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Contact:Miss Cheng

Address:No. 6, No. 18 Zhongtai science and Technology Park, No. A02, Huayuan Road, Garden Road, Baohe Economic Development Zone, Hefei

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Confirmation of Preset Parameters of Marine Pressure Regulating Valve

It is considered that when liquid ammonia (NH3) is properly used to prepare ammonia for SCR denitrification restorer, liquid ammonia is heated by evaporator and converted into gas ammonia, then transported to SCR denitrification area through plant pipeline. If ammonia is transported at too low background temperature, it will liquefy and no normal ammonia supply will occur, which will affect SCR. Operation of denitration.



In order to avoid the liquefaction of ammonia, a marine pressure regulating valve should be added to the ammonia outlet pipeline of the evaporator. Through the marine pressure regulating valve, the pressure of ammonia atmosphere is adjusted to a lower permanent fixed value, so that the condensation temperature of ammonia under this constant pressure is lower than the background temperature at the beginning and end, which can prevent the ammonia from being transported. The liquefaction phenomenon appeared in the process.



The pressure regulating valve of ammonia atmosphere usually adopts self-operated marine pressure regulating valve, that is, it does not need external pressure, and uses ammonia self-energy + wire as power source to control the position of the valve core, improve the pressure difference and flow at the inlet and outlet ends of the valve, and make the pressure behind the valve stable. The selection of self-propelled marine pressure regulating valve is mainly related to medium, pressure, temperature and flow rate. According to the special physical properties of ammonia, its pressure is greatly affected by temperature. The higher the temperature, the higher the pressure, the higher the relationship between the pressure and temperature of ammonia under the condition of gas-liquid two-phase reaching the maximum is shown in the table below. Marine pressure regulator valves are usually installed outdoors and indoors in cold and overcast areas. Their office temperature varies greatly with different office background. If the selection parameters of marine pressure regulator valves are unreasonable and the pressure difference between the inlet and outlet is too large, the pressure behind the valve will not be able to control to the set value. Ammonia in the pipeline behind the valve is in the back. Liquefaction will occur when the temperature is too low.



The corresponding value of pressure and temperature < br />.






2. Confirmation of temperature and pressure parameters



The liquid ammonia enters the evaporator and is heated, then the latent heat liquid is released to gas ammonia. The ammonia gas is transported to SCR ammonia spraying unit through the pipeline of the plant after the pressure is lowered by the marine pressure regulating valve. The temperature of ammonia air at the evaporator outlet is exactly the same as that of liquid ammonia before heating (near the background temperature). Considering the problem, the short time of ammonia gas in the evaporator will cause the temperature to rise slightly. The actual temperature of ammonia gas outlet of the evaporator is slightly higher than that of liquid ammonia, that is, the office temperature of the pressure regulating valve for ships is slightly higher than that of the background In addition to the background temperature, the specific number is also affected by the evaporator structure presupposition, hot coal control temperature and other factors, generally not more than 50 C.



When SCR shuts down, the restraint valve on the ammonia pipeline at the outlet of evaporator closes and the marine pressure regulating valve stops working. At this time, the temperature of ammonia remaining in the evaporator will rise rapidly (20-30 C above the liquid ammonia temperature and no more than 60 C above the upper temperature), which will cause the internal pressure to rise, and the excessive pressure can pass through. The bypass check valve on the inlet pipeline of liquid ammonia flows back to the liquid ammonia pipeline to release the internal pressure of the evaporator and prevent the operation of the safety valve. In this case, the increase of the internal pressure in the evaporator has no effect on the marine pressure regulating valve. The upper pressure in the evaporator can not be used as the preset pressure for the selection of the marine pressure regulating valve. Otherwise, the selection pressure difference of marine pressure regulating valve is too large, and the precision of adjusting minor knuckles decreases in actual operation, even beyond the adjustment range, there is no way to guarantee the set pressure at the outlet.



Because of this, the preset temperature of the self-powered marine pressure regulating valve can be reasonably confirmed according to the background temperature of its office, according to the supreme office temperature and the strongest working temperature, while the imported office pressure can be confirmed according to the gas-liquid two-phase at the corresponding background temperature to reach the maximum pressure.





3. Confirmation of Export Pressure



The outlet pressure of pressure regulating valve in ammonia atmosphere is based on the principle that ammonia does not condensate in normal operation, and the outlet pressure can completely overcome the resistance of pipeline. For most power plants, the outlet pressure of pressure regulating valve in ammonia atmosphere can satisfy the requirement by presupposition of 1bar. At this time, the pressure in ammonia atmosphere can completely overcome the resistance of pipeline, and the background temperature above - 19 C will not show the liquefaction of ammonia gas.





The preset pressure at the outlet of the marine pressure regulating valve can be appropriately increased to 2 bar. However, it is particularly clear that some projects are still incorrect because of incomplete weather data (early weather counts), and the rapid progress of urban construction and industrialization has resulted in background pollution and climatological deterioration. In recent years, air temperatures in parts of the South and North have shown contrast or extreme appearance. Elephant. For this reason, if there is no special requirement, it is proposed that the outlet pressure of the self-propelled marine pressure regulating valve should still be preset at 1bar to prevent the possibility of liquefaction of ammonia due to extreme temperature under extreme climatological conditions.



IV. Concluding remarks



The preset pressure and preset temperature at the inlet of ammonia self-powered marine pressure regulating valve shall be reasonably confirmed according to the background temperature of the locations of the power plant and the installation locations (indoor or outdoor). The setting of outlet pressure of marine pressure regulating valve should ensure that liquefaction does not occur in the process of gas ammonia transportation, and can supply ammonia steadily, satisfying the normal operation demand of SCR denitrification.



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Contact:Miss Cheng
Telephones:86-13524555517  
Address:No. 6, No. 18 Zhongtai science and Technology Park, No. A02, Huayuan Road, Garden Road, Baohe Economic Development Zone, Hefei
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