Concept (need and benefits)
Gaseous flows of a potentially polluting nature are produced by industry, sometimes with particles in suspension, which must be treated before they are emitted into the atmosphere to comply with current regulations. These establish the emission limit values for the emission sources of industries liable to emit pollutants, as well as a measurement frequency to control compliance.
The discharge of potentially polluting emissions to the atmosphere can be focused through a chimney, for example, or diffusely.
Focused emission consists of discharging pollutants into the atmosphere in a continuous, discontinuous or occasional manner and from single or several devices, processes and/or activities, and which can be combined for joint emission into the atmosphere.
Diffuse emission consists of a discharge into the atmosphere from any source capable of producing this contamination which is not from focused, continuous or discontinuous sources, of particles or gases either directly or indirectly. This is the case for non-captured emissions released to the outside environment through windows, doors, vents and similar openings, or directly produced outside.
The selection of the optimal treatment techniques to reduce, minimize or eliminate the amount of contaminants in the gas stream depends on the nature of the pollutants and the emissions regime, whether focused or diffuse, for example.
Technology and the Condorchem Envitech Offer
Condorchem Envitech has a lot of experience designing and building turnkey solutions for the treatment of industrial emissions. The Condorchem Envitech interdisciplinary team selects technologies from the wide range available to provide the optimal results in each case:
A scrubber works by treating the gas stream with a liquid. After contact, the pollutants in the gas are transferred by dissolving in the liquid. This transfer of gas phase components to the liquid phase is called absorption and is an equilibrium operation. The solubility of the contaminants in the liquid determines to what extent the contaminants transfer to the liquid phase from the gas phase. In some cases, the liquid phase consists of water, but sometimes it is possible to use a liquid (often an acid or alkaline solution) that chemically reacts with the contaminants, obtaining transfer yields close to 100%.
Biofiltration is a biological process used for the treatment of volatile organic compounds and also for some inorganic compounds. Its operation requires the use of microorganisms that subject the pollutants contained in the air to biological degradation. During a biofiltration air treatment process, the contaminated air passes through the filter material, which serves as a support for the growth of the biomass. When the contaminants come into contact with the biomass, they are degraded and used as a source of carbon and energy (organic compounds) or as an energy source (inorganic compounds). Thus, the biofiltration process leads to the complete decomposition of the contaminants, creating non-hazardous products.
Biofiltration removes contaminants without consuming chemical reagents or producing liquid waste, which is a very competitive advantage.
Biofiltration is especially effective for the treatment of VOCs and hydrogen sulphide, among other pollutants.
Adsorption is an equilibrium operation by which the pollutants suspended in the gas phase are superficially adhered to the solid particles that make up the support, usually activated carbon, alumina or zeolites, thus cleaning the gaseous current of these pollutants. Once it is exhausted and no more contaminant molecules can be adsorbed, changing the environmental conditions can produce the desorption of the contaminant and thus regenerate the activated carbon for reuse. Adsorption is a non-destructive technology for treating the VOCs and odors present in industrial gases.
Regenerative thermal oxidation (RTO) consists of oxidizing the pollutants under certain conditions of temperature and residence time. For combustion to be complete, it must be carried out at a high temperature, around 800°C. So that the energy cost is not excessive, heat recovery systems are used; this is why they are called regenerative systems. Hot air passes through a bed filled with a ceramic support with a very high surface area. The ceramic support accumulates heat which is released later, after cold air has passed through the bed. Thus, both hot and cold air pass sequentially in time in countercurrent through the same bed. For VOCs, the elimination efficiency of these pollutants is of the order of 98% of the concentration of VOC at the entrance to the RTO. The thermal efficiency of regenerative heat exchange systems with ceramic blocks is of the order of 95%, so that the fuel consumption to maintain the temperature of the oxidation chamber is reasonable, even if the VOC content is very low.
Although it is the most widely used treatment for the elimination of VOCs in industrial emissions, it is an efficient technology for a wide variety of pollutants.
Recuperative thermal oxidation is a technology that makes it possible to remove pollutants from a gas by subjecting it to a sufficiently high temperature. For the process to be effective and for the pollutants to be able to fully oxidised, it is necessary to maintain a high temperature (between 700ºC and 1200ºC). The system consists of a combustion chamber with a burner and a heat exchanger in which the inlet air is preheated with the exhaust air. Because the working temperatures are high and a thermal recovery efficiency of 65% is achieved, the fuel consumption is appreciable. Recuperative thermal oxidation is a VOC treatment technology that requires lower investment costs than the regenerative one, but which has a higher management cost due to a higher fuel consumption.
Catalytic oxidation is a destructive technology for VOC purification that achieves combustion at lower temperatures than the thermal alternative, due to the catalyst in the combustion chamber and a heat exchanger to preheat the incoming air with the purified exhaust air.
Catalytic oxidation is a very efficient technique for the treatment of emissions containing VOCs. This technology seems to be the best way to eliminate VOCs due to its high efficiency at very low pollutant concentrations and very low energy consumption.
This is not a purification process by itself, but it is a step before combustion, which is necessary when there are high airflows with a very low concentration of pollutants. Under these conditions, the fuel consumed for combustion would be very high and this technology is applied in order to reduce it.
Rotor-concentration with Zeolite is a technology that makes it possible to increase the concentration of a pollutant in a gas flow. The pollutant, generally a VOC, is retained through an adsorption process on a Zeolite wheel, obtaining the pollutant-free gas. A fraction of the treated gas, about 5%, is subsequently heated and fed into the rotor-concentrator in a counterflow. Thus, the pollutant that was previously retained on a Zeolite wheel is reabsorbed and the new gas flow is released, the Zeolite wheel being now again free of pollutants. The new gas flow has a pollutant concentration between 15 and 20 times greater than the initial concentration and it is fed into the combustion unit in order to oxidise the pollutant.
Photo-oxidation is a treatment that emulates the chemical reactions that spontaneously occur in the atmosphere which are the basis of its natural capacity for self-purification. The pollutants are oxidized by the use of ozone in combination with high intensity ultraviolet light, which transforms the ozone molecules into hydroxyl radicals. These have a high oxidative capacity and are capable of degrading most contaminants, transforming them into aerosol particles that can be filtered using an electrostatic precipitator. The final stage of the process removes the excess of ozone by means of a catalyst.
The nature of hydroxyl radicals results in a wide capture and neutralization of the different types of pollutants and many harmful chemicals resulting from painting, plastics processing and VOCs emitted by the treatment of waste oils.
The experience of Condorchem Envitech in the use of this technology has led it registering its own photo-oxidation process, CLIMATIC®, which is highly effective.
The system’s operation is based on the natural chemical reactions that occur spontaneously in the gas phase. This allows the CLIMATIC® system not to consume energy to force the air flow through static filters that have a limited treatment capacity. The result is a small drop in pressure and lower energy consumption, as well as a highly flexible treatment system for the load level.
This is applicable in all those industries that are facing problems of contamination and volatile organic compounds (VOC), such as solvents, odorous compounds, dust particles or aerosols, organic hydrocarbons, chlorine and its derivatives, for example.
Selective catalytic reduction is a technology to chemically reduce certain contaminants via the use of ammonia. It is especially efficient for the elimination of NOX and, when ammonia is added under conditions of excess oxygen and an appropriate catalyst, it is transformed into an innocuous substance, such as water and molecular nitrogen. The operation is basic, the liquid ammonium hydroxide is vaporized and diluted with air and injected directly into the stream of gases to be treated through a distributor. By controlling the operating conditions, this technology removes NOX efficiently, selectively and financially.
Cryocondensation consists of refrigeration of a gaseous current with liquid nitrogen until the pollutants in the vapor phase reach their dew point and begin to condense. The liquefied contaminants are easily separated from the gaseous current, which can be emitted into the atmosphere in compliance with regulations. Note that nitrogen is only used as a cooling agent and is not consumed, so it can be used in other processes (for example, for an inert atmosphere).
Cryocondensation treats and recovers a wide variety of solvents, such as toluene, acetone, methanol, chlorinated derivatives and hydrocarbons. It is a technology that can treat different currents, flows and pressures with even customized systems being designed for each case.
The DeNOx® process, patented by Condorchem Envitech, was conceived for the treatment of the emissions from power generation solar thermal plants, by converting the (NOX) pollutants into products re-used in the solar thermal plant process. The process is based on the acceleration of the natural mechanisms of the atmosphere for its own purification.
In recent years, it has been observed that conventional solutions for the purification of industrial emissions, based solely on end-of-line treatments, have not proved effective in all cases. The treatment technologies offered by Condorchem Envitech are sufficient for most of the problems that need to be addressed; however, the priority is not only to have an effective end-of-line specific treatment system, but to address the problem globally and with specific solutions for each case.
For this purpose, the processes producing emissions must be evaluated at source, with a minimization of the flows to be treated (this has a special impact on energy costs), with their proper capture, channeling and possible treatment alternatives. This procedure ensures the selection of the optimal solution, with the lowest implementation and operation costs.
Each case is a different project that Condorchem Envitech will successfully address by a global approach to the situation; along with its vast experience in the implementation of technologies for the treatment of emissions plus an in-depth study of the specifics of the customer’s facilities (for example, availability of space, water, reliability of the systems, simplicity of operation and maintenance). Only this way can success be guaranteed.
Types of polluting emissions
There is a wide variety of polluting emissions, although the most common in industry are those that contain one or more of the following compounds:
- Volatile organic compounds (VOC): e.g. aliphatics, aromatics, alcohols, ketones, esters and organochlorides.
- Compounds derived from nitrogen oxides (NOX)
- Dust and aerosols
- Odorous compounds: e.g. hydrogen sulfide, mercaptans, ammonia and amines.
- Inorganic compounds: e.g. cyanides, chlorides, fluorides, bromides and sulfur oxides.
The generation of polluting emissions occurs throughout industry, especially from the following sectors: