Calculations regarding flash economizers

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Does anyone know the design calculations for a flash economizer (flash tank)? The information available from various sources relates to the design calculations for gas-liquid separators. By using the critical velocity of the gas and its flashing flow rate, it is possible to determine the flow cross-sectional areas for both gas and liquid. In the case of gas-liquid separators, the length of the flash tank is calculated by determining the liquid retention time, thereby finding the volume of liquid; this volume is then used together with the cross-sectional area to calculate the length of the flash tank. The time specified in the book is 10 minutes as the residence time of the liquid in the pre-compressor gas-liquid separator. If we use this value for calculation, the size of the vessel would be excessively large; in reality, a flash tank of such large dimensions isn’t necessary. I’m seeking advice on what residence time should be used as a parameter for calculation – it would be ideal to have some written reference for this. If none is available, I hope reasonable explanations can be provided. Thank you all~~~