Piping, chemical plant design

Chemical plants—Design and construaion. 2. Plant layout. 3. Chemical plants—Piping. I, Hunt, Roger (Roger W.) II, Title. TP155.5.B38 1993... 

Pressure Vessels and Piping. Some of the most critical components of a chemical plant involve pressure vessels. A thorough knowledge of the American Society of Mechanical Engineers (ASME) Pressure Vessel Code (75) is essential for design and maintenance of chemical plants. Some states have their own codes, which usually conform closely to the ASME version (see High pressure technology Tanks and pressure vessels). 

Standard Chemical Pump. In 1961, the American National Standards Institute (ANSI) iatroduced a chemical pump standard (29), known as ANSI B73.1, that defined common pump envelope dimensions, connections for the auxiUary piping and gauges, seal chamber dimensions, parts mnout limits, and baseplate dimensions. This definition was to ensure the user of the availabiUty of iaterchangeable pumps produced by different manufacturers, as well as to provide plant designers with standard equipment. A typical ANSI chemical pump, known as of the mid-1990s as ASME B73.1M-1991, is shown ia Figure 6. 

In recent years new ec]uipment has been invented, chemical processes, piping materials, valve designs, and new teehnologies not eonsidered when these formulas were developed with eold water in the 19th century. There is a need to measure the aetual losses onee an industrial plant is eommissioned and operations begin. I he authors of this book have developed a formula that permits the measurements of these losses in a live functioning system. Here it is ... 

Over-pressure, a pressure exceeding the system design pressure, is one of the most serious hazards in chemical plant operation. Failure of a vessel, or the associated piping, can precipitate a sequence of events that culminate in a disaster. 

Hazard and Operability Analysis (Hazop) (Kletz, 1992) is one of the most used safety analysis methods in the process industry. It is one of the simplest approaches to hazard identification. Hazop involves a vessel to vessel and a pipe to pipe review of a plant. For each vessel and pipe the possible disturbances and their potential consequences are identified. Hazop is based on guide words such as no, more, less, reverse, other than, which should be asked for every pipe and vessel (Table 1). The intention of the quide words is to stimulate the imagination, and the method relies very much on the expertise of the persons performing the analysis. The idea behind the questions is that any disturbance in a chemical plant can be described in terms of physical state variables. Hazop can be used in different stages of process design but in restricted mode. A complete Hazop study requires final process plannings with flow sheets and PID s. 

In this volume, there is an account of the basic theory underlying the various Unit Operations, and typical items of equipment are described. The equipment items are the essential components of a complete chemical plant, and the way in which such a plant is designed is the subject of Volume 6 of the series which has just appeared. The new volume includes material on flowsheeting, heat and material balances, piping, mechanical construction and costing. It completes the Series and forms an introduction to the very broad subject of Chemical Engineering Design. 

The chemical reactor is the most hazardous unit in any chemical plant because most accidents occur by uncontrolled reaction, either within the reactor or after reactants have escaped the reactor and perhaps reacted with oxygen in air. Obviously no reactor or piping can withstand the temperatures and pressures of total combustion unless designed specifically for these conditions. We will consider the energy balance and temperature variations in continuous reactors in more detail in Chapters 5 and 6, while flames and explosions will be considered in Chapter 10. 

Design and fabrication of tanks, vessels, piping and other equipment which are required to be protected with rubber lining against corrosion need special consideration in chemical plant construction. Certain features are to be incorporated in the design, and precautionary methods should be taken while fabricating the mild steel equipment to be suitable for rubber lining application. These are discussed below. 

In a chemical plant the capital investment in process piping is in the range of 25-40% of the total plant investment, and the power consumption for pumping, which depends on the line size, is a substantial fraction of the total cost of utilities. Accordingly, economic optimization of pipe size is a necessary aspect of plant design. As the diameter of a line increases, its cost goes up but is accompanied by decreases in consumption of utilities and costs of pumps and drivers because of reduced friction. Somewhere there is an optimum balance between operating cost and annual capital cost. 

F.L. Evans, Equipment Design Handbook for Refineries and Chemical Plants, Gulf, Houston, 1979, Vol. 2 piping, pp. 188-304 valves, pp. 315-332. 

Numerous developments in mechanical equipment, piping, control systems, and electrical systems have contributed to the design of safer chemical plants. However, they also have made the designer s job more difficult. With so many choices, how is the designer to choose the best one ... 

Piping systems may be relatively simple or complex and may convey utility services and chemical fluids that can be highly flammable, highly toxic, corrosive, erosive, or any combination of these properties. Piping systems within chemical plants handling hazardous Iluids must be designed, fabricated, tested, operated, and maintained consid-... 

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