Material flow analyses are performed by model calculations. Data used for these calculations are representative of operating values for technical-scale plants. As starting point a model plant with grate firing is considered. For this plant 10 different flue gas cleaning systems are analysed, 6 of them being equipped with a wet cleaning system. Additionally, 2 systems operating in a semi-dry sorption and 2 systems operating in conditioned dry sorption are taken into account. The system boundaries for the material flow analysis performed include the entire flue gas cleaning system, starting with the raw gas downstream of the boiler and ending downstream of the stack. The elements chlorine (Cl), sulfur (S), mercury (Hg), cadmium and lead are considered.
The balances calculated for chlorine and sulfur are different for the considered flue gas cleaning systems - nevertheless limit values of legal regulations are not exceeded. In contrast, no such dependence on the type of flue gas cleaning system can be seen for the heavy metals balanced in this study. The wet flue gas cleaning systems with fine purification downstream show the lowest emissions, the emissions of the semi-dry and conditioned dry sorption are slightly higher.
The need of auxiliary chemicals and therefore the amount of residues is lowest for the wet cleaning system and highest for the conditioned dry sorption. Moreover, the balances show that the emissions of the semi-dry and conditioned dry sorption can be controlled by plant operation, particularly by the auxiliary chemicals used.
For cost analysis, only the investment costs for pure plant components of the flue gas cleaning system are taken into consideration - construction work, control engineering etc. are not included. In the last few years a collapse of prices for investment costs of flue gas cleaning systems occurred. There are only slight differences in the investment costs between semi-dry and conditioned dry sorption systems. These plants have the lowest investment costs. A wider range for the investment costs is calculated for wet flue gas cleaning systems. A wet system constructed in a relatively simple manner is only slightly more expensive than a semi-dry sorption system.
As a result of this work, two flue gas cleaning concepts seem to be very interesting for the construction of new plants: A plant with a wet flue gas cleaning system equipped with fabric filter followed by a two-stage scrubber system generates small amounts of residues by low investment costs. Moreover, semi-dry sorption seems to be a respectable alternative, but this study shows that the operation of the semi-dry sorption can be optimised.