Differential pressure sensor on flammable gasses

Calistodwt said:

So the area where the orifice plate is installed is probably a hazardous area?
You have the following options:
1. Install an explosion proof transmitter.
2. Install an intrinsically safe transmitter and associated loop.
3. Install your transmitter in an air purged box. This will introduce further requirements to monitor the air purge and take appropriate action should the purge be compromised in some way. (these systems are generally a pain in the butt).
4. Don't install a transmitter.

The cost of a certified transmitter will generally be fairly expensive compared with the one you indicate.

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lfe said:

The electrical material for measurement and control in natural gas installations, such as transmitters, valves, pressure switches, flow counters, etc. does not need to be Ex-proof but the space where it is installed must be ventilated with openings to the outside of a minimum section that the standards indicate.

Just use a normal process differential pressure transmitter like a Siemens or a Rosemount 3051 and install it in a support near the orifice and use metallic tubing.

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cardosocea said:

The reason why it doesn't need to be Ex in your opinion is precisely because the place has to be ventilated enough where a leak would never achieve the minimum ignition mixture with air.
Is the standard for NG different than IEC600079?

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lfe said:

Areas with Natural Gas regulating, measuring and also combustion equipment in which I worked for many years are not considered areas with risk of explosion, therefore that IEC600079 norm is not applicable.

In fact, electric and electronic devices for use with GN that brands such as Kromschroeder or Eclipse sell are not Ex-Proof

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NetNathan said:

Usually there is a High Gas PS and Low Gas PS required.
We use a Dungs PS.
https://www.dungs.com/en/productgroups/pressure-switches-for-gas-and-air/

If the location has 5 changes per hour of the atmosphere, you do not need to go explosion proof.
Worked on MANY gas fired furnaces that wiring and components are not required to be explosion proof.

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This installation would not require explosion proof equipment. It is well-enough ventilated.

NetNathan said:

Usually there is a High Gas PS and Low Gas PS required.
We use a Dungs PS.
https://www.dungs.com/en/productgroups/pressure-switches-for-gas-and-air/

If the location has 5 changes per hour of the atmosphere, you do not need to go explosion proof.
Worked on MANY gas fired furnaces that wiring and components are not required to be explosion proof.

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The pressure switches for those functions are installed in the gas train and wired in the proper manner. The pressure sensors I was looking to add were to monitor flow rate.

While the pressure switches on this particular furnace are not Dungs, I have them on other equipment, and like them.

Brian123 said:

I was looking to monitor the flowrate in a natural gas supply line to a furnace. I was hoping to detect changes in total flow over time in an automated way. The furnace itself is under 1 million BTU/h input. If the sensors were reasonable in cost, I could expand the monitoring to each of the 8 burners individually.

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A. Measuring flow rate with DP has a couple downsides:

1. low turn down (1:4) due to flow being a square root function. Flow rate readings are noisy and inaccurate at low flow, where low flow is generally less than 25% full scale.

2. Volumetric flow only values only, because DP is not temperature compensated, not pressure compensated. You can only get inferred mass flow values when static pressure and temperature measurements are made simultaneously and mass flow is calculated in a PLC or flow computer (or a multivariable DP is used which measures the temperature and static pressure).

3. The inexpensive low DP transmitters designed for HVAC are spec'd for air only; they not designed for combustible gases.

B. Thermal dispersion
Thermal Dispersion does inferred mass flow out-of-the-box. Insertion or in-line models available. Generally excellent performance very good at low flows, in fact, you need to make sure that the high end of the flow rate is doable.

Neither technology is cheap. Any vendor is playing in the market where approvals and ratings are expected, so the products are industrial grade with approvals and ratings.

Monitoring all 8 burners is not likely affordable.

Some flow elements claim greater turndown than pitot tubes or orifice plates, like venturis or V-cones.