How to calculate the water content in gases; those who provide perfect answers will receive a large financial reward
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For a certain single gas, after being washed with water spray, compressed (to 0.3 MPa), and cooled (to 40°C), what is the water content in the gas? Without conducting any analysis, what data can be used to estimate the approximate content? For example, what is the moisture content of carbon dioxide gas after the above treatment? What would the values be if other gases such as acetylene, methane, hydrogen, etc., are used instead? Do different gases have the same water content?
To calculate the water content in a gas, it is necessary to know the saturated vapor pressure of the gas and the actual temperature. The maximum water content that a gas can achieve at a specific temperature is determined by its saturated vapor pressure. The water content that a gas may reach after cooling can be determined by consulting a table of the saturated vapor pressure of water and using formulas. Information on carbon dioxide gas can be found by consulting gas property tables. When using other gases such as acetylene, methane, hydrogen, etc., their water content may vary, as different gases have distinct physical properties, including saturated vapor pressures. In addition, it is also necessary to know the pressure and temperature conditions of the gas before and after treatment, as well as whether it is saturated. If the gas is in a saturated state, its water content will be higher than that in an unsaturated state. In short, the main data required are the saturated vapor pressure of the gas, temperature, and pressure. Different gases have different water contents. .
Water content (vol.%) = Saturated vapor pressure of water at 40°C / System pressure (absolute pressure) x 100； For this case, the saturated vapor pressure of water at 40°C is 0.007375 MPa; the system pressure is 0.3 + 0.1 = 0.4 MPa. The water content (in vol.%) is calculated as 0.007375/0.4 x 100 = 1.844%. Since CO2 dissolves in water, the calculations above are approximate values. The calculations are more accurate for methane and hydrogen, which do not dissolve in water. Acetylene has a high solubility in water, so it is necessary to refer to tables showing its solubility levels and use the corresponding saturated vapor pressure data for calculations
Calculations using Aspenplus: For the carbon dioxide and water system, carbon dioxide accounts for 99.0111% and water accounts for 0.9888%; for the acetylene and water system, acetylene accounts for 98.3582% and water accounts for 1.64179%; for the methane and water system, methane accounts for 97.2618% and water accounts for 2.73816%; for the hydrogen and water system, hydrogen accounts for 81.5968% at Seikazi Station, with water accounting for 18.4032%