A condenser is an important device in steam power plant. It is responsible for condensing the steam that exits the turbine. It plays two vital roles.
It generates a substantially low pressure at the turbine’s exhaust that inturn allows for the steam in the primary mover to expand to an exceedingly low pressure. This process facilitates the conversion of the steam’s thermal energy into mechanical energy in the primary mover.
The condensed steam can be utilized as feedwater for the boiler.
Condensers are primarily classified into two types: Jet type and Surface type condensers.
Jet condenser
In the case of a jet condenser mixing of cooling water and exhausted steam takes place together, resulting in the same temperature of both the cooling water and condensate when leaving the condenser. The jet condenser has several advantages, including low initial cost, a small floor area requirement, the requirement of less cooling water, and low maintenance charges.
Apart from the advantages, there are some disadvantages while employing a jet condenser. The condensate is wasted and high power is required for pumping water.
Surface condenser
A surface condenser operates without any direct contact between the cooling water and exhausted steam. Instead.
Its basic construction involves bank of horizontal tubes enclosed in a cast iron shell.
Cooling water flows through the tubes, while exhausted steam passes over the surface of the tubes.
As the steam gives up its heat, it condenses and can be collected as condensate, which can be used as feed water.
Major advantage of surface censers is that it requires less pumping power and creates a better vacuum at the turbine exhaust.
However, there are some disadvantages while employing a surface condenser.
The initial cost of surface condenser is high and it requires a large floor area, and the maintenance charges can also be high.
Given below is a tabulated comparison by ElectricalEngineering.xyz for Jet and Surface condensers.
| Jet condenser | Surface Condenser |
|---|---|
| Also known as Direct Contact condenser OR Mixing type condenser | Non-mixing type condensers |
| Direct contact heat exchanger | Indirect contact heat exchanger |
| Simple design with low manufacturing and maintenance costs | An indirect contact heat exchanger has a high manufacturing and maintenance cost |
| Involves mixing vapor and a condensing medium | No mixing of vapor and condensing medium occurs, they are separated by a wall or surface |
| Mixing can result in impurities in the condensate, which must be purified before recirculation | Condensate is free from impurities and can be recirculated without purification treatment |
| Cooling medium should be pure | Quality of the cooling medium is not important, because there is no mixing |
| Fast condensation, requiring less condensing medium | Condensation process is slow and requires a large amount of condensing medium to condense a unit amount of vapor |
| Less suitable for high-capacity plants | Suitable for high-capacity plants |
| Low vacuum efficiency | High vacuum efficiency |
| Requires a condensate extraction pump, and failure of this pump can cause flooding of the condenser | Does not require a condensate extraction pump |
| Requires small floor space | Large floor space is required |