Capacity loss

Adsorption (qv) of gases has been reviewed (40,50) (see also Adsorption, gas separation). Adsorption, used alone or in combination with other removal methods, is excellent for removing pollutant gases to extremely low concentrations, eg, 1 ppmv. When used in combination, it is typically the final step. Adsorption, always exothermic, is even more attractive when very large gas volumes must be made almost pollutant free. Because granular adsorbent beds ate difficult to cool because of poor heat transfer, gas precooling is often practiced to minimize adsorption capacity loss toward the end of the bed. Pretreatment to remove or reduce adsorbable molecules, such as water, competing for adsorption sites should also be considered (41). 

Poor performance can result from fan inlet eccentric or spinning dow, and discharge ductwork that does not permit development of hiU fan pressure. Sometimes inlet restrictions starve a fan and limit performance. To obtain rated performance, the air must enter the fan uniformly over the inlet area without rotation or unusual turbulence. This allows all portions of the fan wheel to do equal work. If more air is distributed to one side of the wheel, such as with an elbow on the inlet, the work performed by the lightiy loaded portions of the wheel is reduced and capacity is decreased by 5—10%. The use of an inlet box duct on a fan can reduce capacity by as much as 25% unless there are turning vanes in the duct. Use of the vanes reduces the capacity loss to around 5%. 

PAG sludge can be regenerated by wet air oxidation (WAO) or by a multiple-hearth furnace. Capacity losses might be high in WAO, particulady with low molecular weight organics. Weight loss in a furnace may exceed 20%. 

While the axial position of multistage impellers to their diffusers is not critical, they should line up reasonably well. Impellers are not extremely sensitive to leading-edge dings and minor damage, but anything, such as erosion on the exit tips, that tends to decrease the effective diameter of the impeller is more serious. Front shroud clearance on open impellers should be maintained close to the design values to minimize capacity loss. 

For compressors in general and for some types in particular, the cleanliness of the gas stream is the key factor in a reliable operation. Moisture or liquids in various forms may be the cause of an early failure or in some-cases a catastrophic failure. Corrosive gases require material considerations and yet even this may not entirely solve the loss of material issue that can certainly cause early shutdowns or failures and high maintenance cost. Fouling due to contaminants or reactions taking place internal to the ( i-pressor can cause capacity loss and the need for frequent shutdowns. 

The cycle life of the hydrogen-containing samples also appears to be limited as shown in ref 8. This is unacceptable for a practical application. The capacity loss is mostly due to the elimination of the excess capacity which exhibits hysteresis. Since this portion of the capacity appears related to the incorporated hydrogen, its elimination with cycling may not be unexpected. We do not understand this point fully yet, and further work would appear to be warranted. 

I here is little capacity loss upon cycling, and the materials show adequate rate capability. 

The slip S is the fraction of suction capacity loss. It consists of the volumetric efficiency loss fraction 1, the stuffing box loss fraction 1, and the valve loss fraction 1. The slip S is... 

Example 35.1 An ammonia compressor is rated at 312 kW with saturated suction at -15°C. It is installed with a very long suction line, causing a pressure drop of 0.4 bar, and picks up 6 K superheat from its evaporator condition. Estimate the capacity loss. 

So the capacity loss is of the order of 19%, or 59 kW. There may also be a slight drop due to the higher compression ratio, ignored here as the condensing pressure is not known. 

Figure 6. Arrhenius plots for various hattery systems. The percentage capacity losses per year and per day are given on a logarithmic scale. The Li-MnO, cell, which has excellent shelf-life characteristics, is a primary cell, not a rechargeable Li cell...

Sealed batteries have made little entry into this market with heavy cycling service, since the lead-calcium alloys required for these versions tend towards premature capacity loss, a phenomenon intensively investigated in recent years and possibly close to a solution. 

For the separation of such batteries, gel construction and microfiber glass fleece separators again compete because of the deep discharge cycles, the gel construction with its lower tendency to acid stratification and to penetration shorts has advantages for the required power peaks, microfiber glass fleece construction would be the preferred solution. The work on reduction of premature capacity loss with lead-calcium alloys has shown that considerable pressure (e.g., 1 bar) on the positive electrode is able to achieve a significantly better cycle life [31-36], Pressure on the electrodes produces counter pressure on the separators, which is not unproblematic for both separation systems. New separator developments have been presented with... 

It is possible that all three phenomena contribute to the capacity loss of 4V Lix[Mn2]04 electrodes. Nonetheless, all three can be at least partly circumvented by slightly modifying the composition of the spinel electrode. For example, cell performance can be improved by increasing the amount of lithium in the spinel structure [107, 123, 130] and, in particular, by substituting a small amount of manganese on the B sites with lithium [107], which drives the composition a small way down the stoichiometric spinel tie-line, towards... 

In practical cases, however, the excess weight and volume due to the use of alloys may not be very far from those required with pure lithium electrodes, for one generally has to operate with a large amount of excess lithium in rechargeable cells in order to make up for the capacity loss related to the filament growth problem upon cycling. 

In order to improve the electrochemical performance with respect to lower irreversible capacity losses, several attempts have been made to modify the carbon surface. Here the work of Peled s [38, 130-132] and Takamura s groups [133-138] deserves mention. A more detailed discussion can be found Chapter III, Sec. 6. 

This difference is the irreversible capacity loss (<2jr). Dahn and co-workers [71] were the first to correlate <21R with the capacity required for the formation of the SE1. They found that <2ir is proportional to the specific surface area of the carbon electrode and, assuming the fonnation of an Li2C03 film, calculated an SEI thickness of 45 5 A on the carbon particles, consistent with the barrier thickness needed to prevent electron tunneling [1,2]. They concluded [71] that when all the available surface area is coated with a film of the decomposition products, further decomposition ceases. 

It was concluded [93, 94J that, on long cycling of the lithium-ion battery, the passivating layer on the carbon anode becomes thicker and more resistive, and is responsible, in part, for capacity loss. 

The solubility of nickel chloride in the molten electrolyte is of interest because high solubilities of nickel chloride will cause capacity loss over the lifetime. Dissolved nickel chloride will not be contacted by the electronically conductive backbone nickel and cannot participate in the discharge reaction. Therefore it is essential that the nickel chloride is formed... 

Most types of ion-exchange resin suffer some breakdown and volume loss over time because of attrition, excessive heat, or other factors. Water softeners should be inspected annually, and a double backwash procedure should be provided. This generally lifts the broken resin ( fines ) to the top of the bed, where it can be removed and replaced to restore capacity. Allow for 5 to 10% resin operating capacity loss per year because of physical breakdown. At many sites the resin is unfortunately not inspected regularly but merely replaced when a serious decline in operating capacity is noticed. Here a resin life expectancy of, say, 6 to 8 years probably is the norm. 

Figure 5. Integrated capacity losses of LiCn in PC electrolytes without and with electrolyte additives (CO2, N2O, S ). Electrolyte 0.5 M UCIO4 inPC, Carbon Highly graphitic carbon fiber PI00 (Amoco), i = 50 pA mg1, cut-off 0-2 V vs. Li/Li+ [4],...

Integrated Capacity Losses / mAh g"1 Integrated Capacity Losses / mAh g... 

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