Operation Difficulties

There is no sharp demarcation between this and the previous chapter. As an arbitrary demarcation criterion, considerations primarily related to startups and shutdowns were treated in the previous chapter, while this chapter deals with difficulties that frequently affect normal operation as well as startups and shutdowns. Because of this vague distinction, the reader is well-advised to review both chapters when examining either startup/shutdown practices or when reviewing operation difficulties. 

Introductory comments made in the previous chapter also extend to this chapter. Failure to recognize and eliminate operation pitfalls or hazards has caused catastrophic accidents, loss of life, iiyuries, damage to colmnns and their internals, and lengthy shutdown periods. 

This chapter reviews common difficulties in column operation, outlines practices for overcoming them, highlights the consequences of poor practices, and supplies general guidelines for avoiding the hazards and pitfalls. As in the previous chapter, hazeu ds and pitfalls specifically related to the nature of the chemicals processed (e.g., toxicity, flammability) are outside the scope of this distillation text. The safe handling procedures of the relevant chemicals must be followed to cater for the latter hazards and pitfalls. 

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The metal is a source of nuclear power. There is probably more energy available for use from thorium in the minerals of the earth s crust than from both uranium and fossil fuels. Any sizable demand from thorium as a nuclear fuel is still several years in the future. Work has been done in developing thorium cycle converter-reactor systems. Several prototypes, including the HTGR (high-temperature gas-cooled reactor) and MSRE (molten salt converter reactor experiment), have operated. While the HTGR reactors are efficient, they are not expected to become important commercially for many years because of certain operating difficulties. 

An example of the concentration effect on the specific cake resistance is available (12) that reports results of some experiments with a laboratory horizontal vacuum belt filter. In spite of operational difficulties in keeping conditions constant, the effect of feed concentration on specific cake resistance is so strong that it swamps all other effects. 

Liquefaction. Siace the 1970s attempts have been made to commercialize biomass pyrolysis for combiaed waste disposal—Hquid fuels production. None of these plants were ia use ia 1992 because of operating difficulties and economic factors only one type of biomass Hquefaction process, alcohohc fermentation for ethanol, is used commercially for the production of Hquid fuels. 

Intermediate Rate. At 0.43—1.08 mr / (ha-s) [46—115 gal/(acres)], certaia operational difficulties were frequently encountered and therefore this range was avoided for many years. It now appears that these difficulties stemmed primarily from the iaabiHty of the hydrauHc load to keep the filter slimes from becoming too thick and thereby clogging the filter. The use of relatively large filter stones solves this problem. 

A very important parameter ia routine control of the process is the ratio of the MLSS volume to the dry weight, called the Sludge Volume Index (SVI). A weU operating plant has an SVI of 50 to 100, but operational difficulties occur when the SVI approaches 150. At this poiat the sludge settles poorly. 

SASOL has pursued the development of alternative reactors to overcome specific operational difficulties encountered with the fixed-bed and entrained-bed reactors. After several years of attempts to overcome the high catalyst circulation rates and consequent abrasion in the Synthol reactors, a bubbling fluidized-bed reactor 1 m (3.3 ft) in diameter was constructed in 1983. Following successflil testing, SASOL designed and construc ted a full-scale commercial reac tor 5 m (16.4 ft) in diameter. The reactor was successfully commissioned in 1989 and remains in operation. 

To avoid operating difficulties, the torsional critical frequencies of the combined engine and driven equipment should be calculated or measured to assure that operating speeds are removed from these criticals or that vibration dampers are provided or that the equipment is designed for the resulting cyclic stresses. 

Other terms and conditions provisions for payment terms, freight, taxes, packaging and operational difficulties, and insurance... 

Clay - The use of elay based floeculating agent(s) in eonjunetion with a strong metal preeipitator has proven sueeessful in many wastewater treatment applieations where the objeetives are aimed at metals removal. Clay based floeeulants eleans the wastewater and in some eases replaees multistage conventional treatment system and saves the traditional operational difficulties of treatment with several chemicals such as metal hydroxide precipitation, coagulant, floeeulants and other methods. Commercial clay-based floeeulants usually consist of bentonite and other... 

The problem was an operational difficulty concerning the production department. Two root causes were identified based on the investigation. 

In many instances, the design of suction and discharge pulsation dampening drums (or bottles) for reciprocating compressors is based on piston displacement and volumetric efficiency, and this design normally will suffice to reduce peak pulsation to approximately 5% of the line pressure. In special or other cases, experience has shown that operational difficulties (vibrations, meter pulsations, etc.) may indicate that the peak pulse pressure of 5% line pressure is inadequate. Thus, the pressure in pulsation-reduction design selection is... 

In general, it is fair to state that one of the major difficulties in interpreting, and consequently in establishing definitive tests of, corrosion phenomena in fused metal or salt environments is the large influence of very small, and therefore not easily controlled, variations in solubility, impurity concentration, temperature gradient, etc. . For example, the solubility of iron in liquid mercury is of the order of 5 x 10 at 649°C, and static tests show iron and steel to be practically unaltered by exposure to mercury. Nevertheless, in mercury boiler service, severe operating difficulties were encountered owing to the mass transfer of iron from the hot to the cold portions of the unit. Another minute variation was found substantially to alleviate the problem the presence of 10 ppm of titanium in the mercury reduced the rate of attack to an inappreciable value at 650°C as little as 1 ppm of titanium was similarly effective at 454°C . 

Control of waterside chemistry starts in the pre-boiler section because the lack of, or inappropriate methods for, water treatment creates significant operational difficulties and impacts the economics of the entire process from start to finish. 

Because HQ has limited volatility at lower pressures, when acting as a catalyst with other more volatile oxygen scavengers, it will not always follow the primary scavenger around the boiler cycle system. This creates operational difficulties because scavenging reaction rates are slowed and, in lower pH condensate systems, the post-boiler oxygen scavenging reaction may cease entirely. 

Organic matter other than oil may be innocuous in a boiler depending on the temperature of operation and the amount and type of organic matter. Maximum values that would be universally applicable cannot be stated, and the operator should therefore be alert to the operating difficulties that may be associated with the presence of organic matter these are as follows ... 

Analytical-operational Difficulties. In order to work close to the conditions in natural waters, very low concentrations of metal ions (in the nanomolar range) and of particles as well as pH values in the neutral range have to be used. Analytical difficulties occur because of undesired adsorption of metal ions to the experimental devices (walls of beakers, glass filtration devices, etc.) and of insufficient separation of the particulate and dissolved phase (particles in the colloidal size range). 

The major operating difficulties that confronted Bergius s promising research on coal hydrogenation were not entirely technical, however. Obtaining sufficient research funds proved a serious problem in postwar, inflation-plagued Germany. To... 

Demonstrate that the mixers will size-reduce the crystalline solids that caused most of the operational difficulties in the plant during the Demo II tests. 

Demonstrate that the mixers will operate without operational difficulties with a slurry that contains M28 propellant. 

Operational difficulties encountered while processing mixed dunnage containing carbon... 

Both the failure of the isolation valves to hold and the difficulty in draining the system were due to solid build up in the circuit. In the previous two-year period, the refinery had changed its crude feedstock resulting in operating difficulties on the unit desalter. Carryover of salts led to accelerated corrosion in the crude column and associated piping circuits. 

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