Review of recycling of plastic packaging material waste in various countries (7)

5.3 Waste Plastics Used for Heat Recovery

Plastic heat output is as high as 8000~9000kcal/kg, which is higher than that of coal and slightly lower than that of specific gravity oil. Therefore, foreign waste plastics are used in blast furnaces instead of coal, oil and coke to substitute coal for cement rotary kiln and waste solid fuel. (RDF) generates electricity and burns cement and has received good results.

(1) The use of blast furnaces for the treatment of waste plastics in Germany is effective and is being promoted. Firstly, after more than one year of tests, Bremen Steel Company officially approved the construction of a 70kt/a waste plastic pellet injection device for blast furnaces. The company can produce 70kt of heavy oil each year. This investment alone can recover the investment within about 2 years. In addition, the cost of recycling and producing waste plastic pellets is only 1/2 of the landfill disposal fee, so it has better energy-saving and social benefits. As the composition of waste plastics is similar to that of oil and coal, but the content of chlorine is high (Table 1), in order to prevent the pollution of furan and dioxins caused by chlorine, the plant also controls the chlorine content of waste plastics by 2%. A rigorous test was conducted. As a result, the dioxin content was only 0.0001 to 0.005 μg/m3, which was far below the emission standard of 0.1 μg/m3, and was officially approved by the government.

Table 1 Composition of Waste Plastics and Heavy Oil and Coal (Unit: %)

The company's No. 2 blast furnace used 3 kt of waste plastic pellets, which has been used for 18 months. Therefore, from the end of 2000, it will be promoted to No. 1 blast furnace and will soon reach the level of 70 kt. Driven by the plant, Krupp Tsoi Steel Co., Ltd., which began trial spraying, improved the process and proposed a target of 90kt per year. Then large steel companies such as Mannesmann and Thyssen began to promote it.

(2) Japanese NKK Corporation successfully injected 1.6 billion yen in blast furnace No. 1 blast furnace (4093m3. annual output of iron 3000kt or more) in the blast furnace for injection of waste plastic pellets into coal powder, and built 30kt/a waste plastic broken and selected. The pellets were set up and 200 kg of large injections per ton of iron were started. It was hoped that they would all replace pulverized coal and replace some of the coke. In order to prevent the harm of chlorine, only industrial waste plastics containing no vinyl chloride were sprayed in the initial stage. Afterwards, the agricultural plastic film used for waste was also tested under the entrustment of 4 Yexian County. The result was good. It has been decided that the county's 1kt/a agricultural film will be eaten out of the county, and it will be treated in other counties. Then, the test of spraying PET powder was performed, and the effect was also good. It is also planned to try other varieties in the future.

Japanese environmental protection and public opinion circles have high hopes for this, claiming. If the 200kg/t iron target is reached, the blast furnace can process 600kt of waste plastics in the year. If 10 blast furnaces are involved in the country, all the nationwide waste plastics can be disposed of. This not only saves landfill land, but also has a significant effect on energy saving and CO2 emission reduction. Japan Iron & Steel Alliance has incorporated this into the 2010 energy-saving plan, requiring that the annual spraying be more than 1000 kt.

(3) Japan's cement rotary kiln has successfully tested the injection of plastic waste. Japan’s cement industry is a big waste player. It produced 90 kt of cement last year and used 25,000 kt of waste, of which 250 kt of waste rubber tires accounted for 29% of the annual production. In addition to replacing part of the fuel with used tires, the steel wire of radial tires can also replace iron ore fines after melting.

The Deshan Cement Plant carried out tests on waste plastics injected into rotary kiln under the cooperation of the Waste Plastics Processing Promotion Association on the basis of long-term consumption of waste tires. The waste plastic was crushed into pellets < 25 mm and sprayed from the open top of the pulverized coal burner. In order to prevent the impact of chlorine on clinker, PVC is temporarily not used. The ingredients for each batch are shown in Table 2.

Note: PP mixed waste refers to mixed waste plastics of PP, PE, PC, and KBS.

After each batch of continuous incineration of 10 to 24 hours, the following points are clearly defined:

·Injected 6kg/t plastic, it can be used as a substitute for 7-8kg/t pyrolysis of coal, and the total thermal energy utilization is equal to that of full-fired coal.

· The amount of waste plastic injected is 1 to 10 t/h. The comparison between batches #1 and #2 shows that the particle size of less than 25 mm is slightly better.

· The effect on smoke emission from the kiln tail is not obvious and no special measures are required.

· There is no impact on the operation of rotary kiln, clinker and cement quality.

(to be continued)