Startups

In reactor startup, it is often very important limv temperature and concentrations approach their steady-state values. For example, a signihcani overshoot in temperature may cause a reactant or product to degrade, or the overshoot may be unacceptable for. safe operation such as a secondary reaction runaway. If either case were to occur, we would say that the system exceeded its practical stability limit. The practical limit is specific to the specific reaction and conditions under which the reaction is carried out and is usually determined by the reaction safety engineer. Although we can solve the unsteady temperature-time and concentration-time equations numerically to see if such a limit is exceeded, it is often more insightful to study the approach to steady slate by using the temperature-concentration phase plane. To illustrate these concepts, we shall confine our analysis to a liquid-phase reaction carried out in a CSTR. 

Again we consider the production of propylene glycol (C) in a CSTR with a heat exchanger in Example 12-3. Initially there is only water, C ,- = 3.45 lb-moI/ft at Tf = 75°F and 0.1 wt % H SO in (he 500-gallon reactor. The feed stream consists of 80 Ib-mol/h of propylene oxide (A), 1000 Ib-moi/h of water (B) containing 0.1 wt % H2SO4. and 100 Ib-mot/h of methanol (Ml. 

Plot the temperature and concentration of propylene oxide as a function of time, and a concentration vs. temperature graph for different entering temperatures and initial concentrations of A in the reactor. 

(he temperature of the mixed reactant streams entering the CSTR is To = 75 F. 

Unsteady-Slate Nonisottiermat Reactor Design Chapter 13 

More has been written about plant startup than one might imagine. Since considerable troubleshooting is needed during startup the two subjects tend to overlap. Therefore, the reader is encouraged to seek startup techniques also within the troubleshooting chapter. 

Kiorpes, S. A., and Fitzgerald, F. A., Plant Startup-Step by Step, Chemical Engineering, October 3, 1983, p. 74. 

Anderson, G. D., Initial Controller Settings to Use at Plant Startup, Chemical Engineering, July 11, 1983, p. 113. 

Talley, D. L., Startup of a Sour Gas Plant, Hydrocarbon Processing, April 1976, p. 90. 

Matley, J.. Keys to Successful Plant Startups, Chemical Engineering, September 8, 1969. p. 110. 

Installation began in June 1988 and was accomplished in four months. The waste treatment area was prepared and coated with a chemically resistant vinyl ester. Only after this coating had cured was the equipment brought to the site. Both Aeroscientific and TRSI supervised the installation. Plumbers and electricians logged abcut 2,000 hours over a 12 week period. 

Installation was timed to match startup of the automated plating lines. The waste treatment system was started up in manual mode under TRSI supervision. During this period a number of small glitches were encountered, as is common with projects of this size. These were quickly resolved. The system progressed to its fully automated capabilities with no major interruptions to production. 

This test shall demonstrate that the incinerator can be operated safely in accordance with the design assumptions and intent, and the operating limits and conditions, as well as with the requirements of the regulatory body. Thermal commissioning with radioactive waste shall be continued until all the required tests are carried out and satisfactory functioning of the entire system is verified. 

As a minimum requirement, the incineration system shall be operated according to the manufacturer s instructions and recommendations, provided that they are within the authorized operating limits and conditions. 

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Thermal power plant components operated at high temperatures (>500°C) and pressures, such as superheater headers, steamline sections and Y-junctions, deserve great attention for both operation safety and plant availability concerns. In particular, during plant operation transients -startups, shutdowns or load transients - the above components may undergo high rates of temperature / pressure variations and, consequently, non-negligible time-dependent stresses which, in turn, may locally destabilize existing cracks and cause the release of acoustic emission. 

The results of over 1 year of continuous, on-line acoustic emission (AE) structural surveillance of high temperature / high pressure steam headers, gained on 2 M-scale 600MW supercritical multifuel ENEL power units in normal operation, are presented in the paper. The influence of background noise, the correlation between plant operating conditions (steady load, load variations, startup / shutdown transients) and AE activity and the diagnostic evaluation of recorded AE events are also discussed. 

Steam headers and steamline sections may undergo high rates of temperature / pressure variations during plant operation transients - startups, shutdowns or load transients - and are... 

Different plant operating conditions (steady load, load variations, startups / shutdowns) have been encountered during the monitoring period. Electrical load, steam pressure and steam temperature values vs time have been acquired and stored during the entire period. At the same time, the RMS values of the acoustical background noise were have been continuously checked and stored, thus providing a quick check of proper instrumentation condition and a correlation between variations of plant parameters and the acoustical behaviour of the components. 

Localized AE sources appear during load variations, startups or shutdowns, but their positions are uniformly spread over the length of the two bodies of the header this can be seen from the histogram of the localized AE events for the front body (fig.S) and for the rear body (fig.9). 

The Operation manual accompanying each analy2er should be consulted for the recommended startup, installation, and caUbration procedures. 

Because of projected nylon-6,6 growth of 4—10% (167) per year in the Far East, several companies have announced plans for that area. A Rhc ne-Poulenc/Oriental Chemical Industry joint venture (Kofran) announced a 1991 startup for a 50,000-t/yr plant in Onsan, South Korea (168,169). Asahi announced plans for a 15,000-t/yr expansion of adipic acid capacity at their Nobeoka complex in late 1989, accompanied by a 60,000-t/yr cyclohexanol plant at Mizushima based on their new cyclohexene hydration technology (170). In early 1990 the Du Pont Company announced plans for a major nylon-6,6 complex for Singapore, including a 90,000-t/yr adipic acid plant due to start up in 1993 (167). Plans or negotiations for other adipic acid capacity in the area include Formosa Plastics (Taiwan) (171) and BASF-Hyundai Petrochemical (South Korea) (167). Adipic acid is a truly worldwide... 

Investments in plants to produce refrigeration alternatives have been aimounced by a variety of companies. ICI has an HPC-134a plant built in St. Gabriel, La. and is scheduled for 1993 startup. Their HPC-134a plant in Runcorn, UK is operational another one is plaimed for the Mihara, Japan site. 

T. P. Cotter, Heat Pipe Startup Dynamics, TA-DC-9026, Los Alamos Scientific Laboratory, University of California, Los Alamos, N.M., 1969. 

In the multistep production of IPDI, isophorone is first converted to 3-cyano-3,5,5-trknethylcyclohexanone (231—235), then hydrogenated and ammoniated to 3-aminomethyl-3,5,5-trknethyl-l-aminocyclohexane (1) (236,237), also known as isophorone diamine (IPDA). In the final step IPDA is phosgenated to yield IPDI (2) (238). Commercial production of IPDI began in the United States in 1992 with the startup of Olin s 7000 t/yr plant at Lake Charles, Louisiana (239), and the startup of Hbls integrated isophorone derivatives plant in Theodore, Alabama (240). Hbls has a worldwide capacity for IPDA of 40,000 t/yr. 

PWR Primary Shutdown and Startup Chemistry Guidehnes," Report TR101884, Electdc Power Research Institute, Palo Alto, Calif., 1993. 

The Model 412 PWR uses several control mechanisms. The first is the control cluster, consisting of a set of 25 hafnium metal rods coimected by a spider and inserted in the vacant spaces of 53 of the fuel assembhes (see Fig. 6). The clusters can be moved up and down, or released to shut down the reactor quickly. The rods are also used to (/) provide positive reactivity for the startup of the reactor from cold conditions, (2) make adjustments in power that fit the load demand on the system, (J) help shape the core power distribution to assure favorable fuel consumption and avoid hot spots on fuel cladding, and (4) compensate for the production and consumption of the strongly neutron-absorbing fission product xenon-135. Other PWRs use an alloy of cadmium, indium, and silver, all strong neutron absorbers, as control material. 

In the startup of a reactor, it is necessary to have a source of neutrons other than those from fission. Otherwise, it might be possible for the critical condition to be reached without any visual or audible signal. Two types of sources are used to supply neutrons. The first, appHcable when fuel is fresh, is califomium-252 [13981-174-Jwhich undergoes fission spontaneously, emitting on average three neutrons, and has a half-life of 2.6 yr. The second, which is effective during operation, is a capsule of antimony and beryUium. Antimony-123 [14119-16-5] is continually made radioactive by neutron... 

United States. In 1980, Unocal began constmcting the Parachute Creek Project, designed to produce 1600 m (10,000 bbl) of upgraded shale oil per day. The project included a conventional underground room-and-pikar mine, the Unishale B (see Table 7) retort, and a special Unocal upgrading facihty. Plant startup occurred in 1986, and daily shale oil production reached 1100 m /d (7000 bbl/d). By 1991, total production exceeded 0.6 x 10 m (four million barrels). However, the Parachute Creek Project was shut down in mid-1991 for economic reasons. 

WU lowest cost SO2 produced in situ catalyst requires startup time higher most every sulfonation and sulfation ... 

Most sulfonation plants monitor and control operations by computer. Sulfur-buming catalytic SO -generating equipment may require a 1—2 h stabilization period on startup. The unit can be kept in a standby position by maintaining heat to the unit when it is off-line. Liquid SO -based sulfonation plants do not require such a stabilization period and hence are more flexible to operate than sulfur-buming sulfonation plants. 

Pretreatment of membranes with dynamically formed polarization layers and enzyme precoats have been effective (12,13,39). Pretreatment with synthetic permeates prevents startup instabiUty with some feed dispersions. 

During startup, the baseplate heat shields ate lowered, thereby allowing pump-down through a large gap. The heat shields can then be raised to produce a narrow gap when maximum temperature is requited. 

Besides being slower, anaerobic treatment is more difficult to manage and can generate by-products that are more mobile or toxic than the original compound, for example, the daughter products of TCE, ie, dichloroethenes and vinyl chloride. It requires a longer acclimation period which means slower startup times in the field. The microbial processes are less well understood, and hence, ate less controlled than for aerobic systems. 

M. Ramanathan and W. E. Vedey, Evaluation, Design and Startup of an Innovative and Cost-effective Wastewater Treatment Plant at Concord, New Hampshire, paper presented at the 36th Annual Meeting, Virginia Water Pollution Control Association, Inc., Charlottesville, Va., 1982. 

Stress Corrosion Crocking. Stress corrosion cracking occurs from the combined action of corrosion and stress. The corrosion may be initiated by improper chemical cleaning, high dissolved oxygen levels, pH excursions in the boiler water, the presence of free hydroxide, and high levels of chlorides. Stresses are either residual in the metal or caused by thermal excursions. Rapid startup or shutdown can cause or further aggravate stresses. Tube failures occur near stressed areas such as welds, supports, or cold worked areas. 

C. J. Macedo, E. A. O. d Avila, and J. G. Brosnan, Startup of a Closed Carbide Furnace Using Charcoal as a Reducing Mgent, Vol. 43, Electric Furnace Proceeding, Atianta, Ga., 1985. 

The analyses of the solutions in the electrolytic circuit and ceU operating data are given in Tables 5 and 6, respectively. The current efficiency of 45% shown in Table 6 includes low efficiencies that always prevail during the startup of a reconditioned cell. The 2.1—2.4 pH range used in the plant also results in somewhat lower current efficiency but provides a safe operating latitude. 

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