Impact of Co-combustion of Mercury-containing Secondary Fuels on Flue Gas Desulfurisation (Pre-project)

Project Number 293

In the light of increasing energetic utilisation of wastes by co-combustion in power plants it is necessary to further investigate the impact of mercury emission reduction by means of wet FGD, because some wastes contain a high percentage of mercury traces. Due to interaction with several parameters, mercury-reduction rates vary. In this pre-project, all important factors influencing mercury-separation are to be investigated in the laboratory.

Questions on mercury separation and -emission in the FGD area cannot be thermodynamically recorded. The data required for their kinetic modelling are not available. The pre-project will thus elaborate on an experimental basis the basic parameters for description of the mercury chemistry and process technology in FGD scrubbers. Laboratory tests with model and real FGD suspensions will be realised under controlled conditions; they will be supplemented in the main project by investigations at technical FGD.

To this end, in the pre-project the process-technical parameters are to be investigated which

  • determine the separation degree of the oxidised mercury in the raw waste gases in the FGD scrubber without re-emissions,
  • avoid integration of the mercury in the FGD gypsum and support discharge in the FGD waste water scrubbing plant (RAA),
  • affect separation of the mercury from the residual gypsum and from the RAA sludge.

The vital scientific aims of the project are clarification of the factors which

  • influence solubility and steam pressure of the mercury in the FGD,
  • reduce integration of the mercury into the FGD gypsum and
  • facilitate separation of the mercury from the sludge in the RAA.

Based upon these basic results, technical concepts for better regulation of mercury separation and -emission are to be developed and tested in operational tests in the course of the main project.

The results of the pre-project are useful to determine in the planned main project the marginal conditions for transformation into the large-technical wet FGD, by means of which the demands to mercury emissions into the air and/or the draining ditch can be observed and the side product quality can be maintained. Realisation of the main project will be mainly determined by the results of the pre-project. The overall project aims at the economic and operationally secure reduction of mercury emissions into the air and waste water during co-combustion of secondary fuels in power stations.

The project will be realised in 2007 by the Institute for Environmental Technology of the Halle-Wittenberg Martin-Luther-University and headed by Prof. Heinz Köser. The investigations will be supported by a working group of the VGB Working Panels “Flue Gas Cleaning Technology”, “Chemistry of Water Treatment”, “Water Management” and “Power Plant By-products”.