1. Equipments for preventing air pollution
(1) Flue gas desulfurization (FGD)
Preventing air pollution is a cross boundary global problem. The emission of Oxysulfide sulfoxide _X,nitrogen oxide（NO_X）, carbon dioxide , chlorofluorocarbon and other effluent will cause severe harm to human as well as to ecology environment, thus the emission must be limited. Among these, the emission of SO₂ is the earliest problem people paid attention to, for the purpose of solving the harm caused by acid rain. Statistics show, the annual artificial emission of SO₂ is about 140 million tons/ year; in order to reduce the loss caused by acid rain, the global SO₂ emission each year should be reduced by 40 million tons. The emission of SO₂ mainly comes from power plants that burn fossil fuel. The method of using pre burn treatment, heavy oil desulfurization and adopting natural gas can only solve half of the emission, and the rest emission must be solved by way of flue gas desulfurization. In the end of the twentieth century, the capacity of all the flue gas desulfurization of the world is tantamount to 0.2 billion kw, each year, which can delete an SO₂ amount around 10 million tons, and large quantities of FGD are required to be installed in order to achieve ideal effect.

The flue gas desulfurization (FGD) processes include dry method and wet method, see the following table:

FGD process type

Wet method	Process type	absorbentabsorbent	Status of absorbing liquid	Material		Byproduct
	Lime-plaster method	Calcium sulfite CaSO3	Serosity	Calcium carbonate White lime Calces	CaCO3 Ca(OH)2 CaO	Plaster CaSO4·2H2O
	Mg-plaster method	Magnesium sulfite MgSO3 calcium sulfite CaSO3	Serosity	magnesium hydrate white lime calcium carbonate	Mg(OH)2 Ca(OH)2 CaCO3	Plaster
	Na2SO3-Glauber salt method	sodium sulfite Na2SO3	Solution	Caustic soda	NaOH	exhaust the Glauber salt liquid
	Sodium sulfite reclaim method			Caustic soda	NaOH	Na2SO3
	Sodium sulfite plaster method			Calcium carbonate White lime	CaCO3 Ca(OH)2 CaO	Plaster
	Sodium sulfite-sulfuric acid method			Caustic soda	NaOH	Sulfuric acid
	Diluted sulfuric acid-plaster method	Diluted sulfuric acid	Solution	Sulfuric acid Calcium carbonate	H2SO4 CaCO3	Plaster
	NH3-ammonia sulfate method	Ammonium sulfite (NH4)2SO3	Solution	Ammonium hydroxide	NH4OH	Ammonium sulfate (NH4)2SO4
	NH3- NH3-plaster method			White lime	Ca(OH)2	Plaster
	Al-plaster method	Alkalinity aluminium sulfate Al2(SO4)3Al2O3	Serosity	Aluminium sulfate Calcium carbonate	Al2(SO4)3 CaCO3	Plaster
	Mg method	Magnesium sulfite MgSO3	Solution	Magnesium hydrate	Mg(OH)2	Exhaust the bitter salt liquid MgSO4
Dry method	Activated carbon absorption method	Activated carbon		Activated carbon		Sulfur
	Spray drying method	Ca(OH)2 Na2CO3	Serosity	White lime Sodium carbonate	Ca(OH)2 Na2CO3	Plaster and others

The FGD in firepower plant mainly refers to the limestone-plaster technique, and the less used is sodium sulfite technique. In Japan, 60% of FGD is limestone-plaster technique, 30% is sodium sulfite technique, and 10% is vitriol sorbent technique; in Germany, 80% is limestone-plaster technique.

In the FGD technique process, the environmental conditions have large variations, and for different fuel, the content of corrosive medium contained in the flue gas is different, see the table below. In some desulfurization techniques, sulfuric acid must be added, and the corrosion can be more severe, thus under condition that the nonmetal lining cannot satisfy the requirements, stainless steel should be chosen. Under strict condition, Nickel-base anti-corrosion alloy must be chosen, and different anti-corrosion materials shall be chosen according to the content of chloride and PH value of the environment. In the desulfurization process, the components in the flue gas will be concentrated, at some points they can reach a very high concentration, for example, the chloride can sometimes arrive at more than 100 thousand ppm. And the right anti-corrosion material should be chosen according to the detailed situation.

Flue gas components

Medium components	Fire coal	Heavy oil
SOX，ppm NOX，ppm HCl，ppm HF，ppm dust，mg/m3	300-1000 100-200 10-40 5-30 100-200	500-2000 60-100 <2 <3 20-50

The anti-corrosion material in FGD equipments commonly involve general stainless steel, high performance stainless steel and nickel-base anti-corrosion alloy, see the following Table 1. And it commonly follows the principle in Table 2 for choosing material for the different equipments in FGD.

Table 1 - The anti-corrosion material for FGD

Material name	Main alloy components
316L 317L 317LM 317LMN 2205 double phase steel Alloy 255 254SMO 654SMO Incolog825 904L Soniero-28 20Nb-3 20Mo-6 HastellogG HastellogC-276 HastellogC-22	00Cr17Ni14Mo2 00Cr19Ni13Mo3 00Cr19Ni15Mo4 00Cr19Ni15Mo4N 00Cr22Ni5Mo3N 00Cr25Ni5Mo3Cu2N 00Cr20Ni18Mo6CuN 00Cr24Ni22Mo7NCu 0Cr22Ni42Mo3Cu2 00Cr21Ni25Mo5Cu2 00Cr27Ni31Mo3Cu 00Cr20Ni34M2Cu4N 00Cr23Ni34Mo6Cu3 0Cr22Ni44Mo7Cu2Nb2w 00Cr16Ni56Mo16w4 00Cr22Ni61Mo13w3Fe3
YUS 260 (Japan) YUS 270 (Japan)	00Cr20Ni15Mo3Cu2N 2Cr20Ni18Mo6CuN

Table 2 - The guide for choosing stainless steel and nickel alloy to make FGD washing tower

		Weak	Medium	Strong	Super strong
	Chloride ppm	100　　　500	1000　　　5000	10000　　50000	100000　　200000
Weak	PH6.5	316L　 　316L	316L 　　317M	Alloy 904L Alloy G3	Alloy G3　 Alloy 625
Medium	PH4.5	316L　 　316L	317M 　　Alloy 904L	Alloy G3　 Alloy G3	Alloy 625　Alloy 625
Strong	PH2.0	317LM　　317LM	Alloy 904L Alloy G3	Alloy G3　 Alloy G3	Alloy 625　Alloy C276
Super strong	PH1.0	Alloy 904L Alloy 904L	Alloy G3　 Alloy G3	Alloy G3 　Alloy 625	Alloy C276 Alloy C22

The status of stainless steel and anti-corrosion alloy of the operating FGD is shown in the table below. For the differences between fossil fuel and minor discrimination between desulfurization, in different countries, there exist differences in material application for the purpose of solving problems of flue gas desulfurization including uniformed corrosion, corrosion pitting, crevice corrosion, and condensate corrosion, but in consideration of anti-corrosion and cost of stainless steel, the super austenite stainless steel（654SMO）has better performance and price advantages.

The operating situation of stainless steel and anti-corrosion alloy in FGD equipments

Name of equipment	Material
Pre-washing tower container	00Cr17Ni14Mo2，HastellogG，00Cr19Ni13Mo3 C-276 alloy
Chill/absorbing tower container	HastellogG，Js-700，00Cr17Ni14Mo2 C-276，00Cr19Ni13Mo3，904L，317LM，Inconel625,654SMO，254SMO
Outlet pipe and reheater	Hastellog C-22 ( outlet pipe lining ), reheater pipes and the hull of 00Cr17Ni14Mo2, C-22, C-276, Inconel625, 317LM, 904L, 654SMO
Chimney	C-276, wallpaper steel lining YUS260, YUS270

2. Dust removal equipment.
In the industry areas including chemical processing, food and metallurgy, dust removal equipment is widely used. In some industries, the purpose of dust moving is to prevent pollution to the products by dust, and in most industry, the purpose is to reduce the dust pollution to the environment. Stainless steel is widely used to make anti-corrosion and heat resistant components in various dust removal equipments, see the following table:

Stainless steel in dust removal equipments

Name of the equipmet	Material
Cyclone dust collecting equipment	0Cr18Ni9 is used to make the dust receiving equipment and components that contact with corrosive gas
Venture scrubber	0Cr18Ni9: used when temperature >600℃ , to make air channel, air blower hull 0Cr17Ni12Mo2 00Cr17Ni14Mo2: scrubber, blade of the blower
Electric dust removal	0Cr17Ni12Mo2: scrubber hull, dust collector, blower hull, blower blade 0Cr17Ni14Mo2: discharge electrode

3. Waste water treating equipments
Living waste water and industrial waste water are the main sources for causing water contamination; for environmental protection, the waste water must be treated to reach qualified standards before exhausting or must be regenerated for usage. The treating methods include physical method, chemical method and biochemical method. These methods are commonly not used singly, but in combination, thus to achieve ideal results. The waste water treating technique does not use a lot of stainless steel, and only at some corrosive points that stainless steel is used. The application of stainless steel in waste water treating industries is shown in the following table:

The application of stainless steel in waste water treating industry

Name of equipment and part	Material
Filtration web, filter	0Cr18Ni9: Minutia filtration web , frame chain, slag filtrating components inside the filter
Precipitation slot, separating slot	0Cr18Ni9，0Cr17Ni12Mo2: For making the collector of corrosive waste water mud , stirrer
Neutralizing slot, drug adding container	0Cr18Ni9，0Cr17Ni12Mo2: For making the axis, wings of stirrer,
Filter	fastening piece
Centrifugal separator	0Cr25Ni6Mo2(SCS11), CD-4MCu cast copper
Pump, valve, instrument	0Cr18Ni9，0Cr17Ni12Mo2: The pump for transporting corrosive waste water, bobber of tank gauge, flow test riser
Ion exchanging equipment	0Cr18Ni9，0Cr17Ni12Mo2: Used to make the baffle for preventing resin over brimming

4. Ordure treatment.
The PH value of ordure is 7-9, but it contains small sums of H₂S and will require large sum of water for flushing, the environment is comparatively corrosive, some treating devices and equipments are made of anti-corrosion stainless steel, and the application of stainless steel in ordure treatment is shown in the table below:

The application of stainless steel in ordure treatment

Name of the equipment	Material
Filtration web for eliminating impurities	0Cr18Ni9
Spin-drier, screw punch, disintegrator	0Cr18Ni9
Heat exchanging pipe for deodorization with burning	0Cr18Ni9
Burning deodorization reaction room	0Cr18Ni9，0Cr25Ni20
Valves for digesting treatment method, inlet part for the air absorbed by booster	0Cr18Ni9
Deposit mud carrier for second treatment at the sedimentation basin	0Cr18Ni9