Vaporizers, operating problems

Many of the above factors that affect column operation are due to vapor flow conditions being either excessive or too low. Vapor flow velocity is dependent on column diameter. Weeping determines the minimum vapor flow required while flooding determines the maximum vapor flow allowed, hence column capacity. Thus, if the column diameter is not sized properly, the column will not perform well. Not only will operational problems occur, the desired separation duties may not be achieved. 

The importance of the downcomer seal is to prevent vapor from the tray from bubbling into the downcomer (see Figure 8-63), whether the trays are bubble cap, valve or sieve types. If a seal weir is not included in the tray design, then operation problems to avoid flooding, weeping and unstable performance, including pressure drop, are increased, particularly during the start-up phase. 

As mentioned earlier, the Petlyuk column (Figure Ic) poses potential operational problems because of the two directions of the interconnecting vapor... 

Operational problems with the freshwater vapor quenching system may cause high particulate emissions. 

CNG fuel systems can thus be subjected to compressor oil and condensed water vapor that would not occur otherwise if the gas had not been compressed. The compressor oil is probably more of an operating problem than a materials compatibility problem, though new CNG vehicle fuel systems that use multi-point fuel injectors may encounter some problems. 

An increase in the concentration of steam in the feed can alleviate carbon-induced deactivation of Ni. Steam enhances the rate of carbon oxidation, thus leading to carbon removal in the form of CO or CO. However, the increase in the S/C (steam-to-carbon) ratio introduces a number of operational problems. For example, the additional steam increases the flow rate through the reformer, thereby escalating the size and capital cost of the equipment [18, 36], In addition, substation energy is required to vaporize water and increase its temperature to the operating conditions of the reactor. In SOFCs, the addition of steam lowers the energy density of the fuel stream. Also, the need for additional steam lowers the flexibility to manipulate the CO/H ratio in the effluent stream via the water gas-shift reaction. 

Two-phase flow often presents design and operational problems not associated with liquid or gas flow. For example, several different flow patterns may exist along the pipeline. Frictional pressure losses are more difficult to estimate, and in the case of a cross-country pipeline, a terrain profile is necessary to predict pressure drops due to elevation changes. The downstream end of a pipeline often requires a separator to separate the liquid and vapor phases, and a slug catcher may be required to remove liquid slugs. 

The postscript to this story is that at least one of the large new glycol distillation columns built in the last two years has (supposedly obsolete) bubble caps. The plant manager s reluctance to experiment with new designs is understandable. There are a large number of potentially unpleasant operating problems that can make life difficult for him, and, at one time or another, he has probably seen them all. Packed column vapor-liquid contactors can ... 

Pluggng of overhead system top temperature not within the operating window for sour water strippers temperature < 82 °C at which ammonium polysulfides form but temperatures too high give excessive water in overhead vapor causing problems for downstream operation/overhead lines not insulated/insuflicient steam tracing on overhead vapor lines. 

It should be noted that the utihzation of a reflux condenser for heat removal in the VCM suspension polymerization introduces some operational problems. For example, noncondensable gases maybe concentrated in the condenser, which can reduce its heat removal capacity. The level of non-condensable gases in the reactor vapor phase will depend on the quality of the monomer, how well the reactor has been evacuated prior to polymerization and whether or not the polymerization process generates inert gases [20]. For example, the use of azo initiators will result in the formation of nitrogen as a byproduct of the initiator... 

Hexene reactivity Catalyst reactivity with 1-hexene is important in order to reduce the amount of 1-hexene needed in the reactor. Ziegler-type catalysts based on Ti/Mg compounds exhibit relatively poor reactivity with 1-hexene compared with many other catalysts. Such catalysts can require a 1-hexene/ethylene vapor phase ratio of about 0.12 and higher in a commercial reactor, thus limiting the ethylene partial pressure in the reactor and leading to lower production rates and/or lower catalyst productivity. However, with the super-condensing mode of operation, comonomer fed concerns are rare. Most other catalysts used in a fluid-bed reactor exhibit higher 1 -hexene reactivity and, therefore, require lower 1 -hexene feed rates and fewer operational problems... 

Process engineer One who uses the principles of heat balance, hydraulics, vapor-liquid equilibrium, and chemistry to solve plant operating problems and optimize operating variables. Your authors are process engineers. 

The two principal problems of this process are oxidation of sulfur dioxide to form ammonium sulfate and loss of ammonia by vaporization. The oxidation problem can be alleviated by acidifying a portion of the circulating absorbent to release sulfur dioxide and produce anunonium sulfate solution or by carefully controlling the ammonium sulfate concentration in the circulating stream so that the required amount can be removed by a crystallization step. At the Trail plant, the first operation was used because ammonia acidification units were available elsewhere in the plant. Control of the ammonia-vapor-loss problem requires maintenance of minimum temperatures in the absorbers and careful adjustment of solution concentrations. 

Another Claus plant operating problem is condensation of sulfur on the catalyst resulting in rapid deactivation. This can be avoided by maintaining the temperature in the catalytic converters above the sulfur dew point of the gas mixture. Should sulfur condense on the catalyst, raising the gas temperature 50°F is usually sufficient to vaporize the condensed sulfur and reestablish catalyst activity (Norman, 1976). 

---