Re: Active Coal Handling
Dear Sir
In reveiwing your posted issue on Bulk Online regarding explosion hazards related to handling/storing coal I would like to invite you to visit www.fike.com or www.fike.es for details with regards to explosion protection options available to you. The ATEX-directives require the creation of an explosion protection document and identification of necessary explosion protection measures.
Fike is one of the leading manufacturers of explosion protection systems, offering more than 30 years of experience in handling such applications as you have described on the forum.
I would be happy to remain in contact with you and work with you towards a suitable solution and assist you where required. You may also want to consider visiting us at the upcoming Expoquimia (Barcelona November 14 till 18) where Fike will be organizing a major ATEX-conference. Details are available on our website.
Kind regards
Roger Bours
Fike Europe
roger.bours@fike.com ■
Process Control In Explosive Environments
Dear Sir,
We have, for over 85 years, been designing interlocking systems to control processes within hazardous areas. This includes areas subject to explosion and fire hazards. We have a range of ATEX compliant and zone rated interlocking products for the control of electrical, hydraulic and pneuatic power as well as for the control of access and movement of people, vehicles and equipment.
We have many years' experience in the design of process control systems that ensure effective risk management in aggressive environments and would be pleased to meet at your convenience, to discuss the issues that you face.
You can see some of our products and applications at www.castell.com
Regards.
David Milner
Managing Director ■
Coal.
Active coal handling .
le me see if I get the image clear , you have coal that somehow ha to be injected into a flue system , possibly to absorve some kind of organic compound, you will also use lime or limestone to dilute the coal and possibly to help out absorving suphur compounds.
you are designing a grinding station, a silo and a lock hoppper or using some kind od dosing device.
handlimg the coal in a pneumatic conveying system.
the flue system atmosphere is escentially co2 , and nitrogen with minor traces of oxigen.
you will inert your silos , you can convey with air, inert gas or flue gases , the coal will not ingnite in the conveying line , if you ere worried abouth that , do not be , it could ignite in the flue system or in the dust collector , if enough temperature , oxigen is available , and once it slows down and the mack speed reduces ,
I have conveyed hot 500 C pyroforic solids with oxigen enrriched gases., not a problem,
Be carefull if your active solid forms crusts, then during startup and shuttdown you can have a hazzardows situation , when there are no solids moving in the line and if your conveying gas has oxigen , your line can burn.
Only if you buildup a crust, do not run your gas with an empty line.
Regards
Marco ■
Re: Active Coal Handling
Although it is not completely clear from your post, it sounds as though the system would have a reduced oxygen concentration and may be safe. Do you know what the oxygen concentration design goal is? If oxygen concentration is kept below approximately 12% there is no possibility for fire or explosion.
In terms of an ignition source things are not so easy for coal. Coal can self heat, due to an exothermic chemical reaction, to the temperature for spontaneous ignition. You need to take steps to ensure that your coal is kept dry. If you are storing it in an enclosure such as a silo, you need to monitor for self heating activity and you need a way to disturb the bed of coal to interrupt that activity. This is usually done with a carbon monoxide detector and a series of thermocouples suspended down through the coal bed.
Disturbing the bed usually can be accomplished by dumping part of the contents.
Regards,
Bill Stevenson ■
Re: Active Coal Handling
I concurr.
but the termocouples are not a reliable warning system.
You can have runaway reaction before the termocouples notice , Coal in bulk form has high insulation properties.
Ignition sources can come from the lamps if dust is allowed to collect there , or by slow oxidation in a highly insulating environment . and core temperature buildup. even static electricity can ignite the dust .
You will find many references in the literature .
How large is your feed silo, can you keep it sealed and oxigen starved?
is your feed silo mass flow?
or funnel flow ?
you need to think on first in first out criteria when handling active coal. and if you want to have a possibility of recovering after incipient ignition.
Marco ■
Re: Active Coal Handling
I concur too, but carbon monoxide detectors are also not completely reliable as the probes get contaminated in a coal dust environment. While there is no 100% reliable solution, the use of both thermocouples and CO analyzers has proven to be effective and to the best of my knowledge there is no record of loss where both were employed to monitor for self heating.
Regards,
Bill ■
Active Coal Injection System
Mr. Flores and Mr. Stevenson,
thanks a lot for all the help and advices that you are providing
I will try to give a little bit more detailed explanation about the work we are involved in:
we work at an steel industry, and at this moment we are developing one project for an existing sinter plant. This kind of facility is an important source of dioxins; these compounds are formed during the sinter process and are dragged by the main flue gases to the atmosphere through the main stack. Before the stack there is a dust collecting system (in our case an ESP) but, since the dioxins are in a gaseous form, they can not be grabbed by the ESP.
According to the BAT (Best Available Technologies) for sinter plants and the experience that we know in other similar facilities, we are going to install an Active Coal Injection System. This consists on injecting active coal in the sinter flue gas ducts;a right combination of the macro and micro pores of the active coal makes this material very suitable for trapping the dioxins. Then, the active coal with the dioxins inside is dragged by the flue gas and can be retained in the ESP preventing the dioxins to be thrown to the atmosphere.
The injection system includes:
- main storage silos, one for active coal and one for limestone
- smaller dosing silos
- screw feeders
- pneumatic conveying (by using the suction pressure of the main blower of the sinter plant) from the dosing system to the injection point (in the main flue gas duct)
The size of the main silos is around 120 m^3, and our idea is to design it for mass flow
About safety measures, we are considering the following:
- Inertisation of the active coal silo with nitrogen (a continous flow of around 10 Nm3/h)
- Fluidisation of the active coal with nitrogen
- Injection of limestone together with the active coal in order to reduce the concentration of active coal in the dust picked up in the collecting dust system.
- Since we know that the active coal ignition temperature will be around 220ºC, we are going to measure the temperature in the injection point, shutting down the system if the temperature in that point is higher than 160ºC
- Besides, we will control too the inlet temperature to the ESP
- We will take samples of the dust inside the ESP, increasing the amount of limestone if the content of active coal in the sample is higher than 18%.
Anyway, there are still some points we are not completely sure about:
- As you are suggesting, the main point we are concerned about is the behaviour of the active coal inside the dust collecting system. We are using an ESP, so if some material builds up in the collecting plate and at the same time we got any spark, maybe we can have some troubles. Besides, in the hoppers of the ESP we will have a high volume of dust containing active coal with the corresponding risk of fire.
- Inside the storage silo, in other similar equipment we know that they tried to use termocouples to control the internal temperature but, as you have said, they found some problems because of the insulating power of the coal; anyway, maybe we can do as you suggest and use both systems (thermocouples and carbon monoxide detectors) to increase the safety. About disturbing the bed, I understand that mass flow should be mandatory, isn´t it?
- About keeping the coal dry inside the silo, we will use compressed air for unloading the trucks. We will use our own compressors (not the ones from the truck), do you think that is important to have a compressed air with a very low dew point (i.e. -20ºC)?
- About preventive actions, do you consider that these are enough or you would recommend something else? And would you consider necessary to install some other protections in case the explosion finally happen (venting systems, supressors,..)?
I hope I will not be boring you with too long posts like this, anyway, thanks a lot for your attention, and I will appreciate any kind of suggestion you can make
Regards ■
Active Coal.
Seems you are in the right trak.
Mas flow is not madatory but you need to make sure you move the whole mas of coal in the silo and the dust collector bins , the mass does not need to move at the same rate. you can use a bottomless bucket inside your silos to increase the flow near the walls and reduce it on the center, do not use inserts that close the center lane , you will (politacly acceptable word will be you might) create a collumn of packed material on top of the insert.
take your coal out of the collector bins as soon as possible, sooner if possible. be very carefull with your lime dosing to keep the coal diluted and not layered in the collector.
can you divide the collector plennum?
no need to use nitrogen but you must have surplus fron the oxigen plant.. no need to have ultra low dewpoint conveying air, but try not to unload under the rain. and look at your blower intake avoid intaking water.
look into the detail design of the dust collector bins , minor changes can make a big diffrence .
look into your piping, no stagnant points.
select a point for your pressure relief ( rupture panell) that is safe, you might have spaks comming out and falling to the floor , not only flames.
Keep us posted on your questions and progress.
Marco ■
Re: Active Coal Handling
Dear Pablonici,
I would like to know the size of your coal dust silos and the arrangement between silos and conveying system to furnace.
There may be a more reasonable way to protect your silos from falling apart during an explosion, however, I cannot help you with the protection for the converying system.
Regards,
Dieter M Blaufelder
Product Manager - Safety Products
HOERBIGER KT Asia Pte Ltd ■
Active Coal Injection
Dieter,
the storage silo for active coal will be designed for 120 m^3. It will be placed on top of a supporting structure. This silo will be gravity discharged through discharge valves to another two smaller dosing silos (cause we have to feed two sinter plants) of around 2 m^3 each. The silos discharge will be controlled by three weighing cells installed in each silo. Finally, in the ground floor there will be one screw feeder for each silo, feeded by gravity from the dosing silos.
This is for the active coal, and more or less the same for the limestone. So we will have two main storage silos, one for active coal and one for limestone and four dosing silos (two each). The material dosed by each couple of dosing silos (active coal-limestone) will be mixed in a mixing duct and pneumatically conveyed to the main flue gas duct by a suction pressure blower. The conveying distance will be around 200 metres.
I think this is, aproximately, the system that we´ll develop
Regards ■
Re: Active Coal Handling
Dear Pablonici,
I apologize for the delay in response. We had Hurricane Wilma pay us a visit and have been out of commission until today. Anyway, I concur with the comments of Marco Flores and would only like to add that the only type of sparks that you could generate inside the dust collector itself are brush discharges. It is not possible for brush type ESD (electrostatic discharge) to ignite pure dusts. Hybrid mixtures of dust with flammable vapors or fumes could be ignited by brush ESD, but not dusts.
It sounds to me like you are on the right track.
Regards,
Bill ■
Active Coal Injection System
Dear Bill,
I hope Wilma is not causing too much troubles over there;
by the other hand, that issue you are referring to is very important for us, since our ESP is the point where we are more concerned about, from the safety point of view, when designing our system.
Thank you all for your support, I will keep you informed of our progress and I will be much pleased to keep on learning with your experience.
Best regards ■
Re: Active Coal Handling
Dear Sirs,
Thorwesten Vent GmbH, active in the field of explosion protection, might be able to assist.
Please contact:
Thorwesten Vent GmbH
Daimlerring 39
59269 Beckum
Germany
Contact: Mr Vincent Grosskopf (Sales Manager)
Phone: +49 (0) 25 21 - 93 91 - 0
Fax: +49 (0) 25 21 - 93 91 - 33
E-mail: thorwesten.vent@thorwesten.com
Best regards,
Thorwesten Vent GmbH ■
Active Coal Injection
Dear Pablonici,
Thanks for your reply and the indication of the set- up. Do you have Kst values for the active coal dust and other pertinent data like grain size distribution and minimum ignition temperature?
Can you presume that the blend of coal and limestone will not be explodible any more?
The coal storage bins can definitely be protected against destruction in case of an explosion with our explosion relief valves. The structure is outside or inside an enclosed building?
The screw conveyor may also be protected with the same principle. Do you have vessel strength data?
The advantage of these explosion relief valves lies in the fact that they require virtually no maintenance and are "multi- event devices" (unlike bursting panles). A flame filter is also fitted which permits indoor use (ATEX approved).
Do you also have a (coal) dust collector built into the system? It also is worth protecting.
Still interested?
Regards - Dieter ■
Active coal handling
We are preparing a system for injecting active coal in a flue gas duct.
We know that handling active coal exists a risk of fire and/or explosion (depending on three factors: coal concentration, oxygen level and existence of ignition source).
The system that we are designing includes four areas:
Silo storage, pneumatic conveying of material, injection of the material in the flue gas and processing in ESP.
Some facilities similar to ours use nitrogen for inertisation during storage and for fluidisation of the active coal, and they control the temperature of every area in order not to reach the ignition temperature, besides, we are thinking of mixing tha active coal with another material (i.e. limestone) in order to reduce the concentration of active coal in the dust inside the ESP; but, on the other hand, we have contacted some active coal suppliers that consider that some of this measures are not needed.
Anybody with experience in the pneumatic handling of active coal can advice me regarding this safety issue? are there any other measures we should have to take into account in any of the four stages of our system?
Regards ■