LU88553A1 - Process for burning plastic waste in a blast furnace - Google Patents

Description

METHOD FOR BURNING PLASTIC WASTE IN

BLAST FURNACE

The invention relates to a method for burning

Plastic waste in the blast furnace. It relates in particular to a method for blowing shredded plastic waste, with a granulometer from 0 to about 5 mm, over the nozzle blocks of the blast furnace.

In Germany alone, around 800,000 tonnes of plastic waste are generated each year, which can neither be recycled nor disposed of in domestic waste incineration plants without expensive exhaust gas filtering. Burning these plastics in the blast furnace is certainly an environmentally and economically interesting solution to reduce the mountains of waste. The high temperatures in the blast furnace prevent the release of toxic substances (e.g. dioxins and furans). At the same time, one kilogram of plastic waste allows one kilogram of coke to be replaced.

In the meantime, a blast furnace has been experimentally equipped for the incineration of plastic waste. For this pilot plant, the plastic waste is crushed in mechanical crushing machines to finally have a granulometer of 0 to 5 mm. The shredded plastic waste is transported from a silo system via a pneumatic transport system to the blast furnace, where it is blown into the hot wind in the nozzle blocks.

The incineration of plastic waste in the blast furnace is on the one hand an interesting solution to remove non-recyclable plastic waste in an environmentally friendly and energy-wise manner, but on the other hand the blast furnace operation must not be dependent on the supply of plastic waste. In other words, it must be possible to replace the plastic waste with a classic fuel at any time without adversely affecting the operation of the blast furnace. In the pilot plant mentioned above, eight nozzle blocks of the blast furnace are equipped for blowing in the shredded plastic waste, the eight remaining nozzle blocks are provided with a classic oil injection. The eight nozzle blocks of the blast furnace, which are equipped for blowing in the shredded plastic, also have a device for injecting oil, so that these nozzle sticks can alternatively be filled with shredded plastic waste or oil.

The blast furnace of the pilot plant is therefore suitable for the following operating modes: 1) injection of oil in the first eight nozzle assemblies,

Blowing plastic into the remaining eight nozzle sticks; 2) Inject oil in all 16 nozzle assemblies.

This mode of operation of the test facility is not necessarily optimal, as was found in the elaboration of the present invention.

Plastic and oil have approximately the same energy value. In other words, one kilogram of plastic and one kilogram of coal can each replace the same amount of coke (approximately one kilogram) in the blast furnace. Experiments have shown, however, that blowing plastic into the hot wind influences the flame temperature to a much lesser extent than injecting oil. Injecting one gram of oil into a standard cubic meter of hot wind lowers the flame temperature by around 3.2 ° C; blowing one gram of plastic into a standard cubic meter of hot wind, on the other hand, only lowers the flame temperature by about 2.4 ° C. In order for the flame temperature to be the same for both fuels, a standard cubic meter of hot wind would have to be subjected to approximately 33% more plastic than oil. However, this would mean that the energy supplied when blowing in plastic is also 33% higher than with oil injection. This difference would of course completely change the thermal balance of the blast furnace when switching from plastic / oil operation to 100% oil operation, which would inevitably lead to problems. In order to avoid these problems, the flame temperature in the oil injection system is artificially raised by the addition of oxygen, so that the plastic throughput and the oil throughput in the blast furnace can be the same. Injecting oxygen to raise the flame temperature naturally entails additional costs.

Another problem with the pilot plant is that the plant for blowing plastic is very susceptible to blockages. These blockages are caused by the fact that the plastic particles: 1. are very difficult to keep in a fluidized state; 2. have the property of aggregating in the pneumatic transport system into indissoluble plugs.

The present invention has for its object a method for the industrial blowing of shredded plastic waste into one

To create a blast furnace that enables the aforementioned problems to be eliminated or at least alleviated.

This task is solved by mixing the shredded plastic into coal dust and blowing it into the blast furnace as a coal dust / plastic mixture.

In the process according to the invention, the mixing ratio of coal dust / comminuted plastic can be selected such that the mixture only gives an insignificantly higher flame temperature than coal dust alone and only has an insignificantly higher energy value than coal dust alone. This can, e.g. if there is insufficient supply of plastic waste, you can switch to 100% coal dust combustion without having to compensate for a significant discontinuity in the flame temperature or the thermal balance of the blast furnace.

The coal dust / shredded plastic mixture is also less prone to clogging than the shredded plastic alone.

The present invention is described in more detail with reference to the accompanying drawings.

- Figure 1 shows a first embodiment of a system for mixing crushed plastic under the coal dust; - Figure 2 shows a variant of the embodiment of Figure 1.

Reference number 10 shows a storage silo for holding solid, pneumatically conveyable substances, in this case a mixture of coal dust / shredded plastic. This storage silo 10 is constructed in such a way that a mass flow forms when emptied, i.e. that the entire filling is in motion. This is advantageously achieved in that the storage silo 10 has an outlet funnel 12 with a smooth inner wall and a relatively small opening angle 13 (an opening angle of approximately 40 ° is advisable). Due to the special shape of the outlet funnel 12, no drain funnel is formed when emptying, so that segregation of the filling material is avoided during emptying.

The storage silo 10 is connected to a plurality of pressure containers 14i, 142, 143, which it can optionally load with its contents. Each of the pressure vessels 14, 142 and 143 has a fluidization chamber 16i, 162, 163 via which it feeds the fluidized filling material into a pneumatic main delivery line 18. This main conveyor line 18 opens into one

Verteller 10, where the material to be conveyed is divided over several connecting lines 22. Each of these connection lines 22 is connected to a blowing lance (not shown) which is introduced into the nozzle assembly of a blast furnace.

According to the invention, a mixture of coal dust / shredded plastic is blown into the blast furnace. This mixture is advantageously created in the storage silo 10.

A pneumatic conveyor line 24 connects the storage silo 10 to a storage bunker (not shown) for coal dust. This coal dust has a granulometer of 0 to a maximum of 1 mm. In this line 24, the coal dust is transported in a gas as a carrier medium to the upper end of the storage silo 10, where it is blown into this storage silo.

A store of shredded plastic is stored in a separate storage silo 30. This mechanically crushed plastic has a granulometer of 0 to 5 mm. Due to the mechanical comminution, the plastic particles have a very irregular, shredded shape, so that they easily cling to each other. The storage silo 30 can be refilled, for example, via a tank truck 32.

According to the embodiment according to FIG. 1, the comminuted plastic is fed pneumatically from the storage silo 30 into the storage silo 10. For this purpose, the storage silo 30 alternately feeds one of several pressure containers 34i, 342 with shredded plastic. Each of these

Pressure vessel 34 !, 342 is equipped with a fluidization chamber 36i, 362, via which the comminuted plastic is fed into a pneumatic delivery line 38. Like the pneumatic conveying line 24, the pneumatic conveying line 38 also opens into the upper part of the storage silo 10.

The coal dust and the shredded plastic are blown into the storage silo 10 at the same time. The ratio of mass throughput to coal in line 24 to mass throughput plastic in line 38 determines the mixing ratio in storage silo 10. The introduction of lines 24 and 38 into storage silo 10 is such that swirling of the coal dust and the comminuted plastic in the upper Part of the storage silo 10 takes place, and that no bulk cone forms in the storage silo 10.

The device according to FIG. 2 differs from the device according to FIG. 1 only in that the pneumatic conveying of the comminuted plastic between the storage silo 10 and the storage silo 30 has been replaced by a pneumatic conveyor 50. In this embodiment, which requires less installation work than the system according to FIG. 1, the swirling of the comminuted plastic is generated in the upper part of the storage silo 10 by blowing in the fluidized coal dust. However, fluidization gases can also be additionally blown into the storage silo 10.

Example:

Blast furnace output: 5,0001 pig iron per 24 h blowing rate of coal dust: 150 kg per t pig iron quantity of coal dust: (5000 * 150) / 24 = 31,250 kg / h mixing ratio of coal dust to shredded plastic: 4: 1 mass flow rate of coal dust in line 24: 25,000 kg / h mass flow rate of shredded material Plastic in line 38: 6,250 kg / h The blast furnace can burn about 50,000 t of plastic per year.

Substitute relationships in Bezuq on coke:

Coal (mean): 0.80 plastic: 1.00

Mixture (4: 1): 0.8 * 0.8 + 0.2 * 1 = 0.85 decrease in flame temperature:

Coal alone: approx. 2 ° C per g of coal, which is blown into 1 Nm3 hot wind;

Plastic: approx. 2.4 ° C per g plastic, which is blown into 1 Nm3 hot wind.

Mixture (4: 1): 0.8 * 2 + 0.2 * 2.4 = 2.08 ° C per g mixture, which is blown into 1 Nm3 hot wind.

Comment: 1. Replacing 20% coal dust with the same amount of shredded plastic only slightly changes the energy balance of the blast furnace and the flame temperature. The replacement ratio with regard to coke is only increased by about 6%. The flame temperature only increases by about 4%.

2. A 4: 1 mixture of coal dust / shredded plastic significantly reduces the risk of clogging of the pneumatic transport system.

Claims (5)

1. Process for incinerating plastic waste in the blast furnace, whereby the plastic waste is crushed up to a granulometer of 0 to 5 mm and blown into the hot wind in nozzle sticks of the blast furnace, characterized in that the crushed plastic is mixed into coal dust and as coal dust / Blown plastic mixture. 2. The method according to claim 1, characterized in that the coal dust / plastic mixture has less than 50% by weight of plastic. 3. The method according to claim 1 or 2, characterized in that the mixing of the shredded plastic into the coal dust is carried out by simultaneously feeding the shredded plastic and the coal dust into a reservoir of a pneumatic transport system. 4. The method according to claim 3, characterized in that the feeding of the shredded plastic and the coal dust into the reservoir is carried out pneumatically. 5. The method according to claim 3, characterized in that the feeding of the shredded plastic into the storage container is carried out by means of a mechanical conveyor, and the feeding of the coal dust into the storage container is carried out pneumatically, the coal dust being blown into the stream of the shredded plastic in such a way that swirling in the reservoir occurs.