Process Need

As with heat pumping, the grand composite curve is used to assess how much heat from the process needs to be extracted into the refrigeration system and where, if appropriate, the process can... 

Specialized equipment for industrial measurements and automatic control have been developed (18) (see Process control). In general, the pH of an industrial process need not be controlled with great accuracy. Consequendy, frequent standardization of the cell assembly may be uimecessary. On the other hand, the ambient conditions, eg, temperature and humidity, under which the industrial control measurements are made, may be such that the pH meter must be much more robust than those intended for laboratory use. To avoid costiy downtime for repairs, pH instmments may be constmcted of modular units, permitting rapid removal and replacement of a defective subssembly. 

The NaAlCl formed in this process needs to be removed by washing with water, in order to achieve the desired improved stabiUty. A more convenient method for replacing framework-Al with Si is the reaction with ammonium hexafluorosiUcate (35). 

When the dryer is seen as a heat exchanger, the obvious perspective is to cut down on the enthalpy of the air purged with the evaporated water. Minimum enthalpy is achieved by using the minimum amount of air and cooling as low as possible. A simple heat balance shows that for a given heat input, minimum air means a high inlet temperature. However, this often presents problems with heat-sensitive material and sometimes with materials of constmction, heat source, or other process needs. AH can be countered somewhat by exhaust-air recirculation. 

Good design ideas for new plants are also good for existing plants, but there are three basic differences. (/) Because a plant already exists, the capital—operating cost curve differs. Usually, this makes it more difficult to reduce utiHty costs to as low a level as in a new plant. (2) The real economic justification for change is more likely to be obscured by the plant accounting system and other nontechnical inputs. (2) The real process needs are... 

The level of technical service support provided for a given product generally tracks in large part where the suppHer considers thek product to be located within the spectmm of commodity to specialty chemicals. Technical service support levels for pure chemicals usually provided in large quantities for specific synthetic or processing needs, eg, ammonia (qv), sulfuric acid (see SuLFURic ACID AND SULFURTRIOXIDe), formaldehyde (qv), oxygen (qv), and so forth, are considerably less than for more complex materials or blends of materials provided for multistep downstream processes. Examples of the latter are many polymers, colorants, flocculants, impact modifiers, associative thickeners, etc. For the former materials, providing specifications of purity and physical properties often comprises the full extent of technical service requked or expected by customers. These materials are termed undifferentiated chemicals (9),... 

Abundant supplies of fresh water are essential to the development of industry. Enormous quantities are required for the cooling of products and equipment, for process needs, for boiler feed, and for sanitary and potable water supply. 

Charcoal—sulfur processes need low ash hardwood charcoal, prepared at 400—500°C under controlled conditions. At the carbon disulfide plant site, the charcoal is calcined before use to expel water and residual hydrogen and oxygen compounds. This precalcination step minimises the undesirable formation of hydrogen sulfide and carbonyl sulfide. Although wood charcoal is preferred, other sources of carbon can be used including coal (30,31), lignite chars (32,33), and coke (34). Sulfur specifications are also important low ash content is necessary to minimise fouling of the process equipment. 

Mutual Exclusion (MUTEX). The idea of multiple entities all working on the same piece of work raises this issue of coordination and communication among the individual processes. A weU-known example from banking is instmctive. Consider two bank tellers simultaneously performing withdrawals from the same bank account. Both read the account balance and determine that the balance is 100, and so a withdrawal of 100 is allowed. Both then withdraw 100 from the account. Clearly this process needs some means by which the actions of the independent processes can be synchronized and coordinated. 

The cleaned and microetched boards are cataly2ed and activated in the same manner as for POP. The same coppers are used as for POP, but these are usually formulated to give greater deposition rates and thicknesses. Copper is typically deposited in 0.25—35 p.m thickness, depending on the process. Fully additive processing needs thicknesses of 25—35 p.m subtractive processing needs thicknesses of 0.25—2.5 p.m. 

It is seldom possible, either economically or timewise, to study eveiy potential mixing variable or to compare the performance of many impeller types. In many cases, a process needs a specific fluid regime that is relatively independent of the impeller type used to generate it. Because different impellers may require different geometries to achieve an optimum process combination, a random choice of only one diameter of each of two or more impeller types may not tell what is appropriate for the fluid regime ultimately required. 

Often batch process equipment needs to be located inside buildings. This is usually the case when the process needs to be shielded from extreme heat/cold conditions, the elements, and/or needs to be kept sterile. This leads to the need to provide adequate building ventilation to avoid buildup of hazardous material due to leaks and other process emissions. When the operation of a process involves opening, cleaning, charging etc., point source ventilation may also need to be provided. 

An overall review of the management of change documentation package should be performed to ensure documentation update items (including material safety data sheets) are addressed and that PHA action items are complete. This can be done by one person but is often best achieved by a PSSR Team. The process needs to account for ... 

Since the motor s fixed parameters can now be varied to suit a particular load requirement, there is no need to pre-match a motor with the load. Now any motor can be set to achieve the required characteristics to match with the load and its process needs. Full-rated torque (TJ at zero speed (during start) should be able to pick up most of the loads smoothly and softly. Where, however, a higher 7 s, than is necessary, a voltage boost can also be provided during a start to meet this requirement. (See also Section 6.16.1 on soft starting.) The application of phasor (vector) control in the speed control of an a.c. motor is shown in a block diagram in Figure 6.12. 

The above tiiethod is used to vary Ihe frequency and the voltage of the inverter output (motor side) according to the process needs, irrespective of Ihe electronics scheme adopted to obtain the required speed control. 

Moderate to accurate, depending upon the accuracy of controls. Stepless up to 20% of V, at constant h.p. and up to 33% of N, at constant torque is possible. Pumps, ID fans etc., that call for speed variation during a process need may not necessarily be too accurate. Or variation in flow of fluid, gas or temperature etc. not calling for very accurate controls, that such drives find their extensive use. It may be made more accurate, but at higher cost of controls... 

Central processing unit (CPU) This is in the form of a micro controller and can be called the brain of the PLC. It computes and analyses the various data fed into it. It acts like a comparator and makes decisions on the corrective action necessary to fulfil process needs according to the instructions received from the program stored in the memory and generates the output commands. 

The merits of a variable-speed motor would appear to be obvious, as many compressors in the past have benefited from the variable speed available in a steam turbine. A compressor may be adjusted as required to meet the process needs. The advent of the variable-frequency drive returns some of the benefits to the process operator that were lost when the more favor able electric energy caused motors to replace steam turbines. 

One such process is the TAP process, the basic patent being held by Dow. It was developed in Japan by Asahi in conjuction with Toshiba. Foam expansion after mould filling is made possible by use of retractable mould cores. Because of the difficulty of allowing expansion in more than one direction this process has been largely limited to the production of flat products. Efficient gas sealing systems are also vital and the process needs close control. For this reason it has not been widely used in either Europe or North America. 

There is an intermediate mechanism between these extremes. This is a general acid catalysis in which the proton transfer and the C—O bond rupture occur as a concerted process. The concerted process need not be perfectly synchronous that is, proton transfer might be more complete at the transition state than C—O rupture, or vice versa. These ideas are represented in a three-dimensional energy diagram in Fig. 8.1. 

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