Seal pans

Liquid level above seal pan in bottom of column. Poor stripping of bottoms product. High pressure drop across section. Board mounted instrument improperly calibrated. Level gauge in field not properly blown down or even checked. Operation problem. 

These contribute to the uniform distribution of liquid as it enters the tray from the downcomer. There are about as many tray designs without weirs as with them. The downcomer without inlet weir tends to maintain uniform liquid distribution itself. The tray design with recessed seal pan ensures against vapor backflow into the downcomer, but this is seldom necessary. It is not recommended for fluids that are dirty or tend to foul surfaces. The inlet weir is objectionable for the same reason. 

The bottom tray of a tower must have its downcomer sealed to prevent upflow of reboiled vapors. The downcomer of this tray is usually equal to or 6 in. longer than the other downcomers to ensure against bottom vapor surges or pulses in pressure breaking the seal. The seal pan is designed to avoid liquid back pressure and minimum restrictions to liquid flow. 

Provide drainage holes in seal pan to allow adequate drainage, flushing and cleaning, but not too large (number) to prevent liquid backup sufficient to maintain a seal on the tray. 

Anti-Jump Baffles Yes / No / Vendor Preference Recessed Seal Pans YeS / No / Vendor Preference Specify Equal Bubbling Areas / Flow Path Lengths per pass Design Load ... 

This unit is usually used as the reboiler for the distillation column and, in this service, operates by the thermosiphon action of the difference in static head in the column and in the vapor-liquid phase leaving the reboiler. When tied into the bottom chamber, the liquid is usually recirculated many times, vaporizing only 10-25% of the reboiler feed per pass however, when used as a draw-off from the bottom tray seal pan, the feed to the reboiler is not recirculated flow. The basic operation is the same, however. 

Any chemical reaction that is accompanied by enthalpy changes can be followed by calorimetric methods [3,24,29], DSC is widely used to study polymerizing systems, especially epoxides [55-57]. Both the rate and the extent of reaction can be monitored using either isothermal or scanning modes of operation [3,24,29]. If volatile products are formed, the reaction must be carried out in sealed pans or under pressure [58] to conserve mass and avoid an uncertain correction for vaporization or to pressure-shift simultaneous vaporization events. 

The sample containers most commonly used are cylindrical pans pressed from pure aluminium foil. Alternative materials are used for very high temperatures or corrosive substances, and hermetically sealed pans to withstand several atmospheres pressure can be used for volatile materials. Some heat flux DSC instruments are available which are capable of operation at high pressures, by means of containment of the DSC cell within a pressure vessel. 

Bottom tray, seal pan, or draw-off pan damaged, s Reboiler partially plugged. 

Table 6.1. Comparison of the high pressure (HP) and sealed pan differential scanning calorimetric techniques (SP-DSC/ HP-DSC) and the colorimetric technique for oil change requirements (Kauffman and Rhine, 1988a)...

The need for positively sealing the downcomer is determined in this phase. This could be achieved by installing an inlet weir, which is a weir installed at the tray inlet to keep the downcomer outlet immersed in liquid. A similar device, which extends below the tray floor, is a seal pan (Fig. 17). Both devices provide positive assurance against vapor rising up the downcomer, but they may also trap solids and dirt and cause blockage. A seal pan must always be used in the downcomer from the bottom tray otherwise there is nothing to prevent vapor from rising up the bottom downcomer. 

Different sample pans are used in DTA and DSC measurements for samples of various shapes and physical states. The sample pans are of two types open pans for solid samples and sealed pans for liquids or volatile samples. The materials used for making sample pans are mostly aluminum, silver, gold, stainless steel, and carbon. When aluminum and silver sample pans are used for samples containing water, the sample pans should be pretreated with water in a small pressure vessel to avoid reactions between the pans and water during subsequent heating. 

Waxy maize Speciality Oxidised waxy maize Sealing panned centres... 

The intensity of the 120°-130°C endotherm increases as stratum corneum moisture content increases there is a corresponding decrease in the high temperature meltings at 194° and 210°C (Figure 20). Highly hydrated corneum displays the 120°-130°C endotherm while below 15 to 20% water content, the transition is quite small. These DSC measurements were performed in hermetically sealed pans to avoid the endothermic loss of water. The transition in the presence of water is a cooperative one in that water facilitates the magnitude of the observed transition. The heat change associated with the 120°-130°C transition... 

Great efforts have been made in recent years in order to validate the different instruments not only in comparing principle and results but also in determining the critical parameters such as heating and cooling rates, particle size, weight, resolution, atmosphere, and type of pans (crimped pan, sealed pan, open pan, etc.). 

Fig. 17 Influence of the water content on the glass transition temperature of HPMC 4000 measured by DSC in sealed pans.

The segmental, or chord downcomer, shown in Figure 11.26a is the simplest and cheapest form of construction and is satisfactory for most purposes. The downcomer channel is formed by a flat plate, called an apron, which extends down from the outlet weir. The apron is usually vertical but may be sloped (see Figure 11.26b) to increase the plate area available for perforation. If a more positive seal is required at the downcomer at the outlet, an inlet weir can be fitted (see Figure 11.26c) or a recessed seal pan used (see Figure 11.26d). Circular downcomers (pipes) are sometimes used for small liquid flow rates. 

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