3 replies to this topic

[DAIALOS]

Hi

I have been having some situations with one of our boilers in our plant. The boiler is a Water Tube boiler of 600 psi; we currently use a mixture of petroleum + methane (biogas) as our fuel.

The problem is that when we are trying to start it up and we in some way stabilize the boiler around 600 psi, then it suddenly increases the furnace pressure in a matter of some seconds and then it shut downs due to safety controls because of excess pressure inside the furnace. It looks like in some way it does some kind of uncontrolled combustion of accumulated fuel which results in this suddenly increase of pressure in the furnace or at least that’s one of my theories of possible reasons.

We use 50 psi vapor to atomize the petroleum. What kind of factors could create this kind of effect inside a boiler furnace? Could it be a problem with condensation in the vapor system atomizing the petroleum? Or maybe some accumulation of fuel inside the furnace that instantly ignites creating this kind of explosion?

The combustion gases are also used to heat the vapors on superheater. Could it be some kind of obstruction of the flue gases? Maybe if this were true then some gradually increase in pressure would be the effect, but we are seeing a big increase in pressure in a matters of 1 or 2 seconds like if it were some kind of explosion.

Thanks in advance. Any other important information or data can be given if needed.

Edited by Art Montemayor, 07 December 2012 - 01:00 PM.

[rychurek]

Hi
Drawings for investigation will be helpfull.
As you mention furnance pressure goes up when boiler system reach 600 psi pressure. Maybe there is leakage in biler system acting like PSV. Did you notice rush pressure fluctuaction when its occur?

[DAIALOS]

The problem is that when it is stabilized at 600 psi and running "normally" some minutes after reaching 600 psi then it suddenly shut down because of a increase in furnace pressure almost instanly. is not even a gradual increase in pressure.

[Art Montemayor]

DAIALOS:

I presume you are the same young Puerto Rican ChE student we helped some time ago and you are now a practicing engineer. Welcome back. Now, I address your specific problem:

DO NOT - I REPEAT - DO NOT PROCEED TO TRY TO ESTABLISH FURTHER NORMAL FIRING OPERATION WITH THIS BOILER.

This is, in my experience, the best advice and recommendations I can give you for now based on the basic data and background you have furnished. We would need more specific and detailed information to further comments, such as:

• Are both boilers 100% identical in all aspects? If so, is the same incident appearing in the other boiler?
• How old are the boilers and how long have you operated with the affected boiler – assuming that its normal operating pressure is 600 psig?
• Has this affected boiler operated before under the same fuel and startup conditions? If so, for how long, and when did the reported startup failures begin to appear?
• If the affected boiler recently start to exhibit this failure (and it has been operating and starting up normally in the past), was it subjected to any maintenance, modifications, or repairs (especially in its burners and combustion control instrumentation) prior to this startup incident?
• How are you burning the two fuels? Do you have two independent burners – one for fuel oil and the other for biogas? How do you feed and control the combustion air if you have two independent burners? Do you have forced combustion air feed? Is there any additonal blowers employed in the boiler – such as an auxiliary induced flow flue gas blower prior to the flue stack?
• How was the boiler purchased? Was it a “Packaged steam generation design and supply”? In other words, did the same supplier furnish and take the responsibility for the dual fuel combustion, the equipment design and supply, the installation and initial startup, and the performance tests on site?

Now I offer my experience in attacking the problem based on what you have described:

• After establishing what I note above, immediately get in contact with the responsible supplier(s) of the combustion burners and all the combustion controls. Ideally (and logically) this should be ONE supplier. Immediately inform them of what is happening - IN DOCUMENTED WRITING. Normally, today, I would do this with an immediate email, followed up with a hard-copy, documented letter on company letter-head. Do this as soon as you read this post. Be sure to explain in detail what you have experienced and your concern as well as your request for help in resolving this very important and DANGEROUS situation.
• I strongly suspect that what is occurring may be due to a variety of reasons – all of which are definitely NOT SAFE and very hazardous to your facilities, your personnel and yourself included. A sudden combustion chamber pressure increase as you have described is not to be taken lightly and constitutes what may be an accumulation of volatile fuel in the chamber and spontaneously combusting without any warning or controls. This is a probability of gaseous fuel post-ignition or, in some instances, a post-ignition of liquid fuel that has inadvertently been dumped into the combustion chamber for one reason or another. If you have diligently studied and mastered the startup and shutdown procedures of your boilers, you are aware that two of the most important safety procedures employed BY LOCAL CODES are the pre-purging of the combustion chamber and the post-purging of the combustion chamber. This, of course, is to eliminate the possibility of having fuel exist and ignite inside the chamber without it being controlled or accounted for. This situation, in the past, has been the cause of many countless boiler explosions and human fatalities – and it has had nothing to do with the relative high steam pressures generated. It has very thing to do with logical, code-regulated, safe combustion controls on every boiler.

I strongly urge you to consider what I have advised and to take a quick, effective and pro-active role in ensuring that your operations are not endangered by what is perceived to be a potential and dangerous hazard. Concentrate on the application of proper, specified and code-regulated startup and shutdown procedures on your boiler(s) as well as confirming that your combustion controls are not only in proper operating condition, but are operating as they were designed and intended to operate. You should take direct accountability for ensuring the first of these functions. The second function – related to the boiler controls – is one that can only be addressed and confirmed by the original designer and installer. If the original supplier is not available, then work with your manager or upper management to establish an acceptable, recognized, and experienced expert to confirm the proper combustion controls and operation.

Above everything else, obtain a concurrence with your management that this is a very dangerous and hazardous situation that can’t be set aside until the actual reasons are discovered and resolved safely. The risks in continuing to try to overcome this obvious hazard locally and by yourself are far too dangerous and never recommendable.

I hope I have made my comments clear and direct and hope that they are of help and assistance in the immediate steps you must take as a professional and responsible engineer. Your management and personnel depend on your decisions and actions from this point on. It is important that you keep them informed and aware of the hazard(s) involved. You are going through a test of fire that often is not available to other young engineers. Your logic, hard dedication, and insistence on safety for your personnel will determine the outcome. I believe you are up to that challenge and will overcome it. Please let all of us know on this Forum if our members can be of help.