Gas purification technology

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This post was last edited by B0SS on 2017-3-19 21:30. Introduction to flexible membrane technology: The core of flexible metal membrane separation technology lies in intermetallic compound porous membrane materials, which are sheet-like in shape, with a thickness of 0.5–0.8 mm, and are flexible enough to be rolled into various shapes. It features good comprehensive mechanical properties, a high porosity rate, high separation efficiency, large flow capacity, and low filtration resistance. It is suitable for gas dust removal over a wide temperature range, with high precision and efficiency. It is widely used in the recovery of valuable dusts and in the separation of gases and solids at medium to high temperatures. It represents an upgraded version of bag filter and electrostatic precipitator technologies, addressing issues such as low filtration accuracy, bag burnout, insufficient processing capacity per unit area, and large equipment footprint. Principle: The dust removal mechanism of the flexible metal film dust removal system is as follows: Dusty, high-temperature gas enters the filter, where the dust is trapped by the flexible membrane, while the clean gas passes through the membrane pores and is sent to subsequent processes. The filter cake formed by the retention of dust by the flexible membrane is removed through backblowing and falls into the ash bin for reuse. Comparison of flexible membrane material parameters: Serial No., Item, Flexible Membrane, P84 Glass Fiber, Fluorocarbon Membrane, Glass Fiber, PPS Needle-Punched, Metas Needle-Punched. 1. Weight (g/m2): 800–1000, 800–900, 850–950, 900, 500, 600. 2. Thickness (mm): 0.5–0.8, 2.5–3, 2.4–3.2, 2.3, 2, 1.8. 3. Average pore size (um): 5–10, 60–120, 60–120, 60–120, 60–120, 60–120. 4. Porosity (%): 38–40, 20–25, 20–25, 20–25, 20–25, 20–25. 5. Pore size consistency: Consistent, Inconsistent, Inconsistent, Inconsistent, Inconsistent, Inconsistent. 6. Smoothness of pores: Smooth and smooth, Rough, Rough, Rough, Rough, Rough. 7. Air permeability (m3/m2·h): 1200–1300, 500–700, 200–800, Approximately 500, Approximately 700, Approximately 800. 8. Tensile strength in the machine direction (N/5×20cm): 8000, 1800, 1800, 2100, 1200, 800. Advantages of flexible membranes: ① High temperature resistance: up to 400°C (the bag does not burn). ② Corrosion resistance: Resistant to corrosion caused by H2S, SO2, SO3, etc. ③ High precision: 0.1μm, membrane pore size 10μm ； After filtration, it can reach up to <5mg/Nm3 ； ④ High flux: The flux per unit membrane area is more than 1.5 times that of cloth bags. ⑤ Low resistance: When handling the same volume of air, its resistance is 300 Pa lower than that of bag filters, resulting in approximately a 10% reduction in power consumption. ⑥ Smooth surface: Backflushing for dust removal is easier (bag filters suffer from severe dust accumulation). ⑦Long lifespan: No damage occurs with normal use (its lifespan is 1-2 years longer than that of high-quality cloth bags). ⑧ Good environmental performance: Equipment for processing the same volume of gas occupies about half the space required by bag filters; steel consumption is reduced by approximately half. The metal resources in the filter bags can be recycled once they reach the end of their useful life, eliminating the secondary pollution associated with bag filters. 2. Rigid membrane: A rigid metal membrane separation system that uses asymmetric membranes made of FeAl intermetallic compound porous materials, for which independent intellectual property rights exist, as the filtering elements. It is a **key new product incorporating over 30 patented technologies. The device features high-temperature resistance (up to 800°C), high filtration precision (with a minimum dust capture particle size of 0.1μm), online backwashing at high temperatures, high-temperature ash discharge, protection against high and low temperature inlet conditions, dew prevention, and prevention of tar film formation, as well as automatic detection and control functions. Meanwhile, the filter elements possess advantages such as high-temperature oxidation and sulfidation resistance, heat shock resistance, and wear resistance. Advantages of rigid membranes: ① The filter element is easy and convenient to install, with reliable sealing. ②The filter element can withstand high temperatures, enabling stable filtration at temperatures ranging from 200°C to 800°C; it is energy-efficient and does not cause the membrane to clog. ③The filter element has good thermal shock resistance and resistance to pressure fluctuations, and can adapt to variations in system temperature and pressure. ④The filter element exhibits good resistance to high-temperature oxidation and high-temperature sulfidation corrosion, making it suitable for the purification of high-temperature gas and gases from various industrial furnaces. ⑤The filter element is resistant to carbonization, with no high-temperature catalytic cracking. Rigid membrane filtration system – Key functions of the large-scale system: ① The filter elements exhibit resistance to oxidation at high temperatures, resistance to sulfidation, as well as tolerance to thermal vibrations and wear ； ②、Low-temperature intake protection ； ③, anti-dew, anti-tar film formation ； ④High-temperature online backblowing, automatic online ash discharge ； ⑤, automatic detection and control ； Application areas of intermetallic compound films: Serial number, Product model, Filtration temperature, Applicable industries, Functions and advantages: 1 SDN-800, 400–800°C, Hermetically sealed electric arc furnaces (ferroalloys, high-titanium slag, yellow phosphorus); High-precision filtration, capable of high-precision filtration at high temperatures ； Waste heat utilization, product recovery, purification of high-temperature flue gas, prevention and control of heavy metal pollution. Coal chemical industry (coal-to-oil, coal-to-gas, gasification furnace gas purification). Separation and recovery of arsenic during the smelting of non-ferrous metals. 2 SDN-400, 250–400°C; open-type electric arc furnaces (ferroalloys). High-precision filtration, compact design ； Achieve high-temperature filtration ； Waste heat utilization, product recycling, and environmentally friendly ultra-low emissions. Before the SCR process (power plants, steel mills, glass factories, cement plants): calcium carbide; coal chemical industry (conversion from wet to dry dust removal in gas stations); arsenic removal through pyrometallurgical processes (for metals such as copper, lead, tin, antimony, etc.); drying industries (titanium dioxide, feed, glass, ceramics, etc.); boiler industry (ultra-low emissions from industrial boilers, near-zero emissions from coal-fired power plants); coking industry; waste heat utilization. 3 SDN-250: 150–250°C; recovery of precious metals (indium, germanium, gold, silver, tungsten, molybdenum, etc.); high-precision filtration, suitable for small spaces ； Solve the problem of bag burnout; recycle products while ensuring environmental protection and ultra-low emissions. Recovery of valuable metals (comprehensive recovery of copper, lead, tin, antimony, etc.) Flue gas purification (in industries such as steel, calcium carbide, ceramics, cement, and glass) Carbon plants 4 SDN-100 Temperatures below 150°C Flue gas purification (in steel mills, power plants, calcium carbide plants, ceramics industries, etc.) High-precision filtration; compact in size; environmentally friendly with ultra-low emissions. Introduction to the main desulfurization process technologies 1. In-furnace desulfurization: Process principle: CaCO3 powder is sprayed into the furnace via pneumatic conveying; after CaCO3 decomposes and is calcined into CaO, it reacts with SO2 in the flue gas to form CaSO4, which is then removed along with the slag, thereby achieving desulfurization. The typical desulfurization efficiency is 60%-80%. Factors affecting performance: 1) Bed temperature: The optimal range is 850–900°C. 2) Particle size: The optimal range is 0.2–1.5 mm. 3) Ca/S ratio: The optimal range is 2–2.5; effects become minimal above 4.5. 4) Quality of limestone. 5) Method of adding limestone. 6) Sulfur content in coal. System advantages: 1) The system is simple and reliable in operation. 2) Desulfurization costs are low, as are the initial investment and operational maintenance costs. 3) The desulfurization products are found in fly ash and bottom slag; no by-products such as wet gypsum are generated, resulting in no secondary pollution. 2. Calcium–calcium double-alkali process: Principle – Desulfurization is carried out in a tower using a calcium sulfite suspension, which results in the formation of calcium bisulfite with high solubility (thus preventing scaling in the equipment). Then, calcium hydroxide reacts with calcium bisulfite in a circulation tank to regenerate calcium sulfite for reuse in desulfurization. Significance: This method theoretically explains and practically solves the problem of equipment scaling in conventional desulfurization processes, thereby ensuring the reliability of plant operation. Simplified process flow for calcium-calcium double-alkali desulfurization; Comparison with other methods: 1) Differences between calcium-calcium double-alkali method and foreign low-pH desulfurization methods. Calcium-calcium double-alkali desulfurization vs. Low-pH desulfurization: pH range – 6.5–7.5 vs. 4.5–5.0; Reaction mechanisms – CaSO3·1/2H2O + SO2 + 1/2H2O → Ca(HSO3)2; Ca(OH)2 + Ca(HSO3)2 → 2CaSO3·1/2H2O + H2O; HSO3- + 1/2O2 → H+ + SO42-; CaCO3 + H+ + SO42- → CaSO4·1/2H2O + CO2; Liquid/gas ratio – 3.0–5.0 (L/m3) vs. 10–26 (L/m3); Energy consumption – low vs. high. 2) Comparison between calcium-calcium double-alkali method and traditional Na-Ca double-alkali method. Purpose of each method – to prevent scaling; Desulfurizing agents inside the tower (first alkali) – CaSO3·1/2H2O (derived from Ca(OH)2) vs. Na2SO3 (derived from added Na2CO3); Desulfurization reactions inside the tower – CaSO3 + SO2 + H2O → Ca(HSO3)2; Na2SO3 + SO2 + H2O → 2NaHSO3; Scaling prevention mechanism – The product Ca(HSO3)2 has high solubility and does not crystallize; the product NaHSO3 also has high solubility and does not crystallize. Regenerants used in the regeneration tank (second alkali) – Lime vs. Lime; Regeneration reactions in the tank – Ca(HSO3)2 + Ca(OH)2 → 2CaSO3·1/2H2O + 1/2H2O; 2NaHSO3 + Ca(OH)2 → CaSO3·1/2H2O + Na2SO3 + 3/2H2O. Main advantages of the calcium-calcium double-alkali method: Use of lime or limestone as desulfurizing agents, no need for sodium-based chemicals, resulting in lower operating costs; prevention of scaling in the system, enabling continuous and stable desulfurization and dust removal; high desulfurization efficiency, ranging from 85% to 96.2% ； The liquid-gas ratio is relatively low, and the power consumption of the circulation pump is minimal. The internal components of the tower are made from imported materials, making them corrosion-resistant and durable. The system resistance is low; in most cases, there is no need to replace the induced draft fan. The removed SO2 separates from the water as insoluble solids, thus preventing any secondary pollution of the water body. 3. Zinc oxide process 1) Process description: This process is similar to the calcium–calcium double-alkali process. Utilize the zinc oxide dust available in the metallurgical industry for desulfurization, and recycle the by-products of this desulfurization process. 2) Process characteristics: This process is highly targeted; it offers significant advantages for enterprises that produce zinc oxide dust themselves. It enables “using waste to treat waste” and the reuse of waste materials. 4. Ammonia-based desulfurization: Process description: Ammonia-based desulfurization uses ammonia-containing substances such as aqueous ammonia (waste ammonia water), liquid ammonia (gaseous ammonia), urea, and ammonium carbonate as desulfurization agents. Its main by-product is ammonium fertilizer, and the desulfurization facilities do not generate any secondary pollution. Its basic technical principle is as follows: In the first step, there is an absorption process based on the reaction between SO2 and NH3 in an aqueous solution: SO2 + H2O + XNH3 = (NH4)XH2 – XSO3 (1). Thus, ammonia is used to remove SO2 from exhaust gases, yielding sulfurous acid as an intermediate product. The carriers of ammonia can be alkaline substances capable of producing ammonia, such as liquid ammonia (gaseous ammonia), aqueous ammonia, ammonium carbonate, urea, etc. In the second step, forced oxidation of ammonium sulfite is carried out using air: (NH4)XH2-XSO3 + 1/2O2 + (2-X)NH3 = (NH4)2SO4. This process converts the unstable intermediate product, sulfurous acid an, into the stable sulfuric acid an, thereby producing ammonium sulfate fertilizer for agricultural use. Ammonium sulfite can also be acid-hydrolyzed using sulfuric acid, nitric acid, phosphoric acid, etc., with by-products such as sulfur dioxide, sulfuric acid, *ao acid an, ammonium phosphate, and other products. Process flow: Characteristics of the ammonia-based desulfurization method – High desulfurization efficiency, with stable results of over 98%. Waste is converted into useful products, as the by-products of desulfurization are sulfuric acid and ammonium fertilizers. The system operates in a closed loop, resulting in “zero” wastewater discharge. The absorbent does not contain carbon, so it does not contribute to carbon dioxide emissions. The system has a short process flow, is easy to operate, and reliable in performance. Its energy consumption is low, only 50% that of the limestone-gypsum method. Operating costs are also low, and there is great market potential for sulfuric acid and ammonium fertilizers.

Introduction to denitrification technologies: Several methods for reducing NOx levels in flue gases: 1. Air staging combustion technology; 2. Fuel staging combustion technology; 3. Low-nitrogen burners; 4. Selective non-catalytic reduction (SNCR); 5. Selective catalytic reduction (SCR); 6. SNCR+SCR hybrid technology.

Principles of denitrification technologies: 1. Principle of the SNCR process – SNCR (Selective Non-Catalytic Reduction) involves injecting ammonia or urea at an appropriate temperature, where NH3 reacts with NOx to produce N2 and water, thereby removing NOx from the flue gases. Ammonium hydroxide (20%–25% concentration) is often used as a reducing agent. Optional reducing agents include aqueous ammonia, liquid ammonia, urea, and sulfuric acid solution. The performance of an SNCR system depends on temperature, residence time, turbulence level, oxygen content, and several other factors. The chemical equations for SNCR in removing NOx are as follows: 4NO + 4NH3 + O2 → 4N2 + 6H2O; 4NH3 + 2NO2 + O2 → 3N2 + 6H2O. Since 90% to 95% of the NOx in flue gases is in the form of NO, the first equation is the primary reaction equation. 2. Principle of the SCR process: Selective catalytic reduction (SCR) is a process in which, in the presence of a catalyst, ammonia or urea is injected to selectively reduce NOx levels in flue gases. The SCR process is widely used in internal combustion engines, power plant boilers, etc. In an SCR system, air-diluted ammonia is injected into the system, where it removes NOx from flue gases as it passes through the catalyst. The catalyst is not consumed during the reaction; its role is to enable the chemical reaction between NH3 and NOx to take place at lower temperatures. When the SCR process is used, the following two reactions occur: 4NO + 4NH3 + O2 → 4N2 + 6H2O and 4NH3 + 2NO2 + O2 → 3N2 + 6H2O. Similarly, since 90%–95% of the NOx in flue gases is in the form of NO, the first equation is the primary reaction equation. The NCR+SCR denitration technology combines SNCR and SCR methods. In other words, SNCR denitration is used inside the furnace to remove a portion of the NOx, thereby reducing the concentration of NOx entering the SCR reactor, decreasing the amount of catalyst required, and saving on operating costs. The reaction principle of SNCR+SCR is the same as that of SNCR and SCR introduced earlier. Comparison of the advantages and disadvantages of several denitrification technologies
| Item | SNCR | SCR | SNCR+SCR |
|------|------|-----|----------|
| Reactants | Ammonia water or urea | Gaseous ammonia or urea decomposition | Ammonia water + gaseous ammonia or urea decomposition |
| Catalyst | Not required | Required | Only a small amount of catalyst is needed |
| Denitrification efficiency | 25–50% | Can reach 95% | Can exceed 90% |
| Injection locations for reactants | Combustion zone inside the furnace (850°C–1050°C) | Flue gas duct at the economizer outlet (300–400°C) | Both of the aforementioned locations |
| SO2/SO3 oxidation | Does not cause SO2/SO3 oxidation | SO2/SO3 oxidation can be controlled | Minimal SO2/SO3 oxidation occurs |
| Impact on air preheater | Does not lead to conversion of SO2/SO3; likelihood of blockage or corrosion is the lowest among the three methods | NH3 readily reacts with SO3 to form NH4HSO4, which may cause blockage or corrosion of the air preheater | SO2/SO3 conversion rate is lower than that in SCR processes; thus, the risk of blockage or corrosion is also lower compared to SCR |
| Ammonia slip rate | High (8–10 ppm) | Very low (≤3 ppm) | Low (5–10 ppm) |
| Construction costs | Low | High | High |
| Operating costs | High; requires heating to vaporize liquid ammonia | Low | Lower than those of SCR processes |
| Safety equipment requirements | Required | Mandated by regulations | Mandated by regulations |

Introduction to dust removal technology
We have introduced Fluorme® needle-punched felt, a new type of high-temperature, high-efficiency filter material featuring a rational structure and excellent performance. It boasts resistance to acid and alkali corrosion, dimensional stability, and high strength. Its filtration precision reaches as high as 99.99%. Currently, it is the preferred product for purifying blast furnace gas and filtering flue gas in industries such as steelmaking. It is the preferred technology for the advanced purification of industrial flue gases. The adoption of this technology enables the attainment of pollutant emission standards that are difficult to achieve with existing industrial flue gas purification methods. Its main application areas include the advanced purification of high-temperature gases such as those generated in coal gas production, biomass gas production, traditional coal chemical processes, electric arc furnaces, yellow phosphorus production processes, TiCl4-related high-temperature gases, and gases produced during the roasting of non-ferrous metals, as well as the upgrading of existing dust removal systems and the control of PM2.5 pollution. CDL type long-bag offline pulse bag filter: The CDL type long-bag offline pulse bag filter is a high-performance pulse bag filter developed specifically to meet the needs of cleaning large volumes of air, based on the technology of pulse jet dust removal. It possesses the advantages of pulse jet dust filters, such as strong dust removal capacity, high efficiency, and low emission concentrations, in addition to being stable and reliable, having low air consumption, and requiring little space – making it particularly suitable for handling large volumes of flue gas. The CDL type long-bag offline pulse bag filter is a large-scale dust removal device featuring high air handling capacity, excellent dust cleaning performance, high dust removal efficiency, reliable operation, easy maintenance, and low floor space requirement. It is used for dust control and material recovery in industries such as metallurgy, building materials, power generation, chemicals, carbon black, asphalt concrete mixing, and boilers. Working principle of the dust collector: The long-bag offline pulse bag dust collector is located on the negative pressure side of the fan; it features an external filtration structure with air intake at one side and air outlet at the other side. The dust collector is mainly composed of an upper box, a middle box, an ash hopper, an ash discharge device, air inlets and outlets, a blowing device, and a control system. The dust-containing flue gas enters the inclined flue, and within the pre-separation chamber formed by the wind baffle, larger particles of dust fall into the ash hopper due to inertia. The flue gas reaches each filter bag chamber through the ash hopper, while the dust is retained outside the filter bags. Clean flue gas enters the filter bags, and then passes through the bag openings and the upper box, being expelled through the exhaust chimney by a fan. As the dust on the surface of the filter bag continues to accumulate, causing the equipment resistance to rise to the set value (or when the preset time is reached), the differential signal device generates a signal; the controller then sends a signal to activate the solenoid valve, which in turn causes the diaphragm of the pulse valve to move, thereby releasing pressure from its chamber and opening the blowing outlet, so that compressed air can be used for dust removal. Flumece filter bags: Flumece needle-punched fabric is made from 100% alkali-free glass fiber; it is produced by splitting high-count glass fiber strands into filaments and then needle-punching them together. It boasts excellent heat resistance, flame retardancy, and corrosion resistance. It presents low gas filtration resistance, an dust removal efficiency higher than that of woven filter materials, and a filtration speed roughly twice that of woven filter materials. The glass fiber base fabric has a weight of >850 g/㎡, good air permeability; it can be used at temperatures ranging from 220–240°C, with temporary use possible at 280°C, and it offers a filtration efficiency of 99.99%.