Process design steam supply

At the low-pressure side of the reducing valve it is usually essential to fit a relief or safety valve. If any of the steam-using equipment connected to the low-pressure range is designed to withstand a pressure below that of the upstream steam supply, then a safety valve is mandatory. Further, it may be called for when it is sought to protect material in process from over-high temperatures (Figure 22.9). 

Utilities Design steam, water, electricity, and air supplies to be available during emergencies. Place substations away from process areas. 

Pressure relief valves are provided to cater to two main conditions of the process -normal conditions and emergency conditions. Normal conditions relate to the designed operation of the process which emergency conditions can be caused by either (1) external fire conditions, (2) failure of reflux or cooling, (3) Failure of the power supply, (4) failure of steam supply, (5) heat exchanger failure (6) introduction of incompatible materials, (7) thermal expansion with outlets closed. 

Most heat transfer systems are of a closed loop design that circulates a heat transfer medium between heaters and heat exchangers. Circulation pumps provide flow and regulating valves are used for process control. The heat transfer medium is usually steam, a high flash point oil, or in process plants flammable liquids and gases. Inherently steam is a safer medium to use and is preferred over other mediums. When steam supplies are unavailable high flash point oils (organic or synthetics) are sometimes used. 

As mentioned earlier, these bottlenecks are only partly applicable when we consider supply-level integration naturally process temperatures will have an impact on the supply line temperatures and return flow temperatures will as well be influenced by the process design however, this is most true for water-based distribution systems and less for steam systems. High-energy peaks and varying loads will pose no challenge for supply... 

One additional load variable which if allowed to pass through the process would upset the controlled variable is steam enthalpy. In some applications the steam supply may be carefully controlled so that its energy is uniform in other applications substantial variations in steam enthalpy may experienced. The objective is to consider the factors that influence the energy level of the steam supplied and to design a system that will protect the process from these load variables. 

In the present chapter, we shall first consider the details of the heat generation process within the reactor core. The transfer of heat from the fuel elements to the coolant will then be covered for both the nonboiling and boiling cases. Finally, the overall design of the nuclear steam supply system (NSSS) will be discussed. 

Thus, a cogeneration system is designed from one of two perspectives it may Be sized to meet the process heat and other steam needs of a plant or community of industrial and institutional users, so that the electric power is treated as a by-produc t which must be either used on site or sold or it may be sized to meet electric power demand, and the rejected heat used to supply needs at or near the site. The latter approach is the likely one if a utility owns the system the former if a chemical plant is the owner. 

It is important for crosstied systems that a sufficient condensate network is provided for balancing the mix of condensate return and makeup treated water as required. The author has seen a system designed with process area and utility area fired boilers of the same pressure. Periodically, the utility area was required to supply makeup steam to balance a shortage in the process area, but no provisions were made to return equivalent condensate from the process to the utility area. The earlier such a mistake is caught, the better. 

Traditionally, the steam reforming reactor has a tubular design in which vertical tubes, loaded with catalyst, are surrounded by furnaces to supply the heat required for the strongly endothermic process, see Fig. 8.2. Combustion of natural gas supplies the heat to the tubes. 

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