Plant vacuum distillation units

Figure 6.5 Modern refinery vacuum distillation unit. One of the product streams is the feed to the plant prodticiny lubricating oils... 

As shown in Figure 1, hydrocracking often is an in-between process. The required hydrogen comes from catalytic reformers, steam/methane reformers or both. Liquid feeds can come from atmospheric and/or vacuum distillation units delayed cokers fluid cokers visbreakers or FCC units. Middle distillates from a hydrocracker usually meet or exceed finished product specifications, but the heavy naphtha from a hydrocracker usually is sent to a catalytic reformer for octane improvement. The fractionator bottoms can be recycled or sent to an FCC unit, an olefins plant, or a lube plant. 

British Columbia, and three at the U.S. Army Ordinance Works operated by the DuPont Company at Morgantown, West Virginia Cluldersburg, Alabama and Dana, Indiana. The plant at Trail used chemical exchange between hydrogen gas and steam for the initial isotope separation followed by electrolysis for final concentration. The three plants in the United States used vacuum distillation of water for the initial separation followed by electrolysis. Details of these plants and their operations may be found in the Hterature (10). 

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. 

On July 24,1994, an explosion followed by a number of fires occurred at 13 23 at the Texaco refinery in Milford Haven, Wales, England. Prior to this explosion, around 9 a.m., a severe coastal electrical storm caused plant disturbances that affected the vacuum distillation, alkylation, butamer, and FCC units. The explosion occurred due to a combination of failures in management, equipment, and control systems. Given its calculated TNT equivalent of at least 4 tons, significant portions of the refinery were damaged. That no fatalities occurred is attributed partially to the accident occurring on a Sunday, as well as the fortuitous location of those who were near the explosion. 

In 1966, a plant with a capacity of 380 Mg D20/yr was commissioned at Port Hawkesbury, Nova Scotia, and production started in 1970. The plant at Glace Bay, Nova Scotia, built in 1963, faced numerous problems caused by seawater feed. The plant was rehabilitated in 1976. The Bruce HWP (BHW-A) at the Bruce site on Lake Huron was built in 1971. Two identical enriching units in parallel were used to double the plant capacity. The final enrichment was achieved by vacuum distillation. Three additional identical plants (BHWP-B, BHWP-C, and BHWP-D) were constructed at Bruce, Ontario, and at Le Prade in Quebec. BHWP-B was commissioned in 1979. Owing to lack of demand, the remaining plants were cancelled. ... 

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. 

An existing lube hydrocracker can be operated at higher severity to make this special product, but the sharp reduction in yield may not be attractive for the base oil plant economics. However, an alternative source of hydrocracked base oil is available from some of the many existing fuel crackers. These hydrocrackers are important refinery conversion units and are used to make a range of fuel products from vacuum distillate feedstocks. Some plants do not fully convert the feed in one pass to low-boiling products and the limited amount of residue which remains, 5-10%, can be recycled within the plant, used as a fuel oil blending component or upgraded to make the special base oils. 

The extraction plant was quite complex since it is essential to the economics of the process to recover the quaternary ammonium salt as well as to isolate pure adiponitrile and unreacted acrylonitrile. The sidestream from the catholyte reservoir was cooled and the adiponitrile and unreacted acrylonitrile extracted with further acrylonitrile in a sieve tray column. The organic phase from this unit was counter-currently extracted with water to recover the quaternary ammonium salt and the acrylonitrile was then removed by distillation. The final stage is the vacuum distillation of the adiponitrile. The total process is shown in Fig. 6.5. 

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 ... 

Shantou Ocean Enterprise Group (SOE Shantou), China s biggest producer of polystyrene, plans to build a US 3.7 billion refining and integrated petrochemicals complex at Shantou. The project will consist of a 6.5 million tpa vacuum crude distillation unit and an olefins plant with capacity for 600 000 tpa of ethylene, 400 000 tpa of propylene and 200 000 tpa of butadiene, as well as aromatics units. Completion of the refinery is expected by 2007, and construction of the petrochemical units will take place between 2008 and 2012. SOE also recently started up a 100 000 tpa polystyrene plant at Quanzhou. 

The simplest unit employing vacuum fractionation is that designed by Canadian Badger for Dominion Tar and Chemical Company (now Rttgers VFT Inc.) at Hamilton, Ontario (13). In this plant, the tar is dehydrated in the usual manner by heat exchange and injection into a dehydrator. The dry tar is then heated under pressure in an oil-fired hehcal-tube heater and injected directly into the vacuum fractionating column from which a benzole fraction, overhead fraction, various oil fractions as side streams, and a pitch base product are taken. Some alterations were made to the plant in 1991, which allows some pitch properties to be controlled because pitch is the only product the distillate oils are used as fuel. 

The Fina/Badger distillation section consists of three distillation columns. All the columns are designed to operate under vacuum to minimize temperature and polymer formation. The first column in the sequence splits the benzene and toluene byproducts from the unconverted EB and styrene product. The benzene and toluene mixture is typically sent to an integrated EB plant where it is further fractionated. In this case, the benzene by-product is ultimately consumed in the EB unit and the toluene becomes a by-product stream from the EB plant. 

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