A compact condenser and reboiler solution is a natural fit for a Syzran oil refinery.
When a new stripper tower was required for the gas sweetening process at the Syzran oil refinery in Russia, condensers and reboilers that took up little space were a natural fit. The refinery, run by the Rosneft, has a capacity of 150,000 barrels of crude oil per day. When the plant was extended, Rosneft installed Alfa Laval Compabloc reboiler and condenser units instead of traditional shelf-and-tube units.
The thermosiphon reboilers were installed at the base of one of the stripper columns, and a reflux condenser was mounted directly on the top of the column. The stripper column is used in the gas sweetening process, in which hydrogen sulfide (H2S) is absorbed in 15 percent MEA solution and then removed at the top of the stripper. The reboilers operate at 257°F (125°C) and 2.3 bara, and the condenser at 239°F (115°C) and 2.1 bara. The H2S is subcooled down to 104°F (40°C) in the condenser.
The Compabloc condenser and reboiler consist of a welded stack of corrugated plates made of stainless steel. The corrugated pattern in the unit creates a high level of turbulence that results in efficient heat transfer. The heat transfer coefficient of Alfa Laval’s reboiler is normally two to four times higher than that in a shell-and-tube unit, according to Patrik Arvidsson, a business manager with Alfa Laval in Sweden. Consequently, Arvidsson adds, the required heat transfer area is two to four times less. In addition, the Compabloc design is compact, which makes it possible to reduce the total space occupied by the reboiler by a factor of five or more. Inspection and cleaning are seldom required, but these tasks are simplified due to the minimal space requirements. Downtime thus is reduced compared with shell-and-tube units.
Condenser. The reflux condenser installed at the Rosneft plant is a good example of the versatility of a Compabloc solution, says Arvidsson. The reflux condenser is mounted directly on the stripper column, which saves costs in connection with installing foundations, piping and pumps. The alternative is a shell-and-tube unit mounted at ground level with piping for the vapor going down, and a pump and piping for the reflux going back up to the top of column.
Vapor enters from the bottom and condenses on the cold plates, with noncondensable gases being removed at the top, and the condensate flowing back to the column. The cooling water is forced through several passes to minimize fouling.
Reboiler. Compabloc also is a compact reboiler solution, says Arvidsson. The reboilers installed at the Rosneft plant are an example of the thermosiphon concept. While one unit would have been adequate, the refinery chose to install two parallel units to prevent any unnecessary shutdowns during cleaning procedures.
Circulation of the media streams is carried out by means of the thermosiphon system: The process medium enters at the bottom and is distributed through the channels. As the liquid passes through, it is brought to the boiling point, and a mixture of vapor and liquid exits from a larger connection at the top. The service medium - in this case, steam - meets the process medium in a crossflow arrangement.
The decision to install a compact solution instead of shell-and-tube units enabled Rosneft to save critical space. The reboilers have been in operation since January 2002, and the general consensus of opinion at the refinery is that the units work extremely well.