Refrigeration process expander

Substituting the throttle value in a compression refrigeration cycle by a process expander both increases the efficiency of the cycle and allows power recovery. However, this is at the expense of increased capital cost. 

Fig. 1.2 Pareto-optimal solutions for the optimization of the dual independent expander refrigeration process (a) objectives and ,0 1) to be minimized, and (b) and (c) two decision variables. See Chapter 8 for further details.

Fig. 8.6 Schematic of the dual independent expander refrigeration process.

Fig. 8.17 Algorithm to calculate the number of natural gas and number of nitrogen refrigeration stages for the dual independent expander refrigeration process for LNG.

The Linde>Hampson process uses a thermodynamic process. Isothermal compression and subsequent cooling along an isobar is done in a heat exchanger. Joule-Thomson expansion connected with an irreversible change in entropy is used as the refrigeration procedure. Despite its simplicity and reliability, this method is now less attractive compared with new ones where cooling is primarily carried out in reversible processes (expander) and where less energy is required. 

The refrigeration process uses compressors and an expander system. The proximity of the refrigeration machinery enables the compressed hot ammonia to be used as a source of heat in the etinol plant. Thus, the acetylene desorption column used to drive off dissolved aratylene is heated by waste heat from the refrigeration machines. Only the excess heat is removed by a cooling tower, and this requires a minimum amount of cooling water. 

In order to calculate the refrigeration work requirements of oxygen plants, it is necessary to focus attention on specific refrigeration cycles. Two Claude type cycles are used in this report. One is a low pressure cycle in which all of the process air is used to produce the refrigeration. The expander exhaust is at 6 atm. Such a system involves about the lowest pressure that would be used in any air plant refrigeration system. This cycle is shown in Figs. 1 and 2. 

All of the mixed refrigerant processes use a multicomponent refrigerant mix, which is repeatedly partially condensed, separated, cooled, expanded. 

Joule-Thomson valves, besides being widely used in refrigeration processes, now are offering an attractive alternative to the turboexpander for small-scale light hydrocarbon (LPG) recovery applications, provided that ethane recovery is limited to below 30%. In a Joule-Thomson plant, the expander would be eliminated, but to obtain the same level of recovery as in a turboexpander plant, the compressor would have to be scaled up. Another advantage attributed to a Joule-Thomson plant besides overall simplicity of operation is the ability to operate under more widely varying inlet gas flow rates. 

Open-Cycle Operation. In many chemical processes, the product to be cooled can itself be used as the refrigerating Hquid. An example of this is in gathering plants for natural gas. Gas from the wells is cooled, usually after compression and after some of the heavier components are removed as hquid. This Hquid maybe expanded in a refrigeration cycle to further cool the compressed gas, which causes more of the heavier components to condense. Excess Hquid not used for refrigeration is drawn off as product. A typical open-cycle is shown in Figure 12. 

---