Packed capital cost

At these lower conversions, the previously described multi-bed down-flow reactor may not be the best design. At the higher space velocities it is more expedient to have the liquid in up-flow, and the reduced penalty from axial (particularly) forward mixing means also that the necessary conversion can frequently be achieved in a single catalyst bed. Thus, the reactor design is considerably simplified, with an associated reduction in the capital cost for a given catalyst volume. The development of the design for an up-flow-packed bed reactor for the decomposition of sodium hypochlorite is described elsewhere [6] and will not be considered in detail here. 

In order to obtain a good rate of transfer per unit volume of the tower, a packing is selected which will promote a high interfacial area between the two phases and a high degree of turbulence in the fluids. Usually increased area and turbulence are achieved at the expense of increased capital cost and/or pressure drop, and a balance must be made between these factors when arriving at an economic design. 

In designing industrial scale packed columns a balance must be made between the capital cost of the column and ancillary equipment on the one side, and the running costs on the other. Generally, reducing the diameter of the column will reduce the capital cost though increase the cost of pumping the gas through the column due to the increased pressure drop. 

Case Study 1. Pump-and-Treat System with a Packed-Tower Air Stripper, McClellan Air Force Base Superfund Site, California, Operable Units B/C, 1987. The costs associated with pump-and-treat system used at the site were estimated in 1994. Costs were approximately 80 per pound of removed volatile organic compounds (VOCs) based on operating costs alone and approximately 150 per pound when capital costs were included (D141286, p. 135). It should be noted that the operation and maintenance costs for the an air stripper could not be separated from the total cost of the project. Capital cost and operating cost information for this project are summarized in Case Study 1. 

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. 

As shown in Table 5.33, the combination of IMTP packing and the ACT-1 activator results in smaller columns, less packing and lower capital costs. Packing volumes are 25% to 35% smaller, and capital costs are reduced by about 10%206. 

Hollow Fiber Small footprint Low capital cost Can be backwashed Can easily be integrity tested High membrane area per unit volume (high packing density) Plugging of fiber (inside-out feed) Bridging of fiber bundle (outside-in feed) Difficult to clean... 

Supplies, which are not raw materials or maintenance supplies, are considered as operating supplies. Examples are custodial supplies, safety items, tools, column packing, and uniforms. The cost of operating supplies will vary from 0.5 to 1% of the fixed capital cost per year [5]. Use an average value of 0.75%. 

Static extraction columns Spray column Baffle column Packed column (random and structured packing) Sieve tray column Deliver low to medium mass-transfer efficiency, simple construction (no internal moving parts), low capital cost, low operating and maintenance costs, best suited to systems with low to moderate interfacial tension, can handle high production rates Petrochemical Chemical Food... 

Table 1 Economic factors in packed tower design operating and capital cost factors...

The study by Hitzler et al. has illustrated the broad scope of potential hydrogenation reactions in SC-Some of the substrates investigated included m-cresol, benzaldehyde, acetophenone, 1-octene, and cyclohexene. Reactions were performed in 5 and 10 ml packed bed reactors and space times of up to 300 hr were achieved. Residence times of this magnitude render the issue of scale-up largely irrelevant for small (kilogram) quantities of product in a continuous process. This is advantageous for the commercialization of SCF reaction processes because it minimizes development and capital costs. 

In the design of industrial-scale packed towers, an economic balance is important between the capital cost of the column, its ancillary equipment, and the operating cost. If the diameter of the tower is reduced, the capacity cost will also be reduced, but the cost of pumping the gas through the column will increase because of the higher AP. 

A comparison of all the equipment is presented in Table CS7.3. For all the cases, the reactor volume and power consumption are given. The former indicates the capital cost, whereas the latter indicates the operating cost. A preliminary comparison reveals that SBC and EL-ALR are comparable but superior to the conventional BC. The volume of HSR is approximately 5.4 to 5.8 times higher than SBC or EL-ALR. However, the power consumption is low (0.25 and 0.362 times lower, respectively). Although the power consumption of the PC is very low, the capital cost of the packed volume would be prohibitive. 

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