Chemical product recovery process

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Chemical product recovery process – Section 1: Drum cooling unit 1.1 Brief description of the process flow 1.1.1 Initial cooling unit for gas: Raw gas at around 820°C from the coke ovens, containing tar and ammonia water, flows through the gas absorption pipeline to the gas-liquid separator. After separation, the liquid goes to the condensate treatment unit, while the gas exits from the top and enters the cross-tube coolers (one in operation and one as backup). The gas is cooled in two stages, with the upper stage being cooled using circulating water； The lower section is cooled by low-temperature cooling water, reducing the temperature of the gas to 22±10°C, and the gas is discharged from the bottom. The condensate formed in the upper and lower sections of the primary cooler flows into the condensate tank, while part of the light tar flows into the light tar tank. To ensure the cooling efficiency of the primary cooler, its upper and lower tube banks are regularly flushed on the gas side with hot ammonia water and light tar in order to remove impurities such as tar and naphthalene from the tube walls. The condensed liquid resulting from these flushes is discharged through the condensate tank and the light tar tank to the subliquid tank, and is ultimately sent to the mechanical clarifier by a subliquid pump. 1.1.2 Condensate treatment unit: The liquid discharged from the bottom of the gas-liquid separator, as well as the condensate at the bottom of the electrostatic precipitator, the spin precipitator, and below the blower, enters a mechanical clarifier. There, tar is separated from ammonia water. Due to their higher density, tar and tar residues accumulate at the bottom of the tank; these tar residues are removed by continuously moving scrapers. The mechanical clarifier regulates the amount of tar discharged by controlling the interface between tar and ammonia water. The ammonia in the ammonia separator flows into the circulating ammonia intermediate tank and then to the circulating ammonia emergency tank; part of it is sent to the coke oven, while the rest flows into the residual ammonia tank from where it is pumped to the ammonia vaporization unit for treatment. The tar from the mechanical clarifier is transferred to the intermediate tar tank, where it is pumped to the tar storage tank; there, the tar is further dehydrated and desludged before being sold. 1.1.3 Blowing unit: The gas coming out of the pre-cooler enters the blower; the motor drives the hydraulic coupling, and an inverter is used to control the operation of the blower. An electric actuator is installed on the hydraulic coupling, and when the suction pressure in front of the blower changes, the actuator adjusts the size of the valve, thereby regulating the blower’s speed. Condensate pipes are provided in the pipes ahead of, behind the blower, as well as in those for gas inlet and outlet, leading to the sealing groove. 1.2 Technical Operating Procedures for the Condensation Station 1.2.1 Operating Procedures for the Condensation Station 1.2.1.1 Responsibilities of Workers at the Condensation Station 1) Under the supervision of the direct team leader, these workers are responsible for the maintenance and use of the equipment in their area, as well as maintaining cleanliness within that area. 2) Strictly follow the operating procedures and safety regulations to maintain normal production processes. 3) Responsible for the transportation of tar, its preliminary dehydration, and loading for sale. 4) Responsible for supplying circulating ammonia water to the coke oven that meets the process requirements. 5) Be responsible for the start-up, shutdown, and vehicle change operations for this position, and keep records in a timely, accurate, and truthful manner. 6) Responsible for supplying qualified light tar to the primary cooler. 7) Responsible for the storage and maintenance of the tools, fire-fighting equipment, and other shared items related to this position. 8) In the event of an accident at this position, report it to the shift leader and the workshop promptly and handle it properly. 1.2.1.2 Normal process parameters for this position: 1) Temperature of circulating ammonia water: 75–80°C. 2) Pressure of the circulating ammonia water pump: ≥0.3MPa. 3) Tar moisture: ≤49. 4) Tar storage tank temperature: 80-900°C. 5) Tar level in the mechanical clarifier: 1.4-1.6M. 6) Pump bearing temperature: ≤700°C; Motor temperature: ≤650°C. 7) The motor current shall not exceed the rated current. 1.2.1.3 Normal operation: 1) Regularly check and adjust the temperature, pressure, flow rate, and liquid level of various components to ensure they meet the process requirements. 2) Check that the lubricant level is not below the specified level. 3) The operation of each pump and motor should be regularly inspected, and any abnormalities should be addressed promptly. 4) Check that all pipelines are unobstructed. 5) The bearing oil should be replaced if it turns black. 6) The various liquid levels in the mechanical clarifier must be maintained at normal levels, so that tar is not mixed with ammonia, and ammonia is not mixed with tar. 7) Ensure that the tar intermediate tank, ammonia water intermediate tank, and submersed tank are not at full flow. 8) Regularly discharge the tar at the bottom of the ammonia water intermediate tank. 9) Except in special cases, it is strictly prohibited to add fresh water to the circulating ammonia solution. 10) At the time of handing over, it is necessary to ensure that the process is stable and operating normally; otherwise, adjustments must be made before handover is possible. 11) Maintain good hygiene at the work station and take care of all the equipment there; each shift should thoroughly clean all the equipment and turn the standby pumps manually. 12) It is required to fill in job records carefully, accurately, and promptly, with clear and neat handwriting and clean record paper. 1.2.1.4 Startup and shutdown operations 1) Startup of the circulating ammonia water pump ① Inform the relevant personnel to prepare for startup. ②Check whether each pump is functioning properly and whether the lubricating oil meets the specified requirements. ③Open the inlet valve and the pump casing vent hole, and after venting the air, tighten the plug. ④Start the machine by closing the switch, and check whether there are any noises from the motor and pump, whether the bearing temperature has increased, whether the current is stable, and pay attention to the outlet pressure. ⑤Open the pump’s outlet valve slowly as required, and adjust it using the outlet valve to control the flow rate based on the increase in outlet pressure. 2) Shutdown of the circulating ammonia water pump ① Notify the relevant personnel to prepare for shutdown. ②Slowly close the inlet valve to reduce the flow rate. ③Stop the pump after closing the inlet and outlet valves. ④If parking for an extended period, the liquid in the pipelines and pump casing should be drained. 3) Switching of the circulating ammonia water pump ① Notify the relevant stations and personnel to prepare for pump switching. ②Check the lubricating oil level of the standby pump and turn it over. ③Remove the gas from the standby pump. ④Start the backup pump and adjust the pump pressure and flow rate. ⑤Once the standby pump is operating properly, stop the pump by following the normal shutdown procedure. ⑥Adjust the flow and pressure of the standby pump to meet the process requirements. 1.2.1.5, Operation and maintenance of scrapers: 1) Clean the equipment and its surrounding area at the end of each shift. 2) Keep the reducer and motor drive unit clean. 3) Check whether the reducer operates smoothly, and whether the vibration noise and temperature are normal. 4) Check for any abnormalities in the motor’s vibration, temperature, and noise. 5) Regularly check whether the engagement between the chain and sprockets and the gears is proper, as well as the lubrication of the chain. 6) Check during each shift whether the oil levels in the oil cups of all bearings of the scraper are sufficient, and whether the oil pipes are unobstructed. 7) Check the tightness of the chain and scraper chain, as well as for any signs of misalignment. 8) If jamming or severe friction occurs, stop the machine immediately for repair. 1.3 Operating Procedures for the Blowing Position 1.3.1 Responsibilities of the Blowing Position Staff 1) Work under the supervision of the direct team leader, responsible for the production operations of the team as well as the use and maintenance of equipment. 2) Responsible for adjusting the suction pressure of the gas system in a timely manner to ensure that all technical parameters of the blower system meet the process requirements. 3) Responsible for the maintenance and daily upkeep of the equipment in this position, to ensure that backup equipment is in good condition. 4) Responsible for cleaning the area assigned to this position. 5) Cooperate with relevant personnel in the trial operation and acceptance of the fan after maintenance. 6) Ensure stable suction during the initial cooling stage, thereby maintaining a stable pressure level in the coke oven gas collection system. 7) In accordance with the shift handover system, carefully carry out the handover process. 8) Strictly follow job procedures and safety regulations, avoid any violations of rules and disciplines, to ensure safe production. 9) The spare equipment should be turned over once per shift. 10) After draining waste from each drain pipe, clean it promptly with steam. 1.3.2 Main technical specifications of the blower: 1) Pre-blower suction pressure: 200–4000 Pa. 2) Pressure after the blower: ≤30 kPa 3) Pressure in the gas collection duct: 70–90 Pa 4) Current of the fan motor should not exceed the rated value: ≤50 Hz 5) Oil type: Medium extreme pressure industrial gear oil, grade 150# 6) Temperature of the gas before the primary cooler: 80–85°C 7) Temperature of the gas after the primary cooler: 20–22°C 8) Volume of gas processed by the electrostatic tar catcher: 25,000–30,000 m3/n 9) Oxygen content in the gas fed to the electrostatic tar catcher: ≤0.8% 10) Temperature of the insulating box of the electrostatic tar catcher: 90–110°C 1.3.3 Normal operation: 1) Adjust the gas suction pressure in a timely manner to meet the requirements of coke oven production. 2) Conduct inspections every half hour to check the operation of the equipment instruments. 3) Pay attention to whether the sound of the fan and motor is normal, and check for any vibration in the unit; address and report any abnormal phenomena promptly. 4) Check whether the motor vibration and temperature rise are normal, and whether the current meets the specified values. 5) Carefully check the fan oil tank and the oil level. 6) The standby fan should be turned 1/4 turn per shift to ensure it can be started at any time. 7) Regularly check the inlet and outlet gas temperatures of the primary cooler, and adjust them to meet the process requirements. 8) Check the temperature, pressure, and suction at various parts of the blower every hour, and keep records. 9) When the gas resistance of the cooler and electrostatic precipitator exceeded the specified values, they were cleaned promptly, and the cleaning liquid was removed in a timely manner. 10) The blowers, electrostatic precipitators, and the condensate pipes before and after them should be cleaned once per shift in summer, and twice per shift in winter, to ensure unobstructed flow. 1.3.4 Starting up the blower 1.3.4.1 Starting up 1) Inform the relevant staff to get ready for startup. 2) Coordinate with the coke oven, get everyone in position, and the dispatcher will give the order to start operation. 3) Turn the start switch knob, and the motor will start operating. 4) Once the motor speed stabilizes, open the gas inlet valve to adjust the gas suction to normal levels. 5) Conduct a thorough inspection, pay attention to current changes, and check the condition of all parts of the motor; once no issues are found, proceed with normal operation. 1.3.4.2 Shutdown 1) First, report to the workshop and the dispatch team, and get in touch with the coke oven; everyone should take their positions, after which the dispatch team issues the shutdown command. 2) After stopping the fan, quickly close the inlet and outlet valves and open the bypass valve. 3) Turn off the motor power supply. 4) Condensate exhaust pipe of the steam purge fan. 5) Within 2 hours after shutdown by steam purging, turn the machine every 15–20 minutes; after 4 hours, turn it once per shift. 1.4 Knowledge Quiz 1.4.1 How to perform the initial cooling of a coke oven? The raw gas coming out of the carbonization chamber is first sprayed with a large amount of circulating ammonia water at the bridge pipe. During this process, the hot gas comes into contact with ammonia water in the form of a fine mist at 70–750°C. The high-temperature gas releases heat, causing the ammonia water droplets to warm up and vaporize rapidly. As a result, the temperature of the gas drops to 80–850°C, while the temperature of the unvaporized ammonia water rises to 75–780°C. Approximately 50–60% of the tar present in the gas is condensed, and this tar mixes with coal dust and coke particles to form tar residue. After spraying with circulating ammonia water, the temperature of the gas dropped to 80–850°C, but it was still too high; the coke oil vapor and water vapor had not yet completely condensed. To further recover chemical products, facilitate transportation, and reduce the power consumption of the gas blowers, the gas is cooled in a primary cooler before reaching the blowers. Primary cooling generally includes two types: indirect cooling. In recent years, a pre-cooling process that has been used together with intercooling has also been developed; the temperature of the gas after passing through the pre-cooler can be reduced to around 300°C, at which point light tar and ammonia water condense. 1.4.2 How is tar recovered in the recycling workshop? Most of the tar gases in the waste gas are found in the bridge pipes and gas collection pipes. Under the condition of circulating ammonia water for spraying, the tar that condenses flows into the tar-ammonia water clarification tank together with the hot ammonia water. The remaining tar is also recovered successively in devices such as the primary cooler, blower, and electrostatic tar collector. All the tar recovered from these devices enters the tar-ammonia water clarification tank, where ammonia water separates from the tar and tar residues. Most of the ammonia water discharged from the upper layer of the clarification tank is recycled to the bridge pipes and gas collection pipes for cooling the coal gas, while the remaining ammonia water (about 14% of the coal used in the furnace) is taken out and disposed of after treatment. The mechanized tar-ammonia water clarifier is equipped with a scraper for removing tar residues, which continuously discharges the tar residues. The clarified tar is discharged to the tar intermediate tank through a level controller, and can then be pumped using a tar pump to the tar storage tank in the tar processing plant. 1.4.3 What are residual ammonia water and recycled ammonia water? Coking coal contains 8-10% of external moisture. Additionally, during the coking process, the oxygen present in the coal combines with hydrogen at high temperatures to form combined water, which accounts for 2-4% of the weight of the dry coal. These two types of moisture turn into water vapor during coking and are released along with the raw gas; after condensation, aside from compensating for a small amount of ammonia loss, the remaining ammonia is sent to ammonia distillation towers and extraction towers for further processing. The hot ammonia water used for spraying into the bridge pipes and gas collection pipes in order to cool raw coal gas is circulated in a quantified manner as needed; it is therefore referred to as circulating ammonia water. The amount of circulating ammonia water is generally around 5–63 liters per ton of coal used. 1.4.4 What are the characteristics of centrifugal pumps? It features a simple structure, uniform flow rate, easy adjustment and control, and a wide range of applications; therefore, it is a commonly used liquid transfer machine in chemical production. 1.4.5 What is the working principle of a centrifugal pump? It relies on a high-speed rotating impeller, which enables the liquid to gain energy under the effect of inertial centrifugal force, thereby continuously sucking in and discharging the liquid. 1.4.6 What is the gas entrapment phenomenon? When a centrifugal pump is started, if the pump is not filled with liquid and contains a large amount of air, the density of air is much lower than that of liquid; as a result, the centrifugal force generated by the rotation of the impeller is very small. The low pressure at the center of the impeller is not sufficient to create the pressure difference required to draw in liquid, which prevents the pump from transporting liquid. This phenomenon is known as air locking. 1.4.7 How are the initial cooler started and stopped? Start-up: 1) Fill the water seal tank of the primary cooler with water ； 2) Close the drain pipe at the bottom of the cooler ； 3) Open the vent pipe and introduce steam to drive out all air until white vapor emerges from the vent pipe; after about 45 minutes, take a sample for oxygen content analysis until the results are satisfactory ； 4) Once the oxygen analysis shows satisfactory results, stop supplying steam, close the vent pipe, and open the gas inlet valve ； 5) Open the cooling water outlet valve, pour hot water into the cooler, and then open the inlet valve ； 6) Slowly open the gas outlet valve, and inform the blower operator to pay attention to any changes in the gas suction force. Shut down: 1) Sequentially close the valves for the gas outlet, cooling water inlet, gas inlet, and cooling water outlet ； 2) Open the cooling water drain pipe and drain the water ； 3) Open the cooler vent pipe and slowly introduce steam for cleaning for 2–4 hours; the steam pressure must not exceed 4.9×104 Pa (0.5 kg/cm2). 1.4.8 Why are blowers installed in the gas process of coking plants? Coke oven gas coming out of the coke ovens passes through a series of devices such as gas collection pipes, suction pipes, primary coolers, tar catchers, and systems for recovering ammonia and benzene, before it can be turned into clean gas to be supplied to various users or stored in tanks. In this process, gas must overcome many obstacles to reach the user’s location; therefore, it should have sufficient residual pressure. Furthermore, in order to extract the raw gas from the coke oven at the specified pressure level, a certain suction force must be maintained in the gas pipeline. Therefore, it is necessary to select an appropriate location within the coking process flow to install the blower, so that negative pressure exists ahead of the blower and positive pressure behind it. In most coking plants, the blower is placed after the primary cooler and before the electrostatic tar catcher; this is because the load on the blower is lower at this point, and the electrostatic tar catcher operates under positive pressure, which makes it safer. 1.4.9 After the blower starts up, is gas being drawn in? What is the reason? How to handle it? When the blower starts up and no gas is drawn in, if all other conditions are normal, there are mainly two reasons: 1) The water at the bottom of the unit has not been completely drained, thereby blocking the gas passage before and after the unit ； 2) The two blowers compete for gas; the blower that is already in operation has too strong a suction force and draws too much gas, resulting in very little gas reaching the blower that has just started operating. The handling method: 1) Stop the vehicle to drain the water accumulated at the bottom of the engine; after the water has been drained, start the vehicle again ； 2) Reduce the suction force of the blower that is rotating inward. 1.4.10 What is the critical speed of a blower? What is rated speed? When the operating speed of a blower falls within a certain range, issues such as uneven operation, fluctuations in flow rate, and vibration can occur. This speed is known as the critical speed, while the maximum speed at which the blower can operate is referred to as the rated speed. 1.4.11 What tasks should the blower operator carry out during normal operation? During normal operation, the blower operator has many tasks to carry out, but the main responsibilities include the following: 1) Regularly check and adjust the suction force of the blower to ensure that temperatures and pressures in all areas meet the technical specifications ； 2) Check whether the sound is normal and whether the machine is vibrating; address any abnormalities promptly ； 3) Regularly check the operation of the electric blower, paying attention to whether the motor temperature rise and vibration are normal, and whether the current is within the specified range. If sparks appear at the motor wires, the electrician should be notified promptly to handle it ； 4) Regularly check the operation of the motor fan, ensure that air supply is not interrupted, and keep spare parts in good condition ； 5) Make sure to check for leaks in the oil system and that the pipes are unobstructed. Drain any water accumulated in the oil tank once per week during regular working hours, to ensure that there is an adequate level of oil in the tank ； 6) The spare blower should be rotated 1/4 turn per shift, and the oil pressure system should be tested once per week during regular working hours to ensure it can be started at any time ； 7) Regularly check whether the drain valves and traps are unobstructed ； 8) Record the temperature, pressure, suction force, current, and rotational speed of various parts of the blower once per hour ； Record the gas temperature, pressure, and resistance at various locations once per hour ； 9) Record accurately the work progress and issues that occur in this class. 1.4.12 What is the function of the blower drain pipe? The liquid discharge pipe at the lower part of the blower has three main functions: 1) Since coal gas contains tar mist, water vapor, naphthalene, and other substances that condense as it passes through the blower, these condensed liquids must be removed through the discharge pipe; otherwise, the blower cannot operate properly ； 2) Drain the water accumulated at the sealing inlet and outlet through the drain pipe before starting the blower ； 3) Acts as a water seal. 1.4.13 What are the causes of fluctuations in blower suction? How to handle it? There are few reasons that cause fluctuations in the suction force of the blower, but under production conditions the main causes are factors such as the amount of gas, the tightness of the piping equipment, whether condensate is discharged in a timely manner, and pipe blockages. 1.4.14 What is the working principle of an electrostatic precipitator? The sedimentation tube of the electrostatic precipitator serves as the sedimentation electrode and is connected to the positive pole of the current; the corona wire functions as the corona electrode and is connected to the negative pole of the power supply. When high-voltage direct current is applied, a non-uniform electric field is formed between the two electrodes. An area around the corona electrode becomes the corona zone where a corona phenomenon occurs. The gas near the corona electrode undergoes impact ionization, resulting in coal gas molecules that can carry both positive and negative ions. Outside the corona zone, there are negatively charged ions that attach themselves to the tar droplets in the gas, causing these tar particles to move toward the inner wall of the sedimentation tube. Along this wall, they fall under the influence of gravity to the bottom of the electrostatic precipitator. Since the sedimentation electrode is grounded, electrons are conducted into the ground, and the gas ions revert to neutral molecules before leaving the electrostatic precipitator through its top. 1.4.15 What should be noted during electrostatic capture operation? 1) Whether it is steam purging or introducing gas, it must be done gradually; it is strictly prohibited to open the valves suddenly to avoid disturbing the corona wire and causing accidents ； 2) It is necessary to ensure that the tar pipe at the bottom of the electrostatic tar catcher remains unobstructed; it is strictly prohibited for tar to accumulate inside the electrostatic tar catcher. Section 2: Refrigeration Cycle Water Unit 2.1 Brief Description of the Process Flow 2.1.1 Process Flow of the Refrigeration Unit (Refrigeration Cycle) The dilute solution in the absorber is pumped by a solution pump to the high-pressure generator; along the way it passes through the low-temperature heat exchanger and the high-temperature heat exchanger. The dilute solution that enters the high-pressure generator is heated by the heat generated from combustion, resulting in the formation of high-temperature refrigerant vapor. This vapor is then concentrated into an intermediate solution. The intermediate solution flows through the heat exchange tubes of the high-temperature heat exchanger, heating the dilute solution flowing toward the high-pressure generator; as a result, the temperature of this solution drops. It then enters the low-pressure generator, where it is heated again by the high-temperature refrigerant vapor coming from the high-pressure generator. This process leads to the separation of low-temperature refrigerant vapor, and the remaining liquid is concentrated into a concentrated solution. This concentrated solution flows through the heat exchange tubes of the low-temperature heat exchanger, heating the dilute solution inside those tubes; after its temperature drops, it returns to the absorber. The high-temperature refrigerant vapor produced by the high-pressure generator heats the intermediate solution outside the heat exchange tubes of the low-pressure generator, causing it to condense into refrigerant water. After throttling, this refrigerant water enters the condenser. The refrigerant vapor produced in the low-pressure generator also enters the condenser, where it is condensed into refrigerant water by the cooling water flowing through the heat exchange tubes of the condenser. The heat is released into the atmosphere. These two streams of refrigerant water enter the flash tank after being throttled through U-tubes. Part of this refrigerant water vaporizes into refrigerant vapor, which flows into the reabsorption tank at the bottom of the absorber, while the other part cools down to become low-temperature refrigerant water, which then flows into the liquid chamber of the evaporator. The refrigerant water that enters the liquid chamber of the evaporator is pumped out by the refrigerant pump and sprayed onto the surface of the heat transfer tubes in the evaporator. There, it absorbs the heat from the cold water flowing through these tubes, causing it to boil and evaporate into refrigerant vapor. This vapor then enters the absorber, where it is absorbed by the concentrated solution returned to the absorber. Meanwhile, the cold water loses heat to the refrigerant water, its temperature drops, and it flows out of the unit to return to the user’s system. After absorbing the refrigerant vapor, the concentration of the concentrated solution decreases, resulting in a reduced amount of dilute solution. This dilute solution flows through a reabsorption flash tank, where it comes into contact with refrigerant vapor; thereafter, it is sent back to the high-pressure and low-pressure generators by a solution pump for heating and concentration. This process repeats continuously, allowing the evaporator to produce cold water at the desired temperature on an ongoing basis. 2.1.2 Circulating water process: The circulating water, after being cooled in the cooling tower, is pumped by a circulation pump to the drum-type cross-tube cooler to cool the gas; thereafter it returns to the cooling tower, where it is cooled again before being reused. Another portion is sent to the benzene elution section; after being cooled by spiral plates, it is cooled in the recirculation tank before being reused. 2.2 Technical Operating Procedures 2.2.1 Refrigeration Unit 2.2.1.1 Job Responsibilities 1) Study the safety operating procedures carefully and work only with a valid certificate. 2) Be familiar with the process flow of this position, the names of equipment, their structure, working principles, and process parameters. 3) Strictly follow the operating procedures, safety regulations, as well as fire and explosion prevention rules. 4) Strengthen water quality management; discharge wastewater and replenish soft water in the power plant based on water quality test reports. 5) Adjust the water temperature, water volume, and liquid level in a timely manner to supply water to the drum cooler and crude benzene, ensuring an adequate supply of water for production. 6) Turn on the vacuum pump in a timely manner based on the vacuum display. 7) Responsible for maintaining mechanical and electrical equipment, and keeping proper operation records for this position. 8) Maintain hygiene in industrial areas. 2.2.1.2 Process technical parameters: 1) Evaporation temperature: ≤40°C 2) Cold water outlet temperature: ≤160°C 3) Cooling water inlet temperature: greater than 180°C 4) Temperature of the high-temperature intermediate solution: ≤1650°C 5) Temperature of the melting crystal tube: <650°C 6) Motor temperature rise: ≤650°C 7) Pressure of the cooling water pump: 0.3–0.6 MPa. 8) Exhaust temperature: <2450°C 9) Condensation temperature: <480°C 2.2.1.3 Refrigeration operation procedures 1) Startup procedure ① Close the air switch on the unit control panel; ensure that no fault lights are illuminated on the unit’s “Fault Monitoring” screen (except in the case of a cold water supply failure), then switch to the “Unit Monitoring” screen. ②After confirming that the outlet valve of the cold water pump is in the closed position, start the cold water pump. Slowly open the outlet valve of the cold water pump and adjust the cold water flow rate (pressure difference) to the rated flow rate (or pressure difference) of the unit. ③Slowly open the inlet and outlet valves of the cooling water unit, and adjust the cooling water flow to the unit’s rated flow rate. ④Open the unit’s fuel inlet valve and start the air compressor. ⑤On the “Unit Monitoring” screen, press the “System Start” button, then press the “Confirm” and “Done” buttons to bring the unit into operation. ⑥Make rounds to check the operation of the units, recording data every hour. Note: When the cooling water is at a low temperature or the system is operating under light load, the amount of cooling water must be reduced. 2) Shutdown procedure ① Press the “System Stop” button, and the unit enters dilution operation mode. ②Manually close the fuel inlet valve. ③After 3-5 minutes, close the cooling water inlet and outlet valves. ④After the unit stops operating in diluted mode (after 15 minutes), shut off the outlet valve of the chilled water pump and then stop the chilled water pump. ⑤Cut off the power to the unit control box. Note: It is strictly prohibited to stop the cold water pump first and then close the cooling water valve. 2.2.2, Circulating Water Department 2.2.2.1, Job Responsibilities 1) Study the safety operation procedures carefully and work only with a valid certificate. 2) Be familiar with the process flow of this position, the names of equipment, their structure, working principles, and process parameters. 3) Strictly follow the operating procedures and safety regulations. 4) Strengthen the management of circulating water and water quality, and discharge waste water and replenish water in a timely manner. 5) Adjust the water volume and temperature in a timely manner to ensure proper water supply for drum cooling and crude benzene processing. 6) Adjust the cooling tower and axial flow fans in a timely manner based on the temperature of the initially cooled gas, in order to reduce the temperature of the circulating water. 7) Responsible for maintaining mechanical and electrical equipment, and regularly lubricating and servicing the equipment and valve stems. 8) Maintain hygiene in the industrial area and keep proper records of operations for one’s own position. 2.2.2.2 Process technical parameters 1) Cooling water pump pressure: 0.2–0.4 MPa. 2) Cooling water pump outlet temperature: 25-300°C. 3) The temperature rise of the pump bearings shall be less than or equal to 650°C, and the temperature rise of the motor shall be ≤650°C. 4) Motor current: <160A. 5) Axial flow fan current: ≤25A. 2.2.2.3 Circulating Water Operation Procedures 1) Normal Operation ① Check the operation of the pump and motor, as well as the temperature rise of the bearings and any vibration; also verify whether there is any leakage of water or oil. If any abnormalities are detected, stop the machine immediately for treatment. ②The motor bearings should be lubricated once per quarter. ③Maintain the spare equipment well by turning it over once per shift to keep it in good condition. ④Adjust the outlet pressure of the pump to meet the technical specifications. ⑤Regularly check whether the axial flow fans in the cooling tower are operating properly and whether the water distribution is even; remove any water that accumulates on the tower during winter. ⑥Adjust the flow rate of the water tower to maintain a stable liquid level in the tank, and replenish fresh water regularly. ⑦The water temperature at the outlet of the cooling water pump should be kept below 30°C. ⑧Clean the scale from the cooling tower fins in a timely manner. 2) Startup operation: ① Once the blowing and condensation are operating normally, make timely adjustments to ensure proper operation and normal pressure. ②The water volume is adjusted to meet the process requirements. ③Adjust the crude benzene and drum cooling water supply valves to ensure proper water supply for all processes. ④Ensure that the gas temperature behind the tower remains below 280°C. 3) Shutdown procedures ① Prepare for shutdown after receiving notification from the workshop. ②After the blowing and condensation processes have stopped, shut down the circulation water pump. ③Stop the pump in accordance with the prescribed sequence. ④Turn off the power supply and place a warning sign. ⑤Close the inlet and outlet valves of the cooling water pump. ⑥Shut off the valves of each instrument. 3.3 Knowledge Quiz 1) Production characteristics of my workshop: high temperature, flammability, explosiveness, corrosivity, and toxicity. 2) What are the methods to stop a substance from burning? ①asphyxiation method ； ②Isolation method ； ③Cooling method ； ④Inhibition method 3) What are the components of a direct-fired refrigeration unit? It consists of a high-pressure generator, a low-pressure generator, a condenser, an evaporator, an absorber, and a solution heat exchanger. 4) What are the measures to reduce corrosion of the units? ①Isolating oxygen is the most fundamental measure to slow down the corrosion of the unit. ②Maintain the pH of the solution between 9.0 and 10.5. ③In the solution, molybdenum, acids, lithium, molybdate salts, as well as oxides of Te, Pb, Sn, etc., are added as corrosion inhibitors. ④During unit operation, the solution temperature does not exceed 1650°C. 5) What are the operating steps for the vacuum pump (PVD-360)? ①Before using a vacuum pump to evacuate the unit, it should be operated for about 20 minutes; once the oil temperature rises, the evacuation valve of the unit can then be opened to start the evacuation process. ②When evacuating the unit, the gas trap valve should be opened to allow water vapor to evaporate promptly ； And periodically open the drain port to release condensed water (once every 20 minutes). ③During operation, if the vacuum level of the host is very low, the evacuation valve should in principle not be opened too wide or too quickly, otherwise the LiBr solution may easily be drawn out of the pump. ④The condensate at the bottom of the oil trap should be drained promptly to prevent it from entering the vacuum pump and damaging it. ⑤Before shutting down the vacuum pump, after closing the unit’s exhaust valve, the pump should continue to operate for 20 minutes to allow any water vapor inside it to evaporate completely, thereby preventing corrosion within the pump. ⑥The vacuum pump can be started to create a vacuum only after confirming that there is non-condensable gas in the unit’s interior. ⑦It is strictly prohibited to evacuate the main unit blindly, as this may damage the vacuum pump and disrupt the vacuum in the main unit (evacuate it once a week). 6) Handling after a short power outage (within 1 hour) ① If the cold water pump and the cooling water pump also stop due to the power outage, ensure that the outlet valves of the pumps are closed, then start the cold water pump following the normal operating procedures, open the outlet valves, and adjust the flow rate to the specified value. ②The unit is manually controlled; its solution pump and refrigerant pump operate in dilution mode before shutting down. ③Automatic unit control, starting the unit in normal sequence. ④Check the refrigerant water; if its relative density is greater than 1.02, regeneration should be carried out. 7) What surfactant is commonly added to lithium bromide solutions? To improve the heat and mass exchange efficiency of heat exchange equipment, isooctanol (red) and n-octanol (colorless) are often added, which increases the cooling capacity by approximately 10%–15%. Section 3: Benzene Elution Unit 3.1 Process Flow for Ammonia Washing 3.1.1 The gas coming from Phase 1 enters two series-connected ammonia washing towers; after being cooled by ammonia wash water to remove naphthalene, it proceeds to the benzene washing tower. The upper section of Tower 1 for ammonia washing is directly flushed with the ammonia washing liquid from Tower 2, thereby cooling the gas. This ammonia washing liquid flows straight down through the tower and fills the naphthalene recovery tank; thereafter, an ammonia washing circulation pump is used to draw out the ammonia washing liquid from this tank. Part of it undergoes a \"middle circulation\" via a spiral plate cooler and is sent to the middle section of Tower 1 to cool and wash the gas, while the excess portion goes into the ammonia-rich liquid tank. The upper section of Tower 2 for ammonia washing is washed with ammonia-containing wastewater, while the lower section operates in the same manner as Tower 1, using a \"midsection circulation\" approach; however, no spiral plate cooling is used, and any excess ammonia water from the lower section is sent to the upper part of Tower 1. 3.1.2 Process flow for ammonia vaporization: The remaining ammonia water from the air-cooling condensation section and the ammonia-rich water from the washing section first enter a raw material tank where they are mixed and clarified to remove tar. From there, they are pumped to two filters to further remove tar and other impurities. Subsequently, they are sent to a wastewater heat exchanger to exchange heat with the ammonia vaporization wastewater; once the temperature reaches 60–700°C, they are fed into the ammonia vaporization tower. Direct steam is introduced at the bottom of the tower, while the ammonia vapor escaping from the top contains ammonia, water vapor, carbon dioxide, hydrogen cyanide, etc. The wastewater at the bottom of the tower enters a wastewater tank after passing through the heat exchanger; part of this wastewater is sent to the washing units for further treatment, while the rest is sent to biological wastewater treatment facilities. The treated wastewater is then used for coking quenching. 3.1.3 Process parameters for ammonia washing and steaming 3.1.3.1 The gas inlet pressure at Tower No. 1 for ammonia washing is 10,000–20,000 Pa. 3.1.3.2 The gas outlet pressure of Tower 1 for ammonia washing is 10,000–20,000 Pa. 3.1.3.3 The gas outlet pressure of Tower 2 for ammonia washing is 10,000–20,000 Pa. 3.1.3.4, Gas inlet temperature of 1# ammonia washing tower: 28~350°C. 3.1.3.5 Ammonia outlet temperature of the ammonia water circulating cooler: ＜280°C. 3.1.3.6, Ammonia scrubber resistance: not greater than 785 Pa. 3.1.3.7 Ammonia content in ammonia-rich water: 6~8 g/L. 3.1.3.8 The temperature of the cooling water in the spiral plate heat exchanger: ≯160°C. 3.1.3.9 The internal pressure at the bottom of the ammonia vaporization tower: ＜0.04 MPa. 3.1.3.10 The temperature at the bottom of the ammonia vaporization tower: ＞1050°C. 3.1.3.11 The outlet pressure of the feed pump: ＜0.4 MPa. 3.1.3.12 The outlet pressure of the wastewater pump: ＜0.5 MPa. 3.1.4 Operating procedures for the ammonia washing station. 3.1.4.1 Startup. 3.1.4.1.1 Check that all equipment, pipelines, valves, instruments, etc. are in good working condition. 3.1.4.1.2 Lubricate each pump and ensure smooth rotation of the shafts. 3.1.4.1.3 Before starting up, the direct gas valves of each tower and the top vent valves shall be opened, while the inlet and outlet valves shall remain closed; upon receiving the instruction, preparation for gas displacement shall be carried out. 3.1.4.1.4. Steam cleaning of various towers and return water. “After the U-shaped pipeline has been cleaned successfully, close the steam valve. 3.1.4.1.5 Open the gas inlet valve of the ammonia washing tower; once coal gas is detected in the vent at the top of the tower, close the vent. 3.1.4.1.6 Check whether the water pipelines and valves in the ammonia vaporization tower are flexible and functional, and contact the person responsible for supplying water to the ammonia vaporization process. 3.1.4.1.7 Check whether the “U”-tube valve is in the open position, and whether the pipeline is unobstructed with return water. 3.1.4.1.8 When the water level in the bottom tank reaches 1/2, start the pump for Stage I to facilitate the circulation of ammonia water in Stage I. 3.1.4.1.9 When the tower temperature drops to 30–400°C, open the gas outlet valve and close the direct-through valve. 3.1.4.1.10 Adjust each ammonia washing pump according to the specified circulating ammonia volume for each tower to maintain stability. 3.1.4.1.11 Notify the analysis laboratory to take samples for analysis, as necessary, to determine the ammonia and naphthalene content in the gas downstream of the tower. 3.1.4.1.12 Adjust various process parameters to achieve normal stability. 3.1.4.1.13 Keep driving records. 3.1.5 Normal operation 3.1.5.1 Regularly check and adjust the water volume and temperature in each tower. 3.1.5.2 Regularly check the water levels in each tower and the naphthalene collection tank to ensure that there is no overflow of liquid. 3.1.5.3 Check the naphthalene collection tank; remove any naphthalene present as soon as possible. 3.1.5.4 Regularly conduct routine inspections of the operating conditions of various equipment as well as the process parameters. When resistance exceeds the specified limits or mechanical problems are detected, they should be addressed promptly. 3.1.5.5 Regularly check the lubrication oil level of each pump, and top up the oil when it is low. 3.1.5.6 Regularly check the heat exchange performance and resistance of the spiral plate. 3.1.5.7 Clean blocked equipment and pipelines promptly using steam. 3.1.5.8 Prepare production records on time. 3.1.6 Shutdown: Upon receiving the shutdown command, contact the relevant departments to prepare for shutdown. 3.1.6.1 Stop ammonia evaporation and cease water supply to Tower 2; shut down each circulation pump following the pump shutdown procedure. 3.1.6.2 Close the inlet and outlet valves of the ammonia washing pumps in each tower, as well as the water supply and drainage valves of the spiral plate coolers. 3.1.6.3 Open the direct gas flow valves of each tower, and close the gas inlet and outlet valves of each tower. 3.1.6.4. Open the relief valve and clean the tower as appropriate. 3.1.6.5 When the vehicle is parked for an extended period in winter, drain the ammonia solution from within the pump, pipelines, and equipment. 3.1.7 Special Operations 3.1.7.1 In the event of a sudden power outage, the circuit breaker should be turned off immediately, the inlet and outlet valves for the process media in various devices should be closed, and contact should be made with the control room. Appropriate actions should be taken depending on the duration of the power outage to prevent pipe blockages. 3.1.7.2 When the bearing temperature of the pump motor is too high, check whether too much oil has been added or there is no oil at all; oil should be added, removed, or replaced, otherwise consult an electrician. 3.1.7.3 When poor water flow leads to water-sealed gas, the pump should be stopped immediately for handling; it can be restarted once normal operation is restored. 3.1.8, Tower Cleaning 3.1.8.1, Stop the tower according to the shutdown procedures. 3.1.8.2: Turn on the gas release valve, close the return water valve of the \"U\"-shaped tube, and open the exhaust valve of the \"U\"-shaped tube to release a small amount of air. 3.1.8.3 Introduce steam from the bottom of the tower for cleaning; once a large amount of steam is emitted, open the steam cleaning valve on the gas outlet pipeline to carry out cleaning as well. 3.1.8.4 When cleaning the tower, it is necessary to prevent blockage of the “U”-shaped tubes; naphthalene liquid should be drained from the discharge valve in a timely manner to maintain unobstructed flow. 3.1.8.5 Once cleaning is complete, stop cleaning and proceed with starting the machine according to the startup procedures. 3.1.8.6 Keep records. 3.1.9 Starting, stopping, and switching of the ammonia water pump 3.1.9.1 Check that the pump’s foot screws are tight, that there are safety guards in place, that the grounding wires are secure, that the equipment is in good condition, and that the piping and valves are arranged correctly. 3.1.9.2 Check the lubricating oil level and top it up if it is insufficient. 3.1.9.3 The barring gear operates smoothly without any abnormalities. 3.1.9.4 Open the inlet valve of the pump slightly to check whether there is liquid inside the pump and to release any air. 3.1.9.5 Start the pump. 3.1.9.6 Once the pump pressure rises to 0.3–0.4 MPa, gradually open the pump’s outlet valve and adjust the flow rate using the inlet valve to meet the process requirements. 3.1.10, Stopping 3.1.10.1, When it is necessary to stop the operation, first reduce the flow rate by closing the inlet valve of the pump. 3.1.10.2 Close the pump’s outlet valve tightly. 3.1.10.3 Stop supplying power to the pump. 3.1.10.4 Close the inlet valve. 3.1.10.5 In winter, to prevent freezing, the liquid inside the equipment must be drained by pumping it out. 3.1.10.6 First, start the standby pump following the pump-starting procedures, and check that all process equipment is functioning properly. 3.1.10.7 Stop the pumps that need to be stopped according to the shutdown procedure. 3.1.10.8 Keep records of starting, stopping, and switching pumps. 3.2 Operating Procedures for Ammonia Vaporization Station 3.2.1 Startup, upon receiving the startup command 3.2.1.1 Check that all equipment, pipelines, valves, instruments, etc. are in good working condition. 3.2.1.2 Check that the raw water is normal. 3.2.1.3 All equipment pipelines and valves are brought into operation mode. 3.2.1.4 Open the inlet valve of the pump to fill the inlet pipeline and the pump with liquid. 3.2.1.5 The turning gear operates smoothly. 3.2.1.6 Start the pump. 3.2.1.7 Once the pump pressure rises to 0.3–0.4 MPa, gradually open the pump’s outlet valve to bring it in line with the process requirements. 3.2.1.8 Once the raw materials have entered the ammonia vaporization tower and water has reached the wastewater tank, turn on the steam supply for the tower; it is strictly prohibited to increase the steam flow all at once to meet the process requirements. 3.2.1.9 Adjust to meet the process specification requirements. 3.2.1.10 Once the wastewater tank is full, notify the washing unit and supply water to it. 3.2.1.11: Open the valve of the normal washing wastewater cooler to start the wastewater pump for water delivery. 3.2.1.12 Adjust the water supply to meet the process specifications. 3.2.2 Shut down the system upon receiving the shutdown command. 3.2.2.1 Notify the relevant positions and have the control room prepare for shutdown. 3.2.2.2 First, stop the water supply for washing. 3.2.3 Normal Operation 3.2.3.1 Regularly check the source of raw materials. 3.2.3.2 Check the wastewater flow rate and the water supply temperature. 3.2.3.3 Regularly check the operation of the pump and its pressure. 3.2.3.4 Regularly check the pressure and temperature inside the tower, as well as the heat exchange temperature of the heat exchanger. 3.2.3.5 Steam consumption. 3.2.3.6 Remove tar impurities from filters, the bottom of towers, and wastewater tanks at regular intervals as required. 3.2.3.7 Check the steam heating of the jacket. 3.2.3.8 Check the lubricant level in each pump and top up the lubricant as needed. 3.2.3.9 In the event of a process failure, it must be addressed promptly. 3.2.3.10 Keep proper production records. 3.3 Q&A on ammonia washing and steaming. 3.3.1 Why is ammonia removal necessary during gas purification? Answer: There are mainly three reasons: ① Ammonia is a good agricultural fertilizer ； ②Ammonia has a severe impact on the quality of the washing oil used to absorb crude benzene from gas, as it easily causes the washing oil to emulsify and deteriorate ； ③Ammonia has a severe corrosive effect on equipment used in crude benzene production as well as on gas pipelines. 3.3.2 What are the safety regulations for the ammonia washing section? Answer: ① No hot work is permitted on gas pipelines and equipment without approval, and smoking is prohibited in the operation area. ②Firefighting tools and equipment must always be kept in a ready state. ③Oil and other flammable materials must not accumulate in the operation area; if they are present, they should be removed promptly. ④The safety devices for each pump motor should be complete. ⑤Prevent leaks, spills, drips, and seepages from gas pipelines and equipment. ⑥All water seals should remain unobstructed. ⑦When maintaining gas pipelines and equipment, the connected steam pipelines are always disconnected and blocked with blind flanges; maintenance can only proceed after checking and confirming that there is no gas present. 3.3.3 What is the principle of washing ammonia? Answer: Ammonia is highly soluble in water, existing mainly in a molecular form in aqueous solutions, with only a small amount present in ionic form. In the process of absorbing ammonia using water, physical absorption plays a dominant role; the extent of absorption depends on the equilibrium relationship at the gas-liquid interface under the given absorption conditions. The driving force for this absorption process is the difference between the partial pressure of ammonia in the gas stream and the partial pressure of ammonia vapor at the solution surface. 3.3.4 Where does the remaining ammonia water come from? What is the typical quantity? Answer: The remaining ammonia water originates from the moisture in the coking coals and the combined water produced during the coal carbonization process. Under normal circumstances, the remaining ammonia water accounts for 10–14% of the total amount of coal used in coking (with the moisture content of the coal being 8–10% and the combined water content being 2–4%). 3.4 Operating Procedures for the Crude Benzene Unit 3.4.1 Process flow for benzene washing: The coal gas exits from Tower No. 2 for ammonia washing and enters the bottom of the benzene washing tower, where it comes into counterflow contact with the washing oil that is sprayed from the top of the tower. The benzene-containing hydrocarbons in the coal gas are absorbed by the circulating washing oil; the coal gas that emerges from the top of the tower is used internally by the plant, while the remainder is sent outside. The rich oil at the bottom of the benzene washing tower is pumped by a rich oil pump to an oil-gas heat exchanger, where it exchanges heat with the benzene vapor coming from the debenzing tower; this process heats the rich oil to around 700°C. It then goes to an oil-to-oil heat exchanger, where it exchanges heat with the hot poor oil coming from the debenzing tower, raising its temperature from 700°C to 900°C. Finally, it enters a tubular furnace for crude benzene, where it is heated to 140–1800°C. The benzene vapor mixture emerging from the top of the benzene removal tower enters the oil-gas heat exchanger; there it exchanges heat with cold rich oil, and is then cooled by 220°C circulating water to around 300°C. After that, it goes into a benzene-oil-water separator where benzene and water are separated from each other. Benzene is fed into the reflux tank; it is pumped by a benzene reflux pump to the top of the benzene stripping tower as reflux. The remaining benzene flows into an intermediate benzene tank and is sent to the storage area. The oil-water mixture obtained is sent to a control separator, where the separated washing oil is directed to an underground vent tank, and from there it is pumped by an underwater pump into an oil-poor tank. The separated water is sent to a condensate storage tank. The heat-poor oil after benzene removal flows out from the bottom of the benzene removal tower; it then enters an oil-to-oil heat exchanger where it exchanges heat with rich oil, causing its temperature to drop to around 1200°C. It subsequently enters a poor oil tank and is pumped by a poor oil pump to the first and second poor oil coolers, where it is cooled by circulating water at 220°C to around 30–35°C before being sent to the benzene washing tower to spray and wash the gas. Steam at 0.4-0.5 MPa is heated by a tubular furnace to around 400°C; part of it serves as a heat source for the wash oil regenerator, while the rest is fed directly into the bottom of the debenzing tower as a heat source there. During the processes of wash benzene and debenzing, the quality of the circulating wash oil gradually deteriorates. To maintain its quality, 1.0%-1.5% of the wash oil is taken out before it enters the debenzing tower and sent to the regenerator for regeneration using superheated steam; the oil vapor generated is then discharged as residue from the debenzing tower. To reduce the naphthalene content in the washing oil, naphthalene is taken off via a side stream in the middle of the benzene removal tower; the naphthalene oil flows into the naphthalene liquid holding tank, from where it is extracted using steam and sent to the cold drum mechanical ammonia water clarification tank. 3.4.2 Main process parameters: 3.4.2.1 Temperature of the lean oil entering the benzene washing tower: (in winter) it is slightly higher than the gas temperature by 4~70°C; (in summer) it is slightly higher than the gas temperature by 2~40°C. 3.4.2.2, Benzene content in lean oil: ≤0.3%. 3.4.2.3 Benzene content in the rich oil at the bottom of the benzene washing tower: 1.6~2.5%. 3.4.2.4 Temperature of bearings of each pump: ≤65°C. 3.4.2.5 The temperature rise of each motor shall not exceed 45°C. 3.4.2.6 Oil-rich temperature of the crude benzene cooler: 50~60°C. 3.4.2.7 Oil-rich temperature in the oil-to-oil heat exchanger: 90~100°C. 3.4.2.8 Oil-rich temperature in the tubular furnace: 140~180°C. 3.4.2.9 Top temperature of benzene removal tower: 88~93°C. 3.4.2.10 Top temperature of the regenerator: 180~200°C. 3.4.2.11 Temperature of superheated steam entering the regenerator: 300~400°C. 3.4.2.12 Temperature in the convection zone of the tubular furnace: 450°C. 3.4.2.13, Pressure at the bottom of the benzene removal tower: