Many industrial processes generate flue gases containing pollutants that can adversely impact people and the environment. We offer cost-effective solutions for their capture and neutralization.
Sulphur dioxide (SO2) is an acid gas, also called sulphur oxide or sulphurous anhydride. It is non-flammable and non-explosive. This pollutant, which has a pungent odour, is toxic and a respiratory irritant. In plants that burn sulphur-containing fuel, SO2 can, for example, be removed from the flue gas through dry sorbent injection, where SO2 reacts with hydrated lime (Ca(OH)2) to form calcium sulphite (1) or calcium sulphate (2):
Ca(OH)2 + SO2 → CaSO3 + H2O (1)
Ca(OH)2 + SO2 + ½ O2 → CaSO4 + H2O (2)
Where does it comes from
SO2 is released by the combustion of coal and heavy oil in power stations, as well as within the processes of municipal solid waste incinerators (MSWI), biomass plants, glass, brick, cement production, and metal smelting among other types of industries.
Lhoist solutions
Calcium compounds – in the form of limestone (CaCO3), quicklime (CaO) or hydrated lime (Ca(OH)2) – continue to be the dominant sorbents to control SO2 emissions. The choice of calcium sorbent depends on the type of capture process used. Trade-offs on capital cost vs. operational cost for the various processes must be considered.
Properties
- Molecular formula: SO2
- Molar mass: 64.066 g/mol
- Appearance: colorless gas
- Odor: pungent
- Acidity: 1.71 pKa
- Hazards: toxic
- Boiling point: -10°C
Hydrogen chloride (HC) is a colourless and odourless acid gas, also called hydrochloride or hydrochloric acid.
Non-flammable and thermally stable, HCl is toxic and corrosive. HCl is very soluble in water. Dissolution generates large amounts of heat.
Hydrogen chloride can be captured efficiently with calcium hydroxide (Ca(OH)2) sorbents. Optimum capture performance depends on the flue gas composition, flue gas treatment system, and process temperature. The reaction mechanism is complex and takes place through the formation of calcium hydroxide-chloride (CaClOH) according to:
Ca(OH)2 + HCl → CaClOH + H2O
CaClOH + HCl → CaCl2 + H2O
Where does it comes from
HCl is released during the combustion of PVC waste and chlorine-containing coal. It is also possible to find chlorine in the form of inorganic salts (NaCl) in wood, paper and cardboard or in food and biomass waste containing salt.
Lhoist solutions
Hydrated lime has been used for many years in various dry sorbent injection processes. Industrial results have proven that our products are capable of HCl capture above 98%, suitable for meeting regulatory requirements in the most challenging applications. In municipal and medical waste incinerators, HCl capture of more than 99% is achieved. The appropriate solution can be tailored to meet the needs of any flue gas treatment installation.
Properties
- Molecular formula: HCI
- Molar mass: 36.46 g/mol
- Appearance: colorless gas
- Odor: pungent
- Acidity: -6.3 pKa
- Hazards: corrosive, toxic
- Boiling point: -86°C
Hydrogen fluoride (HF) is a non-flammable and non-explosive gas, also called fluoric acid, hydrofluoride, hydrofluoric acid or fluorine monohydride. It has a pungent odour and is corrosive, irritating and toxic. Hydrogen fluoride in flue gas reacts readily with hydrated lime:
Ca(OH)2 + 2HF → CaF2 + 2H2O
Where does it comes from
Hydrogen fluoride is released due to the presence of fluoride in raw materials or combustibles. HF emissions can be generated from the combustion of coal, fluorinated polymers or textiles, and by the decomposition of CaF2 and raw materials such as brick or glass. HF is also present in such waste as inert material, aluminium cans and synthetic fabrics.
Lhoist solutions
Our sorbents can capture over 99% of HF emissions using dry and semi-wet processes. All our calcium-based sorbents can capture HF depending on your requirements and your specific operating conditions. Hydrated limes are superior to sodium sorbents such Sodium bicarbonate for high and efficient HF removal. Today, a number of glass manufacturers worldwide use our sorbents for this particular high removal performance.
Properties
- Molecular formula: HF
- Molar mass: 20.01 g/mol
- Appearance: colorless gas or colorless liquid (below 19.5°C)
- Odor: sharp, pungent, irritating
- Acidity: 3.17 pKa
- Hazards: corrosive, toxic
- Boiling point: 20°C
This compound is also called sulfuric anhydride or sulphur trioxide. SO3 is a clear, oily liquid, often present as a gas. It should be handled with extreme care as it reacts violently with water to produce a highly corrosive sulfuric acid. SO3 reacts with hydrated lime to form calcium sulphate:
Ca(OH)2 + SO3 → CaSO4 + H2O
Where does it comes from
This pollutant is mainly generated in power plants; glass, brick and non-ferrous metal manufacturing; municipal and industrial waste incineration; and boilers fired with heavy fuel oil. In addition, SO3 concentrations can increase when selective catalytic reduction is used for NOx control, as this typically catalyzes oxidation of SO2 into SO3.
Lhoist solutions
Dry calcium hydroxide products are typically used for SO3 capture and address both the visible plume and the operational concerns that are commonly associated with this pollutant.
Hydrated lime is normally capable of maintaining SO3 below the usual target of 5 ppm. However, advanced products are needed to achieve levels of SO3 lower than 2 ppm.
Properties
- Molecular formula: SO3
- Molar mass: 80.066 g/mol
- Appearance: colorless liquid (room temperature)
- Odor: sharp, irritating
- Acidity: < -10 pKa
- Hazards: oxidizing agent
- Boiling point: 45°C
Selenium dioxide (SeO2), also called selenium oxide, is an acid gas. It is non-flammable and non-explosive. This pollutant is toxic and a respiratory irritant. In plants burning selenium-containing fuel, SeO2 can be removed from the flue gas through dry sorbent injection, where SeO2 reacts with hydrated lime (Ca(OH)2) to form calcium selenite (1) or calcium selenate (2):
Ca(OH)2 + SeO2 → CaSeO3 + H2O (1)
Ca(OH)2 + SeO2 + ½ O2 → CaSeO4 + H2O (2)
Where does it comes from
Selenium is used as an additive in glass-making and is released as SeO2 during the manufacturing process. SeO2 is released by coal combustion in industrial processes, such as in power plants.
Lhoist solutions
As for SO2 removal, calcium in the form of quicklime (CaO) or hydrated lime (Ca(OH)2) is the dominant chemical used to control SeO2 emissions. Selenium compounds are inherently more stable on calcium sorbents than sodium sorbents. The choice of calcium sorbent depends on the type of capture process used.
Properties
- Molecular formula: SeO2
- Molar mass: 110.96 g/mol
- Appearance: yellow-green
- Odor: pungent
- Hazards: corrosive, toxic
- Boiling point: 315°C
Mercury (Hg0, Hg2+) is the only metal that is liquid at standard temperature and pressure conditions. It is highly toxic through ingestion or inhalation.
Where does it comes from
Mercury is present in coal and is released by industrial processes, such as in coal power plants, waste-to-energy, and cement plants.
Lhoist solutions
In dry sorbent injection, mercury can be removed by physical adsorption onto the surface of suitable sorbents. These are typically carbon-based materials with very high surface areas. They include pulverized activated carbon, specialized surface-treated (or impregnated) activated carbon, activated lignite coke and blends. Lhoist offers a large range of blends with similar sorbents and selected components such as hydrated lime (Ca(OH)2) and mineral products tailored to meet the needs of any flue gas treatment installation. This offers a simple, flexible, economic and effective way for simultaneous removal of micropollutants such as mercury, and acidic gas components.
Properties
- Molecular formula: Hg
- Molar mass: 200.59 g/mol
- Appearance: silvery
- Odor: no odor
- Hazards: toxic
- Boiling point: 357°C
Lhoist supplies tailor-made blends based on the amount of each micropollutant (and possibly acidic gases) in the flue gas to be treated.
This group of micropollutants (PCDD & PCDF) is classified as polychlorinated dibenzo dioxins/furans. They consist of chlorinated biphenyl molecules linked with different oxygen bridges and are highly toxic.
Where does it comes from
Dioxins and furans are generated in flue gases when both chlorides and organic matter are present at relatively low temperatures.
Lhoist solutions
In DSI processes dioxins/furans are removed by physical adsorption onto the surface of suitable sorbents. These are typically materials with very high surface areas, such as pulverized activated carbon, activated lignite coke, or specialized minerals and blends. At Lhoist, we have a large range of blends with similar sorbents and selected components such as hydrated lime (Ca(OH)2) and mineral products tailored to meet the needs of any flue gas treatment installation. They offer a simple, flexible, economic and effective way for simultaneous removal of micropollutants such as dioxins/furans, and acidic gas components.
Lhoist supplies tailor-made blends based on the amount of each micropollutant (and possibly acidic gases) in the flue gas to be treated.