Changeover

Process operations. The third source of process waste we can classify under the general category of process operations. Operations such as start-up and shutdown of continuous processes, product changeover, equipment cleaning for maintenance, tank filling, etc. all produce waste. 

In continuous processes, all those sources of process waste associated with start-up and shutdown also apply to product changeover in multiproduct plants. 

Changeover between products causes waste because equipment must be cleaned. Such waste can be minimized by scheduling operation to minimize product changeovers. 

Knowing where waste is going is the key to reducing it. When reducing waste from process operations, a steady-state mass balance is not usually comprehensive enough. A balance that takes into account start-up, shutdown, and product changeovers is required. 

Designing for a minimum number of shutdowns and product changeover s. 

Other techniques for mass measurement are available, but they are not as popular as those outlined above. These other methods include mass measurements on a standard substance to calibrate the instrument. The standard is then withdrawn, and the unknown is let into the instrument to obtain a new spectrum that is compared with that of the standard. It is assumed that there are no instrumental variations during this changeover. Generally, this technique is less reliable than when the standard and unknown are in the instrument together. Fourier-transform techniques are used with ion cyclotron mass spectrometers and give excellent mass accuracy at lower mass but not at higher. 

Fig. 3. Multipurpose plant capacity utilization where D represents products A, B, C, D, and E U the changeovers and X the time the plant was idle.

Particularly ia the case of frequent product changes, great attention has to be paid to the reduction of changeover time, which may take up to 10 days (2). 

Below a certain critical temperature, which varies with pressure and stoichiometry, cool flames for several hydrocarbons propagate from the wall inward above this temperature, they propagate from the center of the vessel (78). This transition is interpreted as evidence for a changeover from a predominantly heterogeneous preflame mechanism to a homogeneous one. 

The changeover from ROO radicals to HOO radicals and the switch from organic peroxides to HOOH has been shown as temperature is increased in propane VPO (87,141). Tracer experiments have been used to explore product sequences in propane VPO (142—145). Propylene oxide comes exclusively from propylene. Ethylene, acetaldehyde, formaldehyde, methanol, carbon monoxide, and carbon dioxide come from both propane and propylene. Ethanol comes exclusively from propane. 

Papermaking Use. PAG is widely used in Europe in papermaking processes. The gradual changeover from acid to alkaline systems in U.S. paper mills is expected to be accompanied by an increase in the use of PAG as an alum replacement (35). 

Even when their shells are closed, the animals continue to sense their environment, and as soon as the oxidant level decreases, they reopen and resume siphoning. Continuous chlorination often fails to eradicate these macrofouling creatures because of iatermptions ia the feed, which can occur for various reasons, such as chlorine tank changeover or plugging of feedlines. If the iatermption lasts long enough (1 h or possibly less), the animals have time to reoxygenate their tissues between the extended periods of chlorination. Any oxidant, such as chlorine, bromine, or ozone, eUcits the same response from these creatures. Therefore, only continuous, unintermpted appHcations are successful. 

Resistivity measurements of doped, alpha-siUcon carbide single crystals from —195 to 725°C showed a negative coefficient of resistivity below room temperature, which gradually changed to positive above room temperature (45). The temperature at which the changeover occurred increased as the ionization of the donor impurity increased. This is beUeved to be caused by a change in conduction mechanism. 

Nonimpact Printing. Interest is growing ia the use of nonimpact styles because of the quickness of color changeover and the abiUty to iaterface these machines to computer-aided design systems. Two basic types exist drop on demand and constant drop techniques. 

Lavish provision of installed spares with the accompanying isolation and changeover valves. 

In addition to using an arrester element with greater flow capacity, it is common to use two arresters in parallel where frequent cleaning is required, with one arrester in standby. A three-way valve can be used to allow uninterrupted operation during changeover. Where elements have an intrinsically high pressure drop, suA as sintered metal elements used in acetylene sei vice, multiple parallel elements can be used. 

In a rapid changeover to make another product the meter was not recalibrated for the new monomer, monomer B. This led to a large overcharge of monomer B and the subsequent runaway reaction. 

Is the new hazard a result of production changeovers to different products ... 

F = changeover of speed by electrical braking / = at rest and de-energized,... 

A. (i) ob is the current transient during changeover from y to a in an open transient condition. 

Current overshoot during changeover from Y to A, point, a, on Y current curve (Figure 4.. ))... 

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