Flue gas treatment

An undesired effect of this, has been the increase in the content of chlorine and its compounds in flue gases.
In order to ensure the abatement of these substances, a specific bypass system is installed that typically extracts up to 10-15% of the gas flow rate in the first few metres of the riser, the area where the highest concentration of these compounds in gaseous form and a temperature in the range of approximately 950 to 1100°C occur.

This gas stream is rapidly cooled with air in a mixing chamber, from which the gases exit at around 400°C, with the condensation and solidification of the chlorine compounds, which will be captured in the filtration state that follows.
Area Impianti is already well established in this application with both ceramic candle filters (which can be directly crossed by gases at 400°C) and bag filters (which require subsequent cooling to around 200°C of the gases exiting the mixing chamber).

The choice of the filter technology to be used will be discussed with the customer with a view to energy optimisation and integration of the chlorine bypass into the entire cement production plant.

Bag filters can achieve emission levels of less than 1 mg/Nm3. Depending on the application, they can also act as a “reactor” with reagent injection.

With the ALL IN ONE series, Area Impianti has revolutionised this historic technology, combining several functions in a single housing, optimising space and costs. With vertical, round or oval bags, they guarantee high durability and safety. The filter media is selected according to the flue gas specifications. The modularity of our filters facilitates access and maintenance, while the PPOD cleaning system optimises the cleaning pressure according to the fouling level, maximising efficiency and energy savings and ensuring less stress on the bags

Ceramic candle filters are the ideal choice for applications where low dust emissions are required, even for high temperature flue gases.

Thanks to the use of catalytic candles, ceramic candle filters allow integration of the selective catalytic function of nitrogen oxides.

Our optimised filter design facilitates access and maintenance, while our cleaning system ensures that each candle always operates at peak efficiency, prolonging service life and minimising operating costs.

Our installations have been used for many years in several industrial sectors, proving their reliability and high-performance levels.

Cyclones can be used as dust pre-separators, spark risk reduction systems.

They are an effective solution for several sectors, including cement and biomass.

Used as pre-separators, our cyclones reduce the dust load on high efficiency air filtration systems, extending their life expectancy. Our design also allows the installation of single or multiple low load loss axial cyclones, suitable for the different characteristics of the flue gases to be treated.

SCR (Selective Catalytic Reduction) systems are designed to selectively reduce NOx (nitrogen oxides) in many applications. Using a reagent, typically ammonia or urea, in the presence of a catalyst, SCR systems convert NOx into nitrogen and water vapour, two environmentally harmless compounds. SCR technology is recognised for its high efficiency and reliability, making it the optimal solution for controlling harmful emissions.

Area Impianti manufactures low and high temperature SCRs, compartmented or not, with or without auto regeneration. We specialise in hybrid systems ideal for incineration, self-cleaning systems ideal for glass and innovative SCR tail ends for the cement industry. We also supply BAC (Bag and Catalyst) systems, where the DeNOx function is integrated into the filter through compact solutions.

Area Impianti can integrate the SNCR (Selective Non-Catalytic Reduction) system with the boiler, to optimise the first post-combustion reduction section, studying the thermal profile and optimising the injection points.

The SNCR treatment of nitrogen oxides takes place through reaction with ammonia activated by high temperature (850-1050°C). These temperatures are usually reached immediately downstream an incineration or calcination furnace.

Dioxins and furans are dangerous chemical compounds produced during incineration. They decay very slowly, which makes them serious environmental pollutants.

Area Impianti offers two treatment methods:

• Dry injection of adsorbents: this method fixes the substances in the solid phase, so that they can be captured and disposed of. It is most effective at low temperatures and uses adsorbents such as activated carbon, lignite coke and dolomite and clay mixes.
  
• Catalytic destruction in SCR systems: using the same catalysts as in DeNOx SCR systems, the process destroys dioxins and furans (PCDD/F) and prevents their reformation.

The abatement of carbon monoxide (CO) and the oxidation of organic substances (TOC and VOC) can be thermal or catalytic. Area Impianti can supply modern catalytic methods, integrated in processes with DeNOx – DeDIOX modules or, if required, thermal oxidisers.

These systems are used in the chemical industry, in incinerators, in diesel engines (including vegetable oil) and in any process where the conditions for complete combustion are not optimal.

The process for the abatement of CO and organic substances is an exothermic oxidation that converts these compounds into CO2 and water. This process can also improve the efficiency of unburned dust removal. Thermal combustion takes place at minimum 700°C for CO and 800-900°C for more complex compounds. However, with the use of catalysts, these temperatures can be reduced to 200°C for CO and 200-400°C for more complex compounds.

Operating temperatures are achieved with:

• Self-support, thanks to the heat generated by the exothermic reaction.
• Heat exchangers, recuperators and burners.
• Thermal capacity of two or more catalytic modules in a regenerative thermal oxidiser.

Acid gases present in the flue gases (SOx, HCl, HF) can be effectively removed by dry injection of solid basic reagents of small particle size. Area Impianti uses hydrated lime, sodium bicarbonate and carbonate, with the possibility of double injection for greater efficiency.

The choice of the most suitable reagent depends on the required efficiency levels, the type and concentration of the acids to be neutralised, the temperature of the flue gases and the treatment of the residues. With its wealth of experience, Area Impianti is at the service of the customer to find the best solutions.

The recirculation of reaction by-products can bring significant benefits in terms of consumption, improving the overall efficiency of the process.

Wet deacidification is an advanced technology based on the absorption of acids by an aqueous solution, allowing a significant reduction in pollutant emissions.

The process uses a flue gas scrubber for high efficiency capture and neutralisation of acid gases, with low residual emissions. The wet system generally consists of “scrubbing towers” or columns. The absorption stage can be acidic, for the treatment of hydrochloric acid and possibly mercury, or basic/neutral for the treatment of sulphur dioxide.

Wet deacidification systems use “scrubbing towers” or columns, which can operate in acid mode to treat hydrochloric acid and mercury, or in basic/neutral mode to treat sulphur dioxide. Commonly used basic reagents are milk of lime and soda.

Our company offers customised wet and semi-wet deacidification solutions designed to meet the specific needs of various industries. Thanks to its experience, Area Impianti can offer systems that optimise performance and extend the life of the equipment, while reducing the accumulation of residues and ensuring effective plant management.

Following an intensive period of research and development, we have created and patented a technologically advanced and economically sustainable system for the abatement of mercury emissions with the ComPOD (Cut Of Mercury Peak – ON DEMAND) system.

The ComPOD system uses a fixed bed of chemi-adsorbents and operates discontinuously (ON DEMAND). This technology is designed for use on existing plants when upstream process analysers detect abnormal mercury peaks.

Water cooling can be achieved by direct channel injection for simpler applications, or with quenching towers using atomisation and complete evaporation. The injection nozzles used can be of the spill-back or twin-fluid type and can operate with upward or downward flow, depending on the specific requirements of the process.

The water used for cooling can be process water, thus contributing to the reduction of liquid purging in the system. Area Impianti is recognised for its expertise in implementing water cooling solutions in a wide range of sectors, ensuring efficiency and reliability.

Heat exchangers are an ideal and very flexible solution for various sectors. Their application limits flow rates, allowing lower sizing of the downstream equipment.

Thanks to specific design details, the proposed cooling/heating systems can also function as reactors or be integrated into the process.

Area Impianti uses tubular or plate heat exchangers, ideal for high dust levels. Cleaning is made easier by a design that has been optimised over the years, equipped, where necessary, with chain or compressed air systems with solid references.

These systems can be used for:

• Flue gas/air or flue gas/flue gas heat exchange
• Flue gas/water or oil heat exchange
• Flue gas/flue gas heat recovery
• Condensate preheating
• ORC (Organic Rankine Cycle)

The extracted dusts and ashes, often hygroscopic and complex to handle, indeed require the in-depth knowledge that we have refined over time.

Dust is stored in silos with automatic filtration systems to ensure compliance with emission limits. For transport, we use both mechanical and pneumatic technologies. Mechanical solutions include closed chain conveyors (redler), screw conveyors and bucket elevators for vertical sections. For biomass and combustion residues we use conveyor belts.

We are ready to work with our customers to design and implement the most effective dust management solutions.