The Conceptual Design Process

The conceptual design process for a safety instrumented function begins with a Safety Requirements Specification (SRS). The SRS is an important document. It should contain complete specifications for designing all the safety instrumented functions. For each SIF the following information should be included  

Other items may be required for specific applications including any local regulatory requirements (must meet NFPA85 [Ref. 1] for example), references to company specific requirements or other requirements. 

The standards allow any internationally accepted methodology for the purpose of performing the probabilistic calculations and the most common methods are described in this book -- simplified equation, fault trees and Markov models. 

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The flowsheet synthesis of continuous chemical-like process can be performed following a systematic strategy known as the hierarchical approach. The procedure, initially proposed by Jim Douglas and coworkers in the decade 1980-90 [1, 2], describes the conceptual design process as a logical sequence of analysis and synthesis steps grouped in levels. Each level involves a flowsheet development mechanism based on design decisions. The result is not a unique solution but a collection of alternative flowsheets from which an evaluation procedure eliminates the less attractive ones. 

A general outline of Inventive Engineering, with an understanding of the conceptual designing process and its various stages... 

Conceptual Design, Fig. 3 The conceptual design process (Adapted from Coatanea (2005) Yannou (2000))... 

After equipment is selected, the next step in the conceptual design process is the decision to use multiple instruments to serve the same purpose -redundancy. Redundancy is configured to provide continued system operation even though one or more specific instruments may fail - fault tolerance. Some redundant architectures provide fault tolerance against a... 

Derived requirements are fed back to the conceptual design process or other appropriate processes. o o Hardware Requirements 10.3.1 HCl HCl HCl HCl... 

The flowchart in Fig. 10.5 presents an idealized view of the conceptual design process. 

Thus, in the first step of the conceptual design process, the broad performance requirements were translated into a larger set of clearly defined functions along with the associated factors (Fig. 13.1). 

Turbine creep is considered one of more likely life limiting failure modes and should be continually studied through the conceptual design process. 

This system also offers automatic functions to assist the conceptual-design process. It automatically checks component interference and calculates the size of the model to further determine the size of the mold base (Figure 13). 

Once the candidate corrective measure alternatives have been identified, a more detailed evaluation of each alternative needs to be undertaken. From an engineering perspective, the first step in the evaluation process would include the development of a conceptual design for each alternative. The conceptual design would consist of a process description, a process flow diagram and a layout drawing. Preliminary sizing of equipment and utility and land requirements would be developed. In addition, chemical requirements and residuals produced can be estimated. From the conceptual design, permitability and residuals disposal issues can be identified and addressed. 

Rajagopal, S., Ng, K.M. and Douglas, J.M., 1992. A liieracliical decision procedure for the conceptual design of solids processes. Computers and Chemical Engineering, 16, 675. 

The conceptual design and operation were stated to be based on experiences AEC has accumulated in its operations. 7 In fact the design was based on the ORNL pilot plant concept incorporated in the Idaho Chemical Processing Plant which cost about 20 million TOE was based on experiences at Hanford and SRP in plants that cost about 100 million. The TOE for the ICPP was not 80%, but 3%8,and there were major safety deficiencies. 

An exact calculation of inventory is difficult in the conceptual design phase, since the size of equipment is not usually known. The mass flows in the process are however known from the design capasity of the process. Therefore it is practical to base the estimation of inventory on mass flows and an estimated residence time. Consequently the inventory has been included to the ISI as a mass flow in the ISBL equipment including recycles with one hour nominal residence time for each process vessel (e.g. reactor, distillation column etc). For large storage tanks the size should be estimated. The total inventory is the sum of inventories of all process vessels. 

Many different alternative process configurations can be created for a process in the conceptual design phase. In choosing the most feasible alternative safety should be one of the major evaluation criterias. Therefore information on the safety features of alternative process structures are needed on preliminary process design. 

The conceptual design phase is the most critical when designing inherently safer plants, since the alternative process concepts are created and analyzed in this phase. This emphasizes the need to introduce safety evaluation tools into the preliminary process design. Time and money is saved when fewer expensive safety modifications are needed during the later stages of design. 

The Inherent Safety Index, ISI, was developed to consider a wider range of factors affecting the inherent safety of the process (Ch. 8). The ISI allows the evaluation of inherent safety of process alternatives to be done in a computerized process synthesis environment. The represented synthesis approach allows the inherent safety comparison of process alternatives to be done flexibly and interactively in the conceptual design phase. 

This evaluation represents the committee s understanding of the conceptual design of the modified baseline process based on information made available at the time the report was prepared. Because preliminary cost estimates and schedule information were not made available, the committee could not evaluate cost and schedule implications. 

The test results with the ultrasonic nozzle were obtained with an estimated steam to copper (S/Cu) ratio of 23 and the humidified Ar was injected co-currently with the CuCl2 solution. Several variables remain to be investigated, i.e. lower S/Cu ratios, counter-current instead of co-current operation, and subatmospheric pressures. LeChatelier s Principle predicts that reducing the pressure in the hydrolysis reactor should reduce the S/Cu ratio. The effect of a reduced pressure was quantified by the results of a sensitivity study using Aspen. Aspen predicts that a S/Cu ratio of 17 is needed for essentially complete conversion at 375°C and atmospheric pressure while a S/Cu ratio of 13 is required at 0.5 bar. The conceptual process design specifies that the hydrolysis reactor be run at 0.25 bar. The pressure drop in the reactor is achieved by adding a low temperature steam ejector after the condenser at the exit of the hydrolysis reactor in the conceptual design. 

The book is divided into three parts. Part I surveys concepts for heat-integrated chemical reactors, with special focus on coupling reactions and heat transfer in fixed beds and in fuel cells. Part II is dedicated to the conceptual design, control and analysis of chemical processes with integrated separation steps, whilst Part III focuses on how mechanical unit operations can be integrated into chemical reactors. 

Evidently, the design philosophy that was adopted for the conceptual design of the Synthane process was this Inasmuch as "unlimited" amounts of char are available — as an inherent byproduct of the Synthane gasifier and therefore at "no cost" —the... 

An exergy analysis of the conceptual design of the synclude mode H-Coal process for bituminous coal of Illinois No.6 has been carried out based on the data reported by the Fluor Engineers and Constructors, Inc.,(31). The plant is designed to convert 14,448 tons (short ton) of coal per day. 

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