Originally Posted by joewang

In coal grinding plant,There's many analysers for Oxygen content and Carbon-Monoxide content at some places in the system, like bagfilter, grinding mill, coal bin.

I want to know the operating range of the Carbon-Monoxide, as well as the value for alarming.

Is there criteria or standards on this?

Joe Wang

The rule is you have to have 21 percent oxygen in an atmosphere to support life in a confined space.

Where are you getting carbon monoxide in a coal grinding plant?????????????????????????

Are you using a gasoline or diesel generator to power this plant???????????????????????

Please contact Mine Safety Appliances to obtain more information. ■

Leon is quite right to ask how you get CO in a coal grinding operation. CO used to be the product from a gasworks where the coal was distilled. Grinding is unlikely to reach the temperatures associated with coke ovens. I suspect methane detection would be more useful, far more so. However it is as well to consult your local Health and Safety authorities about the matter. Usually it takes them about 6 months of internal miscommunication before they reach a mis-conclusion and quote something that the average 14 year old knew already. Endress & Hauser can advise you faster and better, properly even.

But to the case in point: it reads that your plant has installed detectors and read neither the O & M nor the Commissioning manuals or now chooses to ignore them. If the books say 300ppm that is your legal reference. In case of disaster you then have the fallback. If you, guessing now, quote a higher figure then perhaps rich extinction plays a part. You cannot rely on rich extinction during start ups and shut downs. ■

Originally Posted by joewang

In coal grinding plant,There's many analysers for Oxygen content and Carbon-Monoxide content at some places in the system, like bagfilter, grinding mill, coal bin.

I want to know the operating range of the Carbon-Monoxide, as well as the value for alarming.

Is there criteria or standards on this?

Joe Wang

As you are using coal that is friable and quite gassy the problem is the need for fire suppression.

You have the three corners of the fire triangle which are fuel, air, and heat from decompostion

of the coal from storage and nearing the furnace.

In the United States we refer to the national fire underwriters for a problem like this as they have all the answers.

IF your country has no standard agency for fire regulation underwritting for fire suppression you are in a bit of a fix.

ANY chemistry professor can help you with this to provide you with the information you need to prove your case.

Short of spraying the coal with water as it travels from the stockpile to the bin and then into the grinding circuit

prior to firing you have no real options. ■

The generation of Carbon monoxide in coal milling is quite common - particularly with large ball mills. The concept of monitoring the CO concentrations is to establish the extent of incomplete combustion taking place in the process. At certain points in the process the level of up to 400 ppm can be normal - but this level should be diminishing as the PF passes through the system. IF the CO level is increasing or at high levels well after the mill then an ember has been generated and fire protection measures need to be activated. In my experience 400 ppm is the maximum concentration of CO that would be allowable at the exit of the mill. Any value approaching this level after the mill would be an alarm condition - and would indicate a continuing combustion event.

Naturally - I can only speak of Australian coal in local conditions here. I have heard of higher CO levels being generated in Lignite processing in Indonesia.

I hope this is of assistance.

Cheers,

Tony Vierboom. ■

Hi Joe,

As far as I know there are no specific levels of CO recommended as thresholds or maximum allowable concentrations. When we set up this type of monitoring we always use a differential measurement to provide any alarm condition. To clarify - we measure the CO concentration on the inlet of each vessel in the chain and then compare the CO concentration in the outlet. In this way we can identify any growth in the CO level and thus isolate the location of any smouldering material.

Differential Co measurement is done at vastly reduced levels to course measurement. If we have 50ppm on the inlet and 60ppm on the outlet then it almost always points to a combustion event inside the vessel. A number of measurements are taken and if the generation of CO continues then steps must be taken to investigate and alleviate the situation. This is a form of early warning fire detection and is well researched -- but not well identified in standards.

Cheers,

Tony. ■