Steam Condensers

Introduction:

• Condenser is a device in which steam coming out from the turbine condenses into liquid state at constant pressure.

• In the condenser, steam rejects latent heat and gets converted into water. (condensate)

• Cooling is obtained by circulating cooling water

Functions of Condenser:

• It lowers back pressure at turbine exhaust. Hence the steam expands through high pressure ratio. (increased work done, more efficiency)

• Enables recovery and reuse of pure feed water to boiler. Hence saves cost of water treatment and cost of fresh water

• Enables removal of air and non-condensable gases from steam. Hence improved heat transfer.

Elements of Condensing Plant:

Types of Condensers:

• Jet condenser: Water and steam come in direct contact. Water sprayed on steam

• Surface condenser:Water and steam do not come in direct contact. Water can be reused. Costly compared to jet condensers.

Types of Jet Condensers:

• Low-Level Jet Condenser1.Counter-flow type2.Parallel-flow type

• High-level jet condenser• Ejector jet condenser

Low-Level Counter-Flow Jet Condenser

Low Level Parallel-Flow Jet Condenser:

High Level Jet Condenser:

Advantages and Disadvantages of High Level Jet Condenser:

• Advantages:1. Less floor area2. Requires only Circulating Pump

• Disadvantages:1. Due to high level, long pipes needed2. Not readily accessible for maintenance

Ejector condenser:

Surface Condensers:

• No direct contact of water and steam.• Hence, condensate can be reused.

Types of Surface Condensers:

• Shell and tube type– Down flow condensers– Central flow condensers– Inverted flow condensers

• Evaporative Condensers

Arrangement of Shell and Tube condensers:

Down-flow Condensers:

Down-flow Condensers:

• Exhaust steam enters the top and flows downward over the water tube

• Cold water flows in lower tubes first and then in upper side in reverse direction

• Extraction pump is connected at the bottom to draw condensate out of condenser.

• Air extraction pump is located at the bottom to separate air and non-condensable gases.

Central Flow Condensers:

Central Flow Condensers:

• Air extraction pump is located in the centre of condenser tubes.

• Steam flows radially inwards.• Condensate extraction pump is located at

bottom to collect the condensate.• More heat transfer rate compared to down

flow condensers.

Inverted flow Surface Condensers:

• Steam enters the bottom of the shell and moves upward

• Air extraction pump is located at the top• Steam condenses to water and condensate

flows down • Condensate extraction pump is located at the

bottom

Evaporative Condensers:

Advantages of surface condensers:

• High vacuum efficiency, hence suitable for large power plants.

• Pure condensate• Saving in cost of water treatment and cost of

fresh water• No direct contact of water and steam, hence low

quality cooling water can be used• Low power air extraction pump can be used• Controlled condensation

Disadvantages of Surface Condensers:

• Indirect cooling-hence large amount of cooling water required

• High cost (Installation and maintenance)• Large floor area