There are certain common problems affecting industrial furnaces that need to be addressed as rapidly as is possible, since otherwise they can significantly impair the equipment’s operation.

So, in this article, we would like to talk you through some of these problems and how to resolve them.


Article content: 
1.- Burner ignition failure
2.- Flame detection failure
3.- Problems with the equipment’s safety limit switches
4.- Temperature uniformity problems
5.- Temperature control problems during the heating cycle
At Nutec Bickley we can assist you

1.- Burner ignition failure


To obtain a flame we need to have three things in place:

  • A spark
  • Fuel (natural gas, LP gas, diesel, etc.)
  • Air or oxygen

An additional factor that also influences this process is the way in which the above are combined.


How can a problem occur?

When one of the four factors mentioned above fails, problems can occur in burner ignition.

Spark

  • The ignition transformer is not generating the spark or the spark plug is not grounded properly.
  • Perhaps the transformer is grounded from the base, so the voltage no longer passes to the spark plug.
  • If the spark is generated by a pilot, the pilot may not be lighting due to lack of air, gas, spark, etc.

Fuel

  • Check that you have fuel because the gas supply may not be providing the proper flow or pressure.
  • Perhaps more gas than necessary is being delivered, preventing the burner from lighting (incorrect air/gas ratio).

Air

  • Check that there is sufficient air supply and that the correct air ratio is achieved, reaching a certain pressure and flow.


Means by which these above elements combine (status)

  • The burner block may be broken or have cracks.
  • One of the burner’s internal components might have suffered some damage.



2.- Flame detection failure


There are different types of flame detection; at Nutec Bickley we mainly use photocells and detector rods.

How can a problem occur?

Photocells

  • The photocell fails to detect the flame because the air/gas ratio is not correct, so the flame spreads or enters the burner, putting it out of range of the photocell.
  • The photocell is poorly located, due to checks not having been made to ensure it has been placed in the position indicated by the manufacturer, so again putting it out of range.
  • Failures occur in the photocell because the cable isn’t sending the correct signal, so the photocell becomes ‘blind’ due to being exposed to the flame for too long.

In processes of more than eight hours duration, the ideal plan is to use a self-checking photocell to avoid the above problems.

Detector rods

  • The rod is not in contact with the flame due to an incorrect air/gas ratio.
  • Poor rod location.
  • Because of its physical nature, as the rod is exposed to heat then after a certain period of time it weakens and ends up bending.
  • When bending, it touches a steel component and short-circuits, adversely affecting operation and leading to erroneous readings.

 


3.- Problems with the equipment’s safety limit switches


Failure to comply with the required safety measures exposes personnel to possible explosions.

Depending on the type of furnace, safety limits vary, but generally speaking are usually the following:

  • Gas: High and low gas pressure switch.

  • Liquid fuels (diesel): High pressure switch.

  • Air: Flow and low air pressure switch.

  • High temperature: Maximum temperature limit of the furnace (controller and thermocouple).

  • Recirculation furnaces: Recirculator low pressure switch.

  • Class A furnaces (with potential for explosions): Low pressure switch of the incinerator extractor.

  • Electrical safety elements: These depend on the combustion equipment manufacturer and the safety standard or guidelines of the country in question. The most common are the purge timer, the safety valve closing test switch, the watchdog switch (burner ignition time limit), among others.

In some special cases: Detection of the furnace’s internal pressure.

How can a problem occur?

You could have a problem with these devices when:

A.- They detect something: They detect low pressure or some other abnormal indicator, so they close the equipment down. Check which safety feature was activated, and analyze the cause of that failure.

Example: the furnace was turned off and the combustion air low pressure switch was activated.

In this case you have to check:

  • Turbo combustion fan: perhaps the rotor belt disengaged and stopped supplying air.
  • Air intake valve: perhaps it was closed, preventing the flow of gas.
  • Disconnection: perhaps the device has been electrically disconnected, preventing flow.

As a general rule, if a limit switch is activated, you have to check what triggered it to resolve the issue.

B.- Electrical shorts: Where these occur, we must check the relay that feeds these safety devices, etc.


4.- Temperature uniformity problems


This will depend on the type of furnace and combustion system you have installed.

How can a problem occur?

In low temperature furnaces there are three main reasons why uniformity problems can occur:

  • You do not have enough heat because the burner is not providing the necessary energy; it may not be calibrated correctly, etc.
  • You do not have the recirculating air flow necessary for temperature uniformity because the recirculator has vibration problems. An imbalance problem; grilles through which the air passes poorly balanced or elements blocking the hot air outlet.
  • There is air infiltration in the furnace due to a poorly sealed wall, damage to the thermal insulation through which heat escapes, or lack of a correct seal somewhere where cold air is entering.


These three elements must be checked and any fault repaired, so that you are able to confirm that:

  • The furnace provides the changes per minute for which it was designed.
  • That there are no air infiltrations.

 

5.- Temperature control problems during the heating cycle


The PID parameters in the PLC or installed temperature controller are not optimally calibrated.

There are equations to find the ideal PID in various tests, cycles, or different PID configurations.

To find out which one is suggested in order for you to get the best production results, consult our department.

6.- Internal pressure of the furnace


The internal pressure control helps to homogenize the temperature or temperature transfer to the product by controlling the damper, lengthening the residence time of the combustion gases inside the furnace.

Problems can occur if the pressure transmitter is not suitably calibrated or does not provide the proper parameters; this can occur when some physical element of the damper is damaged.

We recommend checking that the pressure transmitter is sending the correct signal and that there is no physical element generating an obstruction.

At Nutec Bickley we can assist you


We are experts in resolving all kinds of furnace and combustion system problems. Our service includes:

  • Support: This can be carried out face-to-face or remotely. We have expert staff covering various industries, equipment, brands and processes.

  • Tools: We have specialized instruments to review a wide range of problems.

  • Regulatory compliance: We work with world-class safety standards and in compliance with the NFPA 86 standard.

  • Reports: We provide reports with the diagnosis of your problem and our suggested solution.

  • Follow-up: We follow up on your case for any possible questions you may have.


At Nutec Bickley we are specialists in industrial furnaces and their diverse components. Contact our expert advisers so they can let you know about all the solutions that we have for you.

Author: Luis García, Service Manager

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