Abstract
For the purpose of improving the collection efficiency of high resistivity dust, moving electrode electrostatic precipitator (MEEP) was developed.  It is well known that collection of high electrical resistivity dust in a EP have several problems such as back ionization, reentrainment, and excessive sparking.  Avoiding these problems some countermeasures are designed such as wide pitch EP, pulse power supply and MEEP were proposed.  Pulse energization was proposed in the 1950’s, and its industrial applications are expending these days.  MEEP was developed in 1979 and applied many industries such as Oil Refinery and Coal Fired Boiler to collect the high electrical resistivity dust.  MEEP has moving collection plate and brush which dislodges the collected dust layer on the collecting plate, therefore collecting plate can be maintained clearly.

In this study several parameter was investigated to know the characteristics of moving electrode electrostatic precipitator such as collecting plate velocity, applied voltage, gas velocity, particle load and applied voltage waveform.

The experimental results show that collection efficiency and V-I characteristics of MEEP for high resistivity fly ash are very stable. Thus collection efficiency is high in comparison with the conventional EP.  The effect of intermittent pulse discharge on the collection efficiency and specific corona power increase with pulse period in the experimental condition.

Abstract
The ever-increasing concern of particulate emissions and the increasing demand for electricity call for higher collecting efficiencies from electrostatic precipitator (ESP).  One of the difficulties is meeting lower outlet emission limits with pulverized coal-fired boilers burning low sulphur coals, because the corresponding fly ash often has a high resistivity.  The high resistivity ash causes back-corona conditions within the ESP and lowers collection efficiency.  Larger precipitators have to be supplied to address this problem.

Predictions of severe corona suppression due to high concentration of ultra-fine ash (space charge effect) and of the dust cake resistivity can be improved with better knowledge of the characteristics of the particulate entering the ESP.  A more efficient and reliable ESP can then be designed even for the low emissions that are demanded now.

This paper briefly describes investigations that have been conducted by ABB to combat the problem of high resistivities in ESPs.  Various approaches to superior design such as flue gas cooling, use of spiral discharge electrodes and micro-second pulse energization are described.

Specifically, the performance behavior in the ESP for a large number of worldwide coals is presented in the context of the detailed ash particulate size and composition.  A drop-tube furnace was used to produce ash particles similar to those generated in a pulverized coal-fired boiler.  Particle size and fly ash composition distribution varied substantially even for coals with similar bulk ash composition.

The effect of different boiler conditions on the ash properties is also presented.  A high flame temperature generates a high amount of ultrafine particles, ~0.1.  The resulting high surface area of the ash, in some cases, may not be fully conditioned by the available sulphur trioxide in the combustion flue gas, resulting in high dust cake resistivity.

Measurements of the independent effects of flue gas temperature and humidity have been evaluated during controlled conditions in pilot-scale tests.  This provides a good basis for implementing designs with reduced ESP size.  A review of experience of ESP operation at low gas temperatures is presented in this context.

Abstract
Traditional discharge electrodes in electrostatic precipitators with horizontal gas flow are vertical wires, sometimes weighted-wires, vertical barbed wires or strips, or vertical rigid tubes fitted with discrete emitter points.

Horizontally aligned discharge electrodes have advantages with respect to production, packing, transportation, erection and maintenance over vertically aligned electrodes.  Simple theories of the electrodynamic process mention the concept of “electrical sneakage”, which should exclude designs applying horizontally aligned discharge electrodes in horizontal gas flow precipitators.  Yet, it seems that reality is more complex, and laboratory experiments have revealed that such type of discharge electrode is at least as efficient as discharge electrodes of traditional design.

The present paper will report laboratory results with horizontal discharge electrodes and attempt to explain why the precipitator operates well in spite of “electrical sneakage” and in spite of the risk of provoking more intense secondary flow such as longitudinal rolls.

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