Miljøprojekt, 1133 – Undersøgelse af mulighederne for termisk oparbejdning af mekanisk separeret shredderaffald

Undersøgelse af mulighederne for termisk oparbejdning af mekanisk separeret shredderaffald

Summary and conclusions

The project objectives has been to investigate the possibilities for utilizations of shredder waste as well as flue gas products from a municipal incineration plant (RGP) by applying a thermal process to a mixture of the two types a waste.

The yearly production of shredder waste in Denmark has been estimated to around 100.000 tons. This shredder waste is to day disposed in a special landfill site. The calorific value of shredder waste has been estimated to more than 10MJ/kg. This amount of energy, which yearly is more than 1.000.000GJ should be used for power production.

The amount of flue gas products from municipal incineration plants (RGP) in Denmark have been estimated from yearly green accounts from the three biggest incineration companies in Denmark, which are Amagerforbrænding, Vestforbrænding and Elsam. The amounts for these three companies were for the year 2003 57521 tons. The capacity for the three companies is a little less than 60% of the total municipal incineration capacity in Denmark. Under the assumption that the rest of in Denmark produce similar amounts of RGP, the yearly production of RGP in Denmark is approximately 100.000 tons. This hazardous waste has to be deposited in special landfill sites in Norway or Germany. In the trials in the present project, only fly ash from MSW has been investigated, but it is expected that all types of RGP produced in Denmark be suited to treat in the process described.

The original objective of the project was to investigate two different processes for thermal treatment of a mixture of RGP and shredder waste. The two processes were KSK and CTU. They are described in chapters 6 and 7 respectively.

The course of the project was somewhat different from the planed. KSK jumped during the initial planning out of the project, probably because the management of the company realised, that the process had not yet reached the level of development necessary for the purpose. On top of that a method for producing briquettes of shredder waste and RGP was not available, and a method for making briquettes of only a part of the shredder waste turned out to be very expensive. Under these circumstances it would be necessary to inject through lances a mayor part of the material directly into the hot zone of the shaft furnace. This method has not been tested by KSK, and the method is probably not suited for a parallel flow reactor.

The proceedings in bankruptcy for the mother company of CTU and the reconstruction of CTU have delayed the planed trials for approximately 2 years. The CTU process and the trials are described in chapter 6 of this report.

Request to other development companies to find a substitute for KSK did not bring any results. Among the companies asked some were bankruptcy and others had stopped further development.

After request to the project steering committee it was in June 2003 decided at the border of the projects original objective to participate in a trial at VTT in Finland. The objectives of this trial are to develop a degassing technique for degassing shredder waste and recovery of energy. VTT and the trials are described in chapter 7.

Accordingly two series of trial are described. Only one of them, the CTU-process is able to treat a mixture of shredder waste and RGP.

The trials at CTU / Mefos were carried out over a 24 hours period. Different relations between the amount of shredder waste and RGP were tested. In one part of the test a smaller amount of RGP was substituted by sand to test the influence on slag quality. In another part of the trials only shredder waste was tested of the same reason.

The process and the pilot plant was during the trials operating with only minor problems and only a few smaller stops were observed during the test period. These stops were caused by faults in the electrical equipment and had nothing to do with the process itself. One problem observed however needs concern when constructing a commercial plant. After some hors operation time a blockage in the gas channels and in the filter system was observed. It was after that time necessary to take one more filter system in operation to secure sufficient air draw from the process.

During the evaluation of the test results it was clear, that the process parameters had not been as planed. The main reason was, that the calorific value of the mixture of wastes was lover than anticipated before the trials. The amount of oxygen was accordingly to high to secure a reducing atmosphere in the reactor. This was obvious after a study of the analysis of the produced slag and dust.

The quality of the produced slag does not fully fulfil the demands for category 2 in the Danish slag legislation. The leaching of chromium and arsenic in two out of three samples are slightly higher than the limit for slag category 2. Part of the project objective was to show, that the demands for slag category 2 could be fulfilled. However by correctly adjustment of the process parameters, it will probably be possible to fulfil these requirements.

The quality and amount of the produced dust is naturally also influenced by the degree of reduction in the reactor, but it is possible to recover Zn and Pb from the dust produced at the test.

The environmental aspects by establishing a plant for treatment of all Danish shredder waste, which amounts to approximately 100000 tons pr. year would be that approximately 200000 hazardous waste consisting of shredder waste and RGP do not have to be put into landfills any more. Instead approximately 120000 tons reusable slag, 27000 tons filter dust from which zinc, lead and cadmium can be recovered and approximately 18000 reusable gypsum will be produced. On top of that approximately 60% of the heating value of the shredder waste can be recovered. This amounts to approximately 660000GJ/year

The process economy is highly influenced by the possible slag price. The gate fee for shredder waste has been estimated to be between 43 and 112 EURO pr. tons by a gate fee for RGP at 80 EURO pr. tons and a depreciation time of 10 years and a rate of interest of 5 % pr. year. If instead of 10 years depreciation time 15 years depreciation time is used, the gate fee for shredder waste will be between 18 and 90 EURO pr. tons. The lowest gate fees for shredder waste respectively 18 and 43 EURO pr. tons can only be achieved if it is possible to produce a high value slag (100 EURO pr. tons). It is at this time uncertainly if this slag price can be achieved. More trials and development of process and plant configuration is necessary before this can be confirmed.

The trials at VTT in Finland (Chapter 7) were carried out in a circulating fluid bed degasser with a capacity of 350 kW.

Part of the objective was to investigate the possible fulfilment of the ELV-directive for the process.

Because of the objectives two different well-controlled samples of shredder waste were produced at H.J.Hansen.

1. Normal produced shredder waste, where only approximately 20 % of the scrap was ELV. (SR)

2. Only ELV. (ASR)

Although the relatively high amounts of bottom ashes caused some problems in the circulating fluid bed degasser, the trials were successfully conducted and brought the following results:

The circulating fluid bed degasser is able to produce a gas from shredder waste suitable as fuel for power plants.
An economical estimation shows, that the gate fee for shredder waste will be between 80 and 110 EURO pr. tons, when the price for the produced gas is at 0 EURO/MWh.
The filter dust amounts to 13 – 15 % of the shredder waste. The filter dust contains relatively small amounts of heavy metals like Zn and Pb, and these amounts are to small to be recovered in the zinc industry. The filter dust must be deposited in special landfills.

It has so far not been proved, that the process is able to fulfil the demands put down in the ELV-directive. To match these demands new methods for recovering metals and other materials from the inorganic part of the shredder waste have to be developed.
New trials are planned. In the planned trials only the organic part of the shredder waste will be used in the degasser.