Miljøprojekt nr. 1186 – Trinopdelt forgasning af imprægneret affaldstræ

Trinopdelt forgasning af imprægneret affaldstræ

Summary and conclusions

This project has been started to verify if the staged gasification process developed by TK Energi A/S with further processing of the residual products (bottom, cyclone and filter ash) could be a sustainable treatment process for waste wood impregnated by Cu, Cr and As.

The project has had four main activities:

Information retrieval
Laboratory tests with high temperature treatment of ashes from impregnated wood
Planning and completion of a 100-hour test run at the pilot plant at TK Energi A/S
Evaluation of environmental impact and the potential of recycling the heavy metals

The information retrieval has given information on which international research teams are working on the problems of fractionating Cu, Cr and As in gasification and combustion processes.

However, the published results from these teams have not contributed with information that could be used for implementing changes in the design of the pilot plant or for interpreting the results from the tests.

The complicated chemistry of Arsenic is still the problem. The information retrieval has not found research on the behaviour of Arsenic at high temperatures (> 1000°C).

The laboratory tests have not increased the likelihood of Arsenic not contaminating the bottom and fly ash from this type of gasifier. On the contrary the content of Arsenic increases with the temperature, and since the partial combustion zone of the TKE gasifier is operating at high temperatures, these results cannot support this concept.

The project has successfully carried out a 100-hour test run on the TKE staged gasifier with impregnated waste wood. During the entire test the running conditions were stable and the process controlled properly without unforeseen occurrences.

The gasifier was continuously producing a steady product gas stream with the quality expected from a co-current gasifier fired with dry wood, in spite of the observation of false air.

The operational costs are still high due to manning requirements.

The gasifier should be improved on the following points:

Automatic control
Design of grate and ash outlet
Design of reactor chamber

The gasifier has a potential - with the right investment and development - to become a technology capable of treating CCA-impregnated waste wood in an efficient and sustainable way.

The process still requires improvement in order to increase the process stability and further development to improve the coke transformation, thereby decreasing the ratio of coke in the ash fraction. The project has not demonstrated the possibilities of processing the residuals from the gasification process in full scale, it has only ascertained that the gasification process separates the metals in bottom ash, cyclone ash and filter ash.

The process should be further developed, and a method of recovering Cu, Cr and As from the ash fractions should be verified. After this an economic evaluation can be completed.