What Is Steam Condenser? – Parts, Working, And Types

What is Steam Condenser?

A surface condenser, also known as a steam condenser, is a water-cooled shell-and-tube heat exchanger designed to condense exhaust steam from steam turbines, primarily in thermal power plants. In this process, steam transitions from its gaseous form to a liquid state at pressures below atmospheric levels.

Functionally, a steam condenser operates as a closed vessel heat exchanger that converts low-pressure exhaust steam from the turbine back into water. This conversion is facilitated by circulating cooling water, typically sourced from a cooling tower, which absorbs the latent heat of the steam.

To improve overall efficiency, the pressure inside the steam condenser is maintained below atmospheric pressure. This reduced pressure helps decrease the backpressure at the turbine’s exhaust, enhancing the turbine’s performance.

In situations where water for cooling is limited, air-cooled condensers are sometimes employed. However, air-cooled systems tend to be more costly and are less effective at achieving the low exhaust pressures and temperatures that water-cooled surface condensers provide.

Beyond power generation, surface condensers find use in various other industrial applications that require steam condensation.

Why it is required?

In thermal power plants, the surface condenser plays a crucial role by condensing the exhaust steam from the steam turbine. This process not only enhances the overall efficiency of the system but also transforms the turbine’s exhaust steam into pure water known as steam condensate which can then be recycled as boiler feed water in the steam generator or boiler.

To understand this better, it helps to consider the steam turbine itself. The turbine’s main function is to convert the thermal energy contained in steam into mechanical power. Essentially, the difference in the heat content of steam per unit mass between the turbine’s inlet and outlet reflects the amount of heat energy converted into mechanical work.

Thus, a turbine’s efficiency improves as more heat per unit of steam is transformed into mechanical power.

When the exhaust steam is condensed at a pressure below atmospheric pressure, the pressure drop across the turbine increases. This larger pressure difference means that more heat energy can be converted into mechanical power within the turbine.

Finally, the heat released during the condensation of the exhaust steam is mostly absorbed and carried away by the cooling medium typically water or air used in the surface condenser.

Functions of the Steam Condenser

The primary function of a steam condenser is to maintain a pressure lower than atmospheric pressure at the turbine outlet. This reduction in pressure enables the extraction of maximum energy from the steam, thereby minimizing the specific steam consumption in a power plant.

Additionally, the condenser plays a crucial role in supplying pure feed water to the hot well. From there, this water is pumped back to the boiler via the boiler feed pump.

Moreover, the condenser enhances the heat transfer process by removing non-condensable gases present in the steam as it exits.

Steam Condenser Parts

To operate a steam condenser effectively, several key components are involved:

• Condenser: At the heart of the system, the condenser’s main job is to transform steam back into water. Here, low-pressure steam comes in contact with cooler water typically supplied from a cooling tower which draws out the heat and causes the steam to condense.
• Condensate Extraction Pump (CEP): This pump sits between the condenser and the hot well. Its role is straightforward: it moves the condensed water (known as condensate) out of the condenser and delivers it into the hot well.
• Hot Well: Think of the hot well as a holding area positioned between the condenser and the boiler. It collects the condensate brought in by the extraction pump. From here, water is ready to make its way to the boiler for the next stage.
• Boiler Feed Pump: Placed between the hot well and the boiler, this pump takes water from the hot well and pushes it into the steam boiler. To do this efficiently, it boosts the pressure of the condensate so it’s higher than the pressure inside the boiler.
• Air Extraction Pump: The presence of air in the condenser can interfere with its operation. This pump’s purpose is to remove any air that might have entered, ensuring the condenser works at its best.
• Cooling Tower: Here’s where the cooling water comes from. The cooling tower supplies cold water, which is then circulated through the condenser to absorb the heat from the steam.
• Cooling Water Pump: Positioned between the condenser and the cooling tower, this pump keeps the cooling water moving. Its job is to maintain a continuous flow of water through the condenser so the steam can keep cooling down efficiently.

How does a Steam Condenser Work?

A continuous flow of cooling water circulates between the condenser and the cooling tower, forming a closed loop that ensures efficient heat removal.

As low-pressure exhaust steam exits the turbine and enters the condenser, it releases its thermal energy and transitions back into liquid water. The cooling water moving through the condenser is responsible for drawing this heat away from the steam.

Within the condenser setup, two main pieces of equipment are at work: the condensate extraction pump and the air extraction pump. The condensate extraction pump plays a crucial role in returning the condensed water to the steam generator, keeping the cycle in motion.

Meanwhile, the air extraction pump helps create a vacuum inside the condenser a pressure lower than atmospheric which makes it easier for the cooling water to flow and helps maintain a steady movement of condensate.

However, because the pressure inside the condenser is so low, air tends to seep in. This results in the condenser containing a mixture of water, air, and any remaining steam.

Types of Steam Condensers

The steam condensers are broadly classified into two types:

• Surface condensers (or non-mixing type condensers). In surface condensers, there is no direct contact between the exhaust steam and the cooling water.
• Jet condensers (or mixing type condensers). In jet condensers there is direct contact between the exhaust steam and cooling water.

1. Surface Condenser

A surface condenser serves a dual purpose in thermal power plants: it condenses and deaerates the exhaust steam from the main turbine, while also functioning as a heat sink for the turbine bypass system.

One of the defining features of surface condensers is that the exhaust steam and cooling water remain completely separate there’s no direct mixing between the two. Instead, steam exiting the low-pressure (LP) turbines is guided over bundles of tubes through which cooling water circulates.

As the steam comes into contact with the cool tube surfaces, it condenses. This process relies on the transfer of heat from the steam to the cooling water, driven by both conduction and convection.

The choice of material for these tubes is important, and typically involves stainless steel, copper alloys, or titanium. The selection depends on factors like thermal conductivity and resistance to corrosion.

While titanium tubes offer the best technical performance, their high price tag means they are often reserved for applications where their advantages truly justify the cost.

Generally, surface condensers come in two forms: water-cooled and air-cooled. In locations where water is scarce, an air-cooled condenser might be chosen.

However, this alternative tends to be much more expensive, and it cannot reduce steam turbine exhaust pressure (and thus temperature) as effectively as a water-cooled design.

After the condensation process, the warmed cooling water is typically released into the plant’s cooling system this might be a cooling tower, river, sea, or pond, depending on the setup.

Meanwhile, the condensed steam, now called condensate, is collected and reused as feedwater for the boiler. The key here is that, since there’s no mixing between steam and cooling water, the condensate can be recovered, and even less-than-ideal water sources can be used for cooling.

Compared to jet condensers, surface condensers allow for the maintenance of a high vacuum, which translates to greater thermal efficiency.

On the downside, these units tend to be bulky, require more space, and involve a higher upfront investment. Yet, the improved efficiency can lead to significant operational savings, often offsetting those initial costs over time.

Given these characteristics, surface condensers are the preferred choice for modern thermal power plants especially where large amounts of lower-quality water are available, but the system demands high-quality feedwater for the boiler.

2. Jet Condenser

In jet condensers, the cooling water is sprayed directly onto the exhaust steam, allowing for immediate and thorough contact between the two. This direct interaction leads to a rapid and highly effective condensation process. However, it also means that the cooling water and the condensed steam end up mixed together.

As a result, the condensate produced cannot be recycled as boiler feedwater. The temperature of this condensate matches that of the cooling water as it exits the condenser.

One notable advantage of jet condensers is their efficiency: because the steam and cooling water mix so thoroughly, less cooling water is needed to condense the steam compared to other systems.

Typically, jet condensers also take up less space, are simpler in design, and come with a lower initial cost.

Even with these benefits, jet condensers are not commonly used in thermal power plants mainly because the mixing process prevents the reuse of condensate, which is a significant drawback in such settings.

Advantages of a condenser in a steam power plant

The integration of a steam condenser within a steam power plant offers several notable benefits:

• Improved Efficiency: By allowing for a greater enthalpy drop, the condenser plays a direct role in enhancing the overall efficiency of the power plant.
• Lower Back Pressure: The presence of a condenser helps reduce the back pressure exerted on the turbine by the steam, which translates into an increased work output from the system.
• Reduced Exhaust Steam Temperature: Lowering the temperature of the exhaust steam is another outcome of using a condenser, and this, too, leads to additional work being extracted from the steam cycle.
• Recycling of Condensed Steam: One practical advantage is the ability to reuse the condensed steam as boiler feedwater. This practice not only helps conserve resources but also contributes to a reduction in the overall cost of power generation.
• Higher Condensate Temperature: Unlike fresh water, the condensate that returns to the boiler is already at an elevated temperature. As a result, the amount of heat required to produce steam per kilogram is reduced, leading to further energy savings.

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