KPa and 84.8KPa when graphite heat exchanger stopped; The cycle of operation of system was respectively 24 days and 28 days, and the cycle of operation has had and significantly improves, and the shell side pressure before stopping has also had remarkable reduction.

Because the running effect of concentration systems takes a turn for the better, produce also corresponding being improved of load.Add before the Scale inhibitors, per hour quantity of steam can only be controlled at 17.5 tons, and also needs progressively decrement to the later stage, otherwise the graphite heat exchanger shell presses and rise comparatively fast, can not satisfy cycle of operation of 15 days.And after the interpolation Scale inhibitors, per hour quantity of steam all is controlled at 18.0～18.5 tons.In addition, carbon tube fouling situation also is under control, and is not using under the situation of Scale inhibitors, the situation of an every production cycle of experience carbon tube fouling just increases the weight of to some extent, and after using Scale inhibitors certainly, carbon tube fouling situation is not obvious, and can keep the situation before driving substantially.

In sum, the present invention has determined to improve the best approach of yield of concentrated phosphoric acid.The invention will be further described below in conjunction with specific embodiment, but the present invention is not limited to following examples.

Embodiment 1,

Carry out concentrating of phosphoric acid according to following step:

Concentration systems adopts vacuum-evaporation, pump circulation flow process.Circulation loop is made of flashing chamber, graphite heat exchanger, axial-flow type recycle pump (rotating speed is 500 rev/mins) and connecting tube.To be the 26-28% dilute phosphoric acid add circulation loop by the diluted acid feeding pump before recycle pump mix with a large amount of circulation concentrated acid with mass percentage concentration.Low-pressure steam enters graphite heat exchanger and recycle acid carries out heat exchange; add Scale inhibitors phosphono-carboxylic acids polymkeric substance in the described graphite heat exchanger; the admission pressure of graphite heat exchanger is 105KPa; advancing sour temperature is 77.3 ℃; vapor temperature is 121 ℃, and system is under the absolute pressure about 13KPa, and phosphoric acid acutely seethes with excitement; moisture in the diluted acid is evaporated to be taken out of, to reach the purpose of producing qualified strong phosphoric acid.The operation liquid level of flashing chamber in the design, causes the tubulation breakage, so will be higher than 1～1.5 meter of the outlet of graphite heat exchanger for prevent that recycle acid from seething with excitement in the graphite heat exchanger tubulation.The concentrated acid product acid is pumped to tank field clarification storage from the overflow spout of flashing chamber by strong phosphoric acid.

Because recycle acid moisture content in the process of concentration and evaporation is constantly removed various salt impurity and can be separated out gradually, graphite heat exchanger and circulation loop have the trend of fouling, can cause graphite heat exchanger tubulation inwall dirt layer progressive additive even blocked, rate of heat transfer and heat are declined to a great extent, produce load and do not reach requirement, necessary parking cleaning, infusion, cleaning.

According to the enrichment step that above-mentioned steps is carried out, the concentrated cycle of operation is 30 days, and the concentration of gained strong phosphoric acid meets industry standard, is 45-50%.

Before adjusting above-mentioned processing parameter from bringing into operation in 05 year in April, 07, the production peak of this concentrated phosphoric acid step is 13643.72 tons of P in 07 year February ₂O ₅, in January, 07 and March the Phosphoric Acid Concentration step output be respectively 8941.77 tons and 12377.83 tons.And after the adjusting process parameter, the yield of concentrated phosphoric acid in April, 07 and May reaches 18253.82 tons and 18542.02 tons respectively; Calculate through system, increased production 2.6 ten thousand tons of P at concentrated phosphoric acid in 2007 ₂O ₅More than, and cost has had significantly reduction.With the steam consumption is example: 07 year 1～March, the steam average quantity used in unit volume blasted was respectively 1.328,1.363 and 1.339, the steam average quantity used in unit volume blasted in 4～May be respectively 1～March in 1.279 and 1.244,07 the steam average quantity used in unit volume blasted and 4～May by speed-raising with add the later steam average quantity used in unit volume blasted of the Scale inhibitors 0.098t/t that descended; Calculate by 100 yuan/ton steam costs, only with in May, 07 yield of concentrated phosphoric acid and steam consumption be example, reduce steam consumption about 160,000 yuan, the annual steam cost that reduces was more than 1,800,000 yuan in 2007.

Claims (3)

1. a method that improves yield of concentrated phosphoric acid is in the enrichment step of phosphoric acid production method phosphoric acid to be concentrated, and it is characterized in that: in the described enrichment step, the rotating speed of propeller pump is 500-510 rev/min; Add Scale inhibitors in the graphite heat exchanger; The admission pressure of interchanger is 100KPa-110KPa, and vapor temperature is 120-122 ℃, and the flashing chamber absolute pressure is 10-16KPa, and the sour temperature of advancing of interchanger is 75-80 ℃.

2. method according to claim 1 is characterized in that: the rotating speed of described propeller pump is 500 rev/mins; The admission pressure of described interchanger is 105KPa, and described vapor temperature is 121 ℃, and described flashing chamber absolute pressure is 13KPa, and the sour temperature of advancing of described interchanger is 77.3 ℃.

3. method according to claim 1 and 2 is characterized in that: described Scale inhibitors is the phosphono-carboxylic acids polymkeric substance.