The latest and most practical technologies for ammonium-based desulfurization

Ammonia-based desulfurization or ammonium-based desulfurization? Could you provide a detailed explanation?

(1) System overview and design principles ① Flue gas flow: The flue gas emerges from the outlet flue of the boiler’s exhaust fan, passes through the original flue for FGD before entering the desulfurization tower where it is cooled further in the concentration section, desulfurized in the desulfurization section, and dehumidified by the demister. The resulting clean flue gas then enters the clean flue gas duct. A condensate collection tank is installed at the lowest point of this duct, and the condensed liquid is discharged back to the desulfurization tower； Then it is emitted through the chimney. The flue gas in the desulfurization system operates independently. The flue gas system within the FGD is divided into the inlet flue before the desulfurization tower (i.e., the original flue) and the outlet flue after the desulfurization tower (i.e., the cleaned flue). The designed wind speed in these flues is 14.5 m/s, with a designed pressure of ±5000 Pa. ② Principles for flue insulation design: All flues through which the flue gas passes, including the original flue gas flue and the cleaned flue gas flue, are insulated. The insulation material used is 100 mm thick high-temperature centrifugal glass wool, with a 0.8 mm thick color-coated steel sheet protective layer. (II) Flue ducts: Overview: Both the original flue ducts and the cleaned flue ducts are made of 6mm carbon steel, with steel sections used for reinforcement on the outside ； Pressure gauges and thermometers are installed in the original flue and the clean flue respectively for operation and monitoring; ash removal holes are provided at appropriate intervals, along with operation platforms and inspection manholes. (III) Baffle Doors: Overview: The desulfurization system of this entire project is equipped with 12 electric rectangular, double-layer gas-sealed baffle doors, which are located in the original flue and the cleaned flue, respectively. Both the raw flue gas damper doors and the clean flue gas damper doors are of the switch type ； All bypass flue gas damper doors are of the adjustable type ； All baffle doors can be operated remotely via DCS or locally. Swiss SiBe electric actuators shall be used in accordance with the requirements of the tender documents. 1. The frame material of the original flue gas damper door is made of section steel ； The shaft material is carbon steel (35#) ； The blade material is carbon steel. The flap doors are equipped with Swiss SiBe electric actuators of the direct-drive type, which provide a 4–20mA output signal. They can be operated remotely via DCS, locally, or manually. 2. The frame material for the clean flue gas damper doors and the bypass flue gas damper doors is carbon steel lined with a corrosion-resistant alloy (including the flange surfaces); the alloy used is 316L or an equivalent material, with a thickness of 3 mm ； The shaft is made of carbon steel (35#), with a corrosion-resistant alloy coating; the alloy used is 316L or an equivalent material, and the thickness of the coating is 3 mm ； The blade material is 316L; the internal bolts are also made of 316L, while the external components are fabricated from ordinary carbon steel. The flap doors are equipped with Swiss SiBe electric actuators of the direct-connected type, which allow for remote DCS operation, local operation, as well as manual operation. (IV) Flue expansion joints: The materials for the primary flue gas expansion joint 1, the primary flue gas expansion joint 2, and the bypass flue gas expansion joint are all Q235 + canvas + fluororubber + insulation cotton, etc ； The material of the clean flue gas expansion joint is Q235, with a lining of 316L + canvas + fluororubber + thermal insulation cotton, etc. The expansion joint compensation amount is 50 mm. (5) Supports: The flue supports are concrete supports. (VI) Flue anti-corrosion: 1. For the main flue and backup flue: After construction, the external surfaces are mechanically rust-removed to a standard of St3; two coats of high-temperature resistant primer are applied. 2. Clean flue: After fabrication, the inner surface is sandblasted to remove rust; the rust removal standard is Sa2.5 level, and glass flake coating is applied for corrosion protection ； Mechanical rust removal on the outer surface; rust removal standard at grade St3; two coats of high-temperature resistant primer. (7) Flue insulation: The flue insulation is designed to consist of 100 mm thick centrifugal high-temperature glass wool, with a 0.8 mm thick color-coated steel sheet protective layer on top. (8) Platforms: All steel structure platforms are covered with purchased steel grating plates, with a grid height of 40 mm. The steel grills should be arranged horizontally and maintain a uniform appearance from any direction. Each steel grill is fixed with screws welded to the platform; the use of screw clamps is not allowed. All and major platforms are designed for live loads of 4 kN/m2. All grills are hot-dip galvanized; if the steel grills need to be cut or welded, they must be galvanized again. All platform edges are equipped with skirtings that are 100 mm higher than the platform, with a thickness of 4 mm. 10.3 SO2 absorption system The SO2 absorption system consists of the following components: desulfurization tower, spraying system, demister, etc. 1) Desulfurization tower: The desulfurization tower is the main equipment for SO2 absorption. Its functional zones include: ① concentration section, ② desulfurization section, ③ washing section, and ④ demisting section. To ensure that the flue gas is evenly distributed across the entire cross-section of the desulfurization tower and to prolong its residence time. Sulfur dioxide in the flue gas is absorbed through thorough contact with a 3-layer spray of a circulating solution mixed with ammonium sulfite (NH4)2SO3, ammonium bisulfite (NH4HSO3), and ammonium sulfate (NH4)2SO4. Two desulfurization towers are installed, with specifications of Φ8500×33000 mm. The material used for the tower bodies is Q235B. The anti-corrosion material used inside the tower is glass flake anti-corrosion material, and the warranty period for this internal anti-corrosion material is no less than 15 years. 2) Demister: This project uses a two-stage demister; the first stage is a baffle demister (made of reinforced polypropylene), and the second stage is a swirl plate demister (made of FRP). Both layers of the demister are equipped with a flushing water system, which allows for the separation of any remaining mist in the flue gas, ensuring that the amount of liquid droplets carried in the flue gas is ≤75mg/Nm3. 3) Spray system: The spray system includes a storage tank for the desulfurization liquid in the desulfurization tower, slurry tanks, agitators, circulation pumps, pipelines, nozzles, supports, reinforcements, and accessories, etc. The design of the spray system ensures that the arrangement of the spray layers achieves the desired coverage rate of the spray slurry, allowing the absorption solution to come into full contact with the flue gas; this in turn guarantees the reliable achievement of the desired desulfurization efficiency at an appropriate liquid/gas ratio (L/G). The design and arrangement of the spraying components and nozzles ensure that the liquid mist covers the cross-section of the desulfurization tower evenly. Each spray layer consists of a main pipe with connecting branches, solution distribution pipes, and nozzles. The design of the operating liquid level in the desulfurization tower ensures optimal performance of the pump, with no cavitation occurring behind the pump’s impeller ； At the same time, selecting a larger pump inlet pipe diameter can effectively prevent cavitation and extend the pump’s service life. 10.4 Absorbent Storage, Preparation, and Supply System (I) System Overview (1) System Overview: The liquid ammonia delivered through pipelines is prepared into ammonia water at the concentration required for the process (approximately 25%) using an ammonia absorber, and this ammonia water is stored in an ammonia storage tank. (2) Design principles: Safety and practicality, to minimize the leakage or evaporation of ammonia in the desulfurization zone. (3) Design specifications: The capacity of the ammonia storage tank is determined based on the amount of ammonia required over 8 hours of operation at full load of the desulfurization unit (using the designed coal type), while also ensuring sufficient supply for flue gas denitrification; this amount is tentatively set at around 120 kg/h. (4) Load range: The preparation and supply of the absorbent meet all possible load ranges for FGD. (II) Equipment Configuration: The ammonia preparation system is equipped with the ammonia absorber unit itself, exhaust gas absorbers, control valves, etc. The ammonia storage system is equipped with 1 ammonia tank. Two ammonia water pumps, configured in a one-operational-one-redundant setup. (III) Technical specifications: In compliance with the current relevant design codes, regulations, and technical standards issued by **, and taking local conditions into account, the newly constructed installations and facilities are arranged in a compact manner to reduce investment costs. These arrangements meet the requirements of relevant norms regarding fire safety, explosion prevention, safety, and hygiene, thereby creating favorable conditions for production and ensuring smooth operation of the industrial processes. The complete absorbent preparation and supply system meets all possible load ranges for FGD. Provide the design of all pipes, valves, instruments, control equipment, and accessories required by the system, as well as the supply of the relevant instruments and accessories. 10.5 Oxidation System: This process technology employs an external tower oxidation process. An oxidation circulation pump is installed to oxidize the unoxidized HSO3- and SO32- in the solution into SO42-. The sulfuric acid an by-product generated as a result of this oxidation is sent to a sulfuric acid an recovery system for processing. The multi-functional oxidizer features a carbon steel interior lined with glass flake anti-corrosion material, and is designed for two-stage oxidation. 10.6 Sulfuric Acid An Post-treatment System (I) Crystallizer The crystallizer is a device that utilizes the gravity of the solution to further separate the crystals from the mother liquor. Quantity: 2 units. Specifications: Φ3000×2500/1500 mm. Material: FRP. Each unit is equipped with 1 mixer. (II) Centrifuges: Type – piston-fed centrifuge. Quantity: 2 units in total. Material: All components in contact with the sulfuric acid mother liquor are made of 316L stainless steel; the centrifuge screens are made of 2205 material. (III) Drier: For the drying of the sulfuric acid an product, a vibrating fluidized bed dryer is selected for this project. Composition: It consists of a vibrating fluidized bed dryer along with its associated equipment. Material: The parts in contact with wet materials are made of 316L material, while those in contact with dry materials are made of 304 material. The material of the dry machine frame and upper housing is stainless steel 304 or 316L; the lower housing is made of carbon steel with anti-corrosion treatment. Quantity: 1 set. (IV) Packaging machine: Semi-automatic packaging machine – automatic material feeding and weighing, manual bagging, manual assistance in sealing the bags, and manual stacking. Quantity: 1 unit. Material: The parts in contact with the material are made of 304 stainless steel, while the rest are carbon steel coated with anti-corrosion paint. Packaging specification: 50 kg/bag. 10.7 Water supply for desulfurization unit and emergency system. (I) Function of process water system: The process water is stored at the bottom of the desulfurization tower, providing water for the system’s operations. The process water system supplies water to the following equipment: • Make-up water for flue gas evaporation ； •Washing water for the demister and all slurry transfer equipment, transfer pipelines, and storage tanks ； •Flushing of desulfurization sites • Various other water requirements in the design (II) Functions of the desulfurization unit’s discharge system The functions of the discharge system are as follows: (1) During periods when the unit is not in operation, flushing and drainage systems are installed at locations prone to crystallization-induced blockages; these include water for flushing equipment, pipes, the desulfurization tower area, and other areas, with the flushing water being returned to the desulfurization tower. (2) The capacity of the drainage facilities is designed based on the expected flow rate. The maintenance fluid for system equipment is discharged into the accident tank, while the maintenance fluid from the pumps in the pump room is discharged into the sump. (3) The wastewater generated during the flushing and cleaning of equipment (such as equipment and pipelines in the sulfuric acid slurry system) is collected in the accident tank on the desulfurization island, and then sent to the desulfurization tower system for reuse; thus, no wastewater is discharged from the system. (4) Rainwater drainage.