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Sun Sep 8, 2019, 04:22 PM

Unexpectedly Increased Particle Emissions from the Steel Industry Using Desulfurization Technology.

The paper I'll discuss briefly in this post is this one: Unexpectedly Increased Particle Emissions from the Steel Industry Determined by Wet/Semidry/Dry Flue Gas Desulfurization Technologies (Li et al, Environ. Sci. Technol. 2019, 53, 17, 10361-10370)

Although extreme weather is likely to overtake it in the near future, the deadliest component of dangerous fossil fuel waste has been air pollution, which kills 7 million people per year, a portion of the death toll resulting not from the combustion of dangerous fossil fuels, although they dominate air pollution, but from the combustion of biomass. The chief component of air pollution that kills people is particulate matter, although the acid gases (sulfur oxides and nitrogen oxides) and ozone also contribute on a fairly grand scale.

There are many technologies for addressing sulfur oxides and I've written about some here recently. Not all dangerous fossil fuels are consumed for power plants and transport devices; some are consumed for material usage. The paper under current discussion suggests that there is no free lunch, using one technology can impact others.

From the introduction:

Severe haze pollution associated with fine particulate matter (PM), i.e., PM2.5 (PM with an aerodynamic diameter less than 2.5 μm), has frequently occurred in China in the past 2 decades.(1−3) Aiming to reduce PM emissions from anthropogenic sources and improve air quality, the Chinese government has promulgated strict regulations and standards for most major emission sources and updated them every few years. The strictest regulation, also called the “ultralow-emission” standard, has been implemented for pollutant emissions from coal-fired power plants (CFPPs) since 2014.(4) By the end of 2017, approximately 71% of CFPPs had already met the ultralow-emission standard (PM < 10 mg/Nm3, SO2 < 35 mg/Nm3, and NOx < 50 mg/Nm3) by employing various ultralow-emission technologies. Ultralow-emission technologies for high-capacity CFPPs mainly include selective catalytic reduction (SCR), electrostatic precipitators (ESPs), and flue gas desulfurization (FGD) combined with wet ESPs, while air pollution control devices (APCDs) for low-capacity CFPPs are more diverse, including circulating fluidized bed (CFB)-FGD, selective noncatalytic reduction (SNCR), electrostatic fabric filters (FFs), and semidry limestone FGD.(5−9) As a benefit of the ultralow-emission standard, the amounts of the pollutants PM, SO2, and NOx emitted from CFPPs in 2017 were approximately 18.6, 70.0, and 46.8% less than those in 2013, respectively.(10)

Pollutant emissions from the nonpower industry have recently attracted increasing attention as CFPPs have significantly reduced their emissions, especially those from one of the major industrial sources, i.e., steel plants.(11−13) A total of 17.1–36.9% of the atmospheric PM2.5 in many industrial cities has been attributed to emissions from steel plants, as suggested by source apportionment investigations.(14−16) China has been the largest steel producer in the world since 1996 (837.7 Mt in 2017, approximately 49.2% of the total production in the world).(17,18)Figure S1 shows that the relative contribution of primary PM2.5 emissions from the steel industry to total anthropogenic emissions grew from 5.4 to 8.2% from 2005 to 2014 in mainland China, while the relative contribution from CFPPs decreased from 9.5 to 5.1% in the same period, mainly attributed to the ultralow-emission requirement. Because steel emission standards lagged behind those for CFPPs during this period, the steel industry has emitted more PM2.5 than CFPPs since 2008.(17,18) Aiming to improve local air quality, Hebei Province in North China has implemented an ultralow-emission standard for steel plants starting in 2019.(19) The emission parameters for sinter flue gas in the Hebei ultralow-emission standard are the same as those for CFPPs. Although there is still no national standard for steel plants similar to the ultralow-emission standard for CFPPs deployed in mainland China, the detailed requirements of pollutant emissions for the steel industry have recently been under discussion with regard to standard feasibility and flue gas complexity.

The whole iron and steel producing process, mainly including sintering/pelletizing facilities, blast furnaces, basic oxygen furnaces, electric arc furnaces, and steelmaking furnaces, can generate pollutant emissions.(20,21) The sintering process is the major emission source of most pollutants, including PM, SO2, and NOx, with relative contributions of approximately 30–45, 70, and 90%, respectively, in the whole process.(13,22) Sintering flue gases are generally much more complex than those of CFPPs, exhibiting traits such as variable concentrations/compositions of pollutants, including SO2 and unknown corrosive gases, large temperature fluctuations ranging from 80 to 180 °C, and high variations in oxygen content ranging from approximately 10 to 15%...

It appears that desulfurization technologies designed to address acid gases have had an effect on the particulate emissions.

The wet flue gas desulfurization discussed herein involves the use of limestone and ammonia.

Some pictures from the text:

The caption:

Figure 1. Schematic configuration of APCDs and sampling sites. (a) Limestone and ammonia WFGD system combined with a WESP. (b) Semidry CFB-FGD system combined with an FF. (c) Activated coke dry FGD system

The caption:

Figure 2. Mass concentrations of PMs (a) and species concentrations in PM2.5. WSIs (b), elements (c), and carbonaceous components (d) at the FGD inlets/outlets of the five tested sinters. Note: “Other” WSIs include F–, Br–, NO3–, Na+, and Mg2+; HMs include Mn, Cd, V, Cr, Ni, Cu, Zn, As, and Pb; OC1-3 is the sum of OC1, OC2, and OC3; other elements include P, Sn, Sb, Sc, Ti, Co, Se, and Br.

The caption:

Figure 3. PSDs of PM sampled at the inlets (black line) and the outlets of the five tested FGD systems via high-temperature DLPI+.

The caption:

Figure 4. Chemical composition of segregated-size PMs collected at (a) the FGD inlet (S-1,2,3) and 3 stacks after different FGD systems: (b) limestone, (c) ammonia, and (d) activated coke. The PM was sampled via high-temperature DLPI+.

The caption:

The caption:

Figure 5. Relative contributions of desulfurization byproducts with major chemical compositions and primary PMs from various FGD processes ((a) limestone, (b) ammonia, (c) activated coke, and (d) CFB) in averaged PM2.5 emissions in flue gases at stacks.

It must be said however, that the authors state that it is not clear that the particulates involved desulfurization technology while contributing to Chinese haze, are not the normal carcinogens associated with coking.

Some text:

The FGD system, an end-of-pipe technology before the stack currently used in the steel and iron industry, determines the emission characteristics of PM to different degrees. WFGD systems carry part of the desulfurization slurry and the water-soluble byproducts, which contribute to the emitted PM concentration after desulfurization and subsequent WESP treatment. Compared to the limestone WFGD, the ammonia WFGD system contributes a higher mass ratio of emitted PMs after desulfurization due to the high solubility of its byproducts and slurry, as well as the heterogeneous byproducts from the reaction between the desulfurizers and acid gaseous species. The semidry and dry FGD systems remove pre-existing particles from the FGD inlets with high efficiency, mainly via physical processes of collision and filtration, while the number of new particles in the FGD devices is directly increased by powders of the desulfurizers and their byproducts.

Figure 5 summarizes the relative contributions of the newly generated components from the FGD systems to PM emissions in the stack. The estimation of newly generated components originating from FGD systems is estimated based on the assumption of the most abundant metal elements (i.e., K and Fe), which are increased by FGD desulfurizers and their byproducts (see the description in the Supporting Information text). Relative mass ratios of 16.5, 63.4, 59.4, and 70.7% in the emitted PM2.5 components are replaced by FGD desulfurizers and their byproducts for limestone WFGD, ammonia WFGD, semidry CFB-GFD, and activated coke dry FGD systems, respectively. The 16.5% replaced components of PM2.5 in the limestone WFGD outlet are occupied by SO42– (9.1%) and Ca (2.3%), while the 63.4% in the ammonia WFGD outlet are dominated by SO42– (43.1%) and NH4+ (14.2%). The 59.4% increase in components in the CFB semidry FGD outlet was mainly attributed to Ca (22.6%) and SO42– (13.1%), and the higher proportions of other compounds may be derived from impurities of the desulfurizer itself or unreacted hydrated lime. The PM2.5 in the activated coke dry FGD outlet possesses a high ratio of EC (39.9%), OC (14.4%), and NH4+ (14.2%). The proportion of byproducts in PM2.5 in the ammonia WFGD, activated coke dry FGD and CFB semidry FGD is over 60%, but this is not the case in the limestone WFGD. The smaller effect on PM2.5 component characteristics at the limestone WFGD outlet could be attributed to its relatively mature desulfurization process (optimal size of spraying slurry droplets) and the efficiency of removing entrained droplets of enriched byproducts by its demister and WESP. Limestone WFGD is the dominated technology (about 90%) for reducing SO2 in CFPPs. Since the concentration of PM is greatly influenced by the scouring intensity of desulfurization slurry and the effect of flue gas carrying. High-efficiency WESP has been commonly installed in front of the stack to effectively reduce the final PM emission to meet the “ultralow-emission standard” in CFPPs recently.(5) Compared to that of CFPPs, more attention about the newly generated components from the FGD systems to PM emissions should be paid for the steel industry.


In any case, the steel industry is an environmental problem that is not generally addressed in some of the wishful thinking we hear about climate change.

Have a pleasant Sunday evening.

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