05-10-2012, 10:51 AM
Steam Systems
Steam.ppt (Size: 2.56 MB / Downloads: 63)
Classes of Steam
Low Pressure Heating Steam – 15 psig
Used Mainly for Space Heating Systems and Single Effect Absorption Chillers
Actual Code is More Restrictive
Medium Pressure Steam: 15-150 psig
Used in Hospitals, District Steam Systems, Some Industrial Heating
High Pressure: Above 150 psig
Strictly Industrial and Power Generating Applications
Each Class has Piping and Valve Requirements
Increase in Expense with Each Higher Class
Generation
Fire tube
Scotch Marine – most popular
Two, three, and four pass designs
Constant pressure with wide load fluctuations
Steam pressure limited to under 350 psig
Preferred between 3,500 to 35,000 lbs/hr (120 Bhp – 1,200 Bhp)
Water tube
Fuel burned within combustion chamber
Combustion gas surrounds water tubes within vessel
Low water content allows rapid steam production
Capable of high pressure and superheated steam
Preferred ranges are below 3,500 lbs/hr (120 Bhp) and above 35,000 lbs/hr (1,200 Bhp)
Typical Applications
Steam is not commonly used for space heating only
hot water systems are less maintenance intensive
Exceptions
Hospitals – need steam for sterilizers
Older district heating systems
Industrial plants which require process steam
Efficient Steam Systems
Proper performance yields
Low operating costs
Minimal downtime
Reduced emissions
Effective process control
Effective maintenance is the best strategy!!
Boiler Recuperator
Boiler efficiency indirectly proportional to stack temp
Causes of excess stack temps:
Excess air
Fouled waterside surfaces
Fouled fireside surfaces
Overfiring
Insufficient heat transfer surface
High steam pressure
Only insufficient heat transfer surface or high pressure justify a recuperator:
Excess air - adjust air/fuel ratio
Fouled surfaces - can be detected by visual inspection
Overfiring
Flue temp must be at least 50°F over the minimum allowable