Acid gas purification by dry method: HCL, HF and SO2 control
The flue gas desulfuration (FGD) processes responsible for processing acidic compounds are generally based on absorption by alkaline substances of lime.
Dry scrubbing is the alternative to wet scrubbing for the control of acidic gases such as SO2, HCl and HF, which are mainly found in the combustion gases of the boilers of thermoelectric power plants and kilns.
Dry purification consists of the dispersion of an alkaline reagent based on bicarbonate or hydrated lime (depending on the composition of acid gases to be treated), which are injected into the gas stream before the bag filter. The final neutralisation reaction concludes in the bag filters impregnated with the reagent.
The main advantages of the dry route compared to the wet route are:
- Lower CAPEX, due to cheaper construction materials and more compact equipment.
- Minor water and electricity OPEX.
- Dry waste products.
- Application in smaller units.
- Operational simplicity.
- Less time to complete assembly and commissioning.
The temperature of the gases leaving the combustion unit must be kept high to avoid corrosion phenomena due to the condensation of acidic gases.
Our neutralisation system
Our gas treatment systems are capable of removing polluting acids such as sulfur dioxide (SO2), sulfur trioxide (SO3), hydrogen chloride (HCl) and hydrogen fluoride (HF), at an efficiency of greater than 92%.
Regulations against these pollutants are increasingly restrictive and in the sights of governments and public administrations, especially in thermal waste incineration plants, steel mills, for biomass, pulp and paper and cement plants, among others.
At GORCO we carry out an exhaustive study of each case, carefully analysing the gas stream to be treated and the layout of the main plant equipment to find the best possible on-line integration, while understanding the technical and financial needs of the customer.
The main pieces of equipment in our dry treatment systems are:
- Reagent silo with a dosing system based on the continuous measurement of pollutants in the flue.
- Pneumatic reagent transport, injected and dispersed in the gas stream before the bag filter.
- Vertical mixing reactor (optional).
- Off-line bag filter.
- Filter residue collection and silos for storage.
- Reagent recirculation (optional)
– Main fan
Depending on the project or facility under study, we mainly handle 3 types of reagent injection systems:
a) Direct injection into dirty air duct
The reagent mixture injected into the acidic gas stream must be as homogeneous as possible with a minimum reaction time.
A mixing reactor is not needed if the pipeline length between the kiln/boiler and the bag filter is sufficient for a reagent residence time of 1-3 seconds.
The reagent is injected and dispersed by a system of jets directly inside the dirty air duct connected to the bag filter.
b) Reaction tower
Some systems or projects do not have a sufficient distance between the boiler and the filter. In these cases, it is recommended to install a vertical reaction tower to guarantee a homogeneous mixture of the product. This reactor has two effects: firstly, it produces turbulence in the gas stream, which promotes mixing and, secondly, it increases the contact time with the reagents before reaching the bag filter.
c) Reaction tower and reagent recirculation
This third case is considered especially biomass and waste incineration thermoelectric power plants where reagent consumption is higher. Recirculation and reinjection of part of the unreacted product reduces reagent consumption and improves removal efficiency.
Activated carbon
Volatile organic compounds (VOC) are gaseous hydrocarbons derived mainly from the burning of fuels and evaporation of organic solvents produced in industries such as steel, wood, paints and varnishes, cosmetics and pharmaceuticals.
Activated carbon physically adsorbs the VOCs, such as dioxins and furans, as well as mercury and other trace heavy metals in the gas emission.
The dry injection of this reagent is similar to that of hydrated lime or bicarbonate described above. Both systems are complementary.
