University, Western Washington University, Gonzaga University, Auburn University, and Education Services of the American Institute of Chemical Engineers. Dunn, PhD, PE, is a professor of the practice of chemical and environmental engineering at Vanderbilt University.
A BRIEF HISTORY OF THE AIR POLLUTION PROBLEM
October 1948 marks the start of a more vigorous program of air pollution control in the United States. During World War II, a new type of air pollution had been discovered in the Los Angeles atmosphere.
FEDERAL INVOLVEMENT IN AIR POLLUTION CONTROL
Required development of air quality criteria which would be used as guides in setting ambient and emission standards. Required states to established air quality standards consistent with air quality criteria in a fixed time schedule.
CHARACTERIZING THE ATMOSPHERE
Encouraged state and local programs for the control and abatement of air pollution while reserving federal authority to intervene in interstate conflicts. Set the following basic control strategy to be employed, establishing – National Ambient Air Quality Standards (NAAQS).
RECIPE FOR AN AIR POLLUTION PROBLEM
The effects in London are to produce bronchial irritation, whereas in Los Angeles, the effects are to produce eye and skin irritations. In Los Angeles, the smog is primarily produced through photochemi- cal oxidation of the hydrocarbons by the ozone and nitrogen oxides that are in the atmosphere.
HISTORY OF THE CLEAN AIR ACT
National Ambient Air Quality Standards
Specifying lead as a criteria pollutant instead of a hazardous air pollutant is interesting, and this distinction proved to be effective. Controlling the spread of lead molecules throughout the environment as gasoline was burned was accomplished effectively as a criteria pollutant.
New Source Performance Standards
The NAAQS for criteria pollutants were to be established by the EPA at two levels:. 1) primary standards to protect health and (2) secondary standards to protect welfare (e.g., crops, vegetation, buildings, visibility). Conversely, the hazardous air pollutant program, NESHAP, became bogged down in establishing health-based standards.
Citizen Suits
Second, establishing an ample margin of safety was problematic, especially for the portion of the public that is sensitive to air pollution. An approved PSD air permit allots a portion of the available increment for deterioration to that source.
Offsets in Nonattainment Areas
Later, new sources wishing to locate in the area, or major modifications of existing sources, must consider the amount of the increment that has already been consumed. They have been hailed3 as “one of the most significant pieces of environmental legislation ever enacted.”.
T ITLE I: P ROVISIONS FOR A TTAINMENT AND M AINTENANCE OF NAAQS The 1990 CAAA recognized that many urban areas were not in attainment of the The 1990 CAAA recognized that many urban areas were not in attainment of the
- NAAQS Revisions
The new standards followed a lawsuit by the American Lung Association that the EPA missed the deadline for the required review of the particulate standard. Circuit Court of Appeals said that the EPA lacked any determi- nate criterion for establishing where the standard for a nonthreshold pollutant should be set, so choosing a standard was capricious and arbitrary.
T ITLE II: M OBILE S OURCES
- Source Categories
- Establishing MACT Standards
- Risk Management Plans
The new technology-based NESHAP program requires the EPA to determine maximum achievable control technology (MACT) standards for major sources of HAPs. The EPA must establish technology-based MACT standards for new and existing sources in the source categories.
T ITLE VII: E NFORCEMENT
The law also requires the EPA to publish a list of safe and unsafe substitutes for Class I and Class II chemicals and to ban the use of unsafe substitutes. Company officials must certify either compliance or acknowledgment of being out of compliance with regulations.
T ITLE VIII: M ISCELLANEOUS P ROVISIONS
These penalty maximums are increased for infla- tion by the Civil Monetary Penalty Inflation Rule, mandated by the Debt Collection Improvement Act of 1996. 37,500 and $320,000, as codified by 40 CFR Part 19.When assessing penalties, EPA is required to consider the size of the business, compliance history, duration of the violation, good faith efforts to comply, payment of penalties previously assessed for the same violation, the economic advantage to the company for noncompliance, and the seriousness of the violation calculated pursuant to the Stationary Source Penalty Policy available on EPA’s website at http://www2.epa.gov/enforcement.
T ITLE IX: R ESEARCH
Certification adds personal liability and causes many managers to be much more concerned about compliance than they had been in the past. An award of up to $10,000 also was estab- lished for information leading to criminal conviction or administrative penalties for violations emissions standards or limitations imposed through the hazardous air pollutant, acid deposition, operating permit, or stratospheric ozone programs.
T ITLE X: D ISADVANTAGED B USINESS
T ITLE XI: E MPLOYMENT T RANSITION A SSISTANCE
A facility that proposes to add or modify a source of air pollution may be required to obtain an approved air permit before starting construction of the new source. The pro- cess for evaluation and approval of a new major source permit application is called new source review (NSR).
ELEMENTS OF A PERMIT APPLICATION
- Potential to Emit
- Fugitive Emissions
- Secondary Emissions
- S IGNIFICANT E MISSION R ATES
Increased secondary emissions at the quarry would not be included in the cement plant’s PTE. In attainment areas, any new or modi- fied source emissions at a major source facility that increases the PTE of any of these pollutants by the significant emission rate triggers the requirement for a PSD permit.
BEST AVAILABLE CONTROL TECHNOLOGY
S TEP 2: E LIMINATE T ECHNICALLY I NFEASIBLE O PTIONS
Some of the potential control technologies may not work in the specific application being proposed. The longer flame length produced by low NOx burners may impinge on the back wall of the heater.
S TEP 3: R ANK R EMAINING O PTIONS BY C ONTROL E FFECTIVENESS
- Energy Impacts
- Environmental Impacts
Also, it is generally presumed that demonstrated levels of control can be achieved unless there are source-specific fac- tors that limit the effectiveness of the technology. Energy and energy conservation is considered by the government to be important to the economy of the nation, and the energy analysis assures that energy has been considered.
S TEP 5: S ELECT BACT
The incremental cost-effectiveness is the difference in cost between two dominant tech- nologies divided by the difference in the pollution emission rates after applying these two technologies. An extraordinarily high incremental cost-effectiveness can be used as justification that a control technology having only slightly higher removal efficiency than the next technology, but which has significantly higher cost, is not cost-effective.
AIR QUALITY ANALYSIS
P RELIMINARY A NALYSIS
The levels of significance for air quality impacts in Class II areas are listed in Table 3.3. If the projected increase in pollutant concentration is less than the significance level for the appropriate time averaging period, then it is considered insignificant, and an evaluation of PSD increment con- sumption is not required.
F ULL A NALYSIS
NSR REFORM
INTRODUCTION—METEOROLOGICAL BACKGROUND
- Surface or Radiation Inversions
- Evaporation Inversion
- Advection Inversion
- Subsidence Inversion
- D IURNAL C YCLE
- P RINCIPAL S MOKE -P LUME M ODELS
When the sun appears in the morning, it heats the earth by radiation, and the surface of the earth becomes warmer than the air above it. Furthermore, the urban inversion will form in the upper atmosphere, which loses heat to the outer atmosphere faster than it can be supplied from the surfaces of the city.
TALL STACK
Under these conditions plumes tend to loop upward and then down to the ground in what are called looping plumes. When the day is dark with steady relatively strong winds, the temperature profile will be neutral, so that the convection currents will be small.
CLASSIFYING SOURCES BY METHOD OF EMISSION
D EFINITION OF T ALL S TACKS
Most tall stack sources will be associated with fossil fuel-burning steam electric power-generating facilities. In general, this is the kind of stack that is found in a chemical or a petroleum processing plant.
ATMOSPHERIC-DIFFUSION MODELS
O THER U SES OF A TMOSPHERIC -D IFFUSION M ODELS
The models can serve to locate areas of expected high concentration for correlation with health effects. The models can be employed in preconstruction evaluation of sites for the location of new industries.
ENVIRONMENTAL PROTECTION AGENCY’S COMPUTER PROGRAMS FOR REGULATION OF INDUSTRYPROGRAMS FOR REGULATION OF INDUSTRY
I NDUSTRIAL S OURCE C OMPLEX M ODEL
Procedures from former models are used to account for variations in terrain height over receptor grid. If terrain height exceeds stack height, the ISC Programms truncate the ter- rain to stack height.
S CREENING M ODELS
A wind-profile law is used to adjust observed wind speed from measurement height to emission height. SCREEN3 allows a group of sources to be merged into one source, and it can account for elevated terrain, building downwash, and wind speed modifications for turbulence.
SOURCE-TRANSPORT-RECEPTOR PROBLEM
S OURCE
From these data, we can calculate the flow rate of the total stream and of the pollutant in question.
T RANSPORT
- Bulk Transport of Pollutants
- Dispersion of Pollutants
Specification of the wind speed must be based on data usually taken at weather stations separated by large distances. For the future, progress in modeling downwind concentrations will come through increased knowledge of wind fields and numerical solutions of the deter- ministic models.
R ECEPTOR
Since wind velocity and direction are strongly affected by the surface conditions, the nature of the surface, predominant topologic features such as hills and valleys, and the presence of lake, rivers, and buildings, the exact path of pollutant flow is difficult to determine. The Gaussian concentration model does not take into account wind speed variation with altitude, and only in a few cases are there algorithms to account for the varia- tion in topography.
INTRODUCTION
CODE OF FEDERAL REGULATIONS
REPRESENTATIVE SAMPLING TECHNIQUES .1 G ASEOUS P OLLUTANTS.1 GASEOUS POLLUTANTS
Determination of oxygen and carbon dioxide concentrations in emissions from stationary sources (instrumental analyzer procedure). 17 Determination of particulate emissions from stationary sources (in-stack filtration method) 18 Measurement of gaseous organic compound emissions by gas chromatography.
AMBIENT AIR-QUALITY SAMPLING PROGRAM
OBJECTIVES OF A SAMPLING PROGRAM
MONITORING SYSTEMS
The chief advantage of mobile sampling is that air-quality measurements can be made at many sites—far more than would be feasible in a fixed sampling program. The selection of the methodology to be used is an important step in the design of the.
FEDERAL REFERENCE METHODS AND CONTINUOUS MONITORINGMONITORING
Reference Method Principle and Calibration Procedure for the Measurement of Sulfur Dioxide in the Atmosphere (Ultraviolet Fluorescence Method). Reference Method for the Determination of Sulfur Dioxide in the Atmosphere (Pararosaniline Method) Particulate Matter.
COMPLETE ENVIRONMENTAL SURVEILLANCE AND CONTROL SYSTEMAND CONTROL SYSTEM
TYPICAL AIR SAMPLING TRAIN
INTEGRATED SAMPLING DEVICES FOR SUSPENDED PARTICULATE MATTERPARTICULATE MATTER
Air then flows through the first-stage vent tubes and then through the second fractionation stage. More noninhalable particles are removed, and the remaining aerosol is drawn through the usual 8 × 10 in.
CONTINUOUS AIR-QUALITY MONITORS
- N ONDISPERSIVE I NFRARED M ETHOD FOR CO
- F LAME P HOTOMETRIC D ETECTION OF T OTAL S ULFUR AND SO 2
- F LUORESCENT SO 2 M ONITOR
- C ALIBRATION OF C ONTINUOUS M ONITORS
- Specifications for Continuous Air-Quality Monitors
- Steady-State Calibrations
Radiant energy: In the sample cell, part of the original energy of the sample beam is absorbed by the component of interest. However, since energy of the reference beam is greater, gas in the reference chamber is heated more.
TIME VALUE OF MONEY
Cost is the basic and crucial decision-making factor in the selection of air-pollution control equipment. The Vatavuk Air Pollution Control Cost Index begins in the first quarter of 1994 with a baseline value of 100.
TYPES OF COST ESTIMATES
OAQPS C ONTROL C OST M ANUAL
O THER C OST -E STIMATING R ESOURCES
Common sources of equipment cost estimates include Perry’s Chemical Engineers’ Handbook5 and Richardson’s Process Plant Construction Estimating Standards.7 Additional material has been published by Vatavuk,8 who is also the primary author and editor of the OAQPS Control Cost Manual. A large amount of detailed cost information on utility flue gas desulfurization systems has been sponsored and published by the Electric Power Research Institute.9,10.
INTRODUCTION TO PROCESS DESIGN
STRATEGY OF PROCESS DESIGN
P ROCESS F LOWSHEETS
As the process design develops, the recycle streams can be added to this input–output sketch. The flowsheet should then be modified and moved toward the final document to be used for the detailed design and cost estimation.
MASS AND ENERGY BALANCES
M ASS -B ALANCE E XAMPLE
It is also known that the ratio of the flow rate of Stream 2 to Stream 1 is 5/1. A is a tie substance, which can be used to determine how much of the total flow goes into Stream 3.
SYSTEMS-BASED APPROACHES TO DESIGN
A heat-induced separator is defined as an indirect-contact, countercurrent unit that employs an energy-separating agent ESA to allow the removal of the pollutant from the gaseous emission stream by using a phase change. The design task of synthesizing heat- induced separation networks (HISENs) for air-pollution control process design is to systematically identify a cost-effective system of heat-induced separators and heat exchangers that can achieve a specified pollutant reduction task (single component or multiple component waste streams) by heating/cooling the streams to produce a separation by a phase change of the pollutant.9 Figure 8.8 is included as a general representation of the HISEN synthesis task for end-of-the-pipe waste minimization process design.
INTRODUCTION—PROFIT GOAL
PROFITABILITY ANALYSIS
Example of IROI Comparing Two Cases
One manufacturer proposes a carbon steel cyclone to do the job; the other manufacturer proposes a stainless steel cyclone that costs more but has a longer service life and lower maintenance and power cost.
Example of IROI with Four Cases
EFFECT OF DEPRECIATION
D ESIGN D EVELOPMENT
If the pollutant content of the cleaned stream meets the effluent emission standards, the cleaned stream can be discharged to the atmosphere. If a suitable coolant is available and the pollutant concentra- tion is high enough, condensation can be very effective in recovering material that may be used again.
ABSORPTION AND ADSORPTION
F LUID M ECHANICS T ERMINOLOGY
Therefore, determining the unoccupied tower cross-sectional area is dif- ficult, and it becomes advantageous to base the velocity on the total tower cross section, which is the usual way to calculate tower flow, especially in absorption design. If G is defined as the mass rate of gas flow, then a superficial mass velocity can be defined as G, where.
Furthermore, gases to be treated may have liq- uid or solid particles present or have a high humidity. Gases to be treated may also be required to be cooled if the temperature is greater than 120°F–130°F and the possibility of exothermic reac- tions exist.
PROCESS SYNTHESIS TECHNOLOGY FOR THE DESIGN OF VOLATILE ORGANIC COMPOUNDS RECOVERY SYSTEMSVOLATILE ORGANIC COMPOUNDS RECOVERY SYSTEMS
To apply this approach to the design of volatile organic compounds (VOC) recov- ery systems, the designer must be aware of two key points. Second, the designer must understand that the ther- modynamic effectiveness (not necessarily related to the cost-effectiveness) of the system is based on the system equilibrium data.
INTRODUCTION
A DVANTAGES
It may result in column packing plugging or fouling if particulates are pres- ent in the gaseous waste stream.
AQUEOUS SYSTEMS
Some of the liquid absorbent may be transferred to the exit gas stream, thus creating a new pollution concern. For pollutant gases with limited water solubility, such as SO2 or benzene vapors, the large quantities of water that would be required are generally impractical on single-pass basis, but may be used in unusual circumstances.
NONAQUEOUS SYSTEMS
In plate columns, contact between gas and liquid is obtained by forcing the gas to pass upward through small orifices, bubbling through a liquid layer flowing across a plate. Baffle tower design may use alternating segmental baffles (Figure 11.5) or disk and doughnut plates, in.
DESIGN TECHNIQUES FOR COUNTERCURRENT ABSORPTION COLUMNSABSORPTION COLUMNS
If it is assumed that the flow rates do not remain constant through the column, Equation 11.22 can be written as. The material balance of Equation 11.24 can be rewritten in terms of these solute-free flow rates as.
O RIGIN OF V OLUME -B ASED M ASS -T RANSFER C OEFFICIENTS
- Steady-State Molecular Diffusion
Then for component A with mole fraction yA, the sum of the bulk flux and the flux due to molecular diffusion in the z-direction is given by. Mass transfer in real absorption equipment resembles a molecular diffusion process only in the basic idea of a concentration difference driving force.
O VERALL M ASS -T RANSFER C OEFFICIENTS
We can now rewrite Equation 11.36 in terms of a differential rate of mass transfer dNA, with units (moles/unit time) = (moles/unit time − area) × (area),. The integral portion of Equation 11.54 is designated as the number of overall mass-transfer units, or, for the gas phase, NOG.
COUNTERCURRENT FLOW PACKED ABSORPTION TOWER DESIGNABSORPTION TOWER DESIGN
T OWER P ACKINGS
- Random or Dumped Packing
- Types of Random Packing
- Structured Packing
- Types of Structured Packing
- Grid-Type Packing
- Packing Support Plate
- Liquid Distributors
- Liquid Redistributors
- Bed Limiter
The Intalox™ saddle (Figure 11.17) was created by modifying the Berl saddle, so that adjacent pieces of packing would not blank off any portion of the liquid wetting the packing. Intalox™ high-capacity structured packing (Figure 11.22) is an example of the corrugated structured packing type.
Since L/G is known, we can calculate the value of the abscissa in Figure 11.31, if the gas density ρG and the liquid density ρL are known. In Figure 11.31, the abscissa is defined as the flow parameter X and is given by Equation 11.69.
For any given B and percent removal, knowing G and K ayo , HOG can be calculated, and the height of the column can be calculated from Equation 11.57. Since Equation 11.80 is derived for the dilute solution, examination of Figure 11.29 shows that the number of transfer units, NOG, cannot be greatly reduced by increasing B, the multiple of the mini- mum L/G ratio, above 1.70.
