System pressure, troubleshooting

Shortly after the valve to the sump was opened and the valve to the hopper was closed, the No. 4 reactor began experiencing erratic pressure problems. The system pressure troubles continued for about 15 minutes. As the supervisor and operator were troubleshooting the problem the relief valve on the reactor heat transfer chest opened with a loud report, signaling real troubles. The two employees started to head out of the unit. About 20 seconds later a large section of a 9 ft. (2.7 m) in diameter expansion joint burst. The initial explosion and the resulting thrust shifted the massive reactor. 

Because of its small size and portabiHty, the hot-wire anemometer is ideally suited to measure gas velocities either continuously or on a troubleshooting basis in systems where excess pressure drop cannot be tolerated. Furnaces, smokestacks, electrostatic precipitators, and air ducts are typical areas of appHcation. Its fast response to velocity or temperature fluctuations in the surrounding gas makes it particularly useful in studying the turbulence characteristics and rapidity of mixing in gas streams. The constant current mode of operation has a wide frequency response and relatively lower noise level, provided a sufficiently small wire can be used. Where a more mgged wire is required, the constant temperature mode is employed because of its insensitivity to sensor heat capacity. In Hquids, hot-film sensors are employed instead of wires. The sensor consists of a thin metallic film mounted on the surface of a thermally and electrically insulated probe. 

To ensure the required eonstant pressure, a loeal pressure eontrol loop is provided on eaeh system—turbine lube oil, eompressor lube oil, and eontrol oil. Eaeh oil pressure system should be reeorded in the eontrol room to provide troubleshooting information. The sueeess of the oil system depends upon not only the instrumentation, but upon proper instrument loeation. 

Problems that arise with HPLC experiments are usually associated with abnormally high or low pressures, system leaks, worn injectors parts, air bubbles, or blocked in-line filters. Sometimes these manifest themselves on the chromatogram and sometimes they do not. In the following subsections, we address some of the most common problems encountered, pinpoint possible causes, and suggest methods of solving the problems. You can also refer to the troubleshooting guide in Chapter 12 for possible solutions. 

Hollow fiber modules, or permeators, are precisely machined units containing bundles of hollow fine fibers positioned parallel to and around a perforated center feed-water tube, with only one or two bundles per pressure vessel. They are widely used for brackish and seawater applications. Hollow fiber modules exhibit a low flux rate (permeate flow per unit membrane per unit time) and can foul easily but tend to have high conversion factors (the percentage of feed flow converted to permeate), typically 50 to 55%. This makes them suitable for both small and large RO systems. They are easy to troubleshoot, and bundles are easy to change in the field. 

The first step is to locate the point of the pressure increase. Since most problems are column problems, we can simplify our task by eating the elephant one bite at a time. Remove the column from the system and turn on the pump. If the pressure problem goes away, it was in the column. If not, it s in the system leading up to the column. I ll deal here only with the column pressure problems, the system problems will be dealt with in Chapter 10 on troubleshooting. 

The final component we need to consider is the instrumentation and control system (Figure 14-10). Good instrumentation is vital to ensure that an extrusion line is operating efficiently and to troubleshoot extrusion problems. Because we cannot see inside the extruder, nor would we leam much even if we could, instrumentation serves as a window onto the process. Monitoring an extrusion system has been compared to monitoring a patient in the hospital you always need to measure vital signs, like blood pressure and body temperature. Likewise, an extrusion line that is not properly monitored can... 

The fourth column provides some general discussion to do with the step just described. In addition, troubleshooting information can be provided in this column, which can also be used to describe the anticipated response of the system to the action taken. For example, if the instruction is to do with starting a pump, then the response could be that the discharge pressure should be above a certain value, and that the pump motor should be drawing a specified number of amps. If actoal results do not correspond to these anticipated values, the operator knows that he needs to identify the cause of the discrepancy. 

The purpose of the instrumentation and control system (Fig. 2.14) is to measure and control important processing parameters. Without the data provided by this system, it would be very difficult to maintain a safe and efficient process and to troubleshoot extrusion problems. The data provides a window to the process, since we cannot see inside the extruder (and probably would not find it very useful if we could). Monitoring an extrusion line has been likened to monitoring a patient in a hospital we certainly want to measure the patient s vital signs, such as body temperature and blood pressure. Similarly, we need to monitor extrusion parameters, so the system does not become unstable, leading to a dangerous situation or to the production of costly scrap. 

---