Typical process plant

The historical data is sampled at user-specified intervals. A typical process plant contains a large number of data points, but it is not feasible to store data for all points at all times. The user determines if a data point should be included in the list of archive points. Most systems provide archive-point menu displays. The operators are able to add or delete data points to the archive point hsts. The samphng periods are normally some multiples of their base scan frequencies. However, some systems allow historical data samphng of arbitraiy intei vals. This is necessaiy when intermediate virtual data points that do not have the scan frequency attribute are involved. The archive point lists are continuously scanned bv the historical database software. On-line databases are polled for data. The times of data retrieval are recorded with the data ootained. To consei ve storage space, different data compression techniques are employed by various manufacturers. 

Some of the cases below reflect situations that might be encountered in a typical process plant. Others are less obvious and may only appear remotely connected to an operating plant. The Concorde crash and the Challenger disaster are examples of this latter category. These clearly demonstrate loss of containment scenarios that could be encountered in any operating environment. 

The largest component of the constant C is the return on investment of the fixed capital. In order to make comparisons easier, a standardised methodology is adopted which is detailed in the Appendix. Typically process plants are assumed to take a similar (3 year) construction period to operate at full output over the project lifetime with zero residual value. The capital payback is then over this operating life. 

For typical process plants, use 47,000 U.S. (CE instruments = 1000) per MPI for highly automated batch processes, use 69,000 to 82,000 U.S. (CE instruments = 1000) per MPI. CE instruments is the Chemical Engineering inflation index for process instruments. Details are given in Section c and in Table 16.12. Scale the instrument cost to the correct time. 

Equation (4.23) applies to a theoretical pipe, but for a real pipeline additional allowances need to be made for pipe entry and exit losses, bends and fittings. Consider a fluid flowing in a typical process plant pipeline as shown in Figure 4.2. 

VALVES. A typical processing plant contains thousands of valves of many different sizes and shapes. Despite the variety in their design, however, all valves have a common primary purpose to slow down or stop the flow of a fluid. Some valves work best in on-or-off service, fully open or fully closed. Others are designed to throttle, to reduce the pressure and flow rate of a fluid. Still others permit flow in one direction only or only under certain conditions of temperature and pressure. A steam trap, which is a special form of valve, allows water and inert gas to pass through while holding back the steam. Finally, through accessory devices, valves can be made to control the temperature, pressure, liquid level, or other properties of a fluid at points remote from the valve itself. 

Figure 8-1. Typical process plant sewer system.

Most of the raw water to the plant is used for cooling, with smaller amounts becoming boiler feed water and process water. Figure 1 illustrates a water balance for a more or less typical process plant. 

Even though the reactor typically represents between 5% and 15% of capital and operating costs of typical process plant, its choice determines both... 

Fires and explosions are the large-scale accidents most to be feared in the typical process plant. For diorough coverage of the vital topic of protection from these hazards, the reader should consult the large body of specialized literature. The National Fire Protection Association (NFPA), the publisher of the National Fire Codes, provides good summaries of codes and safe practices. 

COMMERCIAL OPERATION Figure 1.1 Typical process plant project. 

A typical process plant can include a large number of pressure vessels completely manufactured and tested in the Supplier s premises and delivered on site as a complete finished item. Exceptionally a large vessel may be delivered in two pieces to facilitate transport and then be welded together on site. This operation would almost certainly be carried out by the supplier s personnel. For pressure vessels the requirements of the concerned authority will be very much to the forefront. There will be a quality file established in the country of manufacture with records of materials used, manufacturing processes, in particular concerning welding, with trace-ability, and the records of inspections and tests carried out. Cold-stamping on the vessel itself and on the name/data plate may be an indication of its conformity and acceptance status. 

There is a bit of a problem here for the typical process plant end user because this model and all the detailed requirements laid down in lEC 61508 part 3 are directed at situations where a completely new and customized product may have to be produced. Hence it is not always as clear how the end user should proceed in the case of a product with embedded software. However lEC 61511 helps to resolve this issue. 

As we will see later in this chapter and elsewhere, the equations that govern the dynamics of some of the unit operations in typical process plants can be quite complex. Despite... 

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