Air Pollution Control – Design Considerations: General Objectives: Background for equipment design To be conversant with equipment manufacturers Understand expectations for normal operation

Specific objectives & expectations: Develop models for air pollution control equipment and implement these models in spreadsheet-based calculations. Capability and reliability of these models will vary depending on the system complexity, but factors affecting equipment performance should be evident.

Unit operations of interest: Gravity settling chambers (GSC) Cyclones Electrostatic precipitators (ESP) Filtration units – baghouse filters Wet scrubbers

Basic input information: Gas properties – temperature, pressure and composition. Derived gas properties – density, viscosity, continuum conditions ( ) and dew point. Particulate properties – size, shape and density. Derived particulate properties – aerodynamic drag and behaviour in non-continuum conditions.

Basic assumptions: Particulates are transported to the collection units in the process – requires minimum transport velocities and “pick-up” velocities. Gas streams, even with heat recovery systems, will probably be above the dew point temperature of the gas (this reduces corrosion in equipment).

Single Collection Systems: A single collection system will process a total gas flow rate, Q f (m 3 /s), and particulate loading, m P (g/s). It will be characterized by a collection efficiency,  (mass fraction- weighted for all particle sizes), and pressure drop,  P f.

Overall collection efficiency (mass-fraction weighted): Overall collection efficiency is a function of: (i)Particle size mass fraction, and (ii)Grade efficiency (  for each particle size)

Multiple collection systems in series: The overall collection efficiencies for the individual systems will not be equal and generally,  1 >  2 (and this inequality continues for additional units in the series sequence). The reason for this is that larger, easier to remove particles are captured in the upstream systems. A drawback for this series arrangement is that the pressure drops add, increasing the overall operating costs. If a single system does not give adequate collection efficiency, we may use systems in series:

Multiple collection systems in parallel: When pressure drop considerations are important, the inlet flow stream can be split into parallel streams. Since  P f  ~(Q f ) 2, this can lead to substantial cost savings. Increased efficiency can be realized when the collection efficiency increases with lower gas flow rates through the units (true for most collection devices except cyclones)

Multiple collection systems in series and parallel: A combination of series and parallel arrangements might be used to give optimum collection efficiency and pressure drop. This method often involves components of the same type of collection device (or elements of the same type of device). The parallel lines can be turned off (or isolated) in a regular timed sequence for periodic cleaning (baghouse filtration units) or routine maintenance.

Gravity Settling Chambers – Chapter 7 Relies on the terminal velocity of a particle to settle out of a gas stream … A conventional design based on flow cross section expansion and dust collection hoppers.

Novel designs based on multiple chambers in parallel

Design analysis similar to a problem previously examined (pg )