The sooner, the better: measuring mercury in raw gas

11. June 2015

Stricter limits for mercury emissions?

The thresholds for mercury emissions are already as low as the μg spectrum. To be able to monitor even tighter restrictions, measuring devices need to be extremely sensitive, accurate, and reliable. The MERCEM300Z mercury measuring system monitors Hg emissions in flue gases with high reliability within the smallest measuring ranges.


These days, it is hard to believe that mercury  (Hg)  was  still  being  used  to cure illnesses  at  the  beginning  of  the  20th  century. Due to its deeply harmful properties, strict regulations regarding the use of this heavy metal  now  apply in a number of areas. In its liquid form, mercury evaporates at temperatures as low as room temperature.  Impossible to see  or  smell,  it  is  also  a  neurotoxin when inhaled  into  the  lungs.  As an exceptionally volatile substance, mercury can spread across large areas. Scientific institutes are currently taking measurements in Polar Regions to find maximum mercury values. As a result, UN climate policies are now demanding even stricter  requirements  to  keep  emissions  of this  toxic  substance  to  a  minimum.  In January 2013, a total of 140 countries signed up to the Minamata convention in Geneva, switzerland, pledging to limit the mining of mercury, cut the amount of mercury emissions, and monitor waste.

Monitoring of mercury emissions

Emission monitoring requirements  focus primarily on power plants, incineration plants, and cement kilns that burn fossil fuels or waste. Waste incineration plants, for instance, have to pay special attention to  items  like  batteries  that have not been disposed of correctly and other  electronic  devices  that  contain mercury.  Plant operators  are  adapting to these changes by employing better filter systems, improved gas cleaning systems, and even more accurate emission measurement devices  to  remain  below the  thresholds.  The US  government  already  drastically  cut  the  limit  for  mercury emissions back in 2012 in light of the health risks posed by the substance.  In  Europe,  the  limit  is  specified  by  IED 2010/75/Eu  and  is  still  a  little  higher than in the US. However, plant operators all over  the  world  should  already  start preparing themselves for lower measuring ranges. There are a number of products on the market that promise  users  accurate emissionmeasurements.  However, not all of these products are suited to meet the complex requirements.  All  statutory requirements are based on absolute emissions  values,  in  other  words,  the sum total of elemental mercury Hg0  and oxidized mercury Hg+. The amounts and ratios of these two mercury forms in the flue gas depend largely on the raw materials being incinerated, the additional fuels, the gas flow in the process, and the  purification  process  used  for  the flue  gas.  A  quick  and  reliable  mercury analyzer  that  can  monitor  both  forms of  mercury  is  therefore  crucial  to  the measurement process.



This is where the MERCEM300Z by SICK comes in.  The gas analyzer provides extremely reliable monitoring of mercury emissions  down to the lowest certified measuring range of 0 up to 10 μg/m3 . It is the only product on the market able to cover this measuring range;  in  fact,  the  range  is  almost five times lower than other Hg analyzers.  The MERCEM300Z combines thermal conversion at temperatures of around 1,000 °C with the fast measurement of trace or low Hg concentrations directly inside the heated converter. This enables it to supply reliable and continuous readings for actual flue gas concentrations. Continuous measurement directly in the hot converter combined with Zeeman atomic absorption spectroscopy (AAs) is patented and has been licensed exclusively for the MERCEM300Z from SICK. No chemical conversion, no particulate converter, and no gas cooling that may quickly distort the measurement result. Thanks to AAs technology, the measurement will not be affected by any other interfering components either. The certified maintenance interval of six months makes the MERCEM300Z truly unique.


In the US, cement and power plant operators are also very happy with the mercury analyzer by SICK. In the US, emission limits are not based on a daily average but instead look at a 30-day average. Another difference between the two regions is that the us has once again tightened its emission limits, posing an even greater challenge for gas analyzers. To get a clearer view of the situation, one simply has to look at the limits set there. The emission limits for a newly-constructed coal-based power plant are 30 times smaller than the current limit in Europe.



MERCEM300Z uses hot extractive measurement: the flue gas is extracted using a sampling probe and then transported to the analyzer via a sample gas inlet. Any of the analyzer’s com- ponents that come into contact with the sample gas (the probe, sample gas inlet, converter) are heated to above the dew point.

The sooner, the better: measuring mercury in raw gas

Reducing the level of mercury during the treatment process is a sure way of adhering to emission limits at the end of the process.  Improved measures  for  cleaning the raw gas enables plant operators to save additional costs and increase the safety of their systems. And this applies no matter what type of system is used.




In  comparison  to  emission  measurement, measuring mercury levels prior to the electric filter or prior to the scrubber requires a lot more effort due to the higher levels of dust and high concentrations of interfering components such as sulfur dioxide  or  hydrochloric  acid.  Nevertheless, the Hg value still has to be recorded at  levels  as  low  as  the  mg/Nm³  range. Measurement methods using an additional amalgamation step can be ruled out from the outset. This option would take too long to respond to Hg peaks. Thanks to Zeeman AAs technology, the MERCEM300Z is also ideally equipped to take measurements in raw gas. The gas analyzer enables measurements to be taken without any further settings, without any additional equipment, and without any complicated operations. The set-up is exactly the same as for emission measurement. The MERCEM300Z is consistently accurate, detecting even the smallest milligram of mercury. It also boasts fast response times so that operators can react quickly to fluctuating concentrations of mercury.


The majority of all flue gas cleaning units tend not to come with a cleaning stage designed especially for mercury. Injection of activated carbon prior to the electric filter or  precipitants  for  the  scrubber  remove mercury from the process gas. However, these  chemical  additives  are  expensive and are often cut out of the process just for safety reasons. operators are able to cut costs if they adjust the dosage according to current needs. The MERCEM300Z supplies reliable measured values for this purpose. If high levels of mercury collect over a longer period, this may lead to an excess of mercury in the flue gas scrubber and ultimately end up contaminating the entire system. In a worst case scenario, the entire facility may have to be brought to a stop. However, this can be avoided. If an accurate measurement process enables high  Hg  concentrations  to  be  detected in the raw gas, measures can be introduced to counteract them.




Umweltberater auf internationaler Ebene: Josef Waltisberg

The Swiss mechanical engineer Josef Waltisberg understands the cement industry and its measurement technology needs better than most. Employed as a project manager and selection consultant at an international cement company, the cement expert spent the past 30 years working all over the world. He was happy to talk to SICKinsight for an interview:





SICKinsight: Mr. Waltisberg, are there any special requirements when it comes to measuring harmful emissions for cement plants?

Josef Waltisberg: Of course there are! In power plants that use coal, the composition of harmful substances is always the same  up  to  a  certain  point,  regardless of the type of coal being burned. In cement plants, nearly all of the emissions (apart from nitrous oxides) are generated primarily by  the  raw  materials.  And the trace elements from a quarry in, say, Switzerland could  be  completely  different to those from a quarry in the us. As such, you have to really put your gas matrix under the microscope as it can influence  the  selected  measurement  principle in ways that you could never predict.

SICKinsight: Could you give us an example of what might happen?

Josef Waltisberg: You never know what traces are in the stones or admixtures. For example, we once found traces of iodine which was distorting our mercury measurements. Iodine is never really the first thing you think of when red smoke suddenly starts appearing from your stack. But this is what happened at a waste incineration plant near Zurich a little while ago.

SICKinsight: When  will  the  current  systems reach their limits?

Josef Waltisberg: Not long. This is an area that requires constant development. Take mercury for instance. At the moment, there are around five devices with QAL1 certification for mercury-based requirements in Europe. The European limit for the co-incineration of waste is currently 30 µg/m3 . However, the US is planning to cut its limit to below 10 µg/m3 . This will also affect Europe and ultimately means that measurement devices will also be subject to stricter requirements. The MERCEM300Z mercury gas analyzer from SICK already meets these requirements. Ten years ago I was telling  the audiences  at my talks that we needed a measuring device that could measure mercury at very high temperatures above 800 °C. And SICK has done it!



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