Forced Draft Boiler Flue Gas Venting: Problems & Solutions Presented by Steve Connor and Patrice Gouin January 27, 2016
What Will We Be Covering Today? Pressurized Non-condensing Vent Systems Venting s impact on Efficiency, Reliability and Safety Stack categories and codes Venting dynamics, the what and how Combustion air supply requirements Contaminants in the fuel Venting components making up the system Draft and the factors causing its variance Insulation Two scenarios 2
Increased Operating Cost
4 Excess Air
Efficiency, Maintenance & Downtime Pilot Failure Poor Combustion 5
POSITIVE NEGATIVE Categories Based On Boiler Design and Operation CATEGORY I APPLIANCE CATEGORY II APPLIANCE NON-CONDENSING CONDENSING CATEGORY III APPLIANCE CATEGORY IV APPLIANCE 6
POSITIVE NEGATIVE Today s Focus CATEGORY I CATEGORY II Atmospheric Boilers Fan assisted Boilers Fan assisted, near condensing Boilers NON- CONDENSING CATEGORY III CONDENSING CATEGORY IV Forced draft Boilers Fan assisted Boilers Forced draft Boilers 7
UL & NFPA Code Compliance UL 103 (1400 deg. F) UL 1738 (National Fuel Gas Code, ANSI Z223.1/NFPA 54) 8
Code Listings UL 103 Industrial Positive Pressure Can/ULC C 959 1400 F continuous operation 60 in. wc. UL 1738 Special Gas Vent 550 F continuous operation 2.5X manufacturer tested pressure (minimum 1.25 in. wc.) NFPA 54 & 211 9
Applications for Low and High-Pressure Steam 10
What is The Exhaust System Doing? Channel for products of combustion to exit Provide adequate draft Allow for corrosion resistance -(Carbonic acid, Sulphuric acid, Nitric acid) Allow for expansion Allow for weight bearing Allow for possible overpressure Allow for draining & cleaning 11
How Draft is Accomplished Pressure/density differential Natural (atmospheric) Forced draft Balanced (power burner and induced) Induced (draft fan) applied to: Natural Positive Balanced Induced 12
Rule of Thumb for Boiler Room Air Comb. Air - 8 CFM/BHP Vent. Air - 2 CFM/BHP Total = 10 CFM/BHP Divided by Velocity: (7) foot ceiling above floor 250 FPM > (7) feet 500 FPM = Cross sectional area required Two (2) openings, either side of room, Minimum 5 feet above floor 13
Fuels We Will Be Considering Today Include Natural gas No. 2 oil 14
Fuels and Related Combustion Products All volatized carbon fuels create CO2 15
Venting Component Systems Vertical stacks (metal & masonry) Breechings Liners 16
Vertical Prefabricated Stack Carbon steel Stainless steel Cor-Ten Single or double wall Insulated 17
Breeching Expansion Joints Note: Breeching expands approx. 1 per 100 feet for every 100 deg. F increase in temperature over the ambient temperature surrounding its outer surface. 18
Stack Liner Liners 19
Point of draft measurement / estimation Factors Increases draft Decreases draft Mass flow Exhaust temperature Horizontal length Vertical height Fittings Diameter Heat loss Site elevation Cold Vs Hot weather 20
Venting Solutions Vary Greatly 21
Varying Atmospheric or Operating Conditions Vent outlet 22
Modulating Damper in Boiler Vent Outlet Process variable Modulating damper 23
Induced Draft Fan In-line Top mount 24
Stack Insulating Material 25
Insulation Material For Double Wall Venting Systems When to use what? Air Mineral fiber Ceramic fiber 26
Insulation Types and Limits Air Space Mineral Fiber Ceramic Fiber UL Approved for 1400 F continuous Peaks of 1800 F for 10 mins. UL Aprroved for 1000 F continuous Peaks of 1400 F for 10 mins. UL Approved for 1400 F continuous Peaks of 1800 F for 10 mins. 27
28 Venting System Choices
Different Vent Joining Systems Flanged Male/female 29
30 Patrice Gouin
Both with Category III boiler venting Both burning natural gas & #2 oil Both with boilers on common breeching One with prefabricated chimney sections One with a liner in a masonry stack Two Scenarios
1 st Scenario - Exhaust System Layout & Sizing Longest breeching length is 43 10 long. (25 1 ¼ + 9 6 + 9 2 ¾ )
1 st Scenario - Space Constraints End Cap for inspection 45 Deg. Tee Tee w/drain cap Adapter with elliptic edge and drain
1 st Scenario Inspection & Site Preparation Aeration grid Utility shaft Utility tunnel
1 st Scenario Inspection & Site Preparation Damaged bricks no longer reliable to anchor a chimney Utility shaft prepared for new bricks and chimney installation
1 st Scenario Chimney Installation Wall Support Variable Length Section Wall Support Variable Length Section
2 nd Scenario Masonry Stack Liner
Sizing the system 2 nd Scenario Masonry Stack Liner
2 nd Scenario Masonry Stack Liner Exhaust system components Chimney sized to get the most Negative draft pressure of the system at this point. Chimney sized to get Zero draft pressure at this point. Draft pressure at this point normally stays slightly positive because of forced draft
Breeching & Liner Installation 2 nd Scenario Masonry Stack Liner
Summary Category of boiler is determined by temperature & pressure @ vent stub @ full rate Category III venting reference is UL 103 in the US and ULC C-959 in Canada Insulation materials are selected to prevent detrimental heat loss Venting systems must allow for expansion Venting system diameter selection is impacted by various factors Condensation in the venting system is highly probable and must be accounted for Deciding to go pre-fabricated stack system or liner involves several trade-offs; Consult an expert before proceeding With multiple boilers using a common breeching/stack, it is often desirable to have controlled dampers on each boiler.
Patrice Gouin Technical Applications & Management Exhaust Solutions pgouin@cleaverbrooks.com 229-319-9646 42