Reasons for the higher steam consumption in the gas column compared to the design value in CO2 stripping production
Thread Content
Our factory uses the CO2 stripping method for production; the gas consumption in the gas tower is much higher than the steam consumption specified in the design. What are the reasons for this and what are the solutions?
1. Are the tubes fouled?； 2. Is there an issue with the opening of the shell-side condensate level valve? ； 3. Is the conversion rate of the synthesis tower low?
Additional note: Is the ammonia-to-carbon ratio within the specified range?； Is the carbon dioxide temperature in the gas lift tower too low?
Is N/C normal, and what is the type of steam?
The design value represents the conversion rate under the design load, as well as the amount of steam required under those design conditions. It is recommended to analyze the conversion rate, the gas-liquid ratio, the water-carbon ratio, and the quality of the steam to determine the extent of deviation from the design specifications
The CO2 stripping process carries out decomposition and recovery directly from high pressure to low pressure, omitting the medium-pressure decomposition and recovery stage, because the ammonia-to-carbon ratio does not exceed 3.0 and the water-to-carbon ratio should be below 0.4. However, in actual production, due to the reasons mentioned by Haiyou, both the ammonia-to-carbon ratio and the water-to-carbon ratio exceed the values specified in the original design; as a result, steam consumption is inevitably higher than what was planned in the original design. Thanks to years of experience, we are now capable of handling everything from processes and design to static and dynamic equipment, and can undertake design, manufacturing, and installation tasks domestically. In plants with extensive operating experience, ammonia consumption and utility consumption have been reduced to quite low levels; however, such plants are still a minority. The concentration of their ammonia tank has dropped below 6%. The reason for the high consumption is a problem with the entire system, not just one specific aspect. For example, low stripping efficiency leads to an increased load on the low-pressure system; ammonia and carbon recovery requires water to be returned to the high-pressure section, resulting in an increase in the water-to-carbon ratio. To maintain a certain conversion rate, it is necessary to raise the ammonia-to-carbon ratio. These passive measures further increase the load on the stripping tower and also raise the load on the low-pressure system. As a result, the entire urea production system operates under conditions of high consumption. The fundamental reason is the inability to actively control the water-carbon ratio of the system. If the water-to-carbon ratio can be controlled, the ammonia-to-carbon ratio can also be controlled accordingly, thereby increasing the conversion rate and allowing the system to operate in an optimized state with all consumptions at the designed levels.
The key is to maintain balance among all the systems (high-pressure, low-pressure, hydrolysis, evaporation and granulation), without neglecting any of them.