Equipment variations, causing process

The waste flow and composition will vary for a number of reasons. Wide variation in the waste stream characteristics may cause process upsets that could take the system out of control and cause equipment failure. The primary method for reducing this variability is to install a tank to collect the waste from the clean room. The tank serves several purposes ... 

Although it is not unusual for equipment to cause excessive variations occasionally, defects can often be related to maintenance faults (e.g. seals not replaced at specified times, volumetric adjustment controls not secured after adjustment). One of the most important process checks is at the start of the batch, particularly after a change-over from a different fill quantity or after a maintenance period. This start-up check is the best opportunity to find the gross error and to ensure that all filling heads are set correctly. 

Furnaces, also referred to as heaters, are one of the main pieces of equipment in a process complex. A furnace may raise the temperature of a gas or hydrocarbon liquid to meet specific processing needs or, in the case of pyrolysis and reformer furnaces, cause a chemical or physical change to the medium. A circular or box-type configuration is primarily used variations to each design are covered throughout this chapter. In addition, because of the various types of furnaces, this chapter covers some basics of furnace design and discusses how to approach a piping layout as it relates to maintenance, operation, and safety. 

Ideally, every manufacturer would like to see the manufacturing process controlled to a degree where he could produce identical parts day in and day out. In the real world, this is not possible. The difficulties in controlling the process arise from inherent variations caused by equipment and tool wear, operator skill, and manufacturing environment. Statistical quality control techniques, through the use of control charts, allow us to achieve the following ... 

The development phase provides a device-independent process plan. The plan may not address the specific semp of each production machine or measurement system (both in common are named equipment) in the production system. This need is caused by the differences between the equipment of the volume production line (the targeted production system) where occurrences of the product shall be produced and the equipment of the pilot line (original production system) where only the first occurrences of the new product were created for development and evaluation purposes. The differences are caused by equipment, which was acquired from different suppliers during different times. Equipment variations are therefore caused by the variation of equipment strucmre across vendors, as well as by the age and thus the different stages of technical progress of equipment. 

The most common cause of process variations on a large scale is equipment variations the material of construction, the shape and size of the equipment, the design of the agitator, the baffle system, and the isolation technique. In controlling or monitoring temperature, the location of the sensors is very important. Is the sensor in the bottom valve or in the baffle Many things are... 

Adaptive Control. An adaptive control strategy is one in which the controller characteristics, ie, the algorithm or the control parameters within it, are automatically adjusted for changes in the dynamic characteristics of the process itself (34). The incentives for an adaptive control strategy generally arise from two factors common in many process plants (/) the process and portions thereof are really nonlinear and (2) the process state, environment, and equipment s performance all vary over time. Because of these factors, the process gain and process time constants vary with process conditions, eg, flow rates and temperatures, and over time. Often such variations do not cause an unacceptable problem. In some instances, however, these variations do cause deterioration in control performance, and the controllers need to be retuned for the different conditions. 

From this relatively simple test, therefore, it is possible to obtain complete flow data on the material as shown in Fig. 5.3. Note that shear rates similar to those experienced in processing equipment can be achieved. Variations in melt temperature and hypostatic pressure also have an effect on the shear and tensile viscosities of the melt. An increase in temperature causes a decrease in viscosity and an increase in hydrostatic pressure causes an increase in viscosity. Topically, for low density polyethlyene an increase in temperature of 40°C causes a vertical shift of the viscosity curve by a factor of about 3. Since the plastic will be subjected to a temperature rise when it is forced through the die, it is usually worthwhile to check (by means of Equation 5.64) whether or not this is signiflcant. Fig. 5.2 shows the effect of temperature on the viscosity of polypropylene. 

A certain potential is applied to the electrode with the potentiostatic equipment, and the variation of current is recorded as a function of time. At the very beginning a large current flows, which is due largely to charging of the electrode s EDL as required by the potential change. The maximum current and the time of EDL charging depend not only on the electrode system and size but also on the parameters of the potentiostat used. When this process has ended, mainly the faradaic component of current remains, which in particular will cause the changes in surface concentrations described in Section 11.2. 

One of the major problems associated with bonding plated parts is the different surface conditions that can be caused by variations in plating equipment, process methods, and solution concentrations. These variables result in plated surfaces with broad conditions of surface finish and inconsistent metallurgical and adhesion properties. 

Your preparation should also include following a realistic simulation of a process through a complete phase of eight to ten cycles. Realistic simulation implies that measurements of the response to be optimized (e.g., yield, profit, etc.) include some error, or noise, t)-pical of that caused by such factors as raw-material variations, equipment fluctuations and instrument deviations. Because of the conservative nature of EVOP, the response changes and the noise may occasionally have comparable values however, as the number of cycles increases, the simulation will show that even though the best run may vary from cycle to cycle, the effects of the noise will eventually average out so that the true responses and variable effects can be determined. At the completion of a phase, the worksheet calculations... 

As in most processes, a distillation column and other separation processes must be maintained at operating conditions that result in products meeting certain specifications. To achieve this objective on a continuous basis the process is equipped with an automatic control system. Various disturbances can occur during the operation of the process, such as variations in ambient conditions or in the feed flow rate or composition. This can move the process away from design steady-state conditions, causing the products to be off-specification. The automatic controller counters the disturbances by adjusting the operating conditions such as to maintain the process variables at acceptable values. 

VALIDATE To provide documented evidence that an item of equipment, process, system or method is in a state of control (i.e., that all assignable causes of variation have been eliminated) and is able to consistently deliver specified results. 

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