The chemical sector is a sector with high environmental risk. Emissions elimination in the chemical sector has become a critical issue in the recent decades. The excess of pollutants in the atmosphere derived from production processes brings consequences and harmful effects for the environment and for people’s health.
Peculiarities of the processes in the chemical sector
The chemical sector is facing several challenges nowadays. The mixture of fine raw materials, distillations and physicochemical reactions are constant in this sector. It is common to find combustion installations such as steam production boilers used in distillation operations, and in many cases explosive mixtures can even be generated. These conditions require counting on environmental experts for emissions treatment for safe operation.
In line with the great diversity of manufactured products, several processes are developed in the chemical sector: production of resins, composite materials, fertilizers, derivatives, lubricants, products and chemical substances, etc. And there are a wide range of pollutants, usually both organic or inorganic compounds, fluorinated, halogenated, etc.
BAT and RTO: an EU workframe for emissions elimination
The greenhouse effect, acid rain and global warming are just some examples of the negative effects of air pollution. Those long-term and medium-term effects have become problems that are critical to solve.
And that’s when technologies for emissions elimination become vital.
Taking into account the polluting emissions that must be eliminated in the chemical sector, and regardless of whether their origin is a fixed source or a stationary source and the explosive risk that many of them have, Regenerative Thermal Oxidation (RTO) environmental technology is the best option to guarantee polluting emissions elimination in this sector.
There are several technologies available in the market, each of them suitable for certain specific cases and requirements.
According to the latest Best Available Techniques (BAT) document of the European Commission, the incorporation of Regenerative Thermal Oxidation (RTO) technology for emissions treatment in the chemical industry is highly recommended.
A BREF (which stands for BAT Reference) document gathers all the information related to the BAT for the prevention and control of environmental pollution by European industries. Those documents must be updated every 8 years by technical working groups of the European Commission.
Within the Industrial Emissions Directive 2010/75 / EU, in the latest BAT known as “Best Available Techniques (BAT) Reference Document for Common Waste Gas Management and Treatment Systems in the Chemical Sector” the technology of Thermal Oxidation was included in chapter 3 (“Techniques to consider in the determination of BAT”). This chapter describes techniques that have the ability of achieving a high level of environmental protection regarding polluting emissions.
Thermal Oxidation is described in this BREF document as a very useful technique to reduce emissions together with other techniques such as Selective Catalytic Reduction (SCR) or Selective Non-Catalytic Reduction (SNCR). Thermal oxidation is used alone or in combination with other waste gas treatment techniques (e.g. combined with pretreatment by condensation or adsorption or with post-treatment by absorption). Removal efficiencies for organic compounds typically range from 95% to more than 99.99 %
Thermal oxidation is an abatement technique that oxidises combustible compounds in a waste gas stream with air or oxygen. The waste gas stream is heated above its auto-ignition point in a combustion chamber and maintained at a high temperature long enough to complete its combustion to carbon dioxide and water. The typical combustion temperature is between 800°C and 1000°C.
Types of Thermal Oxidation
There are several types of thermal oxidation:
- Direct thermal oxidation: thermal oxidation without energy recovery from the combustion.
- Recuperative thermal oxidation: thermal oxidation using the heat of the waste gases by indirect heat transfer.
- Regenerative thermal oxidation: thermal oxidation where the incoming waste gas stream is heated when passing through a ceramic-packed bed before entering the combustion chamber. The purified hot gases exit this chamber by passing through one (or more) ceramic-packed bed(s) (cooled by an incoming waste gas stream in an earlier combustion cycle). This reheated packed bed then begins a new combustion cycle by preheating a new incoming waste gas stream.
Some achieved environmental benefits are reducing emissions into the atmosphere and a possible energy recovery.
Optimisation of thermal oxidation can reduce the emissions of NOx and CO. This is carried out by:
- Optimising the design of the oxidiser:
- residence time
- mixing of the flows (e.g. natural diffusion between turbulent streams, changes in flow direction)
- combustion chamber
- Monitoring the combustion parameters:
- oxygen content
- carbon monoxide concentration
- temperature
- Checking the burners regularly, and cleaning them when necessary
When the oxidised VOCs contain sulphur and/or halogens, further emissions of sulphur dioxide and/or hydrogen halides might be expected. This might require an additional waste gas treatment after thermal oxidation (e.g. absorption).
Advantages of Thermal Oxidation
Energy recovery can be achieved while maintaining the same VOC removal efficiency. This use is due to the fact that the ceramic towers store a large amount of energy in each sequence, a fact that makes the air or process gas heat up. Thus, there are thermal efficiencies of around 90 to 95%.
This implies that under normal operating conditions, fuel gas is not consumed, since the process is autothermal. An autothermal process means that, without the input of external energy in the form of fuel in the burner, the combustion chamber maintains the operating temperature. This is because the energy released by VOCs when oxidizing is sufficient to keep the chamber at a high temperature.
RTO equipment have several other technology advantages when it comes to VOC emissions abatement compared to other techniques, such as: they are adaptable for small, medium and large air flows while they can treat a wide range of VOC emissions. They also have a low operating and maintenance cost and a have very high thermal efficiency. And it guarantees low emissions in a constant way.
As a conclusion, with regards to air pollution treatment in the chemical sector, Regenerative Thermal Oxidation (RTO) is the most recommended solution currently used and installed in production plants to efficiently reduce pollutant emissions. Moreover, it is backed up by the European Commission’s BAT document.
At Tecam we are convinced that environmental sustainability is the only viable path for the future of the industry. We know that the only possible answer is to implement technologies that combine maximum efficiency in eliminating emissions with the highest efficiency in its implementation and use, in order to help production plants become cleaner spaces, safe for people and the environment.
Contact us today if you need help with your emissions treatment: info@tecamgroup.com or +34 93 428 11 54.
