| Popis: |
Pilot plant electrostatic precipitator experiments have shown that the collection of pulverized fuel ash was aided by a number of additives, including sulphur trioxide, sulphuric acid, ammonium sulphate, ammonium bisulphate, sulphamic acid and, in certain circumstances, ammonia. The first three are economically the most attractive for use in power station precipitators. Sulphuric acid and ammonium sulphate are easily injected in the form of aqueous sprays and the effectiveness of the latter has been confirmed in full-scale tests. Other additives studied were sodium chloride, calcium chloride, sodium sulphate, lithium iodide and hydrogen chloride. Additives improved precipitator performance by increasing the flashover voltage. It is suggested that changes in resistivity due to an additive affected the electron charge on the ash layer, which in turn influenced the surface work function and raised the flashover voltage. Nevertheless, some additives increased the flashover voltage and efficiency without altering resistivity. Where performance correlated with resistivity a better correlation was obtained at an arbitrary bulk density rather than at that of the precipitated layer. The cohesive properties of ash were related to efficiency only when the resistivity was low. |
