Choosing the Correct Condenser Materials for Power Plants

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Condensers are pivotal in various industrial and HVAC applications, playing a critical role in converting vapour streams into liquid. They function through heat transfer and compression techniques. They find applications in cooling gases and process fluids and are integral components of systems designed to cool external environments, including air conditioners.

Condenser in Power Plant: Understanding Different Types

The condenser in power plant: Every condenser is built to specific standards, considering flow rates, operating pressures and temperatures and condensing capacity. They are versatile, finding use in automotive air conditioning, central air systems for buildings, process cooling, refrigeration and steam power turbines in power plants.

Heat Exchangers

These can transform gas into liquid via heat transfer. There are two primary types:
Direct Contact Condensers: These facilitate heat transfer through the direct interaction of gas and liquid, typically of the same material.
Indirect Contact Condensers: They use a conductive boundary, like a shell or tube, for heat transfer, avoiding fluid mixing.Large surface condensers with &#;U&#; bent tubes are used in coal-fired power stations and nuclear power stations.

An In-Depth Look: Surface Condenser

A surface condenser is a type of heat exchanger integrated into the steam boiler exhaust which drives the turbines in power stations. The process of gaseous-liquid conversion condenses superheated steam into pure water. In addition, the condenser recovers heat and generates energy. The pure water and the recovered energies are recirculated into the steam generators and boilers, making the condenser performance a significant factor in the overall efficiency of power plants.

Condenser in Power Plant: Corrosion

Corrosion in condensers is a serious issue which can cause expensive equipment damage and threaten operational efficiency and safety. Therefore, alloys used in the construction of the &#;U&#; bent tubing condensers must be strong and practically immune to all corrosion processes in challenging operational conditions, e.g. hot, cold and cyclical changes in temperatures.

Alloy Selection

Titanium is the best technical choice for condenser tubes as it exhibits corrosion resistance to all types of water and significant resistance to general pitting corrosion, crevice corrosion and stress corrosion. The corrosion resistance of this low-density, high-strength material in a boiling water environment is significantly higher than that of copper-nickel alloys. Due to increasing environmental concerns the copper-bearing alloys are now rarely used.

Several million metres of titanium welded tubes, especially Ti Grade 2, (ASTM B 338, ASTM B 861, ASME II Part B SB) are in service worldwide. The power industry has proved titanium to be the most reliable choice for condenser tubing. While Titanium tubes constitute the main part of a condenser, a lot of titanium sheet and plate products are used in the construction of baffle plates and vessels as well as cladding for the condensers&#; shells. This avoids the need for cathodic protection and issues with galvanic corrosion.

Experience gathered from these condenser units in various conditions has guaranteed a long-life expectation of titanium components which virtually eliminates condenser corrosion problems from power plant economics. However, due to the high price and installation cost of titanium tubes, they are generally only used in coastal and nuclear power stations.

Stainless Steel Tube (ASTM A 249 / ASME SA 249) is also used extensively, when possible, and has good mechanical properties, corrosion resistance and economy. Alloy 800H/AT (ASTM B 407, ASME SB 407) is another austenitic heat-resistant alloy. Designed for high-temperature structural applications, the strength of 800H/AT is achieved by controlled levels of carbon, aluminium and titanium along with an °C minimum anneal to achieve a grain size of ASTM 5 or coarser.

Alternative Materials: Stainless Steel and Alloy 800H/AT

While titanium leads in performance, stainless steel tubes (ASTM A 249 / ASME SA 249) are also widely utilised. They offer a balance of good mechanical properties, corrosion resistance, and cost-effectiveness. Another notable material is Alloy 800H/AT (ASTM B 407, ASME SB 407), an austenitic heat-resistant alloy designed for high-temperature structural applications. It gains its strength from controlled carbon, aluminium, and titanium levels, and a specific annealing process.

Duplex Stainless Steels

Duplex stainless steels, , (ASTM A789, ASME SA789) have excellent corrosion resistance, good mechanical, and welding properties with high thermal conductivity, but processing can be difficult with high costs.

We&#;ve looked in-depth at a surface condenser, the importance of the correct condenser in power plant and understanding the various aspects of condensers. From types and material properties to technical specifications and standards, is vital to select the right component for your plant. For further help and support, get in touch today.

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FAQs

What does a condenser do in a plant?
Condensers are essential in power plants for their pivotal role in the steam power cycle. They recover heat energy from steam, significantly enhancing the efficiency of the power generation process.

Why does a plant need a condenser?
Surface condensers in thermal power plants serve a dual function. They are designed to condense the steam exiting a steam turbine, maximising the plant&#;s efficiency. Additionally, they transform the turbine exhaust steam back into pure water, known as steam condensate. This recycled water can then be reused in the steam generator or boiler as feed water, promoting efficient resource utilisation.

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What is air cooled condenser in power plant?
An Air Cooled Condenser (ACC) operates as a direct dry cooling system where steam condenses within air-cooled finned tubes. The key to its functionality lies in the cool ambient air that flows outside these finned tubes, effectively removing heat and enabling the ACC&#;s operation.

The condenser is important auxiliary equipment in the thermal generator set. The condenser is generally composed of neck, casing, water chamber, tube bundle, tube plate, support rod, steam baffle, air cooling area, hot well and other parts, which is the key equipment to determine and affect the load and thermal efficiency of a steam turbine. The heat exchange tube, as the main heat transfer component of the condenser, is the key component of the condenser. With the increase of suspended solids, chloride ions and sulfur ions in the cooling circulating water, there is a higher requirement for a condenser cooling pipe.

Condenser heat exchanger pipe should have excellent heat transfer performance, good corrosion resistance, erosion resistance and wear resistance, but also should have good strength and stiffness, as well as economic and good processing performance. The materials of condenser heat exchange pipe are mainly copper alloy pipe, Austenitic stainless steel pipe, Ferrite stainless steel pipe, Duplex stainless steel pipe, titanium and titanium alloy pipe. The copper alloy pipe mainly includes military brass pipe (C), tin-brass pipe, aluminum-brass pipe, nickel-copper pipe, etc. Stainless steel grades mainly include Austenitic stainless steel tube TP304, TP316L, TP317L and Ferrite stainless steel grades TP439, TP439L, and duplex stainless steel tube , , titanium and titanium alloy tube mainly includes GR1, GR2, GR5, etc..

Pipe materialsProsConsCopper tubingGood processing performance, moderate pricePoor tolerance to complex water quality, poor strength, stiffness, welding workability. Austenitic Stainless steelExcellent erosion resistance, good strength, plasticity, machinability and weldabilityCr-Ni Austenitic stainless steel has poor resistance to chloride ion corrosionFerrite Stainless steelLarge thermal conductivity, small expansion coefficient, good oxidation resistance and stress corrosion resistance, insensitive to chloride ionsPoor plasticity and toughness, especially after deep drawing and other large deformation of cold processing, welding and other high temperature plasticity and corrosion resistance significantly reducedDupex stainless steelExcellent corrosion resistance, comprehensive mechanical properties, welding properties, high thermal conductivity.Processing is difficult and the high costTitanium tubingExcellent corrosion resistance, low density, light weight, good comprehensive performance.Expensive Pros and cons of difference materials for condenser tubing

Different materials of the heat exchange pipe because of its own characteristics and cost factors, its application scope and working conditions are not the same. The corrosion in the Condenser is always an important problem in boiler accidents in power plants. The condensers of power plants in offshore areas generally use Cu-Zn tubes and Cu-Ni alloy tubes. The corrosion resistance of the latter is better than that of the former, because the thermodynamic stability of Ni is close to that of Cu, and the nanoscale compact and stable surface film will be generated on the surface in water or air. Therefore, the Cu-Ni tube in high saltwater (or seawater) and dilute acid, alkali medium is not easy to corrosion. But once there is an attachment on the surface of the copper tube, pitting will occur. Pitting corrosion is autocatalytic and latent, which will bring great damage. The condenser tube blockage and leakage frequently occur in the offshore area due to seawater backfilling, corrosion, dirt and other reasons. Yongxiang operates the generator set. Why is the brass condenser tube so easy to corrode? It depends on the type of corrosion. The corrosion of copper alloy condenser tube is affected by many factors, and the corrosion types are various, mainly including the following items:

Selective corrosion

Because the condenser copper tube is mostly composed of copper zinc alloy, zinc potential is lower than copper, so zinc is easy to become the anode of corroding battery, so that zinc selectively dissolved to corrode the copper tube. The theory and practice show that the corrosion process of copper tube is closely related to the performance of the protective film on the surface of copper tube. If the initial dense protective film is not formed, the corrosion of copper tube is more likely to occur. If there is no initial coating treatment of FeSO4 on the condenser copper tube, it is also easy to lead to local dezincification corrosion.

Electrocouple corrosion

Coupling corrosion may occur when two different metal materials come into direct contact in a corrosive medium. In the condenser, the copper alloy condenser tube material is different from the carbon steel tube sheet material in the cooling water potential, there is the possibility of galvanic corrosion between them. The potential of the condenser copper tube is higher than that of the tube plate, which will accelerate the corrosion of the tube plate. But because the thickness of the carbon steel tube plate is larger, generally 25~40mm, the galvanic corrosion won&#;t affect the safe use in clean freshwater, but in the environment with a high salt concentration of water galvanic corrosion is more likely to occur.

Pitting corrosion

This corrosion is prone to occur on the surface of the copper tube protective film rupture. Because the cooling water contains Cl and Cu oxidation generated by Cu+ to generate unstable CuCl, can be hydrolyzed into stable Cu2O, and make the solution local acidification thermal equipment corrosion. If the condenser copper tube is not cleaned on schedule, the uneven surface deposits promote corrosion and eventually lead to punctate corrosion perforation. In the operation of the condenser copper pipe in frequent start-stop, load change is bigger, the impact of the high-speed turbine exhaust steam, the role of copper tube by alternating stress, easy to make the brass surface membrane rupture, produce local corrosion, pitting corrosion pit formation, reduce material fatigue limit, and because the stress concentration at the corrosion, pitting bottom is easy to crack, Under the erosion of NH3, O2 and CO2 in water, the fracture is gradually expanded.

Erosion corrosion

This type of corrosion can occur on both the waterside and the steam side, mainly in the waterside. Suspended solids, sand and other solid granular hard objects in circulating cooling water impact and friction on the copper tube at the inlet end of the condenser. After a long time of operation, the inner wall of the front section of the copper tube at the inlet end is rough. Although there is no obvious corrosion pit, the surface is rough, the brass matrix is exposed and the copper tube wall becomes thin. The anodic process of erosion and corrosion can be said to be the dissolution of copper, and the cathodic process is the reduction of O2. The high flow rate will hinder the formation of stable protective film, is also the cause of erosion-corrosion, the general flow rate is not more than 2m/s.

NH3 corrosion

Excess NH3 enters the condenser with steam and concentrates locally in the condenser. If O2 is present at the same time, NH3 erosion will occur on the steam side of the copper tube in this area. Its characteristic is uniform thinning of the tube wall, and NH3 erosion is easy to occur when ammonia content in water reaches 300mg/L. The condensate at the baffle hole is too cold and the dissolved ammonia concentration is increased, which will also cause the annular strip ammonia erosion in the copper tube.

Stress corrosion cracking

When the condenser copper tube is not installed properly, vibration and alternating stress will occur in the operation of the copper tube surface to destroy the protective film and corrosion, finally, produce transverse crack to break the copper tube. This is mainly due to the relative displacement of grains inside the copper tube under the action of alternating stress, and the formation of anodic dissolution in the corrosive medium, mostly occurring in the middle of the copper tube.

Microbial corrosion

Microorganisms can change the medium environment in local areas of the condenser wall and cause local corrosion. The electrochemical corrosion process of metal in cooling water is promoted by the biological activity of microorganisms, which generally occurs on the carbon steel tube plate at the inlet side of the condenser. Cooling water often contains bacteria that thrive on Fe2+ and O2, called iron bacteria, which form brown slime. The anoxic conditions at the bottom of the slime provided a suitable environment for the survival of anaerobic sulfate-reducing bacteria. The combined action of iron bacteria and sulfate-reducing bacteria promotes metal corrosion. Operating temperature on the high side, the corrosion scale inhibitor and water quality and operating temperature are not appropriate, inadequate dosage or concentration fluctuations in the scale, will cause the condenser tube wall local Cl &#; easy through scale layer, caused the corrosion of the metal matrix, and the corrosion of metal ion hydrolysis, leading to higher medium H + concentration of algae and microbial activities also cause increased acidity of medium, The passivation film on the metal surface is destroyed and the metal matrix is further corroded.

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