1 Test scheme The compression station operator slowly increases the air compressor outlet pressure setting value, thereby increasing the air compressor air volume, allowing more air to gradually enter the oxidation furnace, each adjustment amount is 10 kPa; at the same time, the main control operator Slowly turn on the oxidation furnace temperature control valve TCV 119 to maintain the oxidation furnace temperature in the normal process specification (921), and adjust the process water supply in time until the entire process system is stable. After each adjustment, the system will run stably for 1 d before making the next adjustment. During the period, the contact center laboratory conducts a full analysis of the relevant analysis project to confirm the impact of the test on the system.
2 Test requirements During the test, the speed of the air compressor pressure setting should be slower, and the parameters such as vibration and displacement of the air compressor should be strictly monitored to ensure safe and stable operation of the device; the main control operator should open the gas ammonia flow regulating valve. The speed must be as slow as possible to prevent the platinum net from burning out; the on-site operators should strengthen the inspection during the whole test process, and timely grasp the operation of the air compressor, the combustion situation of the platinum net, the change of process parameters and the exhaust situation; It is necessary to pay close attention to all process indicators and the operation of equipment and regulating valves. If there are any abnormalities, they should report and handle them in time; technicians track and monitor relevant parameters, and once an abnormality is found, immediately organize relevant personnel to analyze and take emergency measures.
3 When the test condition is met, the test is stopped immediately and the air compressor outlet pressure is restored to the value under the last stable operation condition: when the air compressor vibrates, the displacement value increases significantly or fluctuates greatly; when the system When the regulating valve PCV 108 (gas ammonia pressure control valve), the oxidation furnace temperature control valve TCV 119, and the ammonia evaporator circulating water regulating valve TCV 167 have one valve opening exceeding the regulation sensitive zone; when the ammonia evaporator capacity is insufficient; When the chimney is yellow smoke or the exhaust NOx content is 200 10 - 6; when the liquid ammonia consumption is significantly increased; the absorption tower outlet temperature TI 135 is greater than 20; other abnormal conditions that cause the test to fail.
4 Test and summary According to the requirements of the test plan, the test was completed from December 29, 2008 to January 4, 2009, and the air compressor outlet pressure was increased from 1 203 kPa to 1 260 kPa. On the New Year's Day holiday 3 days, stop the boost), the air compressor outlet flow rate reached about 17,350 m 3 /h, and the final nitric acid load reached 110% of the design load. Due to the downstream equipment load reduction, the nitric acid plant load was on January 4, 17: 41 returned to 100%, this overload test ended early.
(1) During the test, the temperature of the oxidation furnace was normal, the ammonia-air ratio was stable, and the various control indicators did not change much. The system production was basically normal.
(2) During the test period, the nitric acid concentration, the NOx content in the exhaust gas, the O 2 content in the exhaust gas, and the nitrous content in the finished acid were all maintained at the pre-test level, which could provide qualified products for the downstream equipment.
(3) During the test, the compressor outlet pressure increased by 40 kPa, the compressor pumping volume increased by 150 m 3 /h, and the highest daily nitric acid output reached 122 06 t, setting a new historical high in winter production since the start of the car. The highest daily output is 122 06 t (110 91% of designed Nissan) and the highest class is 40 92 t (111 54% of design class).
(4) During the test, the operation of the air compressor was mainly focused on. During the test, the vibration and shaft displacement of the compressor shaft were basically unchanged, and the four-stage X-direction and Y-axis vibrations increased. The four-stage bearing temperature is normal, up to 74.
The rest of the process parameters are normal, the inlet valve opening is up to 34%, and there is a certain amount of load space.
(5) The liquid ammonia consumption is reduced. From the statistical data, when operating under high pressure, the liquid ammonia consumption is significantly reduced. The average unit consumption of liquid ammonia before the test is about 0 291 5 t, which drops to 0 285 during the test period, and t is reduced by 0 006 5 t before the test. According to the average daily production of 121, 41 tons of nitric acid and 3,000 yuan / t of liquid ammonia, the daily increase in liquid ammonia consumption can save 2,367 yuan.
The analysis believes that the reason for the decrease in liquid ammonia consumption is: increase the outlet pressure of the air compressor, increase the absorption pressure, and increase the absorption efficiency of NO 2 .
(6) Daily production of nitric acid increased. After the air compressor outlet pressure is increased to 1 260 kPa (design pressure is 1 203 kPa), it is estimated that the average daily production of nitric acid can be increased by 6 yuan. According to the profit of 500 yuan per ton of acid, the annual benefit can be increased by 3,000 yuan.
(7) The cost of public works for tons of acid has not increased substantially. The outlet pressure of the air compressor is increased. After the increase in output, in addition to the increase in power consumption, the amount of other public works has not increased. Compared with before the pressure is raised, the air current of the air compressor drive motor increases by about 3 A, and the daily expenditure increases by about 299 yuan due to the increase in power consumption.
(8) Platinum net consumption costs increase. Due to the short test time, it is impossible to calculate the platinum net consumption of the catalyst. However, the platinum consumption of the platinum network during the test period can roughly calculate the cost increase caused by the platinum consumption. The consumption of platinum per ton of acid is 0 44 g, increasing by 0 06 g. The daily cost increase is: 0 06 120 300 = 2 160 yuan. This fee does not take into account the associated costs associated with increased frequency of platinum network replacement.
In summary, the economic benefits are increased approximately every day during the test period: 2367 5+ 3000- 299 3- 2160 = 2 908 yuan.
5 problems (1) The supply of gaseous ammonia does not meet the production needs well. When the air compressor pressure is 1 220 kPa and the gas ammonia pressure control valve PCV 108 is set to 1 335 M Pa, the opening of the TCV 119 has reached more than 70%. This opening is no longer within the ideal adjustment range of the regulating valve. With the increase in load and the increase in ammonia intake, TCV 119 is no longer sufficient. In this test we maintained the opening of the TCV 119 by increasing the set pressure of the PCV 108. At the end of the test, the PCV 108 set pressure increased from 1 335 MPa to 1 380 M Pa, an increase of 45 kPa, while the TCV 119 opening was still above 70%.
(2) Whether the compressor itself can operate safely under high pressure for a long time needs further observation and discussion. The four-stage vibration of the compressor showed an upward trend during the test. In March 2009, we used the favorable timing of liquid ammonia tank inspection to re-load the compressor in four stages and then reload it, and maintain it under the design pressure. The four-stage vibration can be stabilized at 7 8.
(3) The separation capacity of the steam drum is insufficient, resulting in a decrease in the quality of the high-pressure steam of by-products and a large water content in the steam. According to the statistical data, the boiler water consumption during the test period is about 400 kg / h more than the steam production before the load increase, reaching 1 050 kg / h.
(4) Whether the processing capacity of the ammonia evaporator can be further satisfied, it also needs to be observed. During the lifting process, the highest flow rate of liquid ammonia reaches 1 460 kg / h, which is 113% of the designed amount, while the circulating water used to evaporate liquid ammonia is only 49 water, especially when the liquid ammonia quality is poor, oil content, When the water content is high, the problem of evaporator effluent will be highlighted. At this time, the liquid ammonia pressure setting value is higher, and the TCV 119 opening degree is also larger. The system is prone to unstable operation and is likely to cause parking accidents. occur.
6 Test conclusions Based on the above analysis, as long as the bottleneck factors of the high-load operation of the control device are solved, especially how to ensure the stable operation of the compressor and the large opening degree of the TCV 119, a careful operation plan is prepared to improve the outlet pressure of the air compressor. The existing high-load operation of the existing nitric acid plant in winter is achievable, and the benefits are considerable.
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