| Forside | | Indhold | | Forrige | | Næste |

Metoder til behandling af tungmetalholdigt affald - Fase 3

Summary and conclusions

• Background and objectives
• Identification and investigation of relevant technologies
• Conclusions
• Comparison of technologies for waste treatment
• Danish strategies
• Formation of Scaling and corrosion
• Final conclusion

Background and objectives

The project ”Methods for Treatment of Waste Containing Heavy Metals” was started on the initiative of the Danish Environmental Protection Agency on the basis of the discussion paper “Industrial waste and selected waste fractions” from 1997. The discussion paper points out the development in alternative methods for treating wastes as a necessary contribution that makes it possible to recover resources in the form of energy and raw material.

The objective of the project is to give players in the Danish waste sector fully updated knowledge about international experience in technologies for treating shredder waste, impregnated waste wood, and tannery and leather waste. This new knowledge will be used to form the background for a new Danish strategy for waste handling and the choice of technology to be introduced in or to be developed for Denmark.

Identification and investigation of relevant technologies

The project has identified, investigated and compared international plants and technologies for treating wastes with high content of heavy metals. Based on these studies, the project proposes strategies for treating and handling especially shredder waste, waste wood and tannery and leather waste in Denmark. An evaluation of the different technologies and their possibilities to treat other problematic waste streams has also been made. Finally, focus has been on possible solutions for avoiding corrosion and deposits in plants for energy production.

The technologies have been evaluated on the basis of following criteria:

• The effectiveness of the technology to recover and reuse metals and other materials.
• Economy.
• Environmental impact.
• Working environment.
• Dependability.
• Energy yield.
• Possibilities to fit in the technology in the Danish waste structures.

The project includes the phases: 1, 2A, 2B and 3.

Phase 1

Phase 1 was finished in 1999, and the tasks in this part were:

• Estimation of the amount of the selected wastes, and estimation of the potential for reuse of metals and materials from the selected wastes.
• Estimation of expected present and future composition of relevant waste fractions.
• Gathering of information about international experience in treating waste fractions with high content of heavy metals.
• Evaluation of such experience.
• Selection of the most promising technologies for further investigation.

The results of the work in phase 1 are published in the report ”Methods for Treatment of Waste Containing Heavy Metals - Phase 1”. The main conclusions in this report were that further investigation should focus on treatment of shredder waste, impregnated waste wood, and tannery and leather waste. During the project period, 11 relevant technologies for treating shredder waste were identified, while no full-scale experiences for treating impregnated waste wood or tannery and leather waste were identified.

The most promising plant suppliers or plant operators for treating shredder waste (at that time, 1999) were:

Only three technologies were identified as being possibly qualified for treating impregnated waste wood. The reason why these technologies are only possibly qualified is that none of them recycle the metals in the waste or stabilise the metals. Only the energy content is utilised.

Phase 2A

The objectives of phase 2A of this project were:

• Contact to all companies with priority from phase 1, in order to:
  => determine the status for the development,
  => update technical and economic information from phase 1,
  => collect detailed information on new processes,
  => describe and evaluate these new processes,
  => make agreements for participating in trials at relevant plants,
  => make agreements for visiting relevant plants
• Select the five most interesting plants for a long visit, and
• Select one or two relevant plants for short visits.

The result of phase 2A was an action plan and a budget for visiting the following plants / companies: (L: long visit. S: short visit)

During the entire project period, a very rapid development of technologies for treating heavy-metal contaminated waste has occurred. New technologies have been developed, other technologies have been taken over by new owners, and some have stopped further development or have gone bankrupt. In all the phases of the project, close contact has been established with all the interesting players, and priorities have been currently changed, depending on the development within the most relevant technologies. However, some of the relevant technologies were in operation with other but still comparable types of waste.

Phase 2B

Phase 2B was finished in 2001, and the long visits, which were reprioritised several times in this phase were:

And shor visits were paid to:

All the visits were planned with a view to focusing on thermal treatment of shredder waste. The visits relating to the seven relevant technologies are reported in the report: ”Methods for Treatment of Waste Containing Heavy Metals – Phase 2B”. In addition, this report contains descriptions of technologies developed by Citron AG and EPR. It is concluded that these two technologies are not qualified for treating shredder waste, impregnated waste wood, or tannery or leather waste.

Phase 3

Phase 3 of the project is described in the present report, which is a direct follow-up of the report for phase 2B. The present report contains descriptions of detailed studies of 11 technologies: partly technologies that, for economic reasons, could not be investigated in phase 2B – especially mechanical separation technologies for shredder waste – and partly new interesting technologies for treating impregnated waste wood and leather and tannery waste.

Phase 3 includes the following tasks:

1. Update of know-how on technologies.
2. Investigation of technologies.
3. Comparison of the investigated technologies.
4. Proposals for a Danish strategy.
5. Investigations of possible solutions to avoid corrosion and deposits in boilers.

During task 1 in phase 3, several new mechanical separation technologies were found, for example R-plus, S+S, and SSE. In addition, some previously known technologies have developed further, to a level that now makes them interesting for more detailed study. These are, for example, the Pyroarc process, Procone and Salyp.

In phase 3, the following priority and visits were made:

The 11 technologies are described in more detail in the reports from visits shown in annexes B-L.

Conclusions

At the beginning of this project in 1998, a large number of technologies and companies were presented, which apparently were able to treat the prioritised fractions of waste. Now, at the end of this investigation, almost five years later in 2003, it must be concluded that only a small handful of apparently surviving technologies and companies is interesting for Danish investors and operators of waste treatment plants.

Investments in one or more of these technologies will still have to be regarded as risky, and the proposed Danish strategy should be regarded more as an strategy of development than as a complete and clearly described way of treatment of the relevant Danish waste fractions.

Comparison of technologies for waste treatment

Treatment of shredder waste

All the processes investigated for shredder waste produce free metals of the waste and utilise the energy. A number of processes produce entirely stable products that can be sold, be used as road construction or building materials - or be disposed of at an ordinary landfill.

The treatment costs vary from about DKK 470 to 1,091/t SHR for a plant with a capacity of 50,000 t SHR/year.

The process technologies for shredder waste falls in two groups:

1. Mechanical separation succeeded by a thermal process (pyrolysis, gasification, combustion, etc.)
2. Thermal process without pre-treatment

Mechanical separation succeeded by a thermal processMechanical separation

The methods used at H.J. Hansen and R-plus reach the same results. Both processes function well and separate so many metals from the shredder waste that the residue is suitable for thermal treatment.

If the methods are complemented with separation of plastic (i.e. Salyp) or a simple separation based on density, plastics could be produced from the coarse fraction.

The development of mechanical separation processes is very fast - both as regards sensor systems and sorting mechanisms (Salyp, SSE, S+S, LLA, etc.).

Succeeding thermal processes

CT-Environment and von Roll have, in large-scale pilot tests, shown that their technologies can process pre-treated shredder waste.

CT-Environment has shown, in full scale tests, that their melting cyclone can treat shredder waste and flue gas cleaning product from MSW incineration simultaneously. The process produces a metallic melt and glassy mineral slag, with a composition that can possibly meet the Danish limit values for slag category II. CT-Environment has not demonstrated that they themselves master the technology of mechanical pre-treatment. In the middle of 2002, the Swiss authorities chose the technology of CT-Environment for treatment of shredder waste. The parent company of CT-Environment, Babcock Borsig Power, is at the moment under liquidation. Recently, CT-Environment was reconstructed with new owners.

Von Roll masters technologies for processing of shredder waste (including grate-pyrolysis). Von Rolls slag processing oven allows control of the composition of the slag - an interesting option that is not offered by others. Von Roll offers both the grate-pyrolysis process and their melting technology at commercial conditions for processing of shredder waste.

Comparison of CT-Environment and Von Roll:

• The process of von Roll requires an extra mechanical pre-separation process, if metals of high quality have to be produced.
• The melting technology of von Rolls is able to reduce oxides of cupper and iron to free metals. In the CT-Environment process, oxides of iron and cupper end up in the slag.
• It is estimated that the treatment costs of a von Rolls plant is DKK 1,091/t SHR at 45,000 t/year, while CT-Environments costs are lower, approximately DKK 470/t SHR at 100,000 t/year, because CT's plant simultaneously processes an equivalent amount of flue gas cleaning product from MSW incineration.
• Both technologies are working reliably when processing other materials, but long-term experience with shredder waste has not been found.
• The plant capacity of both technologies can be tailored to the structure of the Danish waste management system. Both technologies will also be able to process other waste fractions simultaneously, as demonstrated by CT-Environment.

The SVZ, KSK and PyroArc shaft furnace process and the Kawasaki combination of pyrolysis in a duct and a shaft gasifier, can with certain constraints, process shredder waste. All shaft furnace processes require that the shredder waste is feed as briquettes that are stable at temperatures above 1,000 °C. SVZ and PyroArc claim that they have solved this problem, but actual experience has not been found. The process of Kawasaki requires additional supply of coal. The pyrolysis duct and the feeding system of the Kawasaki process have problems with shredder waste.

Thermal processes without pre-treatment of shredder waste

Ebara and Takuma are the only two documented well-functioning thermal and mechanical processes that are able to treat shredder waste. Both Ebara and Takuma have three and four years of production experience from one commercial plant, and offer the plants with guarantees all over the world.

Comparison of Ebara and Takuma:

• Both processes produce iron, copper and aluminium in mixtures from the waste, and both processes produce a mineral granulate that can probably meet the Danish limit values for slag category II. Most of the Zn and Pb end up in the flue gas-cleaning product, which has to be disposed of.
• The treatment costs of both processes are expected to be in the order of DKK 880/t SHR.
• Both technologies can, without any problems, meet the Danish requirements laid down for the working environment and for emissions.
• The Takuma plant has been in operation for four years and has processed approx. 100,000 tons shredder waste. The EBARA plant has been in operation for nearly three years and has treated more than 120,000 tonnes shredder waste.
• The processes of Ebaras and Takumas have the same energy efficiency.
• Both technologies can be adapted to the structure of the Danish waste management system. The desired plant capacity is not at problem, and both processes will be able to process other types of waste, like flue gas cleaning products, simultaneously.

PKA has developed a process, where the energy output is a combustible gas. PKA has no full-scale experience with shredder waste, but has performed pilot plant tests. The liquidation proceedings of PKA are ongoing.

The process of Mitsui is almost identical to Takumas, but Mitsui has concentrated on the processing of MSW.

Processing of CCA-impregnated waste wood

Only one commercial process for treatment of CCA-impregnated waste wood was found: a Finish recycling system for impregnated poles, sleepers, etc. However, it has not been possible to get any kind of detailed information about the technologies. The process consists of a patented combustion process succeeded by chemical processing of the ashes into a new impregnation liquid. The process cannot be immediately transferred to Denmark, and the type of chemical process is unknown.

A number of processes are developed:

• Kommunekemi A/S has performed pilot plant tests with counter-current gasification succeeded by a chemical processing of the ash, and is also developing a process based on low temperature pyrolysis.
• Watech A/S is working with separation processes that can extract the heavy metals in the ash from CCA-impregnated waste wood, PVC, shredder waste, etc.
• The development of the PyroArc process indicates that this and similar shaft gasifiers will probably be able to process CCA-impregnated waste wood together with iron-containing materials, like pre-treated shredder waste. The process will then produce a strongly bound arsenic residue and a slag, which could probably be sold.

Treatment of leather- and tannery waste

Borge tannery, Norway, operates the only commercial plant treating leather-and tannery waste. The process is based on the shaft gasifier (Pyroarc) from the company Enviroarc, and the product is an iron-chromium alloy and a melted slag for recycling. The plant has been in operation for approximately one year. Enviroarc has successfully tested the process in pilot scale with shredder waste and impregnated waste wood.

Danish strategies

Strategy for treatment of shredder waste

It is expected that approximately 100,000 t SHR/year will have to be treated in Denmark in the near future. The composition of the waste will roughly be as in 1996, but with a slightly lower heating value (12 MJ/kg).

The process technologies for shredder waste can be divided into two groups:

1. Mechanical sorting followed by a thermal process (pyrolysis, gasification, combustion, etc.).
2. Thermal process without pre-treatment.

Today's technologies recover energy and materials from shredder waste in amounts that are sufficient to meet the demands laid down in the EU Directive concerning end-of-life vehicles, in 2006 as well as 2015.

The now available technologies from group 2 are: EBARA and Takuma which are first-generation processes. A possible solution from group 1 is CT-Environment in combination with mechanical sorting processes like R-plus or H.J. Hansen. However, the CT-Environment process is not yet established as a first-generation plant in operation.

In the preparation of a strategy for treatment of shredder waste in the future, the following subjects should be considered:

• Treatment of shredder waste in melting processes together with other problematic wastes (for instance residues from flue gas cleaning)
• New possibilities for sorting plastics, metals with new sensor and computer technologies
• Reduced heat value caused by recovery of plastics
• Treatment in a combined process with impregnated wood where the wood is added in the melting process in order to obtain sufficient heat value to melt the slag. (For instance in shaft gasifiers similar to Pyroarc).

Before a technology is chosen, studies should be made of:

1. The economic and environmental possibilities for further sorting and recovery of plastics.
2. The relevance of recovering heavy metals either in mechanical pre-sorting or in the following thermal process.
3. Alternative possibilities for other energy recovery than production of heat/power.
4. Possibilities for upgrading the slag from the thermal process to construction material or raw material of higher value.
5. Economic and environmental aspects of co-treatment with municipal solid waste and industrial waste.

Strategy for treatment of CCA-impregnated waste wood

The main effort in treatment of CCA- impregnated waste wood should be concentrated on solving problems with the toxic arsenic. Arsenic should be stabilized in the cheapest way where it can still be deposited without risk for the surrounding environment. One possibility is to treat the waste wood together with a smaller amount of shredder waste where free metals has been removed, or leather and - tannery waste with iron content from sludge treatment in a process which binds Arsenic in stable iron/copper compounds.

The heat value of the waste wood must be efficiently utilised to ensure the highest possible CO₂-displacement.

The recovery of Copper and Chromium from CCA-impregnated waste wood must be prioritised in relation to the treatment costs associated with the recovery. To the extent that Copper and Chromium are not recycled, they should in all circumstances be stabilized in such a way that slag and other residues do not present an environmental hazard.

The details concerning the Finnish recycling system, producing new substances for impregnation of wood, are not known. Due to the lack of information on the process, transfer of the system to Denmark cannot be recommended.

In the preparation of a strategy for treatment of impregnated waste wood in the future, a combined process should be considered, in which impregnated waste wood is treated with shredder waste where free metals have been removed or with tannery waste (for instance in a shaft gasifier such as Pyroarc).

Strategy for treatment of leather- and tannery waste

The process of Enviroarc, as demonstrated at Borge Tannery, can be utilised in Denmark. The Danish potential for this type of waste is only approximately 4,700 t waste/year, which is expected to lead to rather high treatment costs approx. DKK 1,500-2,000/t waste. If other waste is added, the treatment costs can be reduced.

In the choice of strategy another possibility for treatment of leather waste should be considered in which the waste is treated together with downsized impregnated wood waste in gasification plants, fluid bed combustion plants or other plants without melting units - followed by recovery of chromium and copper from the residues.

Formation of Scaling and corrosion

The large content of chlorine, alkali and heavy metals in shredder waste in comparison with the content in normal municipal solid waste and industrial waste, presents a drastically increased risk of corrosion - or scaling problems in boilers for production of heat and power.

Only scarce experience of operation exists under the right conditions and in the one or two years required. Therefore, the above-mentioned problems cannot be quantified yet.

The report presents a number of possibilities for solving the most likely problems with break-down of fireproof lining, corrosion of evaporator heating surfaces either under the fireproof lining or in areas without fireproof lining and corrosion of evaporator tubes.

It is assessed that corrosion protection of especially evaporator heating surfaces can be obtained by welding on to the surfaces a layer of Inconel steel, which reduces the costs of maintenance and increases the service intervals, with savings that by far exceed the extra costs for the protective layers.

Final conclusion

At the closing of the project further operational experience with the plants in operation is still required before they can be considered as thoroughly tested and sturdy technologies.

The Ebara and Takuma processes may be characterized as first-generation plants, while the CT-environment process must be characterized as a 0. generation plant.

This means that unknown problems can be expected after longer periods of operation, but also a large potential for optimisation. Better plant design, operation and product qualities will probably lead to significantly lower treatment costs pr. treated tonne of waste.

There is still a need for following the experience of the commercial plants and the plants under planning or construction. Several interesting technologies are being developed at Enviroarc, Kommunekemi, Watech and other companies.

There is a need to draw up requirements for ideal plants, which are to treat the prioritised waste fractions.

It should be considered where Danish companies and development environments could participate in the development and test of new technologies

Many of the processes will, with few or no adaptations, be able to treat normal municipal solid waste and industrial waste.

| Forside | | Indhold | | Forrige | | Næste | | Top |

Version 1.0 Februar 2006, © Miljøstyrelsen.