Utilities refrigeration cost

A low temperature of approach for the network reduces utihties but raises heat-transfer area requirements. Research has shown that for most of the pubhshed problems, utility costs are normally more important than annualized capital costs. For this reason, AI is chosen eady in the network design as part of the first tier of the solution. The temperature of approach, AI, for the network is not necessarily the same as the minimum temperature of approach, AT that should be used for individual exchangers. This difference is significant for industrial problems in which multiple shells may be necessary to exchange the heat requited for a given match (5). The economic choice for AT depends on whether the process environment is heater- or refrigeration-dependent and on the shape of the composite curves, ie, whether approximately parallel or severely pinched. In cmde-oil units, the range of AI is usually 10—20°C. By definition, AT A AT. The best relative value of these temperature differences depends on the particular problem under study. 

The effect of utilities costs on optimum operation was noted by Kiguchi and Ridgway [Pet. Refiner,. 35(12), 179 (1956)], who indicated that in petroleum-distillation columns the optimum reflux ratio varies between 1.1 and 1.5 times the minimum reflux ratio. When refrigeration is involved, 1. IRmm < flopt < 1 is used in the condensers, 1.2Rrniii < fLpt < 1 -4Rrn... 

The next step is to screen the candidate refrigerants with the objective of minimizing the utility cost. This step can be accomplished by examining the cost of... 

In addition to the fixed capital investment needed to purchase and install process equipment and auxiliaries, there is a continuous expenditure referred to as operating cost, which is needed to operate the process. The operating cost (or manufacturing cost or production cost) includes raw materials, mass-separating agents, utilities (fuel, electricity, steam, water, refrigerants, air, etc.), catalysts, additives, labor, and maintenance. The total annualized cost of a process is defined as follows ... 

Refrigerant temperatures greater than 32°F suggest the steam jet or lithium bromide absorption system. Between 30°F and —40°F, the ammonia-water absorption or a mechanical compression system is indicated. At less than —40°F, a mechanical compression is used, except in special desiccant situations. The economics of temperature level selection will depend on utility (steam, power) costs at the point of installation and the type of pay-out required, because in some tonnage ranges, the various systems are competitive based on first costs. 

The utilities required for steam jet refrigeration operation often determine the selection of these units, between manufacturers and between types of refrigeration. As the chilled water temperature off of the unit approaches 32°F, the cost of the basic unit and its steam and cooling water requirements rise rapidly. 

Operating costs can be estimated based on statistical analysis of operating costs in existing plants. Costs of waste disposal can be evaluated in the same way as costs for any chemical process since procedures for disposal include, in fact, unit chemical processes and operations. Costs of utilities and maintenance are best assessed based on the company data banks. Typical utility figures per m capacity of reactors in MPPs are 800-1100 kg steam/h, 60-80 kW power, and 7,000-8,000 kJ/h refrigeration capacity. 

Assume heat rejection from refrigeration is to cooling water. Calculate the total energy cost of the utilities,... 

The application of activated carbons in adsorption heat pumps and refrigerators is discussed in Chapter 10. Such arrangements offer the potential for increased efficiency because they utilize a primary fuel source for heat, rather than use electricity, which must first be generated and transmitted to a device to provide mechanical energy. The basic adsorption cycle is analyzed and reviewed, and the choice of refrigerant-adsorbent pairs discussed. Potential improvements in cost effectiveness are detailed, including the use of improved adsorbent carbons, advanced cycles, and improved heat transfer in the granular adsorbent carbon beds. 

The utilities required for the refrigeration system other than power are therefore very much less than for recompression with steam, although the capital cost and the cost of power will be much higher. 

An HD CatOx system having a capacity of 200 standard cubic feet per minute (scfm) is priced at approximately 150,000 (1992 dollars). Daily operating costs for utilities and the caustic for hydrochloric acid neutralization are about 200 (1992 dollars). The preheater s monthly operating cost would be 220. Monthly electrical costs for the extraction blower and refrigeration unit would be approximately 800 (D135319, p. 530 D13108Y, p. 50). 

Reactions are performed at temperatures of approximately 50°F (10.0°C) or lower to minimize polymerization and SO formation a costly refrigeration system is utilized to maintain low temperatures... 

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