Boilers 101. Asit Patel ANP Energy Consulting Services

Transcription

1 Boilers 101 Asit Patel ANP Energy Consulting Services 1 Learning objectives Define what is a boiler? What are different classification of boilers? Define combustion efficiency, thermal efficiency, and fuel to fluid efficiency. Identify different type of boilers Criteria for boiler selection 2 1

2 Lets look at what the Merriam-Webster dictionary says the BOILER IS 3 What is a boiler? A boiler is a closed metal container (pressure vessel) in which water is heated to produce steam and heated water 4 2

3 Boiler Classifications Low Pressure: Section IV of ASME Code (Heating Boiler) Steam: Up to 15 PSIG Water: Up to 160 PSIG and or 250 F High Pressure: Section I (Power Boiler) of ASME Code Steam: Above 15 PSIG Water: Above 160 PSIG and or 250 F 5 Boiler Efficiency Classification Standard Efficiency (80-84%) Most Steel and Cast Iron Boilers Mid Efficiency (85-90%) Copper Fintube Boilers Non- Condensing High Efficiency (90%+) Condensing Boilers 6 3

4 Defining Boiler Efficiency Combustion Efficiency - indicates a burners ability to burn fuel measured by unburned fuel and excess air in the exhaust. Thermal Efficiency - indicates the heat exchangers effectiveness to transfer heat from the combustion process to the water or steam in the boiler, exclusive radiation and convection losses. Fuel to Fluid Efficiency - indicates the overall efficiency of the boiler inclusive thermal efficiency of the heat exchanger, radiation and convection losses - output divided by input. 7 Where do we get input and output information for a boiler? Boiler Brochure 8 4

5 Boiler Capacity Units of Measurement Input (Firing rate) GPH Gallons per hour MBH (M = 1,000 btu) Output BHP = Boiler Horse Power = 33,475 btu Sqft of steam = 240 btu lbs/hr (34.5 lbs of steam = 1 BHP) 9 What is a BTU? British Thermal Unit (btu) = Unit of measurement of heat energy. Amount of heat energy required to raise one pound of water by one degree Fahrenheit. one gallon of water = 8.33 lbs Approximate amount of heat released by one kitchen match. 10 5

6 Types of Boilers Cast Iron Sectional Scotch Marine Steel Firetube Firebox Watertube Low water content copper fin tube type Condensing boilers 11 Types of Boilers 12 6

7 Types of Boilers Cast Iron Sectional Scotch Marine Steel Firetube Firebox Watertube Low water content copper fin Condensing boilers 13 Boiler Types Cast Iron Sectional 14 7

8 Boiler Types Cast Iron Boilers Advantages Modular Design High Number of Options Low Initial Cost Durable Construction Disadvantages Low Pressure Only Limited to 200 horsepower Not Recommended For Process Applications Medium to High Level of Maintenance Low Efficiency in Field 15 Types of Boilers Cast Iron Sectional Scotch Marine Steel Firetube Firebox Watertube Low water content copper fin Condensing boilers 16 8

9 Boiler Type Steel Firetube Scotch Two Pass Dryback Three Pass Wetback 17 Boiler Type Steel Firetube Scotch - Four Pass - Wetback 18 9

10 Boiler Type Steel Firetube Scotch - Wetback Design Principles Rear turnaround is totally surrounded by water No expensive refractory to maintain Rear doors are either lightweight lift off type or split-hinged 19 Boiler Type Steel Firetube Scotch - Dryback Design Principles Rear turnaround is a refractory wall Door refractory is a maintenance item Rear door is vessel-sized in diameter, extremely heavy, and hinged or davited 20 10

11 Boiler Type Steel Firetube Scotch - Dryback 21 Boiler Type Steel Firetube Scotch Advantages Wide range of sizes Both high and low pressure Higher Efficiency Easy to clean No mud legs Longevity No refractory floor No rear door refractory (3-Pass & 4-Pass Wetback Only) Disadvantages Operating weight Requires more floor space Space required for tube removal & cleaning Refractory Maintenance (dryback design only) 22 11

12 Types of Boilers Cast Iron Sectional Scotch Marine Steel Firetube Firebox Watertube Low water content copper fin Condensing boilers 23 Boiler Type Steel - Firebox 24 12

13 Boiler Type Steel - Firebox Advantages Wide range of sizes Compact (for places where Scotch will not fit) Easy to clean Longevity Disadvantages Low Pressure ONLY Operating weight Refractory maintenance costs Space required for tube removal & cleaning (but not as much as Scotch) 25 Boiler Type Modified Firebox (fits through 36 door) 26 13

14 Types of Boilers Cast Iron Sectional Scotch Marine Steel Firetube Firebox Watertube Low water content copper fin Condensing boilers 27 Boiler Type Flexible Watertube 28 14

15 Boiler Type Flexible Watertube Advantages Lower Cost Lower operating weight Long life expectancy (40 Years) Wide range of sizes Knockdown capability Minimum space required for tube removal & cleaning Tubes easily replaced Disadvantages Low Pressure Application ONLY Water treatment more critical (difficult to clean) 29 Boiler Type Steel - Watertube D Type S Type A Type O Type 30 15

16 Boiler Type Steel Watertube 31 Boiler Type Steel - Watertube Advantages High Pressure up to 900 psig Fast Steaming Low Water Content Quick Response to Load Demands Disadvantages Steam Only Process Only 32 16

17 Types of Boilers Cast Iron Sectional Scotch Marine Steel Firetube Firebox Watertube Low water content copper fin Condensing boilers 33 Boiler Type Copper Fin Tube Horizontal Lay-out Source: Hydronic Institute Installation Guide: Residential hydronic heating Guide

18 Boiler Type Copper Fin Tube Vertical Lay-out 35 Boiler Type Copper Fin Tube Advantages Medium efficiency Low initial cost Low Mass Low operating weight Small footprint Lower stand-by losses Disadvantages Gas only Water only Special vent requirements 36 18

19 Types of Boilers Cast Iron Sectional Scotch Marine Steel Firetube Firebox Watertube Low water content copper fin Condensing boilers 37 Boiler Type High Efficiency Condensing Boilers 38 19

20 True Operating Efficiency of Condensing Boiler Condensing boilers actually operate at higher part-load efficiency while in condensing mode. 39 Boiler Type High Efficiency Condensing Boilers Advantages Highest Efficiency Can be used in low RWT systems Various types Condensate will not harm properly designed boiler Standard features & Controls Smaller Venting Disadvantages Water only Gas only Special venting Costly??? 40 20

21 TYPES OF BOILERS Atmospheric - Gas Increased standby losses Air from building free to move through units and up through stack at all times 41 Types of Boilers Knockdown Boiler (vessel) only Packaged Boiler and burner May be the same manufacturer or may be two different manufacturers Mostly two different manufacturers Integral unit Boiler and burner is one unit Most condensing boilers 42 21

22 Criteria for boiler selection Application Heating/Process Steam/Hot Water High Pressure/Low Pressure Fuel availability and venting options Space availability Budget Efficiency 43 What makes one boiler more efficient than other? Capability to transfer more BTU s from combustion process to make hot water or steam. Heat exchanger design and construction Lower jacket and stand-by losses Better insulation and heat exchanger isolation during off cycles. Capability to match the boiler s output to actual load Better modulation capability (higher turn-down ratio) 44 22

23 From operating perspective.. The best boiler for your application is the one that is properly sized to match your load. A boiler that runs non-stop. 45 How do we achieve that Multiple smaller capacity boilers Larger boiler(s) with modulation burner Turn down ratio Typical 4:1 (100% 25%) 5:1 (100% - 20%) Highest - 20:1 (100% - 5%) But then, what about part load efficiency? 46 23

24 Part-Load Efficiency Curves of Non-condensing High Mass boiler Typical high mass boilers have low partload efficiency. Another concern is flue gas condensation. 47 Part Load Efficiency of Condensing Boiler Condensing boilers actually operate at higher part-load efficiency while in condensing mode

25 So What Makes Condensing Boiler Efficient? Condensation of water vapor. Extraction of latent heat that is otherwise going up the chimney in form of water vapor. 49 Fuels and Combustion Fuels are Hydro-Carbons Oxygen is 21% of air (78% is Nitrogen) HC + O2 Good, complete combustion CO2 + H20(vapor) + heat Flame Quality Carbon Monoxide hazard Incomplete combustion of gas CO2 + CO + H2O + heat Incomplete combustion of oil CO2 + CO + C + H2O + heat Soot = $ lost 50 25

26 Energy Improvement Opportunities Associated with Boilers/burners Maximize combustion efficiency Minimize excess air Maximize heat exchange Clean up fireside and waterside fouling Minimize stand-by losses Jacket losses and cyclical losses 51 How much excess air should we strive for? FEMP O&M Manual Ver. 3 P

27 Opportunity in field Lowering of excess air results in lower exhaust gas temperature and higher efficiency 53 Heating System Efficiency Soot on Heat Exchanger Acts as an insulator Increases amount of heat lost through chimney 54 27

28 Heating System Efficiency Scale on Water Side of Heat Exchanger Acts as an insulator More heat lost through chimney 55 Just so that you know that I am not making these things up

29 Optimization Opportunity (Minimize stand-by losses) If this damper is left in open position, it can significantly impact the stand-by losses and if not adjusted properly can have significant impact on combustion process. 57 Thank You 58 29

30 Q & A 59 30