Process boundaries

Safe work practices for hazards control lockout/tagout, confined space entry, procedures for opening process boundaries and entrance control for maintenance... 

With respect to the physical processes, boundaries can be subdivided into just three classes. The distinction will be made according to the nature of the resistance to mass transfer across the boundary. We must recognize that this transfer is usually mediated by random motions. Thus, the resistance is like the inverse of a generalized diffusivity or transfer velocity, since both these quantities have the function of a conductivity (of mass, heat, momentum, etc.). For simplicity, the following discussion will be focused on the diffusion model (Eq. 18-6), although everything which will be said can also be adapted to the transfer model (Eq. 18-4). 

The external processes (boundary fluxes) can be combined into four pairs of generalized exchange fluxes that is (a) input/output by streams, rivers, or ground-water, (b) air-water exchange, (c) sediment-water exchange, (d) exchange with adjacent water compartments. If the box represents a pond or lake as a whole, flux (d) does not exist. The fluxes into the system are controlled by external parameters such as the concentration in the inlets, the atmospheric and the sedimentaiy concentrations. These concentrations can be constant or variable with time. 

Early design assessments similar to those presented in previous sections of this chapter have the following limitations (1) they tend to focus on the reaction step and neglect the impacts of downstream units, (2) the assessment includes one or a small number of environmental indicators, and (3) the early assessment typically does not consider impacts beyond the process boundary, for example, the environmental burdens associated with the life cycle of materials used in the process. In this section we will explore some approaches to address these limitations. 

The problem really centers on understanding that these polymers are reactive chemical systems. They have variable kinetics, form numerous adducts and phase morphology as a function of the actual process (time, temperature, pressure, etc.) pathway incurred. The ability of a material to uniformly exhibit consistent process behavior and mechanical properties will therefore depend on controlling the variations within a materials chemical process boundaries. 

The next type of test is a heat rate effect evaluation. Here the sample is heat at various rates over the process range to define any effects on reaction initiation temperatures or kinetics. Figure 9 illustrates the effect of low rates allowing sufficient time for chemical reactions to change the process behavior. The higher heat rates indicate that no significant reaction products have had the opportunity to influence the process behavior. This type of information is useful for the engineering staff to set process boundary limits to maintain flow consistency. 

Many problems arise when the design fails to take account of processing boundaries, such as dam entry, maximum storage requirements, and maximum variables scanned at the highest scan frequency. 

Seals are those elements that create or maintain process boundaries between system components and/or subassemblies in order to ensure system integrity in validated process and utility systems. Seals must be biocompatible (able to be in contact with bacteria or mammalian cells without interfering with their metabolism or ability to live and multiply), must be corrosion and permeation resistant, their surface finishes must be free of molding imperfections and foreign matter on surfaces within the sealing area, and shall not generate particulate that may entrain the product. 

DOE is the only technique that enables scientists and managers to find, see, and use interaction effects that can improve product quality and yield or help set process boundaries to prevent failure. The well entrenched views that only one factor at a time can be studied and the widely held management maxim that if it ain t broke, don t fix it are not only wrong but, in some cases, dangerous a process can drift into failure, or periodically have an unexplainable failure, due to interaction effects. DOE permits scientists to conduct small scale, low cost process improvement experiments to model large scale, unbroken commercial processes without endangering current production runs and product supply. These same experiments can also generate data that drives continuous process improvement (read make more profitable ) of a process that ain t broke. ... 

Limiting Current Density. In the membrane process, boundary layers form at both sides of the membrane due to its cation permselectivity. Such boundary layers do not occur in the diaphragm process. For the boundary layer at the surface of the membrane facing the anolyte, the following basic equation is established (73). 

What are the identifiable risks from the know process hazards Where are the safe processing boundaries (i.e., the safe processing envelope described in Fig. 19 of Chapter 2) ... 

Process validation would not be expected until commercial batches are produced but information on process boundaries and critical parameters should be obtained at this stage. It should also be pointed out that if the pivotal stability studies to be listed in the final registration (on the drug product or API) are performed on pilot batches, then this data certainly could become subject to inspection. It is becoming inaeasingly common in Europe and the USA for R D facilities to be audited as well as the commercial facility before approval of a manufacturing licence, even though the R D facility has not manufactured any commercial supplies. 

Upon completion of characterization, a platform s true capability can be determined. This capability provides design organizations with tolerances to design within. These capabilities must be defined relative to appropriate constraints on process conditions. These constraints are termed boundary conditions. Process boundary conditions must be defined that clearly specify any restrictions necessary to achieve the capability and benefits of the platforms. These boundary conditions can include restriction to process settings, fixture requirements, environmental conditions, process methods or sequences, and so on. Thus, these conditions provide design groups with what a process can and cannot achieve. 

FIGURE 61.4 Schematic drying process boundary used for this LCA. 

The goal of the model for membrane unit for gas separation is to predict the flow rate and composition of retentate and permeate streams, for a given feed stream containing n components, membrane type and area, and permeate pressure. Here, the process boundary and variables are limited to one of the membrane modules shown in Figure 4.5. In this section, the solution-diffusion mechanism is used to predict the separation behavior of the membrane. In the development of a membrane model, it is assumed that the process is at steady state, pressure is constant on feed side, and permeability of a component through the... 

Determine the process boundaries— starting and ending, and note them here. 

Organizational Process Boundaries Areas of primary supply chain process responsibility... 

Second is expansion of the concepts of pollution prevention to a level transcending unit process boundaries, and even transcending facility or corporate boundaries. This is sometimes very difficult because of business issues but is beginning to see some progress. 

The common mistake in determining ATmin opt is optimizing subsystems. To avoid this, the battery boundary for a process unit should be determined from the feed to products. The following issues should be addressed to define the process boundary ... 

Over the last 15 years, substantial research on small-scale structured devices for chemical applications has been undertaken and a host of academic studies have established a solid scientific basis for the fabrication of individual (generally unconnected) units. A number of reference books are now available [8, 9] as a substantial contribution to the already well-established general area of process intensification [10]. This research has demonstrated that miniaturized components can be exploited to act on the specific length scales (several tens to hundreds of micrometers) that are particularly relevant to chemical processing boundary layers, transport processes, reaction and mixing zones. 

The less severe conditions selected in the first four HIP runs were intended to explore lower HIP process boundaries to produce weaker interfacial bonds. The HIP ed samples showed a range of densities (reported in the last Semi-Annual report), consistent with the expected effects of HIP parameters, whisker content and sintering aid level. Additional analyses were conducted during this reporting period, and the results are presented below ... 

A wealth of techniques exists for designing molecules with desired characteristics. Despite the plethora of approaches, most approaches focus on designing materials with the required processing properties without explicitly considering the plant-wide implications. In an attempt to address this limitation, Buxton (2002) proposed that only with an expanded process boundary, the selection of materials can lead to consistent cost optimal and environmentally benign improvements. Within this context, he developed a procedure for designing solvents using process and plant-wide environmental objectives. 

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