Some experience sharing on the operation of auxiliary boilers in ammonia synthesis plants

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1. When starting the auxiliary boiler, press “RPB-C” on the auxiliary control panel of the DCS screen, or press the “Reset” button on the DCS flame detection screen. Note: After pressing the “RPB-C” reset button, wait for 5 minutes of purging time, then press the “RPB-C” reset button again; this will cause XV-1258 to open and FCV-1002 to become energized, after which FCV-1002 can be operated. 2. Before starting 2.101-BJA, contact the instrumentation team to confirm that the interlock for \"101-BJA stopped\" has been short-circuited; then press the reset button for the air preheater, so that the dampers of MCV-31 (1–4) and MCV-30 can be operated. After 101-BJA is started, it is possible to determine whether to reduce the air damper opening and by how much, based on the oxygen level and negative pressure. 3. When igniting 3.103-B, activate the interlocks of instruments PSL-04117 and PSL-04119 to confirm that 103-BJ and 103-BJA are operating properly, and control the pressure of PIAS-04115 to be above 1.5 KPa in order to prevent interlocks due to low pressure of the combustion air ； Control PRCA-04122 pressure at -100 Pa to prevent the furnace negative pressure low interlock. To reset Control Center 103-B, press the HS-04101 button on the auxiliary control panel. Confirm that KV-04101-2 is off (turns red), and KV-04101-1, KV-04101-3～6 are on (turn green) ； Confirm that KV-04102-2 is off (turns red), and KV-04102-1, KV-04102-3～6 are on (turn green). 4. The auxiliary oil pump is operating normally, and its color on the central control DCS screen is green ； The stop color is: red. The auxiliary oil pump can be operated in “automatic” or “manual” mode, similar to the “normal” and “bypass” modes of interlocks. 5. During operation, due to factors such as temperature, the pressure in the drum can experience significant fluctuations; therefore, special attention must be paid to the drum liquid level to prevent low-level interlocks from triggering, which could cause the system to stop and delay the start-up process. At the same time, attention should be paid to temperature changes in TI-1-43 to prevent interlocks from being triggered due to excessively high temperatures in the steam coil. When a significant increase in temperature is detected, the control room can adjust the situation by opening the PCV-13 pressure relief valve to increase the flow of steam; on-site adjustments can also be made by opening the air ducts. 6. The fuel gas flow rate FCV-1002 of the auxiliary boiler is linked to the high-pressure steam pressure PCV-1018; this is a rather complex automatic control system. When the pressure at PCV-1018 is low, FCV-1002 increases its output, thereby raising the steam production and the steam pressure ； The fuel gas flow rate FCV-1237 of the superheated burner and the superheated steam temperature TCV-1238 are linked together; when the temperature of TCV-1238 is low, FCV-1237 increases its flow rate to achieve automatic adjustment. The fuel gas flow rate FCV-1002 of the auxiliary boiler is linked to the combustion air flow rate FCV-1003 as well as the oxygen content ACV-6, enabling automatic adjustment to achieve optimal control; this ensures that combustion does not occur under conditions of excessive oxygen, while also preventing secondary combustion or even detonation due to too low an oxygen level. Consistent with this, the fuel gas flow rate FCV-1237 of the superheated burner and the combustion air flow rate FCV-1004 are linked together to form an optimized control loop. 7. The auxiliary boiler and the first-stage furnace share one flue duct and the convection section, as well as the same supply fans and exhaust fans; their combustion air and negative pressure levels influence each other (the impact of oxygen content is not significant). The air damper MCV-31-1～4 is located in the air duct of the blower; therefore, when the first furnace unit is just started up, as long as the damper remains open, an adequate amount of air can be drawn in to ensure proper combustion in the burners. Since the dampers MCV-31-1～4 are located in the air duct of the blower, once the blower is operating properly, these dampers should be closed promptly to prevent the combustion-supporting air supplied by the blower from escaping into the atmosphere through the dampers, thereby affecting the combustion in that section of the furnace. The two oxygen content meters for a furnace section, ACV-8-1 and ACV-8-2, are located on the east and west sides of the furnace chamber behind the air dampers; the value displayed on the control panel is the average of these two meters. The auxiliary boiler is similar to the first-stage furnace. Negative pressure is achieved by adjusting the damper (i.e., PCV-21) that controls the flow of flue gas from the auxiliary boiler into the convective section of the furnace. If the opening degree of the baffle is too small, the negative pressure in the furnace decreases or even turns positive; as a result, the amount of air drawn in by the burners is insufficient (the burners in auxiliary boilers are self-priming, using the negative pressure in the furnace to draw in air), leading to incomplete combustion and waste, as well as an increase in furnace temperature. Conversely, if the baffle opening is too large, an excessive amount of air is drawn in, causing the furnace temperature to drop. Furthermore, an excessive oxygen content in the flue gas causes corrosion to the furnace tubes.