Machines shutdown

As fabrication shops have accomplished effective safety measures to protect the primary operator, safeguarding only the machine or process operator has been extended toward providing hazard protection for nonoperators, maintenance personnel, and others. Particularly effective in reduction of injury to maintenance personnel and die setters has been the lockout-tagout programs established to assure that nonoperators are not injured during machine shutdown and reconfiguration. 

Because of increased emphasis on maximizing cogenerated power, newer plants are trying to utilize back-pressure turbines only in applications where efficiencies above 70% can be attained. This typically means limiting the applications to the large (>1000 kW) drives, and usiag small machines only where they are necessary for the safe shutdown of the unit. Multistage turbiaes are used even on the smaller loads. 

In selec ting the machines of choice, the use of specific speed and diameter best describe the flow. Figure 10-67 shows the characteristics of the three types of compressors. Other considerations in chemical plant service such as problems with gases which may be corrosive or have abrasive solids in suspension must be dealt with. Gases at elevated temperatures may create a potential explosion hazard, while air at the same temperatures may be handled qmte normally minute amounts of lubricating oil or water may contaminate the process gas and so may not be permissible, and for continuous-process use, a high degree of equipment rehability is required, since frequent shutdowns for inspec tion or maintenance cannot be tolerated. 

Padlocking arrangements may be required to lock the feeder in the OFF position when the machine is undergoing a shutdown or repairs. 

Safe shutdown earthquake (SSE) test This is defined by the most severe earthquake that could occur, producing the maximum vibratory ground movements at the place of installation. Safety-related machines, devices and components should remain functional during an earthquake of this magnitude and maintain the safety and integrity of the plant until a safe... 

The armature of the machine will normally have a residual voltage of around 8 V (for LT machines) across the terminals when running at the synchronous speed. If not, as when the generator is operated after a long shutdown, a d.c. voltage of 12 V can be applied through a battery for a few seconds to obtain the required residual voltage. 

When there are two or more machines it is also possible to program the PLCs to select the machine to perform in a particular sequence so that each machine has almost the same number of hours of operation. This makes it easy to identify the next machine for routine maintenance shutdown. A PLC is fully capable of performing the following ... 

As a result of these poorly designed control systems, users experience significant operational problems, including machine and process shutdowns. As with any process plant, the first objective is to achieve reliable production from the FCCU. Only with reliable production will operators start optimizing the unit. Users, therefore, are not using the... 

In a hot gas expander, the major problems associated with catalyst fines are centered on erosion of components and particulate plugging. Either problem can cause machine vibration and sometimes power train emergency shutdown. Because many failures have resulted from these factors, machinery manufacturers recommend that the maximum permissible solids concentration upstream of an expander not exceed 200 ppm. It is further stipulated that 97% of the particles be smaller than 10 p. Allowing concentrations of 160 ppm with 95% of the particle less than 10 p is considered reasonable. 

In order to operate the prime movers described in the previous sections it is necessary to provide auxiliary equipment for the start-up, steady operation and shutdown of the basic equipment as well as for monitoring and controlling its performance. The need also arises for the maintenance of the plant that invokes the provision of cranage and lay-down areas in the engine room. The following describes these features for the various types of prime movers. The driven machines (i.e. the electrical generators) are also reviewed in detail so that the complete picture of industrial generating stations can be obtained. 

Load factor is particularly important with air-cooled machines where sustained full-load operation results in an early build-up of deposits on valves and other parts. This build-up increases the frequency of maintenance required to maintain compressor reliability. Intermittent operation is always recommended for these units. The frequency and duration of unloaded operation depends on the type, size, operating pressure of the compressor. Air-cooled compressors for higher than 200-psig-pressure application are usually rated by a rule that states that the compressing time shall not exceed 30 minutes or less than 10 minutes. Shutdown or unloaded time should be at least equal to compression time or 50 per cent. 

Repeated twisting of the spindle s tube or the solid shaft used in jackshafts results in a reduction in the flexible drive s stiffness. When this occurs, the drive loses some of its ability to absorb torsional transients. As a result, damage may result to the driven unit. Unfortunately, the limits of single-channel, frequency-domain data acquisition prevents accurate measurement of this failure mode. Most of the abnormal vibration that results from fatigue occurs in the relatively brief time interval associated with startup, when radical speed changes occur, or during shutdown of the machine-train. As a result, this type of data acquisition and analysis cannot adequately capture these... 

A hot alignment check is performed exactly like an ambient alignment check with the added safety precautions required for hot machinery. The accuracy of a hot alignment check depends on how soon after shutdown dial indicator readings can be taken. Readings may be taken within a few minutes with the use of shaft-mounted brackets that span a flexible coupling. To speed up the process, assemble the brackets to the fullest extent possible prior to shutdown so that they need only be bolted to the shafts once the machine stops rotating. 

In lithium-based cells, the essential function of battery separator is to prevent electronic contact, while enabling ionic transport between the positive and negative electrodes. It should be usable on highspeed winding machines and possess good shutdown properties. The most commonly used separators for primary lithium batteries are microporous polypropylene membranes. Microporous polyethylene and laminates of polypropylene and polyethylene are widely used in lithium-ion batteries. These materials are chemically and electrochemically stable in secondary lithium batteries. 

A demonstration of a promising flash-lamp detritiation method has been carried out for the JET 2004 shutdown. Without established fast and efficient tritium removal method a satisfactory schedule of burning plasma operations in a machine with carbon PFCs appears impractical. 

Synchro-Self-Shifting ( SSS ) Clutches The automatic freewheel action of an SSS clutch simplifies plant startup and shutdown sequences. It is, of course, receiving its power input from a gas turbine or similar driver, while its output is connected to a driven machine. The drive disengages automatically when the driven machine speed exceeds that of the driver. Since large gas turbines are usually brought up to speed with either a startup gear motor or a helper turbine, thousands of SSS clutches (Fig. 29-77) are finding application here. 

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