Carbon dioxide emissions from industrial processes come from chemical reactions or physical changes in the production of cement, lime, steel and calcium carbide (except for energy activities).In 2019, China produced 300 million tons of lime annually, accounting for 70.75 percent of the world’s total.According to the China Building Materials Association released “China Building Materials Industry Carbon Emissions Report (2020)” : In 2020, the cement and lime industries ranked the top two building materials industry carbon dioxide emissions, respectively, up 1.8% and 14.3% year on year.In 2020, carbon dioxide emissions from the cement industry were 1.23 billion tons, up 1.8 percent year on year, with coal combustion emissions up 0.2 percent and industrial production emissions up 2.7 percent.In addition, the electricity consumption of the cement industry can be indirectly translated into about 89.55 million tons of CO2E. Carbon dioxide emissions from the lime-gypsum industry were 120 million tons, up 14.3 percent year on year, among which coal combustion emissions rose 5.5 percent year on year, and industrial production emissions rose 16.6 percent year on year.In addition, the electricity consumption of the lime-gypsum industry can be indirectly translated into approximately 3.14 million tons of CO2E. That adds up to about 20 percent of domestic carbon dioxide emissions.

 

In lime production, according to the quality requirements of desulfurized limestone, calculated according to the purity of 90%, each ton of lime calcined produces carbon dioxide ~ 400kg. To burn one ton of lime in a vertical kiln, about 140 kg of standard coal is used. If the calorific value of coal is 6000 kcal, it will increase by 15%, consume ~ 160kg, and emit 470kg carbon dioxide according to 80% carbon content. The combined CO2 yield of the two can reach 870kg.

 

CaCO3=CaO+CO2(g)

MgCO3=MgO+CO2(g)

2C+O2(g)=2CO(g)

2CO(g)+O2(g)=2CO2(g)

CaO+H2O=Ca(OH)2

Ca(OH)2+SO2(g)=CaSO3+H2O(g)

 

In addition to building materials industry, lime is also widely used in flue gas purification field. In hazardous waste disposal industry, when lime is directly used for dry deacidification, the utilization rate is usually below 30%. In the waste-to-power industry, when lime is used for semi-dry deacidification, the utilization rate is usually around 50%. According to lime content > 85% calculation, this equivalent to the removal of a ton of sulfur dioxide requires about 2.1 ~ 3.5t of lime, the total emissions of carbon dioxide 1.8~3.0t.

 

When using sodium based dry deacidification, take the baking soda desulfurizer launched by Al Environmental Protection as an example, each ton of sulfur dioxide removal needs to consume 2.63t baking soda, release 1.38t carbon dioxide. Because baking soda is made by reaction of soda as raw material and recycled carbon dioxide in a ratio of 1:1, the actual release amount is reduced by 1/2, that is, the release amount is 0.69t.

 

Na2CO3+CO2(g)+H2O=2NaHCO3

 

2NaHCO3+SO2(g)+1/2O2(g)=Na2SO4+H2O(g)+2CO3(g)

Comparing the two methods, it can be seen that for each ton of sulfur dioxide removed, the sodium-based drying method can reduce carbon dioxide emissions by 1.1 ~ 2.3t compared with the calcium-based drying method. If the power consumption of lime, slavered lime and other pulverizing processes is added, the carbon dioxide reduction will be even more significant.

 

The actual annual capacity of our municipal solid waste incineration plant has increased to more than 110 million tons. According to the estimate of 6 ~ 10kg of slaked lime used per ton of waste incineration, the annual consumption is about 1 million tons. If it is replaced by baking soda dry deacidification, it can reduce carbon dioxide emissions by 1 ~ 2 million tons per year.In hazardous waste disposal, coal-fired power generation and other industries, a large number of slaked lime is also used in flue gas purification. With the increasing environmental protection requirements for lime mining, crushing and calcination facilities, more energy saving, environmental protection and emission reduction of sodium based dry deacidification will be applied in more industrial scenarios, which is expected to reduce carbon dioxide emissions by more than millions of tons.

When talking about halogen free radicals (especially chlorine free radicals), one must think of the stratospheric ozone hole caused by halogen elemental compounds (freon, etc.).However, over the last 10 years of studying the troposphere, scientists have gradually discovered that halogen radicals play a different role.They can affect the concentration of classical free radicals (OH, HO2.RO2) in the atmosphere by rapidly oxidizing a range of hydrocarbons, thereby promoting the production of ozone and controlling the concentration of a variety of atmospheric pollutants.At present, most studies on halogen free radicals focus on nitacyl chloride (CINO2) and chlorine gas (CI2). The chlorine free radicals produced by their photolysis can affect the atmospheric oxidation.But are there other halogen activation channels in contaminated areas that contribute halogen radicals? How big is their impact? None of this is clear.

 

In the winter of December 2017, our research team carried out a comprehensive field observation experiment on active halogens (Cl2, Br2, HOCI, HOBr and BrCI) in China in the North China Plain (Wangdu, Hebei Province), and unexpectedly found a large number of unexpected active halogens in this region. The most active Brcl (the highest concentration of Brcl was 482ppt).BrcI can be photolysis in atmosphere and release bromine radical and chlorine radical.Thus, BrCl is both an active bromine compound and an active chloride. This study is the first ground observation in the world to report a persistent high BrCl concentration, which is 10 times greater than the maximum observed on the ground in the Arctic region, except the Arctic study. The discovery was shocking.In addition, in March 2018, the research team also observed a high BrcI(up to 190 PPT) at the top of Mount Taishan (1465 Ma.S. 1.), 300km from the observation site in Hebei Province. But where do such high concentrations of active halogens come from?

The analysis of the observed data shows that there is a strong correlation between the active bromine substance and the emission indicator of coal burning. Based on further analysis of the observed data, the researchers confirmed that coal burning in the region during winter can emit large amounts of chlorine and bromine particulate matter and active bromine compounds.Furthermore, by further calculating the chlorine and bromine content of loose coal reported in China in 2017 and the literature, the high concentration of active bromine compounds and chlorine and bromine particulate matter observed in the North China Plain in winter of 2017 can be reasonably explained by the amount of loose coal burned in the region where the observation was made.The heterogeneous reaction between active bromine compounds and chlorine-containing particles leads to the generation of BrCl, which contributes both bromine and chlorine free radicals through photolysis.

In addition, a nitrate-related photoactivation pathway was found to maintain the diurnal concentration of active bromine substances. Therefore, high concentration of active halogen substances (especially BrCl) may be prevalent in coal burning areas in northern China in winter.

What effect does such a high concentration of active halogens have on the atmosphere?

In order to further explore the contribution of active halogen compounds to atmospheric oxidation and ozone generation, the research team independently built and developed a chemical box model containing chlorine and bromine. This model is the most comprehensive model including chlorine bromide chemical vapor phase mechanism in the world. The study found:

1. The contribution of BrCl to chlorine and bromine free radicals in the atmosphere is more than 50%. In previous studies, nitryl chloride is mainly activated at night, so the contribution of daytime to chlorine free radicals is limited. However, BrCl has a diurnal activation mechanism and can continuously release chlorine and bromine free radicals, which can not be ignored.
2. The two free radicals chlorine and bromine can greatly enhance the oxidation rate of volatile organic compounds (alkanes up to 180%, aldehydes and ketones up to 90%), at the same time can increase the average concentration of classical oxidants (OH, HO2, RO2) in the atmosphere by 25%, 50% and 75%, and increase the net ozone generation rate by 55%. The enhancement of atmospheric oxidation can accelerate the generation of secondary particulate matter.
3. In addition, the resulting bromine free radicals can greatly enhance the oxidation of elemental mercury to divalent mercury. Oxidized divalent mercury is toxic, soluble in water, and easy to enter the ground and ecosystem through deposition. The North China Plain is one of the regions with high concentrations of elemental mercury in the world. Therefore, divalent mercury generation and rapid deposition facilitated by high concentrations of bromine free radicals may significantly increase the risk of toxicity to humans and ecosystems in the areas of discharge.

 

As a result, the study suggests that in the future, in addition to carbon dioxide, particulate matter, and sulfur-nitrogenous substances from coal-burning activities, close attention should be paid to halogens and mercury. This study provides a new scientific basis for controlling rural coal burning in northern China and promoting clean heating work such as “coal to gas” and “coal to electricity”.

 

The co-first authors of the paper are Xiang Peng and Weihao Wang, PhD students in the group of Professor Tao Wang of the Hong Kong Polytechnic University, who is the corresponding author of the paper.Jianmin Chen, Fudan University; Yujing Mou, Ecology Center, Chinese Academy of Sciences; Likun Xue, Shandong University; Jinhe Wang, Shandong Jianzhu University; Academician A.R.Ankara, USA; Alfonso Saiz-Lopez, Spain; and Christian de France Professor George and other institutions and many scientists participated in this research, which provided important observational data and analysis support for this research.

1. Basic concept of PM2.5

In recent years, China has become one of the most smoggy regions in the world, with a high concentration of PM2.5. According to a research report by Ma Guojun, professor senior engineer of Guodian Environmental Protection Research Institute and a consultant to the World Bank’s FGD project, there is still much room for improvement in the reduction of PM2.5 in coal-fired power plants.

PM2.5: particulate matter with an aerodynamic equivalent diameter of 2.5 microns or less;

PM2.5 comes from natural and man-made sources of pollution;

PM2.5 is not a single component of air pollutants, but a complex and variable air pollutant composed of a large number of different chemical components

 

The main components of PM2.5 are sulfuric acid, ammonium bisulfate, ammonium sulfate, ammonium nitrate, elemental carbon C and organic carbon. PM2.5 emitted directly by pollution sources is called “primary particle”; Gaseous pollutants discharged from pollution sources condense or undergo complex chemical reactions in the atmosphere to produce PM2.5, which is called “secondary particles”.

 

According to the “Beijing Air Quality Standard Strategic Study” carried out to ensure the air quality of the 2008 Beijing Olympic Games, the composition of PM2.5 in Beijing is as follows:

29% Industrial coal

15% biomass combustion

13% secondary sulfate

10% motor vehicle

9% secondary nitrate

8% Dust

16% Others

 

2. Influence of PM2.5

2.1 Health hazards of PM2.5

PM 2.5 can be directly into the human alveoli, also known as pulmonary particulate matter;

PM2.5 causes three respiratory diseases:

As the carrier of viruses and germs, PM2.5 causes colds, tuberculosis and pneumonia;

PM2.5 can cause respiratory allergies, such as asthma and alveolitis.

PM2.5 can lead to weakened immunity and increase the incidence of lung cancer.

 

2.2 Influence of PM2.5 on atmospheric visibility

Atmospheric visibility is determined by the scattering and absorption of light by particles in the atmosphere:

If there are no particles at all, the scattering of light by atmospheric molecules is very small, and the visibility can reach 100-300km. Visibility can reach 30km in the ultra-clean city air; When the atmospheric visibility decreases to l0km and the relative humidity of the atmosphere is below 80%, it is defined as haze.

3. Coal burning flue gas and PM2.5

The contribution of coal flue gas to PM 2.5 varies between 10% and 25% depending on the region.

Characteristics of flue gas emission from coal burning:

Fixed point source; Large flue gas discharge; Organized discharge; Controllable emissions;

Reasonable inference: Coal enterprises will become the “leader” of strict control.

PM 2.5 emissions from coal flue gas can be divided into:

Filter particles (primary PM) : mechanical particles; The particles are large, 1~ 2.5μm;

Condensable particles (secondary PM’) : gas, vapor state; Generate a second PM in the environment.

The ratio of filtrable particles to condensable particles is about 1:3~1:1.

There is currently no control technology specifically for PM 2.5. Existing and mature APCs in the industrial sector are capable of removing PM2.5. But there are limits to efficiency or capacity.

 

4. SCR flue gas denitrification system

Impact of SCR flue gas denitrification system:

While reducing NOx in flue gas, SCR catalyst will catalyze the oxidation of about 1~ 3% SO2 into SO3, which will increase the condensable sulfuric acid aerosol in the coal flue gas with high sulfur content. The escape of excess ammonia will increase the concentration of ammonia salt in the flue gas.

There are the following methods to reduce the impact of SO3 generated by SCR on PM2.5:

Catalysts with low oxidation capacity for SO2 were selected. Disadvantages: expensive, unfavorable to flue gas mercury removal;

The disadvantages of setting DSI device in front of air preheater to remove SO3 in flue gas are: increased investment is needed, high price of absorbent and high operating cost.

 

5. cloth bag filter

In 2003, Lillieblad tested PM2.5 and mercury emissions from a high gas ratio bag filter in a Finnish coal-fired power plant. The bag was made of PTFE-coated PPS (polyphenylene sulfide) and had been in good condition for 31,000 hours. The test results are shown in the table:

The test results show that:

In the flue gas of bag filter outlet, PM1.0 is 3 ~ 6%, PM2.5 is 15 ~ 20% and PM10 is 79 ~ 88%. The increased emission of sub-micron particles in the tested bag dust collector is due to the small hole with a diameter of about 0.4μm in the bag coating.

The conclusion is that the collection efficiency of cloth bag filter is about 99.5% when the particle diameter is 0.2-3 μm.

6. Condensable particulate matter

6.1 Aerosols and colored plumes

The main sources of condensable particles from coal flue gas are SOx and NOx, and SOx is the main one. SO3 in flue gas combines with water in flue gas to form sulfuric acid aerosol with particle size < 0.3μm;After the sulfuric acid aerosol is discharged from the chimney and first enters the atmosphere, it reacts with the positive ionization in the environment to produce secondary PM2.5 (near-ground pollution). SO2 in flue gas is oxidized to SO3 by photochemical oxidation, liquid phase oxidation and particle oxidation in the environment, and sulfate aerosol is formed. While SO2 has a lifetime of several days in the atmosphere, sulfate aerosols can migrate more than 1000km (long-range pollution).

Dry ESP and bag precipitator cannot remove condensable PM2.5!

6.2 Wet scrubber

The conventional wet FGD can not effectively remove fine particles: the conventional wet FGD will increase the concentration of discharged particles due to the removal of solid matter in the slurry. Conventional wet FGD could not effectively remove SO3.

Therefore, the wet scrubber of flue gas desulfurization has low removal efficiency for PM2.5. Wet desulphurization may also increase the emission of particulate matter, and ammonia desulphurization increases the risk of ammonia escape. Effective measures to reduce PM2.5 in the export flue gas of wet FGD:

 

1) WESP installed downstream of FGD has limited capacity and poor effect on ammonia desulfurization;

2) Install the dry FGD upstream of the FGD.

 

6.3 Dry FGD

Dry FGD can effectively remove acid gases such as SO3, HCl and HF while removing SO2. Most of the terminal equipment of dry FGD is dust collector. If cloth bag dust collector is used, the problem of PM2.5 emission can be solved.

 

The dry FGD products of Solway, a Belgian soda manufacturer, introduced by Aier Environmental Protection, combined with its rich engineering technology and experience in atmospheric management, have built dozens of sets of dry FGD devices in China and run them reliably, making a contribution to the cause of atmospheric environment management in China!

According to the “Notice of Guangdong Provincial Department of Science and Technology on the Work of 2020 Guangdong Science and Technology Award” (Guangdong Science Letter District word [2020] 391), Now, the South China Branch of our company Guangzhou Aier Environmental Protection Engineering Co., LTD and the project partner Professor Wu Junliang participated in the 2020 Guangdong Science and Technology Award winning project “High air volume Low concentration industrial volatile organic pollution control strategy and key technologies and applications”. See the attachment for details.

 

Public notice: from August 7, 2020 to August 14, 2020, a total of 7 days.

 

During the publicity period, if you have any objection to the publicity content, please report in writing to the Science and Technology Office of the University (High and New Technology Development Section). If you reflect the situation in the name of an individual, please provide your real name (and signature), contact information and supporting materials of the reflected matters. If the situation is reflected in the name of the unit, please provide the name of the unit (with official seal), contact person, contact information and the supporting materials of the reflected matters. Any anonymous objection or objection beyond the time limit shall not be accepted.

 

https://s2.d2scdn.com/2020/08/07/Fl7AWfO3PCKkVrIlQ2CTYHXe3u9c.pdf

On July 24, 2020, Kargon, the world’s top activated carbon brand manufacturer, brought its technical team, and Solvy, the world’s top group, brought baking soda technical elites to our company for communication.

General Manager Liu Liyan led the Aier team to receive, and the three parties fully exchanged views on “flue gas purification at the back end of incinerator” and “market application of activated carbon”.

Calgon, Solway and Aier are all leaders in their respective industries, consistently leading the way in the rapid pace of technological change. Our products are very expensive, which means the sustainable development of industrial products is expensive, aiming to provide customers with more cost-effective products and services.

Next, General Manager Liu Liyan will lead the Aier team to continue to carry out profound technical exchanges with leading enterprises in various fields, constantly upgrade and enrich the team experience, and provide customers with more professional technical services.

On June 4, 2020, Mr. Liu, the general manager of Aier Environmental Protection, and his team visited the hazardous waste plant in Huai ‘an. The plant was the first enterprise in the hazardous waste industry that successfully used baking soda to desulphurize.

In this project, baking soda drying method was used instead of slaked lime drying method, and part of the lye consumption was reduced, and 50% of the load of deacidification was undertaken. For more than half a year, the baking soda dry system has been running well, the sulfur and chlorine indexes have all reached the ultra-low emission requirements, and there has never been any gridding phenomenon, which greatly reduces the daily maintenance pressure on the site. At the same time, due to the reduction of the amount of lye, the pressure of the wet process and the three-effect evaporation at the back end has been significantly reduced, and the corrosion problem has also been significantly improved.

For the solutions and products provided by Aier, the owner’s Deputy General Manager Cheng expressed his high praise and sincere gratitude. Baking soda drying method not only brings environmental compliance, easy maintenance and stable operation, but also brings huge economic value.

1. Overview

At present, most domestic waste incineration power plants adopt the conventional flue gas purification process as follows:SNCR+ lime milk rotary spray semi-dry deacidification + slaked lime dry deacidification + activated carbon jet + bag dust collector + induced draft fan + chimney discharge.With the increasingly strict environmental protection requirements around the country, the emission standards for the waste incineration and power generation industry continue to improve, especially the NOx emission limit set by some provinces has been far lower than the European Union industrial emission directive（EU2010/75/EC），For example, the limit of nitrogen oxides in the Pollution Control Standard of Hainan Municipal Solid Waste Incineration (DB46/484-2019) is 120mg/m3, and the limit of nitrogen oxide emission concentration of waste incineration flue gas is below 80 ~ 120mg/m3.So more efficient, more applicable flue gas desulfurization and denitrification technology needs more and more prominent.

Comparison of emission standards of domestic waste incineration

2. SCR denitration traditional technology solution

2.1 Process Technology

Because the flue gas of waste incineration has the characteristics of high dust content and strong corrosion, the SCR denitration system must be set after the deacidification and dust removal system to ensure the normal operation of the catalyst.Catalyst is the core of SCR denitrification process, and the reaction temperature of catalyst is mainly divided into high temperature, medium temperature, medium low temperature and low temperature. Table 1 shows the main applications of catalysts at home and abroad:

At present, the domestic waste incineration and power generation industry mainly uses low-temperature catalyst. However, since the flue gas temperature after the rotary spray semi-dry deacidification and dust removal is below 140℃, and the appropriate temperature of catalyst reduction reaction in low-temperature SCR system is 160 ~ 180℃, it is necessary to consider adding the flue gas reheat system to heat the flue gas.

For the flue gas purification system with wet washing device, it is also necessary to set one or two GGH to recover part of the heat and reduce the heating steam consumption. The flue gas temperature needs to be raised is still around 30℃. Because the high pressure steam can be directly used for steam engine power generation, the value is very high, and the equipment and pipeline maintenance requirements are high, the heat loss is very large, so that the economic benefit level of the device is greatly reduced.

 

2.2 Existing Problems

(1) The flue gas temperature of rotating spray semi-dry deacidification and dust removal is below 140℃, while the optimal temperature of catalyst reduction reaction in low-temperature SCR system is 160 ~ 180℃,Therefore, it is necessary to increase the flue gas reheat system to heat the flue gas. If the flue gas temperature rises by 30℃, it needs to consume steam ~ 130kg/ ton of garbage. If this part of steam enters the steam turbine to generate electricity, according to the steam consumption of 5kg/ (KW·h), this part can generate 26KW·h/t of garbage.As a result of a large amount of steam consumption, resulting in a large increase in operating costs.

(2) The precision of rotary spray semi-dry deacidification and desulfurization is not high, and the efficiency of SO2 removal is generally about 85%. Although it can stably meet the requirements of the national standard, it is very unfavorable if the residual SO2 is oxidized into SO3 in the SCR catalyst bed.Because SO3 reacts with water and NH3 in the flue gas, ammonium sulfate and ammonium bisulfate will be generated. These sulfates, especially ammonium bisulfate, are a kind of sticky substance, which will cause corrosion, blockage, poisoning of the catalyst and shorten the service life of the catalyst.

 

3. Baking soda dry deacidification technology

3.1 Process Technology

This technology uses about 70 mesh special baking soda for desulfurization, and then grinds it into d90=30μm super fine soda powder,With air as the medium, it is sprayed into the deacidification tower by means of pneumatic conveying and mixed with high temperature flue gas of 180℃ ~ 210℃. At high temperature, sodium bicarbonate is decomposed into sodium carbonate Na2CO3, H2O and CO2,Due to the “popcorn” effect during decomposition, the surface area of the particles increases by more than 4 times, and they become extremely loose and porous highly active particles, which react quickly with various acidic gases such as SO2 and HCl in the flue gas，The removal rate can reach 95 ~ 99%, the reaction products are removed by the bag filter, the purified flue gas can reach: dust content ≤5mg/m3, SO2≤10mg/m3, HCl≤5mg/m3, temperature ≥170℃, and then enter the SCR denitration system.

 

3.2 Technical application advantages

(1) After using baking soda dry deacidification, the flue gas temperature entering SCR denitration system should not be lower than 170℃, which can meet the optimal temperature of catalyst reduction reaction in low-temperature SCR system and does not need additional steam to heat it up.

(2) Baking soda can not only remove SO2, HCl, HF, HBr and other substances, but also effectively remove the existing SO3 in the flue gas, reducing the content of SO3 into the SCR denitrification system, reducing the production of ammonium sulfate and ammonium bisulfate, ensuring the life of the catalyst and reducing the cost.

(3) Baking soda also has a certain synergistic denitrification effect. Sodium sulfite produced by the reaction of baking soda and SO2 has strong reducibility and can partially REDOX reaction with nitrogen oxides. The synergistic denitrification efficiency of baking soda is about 10 ~ 20%.

(4) With the mainstream configuration of rotary spray semi-dry deacidification, the efficiency of SO2 and HCl removal can reach 85% ~ 95%, which can stably meet the current national standard requirements.When the emission concentration is further reduced, the pursuit of higher deacidification efficiency often brings about a series of technical and economic problems, such as the increase of desulfurizer consumption, the increase of fly ash production, and the risk of clotting bags.At this time, the efficiency of SO2 and HCl removal can reach 95% ~ 99% by using baking soda dry deacidification with higher activity, and the best overall technical and economic results can be obtained.

 

4. Closing Remarks

Along with the continuous strengthening of our environmental management work, it is believed that in the near future, as itself is the green environmental protection project of household garbage incineration power generation industry, flue gas emission standard will be more strict, baking soda dry acid removal and SCR denitration system will be gradually promoted application, technical and economic advantages will be further developed.