VOC, CO and NOx separation
The requirements for integrated exhaust gas cleaning clearly show that a given plant configuration cannot be applied equally to every cement plant because of plant-specific process parameters. In its capacity as an expert provider of NOx exhaust gas reduction solutions, therefore, Scheuch's aim is to work with the customer in order to develop the right process and provide a turnkey installation – all from a single source. In pursuing this aim, we look at all kinds of technologies from the outset in order to ensure that we are creating the very best solution for every application case.
The deconox process combines regenerative thermal oxidation (RTO) with a low-dust SCR (selective catalytic reduction) – two proven technologies in a single system. With deconox, nitrogen oxides and organic carbon compounds can be reduced at the same time.
deconox, the novel process for industrial exhaust air cleaning, uses energy from exhaust air containing pollutants to break down other pollutants such as nitrogen oxides and organic compounds. This results in significantly lower emissions in industrial environments, and prevents unpleasant odours. As the residual energy can also be fed back into the production process or recycled in other ways, this procedure also makes a huge contribution towards energy-saving measures.
Performance at a glance:
- A single system for NOx, VOC and CO reduction
- Up to 90 % NOx reduction
- 98–99 % CO/VOC reduction
- Long catalyst service life
- Autothermal operating option
- Secondary fuels or secondary raw materials can be used
Regenerative Thermal Oxidation plants (RTOs) efficiently reduce pollutants such as VOCs and unpleasant odours. Moreover, since the energy required for thermal oxidation can largely be recovered when it flows through the ceramic heat exchanger towers, this saves on fuel use and the associated operating costs.
In a high-dust circuit, the exhaust gas from the cement kiln exits the preheater at a temperature of 300–380 °C, which is the ideal temperature range for catalytic denitrification. Depending on the specific requirements, multiple catalyst layers can be integrated into a single reactor to allow the required emissions level to be maintained. The dust-laden exhaust gas (dust content up to 200 g/Nm³) is conveyed vertically downwards. To prevent the channels from becoming clogged, each catalyst layer is cleaned during operation by means of an efficient cleaning concept. By taking advantage of the temperature level, heating of the exhaust gas is unnecessary, which has a positive effect on operating costs.
Scheuch has developed the semi-dust circuit on the basis of experience and findings gained from high-dust and low-dust circuits operated in parallel to one another in pilot plants. The process involves installing a pre-separator in the form of a dry electrostatic precipitator for temperatures up to 400 °C upstream of the catalyst – and directly downstream of the heat exchanger, as is the case in high-dust circuits. A gas conditioning tower, which can be integrated into the catalyst system as an option, then ensures that the maximum filter inlet temperature for the emc bag filter is adhered to.
A significant proportion of the exhaust gas heat from a cement plant is used for drying raw materials and fuels, and leaves the kiln filter at a temperature of 100–120 °C. The temperature of the dedusted exhaust gas is usually too low for breakdown to take place in the catalyst. For breakdown to occur, temperatures of 220–300 °C are required. With heat exchangers, some of the energy that must be used for heating can be recovered. In normal operation, only the temperature loss of the heat exchanger needs to be compensated using an external energy source (heat displacement from other exhaust gas flows, natural gas burners). The advantage of this circuit type is that relatively low catalyst volumes can be used thanks to the dust-free exhaust gas. As a result of this absence of dust pollution, the catalyst can be expected to offer a long service life.