Hydrocarbon Processing - April 2021 - GP-17

SPECIAL FOCUS: GREEN TECHNOLOGIES

Obtain accurate NOX values for strategies
to reduce emissions from combustion
G. Y. ZHAO, L. LIU and M.-S. LI, Sunree Technology Development Co., Ltd., Dalian, China

In the process of developing low-nitrogen-oxide-emissions
(NOX ) combustion appliances, the request for the volume of
NOX emissions from the tail flame is given in milligrams/kilowatt hour (mg/kWh) in almost all national and regional standards and related certifications. However, the instrument that
measures NOX in the exhaust tail flame of the combustion reports only in ppm or mg/m3. This requires the calculation of
the NOX in mg/kWh, based on the measured NOX in ppm or
mg/m3 and related data for these specific combustion systems.
This article summarizes how the combustion industry presently converts ppm to mg/m3 and introduces a concept for
measuring the emission rate of a combustion system. With this
concept, a formula can be derived to calculate the NOX produced by combustion in mg/kWh. The combustion of methane and propane are used as examples in a demonstration of the
measured ppm or mg/m3 concentration of NOX , along with the
the CO2 or O2 concentration in the tail flame, to calculate the
NOX emissions in mg/kWh.
This discussion explains how, when applying various methods to reduce NOX emissions from the combustion process, the
traditional measurement results of NO2 content (accounting
for 5%-10% of NOX) can give an estimated result. However, to
obtain accurate NOX values, it is necessary to precisely measure
NO value, as well as NO2 value. More accurate measurement of
emissions values and amounts aids in emissions reductions for
combustion, thereby helping control air pollution.

Incentives for accurate emissions measurement. Immense
economic growth in China since the 1980s has resulted in significant air pollution in major cities, which poses a serious
threat to public health. However, decades of hard work and investment by the municipal government have paid off, resulting
in a dramatic reduction in air pollution.
The Beijing 2013-2017 Clean Air Action Plan1 is the most
comprehensive and systematic pollution control program
put into practice in Beijing to date. From 2013-2017, emissions of SO2 , NOX , volatile organic compounds (VOCs) and
particulate matter (PM2.5) decreased by 83%, 43%, 42% and
55%, respectively (FIG. 1, left). However, during the same time
period, changes in major air pollutant emissions in the areas
surrounding Beijing (including Tianjin, Hebei, Henan, Shandong, Shanxi and Inner Mongolia) were not as desirable (FIG. 1,
right). Other areas in the country face the same problem. To
clean China's air supply, numerous issues must still be addressed; this article was written with this task in mind.
NOX emissions caused by combustion are an important factor in the formation of air pollution and smog.2-5 NOX , which
comprises mainly NO and NO2 , is the general term for a group
of highly reactive gases. Most nitrogen oxides are colorless and
tasteless; however, in many cities or densely populated areas,
the pollutant NO2 and other particles in the air often form a
reddish-brown smog or haze.
When NO reacts with O2 in the air under sunlight, ozone

350

Pollutant emissions in Beijing, kitotons

300
250

-42%

200
-43%
150
100
-59%

-83%
50
0

Pollutant emissions in areas surrounding Beijing, kitotons

12,000
Dust
Solvent use
Transportation
Residential
Industry
Power and heating

Solvent use
Transportation
Residential
Industry
Power and heating

10,000
-24%

0.2%

8,000
-59%
6,000
4,000

-34%

2,000
0

2013

SO2

2017

2013

NOx

2017

2013

VOCs

2017

2013

PM2.5

2017

2013

SO2

2017

2013

NOx

2017

2013

VOCs

2017

2013

PM2.5

2017

FIG. 1. Changes in anthropogenic emissions of SO2, NOX, VOCs and PM2.5 in Beijing, 2013-2017 (left). Changes in major air pollutant emissions
in the areas surrounding Beijing (including Tianjin, Hebei, Henan, Shandong, Shanxi and Inner Mongolia), 2013-20171 (right).
Gas Processing & LNG | MARCH/APRIL 2021

Hydrocarbon Processing - April 2021

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