Systems Design

The simplest design is the dead-end operation (figure Vin - 14a). Here all the feed is forced through the membrane, which implies that the concentration of rejected components in the feed increases and consequently the quality of the permeate decreases with time. This concept is still used very frequently in microfiltration. 

The design of nuclear power plant systems should be based on the feedback of experience gained in reducing radiation exposure at operating stations. 

The following measures for reducing radiation exposure should be adopted in the system design  

Pipelines containing radioactive fluids should not be located near clean piping and they should be located at a suitable distance from items that need maintenance. Sufficient space for making inspections as well as repairs and modifications should be left between the pipeUnes and the walls. 

The uncontrolled buildup of particles containing radioactive substances should be prevented by means of appropriate design for fluid flow and chemistry control and also by the use of piping with a smooth and even inner surface. 

Pipelines should be so designed that few venting and drainage Unes are needed. Drainage should lead to a sump or a closed system. Pipelines should be designed to avoid causing fluid to collect in places.. 

Feed Pretreatment. The type and complexity of the feed pretreatment system depends on the content of the water to be treated. As in reverse osmosis, most feed water is sterilized by chlorination to prevent bacterial growth on the membrane. 

Two membranes and two gasket spacers form a single cell pair. Holes in the gasket spacers are aligned with holes in the membrane sheet to form the manifold 

Power Supply and Process Control Unit. Electrodialysis systems use large amounts of direct current power the rectifier required to convert AC to DC and to control the operation of the system represents a significant portion of a plant s capital cost. A typical voltage drop across a single cell pair is in the range 1 -2 V and the normal current flow is 40 mA/cm2. For a 200-cell-pair stack containing 1 m2 of membrane, the total voltage is about 200-400 V and the current about 

400 A per stack. This is a considerable amount of electric power, and care must be used to ensure safe operation. 

Since the first plants were produced in the early 1950s, several thousand brackish water electrodialysis plants have been installed around the world. Modern plants are generally fully automated and require only periodic operator attention. This has encouraged production of many small trailer-mounted plants. However, a number of large plants with production rates of 10 million gal/day or more have also been installed. 

When cleaning needs have been defined, the next step is to determine how they can be met. The design and installation of equipment and piping are critical here. 

The designer must consider also the choice of materials of construction [1-5]. The system must be resistant at cleaning temperatures and pressures to all materials used in the process. These include process ingredients, individually and in combination, reaction products at process temperatures and pressures, and substances used in chemical cleaning. 

The chief concern in selection of materials of construction must be the prevention of corrosion and equipment failure. In some cases, minor corrosion may also cause contamination of a product. Such corrosion cannot always be predicted during the design phase and therefore must be studied during process development. A more subtle problem can arise with compound materials. The base material (e.g., a rubber or a plastic) may be inert to corrosion however, other components of the compoimd material may cause a problem. The same compoimding materials used in product development should therefore be specified for use in production nms. This may be best ensured by using the same brands in all stages of production. 

Other important design considerations can be grouped under the heading of mechanical or detailed design of process equipment. 

Cleanout nozzles have a vital purpose. Unless the equipment can be cleaned properly and thoroughly, a production campaign may fail or a hazard may be created. The nozzles must be sized and positioned properly. Access should be specifically provided to all parts that may require cleaning. 

After the feasibility of in situ groundwater bioremediation has been established, the engineering design can proceed. Detailed design documents should be based on  

The flow diagram in Fig. 3.1 will be familiar to anyone using low pressure liquid chromatographic systems with the exception of the pressure monitor however, each user will have their own specific requirements. For example, a user who wants a machine as a general all-purpose tool on which a multitude of tasks can be performed (thereby exposing the equipment to a variety of aqueous and non-aqueous solvents) will perhaps not require the same degree of sophistication as someone requiring a dedicated instrument, e.g. for quality control purposes. 

Each of the components detailed in Fig. 3.1. will be considered in turn to try to create an understanding of how to design a system. A detailed description of the development of HPLC equipment can be found in McNair (1984). 

The location in which the system is being utilized needs to be considered. On the one hand the system needs to be designed or selected for reliable operation in such locations, eg, cold room on the other hand the quality and stability of the services (power, air) need to be ensured. Particularly with automated systems in industrial situations, the susceptibility to, and implications of, power drop outs and other potential electrical problems, need to be considered. Be cautious of scaled up analytical components that may not be rugged enough. 

Systems should be designed with the aim of minimum service requirements but routine adjustments and calibration of sensors will be necessary. Layout of the various components should be such as to facihtate access to those items such as filters, pH probes, and detector lamps which will require periodic replacement. 

In selecting instrumentation, attention should be given to its stability, requiring less frequent recalibration and to its ease of recalibration when required. Certain pH and conductivity probes for instance can only be calibrated accurately under flow conditions which is not as easy to perform as static calibration. Design of the system should also address this need to facilitate recalibration. 

In production it is usual to implement routine preventative maintenance to reduce the likelihood of component failure during a run. The requirements and frequency of such servicing should be advised by the manufacturer or compiled from individual component manuals. 

Bearing in mind the general requirements, the next stage in designing a system is to produce a functional or block flow diagram of the process. This will usually also take into account not only the chromatography step but also the upstream and downstream requirements of the process. This identifies the number and volumes of solvents, sample, and fractions, together with column size. 

The development of an incineration system process flow diagram is one of the most important aspects of the conceptual design. This activity includes the determination of individual process steps and subsystems, and their relative sequence. A generic block diagram of a radioactive waste incineration system is shown in Fig. 1. 

An overall incineration system consists of a number of subsystems, such as waste feed, combustion chamber, off-gas treatment, and ash handling systems. Each of these subsystems consists of several components or process steps. In the overall system design, as represented by the process flow diagram, the suitability of each subsystem and its components needs to be carefully established from the viewpoint of mutual compatibility, equipment layout and system controls. Often, the interfacing requirements will dictate the final selection of components. Further direction on subsystem and component selection can be found in Sections 6 and 7. 

The design of systems and components important to safety shall be prepared, reviewed and documented in accordance with the applicable design codes and QA requirements and shall be submitted to the regulatory body for approval before construction begins. Modilications of the above systems and components shall follow a similar procedure. 

The process flow diagram shall be revised to reflect the revised configuration of the installed equipment following any modification of the system. 

The combustion technique should be selected according to the waste feed characteristics, with the objective of achieving complete combustion and of meeting the primary goal of selecting incineration as a treatment method. An off-gas treatment system can subsequently be chosen on the basis of the particular combustion technique selected and the specific environmental and occupational requirements. 

Another technique for overcoming the solids/viscosity conundrum is demonstrated in a patent by American Cyanamid. Here a conventional water soluble acrylic is prepared as a dispersion and is then used as a colloid stabiliser for further emulsion polymerisation. This polymerisation occurs within the dispersion droplets that have already been formed. This allows higher solids solutions to be formed with low viscosities, and low cosolvent contents  

Emulsions resulting from the emulsion polymerisation of acrylic or vinyl monomers are unique compared to other resins used for surface coating applications. As such they have properties which are totally different to a conventional solution acrylic, polyester or alkyd resins. Their mechanism of film formation is totally different to other types of resins. Because particles are present it is necessary for them to coalesce to film form and pigmentation is also different to conventional solution polymers. Consider first the unique properties and test methods of emulsion polymers. 

Span AB = 140 feet expansion = (140)(3.4)/10C = 4.8 inches. A single-end joint with an 8-indi traverse is suitable at point A. Span BC is 90 fee long and has an expansion of 3.1 inches when figured as above. Hence, the joint C is a single-end with a 4-inch traverse. The span CE is 430 feet long with 14.7 inches of expansion. A double-end join with an 8-inch traverse at each end is suitable at D. the approximate mid-point. Span EF is 100 feet long with 3.7 inches of expansion for which a single-end, 4-inch traverse joint will be adequate. 

Distance between guide and expansion joint For internally guided joints For internally.externally guided 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12 12 

Anchor Loads. Intermediate anchors at A, D, and F are subject to possible maximum loads of 

000 pounds along the solid arrows with an 11,300-pound resultant. 

Note Anchor loads with corrugated joints will be somewhat higher or lower depending on pipe size, pressure, etc. Consult manufacturer s instructions. 

The eurliestcleanrooms were once through units. These rooms were heavily filtered. When the maximum cleanliness achieved became inadequate, the individual rooms had clean zones added where the cleaner air in the cleanroom was again filtered at the point of use. There was no recirculation of the air within these rooms. These rooms had limitations on the cleanliness they could achieve. The cleanliness was limited to the efficiency of the HEPA filter. It also was costly to treat the air and then release it outside the building. 

The best protection against smoke is proper design of the cleanroom and air handling system. The importance of noncombustible components and elimination of plastics has already been discussed but cannot be overstressed. 

With any exhaust system, the fire department should have a manual override. This could be to actuate the system if there is a smoke buildup that hasn t tripped the system automatically or it could be to shut the system off if they deem it necessary to enhance the manual fire fighting. The smoke exhaust systems should be automatic. This allows the plant personnel to 

Before makeup air is added to the cleanroom, it is pretreated. Here, Class 1 filters should be used. Temperature and hmnidity should be adjusted at this point, not at the recirculating air handling units. 

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R. W. Haines, HTAC System Design Handbook, TAB Books, Blue Ridge Summit, Pa., 1988. 

Alkylated aromatics have excellent low temperature fluidity and low pour points. The viscosity indexes are lower than most mineral oils. These materials are less volatile than comparably viscous mineral oils, and more stable to high temperatures, hydrolysis, and nuclear radiation. Oxidation stabihty depends strongly on the stmcture of the alkyl groups (10). However it is difficult to incorporate inhibitors and the lubrication properties of specific stmctures maybe poor. The alkylated aromatics also are compatible with mineral oils and systems designed for mineral oils (see Benzene Toulene Xylenes and ethylbenzene). ... 

Chemical Regeneration. In most MHD system designs the gas exiting the toppiag cycle exhausts either iato a radiant boiler and is used to raise steam, or it exhausts iato a direct-fired air heater and is used to preheat the primary combustion air. An alternative use of the exhaust gas is for chemical regeneration, ia which the exhaust gases are used to process the fuel from its as-received form iato a more beaeftcial oae. Chemical regeaeratioa has beea proposed for use with aatural gas and oil as well as with coal (14) (see Gas, natural Petroleum). 

MaintainabiUty is a characteristic of design, installation, and operation, usually expressed as the probabiUty that a system can be restored to specified operable conditions within a specified interval of time when maintenance is performed in accordance with prescribed procedures. The ease of fault detection, isolation, and repair are all influenced by system design and are principal factors contributing to maintainabiUty. Also contributing is the supply of spare parts, the supporting repair organization, and preventative maintenance practices. MaintainabiUty must be designed into the equipment. Some factors to consider foUow. 

Failure Mode and Effects Analysis. The system design activity usually emphasizes the attainment of performance objectives in a timely and cost-efficient fashion. The failure mode and effects analysis (FMEA) procedure considers the system from a failure point of view to determine how the product might fail. The terms design failure mode and effects analysis (DFMEA) and failure mode effects and criticaUty analysis (EMECA) also are used. This EMEA technique is used to identify and eliminate potential failure modes early in the design cycle, and its success is well documented (3,4). 

System rehabihty is improved by providing alternative means for performing the same task. For example, automobiles were equipped with hand cranks even though they had electric starters. This back-up equipment was provided because at that time starters were unrehable. In contemporary system design, factors such as added cost, weight, and space may prohibit the use of redundant systems. 

The rate of heat-transfer q through the jacket or cod heat-transfer areaM is estimated from log mean temperature difference AT by = UAAT The overall heat-transfer coefficient U depends on thermal conductivity of metal, fouling factors, and heat-transfer coefficients on service and process sides. The process side heat-transfer coefficient depends on the mixing system design (17) and can be calculated from the correlations for turbines in Figure 35a. 

Concepts and Processes. Contemporary dosage forms are dmg dehvery systems, designed and manufactured to achieve safe and effective therapeutic responses each time the forms are used as part of an appropriate regimen. Thus, the intent of the prescriber is accompHshed when the product is used compliantly by the patient (12—14). Each dmg product involves several interrelated concepts that must be considered in its design and manufacture (15). Examples include the following ... 

J. A. Wilkinson and B. W. Balls, "Microprocessor-Based Safety Systems Designed for Fine and Gas and Emergency Shutdown AppHcations,"... 

Reviews of concentration polarization have been reported (14,38,39). Because solute wall concentration may not be experimentally measurable, models relating solute and solvent fluxes to hydrodynamic parameters are needed for system design. The Navier-Stokes diffusion—convection equation has been numerically solved to calculate wall concentration, and thus the water flux and permeate quaUty (40). 

The intrinsic rejection and maximum obtainable water flux of different membranes can be easily evaluated in a stirred batch system. A typical batch unit (42) is shown in Figure 5. A continuous system is needed for full-scale system design and to determine the effects of hydrodynamic variables and fouling in different module configurations. A typical laboratory/pilot-scale continuous unit using computer control and on-line data acquisition is shown in Figure 6. 

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