SO3 Mitigation - Dry/Wet Sorbent Injection
There are many Balance-Of-Plant (BOP) impacts from the presence of SO3 in the Flue Gas. These include:
Therefore it is sometimes necessary to capture and bound the SO3 in a form that mitigates its harmful effects and can be captured in the ESP or baghouse.
SO3 forms an acid in the flue gas and therefore in order to capture and bound it into harmless compounds, one needs to inject an Alkali into the gas stream. The typical Alkalis currently used for this process are Mg, Na and Ca based Alkali. These alkalis can be injected in a solution or Wet Slurry form or in the form of a dry powder.
Mg is typically injected in the form of Magnesium Oxide (MgO) in an Oil emulsion or as Magnesium Hydroxide (MgOH) in a water based slurry. It is typically injected in the upper furnace and provides a dual effect of minimizing slag formation in the Superheat Reheat sections as well as reducing SO3 at the economizer outlet. Typical injection rates can deliver about 50% reduction of furnace generated SO3, although higher rates can deliver more at reduced efficiencies. If there is an SCR in the gas stream, additional SO3 will be generated in the SCR, which the MgO will not mitigate. Therefore, this is a partial solution for SO3 mitigation and is highly applicable when the dual intent of slag mitigation is involved.
Breen Energy has formed a relationship with the chemical supplier, Lubrizol, and has developed a process to inject highly micronized MgO in an oil emulsion in the upper furnace for slag and SO3 control.
Na can be injected in a wet solution or as a dry material. Trona, a naturally occurring form of Sodium Carbonate / Sodium BiCarbonate, also known as Sodium Sesquicarbonate, is typically injected as a dry powder. Sodium has a tendency to form a highly viscous sticky condensable, Sodium Bisulfate (NabS), at temperatures between 500 and 350 DegF. Therefore typical applications for Sodium injection are below 350 DegF, which is after the Air Heater. Injection at higher temperatures requires much higher molar ratios and good mixing to prevent the formation of Sodium Bisulfate. Milling Trona can improve reaction efficiency as well as mixing. In the case of Hot-Side ESP, injecting the Trona at the Economizer outlet is very beneficial both for ESP performance and SO3 removal and is the ideal solution. There is no concern of NabS formation at that temperature.
Calcium is typically injected as Calcium Oxide (CaO)- Lime - in a Dry Hydrate form. The particle size and porosity of the hydrate has a large impact on capture efficiency and thus not all Hydrates are created the same. Lime is a very good alkali sorbent for injection at all temperatures however the efficiency of capture goes down at higher temperatures due to competition with the Lime-CO2 reaction. Lime may be injected at:
There are many Balance-Of-Plant (BOP) impacts from the presence of SO3 in the Flue Gas. These include:
- SCR Minimum Operating Temperature
- SCR/SNCR Performance
- Air Heater Fouling / Unit Heat Rate
- Back-End corrosion
- ESP Performance / Opacity
- Blue Plume / Visible Stack emissions
Therefore it is sometimes necessary to capture and bound the SO3 in a form that mitigates its harmful effects and can be captured in the ESP or baghouse.
SO3 forms an acid in the flue gas and therefore in order to capture and bound it into harmless compounds, one needs to inject an Alkali into the gas stream. The typical Alkalis currently used for this process are Mg, Na and Ca based Alkali. These alkalis can be injected in a solution or Wet Slurry form or in the form of a dry powder.
Mg is typically injected in the form of Magnesium Oxide (MgO) in an Oil emulsion or as Magnesium Hydroxide (MgOH) in a water based slurry. It is typically injected in the upper furnace and provides a dual effect of minimizing slag formation in the Superheat Reheat sections as well as reducing SO3 at the economizer outlet. Typical injection rates can deliver about 50% reduction of furnace generated SO3, although higher rates can deliver more at reduced efficiencies. If there is an SCR in the gas stream, additional SO3 will be generated in the SCR, which the MgO will not mitigate. Therefore, this is a partial solution for SO3 mitigation and is highly applicable when the dual intent of slag mitigation is involved.
Breen Energy has formed a relationship with the chemical supplier, Lubrizol, and has developed a process to inject highly micronized MgO in an oil emulsion in the upper furnace for slag and SO3 control.
Na can be injected in a wet solution or as a dry material. Trona, a naturally occurring form of Sodium Carbonate / Sodium BiCarbonate, also known as Sodium Sesquicarbonate, is typically injected as a dry powder. Sodium has a tendency to form a highly viscous sticky condensable, Sodium Bisulfate (NabS), at temperatures between 500 and 350 DegF. Therefore typical applications for Sodium injection are below 350 DegF, which is after the Air Heater. Injection at higher temperatures requires much higher molar ratios and good mixing to prevent the formation of Sodium Bisulfate. Milling Trona can improve reaction efficiency as well as mixing. In the case of Hot-Side ESP, injecting the Trona at the Economizer outlet is very beneficial both for ESP performance and SO3 removal and is the ideal solution. There is no concern of NabS formation at that temperature.
Calcium is typically injected as Calcium Oxide (CaO)- Lime - in a Dry Hydrate form. The particle size and porosity of the hydrate has a large impact on capture efficiency and thus not all Hydrates are created the same. Lime is a very good alkali sorbent for injection at all temperatures however the efficiency of capture goes down at higher temperatures due to competition with the Lime-CO2 reaction. Lime may be injected at:
- Econ Outlet - SCR inlet for SCR MOT and efficiency effects
- SCR Outlet - AH inlet for AH Fouling Mitigation and backend corrosion
- AH Outlet - ESP Inlet for ESP Performance, Opacity, Blue Plume and corrosion
- ESP Outlet for Blue Plume