Process Technology Operation Standards for the Desulfurization Section in the Recycling Workshop

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Process overview: This unit employs ammonia present in coal gas as the alkaline source, and cobalt phthaloate sulfonate as the main catalyst for the wet oxidation desulfurization of coke oven gas; it is also known as the combined ammonia-sulfur washing method or HPF method. The process is as follows: The gas sent from the blower section enters a direct-cooling pre-cooling tower, where it comes into counter-current contact with the circulating cooling fluid sprayed from the top of the tower, thereby being cooled to 27–28°C. The circulating cooling fluid is pumped out from the bottom of the tower and sent to a circulating water cooler, where it is cooled to 27°C using refrigerated water before being circulated and sprayed back at the top of the tower. Part of the excess ammonia water is used to update the circulating cooling water, while the remaining circulating water is returned to the condensation and blower section. The gas coming from the pre-cooling tower enters two desulfurization towers in parallel, where it comes into countercurrent contact with the desulfurization liquid sprayed from the tops of the towers, thereby absorbing H2S and HCN from the gas (while also absorbing ammonia from the gas to replenish the volatile ammonia in the desulfurization liquid). After desulfurization, the gas passes through the desulfurization liquid mist catcher at the outlet of the desulfurization tower before being sent to the ammonium sulfate production unit. The desulfurization fluid, which has absorbed H2S and HCN, flows from the storage tank at the bottom of the desulfurization tower to the reaction tank by gravity. It is then pumped by a desulfurization fluid circulation pump to the bottom of the regeneration tower, where it is fed into the regeneration tower through the premixing nozzles ； The temperature of the desulfurization solution is maintained about 3°C higher than that of the gas entering the tower; at the same time, compressed air is injected at the bottom of the regeneration tower through premixing nozzles, enabling the solution to be oxidized and regenerated within the tower. The regenerated solution flows automatically to the top of the desulfurization tower via a level controller, where it can be reused. The sulfur foam floating on the expanded section at the top of the regeneration tower flows automatically into the foam tank due to the difference in pressure ； After being heated and stirred in the foam tank, it is pumped to the sulfur melting vessel using a foam pump. After heating and dehydration, the clear liquid overflows through the clear liquid pipe at the top of the sulfur melting tank into the waste liquid tank. Most of it is pumped by the waste liquid pump to the desulfurization liquid cooler for cooling before being fed into the reaction tank, while a small portion is pumped by the waste liquid pump to the coal yard for spraying. After the sulfur paste is melted in the sulfur melting tank, it is discharged through the discharge valve of the tank onto the sulfur cooling tray; once cooled, it is packaged and sold externally. The catalyst consumed during the desulfurization process must be replenished in a timely manner, with the amount added determined based on the test results showing the catalyst concentration in the desulfurization solution. After being dosed, the catalyst is added to the dissolution tank located above the reaction tank; after mixing it thoroughly with water, it is gradually poured into the reaction tank to minimize unnecessary waste of the catalyst. With this process, the growth rate of by-product salts is extremely slow; thiosulfate and ammonium thiocyanate can be kept within certain concentration ranges without affecting the catalyst’s activity, which offers the advantage of eliminating the need for by-product salt extraction ； To prevent the accumulation of by-products in the desulfurization liquid from affecting its efficiency, a small amount of this liquid can be appropriately discharged and used to spray the coal seams in the coal preparation area. 2 Principles of desulfurization processes 2.1 Wet oxidation desulfurization using ammonia as a base source is a liquid-phase catalytic oxidation reaction. The catalyst plays a catalytic role in both the desulfurization and regeneration processes; it possesses high catalytic activity. Moreover, it is easily soluble in water and has good fluidity, which helps to prevent blockages in the equipment pipes. 2.2 The ammonia-based desulfurization process is employed; during the absorption of H2S, it is not necessary to use pure soda ash – the ammonia present in the gas itself can serve as the alkaline source. With an appropriate addition of concentrated ammonia solution, H2S and HCN in the gas can be absorbed quite completely. Meanwhile, under the catalytic action of a catalyst, the oxygen in the air is used to oxidize NH4HS in the absorption solution into elemental sulfur, thereby allowing the absorption solution to be regenerated for reuse. 2.3 Several major chemical reactions in the desulfurization process: 2.3.1 Absorption reactions: NH3 (gas) → NH3 (liquid); H2S (gas) → H2S (liquid); HCN (gas) → HCN (liquid); CO2 (gas) → CO2 (liquid). Reactions include: NH3 + H2O → NH4OH (ammonia water); NH4OH + H2S → NH4HS + H2O; 2NH4OH + H2S → (NH4)2S + 2H2O; HCN + NH4OH → NH4CN + H2O; CO2 + NH4OH → NH4HCO3; NH4OH + NH4HCO3 → (NH4)2CO3 + H2O. 2.3.2 Catalytic chemical reactions: NH4HS + NH4OH + (X-1)S → H2. P. F (NH4) 2Sx + H2O → 2NH4HS + (NH4)2CO3 + 2(X-1)S·H. P. F 2(NH4) 2Sx + CO2 + H2O → NH4HS + NH4HCO3 + (X-1)S·H2O. P. F (NH4) 2Sx + H2O + CO2 → NH4CN + (NH4) 2Sx·H2O. P. F NH4CNS + (NH4) 2SX-1 → (NH4) 2SX-1 + S H. P. F (NH4) 2Sx 2.3.3 Catalytic regeneration reaction: NH4HS + 1/2O2 → S↓ + NH4OH; (NH4)2S + 1/2O2 → 2NH4OH + S↓; (NH4)2SX + 1/2O2 → Sx↓ + 2NH4OH. NH4CNS → H2N—C(=S)—NH2; H2N —C(=HS) = NH; H2N —C(=S)—NH2 + 1/2 O2 → H2N — C(C =O) —NH2 + S; H2N—C(=O)—H2N + 2H2O; (NH4)2CO3 + H2O → 2NH4OH + CO2. 2.4 Side reactions: 2NH4HS + 2O2 → (NH4)2SO3 + H2O; 2(NH4)2SO3 + O2 → 2(NH4)2SO4 + 2S↓. 3 Process characteristics 3.1 The desulfurization unit is placed in the overall coal gas purification process before ammonium sulfate and crude benzene, resulting in a rational technical approach with a short and simple process flow. 3.2 By using ammonia in the gas as a base source, operating costs and production costs are reduced. It also replenishes the ammonia vapor generated after the evaporation of excess ammonia water, thereby effectively controlling the ammonia content in the desulfurization solution and contributing to the stability of desulfurization efficiency. 3.3 By using cobalt phthaloate sulfonate catalysts in combination with KHSS-1 type fillers in the desulfurization tower, this process achieves good desulfurization and decyanation results, with a desulfurization efficiency of ≥99% and a decyanation efficiency of ≥75%, offering significant social and environmental benefits. 3.4 The sulfur foam formed is easily separable from the clear liquid, making the sulfur melting process convenient; the method of adding catalyst is simple. Meanwhile, during the desulfurization process, the growth rate of by-product salts is slow, so it is not necessary to install a device for recovering these salts. 4 Main technical parameters 4.1 Gas temperature entering the desulfurization tower: 27-28℃ ； 4.2 Temperature of the solution in the desulfurization tower: 30-35℃ ； 4.3 Maximum liquid-to-gas ratio in the desulfurization tower: 0.33 t/Nm3 ； 4.4 Air flow rate into the regeneration tower: 2000 m3/h ； 4.5 Desulfurization tower resistance: ≤1000Pa ； 4.6 Pre-cooling tower resistance: ≤1000Pa ； 4.7 Solution pH value: 8-9 ； 4.8 Catalyst concentration: 30-50ppm ； 4.9 Steam pressure: 0.4-0.6MPa ； 4.10 Compressed air pressure: 0.5-0.6 M 4.11 Foam tank heating temperature: 80-90℃ ； 4.12 Temperature in the gap of the sulfur melting tank: 130-150℃ ； 4.13 Pressure inside the sulfur melting tank: ＜0.6MPa ； 4.14 Liquid level in the reaction tank: 1/2-2/3 ； 4.15 Total content of by-products: ＜300g/L ； 4.16 Suspended sulfur content: ≤1.5g/L ； 4.17 Free ammonia content in the desulfurization circulation fluid: 4–5 g/L ； 4.18 H2S content after the tower: ＜300mg/m3 ； 4.19 Desulfurization cycle pump shaft temperature: ＜75℃ 4.20 Desulfurization efficiency: ≥98% ； 4.21 Decyanation efficiency: ≥80 ； 4.22 Liquid level at the lower part of the pre-cooling tower: Maintain it at the middle position of the level gauge ； 5 Technical Operation Standards 5.1 Operating Standards for Circulation Pump Operators 5.1.1 Operation under normal conditions 5.1.1.1 Items to be checked hourly: pump outlet pressure and bearing temperature, motor operating current and casing temperature, sound of the pump, solution temperature and circulation rate, gas temperature and pressure, cooling water circulation rate in the pre-cooling tower, etc. Circulate ammonia water from the drum cooling section (cooled to 27–28 degrees Celsius by an ammonia water cooler) until the liquid level in the tower level gauge reaches 3.5 m, after which the supply is stopped. 5.1.1.2 Items to be checked every half hour: liquid levels in tanks such as accident tanks, underground tanks, and reaction tanks, as well as the amount of regenerative air and air pressure. 5.1.1.3 Items to be checked every two hours: Check whether outdoor equipment is leaking air or fluid; any abnormal conditions must be addressed promptly. If they cannot be resolved, it is necessary to report them immediately, and regular inspections should be carried out until the abnormal conditions are resolved. 5.1.1.4 Clean the gas water seal and the outlet pipe of the mist catcher regularly once a week (during the day shift). 5.1.1.5 The catalyst is added during the day shift on a daily basis. The method of adding the catalyst involves calculating the required amount based on the catalyst concentration determined through testing each day. Then, water is added and stirred in the dissolution tank above the reaction tank; once the catalyst is completely dissolved, it is added drop by drop into the reaction tank to avoid uneven catalyst concentration within the system and catalyst loss, thereby reducing catalyst consumption. 5.1.2 Startup of the desulfurization circulation pump: 5.1.2.1 Before starting, it is necessary to check that the pipeline valves are in their normal condition prior to operation, as well as to inspect the lubricating oil in the bearings and motor. The coupling should be turned by hand to verify that it rotates smoothly. 5.1.2.2 Before starting, open the inlet valve of the pump. Open the exhaust valve on the pump body to release the air inside it, then close the exhaust valve. Close the pressure gauge valve as well, and subsequently start the motor. Once the pump is rotating properly, open the pressure gauge valve and the inlet valve. After the pressure gauge shows normal pressure, gradually open the outlet valve until the desired flow rate is achieved. 5.1.2.3 Pay attention to changes in motor current, sound, motor temperature, etc. 5.1.3 Shutting down the pump: First, reduce the flow rate by closing the pump’s outlet valve; after shutting off the power supply to stop the pump, then close the inlet valve ； The liquid inside the pump should be drained during winter or during maintenance. 5.2 Operator Standards for the Tower 5.2.1 Starting up the pre-cooling tower: 5.2.1.1 Before starting the ammonia vaporization tower, supply circulating water and low-temperature water to the front of the tower; check that the manholes are properly sealed, that the water seal tank is filled with water, and that the drain pipe connecting the gas pipeline to the water seal tank is closed. Open the vent valve at the top of the tower, while keeping the inlet and outlet valves of the pre-cooling circulation pump closed. 5.2.1.2 Open the nitrogen valve connected to the tower and the nitrogen valve on the coal gas outlet pipe, and supply nitrogen into the tower and the coal gas pipe to displace the air. Once a large amount of nitrogen begins to flow out from the tower’s vent pipe, reduce the valve opening of that vent pipe in order to maintain a nitrogen pressure of 50 Pa inside the tower; then remove the blind flanges on the inlet and outlet coal gas pipes as well as the blind flange for ammonia gas ； 5.2.1.3 Close the tower vent line valve ； 5.2.1.4 Slightly open the gas inlet valve to use gas to displace nitrogen in the tower; once the oxygen content of the gas at the outlet of the vent pipe is within acceptable levels, close the vent valve ； 5.2.1.5 Open the gas outlet valve of the pre-cooling tower, slowly open the gas inlet valve, and gradually close the gas transfer pipe valve. Pay attention to changes in the gas resistance inside the tower, and keep the resistance of the pre-cooling tower below 1 kPa ； 5.2.1.6 Once the gas operation is stable, start the pre-cooling circulation liquid pump to ensure normal circulation of the liquid; at the same time, supply low-temperature cooling water to the cooler, and continuously feed in the cooled circulating ammonia solution. The excess circulation liquid should be sent to the drum cooling section (to determine the optimal amount), in order to maintain the liquid level at the middle position indicated by the level gauge ； 5.2.1.7 Open the ammonia vapor inlet valve of the pre-cooling tower to feed in the ammonia vapor from the ammonia vaporization unit ； 5.2.1.8 Adjust various control parameters to meet the requirements specified in the technical regulations ； 5.2.1.9 Open the drain valve of the gas pipe leading to the water seal tank, and plug the nitrogen blind flange ； 5.2.2 Shutdown of the pre-cooling tower: 5.2.2.1 Stop supplying circulating ammonia water to the drum cooling section; stop the cooling water flow to the ammonia water cooler; cease feeding circulating liquid to this section. For ammonia vapor generation, stop supplying ammonia vapor and close the valve for ammonia vapor entering the tower ； 5.2.2.2 Open the gas bypass valve, close the gas inlet and outlet valves of the tower, stop the circulating liquid pump, close the inlet and outlet valves of the pump, and stop the low-temperature cooling water flow ； 5.2.2.3 In the case of a short-term shutdown of the tower, keep the gas outlet valve slightly open to maintain positive pressure inside the tower ； 5.2.2.4 When the tower is to be shut down for an extended period and maintenance work is required inside it: First, steam is introduced and the vent valve is opened until a large amount of steam emerges from the vent. With the vent valve set to maintain a positive pressure of 50 Pa inside the tower, the blind valves for the inlet and outlet gases, as well as those for ammonia vapor and nitrogen, are closed. The liquid present in the tower is drained, and the vent valve at the top of the tower is opened to clean it using steam. After that, the steam supply is turned off, and the manholes on the tower are opened for ventilation. Maintenance work can only begin after samples taken show satisfactory results. 5.2.3 Starting the desulfurization tower and regeneration tower: 5.2.3.1 Fill the water seal tank of the coal gas pipe in the desulfurization tower with water; close the valve of the drain pipe connecting the coal gas pipe to the water seal tank. The electrostatic tar catcher is already in operation and functioning properly ； Fill the reaction tank with water, and fill the bottom of the desulfurization tower to full flow. 5.2.3.2 Open the valves on the vent pipes at the top of the regeneration tower and the desulfurization tower; close the drain valve located at the lower part of the \"U\"-shaped pipe connecting the regeneration tower and the desulfurization tower. Set the liquid level regulator of the regeneration tower to its lowest position, and close the valve connecting the regeneration tower to the foam tank ； 5.2.3.3 Open the nitrogen valves on the desulfurization tower and the coal gas outlet pipe; use nitrogen to displace the air inside the tower and the coal gas outlet pipe. By adjusting the opening degree of the vent pipe at the top of the desulfurization tower, maintain a nitrogen pressure of 50 Pa inside the tower, and then remove the blind flanges from the inlet and outlet of the coal gas in the desulfurization tower ； 5.2.3.4 When fresh water added to the reaction tank raises its level to 2/3 of the total capacity, start the desulfurization liquid circulation pump (ensure that the flow rate at the pump outlet is not too high). As the desulfurization liquid flows from the bottom and top of the regeneration tower, back to the top and bottom of the tower again, stop the desulfurization liquid circulation pump. Once the liquid level in the reaction tank remains stable at 2/3 of its capacity during this circulation process, it is possible to cease adding fresh water, and then close the nitrogen valve ； 5.2.3.5 Slightly open the gas inlet valve of the desulfurization tower and use gas to displace nitrogen from within the tower; once the oxygen content in the gas at the outlet of the vent pipe is found to be within acceptable limits, close the vent pipe valve ； 5.2.3.6 Open the gas outlet valve of the desulfurization tower, slowly open the gas inlet valve, and gradually close the gas bypass valve; pay attention to changes in gas pressure and keep the resistance in the desulfurization tower below 1 kPa ； 5.2.3.7 Once the gas operation is stable, start the desulfurization circulation liquid pump to maintain the liquid level in the reaction tank between 1/2 and 2/3 of its capacity ； 5.2.3.8 Feed compressed air into the regeneration tower, and add catalyst dropwise to the reaction tank ； 5.2.3.9 Adjust various control parameters such as flow rate, pressure, and temperature to their optimal levels ； 5.2.3.10 Open the valve of the drain pipe from the gas pipeline to the water seal tank, and plug the nitrogen blind flange ； 5.2.4 Shutting down the desulfurization tower and regeneration tower: 5.2.4.1 Complete the removal of sulfur foam from the system before shutting down the towers ； 5.2.4.2 Open the gas traffic valve of the desulfurization tower, slowly close the inlet and outlet valves of the gas in the desulfurization tower, stop supplying compressed air, and stop the circulation pump for the desulfurization liquid ； 5.2.4.3 During a short-term shutdown of the tower, a slight opening of the gas outlet valve of the desulfurization tower can be used to maintain positive pressure inside the tower. 5.2.4.4 When the tower is shut down for an extended period for maintenance work inside it: Steam should be introduced, and the vent pipe at the top of the desulfurization tower should be opened. The steam pressure inside the tower should be maintained at 50 Pa by adjusting the opening degree of this vent pipe. The gas inlets and outlets of the desulfurization tower as well as the nitrogen supply valves should be sealed, and all liquid present inside the tower should be drained. After that, the vent pipe at the top of the tower should be opened further to use steam to clean the tower; once the steam supply valve is closed, the manholes on the tower should be opened for ventilation. Only after gas samples taken from inside the tower show satisfactory results can maintenance work proceed inside the tower. 5.3 Operating Standards for the Sulfur Foam Tank 5.3.1 Regulation of the Regeneration Tower Overflow Volume Regularly check the overflow condition of the regeneration tower. Under normal circumstances, the overflow level of the level controller is adjusted to control the overflow volume ； In some cases, it is also possible to adjust by regulating the circulation volume of the solution or the amount of compressed air ； When the concentration of the liquid in the foam tank is high, lower the overflow height; when the concentration is low, raise the overflow height. 5.3.2 Normal operation of the foam tank: 5.3.2.1 The sulfur foam overflowing from the regeneration tower is directed to the foam tank; when the foam tank is nearly full, another sulfur foam tank is used to continue collecting the foam. 5.3.2.2 Heat the filled tank and introduce indirect steam until the temperature reaches around 80-90°C. During the heating phase, it is necessary to run the mixer to prevent large localized clumps of sulfur powder from forming and blocking the pipes ； 5.3.2.3 After heating is completed, allow the mixture to stand and separate for half an hour; the sulfur slurry obtained through sedimentation should be reported to the staff in charge of the sulfur melting tank, who will then pump it into the tank using a foam pump. The liquid level in the foam tank should be kept below the full-flow level indicator. 5.4 Operating Standards for the Sulfur Melting Vessel 5.4.1 Check and close the valve at the bottom of the vessel, then open the feed valve of the sulfur melting vessel to start feeding material. 5.4.2 Open the sulfur melting drainage valve to discharge the liquid. It is strictly prohibited for the clear liquid to contain sulfur foam (which can be observed at the funnel opening); when sulfur slurry flows out of the funnel, close the clear liquid vent pipe and the feed valve. 5.4.3 Heat the sulfur melting tank’s jacket with steam to melt the sulfur; maintain the temperature at around 130–150°C for 4 hours. 5.4.4 Allow steam to flow into the jacket surrounding the feed valve for about 15 minutes, then open the feed valve. Once all the sulfur has been discharged, close the feed valve. Open the slag discharge valve to remove the slag; after all the slag has been discharged, close the slag valve ； Open the feed valve to continue feeding. 5.4.5 Steam shutdown procedure: 5.4.5.1 When releasing sulfur, the steam should be shut off, and the discharge valve must be closed immediately ； 5.4.5.2 Stop the steam when discharging the slag liquid; drain all of the slag liquid before closing the slag discharge valve. 8 Safety Operating Procedures 8.1 Strictly abide by all safety management regulations established within the factory. 8.2 Before entering towers or tanks for work, relevant procedures must be followed, and protective measures must be put in place before work can commence. 8.3 It is strictly prohibited to dry clothes in equipment, pipelines, and operation rooms. 8.4 When working at heights on the tower, hold onto the handrails and guardrails to prevent falling from great heights. 8.5 Open flames and smoking are strictly prohibited in the production area. 8.6 Cleaning and repair are prohibited on the moving parts of the equipment. 8.7 Regularly inspect safety valves and pressure gauges to ensure that the safety valves are safe and reliable to use, and that the pressure gauges are accurate. 8.8 The sulfur melting furnace equipment must be pressure-tested regularly in accordance with relevant regulations to ensure safety. 8.9 When handling molten sulfur, be careful to avoid burns and pour it slowly. 8.10 The protective covers for the transmission components are complete and in good condition; the maintenance of fire-fighting equipment is addressed at the end of this post, last edited by ryn on 2009-2-13 11:11]