Sequence of Operation

At the beginning of operation a defined operating pressure at low vacuum is set to evacuate the entire machine using a vacuum pump. To ensure a safe operation of the plant without inertisation, the system has to be operated at a pressure below the minimum ignition pressure of the corresponding organic solvent to fulfil explosion protection demands (Table 13.1) [2]. 

The actual sequential steps involved in taking a pH measurement are simple. They may be a source of problems, however, since the steps include all possible sources of error previously discussed. The main considerations for establishing proper technique are to ensure proper working and noncontaminating electrodes, and to require stable readings before recording the pH value. 

The frequency of standardization will depend on the sample, the electrodes, and the desired accuracy. For example, a relatively clean sample measured with low potential drift electrodes would require standardization once a day if only 0.1 pH accuracy is required. If the standardization is a stable, reliable pH value, and the electrode exhibits low potential drift ( 0.01 pH/hour) in buffers, there is no need for more frequent restandardization. In fact, what often occurs is that restandardization is a source of error 

There are a number of precautions an operator should observe in order not to damage the electrodes or pH meter and in order not to affect unknowingly the results of the pH measurement. 

Protection of the equipment is maximized with the following precautions  

---

The total time taken to carry out a sequence of operations (or instructions) is the average time for one operation multiplied by the number of operations. To carry out 100 instructions, each taking 100 nsec, requires a total of 10,000 nsec. 

Top-Feed Procedure The sequence of operations with a top-feed leaf test is the same as in a bottom-feed test, except that the leaf is not immersed in the sluriy. The best method for transferring the slurry to the top-feed leaf is, of course, a function of the characteristics of the sluriy. If the particles in the sluriy do not settle rapidly, the feed can usually be transferred to the leaf from a beaker. If, however, the particles settle veiy rapidly, it is virtually impossible to pour the slurry out of a beaker satisfactorily. In this case, the best method is to make use of an Erlenmeyer flask, preferably one made of plastic. The slurry is swirled in the flask until it is completely suspended and then abruptly inverted over the leaf. This technique will ensure that all of the sohds are transferred to the leaf. 

Various techniques are available to separate the different types of particles that may be present in a sohd mixture. The choice depends on the physicochemical nature of the sohds and on site-specific considerations (for example, wet versus diy methods). A key consideration is the extent of the liberation of the individual particles to be separated. Particles attached to each other obviously cannot be separated by direct mechanical means except after the attachment has been broken. In ore processing, the mineral values are generally liberated by size reduction (see Sec. 20). Rarely is liberation complete at any one size, and a physical-separation flow sheet wih incorporate a sequence of operations that often are designed first to rejec t as much... 

They are suitable for stepless speed variation and can be controlled through speed, torque, temperature or flow of a process. They can also be programmed for any sequence of operation. 

The table of results is laid out in a column, and a second column is constructed in which in the hrst four rows the results would be added sequentially in pahs, e. g. Xi + X2, xj, + X4, x + jcg etc., and the lower four rows are calculated by subuacting the second value from dre preceding value thus, JC2 — JCi, JC4 — JC3 etc., a thh d column is prepared from these results by canying out the same sequence of operations. The process is continued until there are as many columns as the number of variables. Thus in the present tluee-variable, two level-study the process is repeated tluee times (Table 15.1), and in the general -variable, two-level case it is repeated n times. (The general description of uials of this kind where tlrere are n variables and two levels, is 2 factorial uials ). 

In ntosl respects the process is similar to the injection moulding of thermoplastics and the sequence of operations in a single cycle is as described earlier. For thermosets a special barrel and screw are used. The screw is of approximately constant depth over its whole length and there is no check value which might cause material blockages (see Fig. 4.50). The barrel is only kept warm (80-110°C) rather than very hot as with thermoplastics because the material must not cure in this section of the machine. Also, the increased viscosity of the thermosetting materials means that higher screw torques and injection pressures (up to 200 MN/m are needed). 

Where two or more procedures share a common sequence of operations, or working environment, do they contain checks that the worker is continuing to use the correct procedure ... 

If the procedures were not regularly updated or were otherwise incorrect, or if training was inadequate, PI errors could occur. P2 errors would often arise as a result of misdiagnosing a situation, or if the entry conditions for executing a sequence of operations were ambiguous or difficult to assess and therefore the wrong procedure was selected. It is important to note that if a planning error occurs, then this implies that a detailed analysis needs to be conducted of the alternative course of action that could arise. 

Sequences of operations in different tasks which are very similar, apart from the critical steps which could have critical consequences when performed in the wrong situation (strong habit intrusions)... 

If the kick is gained while tripping, the only warning signal we have is an increase in fluid volume at the surface (pit gain). Once it is determined that the pressure overbalance is lost, the well must be closed as quickly as possible. The sequence of operations involved in closing the well is as follows ... 

Depending upon the drilling rig type and company policy, the sequence of operations described above may be changed. 

The sequence of operation for automatic burners is based on that which a knowledgeable, conscientious and alert... 

All gas-fired plant should be provided with operating instmctions for shutting down as well as starting up. Such instmctions will ensure that the correct sequence of operations is carried out to both avoid a hazard during the shutdown and to leave the plant in a safe condition. These procedures should also contain instmctions for actions to be carried out in emergencies. Such actions may differ from the normal shutdown. 

Sequence valves control the sequence of operation between two branches in a hydraulic circuit. In other words, they enable one component within the system to automatically set another component into motion. An example of the use of a sequence valve is in an aircraft landing gear actuating system. 

The wide application of hydraulic systems has undoubtedly been stimulated by the increasing use of fully automatic controls for sequences of operations where the response to signals must be rapid and the controls themselves light and easily operated. These needs are met by hydraulic circuits that, in addition, provide infinitely variable speed control, reversal of high-speed parts without shock, full protection against damage from overhead and automatic lubrication. 

Sheet steel is normally prepared for application of enamel by a sequence of operations including thorough degreasing, acid pickling and neutralisation. A nickel dip stage is often included to deposit a thin, porous layer of nickel applied at about 1 g/m especially when conventional groundcoat is not used (see Section 13.7). 

It is often desirable to recover product and to choose a suitable strain of microorganism which produces extracellular rather than intracellular product. If the product stays inside the cells, the cells must be ruptured, so freeing intracellular enzyme, after which extraction or purification is performed to recover the valuable product. The fermentation broth has to be processed, and pass through several stages for separation and purification. The product requites a sequence of operations for high purification. Hie usual steps to follow are as follows. 

The solution of Problem-1 requires extensive search over the set of potential sequences of operations. Prior work has tried either to identify all feasible operating sequences through explicit search techniques, or locate the optimum sequence (for single-objective problems) through the implicit enumeration of plans. The former have been used primarily to solve planning problems with Boolean or integer variables, whereas the latter have applied to problems with integer and continuous decisions. 

Using the initial and goal states as indicated in Fig. 3, it is easy to construct the following sequence of operations that satisfy the desired objectives ... 

Operators, describing process operations, can be declared at any level of abstraction, but they should maintain consistent relations with each other, since they refer to the same process. For example, the top-level operator, (START UP PLANT), could be refined to the following sequence of operators (see also Fig. 5) (START UP RECOVERY), (START,UP REFINING), (START.UP FEED PREPARATION), and (START. UP. REACTION). Clearly, the preconditions of (START.UP.PLANT) are distributed and represent a subset of the preconditions for all four more detailed operations. Similarly, the postconditions, derived from the startup operation of the four sections, should be... 

If the initial concentrations of the raw material were (in moles per liter), [HCNlo = 1, [H2S04]q = 1.5, and [HCHO]q = 2, then the preceding sequence of operations would immediately have violated Constraint-2, since [HCN] = 1 > 0.1. Similarly, Constraint-3 is violated by the preceding sequence, since [HSO4] = 0 < 1.5. In Section III,D, we discuss the notion of demotion of Clobberers. Let us see how it works here and leads to temporal ordering of operations ... 

Plan and schedule sequences of operating steps to bring the plant at the desired operating level, e.g., recover from safety fallback position, return to feasible operation after a fault. 

The assembly of complex glass apparatus is comparatively easy provided it is done in a systematic manner. It is most important to work out the general arrangement of the various parts of tlK system before starting to assemble them, and the sequence of operations should be planned in detail. 

Whatever the problems and however complex the apparatus to be constructed, the sequence of operations should be carried out mentally before any practical work is started. The time spent in planning any piece of practical work is well spent and will probably save time eventually. 

---