Explosion in Boiler

Dear Rajant-2001,

What is the burner manufacturer of this boiler? What type of burner programmer is installed? Please take a look and observe the ambient temprature of the panel where the burner programmer is installed. The programmer might have malfunction. you need to understand the combustion cycle of the burner in a boiler equipment.

What is the Boiler turn-down? Is this boiler is equiped with full modulation controls?

please let me know or email me jojie_oak@yahoo.com

regards

Dear Mr. jojie oak,

There is no oil or gas burners in this Boiler. Initial firing is only by manual torching.

There is no specific Burner control system.

Boiler was operating on 50% load and turn down was much less.

Regards

rajant_2001

Mr Rajant,

If Manual Torching is the method, then am sure pre-furging was not initiated. This boiler will cut-off on its high limit pressure setting. the boiler then will start if the pressure reach to its lower limit setting and the manual torching will start. However, pre-purging should be done first by starting the blower to remove the unburned gasses in the combustion furnace. sometimes this will take upto to 35 seconds before firing or start the torching.

Back firing occurs because the pre-furging process was not initiated and the manual torching occurs.

I think thats the answer of your question.

regards

Installation of pressure releif valve.

I believed this boiler is a water tube type. There is no pressure relief valve on the furnace side of the boiler, hot gasses is free flowing up to the chimney.... Explosion occurs only on the furnace side (combustion area).

I have done some inspection of the boiler with the same same problem.

Sorry to hear about your explosion. I hope no one was injured. You said that the fuel was excessive but that the unit was at low turn down. Explosion could have been caused by pyrolysis gasses building up in the fire box and assisted by water vapor.

"Boiler parameters 45 tons/hour; 65 kg/cm2; 490 c"

"Fuel - eucalyptus bark".

Obviously, this is a solid fuel type of boiler, eucalyptus bark is only one of the many kinds of solid fuel that can be used to operate this boiler. You also added that there is no secondary burner used for this boiler so that no combustible gas or fuel is present.

The explosion could mainly be caused by a low water level due to a malfunction of a pump or a level gauge or sensor. When a boiler runs out of water and the operator or the controls opens the water valve immediately, there will be a sudden vaporization of a lot of water to steam, like quenching a red hot iron and a rapid build up of pressure in the tubes, as well as excessive stress in the metals that could cause its failure and rupture.

The operating pressure of 65 kg/cm² is also very high for this kind of boiler, an equivalent approx 65 bars or 975 psi, wow!

I agree about the sudden opening of the water valve.

It looks quite possible.

Are there the graphs of the levels? DCS should keep recordings of the last 24h (at least).

Regards,

Abel

In my opinion, the method of firing the manuel fuel is to blame- the fact that excess O2 was present was just an explosion waiting to happen WHEN EXCESS FUEL WAS LOADED & FIRED!.

"In my opinion, the method of firing the manuel fuel is to blame- the fact that excess O2 was present was just an explosion waiting to happen WHEN EXCESS FUEL WAS LOADED &I FIRED!."

Sorry, I do not agree! Which fuel? as mentioned, this is a solid fuel boiler, there can be no explosive nature in an excess of wood or any solid fuel. If you pack the furnace or the stoker, real full with wood, you might even have reduced the heat generated. The excess O₂ is just the result of excess air. The heating control in a solid fuel boiler is basically a diversion of the hot air or gas towards the atmosphere (chimney) by means of a diverting flap to bypass the heating chamber. In some installation, a secondary air blower is activated to provide some cooling air to the tube bundle.

Rajant,

What is the latest investigation of the boiler after explosion? in mechanical side, how is the condition of the tubes and the drums? Is there any ruptures on the tubes & drums?

==== Jojie

Findindings.

Lower portion - waterwall caved in and slightly above waterwall bent outside.

bottom header lifted by about 25mm

One waterwall tube opend inwardly & another opened outwardly (on the refractory side)

It was also noted that Boiler was operating without the seal plates (seal plates removed)

I agree with jojiie, examine your tubes carefully to determine if any ruptured outward. This will help you determine if the explosion was caused on the fire side or the water side of the tubes.

Also what was the moisture content of your bark? What is normal for your boiler?

I'd be examining your bark supply. I suspect it may containthe wrong eucalyptus variety. Some burn very hot, realeasing Oxygen. This burns out the tubes. if your in Oz I'd suspect you had wattle mixed in. Also some eucalypts produce large quantities of oil vapour, elongating the high heat flame containing Dissociated hydrogen into the flame tube area, again burning the metal out of the tubes. I presume its a flame tube boiler as water tube tend to blow single tubes, reducing the speed of the depressurisation and therefore damage. either way a change in the thickness under heat will wreck the tube. Check for water damage and blockages given the pressure you are running???? I can't quite get those numbers to read right on the steam tables??

Fire tube boiler? A simple view of a fire tube boiler.

In a fire-tube boiler, the entire tank is under pressure, so if the tank bursts it creates a major explosion.

In a solid fuel boiler, whether fire tube or water tube, once the furnace is fired or fuel is already burning, the flames are always there and very seldom are put out or extinguished, unless you stop or shutdown the boiler. Since the boiler described by Mr. Rajant is manually torched and there is no internal burner, an explosion would likely occur from within the water side, which is is an excessive steam pressure buildup beyond the safety design of the tubes.

Historical records in boiler accidents shows that the main cause of explosion is that when the boiler runs out of water and the operator unknowingly opens a valve or runs a secondary pump or the controls automatically opens the water, and boom! the
boiler explodes. Likewise, even if no water is pumped in, because of the heat continuously applied to the tubes, these get deformed and stressed out which results in failure and its rupture.

"One 45 tons/hr spreader stoker fired boiler had an explosion with a loud noise causing furnace water wall damage."

Does this news describe the same incident? or just similar to your Post?

"One person died and about 30 were injured when a boiler of the Riddhi-Siddhi Gluco-Biols Ltd in Gokak exploded on Friday night. The condition of about 20 of the injured — with 80% burns — is reported to be critical. Some 40 workers were inside the factory when the disaster occurred. The impact of the blast was so great that the roof of the factory blew off and fell 100 metres away. Everything in a 100-metre radius of the factory was destroyed. Eyewitnesses said they heard a loud explosion at the factory and, some time later, saw factory employees carrying out colleagues who had suffered burns. Police officials at the factory site said they could not see any bodies in the debris as it was pitch dark. The extent of casualties would be known on Saturday morning. Fire fighters had controlled the fire by midnight. Rescue operations were on. The injured are being treated at hospitals in Gokak. The critically injured were shifted to Belgaum, sources said. Four fire engines were rushed to the spot, B G Chengappa, joint director of Karnataka Fire and Emergency Services, informed TOI in Bangalore. The fire force received the call at 8.58 pm. The company manufactures starch and glucose. Besides Gokak, 60 km from Belgaum, the company has a plant at Viramgam, Gujarat."

Gentlemen,

This issue brings us the awareness of Direct-Fired Pressure Vessel. Safety requirements will always pravail to avoid explosion such as this incident. We always argue and discuss details of safety devices. However, Most operators/owners are sometimes reluctant to consider the future effect of disaster such this.

I recon a friend told me, one Japanese consultant doing the supervision of equipment assembly. The technicians is quite expert as we can say. The technicians no longer seing the procedure of assembly as he is expert in doing the work.

However, the Japanese Consultant insist that he has to follow the written procedure to avoid mistakes. The japanese comment, The vital mistakes always relies on human error.

I do agree on his principle. A log sheet for monitoring is the output of the data that can be verified and conclude where the root of the problem. Only expert can sit on the table and analyse the cause, and possible solutions.

Many thanks for this issue that have brought on this forum. Its quite satisfying to have the discussion based on our experience.

I have been observed many incident like this here in KSA as this is our part of company business services.

Tell next forum issues will meet again....

regards === Jojie

The reason for furnace explsion is due to accumulation of volatiles released from the excessive fuel.

Positive furnace pressure is an indication of inadequte draft maintained. Continuous feeding of fuel (Wood ) does not allow full combustion of fuel. This conditionleads to generation CO and when the gas gets ignited it results into an explosion.

To avoid this kind of situation the following is required:

1. Automatic furnace excessive pressure alarm and trip arrangement.

2. If excessive persists beyond permissible duration feeding should stop automatically.

3. By monitoring flue composition correctly necessary alarms can be initaied.

More details can be discussed once you provide your details.

Our contact details:

P.Rajendran

Megaserve Energy Systems Pvt Ltd.

Cell: +919848018460

Tel:+914023736834

Email: megaserve@vsnl.net

In my opinion, I will link the explosion/birst to the following.

1. The quality of the Boiler Tubes.

2. Localised over heating and high skin temp. of the tube and when the temp. of metal increases, the hoop stress of the tube will fall and cause bursting/explosion.

3. The positive pressure in the furnace should have been released for which the general procedure/method is to provide "explosion doors" and this door will not be bolted/hinged. The door rests on a support at the frame of door having 5 to 8 slope.

For this slope under normal pressure of furnace stay intact. When the excess pressure develops in the furnace, it will push the door outside from its position and release the excess furnace pressure by which the product of combustion will be spewed and drastically bring down the combustion of fuel as well as the furnace temp.

Whether the explosion door was in the original drawing is installed or not is to be checked.

DHAYANANDHAN.S