Report Provided to Client:

 

Site / Location: Confidential South Carolina

Equipment: Confidential Industrial Oven/Furnace exhausting to atmosphere (subject to NFPA 86)

 

Reference:

1. Job# XXX - Confidential

2. Installation # XXX - Confidential

 

Issue(s):

1. Intermittent MFT (master fuel trip) from newly installed (March / April shutdown of 2020) exhaust flow proving switch, Mfg. part #: FLT93B-AC00, Fluid Components International

 

Suspected Contributing Factors(s):

1. Eddy in flow stream created by the louvered BFV (butterfly valve), duct transition, & the proximity of the FSL (flow switch limit) to the fan.

2. Current location does not provide consideration to device manufacturer “Best Practices” for installation location of upstream (15D - 15 times diameter) & downstream (7.5D - 7.5 times diameter) straight-runs in perspective to pipe / duct diameter (supporting device manufacturer literature provided).

Note: The proposed re-location of the FSL cannot meet the exact prescribed upstream (15D) & downstream (7.5D) straight-runs due to restrictions in ducting length & considerations for accessibility (Place FSL at or above flow testing ports added 7/22/2020, Please refer to attached scanned P&ID for suggested placement).

 

Site Speculated Contributing Factor(s):

1. Moisture & product (fine Confidential type material) in air stream making contact with & building up on the FSL (Note: this would also present the possibility of the same vented to atmosphere… Which would also be an SCDHEC concern) and creating an MFT due to an inaccurate switch reading.

 

Question(s) Posed:

Q(s): Does flow during operation need to be proven &/or interlocked? NFPA code requirements?

A: Yes, flow does need to be proven during operation.

 Reference:

• NFPA 86,2019 code 8.6.1* Where a fan is essential for purge or safety ventilation of an oven or allied equipment, fan operation shall be proved and interlocked into the burner management system.

 

• NFPA 86,2019 code 8.6.1.1 Electrical interlocks and flow switches shall be arranged in the safety control circuit so that loss of ventilation or airflow shuts down the heating system of the affected section, or, if necessary, loss of ventilation shall shut down the entire heating system as well as the conveyor.

 

• NFPA 86,2019 code 6.2.2.1 The fuel-burning system design shall provide a supply of clean combustion air delivered in amounts prescribed by the furnace designer or burner manufacturer across the full range of burner operation.

 

• NFPA 86,2019 code 6.2.2.4* Where primary or secondary combustion air is provided mechanically, combustion airflow or pressure shall be proven and interlocked with the safety shutoff valves so that fuel gas cannot be admitted prior to establishment of combustion air and so that the gas is shut off in the event of combustion air failure. (See 8.5.1.2 and 8.7.4.)

 

• NFPA 86,2019 code 7.3.6 Operating procedures shall be directly applicable to the equipment involved and shall be consistent with safety requirements and the manufacturer's recommendations.

​

• NFPA 86,2019 code 8.7.4* Combustion air minimum pressure or flow shall be interlocked into the burner management system by any of the following methods:

  1. A low pressure switch that senses and monitors the combustion air source pressure

  2. (2) A differential pressure switch that senses the differential pressure across a fixed orifice in the combustion air system

  3. (3) An airflow switch

 

Note: By manufacturer burner design the Confidential # blower provides the primary source of combustion air (Please refer to attached literature).

 

Recommendation(s):

• Re-locate the FSL device to a new location considering manufacturers “Best Practices” for upstream & downstream straight-runs and apply judgement / testing for the best location given the application constraints (Current & proposed locations noted on attached scanned P&ID).

Reference:

• NFPA 86,2019 code 8.2.3* Safety devices shall be applied and installed in accordance with this standard and the manufacturer's instructions.

 

• Employ the FSL device to be interlocked within the safety limits and prove flow both during purge and throughout operation.

 

 

History of events leading to current discussion:

 

The FSL was recommended to be installed during the 2020 upgrade to meet NFPA 86, 2019 code 8.6.1* Where a fan is essential for purge or safety ventilation of an oven or allied equipment, fan operation shall be proved and interlocked into the burner management system. The recommendation was made in understanding the design of the system in which the Confidential # blower is the air flow device which is required for system purge due to its higher volume capability in comparison to the Confidential blower – Confidential # (Please refer to NFPA 86, 2019 code 8.5.1 Preignition (Prepurge, Purging Cycle).

 

The use of the FSL for operational flow proving was not the original intended use, it was decided during start up that it would also be used to satisfy NFPA 86, 2019 code 8.6 Ventilation Safety Devices and was wired to be in the safety limit circuit continuously. When the FSL switch intermittently failed and shut down the Confidential Equipment several times, a more reliable solutions needed to be found. A discussion was had with Confidential E&I Programmers which led to deciding to monitor the FSL only during purge with a failure delay of 5 seconds (NFPA 86, 2019 code 8.2.7.2) and to monitor operational flow with another DP device which would prove system flow and be interlocked within BMS. DPI Confidential # (which is the DP transmitter across the scrubber) was already in the PLC and could be adapted fairly easily / quickly and was already being used to prove flow for SCDHEC requirements.

 

In further exploring the process and the use of the DP transmitter across the scrubber as the operational exhaust flow limit, our analysis has revealed:

 

• A concern of a screen which had a potential for clogging (speculation info from site) – after looking closer at the system onsite - a screen does not exist on the scrubber, but is in fact a mesh material used internally at the Demister which is downstream of the scrubber (Please refer to attached P&ID’s). If clogged at the Demister the Scrubber DP would be driven low until it reached 11”WC (or the trip setpoint) and a MFT would occur. This would be an acceptable application if the second / next concern did not exist. 

 

• Questionable reliability of the DPI Confidential # in regard to NFPA 86, 2019 8.6.1.4, "Switches used to prove airflow on systems where the air is contaminated with any substance that might condense or otherwise create a deposit shall be selected and installed to prevent interference with the performance of the switch." There is a concern of contamination from water scale &/or product – other, which can create a false high DP reading depending on the port (+ or -) that would become “clogged”. The existing DP device / application has the potential for contaminants to create a false DP and is not an acceptable manner to prove flow through the system.

 

• Additionally, in my investigation, the presence of both water & product are present downstream of the Demister which will affect the operation of any device installed for flow proving. To what degree the effects will be noticed by operations and with what required maintenance intervals will need to be learned.

 

Ultimately, the re-location of the existing FSL will decrease its exposure to contaminates and increase its reliability due to the more laminar flow in the new position in the ductwork as recommended above.    

 

Considerations in re-locating the FSL:

 

 

1. Weld in place and provide a clearance hole for a 1.0” NPT threaded half coupling to be used in conjunction with a 1.0 to 0.75” NPT reducing bushing. (Note: This will ensure maximum insertion of the sensing end of the FSL and provide adequate clearance for the shaft diameter.)

2. The switch will need to be re-set / calibrated under operational conditions (Confidential to perform).

3. Follow manufacturer installation instructions (Please refer to attached literature).

4. Fluid Components International, Mfg. part #: FLT93B-AC00, FSL.

 

 

Please feel free to schedule a conference call to review and solidify so that the site may move forward with the FSL re-location.

​

Note

​

Research & Information provided:

​

• Field interviews & investigation

• Field pitot tube air flow test #1

• Field pitot tube air flow test #2

• NFPA 86 Code & Standard research

• Review & mark up of existing P&ID to illustrate locations discussed (Equipment, baghouse, scrubber)

• Device manufacturer research & provided supporting literature (Instructions, installation, best practices)

• Burner manufacturer research & original commissioning values

• A complete "walk through" video teleconference for clarification with all invested parties

​

​

Client Response:

​

"Hello Shawn,

​

Well done – very professional."  "Thank You!"

 

"We recently assembled a group of SIS engineers to serve as the Confidential Committee here in North America for BMS. Confidential is chairing. This document will be part of the team’s “precedent” library as a good interpretation of NFPA 86."

 

"The way I read your memo, you want me to incorporate this analysis in a communication to Confidential Engineer and set a date/time for a video conference to answer questions and to make sure everyone is on the same page." " Correct?"

 

"Have a good weekend."

 

"Confidential,"

​

​

Reply to Client:

​

Thank You very much Confidential!

 

Yes Sir, I believe that a conference will bring the discussion to a close so that the site and Confidential Engineer may make plans sooner than later to have the work completed.

 

Have a great weekend,

​

​