Superheated vs saturated Steam - chemical plants
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The document discusses the differences between superheated and saturated steam, emphasizing their enthalpy values and implications for boiler performance and steam systems. Superheated steam offers advantages such as reduced condensation in pipelines and the ability to operate at higher velocities, but saturated steam is cheaper for heat exchangers due to better heat transfer coefficients. Desuperheating, the process of converting superheated steam back to its saturated state, is also explained, along with its types, which include indirect and direct contact methods.
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Superheated vs saturated Steam - chemical plants
- 1. Superheated vs Saturated Eng Abdelrahman Kamal
- 2. Superheated vs Saturated Superheated steam at 10 bar a and 300°C: ➢ Enthalpy of water = 763 kJ/kg ➢ Enthalpy of evaporation = 2 015 kJ/kg ➢ Enthalpy of superheat = 274 kJ/kg
- 4. Saturated Steam 1. It places a heavy demand on the boiler because a large amount of water must be evaporated per unit volume of steam 2. It contains small droplets of water that must be periodically drained from the cylinders 3. It inevitably condenses in the steam pipes and cylinders outside the boiler, causing a loss of steam volume as it does so Disadvantage Advantage
- 5. Advantage of Superheated steam ➢ At continuously running plants, superheated steam means there is no condensation in the pipework, therefore, there is only a requirement for steam trapping during start-up ➢ It can be used at higher pipeline velocities (up to 100 m/s). This means that smaller distribution pipelines is applied and pressure drop is not excessive . ➢ Wet steam within a turbine would result in water droplets and erosion of the turbine blades, as well as increased friction. SUPERHEATED
- 6. The presence of high heat transfer coefficients associated with saturated steam leads to smaller and cheaper heat exchangers than those which utilize superheated steam. So, Superheated steam is not properly applicable but also saturated steam may cause severe problems due to condensation and droplet formation n piping network and compressors. Superheated steam has a lower density, so lowering the temperature does not revert it back to its original liquid state. Dropping the temperature of saturated steam, however, will revert it back to its old form of water droplets. So, Saturated steam can’t be applicable to pumped in plant piping network due to heat loss and condensation. Then, an operation is applied to the process to treat both problems. It’s Desuperheating. Let’s Recognise Desuperheating
- 7. Desuperheating ➢ Desuperheating is the process by which superheated steam is restored to its saturated state, or the superheat temperature is reduced. ➢ Most desuperheaters used to restore the saturated state produce discharge temperatures approaching saturation (typically to within 3°C of the saturation temperature as a minimum). ➢ Designs for discharge temperatures in excess of 3°C above saturation are also possible and often used.
- 8. Types of Desuperheaters Indirect contact type – The medium used to cool the superheated steam does not come into direct contact with it. A cooler liquid or gas may be employed as the cooling medium, for example, the surrounding air. Examples of this type of desuperheater are shell and tube heat exchangers. Direct contact type – The medium used to cool the superheated steam comes into direct contact with it. In most cases, the cooling medium is the same fluid as the vapour to be desuperheated, but in the liquid state. For example, in the case of steam desuperheaters, water is used.