Flow vacuum distillation unit

Figure 3-1. Flow diagram of atmospheric and vacuum distillation units (1,3) heat exchangers (2) desalter, (3,4) heater (5) distillation column, (6) overhead condenser, (7-10) pump around streams, (11) vacuum distillation heater (12) vacuum tower.

In order to overcome these problems, the flow schemes as shown in Figures 1 and 2 were developed. These incorporate the use of Kerr-McGee Corporation s Critical Solvent Deashing and Fractionation Process (CSD) for recovery of the SRC. The Kerr-McGee Process adds extra flexibility since this process can recover heavy solvent for recycle, which is not recoverable by vacuum distillation. EPRI contracted with Conoco Coal Development Company (CCDC) and Kerr-McGee Corporation in 1977-1978 to test these process concepts on continuous bench-scale units. A complementary effort would be made at the Wilsonville Pilot Plant under joint sponsorship by EPRI, DOE, and Kerr-McGee Corporation. This paper presents some of the initial findings. 

Slurry drawn from the crystallizing columns is filtered in rotary vacuum filters where the NaHC03 crystals are water-washed. The filtered liquor then flows to the distillation unit for recovery of ammonia. The crude bicarbonate filter cake contains 3 percent... 

The connection between pump and distillation unit also requires consideration. As large gas volumes are present under vacuum, pipe connections have to be short and wide. If the pipe diameter is too small, a pressure loss results and the pump s suction efficiency decreases. The pressure loss due to the flow conductance is the reciprocal sum of all connecting parts from the pump to the distillation unit. With short pipes at least the diameter of the pump s intake port has to be selected longer pipes require correspondingly larger pipe diameters. Pump manufacturers (see 2.1.3.5) usually provide the necessary information. 

Figure 1.6 indicates where a lubricant base oil plant fits into the process flow scheme of a typical refinery - if ever there is such a thing. Although the scheme is simplified, the inter-relationship between the base oil plant and other process units and product streams is evident. In a sense, the base oil plant and the fuel-upgrading plant, such as the catalytic cracker, compete for feedstock from vacuum distillation. These interactions are very important to the logistics and production economics of producing base oils. 

Regardless, I tried culling ihe steam back to 5,000 Ib/hr to see how much the vacuum distillate rate would increase. Surprisingly, the flow of vacuum distillate remained constant. The only notable result on the crude unit was a drop in flow of wet gas from the reflux drum. The 3,000 Ib/hr cut in the bottom s stripping steam had unloaded the overhead condenser. This caused the reflux drum temperature to drop and hence reduced the flow of wet gas to the off-gas compressor. 

Cavitation occurs wherever irregular water flow takes place, particularly if high pressures and vacuum are involved in the flow systems. Cavitation is a serious problem in desalination plants. In multi-stage flash distillation units, cavitation occurs in ... 

Figure 1-11 General flow diagram for a distillation section (atmospheric and vacuum), including a primary flash unit, in a refinery. 

High vacuum is not and should not be regarded as a unit operation in itself. Rather, it should be viewed as a very low pressure range in which conventional unit operations such as heat transfer, fluid flow, distillation, and extraction are put to use in the light of physical and chemical equilibria, reaction rates, and transfer rates characteristic of this pressure range. 

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