Introduction to Emissions

• The term of Emissions is used to describe the gases and particles which are put into the air or emitted by various sources.
• An emission comprises one or more specific greenhouse gases or air pollutants originated from all source categories in a certain geographical area and within a specified time span

• Hot gases and particles emitted from coal-fired thermal power plants. Solid  Fuel contains a high carbon index and unburnt carbon particles are exhausted at higher altitudes

 Quantification of Emissions

• Emission index” (EI): The EIi for a certain chemical species is defined as the ratio of the mass of the pollutant species i to the mass of fuel burned

• Assuming that CO2, CO, and unburned hydrocarbons are the major combustion products and all other species are negligible Emission index” (EI)

•   EI for automobile or power generation applications: mass species emission(MSE, units g/(kW-h)) is used and its definition is

where  mf is the fuel mass flow rate (kg/h), W is the brake power generated (kW)

•  For furnace applications: the level of pollution is often expressed as

•      The natural gas industry uses the following expression

Major Types of Air Pollutants

•  Mole fraction of species for τres >= τchem

 

•         τres <  τchem : Combustion is incomplete. CO emissions will be high.
•          Mole fraction of species for τres < τchem

 Effect of Temperature on Emissions

• Temperature peaks near the stoichiometric equivalence ratio, ϕ = 1
• Trends of emission versus ϕ show that lean combustion can achieve low emissions
• Emissions reductions and potential difficulties in achieving lean combustion: flame stability becomes an issue when combustion temperature is low
• Effect of flame temperature on emissions

• Effect of flammability on emissions 

• Effect of flame temperature on emissions

• CO emissions are minimized at slightly lean equivalence ratios;
• The reaction rate constant of the “wet” CO oxidation route increases with temperature but not a strong function of temperature

• Effect of equivalent ratio on CO emissions

• Effect of temperature on reaction rate

Methods of NOx Formation 

 Effect of Temperature on NOx

• Predicted NO formation rate versus temperature showing less thermal NO formation when temperature is below 1,800 K.
• The right branch is for rich mixtures (equivalence ratio >1) and the left is for lean combustion
• Effect of equivalent ratio and temperature on NOx emissions

•        Effect of  temperature on types NOx emissions

 Technical Methods of NOx Reduction

•  Many industrial practices have been developed to reduce NO pollutions

Combustion Modification and Post Combustion Controls

 

 Using Staged air for combustion in Boiler

 Air staging in boiler to control NOx

 

 

 

 Ammonia (NH3) Injection in Flue Gases

                      

Staged Air/Fuel Burner

       

Water Injection

 Flue Gas Re-circulation

Measurement of Emissions 

Vehicular Emissions:

Flue gas analyzers and measurement principles

Power Plant Emissions

• Power plant emissions can be measured by sampling flue gases generated by boiler at different locations of ducts.

• The following parameters are commonly measured or conterminously monitored in thermal power plant to control the emissions
•  Flue gas monitoring systems for boiler

• The Continuous Emission Monitoring System (CEMS) is a facility to measure flow, dust, the concentration of air pollutants (such as SO2, NOx, CO etc), and other parameters according to requirements. Required parameters depend on the type of stationary source.
• Fore more details, click here: Horiba Continuous Emission Monitoring System

 Measurement points for thermal power plant

 CFD Modeling of Pollutants

For more detail refer: Rection Eng.International Pollution Modeling

1 Modeling Emission from the Terrain

Using CFD for Cleaner Fireplace Design

• • J. Valentine, M. Cremer, K.Davis,J. J. Letcatvits, S.Vierstra, CFD Modeling for Design of NOX Control System for Two Boiler, Reaction Engineering International

• • Z. Man, F.U/Zhenbo, L. Yuzven, Li Jibao, CFD Study of NOx Emissions in a Model Commercial Aircraft Engine Aircraft, Chinese Journal of Aeronautics, 25 (2012) 854-863

• • R. Zadghaffaria J .S. Moghaddas, Z. Rahimiaharas, Numerical Investigation of a Burner Configuration to Minimize Pollutant Emissions, APCBEE Procedia, 3 (2012) 177-181(2012) 854-863