Distribution trays

The entrance of a liqmd-flashing vapor mixture into the distillation column feed location requires a specially designed distribution tray to separate the vapors from the liquid, w hich must drop onto the packing bed for that section in a uniform pattern and rate. 

Vapor Channeling All the correlations in this section assume an evenly distributed tray vapor. When the vapor preferentially channels through a tray region, premature entrainment flood and excessive entrainment take place due to a high vapor velocity in that region. At the same time, other regions become vapor-deficient and tend to weep, which lowers tray efficiency. 

Packing liquid distribution trays and limiting packing height... 

An atmospheric multiple-tray aerator consists of distribution trays, coke tray, and fine gravel tray. The removal of carbon dioxide by multiple-tray aerator (gravity ventilation system) can be estimated by an empirical equation, developed by Scott (19) ... 

Tokyo Gas Company, 246, 381 Topsoe Dense Pattern Flexible Distribution Tray, 241... 

Attention turned to liquid and gas distribution between the catalyst beds. The precise arrangement of the distribution trays is known to have a marked effect on liquid distribution and hence catalyst effectiveness. A close examination of the distributor trays suggested that leakage between sections of the trays may have been significant, leading to uneven distribution of liquid onto the catalyst below. 

Figure 1,14 . Expanded view of a multi-bed HDS reactor showing the gas distribution tray at the top and the catalyst support tray in the middle these reactors can range in diameter from 13-5 m. Courtesy of UOP LlC.

Thermowell Support -3 Layer of 1/8 Inerts >3 Layer of 1/4 Inerts CaU st Support Grid and Beams Upper Quench and Splash Trays Lower Distribution Tray... 

Boxing up—fitting internal distribution trays, tower packings, catalysts, thermowells, and instrument cables. 

Tower internal distribution trays not levelled properly—can result in poor absorption or distillation performance. 

If the only consideration is to reduce sulfur, the preferred solution would probably be to add reactor volume as in Case 3, but this assumes that the existing gas recycle system can manage the increased pressure drop and that the diesel yield loss due to cracking is acceptable. It may be necessary to revamp the recycle gas system and the overhead fiactionator. In many cases, the performance of the existing reactor can also be improved by installing state-of-the-art liquid distribution trays and quench mixers. " ... 

The improvement in vapor-liquid contact can enhance the performance of distillate hydrotreaters. As an example, in testing of an improved vapor-liquid distributor in commercial use, Haldor-Topsoe and Phillips Petroleum found that the new Topsoe Dense Pattern Flexible Distribution Tray (installed in 1996 to replace a chimney type distributor installed in 1995 in a refiney) allowed a 30% higher sulfur feed to be processed at 25°C lower temperatures, while reducing the sulfur content of the product from 500 to 350 ppmw . Albemarle estimates that an improved vapor-liquid distributor can reduce the temperature necessary to meet a 50 ppmw sulfur level by 10 °C, which in turn would increase catalyst life and allow an increase in cycle length from 10 to 18 months. Based on the above data from Haldor-Topsoe, if temperature were maintained, the final sulfur level could be reduced by 50%. Maintaining temperature should have allowed an additional reduction in sulfur of more than two-thirds. Thus, ensuring adequate vapor-liquid contact can have a major impact on final sulfur levels. 

Inlet Impingement Device The purpose of the inlet impingement device is to diffuse the velocity profile of the fluids entering the reactor inlet nozzle and create an even pattern of liquid dispersion across the top liquid distribution tray. 

Top liquid distribution tray The top liquid distribution tray evenly distributes the liquid charge across the surface of the top catalyst bed. 

Liquid re-distribution tray The re-distribution tray evenly distributes the quenched liquid and vapor exiting the mixing chamber across the surface of the subsequent catalyst bed. 

When Haldor Topsoe began to investigate the design of a high performance distribution tray, several parameters were recognized as critical to achieve the desired performance efficiency. These are as follows ... 

Due to changes in the plant operation subsequent to the initial installation, the performance of the impingement-type quench mixing chambers deteriorated and the distribution trays could no longer maintain an even flow distribution across the catalyst beds. The degradation in performance of the reactor internals resulted in wide radial temperature variations ranging from 7- 10°C at the catalyst bed inlets to 15 - 40°C at the catalyst bed outlets. The flow/temperature mal-distribution is documented by temperature profiles plotted from thermocouple measurements (Figure 5). 

To improve unit performance, the existing reactor internals were replaced by high performance vortex t) e mixing chambers to optimize liquid-liquid mixing and VLT distribution trays to increase the number of drip points and minimize the dead flow zones adjacent to the reactor wall (Figure 6). The VLT distribution trays also offered low sensitivity to tray levelness and improved stability over a wide operating range. 

High performance reactor mixing chamber and distribution tray designs have been developed by some licensors which can often be incorporated into existing reactors to improve their performance. 

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