Costs Vacuum systems

Patton, P.W., Joyce, C. F., Lowest Cost Vacuum System, Chem. Eng.,... 

We have a serious problem with styrene. If any stream contains more than 50 wt% styrene, the temperature of the stream must not exceed 145°C. Otherwise, the styrene will polymerize. This must be carefiilly considered when establishing the operation conditions for the two distillation operations. You may have to operate one or both colunms under vacuum. This will require you to estimate the amount of air that leaks into the vacuum columns and select and cost vacuum systems. In designing the distillation system, you are to consider the direct sequence and the indirect sequence. 

Because of the low efficiency of steam-ejector vacuum systems, there is a range of vacuum above 13 kPa (100 mm Hg) where mechanical vacuum pumps are usually more economical. The capital cost of the vacuum pump goes up roughly as (suction volume) or (l/P). This means that as pressure falls, the capital cost of the vacuum pump rises more swiftly than the energy cost of the steam ejector, which iacreases as (1 /P). Usually below 1.3 kPa (10 mm Hg), the steam ejector is more cost-effective. 

Other factors that favor the choice of the steam ejector are the presence of process materials that can form soflds or require high alloy materials of constmction. Factors that favor the vacuum pump are credits for pollution abatement and high cost steam. The mechanical systems require more maintenance and some form of backup vacuum system, but these can be designed with adequate reflabiUty. 

The cost of the filter station includes not only the installed cost of the filter itself but also that of all the accessories dedicated to the filtration operation. Examples are feed pumps and storage facihties, precoat tanks, vacuum systems (often a major cost factor for a vacuum filter station), and compressed-air systems. The dehvered cost of the accessories plus the cost of installation of filter and accessories generally is of the same order of magnitude as the dehvered filter cost and commonly is several times as large. Installation costs, of course, must be estimated with reference to local labor costs and site-specific considerations. 

Air is usually the basic load component to an ejector, and the quantities of water vapor and/or condensable vapor are usually directly proportional to the air load. Unfortunately, no reliable method exists for determining precisely the optimum basic air capacity of ejectors. It is desirable to select a capacity which minimizes the total costs of removing the noncondensable gases which accumulate in a process vacuum system. An oversized ejector costs more and uses unnecessarily large quantities of steam and cooling water. If an ejector is undersized, constant monitoring of air leaks is required to avoid costly upsets. 

It is necessary to consult manufacturers for final and specific selecdons. However, the followang guide data is reliable and should serve to check recommendations or to specify a system. It is advisable to try to accomplish the specific operation wth as few ejectors as possible, because this leads to the most economical operation and lowest first cost in the majority of cases. Figures 6-9A, B, and C are a basic comparison guide for vacuum systems. 

In many cases design modifications can substantially improve the productibility of the products and reduce their cost with improved product quality. As an example if voids exist the problem can usually be corrected by modifying or changing the plastic s composition and/or the use of a vacuum system during the casting. Understanding the effects of the process on the product is essential in making successful products. 

Accounting, plant construction costs, 48 Cost accumulation, 49 Affinity laws, 201, 202, 203 Air Inleakage, vacuum systems, see vacuum systems Air pressure drop, table, 106 Chart, 114 Orifice flow, 107 Air, absolute viscosity, 132... 

CVD does not usually require the low pressures which are necessary with sputtering, MBE, and other PVD processes. Consequently the vacuum system is simpler and less costly. Mechanical pumps are adequate for many operations. Vane pumps, built with corrosion resistant material, are preferred. If properly maintained, these pumps will operate for long periods of time. 

The importance of the first three of these factors has already been discussed. The temperature factor would include the cost of insulation plus the increase in metal thickness necessary to counteract the poorer structural properties of metals at high temperatures. Zevnik and Buchanan17 have developed curves to obtain the average cost of a unit operation for a given fluid process. They base their method on the production capacity and the calculation of a complexify factor. The complexity factor is based on the maximum temperature (or minimum temperature if the process is a cryogenic one), the maximum pressure (or minimum pressure for vacuum systems) and the material of construction. It is calculated from Equation 2 ... 

One practical advantage of pressure purging versus vacuum purging is the potential for cycle time reductions. The pressurization process is much more rapid compared to the relatively slow process of developing a vacuum. Also, the capacity of vacuum systems decreases significantly as the absolute vacuum is decreased. Pressure purging, however, uses more inert gas. Therefore the best purging process is selected based on cost and performance. 

Quadrupole Energy and spatial distribution of ions produced in the ion source is not critical Low cost and easy to couple to LC Tandem MS experiments available in triple quadrupole or Q-TOF systems for sub-structure information and/or quantitative analysis Vacuum system demands are minimum Low resolution and low accuracy in mass measurement except in Q-TOF systems Mass range limited to approximately 4000... 

There are two basic evaporator designs that are typically used atmospheric and vacuum evaporation (Metals Handbook 1987). Atmospheric evaporation principles are similar to those of a heated open tank, with the exception that the heated liquid is sprayed over plastic packing in order to increase its surface area and accelerate evaporation. Atmospheric evaporators on chrome plating lines have sometimes been used simultaneously as evaporators and as plating bath fume scrubbers. Atmospheric evaporators are considerably less expensive than vacuum evaporators. Typical atmospheric evaporator capital costs range from 2500 to 4000, while vacuum evaporator costs can be an order of magnitude or more higher. In atmospheric evaporator systems, however, vaporized water is not recovered, as it can be in vacuum systems. 

Due to the high deposition rates possible at atmospheric pressure, approximately 1000 A/mtn, wafer throughput can be as high as 200 to 400 per hour. Also, since this is an atmospheric pressure reactor, there is no expensive vacuum system, and the capital cost of the reactor system is modest. These two facts contribute to a low cost per wafer processed, and has allowed this system to remain in commercial use for over 13 years. 

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