Process Introduction and Process Control Parameters for the Desulfurization Section in the Chemical Production Workshop

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I. Process Flow: The gas coming from the cold drum section is cooled in a gas pre-cooling tower, then enters the lower part of the desulfurization tower where it comes into counter-current contact with the desulfurization liquid sprayed from the top of the tower. After hydrogen sulfide is removed from the gas, it is sent to the sulfur ammonia section. The desulfurized rich liquid flows from the desulfurization tower into the solution circulation tank via a liquid seal. After catalyst and concentrated ammonia water are added, it is pressurized by a solution circulation pump and cooled in a solution heat exchanger (in summer) or heated (in winter) before entering the regeneration tower for regeneration. Inside the regeneration tower, the desulfurization-rich liquid flows upward in parallel with the compressed air from the air compressor station, thereby oxidizing and regenerating the desulfurization liquid. The regenerated desulfurization-poor liquid is returned to the top of the desulfurization tower for spraying, to continue the cycle of washing H2S out of the gas. The sulfur produced through oxidation is blown to the top of the regeneration tower by air, where it forms a sulfur foam that flows into the foam tank due to the difference in pressure. In the foam tank, sulfur foam is stirred, broken apart to release air, thereby forming a solid-liquid mixture. This mixture is then pressurized by a foam pump and sent to the sulfur melting tank or centrifuge, where sulfur or sulfur paste is produced; the liquid residue is returned to the solution circulation tank. Due to various losses during production, the catalyst needs to be replenished periodically. PDS and hydroquinone are added to the catalyst storage tank in a certain ratio; after being stirred evenly to dissolve, the mixture is continuously fed into the solution circulation tank. During the continuous circulation of the desulfurization solution, side reactions cause by-products such as NH4CNS and (NH4)2S2O3 to accumulate continuously, resulting in an increase in the solution’s viscosity and crystal precipitation. This leads to tower blockage and a decline in desulfurization efficiency; in severe cases, it can even cause the system to fail. Therefore, it is necessary to remove some of the desulfurization waste liquid and add fresh liquid to ensure the stable operation of the desulfurization system. The remaining ammonia water from the cold drum passes through an ammonia filter, which removes impurities such as tar from the ammonia water, before entering the ammonia heat exchanger. There it exchanges heat with the ammonia vapor wastewater coming from the bottom of the ammonia vaporization tower; after being heated, the remaining ammonia water enters the ammonia vaporization tower. The ammonia vapor evolved enters the ammonia fractionator for cooling; some of the liquid that condenses flows back automatically to the top of the ammonia evaporation tower as reflux. The uncondensed ammonia vapor (containing about 10% ammonia) passes through the condensing cooler and enters the solution circulation tank, where it is used as a supplementary liquid for desulfurization. The ammonia-vapor wastewater discharged from the bottom of the ammonia vaporization tower is sent to the exhaust gas cleaning tower or for biochemical treatment via an ammonia water heat exchanger, a wastewater tank, an ammonia-vapor wastewater pump, and a wastewater cooler. Tar is regularly discharged from the bottom of the ammonia distillation tower and sent to the coal yard to be mixed with coal for coking. The purchased alkaline solution (40%) is poured into the alkali discharge tank, from where it is pumped via a pump located beneath the tank into the alkaline solution storage tank. From there, it is sent by an alkaline solution transfer pump into the pipeline carrying the remaining ammonia, where it mixes with that ammonia and enters the ammonia vaporization tower in order to adjust the pH value and ensure the decomposition of fixed ammonia. II. Process Parameters
1. Temperature parameters
(1) Temperature of desulfurization solution: 35–45°C
(2) Temperature of coke oven gas at the inlet of the desulfurization tower: 3–5°C lower than that of the solution
(3) Operating temperature in the sulfur melting tank: 140–150°C
(4) Temperature at the top of the ammonia vaporization tower: 101–103°C
(5) Temperature of ammonia vapor after the ammonia condenser: 85–92°C
(6) Temperature of concentrated ammonia water after the condensation cooler: 30–70°C
(7) Temperature of wastewater after the wastewater cooler: 60–70°C

2. Pressure parameters
(1) Outlet pressure of the solution circulation pump: >0.5 MPa
(2) Air pressure entering the regeneration tower: 0.5–0.6 MPa
(3) Resistance in the desulfurization process: <3500 Pa
(4) Steam pressure entering the process section: >0.4 MPa
(5) Steam pressure entering the ammonia vaporization tower: ≤0.2 MPa
(6) Operating pressure at the bottom of the ammonia vaporization tower: ≤0.035 MPa
(7) Operating pressure at the bottom of the ammonia vaporization tower: ≤0.025 MPa
(8) Operating pressure in the sulfur melting tank: 0.4 MPa

3. Flow rate parameters
(1) Blowing intensity in the regeneration tower: 100–120 m3/m2·h
(2) Solution circulation volume: 30–35 L/Nm3

4. Level parameters
(1) Solution circulation tank: 1/2–2/3 (of height)
(2) Wastewater tank: 2/3 (of height)

5. Quality parameters
(1) Quality of gas: H2S at the inlet of the process section: 3–5 g/Nm3; H2S at the outlet of the process section: ≤20 mg/Nm3
(2) Quality of desulfurization solution: Free ammonia content in the solution: 4–6 g/l; PDS content: 10–18 ppm; Resorcinol content: 0.3–0.5 g/l; Suspended sulfur content: 1 g/l; Salt content: <250 g/l; Solution pH value: 8.2–8.5
(3) pH value after adding alkali to the residual ammonia water: 8–9; NH3-N content in the ammonia vaporization wastewater: ≤200 mg/l