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• Tubes are placed vertically with axes parallel to gas flow. It does not obstruct the flow of gas. Possibilities of soot accumulation are less since vertical downward flow of flue gas will help in dislodging the soot particles.

• Tubes are placed horizontally with their axes perpendicular to flow of gas. This results into obstruction to Gas flow & soot particles are arrested on tube surface.

• Natural circulation design. No dependence on any external equipment for circulation. Uninterrupted circulation eliminates possibilities of higher TDS level in evaporator & subsequent scale deposition.

• Forced circulation design. Circulation is dependent on pump. Failure of pump suddenly stops circulation & results into higher TDS level in evaporator & subsequent scale deposition. Pump has to operate at very high suction pressure making the operation critical.

• Bare tubes reduces possibility of soot accumulation. Particularly for gases with high SPM like flue gases of F.O. engine, it is highly recommended to use only bare tubes without finning. Even though manufacturing cost goes up, user gets benefited.

• Finned tube construction invites accumulation of soot between fins. This type of tube is not recommended particularly for flue gases with high SPM. Their use should be restricted for cleaner flue gases like gas engine/turbine.

• Bare tubes used in manufacturing are standard tubes available in market. In case of replacement user is not dependent on manufacturer for supply of tubes.

• Finned tubes used have specific fin size, shape & configuration. These Tubes have to be purchased only from manufacturer & hence user is Completely dependent on Manufacturer for lifetime of boiler.

• Two stage economizer improves Heat recovery. Feed water is heated completely up-to saturation temperature with waste heat after main boiler. This is done while maintaining feed water temperature at economizer inlet Above 122 Deg. C even if temperature in tank is 85- 90 Deg. C.

• Single stage economizer. Hence Limited heat recovery.

• For flue gases of furnace oil with 4% sulphur, it is necessary to maintain metal temperature above 121 Deg.C. We provide auto temperature correction system which ensures that the feed water entering each stage of economizer is at-least at 122 Deg.C. This will ensure that all contact area is above the safe temperature level & will eliminate any possibility of corrosion.

• Water in the tank directly enters Economizer without any temperature correction. Hence the tube wall temperature at economizer Inlet drops below safe level & results into Cold end corrosion. User has to buy the tubes frequently from manufacturer since these tube are not available in market.

• Two alternatives are available. Steam soot blowers are provided as one of the alternatives. As a second alternative, soot removal is done on-line with mechanical knockers. This has negligible operating costs. These soot blowers can operate automatically based on ‘flue gas back pressure feedback signal’ or ‘flue gas outlet temperature feedback signal’.

• Steam soot blower consume almost 3-4% of the steam output per day. This reduces net steam available to Plant. Operation is manual & if not done properly, can create problems.