Process Conditions and Operations

This section covers melt temperature and profile, screw rotation, injection speed and pressure, mold temperature and back pressure, cycle management, clean-out procedure, and shutdown and startup procedures. 

Stress Where the part would not be stressed by bending or by impact. 

Weld lines Where the line would not be critical. 

Finishing Where finishing the gate site would be inexpensive or unnecessary. 

Thickness Where the part is thickest to minimize sink marks and to avoid pushing the melt through a thin section to fill a thicker one. 

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These tests must encompass the complete interlock system, from the measurement devices through the final control elements. Merely simulating inputs and checking the outputs is not sufficient. The tests must duplicate the process conditions and operating environments as closely as possible. The measurement devices and final control elements are exposed to process and ambient conditions and thus are usually the most hkely to fail. Valves that remain in the same position for extended periods of time may stick in that position and not operate when needed. The easiest component to test is the logic however, this is the least hkely to fail. 

Vacuum dryers are used for the processing of different type of products under different process conditions and operation modes. Typical applications are the gentle drying of high-value pharmaceuticals in small batches as well as the removal of high amounts of solvents from waste products. 

A Loss of Containment or LoC of process equipment follows when all barriers fail. The uncontrolled deviations from normal or abnormal process conditions and operations that are so extreme that leaks, cracks, ruptures or failing barriers cause the uncontrolled transport of materials from inside process equipment to the outside. In the current version of Platypus, the LoC s are of arbitrary size. That is to say that Platypus does not predict the size of the leak. The reason for that is the size of the leak is a consequence rather than a cause, which puts it in the right-hand side of the bow-tie. 

Inherent occupational health (lOH) is the prevention of occupational health hazards (i.e., chemical or physical condition) that have the potential to cause health damage to workers by trying to eliminate the use of hazardous chemicals, process conditions, and operating procedures that may cause occupational hazards to the employees. In this context, inherent occupational health hazards can be defined as a condition, inherent to the operation or use... 

A good solids-hquid separator performs well in service, both initially and over time. It operates rehably day after day, with enough flexibility to accommodate to normal fluctuations in process conditions, and does not require frequent maintenance and repair. Selection of such a separator begins with a preliminary hsting of a number of possible devices, which may solve the problem at hand, and usually ends with the purchase and instaUation of one or more commercially available machines of a specific type, size, and material of construc tion. Rarely is it worthwhile to develop a new land of separator to fill a particular need. 

The chemical process industries (CPI), petroleum and allied industries apply physical as well as chemical methods to the conversion of raw feedstock materials into salable products. Because of the diversity of products, process conditions and requirements, equipment design is often unique, or case specific. The prime requirement of any piece of equipment is that it performs the function for which it was designed under the intended process operating conditions, and do so in a continuous and reliable manner. Equipment must have mechanical reliability, which is characterized by strength, rigidness, steadiness, durability and tightness. Any one or combination of these characteristics may be needed for a particular piece of equipment. 

BPCS/SIS functions that produce a trend analysis of input and output functions. Graphic video displays set-up to indicate process conditions and valve positions assure that the status of the process conditions is announced to the board operator, who may then verify the conditions with the field operator. 

Each situation must be evaluated on its own merits or conditions and operating situation, and even its environment with respect to the plant flammable processing equipment. 

Plant and process design, where the materials of construction, equipment design, process conditions and recommended operating practice can all be influenced to minimise the risk of corrosion. This is the most important phase. 

The effort required to specify the materials schedule for a new plant or to check a design very much depends on how much experience there is of similar or identical units in operation. Factors such as process conditions and raw material sources are taken into consideration before extrapolating the experience of another unit. 

Copolymerization and crosslinking processes are very important in the paint and coating industry. The theoretical description of such processes is helpful in understanding the essential parameters in these complex operations and in improving process conditions and product specifications with a minimum of time-consuming systematic experiments. 

Linear, polynomial, or statistical discriminant functions (Fukunaga, 1990 Kramer, 1991 MacGregor et al., 1991), or adaptive connectionist networks (Rumelhart et al, 1986 Funahashi, 1989 Vaidyanathan and Venkatasub-ramanian, 1990 Bakshi and Stephanopoulos, 1993 third chapter of this volume, Koulouris et al), combine tasks 1 and 2 into one and solve the corresponding problems simultaneously. These methodologies utilize a priori defined general functional relationships between the operating data and process conditions, and as such they are not inductive. Nearest-neigh-... 

Fig. 3. Inductive generalization of pattern-based relations between process variables and operating conditions.

The extraction, though, of the so-called pivotal features from operating data, encounters the same impediments that we discussed earlier on the subject of process trends representation (1) localization in time of operating features and (2) the multiscale content of operating trends. It is clear, therefore, that any systematic and sound methodology for the identification of patterns between process data and operating conditions can be built only on formal and sound descriptions of process trends. 

A chemical reactor is an apparatus of any geometric configuration in which a chemical reaction takes place. Depending on the mode of operation, process conditions, and properties of the reaction mixture, reactors can differ from each other significantly. An apparatus for the continuous catalytic synthesis of ammonia from hydrogen and nitrogen, operated at 720 K and 300 bar is completely different from a batch fermenter for the manufacture of ethanol from starch operated at 300 K and 1 bar. The mode of operation, process conditions, and physicochemical properties of the reaction mixture will be decisive in the selection of the shape and size of the reactor. 

Time based commands start processes that require control over a period of time, as in operations that must be repeated at regular intervals. Flow control commands let the control program choose alternative execution paths as needed. They are used to test for the existence of specified process conditions and to change the reaction conditions by branching to other parts of the formula table. 

The scope of this book includes several aspects of safe process design and operation, such as the choice of reactor type, safe operating conditions, and the selection of protective systems, primarily related to chemical reactivity. However, even in a process plant where these aspects have been carefully considered and thoroughly applied, there are still numerous events that can occur and can lead to hazardous incidents. Examples of such events are ... 

The main business of most chemical companies is to manufacture products by means of controlled chemical reactions. The reactivity that makes chemicals useful can also make them hazardous. Chemical reactions are usually carried out without mishap, but sometimes they get out of control because of problems such as the wrong or contaminated raw material being used, changed operating conditions, unanticipated time delays, failed equipment, incompatible materials of construction, or loss of temperature control. Such mishaps can be worse if the chemistiy under both normal and abnormal conditions is not fully understood. Therefore, it is essential that chemical process designers and operators understand the nature of the reactive materials andchemistry involved and what it takes to control intended reactions and avoid unintended reactions throughout the entire life cycle of a process facility. 

Introduction The chemical processing industry relies on many types of instrumented systems, e.g., the basic process control systems (BPCSs) and safety instrumented system (SIS). The BPCS controls the process on a continuous basis to maintain it within prescribed control limits. Operators supervise the process and, when necessary, take action on the process through the BPCS or other independent operator interface. The SIS detects the existence of unacceptable process conditions and takes action on the process to bring it to a safe state. In the past, these systems have also been called emergency shutdown systems, safety interlock systems, and safety critical systems. 

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