DE4111917C2 - Process for the utilization of heavy metals contaminated combustible residues by partial oxidation - Google Patents

Description

The invention relates to a method for the harmless recovery heavy metal contaminated, combustible residues and waste, such as sewage sludge, waste oils, Bohremulsionen or residues from waste pyrolysis by partial oxidation with an oxygen-containing oxidant, wherein a CO and H ₂ -containing raw gas is generated.

Flammable residues and waste materials are often burned. are these materials contaminated with heavy metals, so arise toxic heavy metal oxides, some of which are in the solid combustion back be enriched, sometimes as "smoke", ie in aerosol like form remain in the combustion gases and only with very large technical effort and limited success can be deposited. As a rule, the disposal of the heavy metal-containing combustion Residues only possible in special depots.

It is known to convert fuels by partial oxidation with oxygen in a flame reaction, at high temperatures and usually elevated pressure in a CO and H ₂ -rich gas. The gas produced is used after appropriate cooling, purification and optionally further conversion as synthesis gas, as a reducing gas or for energy purposes. If the fuel contains mineral constituents (ash), this process is conducted under such temperature conditions that the mineral constituents form a molten slag which, after solidification and cooling, is present in a water bath as glassy slag granules. This slag is well landfilled because of their very low leachability, their grain size and bulk density, often also industrially usable.

Gas generating processes of the type described are not limited to the use of high quality fuels, but allow, inter alia, in the Patent DE 28 31 208 and DE 38 20 013, also the recovery of carbonaceous, combustible Residues with high levels of fiber. So is for example, the gasification of contaminated, liquid residues of petroleum and tar processing, coke-like residues or dusty ones Plastic waste possible.

For a number of waste materials used for gasification could be used is a relatively high salary on volatile heavy metals such as lead, tin, zinc and given mercury. An example of this is Sewage sludge, which after drying at a calorific value of about 15 MJ / kg following contents of this fluid Heavy metals have:

lead 460 mg / kg tin 80 mg / kg zinc 3700 mg / kg mercury 2 mg / kg

Under the usual conditions of partial oxidation these proportions are volatile heavy metals at least partially vaporized and go as vaporous Metals or metal compounds (for example as Chloride) in the CO and H₂-rich raw gas over. you cause problems in subsequent cooling and cooling Cleaning stages for the raw gas. It comes with a Heavy metal compounds polluted wastewater and solid, Partly toxic, heavy metal-containing residues, whose Refurbishment or landfill with significant Expense can be connected.  

From US 4,376,108 is a method and an apparatus known for the disposal of sulphurous waste, sulfuric acid being among sulphurous waste, Acid resins and acid slurries are understood in the Refining processes especially in the petrochemical Industry incurred.

Next there are residues and waste products of organic chemistry with sulfur-containing organic Compounds such as mercaptans exist. The prescribed procedure is a multi-level Combustion process in which at the end of the sulfur content of Starting material is completely oxidized to sulfur dioxide. Even if the first stage of these combustion processes in A reducing atmosphere is the process not with the one described and underlying in the application Partial oxidation by means of technically pure Oxygen comparable to a CO and H₂-rich, flammable gas leads.

The object of the invention is, by appropriate Embodiment of the known technologies of gas production by partial oxidation a process for harmless Utilization of heavy metal contaminated, combustible residues and to create waste materials where using simple Volatile heavy metals are controlled, none incurred heavy metal polluted wastewater and the eliminated economic disadvantages become.

According to the task set by the characterizing part of the first claim.

Advantageous embodiments are in the subclaims called.  

The invention provides that the partial oxidation in Presence of such an amount of sulfur any Binding form takes place in the raw gas Hydrogen sulfide partial pressure of at least 10 kPa is reached, the raw gas generated under the increased Pressure brought into contact with water and thereby cooled and saturated by evaporation of a portion of the water being, taking part of the hydrogen sulfide in the water is dissolved, the heavy metals entrained in the raw gas the entrained in the raw gas and dissolved in the water Hydrogen sulfide to form Heavy metal sulfides react and the formed Heavy metal sulfides as sulfide-containing sludge of the remaining evaporated water are separated.

Is essential to the invention that a for setting the Amount of sulfur required additional amount of Sulfur-containing material together with the heavy metals contaminated, combustible residues of Partialoxidation is supplied.

Furthermore, it is essential to the invention that the addition of Sulfur in the form of elemental sulfur takes off a separated from the crude gas hydrogen sulfide fraction is won.

Another advantage is that the addition of sulfur in Form of a sulfur-containing gas, preferably one out the raw gas separated hydrogen sulfide fraction of Partial oxidation takes place.

Furthermore, it is essential to the invention that the Partial oxidation in the presence of slag-forming, mineral compounds from the group SiO, CaO, MgO, Fe₂O₃, Al₂O₃ and under such temperature conditions  that a molten slag is formed, which incorporates part of the heavy metals, the molten slag by contact with the water is solidified, with a Slag granules of vitreous structure forms and the sulfide-containing sludge attributed to the partial oxidation becomes.

The invention is based on an embodiment whose Scheme is shown in the accompanying drawing, explained in more detail. The embodiment relates to Recycling a relatively strong with heavy metals contaminated sewage sludge from the joint clarification of municipal and commercial wastewater. The sewage sludge is with previous mechanical dewatering with following composition:

Water content (as-delivered condition) | 40% Elemental analysis (anhydrous) @ carbon 35.9% hydrogen 4.8% nitrogen 1.5% oxygen 14.8% Sulfur (burnt) 0.5%   ash 42.5% Calorific value (anhydrous) 14.0 MJ / kg

Main ash constituents (related to incineration residue):

SiO₂ | 41% Al₂O₃ 12% Fe₂O₃ 4% CaO 23% MgO 3% Na₂O 0.7% K₂O 1% P₂O₅ 8th% SO₃ 2.3% Cl ^- 2%

Heavy metal content (based on anhydrous sewage sludge):

Ag 20 mg / kg ace 80 mg / kg Ba 1050 mg / kg CD 5 mg / kg Cr 260 mg / kg Cu 180 mg / kg hg 3 mg / kg Mn 7210 mg / kg Ni 60 mg / kg pb 570 mg / kg sn 105 mg / kg V 50 mg / kg Zn 2900 mg / kg

The pre-dewatered sewage sludge is fed from a bunker 1 a dryer 2 and a downstream grinding plant 3 with corresponding vision devices not shown in the scheme and finished to use, dry dust of about 4% water content and a grain size of about 20% residue on the 0, 2 mm sieve prepared. The finished dust is fed via a special feed system consisting of intermediate bunker 4 , cyclically operated pressure lock 5 and a feed and metering 6 as a dense dust-carrier gas mixture via a conveyor line 7 to a burner 8 of a gasification reactor 9 . The carrier gas is nitrogen, which is injected via the supply line 10 and a distributor plate in the lower part of the feed and metering container 6 , there fluidized from the top of slipping dust and enters this together in the delivery line 7 . About the oxygen line 11 technical oxygen reaches the burner 8 , which is also provided with a supply of natural gas, not shown in the picture as an auxiliary fuel. In a built-in reaction chamber 12 in the upper part of the gasification reactor 9 , which is under a pressure of about 20 MPa, react sludge dust and technical oxygen to form a flame with each other. The ratio of oxygen to dust is adjusted so that a substantially consisting of CO and H ₂ existing crude gas and final temperatures of the order of about 1400 ° C can be achieved. It depends on the composition of the sewage sludge and its fluctuation range whether a more or less large auxiliary fuel stream has to be supplied via the burner 8 .

Under the temperature conditions prevailing in the reaction space 12 , the mineral constituents of the sewage sludge dust are transferred into a molten slag which enters the cooling space 13 in the lower part of the gasification reactor 9 together with the hot raw gas. Via a nozzle ring 14 , water is introduced into the cooling space 13 , which comes into contact with raw gas and liquid slag. The crude gas is cooled to about 190 ° C and this temperature saturated with water vapor accordingly. The slag falls into a water bath 15 at the bottom of the cooling chamber 13 and solidifies into granules.

The raw gas leaves the cooling chamber 13 via a side nozzle and enters the waste heat boiler 16 , produced in the low-pressure steam of about 0.6 MPa, the raw gas cooled to about 160 ° C and a large part of the saturated water vapor is condensed from the crude gas. Via cooler 17 , the gas enters the desulfurization system 18th With a portion of the clean gas, the dryer 2 is heated. The remaining amount is used to operate gas engines.

The unevaporated remaining remainder of the cooling water, which collects in the water bath 15 is, if not discharged together with slag on the inter mittent operated slag lock 19 , over an overflow 20 and an expansion valve 21 in a flash tank 22 relaxed. Slag and water content of the slag lock 19 are transferred into a slag tank 23 , from which the slag is discharged via a scraper belt. The effluent from the flash tank 22 and the slag tank 23 wastewater is freed by the filter 24 of finely dispersed solids and repelled after treatment in a wastewater treatment.

The resulting in waste heat boiler 16 and cooler 17 gas condensate is collected in the container 25 and fed via a cooling water line 26 and a booster pump 27 to the nozzle ring 14 . A deficit is compensated by fresh water supply via line 28 .

The desulfurization unit 18 , shown as a block, washes the sulfur compounds present in the raw gas, which are hydrogen sulphide and a very small proportion of carbon oxysulphide, into internal wash cycles and works them up by means of a Claus plant to salable elemental sulfur.

Under the conditions described here, 1050 m ^{3 of} pure gas with a calorific value of 9.9 MJ / m ^{3 in} relation to 1 t of sewage sludge (anhydrous) are produced using 380 m ^{3 of} (in normal state) technical oxygen.

The present in organic and inorganic binding sulfur content of the sewage sludge used is, as already shown, virtually quantitatively converted to hydrogen sulfide and Kohlenoxisulfid in the reaction chamber 12 , wherein a relation between the two compounds of 10 to 20 to 1 is found. Under the conditions shown in the embodiment example, at the point of entry into the cooling chamber 13, a hydrogen sulfide partial pressure of about 4 kPa in the raw gas would be set. To increase the hydrogen sulfide partial pressure, the sewage sludge is added before entering the drying plant calcium sulfate in the form of gypsum from flue gas desulphurisation plants (referred to in the drawing as REA gypsum). The addition is calculated on an anhydrous basis 6%.

The gypsum is under the conditions in the reaction space to form Decomposes hydrogen sulfide so that the hydrogen sulfide Partial pressure approximately doubled. The introduced calcium content goes into the slag and improves its melting and flow behavior.

Depending on the volatility of the element in question, the heavy metal contents introduced with the sewage sludge are incorporated into the slag under different proportions. The remainder passes as vapor into the gas phase. Under the effect of the high hydrogen sulfide partial pressure of about 16 kPa, a part of the volatile heavy metals in the gas phase is converted to sulfides. These non or comparatively only weakly toxic heavy metal sulphides pass into the solid phase during cooling and are taken up in the form of finely dispersed sludge from the part of the water injected into the cooling chamber 13 which has remained unevaporated. The other part of the heavy metal vapors is in contact with the injected water first in solution, is precipitated with the same time taken up by the water Schwefelwas hydrogen as insoluble sulfide and also remains as sulfidic sludge in the remaining water. The sludge with the heavy metal sulfides is, as already shown, deposited in the filter 24 from the expanded wastewater. In order to avoid contamination of the slag by adhering, loaded with sulfides sludge, the slag is rinsed with water, which is removed from the sewage stream after the filter and fed via a wash water line 30 a shower device 29 . This shower device is arranged at the head of the scraper belt with which the slag is discharged from the slag tank 23 .

The part of the heavy metals involved in the slag is with atmospheric waters are not leachable. The grainy and with high Bulk density storable slag is at least easily landfilled, in but usually usable for a wide range of applications.

In the enriched with heavy metal sulfide sludge from the filter 24 silver and lead are enriched to the single-digit per thousand range, zinc to values up to 15%. A metallurgical work-up of the sludge is possible, but can be added to the feedstock or the REA gypsum before entering the dryer 2 and recycled to the process to substantially increase the firmly embedded in the slag fraction of these elements, a large part of the heavy metal sulfide sludge.

It is possible, instead of gypsum, to add a portion of the sulfur produced to the feedstock. The sulfur in an amount of about 1.4% is used in this case in solid form, immediately before the grinding plant 3 . While using 6% REA gypsum yields a salable sulfur yield of about 18 kg / t sewage sludge (anhydrous), this amount is reduced to about 4 kg / t with the exclusive recovery of own sulfur.

Although not shown in the drawing, it is possible, if necessary, instead of sulfur or sulfur-containing material in solid form and sulfur-rich gases such as sulfur dioxide from Rauchgasentschwe felungsanlagen or hydrogen-rich gas fractions from the gas desulfurization of Partialoxydation supply. The supply then takes place after appropriate compression via the burner. 8

List of reference numbers used

1 bunker
2 dryers
3 grinding plant
4 intermediate bunkers
5 pressure lock
6 Feeder and dosing tank
7 support line
8 burners
9 gasification reactor
10 nitrogen supply line
11 oxygen line
12 reaction space
13 refrigerator
14 nozzle ring
15 water bath
16 waste heat boiler
17 coolers
18 desulphurisation plant
19 slag lock
20 overflow
21 relaxation valve
22 relaxation tank
23 slag tank
24 filters
25 containers
26 cooling water pipe
27 booster pump
28 fresh water pipe
29 shower unit
30 wash water pipe

Claims (5)

1. A method for recycling heavy metal contaminated combustible residues by partial oxidation with an oxygen-containing oxidant in the form of a flame reaction under elevated pressure, wherein a CO and H₂-rich raw gas produced, a sulfur content of the residues at least partially converted to hydrogen sulfide, which admixes the raw gas , and at least part of the heavy metals contained in the materials to be recycled is transferred as a vapor into the raw gas, characterized in that the partial oxidation takes place in the presence of such an amount of sulfur any binding form that in the crude gas, a hydrogen sulfide partial pressure of at least 10 kPa is achieved, brought the raw gas produced under the increased pressure in contact with water and thereby cooled and saturated by evaporation of a portion of the water, wherein a portion of the hydrogen sulfide is dissolved in the water, the heavy metals entrained in the raw gas react with the hydrogen sulfide entrained in the raw gas and dissolved in the water to form heavy metal sulfides and the sulfur metal sulfides formed are removed as sulfide-containing sludge from the residual water remaining unevaporated. 2. The method according to claim 1, characterized that one for adjusting the amount of sulfur required additional amount of sulphurous Material together with the heavy metal contaminated, combustible residues fed to the partial oxidation becomes.   3. The method according to claim 2, characterized that the addition of sulfur in the form of Elemental sulfur takes place from one of the Crude gas separated hydrogen sulfide fraction is won. 4. The method according to claim 1, characterized that the addition of sulfur in the form of a Sulfur-containing gas, preferably one of the Crude gas separated hydrogen sulfide fraction of the Partial oxidation takes place. 5. The method according to any one of claims 1 to 4, characterized in that the partial oxidation takes place in the presence of slag-forming, mineral compounds from the group SiO ₂ , CaO, MgO, Fe₂O₃, Al₂O₃ and under such a temperature conditions that a molten slag is formed, which incorporates a part of the heavy metals, the molten slag is solidified by contact with the water, forming a slag granules of vitreous structure and the sulfide-containing sludge is recycled to the partial oxidation.