Desulphurization methods implemented by ZVVZ-Enven Engineering, a.s.
Dry method – Semi-dry method with CFB absorber – Wet limestone scrubbing
The desulphurization technologies have their specifics and each power energy source being desulphurized.
The influencers for selection of an appropriate desulphurization method:
Requirements of customers
Capital and operation expenses
Current technology, operation flexibility, control capacities
Required desulphurization effectiveness
Spatial possibilities for installation of the desulphurization
Availability of suitable sorbent
Complexity of technology
How the FGD product is to be used
Dry method
The principle of this method lies in dosing of the sorbent to the flow of flue gases. Either calcium hydroxide Ca(OH)2 or sodium hydrogen carbonate NaHCO3 may be employed as the sorbent. The SO2 reaction with the sorbent occur mainly in flues and continue in the layer of separated substances established on the filtration bags of a bag filter to lesser extent. The reaction products are solids and separated together with fly ash in the bag filter. Efficiency of the desulphurization depends on the sorbent used.
Emission of acid components is reduced by control of the quantity of the sorbent being dosed.
Chemical reactions of the sorbent and SO2
Semi-dry method with CFB absorber
The principle of the method consists in dosing of the Ca(OH)2 sorbent to the circulating fluidized bed
scrubber (absorber). Process water being used for cooling down the flue gases is fed separately to the
absorber. All process water fed is vaporized by heat from the flue gases.
The absorber consists of upper large-diameter cylindrical part and lower small-diameter cylindrical part,
Wherein both parts are connected through Venturi tube-shaped transition piece. The fluid bed consists
of fresh sorbent and recirculated product. Thanks to high speed of the flue gas at entry to the bottom
part of the absorber, the loose particles may not fall down but they are levitated by the flue gas flow
upwards. Inside the Venturi tube there are loose particles distributed uniformly in the flue gas flow
and accelerated in vertical direction. The speed flow of the flue gases is not as fast in the upper largediameter part of the absorber and flow away forces of the flue gas flow are no linger able to keep all
loose transported and made airborne. In this way, continuous return flow of heavier particles of the
fluid material close the inner surface of the absorber is created. As soon as this loose material, which
returns down again, approaches the bottom Venturi tube, fast flow of the flue gas in this point makes
the material airborne again and rises upwards. Fine fractions leave the absorber in its highest point
Basic technological units
..Storage and dosing of the sorbent
..Bag filter
..Product transport to silo
..Flue gas ducting, flue gas fan
..Potential use of a reactor (sorbent Ca[OH]2)
..Potential use of a reactor and water
The product entrapped in this way is re-circulated from the bag filter in the absorber, and a smaller part transported to the desulphurization product silo. Water and sorbent are transported separately to the process and therefore, there are no operation unpleasant suspensions. The technology works at a temperature over dew point. Hence, compared to wet limestone scrubbing, no special materials need to be used. No waste water problems need to be dealt with in this method because only solid desulphurization product is handled here. Chemical reactions in the absorber
Handling with product and its use
..The desulphurization product contains in particular a mixture of sulphate CaSO4, sulphite CaSO3,
and calcium hydroxide Ca(OH)2. Calcium carbonate CaCO3 is represented to a sufficient level. The
desulphurization product alone is not reusable.
..The desulphurization product can be mixed in the mixing station with fly ash from boilers and
batch water into conditioned fly ash usable in building industry for reinforcement of subsoil, for
closing layers of dumps and disposal sites, for landscape restoration, and more.
..The conditioned fly ash flowing from the mixing station is moist mixture with optimum moisture
suitable for immediate processing. It is recommended to process the conditioned fly ash not later than 1–6 hours from production.
..Following hardening, the conditioned fly ash differs in principle with its technical properties from surrounding unconditioned input materials; its properties are similar to poor concrete.
..The conditioned fly ash meets all requirements not only technical (physical and chemical) as well
as requirements for human health and environment protection according to applicable laws of the EU and Czech Republic.
Advantages of the method
..Circulation of particles in the absorber . reciprocal abrasion . scrubbing of reacted layer .
uncovering of non-reacted material
..The sorbent is delivered in the absorber in dry powder form. The troubles associated with
preparation, storage, and injection of suspension transport routes are eliminated
..Separated feed of water and sorbent to the process. Problems associated with cleaning of pipeline routes are eliminated . all water is vaporized by heat from flue gases
..Ratio of Ca/S = 1.25–1.9 in the wide range of input concentration of SO2
..Desulphurization product recirculation . use of residual hydrate in the product
..Desulphurization efficiency over 90%, suitable for medium-sized to large sources
..Temperature of flue gases over dew point. Installation of special materials is eliminated
.. Solid desulphurization product . troubles with waste water are eliminated
Wet limestone scrubbing: The principle of the method consists in intense “scrubbing” of flue gases with limestone suspension. With fresh limestone added, the mixture of limestone, by-product, and water is re-circulated from the absorber into the spraying blocks. In the spraying nozzles, the suspension is sprayed into drops of defined diameter. When falling back to the recycling tank, the drops remove acid substances – SO2 and SO3 from the flue gases. The flue gases enter the absorber in the lower part and rise up. The drops fall from top to bottom. Hence, the scrubbing process principle is based on counter-flow stream.
The chemical reaction, which removes SO2, occurs in oxidation environment where gypsum crystallizes.
In the course of SO2 removal in the absorber the flue gases are cooled down and saturated with water
from re-circulated suspension to adiabatic saturation temperature. Water loss is compensated by
process water. In order to optimize water consumption in the absorber, the process water is also used
for scrubbing of the drop separator in the upper part of the absorber.
Entrapped SO2 reacts with limestone in the suspension and sulphite HSO3 is formed that oxidizes into
sulphate in the recycling tank (in the lower part of the absorber) through the oxidizing air. Gypsum
crystallization from over-saturated solution follows after this step.
The retention time in the absorber permits production of minor gypsum crystals (CaSO4 × 2H2O). The
gypsum slurry taken from the absorber is pumped into hydrocyclones to dewater the gypsum where
concentrated gypsum slurry forms. The concentrated gypsum slurry is then fed to the belt filter. The
gypsum slurry is dewatered here. A system of conveyors transports the gypsum to the required place
for storage.
Scrubbed flue gases exiting from the scrubbing part of the absorber go through the drop separator where the carried drops are trapped. The liquid obtained in this way is then returned to the absorber. Clean flue gases saturated with water steam are then fed to the wet stack and released to atmosphere. The wet stack may be either a part of the absorber or standalone standing one. As the method works with flue gases temperature under dew point, suitable materials must be used across the technology (stainless steel, plastics, laminate, etc.) or provide corrosion protection (anti-corrosion lining, rubber lining).The final desulphurization process can be described by main chemical reaction among sulphur oxide,
calcium carbonate, and oxygen with presence of water:
CaCO3 + SO2 + 0.5O2 + 2H2O . CaSO4 * 2H2O + CO2.
Dosing device Lime stone slurry tank from drainage system Gypsum storage Fly ash silo Limestone silo Clean flue gasses Hydro cyclone Flue gas fan Gypsum water tank Oxidation air blower Drain pit Belt filter Boiler Raw flue gas Electrostatic precipitator Absorber with wet stack Process water tank Emergency storage tank Diagram
Basic technological units
..Absorber including circulation pumps
..Preparation of limestone slurry
..Dewatering of gypsum slurry
..Oxidation air system
..Emergency and drainage system
..Water management
..Flue gas system
Handling with product and its use
The desulphurization product from this method may be widely applied:
..Production of gypsum, plasterboards or gypsum fibrous boards
..Production of gypsum plasters and blocks
..Hardening regulator for cement production
..Activator in production of porous concrete
..Landscape renewal from underground mining
..Fertilizer and auxiliary substance for soil improvement in agriculture and forestry
..Raw material for production of fillers for glues, varnishes, and paints
..Production of anhydride and anhydride binders (anhydride floor mixtures)
However, its reuse still remains low, and most of the material is dumped usually in the form of the
conditioned fly ash with fly ash and ash.
Advantages of the method
..Cheap and easily available CaCO3 sorbent
..High desulphurization efficiency up to over 95 %
..Lower operation costs compared to desulphurization with fluid absorber
..Low Ca/S stoichiometric ratio
..Possibility to use the desulphurization product, so-called energy gypsum
..Beneficial use for large-scale boilers
..Our experience from installation of heat production plant in Planá nad Lužnicí, use of smaller
boilers for a favourable price is advantageous as well
Summary of desulphurization methods
Dry method Semi-dry method
with CFB absorber Wet limestone scrubbing
Sorbent Ca(OH)2 NaHCO3 CaO, Ca(OH)2 CaCO3
Technology Easy Medium complicated Complicated
Efficiency 50–60 % 90 % Up to 93 % Up to 96 %
Water consumption None Lower, medium** Higher**
Product Dry Dry Moist
Usable product Yes No Yes Yes
Waste water No No Yes
Source of pollution Low, medium, big Medium, big
Maintenance Easy More complex (owing to higher
number of installed components)
Complete supply programme
..Equipment for the cleaning of waste gasses from solid and gaseous pollutants
..Equipment for pneumatic transport of loose materials
..Equipment for air-conditioning and ventilation of nuclear power plants
..Equipment for air-conditioning of buildings and ventilation of industrial facilities, mines, tunnels
and underground railways
ZVVZ-Enven Engineering, a.s.
Sažinova 1339 • 399 01 Milevsko • Czech Republic
Phone: +420 382 551 111* • Fax: +420 382 522 158 • E-mail: info@zvvz-enven.cz • www.zvvz-enven.cz
Selected desulphurization projects of reference
Dry method
ZVVZ Energo, s.r.o., Milevsko boiler room, 2017
Volume of flue gases Max. 122 600 m³N/hour (wet)
Flue gases inlet temperature Max. 198 °C
Inlet concentration of SO2 Max. 3 250 mg/m³R
Outlet concentration of SO2 <1 500 mg/ m³R
Required desulphurization effectiveness 54 %
Fuel Lignite dust
Sorbent NaHCO3
Semi-dry method with CFB absorber
ArcelorMittal Ostrava a.s., Heating plant TAMEH Czech, s.r.o., 2017
Volume of flue gases 147 600–865 000 m³N/hour (dry)
Flue gases inlet temperature 120–205 °C
Inlet concentration of SO2 500–1 700 mg/m³N (dry)
Outlet concentration of SO2 <160 mg/m³R
Required desulphurization effectiveness 90.6 %
Fuel Black coal
Sorbent CaO
Number of absorbers 2 pcs
Actherm, spol. s.r.o., Heating plant Chomutov
Volume of flue gases Max. 165 000 m³N/hour (wet)
Flue gases inlet temperature 130–180 °C
Inlet concentration of SO2 3 830–5 800 mg/m³N (wet)
Outlet concentration of SO2 <400 mg/m³R
Required desulphurization effectiveness 89.7–92.4 %
Fuel Lignite
Sorbent Ca(OH)2
Number of absorbers 1 pcs
Wet limestone scrubbing
C-Energy Planá, s.r.o., Heating plant Planá nad Lužnicí
Volume of flue gases 40 000–110 000 m³N/hour (wet)
Flue gases inlet temperature 120–140 °C
Inlet concentration of SO2 2 680–3 580 mg/m³N (wet)
Outlet concentration SO2 <400 mg/m³R
Required desulphurization effectiveness 93.6 %
Fuel Lignite
Sorbent CaCO3
Number of absorbers 1 pcs
Note
m³N – normal conditions (0 °C, 101 325 Pa).
m³R – reference conditions (0 °C, 101 325 Pa, dry, 6 % O2).