Refrigeration unit

The student undertaking a design for the first time often finds this unnerving. There is often a reluctance to carry out the early stages of the project because the detail required for final decision-making is incomplete. However, it should be apparent that to wait until all information is available, and then make the decisions and carry out the calculations in one-hit is not the best way to proceed. 

Action Adopt a new way of thinking and approaching engineering problems — be prepared to re-assess decisions at every stage of the design, and incorporate necessary changes. Do not assume every problem has a particular method of solution and a single correct answer. 

Elements of Engineering Design An Integrated Approach, Prentice-Hall International, UK (1985). 

and Noble, R.D. (Eds), Problem Solving, AIChemE Symposium Series, Volume 79, Number 228, New York (1983). 

Note For Part II, references are included at the end of each chapter. General references are given in Sections 2.4 and 2.5, and Appendix L. 

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Natural gas Hquids are recovered from natural gas using condensation processes, absorption (qv) processes employing hydrocarbon Hquids similar to gasoline or kerosene as the absorber oil, or soHd-bed adsorption (qv) processes using adsorbants such as siHca, molecular sieves, or activated charcoal. Eor condensation processes, cooling can be provided by refrigeration units which frequently use vapor-compression cycles with propane as the refrigerant or by... 

Many units have waste heat recovery systems that generate low pressure steam from reaction heat. Such steam is often employed to drive adsorption refrigeration units to cool the reactor feed stream and to increase polymer conversion per pass, an energy-saving process that reduces the demand for electrical power. 

Energy source for driving the refrigeration unit (electricity, natural gas, steam, waste heat)... 

The thermocycle system can be operated only when condensing water is available at a temperature lower than the required chilled-water-supply temperature. Modifications for a centrifugal refrigeration unit include the installation of a small liqmd-refrigerant pump, cooler spray header nozzles, and a vapor bypass line between the cooler and the condenser. Without the compressor operating, a thermocycle capacity up to 35 percent of the refrigeration-unit rating can be produced. 

Refrigeration units modified for free cooling do not include the hq-uid-refrigerant pump and cooler spray header nozzles. Without the cooler refrigerant agitation for improved heat transfer, this arrangement allows up to about 20 percent of rated capacity. Expected capacities for both tnermocycle and free cooling are indicated in Fig. 12-21. 

In summary, starting with 105°F gas at atmospheric pressure, the theoretical work necessary to liquify one pound of methane is 510.8 Btu or 352 hp/MMcfd. The simplified liquefaction process, as illustrated, uses a turboexpander/compressor and a small propane refrigeration unit. The 41.25% efficiency breaks down as follows one-fourth contributed by the turboexpander/compressor at 35.8% efficiency one-sixteenth contributed by the mechanical propane refrigeration unit at 43% efficiency, at a moderate temperature where its efficiency is high and a large fraction—eleven-sixteenths—contributed at 58.2% efficiency by compression and Joule-Thomson condensation energy. 

The raw material at this plant is natural gas supplied by the El Paso Natural Gas Company from a nearby pumping station. In each process train, gas is compressed to 850 psig, dehydrated by an adsorption method to remove 100% of the water, then passed through a refrigeration unit to lower the temperature to -60°F. A separator removes liquids upstream of the turboexpander. 

For condensers, especially refrigerated units with high temperature difference, a check should be made for fogging tendency. Branan s Chapter 7 shows how to do this. 

Transport refrigeration - HCFC-22 and CFC-502 have been the refrigerants of choice for transport refrigeration units, although some applications are using ammonia as the refrigerant. The alternatives include various HFC blends. 

Many data cells in the CCPS Taxonomy use equipment boundaries found in available generic data sets in which equipment and service is similar to that in the CPI. The boundaries established for other data cells were generally combinations of normal equipment modules—such as pump, seals, coupling, motor and base plate, or refrigeration units—and functionally interdependent basic and auxiliary components, such as motor controllers. Boundaries may change as greater amounts of equipment reliability data become available. 

Refrigeration is needed for processes that require temperatures below those that can be economically obtained with cooling water. For temperatures down to around 10 0, chilled water can be used. For lower temperatures, down to -30°C, salt brines (NaCl and CaCF) are used to distribute the refrigeration" around the site from a central refrigeration unit. Vapor compression machines are normally used. 

BR — Barometric Refrigeration Unit G — Compressor CP — Gar Puller GT— Cooling Tower GV — Conveyor D — Drum or tank DS — Desuperheater... 

Figure 6-7B. Chilled water refrigeration unit using steam jet ejectors. By permission, Croll-Reynolds Co., Inc.

EVACUATING a SEALING EOUIPMENT FOR. REFRIGERATION UNITS, ELECTRIC LIGHT BULBS, RADIO TUBES AND VACUUM TUBES FOR RADAR EOUIPMENT, TELEVISION SETS, AND OTHER TYPES OF ELECTRONIC EOUIPMENT a RESEARCH APPARATUS... 

WATER VAPOR REFRIGERATING UNITS FOR AIR COND. a PROCESS WORK... 

Figure 11-1. Multibooster barometric refrigeration unit with barometric condenser. (Used by permission Ingersoll-Rand Company.)...

Figure 11-2. Surface condenser steam jet refrigeration unit. (Used by permission Graham Manufacturing Company, Inc.)...

Figure 11-3. Water-vapor relationship in steam jet refrigeration unit.

By means of this relation, the effect of water-flow rate and the required temperature drop in the refrigeration unit can he visualized. Thus, if the water requirement increases, hut is at a smaller At, it is possible that an existing unit may he capable of handling the load. 

Make up water for these refrigeration units is at 80°F, and feed water for the gas cooler unit is available at 90°F. Barometric water is 90°F. Items 1 and 2 are for a closed-circuit operation with return water at 68°F and total 175 gpm. Note that in order to consolidate the temperature levels of water, it is economical to establish a temperature, such as 55°F, which satisfies the bulk of the requirement, and then design the other phases of the plant process to also use this water temperature. Item 3 is an open-circuit operation because the water is sent to waste after absorbing certain corrosive vapors and cooling the bulk of the gas. 

The use of a combination dryer should be investigated when a very low dew point is necessary. Placing a refrigeration system ahead of an adsorption dryer will allow the more economical refrigeration unit to remove most of the vapor and reduce the load on the desiccant. 

Figure 20.1 Self-contained transport refrigeration unit (Courtesy of Fetter Refrigeration Ltd)...

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