Questions regarding the calculation of the cooling load for LNG cryogenic tanks
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How is the cooling load calculated for a cold storage unit designed to produce 300,000 standard cubic meters per day? I calculated it using a natural gas specific gravity of 0.72 kg/nm3, a specific heat capacity of 2156 J/(kg·K), and a temperature difference of 260 degrees, resulting in 1401 KW. Is this result correct? It seems to be 10 times different from what the design institute provided – what’s the issue? I’m thinking that if we assume the energy efficiency ratio of the entire refrigeration system is 3, then the motor power of the refrigeration compressor should be roughly 1/3 of the cooling capacity of the refrigeration chamber. Is that correct to say?
As a supplementary note, the above calculation does not take into account the latent heat of vaporization of natural gas; the latent heat of vaporization for natural gas is 510.25 kJ/m3. Therefore, 300,000 cubic meters per day corresponds to 1771 KW. When this value is combined with the specific heat capacity values mentioned earlier, the load should be 3172 KW, which is still more than three times higher than the value determined by the design institute. According to my calculations, the power of the refrigeration compressor should be less than 1/3 of that, that is, below 1000 KW. What’s the mistake?