Rejection

Rejection is a term used to describe what percentage of an influent species a membrane retains. For example, 98% rejection of silica means that the membrane will retain 98% of the influent silica. It also means that 2% of influent silica will pass through the membrane into the permeate (known as salt passage ). 

Rejection of a given species is calculated using the following equation  

Cf = influent concentration of a specific component Cp = permeate concentration of a specific component 

Note that for exact calculation, the average feed concentration that takes in account both the feed and concentrate concentration rather than just the feed concentration at a single point in time should be used. 

Rejection is a property of the specific feed water component and the membrane of interest. Table 3.2 lists the general rejection ability of the most common polyamide composite RO membranes. Note that ionic charge of the component of interest plays a role its rejection by an RO membrane the rejection of multi-valent ions is generally greater than for mono-valent ions. 

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An additional advantage derived from plotting the residuals is that it can aid in detecting a bad data point. If one of the points noticeably deviates from the trend line, it is probably due to a mistake in sampling, analysis, or reporting. The best action would be to repeat the measurement. However, this is often impractical. The alternative is to reject the datum if its occurrence is so improbable that it would not reasonably be expected to occur in the given set of experiments. 

Fig. 6.7a. Above the pinch (in temperature terms), the process is in heat balance with the minimum hot utility Qnmin- Heat is received from hot utility, and no heat is rejected. The process acts as a heat sink. Below the pinch (in temperature terms), the process is in heat balance with the minimum cold utility Qcmin- No heat is received, but heat is rejected to cold utility. The process acts as a heat source.

Reject the areas of integrity, and operate the process as a single system. 

A more complex utility is combined heat and power (or cogeneration). Here, the heat rejected hy a heat engine such as a steam turbine, gas turbine, or diesel engine is used as the hot utility. 

Most refrigeration systems are essentially the same as the heat pump cycle shown in Fig. 6.37. Heat is absorbed at low temperature, servicing the process, and rejected at higher temperature either directly to ambient (cooling water or air cooling) or to heat recovery in the process. Heat transfer takes place essentially over latent heat profiles. Such cycles can be much more complex if more than one refrigeration level is involved. 

Th = temperature at which heat is rejected from the refrigeration cycle (K)... 

Total power for heat rejection to cooling water = 0.38 -I- 0.44 = 0.82 MW... 

Process cooling by level 2 by this arrangement across the pinch is 0.54 — 0.14 = 0.40 MW. The balance of the cooling demand on level 2, 0.8 — 0.4 = 0.4 MW, together with the load from level 1, must be either rejected to the process at a higher temperature above the pinch or to cooling water. 

Figure 6.40 A two-level refrigeration system for Example 6.6 with heat rejection to cooling water.

Additional separation and recycling. Once the possibilities for recycling streams directly, feed purification, and eliminating the use of extraneous materials for separation that cannot be recycled efiiciently have been exhausted, attention is turned to the fourth option, the degree of material recovery from the waste streams that are left. One very important point which should not be forgotten is that once the waste stream is rejected, any valuable material turns into a liability as an effluent material. The level of recovery in such situations needs careful consideration. It may be economical to carry out additional separation of the valuable material with a view to recycling that additional recovered material, particularly when the cost of downstream effluent treatment is taken into consideration. 

Reverse osmosis is a high-pressure membrane separation process (20 to 100 bar) which can be used to reject dissolved inorganic salt or heavy metals. The concentrated waste material produced by membrane process should be recycled if possible but might require further treatment or disposal. 

By contrast. Fig. 13.46 shows an endothermic reactor integrated below the pinch. The reactor imports Qreact from part of the process that needs to reject heat. Thus integration of the reactor serves to reduce the cold utility consumption by Qreact- There is an overall reduction in hot utility because, without integration, the process and reactor would require (Qumin + Qreact) from the utility. 

Fig. 14.1a. The background process (which does not include the reboiler and condenser) is represented simply as a heat sink and heat source divided by the pinch. Heat Qreb is taken into the reboiler above pinch temperature and rejected from the condenser at a lower temperature, which is in this case below pinch temperature. Because the process sink above the pinch requires at least Q min to satisfy its...

Let us now consider a few examples for the use of this simple representation. A grand composite curve is shown in Fig. 14.2. The distillation column reboiler and condenser duties are shown separately and are matched against it. Neither of the distillation columns in Fig. 14.2 fits. The column in Fig. 14.2a is clearly across the pinch. The distillation column in Fig. 14.26 does not fit, despite the fact that both reboiler and condenser temperatures are above the pinch. Strictly speaking, it is not appropriately placed, and yet some energy can be saved. By contrast, the distillation shown in Fig. 14.3a fits. The reboiler duty can be supplied by the hot utility. The condenser duty must be integrated with the rest of the process. Another example is shown in Fig. 14.36. This distillation also fits. The reboiler duty must be supplied by integration with the process. Part of the condenser duty must be integrated, but the remainder of the condenser duty can be rejected to the cold utility. 

Another design option that can be considered if a column will not fit is use of an intermediate reboiler or condenser. An intermediate condenser is illustrated in Fig. 14.5. The shape of the box is now altered because the intermediate condenser changes the heat flow through the column. The particular design shown in Fig. 14.5 would require that at least part of the heat rejected from the intermediate condenser be passed to the process. An analogous approach can be used to evaluate the possibilities for use of intermediate reboilers. Flower and Jackson," Kayihan, and Dhole and Linnhofl have presented procedures for the location of intermediate reboilers and condensers. 

It was noted earlier that dryers are quite difierent in character from both distillation and evaporation. However, heat is still taken in at a high temperature to be rejected in the dryer exhaust. The appropriate placement principle as applied to distillation columns and evaporators also applies to dryers. The plus/minus principle from Chap. 12 provides a general tool that can be used to understand the integration of dryers in the overall process context. If the designer has the freedom to manipulate drying temperature and gas flow rates, then these can be changed in accordance with the plus/minus principle in order to reduce overall utility costs. 

Dryers are different in characteristic from distillation columns and evaporators in that the heat is added and rejected over a large range of temperature. Changes to dryer design can be directed by the plus/minus principle. 

Project screening means checking that the predicted economic performance of a project passes a prescribed threshold or hurdle . Investors commonly apply a screening value to the project, which is a chosen IRR at a chosen oil price (for example, 20% IRR at 20/bbl). Provided the project IRR exceeds the hurdle rate the project is considered further, otherwise it is rejected in current form. 

The geometrical consistency of all possible triplets of time delays (AT31, AT21 and AT32) is validated and invalid combinations are rejected. 

All AE sources (= elementary AT1,AT2 cell), whose counts are below threshold, are rejected. 

Rejection criteria for the ropes resulting in durability loss, are defined by the regulations character and number of wires broken strand breakes friction wear corrosion ... 

Experiments have shown promising results. For components in sintered state a number of components with different defects have been able to reject based on reference measurements on components without defects. For components in green state the results vary, cracks have been able to detect, but density differences not. For both measurements on components in green and sintered state scatter between measurements was observed to be substantial. 

Real Time Radiography (RTR) is an advanced method of radiography in which the image is formed while the job is exposed to ionising radiation. RTR is often applied to objects on assembly lines for rapid inspection. Accept-or-reject decisions may be made immediately without the delay or expense of film development. The main advantages of RTR are thus, reduction in inspection cost and processing time. 

Two different types of calibration marks are used in our experiments, planar circles and circular balls. The accuracy of the calibration procedure depends on the accuracy of the feature detection algorithms used to detect the calibration marks in the images. To take this in account, a special feature detection procedure based on accurate ellipses fitting has been developed. Detected calibration marks are rejected, if the feature detection procedure indicates a low reliability. 

The fish block will be moved through the X-ray beam and the resulting image is studied on the high resolution monitor. The operator has the ability to judge a block as acceptable, rejectable or downgrade able via push-button. 

Within the preset time limit, the operator can at any time press the reject button, which will close the on/off shutter, open the exit panel and move the block on to an output conveyor At the same time the entrance panel will open to admit the next block awaiting inspection. 

The accept and downgrade buttons are interlocked with a sensor device, so that a block must be scanned at least once before the block can be accepted and loaded out by the operator This function will however always be overruled by the programmed safety time limit, which will automatically reject and outload the block when the allowed exposure time has elapsed. 

If neither the accept, downgrade or reject button is pushed during inspection, the block will automatically be out loaded after the time limit has expired. The accept/reject/downgrade buttons will flash prompting the inspector for a decision. 

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