Doosan Lentjes : Full compliance with BREF regulations
To reduce emissions released during the thermal waste treatment process, Doosan Lentjes offers a full range of cost-efficient flue gas cleaning processes. These include both (semi-)dry and wet processes for the separation of particles and pollutant gases as well as technologies for denitrification and possibilities for heat extraction from flue gases.
The conditioned dry Circoclean® system is a wastewater-free process for removing various pollutants such as SO2, SO3, HCl, HF, dioxins and furans, and heavy metals such as mercury from the flue gas. The technology uses hydrated lime and activated carbon as reagents for adsorption and absorption processes that take place in a Circoclean® reactor. Used reagents and solid particles, which are separated in a fabric filter, are partly returned to the reactor, which improves the consumption efficiency of the consumables. In this way, even the highest pollutant loads and sudden fluctuations in concentration can be handled. The recirculation of the clean gas ensures stable flow conditions and compensates for varying boiler loads. The direct feed of water into the reactor enables the optimisation of the reaction conditions for the absorption process in terms of temperature control and humidity.
If particularly low emission values are to be achieved, single or even multi-stage wet scrubbers can be applied downstream of the Circoclean® system. Depending on individual requirements and goals, Doosan Lentjes offers acidic and alkaline systems. If the pollutant load in the wastewater needs to be separated, acidic and alkaline wet scrubbers are designed as separate cleaning stages. This is done either in a sequential design with separate scrubbing towers or in a combined scrubber design. If the separation of the pollutant load is not necessary, the toxic substances (SOx, HCl, HF, ammonia (NH3) and mercury (Hg)) can in principle be separated in one alkaline system. The combination of a Circoclean® system with a wet scrubber enables the wastewater produced in the scrubber to be evaporated inside the Circoclean® reactor.
The FER-DI® process is especially suitable for moderate concentrations of pollutants such as SO2, SO3, HCl, HF, dioxins, and furans as well as heavy metals. Usable removal agents can either be sodium bicarbonate or hydrated lime. From the solid particles removed in a filter device only a small amount is recirculated into the reaction zone. This allows the plant to feature a compact design with a reduced footprint and, thus, lowering the investment costs.
For the denitrification of flue gases - i.e. the removal of NOx emissions – systems directly integrated into the combustion process (primary measures for nitrogen oxide reduction) and separate (secondary) applications can be installed.
The selective non-catalytic reduction (SNCR) process separates NOx emissions by injecting a reagent into the first pass of the boiler. The reducing agent can be either ammonia water or urea (NH2CONH2), which reacts with the nitrogen oxides (NO, NO2) to form nitrogen (N2) and water. The SNCR process reduces the NOx emissions in the flue gas to values in the upper range of the BREF requirements.
If compliance with stricter NOx emission limits is required, a separate selective catalytic reduction (SCR) system is installed to achieve NOx limits in the lower range of the BREF documents. SCR systems are usually installed downstream of the (semi-)dry or wet processes. NOx emissions are reduced by injecting ammonia water into the flue gas stream upstream of an SCR catalyst, where ammonia water reacts with the nitrogen oxides (NO, NO2) to form nitrogen (N2) and water.
Systems for removing solid particles are an essential element of modern flue gas cleaning and crucial for compliance with applicable emission regulations. Depending on the specific requirements, Doosan Lentjes offers state-of-the-art fabric filters or electrostatic precipitators.
Fabric filters are used to separate particulate matter pollutants. In addition, they act as a fine filter stage for gaseous acidic substances such as SOx, HCl and HF as well as heavy metals, dioxins, and furans in conjunction with the Circoclean® and FER-DI® system. Clean gas values of 5 mg/Nm³ particle concentration and also significantly below can be achieved permanently. The proven electrostatic precipitators can remove particulate matters from the flue gas and achieve clean gas values below 8 mg/Nm³.
For optimised heat recovery, both gas-gas and gas-liquid heat exchangers are integrated, depending on the requirements. This offers the possibility of increasing efficiency through combustion air preheating, feedwater preheating or district heat extraction.
The extraction of district heat can be further increased by flue gas condensation. In this process, the flue gas is cooled far below the dew point and the resulting condensation heat is transferred to the cooling circuit. This can be done in a separate heat exchanger in the clean gas or integrated into a wet scrubber.
In West Bromwich, UK, Doosan Lentjes is currently supplying an advanced Circoclean® system for the new enfinium Kelvin WtE plant to clean the flue gases produced during incineration in accordance with the applicable guidelines of the European BREF requirements. The SOx removal efficiency of the new plant will be over 97%; the HCl and solids removal rate will even exceed 99%.
The fabric filter to be applied has been designed to achieve the required lower dust emission limits in order to retain the heavy metals, which are primarily found in solid form. This design allows compliance with the very demanding heavy metal removal requirements.
In addition, the Circoclean® system in the enfinium Kelvin plant was designed to be "SCR ready". This means that in the event that NOx emission limits are lowered in the future, the planned system can be converted to a FER-DI® process operated with sodium bicarbonate and an SCR reactor can be used at the fabric filter outlet.
Thanks to the flexibility of the Circoclean® system, the thermal treatment of the residual waste generated in the region of West Bromwich will take place safely in the long term, considering all environmental objectives - even in the case of regulations that become stricter in the future.
The basis for efficient flue gas cleaning is always optimisation of the combustion process to reliably destroy toxic components and keep NOx concentrations low. As a one-stop partner, Doosan Lentjes offers not only flue gas cleaning technology but also grate and boiler technologies to achieve the best possible results in this part of the thermal treatment process.