Basis for determining the nitrogen gas production volume in low-temperature methanol washing
Thread Content
In the low-temperature methanol washing process, nitrogen is generally used for stripping during the hydrogen sulfide concentration step. Excessive amounts of nitrogen lead to waste, while too little nitrogen increases the loading on the concentration tower and results in waste of cooling capacity. What is the optimal amount of nitrogen to use? What is the basis for this?
Each set of equipment is different; the amount of nitrogen gas removed by lift ventilation at different loads is calculated based on the design values of that equipment at 100% load! It is also possible to determine whether the amount of nitrogen used in gas stripping is sufficient by analyzing the methanol composition at the bottom of the hydrogen sulfide concentration tower; meanwhile, this can be assessed based on whether the load on the thermal regeneration tower is too high.
A plant with a capacity of 600,000 tons. . . The nitrogen stripping volume at 100% load is 11,000 Nm3/h, which is the design value. . . Since it has not yet been put into operation, the operating values are pending. . .
Based on the temperature in the middle of the H2S concentration tower, the hydrogen sulfide content in the exhaust gas at the top, as well as the opening degree of the pressure self-regulating valve in the regeneration tower, and the H2S content in the methanol-depleted fluid after regeneration.
In general, when designing a process, a design value for 100% load is provided. For the specific changes in quantities during the actual production process, you may refer to the judgments of the people above for convenience.
The purpose of setting up the hydrogen sulfide concentration tower is: 1. To desorb CO2 and recover the cooling capacity of the system； 2. Concentrate H2S in methanol. The purpose of adding stripping nitrogen is to maximize the achievement of this goal. Therefore, factors such as temperature, the H2S content in the exhaust gases, and the H2S concentration in the methanol solution can all be used to determine the amount of nitrogen gas that needs to be added for stripping. In practice, this amount varies depending on the actual load, but it remains close to the value specified for full load operation.
Don’t worry about the actual operation – just add O(∩_∩)O, haha~. As long as you’re not concerned about a low inlet temperature of the feed gas heat exchanger and a high temperature of the lean liquid, and of course make sure not to lower the exhaust gas temperature too much, so as to avoid freezing the exhaust gas scrubber.
When designing the process, a design value for 100% load will be provided to you
The amount of nitrogen used for stripping is determined based on the amount of carbon dioxide in the lower section of the carbon dioxide stripping/regeneration tower; generally, the designed level of carbon dioxide in that lower section is 1%
A plant with a capacity of 300,000 tons. The nitrogen stripping volume at 100% load is 6000 Nm3/h, which is the design value. During the production process, this value generally does not change in response to load variations.
The real* moderator upstairs provided a very professional and logical analysis. Our inlet volume is 17,574 Kmol/h, and the amount of nitrogen used for stripping is 580 Kmol/h. Since the components differ, the amount of nitrogen required for stripping also varies. The purpose of adding an inert gas is to reduce the partial pressure of acidic gases in the gas phase above the phase interface, thereby driving away the remaining acidic gases from the methanol solvent. The amount of nitrogen used for stripping directly affects the cooling balance of the system; the more nitrogen used for stripping, the more cooling capacity is recovered by the system, and thus less cooling capacity is required from the chillers. Therefore, as much nitrogen as possible should be used for stripping, provided that the pipeline network allows it.