Desulfurization process in the coking recovery workshop

Thread Content

Desulfurization process in the coking recovery workshop 1. Brief description of the process flow and flow diagram: The gas sent from the blower station, with a temperature of approximately 20–35°C and a pressure of 5–1.5 kPa, enters the desulfurization tower. The gas enters the bottom of the desulfurization tower, where it comes into counterflow contact with the desulfurization liquid sprayed from the top of the tower; after H2S and HCN are removed, the gas is discharged from the top of the tower and sent to the final cooling tower. The desulfurization liquid discharged from the bottom of the desulfurization tower enters the rich liquid tank through a liquid seal tank, and is then pumped by a desulfurization liquid circulation pump into the oxidation regeneration tank, where air is drawn in to enable the desulfurization liquid to be regenerated within the tank. The regenerated desulfurization liquid flows back to the circulation tank at the top via a level regulator. The sulfur foam floating on the expanded area at the top of the regeneration tank flows automatically into the sulfur foam tank due to the difference in liquid levels; the sulfur foam is then pumped to a plate and frame filter press where it is filtered to form a filter cake, which is packaged and sold externally. The discharged desulfurization liquid enters an underground tank, from where it is pumped to a circulation tank for reuse. The alkali consumed during the desulfurization process is replenished by pumping the alkaline solution prepared in the alkali preparation tank into the circulation tank. The process flow diagram is attached below. 2. Technical specifications and quality standards for raw materials and products
2.1 Technical specifications for raw materials and products
Gas temperature entering the desulfurization tower: 20–35°C
H2S content in the gas entering the desulfurization tower: 4–8 g/m3
Low-pressure steam pressure from the preceding process unit: ≥0.4 MPa
2.2 Quality standards for products
H2S content in the gas after passing through the desulfurization tower: < 1 g/m3
Suspended sulfur content: ≤3.0 g/l
Desulfurization efficiency: >80–95%

3. List of equipment
| Serial No. | Equipment Name | Specification Model | Quantity |
|-------------|----------------|--------------------|----------|
| 1 | Desulfurization liquid circulation pump | Q=500 m3/h, H=60 m, EAP300K5-500 | 3 |
| 2 | Desulfurization tower | DN3200×32500 | 1 |
| 3 | Rich liquid tank | DN6000×15000, V=145 m3 | 1 |
| 4 | Regeneration tank | DN5000/6000/7000, H=6000 mm | 1 |
| 5 | Alkali preparation tank | – | 1 |
| 6 | Foam pump | – | 1 |
| 7 | Filtrate pump | Q=10.5 m3/h, H=42 m, CHZ25-200A | 8 |
| 8 | Foam tank | 2600×5000 | 1 |
| 9 | Underground vent tank | 2600×5000 | 1 |
| 10 | Level regulator | DN=800/600 | 1 |
| 11 | Plate and frame filter press | 30 m2 | 1 |
| 12 | Circulating liquid tank | DN6000×6000 | 1 |
| 13 | Sulfur steaming tank | 1500×4000×1500 | 2 |

4. Process technical parameters for the operation
4.1 Temperature parameters
Gas temperature after the blower: ≤35°C
Gas temperature entering the desulfurization tower: 20–35°C
Temperature of the solution entering the desulfurization tower: 30–40°C
Temperature of the solution in the reaction tank: 30–40°C
4.2 Pressure parameters
Pressure of gas entering the desulfurization tower: 5–15 kPa
Pressure of gas exiting the desulfurization tower: 4.5–14.5 kPa
Pressure entering the regeneration injector: ≥0.4 MPa
Air pressure entering the injector: 0.4–0.6 MPa
4.3 Resistance and flow rate parameters
Resistance of the desulfurization tower: ≤1500 Pa
Flow rate of the solution entering the desulfurization tower: 350–450 m3/h
4.4 Quality parameters
pH value of the desulfurization liquid: 8.5–9.2
H2S content in the gas after passing through the desulfurization tower: < 1 g/m3
Suspended sulfur content: ≤3.0 g/l

5. Normal operation
5.1 Desulfurization unit
5.1.1 Responsibilities
5.1.1.1 Responsible for operating and adjusting the flow rates, pressures, and temperatures of the gas and circulating liquid, in accordance with the requirements of the process parameters ； Responsible for the recovery and preliminary processing of sulfur foam, closely monitoring the bubbling activity at the top of the regeneration tank, and properly adjusting the liquid level ； Reduce the content of suspended sulfur in the system in a timely manner, fully recover sulfur, produce sulfur and supply sulfur slurry, so as to meet the requirements of the process technical specifications. 5.1.1.2 Control the liquid level in the foam tank according to the process requirements. 5.1.1.3 Check the condition of the sulfur foam in the foam tank once per hour, and be responsible for starting, stopping, and ensuring the proper operation of the plate and frame filter press. 5.1.1.4 Carry out chemical dosing in accordance with the workshop’s instructions to ensure that the components of the desulfurization solution meet the requirements of the desulfurization process. 5.1.1.5 Responsible for the maintenance of the equipment in this position as well as the cleaning of the equipment’s surrounding area. Participate in the testing and acceptance processes after repairs to devices such as circulation pumps. Regularly lubricate pumps and valve screws to ensure their proper operation. Frequently check the instruments; any damage or malfunction detected should be reported promptly. 5.2 Daily Operations 5.2.1 Items to be checked hourly 5.2.1.1 Pump outlet pressure, motor operating current, solution circulation rate, and gas pressure. 5.2.1.2 Check whether the temperatures of the front and rear bearings of the pump, as well as the temperature of the motor casing, are normal, and whether there are any abnormal noises. 5.2.1.3 Gas temperature and circulating fluid temperature. 5.2.2 Items to be checked every half hour 5.2.2.1 Liquid levels in underground tanks, waste liquid tanks, and other such tanks. 5.2.2.2 Make adjustments in coordination with the control room staff based on the situation of sulfur foam overflow. 5.2.3 Items to be checked every two hours: Check whether outdoor equipment is leaking air or fluid; increase the frequency of inspections in case of any abnormal conditions. 5.2.4 During each day shift, the operating crew shall clean the drainage pipes of the gas pipelines. 5.2.5 Regulation of the overflow volume from the regeneration tank 5.2.5.1 Regularly check the overflow condition in the regeneration tank; generally, the overflow level of the level controller is adjusted to control the overflow volume, and in some cases, the solution circulation rate can also be adjusted for this purpose. 5.3 Filter Press 5.3.1 Responsibilities 5.3.1.1 This position is responsible for pumping the sulfur slurry from the sulfur foam tank to the filter press, where it is filtered to form sulfur cakes, which are then transported to the sulfur pooling area. 5.3.1.2 Be responsible for discharging materials according to the requirements of operational indicators; it is strictly prohibited to allow sulfur foam to be carried along with the liquid, and records must be kept. 5.3.1.3 Responsible for the maintenance of equipment, valves, instruments, etc. in this position, ensuring they remain in good condition with no leaks; timely lubrication of the oiling points on all screw valves, as well as proper maintenance and cleaning. 5.3.1.4 Responsible for the recovery of solutions and slag, as well as for the cleaning and maintenance of equipment and the premises. 6. Startup and shutdown procedures 6.1 Startup and shutdown of the desulfurization tower 6.1.1 Starting up the tower 6.1.1.1 Inform the electricians, fitters, and instrument technicians to check the associated equipment to ensure it is in good condition. 6.1.1.2 Prepare the desulfurization solution. 6.1.1.3 Notify relevant units such as the drum cooling department and the dispatch team. 6.1.1.4 Before starting operations in winter, all oil and water pipelines must be cleaned. 6.1.1.5 Check whether the manhole of the tower is properly sealed, whether the water seal and the bottom of the tower are filled with water to prevent gas from escaping, and open the vent valve at the top of the tower. 6.1.1.6 Open the steam purge valve to displace the air in the tower with steam, until a large amount of steam emerges from the vent pipe. 6.1.1.7 Start the desulfurization liquid circulation pump to enable the circulation liquid to be sprayed, and adjust the temperatures, pressures, and circulation rates at various locations to meet the technical specifications. 6.1.1.8 Slightly open the gas inlet valve to use gas to displace the vapor inside the tower; once a large amount of gas begins to flow from the vent pipe at the top of the tower, indicating that the explosion test has been successful, close the gas vent pipe valve. After opening the outlet valve and the inlet valve, slowly close the bypass valve, while paying attention to any changes in pressure behind the blower as well as the resistance in the desulfurization tower. 6.1.2 Shutting down the tower 6.1.2.1 Stop the desulfurization liquid circulation pump, and close the inlet and outlet valves as well as the main valve of the regeneration tank’s injection pipeline. 6.1.2.2 Open the gas bypass valve. 6.1.2.3 Close the gas inlet and outlet valves of the desulfurization tower, and open the vent valve at the top of the tower. 6.1.2.4 To carry out work inside the tower, the gas inlet and outlet valves must be fitted with blind flanges, followed by cleaning using steam until steam begins to emerge from the vent pipe. Once the steam supply is turned off, the manholes on the tower are opened for ventilation. Work can proceed inside the tower only after safety inspections confirm that it is safe to do so. 6.1.2.5 In the event of a long-term shutdown of the tower, it is necessary to drain and clean the relevant equipment and pipelines. 6.2 Starting and stopping of the desulfurization liquid circulation pump 6.2.1 Before starting, it is necessary to check that the pipes and valves are in normal condition prior to operation; moreover, the pump bearings must be filled with lubricating grease. The coupling should be turned by hand to ensure normal operation. 6.2.2 Before starting, slightly open the pump inlet valve and close the outlet valve; open the pressure gauge valve as well. Then start the motor. Once the pump is operating properly and the pressure gauge shows the correct pressure, gradually open the pump’s inlet and outlet valves until the flow rate is adjusted to the desired level. 6.2.3 When the pump stops operating, first reduce the flow rate by closing the pump’s outlet valve, then turn off the power supply. After the pump has stopped, close the inlet valve as well. In winter, when the pump is shut down, the water remaining inside it should be drained to prevent it from freezing and cracking. 7. Abnormal Conditions and Handling 7.1 Sudden Power Outage 7.1.1 If a fault occurs in the circuit of a pump’s electrical equipment, the backup equipment shall be activated. 7.1.2 In the event of a short-term power outage, close the pump outlet valve. 7.2 High resistance in the desulfurization tower 7.2.1 Contact the relevant departments. 7.2.2 Open the traffic pipe valve as indicated. 8. Classification and allocation of responsibility for process accidents: Any accident that occurs during the production process due to the operator failing to follow the prescribed procedures or acting carelessly during operation is considered a process accident. 8.1 Failure of the desulfurization liquid circulation pump: If the desulfurization liquid circulation pump fails to operate due to reasons such as an excessively low liquid level in the reaction tank or a sudden power outage, and the on-duty operator fails to detect this in time, thereby affecting the normal operation of the desulfurization process, the on-duty operator shall be held responsible. 8.2 If the resistance in the desulfurization tower is high, which may lead to gas release from the coke oven, the control room should monitor the pressure behind the fan and instruct the operators on duty to adjust the desulfurization valve promptly. In the event that delays in adjustment or handling result in an increase in the resistance of the desulfurization tower, thereby causing excessive pressure behind the fan that cannot be adjusted and forcing gas to be released, the operator on duty shall be held responsible, in accordance with the principle that those who operate the equipment are accountable for any issues that arise. 8.3 Product quality incidents: Any instances in which the product quality at this workstation is substandard due to careless operation, inadequate control of raw material quality, or failure to adjust parameters in accordance with technical specifications are the responsibility of the operator on duty. 8.4 Operational accidents resulting from imperfect process technical specifications are the responsibility of both technical managers and operators