Pump-around flow

Chimneys (risers) blocking flow to draw sump forcing liquid to overflow prematurely. Flooding of trayed section below pump around. Lack of response to pump around flow changes. Design error. 

Group 3 Loss of pump around flow. This grouping comprises malfunctions associated with the circulation of fluids through and around the main fractionator. The loss of one or more pump flows (slurry, light cycle oil, naphtha, and heavy cycle oil) leads to the loss of some of the fractionator heat sink. 

Use pre-flash, feed conditioning, feed-product heat exchange, heat pumps, dividing-wall columns (Premkumar and Rangaiah, 2009), intermediate heat exchangers, optimize pump around flows. Organic Rankine Cycle (ORC) and Kalina Cycle (KC) to recover power (Chew et al., 2014)... 

As shown in Fig. 13-92, methods of providing column reflux include (a) conventional top-tray reflux, (b) pump-back reflux from side-cut strippers, and (c) pump-around reflux. The latter two methods essentially function as intercondenser schemes that reduce the top-tray-refliix requirement. As shown in Fig. 13-93 for the example being considered, the internal-reflux flow rate decreases rapidly from the top tray to the feed-flash zone for case a. The other two cases, particularly case c, result in better balancing of the column-refliix traffic. Because of this and the opportunity provided to recover energy at a moderate- to high-temperature level, pump-around reflirx is the most commonly used technique. However, not indicated in Fig. 13-93 is the fact that in cases h and c the smaller quantity of reflux present in the upper portion of the column increases the tray requirements. Furthermore, the pump-around circuits, which extend over three trays each, are believed to be equivalent for mass-transfer purposes to only one tray each. Bepresentative tray requirements for the three cases are included in Fig. 13-92. In case c heat-transfer rates associated with the two pump-around circuits account for approximately 40 percent of the total heat removed in the overhead condenser and from the two pump-around circuits combined. 

For a fired reboiler, a pump-around system is used with an FRC to maintain constant flow. There will be a low flow alarm plus fuel shutoff. There will also be a high flow alarm plus fuel shutoff, since a tube rupture would reflect itself in a high flow. 

Figure 3-1. Flow diagram of atmospheric and vacuum distillation units (1,3) heat exchangers (2) desalter, (3,4) heater (5) distillation column, (6) overhead condenser, (7-10) pump around streams, (11) vacuum distillation heater (12) vacuum tower.

When chemists talk about an analytical method or when instrument vendors tout their products, they often quote the standard deviation that is achievable with the method or instrument as a measure of quality. For example, the manufacturer of an HPLC pump may declare that the digital flow control for the pump, with flow rates from 0.01 to 9.99 mL per minute, has a RSD less than 0.5%, or a chemist declares that her atomic absorption instrument gives results within 0.5% RSD. The most fundamental point about standard deviation is that the smaller it is, the better, because the smaller it is, the more precise the data (the more tightly bunched the data are around the mean) and, if free of bias, the greater the chance that the data are more accurate. Chemists have come to know through experience that a 0.5% RSD for the flow controller and, under the best of circumstances, a 0.5% RSD for atomic absorption results are favorable RSD values compared to other comparable instruments or methods. 

Flow delivery system will consist of a peristaltic pump providing flow rates around 20-200 pL/min. Models with many rollers (-10, e.g., Minipuls MP-3, Gilson) are preferred as the noise due to pulsation will be reduced. The indicated flow rates apply for common crystals with the diameter of the working electrode around 5 mm. In fact, on the one hand, slower flow will limit consumption of valuable bioreagents on the other hand, faster flow rate will be more appropriate for immunoaffinity studies to avoid influence of slow diffusion on kinetics. In addition, electronically controlled switching and/or multiposition valves or even more complex autoinjectors will enable automatization of performance and provide option for unattended operation. 

If reconnecting the column fails to correct the leak, then other common areas to search for leaks are the detector flow cell, the pump (around the pistons), and the injector valve. The same process should be followed until the source of the leak is identified and corrected. New parts maybe required for example, the pump piston seals may have worn out. Always consult the manufacturer s user manual when attempting to replace any part. If in doubt, contact the manufacturer and ask for installation of the new part. It will be necessary to undertake system performance qualification on the replacement of any worn out or damaged part (see Chapter 8). 

Column Component Flow Column Component Fraction Column Component Ratio Column Component Recovery Column Cut Point Column Draw Rate Column DT [Heater/Cooler) Spei Column Dt Spec Column Duty Column Duty Ratio Column Feed Ratio Column Gap Cut Point Column Liquid Flow Column Physical Properties Spec Column Pump Around Column Reboil Ratio Spec Column Recovery... 

Side columns are used, for instance, in the most important distillation processes worldwide, the fractionation of air (see Fig. 11.2-18) and the distillation of cmde oil (Meyers 1996). The atmospheric tower of oil refineries consists of a main column and four stripping side columns (Fig. 11.2-12). In this tower the crude oil is split into six fractions which are processed further in several subsequent columns. Oil refineries also have some other interesting features. Steam is fed into the bottom of the main column and most of the side columns. This causes a stripping effect and reduces the temperatures in the columns (steam distillation). The overhead fractions of all side columns are fed into the main colunrn thus increasing the vapor flow there. So-called pump arounds effect a partial condensation of the vapor in the main column and, in turn, a reduction of the vapor flow rates in the upper sections. 

El. A system known as a punp-around is shown below. Saturated liquid is withdrawn from stage 2 above the partial reboiler, and the liquid is returned to stage 3 (assume it is still a saturated liquid). Pump-around rate is P = 40.0 kmol/h. The column is separating methanol and water at 101.3 kPa. The feed flow rate is 100.0 kmol/h. The feed is 60.0 mol% methanol and 40.0 mol% water. The feed is saturated liquid. We desire a bottoms product that is 2.5 mol% methanol. The distillate product should be 95.0 mol% methanol. The column has a total condenser and the reflux is a saturated liquid. Assume CMO. Use (L/D) = 2.0 x (L/D)Tnin- Data are given in Table 2-7. Find Xp, the optimum feed stage and total number of equilibrium stages required. 

Figure 3.16 Flow diagram for the distillation of coal tar with bottom pump-around...

For the crude preheat train in the refinery plant, three beneficial modifications are identified. Modifications 1 and 2 add a new shell to each of the feed preheat exchangers serviced by the diesel pump-around (PA). Modification 3 adds surface area to the diesel product run down heat exchanger. Before implementing these changes, it is crucial to make sure that the existing pump can handle the increased diesel PA flow and the increase can be tolerated in product cut points. These modifications can save 47 million Btu/h of fuel in the crude heaters, equating to cost savings of 2.3 million per year. With only a 2.2 million installed cost, this project provides a fast payback. 

In conventional boilers, water is heated by gas burners. It Is then pumped around the central heating system and the hot water storage cylinder. The flow of gas to the burner is controlled by a valve (or valves) which can be operated by a time switch or by a boiler thermostat, hot water cylinder thermostat, or by a 10 thermostat located in one of the rooms. 

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