Other Typical Operating Problems

Previous chapters described poor column performance caused by troublesome column internals and their installation. Earlier sections in this chapter described several other sources of operation difficulties. A number of the simpler sources of problems remained unmentioned so far. Although these sources appear obvious, they must not be overlooked when diagnosing column problems. Some of these sources are 

Column upsets and operation difficulties are often initiated in an upstream unit. For instance, poor column performance may be due to an upstream column experiencing control problems, a malfunctioning pH regulation or additive injection system upstream, or a reactor performing in a different manner than design. 

Several incidents of column problems initiated in an upstream unit have been reported. In one incident (98), solids suddenly appeared in the feed and plugged a column when the feed tank was emptied. This occurred because settled solids from the bottom of the tank were stirred up and entered the feed pipe. In another incident (391), oil from an overflowing inlet separator entered an absorber system it took two days to clean this oil out. 

Poor performance can be caused by leaks (e.g., block valves on connecting pipes, vent valves) into or out of the system. The effects are similar to those described in Sec. 13.14. In one case (2066), a column separating propane from butadiene experienced excessive propane in the bottom. The cause was a seal failure on the reboiler pump the pump used propane as seal gas. 

Poor performance is often suspected due to misleading laboratory analysis, even when the column performs well. Some classic distillation (2066, 268) and nondistillation (131) experiences illustrating this have reported. The author recalls several such experiences. Malfunctioning instruments can lead to similar suspicions. A thorough check of the analjd ical procedure and analytical calculations, and complication of mass, component, and energy balances can determine whether performance is really poor. This is discussed further in Sec. 14.3. 

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Catalyst recovery is a major operational problem because rhodium is a cosdy noble metal and every trace must be recovered for an economic process. Several methods have been patented (44—46). The catalyst is often reactivated by heating in the presence of an alcohol. In another technique, water is added to the homogeneous catalyst solution so that the rhodium compounds precipitate. Another way to separate rhodium involves a two-phase Hquid such as the immiscible mixture of octane or cyclohexane and aliphatic alcohols having 4—8 carbon atoms. In a typical instance, the carbonylation reactor is operated so the desired products and other low boiling materials are flash-distilled. The reacting mixture itself may be boiled, or a sidestream can be distilled, returning the heavy ends to the reactor. In either case, the heavier materials tend to accumulate. A part of these materials is separated, then concentrated to leave only the heaviest residues, and treated with the immiscible Hquid pair. The rhodium precipitates and is taken up in anhydride for recycling. 

Measurement Selection The identification of which measurements to make is an often overlooked aspect of plant-performance analysis. The end use of the data interpretation must be understood (i.e., the purpose for which the data, the parameters, or the resultant model will be used). For example, building a mathematical model of the process to explore other regions of operation is an end use. Another is to use the data to troubleshoot an operating problem. The level of data accuracy, the amount of data, and the sophistication of the interpretation depends upon the accuracy with which the result of the analysis needs to oe known. Daily measurements to a great extent and special plant measurements to a lesser extent are rarelv planned with the end use in mind. The result is typically too little data of too low accuracy or an inordinate amount with the resultant misuse in resources. 

Problems related to sample introduction, high voltage isolation, or other typical of other gradient methods are avoided. Samples can be injected in both electro-kinetic and hydrodynamic mode without affecting other aspects of the instrument operation or causing sample waste. 

Note that Eq. 6.2.1 has three variables the operating time t, the reaction extent Z, and the reaction rate r. The design equation is applied to determine any one of these variables when the other two are known. A typical design problem involves the determination of the operating time necessary to obtain a specified extent for a given reaction rate. The second application involves the determination of the extent obtained in a specified operating time t for a given reaction rate. The third application involves the determination of the reaction rate when the extent is provided as a function of time. Below, we will consider each of these applications. 

Operational Problems of the Pilot Plant. Pilot plant operation began in late August 1971 and initially investigated treatment of a 12% sulfur dioxide gas stream. A number of minor start-up problems were resolved, and a relatively stable, around-the-clock operation was achieved by mid-September. Operation in this mode continued, with some interruptions, until late February 1972. During this period 91 days of operation were logged. Typically, sulfur recoveries averaged 88-92% as compared with a theoretical recovery of approximately 93%. Eleven days of downtime were attributed to curtailed industrial use of natural gas. Other than this, most of the downtime was caused by two problems. 

Water can cause severe operational problems in services which are not meant to handle it. One refiner (296) stated that 99 percent of his fractionator upsets are due to water other refiners (296) agreed with this evaluation. Most problems occur when the column separates water-insoluble materials such as hydrocarbons. The main adverse effects of water in such services are pressure surges, flooding, cycling, corrosion, hydrates, and off-spec products. Typical sources of water in this t5q>e of services are... 

The assessment of trends is one aspect of procedure following that is particularly dependent on operators expectations and evaluations, as time and other boundary conditions are not typically specified. Problems might arise when the operators have to decide whether a plant behavior is the result of known actions (manual or automatic) or of a plant fault. 

These BAHX are constructed with aluminum alloys, these alloys are chosen based on the weld-ability, braze-abiUty and other typical characteristics of usage. Different types of alloys are used for the components ( Fins, Headers, Parting Sheets, Nozzles, Supports, etc.) in the BAHX. All of them differ Ifom the maximum applicable design temperatures. Typically the core of the exchanger, which consists of the fins, parting plates, center bars, side bars etc. are made of an Aluminum alloy ( 3003 ) which has a temperature range of ( -269 C to +204 C ), whereas the header and nozzles are made of 5083 A1 Alloy which can withstand colder temperatures but the operability is limited to +65 C. Because of the pressure drop and the maldistribution problems, nozzle and... 

Troubleshooting a reactor system requires the student to become familiar with the typical operation of the unit. As equipment and instrumentation fails, the student sees the cascading effect a single problem can have on the unit. A single problem can create a series of other problems, so students must learn to identify the primary problem that started the system failure(s). 

The process to solve other motion generation problems is described, to make clear a procedure to apply proposed methods to other problems, and to prove the effectiveness of the methods. The curling around an object was selected as typical example. This is because deformable machines should be good at manipulating an object without damaging by its nature. The problem is only how we realize it. The two-dimensional system and beam-shaped gel with fixing point placed below the array of electrodes were selected. Since the operators are already arranged, we start from the second step. 

The acid gas produced contains more than 45 voI% hydrogen sulfide with the balance being carbon dioxide and a small amount of other impurities such as 0.1 vol% hydrogen cyaiude,. 01 vol% ammonia, and 1.1 vol% aromatics. Consequently, the acid gas is a suitable feed for a typical Claus unit. Operating problems such as plugging and corrosion associated with larger concentrations of these impurities are avoided. As an alternative, the acid gas is a suitable feed for a sulfuric acid plant... 

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