DE3106911C2 - - Google Patents

Description

The invention relates to a method for burning or waste water containing ganic constituents in a cerium dust burner.

Exhaust gases and polymers fall in petrochemical plants contaminated wastewater that needs to be burned.

The exhaust gases mainly contain nitrogen; the combustion stoves are designed accordingly and consist of one Main combustion chamber and several much smaller, regular ones pre-combustion chambers arranged around it. The size of the main burn Room depends on the length of stay that is required is the organic in low concentration Compounds with that also only in low concentration fully implement available oxygen. This is sought for reasons of cost, since every ton of air that must also be heated to the reaction temperature, approx. 30 kg of heating oil required.  

The exhaust gas normally contains approx. 2% residual oxygen. The Temperature at the bottom of the main combustion chamber is through there cold system exhaust gases entering relatively low (approx. 300 ° C).

The pre-combustion chambers contain the actual equipment for the combustion of the polymer-containing waste water, namely Oil burner with coaxial waste water and corresponding air supply guides.

In incineration plants, which in addition to waste water ver burning and heat recovery is the oxidative Zone limited to the small pre-combustion chambers.

In these pre-combustion chambers, the wastewater must Vapor flow through, the polymers contained therein ignite and finally burn them out completely. Becomes if this is not achieved or is achieved only incompletely, polymers arrive coke in the low-oxygen, cooler main combustion chamber there and deposit on the floor of the main combustion chamber.

The conditions for the proper combustion of the Polymers are essentially the following:

• - Largest possible surface of the water to be burned through Formation of tiny droplets, d. H. Increase in evaporation speed through better heat transfer, the same the combustion rate through the more intensive Oxygen / polymer mixture is improved;
• - greatest possible residence time in the oxidation zone, d. H. A setting the lowest possible flow velocity of the Droplet.

The process according to DE-OS 26 12 302 fulfills these conditions largely, by blowing in small amounts of air "Bubble system" is created, which is both the smallest formation Droplets as well as low flow rates guaranteed animals.  

With regard to the pollutant concentration of the smoke However, this system is not yet fully capable of gases to satisfy.

DE-AS 18 13 012 was already a process for burning organic substances in waste water known, but with very high pressures and tempe instruments are required. From DE-OS 25 24 590 is finally, a method of rendering harmless used metal treatment fluids such as drilling oil and Like. Known, which also requires high pressure.

It was therefore the task that only at temperatures Burnout achievable from 900 ° C to a cyanide-free Flue gas also increases reliably at lower temperatures reach and thus the operating temperature of the combustion lower the plant without the need for high pressure.

This object is achieved by the Method according to claim 1.

The cause of a low residual cyanide content bindings in the flue gas of conventional incineration plants to look for droplets through the flame front Shoot through the support firing before it contains polymers are completely burned out. In oxygen poor area of the main combustion chamber these polyme cleaved into highly volatile cyan compounds, which then - incompletely oxidized - with the flue gas into the Atmosphere.

It has now surprisingly been found that with the method according to the invention prevents this process and at the same time the operating temperature of the combustion plant can be significantly reduced.  

An oil burner can be used as the atomizing burner will. The wastewater is heated in the usual way Heat exchangers and is pumped over Mixing nozzles in which the wastewater swirls with air is fed coaxially to the burners. The heating elements temperature is preferably 110 to 130 ° C. Through the between the waste water supply pipe in the burner and the Combustion chamber prevailing pressure difference, the preferential is 0.5 to 3 bar, it occurs after formation of the droplet fluidized bed during relaxation on Burner exit to "explode" the droplet chen.

The zer through this thermal "explosion" smaller wastewater droplets no longer fly exclusively in the direction of the flame gases, but get an impulse in different directions of the room. Both the evaporation rate and also the residence time in the oxidizing atmosphere of the Combustion chamber is significantly increased because of the heating the droplet is brought up to the boiling point of the water, furthermore, the droplet diameter is reduced. At the However, the inventive method is not just about shifting the caloric work from Combustion chamber in the heat exchanger; as experiments showed the overheating cannot be increased arbitrarily. As soon as the energy content of the droplets becomes too large, are fission products up to the relatively cold part of the Pre-combustion chamber wall thrown back at the burner passage where they coke.  

Rather, the method found is based in particular on the additional reduction of the droplets knife and a change in the direction of movement of the Droplet.

The invention is illustrated in Example 1 below explained without restricting them. By ver same as example 2 (comparative example) effect achieved with the inventive method illustrated.

example 1

Up to 420 kg of heating oil S and 150 to 250 kg of steam are injected per hour and burner into a combustion system equipped with conventional oil atomization burners. The wastewater stream from an acrylonitrile production, 1.25 to 2.25 m ³ per hour and burner, with a content of approx. 30% organic polymers, is heated according to the invention to 115 ° C. in a heat exchanger and with the aid of pumps via a mixing nozzle, in which the wastewater is swirled with air, fed to the burners at a pressure of 2 to 4 bar coaxially.

The exhaust gas temperature of the incinerator is raised to 800 ° C set. The oxygen content in the flue gas is 2.4%. The burnout is complete (none Cyanide, acetaldehyde, acetonitrile in flue gas).

Example 2 (comparative example)

In the same experimental setup as in Example 1, however without waste water overheating in the heat exchanger and at 900 ° C exhaust gas temperature of the furnace are in the flue gas measured  

• 5.9 ppm HCN O ₂ = 3.2%
  9.4 ppm acetaldehyde
  11.9 ppm acetonitrile.

Another difference between Example 1 and 2 exists in oil consumption

• Example 1 Oil consumption 0.6 t / h
  Example 2 Oil consumption 1.8 t / h.

In both cases the total waste water flow is 6.4 t / h and the waste gas flow is 66 000 m ³ / h. With the method according to the invention, the burnout can be guaranteed despite the shortening of the flame length (reduction in the use of oil).

Furthermore, the residual oxygen can be reduced, whereby the amount of gas to be heated is further reduced. By increasing the residence time of the organic substance in the oxidizing zone, the operating temperature of the ver incinerator can be lowered. A significant reduction of oil consumption is the result.

Claims (1)

Process for the combustion of wastewater containing organic constituents in an atomizing burner, the wastewater being mixed with compressed air in a mixing nozzle before entering the burner to form a fluidized bed of droplets, and this wastewater / air mixture is injected into the burner flame, characterized in that the wastewater before forming the droplet vortex layer is heated under pressure to a temperature of over 100 ° C to 130 ° C and there is a pressure difference of 0.5 to 3 bar between the waste water supply pipe in the burner and the combustion chamber.