(1) Control the inlet pressure of the feed gas compressor. In any case, the inlet pressure of the raw material gas compressor should be greater than 0.12MPa (0.06MPa jumping), and the anti-surge circulating gas volume should be greater than 26.0km 3 /h to prevent the compressor inlet pressure from being too low and jumping. In the past, when the compressor inlet pressure was 0.11 MPa, the composition of the feed gas suddenly fluctuated, and the inlet pressure of the unit dropped rapidly. When the operator found it, the compressor was skipped and the whole system was stopped.
(2) Control steam temperature and pressure. The original design of the unit was designed to supply high pressure steam (11.2 MPa, 530) from three waste heat boilers and one auxiliary boiler. The high-pressure steam drives the ice turbine turbine and the generator turbine to work into medium-pressure steam (5.15MPa, 420) pipe network, medium-pressure steam-driven feed gas compressor, syngas compressor, and CO2 compressor turbine. Later, with the construction of new projects, most of the high-pressure and medium-pressure steam are supplied by coal-fired boilers. Therefore, it is important to ensure the quality of coal-fired boiler steam supply. It should ensure that a small number of self-produced steam temperature parameters are qualified, and the on-site steam system sprays. The water desuperheater is completely closed, and if necessary, the steam decompression station can be opened less. The superheated high pressure steam is greater than 460, and the superheated medium pressure steam is greater than 380. Otherwise, it is unfavorable to both the unit and the catalyst.
(3) Control system pressure. The system pressure should be greater than 3.2 MPa to ensure the decarburization absorption rate and CO2 purification degree, reduce the moisture brought into the decarburization by the process gas, and ensure the heat exchange efficiency of the reboiler.
(4) Control the temperature of the first and second stage reformers. Due to the low load, the temperature of a section of the furnace is relatively low. At 745~755 (normal 770~780), it can not only ensure the methane conversion rate, but also save fuel, and it is also beneficial to the temperature of the conversion tube wall. Appropriate air addition in the second-stage furnace not only benefits the system pressure, but also enhances the steam quality, and also ensures the conversion rate of methane in the second-stage furnace.
(5) Control the hydrogen to nitrogen ratio of the synthesis loop. The conversion system should control the amount of air added, and the hydrogen recovery unit will add more hydrogen to ensure the hydrogen-nitrogen ratio of the synthesis loop is 60%, which is beneficial to the ammonia synthesis reaction, which can reduce the power consumption of the syngas compressor and increase the waste heat of the ammonia synthesis tower. The amount of saturated steam in the boiler.
(6) Protect the air coil. Because the load is too low, the system process air is relatively small. In order to prevent the convection section air coil from overheating, medium pressure steam is introduced into the coil 5~10t/h. Lowering the outlet temperature of a reformer can reduce the convection section combustion. The air temperature can also protect the air coil.
(7) Adjust the gas turbine load. Due to the low system pressure, the outlet pressure of the air compressor can be controlled to be slightly lower to reduce the load of the turbine turbine. The load on the low pressure shaft of the compressor is required to be greater than 93.5%, and the circulation is greater than 43.5 dam 3 /h to prevent the unit from surging. .
In this way, the gas turbine turbine can save 0.2 dam 3 /h of fuel, and the saved natural gas can be used to increase the load and reduce the consumption of ammonia.
(8) Prevent compressor surge. In order to ensure that the system pressure is greater than 3.2 MPa, the method of reducing the speed of the compressor is often adopted. First, the anti-surge valve is opened to ensure that the circulation of the compressor unit is above the minimum flow to prevent the unit from surging.
2 problems with the device.
(1) The air distributor is damaged. The unit has been operating at 38% to 46% load since the winter of 2006. During the overhaul of the equipment, it was found that the air distributor of the second stage furnace was seriously burned out. The reason for the analysis is: due to long-term low-load operation, the air volume in the air coil is small and the pressure is low, the air flow rate is not uniform, causing the air distributor to vibrate, the nozzle combustion flame length is shortened, the combustion hot temperature zone is moved up, and the high-temperature gas of 1200 will be distributed. The appliance burned out.
(2) Material compressor jumps. When the device is operated at 13.0 dam 3 /h, the inlet pressure of the feed gas compressor is controlled at 0.11 MPa. Since the natural gas component supplied by the oil field fluctuates from 102% to 122%, the inlet pressure of the feed gas compressor drops rapidly, resulting in full System parking.
(3) Affect the decarbonization water balance. When the load is low, the system heat is low, the pressure is low, the decarburization water balance is not well maintained, and the regenerative tower liquid level is high. To prevent the loss of the lye, the regeneration tower return valve is closed, and the regeneration effect is not good, which affects the absorption rate.
(4) Syngas compressor surge. When the load is low, the system pressure is low, the syngas compressor speed, and the flow rate is low. On March 21, 2007, the on-site air compressor anti-surge valve suddenly opened, the system process air exited, the syngas compressor circulation decreased rapidly, and the unit surged. The on-site personnel quickly opened the unit anti-surge valve, closed the air vent valve with the handwheel to restore the air, and the unit gradually returned to normal, thus maintaining the continuous operation of the system.
(5) The hydrogen recovery dryer failed to regenerate. The hydrogen recovery load is low, the amount of regenerative tail gas in the dryer is not up to standard, and the regeneration is unqualified within the specified time, causing trace H2O and NH3 exceeding the standard at the outlet of the dryer, causing the cold box to freeze, the pressure difference is increased, and the pressure is forced to be cold. The tank is defrosted and produces less ammonia 4t per hour. Therefore, when the dryer is regenerated, it is necessary to manually adjust the amount of regeneration gas and regenerate within the specified time.
3 energy saving and reducing operation measures.
(1) Protect the two-stage furnace air distributor. Add medium-pressure steam to the air coil to ensure uniform gas flow rate in the coil, and the air flow rate is greater than 30m/s. When the system load is 38%~46%, the steam volume in the coil is required to be greater than 6t/h, which can protect the air distributor. Safe operation ensures that the air coil is not overheated and is also beneficial to the hydrocarbon steam reforming reaction of the second stage furnace.
(2) Maintain the balance of decarbonization water. When the decarburization water balance is not good enough, you can stop the energy-saving equipment hydraulic turbine to save heat. In addition, the following measures can be taken: increase the system pressure, reduce the process gas to bring in moisture; # absorption tower, the regeneration tower rinse water is reduced to the lowest (1t / h and 4t / h); increase the temperature of the tower solution on the absorption tower, by 70 Increase to 85;% increase the water-to-carbon ratio of the conversion system; & appropriately reduce the circulation amount, reduce the regenerative heat load; turn on the heat exchanger bypass to increase the temperature of the decarburization process gas.
(3) Protect the safety of the unit. When the load is low, do not only reduce the speed. Increase the opening range of the anti-surge valve of the unit to ensure that the unit circulation is greater than the surge. The turbine speed is greater than 8500r/min to prevent the governor from fluctuating and the unit surge.
(4) Reduce the auxiliary pot load. The coal-fired boiler increases the steam supply, reduces part of the burner, and reduces the load to a minimum of 0.8 dam 3 /h (full load 6.0 dam 3 / h). The saved fuel can be used as system load to increase ammonia production and reduce tons. Ammonia consumption.
(5) Ensure the stable operation of the generator set. Low-load operation cost is high. In order to reduce the consumption of tons of ammonia, the generator set driven by high-pressure steam turbine is started. The superheated high-pressure steam power generation of 80t/h is 2500kW, which is used in the internal power grid. The high-pressure steam drives the turbine to work and is reduced to medium pressure. The steam enters the medium pressure steam pipe network. In order to ensure the safe and stable operation of the generator set, it is required that the turbine steam volume is greater than 62t/h and the power generation capacity is greater than 1000kW to prevent the generator set from suddenly stopping.
(6) New process modification increases the synthetic circuit load. The 500,000 t/a methanol of Zhongyuan Dahua has been trial-produced in May 2008. The venting gas from the unit is led to the high-alloy furnace of ammonia (design 30 dam 3 /h), which can increase the output of 4 t/h ammonia.
(7) Enhance the sense of responsibility of the operator. When the ammonia plant is operated under ultra-low load, the operator should be extraordinarily meticulous, meticulous, often patrol the operation, be good at observing small changes in parameters, and take measures to reduce the cost of ammonia in the case of stable production.
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