Seeking the operating procedures for waste heat recovery in the riser tube

12 Operating Procedures for the Waste Heat Recovery Unit in the Rising Tube Section 11.1 Job Responsibilities: Utilize the rising tube heat exchange device to convert the waste heat from raw gas into saturated steam; be responsible for the operation, maintenance, and adjustment of the equipment; be familiar with the structure, performance, and principles of the equipment involved in this role; and master methods for troubleshooting common faults. 11.2 Technical Requirements 11.2.1 The pressure in the drum should be higher than the steam pressure in the pipeline system, and it must fall within the range that ensures the steam quality required for production. The liquid level should be maintained within the specified upper and lower limits, as determined by on-site level gauges and remote transmission level gauges; it is strictly prohibited to allow the level to be too high or too low, as this could cause equipment damage and lead to accidents. 11.2.2 The water level in the desalination tank should be maintained at a normal level. 11.2.3 The level, pressure, and temperature of the deaerator shall be controlled and maintained within the ranges specified by the process requirements. 11.2.4 Flue gas temperature control: Temperature at the inlet of the rising pipe for raw gas coming out of the coke oven carbonization chamber: 830°C; Temperature at the outlet of the rising pipe for raw gas coming out of the coke oven carbonization chamber: 500–550°C, with a minimum of 450°C. 11.2.5 Steam production: The amount of steam produced is calculated based on the daily coke pushing volume, approximately 100 kg per ton of coke ； 11.2.6 Soft water parameters: The feed water shall meet the requirements specified in GB1576/T-2018 \"Water Quality for Industrial Boilers\", with the hardness of the treated feed water not exceeding 0.03 mmol/L. 11.2.7 Desalinated water level: 800mm–4000mm; desalinated water temperature: 104℃±2℃. 11.2.8 Deaerator level: 800mm–1100mm; rated output: 20t/h. 11.2.9 Effective volume of the deaerator tank: 10m3; operating pressure: 0.02MPa ； Temperature: 104°C, oxygen content in the effluent: ≤0.015 mg/L ； 11.2.10 Drum liquid level: 250mm–350mm; drum operating pressure: 0.7–1.2 MPa (G); design temperature: 204°C; operating temperature: 170–192°C; rated evaporation capacity: 14.84 t/h; steam-water circulation method: forced circulation ； 11.2.11 Main parameters of the rising pipe: Design pressure: P=1.8 MPa; operating pressure: Pc=1.2 MPa. Design temperature: 210°C; operating temperature: 192°C (175°C). When the coke oven is operating at full capacity, saturated steam at a pressure of 0.6–1.2 MPa is generated, with 80–100 kg of steam produced per ton of coke. 11.3 Shift handover: The shift handover procedure must be strictly followed. The person handing over the shift should prepare everything in advance, while the person taking over should carefully check and inquire about the operation status of the previous shift, as well as ensure that the equipment and machinery are in good condition and that proper maintenance has been carried out. Only when no abnormalities are detected and all conditions for shift handover are met can the handover proceed. 11.4 Job Responsibilities 11.4.1 Starting up the waste heat boiler 11.4.1.1 Inspection of the electrical system: Check whether the power supply meets the required voltage; turn on the switch and verify that the voltage is at the specified level, as well as ensure that the voltage in the distribution cabinet is also at the rated value. Close the switches one by one in the order of main circuits first and then branch circuits, to check whether the control circuit is functioning properly. 11.4.1.2 PLC system inspection: Check whether all signals are normal, the UPS power supply is functioning properly, and there are no alarms in the PLC system. 11.4.1.3 System inspection 11.4.1.3.1 Check that the valves in the system are in the correct open or closed state; the valve blind plates should be removed, safety valves must have passed calibration and their seals must be intact, and the lower valves should be fully open and not closed ； The manual testing of the electric control valve is normal. 11.4.1.3.2 The lubrication oil level in each pump should be between 1/2 and 2/3 of the capacity; manual rotation of the pump should not result in any sticking or jamming, the cooling water circuits must be unobstructed, and the pump should rotate in the correct direction after being filled with water and subjected to a test run ； 11.4.1.3.3 Check the level gauge: its indication is clear and free of dirt, and the remote level gauge shows normal readings ； The steam valves, water valves, and drain valves are in good condition with no leaks, and they operate smoothly ； The gauge is installed in the correct position and its scale is accurate; there are distinct red marks at the normal water level as well as at the high and low limit water levels ； A protective cover equipped with a flushing water level timer to prevent staff from getting burned ； Adequate and reliable lighting ； Insert the water level gauge. 11.4.1.3.4 Check the pressure gauges; the dials should be clear. Red lines are marked at the operating pressure range on the pressure gauges for the steam drum and those for the superheated steam outlet ； The pressure gauge pointer is at zero ； Passed verification, equipped with a verification mark and a lead seal ； Well-lit ； Install a pressure gauge. 11.4.2 System Startup 11.4.2.1 Startup and Operation of the Deaeration Pump (Power-Frequency Pump) 11.4.2.1.1 Before operation, the desalination water tank must be filled with water. The vent valve at the top of the deaerator can be opened slightly; it should be closed down to a slight opening once steam begins to emerge from it after the system reaches operating temperature, with only a tiny amount of steam escaping. 11.4.2.1.2 Close the outlet gate valve or keep it slightly open to prevent excessive current during pump startup. After starting the pump, gradually open the outlet valve and let it run for about 10 minutes. Check that the outlet pressure remains normal without significant fluctuations. Use a clamp meter to measure the rated current, and monitor the temperature of the motor and bearings to determine whether the motor is under normal load. 11.4.2.1.3 Slowly fill the deaerator with water to 1/2 of its capacity; during this process, check on site for any leaks and address them promptly. Once everything is normal, switch to automatic water filling. 11.4.2.1.4 Check whether the settings of the automatic control parameters are correct. 11.4.2.2 Startup and operation of the drum feedwater pump (power-frequency pump). 11.4.2.2.1 Before operation, the deaerator must be filled with half water; first, air inside the pump should be removed. Once the pump is filled with water, test it to determine whether the rotation direction is correct, and check whether it rotates smoothly without any abnormal noises. 11.4.2.2.2 Check that the valves in the pipelines before and after the drum feedwater pump are unobstructed; the outlet valve should be closed or slightly open. Start the pump, then gradually open the outlet valve. After running for about 10 minutes, verify that the outlet pressure is normal with no significant fluctuations. Use a clamp meter to measure the rated current, check the temperature of the motor and bearings to determine whether the motor load is normal, and record the motor temperature. 11.4.2.2 .3 Slowly fill the drum with water until it reaches the normal level; during this process, check on site for any leaks and address them promptly, and verify that the liquid level display is functioning properly. After that, enable automatic water filling and set the automatic control parameters correctly. 11.4.2.2 .4 Check whether the settings of the automatic control parameters are correct. 11.4.2.3 Force the start-up of the circulation pump (variable frequency). 11.4.2.3.1 Before starting, check that the water level in the steam drum is normal, as well as that the pressure and flow rate in the cooling water system are normal. 11.4.2.3.2 Check that the oil level of the bearing lubricant is between 1/2 and 2/3; there should be sufficient oil, with no signs of leakage. 11.4.2.3.3 Open the inlet valve and check that all air inside the pump has been expelled and the pump is filled with water. Ensure that all air in the shaft seal and cooling system has also been removed. Manually rotate the shaft to see if it moves freely; then conduct a trial start to verify that the rotation direction is correct and that there are no abnormal noises. For hot starts, the pump body must be preheated in advance, with a temperature rise not exceeding 50°C/h. The difference between the medium temperature and the pump casing temperature should not be more than 40°C. 11.4.2.3.4 When starting the water pump, gradually increase the frequency to around 15–20 Hz. Observe whether there are any abnormal conditions during operation; the pressure should remain relatively stable without significant fluctuations ； Once normal operation is achieved, gradually increase the frequency to the appropriate value. During operation, use a temperature gun to check that the surface temperature of the bearing housing does not exceed 90°C, the temperature of the outer ring of the bearings does not exceed 100°C, and the temperature of the motor casing should be below 70°C and no higher than 90°C. 11.4.2.3.5 When the temperature inside the drum exceeds 90°C, close the vent valve, gradually increase the frequency of the circulation pump to normal operating levels, and constantly monitor the water level in the drum to prevent dryness of the water inside due to too rapid an increase in frequency. The system should then stabilize as temperature and pressure rise gradually. 11.4.2.3.6 The deaerator can be fed with heated steam once the drum pressure reaches 0.3 MPa. 11.4.2.3.7 Precautions: Before heating up, start the feed water pump of the water heater to prevent overheating due to dry burning of the water heater. As the heating furnace continues to generate heat, the water temperature inside the waste heat recovery equipment rises. Due to water expansion, it is possible for the water level in this equipment to exceed the maximum allowable level, triggering audible and visual alarms from the level control device. In such cases, it is necessary to activate the drain valve in a sequential manner to lower the water level to an appropriate value; once the high-level alarm is resolved, normal operation can resume automatically. 11.4.2.4 Operation of the deaerator: This system uses a low-pressure rotary film type thermal deaerator. Under normal operating conditions, the pressure is 0.02–0.04 MPa and the temperature is 104±2°C. The deaerator is used to remove oxygen from the water, thereby preventing oxygen-induced corrosion of the equipment and extending its service life. 11.4.2.4.1 Checks before starting the deaerator: The deaerator water level is normal ； Unobstructed water inflow and outflow ； Pressure gauge valve in open position ； The bottom valve of the safety valve (if any) must remain fully open and shall not be closed; the inlet blind flange should be removed for inspection ； Keep the deaerator head vent valve slightly open ； Inspection of the steam heating pipeline valves shows no leaks, and the electric actuators are functioning properly ； When the steam pressure is greater than 0.3 MPa, slowly increase the valve for the auxiliary heating steam supplied to the deaerator. Pay attention to any vibrations in the deaerator; it should not be opened fully all at once. The temperature inside the deaerator should rise gradually, at a rate of about 1–2°C per minute. During this heating process, it is necessary to monitor parameters such as vibration of the device, expansion displacement, water level, and pressure. When the temperature approaches 100°C, observe the steam emission from the vent pipe of the deoxygenation head and adjust the valve opening so that only a slight amount of steam is emitted. 11.4.2.4.3 When the deaerator temperature is close to 100°C, the electric valve can be activated to automatically adjust the steam supply to the deaerator in order to maintain normal operation; at this point, the valve for auxiliary heating steam can be closed. 11.4.2.5 Steam connection operation (supplying steam): When the steam pressure in the waste heat recovery equipment is close to or higher than that of the external steam network, slightly open the valve for supplying steam from the steam drum in order to warm the main steam pipes; at the same time, open the drain valves on these pipes to release any condensed water ； The vent valve can be opened, but the external supply valve cannot. The time required for pipe warming depends on factors such as the length and diameter of the pipes as well as the steam temperature; the end time for pipe warming can be determined when the drain valve stops discharging water. When warming up the pipes, attention should be paid to the expansion of the pipes as well as the condition of their supports. If any abnormalities are detected, the process of warming up the pipes should be stopped, and the faults and defects must be resolved. Only when there is no condensate at the steam trap can the steam valve be opened fully to supply steam; the vent valve should be closed, and opening it should be done slowly. At the same time, pay attention to whether there are any unusual noises from various components of the boiler; if such noises occur, conduct an inspection immediately, and shut down the boiler for inspection if necessary. Always keep an eye on the water level in the steam drum. After the steam valve is opened, the handwheel should be turned back half a turn to prevent it from failing to rotate due to thermal expansion. To avoid steam containing water, it is prohibited to operate the steam drum at high water levels, and the drain valve must not be closed. 11.4.3 Regular Pump Switching Operation 11.4.3.1 Preparatory checks before starting the pump: 11.4.3.1.1 Remove any debris from the pump, motor, and surrounding area; check that the pump’s inlet and outlet flanges, valves, and oil sealing lines are in good condition with no leaks, and ensure that the foundation bolts are tight and intact. 11.4.3.1.2 Check that the knob on the field operation panel is set to the remote mode, and that the DCS start command is in the correct state. If maintenance is being carried out, ensure that the rotation direction of the pumps and fans is correct as well. 11.4.3.1.3 Check whether the pressure gauge hand valve is open and whether the pressure gauge is in good condition; check (replace) the lubricating oil in the bearing box, filling it to 1/2 to 2/3 of the level indicated by the oil sight glass. 11.4.3.1.4 Rotate the pump’s drive shaft 3–4 times; apply even force during rotation to check whether the moving parts move smoothly, without any signs of tightness or jamming, and to listen for any abnormal noises inside the pump. Also, install protective covers on the idler wheels. Check that the cooling water system is stable, the temperature is normal, and the valve positions of the pump heat exchangers and other components are correct. Check to ensure that the centrifugal pump is filled with water, and carry out exhaust work. After the inspection is complete, notify the operator inside to request pump switching. 11.4.3.2 Start the motor to operate the pump. In the control room, monitor the DCS displays; on-site, check the pump starting current and frequency, changes in outlet pressure, the temperature of the pump motor and bearings, as well as any vibrations in the unit. Look for signs of leaks, abnormal noises, or unusual odors. Any abnormalities detected should be addressed promptly. Stop the pump once the readings on the pressure gauge and current meter indicate normal conditions; also, check on-site to ensure that the pump is not running in reverse ； If so, the pump should be stopped immediately; after the outlet valve is closed, the standby pump should be started again. After verifying that the started backup pump is operating normally, adjust it to operate in normal mode. Keep proper records of regular on-site inspections. 11.4.4 Emergency Plans 11.4.4.1 Boiler Overpressure Incidents 11.4.4.1.1 Symptoms of Boiler Overpressure: A rapid increase in steam pressure, exceeding the permitted operating pressure; the gauge pointer goes above the \"red line\", and the pressure continues to rise even after the safety valve activates. 11.4.4.1.2 Handling of boiler overpressure: Manually open the safety valve or electric relief valve. During the pressure relief process, close attention is paid to the water level in the drum, as well as the operation of other related auxiliary equipment such as the forced circulation pump. 11.4.4.2 Boiler water shortage accidents 11.4.4.2.1 Symptoms of boiler water shortage: The dual-color water level gauge indicates a completely gas-filled state, and a low-level alarm is triggered via remote display. To prevent the forced circulation pump from running dry, it should be stopped immediately; the cause must be identified promptly, and if there is significant water leakage in the system, emergency repairs should be organized. Check whether the feed water pump of the drum is operating properly; start the backup pump to supply water. If there is a prolonged lack of water and the coke oven remains in a state of continuous heating, and if the upward tube suffers from dry burning for an extended period (but not more than 48 hours), it is necessary to prevent a sudden increase in pressure inside the upward tube due to the large amount of water being injected into it from the water-cooled system, as this could lead to safety accidents that may injure people or damage equipment. Therefore, before starting the forced circulation pump, allow water to flow slowly into the upward tube through the height difference between the drum and the furnace, thereby gradually cooling the upward tube. First, remove any air from within the pump and from the heat exchangers on the pump body. Open the inlet and outlet valves of the upward tube, slightly open the inlet water valve, and fully open the vent valve (steam will be emitted from this valve, so care must be taken to avoid burns). This allows the temperature inside the upward tube to drop slowly, reducing the temperature difference between the water and the tube walls. Monitor the external temperature of the upward tube; it should gradually decrease over time. As time passes, gradually increase the opening of the inlet valve. Once the conditions are suitable (when water starts to emerge from the vent valve), slowly open the outlet valve to allow water to flow back naturally throughout the system and fill the pipes. During this process, gradually reduce the opening of the vent valve depending on the stability of the water flow. Continuously monitor the external temperature of the upward tube until it reaches a value close to the normal range – usually below 80°C in summer and below 65°C in winter. Check that the temperature inside the drum also increases gradually. Once the drum water level is normal, start the forced circulation pump; the temperature of the outer wall of the rising tube should not exceed the allowable limit. In the event of a short-term water shortage, restart the forced circulation pump once the drum water level returns to normal to restore the system. 11.4.4.3 Boiler overfill accident 11.4.4.3.1 Symptoms of boiler overfill: The dual-color water level gauge shows the water level at its maximum, and the high water level alarm sends an alert signal. In severe cases, a large amount of water is carried along with the steam; water hammer sounds occur in the steam pipes, and steam and water leak from the connecting flanges. 11.4.4.3.2 Handling of a full boiler – Flush the water level gauge to determine whether it is a minor or severe case of overfilling. Method: First, turn off the water level gauge and the water connection valve; then open the drain valve. If the water level line can be seen dropping, it indicates a slight level overload. Stop supplying water, and activate the electric emergency drain valve. If remote operation is not possible, proceed immediately to the site to manually drain water until the normal level is reached. In the event of severe water filling, emergency shutdown measures are taken by closing the steam valves to prevent water from entering the steam pipes and thereby limiting the impact of the incident; personnel then rush to the site to drain the water promptly. 11.4.4.4 Boiler slugging accident 11.4.4.4.1 Phenomenon of boiler slugging The water level in the gauge fluctuates sharply up and down, and the water level line becomes blurred. The alkalinity and salt content of the water in the pot are significantly above the limits. Steam contains a large amount of water, resulting in a decrease in its quality. Water hammer occurs in the steam pipes, and steam and water leakage takes place at the flange connections. 11.4.4.4.2 Handling of boiler steam-water flooding: Reduce the main steam valve to lower the boiler’s evaporation rate, and decrease the load while maintaining stability. Fully open the emergency drain valve of the steam drum, and appropriately perform blowdown at the lower part of the drum. For boilers that use chemical dosing inside the boiler, the dosing should be stopped. Check the drain valve on the open steam pipe. Notify the water treatment personnel to take measures to ensure a supply of qualified softened water, and increase the frequency of sampling and testing of boiler water until it meets the required standards before normal operation can be resumed. After the accident is resolved, the water level gauge should be flushed promptly.