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Published in:
2021 | OriginalPaper | Chapter
Industrial Emissions Control Technologies: Introduction
Authors : Szymon Kwiatkowski, Merve Polat, Weijia Yu, Matthew Stanley Johnson
Published in: Air Pollution Sources, Statistics and Health Effects
Publisher: Springer US
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Excerpt
Aerosol
Aerosols are suspensions of solid or liquid particles in a gas and occur when mixing from diffusion and circulation is more rapid than gravitational settling. In common usage, “aerosol” can refer to the particulate matter. Atmospheric particulate matter can be emitted directly (“primary aerosol”) or formed in the atmosphere by gas-to-particle conversion processes (“secondary aerosol”). Atmospheric aerosol particles range in size from a few nanometers (nm) to tens of micrometers (μm) in diameter [1].
By-Product
By-products are formed in emissions control processes due to incomplete mineralization. Ideally, pollution is completely broken down or trapped; often this is not the case.
Contact Time
The contact time t is a crucial metric in characterizing a pollution control system, aiding design and allowing comparison between different systems. It is the ratio between the length of the treatment system l, for example, the contact region of a scrubber, catalyst, or adsorbent, and the velocity of air flow v. In all, \( t=l/v \). The treatment system can be described using a first-order removal rate k, linking the pollution’s input and output concentrations Cout and Cin [2]:
Cout = Cin · e−kt
Energy Intensity
The energy intensity in the pollution control system can be described using the specific energy input (energy input per mass of air, e.g., J/kg) or the volumetric energy input, also called the energy density (e.g., J/m3).
Explosion Limits and Range
A mixture of a given combustible compound in the air is typically explosive over a range extending from the lower explosion limit to the upper explosion limit [3]. The limits are given in %(v/v). The lower limit is the concentration below which flame cannot spread and vapor doesn’t ignite from a spark. The upper limit is the concentration above which a flame does not spread. For example, the explosion range for ammonia is 15–28% [3]; for methane, 5–15% [3]; for benzene, 1.2–7.8% [3]; and for formaldehyde, 7.0–73% [4].
Exposure Limit
The exposure limit describes the legally allowable average concentration a human can be exposed to for a given period. It can be expressed as an 8-hour time-weighted average or a yearly average. Exposure limits assure workers health and safety in different fields of employment.
Externality
An externality is a cost or benefit imposed on a third party unrelated to those who buy and sell [5]. Positive or negative effects on the third party are called positive and negative externalities, respectively [6]. For example, if one party buys a tree and plants it, the buyer and seller benefit, and others may also benefit from the shade and fruit. Or, if one party buys a leaf blower with a polluting two-stroke engine, buyer and seller benefit, but others may be impacted by air pollution and noise.
Global Warming Potential (GWP)
The global warming potential is a metric that allows direct comparison of many different climate forcing agents. The GWP represents the amount of heat trapped in the atmosphere by a kilogram of the compound of interest relative to the heat trapped by a kilogram of CO2. Heat-trapping is determined by integrating the radiative forcing over a defined time period called the time horizon [7]. For example, the global warming potential for methane is 72 over a 20-year time horizon [8].
Green Chemistry
Green chemistry is a pollution prevention method that focuses on reducing the use and production of hazardous substances.
Pollution
Pollution is any substance introduced into the environment that has harmful effects.
Removal Efficiency
The removal efficiency (RE%) is a measure of a pollution control system. It is determined for a specific component based on its concentration at the inlet (Cin) and outlet (Cout) [2]. \( RE\%=\left(1-\frac{C_{out}}{C_{in}}\right)\cdotp 100 \). Note that the removal efficiency, by definition, does not consider the formation of by-products.
Pressure Drop
Pressure drop is a difference in pressure between two defined points[2].
Δp = p2 − p1.
For example, there will be a pressure drop across any system that resists air flow.