Engineers can also use mathematical models or computer programs to design precipitators.
A mathematical model that relates collection efficiency to precipitator size and various
operating parameters has been developed by Southern Research Institute (SoRI) for
EPA. The (SoRI/EPA) model is used to do the following:
• Design a full-scale ESP from fundamental principles or in conjunction with a pilotplant
study·
• Evaluate ESP bids submitted by various manufacturers
• Troubleshoot and diagnose operating problems for existing ESPs
• Evaluate the effectiveness of new ESP developments and technology, such as flue gas
conditioning and pulse energizing.
Table lists the input data used in the SoRI/EPA Model. Assuming that accurate input
data are available for use, the model usually can estimate emissions within ± 20 percent of
measured values (U.S. EPA 1985). The computer model goes through an iterative computational
process to refine its predictions of emission levels for a particular ESP. First, the
model uses secondary voltage and current levels (corona power) to predict emission levels
leaving the ESP. Then, actual emission levels are measured and compared to the predicted
emission levels. Empirical factors are then adjusted and the process repeats itself until the
predicted emission levels of the model agree with the actual, measured levels. This model
can be used to obtain reasonable estimates of emission levels for other ESP operating conditions
(U.S. EPA 1985). For example, once you create a good, working computer model
for a particular ESP design under one set of operating conditions, you can run the model
for different scenarios by altering one or more of the parameters (precipitator length, number
of fields, etc.) to obtain reasonably accurate emission level predictions.
A mathematical model that relates collection efficiency to precipitator size and various
operating parameters has been developed by Southern Research Institute (SoRI) for
EPA. The (SoRI/EPA) model is used to do the following:
• Design a full-scale ESP from fundamental principles or in conjunction with a pilotplant
study·
• Evaluate ESP bids submitted by various manufacturers
• Troubleshoot and diagnose operating problems for existing ESPs
• Evaluate the effectiveness of new ESP developments and technology, such as flue gas
conditioning and pulse energizing.
Table lists the input data used in the SoRI/EPA Model. Assuming that accurate input
data are available for use, the model usually can estimate emissions within ± 20 percent of
measured values (U.S. EPA 1985). The computer model goes through an iterative computational
process to refine its predictions of emission levels for a particular ESP. First, the
model uses secondary voltage and current levels (corona power) to predict emission levels
leaving the ESP. Then, actual emission levels are measured and compared to the predicted
emission levels. Empirical factors are then adjusted and the process repeats itself until the
predicted emission levels of the model agree with the actual, measured levels. This model
can be used to obtain reasonable estimates of emission levels for other ESP operating conditions
(U.S. EPA 1985). For example, once you create a good, working computer model
for a particular ESP design under one set of operating conditions, you can run the model
for different scenarios by altering one or more of the parameters (precipitator length, number
of fields, etc.) to obtain reasonably accurate emission level predictions.
Another model, the EPA/RTI model, has been developed by the Research Triangle Institute
(RTI) for EPA (Lawless 1992). The EPA/RTI model is based on the localized electric
field strengths and current densities prevailing throughout the precipitator. These data can
be input based on actual readings from operating units, or can be calculated based on electrode
spacing and resistivity. The data are used to estimate the combined electrical charging
on each particle size range due to field-dependent charging and diffusional charging.
Particle size-dependent migration velocities are then used in a Deutsch-Anderson type
equation to estimate particle collection in each field of the precipitator. This model takes
into account a number of the site specific factors including gas flow maldistribution, particle
size distribution, and rapping reentrainment.
These performance models require detailed information concerning the anticipated configuration
of the precipitator and the gas stream characteristics. Information needed to operate
the EPA/RTI model is provided below. It is readily apparent that all of these parameters
are not needed in each case, since some can be calculated from the others. The following
data is data utilized in the EPA/RTI computerized performance model for electrostatic precipitators.
ESP Design
• Specific collection area
• Collection plate area
• Collection height and length
• Gas velocity
• Number of fields in series
• Number of discharge electrodes
• Type of discharge electrodes
• Discharge electrode-to-collection plate spacing
Particulate Matter and Gas Stream Data
• Resistivity
• Particle size mass median diameter
• Particle size distribution standard deviation
• Gas flow rate distribution standard deviation
• Actual gas flow rate
• Gas stream temperature
• Gas stream pressure
• Gas stream composition
0 comments:
Post a Comment