Weaknesses of using space furnaces

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Feeding of the two HT-L demonstration units: In regard to the feeding and commissioning process of these two HT-L demonstration units, relevant personnel from Aerospace Coal Chemical Company conducted discussions and summaries, and established measures for the subsequent commissioning of the two HT-L units. First, the participants identified two common issues associated with the two HT-L units: high temperatures in the upper furnace section and excessive shutdowns due to flow rate interlocks. After analyzing the causes of these main problems, the attendees agreed on corrective measures and suggestions, as summarized below: I. Analysis of the reasons for high temperatures in the upper furnace section and corrective measures 1. Inaccurate measurement by the coal powder pipeline metering device. Cause: No pressure correction was applied during the calibration of the SWR flow meter. Measure: Recalibrate the SWR flow meter under various pressure and load conditions using CO2/N2, and verify it again after applying the pressure correction. 2. Problem of flow fluctuations in the pulverized coal pipeline. Causes: (1) The PID parameters of the pressure control circuit for the feed tank are too small, resulting in slow response when differential pressure control is used for the feed tank; (2) The flow meter in the inflation cone of the feed tank is inaccurate; (3) The flow meter used in the pulverized coal flow regulation circuit is of insufficient capacity, and the flow control valve has a limited range of adjustment; (4) The PID parameters of the numerical coal flow regulation circuit have not been tested for interference effects, and their settings are unreasonable ； (5) On Puyang Coal Powder Line No. 2, the coal flow does not increase when the valve opening is above 47%; it is necessary to check the valve and pipelines. (6) The damping time of the SWR flow meter needs to be reset to 30 seconds. Actions to take: (1) While performing calibration, introduce disturbances into the pressure difference control circuit for the gasifier and feed tank, and increase the proportional value of the feed tank pressure difference adjustment circuit ； (2) Re-calibration of the inflation cone flow meter in the feed tank ； (3) Replace the pulverized coal velocity rotameter with an vortex flow meter; the flow rate is increased from 0–100 Nm3/h to 0–500 Nm3/h. The valve element of the speed control valve is replaced to meet the requirements of the 0–500 Nm3/h range. (4) While calibrating the SWR flow meter, disturbances are introduced to the flow setpoint, so that the flow control loop remains stable within 1 minute for every 10% change in the flow rate of each pulverized coal branch, with the total oxygen/coal ratio fluctuating by less than 10% ； (5) Increase in furnace temperature – high level (6 sensors): shutdown after a 5-second delay at 1200°C; increase in temperature in the conical section – high level (2 sensors): shutdown after a 5-second delay at 800°C. These are two safety interlocks. 3. Impact of high volatile content in coal: Reason: The high volatile content in coal leads to high temperatures in the area around the burner tip. Solution: When using Shenmu coal, adjust the H2O/O2 ratio to 0.1. 4. Impact of coal particle size: Reason: Improper control of the three variables in the coal grinding system results in coal particles whose size does not meet the requirement of 90% being ≤90μm; there are relatively large particles present. Solution: Ensure that the coal particle size stays within the specified range. 5. Impact of temperature in the coal powder pipeline: (1) Low temperature of the gas carrying the coal powder ； (2) Poor heat tracing effect of the pulverized coal storage equipment. Measures: (1) Consider adding a steam heat exchanger to the gas delivery line; it is recommended that the owner install electric heat tracing on the pipeline from the pulverized coal flow control valve to the directional control valve. (2) It is suggested that Lou Yu examine the impact of the steam heat tracing drain valves and the back pressure behind these valves, in order to improve the heat exchange efficiency. 6. Impact of the burner swirl angle. Reason: The original design had a relatively large oxygen swirl angle; actual operation showed that the dark zone in the flame angle was short, resulting in limited operational flexibility. Measure: Based on the simulation results after regression, it was decided through collective discussion to improve the burner. 7. Impact of the matching between gasifier pressure and load: Reason: Fluctuations in the pressure of the gasifier itself can cause variations in the pressure difference in the pulverized coal feed tank, which directly affects the stability of the pulverized coal flow. Meanwhile, large fluctuations in the gasifier pressure can influence the flow rate of oxygen entering the burner, thereby indirectly affecting the shape of the flame. Measures: (1) Adjust the PID parameters of circuit 13PC0013 ； (2) Set 13PV0004 to automatic control; considering the potential impact of subsequent gas introduction on vaporization, set the value of 13PV0004 to be 0.5 MPA higher than that of the subsequent process during gas introduction. Regarding the influence on the heat exchange efficiency of the vaporizer coils, and taking into account the fluctuations in the gas introduction system during startup, it is recommended to operate three water circulation pumps in the medium-pressure boiler during startup, and increase the opening degree of the valves on these three water circuits. Once the system stabilizes, switch to operating two pumps with one as a backup for the water circulation in the medium-pressure boiler. Additionally, Puyang Longyu should recheck the density meter for soda water. Second, regarding the issue of the HT-L vaporization unit shutting down due to flow rate interlocks: in order to prevent the burner cooling water from vaporizing locally when the total pressure is low, the temperature control circuit for the burner cooling water was set at 105°C at the beginning of material feeding; this value was increased to 150°C once the pressure in the vaporization furnace rose to 4 MPa℃ ； The burner cooling water buffer tank still uses differential pressure control. III. Recommendations for the plant owners regarding precautions when operating the plant in the future: 1. Ensure stable pressure in the feed tank. 2. Maintain a stable flow rate in the pulverized coal pipeline. 3. Adjust the load gradually; the actual oxygen flow rate should be as close as possible to the theoretical value provided by the DCS. In the gasification section, it is important to ensure that the pressure controlled by the control system matches the load of the gasifier. 4. Pay attention to correcting any discrepancies between the readings from automatic and manual analyzers. 5. Monitor changes in the slag’s composition as well as its residual carbon content. 6. Analyze the quality of water used for cooling the coal nozzles and the water supplied to the medium-pressure boiler on a weekly basis, and replace or add chemicals as necessary. 7. During normal operation, conduct material balance calculations for the gasification system to detect any errors in the measuring instruments promptly. 8. Adjust the oxygen/coal ratio setting; change the initial oxygen/coal ratio for Shenmu coal to 0.82. When the coal supply increases, the oxygen supply should not increase accordingly; when the coal supply decreases, the oxygen supply should be reduced promptly. Finally, it was decided unanimously that these measures and recommendations should be communicated to the owners of the two demonstration projects without delay, and that more detailed discussions on operational procedures should take place with the owners before restarting the plants. Additionally, while communicating these measures, it is necessary to remind the owners to prepare the following tasks immediately: 1. Set up a limestone addition and measurement system for using coal with a high ash melting point. 2. Test the opening and closing times of the control valves that have been recently replaced. 3. Conduct a trial run of the feeding control process.