Issue of CO content in the process gas after transformation
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I read in some sources that for Texaco water-coal slurry gasification gas at 4.0 MPa, a combination of medium-pressure shift and low-pressure shift is used, enabling the CO content in the outlet gas to be reduced to 0.4%. For gasification gas at pressures higher than 4.0 MPa, due to the effects of the shift reaction equilibrium, the CO content can generally only be reduced to 1.0%. I’m not sure if this is indeed the case; are there any cases of gasification gas at 6.5 MPa or 8.5 MPa where the CO content in the gas after shift is as low as 1.0% or even lower?
Among us, the voltage is reduced from high to low; there are four conversion units, with the CO% level being less than 0.4%, and the operating pressure is 6.5 Mpa
I’m not sure what device is being referred to on the second floor; how are the four furnaces allocated there – how many are medium-voltage and how many are low-voltage?
The relationship between the residual CO level after transformation and the operating pressure is not significant; it is mainly related to the process configuration and the production tasks of the entire system.
Qingdao Lianxin Company uses four series-connected reformers in the Liuhua large-scale fertilizer plant (the gasification unit is a SHELL powder gasifier). Since the CO content at the outlet of SHELL furnaces is much higher than that of GE furnaces, in order to meet the requirements of the process and production, 3–4 shift converters are often used to convert CO to meet the needs for hydrogen supply or ammonia production, whereas GE furnaces generally require only 2 shift converters to satisfy production demands.
6.5 Mpa, three-stage conversion; the CO content in the process gas after conversion is around 1%. In my opinion, around 1.5% is the most suitable value. We are involved in ammonia synthesis, and we use liquid nitrogen for washing – too high a CO level is certainly not desirable, while too low a level means that there isn’t enough cooling capacity provided by the liquid nitrogen washing process.
The relationship between the residual CO level after transformation and the operating pressure is not significant; it is mainly related to the process configuration and the production tasks of the entire system. If the value of t is too low, it results in high conversion costs, high steam consumption, and high system resistance. Each plant should determine an appropriate value based on its own operational conditions: for purified gas, the CO content resulting from methanation should be kept at 0.2%; for copper washing, it is generally advisable to keep this value around 1.0%; for alcohol hydroformylation, the value should range from 1.2 to 7.0%; and for liquid nitrogen washing, it should be around 1.0%
For the gasification process gases at 6.5 MPa and 8.5 MPa, after the shift process, a liquid nitrogen washing step is carried out before they enter the synthesis tower. Can meet the process requirements
If the poster uses the low-temperature method, it is best to keep CO below around 1.5%; if the thermal method, such as methanation, is used, it is best to keep it below 0.5%.
For gas production, we use normal-pressure fixed-bed batch gas generation; the shift reaction is carried out via full low-temperature shift, with an outlet carbon monoxide concentration of around 2.5 – it’s impossible to get lower than that.
In the gas after transformation, the CO content can only be adjusted to a limited extent during production operations, as it is primarily determined by the design. When designing, factors such as equipment investment, the products to be produced in subsequent processes, and the purification processes for the shifted gas (such as the recycling of CO after treatment with liquid nitrogen) must be taken into consideration.