Reducing emissions is one of the most important environmental issues of our time. Flue gas purification makes a significant contribution to this. It removes harmful substances from the process gas that comes from burning before it reaches the atmosphere. As a result, flue gas purification is used in (co-generation) power plants and waste incineration facilities and ensures fresh air and a clean environment.
To keep environmental pollution as low as possible, Scheuch has developed a comprehensive programme for dedusting, pollutant reduction and heat recovery which contains high-quality solutions for state-of-the-art air and environmental technology that are adapted to the process.
"Our integrated system solutions for air pollution control provides well-engineered process engineering, a high degree of operational safety and efficiency. Extensive process expertise, many years of practical experience and the continual optimisation of individual components and procedures guarantee custom technological solutions that are always fully up to date from both an ecological and economical perspective," emphasised Franz Söllhinger, General Manager of Scheuch GmbH's Energy Industry division.
Bag filters for flue gas purification
Due to their excellent filtration properties, fabric filter plants, amongst others, are ideally suited to separating fine dust up to a guaranteed value of < 5 mg/Nm3 and also for reducing other contaminants in combination with sorptive processes.
"Scheuch fabric filters are characterised by their high plant availability, low operating costs and maintenance operations that can be implemented easily. A modular system and parameterised variation models enable the filter plant to be specifically designed and optimally adapted – allowing for an airflow rate ranging from just a few thousand up to several million cubic metres," stated Söllhinger.
The air and environmental experts from Aurolzmünster in Upper Austria have added design details to their filter range especially for this application in order to avoid deposits in the system, for example.
Other factors that play a large role in terms of high availability and low operating costs include choosing the correct filter medium and managing filter cleaning according to the boiler load fluctuations.
Patented sorption procedures
Adsorption and absorption methods are used when cleaning acidic corrosive gas emissions (SO2, HCl, HF) and other gaseous materials such as heavy metals, dioxins and furans when recovering energy from treated and polluted fuels, and waste and residual material.
A distinction is made between the dry sorption process that uses calcium hydroxide or sodium bicarbonate and the conditioned dry sorption process that uses a gas conditioning tower or humidifies the recirculated material directly.
Scheuch has developed and patented its own procedures for these applications. Resource and supply costs, as well as spare part and maintenance costs are taken into account in the economic analysis when determining the appropriate procedure.
Flue gas purification at Migros Aare
Scheuch has installed innovative compact bag filter technology for purifying flue gas in the heating plant of the Swiss cooperative Migros Aare in Schönbühl, Bern. This became necessary as the existing system no longer met the company's high energy and environmental requirements.
Migros Aare is the largest of ten cooperatives of the Swiss retailer Migros. It was formed in 1998 as a result of the merger between Migros Aargau/Solothurn and Migros Bern. Migros Aare generates an average annual turnover of 3.3 billion Swiss francs and has approximately 12,000 employees. In addition to supermarkets, Migros Aare also operates restaurants, "Club School" further education institutions, fitness and leisure facilities, as well as speciality sport and DIY retailers in the Cantons of Aargau, Bern and Solothurn. In accordance with the philosophy of the Swiss company, Migros is dedicated to the quality of life of its employees and customers. It aims to preserve the quality of life for future generations over the long term, which is why environmental and social policy is its number one priority. It is for this reason that Migros has been heavily involved in cultural, social and sustainable projects such as electromobility, solar power plants, and environmentally-friendly products and packaging since the 1950s.
Ultra-compact filter plant
As Migros Aare is heavily focussed on sustainability and environmental and climate protection, the company has invested in the modernisation of the filter plant used in the heating plant in the last year. Scheuch has developed a compact filter for dedusting the grate furnace, which fits perfectly in the limited space available in the biomass heating plant with a 6-MW boiler. A filter casing with a filter area of 582 m2 and a height of 3.5 m was built for this purpose. It has a base area of only 12 m2 and is characterised by its compact structure with a special filter bag geometry. Furthermore, an IMPULS bag filter with an output of 35,000 Bm3/h at a crude gas temperature of 160ºC and peaks of up to 230ºC was attached for collecting particulates after old wood and polluted wood treated by a flue gas scrubber has been burned.
"The new filter plant means that a clean gas dust load of 10 mg/Nm3 can be achieved once the flue gas has been filtered, which is significantly lower than the required limit values. As the crude gas dust load is still 2 g/Nm3 before cleaning, the pollutant load can be reduced to a minimum using the new bag filter system," explains Christoph Medwed, Project Manager in the Energy Industry division at Scheuch GmbH.
Short installation time
To reduce installation time, Scheuch provides modular designs ex factory for its mid-range IMPULS bag filters for outputs up to 200,000 Bm3/h (boiler outputs up to 50 MW). With this compact, pre-assembled system, the individual components such as the casing with filter head, crude gas duct, filter head and trough then simply need to be screwed together on site. Even the filter bags are pre-installed.
The filter, which consists of three units (casing with filter head and trough), was delivered in pre-assembled components, insulated and with trough heating for external assembly in Schönbühl. After seven days of assembly, the filter was ready for operation. Migros Aare needed it to be installed quickly as otherwise an additional gas heating system would have needed to be installed and gas purchased for the meantime.
"As it was largely pre-assembled and the individual filter casing components were insulated in advance, our fitters were easily able to complete assembly and commissioning in just one week. It was actually the construction and implementation of the new ultra-compact bag filter plant that presented a new challenge for us. However, our many years of experience meant that we were easily able overcome it," reported Medwed.
The fact that the bag filter was installed in just seven days at Migros Aare proves that it can be done. Another advantage that goes hand in hand with this short installation time is that the customer incurs lower costs, as, for example, less crane work is required as many of the individual filter components come pre-assembled.
A better quality of life and more sustainability
Since it was commissioned at the end of October 2011, the company has been very satisfied with the filter plant in Schönbühl, as confirmed by Patrick Beyeler, boiler house and heating plant Manager for Migros Aare, "The solid waste incineration plant is up and running and the bag filter has been integrated. The previous management confirms that we have been recommended and received a very high-quality filter."
Hansruedi Brügger, Head of energy supply for the Migros Aare cooperative is pleased to say, "Working with Scheuch went off without a hitch. They largely adhered to the agreed deadlines and met our requests with regard to the limited building space and the high power consumption. The new filter plant means that we can make further contributions to reducing pollutant emissions and to significantly increasing the quality of life in the region for the long term."
Image reference: Scheuch GmbH, may be reprinted free of charge
Image 1: Compact bag filter plant for purifying flue gas
Image 2: Short assembly times thanks to pre-assembled components and pre-insulation
Image 3: Migros Aare in Schönbühl with innovative Scheuch filter technology