Shutdown Period

At the end of production period, a batch distillation column can be shutdown in the following sequence  

3) Condenser holdup may be mixed with the top product or with the reboiler material. 

For all other types of column configurations, the operation procedures in startup, production and shutdown period will be slightly different. 

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The system has been in full use during the shutdown periods of 1996 and 97 in the nuclear industry in Sweden. Performed tests have produced excellent results under sometimes difficult conditions... 

Water chemistry is important to the safe and reflable operation of a nuclear power plant. Improper conditions can lead to equipment and material failures which ia turn can lead to lengthy unscheduled shutdown periods for maintenance (qv) and repair operations. Water chemistry can also have an impact on the radiation levels duriag both power operations and shutdown periods. These affect the abiUty of personnel to perform plant functions. 

Unsteady material and energy balances are formulated with the conservation law, Eq. (7-68). The sink term of a material balance is and the accumulation term is the time derivative of the content of reactant in the vessel, or 3(V C )/3t, where both and depend on the time. An unsteady condition in the sense used in this section always has an accumulation term. This sense of unsteadiness excludes the batch reactor where conditions do change with time but are taken account of in the sink term. Startup and shutdown periods of batch reactors, however, are classified as unsteady their equations are developed in the Batch Reactors subsection. For a semibatch operation in which some of the reactants are preloaded and the others are fed in gradually, equations are developed in Example 11, following. 

Stagnant seawater must not be left in the unit during shutdown periods. This must be worked out at this stage because cost is impacted. 

If for any reason the work as defined by the work order cannot be completed during the shutdown period, the work order should not be signed off. Instead, it should... 

Capital shutdown work This type of work is generated by engineering and requires that all or portions of the job are done during a shutdown period. As this work is received, it is entered in the shutdown log the same as routine expense work request. 

Where low-cost labor is available, operators can provide intensive manual cleaning during the annual plant shutdown period. However, this is not a model for operational efficiency, and low-cost labor is seldom that low when quality and productivity is factored in. In the long run, it usually is far better to aim for a higher operational standard from the beginning. 

In common parlance, there is no difference between a standby boiler and an idle boiler, but where any distinction is drawn, it usually is based on the out-of-service time involved. Where the shutdown period is short, perhaps 2 to 3 days or less, boilers may be described as on standby whereas idle boilers are shut down for prolonged periods. 

In this chapter, we develop the basis for design and performance analysis for a plug flow reactor (PFR). Like a CSTR. a PFR is usually operated continuously at steady-state, apart from startup and shutdown periods. Unlike a CSTR, which is used primarily for liquid-phase reactions, a PFR may be used for either gas-phase or liquid-phase reactions. 

A batch reactor and a single continuous stirred-tank reactor are compared in relation to their performance in carrying out the simple liquid phase reaction A + B —> products. The reaction is first order with respect to each of the reactants, that is second order overall. If the initial concentrations of the reactants are equal, show that the volume of the continuous reactor must be 1/(1 — a) times the volume of the batch reactor for the same rate of production from each, where a is the fractional conversion. Assume that there is no change in density associated with the reaction and neglect the shutdown period between batches for the batch reactor. 

Shrink-resist science/technology development of, 26 391 Shrink-resist treatments, 26 391-393 additive, 26 393 chlorine-based, 26 392 chlorine-free, 26 392-393 Shuiskite, 6 471t Shutdown period, 29 494 Shutdown systems, 20 671-672 Shuttle vectors, 26 482-483 Sialon-bonded silicon carbide, 22 541 Siberian red lead, 6 468 S-iB-S block copolymers, 24 707 SiC-ceramic, 22 525. See also Silicon carbide... 

An assessment was made as to whether the mercury cells only could be replaced, while re-utilising the existing brine, electrical systems etc., but this was rejected due to cost and the duration of the required shutdown period. 

Krupp Uhde (KU) know-how and technology is based on extensive experience in chlorine production and provides clients with short shutdown periods for the conversion of chlorine plants to membrane technology, low-energy consumption and includes special technologies for higher chlorine quality and hydrogen-free production. 

As a result of KU s know-how in this field, the guaranteed shutdown period for converting a 340 000 metric tonne per year NaOH plant from mercury to membrane technology was as short as 8 weeks. This was made possible by a new conversion concept the individual elements were assembled in an adjoining assembly hall and installed in cell racks of 72 elements each. In this way, more than 2600 elements were assembled and installed in 18 two-rack electrolysers, and pressure and leakage tested. As soon as part of the mercury electrolysis plant was dismantled, the completed electrolysers were placed onto the vacated area and connected to the piping already installed beneath the cell rows (Fig. 16.6). 

There is no automatic control on the flowrate of the gas inlet stream or weak-acid condensate stream, since both of these flows are predetermined by feed flowrates earlier in the process. Isolation valves and provision for spectacle blinds are included to enable the column to be isolated during shutdown periods. 

Period 4 was a test of a very mild condition after a weekend shutdown. Period 7 was a test of the liquid feed pump at a low rate. Period 8 was a brief test for decline in activity from period 2, although the entire operation was too short for significant life testing. Periods in the order of 2,1,3,5, and 6 were intended to cover the desired range of increasing upgrading. 

Start-up and shutdown periods will normally increase the NOx content of the tail gas at the stack during the few hours needed for the process to stabilize or for NOx to be cleared from the plant. During the ammonia oxidation some nitrous oxide (NO2) is formed. The amount depends on combustion conditions (pressure, temperature), catalyst composition and age, and design of the oxidation reactor97. 

The solution of the above system of partial differential equations (eqs 4-12) yields the concentration and temperature profiles inside the catalyst pellet, and if necessary across the external boundary layer, as a function of time. However, there are only few cases of practical importance where this complete solution is required, as for instance startup and shutdown periods, dynamic process control options such as the so-called Matros concept with flow reversals (for redox processes), or situations where the catalyst is rapidly deactivated. 

The ratio can be expressed either as a percent or a decimal. For example, if a refinery unit undergoes one shutdown period for one month during a three-year duration, its operating factor is (36 - l)/36, or 0.972, or 97.2%. 

Within various types of the family of plastics (PE, PVC, PP, etc.) each type usually have different heat profiles and other settings (Table 5.1). Experience shows how to set the profile and/or obtain preliminary information from the material supplier. Degrading or oxidizing certain plastics is a potential hazard that occurs particularly when the extruder is subject to frequent shutdowns. In this respect, the shutdown period is even more critical than the startup period. 

In general, prior to each furnace ignition trial, provision shall be made for the removal of flammable vapors and/or gases that may have entered during the shutdown period, per NFPA 86 (sect. 5-4.1.1). In some cases, purging the furnace with a forced-air purge is unacceptable therefore, an inert gas may be required. 

There are other normal maintenance items that require extended shutdown periods but can probably be scheduled during other changeovers. For example ... 

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