Superheaters and Reheaters.

Superheaters and reheaters are specially designed in-line tube bundles that increase the temperature of saturated steam. In general terms, they are simple single - phase heat exchangers with steam flowing inside the tubes and the flue gas passing outside, generally in crossflow. These critical components are manufactured from steel alloy material because of their high operating temperature. They are typically configured to help control steam outlet temperatures, keep metal temperatures within acceptable limits, and control steam flow pressure loss.

The main difference between superheaters and reheaters is the steam pressure. In a typical drum boiler, the superheater outlet pressure might be 2700 psi (18.62 MPa) while the reheater outlet might be only 580 psi (4.0 MPa). The physical design and location of the surfaces depend upon the desired outlet temperatures, heat absorption, fuel ash characteristics and cleaning equipment. These surfaces can be either horizontal or vertical. The superheater and sometimes reheater are often divided into multiple sections to help control steam temperature and optimize heat recovery.

The heat transfer surface in the furnace may not be sufficient to generate enough saturated steam for the particular end use. If this is the case, an additional bank of heat exchanger tubes called the boiler bank or steam generating bank is added. This is needed on many smaller, low pressure industrial boilers, but is not often needed in high pressure utility boilers. This boiler bank is typically composed of the steam drum on top, a second drum on the bottom, and series of bent connecting tubes. The steam drum internals and tube sizes are arranged so that subcooled water travels down the tubes ( farthest from the furnace) into the lower drum. The water is then distributed to the other tubes where it is partially converted to steam and returned to the steam drum. The lower drum is often called the mud drum because this is where sediments found in the boiler water tend to settle out and collect.

Tube bundles пучок труб

To line располагать в одну линию

Crossflow поперечный поток, поперечное обтекание

Configure формировать, придавать форму

Outlet выход, выпуск, вывод

Pressure loss потеря давления

Bent изогнутый, гнутый, кривой, коленчатый

Internals внутрикорпусные устройства

Subcooled недогретый

Mud грязь, шлам

Acceptable допустимый

Task 10

Skim through the text and underline the sentences or the words that best sum up the main idea of the text (key words). Discuss the main idea of the text in the group using key words or sentences.

Date: 2014-12-29; view: 1533