SU791589A1 - Method of phosphoric acid production - Google Patents

Description

(54) METHOD FOR OBTAINING PHOSPHORIC ACID

one

This invention relates to a process for the processing of phosphoric sludge into phosphoric acid and phosphate fertilizer.

A known method of processing phosphorus sludge by burning it in rotating drums in a large excess of air (about; 2-3 and above) at 500-600s. Gaseous products of burning ishama containing phosphoric anhydride (P) are sent to the hydration tower. where they are cooled and hydrated with water, and the resulting mist of phosphoric acid is extracted from the exhaust gases in the electrostatic precipitator. The slag formed after the burn-up of phosphorus from the slurry contains up to 25% P1-O, g 1J.

However, phosphorus compounds of lower oxidation states are present in this slag, which makes the slag unsuitable for use as a fertilizer or feed additive. The resulting slag goes to the dump, leading to unproductive irreversible losses of phosphorus and environmental pollution. The presence in the slag of oxidized forms and elemental phosphorus is a consequence of the low; intensity of heat-mass transfer processes.

during the surface burning of sludge on the walls of the rotating drum, low process temperature and insufficient reaction surface. In addition, in this method it is difficult to organize a continuous process.

Also known is a method of processing phosphorus sludge, previously

10 crushed to a fineness not higher than 1.5 mm, by burning it at 1500–1800 ° C, followed by hydration of the resulting, to produce phosphoric acid and withdrawing the phosphorus-poor molten slag 5 at 1250–1400 ° C 2.

However, this method allows to reduce the loss of phosphorus by reducing the content. P O, Q in the slag to

20 3-5% only when burning phosphorus sludge in the absence of water. The implementation of the method is limited in practice by the fact that in order to eliminate the presence of water, it is necessary to carry out laborious and energy-intensive sludge dewatering operations, for example, by centrifuging. In addition, the resulting slags cannot be used as fertilizers, due to the low content of Р O, Q in them.

The aim of the invention is the use of slags as a fertilizer due to an increase in their P 0, e content in an assimilable form.

This goal is achieved by burning sludge according to the method described above in the presence of water and / or water vapor supplied in an amount of 1-40% by weight of sludge with a specific surface of molten slag from 6 to 12 m (t sludge / h) followed by quenching molten slag at a rate of deg / sec.

Water is served mainly in the composition of the cuttle milk - Electrofilters of phosphoric furnaces or in the composition of watered phosphoric sludge containing at least 1% of water.

When fed for combustion, the phosphorus sludge is crushed by spraying with compressed air or steam to a fineness of 0.1-1.5 mm, which, on the one hand, ensures sufficient separation of molten sludge droplets from the gas suspension and, on the other hand, the complete oxidation of phosphorus.

Conducting a process with a specific surface of less than 6 m (t of sludge / h), as well as the supply of water and / or water vapor in an amount of less than 1% (with reasonable reactor dimensions) do not provide fertilizer with a content of 40% or more. Supply of water and / or steam in an amount of more than 40% does not provide the required temperature for the extraction of molten slag, and running the process with a specific surface area of more than 12 (tons of sludge / h), moreover, results in fertilizer with O content, about 65 % hygroscopic and prone to caking.

Hardening of molten slag at a rate of –– not below –– and deg / ce provides for almost complete fixation of P c. form assimilated by plants and animals. Hardening with b-high speeds is impractical because it does not lead to further improvement of fixation ® in an assimilable form and is technically difficult to maintain.

The invention allows for wasteless processing of phosphorus sludge, eliminating environmental pollution by solid waste, and also saving up to 500 nm of natural gas required to produce 1 ton of similar product by conventional thermal methods (production of feed free-flowing phosphate of calcium fertilizers and calcium polyphosphate)

PRI me R 1. Mixed phosphorus sludge in the amount of 3850 kg / h, containing,%: P 65, water 25 and mineral impurities 10, sprayed

compressed air (600) in two nozzles and in dispersed form is introduced into a water-cooled cyclone chamber connected to the melter accumulator. At the same time, air in the amount of 14400 HN / h is fed through the tangential nozzles into the cyclone. The coefficient of excess air is about 1.4 (including air for atomization). The total surface of the film (37.5m)

The Q and the baths (2.5 m) of the melt are 40 m, which corresponds to / (sludge / h). The average temperature of the gaseous products in the cyclone is 1650s, in the melt collector. The average temperature of the melt in the cyclone is 1270 ° C.

0 Phosphorus fertilizer obtained after quenching is a glassy, greenish particle. The total content of RI in the product is 62%, including the citrate-rat5 of the vorimoy form 60.8%. The gaseous products of the combustion of sludge are directed from the digger along a cooled duct to the hydration tower and further to the electro-filter. As a result of re-processing of gases containing P in the tower and the electrostatic precipitator, -v 9725 kg / h of 75% phosphoric acid is obtained.

Example 2. Phosphorus sludge

- in the amount of 3300 kg / h, containing 76% P,, 16% of water and 8% of mineral impurities are mixed with 500 kg / h of cottrell milk with a density of 1.1 r / CNr, containing 14.8% of cotter dust and 85.2% water. The resulting mixture is recycled as described in the previous example, and -v 800 kg / h of phosphoric fertilizer containing 64% PuTo (62.8% of P in digestible form) and 9720 kg / h of 75% phosphoric acid are obtained.

Example 3. 5500 kg / h of phosphoric sludge containing 40% P, 40% water and 20% mineral impurities is processed into phosphoric acid and fertilizer, burning the sprayed sludge in a flow channel connected to a vortex melt separator. Compressed air consumption

.f on spraying 850. Air consumption for combustion 9560.. The coefficient of excess oxidant oi 1,1. The total surface of the film and the melt bath is 33 M, which corresponds to the specific surface of the molten slag in the film and the bath of the melt 6 (sludge / h). Temperatures, gases in the flow channel, in the wl350 separator C. The melt temperature in the flow channel vl450,

5 in the separator 1200 The quenching rate of the molten slag is about 10-10 degrees / sec. As a result of processing, 2780 kg / h of phosphoric fertilizer containing 41.2% is obtained. (including 40.6% P, in digestible form) and 8175 kg / h of 75% phosphoric acid.

Example 4. To increase the Pd-but phosphate fertilizer obtained by processing the slurry specified in Example 3, it is necessary to increase the total specific surface area of the molten slag in the film and the molten bath, simultaneously replacing the air supplied to the combustion with an equivalent amount of oxygen to maintain the temperature separator. With a specific surface of 12 (tons of sludge / h) and the above costs of sludge, compressed air and oi 1.1, l-4420 kg / h of fertilizer containing 62.7% (including 61.8% O, o in digestible form) and -v. 5180 kg / h of 7% phosphoric acid.

Example 5. 3200 kg / h of phosphorus sludge containing 77.8% of P, 21.2% of mineral impurities and 1% of water are processed in a cyclone with a melter accumulator with a total specific surface of the molten slag in the film and molten bath of 12 m / (t sludge / h). Compressed air consumption 600. Air consumption for burning 15460. The coefficient of excess oxidant is about 1.5. The temperature of the gases in the cyclone is 1800s, in the digger IGOO C, the temperature of the melt in the cyclone is ISOO-c, in the kiln. After quenching the molten slag with water at a rate of 10 deg / s, 1190 kg / h of phosphate fertilizer containing 57.4% (56.6% of the digestible form) and 9540 kg / h of 75% phosphoric acid are obtained.

Claims (2)

1. Postnikov N.N. Thermal phosphoric acid, M., Himi, 1970, with. 162. 2. USSR author's certificate five No. 409957, cl. C 01 B 25/12, 05.01.74.