Performance process measures

A wide variety of particle size measurement methods have evolved to meet the almost endless variabiUty of iadustrial needs. For iastance, distinct technologies are requited if in situ analysis is requited, as opposed to sampling and performing the measurement at a later time and/or in a different location. In certain cases, it is necessary to perform the measurement in real time, such as in an on-line appHcation when size information is used for process control (qv), and in other cases, analysis following the completion of the finished product is satisfactory. Some methods rapidly count and measure particles individually other methods measure numerous particles simultaneously. Some methods have been developed or adapted to measure the size distribution of dry or airborne particles, or particles dispersed inhquids. 

An open-loop system positions the manipulated variable either manually or on a programmed basis, without using any process measurements. This operation is acceptable for well-defined processes without disturbances. An automanual transfer switch is provided to allow manual adjustment of the manipulated variable in case the process or the control system is not performing satisfac torily. 

An expert system is a computer program that uses an experts knowledge in a particular domain to solve a narrowly focused, complex problem. An off-line system uses information entered manually and produces results in visual form to guide the user in solving the problem at hand. An on-line system uses information taken direc tly from process measurements to perform tasks automatically or instruct or alert operating personnel to the status of the plant. 

If the technical staff from the client company recognizes that a toller may be asked to perform new analyses and make operating decisions based upon the results, the client may help the toller develop the needed procedures and skills required to make these decisions. Typically a round robin laboratory qualification exercise will be performed. Samples of known standards and unknown concentrations of the materials to be analyzed for the toll will be prepared and sent to both laboratories. This can help ensure that equipment calibration is synchronized and that the toller is capable of performing accurate measurements. In some cases, the toller may be the party with the chemical, process, or synthesis specific expertise. 

Detailed Evaluation Detailed evaluation is performed by measuring the capture efficiency, either by using the actual contaminant or by using a tracer gas. (In principle, it is possible to use particles as tracers, but gases are usually used as tracers.) The most reliable evaluation is to use the process-generated contaminant, since there are always problems with a tracer, due to the difficulties of feeding the tracer to the source in the same way and in a similar amount as the generated contaminant. ... 

Evaluation can be performed by measuring capture efficiency using real contaminants and applying the real process or by substituting with tracer materials. A simpler, but qualitative, method of evaluation is the visualization of the airflow. If the relationship between capture efficiency and airflow rate is known, a measurement of the airflow rate can be used for frequent evaluation. See Section 10.5. 

Measurement must address end-of-pipe performance (through measures such as injury rates and gallons spilled), process efficiency and indicators of performance (through measures such as in service failure of equipment). Using indicators should make it possible to identify problems before they result in poor performance. Process efficiency measurement helps track implementation of the project and continuous improvement in the use of resources. 

Better measurement of performance. A common frustration in PSM and ESH is that end-of-pipe measurement is all that is available and it is too late to correct a problem once the incident has occurred. Quality Management requires that we seek out in-process measures and leading indicators of performance that will warn of potential problems before they exhibit themselves as incidents. 

Measurement of performance. Quality Management requires that measures of performance be established for every activity. These measures include end-of-pipe measurement, such as amounts of material released into the environment or injury rates, and in-process measures of how efficiently you are managing, such as time to review safety improvement proposals or total resources expended on PSM. Each team should be required to identify potential performance measures for the processes they are developing and the activities these processes manage. Many of the end-of-pipe measures will already exist these should be critically examined to ensure that they truly measure performance and are not unduly influenced by other factors. For example, the number of accidents in a fleet of road vehicles is almost directly dependent on the number of miles driven with no improvement in performance, a reduction in miles driven would reduce the number of accidents. 

Controlling is the central activity during implementation. The most important tool in this process is the plan that was developed to define the three parameters of the project - specifications, schedule, and budget. Performance is measured against these standards. Controlling involves three steps ... 

In Section IV we considered a categorical performance metric y. Although that represents a common practice, especially when y defines the quality of a product or process operation, there are many instances where system performance is measured by a continuous variable. Even when y is quality-related, it is becoming increasingly clear that explicit continuous quality cost models should be adopted and replace evaluations of performance based on categorical variables. 

In conclusion, the following experiments on filtration-washing-deliquoring should be performed to produce data (viscosity of liquids, effective solid concentration, specific cake resistance, cake compressibility, etc.) that are necessary to evaluate times of individual steps of filtration at an industrial scale, i.e. to obtain the proper basis for scale-up of filtration processes measure the filtrate volume versus time make marks on your vacuum flask and take down the time when the filtrate level reaches the mark => no more experiments are needed for preliminary evaluations of filtration properties of slurries initially fines pass the filter medium => recirculate them to the slurry,... 

Filters are designed to remove unwanted information, but do not address the fact that processes involve few events monitored by many measurements. Many chemical processes are well instrumented and are capable of producing many process measurements. However, there are far fewer independent physical phenomena occurring than there are measured variables. This means that many of the process variables must be highly correlated because they are reflections of a limited number of physical events. Eliminating this redundancy in the measured variables decreases the contribution of noise and reduces the dimensionality of the data. Model robustness and predictive performance also require that the dimensionality of the data be reduced. 

One of the most important impacts identified in Po river basin was the loss of water quality as consequence of the extended use of agrochemicals. These compounds are of high concern since they are responsible for adverse effects on human health and the environment. The risk associated with each substance is evaluated during its authorisation process. However, it is not possible to assess the cumulative effects of all the agrochemicals currently in use. Within this scenario, it is mandatory to perform constant measurement of such substances. 

Secondly, rheological measurements can be applied to mimic the way materials are used and so relate to the chemical engineer s actual process. So whilst it may not be possible in practice to perform a measurement that mimics the process it may be possible to transform the data in such a way as to provide an insight into the way the material will behave in such a process. A typical example is encountered in the data handling of many... 

The overall process performance, as measured by photon efficiency (number of incident photon per molecule reacted, like the incident photon to current conversion efficiency, or IPCE, for PV cells), depends on the chain from the light absorption to acceptor/donor reduction/oxidation, and results from the relative kinetic of the recombination processes and interfacial electron transfer [23, 28]. Essentially, control over the rate of carrier crossing the interface, relative to the rates at which carriers recombine, is fundamental in obtaining the control over the efficiency of a photocatalyst. To suppress bulk- and surface-mediated recombination processes an efficient separation mechanism of the photogenerated carrier should be active. 

Some of the earliest work on NIR of bioprocesses was performed on the nutrients and metabolites in a fermentation broth. A classic paper (if 1996 is antiquity) was written by Hall et al.30 on the determination of acetate, ammonia, biomass, and glycerol in E. coli fermentations. This early paper used NIR to simultaneously monitor all the above-mentioned parameters. The correlation coefficients were all better than 0.985 with variable SEPs acetate, 0.7 g/1 ammonia, 7 mM glycerol, 0.7 g/1 and biomass, 1.4 g/1. While later work with more modem equipment has attained better results, this remains as one of the first. The work was performed at line in a cuvette, but rapidly enough to be considered a process measurement. 

The mby fluorescence method allows us to perform pressure measurements in a short time scale (1-10 s), providing a real-time access for pressure control comparing to the time scale of many solid-state chemical processes. As a matter of fact, real-time pressure measurements are necessary when studying kinetic processes [117], but it is also important to minimize the laser power used for measuring the mby fluorescence in order to avoid undesired photochemical effects on the sample, whenever these are possible. In the case of IR absorption studies, which are commonly used for kinetic purposes, the advantage of using the mby fluorescence method, once photochemical effects are prevented, with respect to the employment of vibrational gauges is that no additional absorption bands are introduced in the IR spectmm. 

In Chapter 1, we saw that electrochemistry is the branch of chemistry employed by an analyst when performing electroanalytical measurements, while in Chapter 2, we saw that electrochemical measurements fall within two broad categories, namely determination of a potential at zero current, and determination of a current, usually by careful variation of an applied potential. These two branches of electroanalysis are bridged in this present chapter by showing - on an elementary level - why char ge flows, and also explaining how an analyst can interpret and thus process quantitative data during charge flow. 

The development of the electrodynamic balance and other particle traps has made it possible to perform precise measurements of the properties of small particles by focusing on the single particle. The variety of processes and phenomena that can be investigated with particle traps is quite extensive and includes gas/liquid and gas/solid chemical reactions, chemical spectroscopies, heat and mass transfer processes, interfacial phenomena, thermodynamic properties, phoretic forces, and other topics of interest to chemical engineers. 

Experimental Analysis. The most reliable process measurement is the oscillator frequency from the PAAR densitometer. Along with the frequency, the temperature is also measured ( 0.05 C). These two states are used to interpolate the solute concentration. CSD weight percent information and obscuration measurements were obtained from the Malvern Particle Sizer. Approximately 500 concentration data points and 200 CSD and obscuration measurements were recorded during a run of about 80 -100 minutes. Therefore, the dynamics of the system were well monitored, i.e., the time constant of the crystallizer is much larger than the sampling time. We have performed 25 experimental runs. This section summarizes the analysis of a single, typical experiment. 

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