distribution of gas flow

Distribution of gas flow across the entire precipitator unit is critical to ensure collection of the particles. To assure even distribution, gas should enter the ESP through an expansion inlet plenum containing perforated diffuser plates. In addition, the ducts leading into the ESP unit should be straight as shown in Figure 1. For ESPs with straight-line

inlets, the distance of A should be at least as long as the distance of B in the inlet (Katz 1979). In situations where a straight-line inlet is not possible and a curved inlet must be used (see Figure 2), straightening vanes should be installed to keep the flue gas from becoming stratified. The gas velocity through the body of the ESP should be approximately 0.6 to 2.4 m/s (2 to 8 ft/ sec). For ESPs having aspect ratios of 1.5, the optimum gas velocity is usually between 1.5 and 1.8 m/s (5 and 6 ft/sec). The outlet of the ESP should also be carefully designed to provide even flow of the gas from the ESP to the stack without excessive pressure buildup. This can be done by using an expansion outlet, as shown in Figure 3. Figures 1 and 2 also have expansion outlets.

1. Straight-line inlet

2. Straightening vanes in a curved inlet

3. ESP with expansion outlet