Start-up/shut-down procedures

Table 775Recent research in start-up/shut-down procedures for PEFCs... 

Work is being planned to determine if the CPF in PWR vessels is acceptably low when small surface flaws (approximately 4-6 mm - 0.16-0.24 in - in depth) are postulated at the vessel inner surface and normal reactor start-up, shut-down and system leak testing occur along the allowable P-T boundaries defined by reguiatory requirements, the ASME evaluation procedures, and procedural and hardware constraints. 

In the case of manual control, the operator follows written start-up, shut-down and product changeover procedures. During normal steady-state operation key variables (section 9.1.) are controlled automatically, usually by panel-mounted PID controllers. The operator makes adjustments to set points of the controllers and also adjusts pump stroke lengths in response to... 

The basic principle for a computer-aided start-up (shut-down) is to present the operator with a checklist of procedures that he or she must undertake either just prior to or during the 2 hour pre-heat cycle of the gas-raising plant. Where possible the computer will cross-check the operator actions by ... 

Various modes of operation Preparation, start up, shut down, maintenance, and abnormal condition Procedure, measures, and techniques When to carry out... 

Another serious problem in heat exchangers is corrosion. Severe corrosion can and does occur in tubing and very often with common fluids such as water. Proper material selection based on a full analysis of the operating fluids, velocities and temperatures is mandatory. Very often, heavier gauge tubing is specified to offset the effects of corrosion, but this is only a partial solution. This should be followed by proper start-up, operating and shut-down procedures. 

Table 3 provides recommended start-up and shut-down procedures. Effort should be made to avoid subjecting units to thermal shock, overpressure, and/or hydraulic hammer, since these conditions may impose stresses, that exceed the mechanical strength of the unit or the system in which it is installed, which may result in leaks and/or other damage to the unit or entire system. 

Table 3. Recommended General Start-Up and Shut-Down Procedures...

Fluid Location and Relative Temp. Start-Up Procedure Shut-Down Procedure... 

All processes may be classified as batch, continuous, or semibatch depending on how materials are transferred into and out of the system. Also, the process operation may be characterized as unsteady state (i.e., transient) or steady state, depending on whether the process variables (e.g., pressure, temperature, compositions, flowrate, etc.) are changing with time or not, respectively. In a batch process, the entire feed material (i.e., charge) is added instantaneously to the system marking the beginning of the process, and all the contents of the system including the products are removed at a later time, at the end of the process. In a continuous process, the materials enter and leave the system as continuous streams, but not necessarily at the same rate. In a semibalch process, the feed may be added at once but the products removed continuously, or vice versa. It is evident that batch and semibatch processes are inherently unsteady state, whereas continuous processes may be operated in a steady or unsteady-state mode. Start-up and shut-down procedures of a steady continuous production process are examples of transient operation. 

Consider the segment of tubular reactor shown in Figure 8.3. Since the fluid composition varies with longitudinal position, we must write our material balance for a reactant species over a different element of reactor (dVR). Moreover, since plug flow reactors are operated at steady state except during start-up and shut-down procedures, the relations of major interest are those in which the accumulation term is missing from equation 8.0.1. Thus... 

The decisions should be taken in an optimal fashion subject to the plant topology and the processing constraints with the objective to maximize the profit, given as the difference of revenues for products and costs for the production. The demands are specified by their amounts and their due dates, where the revenues decrease with increasing lateness of the demand satisfaction. The production costs consist of fixed costs for each batch and for the start-up- and shut-down-procedures of the finishing lines, and variable costs for the product inventory. 

Basic engineering final flow sheets final PID data sheets for equipment, piping, process data on equipment, piping and instruments operating, start-up and shut-down procedures Dow F E Index, Mond Index, Hazop, Hazan, Fault tree, RISKAT... 

Review start up and shut down procedures and the consequence of a time delay in any step of the process. 

Supervision instituted new procedures. When slurry feed supply is shut down, procedures require the operators to continue agitation and acid flow for at least 30 minutes. On startup, the agitators and acid feed will be restored before starting up the slurry pumps. Both of these steps were designed to eliminate the possibility of having an undetected layer of calcium carbonate. 

Uniform product quality is also an advantage claimed for continuous reactors. If a continuous reactor can be controlled at a desired steady state, product quality transients should be considerably less than typical batch-to-batch variations. Start-up transients and shut-down procedures can produce off-spec product hence, frequent start-ups and/or product changes represent a real problem for continuous systems. 

Gaming process know-how (dynamic behavior of the plant, start-up and shut-down procedures)... 

Document start-up/operating/shut-down procedures along with set-up/changeover practices. 

For these systems to operate efficiently, they must be completely integrated into all plant operations. Start-up through shut-down procedures for all equipment, limits, and control instructions must be suited to meeting product... 

Installation Site planning environment, process connections, start-up procedures, shut-down procedures, application modifications, implementation of functions in systems already operating. 

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