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MOVING AWAY FROM SURFACE AREA
Presentation for NBIC Chief’s Technical Meeting
RECENT PAST
THINGS CHANGED
NONMANDATORY APPENDIX AESTIMATING PRESSURE RELIEF VALVE
CAPACITY REQUIREMENTSA-100 GUIDE FOR ESTIMATING PRESSURE RELIEF VALVE CAPACITY BASED ON HEATING SURFACEThe minimum pressure relief valve relieving capacity, when provided in accordance with HG-400, may be estimated on the basis of the pounds of steam generated per hour per square foot (kilogram per hour per square meter) of boiler of heating surface, as given in Table A-100. In many cases, a greater relieving capacity of pressure relief valves will have to be provided than that estimated using Table A-100, in order to meet the requirements of HG-400.1(d) and HG-400.1(e) or HG-400.2(e) and HG-400.2(g).
FURTHER BACK IN HISTORY On April 27, 1865, the steamboat Sultana exploded and sank while traveling up the Mississippi River, killing an estimated 1,800 people.
This tragedy was one of the instances that inspired Henry R. Worthington, Alexander Lyman Holley, and John Edson Sweet, and other prominent industrialists and technical innovators to form the American Society of Mechanical Engineers in 1880.
ORIGINAL BOILER CODEThe ASME boiler code was originally adopted in 1914. Manual and conveyor feed systems were common. Heat input rate was basically unregulated.
Minimum relief valve sizing and maximum heating capacity were based on the capacity of the boiler to absorb heat (surface area).
MODERN BOILERSModern boiler input rates are regulated by nozzles, orifices, pumps, regulators and servo actuated controls. Maximum input rates can be controlled within a few percentage points.
This led to publication of ASME Code Case 2583 in 2008 and a Code revision in 2015 removing the requirement to use surface area to size relief valves.
LOGICAL NEXT STEP?
• I proposed removing surface area from the nameplate since surface area was no longer used to determine relieving capacity.
• Inspectors opposed the proposal because surface area is still used to determine applicable requirements by jurisdictional authorities.
• Proposal was dropped.
OTHERS?
MODERN SOLID FUEL BOILERS• Wood Fired• Coal Fired• Biomass
NBIC Part 1, Supplement 4 Installation of Biomass (Wood/Solid Fuel) Fired BoilersIndicates that the owner-user should try to vary the type of fuel as little as possible once the boiler has been set up so the energy input is controlled.
Modern solid fuel firing systems provide various metering methods that control energy input similar to liquid or gas fueled boilers. Such controls include PLC controls (Programmable Logic Controller) to regulate fuel and air input for controlled and balanced combustion.
CAPACITY DETERMINATION FOR SOLID FUEL
Manufacture's ratingOR
HG-512 SAFETY AND SAFETY RELIEF VALVE ACCUMULATION TESTSIf the safety valve or safety relief valve capacity cannot be computed or if it is desirable to prove the computations, it may be checked in any one of the following ways and, if found insufficient, additional capacity shall be provided(a) by making an accumulation test, that is, by shutting off all discharge outlets from the boiler and forcing the fires to the maximum, the safety valve equipment shall be sufficient to prevent an excess pressure beyond that specified in HG-400.1(f) and HG-400.2(f).(b) by measuring the maximum amount of fuel that can be burned, and computing the corresponding evaporative capacity upon the basis the heating
ORA-100 GUIDE FOR ESTIMATING PRESSURE RELIEF VALVE CAPACITY BASED ON HEATING SURFACE
DIFFERENCES IN HEAT EXCHANGER DESIGNS
• Type of heat exchanger as well as other design features such as efficiency and resistance to fouling affect the amount of surface area relative to the rated boiler output.
• Among one manufacturer’s water boilers there is a boiler with 2.2 times more surface area per Btu/hr input than the unit with the least surface area per Btu/hr input. Different manufacturers have over 3 times the surface area per Btu/hr input.
• Comparisons did not include cast iron, cast aluminum, scotch marine, steam or oil boilers; so there could be even more disparity in the surface area and rated boiler input.
29 million Btu/hr(858 BHP)
1,500 sq.ft.Unattended
29 million Btu/hr(858 BHP)
5,000 sq.ft.Continuous supervision
PICKING WINNERS AND LOSERS
• Building design will stipulate the required total boiler input or output.• Jurisdictional rules for boiler plant supervision or frequency of
inspections based on surface area are biased to certain boiler designs that have lower area per Btu/hr input.
• Costs associated with supervision and inspection can dictate the choice of boilers.
• Similarly, selection of boilers can be used to circumvent inspection or supervision requirements.
RECOMMENDATION- A STARTING POINTRevise jurisdictional rules:• Eliminate surface area based thresholds and requirements.• Use total rated boiler input to classify installations.• Use minimum relieving capacity for classification of solid fuel boilers.
Proposed conversion (square feet to new metrics):• Multiply existing square feet limits by 8,000 Btu/hr-sq.ft., or• Multiply existing square feet limits by 0.2 BHP/sq.ft.This should provide similar classification for installations.
Equivalency based on New Jersey boiler code clause 12:90-3.3 “Equipment requiring a licensed operator”.“A steam or hot water heating plant with an indicated or rated capacity that exceeds either 499 square feet of heating surface or 100 boiler horsepower or 1,000 kilowatts or 4,000,000 BTU input regardless of pressure or temperature conditions, and only when the building or building being served is deemed occupied;”
29 million Btu/hr(858 BHP)
Unattended
29 million Btu/hr(858 BHP)
Continuous supervision
New classification based on conversion from surface area to
Btu/hr input (8,000 Btu/hr-sq.ft.)
BENEFITS
• Better aligns requirements with energy input rather than what may be seen as arbitrary dimensional limits.
• Reduces potential surprises for end users.• Surface area is not typically part of specifications or trade literature.• Designers and owners may not know what inspection or supervision
requirements until equipment is installed.
DISCUSSION
• What have I failed to consider?• Risks?• Research needed?• Problems making it happen?
