SU1555276A1 - Method of obtaining thermal phosphoric acid - Google Patents

Abstract

This invention relates to a process for the production of thermal phosphoric acid used in the production of phosphate fertilizers. The aim of the invention is to improve the quality of the acid by reducing the content of oxidized phosphorus in it. The method consists in conducting combustion in the presence of water vapor supplied in an amount that provides the mass ratio of oxygen and steam (7.5-10): 1, when the oxygen concentration in the combustion zone is 40-45 wt.% And the oxygen excess factor is 2.25. -3.0, cooling in the combustion tower of the resulting gases with circulating phosphoric acid, hydration of phosphoric anhydride, pressure of gases into two streams, enrichment of the first with oxygen and supplying it to the combustion tower, cleaning and ejecting the second. 1 hp f-ly, 3 tab.

Description

The invention relates to a process for the production of thermal phosphoric acid used for the production of phosphate fertilizers, and can be used in the chemical industry.

The aim of the invention is to improve the quality of the acid by reducing the content of oxidized phosphorus in it.

Example. The molten phosphorus with the temperature of 70 ° C in the amount of 3526 kg is supplied to the nozzle of the combustion tower. At the nozzle for spraying phosphorus serves 1320 nm / h of compressed air heated to 75 ° C, containing 393 kg of oxygen. As a secondary blow

In the combustion tower, the process gas is supplied after the hydration tower in the amount of 25600 kg / h at 55 ° C, containing 1541 kg of water vapor and 8128 kg of oxygen, which before being fed into the tower, is supplied with technical oxygen in the amount of 4228 kg / h, containing 4017 kg of oxygen . The total amount of oxygen in the mixture supplied with the primary secondary blast is 12,538 kg / h or the oxygen concentration is 40.6 wt.%, The mass ratio of oxygen: steam is 8.14: 1, the excess oxygen ratio is ot. 2.77, the temperature in the combustion zone is 2060 ° C. Into the combustion tower to cool the resulting gases,

cl

hydration of phosphoric anhydride and protection of the tower body against high temperatures supply 75% circulating phosphoric acid at a temperature of 45 ° C to a glass tower in the amount of 612,000 kg / h, to the nozzles 535500 kg / h 45% to the burning tower glass - phosphoric acid from the hydration tower with a temperature of 50 C in the amount of 7350 kg / h and water with a temperature of 25 ° C in the amount of 3200 kg / h.

Gases cooled to 150 ° C from the combustion tower through the cooled flue enter the hydration tower with a temperature of 120 ° C, where they are irrigated with 45% phosphoric acid in the amount of 206400 kg / h, having a temperature of 35 ° C. 3700 kg / h of water with a temperature of 25 C are fed into the hydration tower here.

Part of the acid to the hydration tower (trapped from gases) in the amount of 7350 kg / h is fed to the glass of the combustion tower. The gases cooled to 55 ° C are vented by bromide in two streams: one stream in the amount of 25600 kg / h is sent to the combustion of phosphorus, having previously enriched it with oxygen, and the other in the amount of 2300 kg / h (or 1750 nme / h) they are cleaned and then emitted into the atmosphere.

From the irrigation cycle of the combustion tower

the commercial 75% phosphoric acid is removed in the amount of 14785 kg / h, the content of which in the lower phosphorus oxides is 0.035 wt.%. The specific emission of gases into the atmosphere per ton of recycled phosphorus is 1,750 3,526 t / h 496 yme / t.

According to a known method, the subsoil content of oxidized forms of phosphorus in the product reaches 0.2%, and the volume of gases emitted into the atmosphere is up to 10,000 m3 per 1 ton of processed phosphorus.

In tab. 1 shows the dependence of the process indicators on the ratio of oxygen: steam.

When the ratio of oxygen: steam is less than .7.5: 1, the content of non-dilate phosphorus in the product increases. With a ratio greater than 10: 1, the temperature exceeds 2100 ° C and already at a ratio of 11: 1 it is 2300 ° C. Under these conditions, the equipment requires enhanced cooling of the walls of the tower.

Q

five

Q

 burning in order to avoid their destruction from high temperatures. Thus, the optimal ratio of oxygen and water vapor, providing the content of lower oxides in acid less than 0.05% and the normal temperature in the phosphorus combustion tower, should be considered 7.5-10: 1.

In tab. 2 shows the dependence of the process indicators on the oxygen concentration.

When the oxygen concentration is below 40%, the content of under-oxidized phosphorus forms in the product increases, and at a concentration above 45% the temperature of the gases rises to 2350 ° C, which necessitates increased equipment protection. If the process is conducted with an oxygen concentration in the vapor-air medium of 39% (at the entrance to the combustion tower) while simultaneously increasing the excess air to 3.0, this increases the volume of gases and their velocity in the phosphorus burning zone, which, with the same dimensions of the combustion tower, does not cause reduction of the oxidized forms of phosphorus in acid, but will increase the loss of acid into the atmosphere with waste gases.

In tab. 3 shows the dependence of the process indicators on the excess of oxygen.

The content of lower oxides in the acid, less than 0.05 wt.%, Is reached when the mixture contains 2.25% and higher, while decreasing N to 2, the content of lower oxides increases to 0.06 wt.%. An increase in ОЈ leads to an increase in the amount of gases emitted into the atmosphere, and at ot 3.5, their volume is 1.5 times higher than the volume of gases generated at L - 2.25. With emitted gases, oxygen is lost, which leads to an increase in the cost of acid. Therefore, the optimal values of ОЈ, providing a positive effect, should be considered 2.25 - 3.0.

 Thus, the invention improves the quality of the acid by reducing the content of compounds of lower phosphorus oxides in it, which during the subsequent processing of acid to salt and fertilizer will lead to a decrease in phosphine release at the neutralization stage and will improve the environmental

workplace conditions; reduce the amount of air emissions.

Claims (2)

1. A method of producing thermal phosphoric acid, which includes burning elemental phosphorus using excess oxygen, cooling the resulting gases in a combustion tower with circulating phosphoric acid, hydrating phosphoric anhydride, purifying gases from phosphoric acid mist with output of production acid from the combustion tower, differing from that in order to improve the quality of the acid by 0 reducing the amount of non-oxidized phosphorus in it, burning is carried out in the presence of nagos water supplied in an amount that provides the mass ratio of oxygen: vapor equal to (7.5-10): 1, with an oxygen excess ratio of 2.25-3.0 and the oxygen concentration in the combustion zone is 40–45 wt.%. 2. A method according to claim I, characterized in that, in order to reduce emissions into the atmosphere, the waste gases after hydration are divided into two streams: the first is enriched with oxygen and sent to the combustion tower, and the second is sent for purification and is thrown into the atmosphere. 39.0 40.0 40.6 42.0 45.0 47.0 Table 1 table 2 442 480 496 518 530 550 1810 1940 2060 2080 2140 2350 The ratio of excess oxygen at a mass ratio of oxygen: a pair of 8.28: 1 and an oxygen concentration of 40.6 wt.% 0.060 0.043 0.036 0.021 0.002 Table 3 Phosphorus burning temperature, ° С 2400 2150 2060 1890 1740