Liquefied compressed gases with compressor

It is economic to cool the compressed methane for liquefaction by the gas that does not liquefy in the throttling process. In the Claude process, the gas at an intermediate temperature splits into two parts. One of them enters the expander and exhausts as a saturated or slightly superheated vapor, and produces work. The remaining gas is further cooled in the second heat exchanger and throttled to liquefy. The portion that is not liquefied is combined with the output vapor of the expander and recycled into the compressor. 

Chlorine is first cooled and passed through demisters to remove the water droplets and the particulates of salt. The cooled gas goes to sulfuric acid circulating towers, which are operated in series. Commonly, three towers are used for the removal of moisture. This stream often goes through dry demisters and then to compressors. The compressed gas is then liquefied at a low temperature. The noncondensed gas, called snift gas, is used for producing hypochlorite or hydrochloric acid. If there is no market for hydrochloric acid, the snift gas is neutralized with caustic soda or lime to form hypochlorite. The hypochlorite is either sold as bleach or decomposed to form salt and oxygen. 

The dry gas is usually compressed before use. The level of compression depends on the application. A large fraction of the world s output of chlorine is consumed on site. The production of ethylene dichloride (EDC) is the single largest-volume use. The dry gas supply pressure then is determined by the needs of the EDC process. Merchant chlorine will be liquefied. The choice of compressor output pressure is then an economic/technical balance with the requirements of the liquefaction process. Because some of the impurities in the chlorine gas are noncondensables, a chlorine-containing tail gas always results. Some of this chlorine value can be recovered directly or in the form of various byproducts. A system is also required for safe disposal of any unrecovered chlorine as well as any released from the process during emergencies. 

Nitrogen is liquefied in the process shown in Fieure 6-16. Nitrogen gas is fed at 25 °C, 1 bar (stream 1). The gas is compressed to 180 bar in a compressor with an efficiency of 85%. The precooler uses ambient water as the cooling medium and cools the nitrogen to 30 "C. The precooler uses cold vapor from the separator as the cooling medium this vapor leaves the precooler at 20 °C (stream). Perform the energy and entropy balances on the basis of 1 kg/s of liquid nitrogen produced. 

Direct feed of compressed chlorine to another process is possible only when the quality of the chlorine meets the user s needs. The receiving process determines and controls how much chlorine is taken from the header, but another control valve is necessary at the compressor discharge header in case the user attempts to take more chlorine than is available. The liquefiers normally handle the chlorine not taken by the direct user. It has been common practice to design the liquefaction plant for full cell output, so that the cells can operate at full rate during short upsets in the user s process. This approach may be modified to suit restrictions on maximum chlorine inventory. In any case, the liquefiers should always have some chlorine gas fed to them to keep them operational and ready to handle full chlorine production should the direct user suddenly stop taking gas. In addition, a supply of liquid chlorine may be needed for a suction chiller. A bypass line around the control with a restricting orifice sized for about 10% of full capacity at the control valve drop can meet this requirement. Any chlorine not taken... 

In a Heylandt liquefaction system with air as the working fluid, the gas enters the compressor at 0.101 MPa and 295 K and is compressed isothermally to 7.07 MPa. The expander handles 60% of the high-pressure gas stream and its work output is utilized to reduce the compression work. Determine the liquid yield, the total work per unit mass of gas compressed, and the net work required to liquefy a unit mass of air in this system. 

In a simple Linde liquefier producing oxygen, the liquid yield is determined to be 0.038. The compressor in the system operates between 0.101 and 18.18 MPa with an exit temperature of 300 K. The thermodynamic efficiency of the compressor is 70 %. If the heat leak to the liquefier system is 1 kJ per kg of gas compressed, what is the effectiveness of the heat exchanger and the work requirement per unit mass liquefied ... 

Consider a Claude liquefier with parahydrogen as the working fluid. The compressor operates isothermally at 295 K from 0.101 to 3.03 MPa. The expander flow-rate ratio is 0.7 and the expander work is utilized in the compression process. The condition of the gas at the inlet to the expander is 279 K and 3.03 MPa. What is the quantitative effect on the liquid yield, work per unit mass of parahydrogen compressed, and the work per unit mass of parahydrogen liquefied if the thermodynamic efficiency of the expander is 70% rather than 100% Assume that the compressor has a thermodynamic efficiency of 70% for both situations and the mechanical efficiencies of both compressor and expander can be neglected. 

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