Steam Separator And Steam Trap Are Almost Same In Function.docx

STEAM SEPARATOR AND STEAM TRAP Steam separator and steam trap are almost same in function. Both used to avoid the problem caused by water residue in the steam.

Steam separator     

The steam separator is a device which separates water particle from steam. It used to increase the dryness fraction (quality) of steam before it enters into turbine or engine. They usually employ a chamber to collect condensate and a drain valve which activates automatically as per the pre-set water level in the chamber. Large surface areas exposed to an environment that causes considerable heat loss. Some of them need an insulation jacket to avoid heat loss. They mainly classified into baffle separator, centrifugal separator, and mechanical coalescing separator.

Steam trap     

Steam trap filter out condensate and non-condensate gases such as air, CO2 without leaking of steam. The main function is to avoid accumulation of condensate in steam ducts and pipe. They are simply automatic valves working under different mechanism. Radiation loss is very low as compared to steam separators. They are classified into the thermostatic trap, mechanical trap (or density trap), and thermodynamic trap.

The most common problems associated with the steam system are water hammer, pressure drop, freeze up, air binding, steam bind, dirt, scaling and corrosion. 

Water hammer Steam condensate collected at the lowest point of the pipeline. If it is not removed as soon as it condensed, steam at high velocity will pick up accumulated water and slam against the wall of pipeline and other robust equipment. The kinetic energy of steam converted into pressure energy. Resulting high pressure shock wave can cause devastating damage of steam system, even death of the operator in severe cases. To avoid this problem steam separator and traps must be employed on system pipeline.

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Freeze up It happens to the poorly insulated system. In extreme cold condition water in the drainage pipe to get frozen. Resulting difficulty to start the machine and get the system to optimize production temperature. It will cause stalling entire system. The best solution is the drain water as much as you can. Thermostatic controls also help to beat this problem.

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Air binding Prior to starting up the system already filled with air, during the working it gets mixed with steam. Air is non-condensable; it will not return to the boiler, create air pockets. The air in the pipeline causes the steam trap close and then prevents circulation. Thermostatic air vents used to avoid air pocket.

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Steam binding /Steam locking It is similar to the air binding, here the problem caused by steam instead of air and noncondensable gas. This is a condition usually seen in a long horizontal pipe in which steam traps tend to close and restrict the circulation. It may lead to water hammer. Unlike air binding, it may resolve itself as steam condenses.

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Dirt and scaling

Heat exchanger pipe cross-section with the thick scale crust on the inside wall. It is very difficult to keep feed water pure. Sludge and minerals deposited at narrow passages of boiler equipment. The precipitation interferes heat transfer. It causes scaling in the boiler, kettling, lead to

outages and downtime. The solution of this problem is purification and pre-softening of water, use dirt pocket and strainer. The oil leaking also a reason of dirt.

Corrosion All equipment associated with the steam system suffers corrosion. The main corrosives are dissolved oxygen and carbon dioxide (forms carbonic acid). A poor drainage of condensate plays a relevant role in corrosion. Water treatment is the only way to solve this problem.

Pressure drop For efficient operation pressure must be constant. The pressure drop happens mainly due to the leaking of steam. You need to check pressure relief valves.

Feed Pump The pressure of steam inside the boiler is high, and so the feed water pressure must be raised before its entry into the boiler for consistent operation. Feed pump is a device which raises the pressure of water and forces it into the boiler. Feed water pressure must overcome the steam pressure for a steady flow of water to the boiler.

Injector

Drawing of the injector used in steam locomotives. - credit:wikimedia The function of the injector is same as the feed pump; it is used where space is not available for feed pump installation. In an injector, the Kinetic energy of steam is used to increase the pressure and velocity of feed water in a convergent-divergent nozzle. Advantages: Simplicity, Compactness, High thermal efficiency, Absence of dynamic part. Disadvantages: Low pumping efficiency, Difficulty in operation under extreme variation in steam pressure.

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When large quantities of feed water involved feed pump is preferred over the injector because they are more reliable and need less attention.

Economizer Economizer is a heat exchange device which recover some of the heat from exhaust or flue gas and utilize it for heating feed water. Generally, economizer units are placed between boiler and chimney. Advantages: 1. Stress due to uneven expansion is reduced because the temperature range between boiler parts is reduced. 2. Saving in the Fuel consumption. 3. Overall efficiency increases.

4. Evaporative capacity of the boiler is increased. 5. Protection from chilling of boiler metal.

Air preheater

Tubular type air preheater Air preheater is a device which extract heat from exhaust gas to increase the air temperature before entering the furnace. It accelerates the combustion, enhance the burning of fuel and thus increase thermal efficiency. It is generally placed after the economizer. The degree of preheating depends on the type of fuel and rate at which boiler operates. Another advantage of air preheater is that it Reduce flue gas temperature that allows to simplify the design of ducting for flue gas.

Super heater

Diagram of a locomotive type fire-tube boiler with superheater. - credit: wikimedia The steam generated by a boiler is generally wet or at most dry saturated. Super heater is used to increase the temperature of steam above its saturation point, since superheating result in the increase in efficiency and economy of the steam plant. There are two types of super heater, convective and radiant. Convective type uses heat from flue gases whereas radiant type (placed on combustion chamber) receives heat from burning fuel through the radiant process. Advantages: 1. Steam consumption is reduced. 2. Protection from erosion of turbine. 3. Losses due to condensation of steam in the cylinders and pipes are reduced. 4. Plant efficiency increases.

Steam separator

Baffle plate steam seperator The use of wet steam in a turbine is uneconomical; hence a steam separator, also known as a moisture separator used. The function of steam separators is to remove water droplet from steam. It is installed on the main steam pipe from the boiler.

It is important to remove water residue steam because:

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 Water droplet in steam reduces the thermal efficiency. Water may accumulate in cylinder and cause hydrostatic lock that damages the engine. In thermal power plants, water droplets in high-velocity steam from nozzles erode turbine blades.

According to the principle of operation, they are classified into Impact or Baffle type, Reverse current type, Centrifugal type.

Steam trap Steam traps are used to remove condensate as well as non-condensable gases from the steam with negligible loss of steam. Most of the steam traps are automatic valves. Read: Comparison between Steam Separator and Steam Trap

Pressure reducing valve The function of pressure reducing valve is to maintain constant pressure on its delivery side irrespective of boiler pressure.

Boiler Mountings    

Boiler mountings are components used for ensuring the safety of boiler operation. These are generally mounted on the surface of the boiler. Control fluid parameters at the inside of the boiler shell. The mountings are the essential part of a boiler, without which boiler operation is impossible.

Examples: Pressure gauges, Water level indicator, Safety valves, Stop valve, Fusible plug, Blow off cock, etc.

Boiler Accessories    

Accessories are the auxiliary items required for proper operation of boiler and improve the efficiency of it. These are integral parts of the boiler, but not mounted on it. Control fluid parameters at outside of the boiler. These are not essential parts of the boiler, without which boiler can operate though at lower efficiency.

Examples: Super heater, Feed pump, Injector, Economizer, Steam separator, Air preheater, etc.

Quick Comparison Boiler Mountings and Boiler Accessories Boiler Mountings

Boiler Accessories

Components that ensure boiler safety

Components improve the boiler efficiency

Essential part of a boiler

Boiler Accessories are not essential

Mounted on the boiler surface

Integral parts of the boiler, but not mounted on it

Boiler Mountings control fluid parameters inside of the boiler shell

Boiler Accessories control fluid parameters at outside of the boiler

Examples: Pressure gauges, Blow-off cock, Safety valves, Water level indicator, Stop valve, Fusible plug

Examples: Superheater, Air preheater, Feed pump, Economizer, Injector, Steam Separator