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Application of PentoMuls Emulsion Technology on boilers equipped with OFA, ESP, FGD and SCR

Modern boilers are equipped with a range of technologies to reduce emission.

OFA technology (over fire air) has been developed as a primary means of reducing NOx during combustion.

As a principle, the combustion on the burners is run with low oxygen, leading to lower temperatures at the burners and therefore a lower NOx formation, but with high CO and unburned carbon production.

To overcome CO emission, OFA is introduced after the furnace where additional air is introduced to oxidize the CO.

Unfortunately, this has led to an increase of dust emission and in many cases an overload of the ESP, a unburned carbon reduces fly ash resistivity leading to a short circuit in the ESP.

SCR technology reduces NOx emission by means of a catalyst typically consisting of titanium and vanadium-based elements.

Ammonium is fed to the flue gas stream ahead of this catalyst to react with NO and NO2 reducing it to N2.

This technology is used for more than 20 years and is considered „best available technology“.

No power station is able to reach emission levels of 200 mg/Nm³ or less without this technology.

The catalyst used however has one disadvantage: The oxidation of SO2 to SO3.

While the manufacturers of SCR catalyst elements show utmost care to limit SO2 oxidation to the minimum, measurements have shown that SO2 oxidation becomes more important with aging of catalyst elements.

Pentol offers SO3 measurements to it’s clients and observed increase of SO3 emission of up to 50 ppm.

In addition, with the ageing of the catalyst the ammonium consumption rises with danger of ammonium slip.

This is essentially dangerous in combination with high SO3 emission, as SO3 and NH3 react with each other and form ammonium bi sulfate (ABS), forming large, sticky deposits blocking the flue gas duct.

After the SCR, an electrostatic precipitator (ESP) is installed to capture dust particles.

A high voltage electrical field is applied over a large cross section to electrically charge the dust particles and capture them.

As mentioned above, this technology is limited with high UBC values.

As the electrical resistance in the flue gas becomes too low and the transformers are saturated before the electrical field is strong enough to attract all dust particles.

The SO3 formed on the SCR catalyst is condensing here at low temperatures causing corrosion and sticky layers of deposits on the collection plates.

As a final step, the gas is passing the FGD unit (flue gas desulfurization unit).

Introducing a limestone slurry in a washer system, the SO2 in the flue gas is converted to gypsum and effectively removed from the gas stream.

If the dust load due to an ineffective ESP is high, the gas/gas exchangers get plugged by fly ash particles, forcing the operator to bypass the FGD after short time (as observed in many boilers in Saudi Arabia).

Unfortunately, the FGD is unable to neutralize SO3 as well, whose yet uncondensed part is passing the FGD and leaving the chimney as a blueish white plume, that can extend over many kilometers.

Pentol has equipped many power plants equipped with above mentioned technologies with the PentoMuls Fuel Oil Treatment, as this technology addresses the main problem causing above mentioned problems at it’s core: excess oxygen.

Excess oxygen is the culprit not only for the above-mentioned problems, it is also reducing efficiency of the plant, as thermal energy is wasted to the atmosphere.

The effects of Pentol Fuel Oil Treatment is described in the respective brochure, the basics are not discussed in this memo.

During combustion of the emulsion, the oil spray is burning quicker and more complete while the flame core is cooler.

The reason for this effect is that the water of the emulsion evaporates in the furnace rapidly, virtually ripping apart the oil droplets.

As a consequence, the fuel burns quicker and more complete.

90% reduction of CO and 80% reduction of unturned carbon set the base to reduce excess air, having the same result as an OFA system, however with the advantage of clean combustion.

If OFA is already installed, we recommend continuing using it, however the distribution ratio of the air has to be set such that the burners have enough air not to create any CO.

The reduction of the flame core temperature is a first step of NOx reduction, as is the reduction of the excess air level.

In addition, the Pentol treatment eliminates vanadium deposits from the boiler walls reducing SO3 formation significantly.

As the gas enters the SCR, the SCR profits from the low amount of unburned carbon.

The total quantity of dust in the fly ash is reduced significantly, therefore the catalyst is not blinded by deposits, allowing a reduction of ammonium, reducing the threat of ABS formation.

The ESP profits from the lower amount of unburned carbon and it can effectively absorb the dust before it enters the FGD. Corrosion is eliminated by reducing SO3 to almost zero (this effect is described in detail in the Fuel Oil Treatment brochure).

Combining all the effects described above, the FGD can do its job to eliminate SO2 emission, leading to a clean stack without visible plume and a plant being able to run for an extended time with higher efficiency.

Pentol has equipped the first plant with SCR, ESP and FGD in 2003 and has since then gathered an enormous amount of knowledge in different countries.

As shown above, Pentol Emulsion Technology is essential for any boiler burning heavy fuel oil if SCR, ESP and FGD should be used efficiently.