Membranes costs

Nutrients are released from POLYON-coated fertilizers by osmotic diffusion. The RLC process permits appHcation of ultrathin, hence lower cost, membrane coatings which distinguishes this technology from many other polymer-coated fertilizers. The coating thickness determines the diffusion rate and the duration of release. POLYON-coated urea at a 4% coating (44% N) will release at twice the rate and will have half the duration as an 8% coating... 

UF and MF use energy to depolarize membranes so as to increase flux. As is shown in Fig. 22-55, membranes and mechanical equipment are traded off to achieve an overall economic minimum. Three things can drive a design toward the use of more membranes and less mechanical equipment cheaper membranes, veiy high flux, and veiy low flux. The availability of lower-cost membranes is easiest to understand. In the five years ending in 1995, the cost of both membrane area and membrane housings was driven down by competition. 

In the case of whey, paint, and other midflux process fluids, mechanical energy at the membrane surface produces a larger dividend. For these applications, pumping for depolarization is much more important economically, but the trend toward lower-cost membranes has nonetheless shifted systems toward more membrane area. 

A good estimate is that each of these areas comprise 25% of the capital cost. Membrane replacement and a pump rebuild may be required after 5 to 6 years, so some provision for these costs should clearly be made because they are not insubstantial. 

The membranes used in the present cells are expensive and available only in limited ranges of thickness and specific ionic conductivity. There is a need to lower the cost of the present membranes and to investigate lower cost membranes that exhibit low resistivity. This is particularly important for transportation applications where high current density operation is needed. Cheaper membranes promote lower cost PEFCs and thinner membranes with lower resistivities could contribute to power density improvement (29). It is estimated that the cost of current membranes could fall (by one order of magnitude) if the market increased significantly (by two orders of magnitude) (22). 

There is ongoing work to investigate alternative membranes that not only exhibit durability and high performance, but also can be manufactured inexpensively at high volume. Work at Ballard Advanced Materials Corporation has concentrated on developing low-cost membranes using trifluorostyrene and substituted trifluorostyrene copolymeric compositions (17). 

K. Ledjeff, et al., "Low Cost Membrane Fuel Cell for Low Power Applications," Fraunhofer-Institute for Solar Energy Systems, Program and Abstracts, 1992 Fuel Cell Seminar. 

Novel Processing Schemes Various separators have been proposed to separate the hydrogen-rich fuel in the reformate for cell use or to remove harmful species. At present, the separators are expensive, brittle, require large pressure differential, and are attacked by some hydrocarbons. There is a need to develop thinner, lower pressure drop, low cost membranes that can withstand separation from their support structure under changing thermal loads. Plasma reactors offer independence of reaction chemistry and optimum operating conditions that can be maintained over a wide range of feed rates and H2 composition. These processors have no catalyst and are compact. However, they are preliminary and have only been tested at a laboratory scale. 

It should be obvious from the above that fluid-management techniques which Improve the mass-transfer coefficient (k) with minimum power consumption are most desirable. However, in some cases, low-cost membrane configurations with inefficient fluid management may be more cost effective. In any case, it is important to understand quantitatively how tangential velocity and mem-brane/hardware geometry affects the mass-transfer coefficient. 

PEMFC R D areas include slightly higher temperature (120°C) and lower cost membrane materials, resistant and low-cost catalyst materials, long life. The technology must meet all the basic criteria for performance, durability and cost. Examples of projects include ... 

Slightly highertemperature(80-120°C), lower cost membrane materials for more efficient waste heat utilization for cogeneration in stationary/distributed applications or as process heat in a fuel reformer, reducing radiator size for transportation applications and for reduced carbon monoxide (CO) management requirements. 

Using the CA-CDI process is expected to consume less energy per unit of water purified than conventional methods, does not use costly membranes or pumps, operates at ambient temperature, and is resistant to chemical attack. 

Low-Cost Separator Materials Low-Loaded/Low-Cost Catalysts Low-Cost Membranes MEA Fabrication Simple Assembly Balance-of-Plant... 

High operating costs—membrane must be replaced after each use and disposal can be a problem Operating costs modest—membranes have extended lifetimes if regularly cleaned... 

In addition to PBI, there are many other hydrocarbon membranes that can also serve as proton-conducting membranes. Most of them have been developed for automotive and DMFC applications. The driving forces for hydrocarbon membranes are the need for a low-cost membrane electrolyte with a wide operating temperature... 

Pervs ration Selectivity Reliability Cost Membrane selectivities must be improved and systems developed that can reliably operate with organic solvent feeds before major new applications are commercialized... 

An alternative approach to costing membrane systems for scale-up is based on the volumetric flow rate of the permeate ... 

Hanemaaijer, J.H. Memstil—low cost membrane distillation technology for seawater desalination. Desalination, 168, 355, 2004. 

Membrane separation has advantages of low energy consumption, effective multiple fine particle removal, and small waste stream. Developing of high performance and low cost membranes is a major factor in hindering the advances of membrane processes. 

These types of cellulose acetate composite membranes are of historical interest only. During the period when this research was done the composite membranes made using very thin cellulose acetate barrier layers (under 100 nm) looked attractive for their high flux properties. However, later optimization of the asymmetric cellulose acetate membrane process improved flux and, in general, outdistanced composite CA types for practical, low cost membrane manufacture. 

Performance of NEOSEPTA-F in Sodium Chloride Solution Electrolysis. Figure 5 shows the relationship of the cell voltage and the current efficiency respectively with the concentration of sodium hydroxide in catholyte when electrolysis of sodium chloride solution was carried out at the current density of 30 A/cm. From the economical viewpoint, i.e, the electrolysis power cost, depreciation of equipment cost, membrane cost and so on, the optimum concentration of sodium hydroxide for NEOSEPTA-F C-1000 is about 20 % and that for NEOSEPTA-F C-2000 is about 27 %. 

Polyolefin films have been post-irradiation grafted with materials such as trifluorostyrene or methacrylic acid followed by sulfonation to control ion flow through nickel-cadmium batteries [8, 9], Investigation is underway to use crosslinked films grafted with selected monomers to develop lower cost membranes for fuel cells. A major commercial use of EB grafting has been to modify the surfaces of plastic films and paper with low molecular weight silicones to impart adhesive or release properties. 

Taxes, Insurance, and Space Costs, Membrane systems are compect but space availability and cost ate so variuble that no generalizetion can be made. Taxes and insurance are generally negligible. 

The cost of demineralization can also be reduced by developing lower-cost membranes, since the cost of membranes is a major factor in amortization and membrane-replacement costs. Additional work is also needed to develop membranes that have an operating life of at least 5 years. If the useful life of membranes can be increased from 3 years to 5 years, the cost of demineralization can be reduced appreciably. 

The process design and economics are closely related in electrodialysis. The total process costs are the sum of flxed charges associated with amortization of the plant capital costs and operating costs, such as energy and labour costs. Membrane replacement costs are sometimes regarded as a separate item because of their relatively short life of 5 to 7 years. 

Membrane electrolysis technology is well established and appropriate for smaller scale facilities. One application is its use as an oxygen generator in submarines, where the hydrogen is considered only a byproduct. Drawback is the high-cost membrane production [14]. 

Membrane costs for MF and open UF membranes are comparable, at an increased WQP for UF. A similar trend is observed tor tighter UF membranes and NF, while membrane cost is comparable at a much higher WQP. This shows that NF is very competitive with UF, especially if a high flux membrane is chosen (the high cost membrane is the TFC-ULP membrane which has a low flux and high salt rejection). The TFC-S membrane performs a lot better at higher flux and identical salt rejection. 

Suratt W.B., Pinto T.G., O Keefe B. (1993), Low cost membrane softening-two years of operation with a hybrid membrane system, Proc. of AWWA Membrane Technology Conf., Baltimore, Aug 93, 491-512. 

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