Steam Condenser I

transcript

Prof. Osama El Masry

Steam Condenser I

Mechanical Engineering DepartmentME332 Operation and Management of Power Plants

Prof. Osama A El Masry

Direct Contact Condenser

This type of condenser is suitable where conditions permit condensation of exhauststeam by direct contact with the cooling water. The vacuum is created in the chamber by an air ejector. The cooling water is sprayed into the chamber an the fine spray contacts the steam. The steam condenses and falls to the bottom of the condenser chamber with the injection water. The condensed steam and injection water is withdrawn using a centrifugal extraction pump

Barometric Condenser

Barometric Counter-Current Condensers have no moving parts. Little maintenance is required and provision can be made for internal inspection of the unit. Because of the barometric leg, no water removal pump is required

Barometric Condenser

Multi-Jet Barometric Condensers are generally employed where low cost water is available in ample quantity. It is the simplest design of all barometric

condensers, and requires no auxiliary air pump or pre-cooler. - Recommended for operation under fairly constant loads where there is

relatively little air leakage, and where water is not too scarce and does not need to be recirculated.

Jet-Type Condenser

Multi-Jet Spray Type Barometric Condensers are generally employed where large capacities are required and where wide fluctuations in water temperature or steam load occur.

Surface CondensersSurface condensers are the

most commonly used condensers in modern power

plants. The exhaust steam from the turbine flows on the

shell side (under vacuum) of the condenser, while the plant’s circulating water

flows in the tube side.

Surface Condensers

The source of the circulating water can be either a closed-loop (i.e.

cooling tower, spray pond, etc.) or once

through (i.e. from a lake, ocean, or river). The

condensed steam from the turbine, called

condensate, is collected in the bottom of the

condenser, which is called a hot well. The

condensate is then pumped back to the steam

generator to repeat the cycle.

Surface Condensers

Surface CondensersSurface condensers are basically a shell and tube heat exchanger consisting of water boxes for directing the flow of cooling water to and from horizontal tubes. The tubes are sealed into fixed tube sheets at each end and are supported at intermediate points along the length of the tubes by tube support plates. Numerous tubes present a relatively large heat transfer and condensing surface to the steam. During operation at a very high vacuum, only a few kgs of steam are contained in the steam space and in contact with the large and relatively cold condensing surface at any one instant.

surface condenser have improved by cutting down the bundle to half and making two smaller bundles beside each others to overcome the high pressure drop problem .

Baffles are used to help the steam distribution and accelerate condensation rate

The shell is fabricated from carbon steel plates and is stiffened as needed to provide rigidity for the shell.

Intermediate plates are installed to serve as baffle plates that provide the desired flow path of the condensing steam. The plates also provide support that help prevent sagging of long tube lengths.

At the bottom of the shell, where the condensate collects, an outlet is installed. In some designs, a sump (often referred to as the hot well) is provided. Condensate is pumped from the outlet or the hot well for reuse as boiler feed water.

Shell OutletShell Outlet

Channel InletChannel Inlet

ChannelChannelOutletOutlet

Shell OutletShell Outlet

SINGLE SEGMENTAL TRANVERSE BAFFLESSINGLE SEGMENTAL TRANVERSE BAFFLES

Tube sheets of sufficient thickness usually made of stainless steel is provided, with holes for the tubes to be inserted and rolled. This is to avoid eddies at the inlet of each tube giving rise to erosion, and to reduce flow friction. To take care of length wise expansion of tubes some designs have expansion joint between the shell and the tube sheet allowing the latter to move longitudinally.

Size: modern condensers use 7/8 or 1.0 in tube of 18 gauge thickness

Condensers may have up to four passes; one and two pass condensers are the most common. In a single pass condenser, the cooling water makes one passage from end to end, through the tubes. Single pass condensers have an inlet waterbox on one end and an outlet water box on the other end. Two pass condensers have the cooling water inlet and outlet on the same water box at one end of the condenser, with a return water box at the other end.

A single pass condenser is commonly used where the water is supplied from natural sources such as rivers or oceans. If the source of circulating water is at all limited, a two pass condenser will probably be the best selection since a single pass condenser requires more cooling water per square foot of condenser surface and per kilowatt of electrical generation. Usually, a two pass condenser is used with cooling towers or a cooling lake.

Waterboxes: The tube sheet at each end with tube ends rolled, for each end of the condenser is closed by a fabricated box cover known as a waterbox, with flanged connection to the tube sheet or condenser shell. The waterbox is usually provided with man holes on hinged covers to allow inspection and cleaning. These waterboxes on inlet side will also have flanged connections for cooling water inlet butterfly valves, small vent pipe with hand valve for air venting at higher level, and hand operated drain valve at bottom to drain the waterbox for maintenance. Similarly on the outlet waterbox the cooling water connection will have large flanges, butterfly valves, vent connection also at higher level and drain connections at lower level.

Condenser Temperature Profile

Change in Condenser Temperature Profile

Change in Turbine Load and Condenser Pressure

Variation in Condenser Pressure

Air Cooled Condensers

Inlet Inlet NozzlesNozzles

Return Return HeadersHeaders

Fan RingFan Ring

SupportsSupports

Drive AssemblyDrive Assembly

Tube BundleTube BundleOutlet Outlet

NozzlesNozzles

Outlet Outlet HeadersHeaders

Inlet Inlet HeadersHeaders

Hood or PlenumHood or Plenum

FanFan

Dry Cooling

Steam ducted to air-cooled condenser

Condensation inside finned tubes - analogous to automobile radiator

Cold water approaches dry bulb temperature

Steam Condensers

Water Cooled Condensers

Internal Surfaces

External Surfaces

Tube Fouling

Deposition or Particulates

Scaling or Crystallization

Microbiological

DebrisCorrosion Products

Deposition or Particulates

Natural sediment Bio-growth Coal dust

Crystalline solids

Are fine particulates that settles on the tube surface due to gravity under low flow condition.

Scaling or Crystallization Fouling• Scale occurs when the saturation point of dissolved

constituents in the

cooling water is exceeded.

• Scale can provide sites for local under scale corrosion

Pitting under scale in stainless steel tube

Debris

Caused by any substance whose size is close to, or greater than,

internal diameter.

• Rocks• Cooling tower materials

( Plastic fill , wood )• Large pieces of rusted

steel• Aquatic animals ( Small

fishes )• Any other substance

that enters the circulating water can obstruct

cooling water flow

Examples :

Tubewall

Deposit Layer

Tube Metal Temperature

800ºF785ºF

700ºF

600ºF

500ºF

766ºF Inside Tube Temperature

730ºF Film Temperature

520ºF Bulk Fluid

Temperature

Temperature Profile in Heat Transfer

Cleaning interior surfaces of tubes

Chemical Mechanical

Off Line Cleaning

On Line Cleaning

Chemical treatment

• Several chemicals, often in combination, are used to control

condenser tube fouling.

• PH control ( lowering PH to 5.8 or 4 )

• Scale inhibitors

• Corrosion inhibitors ( Zinc & phosphates for carbon steel )

Chemical treatment methods :

1) The concentration of dissolved constituents is significant,

increasing the

threat of scaling and corrosion.

2) Once-through cooling systems often discharge directly into a

river, lake,

or ocean where chemicals concentrations are restricted.

Utilized for recirculating cleaning system because of :

Disadvantages of chemical treatment:

• Expensive.

• Job duration is excessive.

• Subsequent disposal of the chemicals requires serious

consideration due to potential environmental hazard.

Mechanical cleaning

High Pressure Water

Molded Plastic Cleaners ( Pigs )

Brushes Metal Scrapers

Hydrodrilling

Off line cleaning

High pressure water :

• The water is directed in a high pressure towards the tubes.

• Disadvantages:

The time taken to clean a condenser can become extended.

Could damage tube sheet or tube coatings.

• They are molded plastic cleaners .

• Quit popular for softest types of deposits such as mud , silt and microbiological fouling

Plastic tube cleaners

Brushes

• Used to remove micro / macro fouling, soft organic scales, some corrosion by-products.

• Useful for cleaning tubes with thin wall metal inserts or epoxy type coatings.

Metal Scrapers

• Used for harder types of deposits such as calcium carbonate.

• The blades are mounted on a spindle.

• One end of the spindle is a serrated plastic disc that allows a jet of water to propel the cleaners through the tube.

Metal U-tube Cleaners

How does this technique work?

• Spring loaded tube cleaner (Bullets) are shot through fouled Condenser tubes using specially designed water guns at 1.5-2.5 MPa water pressure with velocities 3-6 m/s.

• Tube cleaners exit at the end of the condensers, hitting a collection screen hung at the other end.

• These cleaners are collected, cleaned and used again. Normally a bullet can be used 10 to 15 times.

Water Gun & its pumping system

Hydrodrilling• Used to remove difficult deposits from the inside of tubes .

• Hard deposits such as ( Calcium, sulfur and oxides).

• Could be used on-site therefore eliminating the need for

bundles to

be sent off-site for cleaning treatments.

• Polishes tube internal diameter to as-new condition.

Advantages of Hydrodrilling• It uses a small a volume of water (2 to 3 GPM at 200 to 300

PSI) that is filtered and recycled through a booster pump.

• Greater heat transfer efficiency.

• Less scheduled cleaning time and cost.

Cleaning effects for a calcium carbonate scale:

Before After

In-Line Mechanical Cleaning

• Balls that are slightly larger in diameter than the tubes.• Ball injection nozzle. • Ball strainer.• Ball recirculating pump.• Ball collector.

• The tube cleaning system consists of:

Ball Strainer

Sponged balls

External surfaces fouling

Dirt, dust & debris

Pollen & Leaves

Insects & bird carcasses

Cleaning External Tubes Surfaces

Fire hose High pressure handlance

Automated cleaning machine

Fire hose

• Uses low pressurized water but with high volume flow rates.

• Has low washing effect.

Advantages:

• The galvanized surfaces of the tubes and fins are not damaged by this method.

Disadvantages:

• Unit must be taken out of service and scaffolding erected.• Improvements are quite small, since only a portion of debris is

removed, remainder being compacted between tube fins

High pressure handlance

• Low water consumption and a high water pressure

• Latter can damage galvanized surfaces and/or snap off fins

• Unit must be taken out of service and scaffolding erected

• Again, improvements are quite small since only portion of

debris is

removed, remainder being compacted between tube fins

Automated Cleaning Machine

• 60 GPM at 1,000-2,000 psi water pressure avoids fin and tube

surface

damage.

• Adjustable nozzle design, distance from surface and jet energy.

• Water contains no additives.

• Fouling removed effectively and uniformly.

• No need to shut unit down or erect scaffolding.

• Nozzle beam optimally matched to tube bundle geometry with

a constant jet angle.

Forms of Automated Cleaning Machine

Permanently installed system

Semi-automatic

system

Portable service unit

Permanently installed system

The system is supplied for each side of the ACC & controlled automatically

Semi-automatic system

• The guide rails are permanently installed.

• The nozzle beam carriage being moved from section to section

by the labour.

Portable service unit

The unit has a portable nozzle beam carriage and control unit

Cleaning Results

Fouled

During cleaning

Cleaned

Conclusion

Surfaces should be kept clean to increase generation capacity & reduce the

associated costs.

Steam Condenser I

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