Equipment design calculations

Specify the final material balance for the overall process and cany out detailed equipment design calculations. Try to add some flexibility (depending on the cost) to allow for some adjustment of the process equipment during operation— to compensate for uncertainties in the design. 

Process calculations for traditional unit-operations equipment can be divided into two types design and performance. Sometimes the performance calculation is caHed a simulation (see Simulation and process design). The design calculation is used to roughly size or specify the equipment. EoUowing the... 

Process simulators stop generally at the process specifications for the equipment. For the detailed mechanical design of the equipment, such as heat exchangers and distillation columns, stand-alone programs are often used. They make process calculations, size the equipment, calculate thermal and mechanical stresses, design mechanical support of the parts of the equipment, design inlet and outlet nozzles, etc. 

Many of the better known shortcut equipment design methods have been derived by informed assumptions and mathematical analysis. Testing in the laboratory or field was classically used to validate these methods but computers now help by providing easy access to rigorous design calculations. 

In this subsection, basic design theory for preliminary sizing and specifying equipment are reviewed. Some sample design calculations are included. References cited at the end of tlie chapter can be consulted for more detailed information and design methods. For solid-liquid separation methods, the reader should refer to Liquid Filtration, 2" edition, by N. P. Cheremisinoff, Butterworth-Heinemarui Publishers (1998). 

Comparative calculations of specific capacities of different filters or their specific filter areas should be made as part of the evaluation. Such calculations may be performed on the basis of experimental data obtained without using basic filtration equations. In designing a new filtration unit after equipment selection, calculations should be made to determine the specific capacity or specific filtration area. Basic filtration equations may be used for this purpose, with preliminary experimental constants evaluated. These constants contain information on the specific cake resistance and the resistance of the filter medium. 

This section examines and reviews some of the basic principles diat engineers and sciendsts employ in performing design calculations mid predicting die performance of plant equipment. Topics include die tlicrmochemistry, chemical reacdon equilibrimii, chemical kinedcs, die ideal gas law, pardal pressure, pliase equilibrimii, and die Reynolds Number. These basic principles will assist die reader in acquiring a better miderslmidiiig of some of the material diat appears later in die book. 

Several basic principles that engineers and scientists employ in performing design calculations and predicting Uie performance of plant equipment includes Uieniiochemistiy, chemical reaction equilibrimii, chemical kinetics, Uie ideal gas law, partial pressure, pliase equilibrium, and Uie Reynolds Number. 

Ejectors, steam/water requirements, 371 Electrical charge on tanks, 537 Electrical precipaiaiors, 280 Applications, 280, 282 Concept of operation, 281 Emergency relief, 450 Engineering, plant development, 46 Equipment symbols, 19—2 L Abbreviations, 25 Instruments, 21, 26. 29 Piping, 22 Valve codes, 26 Equivalent feel (flow), 86 Estimated design calculation time,... 

The work index, Wjr is basically an indication of ore hardness, but also includes equipment efficiency. The Bond method has been the mainstay of size reduction circuit. It still holds a value, specially for initial design calculations, and for simple checks on efficiency. 

This section is a general discussion of the techniques used for the preparation of flowsheets from manual calculations. The stream flows and compositions are calculated from material balances combined with the design equations that arise from the process and equipment design constraints. 

The reactor volume is taken as the volume of the reactor physically occupied by the reacting fluids. It does not include the volume occupied by agitation devices, heat exchange equipment, or head-room above liquids. One may arbitrarily select the temperature, pressure, and even the state of aggregation (gas or liquid) at which the volumetric flow rate to the reactor will be measured. For design calculations it is usually convenient to choose the reference conditions as those that prevail at the the inlet to the reactor. However, it is easy to convert to any other basis if the pressure-volume-temperature behavior of the system is known. Since the reference volumetric flow rate is arbitrary, care must be taken to specify precisely the reference conditions in order to allow for proper interpretation of the resultant space time. Unless an explicit statement is made to the contrary, we will choose our reference state as that prevailing at the reactor inlet and emphasize this choice by the use of the subscript zero. Henceforth,... 

Pseudo homogeneous models of fixed bed reactors are widely employed in reactor design calculations. Such models assume that the fluid within the volume element associated with a single catalyst pellet or group of pellets can be characterized by a given bulk temperature, pressure, and composition and that these quantities vary continuously with position in the reactor. In most industrial scale equipment, the reactor volume is so large compared to the volume of an individual pellet and the fraction of the void volume associated therewith that the assumption of continuity is reasonable. 

Next we need to calculate the inverse of [A A], designated [A A]-1. Because A A is an X3x3 problem, we had better use a computer program suitably equipped to calculate the inverse (2). 

Most field equipment used at remediation sites has a lifetime substantially longer than the length of the project where it is used. When the total cost of new equipment is included in the project, the unit treatment cost increases substantially as the time of treatment decreases. Two solutions to this dilemma are common either lease the equipment or use the equipment on several different projects. Both of these options require the equipment to be of some treatment volume rate such that it can be readily applied to another treatment train, and also that it can be portable. If the designer cannot locate lease equipment, or if there is only one project on which to use the equipment, cost calculations should include a salvage value for the equipment. 

This kind of calculation is called a rating calculation (equipment size is fixed), as opposed to a design calculation in which equipment is sized. 

All equipment designed to measure surface area, adsorption-desorption isotherms or pore volume by adsorption actually determines the quantity of gas condensed on a solid surface at some equilibrium vapor pressure. The surface area or pore volumes and pore sizes are then calculated by means of an appropriate theory used to treat the adsorption and/or desorption data. Depending on the apparatus employed, the adsorbed quantity is measured as volume or weight. The accuracy of an adsorption apparatus is, therefore, dependent upon its ability to correctly measure either of these quantities. 

Powder flow requirements vary with equipment design. To maintain a low weight variation, optimum values of Carr s index (CI) is in the 25 to 35 range for Zanasi and 18 < CI < 30 for H K. Note Carr s Index is calculated from the loose bulk density (LED) and tapped bulk density (TED) of powders. CI = 100[(TED LED)/TED]... 

In process operations, simultaneous transfer of momentum, heat, and mass occur within the walls of the equipment vessels and exchangers. Transfer processes usually take place with turbulent flow, under forced convection, with or without radiation heat transfer. One of the purposes of engineering science is to provide measurements, interpretations and theories which are useful in the design of equipment and processes, in terms of the residence time required in a given process apparatus. This is why we are concerned here with the coefficients of the governing rate laws that permit such design calculations. 

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