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Desulfurization Plant – Principle of the desulfurization production process: The desulfurization method we use is officially known as the modified anthraquinone disulfonate sodium method, abbreviated as the modified A·D·A method; it belongs to the oxidation-based approach in wet desulfurization. The standard A·D·A desulfurization solution is a mixed aqueous solution containing substances such as sodium carbonate, sodium bicarbonate, sodium metavanadate, sodium anthraquinone disulfonate, and sodium potassium tartrate; it has a specific gravity of around 1.10, a boiling point of 105°C at normal pressure, and a red-brown color. The sulfur contained in raw natural gas is mainly inorganic sulfur with a small amount of organic sulfur. Inorganic sulfur includes hydrogen sulfide and sulfur dioxide (SO2), with hydrogen sulfide being the main one, whose molecular formula is H2S. It is a colorless gas with an odor similar to that of rotten eggs; it is toxic, becomes acidic when dissolved in water, and forms salts when reacted with alkalis. H2S can also react with certain metal oxides or salts. Organic sulfur includes thiol (R—SH), thioether R(—S—R’), carbon disulfide (COS), carbon disulfide (CS2), thiophene (C4H4S), etc. (R— represents a hydrocarbon group). Thiols are the main component among them. Thiols have an unpleasant odor and are insoluble in water. Lower thiols can be decomposed into olefins and hydrogen at temperatures of 150–250°C. The chemical reaction in the absorption process involves the use of dilute alkaline solutions to absorb hydrogen sulfide and produce hydrosulfides, within a pH range of 8.2–9.0. Na2CO3 + H2S = NaHS + NaHCO3 (main reaction). Sodium bicarbonate can also absorb hydrogen sulfide to form sodium hydrosulfide, but the reaction rate is much lower than that of sodium carbonate reacting with hydrogen sulfide. NaHCO3 + H2S = NaHS + H2O + CO2↑ (secondary reaction) The chemical reaction involved in sulfur precipitation: In the liquid phase, hydrosulfides are oxidized by sodium metavanadate, resulting in the formation of reduced sodium metavanadate, while elemental sulfur is precipitated. 2NaHS + 4NaVO3 + H2O = Na2V4O9 + 4NaOH + 2S ↓ Chemical reaction for solution regeneration: The reduced sodium metavanadate is oxidized by the oxidized form of A·D·A back to sodium orthovanadate, while the oxidized form of A·D·A is converted back to its reduced form. Na2V4O9 + 2A.D.A + 2NaOH + H2O = 4NaVO3 + 2A.D.A (oxidized state) (reduced state). The reduced form of A·D·A is oxidized by oxygen in the air, thereby being regenerated into its oxidized state. 2A.D.A + O2 = 2H2O + 2A.D.A (reduced form) (oxidized form). Sodium bicarbonate reacts with the sulfur formed in this process to produce sodium hydroxide, which in turn generates sodium carbonate, thereby maintaining the alkalinity of the solution. NaHCO3 + NaOH = Na2CO3 + H2O; the main side reaction that occurs during the absorption process is the reaction of hydrogen sulfide, in an amount equivalent to 2–3% of the absorption rate, to form Na2S2O3. 2NaHS + 2O2 = Na2S2O3 + H2O The trace amount of carbon dioxide present in natural gas reacts with sodium carbonate to form sodium bicarbonate. Na2CO3 + CO2 + H2O = 2NaHCO3. If the carbon dioxide content in natural gas is low, the amount of sodium bicarbonate produced is also low; and a certain amount of sodium bicarbonate together with sodium carbonate forms a buffer solution that can effectively stabilize the pH value of the solution. In this case, the reaction that produces sodium bicarbonate in the system can be considered not to be a side reaction. When natural gas contains hydrogen cyanide (HCN) gas, the following side reactions also occur. Na2CO3 + 2HCN + 2S = 2NaCNS + H2O + CO2↑ When sodium hydrosulfide comes into contact with large amounts of air in the regeneration tank, it is also oxidized to sodium sulfate. 4NaHS + 7O2 = 2Na2SO4 + 2SO2 + 2H2O. The raw natural gas supplied from the gas supply station passes through a raw gas separator; the gas at the bottom of the desulfurization tower uses an ejector to spray the solution along with the natural gas in mist form for preliminary desulfurization, which can achieve an absorption rate of up to 80% for hydrogen sulfide. After further desulfurization through spraying in the middle empty tower section to remove most of the H2S, the gas proceeds to the packing section for further purification. The purified natural gas exits the desulfurization tower via the demister at the top, is separated in a purified gas separator, and then sent back to the gas distribution station. The A·D·A solution coming out from the lower part of the circulation tank is pressurized by a desulfurization pump and then sent to the packing section and the empty tower section of the desulfurization tower. After absorbing H2S, it collects at the bottom of the tower and is reused via an ejector before exiting the desulfurization tower. The solution is injected into the regeneration tank through an automatic control valve. The solution passes through the nozzle at high speed to form a jet, creating a local negative pressure in the suction chamber of the ejector, which draws air from the atmosphere directly in. At this point, since the two-phase fluid is highly dispersed at high speeds and is in a state of intense turbulence, the gas-liquid contact surface **increases and is continuously renewed**, thereby enhancing the mass transfer process and allowing the regeneration reaction to take place within a short time. Thereafter, the solution enters the regeneration tank for sulfur foam flotation; the solution that has been regenerated in the upper part of the regeneration tank passes through a level controller and enters the solution circulation tank for reuse. The sulfur foam floating on the surface of the regeneration tank liquid continuously overflows into the sulfur foam tank, and then flows back to the mixing tank due to the difference in height. Inside the mixing tank, the sulfur foam separates into layers due to their different specific gravities; the sulfur foam gradually breaks apart and settles, while the solution flows to an underground tank through an overflow pipe for recovery and storage. The sulfur foam is then pumped, via a sulfur foam pump, to the horizontal section of the molten sulfur tank; it is indirectly heated to 130°C using steam at 0.5 MPa before being moved to the vertical section of the tank. The solution and liquid sulfur separate due to their different specific gravities; the liquid sulfur settles at the bottom of the vertical tank and is discharged into a holding tank through a sulfur discharge valve. At the top of the vertical reactor, the A·D·A solution continuously flows into the solution recovery tank in the form of superheated liquid. Sulfur melting and solution recovery: The sulfur foam is indirectly heated to around 130°C in a sulfur melting vessel, causing the sulfur to turn into a molten liquid. Taking advantage of the fact that sulfur has a higher specific gravity than the A·D·A solution and is insoluble in water, the solution and sulfur are separated through settling and layering. Water treatment plant – Principle of water treatment process: The raw water is sent from a pump room to a grit chamber where larger particles of sand are removed, after which it enters the distribution well where coagulants are added. It enters the water treatment equipment through two routes. The flow passes through Reactor Tank No. 1, Horizontal Flow Settling Tank No. 1, Inclined Tube Settling Tank No. 1, and Water Intake Well No. 1; after chlorination for disinfection, it is sent respectively to the desulfurization plant, the plant’s domestic water supply, and the valveless filter. After filtration through a valveless filter, the turbidity is less than 10 ppm; ClO2 is then added, and the water is pumped to the residential areas and non-production areas within the plant. The other route goes to the clarifier via Reactor No. 2 with double-layer baffles, Settling Tank No. 2 of the horizontal flow type, Settling Tank No. 2 with inclined tubes, and Suction Well No. 2. Coagulant: Polyferric sulfate, abbreviated as PFS. General formula: 【Fe2(OH)n·(SO4)3−n/2】m n