Tar and dust content after electrostatic capture

Is it because the moisture content in our gas is high? A lot of water comes out from the connection pipe between the sampler and the flow meter. If the water content is high, will the filter membrane yield a lower reading for the tar content in the gas? I hope the expert can provide an answer

The temperature of the gas before electrostatic capture was high, and the tar content in the gas at the subsequent stages of the process was also high; however, the measurement using the filter membrane method showed a value of around 10, which is significantly distorted. It is likely that the sampling tube inserted into the gas pipeline was too thin. The national standard specifies an L-shaped tube with an inner diameter of 8 MM, whose opening faces in the direction of the gas flow. We had not used such sampling tubes on our gas pipelines before; instead, we connected a 5-mm straight tube to the base of the pressure gauge and inserted it into the gas pipeline, cutting an angled end at its top to face in the direction of the gas flow. The measurements obtained in this way were low. Could it be that the flow velocity of the gas inside the pipeline is high, and the sampling tube, lacking the guiding effect of an L-shaped design, being thin as well, results in a lower gas flow rate compared to that of the main pipeline? As a result, the tar mist cannot be properly collected

We take samples directly in front of the fan following electrostatic capture; the sampling tube can only be angled at the front end and cannot be made into an L-shaped tube. Our sampling tube is 7 mm in diameter. Before sampling, be sure to open the sampling tube to its maximum capacity and let it vent for some time to flush out as much debris as possible from inside the tube. If the moisture content in the gas is high, it will reduce the filtering efficiency of the glass fiber filter membrane, to the point where the gas stream cannot pass through. So high moisture content affects your sampling process, and it should not have an impact on the results. Also, the latex tube connecting to the sampler should be as short as possible, as latex tubes can absorb tar. The latex tube should have no kinks. The entire gas circuit must be airtight; there must be no leaks. The volume after sampling must be converted to a standard volume, as the standard volume varies significantly depending on the sampling temperature. The sampling flow rate should be well controlled, the sampling time should be made as long as possible, and whether there is a loss of focus during sampling also has an impact on the sampling process. It is best to use a riser as the main sampling pipeline; horizontal pipes should not be placed at the top, but rather on the sides.

So do you take the gas samples at the negative pressure section after electrostatic capture? I measured the gas temperature at a higher position in the horizontal pipe behind the fan, and it was 40 degrees. The flow meter is placed on the ground; there is a distance of three meters between the sampler and the flow meter. Over time, water accumulates in the connecting pipe in between. Could it be that the sampling tube I inserted into the gas pipeline is too short? According to the standards, we should insert it 40 centimeters into the pipe, but only 25 centimeters have been inserted. We’ll conduct another test using a longer length today. Our altitude is 1600 meters, and the atmospheric pressure is 0.8365 kPa. There is no pressure difference in the U-tube manometer connected to the flow meter with a capacity of 3.5–4 L; therefore, it’s not possible to convert this value to standard conditions. What should we do? Thank you

In the morning, the sampling time was increased, and a total of 1000 L was sampled, yielding a result of 49.2. At noon, the sampling tube was made longer and 800 L was sampled, giving a result of 29. It seems that the problem lies still in the sampling process; previously, with shorter sampling tubes, 500 L of sample gave a result of less than 10. So which step is causing the issue? It’s frustrating; I’ll increase the purging time after installing the sampling tube tomorrow to see what happens (if the purging time is short and the pipes aren’t clean, the readings should be high). Are your sampling tubes fixed directly to the gas pipes, or are they installed on-site each time a sample is taken? At the location where we install the pressure gauge, we have to remove it each time to insert the sampling tube; can such a slight difference in the orientation of the opening have such a big impact?

During the maintenance of coke ovens, when coke pushing and coal charging are not carried out, are the readings also low?

This post was last edited by happyzojn on 2015-8-27 at 13:39. Oops, the unit was wrong; the atmospheric pressure should be 836.5 kPa, which gives a standard volume of 198.15

The temperature is based solely on the flow meter’s temperature, and the calculation uses only the average temperature of the flow meter. Normally, the length of the pipeline behind the sampler has no impact. As for the temperature difference between the pipeline gas and the flow meter, it does not affect the flow meter’s ability to measure volume. You mentioned before that there was water left in the pipeline behind the sampler; this is caused by the temperature difference. The pipeline is longer, so the gas cools down within it, and when water condenses, it remains in the pipeline. It’s shorter; the gas doesn’t have time to cool down, so it remains in the gas. One more thing: your atmospheric pressure should be 83.65 kPa, right? Otherwise, you won’t be able to calculate the value of 198.15. :)

This post was last edited by happyzojn on 2015-8-29 at 18:37. Well, it’s 83.65 kPa. Have you tried using a spectrophotometer to determine the coal tar content separately? I’ll need to turn to you for help more often if I have any questions in the future

And why is it better to take samples from vertical pipes?