Loeffler Boiler
● The difficulty encounter in Lamont boiler of sedimentation and deposition of salt in tube is solved by Loeffler boiler by preventing the flow of water into the boiler tube
● This boiler works on the principle of evaporation of feed water by means of superheated steam from super heater and hot gases from the furnace being primarily used for superheating purposes.
● The boiler drum is constructed outside the furnace setting. The high pressure feed pump feed water through economizer and pickup some heat from outgoing flue gases and discharge it into evaporating drum.
● The steam circulating pump draws saturated steam from evaporating drum and passes it through radiant and convective super heaters where steam is heated to required temperature from super heater approximately one-third of the superheated steam send to the prime mover and 2/3 passes back to the evaporating drum to evaporate feed water.
● About 35% of the steam coming out from the super heater is supplied to the HP. steam turbine. The steam coming out from HP. turbine is passed through re heater before supplying to LP turbine.
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| Loeffler Boiler |
● The amount of steam generated in the evaporator dnum is equal to the steam tapped (65%) from the super heater.
● This boiler can carry higher salt concentration than any other type and is more compact than indirectly heated boilers having natural circulation.These qualities fit it for land or sea transport power generation.
● Since the poor feed water has no detrimental effect on scale accumulation. The boiler steam generating capacity is 100 tonnes/hr and operating pressure at 140 bar.
Velox Boiler
Velox Boiler is a forced circulation water tube boiler. The Velox boiler works on the principle that the velocity of a gas exceeds the velocity of sound, the heat is transferred from the gas at a much greater rate than the rate achieved with subsonic flow. Velox Boiler used this advantage of the theory, it can increase the total heat transfer rate of steam generation rate without actually increasing its given surface area or size. This boiler has a thermal efficiency of about 90 to 95 percent.
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| Velox Boiler |
Construction :
● It consist of Feed water Pump which supply the water at a pressure and pass through the Economizer. Hot fuel gas passes through the Economizer from the Combustion Chamber. When water passes through the Economizer Tube then water is pre-heated. There is another water circulating pump and this pump is connected with the Economizer.
● This water circulating pump is connected with the Tube Evaporating Section. An Axial Compressor and a Steam Separator is connected with the Tube Evaporating Section. The special feature of this boiler is that the flue gases are expanded in a gas turbine before being discharged to the atmosphere, which runs an axial flow compressor.
● Then Steam Separator is connected with the Convection Super Heater where saturated steam from Steam Separator get heated and become Superheated Steam. Velox Boiler uses Pressurized Combustion Chamber
Working:
● In the Velox boiler, air is compressed to 20 to 50 N/cm by an air compressor run by a gas turbine before supplying to the combustion chamber. The object of this compression is to secure a supersonic velocity of the gases passing through the combustion chamber and gas tube.
● As a result of this high rate of heat release are achieved. The capacity of this boiler is limited to about 100 tonns/hour. Because large power (about 6,000 kw) is required to run the air compressor at this output.
● The fuel and air are injected downwards into a vertical combustion chamber which consists of annulus gas tubes and annulus water tubes. The products of combustion are deflected upwards into the evaporator tubes which consist of an outer annulus through which the water evaporated is circulated at a high velocity. The heat is transferred from gases to the water at a very high rate. Here most of the water converted into the steam
● Then the steam is supply to the Steam Separating drum From this, steam supply to the Convection Super Heater. If there is any moisture with the steam then it will be separated in Steam Separating Section and send it to the water Tube Evaporating along with preheated feed water coming from economizer by Water Circulating Pump. In the Convection Super Heater steam temperature increases by the help of the exhaust flue GAS's. Then generated superheated steam, supply to the prime mover for further operation.
● Size of a Velox Boiler is limited with 100 tons per hour. The main reason is, 600 BHP is required to run the air compressor at 100 tons output. The amount of power generated by the GAS Turbine is not enough to run this compressor. For this reason, some external power source must be needed.
Advantages of Velox Boiler:
(i) It has very high rates of heat transfer.
(ii) Steam generating unit is compact and high flexibility.
(iii) It is capable of quick starting.
(iv) It less low excess air requires due to use of compressor
(v) The control is entirely automatic, and a thermal efficiency is high.
Disadvantage of Velox Boiler:
There is a limitation on the size of Velox Boiler.
Schmidt-Hartmann Boiler
● The arrangement of boiler componentare. This boiler is high pressure indirectly heated boiler. There are two pressure circuits used to exchange heat energy. In the closed primary circuit uses a distilled water and the steam is passed through submerged heating coil to evaporate the water. In the secondary circuit, located in the evaporator drum and the steam produced in the secondary circuit is used for running the prime mover.
● The condensate of high pressure primary circuit steam is circulated through the water drum where feed water is heated to its saturation temperature and finally flows back to the primary evaporator. In the primary circuit, natural circulation is used. The primary circuit also includes a steam separator and a non-return valve.
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| Schmidt-Hartmann Boiler |
● The high pressure steam of primary circuit possesses sufficient thermal head to produce steam at 500N/em with a heat transfer rate of 2000 W/m.sq hr °C.
This main steam is passed through a super-heater placed in the uptake and then to the application point.
● For purpose of safety a combined pressure gauge and thermometer are fitted to the primary circuit. There is an arrangement is provided for making distilled water for the primary circuit.
Main advantages of the Schmidt-Hartmann boiler are :
(i) There are very less chances of overheating or burning of the highly heated components due to use of distilled water in primary circuit so no danger of salt deposition.
(ii) There is no chance of interruption to the circulation either by rust or other material, due to use of distilled water in the primary circuit.
(iii) The feed water outside the heating coil and hence it is easy to remove salt deposits
(iv) Due to high thermal and water capacity, wide, fluctuations of load are allowed without undue priming or abnormal increase in the primary pressure.
(v) The absence of water risers in the drum, and the moderate temperature difference across the heating coil, allows evaporation to proceed without priming.
Ramsin Once Through Boiler
It is a supercritical boiler. It is very similar to Benson boiler, except that evaporator section spiral tube instead if straight tubes. Its water circuit.
The boiler consists of inclined evaporator coil arranged in spiral.Forty such coils is paralleled around the furnace. Water is forced into the economiser by a feed water pump where it is heated and then it enters in spiral evaporator tube where water flashes to steam. Steam generated in evaporator flows into headers and then convection supperheaters. The superheated steam is utilized for power generation.
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| Ramsin once through boiler |
Advantages of Ramsin Once Through Boiler:
1. It has high heat transfer rate.
2. Thermal efficiency is high.
3. Corrosion and erosion problem are minimized.
4. Adaptable to load fluctuations.
Disadvantages of Ramsin Once Through Boiler:
● It is costly due to increased requirement for steel for heat transfer surface, pump and feed water piping.
● Generation of steam using forced circulation, high and supercritical pressure.
