DE3815766C2 - - Google Patents

Description

The present invention relates to a method for manufacturing provision of pellets from raw phosphate by drying, baking and cooling of raw phosphate granules using of traveling grates by first filling the granules as a bed on a first traveling grate through partitions from each other go through separate drying, burning and hardening zones, then into one between the first and a second moving grate heat balance zone and finally cooled on the second moving grate serving as a cooling zone with the granules in the drying zone with from above downward flowing hot exhaust gases are pre-dried, the pre-dried granules in the firing zone from above downward flowing heating gases largely ge to pellets be fired in the hardness zone using a top down weak gas flow that is sucked in at the bottom the pellets to the temperature required for solidification temperature are heated, the hardened pellets under Mixing can be entered in the heat compensation zone and the pellets in the subsequent cooling zone by from air flowing downward to be cooled before it finally be carried out.

From US-PS 31 00 106 and US-PS 33 05 226 are a Method and device for drying and burning Granules consisting of raw phosphates are known. Here who which uses two hiking grids connected in series, of which the second is located spatially lower. The first traveling grate has at least one drying and a combustion chamber as well as a retention and hardening chamber, whereby the required amounts of heat are in the range of Gas burners arranged on the furnace vault be generated while the second moving grate is a cooling comb  is going through. The transfer of the pellets from the first to the second traveling grate is carried out via a chute, which in a heat compensation chamber is arranged. By your Transport through the drying chamber will be the humid Granules first with hot flowing from top to bottom Exhaust gases pre-dried. The pre-dried granules are in the subsequent combustion chamber from top to bottom flowing heating gases generated from gas and air burned. The burning of the Pellets completed by sucking exhaust gas through. Finally, the burned, glowing pellets are underneath Mixing introduced into the heat balance chamber by which, after a certain dwell time, renders them second Moving rust and get into the cooling chamber in which they through the air flowing from the bottom up you can feel their warmth me is almost completely withdrawn before it is discharged will.

In the known device, the amounts of heat required in the combustion and hardening chamber are introduced by heating gases drawn through the bed from top to bottom, the heating gases being produced by complete combustion of the combustion gases in the burners and, if appropriate, their temperature by admixing secondary air is reduced to such an extent that neither the upper pellet layer sinters together nor the metallic grate chain of the sintered grate is damaged. Depending on their composition, the pellets begin to sinter together at around 600 to 700 ° C, while the metallic grate chain must not be heated above 400 ° C. The Gewölbetem temperature, which corresponds approximately to the temperature of the uppermost layer of the fill, may not exceed 1100 ° C for reasons of stability of the brick lining. Accordingly, there should be a temperature drop of 1100 to 400 ° C in the material layer through which the heating gases flow and which rest on the grate chains. However, such a temperature gradient means that the upper layer has well-sintered raw phosphate pellets, while the layer close to the rust consists of unsintered granules. Since the sintering of the granules simultaneously removes the carbonate from the raw phosphate and converts the fluorine contained in the apatite into a hard bond, poorly or unsintered pellets cause malfunctions in the operation of the electrothermal reduction furnace by splitting off SiF ₄ and H ₂ SiF ₆ which hydrolyze to form silicic acid in the condensation of the vaporous phosphorus by injecting water and give rise to the formation of the so-called phosphorus sludge.

In the production of yellow phosphorus from phosphate pellets, coke and gravel in an electrothermal reduction furnace, a reaction gas consisting of carbon monoxide and phosphorus vapor is obtained, from which, after being dedusted in electro-separators, the yellow phosphorus in liquid is injected by gradually lowering the temperature of the water or solid form is deposited. The carbon monoxide remaining after the last condensation stage still contains about 300 mg / m ³ phosphorus; This so-called phosphorus furnace gas cannot be stored in Gasome ters because of its phosphorus content, but must be burned immediately after its attack, since the risk of phosphorus separation, which is below 30 ° C, cannot be ruled out in critical parts of the apparatus. The quantities of heat released during the combustion of phosphorus furnace gas can be used, for example, for burning granules consisting of crude phosphates or for the production of alkali polyphosphates from alkali phosphate solutions by drying and condensing in a spray tower.

The phosphorus furnace gas is used to burn granules from crude phosphate in the device described above, so are the jackets of the gas burner and the vault, which consists essentially of chamotte stones are built up, obviously through the burning Formation of the phosphorus furnace formed phosphorus pentoxide grabbed. This attack turns the chamotte bricks partly with the formation of low-melting ver  bonds melted out. The resulting decrease de Thermal insulation of the chamotte bricks leads to so-called Glow spots on the burner coats or on the vaults sheet with subsequent destruction of the coats or Sheets. To avoid consequential damage, the must Brick lining damage immediately present maneuverable repair, which the device temporarily must be shut down.

It is therefore an object of the present invention to provide a ver drive through to the production of pellets from raw phosphate Drying, burning and cooling of raw phosphate granules using of hiking grates, which are covered with chamotte stones insulated vaults and burners run to indicate what melting effects on the chamotte bricks and there with hot spots on the burner coats and the vaults sheet metal and their subsequent destruction can be avoided. This is achieved according to the invention in that the Firing zone from top to bottom heating gases min partially by burning lignite dust with Air is generated above the first moving grate.

The method according to the invention can also optionally be designed in that

• a) at least 20% of the heating energy in the combustion zone of heating gases flowing downwards by burning Lignite dust are generated;
• b) the lignite dust together with hydrogen as Support gas is burned;
• c) 100 to 600 m ³ / h of hydrogen are burned with each t / h of lignite dust;
• d) ver the lignite dust together with phosphorus furnace gas is burned;
• e) the brown coal dust has the following grain spectrum:
  10 to 20% <200 µm
  20 to 50% <90 µm
  30 to 60% <90 µm

Is min at least 20% of the heating energy by burning brown coal dust and 80% from burning phosphorus furnace gas applied, so occurs at the firebrick lining Burner or the vault no erosion; that at the Combustion of the phosphorus furnace gas formed phosphorus In this case, pentoxide does not call for melting Fireclay bricks.

In the method according to the invention, the sintering of the lower layer of the granules lying on the grate chain improved in that the lignite dust was on the ground compared to a gas slower combustion during its passage through the granule layer burns. This makes the full heating heat more even introduced the granule layer without the top layer the bed is overheated.

In the method according to the invention, the time lag combustion of the lignite dust and thus a verb heat distribution over the entire cross cut the fill through the grain composition of the Lignite dust and the specific amount of mitver burned support gas can be controlled.

With the method according to the invention can by substi tutive combustion of lignite dust or carbon monoxide Phosphorus gas for other purposes, for example for manufacturing position of alkali polyphosphates, are released.

Finally, with the method according to the invention Pellets are also made when carbon monoxide or phosphorus furnace gas, for example when not in operation sensitive phosphorus furnace, are not available. In in this case, however, the combustion of the brown coal dust due to simultaneous combustion of hydrogen are supported.  

Contained in the raw phosphate pellets after calcination grain fraction with a diameter of less than 4 mm, the so-called proportion of returned goods, reduced due to its requ the return after grinding and granulation effective capacity of the sintering device. The size of the The share of returned goods is characteristic of the general Ab rub resistance of the raw phosphate pellets and thus for their Inclination on the transport to the electrothermal Reduk tion oven and dust in the oven itself. There dusty raw phosphate pellets the capacity of the Reduk furnace and lower the phosphorus quality, it depends indicates that when calcining the granules on the sintered grate burned-out and thus abrasion-resistant raw phosphate pellets be formed. In the following examples is a measure for burning the granules on the sintered grate and thus as a measure of the abrasion resistance of the manufactured Raw phosphate pellets the proportion of returned goods.

Example 1 (prior art)

43 t / h granules with a diameter of 25 to 35 mm and a compressive strength of 2 to 3 kg, which on two Gra nulate plates made of raw phosphate (33.5% P ₂ O ₅ ) and the accumulated sintering process with spraying with an aqueous A suspension of clay (45% solids) had been produced as a binder, were placed on the sintering grate of the device according to US Pat. No. 3,3 05,226 using a conveyor belt.

The burners located above the sinter grate were charged with 4500 Nm ³ / h phosphorus gas (calorific value: 9660 KJ / Nm ³ ), with a vault temperature of 980 ° C.

The ceramic lining in the area of the burner had to renewed after less than a year of operation will.  

Of the raw phos after passing the cooling grate The phat pellets were the parts with a diameter of less than 4 mm using a wire rack separates and as return material after grinding again on the granu given plate. The share of returned goods was 25%.

After separating the returned goods, the remaining raw material was shown phosphate pellets have the following grain structure:

<4 mm 5.2%
4 to 10 mm 60.2%
10 to 20 mm 26.3%
20 to 25 mm 3.7%
<25 mm 4.6%

Example 2 (according to the invention)

Example 1 was repeated with the change that 40 t / h granules were placed on the sintered grate and the burners with 850 Nm ³ / h phosphorus gas (calorific value: 9660 KJ / Nm ³ ) and 1950 kg lignite dust (calorific value: 21 420 KJ / kg) were charged. The resulting vault temperature was 960 ° C.

The ceramic lining in the area of the burners did not show any significant damage after two years of operation.
The share of returned goods was 20%.

After separating the returned goods, the remaining raw material was shown phosphate pellets have the following grain structure:

<4 mm 5.0%
4 to 10 mm 63.8%
10 to 20 mm 24.4%
20 to 25 mm 3.2%
<25 mm 3.6%

Example 3 (according to the invention)

Example 1 was repeated with the change that the burners with 800 Nm ³ / h of hydrogen (calorific value: 10 500 KJ / Nm ³ ) and 2000 kg / h of lignite dust (calorific value: 21 420 KJ / kg) were applied. The resulting vault temperature was 965 ° C.

The ceramic lining in the area of the burners showed no significant damage after two years of operation.
The share of returned goods was 15%.

After separating the returned goods, the remaining raw material was rejected phosphate pellets have the following grain structure:

<4 mm 5.2%
4 to 10 mm 60.0%
10 to 20 mm 23.0%
20 to 25 mm 2.3%
<25 mm 3.6%

Example 4 (according to the invention)

Example 1 was repeated with the change that 41 t / h granules were placed on the sintered grate and the burners with 600 Nm ³ / h hydrogen (calorific value: 10 500 KJ / Nm ³ ) and 2050 kg / h brown coal dust (calorific value: 21 420 KJ / kg) were applied. The resulting vault temperature was 960 ° C.

The ceramic lining in the area of the burners showed no significant damage after two years of operation.
The share of returned goods was 18%.

After separating the returned goods, the remaining raw material was shown phosphate pellets have the following grain structure:

<4 mm 4.8%
4 to 10 mm 64.7%
10 to 20 mm 23.5%
20 to 25 mm 3.0%
<25 mm 4.0%

In Examples 2 to 4, lignite dust with fol used grain spectrum:

<200 µm 15 to 18%
90 to 200 µm 35 to 40%
<90 µm 40 to 50%.

Claims (6)

1. Process for the production of pellets from raw phosphate by drying, burning and cooling raw phosphate granules using moving grates, by first passing the granules as a bed on a first moving rust through partition walls from drying, firing and hardening zones separated from one another, then into a heat compensation zone located between the first and a second moving grate arrive and is finally cooled on a second moving grate serving as a cooling zone, the granules in the drying zone being pre-dried with hot exhaust gases flowing downwards, the pre-dried granules in the firing zone with being from above downward flowing heating gases are largely burned into pellets, in the hardening zone by means of a weak gas flow sucked from top to bottom, the pellets below are heated to the temperature required for the hardening, the hardened pellets are mixed into the water rmeausgleichszone be entered, and the pellets in the subsequent cooling zone to be cooled by GE bottom upwards flowing air before they are finally discharged, characterized in that in the combustion zone from the top flowing down the hot gases at least in part by burning brown coal dust with air above of the first moving grate. 2. The method according to claim 1, characterized in that at least 20% of the heating energy in the burning zone of heating gases flowing downwards by burning Lignite dust is generated.   3. The method according to claim 1 or 2, characterized net that the brown coal dust together with hydrogen is burned as support gas. 4. The method according to claim 3, characterized in that 100 to 600 m ³ / h of hydrogen are burned with each t / h of lignite dust. 5. The method according to at least one of claims 1 to 4, characterized in that the brown coal dust common sam is burned with phosphorus furnace gas. 6. The method according to at least one of claims 1 to 5, characterized in that the brown coal dust has the grain spectrum:
10 to 20% <200 µm
20 to 50% <90 µm
30 to 60% <90 µm.