(Chapter – 9) Boilers Classification; Specification; Fitting & Accessories: Fire tubes and water tubes boilers.
Boiler क्या है?
- Boiler एक closed vessel है जिसमें water को heat देकर required pressure पर steam उत्पन्न की जाती है।
- Heat source सामान्यतः fuel combustion, electric heating या अन्य heat source हो सकता है।
- मुख्य energy conversion: Fuel/Heat Energy → Water → Steam Energy
- Boiler के मुख्य उद्देश्य: steam generation, required pressure, required temperature और required capacity प्रदान करना।
Boiler Classification
| Basis | Classification |
|---|---|
| Water/Hot gas position | Fire-tube, Water-tube |
| Position of furnace | Internally fired, Externally fired |
| Axis of shell | Horizontal, Vertical, Inclined |
| Water circulation | Natural circulation, Forced circulation |
| Steam pressure | Low, Medium, High pressure |
| Use | Stationary, Portable, Locomotive, Marine |
| Fuel | Solid, Liquid, Gas, Electric |
| Number of tubes | Single-tube, Multi-tube |
| Steam condition | Saturated steam, Superheated steam |
Fire-Tube Boiler
- Hot gases tubes के अंदर flow करते हैं और water tubes के बाहर होता है।
- Heat transfer: Hot gas → tube wall → water
- Generally low/medium pressure applications के लिए suitable.
- Construction relatively simple और compact.
- Water content अधिक होने के कारण steam generation response comparatively slow.
- Examples: Cochran, Lancashire, Locomotive, Cornish
Water-Tube Boiler
- Water और steam tubes के अंदर flow करते हैं और hot gases tubes के बाहर flow करती हैं।
- Heat transfer: Hot gas → tube wall → water
- High-pressure और high-capacity steam generation के लिए suitable.
- Water content comparatively कम होता है।
- Steam generation तेज होती है।
- Examples: Babcock & Wilcox, Stirling, La-Mont, Benson, Loeffler
Fire-Tube vs Water-Tube Boiler
| Feature | Fire-Tube | Water-Tube |
|---|---|---|
| Inside tubes | Hot gases | Water/steam |
| Outside tubes | Water | Hot gases |
| Pressure | Generally lower | High pressure possible |
| Steam generation | Slower | Faster |
| Water content | Higher | Lower |
| Steam capacity | Lower | High |
| Safety at high pressure | Comparatively lower | Better suited |
| Construction | Simple | More complex |
| Starting time | Longer | Shorter |
| Maintenance | Generally easier | More skilled maintenance |
| Examples | Cochran, Lancashire | Babcock & Wilcox, Benson |
Important Fire-Tube Boilers
| Boiler | Important Feature |
|---|---|
| Cochran | Vertical, multi-tubular, fire-tube boiler |
| Lancashire | Horizontal, internally fired, fire-tube boiler |
| Cornish | Single large flue; internally fired |
| Locomotive | Mobile fire-tube boiler |
Important Water-Tube Boilers
| Boiler | Important Feature |
|---|---|
| Babcock & Wilcox | Horizontal water tubes; natural circulation |
| La-Mont | Forced circulation |
| Benson | Once-through, supercritical operation |
| Loeffler | Steam generation using recirculated/superheated steam arrangement |
| Stirling | Multi-drum water-tube boiler |
Boiler Specification
किसी boiler की specification देते समय निम्न parameters important होते हैं:
- Maximum working pressure
- Steam generation capacity — kg/h या tonne/h
- Steam temperature
- Type of steam — saturated/superheated
- Heating surface
- Type of boiler — fire-tube/water-tube
- Fuel used
- Fuel consumption
- Overall efficiency
- Feed-water temperature
- Superheater temperature, if provided
- Boiler dimensions और operating conditions
Boiler Rating
- Boiler rating को steam generation capacity और evaporation performance से express किया जाता है।
- Historical rating: Equivalent evaporation from and at 100°C.
- Factor of evaporation (FE) = Actual heat required per kg feed water / 2257 kJ/kg approximately.
- Equivalent evaporation: Actual evaporation × Factor of evaporation.
Boiler Fittings / Mountings
Boiler mountings वे essential fittings हैं जो boiler की safe operation, control और protection के लिए आवश्यक होते हैं।
| Mounting | Function |
|---|---|
| Safety valve | Excess steam pressure release करता है। |
| Water level indicator | Boiler water level दिखाता है। |
| Pressure gauge | Steam pressure indicate करता है। |
| Steam stop valve | Boiler से steam flow control/isolate करता है। |
| Feed check valve | Boiler में feed water admission control करता है और backflow रोकता है। |
| Blow-off cock | Boiler को drain और sludge removal के लिए उपयोग होता है। |
| Fusible plug | Low-water/overheating condition में furnace protection देता है। |
| Manhole | Inspection और maintenance access. |
| Mud hole | Mud/sludge removal और cleaning access. |
Safety Valve
- Boiler pressure निर्धारित safe limit से अधिक होने पर steam release करता है।
- Main purpose: over-pressure protection.
- Types: dead-weight, spring-loaded, lever safety valve आदि।
Water Level Indicator
- Boiler में water का actual level indicate करता है।
- Low water level से overheating और tube/furnace damage का risk बढ़ता है।
- Gauge glass type water-level indicator common है।
Pressure Gauge
- Boiler shell/drum के steam pressure को indicate करता है।
- Common principle: Bourdon tube.
- Pressure gauge operator को operating pressure monitor करने में सहायता करता है।
Fusible Plug
- Furnace के ऊपर/appropriate low-water protection location पर लगाया जाता है।
- Low water level की स्थिति में plug का fusible material melt होकर steam/water release करता है।
- इससे furnace overheating से protection मिलता है।
Boiler Accessories
Accessories boiler की efficiency, steam quality और overall performance बढ़ाने के लिए उपयोग किए जाते हैं।
| Accessory | Main Function |
|---|---|
| Economiser | Feed water को flue gases की waste heat से preheat करता है। |
| Superheater | Saturated steam को superheated steam में बदलता है। |
| Air preheater | Combustion air को flue-gas heat से preheat करता है। |
| Feed pump | Feed water को boiler में pressure के साथ भेजता है। |
| Injector | Steam jet द्वारा feed water को boiler में भेजता है। |
| Steam separator | Steam से water droplets अलग करता है। |
| Steam trap | Condensate निकालता है और live steam loss को रोकता है। |
Mountings vs Accessories
| Point | Mountings | Accessories |
|---|---|---|
| Purpose | Safety & control | Efficiency & performance |
| Nature | Essential | Performance enhancing |
| Examples | Safety valve, pressure gauge | Economiser, superheater |
Economiser
- Flue gases की waste heat से feed water preheat करता है।
- Boiler fuel consumption कम करने में मदद करता है।
- Overall boiler efficiency बढ़ती है।
- Economiser boiler में जाने से पहले feed water को गर्म करता है।
Superheater
- Saturated steam को saturation temperature से ऊपर heat करके superheated steam बनाता है।
- Steam turbine में moisture कम करने में मदद करता है।
- Steam turbine efficiency और work output में लाभ दे सकता है।
- Superheated steam में same pressure पर saturated steam की तुलना में higher temperature होता है।
Air Preheater
- Combustion के लिए जाने वाली air को preheat करता है।
- Heat source: flue gases.
- Fuel combustion improve करता है।
- Boiler efficiency बढ़ाने में सहायता करता है।
Feed Pump vs Injector
| Feature | Feed Pump | Injector |
|---|---|---|
| Purpose | Feed water supply | Feed water supply |
| Driving energy | Mechanical power | Steam jet energy |
| Moving parts | Yes | No major moving mechanical parts |
Natural vs Forced Circulation
- Natural circulation: Density difference के कारण water circulation होता है।
- Forced circulation: Pump द्वारा circulation कराया जाता है।
- High-pressure boilers में forced circulation useful हो सकता है।
- La-Mont boiler → forced circulation का important example.
Important Boiler Examples
| Boiler | Key Identification |
|---|---|
| Cochran | Vertical fire-tube, multi-tubular |
| Lancashire | Horizontal fire-tube, internally fired |
| Cornish | Single large flue |
| Locomotive | Mobile fire-tube boiler |
| Babcock & Wilcox | Water-tube, natural circulation |
| La-Mont | Water-tube, forced circulation |
| Benson | Water-tube, once-through, supercritical |
| Loeffler | Water-tube, steam circulation arrangement |
Boiler Efficiency
- \( \text{Boiler efficiency} = \frac{\text{Heat utilized in steam generation}}{\text{Heat supplied by fuel}} \times 100 \)
- Efficiency बढ़ाने के लिए economiser, air preheater और superheater जैसे accessories उपयोगी हैं।
- Heat losses: flue gas, incomplete combustion, radiation/convection, blowdown आदि।
Important Boiler Terms
- Heating surface: वह surface जिसके एक side पर hot gases और दूसरी side पर water/steam होती है।
- Grate: Solid fuel रखने और burning के लिए support.
- Furnace: Fuel combustion का स्थान।
- Flue gases: Combustion के बाद निकलने वाली hot gases.
- Steam drum: Water/steam separation और storage के लिए drum.
- Water drum: Water circulation/storage में उपयोग।
- Superheated steam: Saturation temperature से ऊपर temperature वाली steam.
- Blowdown: Boiler water का controlled discharge.
Exam-Trap Facts
- Fire-tube: Hot gases tubes के अंदर; water tubes के बाहर।
- Water-tube: Water/steam tubes के अंदर; hot gases बाहर।
- High-pressure boiler: Water-tube generally preferred.
- Cochran: Vertical fire-tube boiler.
- Lancashire: Horizontal internally fired fire-tube boiler.
- Babcock & Wilcox: Water-tube boiler.
- Benson: Once-through supercritical boiler.
- La-Mont: Forced circulation.
- Safety valve: Excess pressure protection.
- Pressure gauge: Boiler pressure indication.
- Water-level indicator: Water level indication.
- Fusible plug: Low-water/overheating protection.
- Economiser: Feed water preheating.
- Superheater: Saturated steam → superheated steam.
- Air preheater: Combustion air preheating.
- Steam trap: Condensate removal.
MASTER REVISION TABLE
| Item | Remember |
|---|---|
| Fire-tube | Fire gases inside tube |
| Water-tube | Water inside tube |
| Safety valve | Excess pressure |
| Water-level indicator | Water level |
| Pressure gauge | Steam pressure |
| Fusible plug | Low-water protection |
| Economiser | Feed water heating |
| Superheater | Steam superheating |
| Air preheater | Combustion air heating |
| Feed pump | Feed water supply |
| Steam trap | Condensate removal |
| Babcock & Wilcox | Water-tube |
| Cochran | Fire-tube |
| La-Mont | Forced circulation |
| Benson | Once-through, supercritical |
ONE-MINUTE REVISION
- Boiler: Water → Steam at required pressure.
- Fire-tube: Gas inside tube.
- Water-tube: Water inside tube.
- High pressure/high capacity: Water-tube.
- Cochran: Vertical fire-tube.
- Lancashire: Horizontal fire-tube.
- Babcock & Wilcox: Water-tube.
- Safety valve: Pressure safety.
- Fusible plug: Low-water safety.
- Pressure gauge: Pressure indication.
- Economiser: Feed water preheat.
- Superheater: Saturated → superheated steam.
- Air preheater: Air preheat.
- La-Mont: Forced circulation.
- Benson: Once-through supercritical boiler.