Industrial Boilers Steam generators Closed vessels made of steel and used for generation of steam vaporizing water combustion of fuels eg. coal,coke,oil,wood,saw dust and begesse etc. Steam used for producing power,for industrial process work or for heating proposes.
Requirements of a PerfectSteam Boilers Should be absolutely reliable,capable of producing maximum steam at required pressure for minimum of fuel consumption,with minimum attention and minimum initial cost and operating cost. Simple constructions Quick starting from cold Strong enough against temp. stress & strains Well design combustion chamber Less floor area, space & light weight Best gauges,safety valves and other mountings Easily accessible for inspection,cleaning and repairs
Classification of SteamBoilers Vertical or Horizontal Stationary(Power plant,industrial,central heating and combined power and heating boilers.),Portable,Locomotive or Marine Internally Fired or Externally Fired (Lancashire and Locomotive Boilers) Solid,Liquid or Gas Fired Fire(Smoke)Tube:Water is outside the tubes while the hot gases are inside the tubes eg.Vertical,Cochran,Lancashire,Cornish,Locomotives,etc ) or Water Tube: Contain a large number of small tubes through which water circulates,the fire and hot gases being outside of the tubes.eg.Babcock and Wilcox, Stirling and High pressure Boilers etc.)
Vertical Boilers Used in small factories,small water supply plants,cranes,excavators,winch engines in mines and on sites of temporary nature such as construction work etc. Required minimum floor space,not required elaborate foundations,and is portable. Cheap,easy to start but inefficient due to large wastage of fuel and less heating surface. Vertical Boilers are:Simple(having one to three cross tubes), fire tubes and water tubes types.
Simple Cross tube verticalboiler consists of a cylindrical shell surrounding a cylindrical fire box. heating surface is about 8-10 times the grate area. 50% efficiency
Cochran Boiler It is well design of a Vertical multitubular fire tube boiler Improvement over the simple vertical boiler as it provides greater heating surface. Total heating surface area is about 10-25 times the grate area Efficiency 70-75% Ranges from 1m dia.X2m high,evaporation 20kg/hr to 3m dia X6m high,evaporation 3000kg/hr.
Lancashire Boiler Is horizontal smoke tube boiler size range from a shell 2m diaX6m long to 3m diaX10m long Working pressure range are up to 20kgf/cm2 Ratio of heating surface to grate area is 24-30 Efficiency is about 56% without economizer and 75% with economizer. Similar to Cornish boiler,in Lancashire Boiler two flue tubes but in Cornish boiler only one flue tubes are there.
Loeffler Boiler Indirect heating is combined with forced circulation
Velox boiler Fire tube forced circulation Boiler
Fire tubes Vs water tubesBoilers Fire tubes boilers has a large volume of water,therefore more flexible and can meet the sudden demand of steam without much drop of pressure. Fire tubes boiler is rigid and of simple mechanical construction,so greater reliability and low in first cost. Fire tube boilers can be made in smallest sizes therefore simple to fabricate and transport, occupies less floor space but more height. Due to mostly externally fired water tubes boiler so furnace can be altered considerably to meet the fuel requirements. Water tubes boilers are more readily accessible for cleaning,inspection and repairs,compared to the fire tube boilers. Modern trend is in the favors of water tube boiler due to continuous increase in capacities and steam pressures.
Boiler Mountings andAccessories Fitting and devices which are necessary for the safety and control are knows as boiler mountings Fitting or devices which are provided to increase the efficiency of the boiler and help in the smooth working of the plant are knows as boiler accessories. Fittings which are essential from the safety point of view are as follows, Water level indicators Safety valves Combined high steam and low water safety valve Fusible plug
Boiler Mountings andAccessories contd…. Fittings which are essential from the control point of view are as follows, Pressure gauge Junction or stop valve Feed check valve Blow-off cock Man hole and Mud Box The important accessories are Superheater Economiser Air-preheater Feed pump or injector